Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas - 149 | Lee Smolin on Time, Philosophy, and the Nature of Reality

Episode Date: May 31, 2021

The challenge to a theoretical physicist pushing beyond our best current theories is that there are too many ways to go. What parts of the existing paradigm do you keep, which do you discard, and why make those choices? Among today's theorists, Lee Smolin is unusually reflective about what principles should guide us in the construction of new theories. And he is happy to suggest radical revisions to well-established ideas, in areas from the nature of time to the workings of quantum mechanics. We talk about time, the universe, the role of philosophy, a new picture of spacetime, and the future of physics. Support Mindscape on Patreon. Lee Smolin received his Ph.D. in physics from Harvard University. He is currently on the faculty of the Perimeter Institute in Waterloo, Canada, where he was a founding member. Among his awards are the Majorana Prize, the Klopsteg Memorial Award, and the Buchalter Cosmology Prize. He is the author of several books, most recently Einstein's Unfinished Revolution: The Search for What Lies Beyond the Quantum. Web site Perimeter Institute page Google Scholar publications Amazon author page Wikipedia

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When you need the right person to cut through the chaos, this is a job for Indeed sponsored jobs. And listeners of this show will get a $75 sponsor job credit to help get your job the premium status it deserves at Indeed.com slash podcast. Terms and conditions apply. Need to hire? This is a job for indeed sponsored jobs. Hello, everyone, and welcome to the Mindscape podcast. I'm your host, Sean Carroll. One of the interesting things about science is that people within science, the working scientists,

can get really quite emotional and tied up in their favorite ideas, even if we don't yet know which idea is right, even if we're convinced that eventually the experiments are going to have the last word and they're going to tell us which ideas are right. Along the way, we get very attached. We care about one idea being right or the other one, which is very different than the stereotype of the cold and analytical science type. Part of that is, of course, that the interesting part of being a theoretical physicist, the kind of scientist that I am, is proposing new ideas for what the fundamental laws of nature might be. A lot of theoretical physics is taking the known laws of nature and working out what their consequences are. So how do stars form?

How do you make a high-temperature superconductor? is DNA split and things like that. But another part of it is proposing entirely better, newer, novel ideas for what the fundamental laws are supposed to be. And when it comes to that, how in the world are we supposed to know? How to best invent new laws? Or if someone proposes some new laws, how in the world are we supposed to say, yeah, that seems plausible to me, or no, no, no, that's completely crazy.

This is a judgment call. This is something people who are completely working in good faith will have different ideas about. So today's guest is Lee Smoll and probably needs no introduction. Very well known to any of you who are interested in theoretical physics. Lee is one of the pioneers of loop quantum gravity. He is one of the founding members of the Perimeter Institute for Theoretical Physics in Waterloo, Canada. And one of the interesting things about Lee is that not only is he working in quantum gravity and related fields, but he thinks very carefully about how to be a theoretical physicist.

And the other interesting thing is, his answer to that question is different than most theoretical physicists' answer is. To be honest, a lot of theoretical physicists have some feelings about what works and what doesn't, but they don't reflect on it that much. They just march forward. I think this idea is good. Let's look at that. Whereas Lee really thinks about the philosophical underpinnings of what he's doing, tries to build a coherent story based on principles that one should follow to say,

here is what should come next. And the reason I like it is because I love that way of working, and yet, Lee and I come to completely different answers about almost all of the interesting issues in theoretical physics. So I think that this is a very interesting conversation to listen to, both because of the substance of the theoretical physics ideas we talk about, and also for the stylistic questions of how physicists or scholars in intellectuals more broadly should proceed in developing new ideas. Anyway, let me remind you that we love it here at Mindscape when you do things like leave reviews of the podcast on iTunes, etc.

Or you can support Mindscape by going to Patreon. Go to patreon.com slash Sean M. Carroll. And you can become a patron that lets you ask, ask me anything questions, get ad-free episodes of the podcast, and generally feel good about yourself. With all that, let's go. Welcome to the Mindscape Podcast. Thank you very much. So it's great to have you on.

You've clearly, you know, written a lot about different topics in physics, many of which overlap with things that I've written about. So before we get to specifics of your recent work, I thought for the audience members out there, for the one or two, who are not familiar with your work, it would be fun just to go through and give some of the positions, some of the basic ideas that you've been thinking about over the years. So why don't we start with the most obvious one, which is quantum gravity. You spent a lot of your physics career thinking about quantum gravity. I bet that most listeners of Minescape understand that quantum gravity is a thing that we need to understand, but let's put those people aside. And for the ones who are not familiar with the problem,

how do you even say what the issue is when it comes to reconciling quantum mechanics and gravity? So the way that I said is that Einstein started this revolution in physics in 1905, and there were two parts of the revolution, quantum theory, which Einstein really got started on, got us started on, and the revolution in thinking about space and time and gravity and cosmology, which came with gender relativity. And my sense is that we're still in the midst of this revolution. And they're particularly challenging our two aspects of it,

Well, I'll say three aspects, which I think are all connected. One is to make sense of quantum mechanics, and of course you and I both have a lot to say about that. But another one is to get a description of the gravitational field and space time in the same terms as the other physical fields. And I say this because I tend to agree with Einstein that bringing together gravity in the other forces will change our description of the other forces as much as gravity. So whether we'll relativize the quantum or quantized relativity, certainly I've thought about both of those things. And then there's another set of problems which I think are deeply related to those, which is how they're.

the universe chose the laws that it seems to have chosen, not just what are the laws, but why were they, why are they the laws? How are they chosen? Right. You, of course, famously have been working, or were a pioneer of loop quantum gravity in particular. What is your, what is your current state of thinking about how loop quantum gravity is doing? Was it a step in the right direction? Is it still on the table, or do we not know yet? Good. So, can I tell a little bit about that story the way that I tell it, which is, I think, different from how some other people tell it. So I wanted to do quantum gravity coming into undergraduate school and graduate school, but I went to graduate school at Harvard during a period when the

standard model had just a few years ago been invented, and it was full of all that wonderful physics. And I particularly got captivated by the physics of Ken Wilson and Sasha Polikov, Sasha Migdal, and a number of other people who were interested in the idea, analogous to the quantization of magnetic flux in a superconductor, that you could have something like the electromagnetic field, naming these gauge fields, where the electric field flux got quantized. and that would lead to a sort of picture of the electric flux being carried along strings that had quartz at the ends of them. And that heuristic picture, as it developed with QCD, had a powerful influence on me.

And I thought, and I think I was just in the right place at the right time, that how natural it would be to apply those same methods and the same ideas to the gravitational field. So that's what I started off doing my first paper, was a version of lattice quantum gravity in which the loops of quantized electric flux on the lattice were the main actors. Now we would call this spinfoam model. So sorry, just to be clear for the people who are not,

this is great stuff because I'm very interested in what you're saying, but it might not be familiar to everyone. So there is this technique for understanding the strong interactions, like you said, the glue-on fields that hold quarks together. that thinks not just about the field at every point in space, but what happens when you go around a loop? So that's an existing thing in the study of the strong interactions, and you're saying, so your inspiration was to do that for gravity.

