Theories of Everything with Curt Jaimungal - Fall Asleep to Physics Theories 10 Hours ★︎ World's Top Theoretical Physicists ★︎ Sleep Playlist

Episode Date: October 7, 2024

Fall Asleep to Theoretical Physics Theories SPONSOR: As a listener of TOE you can get a special 20% off discount to The Economist and all it has to offer! Visit https://www.economist.com/toe CHAPTERS: Roger Penrose - Collapse of the Wave Function Stephen Wolfram - Observer Theory Brian Greene - Faster Than Light Travel and Wormholes Sean Carroll - Crisis in Physics Lee Smolin - Thick Time Neil Turok - Fields and Particles Garrett Lisi - Unification, Spinors, Fermions Roger Penrose - Cosmology and Twistor Theory Jonathan Oppenehim - Observation Causes a Collapse Wolfram/Hoffman - Entropy Ivette Fuentes - Current Developments in Physics Jonathan Oppenheim - Quantum Mechanics and Quantizing Gravity Ivette Fuentes - Quantum Theory and Relativity Carlo Rovelli - Quantum Mechanics Cumrun Vafa - Swampland (String Theory) Sean Carroll - Big Bang, Boltzman, Holography Cumrun Vafa - Swampland (Continued) Tim Palmer - General Relativity and Quantum Mechanics Neil Turok - Singularity (Black Hole vs. Big Bang) Stephen Wolfram - Beliefs Dictate Laws of Physics Neil Turok - Unification, Spacetime, Time Tim Palmer - Infinity Wolfram/Hoffman - Ruliad and Consciousness Fay Dowker - Causal Set Theory Jonathan Gorard - Constructor Theory Chiara Marletto - Constructor Theory Peter Woit - Twistor Theory Lawrence Krauss - Quantum Fluctuations Tim Palmer and Tim Maudlin - Quantum Mechanics & Bell's Theorem Stephon Alexander - Autodidactic Universe Thomas Campbell - Theory of Everything Bernardo and Sabine - Superdeterminism Sabine - Superdeterminism and Bell’s Inequality Salvatore Pais - Superforce / Plank Force Chris Langan - CTMU Tim Maudlin - Superdeterminism and Retrocausality Links to Main Episodes: - Penrose: https://youtu.be/sGm505TFMbU?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Garrett: https://youtu.be/z7ulJmfFvd8?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Oppenheim: https://youtu.be/6Z_p3viqW1g?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Ivvette: https://youtu.be/cUj2TcZSlZc?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Carroll: https://youtu.be/9AoRxtYZrZo?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Cumrun: https://youtu.be/kUHOoMX4Bqw?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Turok: https://youtu.be/-gwhqmPqRl4?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Tim Palmer: https://youtu.be/vlklA6jsS8A?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Hoffman/Wolfram: https://youtu.be/1m7bXNH8gEM?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Fay Dowker: https://youtu.be/PgYHEPCLVas?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Neil Turok First Episode: https://youtu.be/ZUp9x44N3uE?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Gorard: https://youtu.be/ioXwL-c1RXQ?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Wolfram: https://youtu.be/0YRlQQw0d-4?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Lee Smolin: https://youtu.be/uOKOodQXjhc?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Chiara: https://youtu.be/40CB12cj_aM?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Peter Woit: https://youtu.be/9z3JYb_g2Qs?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Krauss: https://youtu.be/g12qyToQ4gI?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Maudlin/Palmer: https://youtu.be/883R3JlZHXE - Stephon Alexander: https://youtu.be/VETxb96a3qk?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Campbell: https://youtu.be/kko-hVA-8IU?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Bernardo and Sabine: https://youtu.be/kJmBmopxc1k?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Brian Greene: https://youtu.be/O2EtTE9Czzo?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Sabine: https://youtu.be/walaNM7KiYA?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Salvatore Pais: https://youtu.be/5E6QyAhTB3o?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Chris Langan: https://youtu.be/N-bRM1kYuNA?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy - Tim Maudlin: https://youtu.be/fU1bs5o3nss?list=PLZ7ikzmc6zlMhlVNkx2c8_6CKqiimjgvy Support TOE on Patreon: https://patreon.com/curtjaimungal (early access to ad-free audio episodes!) #science #sleep Learn more about your ad choices. Visit megaphone.fm/adchoices

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Sign up for your $1 per month trial period at Shopify.com slash theories all lowercase go to Shopify.com slash theories to upgrade your selling today that's Shopify.com slash theories I always thought that didn't like the collapse of the wave function as being I mean so can quantum theory was terribly confused. You see, you've got the beautiful... Well, think of the Schrödinger equation. Schrödinger was as confused... I mean, he understood why he was confused. I mean, he was absolutely on the ball. But lots of people were confused. Anyway, let me not go into that story. You see, take a quantum system. How do you describe it? You take the wave function or vector in Hilbert space or something, the wave function. Take the wave function.

How does that evolve in time? Schrodinger equation. So it evolves in time according to Schrodinger equation. Is that the way the world evolves in time? No, it doesn't because you cheat. You say, no, no, you've got to a certain point and you make a measurement. What does making a measurement mean? I don't know. People have funny ideas about making a measurement. The trouble is the word observation, I think, crept in there a little too... Too sneakily, too early? Too sneakily, too strongly, I would say. Because people think as many, one of the big proponents of this view was Vigna, Eugene Vigna.

And I actually, when I was in Princeton, I did talk to Vigna about it. I had a long lunch talk with him, and I talked about this issue of does the wave function, consciousness, if you like, collapse the wave function. Because that was the V function, consciousness, if you like, collapsed the wave function. Because that was the Wigner view. He was not so dogmatic about that view as I was expecting. He was saying it's a view, but a point of view. I don't think for many reasons it really makes sense. But it was nevertheless, I think a lot of people,

even von Neumann seemed to have that sort of idea too. A lot of people had the idea that it was a conscious being observing the system, which somehow changes the rules. You change your wave function and write it down as a, in terms of its certain basis. And then you give the amplitudes and then you look at these complex amplitudes, square them, square the modulus modulus and that makes your probabilities So then what would they say not to take you off track? But what would they say is that what observes the observer?

And I don't say any of that you see I don't care what they say I don't know what they say because it's not what I say and I think it's wrong So although I think consciousness has relates to, Christian, it's in a completely different way. It's not what collapses the wave function. What collapses the wave function is physics. So there is something in physics which collapses the wave function. The Schrodinger equation, quantum theory as a whole, is wrong.

It's not Einstein was wrong, quantum mechanics is wrong. Now I say this very blatantly because it's a blatant topic. I mean, Einstein and Schrodinger were much more polite. They said it was incomplete. Mm-hmm. Okay, incomplete means wrong. Well, you're telling it like it is. Yeah, you've got to change it so it's wrong.

But incomplete is a more polite way of saying it's wrong. Okay, they're fine. I should be polite sometimes too. Everyone who's watching is an observer and what you published is called observer theory. What's your latest discovery about? About observer theory. What's that about? It's about the question of sort of characterizing what it means to be an observer. We have, for example, when it comes to asking what does it mean

to do a computation, we have kind of a way of understanding that. We kind of start from Turing machines, we know they're equivalent to lots of other kinds of computational models. We have this notion of what it's like to do a computation. So I've been interested in what is it like to be an observer? Why do I care about that? I care about that because in our physics project, it's become an essential thing to understand what we're like as observers because it seems to be the case that what we're like as observers determines what laws of physics we perceive there to be.

So it becomes important to be able to characterize what are we like as observers, because if we were observers that are different from the way we are, we would perceive, I think, laws of physics that are different from the laws of physics that we perceive. So in fact, I think in the end, the picture is going to be that the laws of physics are what they are because we are observers of the kind we are. So that's a kind of a different, it's sort of a reframing of thinking about what does it mean to have a fundamental theory of physics. It's a theory of physics that is the theory that has to be the way it is for observers like us. It couldn't be the case that you could kind of wheel in another theory that, you know, God could have invented

a different theory of the universe for observers like us. It is, I think, inevitable that the laws of physics are the way that they are. So, okay, so how do we understand what is an observer, what is an observer like us? Right? So what is an observer like us? So first we have to kind of ask What is an observer doing the world's a complicated place? We have finite minds the goal of us as observers is to take a complexity of the world and kind of find a way to stuff it into our finite minds. And in a sense, what that's doing is it's saying,

there are lots of details in the world, but they're not gonna fit in our finite minds. We somehow have to compress what we're seeing in the outside world so that it fits in our finite minds. Another way to think about it is, we've got to make equivalences between different kinds of things. Like I'm sitting here staring at this camera

and in the retina of my eyes, there are all kinds of photons falling that are kind of making some elaborate pattern there, but all that my brain is perceiving is, oh, there's this object in front of me. So I'm doing many equivalences. And what I extract from this sort of the raw physicality of what's going on is something that has many things,

that many different arrangements of photons that would lead me to perceive the same thing. And what you realize is that that's a common feature, not only of us human observers, but all the measuring devices we use and all these kinds of things. It's all about there are lots of details in the world. We just want to measure a particular thing. So a quintessential example would be you've got a gas, it's got a bunch of molecules bouncing around trying to measure the pressure of the gas. How do you do it?

Well, maybe you just have a piston on the side of the box and you say, how hard is the piston pushed by the molecules in the box? And there are all kinds of different configurations of molecules hitting the piston and they go this way and that way and the other. But all that matters in measuring the pressure is what the aggregate force on the piston is. So there are all these different configurations of molecules that we equivalence together to deduce that one thing that we care about which is the force on the piston. And so i think the four four as we think about our ourselves that the fundamental feature of server is we're doing lots of equivalence. We are taking many different states of the world and saying we don't care about the differences between these things.

We are just going to extract this essence of what's going on. And that's what we as an observer are thinking about. Now, it's interesting to see when we imagine a computational process going on, we're always generating fresh states of the world. We're going from one state of the world We're going from one state of the world We compute the next state of the world the next one and so on we're always sort of generating fresh states of the world

On the other hand when we are being observers, we're sort of doing the opposite instead of generating fresh states of the world We're trying to equivalence together lots of states of the world We're trying to say there are lots of things which which might think of which in some sense are different, but we are going to treat them for our purposes as equivalent. Now you might say, how could you deduce anything interesting from knowing about these kinds of equivalences? It turns out that the notion of these kinds of equivalences is critical to sort of deducing what we can think of as physical laws, because in some sense, a physical law is an attempt to explain some aspect of the universe in a way that we can understand with our minds. I mean, we could say about the universe, oh, it just does what it does. And it has all these little things going around in it But we don't have any narrative explanation of what's happening

The the kind of the nature of physical laws is we want to take what the universe does And we want to somehow get a description of it that sort of fits in our minds And so for example when it comes to something like I don't know a gas with a bunch of molecules bouncing around The thing that fits in our minds is some aggregate description that talks about pressure and temperature and things like this, not the detailed motions of those molecules. So for us, we're talking about the gas laws. For the system underneath, it's got all these molecules bouncing around.

It's important that we are only able to talk about things at the level of the gas laws, because if we could talk about things at the level of molecules, we'd come to quite different conclusions about what's happening in the world. So this is essential to, for example, the second law of thermodynamics, because what does the second law of thermodynamics say? It basically says, things tend to get more random over time. What's the application of that? If you take some mechanical motion, you're sort of pushing something backwards and forwards. Well, that's a very systematic motion of atoms in the thing, but that systematic motion tends to get sort of ground down into random motion of molecules that we call heat.

Once you have things as heat, it's hard to get them back into systematic motion You don't find that all those molecules that are randomly bouncing around Suddenly line themselves up and start systematically pushing the block of wood or whatever it is So there's this tendency for things to get more random But from the point of view of the individual molecules, that's not what's going on from the point of view of the individual molecules They're just following certain laws of motion molecules, that's not what's going on. From the point of view of the individual molecules, they're just following certain laws of motion. You could even reverse those laws of motion if you wanted to. The molecules are just doing definite things. It's only from the point

of view of observers like us, with our kind of bounded computational capabilities, that we say, we don't know how to follow all of those details. For us, what the molecules are doing should just be considered random, and all we should be able to deduce is something about their average properties, like their average temperature, their average pressure, whatever else. So the fact that we believe that the second law of thermodynamics is right or that the gas laws are right is a consequence of the fact that we are observers of the kind we are. If we were observers who routinely traced every motion of every molecule, we would say,

what do you mean that there's randomness in what's going on? There's no randomness. I can see what every individual molecule does. So in a sense that that's an example of a place where being an observer of the kind we are is the thing that causes us to perceive laws of the kind we perceive. If we were an observer

who followed every molecule, could do every computation to figure out what would happen with every molecular motion, we wouldn't say, oh, it's just random, you can only look at the averages. We would be sort of concentrating on the details of what was happening at the level of molecules. So that's an example. And by the way, the same exact thing seems to happen in space-time and in quantum mechanics. And the thing that for me is like spectacular realization is in 20th century physics, there were three big theories, general relativity theory, gravity theory, space-time, quantum mechanics, and essentially statistical mechanics whose sort of prize exhibit is the second law of thermodynamics, the theory of how systems of very large numbers of components

work. Those three basic kind of achievements of 20th century physics, I think one had thought that maybe the second law of thermodynamics was derivable from something lower level. Maybe just from the laws of mechanics and some mathematics, you could deduce the second law of thermodynamics. People had thought that in the 1800s, by the early 1900s, they were kind of giving up on that idea, and it was just like a mystery that was left hanging out there. But there was some thought that the second law might be somehow derivable from something sort of more fundamental and already known. For general relativity and quantum mechanics,

that really hadn't been the thought. The thought had been, at least as I, you know, the way I always thought of it, is we just happened to get those laws of physics. We, you know, the way I always thought of it, is we just happen to get those laws of physics. We, you know, the universe we live in, just, you know, for reasons we don't understand, happens to have those particular laws of physics. Well, I think that, I think we can say more than that now. I think we can say, and it's really surprising that we can say this, but I think we can,

that all three of those kind of achievements are consequences of the fact that we are observers of the kind we are. That it is inevitable that we have to perceive the physical world to have those particular laws because we are observers like we are. If we were different kinds of observers, we would observe different physical laws, but we observe those laws because we're observers like we are. Now, okay, there's more to say about how this all works, but the kind of the thing that I was trying to do

with sort of my efforts in observer theory is to characterize something about what observers are. It's all about these equivalent things. It's all about taking the complexity of the world and sort of stuffing it in a finite mind by equivalencing many different states of the world to say all we care about are these features. That's one side of it. And then being able to see kind of how you flow through from what characteristics do observers like us really have. And by the way, many of those characteristics are things so obvious to us that we've never

really called them out as things that we actually should say, yes, this is a feature of us. So an example, which turns out to be really important, is we believe we're persistent in time. You know, we believe that we have a thread of experience that goes from the past to the future, and it's still us. Well, really, in our models of physics, for example, you know, at every moment in time, we're made of different atoms of space. And so, in some sense, it's always a different us

at every successive moment. But somehow we have the perception that we have this continuous thread of experience. Something that seems very, very obvious to us, but is nevertheless an assumption. It's not obvious that we would have a consistent thread of experience. We could imagine being some kind of alien intelligence that was different at every moment. It was like we have successive generations of humans and each one has its own separate experience. We could imagine that was somehow compressed. It's very hard to think it through what it would be like to be in that situation where

we don't have any sort of memory for ourselves. I don't really know how it would work. That's kind of a science fiction type scenario that would be interesting to think through. But the fact that we believe we have this persistent, unique thread of experience for each of us is non-trivial. You know, it could also be the case that we could, instead of experiencing things in a single thread, there could be multiple threads. We could have, you know, one could sort of imagine what it would be like to have sort of multiple consciousnesses in the same brain, so to speak.

Would you be able to imagine what that's like, or is it part and parcel of you being the kind of observer that you are that you can't even imagine it? I think it's really hard to imagine. I've been trying to imagine a bunch of these things. I mean, I think it's sort of a very interesting challenge to imagine sort of what it would be like to be an intelligence, very alien, compared to us. And I made some attempts along those lines, actually. And I would say it made a little bit of progress,

but I would say that's a really difficult thing to wrap one's brain around. I mean, I think one of the things, this is sort of a side point, but I've been mostly familiar with the Western tradition of thinking about things and philosophy and so on. I've been curious because people have been telling me for years, oh, the things you're doing resonate with various kinds of Eastern philosophies and so on.

I've been curious to try to understand how that works. And you know, my initial investigation say, yes, there are there are things there that that sound an awful lot like things that I've long been talking about, so to speak. Professor Brian Green, it's an honor to speak with you. I've been researching you since I was young. And also, as I've gotten older, It's an honor. Thank you for coming on Thank you so much What have you been working on in the past year and what do you hope to accomplish in the next year in this year? Well, yeah, I've been working on some strange things of late, which I'm almost afraid to talk about

But since they've been published on I guess I shouldn't at all hold back But it sounds a little kooky. It sounds like the kind of things that I received in emails and crank letters for the past 30 years. It has to do with questioning whether the speed of light really is the limit for signal transmission. We all know that as anyone who's taken basic physics studies for relativity that it's an absolutely well established fact that

locally the speed of light is the limit for signal transmission. Obviously going back to Einstein and a gazillion experiments since. But there are some unusual contexts that theories like string theory suggest. And those contexts suggest that the overall shape of space might be non-trivial in the sense that it might not just sort of go on forever. Space might curve back up itself and you can ask yourself what if the universe. Is in the shape of a loop or at least are dimensions that are loop that you go out in one direction you go far enough you'll come back to your starting point. And so we began to study signal transmission in universes with the signal could go all the way around the universe and route to its destination.

And we found in certain circumstances that I'd be happy to elaborate that you could have signals going in that unusual trajectory that would get to their destination faster than the signal that would seemingly be the quicker one moving right through the space time without traversing these these closed curves. And so we found that there are signals that can go from here to there faster than the speed of light. This is related to the topology of the universe and not the variable speed of light? Yeah this is not a variable speed of light type of contribution. As you know, as you're making reference to, there's been a whole

industry that various physicists pursued over the course of many years, wondering about whether the speed of light might vary through time, a temporal dependence to the speed of light. Very interesting idea. I really don't know that there's much evidence for it, nor is there much evidence for what I'm talking about either. So this is like throwing stones in a glass house. But be that as it may, you're right. It all has to do with the topology of space.

And if that topology is non-trivial, if there are non-contractable loops in that space, then that allows for qualitatively different trajectories for signals. And when you take those into account, you find that the signals can have a net speed that's faster than the speed of light. And moreover, it starts to sound a little bit kooky, but

when you take special relativity, you learn that if signal can go faster than the speed of light, then there are observers according to whom that signal may arrive at its destination prior to the time at which it was emitted. And indeed, we find examples of that. In other words, we find examples where you can send a signal into the past. And again, I hesitate saying this, but you asked me the question, what I've been working on lately, so I feel like I need to answer fully and truthfully. I hesitate to say this because this has sort of been the playground of kind of thinkers who wanted to upset Einstein

become the new Einstein to try to find some flaw in the special relativity. This is not a flaw in the special relativity. It's a feature of the special relativity when applied to a universe that has one of these non-trivial topologies. So a closed time like curve doesn't go against general relativity. Girdle had a solution that has closed time like curves. Are you suggesting some amendment to general relativity or are you just saying, look, the actual structure of space time or the shape of it is different, so you're not proposing

new laws? No, no, no laws. Yeah. And so, you know, the whole notion of closed time-like curves is a tricky one. That's one where there's a full trajectory that gets back to its starting point prior to when it departed. And we don't exactly find those kind of structures in these theories. So if I send a signal out into space and send it somehow into the past and then someone in the past gets that signal and fires back toward

me, the return signal will always get to me in at least no time. In other words, it won't be that I get the signal prior to the moment when I emitted it. So this would allow for interesting things, such as, you know, we've always worried, well, worried is probably too strong a word. We've always noted that if we discover intelligent life out there in the cosmos and it's very far away, how are we going to have a conversation, right?

We send out a signal, hey, how you guys doing? And what do we do? We wait like 100,000 years or a million years for the return signal. And by that point, we've forgotten that we're in a conversation at all. But in the theories that I'm describing now with these universes, with these non-trivial topologies, you can send a signal out into space and the person can get it and respond and you will receive it in virtually no time, in as little time as one can imagine. And so you can have a

real-time conversation with someone who's in an arbitrary distance. So I think that's pretty startling and mind-boggling and kind of wonderful. And who knows if any of these ideas happen to be true it would allow for conversations that in the more usual setting would just be impossible but no it's no amendment to general relativity it's no change at all to the fundamental laws that's the kind of fun thing about this approach you know if you come along and say well let's now bend the laws of physics as we knew it in the past change it in some way sure

Obviously you're gonna get some new effects But then it all depends on the utility of it depends on was that amendment was that change at all? Reasonable, so we're not changing the laws of physics at all. We're just considering shapes of space That are very natural in certain unified theories like string theory, you know, Kaluza-Klein type theories that people studied in the past, and just examining conventional physics in a new setting as opposed to new physics in either conventional or new setting.

Is any of this related to wormholes or is this separate? conventional or new setting. Is any of this related to wormholes or is this separate? It is definitely separate from wormholes in the conventional way that people think about wormholes, but there is a deep association in the following sense. If you are looking at a signal that's traversing, say, a circular dimension of space, one of the most profitable ways scientifically of setting that is to imagine cutting that circle and opening it up into a line, say an infinite line, and then just having global identifications,

0.0 identified with 2 pi r, identified with 4 pi, with 6 pi r, and so forth. In that way, you effectively have a circle because of those identifications, but you've unraveled it into a more conventional shape, a line. Then when a signal goes from zero, say, to 2 pi r, which really in some sense happening is,

the signal is then in essence, jumping through a wormhole and going back to its starting point. And so you can reframe everything that I'm talking about using the language of wormholes, but wormholes are not as essential to the story as it might be in certain other applications where you start to worry about things like, well, is the wormhole traversable? Will it stay open long enough for someone to actually go through or for a signal to

go through? In this case, a wormhole is really more of a technique, a mathematical technique for analyzing the situation as opposed to being fundamental to the whole idea. So this year, your plans are what? To work on this theory some more or? Yeah, we're going to definitely whole idea. So this year, your plans are what? To work on this theory some more or? Yeah, we're gonna definitely pursue, you know, look, what is this called by the way? Sorry, is there a name for this?

Or a paper that people can look up? Yeah, we're written a couple of papers on it. The most recent one has the title, Back to the Future, which the editors at Physical Review D initially sent the paper back and said, we like the paper, but you got to change the title because it's like, we just don't have titles like that. And I have to say, I kind of took a little bit, offense is too strong a word, but we wrote back to them and said, sure, there's a cultural reference. It's kind of fun, but it's not just the cultural reference for a cultural

references sake, we truly are talking about a signal that can travel from us. Back to the past and then into the future. Cause as I said before, the return signal always gets to us in a non-negative amount of time. So it's back to the future. It's like a perfect description of what we're talking about. And to their credit, the editor's physical review D finally said, yeah, okay, you're right, it works. So the paper was accepted with that somewhat perhaps loose sounding title, but one that really does have a descriptive approach to what we're talking about that's spot on. And so yeah, if people want to see the technical Toronto on January 26th if I'm not mistaken.

So that's about a week from now when this is being published when you're seeing this. Can you tell myself a little bit about that in the audience as well? Yeah, absolutely. So it's a talk at Roy Thompson Hall. I've never been there before, but at least the pictures look like it's a quite beautiful venue. And it's a journey that I'm going to take the audience on from the beginning of time up to the present and out toward the farthest that science can take us toward the end, toward eternity. And my point in taking the audience on this journey will be partly to illuminate some of the key scientific ideas that guide the cosmological unfolding on the largest of scales and the largest of time scales. But I also want to give people a sense of what science says about how we fit in to this cosmic order from this broadest, this

largest perspective. And so we will be covering the formation of stars and galaxies, a little discussion about how entropy and life interplay and play off of one another. And then once we get to the present, we'll turn our attention toward the future and see how it all comes crashing down when you look at sufficiently large time scales as entropy gains the upper hand. And I'll conclude the evening with some remarks on how one might interpret this large-scale understanding of the cosmos in more human terms, and how it is that perhaps this perspective can shed light

on the age-old questions of meaning and purpose, which occupy all of us in one way or another. So how does it shed light on those, on meaning and purpose? Well, objectively. So, well, shed light on those on meaning and purpose? Well, objectively. So, well, you should come to the evening, but I'm more than happy to discuss it now in broad strokes. So, look, you said objectively, and I would say I don't know that objectively there is an answer. I think it is ultimately the

subject of search that each human being is ultimately on to try to make sense of their life, make sense of their life, make sense of their existence. But what this perspective does for me, and I found that it resonates with many people, it shows us how unbelievably, astoundingly unlikely our own existence is. Against the spectrum of possible combinations of base pairs of DNA, against the spectrum of possible molecular configurations, against the spectrum of possible outcome of quantum processes that stretch from the beginning until today that each of them could have turned out one way versus the way they

did, yielding a universe in which we wouldn't be here, against these astounding odds we're here. And to me, that's the beginning of the most fruitful, compelling and satisfying approach to finding some sense of purpose or meaning. Because rather than looking out to the universe, which we see in many philosophies and frankly many religions, looking out to the cosmos to bestow upon us some ultimate answer, some ultimate meaning, some ultimate purpose, this understanding of the cosmological timeline and the astounding unlikeliness of our own existence turns the spotlight inward. It turns the spotlight to a recognition of how astounding it is not only that we exist

but we have the powers that our particulate arrangement endow us with. Look what we can do. we can have this conversation. We can figure out the past. There aren't many other life forms that we're aware of that can do that. We can imagine the future. Again, not many life forms have been able to work out a testable science that can give us insight

into things that haven't yet happened to the future. And the power of the human mind to do all that and to create beauty in the world and to illuminate mystery in the world and to experience the wonder of it all, to me, that is where a deep kind of gratitude emerges. And that gratitude is for the mere existence of human beings. And it's not dependent upon whether we're going to have some lasting legacy. It rather is just focused on the fact that we're here at all and that we can do the things that we can do. And with that comes an appreciation, which for me is deeply compelling and satisfying

regardless of my understanding of how evanescent it all is. What is specifically meant when people say, or some people say, and you can pick a person because I'm sure there are many different interpretations of this, that physics is in crisis. What's meant by that? You'll have to ask them because I don't think it's true. I guess that there's different interpretations one could have, either that we're stuck, we haven't gone very far forward in fundamental physics, or they might think that individual physicists are doing things in the wrong way for some reason. But again and again, I'm going to keep saying the proof

of the pudding is in the tasting. The alternatives that I've seen offered up are not that impressive to me. And the comment section, I had a brief skim through, and they were saying that when people say physics is in crisis, they don't mean physics as a whole, they mean fundamental physics, and that the podcast focused on the successes of applied physics like MRIs and lasers and so on to counter the claim of stagnation. So attributing engineering feats to physics and that if we detect the Higgs boson, sure that's cool, it's wonderful, but that's a confirmation

of an old theory. It's not a novel theoretical breakthrough. How do you respond to those comments? No, I mean, I agree. What can I say? In fundamental physics, we've not had any breakthroughs that have been verified experimentally for a very long time. That's just true. Can't argue with that.

Again, most physics is not fundamental physics. If you look up the membership roles of the American Physical Society and figure out what fraction of them are doing quantum field theory or gravity or whatever, it's a small fraction. There's a lot more interesting physics out there. You might personally not be interested in it. Good for you. That's fine. But it is going on. That's what employs most physicists. Would you say that part of the distaste for the phrase, hey, fundamental physics is in

crisis stems from your love for physics, your desire to convey that adoration to other people and this whole meme of hey, physics is in crisis bro is typically expressed by people as you see outside the field who lack a clear understanding of the reason behind what they're saying. They're just jumping on the bandwagon of being iconoclastic. Well I think, you know, everyone... As a creator, I understand the importance of having the right tools to support your business growth.

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slash theories, all lowercase. Go to Shopify.com slash theories to upgrade your selling today. That's Shopify.com slash theories. And as welcome to their opinion about everything, I'm not going to gatekeep who gets to have an opinion about things. I just want people's opinion about things to be as educated as they can be. That's why I tried to offer up my own solo podcast and other efforts. I think it would make sense to say that physics was in crisis if I had a very sensible argument that physicists were working badly, were doing the wrong thing,

were making mistakes. If anything, I think that in the foundations of quantum mechanics, that's an argument that you can make, that we've been ignoring the foundations of quantum mechanics for a long time. But in particle physics, quantum field theory, quantum gravity, I don't see evidence that that is the right attitude towards what physicists are actually doing. So when I was researching this, I could see that the crisis in physics is threefold. So there's what I call the great stagnation, which we just referenced, and then there's

the great schism, which I'll speak about shortly, and then the great silence. So the great stagnation is that there haven't been new discoveries that have pointed the way to physics beyond the standard model or general relativity in a way that resembles a consensus. Okay, cool. That's just one element. The other is the schism that happened approximately in the 80s or so, or especially in the 90s where the field is split and many people don't realize this.

So there are string theorists who literally say string theory is the only game in town. I didn't know that string theorists say that. I thought that that was just a claim from people who weren't string theorists to lob at string theorists to say, hey, you all think this, but they would never say that. But I was speaking to Kuma and Vafa and he explicitly said twice in the podcast, it's the only game in town. So this also then has this element of trial by string theorists where new ideas are also evaluated by string theorists. And I'm speaking specifically about fundamental physics. So I agree, there's no crisis in physics as a whole. It's quite foolish to

say that, especially just look at condensed matter physics. It's booming. And if you want to contribute something new, that's like the, that's the great place to be. But it's partly this derisive and supercilious attitude by the string theorists since the 80s that have cost people jobs and this is in part what Peter Wojt is talking about with his critiques, though his tend to be more mathematical about overhyping string theory. The majority of the time though, the issue is with the string culture. So that is to say that there's a history of its arrogance and its incuriosity and its suppression of alternative ideas.

That's the schism. And then the, well, how about I let you comment on that? Do you see that? Yeah, I mean, I would say that there absolutely are string theorists who sincerely and honestly believe that when it comes to quantum gravity and unification, strength theory is the only game in town. That is not necessarily true.

I don't agree with them, I should say. But I get why they think that. As I said, I think I explained in my podcast about this. It's not as if we fixed all the problems of physics and moved on to trying to do quantum gravity. In the mid 1980s, nobody was interested in quantum gravity for very good reasons. The Planck scale is very large, gravity is a very weak force. We can't collide gravitons and see what happens, the prospect of getting any good theoretical handle on quantum gravity seemed unrealistic. The early 80s I

should say. String theory came along and offered an answer to some of the puzzling aspects of quantum gravity in a very unexpected way. It's a finite theory. You can collide gravitons together in the string theory thought experiment and get a very perfectly well-defined answer. And other theories you just can't. What can you say? So that gave people very, very good optimistic reasons to push the theory forward. And then the other thing about string theory is that even though it clearly has failed in making experimental predictions we could test against data, it also clearly has kept itself alive on the theoretical side.

New ideas keep coming in. ADS-CFT is a perfectly good example, but d-brains and M-theory and various versions of holography, there's lots of examples that you can give. The Swampland idea is arguably such a new idea right now. So it hasn't crashed and burned. Many theories will look promising and then they will crash and burn. String theory has remained frustrating because it doesn't connect with data, but the number of theoretical ideas is enormously rich and that's worth taking seriously.

Now, I do have a little bit of sympathy with the view that you just expressed, but I would express it differently. I mean, I think that the way that it often gets expressed is just clearly sour grapes. It's clearly just being curmudgeonly and people don't like my ideas, therefore I'm going to claim that they don't have a good attitude towards science more generally. I don't think that that's a valid way of arguing, but the way that I would be able to argue it is look, precisely because experiment is not guiding us, we should be a little humble about what theories we like and don't, because we can always fool ourselves, we can always trick ourselves when experiment is not there to set us straight.

And so that's a, it's a very difficult thing to do. But what I would argue is that you should nevertheless, as a field, put some resources into approaches to physics that you think are probably wrong, right? Because you could be wrong yourself. So if there is someone out there who is allocating all of the jobs and all of the grants and all of the experimental work in physics, I would argue very strongly that even in the area of fundamental physics and unification and quantum gravity, they don't just put it into string theory. They should certainly put it into other areas as well. Here's the problem with that. There is no such person. There is no such, you know,

Pope of theoretical physics who decides who gets to be in the College of Cardinals. Instead, you have physics departments, right? And physics departments hire faculty members, and they don't hire them very often in theoretical physics. Maybe, you know, if you're lucky, once every five years, you're hiring a new faculty member. So are you going to intentionally hire a faculty member working on an idea you think is probably wrong? Even if it would be good for the field because it maintains diversity and keeps ideas alive, you yourself are not going to do that.

It's probably not good for your department. So there is an academic tendency to bet too much money on the leading horse, right? To be a little bit too conventional and conservative because you don't know what's going to turn out right. It's easier to go with what is in the mainstream. So that absolutely, I would argue, has the effect of cutting off alternatives. And so I think both that there are good substantive intellectual reasons to be skeptical of the alternatives and that we should nevertheless do a better job than we do of supporting some work on them. So practically speaking, how could we do, how could, how could that be achieved?

How should one allocate resources between different research programs in a data starved field? How could the minority? I don't know. I, that's a very good question. But since I'm not the Pope of physics, I don't have to answer it I mean, I think it's somehow I don't know fellowships prizes grant money. I really don't know Yeah, so if I see what you're saying, it's akin to saying Trees are all born of the same Birth they they're they're fragile sapling at first and maybe even a flimsy seedling and then if someone was to say there are no alternatives to string theory or at least none that are

as developed, well, how do we know? Because there could be saplings, but there's the tree of string theory, which is growing its leaves and then just preventing the growth of others because of however the academic system works. So is that a fair recapitulation or am I misguided? Yeah, no, I think that's basically on the right track. Yet another way I would put it is it's a game theory kind of thing. In many games, it turns out that the best strategy to use is what's called a mixed strategy. So in any particular case, you might think that there's one thing to do that is certainly the best thing to do.

But if you do that thing over and over again, people are going to figure out what you do and you are exploitable. So even though there is something that is the best thing to do, your best strategy is to do mostly that, but also some other things as well. I think that applies to, you know, keeping different fields alive within physics or within other academic areas It's so tricky because if you're someone like Roger Penrose and then you start to branch out in your later years. You have a Nobel Prize Then you're told you have Nobel's curse because now you're a bit too woo. It's a tough rope to walk Roger Penrose is a brilliant, brilliant mathematical physicist who's made absolutely

central contributions to the field. And as a result of that, ideas that he has that are not that promising actually get way more attention than they otherwise would. So I don't think that he gets any disadvantage from being a famous, respected, Nobel Prize winning physicist. I think that he gets any disadvantage from being a famous, respected Nobel Prize-winning physicist. I think that he gets a little bit more respect than the idea itself would if some nobody

who is a postdoc proposed exactly the same idea. I see, I see. Steven Wright, a comedian, said, someone asked me, can you tell me what time it is? And I said, yes, but not now. So what is your idea of the thick present? Good joke, good joke involving time. Now the thick present is an idea of some philosophers, I don't remember who right now, that time has an extension,

that show that it can be two events which are at the same time, but one is to the future of the other way around. So as a technical idea, it's clear when it's, it's to be subtle though, does it violate relativity? And I think it challenges relativity. What's the difference between contradicting relativity and challenging it?

Understanding something and not quite understanding it. Yeah, so There's something that you have invented called doubly special relativistic theory with some friends. Yes What is that and does that violate Lawrence? Um, it extends for instance The idea of doubly special relativity is that, well, let's go back to special relativity. In special relativity, we have one scale, one velocity, which is invariant. So when we travel, if we're traveling, you're going that way, I'm going this way. We have a relativity, Galilean relativity, whereby our length and time measurements change relative to each other. But in doubly special relativity, we impose the constraint that not only is the energy of some part of them,

we can transfer between your measurements and mine, and the transformation will be more complicated in such a way that there are two length scales, or one velocity and one energy, which mean value. So is another way of saying that that there's a universal cosmic speed limit, which all observers agree on, but then also a universal cosmic limit to the length, so the Planck length is somehow also fundamental?

Yes, although I'm trying to keep h-bar in the game. So I'm trying to, I want to pick whether it's an energy that's invariant or a length that's invariant. I don't want to assume that h bar equals one. What you would decide is that what's invariant is the ratio of what we usually call the Planck energy, to what we usually call the Planck energy to what we usually call the Planck length.

Why is it that you don't want to set h-bar to equal one? Is there something that you feel like is lost? Yes, because if we want to have a theory which explains h-bar, this can't be one in which h-bar equals one. Uh-huh. So what led you and your collaborators to develop this? Sabina Hassenfelder, to be short. We had a previous theory, which was doubly special relativity.

And we didn't understand it completely. And Sabina saw that there would have to be non-locality in some field theory if that theory was going to encompass doubly special relative. And so we then, and this was four of us, we were working together a couple of times a year at Lemur, and we realized more or less simultaneously

that the way to answer Sabina was to let simultaneity be relative and also let locality be relative. So whether some interaction took place locally or non-locally was dependent on whether you were close to the system being observed or far from it. Uh-huh. So what did Sabine say to the concept that locality itself is a relative concept? She didn't like it, and we continued to have disagreements.

I think she continues to disagree with us. And her disagreements are? Are that you can have a theory, now we call it theory with these amendments, we call it relative locality because that's a more precise description. Okay, speaking of what's relative, there's something called A and B series of times. I never remember which is which, but in one of them, the one says that relative time positions, so I talk about you yesterday or my future or the dog's past. And those are relative to the dog at some moment. The past of the dog is not the same as the whole future at another time.

And this is one view, that's okay. And the other view is the view that really there is no time, so that there is only, I think I'm saying it backwards, in the one view, let's call it the A view, although I'm not sure that this one's... Sure. You can be an observer to the future of another's world,

and we allow that that is we allow ourselves in the theory to discuss relative times as Realistic real things but relative to an observer If that makes no sense and is this related to your thick time or no, it needs thick time to make it consistent Have you heard of Nicholas? Kissens or Nicholas gissens? Oh sure sure well. What is his concept of thick time is it different? I don't think so, but I haven't said it is okay So explain to me why thick time need or why a or the B series needs thick time

Can we come back to that? Sure. Something that the viewers may notice by now, and I've already mentioned it in the introduction, is the movement. And you mentioned that you don't want to hide any of this. Well, it's would be hard to. Yeah, so can you explain?

What you're seeing is an overcompensation for Parkinson coming from taking a bit too much dopamine, which is, in the context of being interviewed, a good thing to do. Why? Because the other setting, it's a very quick transition. I think it is a phase transition. By the way, I'm doing some work on the brain and the regions of the brain which are relevant.

It seems to be that there is a phase where things seizure in the control of the brain, and a phase where things go uncontrollable nuts. Okay. And you want to be in a kind of critical state between them. Yes. And that's what the dopamine allows you to reach. Yeah. And so right now you're in the critical phase or you're pushed off to one of those directions? I'm in one way overcompensation. Oh, but does that mean that with time it will get better? Or with time it gets, okay, with time throughout this day, I mean? It's coming right up.

Oh, okay. And you'll see it happen because the critical phase, as in most physical systems that have a critical phase, is a cause of critical vibrations. So you'll see I'm making it happen, but you'll see half an hour from now my thing's going critical with critical scaling and then it'll be over. Does it just affect your physical body or does your... It affects everything.

Okay, how does your mental state or your state of consciousness affect it? It makes me... I don't have much of an executive function than it sounds to me. So that's the worst thing. I can overreact. Yeah. So why don't you talk about how you're how you studying physics, well, it's more like researching, researching physics has been impacted, your collaborations even.

It's more irregular. As working with my collaborators, I'm on more and we use the words on and off. So um, but I don't know. You have to ask them, although I don't know if I wanna know the answer. I'm glad to have still collaborated. When we talked, actually, we talked a couple of years ago on the phone briefly, I don't know if you recall,

but I was asking if you had taken a look at geometric unity because I was going to be interviewing you at that time and I was giving an overview of some of the questions and you mentioned Eric is a dear friend. Yes, he has to be. He's not your dear friend. He's not going to be your friend. Yeah. Okay.

So can you please talk to that and then also geometric unity? Well, his strength as a researcher is certainly his commitment and his…he's extremely smart, extremely quick, and he can go at something for years and years and years. And that's very important if you're trying to do original work in physics or anything. So I think. Is this quality of going forward on a single idea or a single theme for years rare? Yes.

So it seems like for me, when I was reading your work, and by the way, you don't know this, but so my background's in filmmaking, I was in math and physics and then I did a film. Okay. What was the film film is a dramedy? So comma dramedy called I'm okay. It's a heavily Toronto based film. Oh, so I may know people them Yeah, cuz I know a lot of something. Yeah So when I was filming it and I had the cinematographer in my car and the sound Recordist in the car, we would be listening

to your book. Oh, wow. Yeah, one of them, one or two of them during the filming of it. Anyhow, that was a fun experience because they would ask me what's a Collie Vial manifold? They wouldn't pronounce it like that, but they would say, so what is that? And why does that have anything to do with background independence? And why does background independence matter? Why does that have anything to do with background independence? And why does background independence matter? Why does gravity have anything to do with curvature?

Curvature of what? Space? No, not curvature of space. Curvature of space-time, which is different than space. Anyhow, this interview itself, just meeting you, it's a dream. I would be listening to you in the car. I had no idea that I could ever not only see you in person, but shake your hand and speak to you like this. So thank you. You're welcome. But that's, that's extraordinary to me because I just, you know, I just live

here and I don't feel very well, the Parkinson's has a way of leveling things. I would say everything is now in question, every interview, every talk is every people is a experience sort of on the edge. Meaning that you don't. I don't, I don't dress down reputation, I can't. But the work that I'm working on now is my favorite work. It's very that I'm working on now is my favorite work. It's very, I'm very impressed with it, which is a funny thing to say, that you're impressed

with your work. And that work is, why don't we just briefly outline it now, we can come back to it later. Well that's 10 years ago, what we're talking about. The work that you're working on now is what? Is, well, why not? I'll tell you before it's in the published paper. But what I've been working on, broadly speaking, is extending the notions of time as real and, well, first time a realist.

So let's get that out of the way. OK. real and, well first time a realist, so let's get that out of the way. Okay. I'm not, I don't believe, I'm not interested in physics, which is, there is realistic people and there are people who make physics too. Subjective? Almost subjective.

Like Bayesian. Yes But Bayesian is the mathematical realization of this idea. Okay, so you're not a Bayesian. I'm certainly not a Bayesian Oh, I'm a good old-fashioned. We love us. I believe this there is a way that the world is and I'm interested in knowing what that is Realism to most people means something's external and objective. Is that what you mean? Yes. But at the same time, I believe that the world has to be understood in a language of what observancy.

But it's very important that, to me, that there are many observers. And so you, Einstein allows you to just have an observer and another observer and talk about their relations between what they see. Einstein is a realist, but he is using the methods of this thing that we can't understand. We can't remember the name of it. So it sounds like there are objective and subjective elements, and what you're saying is that there are some people who believe there are only subjective elements,

and you're not one of those. No, I'm saying that we can, we can talk about and record and work with other people's observations as well as your own observations, and they're all real to you. And this is just a word, which is, it's what Lucian always calls himself, Lucian Hardy. Lucian Hardy?

Lucian Hardy. Yeah, yeah, yeah. Okay. What does real mean in this instance? Because you said it was real to you, which to me sounds subjective. Yes, that's unfortunate. Real means that it's uninterested in what makes up the world and what the world is.

I believe that if you took me out of the world, it would still be the same. But you still have, can make interesting transformations between what one observer will see and describe and what another observer will see and describe. I see. Sabina's one, I'm a recent strong, strong fan of Sabina. Okay.

Sabrina, and one of the things that she likes to say is that every problem in physics is a translation problem. That is, the argument between string people and loop people, which unbelievably we still have going on, is a translation problem for her. There's a difference between a field and a particle. A quantum field is the analog of, let's say, electromagnetic fields.

These are, the way they were initially conceived as a function of space and time, which has some value everywhere in space and time. Okay, that's a field. Like an electric field has some value at any particular point in space and at any time, moment of time. What was discovered by Einstein and others is that you can quantize these fields and so the excitations of a field come in packets or quanta called photons or gluons or weak bosons. So this idea of quantum

field theory is a combination of quantum theory and classical theory of fields. And so traditionally what people have done is describe the quanta and their interactions. Now, there is a sort of very fundamental problem lying at the root of coupling particle physics and the standard model to gravity. And the problem is so extreme that it's usually ignored. Okay. This problem was known about for at least 60 years.

It's been well known about probably 70 years, but it was, uh, it's so extreme that people have grown used to ignoring it. The problem is the following. When you have a field, right? Some function that takes values everywhere in space and and you quantize it so that its excitations come in packets of energy, you find that the field, when quantized, is actually fluctuating in the vacuum. So the vacuum is not empty at all.

The vacuum is full of these, what are called zero-point fluctuations of the field. And so people understood this, you know, going back to the 1940s, 1950s, that every possible excitation of the field is actually sitting there in the vacuum and sort of jangling away. The problem is that if you add up the energy of all these zero-point fluctuations, it is infinite. And bosons, like the force-carrying particles or the Higgs field, a Higgs particle, bosons contribute positively to the vacuum energy and fermions like the electrons or neutrinos or quarks contribute negatively. In each case, whatever field you add, you get an infinite contribution to the vacuum

energy. Because there are more fermions than bosons in the standard model, actually you get negative infinity vacuum energy. Now, this is fine if you don't include gravity, because the total energy in the vacuum, it doesn't matter. It's conserved, and when I do an experiment, I have some vacuum coming in and vacuum, it doesn't matter. It's conserved and when I do an experiment, you know, I have some vacuum coming in and vacuum going out. So the difference energy is conserved to all I see is the extra energy which I added in the difference. So you're not sensitive to the absolute value of

the energy until you add gravity. When you add gravity, gravity responds to the total energy. That's actually why cosmology was used to find the cosmological constant, which is the energy in the vacuum. The way we found it is by looking at the total energy in the largest possible volume we can see so that it's as big as possible, and measuring its energy and what we found is that the energy is there and it's changing the expansion of the universe. So that's how the vacuum energy has been measured is actually by using its influence on gravity.

