Theories of Everything with Curt Jaimungal - Jim Al-Khalili: The Ontology of Time. We Had It Backwards

Episode Date: September 21, 2026

SPONSORS: - Head to https://www.factormeals.com/toe50off and use code toe50off to get 50% off and 1 free breakfast item per box for 1 year. - Get Tidy Today! Try CleanMyMac 7 days FREE and use my code THEORIES for 20% off - https://clnmy.com/THEORIES - Get 15% off OneSkin with the code TOE at https://www.oneskin.co/TOE #oneskinpod - I personally subscribe to The Economist. FLASH SALE through Sep 23, 2026: 60% off the annual subscription! No other podcast has this! https://economist.com/TOE Every episode days early, ad-free, plus my essays: https://curtjaimungal.com This episode is about what physics says is there when nobody is looking, including time itself. Jim Al-Khalili, theoretical physicist and Distinguished Professor Emeritus at the University of Surrey, joins to argue that the arrow of time is fundamental. Entropy increases because the arrow already points that way, and not the other way around. We discuss why he thinks the measurement problem is taught badly. He wants Bohmian mechanics to be right without claiming that it is, since the price is Einstein’s special relativity. He calls the past hypothesis a cheat. The conversation also covers the block universe, where he parts ways with Carlo Rovelli, and why he wants thermodynamics in the search for quantum gravity. I hope you enjoy. FOLLOW: - Spotify: https://open.spotify.com/show/4gL14b92xAErofYQA7bU4e - Substack: https://curtjaimungal.com - Twitter: https://x.com/TOEwithCurt - Discord: https://discord.gg/kBcnfNVwqs - Crypto: https://nowpayments.io/donation/TOE - PayPal: https://www.paypal.com/donate?hosted_button_id=XUBHNMFXUX5S4 TIMESTAMPS: - 00:00:00 - Quantum Measurement Problem - 08:44 - Realist Quantum Interpretations - 18:19 - Scientific Empathy and Explanation - 30:19 - Electron's Ontological State - 41:05 - Minkowski's Block Universe - 51:59 - Flow vs. Arrow of Time - 1:01:01 - Entropy and Past Hypothesis - 1:14:56 - Rovelli and Emergent Time - 1:25:40 - Incomplete vs. Approximate Physics - 1:31:57 - Causal Set Theory LINKS: - Jim Al-Khalili's Website: https://www.jimal-khalili.com/ - On Time [Book]: https://amzn.to/46PNLxK - Jim Al-Khalili's Channel [Video]: https://www.youtube.com/@UnbaffledScience - Quantum Reality Series [Video]: https://youtu.be/sivQ-jbZ2oM - The Decoherent Arrow of Time and the Entanglement Past Hypothesis [Paper]: https://arxiv.org/abs/2405.03418 - Block Theory: https://plato.stanford.edu/entries/time/ - Copenhagen Interpretation: https://plato.stanford.edu/entries/qm-copenhagen/ - Many Worlds: https://plato.stanford.edu/entries/qm-manyworlds/ - Bohmian Mechanics: https://plato.stanford.edu/entries/qm-bohm/ - Bell's Theorem: https://plato.stanford.edu/entries/bell-theorem/ - Collapse Theories: https://plato.stanford.edu/entries/qm-collapse/ - Schrödinger's Cat: https://en.wikipedia.org/wiki/Schr%C3%B6dinger%27s_cat - Loschmidt's Paradox: https://en.wikipedia.org/wiki/Loschmidt%27s_paradox - Thermodynamic Asymmetry in Time: https://plato.stanford.edu/entries/time-thermo/ - Space and Time [Paper]: https://en.wikisource.org/wiki/Translation:Space_and_Time - The Strangest Man [Book]: https://amazon.com/dp/B002LDM8QS?tag=toe08-20 - Beyond the Quantum [Book]: https://amazon.com/dp/0198853742?tag=toe08-20 - The Selfish Gene [Book]: https://amazon.com/dp/B01GI5F2FS?tag=toe08-20 - Universe Today Article: https://www.universetoday.com/articles/quantum-physicist-takes-aim-at-the-universes-mysterious-arrow-of-time Full reading list for this episode (all 37 sources): https://curtjaimungal.com Guests do not pay to appear. #science Learn more about your ad choices. Visit megaphone.fm/adchoices

There's a lot of quantum physics that's misexplained. Time itself doesn't flow in any meaningful sense, according to physics. The arrow of time is different. This is Jim Al-Khalili. Theoretical physicist, fellow of the Royal Society, host of BBC's Radio 4s, the Life Scientific, and author of the new book On Time. Time is real, and the directionality of time is real.