Right. And it was pure theft, basically. And so what was needed was a good formulation of general relativity that made the analog of the gauge fields, that tell you how to move things around what we call parallel transport around space, that those are the variables in Yangmills theory, and we needed a formulation of general relativity that focused on the same kinds of variables in general relativity.

And Abitab is sent in a biashikar provided those in late 1985. And then it was just like snapping a little twice, together, so to speak. And that, so why I want to emphasize that is, for me, it's an idea and it's a powerful idea.

And at the kinematical level, it gave us very interesting insight and results. String theory, which had been developing and had started to get interested in quantum gravity in a big way two or three years before that,

was not different. in my mind. It was also the development of these quantized loops of electric flux. You know, the, sorry, let me just spotted to say, the very first person that I interviewed, not the first episode I published, but the first

person I interviewed for the Mindscape podcast was Carlo Revelli. And at the end, I said, so do you think that there is some hope for, you know, string theory and loop quantum gravity to come together and merge in some common understanding? And he said, no. So you might have put your opinion about that also.

Well, Carlo and I are dear, dear old friends, and we disagree about many, many things. And I don't know how probable it will be, but just my mindset in the way that I looked at the problem of quantum gravity was those were different versions of the same idea. And I certainly tried to bring them closer. And Carlo would be right to say without much success. but the thing that then happened sort of sociologically in which there were these two communities of people who didn't understand each other I was very much against from both sides so so I don't see them really certainly they have different they've taken away different shapes but I think the following thing I would defend saying it the following ways. Each of them, and a number of other approaches as well,

have some brilliant successes, and that makes us really interested. Each of them has roadblocks, which have been there for at least 20 years and longer. And I think it's ridiculous that we continue, and in fact, we're not continuing very much. If you look at what the new people coming into the field are doing, there's very little pure, I would say,

nobody is doing what we were doing 25 years ago, thankfully, or just a handful. The last time I saw a paper or heard of talking with somebody actually calculated a spring amplitude. It's a long time ago. A long time ago, yeah. Some of what the really interesting young people are doing is hard to classify.

It's some of this and some of this, and they walk between the communities and they don't notice that they're barriers. And I mean, somebody like Sabrina Gonzalez-Petianic and Laura Ducela. So that's what I'm hopeful for. I think that's right. You know, I've had a few string theorists on the show also, and I always like to ask them, do you call yourself a string theorist? And they always say no. all the modern string theorists, even Lenny Suskin, who is modern in the sense of pushing the field forward,

but not modern in the sense of when he appeared on the scene, you know, doesn't think of himself under that label, because like you say, the boundaries are falling between them. But let me just go in one further step in that direction, because back in the day, at least, one of the arguments between people who were on the loop quantum gravity side and people on the string theory side was whether or not you could really make progress by thinking about gravity in and of itself, apart from the other forces of nature. And one of the string theory arguments was you can't. I mean, they only made up that argument because they seemed to have a way of doing them all at the same time.

What is your feeling about that now? I mean, does it make sense to think about quantum gravity as a field apart from everything else? Or do you just dive right in and get a theory of everything? I think it happens to make sense to think about. quantizing the gravitational field without matter. But it's much better to try to include matter. The world is full of matter. When you include matter, there are some questions right away

that are really compelling to think about. One of them is that matter comes Cairo, which maybe not everybody knows the words, but looking at the particles in the standard model, especially the neutrinos in a mirror, they're not the same. There's not a symmetry underlooking at nature in the mirror. Right.

And that seems tempting to think of that as fundamental. And there are some reasons we can talk about that. But then we're supposed to connect that up with gravity, which at the classical level is completely left-right symmetry. And that seems odd. And one of the attractions of the original Ashtiqar way of thinking about the gravitational field was that it is also Cairo. And there's this sort of hidden chirality, which is if you look at it in the right twisted way, it looks simpler. And that's true of a number of other developments in space-time theory like Twister theory, Roger Penrose's invention.

So I certainly think this matter in the world. And I'm very interested in the question of why this matter. Right. It's not just that they're gaites theories, but why SC3-X2-2-quess-U-1. Good. And then the other thing I wanted to get on the table was one outgrowth of string theory in the late 90s

was the idea of the multiverse and the anthropic principle. I mean, it was a pre-existing idea, but it became very, very popular with the string theory landscape of different possibilities. You were a critic of the way that that was approached in the string theory community with the anthropic principle, but you have your own ideas about cosmological natural selection and so forth, which to some outsiders seem similar, even though you were criticizing the string theory version. So can you tell the people who don't know anything about these ongoing debates where you come down there? Well, again, let's let me start, if it's not too self-referral. with how I started on this.

So Andy Strominger, who was a friend, called me one day, this is the way I remember it. And there was, so string theory at first in 1984, there were five versions of string theory in 10 dimensions. And then they were, you found out you could curl up the extra six dimensions and with some beautiful, elegant, complex geometry, you could classify some of the different ways to curl them up. And there were supposed to be several hundred thousand variants,

according to Yao, who we all admired, but nobody understood the argument. And there was a sort of idea that we would look and pick among the 100,000 or so and find the one that must be that looks just like the standard model at the one. And Andy had realized that there were, uncountably many more. That was just the tip of the iceberg.

And he wrote a paper about that. And when he called me, he was very despairing about that. He said, we'll never get any phenomenology out of this. Because how are we going to search this vast, huge space to find the standard model? And so

at that point, just there are these serendipitous things. I was reading a lot of theoretical evolutionary theory just for fun. And, you know, you must know the attractiveness of reading Stephen Jay Gould at his prime or Lin Margulis. There was wonderful stuff. So I kind of had it on the brain.

And I started to think, could you attack, the biology solves that problem. There's a huge landscape. And the word comes from there, comes from the population biology. It's a huge landscape that population biologists talk about. and they have basically a mechanism to search. If you think about it like a mathematical geneticist, they have a mechanism to search this landscape and find optimal creatures,

find creatures whose fitness is optimized. So I started thinking along those lines and just ask, can I invent a scenario where there would be something that would be extremized. And one of the things I thought about, which was the thing that I published under cosmological natural selection was that what the universe wanted to do was reproduce itself and reproduced itself through black holes that led to baby universes.

That was an old idea, and that was due to Johnny Wheeler and other people at that time. Also, due to Johnny was the idea that the conscience of nature changed when you went through that transition to new baby. universe. He called it reprocessing the universe, and he imagined that everything was just changing randomly. And all I had to add was a constraint that said, no, on the average for dimensionless constants, the change per generation is small. And then you have a search procedure that will discover those regions of parameters space that lead to universes that have a lot of black holes. So that was the idea. And I, I, I,

then had to learn a lot of astronomy and astrophysics, which was great, and put together some sense of whether that was possible. So I published that idea. It makes a very small number of predictions, and I'm following those predictions. I don't think it's likely right. And I deeply dislike the fact that to work it depends on multiple versions of the universe, although they're rather differently organized than in the internal inflation picture. I'm still certainly, well, not me, but that idea is guilty of propagating many universes to explain our own. And I deeply dislike that. But I will point to the fact that it makes predictions as a kind of proof of concept. Okay, so both the string theory landscape and your version of cosmological natural selection involve many, many different universes with different features.