So but the trouble is that the vacuum energy we measure or call the cosmological constant is really small. It's not zero, it's positive and small, but certainly not infinite. If it were infinite, cosmology would make no sense at all. You try and write down Einstein's equations, you find the universe would re-collapse in a plank time. It's just ridiculous. So what have people done?

There was this terrible problem staring us in the face ever since the 40s that coupling quantum fields to gravity makes no sense. You're just trying to put an infinity into the Einstein equations and not surprisingly you'll get garbage. So what has been done is to invoke a technique called renormalization, which is basically a way to cancel infinities and using renormalization you essentially could find a fancy mathematical way of ignoring this infinity.

Unfortunately, this process leaves you with very little understanding of what's actually going on in the vacuum because you've just subtracted it away. There are other problems. The same renormalization process turns out to spoil the basic symmetries in the standard model. One of the basic symmetries,

say in Maxwell theory of electromagnetism, is scale symmetry. In Maxwell theory, an X-ray, a short wavelength wave is exactly the same as a light wave or a radio wave, which are longer and longer wavelength waves, because the whole theory is invariant under changing scale. So in a sense,

it's nothing really fundamental that distinguishes an X-ray from a light wave, from a radio wave. They're just scaled up and down versions of the same thing. That's a very profound symmetry, wave from a radio wave, they're just scaled up and down versions of the same thing. That's a very profound symmetry, which Maxwell's theory respects. And turns out Dirac's theory of fermions has the same symmetry. And these symmetries are really important for the sort of internal consistency of the theory. Well, Dirac's only if it's free and massless.

Exactly. Absolutely right. So Maxwell's theory does describe massless radiation. Dirac's theory, you insert a mass for the electron. But when you ask, where does that mass come from? It actually is not allowed in the standard model if the full symmetry is realized, if the gauge symmetry is realized. Also doesn't allow mass terms.

The way you get mass terms is by adding the Higgs boson, which breaks the symmetry and introduces a scale. So these masses arise, as far as we understand, by breaking symmetries. So it seems that the way the laws of nature work is they have some underlying, you know, very powerful, very fundamental symmetries, and then physics comes along on top of that and breaks those

symmetries so that at low energies we don't see all those symmetries revealed. Now the reason I'm so interested in the scale symmetry of Maxwell and Dirac for massless particles is if you want to understand the Big Bang singularity, which I do, what happens there is that the size of the universe went to zero, and that makes no sense, okay? Unless the part, all of the fields and particles in the universe actually do not care what the size is. You see, because if the photons actually do not

are insensitive to the size, they don't even know if the universe expanding or contracting, and this is true in Maxwell's theory. You can predict a photon without knowing anything about the expansion or contraction of the universe. You can predict how a Maxwell wave evolves. It doesn't care about the size of the universe. Likewise, Dirac, if it's massless.

So in the very early Big Bang, when everything was effectively massless, the natural way to make sense of the singularity, I think it's probably the only way, is if all the material in the universe actually is completely insensitive to the size of the universe. Then you say, well, it looks like space was shrinking to a point,

but actually from the point of view of all the material in the universe, it didn't see that. The universe is perfectly finite and the material in the universe is evolving smoothly all the way to what we call the singularity. So in other words, the singularity is just a result of a poor description being applied to a phenomenon that inherently doesn't care about the size. So a question that may be in the audience's mind is it's relatively straightforward to

see the difference between something that's this size and this size and being scale invariant. Okay. Right. But then that's for something non-zero. So as soon as you get zero, why doesn't it just yield a trivial equation like zero equals zero? So, in physics we are very used to the idea that the coordinates you use to describe something can be singular.

So let's imagine I'm trying to describe the surface of a sphere, like make a map of the earth. the surface of a sphere, like make a map of the Earth. So I can use polar angle, or we call this, yeah, the polar angle, sometimes called theta in 3D geometry, and azimuthal angle called phi. Now, if I go to the North Pole, where theta is zero, the azimuthal angle is zero, the polar angle is zero, then the same point,

the North Pole is described by the azimuthal angle going from zero to two pi. So it's weird that you have many, it's multi-valued. So basically this whole coordinate system is failing at the North and the South Pole. And we know that very well when you make a map, if you try to make a map of the North Pole, you know, and you try to tell somebody,

you know, what latitude are you at, it's just ill-defined at the North Pole. So we're very familiar with the idea that in physics, your choice of coordinates can sometimes be singular. The way around that is to choose some new set of coordinates that are not singular. If I just put a square grid over the North Pole, I would have X and Y,

and there would be no problem at all. I could tell you exactly which point had which value, and for each choice of x and y, there would be one and only one point. There would be a non-singular coordinate system. In physics, we're very used to the fact, and Einstein's theory of gravity, this is particularly true, that very frequently what looks singular in one coordinate system is actually completely non-singular in another coordinate system. So in the first coordinates people solved black holes in called Schwarzschild coordinates. When you fall into a black hole,

as you cross the event horizon, the metric on spacetime is infinite in Schwarzschild coordinates. But then much later, people discovered coordinates that are completely well-behaved as you cross the event horizon. These are called Kruskal coordinates, for example. And so you realize that what looked singular was just an artifact of a poor choice of mathematical variables.

So in the case of the whole universe shrinking to a point, you see if your fundamental theory is actually insensitive to the size of the universe, then you are absolutely free to blow up the size of the universe by any amount you like, and it doesn't change any of the physics. So what you do is you design a blowing up so that when I'm shrinking towards zero, I'm actually also blowing up the scale in just such a way that when I hit the big bang singularity, the sizes are all finite and you can do that. Uh, and actually that was our very first discovery is that if you solve the

Einstein equations for a universe full of radiation, which is what we believe dominated the hot big bang, the solution is actually regular at time zero at the so-called singularity. The Einstein equations do not see any problem at t equals zero. And this was a big surprise. So people had all assumed that this t equals zero, when the whole universe was zero, that somehow the Einstein equations were singular. They didn't make any sense. Actually we found you can just follow it right through t equals zero. And the solution on the other side is unique.

And that's actually how we came up with the concept of a mirror. We just followed the generic solution of the Einstein equations back to t equals zero and out the other side, and we found there is a generic class of solutions which are completely well-defined and just evolve through that. So now we found a sort of doubled universe in which before the Big Bang is classically identical to what's after the Big Bang. So what we found solving the equations is a mirror universe on the other side of the Big Bang.

What we then did is we elevated this into a principle. We said, okay, maybe the right way to describe the Big Bang is to use what's called the method of images. All right, so the method of images, so imagine I'm trying to solve Maxwell's equations in the presence of a mirror. There are two ways to do it. One is I evolve these waves forward to the mirror and then at the mirror I impose some special boundary condition which forces the parallel electric field

to be zero for example and I will find those boundary conditions cause the wave to reflect. That's one way to do it. It's rather ugly. The elegant way to solve Maxwell's equations with a mirror is if I'm right-handed, I make a mirror image of myself which is left-handed and put it behind the mirror. So I literally mirror reflect myself, put my image behind the mirror, and then I just solve Maxwell's equations as if there were no mirror. And that's what I'll see.

That's what I'll see. That's exactly what I'll see. So this is called the method of images. You make a mirror image and you solve the equations. So what we realized is we can do this in cosmology. We can take the late universe, make a mirror copy of it before the Big Bang, and then we're able to solve the Einstein equations all the way through the so-called Big Bang singularity,

and actually the solutions are completely well-behaved. The mirror image isn't real. The mirror image is just a trick for imposing a certain boundary condition at the Big Bang. So if you talk about this as a sort of mirror universe, it's really legitimate to think about this as a one-sided universe with a mirror at the beginning. But that mirror, the kind of implementation of what that mirror does is most easily done by reflecting our universe before the Big Bang and then just solving the equations as

if there were no mirror. Okay, so let's get to this talk, man. Okay, All right. So, um, going back to what we covered, uh, the most straightforward path forward, uh, for achieving a theory of everything that has, I think a decent chance of success is a fairly simple minded progression of unification of embedding groups and their collections of representation spaces that we know of into larger groups and representation spaces. And ultimately if you can get everything

into one you've ultimately succeeded and said nature is just one thing that symmetry breaks down to everything we see. All right, I should mention all the various criticisms of this. The most successful node example of this is the SO10 Grand Unified Theory, which I figured out in 76 or so. And it just turns out to be a pretty wild, you know, one in a hundred coincidence that the hyper charges of the known fermion multiplets represented over here happen to all combine successfully into a 16 dimensional spinner representation of spin 10 and and this is why the the SO10 gut is considered so nice And this is why the SO10 gut is considered so nice,

but a lot of people hate it. Peter White hates it because you still have the complexity now of figuring out how nature does a symmetry breaking from this to this. Okay, so that says, okay, well, you have this very simple thing, but if you're starting with a simple thing, now you have to break it to get what we know. So there are various mechanisms for that

Also, there's an experimental reason you have new gauge whenever you do unification you end up with new fields That give you new interactions and for SO10 the new interactions give you the possibility for protons to decay Which we don't have in the standard model so there are large experiments looking for protons decay and they've never been seen and model. So there are large experiments looking for protons decay and they've never been seen. And that hasn't ruled out SO10, but it makes it less and less likely, the further and further they push the sensitivity of their detectors. Okay, there are a bunch of people like me, just like holding out. It's like, ah, maybe someday a proton will decay and we'll see it, you know, but maybe it's just not true. Maybe it's there's some other structure. Maybe cuts are just wrong. Well, couldn't the probability just be so low?

Is there constraint in the probability for SO10? Whenever you do symmetry breaking, you have all these parameters. At some point, you can always add more parameters with more massive particles that make it less and less likely to decay. But the thing is, and strength theorists got themselves into this position too. They keep adding more and more levels of complication to explain why don't you see super particles.

Supersymmetry is an intrinsic characteristic of super strength theory. And also they said supersymmetry would let you solve the, give you some cancellations you need for the Higgs particle to break symmetry and give masses away it does. They thought super symmetry would help in that,

but only a super partners had a certain masses, a certain mass. And they did not see super partners with those masses at the LHC. I mean, I visited the LHC It was like they had a giant banner across the top saying welcome home super particles You know waiting for him to come in, but they never showed up They didn't show up to the party because maybe they don't exist

So but you can't extricate super symmetry from string theory happily So what they do is they just add more and more parameters to make those masses higher. So it's like, oh yeah, we'll just never see them. It's like, yeah, it keeps straining credulity when you do that. So it's just a matter of like, how much are you willing to believe in these theories? The third criticism of these sorts of unified theories is part of their motivation is because they're very mathematically beautiful, right? These structures, the exceptional lead groups, when you investigate their structure, they're the most exquisitely beautiful objects in mathematics. Okay, and I'm not saying that lightly and I'm not throwing one into the face of this.

They're just extraordinarily beautiful geometric objects. And the possibility that our universe is embedded and ultimately comes from the symmetry breaking of the most beautiful object in mathematics. That's inspiring, but not for some people. If you're Sabina Hassenwalder, she says this sort of mathematical beauty is completely misleading and will never get us anywhere. It's a matter of taste. I suspect maybe Germans just don't like things that are pretty. They like things that work. I don't know, it's a matter of taste. Well, is there anyone other than her?

Yeah, many people share that view. It's a very pragmatic view, and it also goes hand in hand with why do you assume that there is this more beautiful structure when you don't have evidence for support it, and it predicts particles you haven't seen, and you don't know how to break this beautiful thing down to what we get. Okay, those are all very reasonable concerns.

But Sabina wrote a very good book on, you know, as beauty led physics astray. And I think she was mostly talking about what string theory is considered the mathematical beauty of their theories, but she was also talking about grand unified theory, including this one. So it's a valid criticism and from a pragmatism point of view, it's valid. But from a philosophical point of view, I find it very satisfying that our universe might be special. Yeah, it's always nice to be special. Now, Garrett, for the people who skipped forward, they listened in the beginning, but now they're

here. And they heard you speak at length about the value of spinners and their geometry and so on. Where here in this mess of numbers and letters is a spinner? Like sure, we have the word fermion. So this is a complex two-dimensional spin representation space of SL2C, the special linear group, two-dimensional complex matrices. What is the relationship between a fermion and a spinner? Is every fermion an example of a spinner? Do spinners have fermions in them? Is a spinner tensored with quantum numbers the same as a fermion? Like tell them what is the relationship because they're used often interchangeably by physicists.

In the standard model as it's usually presented, a fermion which is a physical particle like an electron like an electron. It corresponds to a representation space. Well, let me let me add some steps. A physical fermion like an electron corresponds to a field. That field is valued in a representation space and that representation space is called the spinner representation space. And a a representation space and that representation space is called the spinner representation space and a spinner representation space is acted on by rotations in a different way than vectors are so vectors also representation space of rotations okay spinners are different representation space of rotations for example you have to rotate a spinner, not 360, but 720 degrees in order to return it to its original state.

In an abstract space. It's an abstract space. It has a very physical implementation as electrons. Yes. Yeah. So it's more than just an abstract space. Also, when you ask them, these things have an intrinsic angular momentum So it's not like an electron is spinning around in a circle. It's like the electron field itself has angular momentum

Yes, okay Which is strange Also the fields themselves Also, the fields themselves anti-commute, which means if you're operating with them and one goes past another, it changes sign to minus. So they're anti-commuting fields. They're anti-commuting spinner-valued fields.

That's the best way to describe a freon. And then we go to quantum field theory, and these things are quantized excitations of these fields. Yes. Okay, and then that's how we do quantum field theory. But structurally, mathematically, you can think of them as electrons correspond to states. So say you have an electron that has, that's spinning around this way with spin up and it's traveling along the z-axis, then that's a spin up electron.

Let's presume for a second it's massless, then you would say this thing is entirely right-handed if it's not interacting with the Higgs. Because if you're interacting with the Higgs, then electrons bounce back and forth between the right and left-handed parts. But or say if it's a massless neutrino, and then you're talking about right-handed neutrinos, which I also think exists. But anyway, so you have a spin, you have a direction of motion along or counter to the spin that determines whether it's right-handed or whether it's left-handed.

Yes. See, this is going this way and this is going that way. So the spin direction is the same, but here my thumb's in the direction of the spin and here my thumb is opposite the spin. So this one is right handed and this one is left handed. So spinners have this chirality aspect to them and they have spin, spin up or spin down which corresponds to angular momentum. But they're also complex.

If you're a complex drag spinner also has a complex conjugate. And those roughly correspond to particles and antiparticles. So all this mathematical structure lives in a representation space. For spinners, that's acted on by spin 1, 3, which is identical to SL2C. Maybe I should have put SO1, 3 or something here. But that SO1 SO13 in a gravitational grand unified theory combines with SO10 into SO113 and

the spinors and this entire Multiplit of fermions, okay, this is all electrons neutrinos and quarks of one generation all fits now in a 64 spinner, real spinner, of SO11-3. And this is a really wonderful unification. Okay? It's very succinct and it includes gravity and gauge fields. Now there are a lot of people that say this sort of unification should not be allowed.

And that comes down to the Coleman-Mendulo theorem, which says if you think about the S matrix for scattering in spacetime and how this works with gravity and gauge fields, then gravity and gauge fields cannot be unified into a larger and larger group. The response to that is to say, if this is a unifying group, right, unifying gravity and gauge fields, you don't have an S matrix here because you don't have space time yet. In order to get space time, you have to break this symmetry and out of it you get space time which is this four here. So this four is the gravitational frame which is acted on by SO and three and this ten is a Higgs multiplet that's acted on by SO and 3 in this 10 is a Higgs multiplet that's

acted on by SO 10 and space-time has to do with this 4 right here, these four dimensions of space-time. After the symmetry breaking happens then you have space-time then you have particle scattering and so forth and then you can apply the Coulomb-Mendoula theorem and say lo and behold the gravitational and the gauge fields are not unified. That is the case over here. Okay. But here, if you're thinking about a unified theory that hasn't broken yet, so it doesn't have even the existence of space-time yet because it's all been unified, then there is no scattering to think about. You can't apply the Cohn-Mendoula theorem because the conditions of the theorem aren't met. Okay, symmetry breaking has to happen

and then the theorem applies. So this is a perfectly fine, perfectly reasonable structural unification and it's a very pretty one. And something especially pretty about it is that this unification then fits in a specific compact real form of the E8 Lie group. The problem is there's a whole bunch of other stuff in here, okay, and some of the other stuff is what is called mirror matter, which is which are like the standard model,

yeah, it's like the standard model fermions, but it has the opposite chirality, it has the opposite handedness, and we don't see these particles in nature. So this is the criticism that Jacques Dissler and Skip Garibaldi used to say this can't work. You can't get the standard model fermions out of E8 because you also have mirror matter. They didn't call it that and they never admitted that this does embed in E8, which it does. It was very annoying to talk with them and I mostly try to maintain my mental health by not.

But that was a criticism. And this is what killed interest in E8 theory, is it has extra stuff that we don't see. So the task then is to understand. So there's specifically, as well as the 64S plus, there's a 64S minus in E8. That's the mirror matter. And we don't see those 64s. But I'm like maybe there's a symmetry that will transform between this 64 that we know

physically as one generation of fermions and that other 64 that usually you identify as mirror matter could be a transformation of one generation and then there's another 64 in SO12-4 that could be another 64, but it's vectorial. It's not even spinorial. Is that the torch that you want passed on most, the conformal cyclic cosmology? Well, I have a trouble because there's more than one thing. One of the things is Twister theory and its progeny, there's been a conference, you see, this is taken seriously in the sense that there has been a conference going on

all about Twister theory, not just a conference, but a whole, I think, term, whole term, I think, dedicated to the subject of Twister theory, which is something which I sort of started in 1963, I think it was, And it's had many developments and many offspring, you might say. And it's spread out to have interests in different areas. Now, it's one of the things that I've been working on for most of my life. And I can't explain it without being a little technical.

It's just that... You can feel free to be technical on this podcast. Okay. It's a bit like... Well, Emerson discovered quaternions, which was a way of talking about the geometry of three-space. And he introduced this thing called the vector product, which if you have two vectors, well it's really an algebra of vectors, where you have vectors and scalars mixed together, and if you multiply two vectors, you have this thing called a cross product, which gives you a third vector. Now this kind of notion is coming in at a different level with what I call twisters,

or now what I call bitwisters. See, the twisters, the subject took ages to develop. As I said, in 1963, when I first had the concept, which… So I gave a talk in Cambridge just recently where I explained the origin of the ideas, and there was a certain, you might call it, slight misconception. There are two different concepts which get confused in Twister theory, and these two concepts are positive and negative frequency and positive and negative helicity. And the thing is that the positive negative frequency idea

was something that I learned from Engelbert Schucking, who was somebody I shared an office with when I was in a group of people working on general relativity in Syracuse, New York State, in the United States. And there were a lot of people working on relativity theory there, and this is, I think, in 1962. And I learned from Engelbert Schucking two things which I found very interesting.

One of them was this question of what you mean by what's important in quantum field theory. And he said the most important thing in quantum field theory is the splitting of field amplitudes into their most positive and negative frequency parts. You keep the positive frequency and you throw away the negative frequency. And I thought, gosh, that's an interesting idea. The other thing he told me was, and he told me various things, but these were the things of relevance to what I'm saying. The other thing he said was to do with the Maxwell field equations. Maxwell's equations, which are very important, they describe electricity, magnetism, and light. So it's a theory of light as well as how electric

and magnetic fields interrelate to each other. Very beautiful equations, which I learnt about when I was a graduate student. And I was very keen on the Maxwell equations, especially when you write them in this formalism called two-spinner formalism, which I can say a bit more about later. But the Maxwell equations, he told me they are conformally invariant. So they only depend on spacetime structure independent of the scaling. So if you magnify the scale up or down, magnify the metric up or down, if you like, it makes no difference. That's conformally equivalent. So the conformal maps are ones, or the conformal transformations are ones which can change the scale, but they don't change the,

well they don't change the light cones in special relativity terms. So the speed of light is the same. Of course, light after all, the speed of light is the same when you magnify and It's a bit of like just the same when you magnify and change the scale. But what struck me about this, these two facts that I learned from it, is there seemed to be a little of an impasse between the two. I mean, how do you decide what's splitting the positive and negative frequencies? You look at the individual frequencies, which means you do a Fourier decomposition, and you take each individual Fourier component and you split that into its positive and negative parts. That's not conformally invariant. You do a

conformal map, conformal rescaling, the Fourier decomposition just not go into itself. And so I thought it would be lovely to have a way of looking at this, which is they come together and you don't have this sort of impasse between the two. Well, I was aware, I don't know whether I was told or I thought about it myself, I was aware of the fact that if you take the field of complex numbers, fold them up into a sphere, so you've got a point at infinity as well, and you take the real numbers and think of that as the equator. So the real numbers go around the equator, and the complex numbers go up and down.

And if you have a function which is defined on the equator, which extends into one hemisphere, that's positive frequency. It extends into the other hemisphere, it's negative frequency. This is a completely conformally invariant description. You conformally invariant the sphere and it doesn't change the splitting into two halves. So I wanted a way of doing this, but globally for spacetime. So for the whole spacetime, I wanted it to be somehow that the real spacetime is the boundary between two extensions into the complex. But if you just complexify spacetime, make all your coordinates complex, you get an eight-dimensional space. It's not a five-dimensional space.

That's no good. It doesn't split it into two halves at all. You get a thing called the forward tube, which is a little tiny thing at one side or the other, in which you can talk about things being regular there or not. But it doesn't split anything in half in the same sort of way. So it didn't satisfy me. I don't know why. I mean, what was I doing? It didn't seem to have any rational reason for looking at this.

It did seem to me there ought to be a way of exploiting this beautiful way in which you do the positive and negative frequency without having to look at the Fourier components individually. It's a deeper concept, if you like, and it's also a conformally invariant of a scale business that Maxwell theory has. You don't lose that. Okay, well, I had this sort of going around in my mind and didn't know what to do about it. It was a very unfortunate occasion It was a very unfortunate occasion because I was in Austin, Texas, and I was working with various colleagues in Austin, Texas. Engelbert Schucking was running this particular meeting. It was a year-long meeting where people like Roy Kerr, Ray Sachs were there too, and very

distinguished people working on relativity theory. And there were also people in Dallas, Texas, and one of them in particular was somebody I was collaborating on a book, I think I was doing it at that time, on spinners, and this was Wolfgang Rinder. And Ivo Robinson, he was somebody who was a very clever fellow, had wonderful ideas. He never wrote anything down. He relied on getting a co-author to write the paper. It was all done with words.

He had a wonderful way with words. The Americans loved him because he spoke in this way that they weren't used to, which the words all fit together in this beautiful way. Yes, he did have a wonderful way with words, there's no doubt about it. Was he the one that didn't write papers? Yes. But he was important in another story, which is a different story, my story, namely the singularity theorem, because that was walking down the streets and crossing the

road. That's a different story. It was the same person. That was Eival Robinson. Yes. So he obviously was somebody who could take my attention. But what he had told me about was he'd found some solutions of Maxwell's equations, which had a very special character. They're what are called null. They have point in one direction, you see. Usually there you have these two directions, which are called principal null directions, on the light cone. They're light directions.

And if they coincide, it's what's called null. And these are more like radiation fields. And he found a beautiful family of solutions, which he constructed in the following strange way. You take a light ray, one light ray, and you take all the light rays which meet it. When I say a light ray, I mean the trajectory of a photon. So in space-time, it's the space-time picture of a photon, as thought of as a particle. Now, if you think of one light ray and you look at all the light rays which meet it coming in, then you have a family of light rays. And then you construct the solution which is based on those light rays. Now, they have this awkward singularity, which is the light ray that they meet. Why is that a singularity?

Well, they all start coming together and so the nature of the solution is different when they come together. Okay, but it's of a different sort of singularity than the singularity theory. It's not a serious singularity, it's a singularity in the Maxwell. I think things become infinite. I see. I don't remember the details of it. Sure.

They just become infinite on that solution. Just because the light rays don't make this nice family anymore, they got crunched up on the other light ray. But what Ivor Robinson did, he had this clever trick, where you just place the light ray into the complex, make it a complex light ray, then you can keep the light rays which meet it, there's a family which is still real. So you can see those real ones, even though the one they meet is in the complex. And they twist around each other in this wonderful configuration. I thought about this before and I think I knew in detail what this configuration was. It corresponds to what's called Clifford parallels. Clifford

parallels are a beautiful geometrical configuration. If you take a three-sphere, so that's an ordinary sphere, but in four dimensions. So it's a three-dimensional surface in four dimensions. So it's a family of points which have the same distance from the origin in four Euclidean dimensions. I'm not talking about space-time now. That four Euclidean dimensions. I'm not talking about space-time now. That four Euclidean dimensions. So you have a three-sphere and there's this beautiful family of circles which fill the whole three-sphere. No two of them intersect and they all link each other. It's

called Clifford parallels. It has a name which the topological people like better. Well, it's called the fibrations. And it's a sphere's worth of circles. It's a very nice example of a fiber bundle and how you have this diagram that people like to draw where you have the fiber, which is the circle, and the bundle, the entire bundle is the sphere, and the projection down is the two spheres. So each circle corresponds to a point on a two-dimensional, an ordinary two-sphere, an ordinary sphere. So the points, each point corresponds to a circle. So it's a beautiful example of a fiber bundle. It's the most simple and beautiful example you can have in a way.

I was well aware of it. I just liked the geometry. I found it was really elegant. And it's the same kind of thing you get with these, except that now you're talking about light rays. So if you think of the light rays, which are quite the easiest way to each point of the Clifford 3-stair corresponds to a light ray, and the whole family of them twists around in this complicated way. So I was familiar with this configuration, and that this was a sort of way of thinking about

a complex light ray. You push it into the complex and you get this real description of it, which somehow feels out this complex light ray, but only in this real configuration that you can visualize. So I found this very beautiful. Now, is this any use to me? Well, the occasion that I'm talking about here was a particular occasion, was maybe in a sense the most significant thought which I had had, which was, well, there was an event, you see, a very unfortunate

event when Kennedy was assassinated. And this was in 1963, and it was in Dallas. And my Dallas colleagues, including Wolfgang Rinder and Ivor Robinson and other people there, and Pitchtah Oschvart was there, and they were at a dinner. And Kennedy was supposed to go and give a talk at this dinner. And he was awfully late, and they sort of joked that maybe somebody shot him. Somebody had shot him.

And they came, and it was a way of… So that was when they came. It was just about a week later, I think, when we decided to go to southern Texas, to go to a nice place where there was a beach and people could relax and try and recover from this awful occasion. And, uh... And do some math? So we went down there.

I didn't think we talked much math. I don't remember. But I remember coming back and most of the people wanted to talk gossip with each other, including my then wife. They really wanted to gossip. I wasn't interested in the gossip. I wasn't interested in the gossip. I just wanted some peace. And I was the one who was committed, more or less committed, to be in the car driven by Piszczak-Oschwart. Now the thing about Piszczak-Oschwart, he

was a Hungarian who did speak English, but he didn't like to speak, even in Hungarian, I think. He didn't like speaking. He was a silent person. Okay, so he was the Hungarian Dirac. Yes, but he was definitely, he could speak English with a strong Hungarian accent, of course. And he was the driver of the car when I came. And so this was very nice for me because I didn't have to make up conversation to speak to him. He preferred not to have conversation. So I think to myself, I knew about this Robinson-Conglinson's rays, which sort of describe a light ray, which has been displaced in this way.

And I said, the thing to do is to count, and I thought I didn't say anything, to count the number of degrees of freedom this configuration has. How much freedom does it have? And I counted them and it has six degrees of freedom. And that's significant because? Yes, this is very significant because light rays themselves have five degrees of freedom. So it's only one. You make your light ray complex in this sense, and you only drop your dimensionality by one.

It's not really what you do if you're complex around light. We have five complex dimensions. No, no. This only drops it by one. Why is that so important to me? Because this gives me a picture. The light rays themselves are represented by points on this five-dimensional boundary, and the Robinson congruences, as I call them, these twisting congruences of light rays, represent the points. If they go right-handed, they're one side, and if they go left-handed, they're the other side. This is the splitting of the space into two halves, just what I was looking for. Only it does it globally

for the whole of space-time. Don't think of points, think of light rays. And then the complex ones, in this strange, contorted sense, are only one more dimension. So that was the origin of Twister theory. I went back, got back much earlier than anybody else, because they were still gossiping, I guess. And I went to the black, I had a blackboard there, and I worked it out in terms of two component spinners. And it worked beautifully. And this was, this was Tristus. You take two, two component spinners, the way you can think of it, see a two component spinners, spin it ordinarily, points along the line, it way you can think of it. See, a two-component spinner ordinarily points along the light cone.

It has a null vector associated with it. And that null vector points along the light cone. In addition, there's a little flag plane. And the flag plane tells you its phase. So the length of a, not the length, but the sort of extent of the light ray, the extent of the null vector gives you one scale, and the other scale is the phase, which is the little flag plane. So you have this nice geometrical way,

apart from the sign, which you have to add in addition. You've got the nice way of describing two-component spinors. So I was well familiar with that. So the thing about the twisters, as you can think of the light ray, where does it hit the light cone of the origin at some point? And then you look at the light ray going up, it hits that point. That's a thing I called omega. I didn't call it omega at the time, but it's to do with angular momentum, really. It's the moment of the light ray about the origin. And the other is pi, that's the momentum of the photon. So you've got the momentum and the moment, and the two two-component spinors, they give you a four-dimensional entity, this was

a twister. So that was the origin of twister theory. And so you can see what's happening here is that the quantum state is collapsing. It starts off in the plus state, like a Stern-Gerlach, right? So in the Stern-Gerlach, if it's spin is in one direction, the particle moves in one direction. If the spin is in the other direction, the particle moves,

gets a force in the opposite direction. And if we observe this particle, if we observe it having a force in one direction, we will know that it's the zero state. If on the other hand, we observe that this particle moves in the other direction, then we will know that it's the one state. So by observing this classical particle, we in some sense learn whether this quantum system is in the zero state or the one state. So I want to write down what the full interaction looks like.

Oh, just a moment. Sorry. What is the collapse here? The observation collapses it? Yeah, so exactly. Good. Good. So what is doing the observation? Well, it's the classical particle that's doing the observation. The classical particle moves, gets a force in one direction or a force in the other. Based on that, we will learn whether this two-level system is a zero or a one. Because the system is classical, another observer could measure it to arbitrary accuracy

at any point. So we can imagine that an observer looks at this classical particle and tries to see if the force is in one direction or the other direction. And if the force is in one direction, that they will then know that the quantum system is a zero. And if it moves in the other direction, they'll know that the quantum system is in one. So we can imagine that there's an observer who measures the classical particle, but we can also just imagine that it's the classical particle itself that is causing the spin to go from the plus state to the zero state or the one state. So this is why I said that the measurement postulate isn't needed. This dynamics automatically gives the result that if I have an initial superposition, it'll go to the zero state or the one state,

and with a probability given by the Born rule, which is the modulus of the wave function squared. Okay. So the measurement postulate gets replaced with an interaction postulate or no? That's right, or just the the measurement postulate gets replaced with the following postulate. There exists a class school, a genuinely classical system, which maybe I want to take to be the experimenter, maybe I want to take it to be space-time, but if there's a genuinely classical system then it will automatically cause, and there's an interaction, then it will automatically force quantum systems to collapse. Got it.

And so here we have an example of the evolution. You can see that it looks very familiar. So we have the evolution of this joint classical quantum state row hat. We have the ordinary Heisenberg commutation relation which gives the evolution of the quantum state. And now instead of having, so previously we had this Poisson bracket and now we have something called the Alexandrov bracket which is, it looks like a Poisson bracket

but it has an operator ordering ambiguity, and so we take H on the left and H on the right. So this is this Alexandrov bracket. In the example of this particular interaction, which is this magnetic field D1Q sigma, then it looks like this. It essentially gives you motion, acceleration in one direction or acceleration in the other direction depending on the value of the spin operator. Okay, so if the spin operator is up, then it will give you momentum in one direction. If the spin is down, it will give you force in the other direction. There are two additional terms.

There's the terms that roughly speaking are the usual Poisson bracket and the Heisenberg commutation. But there are these two other terms. This term will be familiar to anybody that's studied open quantum systems. This is called the Limbladian, and it results in decoherence. If you've seen the Limblad equation or

the GKSL equation that's sometimes called, this is a double Poisson bracket, and it leads to decoherence. It causes the spin to deco here. And if anyone is studied stochastic dynamics they will recognize this as you know again has a very similar form to the limbo ad equation but it is the fucker plank terms right these two diffusion so in this case it leads to. I'm a diffusion of the momentum to the momentum momentum diffuses and the spin decohes. And in order to keep the density matrix positive, it needs to satisfy this inequality.

So this is what we call the decoherence versus diffusion trade-off. If you have a long coherence time, so you have very little decoherence, then you lead a lot of diffusion. So D2 needs to be very large if D0 is very small. So if you have a little bit of decoherence, you need a lot of diffusion. And that's all in relation to how strong the back reaction is, this D1. So this is the trade-off and it's what is going to allow us to experimentally test this theory and a remarkable thing happens when the trade-off is saturated,

which is that the quantum state stays pure. So I said you have this Lindblad term which represents decoherence and you have this diffusion term which causes the momentum to move around. And remarkably when you saturate this trade-off, when you make d2, d0 equal to d1 squared, then in some sense there is no decoherence because conditioned on the classical system the quantum state stays pure. So what happens is that the quantum state starts in the plus state and it stays pure the whole time conditioned on the trajectory of the quantum system and collapses to being in the zero state or

the one state, but it doesn't actually decohere, it just stays pure the whole time. I can pause there, I would normally pause there for questions. I can do one of two things next. This is what's called a master equation. If people are familiar with the Fokker-Planck equation, or the Heisenberg equation, or the Lindblad equation. These are all examples of master equations. So this is a master equation. And that's one way to describe classical quantum dynamics. I can go through the formalism for discussing classical quantum dynamics through path integrals. But I can also talk about more about the experimental tests and this decoherence versus diffusion trade-off and give a maybe, you know, some intuition as to why we have this trade-off. Entropy, what's the definition of entropy? I mean, in a sense, entropy is basically you

take a system, you know certain things about that system, and then you say, how many states are there of the system that are consistent with the things we know about it? And you take the log of that and that's the entropy. So, let me understand, when you talk about, you know, when we talk about entropy increasing, it's a, I mean, again, this is another layer of complexity in what we're talking about, because I mean, again, this is another layer of complexity in what we're talking about because what we're doing is we're saying the number of states of the system consistent with what we observe is increasing, let's say. But if we have a system, which is a deterministic system, and we know everything about what it's doing, and it's also, let's say, a reversible system, which is a deterministic system, and we know everything about what it's doing, and it's also, let's say, a reversible system, so we can always take a state of the system

and, you know, find previous states of the system as we can find future states of the system. In that case, if we could observe everything about the system, its entropy would always be equal to one, zero, rather, because there's only one possible state of the system. It's the state of the system, future state of the system, and so on. So what leads to our perception of the increase of entropy is that we are not observing every detail of the system. We're instead observing only certain features of the system. And with respect to those features, we say, given these features, there are states that there are more, more

and more states of the system consistent with those features. So can you say again what, cause I didn't understand what, what you meant by, so you, you were saying something about entropy being related to something else. Well, the, the entropy, so one proposal is that the mass of a particle is a projection of the entropy rate of a communicating class. So, the entropy rate, you know the definition of entropy rate for Markov kernel? Tell me it.

Okay, yeah. So, for anybody else who's watching, even if I know it, the chance that everybody watching knows it is incredibly low. Well, the tau audience is quite technical and they not only can keep up but enjoy it. The chance that everybody watching knows it is incredibly long. Well, the toe audience is quite technical and they not only can keep up but enjoy it. So, okay, indulge. So, I have a recurrent communicating class. It's got a stationary measure. So, it means there's a long-term probability of being state one through state M. Okay. So, I got the stationary measure and then each row of the matrix is the, you know matrix is a probability measure.

And so it has an entropy. Hold on, hold on, hold on, hold on. Let's unpack this a bit. So we've got this matrix that says, here's a vector of what's happening right now and a vector of probabilities for right now. And we're going to apply this matrix to get a new vector of probabilities

for the next step, so to speak. Right, right, right. Okay? And now you say, going to apply this matrix to get a new vector probabilities for the next step, so to speak. Right. Okay. And now you say, let's apply that matrix a zillion times. And the result of that is we're going to go some limit and that limit is the stationary measure as you're calling it, that there is a limiting matrix in which every entry in that matrix has some particular value that corresponds to the ultimate limiting set of probabilities. In that state, that's right.

Okay, I got that. Now what? So the stationary measure gives you the ultimate probability of being in state one, state two, and up through state N. And then now if you're in state one, right, there's a transition row, there's a probability measure about where you're gonna go next. That probability measure, you can take its entropy, right? So you can take the probability measure, take its entropy. Now you just multiply that entropy by the stationary weight

and add them all up. So that's all you, so it's a weighted sum of all the entropies of the rows weighted by the stationary. I mean, here's a weighted sum of all the entropies of the rows weighted by the stationary row. I mean, here's where I'm getting into trouble. Because yes, at a mathematical level, you can compute sum of p log p for all these entries in the matrix. What the interpretation of that is, and maybe you don't need an interpretation of that, but for know, the entropy, again, this is, you know, by putting probabilities in, you're, you know, you're kind of cooking things in a certain way. For

me, when I'm talking about entropy, I want to know what are those individual states? It's kind of the frequentest version. I'm not just saying there's a probability, I'm actually saying what are the things underneath that probability. So, you're, but I don't know whether... And I'm not. I'm taking these probabilities as the foundations of this particular theory. Okay. So, it's a purely mathematical thing that you're doing.

So, it's not, there's no interpretation of entropy here. It's merely the mathematics of... That's right. That's right. Okay. And of course, entropy rate, for example, is a big deal in communication theory. really the mathematics of PYP. That's right. Absolutely. Okay. All right. And of course, entropy rate, for example, is a big deal in communication theory.

If the source has an entropy rate that's bigger than the channel capacity, you get distortion and so forth. So it's that kind of thing that comes up in communication. Yeah, it's always fun to trace those things through for like 5G and see how the fact is all these things that people said, it's a theorem that you'll never be able to communicate faster than this. And then somehow, we managed to have cell phone channels that break all those theories. Anyway, that's a separate, different discussion.

But okay. But so I'll just say one little fun thing that comes out of this. If we define the entropy rate, the mass to be a projection of entropy rate, then that forces us to make certain predictions. So a mass zero would correspond to an entropy rate of zero. That would correspond to a Markovian matrix that has only zeros and ones in it, a single one in each row and all has zeros. And well, so we know that in space-time, massless objects must move at the speed of light. So it

better fall out of our theory that you get the maximum travel speed in our theory for the things that have zero entropy rate. And it turns out, if you look at what's called the commuting time between states in a Markov kernel, the maximum commuting time, the fastest commuting times, so the smallest commuting times, the fastest travel times are for the ones with have zero entropy rates. So we actually get that. And the maximum speed is one state per step of the chain. Hold on, you're commuting lots of different concepts here.

I mean, when you're talking about things traveling from here to there in this Markov chain, it's like you have a vector and this thing is moving the probability measure from one part of the vector to another. Paul Matz Yeah, you're going from one state, from one conscious experience to another conscious experience. And the question is how fast can the conscious experiences change? Right. But by conscious experience here, you are taking what I would consider to be a kind of a, you know, I hope that in a sense, I feel my conscious experience is a lot richer than, you know, than this, than your kind of probability vector.

This is, again, one of the things that is difficult about this, the intuition about all these kinds of things. For example, in this idea that you can have richness of things emerge from simplicity. Or another thing that took me a long time to come to terms with, I'm not sure I completely come to terms with it even now, is that the universe is an unbelievably profligate waster of computational resources. And you know, I had always imagined that there would have to be a definite history in the universe, that it couldn't be the case that the universe is just sloughing off these immense

numbers of different histories, most of which are completely irrelevant to us. So, you know, I guess my question here is, you're imagining that you're summarizing conscious experience. I mean, you know, you first, you started off by saying, look, conscious experience is this very rich thing that people can't reproduce from theories and so on. And so, what you're doing is you're flipping that around, as I understand it, and saying conscious experience is the

axiomatic starting point. And then we're going to try and erect a theory around that starting point, which I think is a perfectly reasonable thing to do. Okay, I don't have a problem with that. Adam Lichman There's one is I can make physical predictions that are testable inside space time, right? Yeah, but I think, you know, the question is what goes into it, right? Because as soon as you're saying you've got these families of Markov chains and so on, you know, that's real content. That's not, you know, that's a model like I say, you know, the universe is made of hypergraphs and somebody else says, no, it's made of cream cheese or something. You know, it's, you know, you're making, you're positing something definite.

The atoms of your ontology, so to speak, are these conscious experiences or whatever. I mean, you know, I find that so, by the the way, I mean, to, to either support or attack both of our points of view, you know, I can no more pick up an Eem, one of our sort of atoms of existence and say, here it is, than, than I claim you can pick up that conscious experience and say, here it is. Right, right. So, both of us are in the situation where we have to say, look, the effects of what we're talking about are all very good, even though the thing we're ultimately talking about is not a thing we can pick up.

Now, you know, to me, the problem, the thing, one of the things that's nice about Eames and hypographs and Rulliads and things like that is they're extremely non-human. So we do not have sort of, we don't make the mistake of saying, oh, it's truth, it's falsity, it's experience, it's this, that, and the other, because they are by construction, in a sense, they are deeply abstract and deeply non-human. So we don't come to it with a prejudice about how things should work. What worries me about starting from sort of consciousness as the element, so to speak, is that many, you know, we think, we imagine, and in fact,

even the way you're talking about, you know, the sensation of mint and so on, is we come with a bag of prejudices about how that all works. And so, it is a challenging thing to erect the science without being sort of pulled in the direction of some prejudice or another. Fair enough. And I think that that's a very important point. And what I would say to anybody who wanted to do the research along the lines that I'm doing is to, I would say, the set of experiences that you've had is measure zero compared to the set of experiences that are out there. So don't make the silly mistake of taking your own experiences as comprehensive of all experiences. Really, in some sense, use your experiences to get going,

but then follow the math. Don't follow your experiences. That's a very challenging thing to do. Living paradigms is, you know, I got to say in my life, for example, you know, I started studying simple computational systems, I don't know, in my life, for example, you know, I started studying simple computational systems, I don't know, 40, 45 years ago, basically. And you know, it took me embarrassingly long to realize things that were plainly observable in experiments I did. I mean, I, you know, just it happens to be the, a few years ago, it was the 40th anniversary of my, not my discovery of this

rule 37 automaton that does all kinds of cool complicated things. It would be nice if I could say it was a discovery. It wasn't. It was, the discovery of it was three years earlier. It took me three years to understand what the heck was going on and to not ignore it. And I think this is the, you know, it is a huge challenge to kind of rise above one's kind of, one's assumptions about what's going on. And I mean, maybe one thing I could ask is… I just said that's a clue to what it means to be an observer. That it is hard to rise outside of one's previous impressions of things.

Exactly. But I think, so a question would be, observers like us, human observers, things like that, we have an internal experience of it, we have a way of projecting what human observers might be like. When we go to observers with very different, human observers with very different backgrounds, very different kind of belief systems, kind of ways of thinking about the world, you go, we're talking about very different kind of belief systems, kind of ways of thinking about the world. You know, you go, we're talking about the spirit world, animism, whatever else, or we're talking about, you know, all sorts of Eastern philosophy, ways of viewing

the world. It's even then, it can be difficult, I think, at least it has been for me, to wrap one's, you know, simple Western kind of scientific mind around these kinds of different ways of thinking about the world. 5. That's right. That's right. I agree. I've faced the same thing. But one thing that trying to do that has, I've come to conclude is that, I love science, I love mathematics, I love concepts and being precise and everything. But I've concluded that reality, whatever it is, infinitely transcends anything we can describe. And that's a very humbling thing. Yeah, well, right. You know, I have to say I've had this experience now, you know,

with the Ruliat and thinking of myself as this little tiny bundle of Eames and the Ruliat, I would like to be able to characterize what bundle of Eames is a thing like me versus what bundle of Eames is not an observer like me. I don't yet know how to do that. It will be interesting to understand, for example, and this is why I'm asking a little bit about do there have to be many observers, because, you know, for example, that gets you into, oh, you need kind of self-replication, you need some kind of, you need some way of replicating the number of observers. Do you need the observers to be non-identical? Probably you do. If all the observers are in lockstep

doing exactly the same thing, they're not very interesting observers. And one of the things, again, I sort of haven't seen coming, but I've now realized is relevant is, you know, I happened to, well, I just recently did some things about sort of foundations of biological evolution, which surprised me a lot because I've thought about biological evolution off and on for four decades. And I'd always thought, you know, I'd always had a hard time coming up with sort of a minimal model for what was happening. And I finally have this very minimal model with a cellular automaton with a few simple rules. And you're asking, you know, the fitness is something like how long does the pattern live before it dies out? And what you find is that, you know, with that tiny genome,

a very sort of small number of bits in the rule, it turns out you can evolve, you can adapt to produce these long-lived things that are unbelievably complicated and where there is no kind of, you know, there isn't an, you know, when you say what's the narrative scientific explanation of why the thing lives a long time, there really isn't one. It's just, that's the, you know, the bits do what the bits do. And the answer is it lives for 10,000 steps or something. But, you know, one of the things I've been curious about is whether what it takes to make an observer relate to things that we are used to that are very routine to us, like the idea of life, the idea of sort of replicating multiple similar but not

identical copies of minds, things like this. Is that thing that is routine for observers specifically like us actually something that is sort of critically important in the notion of an observer like us? And, you know, as I say, the big surprise for me has been the derivation of core laws of physics, just from very coarse statements about observers like us. And as we get finer statements about observers like us, what more might we be able to derive? Um, so let me jump and then I come back a little bit here. This is the paper that I mentioned that I wrote with Roger. And what we did in this paper is that we calculated how massive would these super positions have to be if we used the Bose-Sein-Stake condensate.