Please dispel my misunderstandings. No, you've got me worried now. Have I been teaching the Block Universe wrong all these years? On this channel, I, Kurt Jymongel, interview researchers regarding their theories of reality with rigor and technical depth. Today, the professor plunges deep into the mysteries of time, the interpretations of quantum mechanics, and even where he parts ways with Carla Rovelli. What is the electron doing when no one's looking?

You've given me a challenge now. Professor, what is most misexplained in quantum physics? Oh, I mean, there's a lot of quantum physics that's misexplained and told badly and give people the wrong impression. I would say probably what we call the measurement problem. You know, the idea Schrodinger, opening the box with the cat that's dead and alive. And there are lots of different weird and wonderful exotic explanations like the need for conscious observers and so on that are completely outmoded now. And we have sensible ways of explaining it.

But I think still a lot of people get confused about what it means when you make a measurement and collapse the quantum state, it'll be great if we taught our students the measurement problem more correctly. Great. So what is the measurement problem? Well, the measurement problem is essentially whenever a quantum system, be it an atom or collection of atoms

or an electron or photon, whatever, interacts with its surrounding environment. So the old idea was, you know, the founding fathers explained, was that it had to interact with a classical system and there was this irreversible act of amplification. It had to be a measuring device

that was behaving non-quantum mechanically. And then that became confused with a human had to do the measurement and then it became, you had to be a conscious observer and the question was, well, why does Schrodinger have to do the measurement? Why can't the cat measure itself and so on?

We now know that the right way to explain it is that the quantum system becomes entangled with its surroundings. And when those surroundings are very big and made up of many particles, then that entanglement becomes decoherence. So it's a bit like in thermodynamics, when you say you look at individual molecules of gas bouncing around in a box, there's no concept of temperature there or direction to time, but you zoom out looking at lots of molecules and suddenly you can assign things like temperature and pressure and a directionality to time. according to the second orthomodynamics.

The same thing with quantum measurement. When does decaherence set in, when a quantum system interacts with an environment surrounding it that's very complex and big. And the more complex and the bigger it is, the quicker decoherence takes place. And that's essentially what the measurement problem is. Beyond that, it's down to

what's your favorite interpretation of quantum mechanics? You know, what happens? If you open the box and see the cats alive, what happened to the version where it's dead? Well, if you subscribe to one version of explaining quantum mechanics, the many world's interpretation you say, well, it's in another universe instead. There are other versions that don't require more than one universe. But the measurement problem is well understood now, but there's still a lot of confusion

when people try to explain it to it in non-technical language. Wouldn't decoherst explain that you don't have the off diagonal, so I know this is a bit technical, but it still doesn't tell you about why one outcome is selected. Exactly. Yes, exactly. So I always think of it, the off diagonals are killed off. That's what D.K. Harris does. So it kills off the possibility that the cat is dead and alive at the same time. But the option of live cat and dead cat are still there. And it's not that we've removed the superposition so the cat is either dead or alive. I just don't know. know yet because I haven't opened the box. Both options are still there. And so there is still

that final step in the measurement problem, which is, well, when I open the box, I only see one of the possible options available. What happened to the other options? That, by the way, is where the Everettian mini-Well's interpretation, I think, is at its most powerful and persuasive, because it says, well, they don't go away. They just exist in other realities. There are other reasons why I'm not a fan of Everett's many of us interpretation. But certainly when it comes to the measurement problem, I think it gives the cleanest way of saying, how do we remove all the other diagonal elements apart from the one that we see. So what were you a fan of when you started university and then you became a member of the opposing side? I think, I mean, I fell on leveled quantum