But you're saying that, if I understood correctly, because your universes change slowly and you can look for the solution that maximizes their reproductive fitness, and that makes more predictions than the string theory landscape does? Yes, but it's zero versus two. Okay. I mean, I think that any of them would make predictions like the cosmological constant allows for the existence of life, right? Yeah. Yes. But what to be a real prediction, it has to be a feature of the universe that's decoupled from or orthogonal to whether it is life or not. Okay.

So one of those predictions is about the value of the value of the. the strange quark mass and the relation that it has to the upper limit of masses of neutron stars. And as far as I can tell, that's not coupled to whether we exist or not. Okay, that makes sense. With world-class instructors curated music and endless fitness variety, Peloton has created an unmatched fitness experience to keep you motivated, workout after workout. I like Peloton because it's flexible about what kind of workout you're going to get in the moment,

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on your time. So get started on your Peloton journey. Go to one peloton.com to learn more. That's O-N-E-P-E-L-O-T-O-N dot com. And then the final thing to get on the ground, because it's very related to this multiverse question, is the many-world's interpretation of quantum mechanics, one of my favorite ideas. And you've written a book recently, Einstein's Unfinished Revolution, where you talk a lot about quantum mechanics, and you make it clear that many worlds is not on your list of viable alternatives. So maybe you want to share with the audience why you think that's the case. Let me preface that. And I'm not just saying that because this is your program.

If you look at that book, you'll see that the many worlds of the Everett approach has two chapters and there's the longest chapters in the book. So I take you guys. I seriously. Good. And I spent a lot, in fact, that was an agony for me. Because I do not believe, for various reasons that I hope we'll talk about, that that's the way nature is organized. But I think that there's been the, there's a world of things that have happened

since the original Everidge, Bryce DeWitt kind of sense of it. And there's a number of people in Oxford who you know who they are, and yourself and your collaborators and a number of other people who have worked really seriously to make sense of that interpretation or the original claims of that interpretation. And it was really challenging for me to try to understand what was going on because it's pretty subtle, at least for a dumb guy or whatever like me, it's pretty subtle. And I wanted to present this to, you know, when we're writing these books, some of it is to promote her own ideas,

but some of it is the responsibility of presenting it to the public so they can choose, so they can get it right. And so we can talk about the ins and outs of that. but that's that's my preface. Yep. And with that preface on the table, why don't you like many worlds, having done all this agonizing work? What level of personal explanation would you like? So let me start with it cuts off my hopes.

So my hopes are and have always been that quantum mechanics was incomplete. and there was a physical theory that is physical discoveries to be made, which would be enlightening about the nature of space and time. And that's always been the goal of the work that I've been trying to do in quantum foundations. So the minimal thing to say is that if you're right, then there's nothing to do in the direction. I've been working, and I don't, it's not, that I feel like I have a great stake, but it's taken a lot of time and effort, and I still believe

that that's a likely, to me, it's a very possible direction for science. Good. So let me actually, let me just sort of reiterate that in my own words, because you can tell me if I'm understanding correctly. One of the things about Everett, the many worlds interpretation, is it says that we basically do understand quantum mechanics. We understand what the sort of space of quantum states is, how it evolves, there's a tremendous amount of work to be done to quote-unquote interpret it, to figure out how that simple underlying description matches on to the world that we see, but the basic physics is somehow there. And what you're saying is that you have either a hope or a desire or an intuition or a thought that we don't understand the basic

quantum dynamics and that trying different versions of that might help us understand other problems in physics, so you don't want to shut that off in the way that Everett might appear to do. Yes. At least I want to go ahead in my little corner and develop that because I think that that's tied to the question about how the universe chose its laws. I think it's tied to quantum gravity, and especially what ties into quantum gravity, is the hypothesis that space is not fundamental and that space is there for emergent out of something more fundamental

and that something being emergent, the property that we call locality, the things talk with other things nearby them, would be disordered, say, the condensed matter of physicists say, to have not, non-locality appearing in the universe and that non-locality could play a role in the non-locality that we discover in quantum phenomena. And that's an interesting question.

So that is part of the picture I have, the map I have in my head of where I'm going. Well, that makes sense. And in fact, it's a perfect segue because I did want to get into now the specific ideas. Thank you for indulging me with that little set of background questions. But I thought it might be fun to start in your, because in your book, you're very interested in philosophy as well as science, and you've taken seriously a lot of philosophers, not just the most modern philosophers doing quantum foundations or whatever, but the history of philosophy and a lot of thoughts from that. And one of the perspectives you put forward is that you would like whatever our physical theory that we develop, up to be to come from some well-articulated principles. And you say that Einstein did this, you know, with relativity, for example, we should at least

give it a try. And then you list in your book, in Einstein's Unfinished Revolution, you have five principles that you want a theory to follow. Now, I don't want to put you on the spot. Do you want to tell us what the five principles are, or do you want me to mention them, and then you can comment? Well, I have different versions of this, so let's see if it's the same. I'll start off and we'll see if it's the same time.

Good. All of the lists that I've written down start with the idea of relationalism as the first one. That is the principles that Leibniz laid out in his writings about how to make a background independent theory of quantum gravity and quantum cosmology, which is what Leibniz was doing, in my opinion. So by the way, in your book, that's principle number two. That's not principle number one is probably realism then. Nope, it's background independence.

I messed up. I'm sorry. Backhand independence is a clear consequence of my misses principles. Anyway. Exactly. But I mean, I actually, I'm only drawing this out because as a fellow book writer, and we know better than the people who are reading the books that they evolve in time, right? Like the book that you actually read is just a snapshot of what it was.

when you hand it in. But if you were given more time, you'd probably keep tweaking it along the way. Oh, of course. Of course. So what is relationalism then? What does that mean in down-to-earth terms? In down-to-earth terms,

that means that there's no such thing as absolutely where you are in space, is where you are relative to some landmarks, which you have to pick out. There's the same thing as true of time. There's no absolute time which goes. on whether there's any change or motion in the world. The principles of liveness say you have to describe time in terms of change and use some actual, we would say a physical clock.

We don't believe, the way Newton believe, that there's some view of God, which gives absolutely where things are and when things are. that it all comes down to relationship. One of the ways that Leibniz put it is the principle is called, I'll say in other words and it'll come to me. The principle is that there can be no two events in the world that are identical described by the relational properties, or no two objects.

So if you have an event and you look around you and you see a certain view around you. When you have another event which sees exactly the same view around it, then they must be the same event. Is this the identity of indiscernible? This is the identity and discernibles. Thank you.