I'm going to come back to that. But we found that you need at least something like 10 to the 9 atoms in a superposition. And let me tell you where the field is now. So well, people started to put electrons in a superposition of two different locations using like a double slit experiment. I don't know i don't know maybe 90 years ago i don't remember when was the first experiment with electrons and from there they said okay works for electrons amazing let's do it now with atoms and you know then is like how. the states the system gets and the record is hold by Marcus Arndt's group in the University of Vienna as well. Where he has been able to put big molecules in a superposition and by big I mean the molecules have around 2000 atoms. Wow. But you know for gravity to act you need at least 10 to the 9.

Actually for molecules, you need even more. So you can see we're very far from that. What do you mean for gravity to act? I thought the assumption is that gravity acts as long as you have mass. Don't these have masses? Yes, but these are stable superpositions. No, they... Oh, according to the calculation from Penrose?

Yes, this, well, Marcus showed that you can have these superpositions, and I think they lasted milliseconds. I don't exactly remember how long he had them for. So they are stable for that long in the lab. So gravity is not causing the collapse of superpositions at those scales. I see, I see. But now the question is, is Roger right? Because if Roger is right, then that explains why we don't see superpositions in the macroscopic world. And what would be super interesting is to see that, no, that is a big open question in fundamental quantum mechanics, is to understand what takes you from quantum states being in superpositions to the classical world where we don't see quantum superpositions.

It's a very interesting question. Marcus and many other people are trying to address this question in an experimental point of view from the experiment by building, like trying to put more mass into the superpositions. There are many different experiments going on at the moment and they use for example nanoparticles, nanobeats made of silicon or silica, diamonds, little mirrors, roads, even membranes. There are many, many experiments going on. And also a record has been held by Markus Aspenmayer, also in Vienna. So, I spent three years in Vienna because of these amazing people and experiments there. So, I was very lucky to get a visiting professorship for that long and, you know, be in the same environment where these amazing scientists are.

And so Marcus was able to bring one of these nano beads to the quantum regime by cooling it down to lower vibrational states. lower vibrational states, so they're already in the quantum, let's say, scales, but with 10 to the 8 atomic masses, so quite a big beat, but he cannot put them yet into a superposition of two different locations. That has not been possible. Also, one of my colleagues, and I'm in Southampton, so one of my colleagues there, Hendrik Ulbricht, also has a very recent, amazing paper where he takes these little beads and he manages to measure gravity. But this is all classical.

But anyway, I mean, at those scales where quantum starts to kick in, well, what he wants to do is push these experiments so that maybe he sees some quantum gravity. Still far from that, but let's say approaching. But this is where things are at with respect to the experiments with big mass. So what I did with Roger is that when he started to tell me about his proposal and the experiments that people were doing, I noticed that all of these experiments were using solids, mirrors, beads, and so on. And it's very difficult to cool a solid

to very cold temperatures where you have little noise. So they haven't been able to make more progress because of the noise, because you can't cool them enough. Now, a Bose-Einstein condensate is a really beautiful system. I think it's my favorite system because you can reach half a nano Kelvin like the coldest things that we can do and you can get up to 10 to the atoms. I mean, that's not very common, but there's been an experiment using hydrogen in which they cool

10 to the 10 atoms into a condensate. So let me tell you a little bit what a condensate is. So you have a, let's say when you learn quantum mechanics you learn that if you put a particle in a potential well the particle is there moving in the potential but if you cool it to the ground state it will let's say if you manage to the ground state the atom will be completely delocalized within the potential. So you don't know what the position of the atom is in that whole thing no that's So you don't know what the position of the atom is in that whole thing, no? That's really, I don't know, when I did that in quantum mechanics I loved it. Now think about having 10 to the 8, 10 to the 10 atoms,

all cooled down, but atoms are bosons, so they can all occupy the same quantum state, so you can cool them all down to the ground state. And that is what is called a Bose-Einstein condensate. So you have the biggest system that behaves in a quantum mechanical way. And like I said in the experiment, people have been able to cool these systems to half a nano Kelvin. Right. So I was wondering if then this would be a good system to test Roger's predictions. And that's what we did together. We said, okay, how would it go with a Bose-Einstein condensate? And well, also super complicated because you would have to create a superposition of all the

atoms on the left with all the atoms on the right. And although the temperatures are that low, people have not been able to create these superpositions. They're called noon states because you have N00N. And you know what? The record is by one of my colleagues called Chris Westbrook and he's been able to do two atoms. So you can have many atoms in quantum states in a Bose-Einstein condensate, but not many atoms in a spatial superposition of two different space locations. That's where gravity acts. So this is what I now have been working on in the last two years. And well, it's not related to, it's inspired by this work with Roger, but it's a complete new thing.

I hope I can talk about it at a later time with you. But in that previous paper with Roger, with Roger, we studied things like Roger had given formulas for uniform spheres and in a BC you could have pancakes or elongated BCs with different distributions of the density and we studied if these would enhance the effects predicted by Roger and then, well, you have a lot of losses and we studied the losses and so on and that's how we came up with this. Well, with a BC, you need at least 10 to the 9 particles, maybe even 10 to the 10 in order to start being able to actually verify that the energy uncertainty of gravitational origin that Roger predicts

has an effect. So now I'm just going to finish this part with the slides, just telling you of an example of the work that I've done where I brought together quantum field theory and curved space-time to let's say propose a new sensor. And it was quite bold because I came up with a proposal that you could use a Bose-Einstein condensate. So let's say that the sample itself can be a hundred micrometers, 50 micrometers, the cloud of atoms. Sure.

And the experiment is again a tabletop experiment. We could put it in this room. No? Cool. this again a tabletop experiment. We could put it in this room. No. And I claim that you could use the BC because you see an atom, we saw how precise they are. And a BC you might want to see it as 10 to the eight atoms cool down to the ground state. So this is a very precise, it's a system that is very sensitive to space-time distortions. And I made a proposal on how could you use the system to detect gravitational waves.

Wow. That's quite crazy because gravitational waves are detected in LIGO, where the apparatus measures each arm three kilometers. So, it so very bold and i've been like really kind of when i met roger that was in twenty two thousand and seventeen. I was really invested in that and trying to convince you know the community that. You need to do this experiment because it's really open supper a new direction and Roger was trying to convince me to work on the collapse of the wave function due to gravity. I was very reluctant because I thought, no, no, I want to put my time and my energy into this. And well, after the years Roger managed to pull me more into what he's doing.

But yeah so well when you talk about using atoms to measure gravity what we usually do in quantum technologies is an atom interferometer. So let's say you have a atom and you hit it with a laser with a photon and you make the atom you hit it with a laser, with a photon, and you make the atom, you put it in a superposition of two different positions, but they're freefalling. So they follow different trajectories and then you recombine them with lasers. And they recombine at a point. But because they went through different trajectories, they picked information in a phase that depends on the local gravitational field.

And this is what a quantum gravimeter is. Interesting. And I put here a single particle detector because although they throw maybe 10 to the 6 atoms at once into the interferometer, all the atoms are independent and each atom goes through this superposition of trajectories. And then they interfere at a point. So I put here the interference is local because it's at the point where they recombine. And then this is limited by the time of flight. And the equation is very simple. It's just this equation that's here. Basically, it depends with the time of flight squared, which means the bigger the detector, the more precise it is. That's why

LIGO is so big. And they're thinking because they want to go to, well LIGO is with light, but the principle is the same. They now want to make a bigger detector in space called LISA to have more precision. So a lot in physics, the tendency is to go very big, big experiments, of course, are very expensive. And I, my husband says that I'm a rebel, because I like, you know, if everybody's doing one thing, I always want to do something different that applies to everything in my life. Yeah, that's another aspect that unifies us. Yeah, really? Yeah, no, it's like I'm a contrarian at heart.

Yeah, yeah, yeah, yeah. Exactly. So if everybody wants to be make big detectors, I want to make them very small. But it has paid off for me in science. Maybe sometimes in life can make me like a Grinch in Christmas and things like that, because I was like, oh, I don't want to do what everybody does. So socially, I don't want to go to the movie that everybody's watching. But in science, it's been good.

So, well, here I also write that this is compatible with Newtonian gravity because this is an experiment that is described with the Schrodinger equation. And if you treat the local gravitational field by Newtonian gravity, everything works very nicely. And like I said, these are already commercial. My colleague, Philippe Boyer, has founded a company that he now sold called Mucans and their other like Mark Kasibich does that as well, in which, you know, they built these interferometers, these gravimeters, and they sell them there like a meter big, I think,

and so on. And that's like, you cannot make them smaller than that because then you lose precision. So if you wanted to get atom interferometers to apply them to fundamental physics, to learn about the equivalence principle or to measure anything with respect to gravity. So you want to make them more precise, you have to make them bigger. So Philippe Boyer did this amazing experiment in which he put his atom interferometer in a plane. So he flew the plane as well and let it free fall for a bit to get the long baselines. He also has an amazing experiment on the ground called, oh gosh, I forgot the name of it now, but it is like the arms of the Atom Interferometer are

300 meters long, so this is huge. You can see here sort of the tunnels and so on. can see here is sort of the tunnels and so on. And in Germany, you have a drop tower that is like, what is it like this? Like a drop tower. Yeah, so they put up here. Oh, a drop tower. They put up there like an atom interferometer and then they let it drop to get these long

interferometer arms and be able to be more precise. Some other people also look at these atom interferometries and put lasers and slow down the atoms so that they get, so for example, um, this paper by, uh, Guillermino Tino is really beautiful trying to miniaturize the detectors. really beautiful trying to miniaturize the detectors. So what I came up with with this idea was, well, if you're trying to do interferometry in using these sort of, call it spatial interferometry, because the atom goes through two different positions, the precision is going to be limited by how big it is. So you're going to have to make them bigger to be more precise. But if instead of that we do interferometry, not in space, but in frequency, then what is going to limit your precision is time.

So the states, so the sensor can be very small, but you're going to have to produce quantum states that live longer in time. So with this idea that I called frequency interferometry, I came up with a number of sensors and including the gravitational wave detector, and then I applied it to searches for dark energy, searches for dark matter. I also patent an idea on how to use these states to measure the local gravitational field. So this might have commercial applications in the future.

And I like that because I like more fundamental questions. Actually, my favorite question is, what's the nature of reality? What are we doing here? Where am I? Oh, yeah. It's a dangerous question, huh? Yeah, very. All of these things. But, you know, when you're doing that and you find

some interesting things, why not also come up with something that can be, you know, patented and commercialized and so on. And yeah, then when I met Roger, I was really invested in this and I'm still working on it. I have some recent results. One of them is not, it was in the old size, it doesn't matter. But I think I managed to give you a flavor of what you can do by bringing together quantum technologies and apply them to fundamental questions and where things are at. I think I want to finish by saying that this last proposal is an example where we used not quantum mechanics, but let's say a more fundamental theory because it takes into account relativity, which is quantum field theory in curved space time. Although it's not the finished theory because it cannot address the question of superpositions of mass, you can apply it without problem to specific cases like the propagation of space-time of packages in the space-time of the Earth and many other interesting instances. This allows you to come up with, let's say, new sensors.

And the theoretical predictions that we've made is that these sensors are so in principle, they still have to test them, so precise that you might be able to detect a gravitational wave with a tiny system. These are for high frequencies, by the way. They don't really compete with LIGO because LIGO works in a different frequency regime. This would be for frequencies higher than the ones that LIGO detects. But, you know, let's say using these patches of the theory that incorporate relativity, I think already show you that you can in principle make sensors that allow you to go closer to the scales where I was talking about that we don't have the guide to unify. You know when people were trying to detect gravitational waves, the first apparatus that were built in Maryland, you can still

see them, they are these Weber bars. So, Weber predicted that the phonons, so the vibrational modes of these big metallic bars would resonate with gravitational waves, and then he claimed that he actually had detected one, and then this got sort of controversial and then eventually disproved. But actually the proposal that we made in which you have, you can implement it by using a BEC and using the vibrational modes like the phonon modes of the BEC. But because you can cool the BEC to half a nano Kelvin, that's 10 orders of magnitude cooler than the Weber bars were cool initially. Then you can prepare the phonons in a highly quantum state, which you cannot do unless you go to those cold temperatures.

And then you can exploit all the sensitivities that we were talking about quantum technologies to see changes in the space time. And that's how we came up with that proposal. You know, like I think I can talk forever, so maybe it's good to leave it here. I'm gonna be talking about the attempt to reconcile quantum mechanics and gravity or space-time. And this is joint work with a number of my students and Isaac Leighton, Muhammad Sajid, Barbara Soda, Andrea Rousseau, Zachary Davies, Andrew Gurka, etc. So it's a joint project.

We can start by asking just a more simpler fundamental question, which is we have these two frameworks in physics, one is quantum mechanics and the other one is classical mechanics. And we can just ask the question, are these two frameworks compatible? Can we combine them in a consistent mathematical way? So quantum mechanics, we're used to the Heisenberg equation. We have a density matrix sigma and it evolves as the commutator with the Hamiltonian. And classical mechanics has a very similar form if we think of a probability distribution row. So the probability density row evolves with the Poisson bracket with the Hamiltonian. So those two frameworks have a very similar form.

And we can now ask a very, I think, natural question, which is can we have a classical system which interacts with the quantum system? So here we have a phase space q and p. So we have a particle which lives in phase space. And then we could have a quantum system like a two level spin half particle. And we can ask, can we combine these two systems together in a consistent way? Oh, sorry. Can you just go back because I want to make sure that you're seeing what I'm seeing? Can you go back? Okay, so to make sure that you're seeing what I'm seeing? Can you go back?

Okay, so I'm going to screenshot to you what I'm seeing, or I'll describe it, but I can also screenshot it. So what I'm seeing is it's a Q&P, there's a blue box, and then there's nothing inside the left hand side, but then there's an equal sign and then a psi with a dot. Yeah, there's just- Is that not what you see? Oh, yeah, I see that. So this is my bad graphics. So the equal sign is a two-level system.

So there's the graph. Alright, so if any of you are confused as well, so this looks like it's saying nothing equals the wave function and the wave function is up here for some reason. There is, okay, this little dot here is a point particle, is the free particle, and then we have the state of the quantum system, which is meant to be a two-level system. And as you can see, I do my own graphics. I don't have a graphic designer.

Wonderful. Let's keep going. Well, this one's far superior. This is a far superior. Okay, so this one I also did myself. Oh, great. So, and it's just meant to demonstrate that we all the time we combine classical systems and quantum systems.

So for example, in the double slit experiment, we treat the walls of the box and the slits, we treat those classically and the particles quantum. And in this potential here, the potential we treat classically and the quantum system is quantum. That's the case where we have a classical system which acts upon the quantum system. That we can deal with pretty easily and we're used to such systems. What we're not able to do or haven't been able to do until recently is deal with the back reaction. In other words, we have a quantum system

which back reacts on a classical system. And I'm motivated to study this for a number of reasons. One is that these sorts of situations occur all the time where we have a quantum system that we want to treat classically, but it's interacting with another quantum system. But I'm mostly interested in this because I'm interested in gravity. And we know that gravity is famously inconsistent with quantum mechanics. And I either want to think of a reconciliation where I treat space-time as classical and maybe modify quantum mechanics

a little bit. Or I may be also interested in situations where I just treat space-time classically. So an example is in a black hole, then the black hole is evaporating, so the evaporation is emitting these photons which you treat quantumly, but the back reaction is on a classical space time. Another example is in inflation, in the cosmology, we treat the expanding universe classically, but the vacuum fluctuations we want to treat quantumly. So it's often the case that we want to treat one system quantumly and the other system classically.

But I'm also interested in the possibility that maybe we should not be quantizing space-time. And so I want to go over the reasons why gravity is somehow different to the other forces which we want to quantize, and therefore why we might question whether we should be trying to quantize gravity. Okay. I just have a quick question here. So when I was speaking with Sean Carroll, he mentioned to me that the holographic principle

is quantum gravity. And I asked him how does that constitute quantum gravity? And he said, well, it integrates quantum mechanics with general relativity. He said it's into some unified theoretical construct. I said, well, to me, the way that I understand quantum gravity is that you quantize the gravitational field. So that either is you do some canonical quantization of Einstein's field equations, or you employ a path integral over the metrics. What is it specifically that you mean when a massive object bends space-time. And so to quantize gravity has generally meant that the space-time itself, the metric,

the gravitational degrees of freedom, which is how much it bends, that that should be quantized. So that's traditionally what people mean. Now, ADS-CFT claims to resolve this in some situations through a duality. And so people would claim that in certain space times, ADS, that the boundary theory, which is a quantum theory, is a, you know, it's a fully quantum theory. And by definition, you can say, I'm going to define that to be quantum gravity. And then if you have a mapping from the boundary to what's happening inside in the bulk, then you would, I think, be able to claim

that you quantized gravity. Now the issue with ADS-CFT is that we don't really know if the dictionary is consistent. So there's all kinds of rules that we're still, people are still trying to develop. And we don't really know if these rules hold or are consistent. Some people have a lot of confidence in it.

My sense of it is that these rules are still being developed and we still don't really know if they hold. So for example, you need to have a whole bunch of things need to, in my view, hold in order for certain paradoxes in ADS-CFT to be resolved. And we just don't know if that's the case. But I would agree that if ADS-CFT, if the conjecture holds, then that is a quantization of gravity in a certain space time. In that case, it still sounds like you have a classical background space time. How is

that quantizing? Are there other issues? So you know in ADS CFD it's a very strange thing that we require this background space-time and then claim that there's no background space-time, you know, that we kind of don't need it in the bulk and it's somehow emergent. And that may be, you know, that may be successful in the end but it's it's a little bit strange in my view that you need to rely on a background classical space-time in order to get an emergent space-time. I guess what I find interesting about,

say, an attempt to quantize gravity is that if you think about what we're trying to do, you can see in this slide, you start off with say some initial data on a Cauchy surface, so you start off with a space-like hypersurface and you define your initial fields to live on that surface and give your initial conditions and then that evolves forward in time. And even defining that initial space-like surface requires you to know the metric. And so gravity is really different and even posing the initial value problem is different in gravity. And when we, for example, want to say that we define our quantum fields on the spacetime, then we need to, for example, if X and Y are space-like separated, then the two fields

commute. But you need to know that those two points are space-like separated in order to define the commutation relations. So if we're going to quantize the causal structure, then how do we even define the commutation relations? That's part of the problem with quantizing gravity from a conceptual point of view. Okay, so this actually title of this slide, should we quantize gravity or gravitize quantum theory comes from Roger Pendrose.

And what he means by that is, should we keep the principles of quantum theory and modify general relativity? That's what we understand more by quantum gravity. Or should we do the contrary, keep the principles of general relativity and modify quantum theory. So I guess, you know, like most people working on the unification, maybe follow the first line of quantizing gravity. But Roger thinks differently, thinks that quantum theory has a problem anyways, which is the measurement problem. So he supports more, let's say, the root of keeping the principles of general relativity and then trying to modify quantum theory to bring them together. Now we both agree that it's more likely you have to modify both of them, but let's say Roger would always give more priority to general relativity in that sense.

So I was writing here in this slide a few things about both theories. So let's go first to quantum theory. Like same as in classical physics, time is absolute in quantum theory. So clocks tick at the same rate for any observer independent of its state of motion. And this comes from the theory being invariant under Galilean transformations. So the underpinning transformations are Galilean transformations just as in classical physics. So in the same, know that inherits that space and time are very different notions. The Schrodinger equation treats space and time completely different. It has one derivative in time and two in x.

It treats time like a parameter and then positions can be quantized and you use operators which are completely different mathematical structures. So then already from there they would be incompatible with the relativity. And just for some clarification, quantum theory means quantum mechanics and not quantum field theory. Yes, yes. I guess because of my background I use that more when I say I like to use actually more quantum physics But that I I'm just talking about like, you know Schrodinger equation Fields is like a step

Okay more no, yes Well, then in quantum theory, we have the superposition principle. So particles can be in a superposition of two distinguishable locations at a time. And then, well, this is what Roger calls, well, many people call the measurement problem, but in quantum theory, the outcome of measurements is probabilistic, fundamentally probabilistic. And then when we want to measure, let's say, space or time, we have an uncertainty principle that tells us that if you measure positions very precisely, then you cannot simultaneously

measure momentum and so on. Also, it's kind of a bit of a summary of some of these, let's say, fundamental principles of the theory. Yes. Then on the other hand, in which way they're different and why are they incompatible? Well, in relativity, time and length are not absolute, are observer dependent. So the underlying transformations in relativity are Lorentz transformations. And if you look at the, they mixed space and time. So let's say the more radical thing I think that we learned from Einstein is that space and time are not different in the way that we understand them

in classical physics and also in our experience, right? If you tell anyone space and time are like a bit of the same thing, people would be shocked with that. But that's what Einstein showed us that they actually belong together in a higher dimensional object, which is space-time. And they're both dependent on the state of the observer. And then you have relativity.

If you have gravity, for example, it curves space-time. And then if you look at two different points in space, you can see that time flows at different rates, at different points. So already there, you can see that in relativity, you have to treat space and time on an equal footing. So let's say equations, if you're having a second derivative in space,

you should also have a second derivative in time. So that's, you can already see how that is already incompatible with quantum theory. And so a little bit also the question of time is at the heart of our difficulties to unify the theory. Then you could think about things, how would you see if a mass is in a superposition of two different locations and then time flowing at different rates?

The Schrodinger equation has only one derivative in time, it's one time. You cannot think about such questions yet with the theories that we have currently. Another thing, just to finish with the slides, in relativity, we don't have this thing about the outcome of measurements being probabilistic, but it's a deterministic theory in that sense, and we can measure space and time as precise as we want. But in my opinion, the most interesting question that we have to answer is what happens when we have a massive superposition where the mass is in a superposition of two different locations in space. And this is something that you cannot answer with quantum field theory in curved space-time, because well, I'm going to go more into that later, but the theory assumes that you have sort of a fixed background, so a fixed space-time metric, which is a solution of Einstein's equations, but the fields themselves, or the mass itself, doesn't curve it.

So you couldn't answer this question. I think this is really an interesting and important question because we know for example from the experiments that you can have the electromagnetic field in a superposition. So you can take an electron and put the electron in a superposition and then you can see that the quantum fields generated are in quantum states. So we were talking about quantum optics and quantum optics has been a theory that has been tested in many, many experiments. And we know that the electromagnetic field can be in quantum states. Another big question is, can gravity also be in a quantum state in this sense? And well, if the mass is very small, well, yes, because the moment that we have, let's say,

an atom in a superposition, in a way, the gravitational field produced by the atom is also in a superposition, but I think the big question is more like if that's a stable situation or not. No, and that's where Roger, and I'm going to go more into detail of that, comes in and says, well, you can, but that is a very unstable situation and gravity collapses the wave function, which would then resolve the measurement problem. And that would explain more like the transition between the classical world and the quantum world that would explain why we don't see, let's say, this cop in a superposition of here and there and so on.

I'm going to talk more about that in a moment. But I guess my point here is that I think this is the most interesting question to answer. And there are good reasons to believe that gravity could act different to the other forces. And that is because gravity is the only one that has an equivalence principle. So there is not an equivalence principle for the others.

Also in the equivalence principle, if you're in a lift and you don't have any way to look at what's happening, so in a box outside, you could not distinguish when you feel an acceleration, if that is because you're in the presence of a gravitational field or just because the box is being accelerated. That is something that is specific from gravity and that could distinguish gravity from the other forces. That is something also that Roger argues that might hint at gravity being fundamentally different.

Okay so i mean obviously the question is very important percent but also i said it underpins other very interesting fundamental questions in physics. I found this picture of the one with them. This picture, the one with the stars and so on online is a very famous one. Actually, you know, one of the things I lost, because I lost my talk just a few moments ago, were all the credits to the images. So I'm sorry I had done that detail and so on. But when I saw this picture, I liked it very much. And it made me think about how was it when we were trying to make sense of,

let's say if you want cosmology, where are we? What's this, let's say, world that we're seeing? What are those points in the sky that appear at night in a way, what's the universe and so on, without instruments? No, so I can imagine, I like to have a romantic image of that, of, you know, people sitting around the fireplace and looking at the sky and trying to make sense of where are we. Without the telescope, you can imagine how hard that would be and what sort

of theories humanity came up with when the only possibility was to use our own instrument, our eyes, and look at the sky. Then Galileo invented the telescope. It's very interesting that as well that when Galileo invented the telescope, many people didn't want to look through it. And that also makes me think about a lot of the stuff happening in science where people sort of refuse to look at certain theories. That reminds me, I also heard you talk about that and you were talking about, well, I mean,

if you're working in string theory or in quantum gravity, don't you have sort of the moral responsibility of looking at what other options are there? Yes. Right. And that I think it's like refusing to pay attention to competitive theories or other ideas. I think it's a little bit equivalent like refusing to look through the telescope. Interesting. Now somebody comes with a new invention says look at what's happening. You say no, I don't want to even look. But that happened. Now, since then, telescopes have developed incredibly. We have amazing, like the latest pictures that you see are just just amazing what they can do. But now with very good instruments we can look at the sky,

we can look really into the past of our universe, and then see that, oh wow, it looks like the universe is in expansion. And we can come up with more meaningful theories, with better theories, thanks to those observations. Same if you think about the microscopic world. So the Greek came with the idea of the atoms. But again, it's not until you build a microscope and you can look into the microscopic world that you can do better atomic physics.

So I'm trying to make the point here about how important have the instruments been in us making better theories and understanding things better. Right. Um, so when it comes to these scales where quantum mechanics and general relativity interplay, where we're blind, we don't even have our instrument. We don't even have our eyes. We don't have anything. So how do you go about, right, when you do that? So I think I understand string theory and loop quantum gravity and many of these very mathematical approaches in that sense is that you do what you can when you have it at hand and what we're able to do is super powerful studies with mathematics

because our mathematics is very developed and you were also talking about that, how actually string theory has allowed mathematics to develop so much, and so much we've learned about mathematics thanks to those theories. But when you come up with theories and mathematics, well, there's many possibilities. You can make many theories, almost as many as you can think about, but which one is the right one? You know? I can make a theory, but then I need to see if actually nature behaves like my theory predicts.

And then I can have a competing theory, a different one, and which one is maybe even contradicting the two theories in principle and their predictions. How do you know which one is the right one? You need to go to the experiment. You need to go to those instruments. And we, well, I'm going to argue that we sort of have them already and we need to start looking through them for resolving these questions of unification. Yeah. When you asked me, I looked, I decided to watch one and then I said, I liked it. Oh, thank you. A physicist I knew, I think.

But I appreciate the width of your questions and the fact that you went through in detail, but in a good... ...middle ground. You seem to know what you were talking about. Yeah, I seem to. I'm great at pretending. So, Professor, why don't you explain your relational view, your interpretation of quantum mechanics? Wonderful. Thank you, Kurt Kurt for having me here. First of all, please don't call me professor. Everybody calls me Carlo.

And that's how I feel comfortable with. All right. So relational quantum mechanics is the way I think it's more interesting to try to understand quantum mechanics. There are, as you know Kurt, there are a number of interpretations of quantum mechanics out there. I find them all interesting. I think that none of them is wrong. I think they're all, each one is right, but each one has a cost, a price to pay. And the question is, are we ready to pay this price? Is it useful to pay this price to go ahead and better understand the world? And I think the relation quantum mechanics, which I'm going to describe in a moment, also has a price, like everything, a philosophical price, okay?

But I think the best price to pay is if we buy that, then we understand the world better. The mystery of quantum mechanics can be expressed in different manners. One way of presenting it is that what the theory gives us is what we see when we look, when we see when we measure. It gives predictions for measurement. And that's the way it's formulated in textbooks. The textbook quantum mechanic talks about the observer, we talk about the measurement apparatus, we talk about the outcome of the measurement. Now this is okay if you want to use it.

In fact, a lot of people use quantum mechanics in these terms and very happy period, there's no question after that. But of course it's not okay if we, after we have realized, quantum mechanics is 100 years old, after we have realized that quantum mechanics is actually the best theory we have for everything, for galaxies, for star, for structure, for nature in the universe, for what happened inside the Sun. So it's how we want to think about the world at the most fundamental physical level that we have access to today. And then, what the hell is an apparatus and an observer doing into that? There are no observers in the Sun or in the early universe when star formed.

So, something is missing, obviously, in the standard textbook presentation of quantum mechanics, which is who is observed, what is a measurement. And one way of saying that is that in the standard presentation of quantum mechanics there are two postulates, two assumptions, which appear to be contradictory to one another. One is that if you don't look, you have a quantum system, it evolves in a way, which is described by the Schrodinger equation or by unitary evolution, things change. If you look, there is a different postulate, which is a projection postulate, that says that the state does not evolve Schrodinger evolution,

but it just jumps. And the visual way of viewing this is that a particle like an electron is described like a wave that satisfies the Schrodinger equation, so a wave diffuses in space. When you look at it, you see in a point. So the wave collapses in a point. And when does it collapse? When there's a measurement. And when is a measurement? When observer apparatus there's a measurement. And when is a measurement? When observer apparatus measure it. But there are no observer apparatus inside the Sun. There are no observer apparatus inside distant galaxies or in all the cases we use quantum mechanics. So that's the problem. And there are many solutions on the table. Some people think that, you know, it's always waves, so the particle never goes to a point.

And the reality of what happened is that we ourselves are waves and we split in many different copies of ourselves. This is a many-word interpretation. And others. Now the relational, and I'll finally come to your question, the relational interpretation is the idea that we can make sense of that by simply thinking that what happens between the particle and the observer, the particle and the measurement apparatus, is generic and is not because of special property of the server or the measuring apparatus. It's just what happened between any

system and any other system in the universe. So every time two systems, we describe the world by splitting it in systems, physical systems. Okay. Like the Sun, like particle, the molecule, the Earth, you, me, these are all systems from the perspective of the system. Every time two of these interact, so exchange something, one so to say measures the other. So if this is a particle, when it interacts with me, the particle collapses in a point, has a position. Okay? But this is not true, this is only true, the particles are position only with respect to

this system, not with respect to the rest of the universe. So if somebody else in the universe, it's later interacting with a particle and this observer here doesn't have to take into account this collapse. So the collapse and the unitary evolution are both true, good postulates for describing what happened in the universe, they just refer to different systems. The ones which are directly interacting, what is relevant is the projective postulate. The ones which are not involved interacting, which still may have an interest in computing what's going to happen next in the interaction to them,

for them is relevant the unitary evolution postulate. So this is it. I mean this solves completely the quantum mechanical problems because now we know what is a system and now what is an observer. Nothing special. All systems are systems, all systems are observable and now we know when to use one postulate and the other. The price to pay is that the particle being in a position, it's only relative to the system it has interacted with, not relevant to something else. With respect to something else, it's still spread around, still a wave everywhere. So all the variable taking values are always relative, relative to a system. So this means that when we describe the world, we describe the world giving values to variables. I mean, the microphone is here, that color on the screen is red,

you know, the sun is there. These are all variables, values that variables take, the color, the position, etc. These, if you buy the relational interpretation of quantum mechanics, they are not absolute properties of a system. They are properties of the system with respect to me, or with respect to this chair, not me as a human being, me as a physical system. So that's relational. Relational because the suggestion here is don't think at reality as systems with properties, rather think at reality as a system that has properties

where they interact with something else, only when they interact with something else and relatively to this something else. That's a possible solution of the quantum mechanic puzzle. The cost of this is accepting this weakening realism, so to say. The world is not made by a substance with properties. It's made by interacting pieces and the the pieces of properties only will interact. Okay, so firstly, let's remove the word observer and say interaction because observer seems to imply in people's mind a human being, essentially, or something conscious.

Okay. Exactly. So there's that. And then what I'm wondering is, let's say, so I have a bedroom here, and I don't know what's going on. Pretend it's much farther away and I'm wondering is let's say so I have a bedroom here And I don't know what's going on pretend. It's much farther away, and I haven't interacted with it Something's going on in that bedroom now to those people who are interacting in this bedroom right now there Their properties are defined there. They've collapsed their wave function in a sense, okay That's good

Is there and let's say they've come up with some value and it says it could be a or B And they've come up with value a for some like the yeah heads on a coin Now is there a reason that necessarily if I was to interact with them that it consistently comes up with the same answer Or is that not necessarily the case Good Yes, there is a reason. But one has to be careful in formulating things properly. Let's see exactly what it means. Suppose you yourself measure that property and you found A, and then you interact with them and ask them, hey, what have you seen? Then for sure you would get something consistent.

This is the precise meaning of seeing the same thing. In other words, you can compare what you have seen and what the people in the room have seen by talking to them or by asking them or by measuring them. But this interaction is quantum mechanical. So this interaction is itself a physical interaction, not outside physics. You cannot go outside the world and somehow cheat physics circumvent and say, oh, physics is not looking, let me ask you what you've seen. That you cannot do.

That's the point. So yes, there is consistency. And why am I so careful in saying that? Because quantum mechanics is tricky. As you know, if you measure the position of a particle and then they measure the momentum, you destroy the information about the position of a particle and then they measure the momentum, you destroy the information about the position. Immediately after you measure the position again, it's not the previous one.

So we measure the momentum, the position is affected. So you have to be careful because if you ask these people a question which is like the from the position, you might be destroying some of the properties and it might be therefore neither true nor false that the value is A. Like when you do a double slit interference, if you measure the interference you cannot ask anymore which way the particle has gone through, which slit the particle has gone through. So by asking when, there is no answer to the other one. So the point is that when you compare what two different observables have seen, you have to be careful that there are these interference effects that might create a different, might

block the possibility of identifying exactly what the two have seen. So as long as you keep asking questions, which are not like positional moment, that don't destroy previous information, anything is consistent and the observer sees the same world. Earlier when asking about F-theory and how it may or may not be the crescendo of your work and you outlined quite a few different directions like the Swampland and black holes, can you please pick one of them, pick one of those topics? Let's say the Swampland, let's just talk about the Swampland.

Why is it that the Swampl Land has you so fired up right now? Well, Swamp Land is for me exciting because it's the executive summary of all I have learned from string theory. If somebody told you, okay, you have studied string theory, tell me what did you learn, what it is that this quantum gravity is all about, this is what Swamp Land is trying to do. It's exactly the lessons we are supposed to have learned from studying string theory. Now, what does that exactly entail? Quantum gravity is very different from the rest of quantum field theories. So if you take particles like quantum quarks and electrons and how they interact in the context of gauge theories.

We have beautiful theories which describe them very nicely. Quantum chromodynamics describes the theory of strong interactions. Quantum electrodynamics does the same for electricity. And there's the electric weak force, which is another kind of gauge force, which also does as equally a good job for describing the weak forces. Naively, one might have thought the gravity is of the same type. You can take the gravity and do the same thing you do with these other forces, and that just doesn't work. And part of the reason it doesn't work is that a lot of the notions of quantum field theory breaks down when it comes to gravity. Quantum field theory has a hierarchical structure in terms of short and large distance physics.

And the idea is that you're always interested in large distance. What happens at large distance, not at microscopic scale? So you kind of integrate out what we say or basically average out what's happening at short distances to come up with an effective description at larger distances. Sometimes we call this the effective field theory perspective about how things are emerging. This idea works beautifully in corner field theories. Namely, you start with a given large distance physics and ask what kind of symmetries are operative at that scale. And using symmetry arguments, you can more or less write down what the physical action looks like. Except that you don't need to know what was the short distance physics leading to this theory.

So you just ignore it because it's not relevant for your question. So we learned the fact that if you're interested in describing large distance, by and large you can forget what's going on in short distance. And that is why quantum physics has become so powerful because you can just take symmetries and write whatever you want and at a larger scale deal with it. Even if you don't know the details at short distance, that does not affect your calculation at large distances. A very powerful idea. This idea totally fails for quantum gravity.

The idea of separation of scales of short and large, microscopic and macroscopic is what doesn't work for quantum gravity. The idea of separation of scales of short and large, microscopic and macroscopic is what doesn't work for quantum gravity. And the idea why it doesn't work is kind of, one could kind of see why. So let's do the Gidankan experiment, like you wanna describe what happens at short distances. What we do in particle physics is to take two particles

and accelerate and tour each other with ever higher energies. Why? Because when they go at higher energies, they can probe shorter and shorter distances. The distance scale you probe is inversely proportional to the energy in the center of mass of such a collision. So therefore you go at a higher and higher energy, collide them to see what's going on at shorter distances, namely what comes out of such a process of scattering these particles, what is created gives you a hint about what's happening at higher and higher energy scales or shorter and shorter distance scales. This is the idea of quantum field theory. If you try to do this for quantum gravity, this begins to work the same way that we think about quantum field theory. If you try to do this for quantum gravity, this begins to work the same way

that we think about quantum field theory. You take energies of the particles who go higher and higher, until you go to such high energies that something totally unexpected happens. What happens is that instead of particles coming out, suddenly nothing comes out. So you hit them at a very high energy

and what happens instead is that you create a big black hole. A black hole is a solution to Einstein's equation, which is described by long distance physics, not short distance physics. So you are interested in understanding what's going on in short distance, and the physics told you, sorry, you cannot go any further than this.

After this scale, everything is becoming bigger. So higher and higher energies is now Translating to higher and higher distances which is opposite to the way of thinking that we had in other words High energy and low energy kind of are connected The discussion of separating the short and large distances in this way fails So the idea of the effective filter fails in quantum gravity precisely because of black holes So the black holes run the show in this way fails. So the idea of the effective field theory fails in quantum gravity precisely because of black holes. So the black holes run the show in this case. So this is why quantum gravity is very special.

Now I come to SWAMP. So this was just a background about the connection between quantum gravity and why it's so different from quantum field theory. So you say, okay, so okay, they are related, so but what does this relation really mean? How do you actually use this fact? What is the description? This means that you cannot just say, I have this and this symmetry in long distances,

write down for me the action. That you cannot expect to work. String theory tells you that is in fact does not work. In other words, if you just studied with the symmetries, you would have thought about the many, many, many more possibilities than you can actually get from quantum gravity. The short distance physics tells you not all of the things that you thought are okay are actually okay.

There's a conspiracy between that short distance and large distance, which is not apparent, to a field theorist point of view. How do we know this? String theory. So the examples that we have learned from string theory tells us that the things that we get, no matter how we change,

so in the string theory, we choose this extra dimensional geometries because string theory is more than in more than four dimensional space-line. These extra dimensions have their own geometries that we can pick. Kalabiao, this manifold, that manifold, G2 manifold, spin 7 manifold, whatever. You choose it and you see what physics comes out.

You change the manifold, changes the physics. So you say, okay, I want to see different physics. I want to get this kind of physics. Can you give it to me? The answer is almost always no. The kinds of physics you get are very, very restrictive. In fact, among the set of all possible conceivable physical theories that you may have been interested in getting, the ones that you actually get are measure zero.

The ratio of what you can get to what you want to get or you could have wanted to get is zero. That means it's basically minuscule possibilities of what are actually consistent theories with gravity. So our perspective of what is This fails now. Wait, is that a theorem? Well, we have a lot of evidence No, there's a lot of evidence for what I just told you and so in different examples It's a theorem depends on how precise a question you want to ask. So I will give you a few examples of this To try to understand that what are these restrictions is what we call the Swamp Land Program. Swamp

Land Program tells you out of these possibilities which ones are not good. Swamp Land. Now, the other ones are good. The ones which are not bad, we call them landscape. So you might say why are we looking for Swamp Land instead of landscape, which is what the good ones are. The point is what the good ones are. The point is that the landscape are measure zero. So it's like saying you have points on a plane and you want to find these points. Well, good luck. What you can more easily say is, well, you draw a line and say to the left there are points, to the right there are none. Much easier to do that than to say there is a point exactly there.

So Swampland program is trying to find these lines, kind of ideas like to the left is okay, to the right is bad, and this and that. So this narrows what is possible. It doesn't pick you those points because those are very difficult, because they're very rare. So that's the Swamp Land Program is to understand these lines. I will try to tell you some of these lines

or these Swamp Land criteria that we have found over the years. So the first one, which actually happened even before the Swampland program started, was started even back in the, I don't know, 40s or 50s, 1940s or 50s by Wheeler and collaborators, which is the statement that no quantum theory of gravity has symmetries other than gauge symmetries. In other words, you cannot have symmetries in quantum gravity without having electrical fields associated with them. Like in our universe we have of course electric charge which is conserved, but that has electrical field with it.

So what this statement is that you could not have a universe where there's electric charges with no electrical field coming out of it and the charges are still conserved. That is a no-no. That's not possible. Now from the viewpoint of an effective field theorist like you and I, it sounds perfectly fine. Why not? Why can't you have objects you can count but has no electrical field on it? Says quantum gravity says no you cannot. So this is almost at the status of a theorem. Why do we think so? Well because we have ideas having to do with black holes, which tells you that if this was not the case, you would get into trouble because you can send

one of these charges to the black hole and black hole evaporates and you get rid of that charge. So therefore you violate the conservation of charge. So symmetries get disappeared through the black hole evaporation process. And so there are arguments like that. So when you say, can you prove it, of course it presupposes we have a framework

or principles to prove, but we don't have those. So I cannot tell you I can prove it because I don't have the Euclidean principles like the axioms of Euclid or whatnot. So I cannot give you such a proof. But to the extent that we believe the evaporation of black holes works the way we do, which we are very sure of,

this is a proof that there is no global symmetries. Another example is weak gravity conjectures that we have, which we have a huge amount of evidence, which says in any conceivable quantum theory of gravity, gravity is always the weakest force. It's not just in our universe. You could not have had any consistent theory of physics for which gravity was not weaker than other forces. That sounds again strange from a viewpoint of effective theories because you can imagine having two electrons. So the hierarchy problem is then the hierarchy inevitability? No, the hierarchy is more specific question.

Hierarchy just says why is the scale so much smaller? It could have been just a factor of 10 smaller. Oh, I see. Okay. Hierarchy says, why is it, why is the factor of 10 to the 19 or 10 to the whatever smaller? That's a different one. Here, we're just saying the scale is lower, but we didn't say how much lower, but it goes in the direction of making hierarchy possible. Let's say it goes in that direction, but it tells you, it doesn't tell you, you have

to have a huge hierarchy. So, uh, so this idea, the weak gravity conject doesn't tell you you have to have a huge hierarchy. So this idea of the weak gravity conjecture, if you think about it, it's a little strange why it's true, because if you imagine you have two electrons, if you put them at a distance r relative to each other, there's a repulsion between them, which Coulomb taught us. It goes like a square of their charge divided by distance squared. Like we call E squared over R squared, the distance squared. But there's also a gravitational attraction between them, which goes like their mass times mass over R squared. That's Newton's gravitational attraction. So it goes like M squared R squared.

So gravitational attraction is M squared R squared, electrical repulsion is E squared R squared, and we are saying repulsion always wins. In other words, M is always smaller than E. Well, you could have imagined that electrical charge, electrons mass was much higher and it would have been the other way. But we say no, no, no, the theory of gravity would not have worked. You see, that's a positive surprise because you would have thought there's no reason a priori the mass of the electron has anything to do with its charge. This is no, it better be smaller than its charge in the appropriate units and the fundamental units in physics. So these kinds of ideas, and these are just two examples, there are many more examples. Yes.

Perhaps I will say one more example, because it's also one of the most remarkable examples which relates to duality symmetries of string theory. This statement, which I find probably the most difficult to see from an effective theory predictions or perspective, is what is called the distance conjecture or duality conjecture. The statement is that if you take parameters in your theory, first of all, all the parameters in your theory are dynamical. Now what does that mean? That means when we usually think about constants of nature or numbers and so on, we are saying there's no such thing in physics. That means that things that we think are constants or numbers are actually can be changed. They are dynamical. You can change them in one region or space to be bigger or smaller.

It's not in fixed numbers. What was wrong with Boltzmann's argument? And what's meant exactly when you say people should give, or that David Albert showed that people should give equal credit to initial conditions and evolution laws? So the idea that Boltzmann had was that you could start with, and again, not only Boltzmann, but others, you could start with this idea that a gas is actually a bunch of, let's say atoms

bumping into each other, okay? And then you can just use probability and statistics to derive the idea that entropy increases. And he indeed did prove a theorem, the H theorem, that kind of sounds like that. But it makes an assumption, the assumption of what is called molecular chaos. In German, the Stosszahlansatz. And the molecular chaos assumption says that if I have a bunch of molecules going to bump into each other, they are uncorrelated with each other. Okay?

Which makes kind of makes sense. You know, they're moving around randomly in The box of gas etc, but it turns out at the technical level you can make that assumption once But as soon as you make that assumption at one moment of time Then when the molecules bump into each other now, they're correlated Now they're coming in opposite directions from where they were before, right? So you can't remake that assumption again and again. So either there's two, you have a choice of two possible mistakes. One mistake is you remake that assumption again and again and that's usually what

people do because it gets them the right answer, or you just apply it at the beginning of your problem and not the end. The reason why that's usually what people do because it gets them the right answer, or you just apply it at the beginning of your problem and not the end. The reason why that's a mistake is because you're trying to derive the fact that there's a difference between the past and future, and if you assume there's a difference between the past and the future, then you haven't really succeeded, right? And look, again, people are smart. Lo Schmitt pointed this out to Boltzmann. Lo Schmitt had been Boltzmann's professor. And, you know, Boltzmann kind of filibustered.

You know, he never came up with a good answer to this so-called reversibility paradox. And ultimately, the answer is you have to explicitly break time reversal symmetry by putting an initial condition that is low entropy. by putting an initial condition that is low entropy. So, what do you make of approaches that do away with initial conditions or boundary conditions like Hawking and Hartle? And for people who are listening, when they hear Hawking and Hartle, no boundary, and they think in terms of you have an equation and you input something in the equations of the black box and the output, it sounds like there is no input, How can you even have an output?

What does that look like? Help people understand that. Well, so there's two things. Number one, Hardell and Hawking have what is called the no boundary proposal for the wave function of the universe, but it's certainly an initial condition. They certainly apply it at the beginning and not the end. It's called the no boundary condition for technical reasons in quantum gravity. So let's indulge our readers with some technicalities for 30 seconds and then we'll pull back.