mechanics as an undergraduate. In fact, in my final undergraduate year, The professor who taught us, well, I'll tell you, a backtrack a year, I did my first course in quantum mechanics. In the UK, you know, we major in one subject from the very start. So you start as a freshman, you're going to do a physics degree. You don't waste your time doing anything else. There are good and bad things about that particular system. So in my second year, I did a core course on quantum mechanics. I have to admit, like most students, it just sort of meant nothing to me. You know, this Schroding equation and Hamiltonians and I'm. eigen functions and you just have to try and figure out what you need to do to pass an exam. Then in my third year, I took a year working in industry. It's what's called a sandwich course where you do two years of study. You spend a year in a research lab or in industry and then you come back to do your final year.

That year out, I spent consuming biographies of the founding fathers of quantum mechanics. Interesting. Werner Heisenberg, Niels Bohr, Richard Feynman. Paul Dirac. And for me, not for everyone, but for me, that sort of made

quantum mechanics magical and wonderful. And I couldn't wait to get back to it. So when I came back to my final year, I did a course on quantum and more advanced course

on quantum mechanics, you know, it blew my mind. So much so that the professor who taught us there, I stayed on and did my PhD with him. I didn't go to another university. So at that point,

I guess, I was like everyone. You're just taught. the standard textbook version of quantum mechanics, what we call the Copenhagen view, the view that was espoused by people like Niels Bohr and Heisenberg and others. And I didn't question it, but during, as a grad student, during my PhD, I wanted to explore further, a bit more about the philosophy, the foundations of quantum mechanics, the interpretations. And this was in the mid-late 80s at a time when it was really frowned upon

to think about the philosophy of quantum mechanics. You know, there's that famous, you know, if you want to worry about what it all means, go and do philosophy. We're doing physics here, man. You know, we know how to use the equations, look at the technology we're developing and in using quantum mechanics.

Why are you worried about, you know, whether, you know, what the electron's doing when you're not looking? But that did concern me. So from that very start, when I started my research, life as a grad student, I was concerned with the standard view, the Copenhagen view. As a group of PhD students, we set up what we called the Carlsberg Group. Now, this is a nod to the Carlsberg Beer Brewery in Copenhagen in Denmark, which funded Niels Bohr's Research Institute back in

1920. So this was like a nod to thank you, Carlsberg Brewery, because without you, you know, bore wouldn't have been able to gather all these geniuses to develop quantum mechanics. And we would discuss in this group the different interpretations. And gradually, I guess, over my career, I didn't fall very strongly down on one side or another, but I became convinced that a certain subset of interpretations of quantum mechanics had to be right, namely what I are called realist interpretations. There's this argument between, you know, whether there's an objective reality that exists prior to measurement, or whether it always exists and independently of us, there's an objective reality. I believe in the existence of a real, you know, objective

reality out there independently of measurement. Then it becomes a case of, well, even within that subset of realist interpretations, there's a whole host of different possibilities. And these days, the three leading contenders are Hugh Everett's many worlds interpretation developed in 1950s there's Louis DeBroy and David Bowen, what's called Pilotwave Theory or

Bohemian Mechanics, and then there's what's called spontaneous collapse. I'm still probably Boehmian mechanics is the one that I want to be correct, but wanting something to be correct doesn't is not the same as believing that's the correct

idea. We don't know yet And I think those who subscribe to a particular interpretation to the exclusion of all others, that's like religion. You know, you have faith in it. I'm open. I just believe nature does things in a certain way. Regardless of our embarrassment of different ways of explaining the mathematics, nature does have it. But there is one interpretation that's correct. We just don't know what it is yet.

So you have desire for the Bohemian interpretation without belief, without faith? That's right. I like it, but I acknowledge it has its problems, as do all the interpretations. I always think of it. It's like when you're sort of laying a wall-to-wall carpet in a room, and then, you know, you realize you've left your hammer under the carpet. Well, there's a bump in the floor. Well, you can move that bump behind the sofa or behind the TV or whatever. It's still there. That bump is the awkwardness, whatever it is that a particular interpretation suffers that's counterintuitive and illogical. You know, wherever you look, you can't escape the counterintuitiveness of what quantum mechanics means. You might say, well, you know, locality or non-locality is not my issue, but many universes is an issue.