The principle of identity and discernibles. And I find this a very useful principle for constructing theories. And I get the impression from reading those principles in particular, but the whole thing, that part of your intuition is that we make progress by stripping away given elements, right? Like the less the ultimate theory of physics says,

well, this is just fixed once and for all, and we can't change it, the happier you are. And so we went from there from Newton, Newtonian Absolute space, to Einstein and now quantum mechanics, and it's a series of stripping away of absolutes. Yes, and I think more specifically, the way that I'd like to say this is that we live, inside this universe, there's one universe, for purposes of discussion, give me that for the moment,

is one universe. And we're trying to understand its properties. Now, what we do most of this is, is we look at a small part of it, a ball rolling down an incline plane, a rocket shooting off, a solar system, a phone, whatever, and we treat the physics of that in isolation. that as we pretend it's isolated from other things in the universe, but not completely because we like to use big, solid, stable things in the rest of the universe, like the whole solar system itself to give meaning to measurements that we make on these small things. So the way that we actually test the theory implicitly assumes that we're discussing a small part of the universe, which is only weakly interacting with the rest of the universe.

So that's fine and that works very well. But if you're cognizant of that, and like you and I both want to make a theory of the whole universe and understand the universe as something that stands alone and is in some sense a whole closed system, then you've got to find a different starting point. And that's one of the lessons of thinking through these ideas, trying to get good principles to start. Did you want to say anything specific about background independence as a principle?

What does that mean? Sure. That's basically background independence says that in your mathematical description of the system that you're describing, there's no fixed mathematical structures. which don't have a back and forth relation with other things. In other words, if this thing, whatever it is, influences the behavior or the evolution of some degree of freedom, there's a reciprocal interaction by which this thing also changes.

So there's not anything which we just use for reference, for coordinates, for landmarks, that's not also dynamic and not also involved in the analysis of the dynamics. And then this, of course, came from Leibniz. Mark enunciated as what Einstein called Mark's principle. So that's an example. So let's just say it. Newton liked to say that one way he could prove that absolute space was there

is take a bucket half filled with water and hold it up by some strings. and rotate it, and the water would be pushed up on the side of the bucket when it was rotating and not when it was not. And Newton said, you see that proves that when it's rotating, it's rotating relative to something, which I'm gonna call absolute space.

And Mark said, no, you're actually rotating, not in a significant way relative to you, standing or doing the experiment, but you're rotating relative to all the same stars and stuff in the galaxy and the group of galaxies and so forth. And the way you could tell experimentally is that you should just keep the bucket fixed and rotate the whole universe around it. And you would see in that second case, the water go up on the side the same way. And that Einstein called Marx principle. And in general relativity, it's true. Is it?

I knew you were going to ask that, yes. So let me finish the sentence. General relativity describes different kinds of systems with different, what we call, boundary conditions, conditions far away from the systems we're describing. And if we put on what are called ascentotic conditions, so we insist that the universe is just goes to flat space time for some other known space time far away, then this principle is not realized because we're anchoring, we're like tying everything down. It's like tying down the circus tent far away. But if the universe

is conceptualized is closed, then it is satisfied. Okay, fair enough. So let me see. On my list, we have background independence. Oh, wait, I had a sub-question sparked by what you just said. when you talk about background independence and relationalism for that matter, you know, this philosophy that things are not given, things are sort of constructed with respect to other things going on in the world, does that go so far as to include constants of nature, you know, the fine structure constant, the mass of the electron, things like that? Is part of your set of principles that we should expect these things that we, that conventional physics says there are just data, that are given once and for all in the universe

to be more alive and more dynamical. Yes, absolutely. And that's what cosmological natural selection was aimed at. And I'm surprised that more particle physicists aren't interested in that idea because that, philosophers are only good when they're good. They're only useful when they're useful, so we speak. I don't think we should just put up a...

Sure. pay from the shei versions of all the philosophers and bow down to them. But I was shocked when I had had those ideas. And then a friend of mine who was a philosopher, Druselk, now sent me some pages from Perce, Charles Sanders Perce, who was a very influential American philosopher, who in the 1890s said that it's not enough to explain nature in terms of laws. the most important thing is to explain why are those the laws.

And he goes on to say that within science, the only way of explaining why the laws are the laws is if they're the result of some evolution. Now it is to biology. So much for originality. You can always find things. This is why you shouldn't read things written by other people because it makes you sad about your own contributions.

So let me see. So what I have here then is background independence, space and time, are relational, causal complete. was another principle that you mentioned. Yes. So what does that mean? That means there ain't nothing outside the universe. That means that every explanation in terms of causes going back in time has to stay within this one universe.

Are there people who don't believe that, or are you, does it depend on how we define the word universe? Sure. Okay. I mean, does cosmological natural selection fit in with causal completeness? Yes. if you define all that as because there's one causal future. Okay. And then I have reciprocity, which I guess is related to background independence.

So what is reciprocity? That was the word for what I was saying about if A influences. Right. B and B influences A. And it comes from one of Einstein's papers on general relativity. And this just for, again, for the people who are not experts here, it always bothered me about hidden various. approaches to quantum mechanics, pilot wave,

Bohemian mechanics ideas. In these ideas, you have a wave function that does the ordinary thing that wave functions do and everyone else's version of quantum mechanics. You also have some more variables that tell you the positions of the particles. And the wave function influences the particles, but the particles do not influence the wave function. So is it correct to conclude that this bothers you also? Oh, yes. My God.

That's good. No, that probably me a lot. And I mean, the things that I've come up with are not as elegant as Beaum DeBroy, possibly because I'm trying to really, I tend not to have hidden variables in that sense, but use non-locality to introduce non-local interactions between the degrees of freedom that already are there. Do you ever feel like you're drinking from a firehouse?

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This week on the podcast, I am sitting down with Ray Porter, the narrator of Andy Weir's audiobook Project Hail Mary, massive sci-fi adventure about survival and science. And what happens when you wake up alone very far from Earth? I really had to make a decision because I caught myself getting that fraud. in my throat and starting to get teary as I'm narrating some of these sections. And it's like, okay, yo, yeah, yo, is this indulgent? And I really thought about it. I was like, no, at this point, it would kind of be betraying the trust the author and the listener have in telling this story if I don't go through it. But there's places in this book that deeply emotionally affected me

and I left it on the mic. That's great. Because it served the story. People will say like, oh my God, I cried at the end. It's like, yeah, dude, me too. Listen to EIRSA, the Audible and IHeart Audio Club on the IHeart Radio app or wherever you get your podcasts. So I want to ask how we should think about these principles. Here's a list of five principles. They'll evolve over time as we tweak them. Like, even the Ten Commandments aren't exactly the same in the Bible every time they appear, right? So we're in good company there.

But do you take these principles as kind of non-negotiable? Like you're so committed to them that you're only going to consider, physics that satisfies them, or is it more like you're starting with some hypotheses, hypothetical principles, and we'll see whether they take us to the right place or not? Surely more the second. Background independence or relationalism, and we didn't mention realism, but realism, it's not a principle of physics, but it's a principle of doing science, are very important to me.