Feynman told us that we can do quantum mechanics by doing a path integral. That is to say, by summing up contributions from every different possible trajectory the system can take. In this case, because we're doing gravity, the trajectories a system can take are geometries of space-time. Okay? So you would like to sum over every geometry of space-time. That's hard. So the first move that Hawking makes is let's, instead of summing over every space-time, let's sum over every space. So let's just imagine there was no time dimension and just treat everything in a Euclidean way, as we say, but we let it be curved. And then if you have some state of the universe at one moment of time, you can sum over all of

the Euclidean continuations of that to the past that don't have another boundary. They have the boundary that is the moment of time you're looking at, but no previous boundary. And that's the no boundary wave function of the universe. Now, if that's all you ever did, that would be cheating just as much as Boltzmann did. You're putting in an arrow of time. In later years, Hardil and Hawking and also Thomas Hurtog, who wrote a book about this not too long ago, who was their collaborator, they talked to people like me and David Albert and other people who cared about the arrow of time and they realized that they need to be a little bit more careful about what their assumptions were.

And it actually goes back to an even earlier debate between Stephen Hawking and Don Page in the pages of Nature and so forth. But the result is that they now would like to claim that the set of all solutions to their equation is completely time symmetric. But we live in a solution that is not. And that's actually a very sort of plausible, clever possibility to think about. I think it's very alive, but I think that again, quantum gravity is too hard for us to say anything

definitive about it one way or the other. Others like myself have other theories where you don't really focus on the quantum state of the universe, you have a universe that is largely classical, but is also symmetric between the past and future. And the real difference is that we don't see the whole universe. So in our picture, what you and I think of as the Big Bang is not the beginning of the universe. It is the emergence of our little bit of universe out of some pre-existing

thing. And the whole shebang is actually symmetric in time. So again, not cheating the way that Boltzmann did. That's a great wordplay. The whole shebang versus the Big Bang. Yep. So can you explain what, how is one supposed to think of the whole shebang compared to the Big Bang? And are you saying that our experience of the arrow of time is somehow some local phenomenon? It's absolutely in my picture some local phenomenon.

The whole shebang is just a casual word for the multiverse, right? The idea in cosmology of the multiverse is that there are regions of space and space-time that are just far away in either space or in time, so we can't see them, where conditions are very, very different. And so in our picture, that includes not just far away in space, but even before the Big Bang as well. And again, plenty of other people have theories of things that happened before the Big Bang,

but except for our model, I think this is still true, they do one of two things. Either they put in an arrow of time Forever so that there is some directionality to the time evolution of the universe for example pen roses conformal cyclic cosmology does that or They treat our Big Bang as a special moment as a moment of special Conditions low entropy for whatever reason,

because it fits the data or whatever, which is also perfectly fine. But in both cases, you're not explaining the special condition of our early universe, you're putting it in in some way. Our ambition is to not make any assumptions about the speciality of the state of the universe at any one moment of time, and to argue that in almost any initial condition, you could go both forward and backward in time, and get a universe that ultimately looks like ours. So that's an explanation, whereas sometimes people would say,

we explain the fact of fine-tuning because everything happens, and then there's the anthropic argument. So what you're saying is not the anthropic argument. Ours is anthropic only in the following sense. In our whole shebang, the vast, vast majority of places to live have no matter in them, have no matter or energy, just empty space. So of course we're not going to find ourselves there. We're going to find ourselves in hospitable regions of space-time.

So that's anthropic in exactly the same way that we explain why we live on the surface of the Earth rather than on the surface of the Sun. There's a lot more surface to the Sun than the Earth, but it's not a hospitable place to live, so we're not surprised that we find ourselves here. Your recent work on holography, is that, do you consider that to be work in quantum gravity? Or do you consider that to be work in reconciling GR with the standard model, which is different? It is work in quantum gravity, but it is not proposing a new theory of quantum gravity. It is taking a purported feature of quantum gravity, namely holography, which again is descended from Hawking and Bekenstein, etc., and asking

is it possible that that feature in a very robust model independent way has potentially experimentally observable consequences. So it's not a theory of quantum gravity, it's a theory of how quantum fields behave in the presence of gravity. The definition of quantum gravity is that you sum over metrics or possible geometries or that you second quantize, so-called second quantize, Einstein's equations. Does this ring true to you as a definition of quantum gravity? Because that would be distinct from the more broader reconciliation between

general relativity and the standard model. I don't know. That's a definition that you're welcome to or not. For me, whatever the correct quantum theory is that gives rise to gravity is quantum gravity. I see. Okay. So when someone says we need to marry general relativity with the standard model and it could be through some novel mechanism that doesn't involve a path integral over

geometries, then that would still be a quantum theory of gravity. I mean, it would be, yeah. But again, I don't, I'm not going to insist that everyone stick with my definition. I see. I see. Well, the reason is because I know that the string theorists have the concept of string universality. I don't know if you've heard of that. Have you heard of string universality? I mean, yeah, I've heard of it, but I'm not an expert. So I couldn't, I couldn't give you the definition. It just says that any theory of any consistent theory of quantum gravity is can be gotten to by some

low energy limit of a string theory. So sure, there may be other quantum gravities out there, but they will all end up being string theories anyhow. That's a good thing to conjecture. We'll have to figure out whether it's true. Yeah, exactly. Hard to prove. It's a braggadocious claim. Right. Because the sometimes I ask a I ask string string theorists what's the definition of string theory, and then I thought it would just be you have a theory where your fundamental ontology is an extended object, or at least that's where it came from, or maybe it's one of the five flavors, or something

akin to that. But then they would say, well, we're studying quantum gravity. It's any consistent theory of quantum gravity. I think before the second super string revolution, so before the mid 1990s, it was pretty clear what string theory was, but it was a fundamentally perturbative theory. You had strings and you would scatter them and you would calculate the Feynman diagrams and get an amplitude and so forth. But when we started to understand dualities in the mid-90s, these were non-perturbative phenomena that were not based on scattering strings off of each other.

And for better or for worse, the field became much richer. People were trying to understand these dualities and holography and special new kinds of field theories that you could get to by taking limits of these string theories and so forth and so These days if you ask almost any person who you think is a string theorist. Are you a string theorist? They will say no I am thinking about theoretical physics, you know, and I get it because they're thinking more broadly than just the old-fashioned 1980s style string theory What's meant when the term publish or perish is echoed? Publish or perish is somewhat of a supposed

to be a dark joke, right? But it basically is the idea that in academia, you are judged at the end of the day by what you publish, not by being smart or being personable or being friends with anyone. What have you done? What have you done? What have you accomplished out there in the literature, whether it's scientific literature

or humanities or arts or whatever? So if you want to succeed in academia and getting a job and keeping the job, you have to publish things. There's a physicist and he was saying, look, the second question after what is my name is how many citations do I have? And that this just incur in some job application for a postdoc or could be an assistant professor, I don't know. And he was saying that this encourages people to just keep publishing trivial or just what

barely makes the mark instead of monumental achievements. And then also citing your friends. Those are citation cliques. And I believe that's what was referenced in publish or perish. What do you make of this? In the modern era, where you have preprints and everything is electronic, you can figure out not only that someone has a bunch of citations, a bunch of publications, but whether those publications had an impact on the scientific literature and by how many times they are cited.

And that is not a perfect proxy for whether their work is good or not, but it's better than just counting how many publications they have, right? I've never seen any application for any job or anything that asks you how many citations you have, but you wouldn't need to because anyone can go online and figure it out in 30 seconds. Go to Google Scholar and you'll plug in somebody's

name and you'll be told. There are ways to try to exploit the system strategically, right? Like you say, get all your friends to cite your papers or whatever. Those ways are not super effective. You know, once I would, I'd like to think that at a decent university, which I like to think that I'm at now at Johns Hopkins, when you hire someone, it doesn't matter only how many citations you have, you want to look at their papers. Like, are they interesting? Do they say good things, you know, at the end of the day? If, if, you know, it's a big world out there and I can't say that all places work like that, but I cannot imagine hiring somebody just because they have a lot of citations and I

don't know what work they've actually done. What papers are you most proud of? Yeah, the papers I'm most proud of are uncorrelated with how many citations they have actually. You know, I think the paper that I explained about the arrow of time is probably one of the ones I'm most proud of, even though there's some mistakes in there, some calculational things that I think I could improve upon now, but I think the idea was very interesting and might even be right.

You know, ideally being right is interesting. Interesting. I wrote a paper with Chip Sabins about deriving the Born Rule in the Many Worlds Interpretation of Quantum Mechanics, which was like my first philosophy of quantum mechanics paper. So I'm like, I'm personally proud of that just because it's, it's the first one in those, in that direction. Um, and I have one, uh,

called quintessence and the rest of the world, which was an early intervention in theories of dark energy when they became interesting in, you know, 1998 when we just discovered dark energy and I pointed out, um, some, you know, issues of naturalness with many people's theories of dark energy and I pointed out some issues of naturalness with many people's theories of dark energy and I pointed out how to get around them and on the basis of that I made an experimental prediction which they're still trying to test these days. People like Brian Keating and others.

So that always makes you feel good when you make an experimental prediction that people are trying to test. And where do your ideas, what you consider to be the best ideas of yours, where do they come from? When do they occur to you? Is there a pattern to them? Honestly, the best ideas come out of annoyance, because you read other people's papers, you hear what they're talking about, and you think to yourself, like, that doesn't quite work, that doesn't quite fit together. Like the Quintessence paper, there were all these people writing models of dark energy with scalar fields that were very low mass and for some reason weren't interacting with anything else. I thought that was very unlikely,

so I explained that it was unlikely. For the Arrow of Time paper, there are a lot of cosmologists writing papers about what they consider to be natural conditions for the early universe, and I think that they were not actually natural, they were just cheating, just like Boltzmann did back in the day. So I got annoyed with that and I tried to do better. So what would you say is the correct model in your present deliberation of dark matter? Oh, dark matter I'm quite open about.

You know, I was completely of the opinion 20 years ago that there were good arguments for weakly interacting massive particle, dark matter. But those arguments went hand in hand with other arguments that would have led you to believe that the Large Hadron Collider would discover a lot of new particles when it turned on. And so that hasn't happened. So I've updated my credences about that. Like I said, there's plenty of other options on the market. I think axions are probably the most plausible right now. Axions are also good for other reasons.

But we'll have to wait and see. That's an empirical question. Okay, so constants become fields. Constant become fields, or more precisely, the expectation value of certain fields. Right, okay. Even the speed of light? Speed of light is not, we view it in a fundamental unit as one, so we don't even talk about it. It's not the speed of light we view it as one. It's not changing for any discussion that I'm working. In other words, speed of light is not a, let me make it more clear. So in your theory, you don't need to have a parameter for speed of light.

That just sets the units for us. So something else will change, don't need to have a parameter for speed of light, that just sets the units for us. So something else will change, but that will change with respect to the speed of light. Yeah, you could try to do that, but all the parameters in the theory will be somehow related to fields. Now, if you take, if you, so now I haven't stated what distance conjecture or duality conjecture is.

It tells you that if you take this field and take the value of this field to extreme values small or large That means in your physical theory it might have been a coupling becomes extremely small or extremely large Something like that. You always your theory always breaks down always something like that, your theory always breaks down, always. That's a surprise. That means the extreme limits means something breaks down. Yes. Now, what do I mean by breakdown?

It means that if you go to far away corners of these extreme parameters, you get a tower of particles which used to be very heavy, becoming lighter, lighter, lighter and lighter, and as you go to extreme values, these give you an infinite tower of light particles. Very, very little mass, separated from each other by little masses. And so you have a huge number of particles that you had ignored, because back in the middle of the field space, they were very massive, so you could have ignored them. But when you're going to these extreme parameters, they become so light you cannot ignore them.

And if you try to incorporate them one by one, you cannot succeed because there are infinitely many of them. So therefore, if you go far away to the left or to the right or anywhere, any direction you go, your description breaks down. So what happens, a new description comes over and takes over, incorporating those degrees of freedom, which is not your original description at all.

It might mean that some dimensions opened up. It might mean that some extra particles or strings are in the game that you have completely no idea about. This gives us what we call the dual description. So the duality in physics, I just explained to you in the language of this form, is of this form. You start somewhere, you go one limit, you find one description, which is what we call one duality frame.

If you go the other direction, you get a completely different perspective, another duality frame. So these physics between them are describing the same physics, but at different extreme regions of parameter space. So this is the duality or distance conjecture, which is also another example. And this does not have to be true without gravity. It's only there if you have gravity. So quantum gravity changes the whole rule. The rules of quantum field theory are not applicable.

And that's, I think, the most exciting thing we have learned in string theory. String theory tells you that the paradigm that the particle physicists have been operating for the hundred years is wrong, is wrong, is badly wrong because they thought they could ignore the short distance away from large distance. We have learned that you cannot decouple them. The short and large are intricately connected when it comes to gravity. And this is crucial because potentially a lot of the puzzles of particle physics, like hierarchy problem, like all these puzzles that particle

physics has difficulty with, that try to use supersymmetry to answer, for example, someone didn't work. So many of these puzzles, which doesn't look natural to particle physicists, is because they had ignored gravity in the discussion. And the reason they ignored gravity was kind of benign. They said, look, gravity is a weak force. It is not strong until you get to plank energies. And we are not in our accelerators. We are nowhere near plank energy. So forget about that. So we were just talking about other particles. Forget about gravity. They thought that not thinking about them is perfectly fine because the energy that we are doing is not related to that. They were not

thinking about the connection I told you about black hole. The higher energy and low energy are intricately linked with each other and that picture is what is I think at the root of failure of particle physics to try to explain a lot of these fine-tuning or hierarchies that appear. Are particle physicists still thinking that we don't have to incorporate gravity? There's a group and a lot of these fine-tuning or hierarchies that appear. Are particle physicists still thinking that we don't have to incorporate gravity? There's a group, it's beginning to change. So, and I do know that there's a number of particle physicists

are now becoming cognizant of this fact. For example, my colleague here, Matt Rees, is an example of such a group of particle physicists who appreciate the importance of the quantum gravity as being in the mix to get insights into particle physics questions. So there is drawing, but still by and large, I think the majority of particle physics unfortunately are not as much familiar with this. And so it's gradually getting to them. But I think it will get because it's kind of, it actually gives their field of vitality to make predictive powers because, as I just told you, the number of possible allowed ones are measure zero.

So therefore, this gives you predictive power. So if you understand what these rules are, it will give you what paragraph is like because they are looking for such paradigms. So I think they will, when they get to learn a bit more about it, I think they will they will appreciate it even more. So in other words, usually in a treasure map, you have x marks the spot, but we don't have the x. If we had the x, we'd have the answer. But if you can exclude parts of the map, exactly ever more so you encroach on exactly viable region, then you say, okay, so we don't have to dig across the whole earth. We can just dig in this guy's back alley in Panama. Exactly, exactly. And so sometimes what happens is that you get lucky. Like, you know, the thing is the X is on the left of this line, but the experiment finds it very close to this line. And you didn't know whether it's going to you sorry, finds it very much along a line here somewhere. And you don't know whether it's going to be

past this or not. And you say, no, no, no, it cannot be past that. But the experiment says that it cannot be so much to the left either. So therefore you're kind of stuck on that line or very close to it. So in this way becomes predictive. Even though it sounds like you're just excluding something combined with experiments, it actually can become predictive. And that's what we have been using it for. So while the Swamp Land has a negative connotation to its name, it's actually positive because you want to be able to exclude more and more. Exactly. So that you can dig at a place that lessen. Okay.

So when you use the word consistent earlier, when you say that look, we're excluding what's inconsistent. Inconsistent means what? Inconsistent means it does not have a short distance completion. That means it looks fine at large distances, but there's no full theory which you can have answered to questions like what happens at high energy scatterings. It will have answers to some region, but not the rest. It doesn't fit together. So you don't have a complete picture. It doesn't work. Okay, because the way mathematicians use the word consistent or inconsistent is that if

you have a theory that's inconsistent, you can predict everything because you have A and not A at the same time. But that's not the sense that physicists mean inconsistent when they're speaking about this theory of quantum gravity is inconsistent. No, it is the same. It is the same. It is the same. It means that suppose I give you a theory for which you study the scattering of particles of some energy E and it looks perfectly fine and everything is good. But you don't know how to compute when E is very large. And somebody says, no, no, no, the E that you picked,

if you try to do that, at large energy, it gives you nonsensical answers. The answer becomes blows up or becomes zero or something which doesn't make any sense. Therefore you say, well, that means that your other one is wrong. So A and not A also in that sense means, if you thought this A, then you're saying the other one is wrong. So in other words you get one side or the other not

working. So if you if you wanted the way it works at long distance the short distance doesn't work. So it is something like A and not A at the same time. I see that as unintuitive but I don't see that as inconsistent. So if someone predicts infinity I don't see that as being inconsistent. I see that as being not not corresponding to our world but, I don't see that as being inconsistent. I see that as being not corresponding to our world, but mathematically I don't see that as being inconsistent. Can you help me out? No, no, no. I'm not explaining, I'm not perhaps explaining myself clearly to you.

So suppose you have drawn a line and you draw a straight line. Suppose you draw, I'm just giving a boring example. You're drawing a straight line. And for physical reasons, suppose this is something that has to be positive, like a mass of a particle or something. You're drawing as a function of a parameter a straight line. And this mass should, the particle should have a positive mass everywhere. But you have studied it far away along the real line and you find that as you change

this parameter, it linearly grows with that parameter. You say, good, I'm done. The mass of the particle goes linearly, it's finished. And then somebody comes and tells you, no, no, no, no, it's not finished. If you go to the other regime, it's negative mass. It doesn't make any sense. That's what I'm saying. So the thing that you thought, the thing that you thought is fine, it doesn't work on the other side. In that example, the difficulty is that you said for physical reasons in the beginning you prefaced this with for physical reasons we have to assume the mass is positive. So that's what I'm getting at. No, not physical reasons. I mean, I'm just saying suppose in your physical theory,

you come up with a physical theory which says oh mass grows linearly and in this regime is positive and that's worked perfectly fine, you're done. For large, for some regime of panamety of parameters. And your theory doesn't tell you anything about the other regime, but your prediction is that should be linear. Yes. But then somebody comes and tells you that cannot be because of the silly fact that if you take this and continue to negative, the mass will become negative and that's not allowed. And that's all. And therefore, the fact that

simple fact that in this I'm giving a little bit of a silly example so that I can illustrate the point. In one regime you know how to do a computation and you think it's fine but actually fails because you're not looking at the totality of the question. So it's inconsistent as a whole. So it ends up inconsistent. So one side is like large distance physics and the other one is like a short distance physics If you take something as large as in physics and you study it You may not know that you're assuming something about short distance, which is not allowed Okay. Now is that because the the short distance comprises the long distance or vice versa? No, they are connected They are connected. You see I was trying to give you the black hole example. You could not have ignored it

You couldn't say they're independent. I see. They're connected because the higher and higher energy gives you bigger and bigger distances. So they're somehow related. What you thought that you're probing at short distance actually ends up being large distance. Higher energy knows about large distance, not short distance. So what happened there? So that paradigm was wrong that that one was using. So that's what has

so it's a revolutionary, in some sense, really revolutionary. That is, the ideas that we thought about scales, short and large separation, is actually badly badly wrong and it is actually in some sense a good development because that leads to predictive power for us. Well, let me see if I understand by taking your silly example and making it even more silly. So let's take this cup and let's say look, this cup must comprise, if you were to zoom in, elements that have mass because this guy as a whole has mass. But if you keep zooming in and your theory then tells you that there's negative mass

there, well, the way that you get the total mass of this cup is by integrating. So you should get something that's negative mass. However, you have the observation that has positive mass, so there's an inconsistency there. Would that be correct? Yes, yes. Okay, so let's talk about classical versus quantum. Is the notion of classical versus quantum fundamental?

And if not, then why not? No, it's not fundamental. Classical and quantum can interchange, and that mirror symmetry is an example of it. So something which appears classical to one perspective can be quantum to another perspective. fundamental, classical and quantum can interchange and that mirror symmetry is an example of it. So something which appears classical to one perspective can be quantum to another perspective. Because the analog of Planck constant can itself be a parameter. And if you go to very strong large values of that Planck, then the duality example I was telling you about gives you some other description opening up.

So sometimes that becomes a classical picture of somebody else. So something which is highly quantum to one perspective becomes classical to another. It's part of duality example. Professor, what would you say is the definition of string theory? Let me preface this. So in other words, if someone hands you a theory, how do you know this is a string theory? Is it that it has extended objects? Is it as simple as extended objects? Is it

as simple as that? No, I wouldn't say that. I would say string theory attempts to describe quantum, consistent quantum gravity theories. String theory has landed on what we think might be the only constant theory of quantum gravity. But the Swamp Land program that I am studying, for example, does not assume that. So we are open to the possibility that there are other constant theory of quantum gravities. But we haven't, but we have all the evidence we are in other words what I mean by that is that we don't want to say just because string theory cannot give you this physical reality that cannot be obtained period. We try to see

if you cannot rule out a physical reality by some other reasonings like black hole physics beyond string theory is not to do with string theory per se which rules that theory out or not so string theory could be therefore in some sense be derived if everything that is allowed ends up being what you can get in string theory if the totality of what is allowed is exactly equal to what string theory gives you then string theory is the only game in town. But we are not assuming that. And in fact, I think it's healthy not to assume that. We want to assume quantum theory of gravity. So consistency of a quantum theory of gravity. That means gravity is well

defined with the properties involving black holes, with other particles, with the consistent set of rules of scatterings and objects and all that. So we have a set of rules that we can check whether they are consistent, and that's what I mean by quantum gravity being good. If you handed me one of those, I would start asking questions like scatter this, do that, do this, to see if it's consistent. And maybe in some regime I'll see some extended objects, because that's one of the things that I expect, and then maybe a string,

maybe a membrane, maybe something else. So therefore these are the tests I will run this object or theory that you give me about. So string theory by now, I think is, I would say at least to me and many of my colleagues, convincingly perhaps possibly the only theory of quantum gravity, but perhaps possibly the only theory of quantum gravity, but it's always, I think, good to be open-minded in possibilities of other possible theories that could exist. I think also if you even want to understand just string theory, having this perspective is good

because it tells you what are the fundamental things in string theory, what makes string theory tick, what are the basic reasons or ideas that go into it? So you have to step back away from string theory to try to get that formulation. What are some of the other theories that may compete with string theory to describe our universe that you feel like perhaps you don't feel like they're on the right track? Otherwise you would switch gears and just start publishing it. I don't think there's anything comparable to, I mean you hear sometimes loop quantum

gravity and this other I think they're just it's just far off about what we are talking about so I wouldn't say even on par so so yeah I don't think I didn't think right now there's any game in town other than string theory but I think we should keep it open-minded not that not we have found one, but I'm just saying the possibility of having some other structure that's consistent with gravity, we should be open to it. But right now, I think all the evidence is pointing towards that. For example, in the context of Swamp Land, we are finding that the rules that seem to be consistency of black hole physics, unitarity, evaporation, all the things that we think should be true regardless of whether it's string theory. When you use them, you narrow the space of theories down and you find a lot of the cases that we know how to narrow them down,

you end up to be exactly the same set you get in string theory. And so that to us begins to smell like, okay, that's the only game in town. So we are now deriving pieces of it. So with enough supersymmetry, high enough dimensions we actually have accomplished that. That we can actually push this to a classification of possible things and it exactly matches what string theory gives you. So we are very happy with the

fact that now we are finally beginning to quote unquote derive string theory from some first principles. Practically speaking what would it mean to keep one's mind open about other quantum theories of gravity or other unifications of gravity with a standard model? Does that mean a grant body for like an additional grant body or additional department? Like practically speaking, what is meant? No, no, no. I will tell you how it will appear.

Suppose I'm studying possible consistent theories of scattering of gravitons. And I find, I study them and I find some framework, I become so smart, I manage to exactly solve what are the allowed possibilities. And I find there are only two possibilities in ten dimensions. One of them gives you exactly the answer to string theory. And the other one is not. But it looks perfectly consistent. Okay? That other thing is whatever you want to call it, it's not string theory, therefore. And so therefore, we would have found another theory. So if we were there, but more and more,

the way we are doing it, we're always being narrowed down only to the one corner, which is what I recognize, which is string theory. Not in everything we have done that, but in high enough supersymmetry with high enough dimensions, we are being cornered to the string corner. Not in everything we have done that, but in high enough supersymmetry with high enough dimensions, we are being cornered to the string corner. And so this is what we call the string lamppost principle. Sometimes the people told us, well, you guys are studying only string theory and you might be suffering from the lamppost effect,

that is, you're only seeing things string theory gives you. But if everything that we're getting is part of that lamppost, that is everything, that's what we're finding. And this thing we're calling the string lamppost principle, that is, there is nothing else other than the lamppost of strings. When people talk about quantum gravity and you go to different lectures, there's often, well, what we do is we sum over the geometries, like you sum over different paths in the Feynman integral. Is that the correct approach to quantum gravity? You sum over the different possible metrics?

At some level, it seems perfectly okay, but not at fundamental level. I don't think we have a fundamental definition of quantum gravity. At large distances, it might be like that, and you take pieces. But if you come to a short distance like tank scale, I don't think that's the correct description.

At distances for which the space-time geometry itself is a highly bubbly quantum form of geometries bubbling off and so on, I don't think you should think about the summing over geometries, because the notion of geometry doesn't make sense. So you're in a regime where geometry is not even a good approximation. So therefore, I think in some regimes it might be that, but not as a whole.

I don't think the notion of distance and metric universally makes sense. Let's come back to the biggest puzzle of all. How on earth did everything we see come out of a point? And the key, I believe, is a certain symmetry in the laws of physics we already know, namely the laws of those forces of nature, one of which is electromagnetic forces, the laws of light and electric and magnetic fields,

and the laws of light and electric and magnetic fields, and the laws of particle physics we know, which were written down by Dirac, the Dirac equation. Those two theories happen to have a symmetry under rescaling space. So this is actually the reason why a light wave is in fact is essentially the same as an x-ray. An x-ray is just a scale down version of a light wave you know you just shrink the length scale is shrink the wavelength of light and you'll get an x-ray. Expand the wavelength of the light and you'll get a radio wave light is essentially. The same thing scale up and down. It can come

in all forms. They all obey the same equation. They just have longer or shorter. It's uniquely specified by the wavelength. The reason the theory behaves like that is it has a symmetry. And the symmetry is scaling, symmetry, rescaling length, and time. And you get shorter or longer wavelength, higher frequency, or lower frequency light. Now, Dirac's equation has the same property, as long as you ignore the masses of the particles. So in other words, when these equations are taken to be massless limit,

and the Big Bang is exactly such a place because the plasma is extremely hot, so masses are irrelevant there. And so it's very tempting to believe that at the Big Bang Singularity, essentially there was nothing but light and light-like particles, and they all have this scaling symmetry. And what it's telling us in sort of colloquial terms is that the matter did not know about the size of the universe. It evolves in such a way that it doesn't care that the universe is shrinking as we go back in time. And so the matter is evolving as if the universe were in fact not shrinking to a point, or can be described mathematically with ignoring the shrinking away of the universe. And this is what we noticed about the Einstein equations and the laws of radiation, they have the Big Bang singularities, a very particular type of singularity

called a conformal singularity. Conformal, and I'll tell you a little bit more about conformal. Conformal symmetry, this is a picture which sort of illustrates this. So light and particles are described as gauge fields and fermions in the standard model, a la Maxwell and Dirac. Now conformal symmetry is a symmetry

of light and massless particles. Conformal symmetry means that you can actually rescale space and time locally, and the equations are invariant. So here's an example. Imagine I was solving Maxwell's equations inside a cylinder. So the boundary of the cylinder was a circle, as the left picture shows. Alternatively, imagine I was solving Maxwell's equations inside a square pipe. So the cross-section was a square. Conformal symmetry tells you those two situations

are actually identical, as far as the light is concerned. And often, so the grid you see on the right, that's just a coordinate grid. It's useful for writing down equations or putting them on a computer but has no particular physical significance. Now, if I distort the square on the right into the disk on the left with a conformal transformation. That means a local change of scale, which does not change angles. It only changes lengths. I get the

picture on the left. So that's another grid. I could solve the Maxwell's equations on that grid. And then the statement of conformal symmetry is that these two things give exactly the same result. These funny points where you see this pileup of grid points in the left-hand picture, they're a little bit like the Big Bang singularity. There's a pileup of space into a point. What it's saying is you just have to blow that up with the conformal transformation just expand your grid and. The equations are just the same in the in the in the in the new picture so we actually use this picture to make sense of the big bang singularity. I'm.

of the Big Bang singularity. So we go back to the Big Bang singularity. Now imagine blowing up that singularity. I don't mean in the sense of explosion. I mean in a mathematical sense, like changing the scale of space. So one can do this mathematically. And then the singularity actually becomes finite. It's not a point.

It's now a finite patch. And then we impose a boundary condition on that patch, which implements mirror symmetry. So that initial patch at the Big Bang, we treat as if it were a mirror. Normally when we deal with, let's say Maxwell's equations in a mirror, the propagation of the light in the presence of mirror,

there are two ways to do it. Either you impose a boundary condition at the mirror, you say that the electric field parallel to the mirror has to be zero, and you literally solve the equations showing how the light travels to the mirror, bounces off the mirror, and comes back. That's one way of doing it.

It's actually a rather tedious way of doing it. There's a much nicer way of doing it, which is to say, look, I'm looking at myself in the mirror. Let me make a, if I'm right-handed, let me make a left-handed version of myself. Put that behind the mirror. Okay? So it's a fictitious person.

That's literally a mirror image of me. Put it behind the mirror, an equal distance from the mirror. Throw the mirror an equal distance from the mirror, throw the mirror away, and just solve Maxwell's equations for the light coming from that person to me. That's called the method of images in physics. It's a very elegant way of solving boundary value problems. What we're claiming is that you can apply the same method to describe the Big Bang.

The Big Bang is a mirror. So I literally take the post-Bang universe, make an image of it before the Big Bang, and then I would just propagate light and particles from that pre-Bang universe through the big bang singularity because of conformal symmetry that propagation is completely smooth and regular and predictable and I propagate that forward to to see what we see. So we claim that this extended or mirror universe picture is absolutely

compatible with everything we see in the universe. So in a certain sense, when we look back towards the Big Bang, we are seeing our own image, okay, that the Big Bang is a boundary condition. It's not, you shouldn't think about, you see, the conventional way about thinking about the big bang which i think leads to terrible paradoxes is that somebody. Input all the stuff in the universe at the big bang and sort of threw it apart right. What we're doing is the opposite of that we said no the big bang it. What we're doing is the opposite of that. We said, no, the big bang, all that happens in the big bang is a boundary condition,

which the matter has to respect. If you look at this, the traditional way is that someone or something just spurred everything into existence from that single point. Exactly. Then you're saying that this is an improved picture. Yes. However, it just looks like someone or something spurred all from,

at all points at once. So it doesn't seem like much of an improvement. So tell me why this is different. Right. No, good question. You might say our picture looks like somebody made two universes, so surely it's twice as difficult. Yes.

No, good point. What we're saying is that there is a, yeah, in fact, the answer is this. Great. Natural lead-up. Yes. The answer is this. So the most fundamental law of physics we know, which is a direct consequence of quantum mechanics and relativity, is called CPT symmetry. CPT symmetry was discovered in the 30s and 40s as an inevitable consequence of bringing quantum mechanics and relativity together. So it underlies quantum field theory. Now what is CPT symmetry? CPT symmetry says the following, that if I turn, if I look at some physical process,

and I try to make another physical process using a law of symmetry, okay? So take some physical process, turn every particle into its antiparticle. That's what the C does. P inverts space. So literally just send any space coordinate in three-dimensional space to its inverse. X goes to minus x. That's an inversion of space. That's a very dramatic thing to do,

but the laws, you can do this with the laws of physics. T is time reversal. So whatever's going forward in time, make it go backwards in time. The CPT theorem in relativistic quantum physics tells you that the rate for any process and its CPT conjugate process is identical. So this is kind of analogous to time reversal in Newtonian mechanics.

In Newtonian mechanics, you can take any laws of motion and reverse time. And because the second order equations in time, they are invariant. So Newtonian mechanics has no arrow of time. And in relativity, the generalization is CPT. So we take our observed universe, the right hand part of this picture, it has more matter than antimatter. Okay, so it is not invariant under C. And it's not invariant under T, it's going

one way in time. And so the right hand side of this picture violates CPT. But if you apply CPT to the right hand side of the universe, what you get is the left hand side. Namely, every particle goes to its antiparticle. What was going forwards in time moving to the right in the right hand part of the picture is now going forwards in time moving to the left in the left hand part of the picture is now going forwards in time, moving to the left, in the left-hand part of the picture. And so the statement is that if you want the universe to respect the laws of physics in the most obvious way, namely that it is invariant under CPT, then you are led to this doubled picture. And in the doubled picture,

there is then a very natural boundary condition, which is symmetrical under CPT, and the boundary condition is the one that we use. So we're saying the Big Bang is a CPT mirror. And this resolves the fundamental puzzle saying the Big Bang is a CPT mirror. And this resolves the fundamental puzzle of why the universe appears to us to violate its own laws. We send more matter than antimatter.

That looks like the universe is not invariant under C. Likewise, we see time going one way. And that's incompatible with the fact that the laws of physics are invariant under reversing time and changing matter to antimatter. So what we're doing here is an extremely minimal application of CPT to the universe. And the consequence is this mirror universe hypothesis. So to put it differently, anyone who makes any other hypothesis is going to have to violate CPT.

And that's a losing battle. And that's a losing battle. So yeah, so we were very surprised. So in Newtonian mechanics, if you take a ball, and there's no friction, and you drop it, it hits, and then it comes right back up. Exactly. OK, now if you were to look locally, if you were to just look at half a second,

you would say, well, look, there is a difference between the future and the past because in the past it starts to go down, but in the future it starts to go up. But you're saying, well, you have to look at the whole picture. Of course. So let's take the full movie. Of course. So now, philosophically speaking, we use that word earlier. Sure.

What is someone who's watching this supposed to feel? There's some religions that say something or someone or universe started itself and you experience this world once. Then there are some other traditions that say you experience it cyclically, infinitely. And then there's here, which seems to suggest, well, you experience everything twice. No, because you see, when I When I say we're using the method of images to impose a boundary condition at the Big Bang, so this picture is a mathematical picture, a device which is useful in order to impose a particular boundary at the Big Bang.

In this picture, the universe in a certain sense creates itself. Okay, it's extremely minimal. Everything I described could be described by just taking the right half of the picture with this boundary condition, which is in effect the result of doubling it and imposing the symmetry. You see, if I double it and impose the symmetry, the doubling goes away, right? Because the left and right halves are identical. So then to be specific, is it correct to say the Big Bang is a mirror? Yes.

Or that for mathematical convenience, it's useful to model the Big Bang as a mirror? Like, is that the more elaborate correct statement? No. Or the Big Bang as a mirror. Like is that the more elaborate correct statement? Or the Big Bang is a mirror is the correct statement? Correct statement is the Big Bang is a mirror. And for any mirror, it is useful to double the universe. I see. Yeah. The doubling is just a mathematical trick, which you can use for any mirror. And we're saying that literally the Big Bang is a mirror. So I would say that this, I mean, certainly in my experience, and I've worked with Stephen Hawking,

and I've worked with a number of other such people on scenarios for cosmology, there is no doubt this is the most economical hypothesis you can make. Because it's consistent compatible with the laws of physics and extremely minimal. So either it's right or it's wrong. We'll see. That's the attractive feature of this whole setup is that it is eminently disprovable, and that makes it interesting.

So, as I mentioned, these laws, the particles and forces, actually do have this symmetry under local changes of scale, and that allows us to resolve the Big Bang singularity, to blow up the point everything came from into a patch, and then that patch is the mirror at the Big Bang. This is actually all the particles we know. Now, notice something funny about this picture.

So the neutrinos in the bottom left have a superscript L, meaning that they are left-handed. If they are traveling along in the direction of the thumb of your left hand, the spin follows the fingers of your left hand. So, it's rather strange that the light neutrinos we see only come in the left-handed variety. All the other particles have a right-handed and a left-handed version. Now, so that is, you know, what we see in laboratory experiments. We only ever see left-handed neutrinos. However, if we were to imagine the simplest or the most minimal conceivable extension

of the standard laws of physics, what would it be? And I just made it. I went from this slide to that slide by removing the L. Okay? Now all the particles have both left and right-handed versions. Okay? And my claim, our claim, this is with Latham-Boyle, our claim is that removing that L, in other words giving the neutrinos a right-handed as well as a left-handed version, allows you to solve the problem of dark matter, okay, in an extremely minimal way with the mirror hypothesis. So now imagine these are the laws of physics.

There's no L anymore on any particle. Every particle has left and right versions. Now what happens is I take my left-handed neutrino, it's coming in from the left. It then, what we call, we say that it can oscillate into a right-handed neutrino, the new right in the middle, and oscillate back into a left-handed neutrino on the right. Now the left-handed neutrinos are very light.

Neutrinos are very light particles. They don't have much mass. If the right-handed neutrino is very heavy, then this process can only be a virtual process. You can't, you had a certain amount of energy, you can't stay as a right-handed neutrino, you just don't have enough energy to account for its mass. So you've got to go back to being a left-handed neutrino. So this is what we call neutrino oscillations. The left-handed neutrinos can oscillate briefly into a right-handed neutrino, and then they find themselves in, if you like, they've got more mass than they can account for with their energy,

and so they go back into being a left-handed neutrino. This mechanism is a mechanism for giving the left-handed neutrinos a small mass. And neutrino masses started to be measured in the 1970s, and this mechanism was quickly realized as the simplest explanation for those masses. Namely, if there are right-handed neutrinos, which are very heavy, this would explain why the left-handed neutrinos are very light. You see, the heavier the right-handed neutrino, the shorter the time you're going to spend as a right-handed neutrino. And so basically, the heavier you make it, the less and less probable it is that the neutrino oscillates in this way. And so it's called the seesaw mechanism because the heavier you make the right-handed neutrino,

the lighter the mass of the left-handed neutrino. So this was understood in the 70s. And at that time, people could have said, oh, well, maybe the dark matter is a right handed neutrino you see the right hand is a very obvious candidate because it has no electromagnetic charge it doesn't couple to the strong or the weak force at all so the only thing the right hand neutrino couples to is the Higgs field, this thing noted by H, and gravity. For the right-hand neutrino to be the dark matter, all you need do is A, switch off this coupling. Actually, this is the important one.

For the right-hand neutrino to be the dark matter, the only problem is that it can decay. This diagram shows a right-handed neutrino decaying into a Higgs and a left-handed neutrino. So, if you want the dark matter to be stable, you know, it has to have survived for at least 14 billion years, you've got to switch off this vertex. And if you switch off that vertex, you must switch off this vertex because they're the same vertex.

And if you do that, it means the left-handed neutrino cannot oscillate into the right-handed neutrino. And this actually means the left-handed guy must be massless. So just from this picture you can see that if the dark matter is stable and consists of right-handed neutrinos then it's plausible that one of the left-handed neutrinos is massless. It's a kind of a mixed bag I would say but I still think we're facing very fundamental questions particularly in this issue of quantum mechanics and gravitational physics, where we've sort of got to get back to basics, I think, a bit more and start asking the deep questions rather than just ploughing through calculations.

What's the missing link then to solve the issues between quantum mechanics and general relativity? I mean I personally think it's to do with at the sort of deepest level it's to do with understanding the if you like the holistic nature of quantum physics a bit more explicitly and we know that that's the case or many of us believe that's the case in gravitational physics and Marx's principle in gravitational physics is, which I think, although it's not something that's been rigorously proved, I think most physicists are sort of sympathetic to the idea, which is that when you spin round and your arms flail out, or when you watch a Foucault pendulum and its plane of oscillation moves as the earth rotates, and you say, well, what actually is causing that rotation, or what is causing my arms to flail out?

Marx's principle says it's the distant mass of the universe. It's the mass, it's the totality of the universe that is doing that. And I think we have to kind of take that notion and move it more into the quantum regime. And you know, sometimes, I mean, this is not completely new idea, people like David Bohm and Basil Hiley, their famous book on quantum mechanics was called the undivided universe. So it's a concept that's sort of been around, but I think we have to take it a bit more seriously and recognize that both in the quantum world and the gravitational world, the local

laws of physics are probably determined by the large-scale structure of the universe. So what is Mach's principle? Can you state it rigorously or you can't and that's the reason why it's unproved rigorously? Well, as I say, Mach's principle is that the, you see, the question is when we rotate ourselves, if we spin round, our arms flail out or if we drive around a curve in the in the road we kind of get pushed to the side of the car and we say you know that's that's caused by the centrifugal force or something like that but that's just a label and the question is let's take the rotating case. What actually is it that determines whether you're rotating or not rotating? And Mach, I mean, this actually goes back to Bishop Barclay

back in the earlier times. But in the 19th century, Mach said, well, the reason why we say we're rotating is because when we rotate, we see the distance stars moving and he said well that's not a coincidence it's because of the kind of gravitational effect of the distant matter that defines what a non rotating frame is and a rotating frame. And this was a very big inspiration for Einstein in his coming, in his developing his theory of general relativity. And indeed in general relativity there is an effect called the Lenz-Turing effect where if you have a mass, a massive shell if you like, and you rotate it, that rotating mass drags the local frames of reference around with it. So in other words, locally, that tells you whether you're rotating or not. Then you ask the question, does general relativity automatically, is it internally consistent with Marx's principle?

Well, you can have space times where there is no distant matter, so the Schwarzschild solution for an isolated star or black hole doesn't have distant matter. But in some sense you have to define then what you mean by rotating or non-rotating. In the case of the Schwarzschild it's a non-rotating solution. You kind of have to impose that non-rotating condition by a boundary condition at infinity. But I think most cosmologists believe that in the real world where we don't live in, the Earth is not an isolated mass in an otherwise empty universe, it's part of the universe. And I think most cosmologists would accept that Mark's principle probably is the key reason why we experience so-called inertial forces in rotating frames

of reference, because these are the ones moving with respect to the distant stars. But it's hard to prove it because we don't yet know, you know, we don't even know whether the universe is infinite or finite. We don't really know how much matter there is. So it's become Marx, I like to think of it like this, Marx principle has become a little bit like some of these famous sort of conjectures in number theory, like Goldbach's conjecture, you know, that every even number is a sum of two prime numbers. I mean, everybody kind of believes it's true, but nobody knows how to prove it. So it's not very high up in the research agenda because nobody knows how to

prove it. And in a way, I think Mark's principle is similar. It's difficult to know how to prove it rigorously, but I think most cosmologists would sort of accept that it's something, there's some truth in it. And I think, as I say, I think that we've got to get to that sort of stage in thinking about quantum mechanics as well. Okay, fill in this blank for me. Mark's principle is to general relativity as blank thinking about quantum mechanics as well. Okay, fill in this blank for me.

Mach's principle is to general relativity as blank is to quantum mechanics. Well, okay, I mean, I have my own, you know, you're putting me on the spot. I mean, I have my own, you know, ideas about quantum mechanics or quantum physics, let's say. And I've tried to propose an idea which I call the cosmological invariant set postulate. And this is very much motivated by chaos theory that there are systems which exhibit this extraordinarily beautiful geometric structure in their state space. And that they, you know, if you leave these, if you start them from an arbitrary initial condition and just leave them for a long time, eventually they just evolve on this, what's called invariant set,

or sometimes called an attractor. But these are fractal attractors. And my kind of principle, which would be consistent with what I'm talking about here, the holistic nature of quantum physics, would be the universe evolving on a cosmological invariant set. So Marx's principle is gravity as perhaps this cosmological invariant set postulates to quantum physics. And the reason for saying that is that it can explain some of these difficult issues like entanglement and Bell's theorem without having to invoke non-locality or indeterminism, all the sort of things that Einstein hated. So, Professor, I'm a stickler for words and I noticed a few times you were going to say

that, okay, so I have three questions here. Einstein's theory is consistent with Mach's principles and then with Mach's principle. Then you corrected yourself and said, is internally consistent with Mach's principle. So one of the questions I have is, well, what's the difference between being consistent

and internally consistent? Okay, so we'll get to that but just a moment So I don't forget you corrected yourself when you were saying quantum mechanics you switched it to quantum physics So I'm curious what the difference is there that you see and then another time is invariant sets Which is the same as a fractal attractor? Okay, if it's the same as a fractal attractor Why did you rename it as invariant set? Okay. So those are three questions. The first one was about internal consistency versus consistency. Okay, on the first question, there are solutions of Einstein's equations. And I mentioned earlier the isolated body and the Schwarzschild solution.

Another one is what's called De Sitter space, you know, which has no matter in it and yet space is curved. It's curved by the cosmological constant. So you can come up with space times which satisfy Einstein's field equations, which are not Machian, you know, because there's no distant matter for them to be. However, what I'm saying is, the real world, forget what I actually said, because what I'm trying to say is the real world, which is governed, you know, which is governed by, let's say to a good approximation, one of the Friedmann-Robertson-Walker solutions, the cosmological solutions of Einstein's equations, is consistent with Mach's principle. So not all solutions of Einstein's field equations are consistent with Mach's principle, but

the Friedmann type of equations are. And we live in a Friedmann type of universe. We don't live in De Sitter space and we don't live in an isolated Schwarzschild space. We live in something which, at least on the very, very, very large scale, approximates quite well to the Friedmann-Robertson-Walker cosmology. So from that point of view, that's consistent with Marx's principle. Quantum physics versus mechanics. Yeah, no, quantum mechanics is a very specific theory. That's consistent with Mark's principle. Quantum physics versus mechanics. Yeah, no, quantum mechanics is a very specific theory.