Other people may think other things are more important. So I don't have a favored interpretation very clearly because I know they all have suffer from certain problems. So what's realist? You mentioned realist has to do with being mind independent. And then there's this idea that some people have that there are pre-existing values of a quantum system. And contextuality puts a monkey wrench in that.

But those sounds synonymous with being mind independent. So can you tease those two out for me? Well, that there are certain. hidden variables, the electron, we think of the electron prior to measurement as not having a definite position or definite momentum. And then, you know, you measure its position, you get an eigenvalue, you know, a particular value of position, but that means you know nothing about what its momentum is, you know, so it's particle-like rather than wave-like. That's the standard view, and that's what the mathematics seems to be telling us. But there are, you know,

So Burmium Mechanics is a hidden variables interpretation. It's one of the realist interpretations, but it says that that electron is always a particle. It's never a wave. It's carried by some invisible force field, the quantum potential, or we think of it as a guiding wave. But it is always a definite path. So it does have a definite position.

It's just that we're never able to know in advance what that is. that's why these variables are hidden. It's still, you mentioned contextuality, and that's something I've only sort of recently started thinking about and I don't really have a good way of explaining it, so I'll leave that if that's okay. But the notion that boeumian mechanics or hidden variables is still a respectable interpretation is because you're having,

to sacrifice other things. So you have to sacrifice locality. Einstein's dream was that you could find some local, objective reality, that everything was sensible and quantum mechanics wasn't so mysterious. Of course, that was destroyed by John Bell in the 1960s, who showed that, look, if the universe really is local and real and there's no magic going on, then you'd get a certain answer if you carried out a certain experiment. If it wasn't, then quantum mechanics is correct, then you get a different answer. And sure enough, it turns out that, yeah, quantum mechanics is right, and Einstein's dream was wrong. But it doesn't mean we have to give up on hidden variables. It just means that the universe is non-local in instantaneous interactions between

particles. There's a friend of mine, a physicist Anthony Valentini, who is a big advocate of pilot wave theory, bone mechanics. And he's written a book on the subject. But he takes it a step further. He says if really if pilot wave theory, Bohemian mechanics, or DeBroidbom quantum mechanics is correct, then Einstein was, not only was he wrong about quantum mechanics, but it was wrong about relativity too, because it means that instantaneously things can communicate with each other,

faster than light, and that's in violation of Einstein's relativity theory. So most quantum physicists tiptoe around the idea of, you know, when you're having two entangled particles and somehow they're part of the same quantum state, how is it that when you measure one, that affects the results of measurements of the other? Physicists find very clever ways of saying, well, it's not really instantaneous messaging faster than light. But if you push DeBroy-Bome pilot wave theory to the limit, then it says, yeah, they really are interacting faster than light. that's why I get nervous about Boehmocast, despite liking it and wanting it to be correct,

if it means giving up Einstein's special theory of relativity, well, that's a big price to pay. Right, right. Actually, I was just speaking to Tim Modlin, who takes a similar view. He says that Bell's theorem shows that there's non-locality, and then I asked him, look, there's a difference between non-local interactions and non-local correlations. So do you indeed imagine that there's something causative that's going on between these two particles? And then he says, yes. And then I said, okay, but then what about no signaling?

And then he says, I think that you could signal. I don't know how you could signal faster than light. I don't know the experimental setup that you could do. I also imagine it's quite fragile, but I think theoretically you can. Yeah, I think if you're prepared to, you know, know, as Tim Mordland is, if you prepare to give credibility to Dubroybone, pilot wave theory, then, I mean, that's what you have to admit to. There is instantaneous, real physical interaction across space. You know, quantum mechanics is non-local, right? Mathematically it is. The wave

function is non-local. You know, if there's got a wave function describing two entangled particles, or even just one particle that has a wave function that's spread out in space and you measure it and you find it here, well, the way function everywhere else is collapsing to zero because this is the one place where it is. It collapses to a delta function at the point of measurement. But people say, oh yeah, but that's all right. That's just the maths. That's just the abstract wave function that is collapsing. It's not real physical locality.