And if you showed me a film from 200 years in the future, and there was a great successful physics, which violates every one of the things I deeply hold here to me, I guess I'd like to know what else is going on in 200 years. I'd be surprised, but sure. I mean, one of the things for me being this kind of scientist is I'm trying to get someone. I'm trying to discover something. And David Finkelstein, who was somebody else who very much worked with principles, said once to me that the reason why I think about philosophy and principles is it gives me a running start. So when I'm sitting here in 2021 and I'm trying to move forward, if I come with a running start, I have a chance for getting somewhere. Right. It gives you a little bit of a guidepost, right?

Like you're not just failing around randomly. At least you're trying to adhere to your principles. That's something. Right. But there are certainly, I mean, you're somebody else who studied seriously the philosophical literature and so forth. but I would certainly say I'm not a scholar. You don't trust me for what's the right interpretation of any of these people. Don't trust me for the history.

It's all inspiring. And if it fails to be inspiring, if I don't get anywhere, then I would certainly be looking to, one of the things I would question would be these principles. Well, and one of the potential worries that I had, while reading that section of the book was you put right there space and time are relational as one of the principles. And that sort of begs the question, are there things called space and time in our philosophy? Like, certainly, I know that you don't even think that space is

fundamental, nor do I. So is it presuming too much to have the word space and time right there in one of our foundational principles? What's the alternative? Well, you could just have a wave function. Oh, you mean not have. Well, so what seems to me, or at least I'm told, is the least popular of the different positions I've adopted, is the one that says that time is fundamental and goes all the way down, below space, below laws. Right. But there is causation.

So, and I've developed this with different collaborators. in the context of several series of models, the energetic causal sets, the causal theory of views, et cetera. And I like to work with models because they're very concrete. You're not driving abstract things from abstract things. I mean, sorry, maybe even explain to the non-scientists out there what you mean by the word model. Like a model has a specific identity in the mind of a physicist.

So we start by stating some principles, of course, loosely. And then we make models of them. And I want to see this from a theory. A model is something that can be defined by a small list of rules. You can imagine playing it the way that somebody would play a game. a model means that you try to capture in the simplest way the implications of some assumptions or some phenomena but you don't try to get all the details in each model

you try to and there's a it's as I've been a physicist over time I've learned to really admire the people who are good at this which I don't know that I'm physically good at, but for example, Perba, if he knew him, he unfortunately died a long time ago, was a master at making the simplest model that illustrated some idea he had about statistical physics. And so a good model demonstrates or exhibits some idea clearly,

and you can either solve it on a piece of paper or put it in a little computer program and code it up, It's not any more complicated than Minecraft. So Perbach famously considered sand dripping onto sand piles and causing little avalanches. So that's a model. The simple harmonic oscillator is a model. These simple idealized systems that get at some of the principles we're talking about

and you can hopefully learn something by studying them in detail, even if no one pretends, they're the whole universe. Right. Good. And I want to get onto this time being real and having some real. causal power. But before we do that, I need to ask some questions about the principle of sufficient reason, because you say in the book, in some sense, I forget which way it goes. Either all of your principles arise from the principle of sufficient reason or taken together, they imply the principle

of sufficient reason. So what is the principle of sufficient reason, and why are you such a big fan? The principle of sufficient reason is states that for every fact that, for every fact that, about the universe such that is possible to ask, why is it this way and not that way? So an example would be, if you're talking about space, why is the universe here and not 10 feet to the left? If you're talking about time, why did the whole universe start when it did 13.5 billion years ago and not 10 minutes later? And this principle of sufficient reason says either there's a reasonable explanation for that, that is an explanation. In law, they have the reasonable person standards. So a sort of reasonably judicious person would agree that that was an explanation.

Or, and this is the sort of back edge of it, which is its most important use, or your actual. asking a question that really has no meaning. So in the case of those two questions I name, the issue is not, is there a reason why the universe was not created 10 feet to the left, but can you construct a cosmological theory in which there's meaning to how far Los Angeles is from Toronto, but there's no meaning to where the whole universe is right now? Right. Okay, but I'm not a fan of the principal's efficient reason, and I know, you are. So that's why I want to sort of dig into this. Probably you and I care more about whether or not this is true than most of the listeners, but we're going to indulge ourselves.

I think that it all depends on what you mean by a reason, and you tried to invoke a reasonable person standard, but I'm not quite sure that that qualifies because we're very far away from what the reasonable people are familiar with. If I ask a question, like, why are there eight planets in the solar system? It's mostly an accident. I mean, I could trace it back. to the whole initial conditions for the universe and the laws of evolution and so forth. But that doesn't strike me as what someone would call a reason. There's different numbers of planets around different stars and we happen to get eight. How does that fit in to the principle of sufficient reason?

I think you showed how it fits in. It's the result of the history of the bunch of gas and dust that became our solar system. Okay, so in that sense, it's a way of saying that the behavior, is lawlike, right? The behavior follows some rules, and you can find the current situation given the earlier situation plus the laws. Let me give a harder case. These are some things I've been thinking about recently with some collaborators over the last few years. We're trying to write something about these kind of things. Supposing you get interested in biology, which I know you are and you have been. And you're...

We get interested in how proteins get made in the whole story of DNA, DNA and RNA and messenger RNA and that whole complicated thing. And we want to know why is there a particular protein that's prevalent in the biosphere. And we imagine several kinds of explanations. There's the brute force deterministic explanation of there were some initial conditions in the universe. The laws are deterministic. And you compute and you compute. And it just happened that way. Then there's the functional explanation that a biologist might want to give, which says,

and let me, I forgot to say the most important thing. there are something like 20 to the thousand different possible proteins. And those that are found in the biosphere are many fewer, maybe 10 to the 7th or 10 to the 9th or something. So what distinguishes those that are found in the biosphere? And the answer is, if you allow functional explanation, it is not very complicated. this molecule makes something which performs a function for the beings that make it,

that make them more viable, have better fitness, and so forth. So there are functional explanations. And with the interesting challenge, let me start. There's a certain amount of argument, much of which, much of which to me is not to the point of, well, but we believe in the determinism of the laws of physics, so that's already a complete explanation. So the functional bit of the explanation must be not relevant or not enlightening, but in fact, it is enlightening.

And what I would say is that we are blessed by having both. That is, we can make a functional explanation for why those proteins exist. And we can also check do they satisfy the laws of physics and the laws of chemistry at every stage in that explanation. But we can't hope with current technology to just compute from the way function of the universe, whether they would be prevalent to us. You see what I'm going. I do, yeah. Okay. I'm going to bite my tongue because I think it'll get us down a rabbit hole.

But we both put our positions on the table there. And I do want to talk about the reality of time, which I think is very important. I mean, you've written a whole book with subtitle, The Reality of Time, but it means different things when you say that time is real. So there's one sense in which time could be real in which you're just distinguishing fundamental from emergent, right? There's a lot of approaches to quantum gravity, for example, the Wheeler-Dowit equation where time is emergent rather than fundamental. But in my mind, I would still call it real in either case. but you're attached, sorry? Of course.