It's the theory that Heisenberg first proposed almost 100 years ago, next year, I guess, and then Schrodinger very shortly afterwards with his wave mechanics version. So that's what we mean by quantum mechanics. It's a specific theory of quantum quantum phenomena. But I use the word quantum physics in a slightly more generic way which is you know the set of all observations of the world you know involving atoms and particles and

entangled systems where maybe quantum mechanics isn't the final word. I mean, that would be my belief, that it's not the final answer to how to describe quantum physics in as accurate a way as possible. I see. Okay, now the third one was invariant sets versus a fractal attractor. Yeah, well, the concept of an attractor

is that if you start with any old initial condition and you run your differential equations forward in time and just leave it for a very, very, very long time, then the state gets attracted to this special fractal. But the hypothesis I want to put forward is that the universe has always been evolving on this geometry. So it's never been attracted towards it. It was always on it and it always will be on it, potentially for an infinite time in the past or a finite time in the future.

It might end up being cyclical, it might end up repeating itself at some stage. But the point is, I'm not invoking the concept of it being attracted, the states of the universe being attracted towards this geometry, but it's just this is the geometry that it evolves on. And the concept behind this geometry is that it's called an invariant set because if you're on it today you always will be on it in the future and you always have been on it in the past. So the set is in some sense, or the geometry, is invariant under time evolution. It's invariant under the propagating forwards

or indeed backwards in time. So calling it an attractor, I don't like using that word because it implies that I'm thinking about states yeah I think you see the point is if you're outside it you're violating and this is an important point of my reason for believing why this is important for Bell's theorem if you don't lie on the attractor you're inconsistent with your this basic postulate the states which don't lie on the invariant set, by definition don't satisfy the postulate that states of the world evolve on the invariant set. So the concept of being

attracted towards it is not really a useful idea in this respect. I see. So in other words, the invariant set is the attractor, but we just... Our states are always on it. Exactly. That's exactly right. The invariant set is the attractor and states are on it. They always will be. They always have been.

At any point, any hypothetical, this is the point, if you imagine a counterfactual world, a hypothetical world in your head where you've slightly changed the position of that chair hypothetically. You haven't actually moved it, but you say, well, maybe I might have moved it. You've invented a counterfactual world which doesn't really exist. It's a hypothetical world. Now if that hypothetical world, if you've nudged the state of the universe off this invariant set when you're formulating such a hypothetical world, then I would say that's inconsistent with the laws of physics as I myself see it.

You may as well have said, what if this ball lifted up into the air? Like a counterfactual such as moving this chair a nudge that takes you off the tractor set or the invariant set is equivalent to saying, what if there was some elephant that just appeared here? But even in that case, there is some quantum mechanical chance that an elephant can appear here. It's just minute.

Well, there's a quantum mechanical chance. Now, I mean, of course, there is a chance an elephant might walk into this room, right, in five seconds. Who knows? I don't know. It's always possible. Should we wait and see? No, didn't happen.

Anyway, but it could have happened. But that's not quite the point I'm making. Point I'm making is if we took the world as it was 20 seconds ago and said, okay, no elephant walked into the room 20 seconds ago, but is a world where everything was the same, you and me talking, the people in London doing their shopping, the earth going around the sun, the sun going around the Milky Way, everything the same, except that an elephant walks into the room. Is that hypothetical world? Because it is hypothetical, it's not an actual world, because the elephant didn't walk in the room, right? It's just maybe we're hypothesizing the possibility that everything stayed the same, but an elephant walked in

the room. What I'm saying is, if that hypothetical state does not lie on this invariant set, and I don't, I'm not saying that it does or it doesn't, but if it didn't, then that would not be consistent with the way I formulate the laws of physics. The point about this is in quantum physics, this notion of counterfactual worlds actually occurs quite a lot of the time and most of the so-called no-go theorems and the classic one is of course Bell's theorem. Implicitly, there's an implicit assumption and it's not, you know, it's in regular proofs if you like, it's not drawn out terribly explicitly, but there's an implicit proof

when you introduce, for example, a hidden variable model. That that hidden variable model has the property that you can for example, keep your hidden variables fixed, but change the actual measurement orientations that you actually did the measurement with and assume that that hypothetical counterfactual measurement is consistent with the laws of physics that's that's an implicit assumption and I'm trying to draw out an example and my example is based on this notion of an invariant set and therefore it brings in the large scale structure of the universe where those counterfactuals would be inconsistent with the laws of physics. Now that being the case, you no longer have to conclude that the world is non-local or indeterministic or anything like that. It's just that certain counterfactual worlds, which

might seem plausible in your head, are actually technically inconsistent with the laws of physics. Great question. What distinguishes the Big Bang singularity from the one inside black holes is that at least if the Big Bang was dominated by radiation, the fields which have the special local symmetry, if that is what dominates the Big Bang, as observations seem to indicate, then the Big Bang singularity was analytic, it was smooth. When you say something is an analytic function,

you can extrapolate it. So if you have, say say a linear function hitting zero, just y equals x, and you tell me y is an analytic function of x, well, it's no problem to extrapolate it. Y is x and that applies when x is negative as well. Analytic functions have this property of being able to be extrapolated

in a completely unique way. So that's what we discovered that the solution of Einstein's equations describing a radiation-dominated Big Bang are analytic at t equals zero, and they have a unique extension to this pre-bang era. If you look at black holes, that is not true. So the singularity inside a black hole is totally different. It's what's called, it's very anisotropic. You know, as you head towards a singularity inside a black hole, you get squished in one direction

and stretched in the other two. It's very anisotropic, and this actually means it's not analytic, and you cannot forecast what comes out the other side. It's just impossible to forecast. Now, in very recent work, which is not yet published, we have been trying to extend our notion of analytic solutions of the Einstein equations

to black holes. And you can ask yourself, if a usual description of a black hole is not an analytic solution of the Einstein equations Is there one which is? Is there some other description of black hole? Which does describe it as an analytic solution of the of the einstein equations And the answer is I think this is still tentative. I think there is

And what happens is that as you head towards the event horizon, there's some matching process that basically when I fall into the event horizon, I would come out of another event horizon and I would never actually fall into the black hole. This is what we're studying now. the event horizon and it would never actually fall into the black hole. This is what we're studying now. It means there's some other prescription for solving the Einstein equations, which does not mean that when you fall into a black hole,

you fall in and hit the singularity. Because I believe that these singularities, you see the thing about this type of singularity because I believe that these singularities, you see the thing about this type of singularity, which is non-analytic, it does not solve the Einstein equations. The equations fail there, so you cannot claim this is a solution. And if there's sort of any justice in the world, which I think there will be, this principle, the principle that the Big Bang singularity is analytic, that is telling us that we need to concentrate on solutions of the Einstein equations which are analytic.

Okay, okay, wonderful, because my next question was going to be if the universe is analytic at say the zero point of the Big bang and analyticity implies that there's an analytic solution which can be extended from the origin arbitrarily. Yes, yes. Then why would it be that a black hole isn't analytic given that it's presumably at some other space time point? Yeah, so let me put this in another sort of framework. Our picture is that you take a big universe and its mirror image and you ask yourself, is there any solution of the Einstein equations which joins the two?

And I will only call it a solution if it's analytic because then it really solves the equation. If it's non-analytic, then it's ambiguous. It's inherently ambiguous. And why this is so important, it actually relates to path integrals and subtle point theory. The classical solutions of the Einstein equations

are called subtle points of the path integral for gravity. It means that basically they are a history in which the destructive interference is cancelling out. Classical physics arises through destructive interference from quantum physics. In quantum physics, you add up all possible histories, but they all come with different phases, and typically they all cancel out. If all the phases,

so destructive interference cancels out the contributions of all histories except classical ones. Classical ones are defined to be histories where there is no destructive interference. That all goes away. And basically, something is only a legitimate saddle point if it is analytic. Okay, so we're claiming the Big Bang singularity is a legitimate saddle point. In other words, it's not really singular,

it's because it's analytic. When I go to a black hole, and if I believe that black holes form and then evaporate, which we believe based on Hawking's calculations of black hole evaporation, it must be that there is some analytic history solution of the Einstein equations, which interpolates between the stuff falling in to make the black hole and the stuff coming out as Hawking radiation when the black hole has gone away. So there must be an analytic solution.

No one has ever found this solution, but with our ideas of CPT symmetry, we now have some hints as to what that kind of solution might look like. And if we do succeed in finding it, the physical interpretation of a black hole may be very different than the classical one based on the singular solution. The classical one says you just fall into the black hole and you're scrunched to zero and then that's the end of time, you know? So that's the conventional description of what happens to the black hole. If what we're saying is right, I suspect, and I could, I don't have the maths for

this yet, but I suspect that as you approach the event horizon of the black hole, everything becomes much more quantum. You'll go through some realm in which things are very quantum, and then you'll come out in a region of space-time in which everything is sort of classical again. What do you mean you'll go through some realm? Well, okay, so the simple analog is quantum tunneling. So in quantum tunneling, so imagine I've got a particle in a potential and the potential has a minimum followed by a barrier.

And so imagine a potential which kind which comes down to a minimum, goes up to a maximum, and then goes down to arbitrarily negative values. I put a particle in this potential well. If it's got some energy, it can rattle around in the well, but it can't get out. Classically, it can't get out.

Quantum mechanically, it tunnels. Quantum mechanically, it tunnels. Quantum mechanically, it can travel under the barrier and come out the other side. That's how atomic nuclei decay. The protons and neutrons are all stuck in a potential well, but occasionally one of them tunnels out. An alpha particle tunnels out of a radioactive nucleus like uranium and just flies off to infinity. So in quantum tunneling,

what happens is that you do not solve the real equations of motion. I'm using real in this sense of complex analysis. If you put a particle in a potential well with a certain energy and just leave it in there, it will stay there forever classically. Quantum mechanically doesn't stay there forever, it tunnels out.

The way it tunnels out is because it follows a complex solution of the same equations. For example, under the barrier, the wave function is falling exponentially, and that's described by saying that the momentum is imaginary. The particle has imaginary momentum, so e to the ipx is actually e to the minus kappa x, where kappa is real. That only happens because p is i times kappa. So quantum tunneling is mediated by complex classical solutions. And so if the right description of a black hole is that it has these two very classical regions

in the far past, far future, but in the middle you have this much more quantum object, it's quite plausible that that is described by a complex space-time, whatever that means. Okay, so nobody has ever found this. It's a very hard calculation to do, but I think it, my guess is it will exist. My guess is there will exist an accurate description of the formation and evaporation of black holes, but it's one where the real classical solution of stuff falling in and then hitting a singularity, that's, in my view, that will be irrelevant. That's not a real black hole, because it doesn't solve the Einstein equation.

It's not the saddle point of any path integral. It doesn't make sense quantum mechanically. I mean, quantum mechanically makes no sense for time to end. Principle in quantum mechanics is that evolution is unitary. You just see everything evolves with a phase, but everything, if you hit a singularity, time stops. That doesn't make any sense. So now if this picture is true, it of course will be very exciting because it will mean that there should be real predictions for

the behavior of black holes on scales of their event horizon. And we're now seeing these right with telescopes for the first time. You can actually see the event horizon. So yeah, I think we have to come up with a consistent picture of what's going on in black holes. And if we do, it will make definite predictions. Hopefully that can be tested. As you can tell, the whole program we're pursuing is kind of extremely minimal and ambitious. We're taking only the laws that we know and the particles we're confident exist, and we're trying to describe everything we see using those laws. You see, to put it differently, why would you ever do anything else?

I mean, minimalism is a very profound principle in science. And in decorating. And in everything. Occam's razor. You know, if you have a choice between a simple explanation or a complicated one, go for the simple one. It's much more useful. As you make descriptions more and more complex, they become less and less predictive,

and more and more arbitrary. This is exactly what's happened with string theory, supersymmetry, grand unified theories. They become more and more complicated. I'm taking the extreme opposite position. I'm saying just forget about all those frameworks. They never predicted anything anyway. Let's work with what we know and see what is the minimal resolution of these things.

So you mentioned the 36. Yes, doesn't seem minimal to most people. So explain why it is. It's a very amazing clue that we stumbled upon. So we started from the point of view that there's this awful contradiction staring us in the face, which is that quantum fields have infinite vacuum energy and Einstein gravity sees that energy. So what do you do about it? As I mentioned, there are more fermions than bosons in the standard model, so it's actually

minus infinity. The standard model has infinite negative energy density. So how am I going to cure this? Well, the simple solution would be just to add the right number of bosons to bring it back to zero. And it turns out that that number is actually 72, which is a multiple of 36. But that's not what got us excited. We also asked the question about this spoiling of local scale symmetry by renormalization. So this beautiful symmetry of Maxwell's theory

and Dirac's theory, which potentially allow you to describe the Big Bang singularity, this beautiful symmetry which was there got spoiled by renormalization. So, that is known in the jargon as trace anomalies, or sometimes called Weyl anomalies, after Hermann Weyl, W-E-Y-L. So, there are these anom anomalies which tell you that the symmetries which you had in the original theory are spoiled by these infinities in the vacuum. So we said how can we fix, so it turns out there are two of these anomalies which spoil

the symmetries and there's the vacuum energy. So basically there's three quantities and we wanted to set all three quantities zero. What is the minimal thing you could do to the standard model to cancel all these problems, all three problems? And we discovered that if you added 36 of a very particular kind of field, they all went away.

They all cancel. Okay. So it's new numerology. Now what kind of field? So this is a strange kind of field. Okay. Which actually was originally postulated by Heisenberg, Verner Heisenberg in the 50s, as a model for the strong interactions in atomic nuclei.

And so people have been playing with this type of field. It's a rather bizarre kind of field in that although it is a field, it has a value at every point in space, there's a huge degree of symmetry in this theory. So much symmetry that actually you're not allowed to have particles at all. It's literally a theory. Explain. Right. So there are certain basic principles you insist upon when building a quantum field theory. One is relativity, that the whole theory must be invariant under relativity.

Two, the theory must be consistent with quantum mechanics, and quantum mechanics requires that you have a sensible definition of probabilities. Okay, so basically in shorting a picture of quantum mechanics, you take the wave function, you square it, and that gives you the probability of finding any particle at that particular position. So you need a positive notion of what's called a positive metric on Hilbert space. The Hilbert space is the space on which quantum operators act.

So when you quantize this funny theory, it's a funny theory in many ways. The field here is what we call the dimension zero field. It's dimensionless, meaning it's more like an angle. It's not a usual field, quantum field like the Higgs field or the Maxwell vector potential field. These have dimensions, they carry mass dimensions. This kind of field has no dimension. It's a dimensionless field like an angle. It doesn't have any mass dimension. Also an indication of very high degree of symmetry.

You can change the definition of scale and this field doesn't change at all. So the action for this, whereas for a Higgs field, the action is gradient of the field squared, integrated over spacetime. The action of this field is what we call box of the field squared. So box is the Hempholz operator, it's a wave operator, the massless wave operator. So you take the massless wave operator on the field, square it, integrate it over spacetime, that's the action.

So there are actually four derivatives in this theory, not two. So ever since Newton, we've liked equations of motion with only two derivatives, like f equals ma, you know, what is a acceleration is d two x dt squared. So most physical laws are formulated only with two derivatives. This theory has four, four derivatives. Now one of the reasons that in QFT or when you have Lagrangians you have at most two derivatives is because otherwise you have problems with instabilities, Ostrogladsky

instabilities, causality and renormalizability. Right. So people focus on theories with two derivatives for good reasons. Ostrow-Gradski, in I think 1820 or 30, showed that any theory of classical mechanics with more than two derivatives has an energy which is unbounded below. That already suggests that such a system would be unstable. If I couple this theory with more than two derivatives with some other standard theory which has positive energy, I could feed energy from this system with unbounded below energy into the positive energy system forever and create

a perpetual motion machine or whatever. Ostrowski argued you should never use more than two derivatives. Now, so these are called runaway solutions or instabilities and so on. Now, this theory, the one with four derivatives, turns out that when you quantize it in quantum field theory, the one with four derivatives, turns out that when you quantize it in quantum field theory, actually the states of the quantized theory are all positive energy. There is no negative energy state. That sounds okay.

Just saying that the problem Ostergratze was worrying about doesn't exist. There are only positive energy states. However, some of those states have negative norms or negative probabilities. If you take the inner product, it's not positive and can't be interpreted as a probability. What you then say is, well, I'm not interested in wave

functions which have negative norms. I don't want them in the theory. It wouldn't be a sensible quantum theory. So what you have to do, now we're actually used to this engaged theory. Engaged theory, when you quantize them, what's called covariantly, you also get negative norm states. And we're very used in that case to simply working on a subspace of states, which is positive. And we have to show that all the interactions leave you on that positive subspace. And so what we've shown is with these four derivative theories, the same is true, that you can pick a subspace, you have to pick a subspace, and that on that subspace, all inner products are positive.

The only problem is that that subspace only includes the vacuum. Okay, that sounds like a huge problem. No I mean depends what you want to do with it. If you wanted to describe particles you would say it's a terrible problem. I can't describe particles because they all come along with these negative probabilities. But if what I want to do is to describe the energy of the vacuum, I'm completely happy. I say, okay, I throw in these dimension zero fields, they contribute to the energy of the vacuum, but they don't allow any particles.

What we found is if you add 36 of them, they fix the vacuum of the standard model, but you do not have any extra particles. In fact, they do more than this because they give you a possible way of building the Higgs field out of these dimensions here. So I have two questions here. One is what is doing that process of equivalencing? And then number two, you stated the word belief a few times, like we believe that we have a persistence in time and so on.

So mathematically, what is meant in your model by the word belief? Is the belief the same as assumption? We assume so and so like what is belief? Well okay, so first what's doing the equivalent saying the. Different cases different things. You know it's only physical systems like the piston with a bunch of molecules bouncing around the what is the equivalent thing that. There's more to analyze in this and there's about ten000 kinds of measurements we know how to make. And for every one of them, you can ask what's really going on.

And they all turn out to be, they're actually a couple of different categories, but they're pretty much all something is being aggregated. Lots of individual molecules are coming in, but there's an aggregate pressure. There's one different case, which is things like weighing balances, where you're saying, you know, there are many different ways you can make a certain weight, but at some point the balance tips over. So it's kind of a discrete output, kind of like what happens in standard quantum mechanics with qubits and so on.

There is a discrete output, whereas in the case of measuring pressure or something, you just have a continuous number out. But what's happening when you measure pressure? Well, what's happening is every time a molecule hits the piston, it makes some atomic scale deformation in the shape of the piston. And the, but that atomic scale deformation quickly sort of you know

Get smeared out because the speed of sound is high and the solid it's kind of that that defamation is kind of you know the atoms are wiggling around it quickly that that quickly disappears somehow and That's that's sort of a common thing that the the process of equivalency is Happening on a time scale that's short compared to the way that you observe it. So, you know, for our brains with our millisecond, multi-millisecond cycle times, sort of things that happen in less time than that, they are, we perceive them as being atomic things. We don't perceive those as being separated. If things are separated by a millisecond, we don't notice that. They're just the same kind of thing. But this again comes into,

well what, you know, we have this inner experience of things happening and that inner experience has done this aggregation. And you say, what does it mean to believe something? Well, how does that sort of work in a, I think the way to think about it is that the kind of, the thing that you will do to make the decision about what to do next, in a sense, is the thing that you operationally believe, so to speak. That is, if you're making, it's kind of like a blockchain. You're kind of making a succession of decisions, and then you go on and do the

next thing. And I think the issue is, what are those atomic decisions, so to speak? What are those things that you have, you know, you've taken lots of detail about what could be happening, and you've said, I think this happened. And then you go on and say, I think this happened and so on. I think that's, that's the sense in which we mean, and in terms of kind of our attempts to build theories, this point about belief is the question of, well, what exactly can we, what can we observe? What can we talk about? I mean, it's the same thing that happened in the early 20th century when Einstein was inventing relativity and things like this. What Einstein highlighted was what can we

talk about about simultaneity? There are things that we just can't know. And so don't worry about it. Make a theory in which we don't have to know the things we can't know. And we're only talking about the things we can know. And it's the same thing that I'm talking about here. Make a theory that talks only about things we can know. And then it will be a feature of that theory that the theory has to have certain characteristics because it's only talking about the things we can know. In the case of the gas, for example, the fact that we can't know where all those individual molecules go means that we have to concentrate on certain attributes of the gas about which

we can make formulas and things like this. It's the fact that we can't go in, if, okay, if we could go in and look at the individual molecules, we would say, wait a minute, PV doesn't equal RT, because like we can't really define the pressure, because actually it could be this whole battalion of molecules that's going off in this direction.

And we got to worry about that. We can't just say, oh, it's the pressure. Oh, interesting, right, right, right. I'm unclear of if it's your own model that dictates the laws of physics because if that was the case this belief in the persistence of time then someone like Heraclitus who didn't believe that he was a continuous thread throughout time and make some arguments about that does he then perceive physics differently? Yeah interesting question I mean I think we are all so close together in royal space

that observers, you know, do the cats and dogs perceive physics the same? Do the whales perceive it the same? Does the weather perceive physics the same? You know, I'm not sure how we, as I say, us humans, I think are so close together in the ways that we perceive things because we all have the same sensory apparatus, give or take. We have many of the same ideas, give or take. I think that the distance between ways that humans could perceive it is not very great. If we say, what's the physics of the weather, the physics as perceived by the weather, I don't know. Hugely different potentially.

What's the physics as perceived by a mosquito? I don't know. What's important probably to the mosquito is a bunch of air currents and this and that and the other, of which we have no description really. I mean, even if we think about, let's say dogs, which are olfactory, where smell is a much more important sense than vision, for instance. Imagining what the laws of physics the smell laws of physics alike is. I don't know it's it's you know it's a good exercise to think it try and think through what it would be like i mean the fact that we perceive the laws of physics as we do is.

For example our physical size is important to the way we perceive laws of physics if and example, the fact that we talk about space as being a thing is a consequence of various kinds of aspects of our size. Let me explain that. We think, we look around, we say there's an extent of space and the room that I'm in is in this particular state at this particular time, and another time it may be in a different state. But we see space as a unified, extended thing. Right, so we can look around and we just say, space is out there and we have a state of the world,

a state of space. Okay, but the reason that works is because we look around, I can see maybe 100 meters away through a window, okay? The light that's coming to me from 100 meters away arrives in microsecond, in a microsecond or something. That time that it takes the light to arrive is really short compared to the time it takes my brain to process the scene that I'm looking at.

So for me, it is a good way of thinking about things to say that the world consists of a series of frames where, you know, a series of frames in time where it's the state of space at this moment in time, then the state of space at that moment in time, and so on. So it makes sense for me to kind of aggregate up my view of the universe in there's space out there, and things progress through time. Now, if I was, for example, if my brain worked a million times faster than it does,

replace human neural circuitry by digital electronics, it'll be a million times faster. What will the world seem like if we thought a million times faster? Well, then the light that's coming to me from there, I will have already, I will have been able to process by the time the light arrives, I can already make, you know,

think something different, so to speak. So it no longer will seem the case that I, it will no longer be obvious that I should aggregate space as a thing that is at this moment in time. It's something, similarly, if I was much bigger than I am, even with the same processing speed as we have right now, if we were the size of planets, for example, we would, you know, if one person was the size of a planet,

let's say, then we would always be thinking about speed of light we can't think about just we can't think about the whole solar system is just one blob of space. Because the different parts of it we always be thinking oh you know that part of the light signal from neptune hasn't arrived yet type thing and we be able to think about things while we were waiting for that light signal to arrive. And again, it wouldn't make sense for us to aggregate sort of space as this blob that exists, that has a state at a particular moment in time. I mean, we see that very concretely when we start thinking about reference frames for talking about the time on interplanetary spacecraft and things like that, we can see you just can't do it. By the time you're talking about things on that scale with our human scale processing speeds, this idea that we aggregate space at moments in time no longer works. So that's an example of where sort of,

because we are the way we are, we choose to talk about the universe the way we choose to talk about the universe. And by the way, I think there are a whole bunch of other aspects of us that we take for granted. Like that feature of us about our size and the fact that space makes sense to talk about, we completely take that

for granted. And, you know, here's another example of something we take for granted. We take for granted that we have a certain degree of free will. We imagine that we have free will. So for example, we imagine that if there's a science experiment, we could just do any science experiment we choose to do. We imagine that we can take that polarizer in some quantum experiment and we can turn it to 30 degrees or 60 degrees and whatever angle we think we can turn it to, we can turn

it to that angle. We don't imagine that actually the act of turning it to that angle changes the world in such a way that next we'd have to turn it to some other angle. We have the belief that we have free will, and that's important for a bunch of things about our perception of the world. And there's a whole chain of these kinds of things that you might, that seem obvious to us. Another good example is motion. The possibility of pure motion is non-trivial. That is, the fact that we can take a step forward and still be the same us as when we were in

a different place is not obvious. If we were made up from little eddies in a fluid, we might be able to do the same thing, but it might not be surprising to us that we can't just be moved around. We have to be, and you know, so this idea that pure motion is possible is another kind of assumption about the world, another thing about sort of the way that we, because we are the way we are, we sort of choose to describe the world in a certain way. I mean, the discussion about space, because we are the way we are with the scales that we're at, in a certain way. I mean, the discussion about space,

because we are the way we are with the scales that we're at, we can choose to describe the world in terms of space and separately time, for example. So. Explain. You know, I think that the more we understand about the way we are as observers, with all the

arbitrariness of the way biological evolution has taken us to where we are, technology has given us measuring devices of the kind we have and so on, with all that arbitrariness, as we think through what that means, we probably will learn more about how physics has to be the way it is as perceived by us. And you know, we could have a, and so I think that's, you know, I had always assumed that we'd be on sort of a search for what is the rule that gives us the universe as the universe is. And what I've come to realize is, and this is kind of this idea of the Ruliyad, that the universe is running all possible rules. It is merely that we are sampling a slice of all those possible rules.

There's a slice determined by the way we are. There's an analogous thing. We are at a particular place in the universe, physically, in physical space. We don't have a theory for why we're here rather than somewhere else. I'm not sure a theory like that would make sense. We just happen to be in this galaxy, on this planet, et cetera, et cetera, et cetera. And that is, and so our view of the universe is based on the point of view of critters that are on this planet looking up at the sky or whatever else.

And if we were somewhere else, if we lived near the center of our galaxy or we lived somewhere completely different or we lived at a different time in the history of the universe, whatever, we would have a different point of view about the universe. And it's the same story with kind of ruleial space that we have a different point of view about the universe. The non-trivial fact, the real sort of scientific bite here is that once we are observers with certain general characteristics, we can make certain general conclusions about the laws of physics that we will perceive. And so it's kind of what goes in, what comes out.

What goes in is some characterization of us as observers, what comes out as the laws of physics we have to observe. And it's sort of interesting because it's like where do the laws of physics come from? Well, they in a sense come from the fact that we are the way we are. And that's a, you know, for me, that was always a very confusing thing. You know, in the end, why did we get this universe and not another? The answer, I think, is we got this perceived universe because we are the way we are. Why are we the way we are? Well, you can say, well, how do we evolve this way, blah, blah, blah.

In the end, it's like asking why are we on this particular planet and not another one it's a sort of contingent fact about the world that we are here and not somewhere else and so similarly that we are the way we are as observers so to speak is something that that you know so happens to be that way but it's not something for which we will expect to have wouldn't expect to have a theory for that. for which we wouldn't expect to have a theory for that. Stephen, what you're saying is that the question of why these laws and not some other set of laws is tantamount to why this planet Earth and not some other planet like some from the Andromeda galaxy. I don't see what's non-trivial about that. Well, yeah, but the thing that's really non-trivial is that you say, well, why is general relativity correct? Well, for any observer that has these very general characteristics, inevitably you have

those precise laws. That's the non-trivial part. If it was just saying, well, because of the details of the way we are, you know, it's, there's, there's a really a non trivial, sort of heavy lifting piece of science between this impression that we have about, you know, these these very coarse statements about the observers that we are, and the precise statements about what laws of physics we perceive. So, Stephen, you had a variety of breakthroughs recently, especially since COVID remarkably.

If you had to pin a majority of the recent breakthroughs of yours to one key insight, what would it be? So for instance, it could be the introduction of hypergraphs or the coining of computational irreducibility or the hiring of Jonathan Gerard? Jonathan's been very helpful for sure. No, I mean, you know, I think, look, the first statement is sort of, it's computation all the way down.

That you can really, that computation is the way of thinking about the world. You know, if you look at how have of thinking about the world. If you look at how have we formalized the world, it's kind of the invention of human language is a formalization of the world. Logic is a formalization of the world. Mathematics is a formalization of the world. Computation is a formalization of the world. Computation is a formalization of the world. In terms of what has allowed

me to get where I've gotten to, a large part of that is taking seriously that idea of computation as a way of formalizing the world and building tools, building our whole Wolfram language, technology stacker and so on around that idea of computation as a way to formalize the world. Now once you've had that idea, you start thinking about, well, what about physics? How do I formalize that? The next big fact is principle of computational equivalence, computational irreducibility. Those are very closely related. That's a key, intuitional idea that I originally

had in the early 1980s that is a driver for a lot of other things. In more recent times, I would say that this whole business about multi-computation, understanding the Ruliat, understanding the role of observers, understanding the rule yard, understanding the role of observers. This is, it's kind of this idea of the relationship of sort of underlying computation and the rule yard,

the sort of entangled limit of all possible computational processes, understanding the interplay between that and what we're like as observers, the fact that you can derive science from that is really pretty interesting. And I did not see that coming. I mean, if you'd asked me,

even four years ago or something, did I think we will be able to derive general relativity? And well, I knew we could derive general relativity from underlying hypergraph evolution. I've known that since the 1990s. I thought it was graphs back then, but hypergraphs are easier. But The concept that there is some kind of, that there's an inevitability to these kinds of laws of physics for observers like us, I really didn't see that coming. And I think I'm sure that it has echoes and resonances in lots of things that people have imagined particularly a couple thousand years ago or more, in early thinking about philosophy and how it relates to our descriptions of the world.

The main thing that we've achieved in the last couple of thousand years is we can run computer simulations and actually see how this works with some concreteness, so to speak, rather than having just some sort of vaguer idea about what's going on. But I would say that the, I mean, for me, this kind of the role of the observer, the idea of multi-computation, the rouillard, the kind of, you know, the inevitability of science the way it is, those are important ideas.

And I think, you know, we're, I suspect that a lot of the technical detail of hypergraph rewriting, all this kind of thing, is a very useful way to get there. But in the end, it will be possible to state a lot of these things in terms of, it's one of these things where you can think about computation theory. If you don't have Turing machines or something like that, you can't concretely talk about

it. You're just sort of still just vaguely saying things. You need a concrete basis on which to discuss things. But in the end, the core ideas are independent of that basis. And so it is, I think, with the whole observer theory, Ruliat, sort of, you know, inevitability of laws of physics and so on story. Yeah, many of these ideas are like fountains where other ideas cascade out of them. So you mentioned the power of computation or thinking about computation as fundamental

equivalencing, computational irreducibility observers multi computation really add. So let's let's call those ideas fountain ideas for the sake of this conversation. What recipe would you give your former self to have some of these fountain ideas more often? There's a whole bunch of computational irreducibility in what ends up happening as one tries to come up with these things. I don't think I'm batting too horribly in terms of having these ideas with some decent frequency.

Because frankly, some of these ideas, if you have them too quickly, there's not a lot you can do with them. They need a certain degree of development before they're very meaningful. I mean, so I think that there's a maximum rate. In fact, one of the things that has been a frustration to me recently is that there are so many of these things coming that I'm writing about all these different things. And I think these things coming that I'm writing about all these different things

and I think some of the things I'm writing are quite important and seeds for a lot of other things but I'm going so quickly that they don't have as much chance to develop as they probably need. So I think there's a maximum rate of generating sort of these potentially big ideas. And if you exceed that rate, it's kind of just totally confusing and you can't achieve anything.

So it's not that when you saturate it, some just fall to the wayside. It's that somehow it's like spinning plates and all of them fall? No, I mean, if you do it too fast, then it's just like, well, I have this idea, but each of these ideas needs a certain development. I mean, you know, when one first, I mean, one of the things that I personally spend a lot of effort on is sort of cleaning ideas. That is, when I have some vague sense of an idea, it's like, what is the essence of that idea? What is the really simple, I could say it in a sentence or two, version of that idea?

And that takes a while. I mean, maybe a smarter me would be able to do that more quickly, but it's, you know, taking, figuring out what's the essence, what's important, what's not. I mean, I've had the good fortune, I suppose, in my life to do that a whole bunch of times. And in fact, the thing I do for a living, building, designing and building our computational language is a kind of that critically relies on that skill

because that's all about taking kind of all these things that one might think about computationally and kind of Crispening them down to these kind of primitives that we implement in our language and so on So that's a you know I get to do this pretty much every day and I've been doing it kind of every day for 40 years and that's that's a useful Experience to have if your goal is sort of the crisping of ideas for kind of basic intellectual development, so to speak. I think that's one thing.

I mean, another thing for me is tools. And you know, when I can do an experiment with Wolfram language, you know, I've built this whole technology stack. Well, conveniently, millions of other people use it too. But first and foremost, I kind of built it so I could do stuff myself, kind of my sort of personal superpower, so to speak. And it works really well. And it's really necessary for, you know, I could not, many, many things I've discovered,

I would never have had the built-in intuition to figure out that the way they work is the way they actually work. I discovered the way they work by doing experiments, computational experiments, and I wouldn't have had the confidence actually, even if I'd imagined that was the way things might work. I wouldn't have had the confidence to say that really is the way things work without having seen them as the result of an experiment.

I think it's kind of the, I might have imagined, although I didn't back in the beginning of the 1980s, that really simple computational rules could lead to complicated behavior. I didn't imagine that. I actually imagined the opposite. Had it not been for the fact that I had explicit computer experiments where I could just plainly see that's what's going on, I wouldn't have believed it. So that's a necessary piece. If it was purely, I'm going to sit and think about this stuff just in my own mind, I would never have got there.

And it's the same with tons of things I've been doing. So I would say that probably the two things that have been important to me are the tools, having built the sort of tool tower of tools that allow me to do experiments, get intuition and so on, that's one thing, and to even the very act of putting my thoughts into computational language is a way of crystallizing what I'm talking about. It's like, well, I vaguely imagine this and that.

And the other, let me write a function that does and that and the other. Ah, interesting, right, right, right. Let me write a function that does that. It's kind of like when people say, I'm gonna write down a mathematical proof. Yeah, it's kind of relevant to see the proof and to check you got the right answer, but more important is the very fact that you're formulating things,

the setup is the important part. It's kind of like when people are doing, I don't know, math exercises or something and they get the setup totally wrong, it's a different story than if, oh, they did a calculation slightly wrong and they got this minus sign in the wrong place. It's kind of like, can you conceptualize things in this formal way? And by the way, computation and computational language are this amazing superpower that we have developed, so to speak, for kind of crystallizing thoughts, human thoughts, into something that has a lot more power.

And not only because, but both because it's a way of sort of formalizing what we're talking about, and because then we can have a computer help us to zoom forward with what we're talking about. And because then we can have a computer help us to zoom forward with what we're thinking about. But so, you know, for me, it's kind of the tools, the sort of crystallization of ideas from representing them in basically a more often language, then the actual running of it to see what happens

and to get intuition that I wouldn't otherwise have had. And I suppose the other thing is the effort to sort of get to the essence of things, say what is the core point that this all comes from, so to speak. And I suppose that, for me, that is somewhat related to exposition. And I spend quite a lot of effort writing things, trying to explain things, you know, doing live streams, all those kinds of things. And for me, that's a part of the process of kind of grinding things down to their essence. Like even in this conversation we've had, I've said a few things that I haven't thought

to say before, so to speak, that I think are useful ways to kind of crystallize some thoughts that I've had in the past. And that is my typical experience, is that sort of the act of exposition is an important driver for sort of getting to the essence of things. But that's for me, the other big thing is what's the essential point? Now, this question of, I sort of carry around with me lots of things where I mean to figure this out someday, and I'm sort of gradually accumulating knowledge

about those things. Part of what I need to do is in any new field that you work in, there is some kind of sort of local intuition in that field. And unless you've kind of marinated in the thing for a while, it's hard to have that local intuition. I mean, you know, I've been interested in the foundations of biology, foundations of economics, things about neuroscience and so on.

In each of these areas, slowly over the years, I've been trying to get general knowledge and intuition about these areas because otherwise, you really, it's very hard to, when you say, I'm now going to go and figure out the essence of economics, for example. Unless you have some sort of big, intuitional understanding of what economics is about, it's very hard, at least for me, it's very hard to go and do that. If you're just like, well, somebody says the definition of economics is this. OK, that's nice, but they might be wrong.

And unless you've got some sort of more broader view of what's in that field, it's really hard to dig down and not sort of be channeled into the things that people already said were going on. So that's a slow process for me. I mean, there are many fields where I've been following them for, I don't know, some of them nearly 50 years now. And slowly trying to get into it.

I mean, physics, for example, is a good example. I mean, the fact that I can make decent, I can do the things we've done in fundamental physics is, I think, completely dependent on the fact that I learnt research physics as it happens pretty young. You can talk to me about quantum field theory or general relativity or something like that, and I know all the technical stuff.

That's not something that we use every day in moving forward with the physics project, for instance. The fact that one has that background knowledge of roughly how things work. I mean, like Jonathan and I were just talking about some really nice stuff he's been doing with using our models to do simulations of space-time. And we're talking about why do these things happen this way? He sees these things in these simulations, why does it happen that way?

It's very important in those conversations that I, for example, and he also, but kind of knows the kind of the whole sort of shtick of how typical general relativity works, how typical quantum field theory works, and so on. Without that, it's really hard to, I think, to reason rationally in this area. If you have to invent everything for yourself, you'll never get there. But once one is living in this environment of, well, there's a certain amount of ambient knowledge that's been developed, then you have the chance,

if you understand that ambient knowledge well, and that's one of the issues. If you just know kind of the, oh, I read this textbook and I got this one point of view about things, that's not enough. If you want to make foundational progress in a field, you really have to understand it in some quite deep level that isn't, that's typically your own internalized understanding that isn't the thing that you just learned from a textbook type thing. And you know, for a lot of these fields, it takes a while to get there. And it takes, often for me, it takes doing practical projects in these fields where you're kind of like, for example, in economics, you know, working on things related to blockchain

and distributed blockchain and so on helped me. I don't think I'm there yet, but it helped me to kind of get an understanding of, you know, I don't know, the role of liquidity and what that means and the notion of single prices for things and so on. To have that sort of practical in the weeds experience in this area and to see sort of how things work out in practice, really important in being able to get a sort of bigger foundational theoretical idea about what's going on. Just the nature of the whole subject, quite likely.

So you think both Einstein's, both general relativity and quantum mechanics need to be modified? Or primarily quantum mechanics and a tinge to general relativity? I would say more importantly quantum mechanics. You see, people sometimes say to combine these two great theories, you've got to quantize general relativity. Can you explain what does it mean to quantize? You mean to haul it into the framework of quantum theory. So you have you make it into a Hilbert space and operators and goodness knows what.

And you sum over metrics or sum over geometry? Yeah, well lots of people were trying to, Wheeler was trying to do that when I was in Princeton. Yeah, lots of people were trying to do that. Bryce DeWitt was certainly trying to do that. And so when you speak to string theorists, they would say, well, that's quite obviously the approach. We're the only finite quantum gravity game in town. Yes.

I mean, there's nothing wrong with quantizing gravity. It's just the weak, I don't know what I'm saying, I'll read the right adjective. But let me... You don't have to be polite anymore. No, no, I'm not going to be polite here. I'm trying to be more illustrative of what I mean. I mean, I sometimes talk about a space, a planet, a distant planet which has an atmosphere on it, just like, it's a planet very much like the Earth, almost identical. And these spaceship, there's a space probe going out to look at it because it's very interesting because it's just like the Earth. However, there is no life on it. No life has ever evolved on it. There are no butterflies to flap their wings, and weather is

supposed to be a chaotic thing and so even sensitive to the flapping of a butterfly's wing. There aren't any butterflies on this planet. There's no conscious beings on that planet. So all the different weathers that they might have on that planet all coexist in superposition. It's a mess. The probe is going out to take a photograph. It takes a photograph of this mess. It comes back to the Earth, and when it's within distance of being able to send signals to

the Earth, somebody's sitting against the screen, and finally the first picture of the weather on that planet, this person looks at it, snap! His consciousness or her consciousness makes that world into weather into one weather. What could be more absurd? Absolutely ridiculous. It seems light-weather, where it doesn't have any interest in us. Why does its weather become one? Just because this chap's not taking a photograph of it. Absolute nonsense.

I'm just trying to emphasize that I don't believe it is consciousness that collapses the wave function. Instead it's the collapse of the wave function that produces consciousness? Well that's my other story, which I think is another story, and is a story which I also try to pursue to some degree. I don't regard this as what I do most in my life, because it's too much biology and things like that, which I don't know anything about. Are you wedded to microtubules being the mechanism or the place?

Or are you just saying, look, if it's going to occur, it needs to occur somewhere in the brain. This chap named Stuart Hammeroff put up his hand and say, it could be microtubules. I found this in the brain. Then you said, okay, well, maybe brain, and then you said okay well maybe. That's more or less it, yeah. Yes, it wasn't quite like that.

But I do think microtubules are a good candidate for various reasons. But you wouldn't be heartbroken if it turned out to be some other structure. Heartbroken is too strong. I'd be a bit disappointed, yes. Because I think microtubules, no there's various features of microtubules that I find fascinating. I don't think it's a coincidence. Did you see the recent news about the superradiance in microtubules? I did hear something.

I didn't see it. Was that on the... It said that there are quantum effects that are coherent in microtubules. No, there better be, yes. Do you feel vindicated from that? The trouble is I did look at the paper which was referred, I think it's the same one you're talking about. I did look at the paper. Stuart is mentioned, there is a reference to his, but it doesn't really talk about his stuff. It looks like something else. I don't know, I might be connected.

I'm not a biologist. So I'm not even a chemist. I find chemists is too difficult. For chemists, it's full of words that I can't remember. Yeah, same. I was supposed to be a doctor. My parents were both doctors. They thought I should be a doctor. They were both medically trained. I was the one they thought would be the doctor. They won in the end because my little sister eventually got a doctor and she married one too, so they got two for the price of one Now I disappointed them terribly. I would have been hopeless because I don't remember names these things you can tell I forget them immediately

I've been putting the wrong prescription on people's well, we invented quite a few by twisters dual twisters alpha planes I remember they mean more. Well, yes, I remember most of those more easily. Yes Twisters alpha planes. I remember they make more. Yes. I remember most of those more easily. Yes So I'm jumping ahead because the audience is familiar with that gravity has something to do with the collapse of the wave function Let me make that little more specific. Sure, you see I Wasn't so clear on that until much more later. I think run just a little before the turn of the century I can't quite remember when I did I Did took me a little while before I actually wrote the paper on it.

I wrote a paper on it, which was to explain a conflict, let's say conflict, between the two basic principles, one of general relativity, the other of quantum mechanics. What's the basic principle of general relativity? It's the principle of equivalence, which Einstein admitted. He didn't give Galileo credit. I think he should have given a reference to Galileo. I'm not sure he did, because Galileo already noticed the principle of equivalence. And he talked about, I like the one of the fireworks,

he describes his fireworks, go out and they make this beautiful sphere of sparks. As it falls, it remains a sphere. You can get rid of gravity by free fall, locally. I mean, he's very explicit. Not just the big rocks and the little rocks, and why the feather doesn't because of air resistance and all that. I mean, he was right. But of course, you needed special relativity and make that into a four-dimensional spacetime as Minkowski did and then bend it as Einstein did. So the collapse and gravity come in? Nothing there. My argument is that the principle of equivalence, which is the basis of general relativity, is in conflict with the principle of superposition.

And the argument is more or less this. I say, think of an experiment done in the lab on the tabletop, and you want to take the Earth's gravitational field into consideration. Now there are two ways you might do this. The way any sensible physicist would do it, you put a term in the Hamiltonian, if you don't know what that means, don't worry, put a term in the Hamiltonian for the gravitational field,

and just chug away the usual procedures. Fine. Then you notice that Einstein's sitting in the corner or Galileo even. He's telling you, no, no, no, you shouldn't do it that way. The gravitational field of the earth is locally just like free fall. So you can consider your lab, your coordinates are falling and the lab is just accelerating in this thing. And there's no gravitational field. Okay, you do it this other way. It's a different way.

Different coordinates, you do it away, and you come up, eventually, you come up with almost the same answer. The key, of course, is just the same except for the complex multiplier, the phase function if you like, which people would quite like to discard because when they're going to measure anything that you observe, they're taking amplitudes, you take squares and moduli. So you don't worry too much about that. Until you look rather too carefully at this actual factor, which is different between these two procedures, that actual factor involves the time, an exponential of the time cubed.

And that is not that serious if you're really thinking of it. If you're thinking of quantum field theory, that's serious because that's telling you that's a different vacuum. You're actually working in a different vacuum. So you might say, well, you still might say who cares because you say stick to your vacuum and you get the right answer at the end. Okay, so I'm going to change the problem a little bit, rather seriously actually. I'm going to say that in this experiment there was a lump of some sort, which is put into

a superposition of two locations. So it's a little stone which goes into two places, a little bead or something, which is part of the experiment. Now, I tried to use the Einsteinian Galilean Einstein perspective, and I ran into trouble because as I get close to the bead, I see that whether it's here or here, I can't get rid of them both at once. And that's, of course, the Einstein problem, which later was a general relativity. I can't get rid of them both at once by free fall. So what do I do? I do what any sensible physicist would do. I cheat. I say, okay, I know I should be using the Einstein perspective, but let's just try

instead measure the mistake that I'm making by adopting that, by the Newtonian perspective. So I adopt the Newtonian perspective, but keep track of what might be a little error in doing it. Then I integrate that error over space, and I do a little integration by parts and some little bit of fiddling around with it, and I get with an answer which looks like a uncertainty in the mass of a system. It is the mass of the system, but it's not the fact that it's a superposition. It gives me an uncertainty of that mass.

Now I can measure, and now the thing is that's a bit like particle physics, where you have, if you have a decaying particle, its mass is not completely well defined. It has an era of fuzziness in its mass, which is given by the Heisenberg time energy uncertainty principle. So, its lifetime, if it's an unstable particle, is inversely related to this sort of fuzziness in its mass. Now here I have a fuzziness in the energy of the system, the mass energy of the system.