Or, as you say, it's hidden in the, it. in the correlations. You know, we can't use quantum non-locality to signal faster than light because, you know, you don't know what's going to happen is random, right?

You don't know what you're going to get. You can't tell the other particle what it's going to do before has happened. My view is, if there's non-locality in quantum mechanics, then the world is non-local. our tough luck that we can't use it to practically send signals faster than light. But quantum signals, quantum, we say, we call it quantum correlations.

I don't think that word does it justice. It's quantum connectivity is non-local. It's instantaneous. What happens here affects what happens over there. The fact that I can't use it to send signals fast than. And like, tough luck on me. But maybe one day we'll find a way of doing it. Who knows?

Now let's talk about On Time, which is your book. You also have a YouTube channel called Unbaffled, which will place a link on screen and in the description. And I recommend people subscribe, links to which are on my substack. And also in the description, you can click on that. You can go to both Jim's book and then Jim's channel. Wonderful.

Thank you. Okay. So you used two words in your previous... answer, one was explaining. You couldn't explain something, so you didn't want to explain it. And I want to talk about that because you're an expert explainer. So I want to know, well, what the heck is it that separates you? Like, why are you so great at this? I also think you're great at this, but I know that your British humility may get in the way of, I'm giving an answer here. Okay, so that's a question I'm going to ask, but I want to tie that together with something else you said. Use the word magic.

You said, John Bell showed there was no magic in quantum mechanics. And then earlier when you were saying, when you were in university toward your upper years, you went into, the library looked at biographies of famous people, bore, Feynman, and so forth. And you found that they gave you back the magic for quantum mechanics. But I assume you mean, you don't mean the mystification, you mean the richness and an interest into quantum mechanics, but not magic.

Yeah, no, I mean that sense of excitement. Right. That there's something magical, almost in a non-religious sense spiritual, The quantum mechanics is so wonderful and intriguing and fascinating. It's almost magical in how it inspires me and excites me still to this day. September is when the calendar refills. The travel stops, the obligations don't, though.

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And you also get a free breakfast item per box for one year, an entire year, while supplies last until October 31st, 26. That's code T-O-E-5-0-O-F at Factor Meals.com. It's in the description, Toe-50 off at Factor Meals.com. See website for more details. Okay, now I imagine those two are tied together with the explanations. That is, this is why you're such a great explainer. I mean, I could be wrong, but is there something about you understanding the biographies of other people, Or is there a different quality that leads to your expert elucidation? Well, I think, I mean, in part, all good science communicators, A, need to be, don't mind being the center of attention.

You know, I want to stand up and explain, but any good teacher should have that quality. You know, listen to me, I have something interesting to tell you. But you also need to have empathy with your audience. And that's not as obvious as you might think. You need to always almost be in a superposition of being the explainer, but also being the person receiving that explanation. What do they know? Am I saying the right words or putting it in the right terms that would inspire, excite, unbaffle them, right?

You know, they will say, oh, okay, I get it. For me, in part, because most of my social group or friends and family are not scientists. So ever since I was a student, I was used to explaining what I do in non-technical language. You know, I wasn't surrounded all the time by other physicists and talking the same language as them. I was used to talking to people who didn't know anything about physics, who didn't have a, background in science at all. So that helped me hone some of the, you know, the tricks and arguments and use of metaphor and so on to explain it. But I think overall, and this is genuinely true, I derive as much pleasure from seeing someone understand something that I've explained

as I do discovering it for myself. You know, it is. It is. If I find something fascinating about the world, I genuinely am excited to explain it to someone else. And they say, wow, I never knew that. That's great. I've got you to understand why I'm so excited about that particular idea or concept. Now, what is it that separates you from other explainers, other popular science explainers? So, for instance, you mentioned empathy. Without naming names, do you imagine that that is something that distinguishes you from some others?