Yes. And you're attaching something a little bit more significant to your notion of real that I would not want to attach. I mean, I think the time is real, but it's just a label on different things, much like space is, whereas you're giving time some role as exerting a causal oomph in the universe. And why don't you give us the sales pitch for that point of view? Well, thank you. It's been changing over the course of my career in recent years. Over time. Over time.

What I want to say is that what I believe to be the case is that when we're arguing or we're discussing what is fundamental. And let me just reiterate to make sure we mean the same thing. But the question is not whether it's real. There's lots of emergent, manufactured, invented things which are not in the laws of physics, which are real, which are all around me

and so forth. But the question, I think it is something that we know how to do pretty well to go down in levels of dependence that is in science, there are, there's a certain level

where we use by a lot of, explanation, biological concepts, and then we can explain those in terms of molecules and the chemistry of molecules, and we go down a level and certain concepts at this level are reduced to concepts which hold because of the laws of chemistry and physics, and we can go down a series of levels like this. And my belief, and it's interesting that as we go down levels,

concepts get stripped away because they're reduced to concepts at the lower level. And I don't, as a side story, we can talk about is what the different kinds of causation, where the causation can

go up and down both. But let me not say that. Now let me just talk about the kind of ontology of it. There is, you assert, a level or maybe several levels where there's no longer a concept that relates to our experience of time. And my hope is that, or belief, is that that's not the case and that as slow as you go, there will always be time and in a particular sense, and the particular sense is that the world at that level will be a process of events which are created and which then disappear, and the events have causes, which are

prior events. You can talk about who the immediate causes of one event are or some other events that each of them have prior causes. And the events and that structure of who is the prior cause to who is part of what goes all the way down. I'm not done, but that's part of the structure. Then very anachronistically, I believe that there is that the correct level, the correct description involves a notion of now these are the events which are in existence now, which are in the process of being created and about to be in the process of creating future events, and that it's not only possible, but absolutely fundamental to ultimately talk about the world in terms of what is real now.

and that that is the two things make up the meaning of time when I say the time is fundamental. The process of the continual creation of events and the fact that I believe there is something objective and universal in the notion of now it is some time. And in the past, some other things happened. They're no longer happening. and some other things may happen in the future. So a variety of presentism, is it safe to say? It's a variety of presentism.

And in particular, you would say, I think, that what we call the arrow of time is something that's built in to the fundamental nature of reality. And so this is very interesting to be both physically and philosophically. So let me just ask about it in more detail. So a point of view of someone like me, and I'm not alone, is that, of course, there's an arrow of time, in our everyday experience of the world.

Ice cubes melt in glasses of water. They don't unmelt, et cetera, et cetera. But we do more and more understanding of physics. We boil these things down into something like Newton's laws or Schroederger's equation or Maxwell's equations, and suddenly there is no arrow of time there. And that's okay because we can still explain the macroscopic arrow of time as an emergent collective phenomenon.

And somehow you want to put the arrow of time back in at an even deeper level than Newton's laws, Einstein's equations, etc. So to someone like me, that sounds like a step backwards. We have explained the arrow of time as this emergent phenomenon, and now you want to put it back in. So I always think, I always have questions about this for myself, because as we make progress in physics, and we learn that something that was brute and fundamental can now be explained in more fundamental terms. That always seems like progress and we're reluctant to let it go. But sometimes we have to let it go, right?

Sometimes we have to take a step backwards to make progress. So I guess I'm simultaneously asking you why you think it's necessary to undo the progress we made and how you in general feel about this move of sometimes admitting that you have to take a step back to take two steps forward. Good. So let me mention some of the things that we owe, some of the homework we have to do if we take this thing. One of them is we have to explain what was your starting point, which is explain why there are errors in the history of the universe that results from our assumptions, in which to a good approximation, the laws look time symmetric. And we have a story about that, which has to do with the formation of limit cycles and so forth. We have some words, and we've studied this in various models.

And we, by the way, this work is with Marina Cortez. Another thing we have to, so we have a story about that. I'd be happy to expound if you want. The second thing we have to do is we have to ask, looking at us from the other way, if you like going backwards from the present through the Earth's universe, is ask, are there? extensions of the physical theories that we use in the area, particularly general relativity and quantum field theory, do they have modifications or extensions where we

see the symmetry in time reversal failing? So that is there what, I mean a lot of people who are cosmologists who work with to study modifications of general relativity. It's a big activity. are there any sensible modifications that lose the time symmetry when you turn the monification? And can we therefore see a smooth transition described by these theories, and maybe muck around and make some cosmological predictions? And with Andrew Little and Marina, we have some cases on that.

And did you want to say something about the general idea of abandoning progress we think we've made for a greater purpose? I don't know that I have, sometimes, sometimes it's necessary. Good, okay. I don't know that I have a general. What you get, many of the most thoughtful physicists have been concerned about the apparent disappearance of the notion of what they, sometimes they call the now or the present moment. You can find Einstein worrying about that. and trying to put back in the distinction between past, present, and future as a fundamental distinction. So there's a paper that a collaborator and I just posted, hopefully it will appear tonight,

in which we mull over some very interesting quotes of Fennon Dyson and Heisenberg and Schrodinger, in which they say quantum mechanics is really a description of the future. future. And the reason why people get confused about these issues like the measurement problem is they don't understand that the crime description is only a description of a few. Hey, everyone. It's Cal Penn. I'm the host of Earsay, the Audible and I Heart audiobook Club. This week on the podcast, I'm sitting down with Ray Porter, the narrator of Andy Weir's audiobook Project Hail Mary, massive sci-fi adventure about survival. and science, and what happens when you wake up alone very far from Earth? I really had to make a decision because I caught myself getting that frog in my throat and starting to get teary as I'm narrating some of these sections, and it's like, okay, yo, yeah, yo, is this indulgent? And I really thought about it. I was like, no, at this point, it would kind of be betraying the trust the author and the listener have in telling this story if I don't go through it.

But there's places in this book that deeply emotionally affected me, and I left it on the mic. That's great. Because it served the story. People will say like, oh, my God, I cried at the end. It's like, yeah, dude, me too. Listen to Earsay, the Audible and IHeart Audio Club on the IHeart Radio app or wherever you get your podcasts. Okay, I hate to leave that out there, but I'll link to the paper when it comes out when we publish this episode so people can look for it themselves. But in other words, these very thoughtful people have worried about the absence of the notion of the now in our physical theory.

And my collaborator, by the way, is Kahlia Bredaix. And so we're trying to address this quiet that these people in Einstein had over the absence of the now. Well, and it goes, I do want to give you a chance to say a little bit about the specifics of this theoretical structure you've been developing. I boiled it down to a statement that the universe should be thought of as a series of events, not things, and each event has a view of the universe. That's probably too simplistic, but maybe you can elaborate on it. So imagine that the universe consists of a number of events. which are created by some just previous events. Each event has a number of progenitors or parent events,

and each event gives rise to a number of, we can just call them children events, and that this is the basic dynamics of the universe. This is how the universe really runs under everything. Is it fundamentally discreet then? Yes. It's fundamentally discrete. I'm not yet using the language of quantum theory because one of our results is that in several of these models, we can show the emergence of quantum theory. So at the moment, what is real is these events.