So I say that's the reciprocal of that in natural units. When I say natural units, I mean making all the things equal to one that you can do, as Dirac sort of pointed out, I guess. And I say natural units, I mean making all the things equal to one that you can do, as Dirac sort of pointed out, I guess. And I get the formula, which Deoshi had already discovered a couple of years earlier than me. Right, for different reasons. I didn't know he'd done that. It was a different argument.

Uh-huh. But I thought this was a nice argument because it just revealed the tension between these two very basic principles, principle of equivalence and the principle of superposition. And they're a bit in conflict with each other. And the resolution of this conflict comes through allowing your unstable state to collapse into one or the other. Now, it's what you only get from this way of looking at it is an uncertainty in the mass. And I know that Yvette's looking directly at this thing rather than looking at the collapse, which is a powerful

thing to exploit. So the title of my talk is really designed to address the basic question Kurt is asking in this series namely what is unification. Add the answer i would give is that unification. Understanding the laws of physics and the nature of the universe in a unified way. means understanding the universe, that the laws of physics and the arena for physics, namely space and time, are really a single entity. And you might think this was obvious, that our best way of understanding the unified laws of physics is to look at the universe. That's the maximum data we have available. And not to do that is kind of insane. It's that you are trying to invent things about physics which are outside the universe. And perhaps unsurprisingly, this has led people to worry about a multiverse, and this is kind of the road string theory has

gone down. And I feel that road may well be, is likely to be a dead end. And what we have to do is pay much more attention to what we actually see and observe in the universe. And I believe that for some reason we don't yet understand what we see and observe in the universe teaches us about nature at a very profound level. So we have this sort of information coming in about the universe now and I believe this is a ideal moment, very opportune moment, to think about unification. But in doing so, we must take that data very, very seriously. That doesn't mean believing every rumor

or slight difference between the basic picture and observations. Many of those are due to observational problems. These observations are very difficult in cosmology. Sometimes they make mistakes and they eventually get corrected over many years or even decades. So don't take the observations absolutely literally, but do be guided by the broad gist of those observations. And of course, as in every area of science, we may always turn out to be wrong, but I believe this is the best route to progress,

is take our theories very seriously, insist on logical consistency, but equally insist on realism, that these theories do match and are consistent with what we see in the universe. So for me, pursuing unification in its own right without thinking about the universe is unlikely to be a successful strategy. Equally thinking about the universe without thinking about unification, as you'll see in this talk, doesn't really make sense because the universe we see includes logical paradoxes such as the emergence of everything from a single point, namely the Big Bang Singularity.

And without thinking about unification, we really don't know how to begin to address those logical paradoxes. So that's the title of my talk. I thought that since Kurt often has a philosophical flavor to his presentations, which I find fascinating, by the way. Well, that's one word for it. I thought I'd start with a philosophical quote, which is rather nice and echoes what I'll

be saying in the talk, that life can only be understood backwards, namely by looking at our past, that's the only evidence that we have, but it has to be looked forward. Namely the future is of course the most interesting thing about life and what we make of the future. As you'll see in this talk, the past and the future get connected in very profound ways. And I think we're just beginning to understand what that means. Now, as you well know in cosmology, looking out from our vantage point on Earth, looking out into space is also looking back in time.

And that's because light has a finite speed. As we look outwards, we're seeing the universe or the objects in the universe as they were longer and longer ago. As we look outwards, this is what we see. Of course, our solar system nearby, but as we go further, this is a logarithmic scale, by the way.

So the distance scale gets very rapidly longer as you go out in radius. What is the origin of this picture, by the way? Is this yours? Oh, yes. I've given the credit. Pablo Carlos. Oh, yes. I see. Yes. No, it's an artistic picture,

but I think it's a very beautiful picture. Essentially, it's telling us what we see when we look out in the universe. So nearby, we see the solar system. Of course, the most distant planets we're seeing as they were a few minutes or hours ago. ago, but as we go further and further out, we're seeing galaxies and stars as they were forming up to a billion years ago, and going further outwards we see what we call a cosmic web, which is basically structure as it was emerging from an initial smooth, almost uniform,

almost perfectly uniform universe. That's the cosmic web, the sort of fringes on the outskirts of the picture. If we go even further out with the red circle here is what we call the last scattering surface. It's the hot surface of the radiation coming out of the Big Bang as it was radiating the microwaves which we now receive as the remnant radiation from the hot Big Bang. So we're essentially sitting in the middle of a microwave oven and as we look outwards,

we're seeing the hot surface that was emitting those microwaves. When it was emitting them, incidentally, its temperature was about 3,000 degrees centigrade, so only a factor of two different than the sun. So essentially, we're outside the sun, but inside a cavity whose surface looks pretty much like the surface of the sun. And then if we go even further out before that surface, imagine we're using a form of light which can penetrate the hot radiation of the Big Bang,

for example, gravitational waves, which would do so. We reach the white circle, which is the Big Bang singularity. That seems to be the beginning of the universe, which we are surrounded by, although actually it's a point. Now, to see how that works, keep in mind that this picture I'm showing now is really

a cross-section of a four-dimensional universe, namely time and space. We are connected to every point on this picture by a light ray. This is what we actually see. But if I try to draw the full four-dimensional picture, I've got to add the time dimension as well as space. And you see, if we are sitting on the right of this picture, in the center of this patch of space around us,

the green curves here show the trajectory of light or something traveling at the speed of light. As it came out of the Big Bang singularity, it then traveled outwards at the speed of light. But of course, you've got to also take into account the effect that as you go backwards in time, the universe is shrinking in size. So what looks to us in this picture as a big circle on the outskirts of what we can see is actually this focal point on the left, where all those light rays, in fact,

came out of the same point in space. Professor, is there anything special about this point where, if you look toward the middle of this, it initially is going up, it's sloping up to the right, and then it starts sloping down to the right? Yes. Is there anything special about that point where it changes?

No, no, there's nothing special. This is just, if I, you see, so if I had drawn this, the curve for an observer living a billion years ago, you know, only 12.7 years, a billion years after the Big Bang, the light would converge a little bit to the left of where I've drawn it. And so it would bend downwards a bit sooner than the curve I show. So this curve is really, if you like, the curve that we see being where we are in space and time in the universe. It's our past horizon or our past light cone.

So normally in special relativity, you learn about light cones, but they are obtained just by drawing straight lines and then making them into a surface of revolution. The difference in an expanding universe is that the light cones themselves shrink down to a point at the Big Bang singularity because the universe is shrinking as we go back in time. go back in time. So this is what we can see. We see a slice of the universe. And weirdly enough, the outskirts of the slice are actually a single point, which

is the Big Bang singularity. And that's what we want to resolve. And so everything I'm going to tell you about today rests on a resolution of that strange paradox that the whole universe came out, the universe we see came out of a single point. Now, as well as the arena for physics, we need to, of course, think about the laws of physics.

And the laws of physics we visions there are. There are three families of quark, each of them containing an up-type quark and a down-type quark. And then we have leptons, which are sort of generalizations of the electrons, which orbit around atoms. And there are similarly three families of leptons, each with an electron-like particle and each with a neutrino-like particle. So those are the particles. And then we have the forces, which are the electrostatic and strong forces. And those are mediated by gauge bosons. The particles we describe as fermions.

They're described by Dirac's equation. So all of these things are very well established. The Higgs boson somehow connects all of them because the Higgs boson is responsible, or the Higgs field is actually responsible for breaking the symmetry in the standard model. And it contributes mass to all of these particles that you see in this picture. So those are laws of particle physics. Then I've drawn gravity as this blue curve that couples to everything because gravity is really universal and gravity feels everything else in the picture. So we have to somehow combine all of these laws

with this picture of the universe in order to try to make a coherent picture. And where it doesn't work, we have to extend these laws to make it work. Now, as I mentioned, we live outside the Sun, so this is the hot surface of the Sun, and it's completely remarkable that the color of the Sun tells us Planck's constant. I mean, it actually... the fact that the Sun has a single color and it has a temperature of 6,000 degrees, one can infer from the color directly Planck's constant. And so if there were no quantization of photons,

hot objects like the sun simply could not exist. It's the quantization of light which allows hot objects to exist without radiating an infinite amount of energy. If you take the Pines constant to 0, you find the rate of radiation from the sun would go to infinity, and the sun would disappear in a puff of smoke in no time at all.

So this is an example of how the universe teaches us its laws. And this is not how Planck's law of radiation was discovered, because people didn't really understand what the sun was at that point in time, but it could have been. And so by taking the observations as seriously as possible, trying to make them consistent, one actually learns all about the fundamental laws of physics. And right now we're doing the same with the other version of the Sun, if you like, which is this cosmic microwave background sphere within which we live.

It's a hot radiating surface. By looking at it, we can see what happened at the Big Bang singularity. Why do you call it the other version of the Sun? Well, in this picture, you see the Sun is at the center of the picture and we orbit around it. But the red sphere represents, obviously, this is a two-dimensional cross-section of a sphere. And the red circle on this picture represents a sphere which surrounds us, a two-dimensional sphere on the sky which surrounds us, and it's hot. It was radiating radiation at about 3,000 degrees C or Kelvin,

when the radiation decoupled. It's called the surface of decoupling, and so the radiation decoupled from the hot plasma in the Big Bang, and the radiation just traveled freely from that surface to our telescopes at the center of the picture. So we're outside the Sun, we're inside the surface of last scattering or this red surface, and by staring at the red surface, we hope to learn the equivalent of the laws of quantum mechanics, which we could have learnt by staring at the Sun. Let's talk about infinity.

Yeah. Some people think of infinity as just a placeholder, like a heururistic for this is a sufficiently large number beyond our grasp. Right. Okay. The computationalists are fond of that. What do you make of the concept of infinity in physics? And let me ask you a question, Kurt, because we have classical physics, the laws of fluid mechanics, for example, is a good example of classical system. about infinity, as you say, you have two possibilities. One is that actually in physics, we know infinity sort of exists as a concept in mathematics, of course it does, but in physics is infinity, when we use infinity, or conversely one over infinity and infinitesimal, when we use these concepts, do we really mean infinity is absolutely, literally infinitely big, bigger than any finite number? Or is it just a placeholder for a very big number, but we don't particularly care exactly how big it is, but it is a very big number and you know the laws

the laws of physics don't depend sensitively on that number and you know all experiments it doesn't really matter if that number is like a Google or a Google plethora something like that so do you think there's a difference between how infinity is used in classical physics and quantum physics? And if so, how would you see it? Do you think infinity is more of a number? Let's say infinity as a number that's bigger than any finite number, so not a placeholder. Do you think that's more of a concept in classical physics

or in quantum physics? In quantum physics, there are infinite dimensional Hilbert spaces and then because of that there's something like the Stone-von Neumann theorem and that's one of the reasons why QFT is not so trivial compared to quantum mechanics because you have the conjugate variables of x and p. Okay well look I think I agree with your answer but I think you're making it too complicated. I think you're right with what you say, but let me put it like this. So if we, you know, even at high school, when we learn Newton's laws of motion, we, you

know, they're framed in terms of the calculus F equals, I mean, I'm assuming that that's, I'm not even sure today whether high school students do the calculus or not. But anyway, certainly first year university, let's say four sequence mass times acceleration and acceleration is the second, you know, rate of change position with respect to time. So we use Newton's calculus, Newton Leibniz calculus, and the calculus involves, you know, involves infinitesimal numbers like d by dt, dt is an infinitesimal number in calculus. So you might think that infinity or an infinitesimal plays an essential role in classical physics, but people might think, well, in quantum physics physics it's all about discrete jumps, you know, everything's discrete jumps of energy and therefore it's all somehow finite.

Everything is finite. But actually it's completely the other way around. Because in classical physics, I can take a differential equation, you know, for, I mean we do this with weather forecasting of course, where we have partial differential equations that underlie the movement of air, but they're represented on a computer with finite derivatives. So we don't have like d by dt, we have delta by delta t, and these deltas are finite things. And you know, we know that, at least for short range forecasts, that does pretty well. So there's no kind of essential reason in classical physics why we need to be working with the continuum, the real number continuum. We can just work with discrete numbers and we get answers.

If we want to get a slightly more accurate answer, we'll have the time step or quarter the time step. But you tell me how accurate you want to know it and I'll tell you the discretization length and the discretization time that will give me an answer to the accuracy you want. But in quantum mechanics, it's completely different because the basic concept behind a quantum state, sort of you mentioned this effectively, is it's an element of a Hilbert space and a

Hilbert space is a vector space. In fact in quantum mechanics it's a vector space over the complex numbers. But the point about it being a vector space is that you want to be, or you need to be able to add together two vectors, in other words, two different quantum states. And the resulting addition is itself a quantum state. So that's a really important property. Now, if you start discretizing Hilbert space,

you will typically lose that property. You'll add together two vectors, and the resulting vector will kind of lie in between two of your points in your discretized space. Wait, that's not so obvious. So let's see. Let's say you make a grid. Okay. So it's just integer steps. I mean, make a grid and take, take a vector. Say you have an origin and you have two vectors, which point to, um,

to two of the points on the grid and add them together that the sum of the two is going to split the difference. Unless you've got a grid point, which splits the difference, then your, your vector will no longer be in the space. Let's say you have something that's unit one in length and then another that's unit one in length then you get something that's unit two in length but along the same axis. But what's wrong with that? If you imagine, well, if you imagine two, you know, if you discretize say a circle and you imagine two vectors pointing to let's say neighboring grid points and then add together, you're going to split that difference and your vector will typically then not lie on

that, on either. Okay, so it depends on your discretization. It will depend on the discretization, but generically, to get these algebraic properties, you need a continuum space. And actually, I'm not the first to make this point, this was made by Lucien Hardy from Perimeter some years ago when he came up with what he called reasonable axioms for quantum mechanics. And one is this notion that is called the continuity notion that you don't have a space where you can get discrete

jumps even though quantum mechanics is all about discrete jumps in the so-called unitary phase of quantum evolution, you actually need continuity. It's a critical property. Now, but then the question is why is it a critical property? And it's only a critical property if you believe that these Hilbert spaces and Hilbert vectors are the fundamental objects of your theory. In other words, if you say, what is that, you know, if I have my theory of quantum physics, what is at the deepest level? Now in quantum mechanics at the deepest level is Hilbert space. That is the, that doesn't go any deeper than that.

That's it. Okay. So then you have to have the continuum of, of Hilbert space, of Hilbert states rather, to describe quantum mechanics. On the other hand if you say that, which is sort of what I'm trying to suggest by virtue of this cosmological invariant set postulate that there may well be something deterministic that underpins quantum physics. Then the Hilbert states are not really fundamental. All they're doing is they're the mathematical quantities that you would use when you know that there is some inherent uncertainty in your knowledge of the system and you want to represent that uncertainty in a kind of statistical way. So Hilbert states coupled with Born's rule, which is about probabilities of outcomes,

then just becomes, if you like, it's not a fundamental property of your theory, it's just something which is useful to use when you want to describe things in a statistical way. And this is actually again where periodic numbers come in, because on a fractal you can add and multiply using these piadic numbers and the result is a piadic number. So you have this closure under addition and multiplication at this deeper deterministic level. So I have a scheme which leads to a particular type of discretization, which I feel might be a bit too much technically to talk about here. But it exactly has all these properties that you add to vectors and typically the sum doesn't

lie in the discretized space. However, it has this deeper deterministic underpinning. But importantly, it has exactly this property If you try and estimate the, sorry, if you try to define the quantum states associated with entangled particles where you do these counterfactual measurements, then to describe the Hilbert states, you will need strictly irrational numbers, either for the amplitudes or the phases of the quantum state. And those are things that are forbidden in the discretization. So this captures precisely this notion of moving off the invariant set, but now it's framed in terms of rational versus irrational numbers

in the definition of the Hilbert state. So I think actually that is probably a more, an easier way to, you know, for, let's say for a practicing quantum theorist to kind of get to the type of model I'm trying to propose here. Now, what is your view on conscious experiences and their relationship to the Ruliat? Is the Ruliat more fundamental than conscious experiences or is consciousness more fundamental than the Ruliat in your view? Well, I don't know. I mean, I think the Ruliat is just an abstract object. And, you know, the fact,

and it is my sort of assumption, perhaps, but it's working really well, that sort of everything that exists is somehow part of the Ruliat, which means we are too. Which means that the Ruliat is sort of a substrate for everything that we are. Now the question of whether you can go into the Ruliat and say, and point at something and say, that's the Don Hoffman set of Eames and the Ruliat, so to speak. And then what special features that might have, that's something, I mean, we know a certain amount about that. There's a lot more to figure out about that.

But if you're asking, is there something, I mean, for, this is a complicated thing about what science is and what the point of science is and so on. I mean, there's the universe doing its thing and there's us having some narrative about what's going on in the universe. And I think, you know, science, I think, is about sort of taking not what the universe does, but sort of trying to develop a narrative that we can kind of play in our minds that can say things about what the universe is doing. In other words, it's not, you know, I think you mentioned the concept of a sort of a headset for us to perceive what's actually going on out there, so to speak. And I agree that what matters to our science is what we perceive.

I mean, the things that are not... And if you look at the history of science, what has happened in the history of science is we've been progressively able to perceive more kinds of things, you know, telescopes, microscopes, electronic amplifiers, all these kinds of things, you know, telescopes, microscopes, electronic amplifiers, all these kinds of things. And we have then, you know, found ways to describe the world that we can then see, so to speak. And I wouldn't be surprised if in the future, there'll be more kinds of sensors that we somehow manage to transduce into the things that we, you know, into the built-in sensors

that we have. And then we'll want to describe more things about the world. But I think in your question of, I mean, for me, I've always thought of consciousness as an incredibly slippery concept. And so I haven't been that interested in kind of exactly how do I define it, and etc., etc., etc., perhaps to my detriment. But the one thing that has, you know, was interesting to me a couple of years ago

was realizing that I needed sort of pragmatic definitions of consciousness in order to understand more about how physics works. In other words, it's, you know, for example, it's kind of like, if I say, okay, there's consciousness and observers like us have consciousness, what is the, what are the operational consequences of that? For example? So, for example, one of them, I think, is this thing about single threads of experience. I think that's a...now, whether you say that's a defining feature of consciousness or not, I don't know.

That's a question of what you mean by the word. But I think there's a significant feature of us as observers that we have this concept, that we have this belief that we have a single thread of experience. I mean, I don't know, you know, I've sort of wondered what it's like, you know, if you could be in a kind of a multi-way trance, so to speak, where really your brain is thinking about two different kind of, you know, you have two different time narratives going on in your brain. I can't imagine what that would be like.

But if one had grown up with that, maybe one would have some sort of internal, you talk about what the internal feeling of something is. I'm curious what the internal feeling of an observer a bit different from me would be like. the internal feeling of an observer a bit different from me would be like? These are all very interesting topics. I'm interested in something very, very simple like the taste of mint. So the taste of mint as a conscious experience. So to keep a really, really simple set of all the threads and so forth, just a single specific conscious experience that an observer might have and how that would be related to the Rulliad. So, for example, would you want to say that there's a computational substrate

in the Rulliad that is, for example, necessary and sufficient for the experience of mint to occur or not? You know, I don't know what the experience of mint is. I mean, you know, in other words, I don't know what the experience of Mint is. I mean, in other words, I have some experience of it. If you say, let's kind of scientificize that experience, okay, what do we do to make it? And this is the question and part of what science is and what science aspires to be.

Because if we say, how do I make that something that you can also sort of observe, you can also be part of? Because the experience that I have internally, as we discussed before, is not something other than by extrapolation, you don't know what that experience is. Right. So the question is, can I make a transportable version that is kind of a community science version of my experience of mint? Or is it just something that happens inside me that can never be broken out of me, and which is therefore not in some

sense, you know, it isn't community science, so to speak. It isn't what we usually think of as being what we usually aspire to have in kind of the operation of science. So if I say, how do I break out that experience? Well, I could start saying, you know, and by the way, it's going to get complicated very quickly because you could say, okay, I experienced this, a bunch of neurons in my brain, you know, are chirping away. And, you know, what does that mean, for these neurons are chirping away? Well, we can say, no doubt,

the neurons in my brain that chirp away at the taste of mint, will be different from the neurons in your brain that chirp away. And we don't even know how to map, neuron number, if we were nematodes, we might know how to map our neurons, but we're humans with a lot more neurons, and we don't know how to map our neurons, but we're humans with a lot more neurons and we don't know how to map our neurons and there won't be a unique mapping

from one brain to another. In other words, a nematode, sort of interesting thought experiment, could one nematode communicate scientifically to another nematode its internal experience of the taste of mint? Because after all, the nematodes have a fixed set of nerve cells where we can say cell number 312 fired in this case. And then the other nematode would say, oh yeah, I know what cell 312 firing feels like, but it's a very different thing with us. We, in order to communicate a concept from one human brain to another, we kind of have to package it in a robust form that will allow that communication. And the number one robust form that we have is

human language, where we're taking all those random nerve firings that you think of when you imagine the taste of mint, and you're're packaging those up and you're saying to me the taste of mint and that's unpacking in my brain and maybe I get some notion that is something, some correspondence, I don't know what the correspondence is between your version of the taste of mint and my version of the taste of mint. Although if we were nematodes, we might know

because it might be the very same nerve cell that was firing. But we have a more general notion of concepts than that. And I think, you know, to this idea of being able to take a bundle of neural activity and package it up in a robust form so that it can be moved to another brain and unpacked, you know, I think that that's probably one of the key things that sort of our species discovered, which is that you can have things like words that are kind of transportable from one brain to another. And I guess, you know, I, there's sort of a fun analogy that, which is, you know, when you have a particle like an electron

or a photon, a quark or something like this, one of the things it's doing is it is a carrier of existence through space and time. That is, the electron is a thing that you can identify as being the same electron when it moved to another place or another time. And that's sort of similar to this idea that concepts are also sort of transportable things. I mean, in our view of the way this works, you know, an electron is a something capable of pure motion in physical space. A concept is something capable of motion, of pure motion in real space. I mean, by pure motion, what I mean is it is not obvious in our models, for example, that a thing can move without change. So in physical space, you know, you move a book around, for example, and if it's near

a space-time singularity, the thing will be distorted like crazy. But most of the time we say, I move a book from here to there, and it's still the same book. And I think that this possibility of pure motion in our models is something that you have to kind of establish abstractly that that's possible. And by the way, the idea that there is pure motion again depends on observers, because that book, you know, you moved it and some things about it changed. I mean, in our models, it's made of different atoms of space when it moved

to a different place. And yet to us, it's the same book. And so similarly, I would say, you know, when you talk about the, the concept of mint, of the taste of mint, experience of the taste of mint, it is a non-trivial fact if it's true, that that is a transportable thing through time, that there is a consistent, persistent thing that is the engram or whatever it is that represents that that concept and That it is robust and I think that that if you you know the version of it that's locked inside your brain at some moment In time, I don't think that's transportable. I don't think that's Science-sizable. I think that's a thing that you would say it is

I mean if we were thinking about in terms of an LLM, it would be some little, you know, some activation of some neuron at some moment and, you know, then it's gone. And we wouldn't say, you know, and we would argue, was that a conscious experience of the LLM? Well, it isn't robust. It's not something where we can pick it up and say, look, it's a conscious experience because it was a fleeting thing that just was there at that moment and then disappeared. And I would claim that that, um, uh, that absent some way to robustify what you're talking about, you, you, there isn't really a way to extract. I mean, if you say, show me that conscious experience, what is it? You know, physicalize that conscious experience. You

can't physicalize it. So what does that mean, so to speak? I would claim that it is not an obvious fact that things can be made robust enough to be sort of picked out as a separate thing. I mean, I'm sort of reminded of, I have to say, in your kind of, what is that essence of a conscious experience? I'm reminded of something that I kind of feel silly about myself, because, you know, when I was a kid, 1960s and so on, it was, you would run into people who would talk about sort of the eternal soul. And if you were kind of a physics-oriented kid as I was, you would always say things like, but how much does a soul weigh? How

can this be a real thing? How much does it weigh? If a soul departs a body, does that mean you lose a microgram or something? How much does it weigh? There must be some sort of…if it's real, it must have those physical attributes. Of course, I realized later on that that's a very silly thing to have thought, because, you know, computation, the kind of the idea of a sort of an eternal soul is very, is kind of a sort of primitive way, I think, to talk about, you know, abstract computation, and it would be a very foolish thing to ask sort of how much does the abstract computation weigh. And I kind of suspect, and I'm not untangling it in real time as well as I might, but I'm kind of suspecting

that your kind of notion of the intrinsic conscious experience of something and you saying, look, you can't pull it out and physicalize it, is the same kind of mistake. So let me see if I can paraphrase. So in your ontology, the Ruliad is fundamental or close to fundamental and the rules there, the computations, but things, but any color, shape, motion, taste, experiences, those conscious experiences are not part of the fundamental ontology that you're considering.

Is that correct or have I misinterpreted? Well, I mean, okay, so, you know, in matters this fundamental, there are inevitably many different ways to look at the same elephant. Okay. Okay. So, the Ruliyad and, for example, its representation in terms of computation and rules and so on is the way that I understand best and that I think people in general understand best. It is probably not the only way to think

about it. So, for example, just as mentioned before, you can think about physics either as a kind of an underlying mechanistic structure that makes things happen, or you can invent kind of an axiomatic physics where you just say this is a thing that's true that's the thing that's true and then you have to fit all the pieces together so similarly when it comes to the Rulliad there is certainly I I like to think of it and from sort of the bottom up of I can represent it in terms of computations and things like this but in the end sort of observers like us are making various observations about it.

And one could imagine reconstructing it. I don't know how to do it exactly, but one could imagine saying, all I know is what I observe. And that's my reality, so to speak. And now from that reality, I can, you know, I could imagine a theory in which there is this Rulliad thing with computations and so on. In other words, my way of thinking about it, the way I prefer to think about it,

just because I guess that's the way my particular mind is built, is from this kind of hard structure of computation building up to something where I might hope to be able to find somewhere in the Ruliat a thing that corresponds to you know a brain with a feeling of mint and things like this. Right? That's the way that for me is the most sort of gives me the most sort of hope of being able to make scientific progress. But I don't think that's the only way to think about it. I think you could as

well say, all I'm going to do, like the S matrix, for example, you know, forget the mechanism. All we want to know is the transformation from initial states to final states. And we're going to just say there's this thing called S that represents that transformation. And we're then going to talk about the properties of S. I mean, this was the, you know, the, the, in the late 1950s, early 1960s, this was kind of what people thought was going to be the way that particle physics worked in, in the strange cyclicity of science. Those ideas have come back again. But, um, you know, at the time, there was sort of a competition. Would we

describe the world by saying, there's just this S matrix and we're going to figure out properties of the S matrix by having, I wouldn't call them conscious experiences, but particle accelerator experiences of the S matrix? That's door number one. Door number two, are we going to figure out the mechanism, how all these particles are structured and how they you know what the little Interaction vertices are and all this kind of thing that was door number two in in the 1970s door number two one in particle physics, right um in

But I think it's it's not the case that you know I'm with seeing in fact a return to more of the kind of S-matrix approach to saying, we don't really know what's going on inside, but we can describe certain constraints based on what we observe. And I absolutely think that there's a way of constructing kind of sort of the Rulliad. You could invent the Rulliad as the afterthought, having started from something which is just axioms about observers. And my particular way of thinking about it, I like to start from something that I can

run computer experiments on and that happens to, that I at least imagine that I have a reasonably good handle on from the way my mind works. But I don't think it's the only way to think about it. For me, if you say, only start from things that an observer can observe, which is kind of the S-matrix idea, only start from things that are sort of externally observable, sure, one could do that. I don't know how to set up that formalism. I mean, I've got some ideas about that, but that's, I think, for me, it's much more difficult than the bottom-up approach. But I don't think it's, I think both approaches are perfectly viable. It's just a question

of if one's goal is to have kind of a narrative description of how the world works, one can make a choice between those approaches, you know, which is the way that is most likely to lead to a narrative that for example I understand I mean now again that this is and for me the narrative that has to do with the ruley ad and Computation and so on is easier to understand it. It is more grounded for me Than a description in terms of kind of starting with consciousness, so to speak. Oh, okay I see. So now the audience is wondering, okay, so what is causal set theory? Sure, it takes into account the causal structure, but then what is it? I would say there are three pillars to causal set theory as an approach to the problem of

quantum gravity. And they're all equally important. So they go together. And you can start at any one point and somehow get to the other two. So I'll just say what the three are. So one is that space-time is fundamentally discrete discrete, or fundamentally atomic, or granular, or pixelated, or any of those. You can use any of those words or concepts. So that means that any event in space-time, say this whole podcast, that's an event. It has a duration in time and a location in space. Of course, today in modern physics, we don't separate out spatial location and time duration. It's all just one region of four-dimensional space. So there's some event like this podcast. That can be broken up into sub-events. So a sub-event like the first half of it and the second half, that's two sub events.

And you can keep dividing it. So you can divide it into, into the part of the, of the podcast that involves me and the part of the podcast involves you. Sure. So you can keep dividing it into a smaller and smaller bits, smaller and smaller events, smaller and smaller sub-event. Ah, I see. And, you know, so I can do that. And that's a little piece of the podcast.

So that's a sub-event. But that can be divided into itself into sub-events and sub-events. In general relativity, there's no limit to that subdivision. There's no smallest event until you get to the point of the continuum. Right. And then those events, you could call them point events. So the whole podcast event is made of these point events. But in causal set theory, the hypothesis is that you can't subdivide the podcast event into arbitrarily many sub-events.

It's actually made of finitely many atomic events. You can roughly work out how many of these atomic events there are just by measuring the space-time volume of the podcast, which would be in Planck units. That's a four four dimensional space time volume, roughly how long it lasts in plank times, how big it is in space in plank length cubed. And then work out how many plank volumes that is. And that will be the very large number. And that will be the number of atomic events that can compose this podcast event. And that's true of everything. Okay, so if you were to divide space, not space-time, into discrete units, you have

problems with Lorentz invariance, because then you could just boost and then you would have a different smallest unit. But if you have space-time, somehow that's different. Yeah. If you discretize space time itself. Yes, yes, yes. That's the key thing. So many people think that discreteness is incompatible with Lorentz invariance because of exactly what you said that they think of discretizing space, three dimensional space. If you discretize space, as you say, the Planck length is not a Lorentz invariant concept. But space-time volume is a Lorentz invariant concept. So some region of a particular space-time, four-dimensional space-time volume, if you boost it, it remains that volume. It

doesn't change. It's a Lorentz invariant concept. So if you discretize space-time into atomic events, rather than discretizing space into bits of space, then you have no problem with, well, at least it then becomes possible to have a discreteness that is Lorentz invariant. So is the continuum still present implicitly in the notion of volume? No. I mean, volume emerges from the discrete underpinning. So, the idea is that volume is a count, what it actually is, is just a count of the number of space-time atomic events that comprise that region of space-time. Volume is what it seems like to us at the emergent level, at the level of the continuum approximation. It appears to

us in our continuum approximation theory, which is which is our space-time volume. What it really is in the deep theory is just the number of atomic events. So it's like if you have, this is an example that Rafael Sorkin, the physicist who's the main champion of this approach to the problem of quantum gravity, he uses an example of an ingot of gold. So it has a certain mass. But what the mass is, it's just counting the number of gold atoms in the ingot. So that's- I see. So that, so it seems like it's a continuum thing, but really it's a discrete thing in the atomic theory.

You used carefully the word continuum approximation, not continuum limit. So why is that? What would be the difference between those? Oh, that's crucial. So yes, so in causal set theory, I'm still on the first pillar, remember? Yes. In causal set theory, the discreteness is fundamental. So the scale, the Planck scale is a physical which well describes the physics at when there are very, very large numbers of space-time atoms.

So it's an approximation to the underlying theory, just like fluid mechanics is an, and say the Navier-Stokes equations of fluid mechanics, they're an approximation to the underlying molecular theory of the fluid. So the, the, the molecular scale is a, is a real physical scale. You can derive the Navier-Stokes equations by taking a hydrodynamic approximation to the underlying physics. The theory is not a continuum limit because the molecular scale is real. The molecules are not actually physically getting closer and closer together. They're just more and more of them. It's the same paradigm for causal set theory. We want to derive general relativity as a continuum approximation to the underlying discrete theory when we're

in a situation where space-time is large, there are lots and lots of atomic events, but not infinitely many. So it's crucial that the continuum approximation is the concept here. I understand. Okay. And now you mentioned you're on the first pillar. So there's a second one, please. So the second pillar is that causal relations are the fundamental degrees of freedom, physical degrees of freedom, if you like.

degrees of freedom, physical degrees of freedom if you like. So the proposal is that the causal structure of space-time, that is this information about, in GR, which is this information about which events can causally influence which other events, that survives in the deep theory. Some things will not survive. The manifold structure, the continuous manifold, the metric, they don't survive. Those concepts are not there in the deep theory. Topology, that doesn't survive in the deep theory. But what does survive is causal order. So these space-time atoms, they are the elements of this discrete space-time. They're the elements of the set, the causal set that space-time really is, and they have an order relation on them. So they maintain, they keep this structure of being causally ordered. So you can say, take two elements of the causal set, two space-time atoms, then they will either be causally ordered,

one will precede the other or the other way around, or they won't be ordered. This order is a partial order. In the deep theory, the causal set elements have this structure just as the point events of space-time in GR have the structure. So those things are maintained in this correspondence between the deep theory, the discrete theory, and the continuum approximation.

This causal order is the same concept in both the theories, the deep theory and the continuum approximation. This causal order is the same concept in both the theories, the deep theory and the continuum, and GR, the continuum approximation. Sorry, what is the deep theory? Causal set theory. Okay, got it. So I don't know whether that underlying theory, the... Oh, I see what you're saying. I see what you're saying. Okay, okay. saying okay okay like the ultimate theory the one that gives rise yeah the more fun and ultimate might be too strong but deeper even welfare it I see. Yes it it's.

I don't know what, maybe deep structure. So the deep structure of space time is a causal order. Okay. So that's the second pillar. So, so first part of it is discrete, atomicity, finite, that there are finitely many atomic events in this podcast. And the second thing is that the fundamental degrees of freedom, the fundamental physical structure is an order relation, causal order, before and after. The third pillar is that the quantum theory of this entity will be a path integral quantum theory. So the quantum theory of causal

sets will be based on the path integral or the Feynman sum over histories. That's a sort of synonymous phrase for path integral Feynman sum over histories. That's what we will have to find on some of your histories, that's what we will have to base our quantum theory of causal sets upon. That the canonical approach or the canonical theory where there's a state vector in a Hilbert space will not fundamentally be what the quantum theory looks like. Eventually in 2019, Stephen, myself and Max Pisganov, we decided for various reasons that it was kind of the right time for us to do this project in a serious way. Stephen and I had some new ideas about how we could simplify the formalism a little bit. I'd made some recent progress in kind of understanding the mathematical underpinnings of it. Max

had just finished writing some really quite nicely optimized kind of low-level C++ code for enumerating these hypergraph systems really efficiently. And so we decided, like, okay, if we're not going to do it now, it's never going to happen. And so that was then the beginnings of the physics project. And so now I'm less, I guess, less actively involved in the, you know, in the project as a kind of branding entity. But I, you know, I'm still kind of actively working on the formalism and still trying to push ahead in various mathematical directions, trying to kind of concretify the foundations of what we're doing and make connections to, you know, to existing areas of mathematical physics. I see, I see. So I also noticed a similar problem as yourself across society. So across

history that people entwine this prevalent application with some ontological status. So what I mean by that is you'll have a tool which is ubiquitous and usefulness. And then you start to think that there's some reality synonymous with that. So another example would be an ancient poet who would see the power of poetry and think that what lies at the fundament is narrative pieces or a mystic who sees consciousness everywhere almost by definition and then believes consciousness must lie at the root of reality and some people, Max Tegmark would be an example of this, find that math is so powerful it must be what reality is. So it's also not clear to me whether computation is another such fashionable instance of a tool being so powerful that we mistake its

effectiveness with its substantiveness. And I understand that Stephen may think differently. I understand that you may think differently. I understand that you may think differently. So please explain. That's a fantastic point. And I suspect from at least from what you've said, I think I think our views may be quite similar on this that I'm reminded of this meme that circulated on Twitter a little while ago about people saying, you know, immediately after the invention of kind of writing systems and narrative structure, everyone goes, ah, yes, the universe, you know, the cosmos must be a book, right?

And then, you know, immediately after the invention of mathematics, ah, yes, the cosmos must be made of mathematics. And then it's, you know, immediately after the invention of the computer, ah, yes, the converse, the cosmos must be a computer. Um, so yeah, I think that, you know, that's, that's, it's a folly that we've fallen into throughout all of human history. And so, yeah, my feeling about this is always that, you know, we build models using the kind of ambient technology of our time. And when I say technology, I don't just mean, you know, nuts and bolts technology, I also mean kind of thinking technology,

right? So, you know, there are kind of ambient ideas and processes that we have access to, and we use those as a kind of raw substrate for making models of the world. So, you know, it's unsurprising that when people like Descartes and Newton built models of the cosmos, you know, of the solar system and so on, they describe them in terms of clockwork by analogies to clockwork mechanisms, right? And, you know, Descartes even sort of more or less directly wrote that he thought that, you know, the solar system was a piece of clockwork. Whether he actually thought that in an ontological sense or whether it was just a kind of poetic metaphor, I don't completely know. But it's sort of obvious

that that would happen, right? Because the 15th century, 16th century, that was sort of the height of clockwork technology in ambient society. And so we live right now in arguably the zenith of kind of computational technology. And so again, it's completely unsurprising that we build models of the cosmos based largely or partly on computational ideas. Yeah, I agree. I think it would be a folly. And I think you're right.

This is maybe one area where perhaps Stephen and I differ slightly in our kind of philosophical conception. I personally feel like it's folly to say, therefore, you know, the universe must be a computer, right? Or that, you know, that, that, yeah, my feeling about it is the strongest we can say is that, you know, modeling the universe as a Turing machine is a useful scientific model, and it's a useful thinking tool by which to reason through kind of various problems. I think it's, yeah, I would be uncomfortable endowing it with any greater ontological significance than that. That being said, of course, you know, there are also lots of examples where people have made the opposite problem, right? Where, you know, or made the opposite mistake,

I mean. So, you know, the classic example is people say Hendrick Lawrence, right, who invented basically invented the whole formalism of special relativity. But he said, oh, no, no, this is just a mathematical trick, right? He discovered the right form of time dilation and length contraction, but he said, this is just some coordinate change. It doesn't have any physical effect. It's just a formalism. And then really the contribution of Einstein was to say, no, it's not just a formalism.

This is an actual physical effect. And here's how we might be able to measure it. And so Yeah, I you I'm just trying it. I'm trying to indicate that this you have to thread a delicate needle there Yeah, so you mentioned Turing and there's another approach called constructor theory Wait, right generalizes Turing machines or universal Turing machines to universal constructors so-called universal constructors. So I'd like you to explain what those are to the degree that you Have studied it and then its relationship to what you work on at the wolframs physics project And by the way string theory loop quantum gravity, they have these succinct names, but wpp. It doesn't have a graspable Apprehensible name at least not to me to be able to echo that So is there one that you all use not to me to be able to echo that. So is there one

that you all use internally to refer to it? Okay so on that, yeah I'm not a fan of the naming of the Wolf of Physics project or indeed even the Wolfram model, which is a slightly more succinct version. In a lot of what I've written I describe it, I use the term hypergraph dynamics or sometimes hypergraph rewriting dynamics. OK. Because I think that's a that's a more descriptive title for what it really is. But no, I agree. I think I think as a branding exercise, there's still there's still more work that needs to be done. So for the sake of us speaking more quickly, we'll say the HD model. So in this HD model, what is its relationship to what was the category? No, it wasn't category

It was constructed through construct right? Okay. So what is the HD models relationship to constructor theory? Although that's an interesting Freudian slip because I think basically the relationship is category theory, right? So Yeah, okay. So so I mean with the with the proviso that you know, again I know that you've had Chiara Maletto on TOE before, right? So I'm certainly not an expert on Constructor Theory. I've read some of Chiara's and David Deutsch's papers on these topics. But so as you say, I can give an explanation to the extent that I understand it. So with, you know, as I understand it, the central idea with Constructor Theory is rather than describing physical laws in terms of equations of motion, right?

In the traditional conception of physics, we would say you've got some initial state of a system, you have some equations of motion that describe the dynamics of how it evolves, and then it evolves down to some final state. The idea with Constructor Theory is you say rather than formulating stuff in terms of equations of motion, you formulate things in terms of what classes of transformations are and are not permitted. So I think one of the classic examples that I think Deutsch uses in one of his early papers, and I know that Chiara has done additional work on, is the second law of thermodynamics, and indeed the first law of thermodynamics, right?

So thermodynamic laws are not really expressible in terms of equations of motion, or at least not in a very direct way. They're really saying quite global statements about what classes of physical transformations are and are not possible, right? That they're saying you cannot build a perpetual motion machine of the first kind or the second kind or whatever, right? That there is no valid procedure that takes you from this class of initial states to this class of final states that, you know, reduce global entropy that reduce global entropy or that create free energy or whatever.

And that's a really quite different way of conceptualizing the laws of physics. So Constructor Theory, as I understand it, is a way of applying that to physics as a whole, to saying we formalize physical laws not in terms of initial states and equations of motion, but in terms of initial substrates, final substrates and constructions, which are these kind of, which are these general processes that I guess one can think of as being like generalizations of catalysts or, you know, it's really a kind of grand generalization of the theory of catalysis in chemistry, right? That you know, you're describing things in terms of, you know, this enables this process to happen, which allows this class of transformations between these, you know, these classes of substrates or something.

What is Constructor Theory and how is it different now And this was originally proposed by David, I think back in 2011, something like that, as a new mode of explanation. So he wrote a paper that had a very strong philosophical component, which laid the foundations of the theory in the form of a program in a sense. And the key idea there was to modify the way we formulate laws of physics, and so the fundamental laws of physics. So instead of using things like dynamical equations, so laws of motion and initial conditions,

which is what most fundamental theories do, switch to a different mode where the basic fundamental statements are constraints about which transformations can be performed and which transformations cannot be performed and which transformations cannot be performed and why. So what is possible and what is impossible. And then consider dynamics and initial conditions as kind of emergent consequences of these principles. So it's really like a switch of perspective into thinking what is the fundamental element in a physical theory. And this was there, I think that's the key idea, and David was really inspired to do this by the quantum theory of computation, which is a theory that he himself pioneered

in the 80s when he with other people proposed the idea of a universal quantum computer. There I think it's really important to, in that theory, to think of what can be performed by a universal Turing machine and what cannot be performed by it under given laws of physics. So in the case of classical physics, you have a classical universal Turing machine that can do certain things and not others. And then you have a quantum universal Turing machine, which uses the laws of quantum theory, not classical physics. And there you have new different modes of computation available.

And this was a key insight in developing this idea of the universal quantum computer. And construct a theory, one way to see it, and this was already there in David's paper, is to think of it as a theory of a more general programmable machine that is even more general than a universal computer, and this is a universal constructor. So a constructor is an entity that can be programmed to perform a number of tasks that are not necessarily computations. So you can think of a heat engine as a constructor, if you like, um, a 3d printer is a constructor, anything that can be programmed to perform a given physical

transformation, you can think of it as a programmable constructor. It just has to have this property of being able to do the transformation once and then keep its ability to do it again. So that's the key feature of the constructor, which makes it different from a different system that can just simply perform the transformation once and then maybe be destroyed or whatever. And a universal constructor is the most general programmable machine that we can think of and this is what the physicist John von Neumann thought of when he was imagining the ultimate, you know, the most general programmable machine that could be built by humans in a sense.

And constructed theory can be thought of as a way to generalize the quantum theory of computation to cover these machines that are more general than computers. And this is somehow a completion of what phenomena had in mind, because phenomena had this idea of the universe of constructors, but then never really deliver the physical theory of these machines. Whereas we are hoping with constructed theory that we will be able to deliver a theory of these machines at the same time, also deepening our understanding of physical theories, because when you understand what are the fundamental limits of the universal constructor.

So what is it that it can or cannot perform? You've also expressed what are the, um, possible and impossible tasks according to the most fundamental laws of physics. So in a sense, studying the universal constructor and studying what is possible and impossible, um, under the laws of physics is the same. And this is a key insight in David's paper. There are lots of other things in that paper, I think, different ways of thinking about constructive theory as a way to expand on complexity theory and chemistry and thermodynamics and so on.

But back then, and I, well, a few years after, I think later, something like 20, yeah, 2012 or something, I was doing my PhD. Back then, we didn't have any specific application of the theory, so it was more like a program. And what happened between then and now, and let's say what I was really interested in when I started working with David and then kind of develop various things on my own was that I like this idea, this new switch, this sort of switch of perspective. And I thought it was very promising. And then I wanted to find some specific problems that this approach could be applied to. So then I think in partly my thesis and then later on in my research work, I did a few things where I applied this theory to various problems. So initially with David, we

applied it to information theory and we found a very interesting way of expressing with this language of constructive theory, the laws, the principles that underlie physical theories of information. So it's this theory that we developed together, David and I, was to express what are the regularities in nature that are needed for information to exist and also for quantum information to exist. So these are ways of handling both quantum and classical information in the same theoretical framework. And this is very important for direction of research that I'm really keen on nowadays, which is the direction where you're

thinking of systems that are in interaction with objects that obey quantum theory. But may not themselves be quantum maybe they behave according to a new theory maybe they behave according to a post quantum theory sure example gravity is one of these objects because. We don't know we have various proposals for quantum gravity but we don't know which particular quantum theory of gravity is the correct one yet. And so in that case, it's very important to have a theoretical framework to handle the situation where gravity that may or may not be quantum interacts with the quantum object and a framework that can handle both quantum and classical things, let's say in the same unified scenario. And that's what the Constructor Theory information can do for you, among other things.

So it's one direction. Another direction where we made progress was thermodynamics. So there was an application of Constructor Theory to thermodynamics and to expanding on the current formulation of the second law, something that we can discuss later. And then a third direction, broad direction, was an application of constructed theory to the physics of life. So there are these issues about what is the simplest entity that can occur in the universe,

which can be considered as alive? What are the essential features of this entity? So does it have to be programmable in some way? Is it a programmable constructor? What's the minimal structure of this entity. And in that direction, I think I applied constructor theory to tell us under what are, let's say, the necessary and sufficient conditions for an entity to be capable of self-reproducing very accurately, so just like living things do.

So in a sense, when we think of self-reproducing entities, we think of laws of biology. But ultimately, what we can do in biology is really set by the laws of physics that we have available. So it's interesting from the physics point of view, and especially from the constructors' point of view, to ask, considering the laws of physics as we know them, what are the minimal features that are both necessary and sufficient for a living system to be capable of self-reproducing accurately? And this is the kind of stuff that the Constructor Theory can deliver on. I think I developed this branch of Constructor Theory with a view of applying this to the study of, for example, the origin of life and possibly the study of life elsewhere in

the universe. So these are, let's say, the three macro directions in which to build progress on. And then David has also worked independently on various other things to do with the universal constructor itself. And finally, there are a few things in the pipeline with some collaborators of mine, Maria Violares, who is a PhD student, a default student here in Oxford, who's developed some interesting results about irreversibility, so again about thermodynamics. And then some work that they are doing on the constructed theory of time, so this is kind of forthcoming. And then some

extra work on the applications of constructed theory to this area where we have a quantum system interacting with something that may or may not be quantum. And this is something I'm doing with Giuseppe Di Pietro, who is another PhD student here in Oxford. So there's a lot of, there's been a lot of work. And finally, there's also been an interesting application of Construct-a-Theory to the problem of testing quantum effects in gravity which is something I've developed with Vlad Kovetrov who is a physicist here in the physics department. So I think that's an overview of what's going on. Wonderful overview, thank you so much. That's related to the twister stuff that I've been working on for

last few years which I'm still quite excited about. But there's one kind of basic claim at the bottom of what I'm trying to do with the twisters, which is I think to the standard way of thinking about particle physics and general relativity and spinners, it's initially's good. Yeah It's initially not very plausible I should say one reason that I actually didn't it took me a long time to get back to the Euclidian twister stuff from some early ideas years ago was that I didn't actually believe that the this this basic thing that I needed to happen and could happen and

I think lots of other people have had the same problem with this. And the more I looked into the twister stuff, the more I became convinced that, you know, something like this had to work out. But more recently, the last few months, I've come up with an understanding in much simpler terms, not involving twisters, just involving spinners

about the really unusual thing that's going on here. And I think that I've been trying to write up kind of an explanation of the basic idea, and I think it's a fairly simple one. And as I've been writing it up, I keep thinking, well, wait a minute, can this really work? There's no way this can actually really work. But the more I've been thinking about it,

the more I've been convinced, yes, this actually does really work. So I'm hoping within the next few days to have a final version of that paper. Well, not a final version, but a version of that paper I can at least send around to people and try to get comments on and also write about and publicly on my blog. I read the paper. Thank you for sending it. I sent you Yeah, what you have is a very is a very early draft of it, which made even less, hopefully, I'll have something that will make more sense, will be what the public will see, but we'll see. Yeah. Do you think spinners are more simplified or easy to understand than twisters?

Oh, yeah. So spinners are really very basic, very, very basic things. I mean, every elementary particle, like electrons are just the way you describe them. Their spin would have nature as spinners. You have to, electron wave functions are spinners. And so they're in every physics textbook, or if you do quantum mechanics, you do quantum field theory,

you have to spend a fair amount of time to spinners. So spinners. So spinners are very, very basic things. And they're not um, I spent a lot of my career kind of thinking about them trying to better understand them. And I keep learning new things. And it's the last few months, I kind of went I realized something about them, which, yeah, which I think, which I think is new, at least I never seen before. And this is what I'm trying to write about. But they're very fundamental objects.

It's a little bit hard to... Anyway, I can give you a whole lecture on spinners. I'm not sure how much of that you want or where you want to start with that. Right, well, there's one view that we can understand them in quotes algebraically, but that doesn't mean we understand what spinners are. So that's the Michael Attia approach,

where he says it's like the letter i the complex i the imaginary i back in the 1400s or 1500s. It's only now or a couple hundred years later, you realize what they are. And so sure, we have many different ways of describing spinners mathematically, but it's still a mystery as to what they are. So do you feel like, no, we understand what they are, or there's much more to be understood more than the formalism Well, yeah, it's very interesting. Yeah, you bring up at T. Yes at T at various points was um,

Did didn't make this argument that there's something very interesting in which we don't understand going on with the spinners and But yeah, he I think was thinking of it in a much more general context spinners and that yeah he I think was thinking of it in a much more general context spinners you know are really if you try and do geometry of any kind or reminding geometry you re expressing everything in terms of spinners and instead of in terms of vectors and tensors gives you a very different in some ways more powerful formalism, but one that people are not that used to. And it has some amazing properties.

It's kind of deeply related to notions about topology and K-theory and the Dirac operator gets into it. And so the thing that made Atiya really most famous is his index there with Singer. This is the, it's basically saying, you know, you can compete, everything comes down to a certain kind of fundamental case, and that is the fundamental case of the draw operator and spinners.

So he was seeing spinners kind of at the, you know, as this really kind of central thing to the most important thing that he'd worked on. And so there's a lot to say. So there's a lot known about spinners, but there's also a lot, it's a little bit mysterious where they come from. I think the new stuff that I've been more,

and so I've been thinking about that a lot over the years, but the new stuff that has gotten, where I think there's something new that I see going on is not the general story about spinners, but a very, very specific story about spinners in four dimensions. So you have spinners in any dimension. In any dimension you can write down spinners and they're useful. But in four dimensions, some very, very special things happen. And the other very, very special thing, it's interesting thing that's going on in four dimensions is that from the point of view of physics,

there's two different signatures that you're interested in. You're interested in either spinners in the usual kind of four dimensions, where all four dimensions are the same and you're just trying to do Euclidean geometry in four dimensions, which I might sometimes call Euclidean spinners, or you're interested in spinners of the sort that you actually observe in relativistic quantum field theories, where the geometry is that of Minkowski

space. So sometimes we refer to those as Minkowski spinners. And so you have two different versions of four dimensions, one with a totally positive signature and one where one direction has the opposite sign than the others in the in the metric so tight you have to treat time differently than space and that's been caskey space so there's two. There are different things in the general story that i'm interested in here. One is very specific. What have specifically the geometry of four dimensions and the other is very specifically the relation between Euclidean and Minkowski signature spinners. So is it your understanding or your proposal that the world is actually Euclidean and it's been a mistake to do physics in a Minkowski way? When we wick rotate, we see that as some mathematical trick and you're saying no, no,'s actually the real space that's real quote unquote even though there's something imaginary about it and the minkowski case was the mistake like.

An analogy would be we operate in usd and then for some calculations it's easier to go into yen. to go into yen and we think that the actual world is operating in the United States and the calculations are just something to make the numbers easier and then you're saying no no no what's really happening is in Japan and it's been a mistake to go into the USD or the USD is just to make the math easier so is that what you're saying or no well so so this goes back more to the Euclidean twister stuff yes so there well it's been well known in physics that you really kind of that the problem is a problem in Kowski space time, if you try and write down your theory in Kowski space time, you

the simplest story about how a free particle evolves, you write down, you know, the formulas for what's a free particle going to do, what's its propagator, and you see that it's just ill-defined. You've written down a formula which mathematically is ill-defined. It needs more information in order to actually be a well-defined formula. Technically, if you look at any physics book, you'll see they're saying, well, you know, we're going to do the answer is this integral and you look at this integral and this integral is going straight through two poles, and you know, that's just ambiguous. You don't know what, how to define such an ambiguity is about how you define such intervals.

So the one, the ask what you've always known, you have to do something like rotation, you have to do something, you have have to do something you have to. Get rid of those ambiguities and one way of getting rid of those ambiguities is. You know analytically continuing in making time a complex variable and let it continue it. Analytically continuing maybe to you clinton signature and there the formulas are well defined. So it's. And there the formulas are well defined. So it's, yeah, I'm not sure, I'm very comfortable saying one of these is real

and one of these is not. It's the same, it's the same formula. It's just, you have to realize that to make sense of it, you have to kind of go into the complex plane in time. And you can, if you things are analytic, if this is a hol more function in time you can you can. You can either evaluate what happens at a measure a time where you can make time real but you have to take theically continuing a certain direction to get real time. But that's the standard story. That's not me saying this. That's the standard story.

Right. And then there's a, how do you, what sense do you make of this? Is this just a mathematical trick, which a lot of physicists will say, well, that's just some kind of weird mathematical trick. It's not, it has nothing to do with reality. Or do you take this more seriously? So what's always fascinated me is more is that it's fairly clear what's going on if you just talk about scalar fields, if you talk about particles with spin zero

or fields that transform trivially under rotations. You know, what happens when you go to a time is quite interesting in some ways tricky but it's very well understood but it's never actually been very well understood what happens. When you have spinner fields and this is the problem is it. Spinners in your clinton signature and spin in a Casio signature are quite different things. And so you can't just say, oh, I'm going to analytically continue from one to the other because you're in it's not they're not related. Anyway, it's very unclear how you're going to do that. And so there's also a similar story in twister theory, you can, you can do twister theory

and Caskey space time, which is what Penrose and his collaborators mostly did, or you can do it in Euclidean signature space time, which is what Atiya and a lot of other people and mathematicians have done. In principle, the two are related by analytic continuation. But the way that works is quite, I think it's much subtler than you expect. What I've been interested in most recently, quite, I think it's much subtler than you expect. And what I've been interested in most recently, this business about, it really is a claim

that the standard way of thinking about how you analytically continue between these two different kinds of spinners is you're making kind of a wrong choice when you do that. And there's a good reason for the standard choice you're making when you normally when you do that, but there is actually another choice you can make, which is that instead of working with spinners, which are kind of symmetric between, there's two different kinds, which by convention you can call right and left handed or positive and negative chirality. And the standard set up treats this question, symmetrically, but between the plus and minus, the chirality is between right and left spinners.

But it's, what I've kind of realized recently is, it looks like it's quite possible to make this setup completely asymmetric so that you just describe spinners using these right-handed or positive chirality spinners. You just don't use the left-handed ones at all in your construction of space-time. You can do that, it appears to be, and that's why this paper is called Space Time is Right-Handed. Is it the case that you could have called it space time is chiral and you could have equivalently described as

left handed? Or is there something specific about right handedness? No, yeah, yeah, yeah, it's certainly it's a matter of convention, which, but you basically mean, to say a little bit more technically, you know, the the, the, the Laurent symmetry group is this group called SL2C. It's two by two complex matrices, a determinant one. And what you realize is if you work in complex version of four dimensions, the symmetry group

is two copies of SL2C. And you can call it a plus copy and a minus copy, or you can call it a right copy and a left copy, but there's two of them. And the standard convention in order to get analytic continuation to work out the way people expected has been to say that the physical Lorentz group that corresponds to our real world is is not currently symmetric it's it's kind of a diagonal which is use both right and left and you have to complex conjugate when you go from one side to the other but.

It kind of. The rent the rents group the sl2c lorenz group we know is supposed to sit is kind of diagonal thing which is both. to see Lorentz group we know is supposed to sit as kind of a diagonal thing which is both right right and left but um what i'm kind of arguing is that no you can actually set things up so that the um the the Lorentz group is just one of these two factors you call it could have been the right factor left actor you have to make your a choice of convention but but yeah so it is very much a chiral setup um but you only, the strange thing about this is you only really see this when you complexify. If you just look at Minkowski's space time,

you don't actually see this. Anyway, you don't see this problem or you don't see this ability to make this distinction. It's only when you go to Euclidean space time where the rotation group really does split into two completely distinct right and left things. Or if you go to a complexified space time where you have this two copies of SL2C, it's only in those contexts that you actually see that there is a difference between choosing the diagonal and choosing the right-handed side.

So for SL2C, you call that the Lorentz group. Is that technically the double cover of the Lorentz group? People use both terminology. If you're going to work with spinners, you have to use a double cover. But yes, it's also, yeah, sometimes you might want to say that SO31 is the Lorentz group and this is the double cover. But mostly you're interested in working with spinners and then you have to use the double cover really.

Yes. Yes. So is there a reason that triple covers or quadruple covers aren't talked about much? Is it just because of experiment? There's nothing there. Well, it's more than mathematics that they don't. There is I mean, there is, you know, any the rotation groups of any kind, you know, have this to have this twofold nature, there is this spin double cut, there is this have these

spin double covers. In many cases, you can cut one way of seeing this is just a basic topology of the topology of rotations has a you know, has a plus and minus thing in it, which you kind of, and you have to do something about that. So there aren't there aren't any kind of known interesting, mathematically interesting triple covers, etc. Tim Modlin was saying that his favorite parts of most physics courses, most science courses in general are the first lectures, because they're selling you on the course.

So he's like, when I went to quantum field theory, they told me about this is the most impactful theory in science. And then lecture three is on Green's functions. He's like, well, what happened to studying what is? And when you ask what is, they're like, oh, that's philosophy actually. Don't even ask that here. Yeah, well, I mean, you know, there's a lot,

well, quantum field theory has certainly always been, and probably, well, I don't know if it remains, but it's always been the most challenging class to teach in graduate school or to take. And there's just a lot of stuff and a lot of intellectual baggage that you need to do. And you can't, and before you can, philosophy is useful for framing initial questions,

the world, but physics has long gone beyond those initial questions so that it's driven by questions that are often quite mathematical in nature. And people don't realize that you can't just sort of start with those questions and expect to reach anything without going through the remarkable baggage that's been developed, and that has taken you far away

from the questions. So what is is a fancy question, but it actually, as I talked about in universe for nothing, that the whole concept of something and nothing has changed dramatically because of physics. And people don't like that, but I don't care. It's the way it is. It's called learning.

And we now realize as a matter of fact, because of quantum field theory, that the difference between something and nothing is not so great as imagined before, because nothing has lots of something in it. Yeah, let's speak about that for a moment. When I was younger, I remember questioning the universe and I couldn't figure out how anything could come from nothing. And that was something that I had asked my brother who was studying physics at the time. And then he mentioned quantum fluctuations. And I was eight or so and then it was approximately at that point that I became an arrogant and inexorable atheist.

Well, your brother your brother did God's work as we say. I realized years later, that's not an explanation to say vacuum. But I didn't know that at the time. So because I didn't know I thought that that was an explanation. However, you have now figured out some way of making that indeed an explanation. However, you have now figured out some way of making that indeed an explanation. So can you cover that please? How you get something from nothing you mean how the universe can come about from vacuum fluctuation. Yeah, well, I can give you a summary. As I say, I wrote a whole book about it. So it's kind of but look, the key part about the key aspect of quantum mechanics,

which I do talk about in the new book, is that the quantum universe is very, many things are happening at the same time. And in particular, quantum fluctuations are happening all the time. We can't see them, but quantum systems are constantly fluctuating. And when you combine quantum mechanics and relativity,

it's even more exciting because it says that empty space isn't empty. So the key thing about quantum mechanics, when you combine it with relativity, and I've described this in a number of my books, it implies that empty space isn't empty. It may, I mean, it has no real particles, but over time scales that are so short

that you can't measure them directly, and this is the uncertainty principle of quantum mechanics, things can happen that you can't see. And in particular, particles can pop into existence that weren't there before, and then pop out of existence in a time scale so short that you can't even see them. Those are called virtual particles.

It may sound like counting angels on the head of a pin if you say, well, these particles are there, but you can't see them. Well, we can't see them directly, but what we can do is see their effects indirectly. We know they're there because we have an impact on the atomic energy levels of atoms. They allow us to calculate the atomic energy levels

of atoms with an accuracy that's unprecedented in all of science. So we know we have to include the fact that on small scales and small times, particles are popping in and out of existence. It's quantum fluctuations in quantum fields. That's why quantum field theory is relevant. Allow you to produce particles that appear and then disappear. Fine. Well, that's for normal quantum field theory with particles in space and time. But gravity is a theory of space and time. And so if gravity is a quantum theory,

if gravity is a quantum theory, and that's a big if, we don't know for certain, but we have no reason to suspect it isn't, then the variables of that theory, space and time, become quantum mechanical variables. And then space and time can fluctuate. And you can start literally with no space, no time, and then have a little universe with space and time appear and then disappear. Virtual universes can pop in and out of existence. And in quantum gravity that kind of phenomena happens. But it can happen that if a virtual universe pops into existence with zero total energy,

then the laws of quantum mechanics and relativity say that that virtual universe, in fact, can be real. It can exist for an arbitrarily long, long time. And then in order for it to not collapse again, if it starts expanding and not collapses, certain processes have to happen. But if you asked, what would a universe that was almost 14 billion years old,

that spontaneously arose from nothing by quantum mechanical processes, what would it look like today? And the answer is it would look just like the universe we live in. All the properties would be the properties of the universe we live in. Now that doesn't prove that that happened. But it's strongly suggestive that that possibility

could explain the existence of our universe. Now it's all possibilities right now because we don't have a quantum theory of gravity. I if space and time if we have a quantum if gravity is a quantum theory and it's a big if We don't have a theory of quantum gravity We may you know string theory is a good candidate for that But no one knows if it is a theory of quantum gravity in our universe And so that's an open question at the forefront of physics one of them known unknowns if you wish And what's the name of that theory one of the known unknowns, if you wish.

And what's the name of that theory? What you just outlined, which is okay, look, if you have fluctuating quantum fields, and you were to combine general relativity, a fluctuating space time itself, universes can it's just a proposal, a vague proposal, like, or is there what it's, it's, it's a, no, I know, there's no names attached to it. I propose it, other people have proposed it. But it's just a consequence, if you wish, of, of, of, of having a quantum theory of gravity. And lots of people have thought about it, Hawking and Ardell and, uh, and, you

know, Stephen Hawking has obviously thought about it a lot. I have other people have. Now the crucial, the crucial, um, statement that bell makes is that fixing says A or A prime, this is the zero or one, this is the output that determines the measurement setting. Fixing A or A prime indeed fixes something about the input, i.e. whether the millionth digit is odd or even. Now this is the crucial statement. But this peculiar piece of information is unlikely to be the vital piece for any distinctively different purpose, i.e. it is otherwise rather useless. So the point is this, that we've got, you know, we're doing this experiment in a world where, you know, the moons, to use the example again, the moons are going around Jupiter and various other things are happening.

You know, people's a reasonable point. I'm not saying it's not reasonable, but I'm claiming that in the context of quantum mechanics, it is questionable. But his point is that all these other things, the moons of Jupiter, the people going for a walk in the park, the value of the millionth digits irrelevant. They just carry on their lives. of the millionth digits irrelevant. They just carry on their lives. And of course, that's a perfectly, that's the sort of thing that you would expect to be true if the world was governed say by Newtonian physics, because, or indeed by most simple dynamical systems,

because you can take an initial condition where, you know, somebody's about to go into the park where the moon is about to take in a particular phase of the orbit, keep all that stuff fixed and vary the millionth digit. And that's a perfectly reasonable perturbed initial condition and you can carry on solving your Newtonian equations with that slightly different initial condition. So that is a kind of scientific statement, if you like, or scientific justification for Bell's, what he calls his reasonable assumption that the millionth is is unlikely to be. The body would not the word unlikely not definitely not unlikely to be the vital piece of for any distinctively different purpose.

So ready there's kind of an implicit. reference to the fact that this millionth digit is a free variable in the sense it can be twiddled it can change you can keep everything else fixed you can just twiddle that thing and the world will continue. But i want to come back to my example. Where do you see twiddling in this i mean he says it's unlikely to be i mean i have it in front of me as well. unlikely to be I mean, I have it in front of me as well. Yeah, a lot of vital pieces for any distinctively different purpose, ie otherwise rather useless, I take it, what he means there is that it that conditioning on that fact, not asking what would have been the case if it had been different. But just conditioning on that gives you no information, no useful

information about anything else. It will tell you a very important thing in the physical world, namely did Alice pick X or Y in that run? It'll absolutely tell you that important physical fact, but it just won't give you any information. It doesn't really have to be the determinism. It won't change the likelihood that Jupiter's moons are at any particular phase. It won't change the likelihood that people are walking in the park. It won't change the likelihood in that, uh, or, you know, have any effect on, on, on anything else in terms of the statistics. But this is the, but Tim, this is the whole point I'm trying to make.

I can, and I do, claim to have a mathematical model where, and it's just a generalization of the example that I discussed with Lorenz's attractor, where you can't chain the millionth digit of one of the variables and keep the others fixed. But he doesn't say you can't chain the millions digit of one of the variables and keep the others fixed. He doesn't say you can't do that. It doesn't, it leads you to an undefined... This passage doesn't say you can do that.

That's what it says. It says it's not a useful piece of information for any distinctive other thing. A distinctly different purpose. In other words, if you change that information... No, no, you keep saying in other words. I'm trying to find. You keep saying in other words, but he doesn't talk about changing it. He just says it's not useful information

for any other purpose. The whole, Tim, the whole paper is about free variables and a free variable is something that you can change in your theory. That's the whole basis of the paper. Free, what does free mean? If it doesn't mean you can't change it, then it has no meaning. One interesting fact is that if you look at, for example, string theory, and you look at

loop quantum gravity, and you look at other approaches to quantum gravity, even the original ideas of super membrane theory, the idea that the fundamental degree of freedom is really a membrane, not a string. And when people tried to quantize this membrane, they ran into problems and they found out that, oh look at this, this membrane theory could be properly quantized if you turn it into a matrix theory. So at the end of the day, all these approaches to quantum gravity pointed to matrix theories. Okay. And what do I mean by matrix theories? If I'm sure that you might as I understand, I'll just tell you and then you can correct me because I help you learn, especially because I put myself on the line, my ego on the line, they learn better. Okay. So as far as I understand with the matrix models, you just mentioned that it solves a particular issue, but another issue is created in that they're finite dimensional

and what you want to do is take n to infinity. Is that correct? One of the things you can do to make contact with the continuum or, for example, Yang-Mills-like theories, which are, is that you, yeah, that's right, when you take n, where n is the rank of the matrix, so if n is 2, I have a 2 by 2 matrix. So when n goes to infinity, the rank goes to infinity, that it does reduce back to known theories like Yang-M Mills theories, for example. Something occurs to me right now as I think about the in okay, let's take n to infinity, would that not be accountable infinity, whereas the infinities that we deal with with lead groups

and so on are uncountable, they're the reals. So how is it that we can take a matrix, blow it up to n and get something that's something like this real continuum? That's a good question. It's similar to, you know, when you, you do a Fourier series, you know, you have a, you take that sum, and, and you, you, you look at basically the sum of sines and cosines. And then when you take basically N in that sum to infinity, that becomes the integral sign. So it's similar to the continuum hypothesis. I see, I see.

Yeah. Okay, continue. Yeah, no pun intended. Yeah, so in a nutshell, the observation that I made with Lee Smolin and Lee made with me is that how interesting matrix models seem to underlie a couple of what we thought to be disparate approaches to quantum gravity or unification, strain theory, loop point of gravity, and other ways, random matrix models. They all kind of seem, I meant membrane theory. They all pointed to these matrix models.

So maybe we should take more seriously that the matrix models themselves might actually be, well, not actually be, I mean, Banks, Fischler, Schenker, and Susskind, so-called BFSS, and I think IKKT named after some Japanese theorists, actually conjectured that M theory, which is supposed to be the unification of all string theories, M theory or the so-called non-perturbative definition of string theory, it was hypothesized to be a matrix theory. So we weren't saying anything new there,

but to maybe extend that, extend it beyond even M theory, to say that other approaches to quantum gravity might also have this. So that was one observation. The second observation that me, John and Lee made was that if you look at the equations of a matrix model, it has a semblance to artificial some, it has a semblance, it's not identical, but it has a semblance to artificial neural network. It resembles and how it might be useful for me to then to write something. Sure,

please. So, and I'm going to be very schematic here, because I'm right in front memory. And I, so, okay. So just recall that an artificial neural network basically tells me that if I have, you know, a simple two layered, if I have an input, so there's my X, so X is a vector, is an N-toplet, right? That I can, you know, that think of each point here, each dot is a neuron that could be connected, you know, in a forward way, right?

I can have connection to, let me call this thing. Right. So, oops, my bad. I don't know why it's doing that. Um, are you able to hear anywhere it sounds? Yeah, no, no, no. Okay. That's what I did right here. Are you able to hear anywhere it sounds? Yeah, no, no, no. OK.

That's what I get right here. So the equation says that if I, there's some output y, right? And there's a weight matrix that determines how correlated, how connected these neurons are. So for example, X1, right? If I have X, oh sorry, X1 and then I have Y1, for example, right, this WIJ will denote basically this is XJ and this is YI, right?

So this basically tells me how every neuron is connected. Um, you know, the output is connected to the input, right? And then of course there's some bias term here that basically helps out with, um, um, to, to further basically, you know, to help with bias and these connections. All right, so that's, there's a long story here about neural networks. Sure. And, all right, so this is very similar to statistical inference, right? If I basically have, in this case, a line, and I tell you the slope

of the line, I can you the slope of the line. I can adjust the slope of the line, basically, to basically fit some data. Given an input, the output will basically sort of maximize, or the slope will basically maximize in this case, if you try to get the best standard, you know, mean you can basically use this. This is a multidimensional version of statistical inference. I see. I see. Okay. Okay. Now. The mate, so what I want you to take notice of here is that mathematically, I'm basically

performing some kind of linear transformation from one vector to another vector. And the weights basically is this transformation matrix. That's one way I like to think about it, right? Okay. Okay. Okay. So in a matrix model, what we have is something similar, not similar, but what we have is situation where we have. So the analogy first of all, let me let me spell out the analogy the analogy is instead of having neurons That are represented by vectors Right, okay

What were the idea here is that okay we have made we have matrices Which are basically tensor products of vectors. So in other words, I can, for example, I could take the tensor product of, say, two vectors, Xi, tensor Xj, and then I can have a matrix Xij. So likewise, I can have some correspondence where the equation of an artificial neural network, which is mapped in the idea of a perceptron

or an artificial neuron, is represented as a vector. The idea here is that the matrices, right, there's a sense in which I can isolate some components of this matrix, and I could freeze. And this freezing procedure, again, an is spelled out in the paper And it's a long story But I just want to spell out the basic idea sure Is that I can basically isolate vectors in this thing in this matrix model and you when you say you can isolate them

hmm Okay, so let me say another thing here. You mean like how they can be decomposed and then you just pull out one of them? Yeah, yeah. So let's so in the matrix models what we have is basically is let me actually write down one of these matrices. Okay. X so it's X a. So I'm actually X I. So I'm going to make an X, I, M, N. So what is this thing? So basically, it's basically, let's say that I runs from 1 to 3 for now. So this would be X1, X2, X3. And then I'll still have M, M here.

Right. So, so one thing I could do here is assume that MN is say, completely diagonal. Right. So I can basically make some approximation and collapse this MN right into some X. So in other words, here's X MN, right. And what I now want to do is basically only look at these components here, the diagonal components. Okay, I can play with that for now. And then, you know, just look only at the diagonal components of this, you know, this MN matrix. And there's something that allows you to say that it's diagonalizable? Yes, there's something that allows me to say that. Right. So that's one thing you can do. But one of the things that we are currently working on as we speak in the follow-up paper is exactly how to turn this thing into a, you know,

into a bona fide, into a bona fide learning architecture. Tom, why don't you tell the audience what you're working on these days? Okay. Well, I suspect what you're referring to working on these days is the My Big Toe, since you are obviously interested in theories of everything. That's one of your subjects of interest. My Big Toe was called My, not because I'm so proud of it. It's because if it's not your experience, then it can't be your truth. So my Big Toe is basically based on my experience, my research, and my conclusions.

And my Big Toe should just be perhaps a structure or a platform for each person to build their own big toe. It's not something to be believed. Belief is a problem. Belief gets in the way. Where you have a belief, you put yourself behind a wall. You don't then let in other information that conflicts with that belief.

So beliefs are always a problem to understanding the big picture. So I would not encourage anybody to believe my model, but to look at it and see if it applies to their life. So I'm a physicist. Let's just give you a little overview. My big toe, it's a model of everything. It's a big toe, not just a toe. Mostly when you hear about toes, they're not really about everything.

They're a theory of physics. They're a theory of fundamental science within this universe, you know, the science of our universe, that's what they are. And what they leave out is everything that is subjective. In other words, consciousness, you know, attitudes, feelings, emotions, everything that's in the subjective world. And if you think about it, most of our world that is important to us does fall in the subjective side. The objective world of physicists, and I'm a physicist, but the objective world of physics is basically just

a subset of the world that we live in and interact in. And it's, I would say, a minor subset. It's the stage, it's the props, it's all the stuff. Important things in our life like, who should I marry? Should I take this job or that job? You know, that sort of thing. Big things that change our lives, change our thinking. What books should I read? All of these choices are not objective choices. They're all subjective choices. So most of our more meaningful experiences like love, justice, truth, all these things are subjective, or at least

have large components of subjectiveness in them. So a theory of everything has to also be a theory of the subjective world as well as the objective world, otherwise you've just got a little tau, which is just the theory of the objective world. So my tau is a bit different, and mine started with, or I should say, mine starts with consciousness as a fundamental. And the reason that I came to that is that I was in graduate school in physics where they know my PhD in experimental nuclear physics. And I found out just quite by accident that I could debug my computer code. Now back

in those days, these are the old days in computer code, I'm talking about boxes of cards, you know, that sort of thing. And debugging was a huge problem. Not like today where you have debuggers and instant terminals and access to the computers and so on. In those days, there was a big central computer and it took up a whole building and it was not as powerful as your telephone is today. It was probably only a hundredth or a thousandth as powerful as your cell phone is today. It was probably only a hundredth or a thousandth as powerful as your cell phone is today. And the whole school, the whole university ran on that one computer. There were no, there were no desktops. So you got to stand in line in a queue and if you got one or two jobs run a week, well, lucky you. So if that job ran and bombed because you had an error, well, you just lost a week for

your research, you see. So debugging was something people spent a lot of time focused on so that they didn't have to wait forever to get their research done and their ideas worked out. So in any case, I found that in my mind I could bring up a picture in a meditation state. I learned to meditate while I was in graduate school, and I learned because the advertisement said that you could get by with less sleep. And in graduate school, that just was a real big plus for me. So that's why I learned how to meditate. And anyway, in this meditation state, I could bring up a picture of my output, my printout,

scroll through all the lines in code, and the lines that had errors in them, had problems in them would just show up red. That was an intention of mine. I wanted to be able to see them. And I just did this kind of on a wild hair, you know, kind of a lark, well, I'm in a meditation state, let's see what I can do. And I checked it out, and it was correct. Those lines of code were actually the ones that had problems. And in these days, a problem wasn't because necessarily you coded it incorrectly, maybe the key punch was just off a hare.

If those little holes didn't line up exactly right with the reader, you'd get an error. So you may have done all the right things, but the machine was a little off. It punched holes. So that, as a physicist, that hit me with a ton of bricks. What was going on here? How could I do that? There was no physical process going on. It was entirely a mental process. And how could my mental process find things like key punch errors? That was just crazy. So I played with it, and I played with it, and I found that I got better with it, with practice, and that I could decode my stuff very, I mean, you know, debug it very, very

quickly. So, as a physicist, what that told me was that my idea that reality is measurable. If it's not measurable, in other words, this is called a, what's the word for it? It's like if you can't interact with it, you know, if you're talking about something, you say, oh, this is real, but you can't interact with it. You can't see, you can't smell. Pete Slauson Operationalism? Pete Slauson Yeah. It's an operational definition of reality. Exactly. So, I, as a physicist, that was my attitude toward reality. It's an operational definition of reality, exactly. So I, as a physicist, that was my

attitude toward reality. It's an operational reality. So I realized that wasn't true, that there was more to reality than just what you could measure, what you could do operations on. It had another whole component to it that was more tied up to mental than to physical. Just in your blog post or whatever you want to call it that you were trying to criticize the experiment that I proposed, unfortunately you don't seem to have actually looked at the original paper where I proposed the experiment. You quoted the paper from 2019, which refers to a paper from 2011, I believe, in which I have explained exactly how you can circumvent this problem that you don't know how the hidden variables, the state of the hidden variables fall in the

prepared state. You make repeated measurement on the same system and then I made some estimate for, you know, what the size of the system should have to be, how cold it should have to be and so on. Now, you're complaining that you can't falsify it, but of course, if no one makes the experiment to falsify it, then we're not going to falsify it. My point is the experiment cannot falsify it. So Sabina, can you respond to this unfalsifiable claim of the model? Yeah, I mean, you propose a model and then you make a prediction. And if the prediction isn't correct, then you falsified the model. That's not how it will work.

Of course. That's not how it will work. Yeah. Well, that's quite possibly the case. I can explain how and why. You know, if this is a general criticism about falsification, we can have this argument. You know, we can argue that no theory has ever actually been falsified, if that's what you want to say. I would actually agree with this. You know, the ether has never really been falsified, blah, blah, blah, blah.

As I've said a few times, we don't really falsify theories, we implausify them until people give up on them. But I think that's kind of a really tangential point. So can I elaborate on why I made that claim? So let me first, we have to explain the experiment a little bit so people can follow. The experiment is the following. Since we do not know what the hidden variables are, we have to adopt certain procedures to minimize the chance that whatever they are, their values can drift. Because the experiment is based on the following.

If you have a quantum system and you make a series of measurements on that system, according to the Born rule of quantum mechanics, you have a certain statistical distribution of measurements that is not deterministic. If super determinism is right, if there are these mysterious hidden variables, then the series of measurements will be determined

by the system's initial condition. So the experiment is based on the following idea. Even if I don't know what the hidden variables are and I cannot know how to restore the initial conditions of the system, because of course you need to restore the initial condition of the hidden variables too, even without knowing what they are, if I cool down the system and I make a fast series of measurements, stop and immediately do a next series of measurements after returning the initial conditions as best as I can, and then do the same thing and do another series of measurements.

If super determinism is right, the series of measurements will all be determined by more or less the same initial conditions if I do them in rapid succession before the hidden variables have a chance to drift in value. And I will find time correlations between the series, which would then, if that's the case, contradict the Bohr and Ruhl. Now, because the whole thing is based on having to do with these series of measurements in rapid succession, but having enough measurements to find

if there is a correlation between the series, you end up in the following situation. If and when the experiment fails and validates Born rule, one can always say, well, I didn't make enough measurements per series, so I don't know that they correlate, so it's inconclusive. Well, then you make more measurements per series, but then each series becomes longer, takes longer to make, so it will take longer for you to start the next series. And then one can say, well, it's just because the initial state has drifted. I took too long to do the next series.

So whatever happens, one will always be able to claim that the experiment is inconclusive and doesn't falsify the hidden variables. Why? Because it's so loosely defined. We are not saying what the hidden variables are and how they work. We are not saying anything. We are just hoping that there is something that somehow does what it needs to do for this picture of nature, this metaphysical commitment that physical properties should have stand-alone existence to survive. Well, two things. First, as I already said earlier, you're talking about

the wrong experiment. I'm talking about the experiments you talk about. No, you were talking about a change in the initial conditions I told you that the experiment you should be doing is repeated measurement of non-commuting variables on the same state. That alone is sufficient. In the 2019 paper, I was talking about a simplified experiment. I mentioned this in the text, and I can explain why I have reason to think that this is probably enough, but I'm not sure you're actually interested in hearing that. Okay, but… Oh, I'm lying.

Okay, good. I'll tell you. So let me make a more general point, which is that you can't falsify super determinism. I totally agree with that because super determinism is not a theory. It's a property of a class of theories. What you can falsify are specific models and yes, you are entirely right, those models would have to specify what the hidden variables are or at least what their properties are. If you don't say anything about it, you can't make any predictions. So what are the hidden variables? Well, that depends on your model. You know, there are different models that people have put forward. I would say that at the moment, they're all unsatisfactory.

So according to your model, what are the hidden variables in your model? In the model which you already complained about with the past integral, we explained this in the paper. The hidden variables are the degrees of freedom of the detector, which are not the measurement setting. Now I can explain to you why I think that makes sense, because I have a background as a particle physicist.

So I don't like the idea of introducing new degrees of freedom and throw them over the already existing elementary particles in the standard model, you know this whole problem. You know, I get the impression you have some background in particle physics. So it's not a good idea. However, we know just empirically that the measurement setting affects the average value of the distribution. That's Born's through. Okay. So that's the measurement setting. You mean like, like the angular momentum you set to affect the

distribution because everything will fall along the eigenvalues of, of the detector. Is that what you mean? Basically? Yeah. I mean, I mean something much more simple. If you want to calculate the probability of a measurement outcome, you have to say, what is the thing that you measure?

Right? Otherwise, how are you going to project it on the eigenstates? Okay, so that's that. But this brings up the question, like, what's with all the other details of the detector? What happened with them? Like, a detector is not just a measurement eigenstate. It's a complicated big thing that has many degrees of freedom. So the model that I'm trying to develop, which is the thing that you are complaining about with

the quantumness, and that's the discussion in the paper where I say this is the part which I haven't figured out is exactly how those degrees of freedom enter the evolution law. But this is the idea. So the degrees of freedom of the detector, except for the measurement setting itself, are the hidden variables. And now once you buy this, and I agree with you that I don't actually know exactly what the evolution law looks like, you can very precisely estimate how long it will take. I mean, maybe not as precisely as I'm hoping, but in principle, you can estimate how long it will take for them to change. There's one way of getting around Bell's inequality and it's called super determinism. And I'm curious if you heard of it. And if you don't mind explaining it to our audience and then giving what your thoughts are on it.

Yes, I've heard of it. As I said in the very beginning, I'm partly working in the foundations of quantum mechanics and that's what I'm working on. So as you correctly say, super determinism Super-determinism is one of the ways to get around the conclusions of Bell's theorem, which could be summarized as if you have a local and deterministic theory, like roughly speaking, very roughly, like the way that we are used to from Newtonian mechanics. There's no randomness in that. It's all deterministic. There's no spooky action at the distance, that kind of stuff, in which the outcomes of quantum mechanics are actually determined, but you cannot predict them just because you're

missing information. In this case, the quantum mechanics would be probabilistic for the exact same reason that you normally have probabilistic predictions if you're throwing dice or something like this. You just don't hear you're missing information. So Bell's theorem tells you you can't do that because any theory that has these properties will be in conflict with certain experiments that have been done. So there's this thing that's called Bell's inequality and all theories of the type that

I was just talking about tell you have to obey this inequality, but experimentally you know that it can be violated. So this just draws out this type of theory. And a lot of people take this to mean that quantum mechanics is non-local and it's a non-realist theory and so on. Now there is one assumption of in-belt theorem which is called statistical independence. And this is really, really essential to arrive at this conclusion. So if you throw out this assumption of statistical independence, you can very well have a theory that is deterministic and local and still violates Bell's inequalities and is therefore compatible with all observations.

And personally, I think that this is much more reasonable than to buy into all this philosophically mind-numbing stuff about having a non-realist interpretation that is somehow always drawing on macroscopic concepts like detector measurements or agents and their knowledge and that kind of stuff, and yet still somehow compatible with reductionism. The only thing that this requires is that you give up on this rather mathematical assumption of statistical independence. Now, you may ask, well, what does it mean to give up on statistical independence? So, just technically, it means that the outcome of the measurement depends on the setting

of the detector. And if you want to interpret this more broadly, it basically means that there are no places in the universe that are entirely disconnected from each other. Basically, everything is connected with everything else in very, very subtle ways so that you don't normally notice it, like in you know Everyday life we don't notice quantum effects. And so we also don't notice these subtle correlations

But if you do a bell type test or some other quantum experiment then You become you become sensitive to that. How is this congruent with special relativity? That is that you can't break the speed of light. How is it that we can be connected to what is outside the cone? Well, you can have in special relativity, you can very well have correlations between, you know, distant points, they will be within some light cone of something. Just because they're in distant places does not mean they were created at a distance.

You know, they can't have been created locally. Right, right. Do you have any thoughts on the emergence of possible emergence of consciousness or whether or not consciousness is fundamental? Well, I don't think that consciousness is all that mysterious. So, you know, I'm a particular person, I'm a reductionist. Of course, I think that consciousness is weakly emergent, as I guess most people in my discipline. It comes from the way that complex systems process information, I would say. At some level, it becomes beneficial for the system in terms of natural selection to have a self-monitoring process.

So that's the peculiar thing about consciousness is that most of the time we're actually not really aware of a lot of stuff that's going on. So that's all the stuff that we put into the subconsciousness, which basically frees up, I guess, some processing power on the higher levels. I don't think that consciousness is specific to biological forms of life, but that sooner or later there will be some computers that will reach some levels of consciousness. So that is, the Sun even has a level of consciousness and the planets do? Well, you know, there's some, depends on exactly how you define it, right? So if you define consciousness by information processing capacity together with some level of self-awareness, then you may find that pretty much any system has a very, very small level of consciousness at some point, but it's rather meaningless.

I guess that you would have to pretty arbitrarily at some point just say, okay, we call it consciousness. If it's larger than I don't know something. Right. Now, how do we test that? I can see that we can come up with a measurement for consciousness, but it's not as if we can. It sounds like we're simply defining consciousness as being a certain level of self monitoring information processing, but it's not. Well, you know, on this verbal level, of course, you can't test it.

You actually need to write down a particular model that, you know, quantifies just what it takes. What exactly needs to be happening in the brain and so on and so forth. And then I think you can very well go and measure it. Okay, well, what I'm saying is that if you measure it, let's imagine there's someone who has a low level of what we would predict to be consciousness. So let's just give it a number. They have consciousness, we would predict that they have, we can, we can figure out their brain state almost exactly. And we can imagine that from our data, from our theory that they should have consciousness at level 10. But they say, and somehow we have to get, we have to have a way of

saying this. They're like, no, no, no, I have consciousness at level 20. Or someone who we predict at level 10 said, no, no, I'm actually consciousness level five. Well, how does this? It just sounds like a definition. Yes, there's probably something fishy about your definition is what I would say. Of course you want a definition that actually agrees to quite some extent with what we normally mean by consciousness. We have an idea of consciousness, like you're conscious, I am conscious, other people are conscious.

My computer is not conscious, at least not on a noticeable level. You could say that maybe the task manager or something is some level of self-awareness, but it's so tiny that I can't have a meaningful conversation with my computer, let me put it like this. And so if we manage to come up with some definition of consciousness, we will want it to agree with our intuition, basically.

For our audience, do you mind explaining? I know that Wolfram's theory is not something you've studied immensely, but Wolfram does say that the universe is inherently computational. What does that mean? Within quantum gravity is fluctuate. And so you have to it's not as simple as that. I mean, well, it's not as simple as that. Anyway, no, now that I've talked about quantum gravity for a bit too long. Why don't you talk about what the super force is and how you believe that solves some of the problems in quantum gravity? Okay. It's interesting because you can say this would go back to Sir Isaac Newton. I think was 1693. I could be possibly wrong with you. He writes a letter to his friend in which he says,

what if, what if gravity is caused by an agent, capital A, that acts constantly in accordance with given laws of nature? What if this agent, capital A, is the super force? And what I mean by the super force would be like the force of unification, the force that would rule over the other forces and equalize all forces. I believe it does exist at the Planck scale. Now why at the Planck scale? Look carefully at the structure of general relativity formalism that's used by Einstein.

And I shall not use Ricci or Riemannian curvature formalism. I'll use Einstein tensor. So g sub mu nu equals what? 8 pi big G divided by c to the fourth. The whole thing times T sub mu nu, that T sub mu nu again represented of energy density. But look carefully at that scalar constant. It has a term in it, C a blank energy divided by blank length.

So your blank mass times c square, the whole thing divided by gh bar divided by c cube, the whole thing one half, the thing comes up as c to the fourth divided by g. How can you get a Planck force featuring within general relativity? And it goes further. You can find the c to the fourth divided by big G. What's I term the super force, this force of unification in the Dirac equation, which is the relativistic form of Schrodinger equation, the foundational form, formalism of quantum mechanics, which is absolutely remarkable that the c to the fourth divided by g should figure not only that, but the superforce equals the Planck force.

And the Planck force does not have h-bar in it. So it's non-Planckian in nature. It's classical, which means the superforce, which equals the Planck force at the Planck scale, is the bridge between the world of the very large, namely general relativity, and the world of the very small represented by quantum field theory. And according to Professor J. R. Maas, this is what's needed, a force of unification, a bridge that would unify all four known forces, in this case including gravity, even though

some people think of it as non-force. They think of it as a-force. They think of it as a spacetime geometric curvature. But if you look carefully, okay, and now that I've said what I've said with the C to the fourth divided by big G, look carefully at Einstein's equation. It can be reformulated. It actually says that the superforce acting on the spacetime geometric structure gives rise to energy density, hence matter. And you can just see by rearranging the terms of the equation that that's exactly what's

saying. Not only that, if you look carefully at the Bekenstein-Hawking formulation for entropy of a black hole, c to the fourth divided by big G also features in that because your entropy of a black hole would be given as h bar actually k sub b which is the Boltzmann constant divided by h bar c, that term times c to the fourth divided by g times your area of the black hole. That would be your entropy. And you can actually see that I am correct. The actual and the significant again is that it is the super force acting on the area of

the black hole that generates this black hole entropy. Hence, I believe it's the super force that's the bridge, the C to the fourth divided by big G, which is non-plank in nature, acts as the bridge between the world of the very large and the world of the very small. And it is, it exists at the Planck scale at every point in space and time. Okay, so help me understand what does it mean when you say that it acts on it. So firstly, let me make this clear. When you say superforce, you're referring to the Planck force. And people can look at what the Planck force is. Yes. Yes. Okay. Yes. And then secondly, when you say it acts on it. So let's imagine we have G equals k times t. And forget about G's Einstein. Forget I'm just making up some variables. I could have said x equals k times t and forget about g is Einstein forget I'm just making up some variables actually could have said x equals k times y I wouldn't

say k is acting on y but you're saying k is acting on y in that case so what does that mean to me I see that as a proportionality constant so as I conversion factor okay so think of the analogy between the main formula of general relativity, g sub u nu equal that scalar constant times d sub u nu. Now, transform it into dimensional character. Just think of it would be one divided by L square, where your L would be some characteristic length, could be the plant length, equal L divided by E times E divided by L cubed. What's the energy?