We call the processes that continually create them. and we insist on keeping in the description energy and momentum, whereas a lot of people at that level see those as things that go out the door, come back as emerging. There is a notion of the view of such an event. The view is basically, let's define now as an event and look around you and what you see. What's coming at you is a whole lot of photons and hopefully, not to know the other stuff, which has ranges of energies, which impinge on you.

And this is, I'm using this as a kind of metaphor, but see yourself right now as an event. And your view is all these things that are coming to you that inform you of the world in your neighborhood or equivalently in your causal past. And what we do, so this world has no space. So there's no forces that can fall off at one over distance squared or any other factor. There's no functions of space. There's no derivatives. So we can't write any field equations.

So how are we going to do dynamics? And one of the ideas is that these views are the stuff that dynamics acts upon. In particular, the fundamental laws exist that can. give a measure to how different the views of two events are. And the fundamental dynamics is expressed as a certain function of differences between views of different events averaged over the universe as it exists now. And we have an operational meaning of now. Basically, an event is part of now if it has.

been created, but it hasn't yet made all the children that it's going to make. Anyway, that gives us a notion of a present, and that's the, that's the, that's the fundamental So it does seem, I mean, compared to my own more Everettian views, it does seem, even if you can, in some limit, recover quantum mechanics, it seems pretty classical to me in that there is sort of a set of events, and that's it. That's the set. It's not like the sum over every possible set of events. But maybe that is just in concord with your feeling that there is only one universe. And if we really went completely to superimpose all the different universes, that would not be what you're looking for. Well, there's a view that

Claudia Verde and I are trying to make work in this new paper, which brings in some parts of What we say is that the fundamental distinction is not the difference between the past, present, and future. The fundamental distinction is between some properties that are incompletely known or indefinite and some quantities that are definite and some quantities that are definite. And that what an event is is in a moment of transition of some indefinite quantity becoming definite. And we then try to make a very simple picture of the world in which everything stems from that. And you do have a principle in there, or at least, I don't know, a law or whatever you want to call it, that you maximize the diversity of these views, which sounds like a social justice statement from the university. But you have definite physical definitions for diversity and view here.

They're a little bit different. Yes. And that's, of course, getting a little bit of satire in, which given the present crazy world, we thought was useful. But let me give that definition, because it's not very difficult. And this actually was invented with Julian Barber way back in the 80s. Julian was, I don't know if everybody knows who. Julian is a historian of physics and a philosophy of physics and a physicist of physics. and a physicist as well.

And he was the mentor for myself and for other people of my generation to teach us these ideas about relationalism. I mean, the first time I met him, he asked me if I knew Leibnizance. And I said, Leibniz Food. Yeah. And so this is something that Julian and I invented, and the idea is basically that we take all pairs of views in the universe, compare them, give a numerical measure of how different they are,

and some that square that and some that are all pairs. And that's what we call the variety of a system. And this is maximized either by assumption or do you show that it's true? No, we put it, I'll use a technical term in there I'll explain it. We put it in the action, particularly its absolute value is the potential energy. Okay. And its rate of change between events and events just causally prior to them is the kinetic energy.

And so the idea is that we have a bunch of events, and they all have their views, and we can calculate the variety, the diversity, the diversity. diversity amongst the different views, but in a very down-to-earth physical sense, we maximize that. And the hope is our universe comes out. I mean, can I ask how much of our universe has come out so far? Do we recover Einstein's equation for general relativity? No. Here's what we recover. We recover space and actually space time. So what becomes emergent, So originally in the theory there's momentum, but there's no positions. But what emerges is a Minkowski in space time with an embedding that takes these events to points of Minkowski space.

One. Two, motion of particles, of relativistic particles in that Mekowski space. Three, and these are as there's a quantity. which I'll just call one over N, and he can come back and I can tell you more about what it is. For one over N goes to zero or N goes to infinity, we get the classical trajectory. For at leaving order in the correction, so that's one over square root of N, and taking a certain non-relativistic limit, and making certain assumptions about the initial conditions,

we derive a version of quantum mechanics, as we derive the Schroederate equation acting on a complex wave function, with corrections that would look like nonlinear functions of the wave function. Okay. We can confuse. Let me stop there. There are other things that are in progress, but that's what's been published. Okay, but then the hope is to keep going and show that you do get curved space time

and Einstein's equation and maybe even the standard model of part of the, particle physics. Yes, it would be great. We'll see. But with the caveat that you want to imagine that the laws of physics themselves change over time or can change over time. Yes. So does that have an experimental consequence? Do we expect to see slight variations in the fine structure constant or something like that? That's a very, very, very interesting question. The cosmological natural selection, which, just to go way back, as we said, makes two predictions. The idea that the constants of nature change in cosmology, in modern cosmology, goes back to Durac, as I'm sure you know. And he looked for changes in these constants, and they've been looked for repeatedly and not been found.

I don't remember what the level is now, but it's several hours magnitude past G-dodd over G in Hubble units. I don't know. There are so many things about this which, let me put this thing, there are a few things about this stuff which I feel I have under control. And there are a lot of things which I don't know the answer. Okay, well, that's fair. I mean, that's how science goes.

So we can't blame me for that. I'm just asking because I was wondering how things were going. Good. So to finish up, I have two questions. One is you mentioned as we were chatting before we actually came on, that I made an offhand remark that caused you to do a U-turn. And you didn't say what the remark was or what the U-turn was. So maybe let's share that.

Yes. And this I very much thank you for, although I don't think you like that. So something that we haven't touched on yet is the whole issue of the mind, the brain, qualia, and all that, which most of my career I felt like was too hard to, mess with. So I stayed away from that. Consciousness, yeah. Yeah, all that. But I have published one paper, written and published one paper, and it's a result of a remarkingly.

So, ever since college, I was a naive pan-psychist. Or the sophisticated, the fancy word for it is a Rossellian monist. and that is, I believe that qualia and conscious experiences are real, and there are other aspects of the matter which makes up our brain, and therefore you get to have the determinism of the laws of physics explaining everything that happens in the brain, so you know you're not a dualist functionally or causally, but you get to be a dualist as to the kinds of properties that things have.

And there are external relational properties by which things move around. Physics describes, and there are, according to this view, other inner or intrinsic qualities which are like the experience of colors and sound and which we know what they're like for our brain, because we inhabit our brain. But why not just say that the whole world has that dual aspect? So I think now that's a really dumb idea. I respect the people who had it.

But what we said, it's funny how to sound. So this was a momentary conversation going into a talk. And you said that doesn't make any sense because why would nature, whatever qualia and consciousness are, if they have no causal influence in the world because the causes are already explained by physics, why should nature be part of them?