Right. Right. E divided by L cubed, that's your energy density term. Well, what is a force? It's really the gradient of an energy. That's why that E divided by L is really your superforce. And if you just put that term on the other side, it's actually saying it's the superforce acting on

your spacetime geometric curvature that yields your energy density, hence matter. So I believe it is the super force that generates matter based on whatever that spacetime geometric curvature local in that particular domain is. So you could actually have a different idea of what... It's just remarkable what Einstein has come up with. If you just restructure it, you see a whole different meaning of his formula. But still, and it says it is the super force acting on the space-time geometric structure

that gives rise to energy density, hence matter. That is interesting, I think. It's new anyway. It's just a new way of looking. It's just a new perspective on old physics. Okay, so let me state it in my words and see if this aligns with what you're saying. Yes, sir. Okay, so traditionally, in Einstein's equations, you have g which, which colloquially is space time, and so geometry. And then on the right side, there's t which is the stress energy tensor, which is thought of as the matter. Now, these are coupled, but you can think of it as geometry, and then there's some proportionality constant in the matter. Now you're saying that it's eight pi divided by the plankck force. So let's just move the Planck force to this side. So Planck force times the geometry equals 8 pi times the matter distribution. You can think of the super force or the Planck force in this case. What is the super force? It is the Planck force because it acts at the Planck scale. So therefore the super

force equals the Planck force. So what that equation now says it's the superforce that's acting on the spacetime geometric structure that yields your T sub mu nu your energy density, which represents matter. Okay, I'm going to need to think about that some more because I still don't see. So the way that I see it is that okay, cool. These numbers come up in a couple different places. It comes up in quantum mechanics and it comes up in Relativity and these are what we're trying to merge keep in mind C to the fourth divided by big G Why should it come up in the Dirac equation?

by a manipulation of the terms in the Dirac equation or the Schrodinger equation and also in general relativity. And just think of it actually even easier than that. If this force C to the fourth divided by big G, why should it be non-Planckian in a classical realm? Because it is Planck energy divided by Planck length that all of a sudden loses its H-bar term. So it becomes classical. Why?

Because the superforce must exist and it's 10 to the 44th Newton's. I believe it actually acts at what eventually we're going to talk about the Ashtakar bounce point. And you can give more in your podcast. You understand this because you read the right. Yes, so Ashtakar's bounce, what Sal is referring to is this paper called the robustness of key features of quantum of loop quantum cosmology. So people can look that up. That will be in the description. Okay, now you're saying this bounce is relevant to your work because? Because I'm saying it's the super force that acts at the Planck scales, that at this bounce point, this Ashtakar bounce point,

that actually you can think of it as saying thus far and no further by actually saying there are no space-time singularities. It doesn't go to zero, it goes to this Planck scale. It's exactly what Professor Ashdekar talks about when he talks about his bounds. I believe it is the super force that acts at this bounce that prevents any so-called space time singularities from forming. This I still need to think about some more. So I'm going to be thinking about it between now and we speak again. Sure, sir.

And please make sure that you read that conversation. I believe it's number three, by the way, three. I like the number three very much. So go ahead. Okay, so just what Sal is referring to is there's this book called Conversations on Quantum Gravity, which anyone who's interested in quantum gravity should read. And there are different chapters. And each chapter is a theoretical physicist talking about the problem of quantum gravity

from their point of view, which generally contradicts everyone else's point of view. So it's fun to watch because they pretty much are squabbling without speaking to one another. Number three is Ashdekar. Yes. What does the process of coming up with the CTMU look like? Practically speaking, do you have a whiteboard? Do you just sit alone with a pipe? Do you bounce it off your wife? Do you go for walks? How are you coming up with the theory?

Just sort of comes to you sometimes that you know, you start thinking okay I'm very good at recognizing paradoxes and inconsistencies just a little thing that I'm good at and I noticed a lot of paradoxes and inconsistencies just a little thing that I'm good at. And I noticed a lot of paradoxes and inconsistencies from an early age onward in the way people explain things, right? I'd ask them for explanations. They wouldn't be able to explain things to my satisfaction. And I, you know, ask myself, why, why doesn't disappear to make sense? And I would find out there were

certain things that didn't make sense, then armed with those paradoxes, I would work on resolving. And from those resolutions came the CTM. Let's give an example of a paradox that's been resolved by the CTMU. So Newcombe's paradox is one, do you mind explaining the paradox of Newcombe and then also your solution to it? Well, so that's kind of a long paradox, but basically it's you've got this, this predictor who has never been wrong before.

And he's got this game that he plays where he shows you a box with a thousand dollars in it and tells you that you can take either, you know, one of these boxes, the opaque box, so you can take both boxes. But if you do not take this transparent box with a thousand dollars in it, I've put a million dollars, I already know what you're going to do, I've put a million dollars in the opaque box. But if you try to take both boxes and make that extra thousand dollars that you can see right in front of your face here, if you've done that, I've left this opaque box empty. So you're going to get scummed. You're going to get your thousand bucks and you're going to have

a nice dinner someplace and then that's going to be a... All right. That's Newcombe's paradox. But unfortunately, the subject, the one who is running this game has two strategies from which he has to choose. And one of them is, of course, that, well, strategies that he has to do that from which he has to choose. And one of them is, of course, that well, this predictor has, you know, never been wrong, you know, and so therefore, you know, I'd better do that. The other one says, well, wait a minute, nobody can actually predict the future. This is some kind of a lucky run that this guy has said. And you know, I have nothing to lose because that money that he says he's acting as though he's going to, he's predicted what I've, that money is already in that box one way

or another because I'm looking at it. He can't tamper with that box at all. It's already there. So I've got nothing to lose by taking both boxes. So instead of just winning a million dollars, if that's what he put in that box, I'm going to win, you know, 1.0... You know, a million plus 1000. Right. 1., one million dollars. And so that's enough.

You know, the thousand dollars has enough value that he's going to take that instead. He's going to enrich himself more and thusly increase his utility. And of course, increasing your utility is the is the whole raison d'etre of economics, right? And economic theory. That's what you're always supposed to do. Increase increasing utility. So this is considered an important paradox because of its applicability to economics and causation in general. Is it possible to predict the future? Well, Newcomb's demon, which is what I call him, is analogous to the programmer of a simulation. He's already run this simulation in which you think you have free will, but he basically knows what your free will is in advance. Right? So he

is, you know, that is what has allowed him to do this with the boxes. Okay, so that's the paradox. Now, how does resolution come in? The resolution is nobody ever placed it in a simulation before. I was the only person to ever place it in a simulation back in 1989 by saying, okay, well basically now we have to use the idea that reality may be a simulation and that Newcomb's Demon is somehow a programmer of this simulation. This was the first application of the simulation hypothesis. Everybody talks about it now, but you'll never see my name mentioned in connection with it.

But I was the first person to apply it, at least as far as I know, there could have been somebody else that did so. But I've actually looked and I can't find anything. As far as I know, you were the first to self-simulation. Well, and that too. Absolutely. Self-simulation appears, you know, that terminology appears in a paper I wrote 20 years ago. So, yeah, basically I'm Mr. Simulation. Okay? Unfortunately, nobody ever comes to me. They always ask Elon Musk, why the hell they ask Elon Musk? I don't know, you know? Okay, Mr. Moneybags Elon Musk. And then there's another fellow named Nick Bostrand, who I guess is at Oxford or someplace.

He's got something called the simulation argument, which is basically a little bit extreme. It's the simulation hypothesis, how likely the simulation hypothesis is to be true on the basis of how humanity has evolved. How certain, how shall we say, these, the species that is simulating reality for humanity has evolved? Do they have the technology to do it?

Don't they have the technology to do it? That's what Boston. Now, how does posing a paradox in a frame of simulation help it? It basically tells you that you might be in a simulation, so you'd better take a very close look at what Newcomb's demon has actually succeeded in doing. It's got a long, arbitrarily long sequence of correct predictions. You'd better give the demon its due, and you'd better take just the opaque box. That's the only way you're getting your milk. Does that mean that the person being simulated doesn't have free will?

No, it does not. Why would it? Just because the demon knows what he's going to choose, that somehow deprives him of free will? Well, see, this is the problem that I had to solve by integrating this into the CTMU. Okay, you actually have a pre geometric or non terminal domain in which Newcomb's demon actually exists and in which he actually makes his prediction. You see? So that's that's what it amounts to. You see, how does being in the non terminal domain and being able to discern what this person's decision is going to be not violate free will for that person? For that person from their perspective are you saying they have free will but from another

perspective they don't have free will or no matter what they have free will from both vantage points? Well, you have free will period to the extent that the universe has free will. As I said, the universe is self-composed, all right? You are a component of the universe, therefore you have inherited free will from the universe itself. So, you know, everything, even a quantum particle to some extent has free will or freedom, it has degrees of freedom. It's not totally determined. Now, as far as whether, from God's point of view, however, God knows, let's just put it this way, let's

forget about Newcomb's Demon for a second and talk about God. God can see reality as a whole. You know what Einstein's block universe is, right? God sees the universe not as a block. He sees the universe through the eyes of its secondary totals. That's how he's seeing. That's how he's looking and seeing the universe through our eyes. Where God's sensor controls, right, which puts a whole different complexion on that. He waits for us to make up our minds before he knows what he's seeing. In other

words, what we see is what we've decided on. Okay? So God is automatically allowing for our decisions, automatically making them. We see what we decide. Can you explain? Everything we decide, you know, if when we decide to commit an event or commit an act, okay, automatically we know we can see ourselves committing the act. That's what I mean. That doesn't mean that we determine everything that's going on around us, right? But God sees that too through our eyes. So it doesn't mean that we can see whatever we like, that for example, if I wished that

there was no wall here, then I would see no wall. Does that mean that or are there limitations on my perception? Well, of course there are. Okay, there is a state of affairs, an external state of affairs that has been created by other telos. It's not entirely up to you. Okay, so you are constrained in what you can see by the state of the external word When one does psychedelics are they operating now in this geometric pre info cognition plane? Well, what the psychedelics do is they introduce a gap between

the terminal and non-terminal realms and kind of allow you to see things that aren't really in the terminal realm. And that's what those hallucinations are. Okay, you still got one foot in the terminal realm, but the psychedelic has kind of, you know, opened up a gap there and you're sort of in that gap. So you're there is a certain there are degrees of freedom in which you can actually perceive, or should I say hallucinate, you see. You have things that you think are

perceptions that seem like perceptions, but actually there's this gap that has opened up and you're inhabiting that gap, and that's what the psychedelics should do. They've been finding out that basically all chemistry is quantum. And they know, for example, the quantum mechanics is involved in how opiates and morphine heroin, things like that affect psychology. This is basically what we're talking about psychedelics are doing a little bit of the same thing. When one says hallucinations, usually they mean we're seeing apparitions that aren't actually there, that's not real. Now, I bet you have

a qualm with saying that anything is not real. Well, it is. It's mentally real. I mean, what I'm saying is, reality is a coupling of mind and physical reality with non-terminal and non-terminal realities. So therefore, there is such a thing as subjective existence. Syntax exists, for example, any

combination of syntax, you can put it together how you want to. And that has mental existence. Is it realized in the terminal realm? Not necessarily. You don't find me a unicorn. There are unary and slash nullary relations. They have two levels, synthetic and diphyonic. Do you mind explaining that? Well, all relations are syn-diphyonic, right? When you see two different things, or even when you see yourself, right, you're distributing your own cognition over yourself.

Therefore, you've got that synesthes and dipheonesis. You've got basically a property and something instantiating the pride. That's what that means. You mentioned that there are three ways in which the syn-dipheonic relationship is self-dual. There are three ways. But does it have to be three ways? Does it just happen to be that there are three ways, or is that a necessary component for them to exist somehow? I'm talking about general symmetries of the syndephionic relationship. You know what a Minkowski diagram is, right? It's got a space axis, always a more space axis, and then temporal axes that are orthogonal to it, that go up, you know, into the future, into the past.

And just imagine that you could rotate Minkowski's space, right? Well, you can rotate a syndepionic relation in the same way, right? And because the time axis is ordinal, whereas the space axis is all about arity or the number of things that you're seeing in parallel out in the real world, you're actually making transformations between ordinality and arity in the real world, you're actually making transformations between ordinality and erity in the relation. And there are other kinds of duality as well. I could probably find more than three if I looked very hard. So, synetic is ordinal, dipheonic is erity. No, the line, metatime axis that relates one to the other, Okay, that's okay, because you've got a level, it's you've got, you know, the property level, and then you've got the instance level.

You also mentioned that they're dual because they have an active and a passive interpretation. So what do you mean by that? An active and passive interpretation. Okay, well, we recognize things, but have you ever heard of John Wheeler's observer participation thesis? No. Okay, John Wheeler had this idea called the observer participation thesis,

that when we see a quantum event, when we look at a far away star and a photon from that star hits our eye, we are somehow participating in that event. Okay? So that's what we're talking. Basically you cannot just watch something without actively participating.

Okay? You're actually agreeing to it in some way. Actually actively putting yourself, by perceiving it, you are contributing your perception to it. And because of the nature of telepsis, you are contributing your perception to it. And because of the nature of telepsies, it's impossible for you to stop yourself from becoming actively entangled with it. Okay, you can't just passively perceive things. Those things also have you and the thing that you're observing both have an impact on each

other. That's the way it has to work because all of these that this causal symmetry in the CTMU and another theory system. How would that work on a more mundane level where there's a wall let's say whether I look at the wall or not does that have any bearing to the wall does it exist or not exist when I look does it erode more when I look for example. Yesode more when I look, for example? Yes, you are participating in the existence of the wall. Right.

Can the wall not self perceive? Can it not perceive itself? The tertiary syntactors in the wall can and do perceive each other in a limited way, yes. But in terms of the secondary utility of the wall, what it's actually doing in the world, you're participating in that. As a matter of fact, human constructed walls wouldn't exist unless they were useful to tellers like you. You can't look at anything without participating in its existence. That's what a measurement event is. When you measure the spin of a particle up or down, you are participating in the determination. That measurement is yours. You're the one who set up the measurement device. You're asking a yes or no question, and your question is being answered.

You impose the question on them. The reality is answering the question for you. So there's this active passive symmetry in everything. Let's get to one more of these abstract sentences. The maximal generality in brackets, universality, comprehensiveness, criterion of a reality, theoretic identity or ontologically necessary and sufficient theory of everything means that a fully general

formal structure must be selected as the skeletal identity of a toe framework okay so let's break down some of these terms term by term maximal generality. Comprehensive. Okay, reality, theoretic identity. That means when you own an identity, that's something as which that thing exists. Okay, that's good. That's this identity. You exist as a secondary tele, that's part of your identity and the property you can assign to you. So if it's part of your identity, fully general formal structure, is that related to the metaphorical structure you mentioned

earlier? Yes, sometimes I use formal for metaphorical because the metaphorical system is, you know, intrinsically a metaphorical system, but by virtue of its description. But I have to write that description down in a formal way. Okay, it's actually going to be written on a piece of paper and you kind of add the metaformality to it with your own by understanding what it's saying, but it's written down on a sheet of paper and that makes it formal. Okay, it's a form as opposed to the content of the form.

All right, and then skeletal identity. Skeletal means, yes, skeletal means that it's just a set of invariants in which, you know, without interfering with those invariants a lot, there's a lot of variability. Reality can vary, can change, can adapt, okay, without disturbing its essential invariants. So those essential invariants are skeletal reality. You flesh it out. Must a theory of everything explain mental activity? Yes. To a certain extent, it's not going to determine mental

activity. Okay, there's no such thing as a deterministic theory of reality. But you know, it has to explain the wherewithal of metal activity. I'm trying to find out what ingredients, seeing as some people have different definitions of theories of everything, you mentioned this before, a grand unified one, which is more of a physics term for gravity and so on, or one that explains consciousness or one that explains the explanations themselves. The theory of everything has to explain all of those things, everything. It's to be taken literally. Anybody who doesn't take it literally is making an estate.

Do you have any thoughts as to the biological origins of life? Sure, life originated biologically, but it also originated metaphysically. Okay, it comes from the origin. It's part of the structure of the universe. It was inevitable to say that, well, there could have been a universe with no life where life just never got started, never formed. That's obvious. Okay, there is no, basically no reason for such a universe to exist even for itself.

Right? It's it's that is that's an absurdity. It's a little bit like the the anthropic principle, but there's got to be it's the anthropic principle with utility, right? Part of the reason the universe exists is because there are secondary tellers that derive utility from it. Otherwise, what is its reason to exist? The universe just simply exists, and it has baked within it some telos, some purpose,

and one of those purposes is to observe itself through secondary telos? That's its structure. In order to exist, the universe must have certain aspects of structure. It must be completely self-explanatory and self-adjusting, because it's closed. It has to provide all of these things for itself. And if it can't provide those things for itself, then its structure is inadequate to support existence and it will not exist. Why is that inconsistent with the anthropic principle? Why can't it just be that there are multiple universes and we can call that all the collection of universes,

one meta universe or one large universe and call that the true universe, let's say. Well, that's what the CTME does. The CTME incorporates something called a syntactic metaverse. But in terms of how do all those universes that you're talking about, you're talking about putting them all together and collecting them into a set, how do they come into existence? Why? You need to justify it, otherwise it's pointless to to uh, hypothecate their existence. What are your thoughts on many worlds generally? You know, many worlds is basically, you know, if it can exist, it does exist, but it's got things that matter. It's Everett's theory, of course. His idea was, well, the Schrodinger equation is deterministic, you know, and everything that, you know, all of those possibilities that exist in

that equation should continue to exist without quantum collapse. So he converted quantum collapse events into a divergence of universes. In order for this to work, you need certain, you need to have certain things, certain assumptions have to be in place. For example, you need a fixed array in order to parameterize all the events and identify all your particles and events in the universe so that you know just exactly how the eventualities are splitting. Okay? It turns out that that these these assumptions are not orthologically viable. So although Everett was correct in that there is a

metaverse, he sort of mischaracterized it. It's not, you know, infinity upon infinity of pointless universes that are pointlessly diverging in every tiny little quantum event. That's ridiculous. Okay? But the idea of a metaverse, of this per-universe that exists prior to, in some sense, the reality that we inhabit, that's a valid idea. So he sort of hit the nail on the head and then he kind of went off on a tangent in order to make his theory work, in order to get his interpretation of all of these, to interpret the multiverse or the metaverse as being this collection this vast collection of pointlessly diverging universes Because we have telec recursion the way that I understand that is that each conspansion

point in the manifold over time Somehow the points are evolving and including their neighbors and I recall you saying at the speed of light, forget about at the speed of light because that can take us down another route. Regardless, their speed of constant the rate of conspiring is usually okay, cool. So they're absorbing and then that translates to a positive cosmological constant because the universe seems as if it's contracting from one point of view or expanding from another. Okay. Do you happen

to have a prediction for I know that your theory says there should be a positive cosmological constant? Does it have a calculation as to what range it should look like? Yes, there's plenty of positive numbers. I've made calculations. I'm not going to announce them here. I'll publish them first and then we can talk about them. You're watching this channel because you're interested in theoretical physics, consciousness, and the ostensible connection between the two. What's required to follow some of these arguments is facility with mathematics as well as discernment of the underlying physical

laws and you may think that this is beyond you but that's false. Brilliant provides polluted explanations of abstruse phenomenon such as quantum computing, general relativity, and even group theory. When you hear that the standard model is based on u1 cross su2 cross su3, that's group theory for example. Now this isn't just for neophytes either. For example, I have a degree in math and physics and I

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Okay, let's get to some philosophy. Alright, what's meant by existence is everywhere the choice to exist? Well, that's that active passive duality that you were talking about before. Okay, in the CTMU, telors are basically secondary quantum and they've got to nucleate physical bodies, all right? So they actually have to actively participate in their own groups. Do they do so of some proto-will? Or is it happenstance?

They inherit the will of the universe. The will of the universe is to exist. Therefore these, therefore, you know, any part of the universe in the will of the universe is to exist. Therefore, in any part of the universe in the non-terminal domain, you've got things everywhere that are seeking to exist. The terminal domain provides them with resources that they can use to actualize their solution, and this is what happens. And you mean that they want to exist at the dyphonic level, at this terminal level, or you mean to say that they want to exist at all? Because to me, as I hear that, when someone says this entity wants to exist, it implies it already exists. You need a physical in order to

truly exist. In the sense that most people mean you actually need this this form content feedback. that most people need, you actually need this form content feedback. So in order to fully exist, things do require some kind of a terminal body. Where people get confused is they think that their terminal body can only be of a certain kind in a certain world. That's not necessarily true. There can be many different kinds of terminal realization. For example, there can be an afterlife, heaven or hell, for example, in which you can exist and have another kind of terminal body which was generated just for that world or just

for that heaven or hell. You see, it doesn't necessarily have to be right here. One way or another, you need those resources in order to fully instantiate your existence. Otherwise, your existence never achieves full resolution. It is never fully actualized. The universe wants to actualize itself everywhere it can. That's why we have this profusion of life. That's why we have all these different species, all these different organisms. Telesis wants to actualize itself. It wants to exist and this world provides it with the resources to do so. So is it akin to God wanting to exist? God wanting there to be more God?

Yes, that's exactly right. That's why I say reality is closed. It has to be totally self-justified. Existence is the will to exist. All right? You've also heard me possibly use a term called triality. As the identity of reality, this global operated descriptor is not only an object and a relationship, it's also a process or an operative. Right?

In other words, you can imagine that the universe is not just an object, it's also a process or an operative, right? In other words, you can imagine that the universe is not just an object, it's an event. It's a creation of that. That's what the universe is a self-creation event or self-identification event. You see? And everywhere in the universe, the self-creation and self-identification events are seeking to occur, they're trying to occur, particles are being created and annihilated everywhere in the universe, alright, because they're inheriting this will to exist from the universe itself and this is a criterion of existence. Without it, existence is impossible, alright.

You can't just exist for a second and then not be an operation that maintains your existence because that second is meaningless. It's got to be a permanent existence. It's got to be in some sense atemporal or eternal. That's what God is, basically. God is being equated to ultimate reality, so God is eternal in this sense. And to get to Wittgensteinian, when you say eternal, do you mean infinite temporal length or timelessness? Basically, we're not talking about, we're talking about a temporality, which is timelessness. Okay. In other words, it's prior to time, it's pre-temple in the way. Okay, it just exists as a kinetics.

This is an impulse as an imperative, but it is not fully actualized without existence and all that goes into it. And there are these existential criteria are what most physicists and other people leave out of their understanding of reality. I mean, if in order to get out of accepting non-locality, you deny what's required, assumptions that are required to do science, that's not a good deal. Right? That's a really bad deal. Speaking of that, I sent you a video. I'm unsure if you had a chance to yeah. Yeah, I did

Okay, so as a preface for those who are watching the video is by Sabine Haassenfelder and it's on super determinism Either way, I'll give a brief description in the first 20 seconds or so. She says Some people think that if we do away with statistical Independence then all of science is undermined. And she says her attitude is no. So I'm curious to know your thoughts on that. Firstly, on super determinism and perhaps specific comments were, I mean, let me, let me walk through this. Although let me before because I knew you were going to ask this, let me just point out to people, because it's much

better than than listening to me. If you're interested in this, be sure you take this book, John Bell's Speakable and Unspeakable in Quantum Mechanics, and very carefully read chapter 12, which is called Free Vari and local causality. Because Bell nails it. Complete. And any questions you have, just he's really I mean, Bell is an extraordinarily precise writer.

He's not so good, by the way, if you watch Sabina, she talks about some interview he gave and he's not so good in interviews. He sometimes slips up, I would say, when he's talking off the top of his head and says those which I think he, you know, are just a bit sloppy and uncharacteristic. But when he writes, there are only a couple places in his entire book where I think he put a foot wrong in what he writes. Well, that's everyone. Yeah, I mean, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm,

I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, I'm, And the thing that amazes me is I've had discussions with many people who want to talk about super determinism who've never read as part, you know, really have never read this particular thing, which is the thing that Bell wrote about it.

So free variables and local causality. And what I'm going to tell you is basically what Bell says. It has no and let's just start off by saying this had nothing to do with free will I mean all this talk about free will has gotten into this discussion from the beginning. It was irrelevant The term super determinism is bad Because even as Sabina says you can't get more deterministic than deterministic. Okay, that's right The the issue, is the mathematical assumption of statistical independence that's used in the theorem. Now, what is that assumption? Let me just give you an example

and why it's important and why I say if you deny it, empirical science kind of goes out the window. So suppose we're going to do a test and there are different experimental conditions. You might think of them as experimental in control or in our case, you're going to either set up a spin measuring device in the x direction or the y direction or in some other direction. We have these different conditions. And I'm doing tests and I'm doing tests on a large number of items, a large number of rats or a large number of particles or whatever. And I'm looking at statistics, I'm looking at percentages of the ones I experiment on with these different conditions, whether they react this way or that way and when I'm doing

Experiments on pairs on the correlations between the two sides. Okay Now What I do if I want to do just to take the simple case everybody understands if I want to check whether smoking causes cancer in rats I start out with a big group of rats. And then I want to subdivide it into an experimental group and a control group. But I want to subdivide it in a way that there's no bias between the two groups. The two groups before I run the experiment are statistically similar to each other.

Okay. Now there's some ways i can check for that like if there are male rats and female rats i can just kind of count. Okay what percentage of male rats are in this group and what percentage are in this group and i can make sure by distributing them that they have the same percentages. Sure. The thing is i want the groups to be similar in all respects even respects i I'm completely unaware of. I mean, maybe there's some genes I don't know about. How do I do that? Well, I randomly assign the rats to the two groups. This word random is important here. The word random here is absolutely important. What the word random there means it is the condition that Bell uses of statistical independence.

It means that the sorting mechanism does not is not biased or does not respond or is not sensitive to the rats. Okay. So, if I, you know, you can imagine flipping a coin, for example, I mean, that's a physical kind of what Bell would call a physical randomizer. There are other randomizers. I mean, he uses this example, which is very nice because it takes all issues about free will out of it. He says, look, you could use a pseudo random number generator, which works like this.

Start at the millionth digit of pi. And then output a one or a zero, depending upon whether the next digit is even or odd. All right. So that'll give you a sequence of ones and zeros. That is a pseudo random sequence. We call it random because it will pass every statistical test for randomness you can come up with. All right, I'll be about the same number of ones and zeros, but there will be no observable pattern. And you could use that and say, okay, for one comes up in the rat goes this way. If his zero comes up, it goes that way. use that and say, okay, for one comes up, then the rat goes this way. If a zero comes up, it goes that way. Now, why do I do that? Because if the sorting is independent, if

whether the rat went this way or that way is independent of the nature of the rats, then with overwhelmingly high probability that's calculable, each subgroup will be statistically like the original group. If 60% of the rats had some unknown feature in the original group, then 60% in each of the subgroups will have that feature. And therefore the subgroups will be like one another. The really important thing you want is you want the statistically the subgroups to be like one another. The really important thing you want is you want the statistically the subgroups to be like another. And that's why we use randomized procedures for making these groups. Now if somebody says now suppose I do this experiment with the rats. I take this big group I randomly divide them by one of these

sorting mechanisms right by throwing dice or by this... Sure, sure. ...go randomizer or whatever into these two groups. And then I expose one to smoke and I treat the other the same, except I don't expose it to smoke. And then I see a lot more cancer in this group. Then we infer that the smoke caused cancer. Now if somebody says, no, no, no, no, no, no, really what's going on is this. Some of the rats

were predisposed to get cancer no matter what and other the rats weren't. And it just turned out that the ones that were predisposed got sorted over into the ones into the smoke group and the ones that weren't got sorted over into the other group. And so the smoking had nothing to do with it. Now this is the kind of argument that actual lawyers for the tobacco industry used to make when they were trying to argue that scientists had not thought that smoking causes cancer. And obviously, as a purely logical fact, yes, if the sorting didn't work to make statistically similar subgroups, then that could be an explanation. But then you have to go on and say, I don't care how you sort, sort any way you want.

Sort based on pi, sort based on the number of shares of stock sold on the shot stock exchange, sort based on anything you want. No matter how you do it, somehow the cancer-prone rats are going to go this way and the non-cancer-prone rats are going to go that way. Now that will, as it were, as a purely logical matter, count as something that would make the prediction that this group will get more cancer than that group. But we would just say this is lunacy because you have no mechanism. there's nothing you know, you're just, you just don't like the result. You don't like the result. And you don't like what the

result is telling you. So you're just grasping at straws. That's all that's going on here. That's what super different somebody who just says, I'm just going to blankly deny statistical independence, no matter how you do this sorting no matter and in this case. You're doing these experiments. Alice is doing an experiment and Bob's doing an experiment each one is randomly choosing how to set their device. And it's there where the randomness comes in how does the device get set and they could be flipping coins or they could be running off pie or whatever the heck they want. And you're the bells only assumption is. That. flipping coins or they could be running off pie or doing whatever the heck they want. And Bell's only assumption is that statistically the group of particles that meet condition

one will be the same as the group of particles that meet condition two, where condition one and condition two are chosen by one of these pseudo random Kanya processes. Now Bell gives an even more extensive discussion of why this is true, but it's clear that when we say it would undermine science, experimental method depends upon in all cases using this. Now, I should say one more thing. There's another idea, which is retro causation, right? Which is a different idea. It's not just a blank denial of statistical independence.

It says, oh, statistical independence fails because the nature of the particles when I made them, right, is somehow affected by at the time I made them, okay, is somehow affected by what experimental condition they would be exposed to in the future. So that's the future affecting the past. That's retro causation. Okay. And all of this is to save locality. Well, that doesn't save locality. So the first point I want to make is that retro causation violates Bell's locality

condition. Okay. And it would be kind of crazy to think, look, I have Bob and Alice and they're doing their experiments far apart. And I absolutely will not believe that what Alice does can have a causal effect on Bob. But I believe that stuff that happens to the future can have a causal effect on Bob. I mean, that's that's even worse. And it's even worse because if you retro causation, then because you have causation from the you certainly have causation from the past to the future

if you also have causation from the future to the past then you're going to be involved in causal loops and Then it's very hard even write down a coherent theory. I mean Wheeler and Feynman tried to do it It's not clear. They wrote down some equations not clear. They have any solution if You if you just have non-locality, the obvious ways to implement it will not involve any causal loops, you won't have that problem. But the fact is, to say I want to deny non-locality and therefore embrace retrocausation, well first of all, retrocausation violates Bell's locality condition so you haven't gotten out of it anyway, and you've gotten yourself even to a worse problem.

Forgive me because I'm uncertain here and I'll just fumble over my words and then you can perhaps cohere what I'm saying and say it better than I have. How far does this correlation have to be? So when I hear statistical independence, the opposite of statistical dependence, which I assume is correlation, and it seems to me clear that even when we sort rats, if we try to do so randomly by picking the one millionth digit of pi and so on, going forward from there, that there is still some dependence. It's extremely, extremely small. Now how? Well, how do we choose the number one million? Well, okay, this person said, okay, well, let's choose a random

number generator to choose that one million or to choose some number 1 million? Well, okay, this person said, okay, well, let's choose a random number generator to choose that 1 million or to choose some number of the digit of pi. Okay, well, then, when we press on the random number generator, why do we choose to press it five seconds from now versus 10 seconds from now, because it would give you a different number. So essentially, what I'm saying is that the world that we chose the rats from every single thing here is influencing our decision. So every single thing is into the sort of rats temperature is influencing our decision. The fact that the rats have a certain amount of hair is influences our decision and so on.

So just just there's a there's a extremely tiny, extremely tiny amount 0.000000002 but I don't know is that the fact that it's nonzero does that have any implication or does it need to be nonzero sufficiently large? Okay, so let me let me try and address there are two parts for this I think. Let me try and address both parts of it. Let me just take my simple case so everybody can follow. I have a big group of rats and some percentage of them say have a certain gene. I don't even know about the gene, but say 60% in the big group have it. And what I want to do is now partition this into two groups of rats and I want the two

groups to be statistically like each other and therefore Statistically like the original group which had 60% now if I just flip a coin It just standard statistics Will tell you alright. There'll be little fluctuation It doesn't mean that you'll get exactly 60% in each of your subgroups, right? exactly 60% in each of your subgroups, right? One subgroup might end up with 61% and the other subgroup with 59%. Those are just statistical fluctuations.

Using standard statistical methods, you calculate the likelihood of these fluctuations. If you're worried about them, then you use a bigger group, okay? And it makes the fluctuations, the probability of the fluctuation smaller and smaller without limit, right? You can't drive it to zero, but you can drive them below any epsilonic.

Right, right. Just to be clear, what I'm wondering is, is the presence of any epsilon, does that undermine the- No, no, because the violations of bells and bells inequality says a certain observed Correlation in the lab cannot be greater than a given number. I see I see I'm the actual observed Violation of that is so far It's not close right? It's not like gosh It's just a tiny bit over and if if I just have a little epsilonic thing somewhere, no, no, no.

The violation is radically far away from the limit. So if you say, Oh, maybe the subgroups aren't exactly the same. Of course they're not exactly the same, but the chances of them being sufficiently different to account for what's observed, and furthermore, of course, what's observed is exactly what's predicted by quantum mechanics. And if what you were seeing was just the result of some random fluctuation, then you wouldn't be able to predict it. I mean, that's the point about random fluctuations is you can't predict them at all.

But what you observe in the lab is precisely what you get out of a quantum mechanical calculation. Yeah. lab is precisely what you get out of a quantum mechanical calculation. There's one other thing I just want to, if I can find it quickly from, um, from this thing of Bell's, because it's relevant to what you said, well, we could do this, we could do this. He says, um, I actually, here's a relevant, a relevant thing to what you just said. He says, he's talking about you've got some things you treat as free variables. In this case, the choice of whether to do experiment A or experiment B, the choice of both Alice and Bobnick.

He says, of course, there's an infamous ambiguity here about just what and where the free elements are. The fields of Stern-Gerlach magnets could be treated as external. That's then treating those as free variables. So I can just you know, I imagine those I set them when I do the calculation However, I want or fields and magnets could be included in the quantum mechanical system with external agents acting only on external knobs and switches Or the external agents could be located in the brain of the experimenter in the latter case The setting of the instrument is not itself a free variable

It's only more or less closely correlated with one, depending on how accurately the experimenter affects his intention. As he puts out his hand to the knob, his hand may shake and may shake in a way influenced by the variable's V. Remember, now this is now exactly to your point. This is Bell I'm reading, right? Remember, however, that the disagreement between locality and quantum mechanics is large up to a factor of root 2 in certain sense So some hand trembling can be tolerated without much change in the conclusion

Quantification of this we require careful epsilon. It's okay. And I mean there's it but another Thing that he talks about, which I just, all right, again, let me just jump to the end. He's talking about, this is the part that I wanted. Consider the extreme case, he's now talking about random generators. So we want something that's setting this equipment either this way or that way.

For Alice, something that's setting it this way or that way for Bob. It would be a bad idea to have it due to the, as it were, whim of the experimenter because the experimenter would have to be just sitting there in a very boring way going, oh, now up, now down. And probably, as we know, people are not even good at creating random sequences, right? Human beings are not good random number generators. Right, right, right. Here's what he said. He says, consider the extreme case of a random generator,

which is in fact perfectly deterministic in nature. And for simplicity, perfectly isolated in such a device, the complete final state, right? What, what it chooses perfectly determines the complete initial state. Nothing is forgotten. And yet, for many purposes, such a device is precisely a forgetting machine. A particular output is the result of combining so many factors of such a lengthy

and complicated dynamical chain. And this is going, what you were saying, well, what if they do it a little later? If I have, you know, suppose I have like, when they do lotteries, they have these ping pong balls that are bouncing up and down in this cage. Okay, that could be a deterministic system so that some set of causes account for why this ball came up. But that set of causes is huge. It involves all the other collisions with all the other balls and all this other stuff going on. So he says, yet for many purposes,

such a device is precisely a forgetting machine. A particular output is the result of combining so many factors of such lengthy and complicated dynamical chain that it is quite extraordinarily sensitive to minute variations of any one of many initial conditions. It is the familiar paradox of classical statistical mechanics that such exquisite sensitivity to initial conditions is practically equivalent to complete forgetfulness of them.

To illustrate this point, suppose that the choice between two possible outputs corresponding to a and a' depended on the oddness or evenness of the digit in the millionth decimal place of some input variant. Then fixing A or A' indeed fixes something about the input, i.e. whether the millionth digit is even or odd. But this peculiar piece of information is unlikely to be the vital piece for any other distinctively different purpose, i.e. it is otherwise rather useless. With a physical shuffling machine, we are unable

to perform the analysis to the point of saying just what particular feature of the input is remembered in the output, but we can quite reasonably assume that it is not relevant for other purposes. In this sense, the output of such a device is indeed a sufficiently free variable for the purposes at hand. For this purpose, the assumption one, which is the statistical independence assumption in the proof, is then true enough and the theorem follows. Now, if you just understand, if you just read that paragraph carefully and understand it, it puts this whole thing about I'm going to deny statistical independence to bet. I mean, and this is just Bell. Okay. He understood this objection. He understood that logically, yes, he has two premises. So logically,

you can deny either one. But then he says, look, denying statistical independence, that's just not physically the kind of thing a physicist could ever do and remain physicists. Here's what's interesting. I respect you, I respect Sabin, I think you're both extremely bright people. Why is it then that extremely bright respectable people believe in super determinism if it's so obviously incorrect? So here's one answer. Neima Arkani Hamed said that there's this mistake that the public has about physics which is that almost every moment

in time we need some radically new paradigm, that we have to be revolutionary. He said no what is required is conservative revolutionaryism or revolutionary conservatism, whichever. And what he meant by that is well let's take a look at Einstein. People say that with special relativity what he did was extremely revolutionary They said no he was revolutionary about one aspect and was extremely conservative about others He said these are certain aspects that I want to hold on to and here's what I'm willing to give up And then he came up with his theory Do you see it as some people are extremely conservative about locality and they're willing to be

extremely revolutionary in other respects, like let's dismiss with statistical independence? Do you see it as that sort of issue or is it something else? I think it's something else. Look, you have to remember the physicists, of course, philosophers, everybody are human beings and then human beings have their labels. everybody are human beings and then human beings have their

labels. And let me, I'm going to illustrate this. One of the one of the physicists who early on recognized and advertised Bell's result, because you know, you have to bear in mind that, that if not for some kind of very lucky things happening Bell's result might have gone entirely buried and nobody would have even known about it. I mean it was it was published in the first volume of a brand new journal that went out of business within a couple years. So people wouldn't even know about the journal. It happened to fall in

the hands of Abner Shimoni and Shimoni read it and understood how important it was and Shimoni happened to know John Clauser who was looking for an experimental project. Okay, there's a whole history here but it's a very iffy thing, right? That Bell's result could have just completely disappeared. But one of the physicists who early on understood the importance of Bell's result was David Merman. And Merman was a good popularizer, and he wrote some articles,

he also wrote articles that were published even in philosophy journals, explaining what Bell did. And the original Bell result, the one that Bell proves, is a statistical result. It says there's a certain kind of experiment. If you do it over and over and over and over again, you then accumulate statistics about correlations between outcomes on these two sides. This Bell inequality puts mathematical constraints on how strong those correlations can be, and that's what's violated. Merman said he always had a suspicion that the probabilistic nature of these predictions was really essential. The fact that you were dealing not with strict 100% predictions, but only percentage predictions

was somehow very deep to this result. He said he could never quite articulate one. And then some years later, Greenberger, Horn, and Zeilinger came up with this very nice example. It's the one I use all the time now instead of Bell's original example, which instead of involving pairs of particles involves triples of particles. This is in my book if anybody wants to read it. It's a beautiful thing to be explained in five minutes. But the nice thing about it is that the predictions there are not statistical. There are 100% predictions. They say, according to quantum mechanics, you

should get this kind of result every time. Right? So if it even fails once, it's you know, quantum mechanics has failed. You know, unless mechanics is that you know what's the experimental air but. And when when merman saw that. He appreciated he wrote a very nice article about it and he said at the end i used to think the probabilities here were really important i was wrong. Okay. important, I was wrong. Okay. I, you know, this just shows I was wrong because here you have a locality result that doesn't involve probabilities. They're all one in zero. And, you know, you can't ask for more than that from somebody. Okay. He had his suspicions. He aided them publicly when he got reason to see that those were wrong. He retracted

them publicly and he wasn't upset about it I mean why would you be upset about it I mean I often say the nicest feeling you can have when you fall asleep at night is that you understand something you didn't understand in the morning or you've corrected an error in your thinking I mean people don't like to admit errors to different degrees right Um, right. And that's just human beings, right? I mean, that's true of all human beings. You have to try to get familiar enough with at least some of the content that

you can really make an independent judgment of your own about who who's right and who's wrong, and then start more trusting the people who are right and being more leery about the people who are wrong. There's nothing else you can do. It's unfortunate. It's hard work, right? And anybody trying to pick up physics from the kind of public presentation is not going to be in a position very well to do that. As I say,

if you're interested in super determinism, get Bell's book, read chapter, it's only four pages, read chapter 12, read it carefully and think, think for yourself and ask yourself whether you think denying the statistical independence assumption that he uses is Something that is it has any physical plausibility That that it And and if you're wondering, you know, that that's the best thing to do right? I'm not asking take it on my word Sure. Sure. Sure. So let's talk about the PBR theorem mm-hmm do you see it as one of the landmark theorems on par with Bell or second or even perhaps greater than Bell's I I would say I think

it's in a certain way as important as Bell's result but not as surprising that is not a surprising given Bell that we already know about. No, no, not as surprising even before Bell. So let me say why. I mean, the PBR result says we use this thing, the wave function, this mathematical object at the center of the mathematical apparatus of quantum mechanics. Everybody uses it to calculate. And again, you know, one question you should ask yourself, why is that right?

Why are you why are we using this thing? One possible answer is well, because it's a pretty good representation of the of some actual physical reality in an individual system. It represents some physical characteristic of the individual system in front of me and a relevant physical characteristic. Even apart from Bell, if you ask, well, should I take this wave function seriously in that sense or should I rather think it's something merely epistemic that so the wave function is kind of for a single particle, let's just talk about a single particle because it's easier, although it's a little misleading. Single particle, the wave function is defined over all of space, so you can sort of think

like a field and it's spread out and the Schrodinger equation tells you how to revolves and it evolves by a wave equation. Good. Okay, is there anything in it if I send a single particle through a two slit experiment? I represent that single particle in part using a wave function and the wave function is spread out and the wave equation carries that wave function through both slits and from there each slit produces its own, as it were, little wave and then they interfere like water waves and you get this interference pattern. Yeah. And physically what we see if I do this two-slit experiment over and over again with

individual single particles is what shows up on the screen is this interference pattern with these bands through it, light and dark bands. Now as soon as you see that, you say, gosh, okay, well that wave function must really represent something physical that does interact with both slats. That's how interference works right if each individual particle merely went through one slit and nothing nothing. Interact with the other slid. slit, then you couldn't possibly get this kind of interference. So the idea that you should take the wave function seriously as representing a real physical feature of individual systems, so nothing to do with anybody's knowledge, nothing to do with epistemology, nothing to do with statistical characteristics of large groups

of systems. It represents some physical reality that pertains to an individual system. That just from two-slit interference, everybody should believe that. And everybody I know does believe it. This was not something the people that I know that work in foundations, nobody ever questioned that because you just say just the two. Now two-slit interference does not violate Bell's inequality. So this is not nonlocality. This is a different thing. And this is again, another place where, you know, Feynman makes a mistake when he says, well, he wrote this before Bell, but he says all the mysteries of quantum mechanics

are somehow packaged into two-slit. No, they're not. Because Bell isn't. But if you just think about those kinds of familiar interference experiments, done with single particles and where you accumulate the data over time, anybody looking at that is going to say, gosh, that wave function must represent a real physical characteristic of individual systems. Now what the PBR theorem does is it gives you something even sharper. It says if despite all that you want to think that there's something epistemic about the wave function, that it doesn't really represent physical reality of the individual system, it somehow reflects your information or something like that. Then the PBR... This is also called cubism or no?

Well, that's sort of what the cubists say. Cubism is, I mean, cubism is a very difficult doctrine to even understand what it's claiming. Let's leave it aside for the moment. But someone, you know, a common idea was that, no, the wave function is kind of spread out not because anything physical is spread out, but because we're ignorant about where something is, right? And the spread outness

reflects us not knowing where it is, not that there is something in these different regions. So I think anybody who just thought about too slit would say, no, that can't be right. It can't be merely epistemic. And again, David Merman makes this point in one article, he made the point very nice with a dialogue, a kind of dialogue with somebody who was trying to be epistemic. And they say, Oh, you know, the wave function spreading out is just a matter of, of our ignorance. And, and then in response, somebody says,

so it's our ignorance that goes through the two slits Right yours, right and that makes no sense, right? I mean with something physical is interacting with both slits It has to be so what what what PBR did was they they took the observation that I made which is not a proof and They gave a sharp definition of what it is to regard the wave function as representing something real about the individual system as opposed to representing something about merely our knowledge of the system and then they said well if you believe it's epistemic by our definition here's an experiment that you'll make the wrong predictions about I mean you'll make prediction you'll have to make predictions that violate quantum mechanical predictions and by the way they also use the

statistical independence assumption in their proof but that's fine because the statistical independence function is fine. You know, I got a problem with that. They use one as well. And it's a nice proof. I mean, and people who reacted at the time who said this is the most important proof since Bell, I think David Wallace said that. I think he's right. I think if you're doing foundations, it just, I mean, you could say it was the last nail

in the coffin and the coffin was already shut, that you shouldn't have been an epistemicist in the first place for straightforward physical reason. How do you explain these interference bands? But if somebody, again, wanted to be very recalcitrant and stubborn and say no no no I just really think there's something epistemic about this wave function the PBR theorem kind of puts that to rest and so you can move on. So yeah I think it's a very important I think it's an extremely important there I think as I say it's not as astonishing in what it's claimed.