What are they doing in the world? And several years later, I found myself thinking about that. And the conclusion I came to, and this I'm very changeable on because this is very current stuff. But I said, gee, Sean must be right. Therefore, consciousness must actually have. causal power in the world, which is the, which is not the conclusion you drew from it, but it is a natural conclusion to draw.

And therefore, and I basically, so I made then a hypothesis about correlation or representative, which is with the people in this consciousness business are saying they're looking for neural correlates of quality or consciousness. So given the situation I just described to you with views, there's another aspect of the theory of views, which is that not every view has fixed consequences. And you're going to have to give me a little time to justify this. But most views have fixed consequences, which are the same as would have happened to similar views in the past. But in order to believe that the laws can change, I have to believe that some very small minority of views are not, don't have precedent or the laws of nature don't know what to do with them.

and they have to somehow discover novel behavior, a novel response to their situation. And so the hypothesis is those that correspond to events which have to do with quality of consciousness. And so I wrote a paper about that. I was very excited about that. I wrote a paper about it. And I'm glad that paper is out there.

And I did not, And basically, I'm very confused. I don't know how you feel. I feel that we have as scientists, our descendants, that as a scientist of two or three or five hundred years in the future, are going to have to grapple with this. I feel like I grappled with it and I got an idea and put it out there. But I don't wake up in the mornings feeling excited about,

now I'm going to go to work on that idea. I feel like it's beyond where science can be. We can imagine things, but we don't know how to reason about them. Well, Philip Goff was a previous guest on the podcast, a big advocate for panpsychism. Am I correct in thinking that you, like myself, were invited to contribute to this Journal of Consciousness Studies, special issue about his work? Yes. So it made me think of it because I just handed in my paper in which I precisely say that, look, you can either modify the laws of physics to allow consciousness to poke things around and have a causal influence, or you don't. And if you don't, you can say, well, there's still something mental that is an aspect of the world that just has no influence on how things behave, or consciousness is just an emergent property from the true physical behavior of things.

And my attitude was, if you want to modify the laws of physics, if you want to have real mental aspects that have a causal influence, then be my guess. Like, that's hard. There's a large barrier to entry because we know a lot about the laws of physics, but at least it's respectable. But this idea that mental aspects are there and somehow utterly important yet have zero causal influence, that's what I said. I don't even quite consider to be respectable. That's my own personal view. I'm a physicalist myself. I think it can emerge, but the idea that you're not going to have any effect on the standard model of particle physics,

and yet there's this crucial aspect of the universe. I'm not quite sure how that's supposed to work. Yeah, so I, so thank you. Oh, I got to that place. And, yeah, it's, let me say something generally, because we both had the experience of being physicists, and getting interested in and opening up to discourse with philosophers. And sometimes it's certainly been very useful to me, very helpful. I mean, we didn't mention it all, but you started to mention my books on time.

And one of them was with Roberta Mandibara Unger, who has been a very, very important influence on. And is, I think, really an important philosopher that people should pay more attention. And then there's kind of all the people we know, the people in Oxford and New York, both places where they're really excellent philosophers of physics. And I find it very, very, both inspiring and humbling to interact with them.

I mean, they are likely to know what's wrong, what all the arguments are against any view you're going to them. It's frustrating, yes, but it is very helpful to talk to them for exactly that reason. Which leads me very nicely into the very last question I have. You've been very indulgent with me with your time here. So one of the ways in which I think that you and I are a little bit different, but I'm glad that there is diversity of views in the usual sense, not in the physics sense, is that when we have,

have a puzzle in physics when there's something we don't fully understand, whether it's consciousness or the arrow of time or the foundations of quantum mechanics, there's various ways one can go in hypothesizing how to do better. And my first impulse is always, I think, what Wheeler called radical conservatism, right? Like, keep the basic ingredients as solidly as you can. The Schrodinger equation, the physical nature of matter, bolts spawn statistical mechanics, etc. and try to see how from those simple ingredients, we can reach this, a better understanding of the thing that we're trying to get to.

Whereas I get the impression that you and people who are on the similar path are just much more willing to say, nope, let's just throw out everything. Let's just throw out the Schrodinger equation, let's just change the fundamental nature of matter because these are big problems and we're not going to solve them without big solutions.

So do you have any words of wisdom, short or long, about the differences between these two philosophies? Do you think that one is sort of generally better, or do you think that it's just good that different people are trying different things? I think they're both necessary. And one thing that would be very interesting at some point is to have a conversation with you and Carlo, if I may, and maybe a few other people. I put Carlo more and more in that same category, although he didn't start out there. But one of the interesting things about this profession is we get to watch each other evolve over lifetimes.

There were a couple of things that were really formative to me. First, I did part of an undergraduate degree in philosophy, But as I said, you know, I wrote a paper in philosophy of mind which took this view that we both criticized. And I was, to the extent I thought about consciousness at all, I was satisfied with that. It was the problem of the landscape of string theory or any other kind of theory. And how are we going to explain where the choice of Ross come from? had a very destabilizing effect on me. It got me thinking about things that most of my friends and colleagues were not thinking about.

Something that was also destabilizing. And it's hard to, in my life it seems like people play a big role and friends and people who are not friends who I talk with. as illustrated by that story and take a big role. I mean, the first person who argued with me when I was a regular, I mean, after we solved the wheel of the equation, so how could I not love that? Be in love with that, yeah. But then we found out what was hard.

It happens in that approach. You can almost by inspection find solutions of the wheel of the way of equation. But quantum mechanics is more than just the wave functions. It's especially a theory with a lot of vision values. It's the observables and the inner product. And what we never did in conventional Hamiltonian loop quantum gravity was find quantum mechanical observables that were honest giraffe quantum mechanical observables.

And that was, nor did we ever construct the physical inner product. And so that program was very frustrating to me. And that had a big influence. And then I was about to say, Fotiini Marco Pulo was the first person who just came and sat me down and said, look, you're wasting your time. That will never work. You have to think about time maybe being fundamental in space not.

She was the first person who articulated that idea in our community. And she articulated it very, to me, very powerful. Now, of course, she's somebody who was very important to me generally, and I have enormous respect for her. But that intervention played a role. And a few years after that, I started working with Roberto, Anibert Unger, and he basically took me the task and said, what kind of, he wouldn't quite say like that,

but what kind of fool are you? I mean, here you are talking about the law is changing in the landscape. And here you're working on getting time to emerge from the Wheeler-Dilid equation. Like, doesn't that bother you? And so it's been very important who I talk to and listen to.

And I feel like over the last 10 years or so, and it took that long. So there were always these elements, but I was working on in the variable series every few years and so forth. But all of this really coalesced into this research program over the last 10 years. Yeah. Well, whether or not the laws of physics change with time,

I'm glad that our views of the laws of physics are changing over time because we don't know them yet, and we have to be a little bit flexible about it. So, Lee Smoland, thanks very much for being on the Mindscape podcast. Oh, thank you very much, John. Great.