I wouldn't have thought so. I think the most important thing is my exceptional good looks. Of course. No, I mean, look, British modesty aside, you know, I'm well aware that there are plenty of other people who are wonderful at explaining and who are great communicators. And I learn from them as well, you know, wow, that's a really nice way of putting it or you've really inspired me in some way. not all scientists are good science communicators, nor should we expect all scientists to communicate their science. Some are much happier leaving it to others. Those of us who do, I think what has changed in recent years, decades, I guess, the last maybe couple of decades, is that communicating science has become a respectable thing. You know, in the past it used to be that scientists would

reluctantly venture outside, you know, their academia, stick their head over the parapetal, their ivory tower. There were exceptions, you know, the Richard Feynman's, the James Jeans, the James Jeans, going back to the early 19th century, George Gamov, you know, these are great names in physics who were great scientists and researchers, and they're famous for that, but they were also famous for their science communication. But beyond them, there weren't that many around. When I was a student, the popular science books that I would read were really, I mean, and most of the authors were, I guess, British. Paul Davies, John Gribbon, Martin Rees, John Barrow, these are all popular science writers who've written popular physics books very often about quantum mechanics or cosmology or so on that inspired me. but not many of them

apart for maybe Paul well Paul Davis and Martin Rees had done for themselves academically but you sort of had to make a choice and if you chose to go down the route of science communication then there was that perception that you're lost to serious science

you're just an explainer you know and you know people like Richard Dawkins I mean we've been talking about physics now talk about biology but he was very a very famous Nobel Prize winning biologists who shall remain nameless, when I asked him about Dawkins, he said, well, the difference is I'm a biologist. Dawkins is a journalist.

Right. Wow, cutting. I mean, admittedly, people like J. Dawkins, Carl Sagan is a fantastic example. You know, great scientists, but when they went into science communication, that became their main job, right? They stopped being seriously, serious academic researchers. My generation, you know, I'm thinking of guys in the US, you know, friends of mine, Brian Green, Sean Carroll, continue their research.

They're great explainers too. They're, you know, very talented science communicators, but they've managed to maintain their academic credibility alongside it. And I think that's also part of what. makes for a good science communicator if you are still embedded and engross within the subject as well. Not just so that you can talk about your own research, but you have that perspective of what it's like to be doing research. And you're always there for finding ways of trying to explain that to a lay audience. What do you think is or was at the root of this trading of public notoriety with academic respectability.

Seems like you have to earn your academic credit in order to spend it on the public. It's not independent. I think that's right. I think, you know, I'm often asked by, you know, my own students or young postdocs, early career scientists. You know, I'd love to get into science communication.

What do I have to do? And particularly if they're still doing their PhDs, I say, well, look, the first thing you want to do, but the first thing you have to do is make a distinction, make a choice. Do you want to be a science? communicator, which is a perfectly good, respectable career, right? You know, you can have a science background, but you can be a communicator. You can be a science writer, a science journalist,

working in science policy. That's one route. Or you could be a scientist who communicates. If you choose the latter, because that's the path that I chose, then you better earn your, you know, your stripes first, right? Get your PhD. Maybe even, you know, you know, be doing some research, do a postdoc. Not necessarily. People work very hard to try to get an academic position to get a full-time professorship at a university. You don't do that just as a means to an end

to allow you the respectability of then venturing into science communication. But yeah, you have to sort of try and do both at the same time. And so the science communication can start to take over later on in your career like it has for me. But in my early career, I was a jobbing, you know, PhD student, postdoc, trying to get a lectureship, doing the teaching, doing all the academic things that academic has to do. And the communication side was something that I, rightly now, Luna, looking back at it, kept constrained and restricted. Exactly, as a site. And then gradually, once I'd reached a level in academia where I felt safe, I had a full professorship, I could then devote my time 50-50 between them.

And later in my career, my science communication is something that I've now, I now regard myself as the gentleman scientist. I can do my research as a when, but I, you know, I do the writing and the broadcasting as well. What is the electron doing when no one's looking? Well, if you're a Bohemian, it's doing whatever, you know, it's a particle. It might be moving. It might have a certain energy. It might be orbiting an atomic nucleus.

It might be traveling through space, bumping into another electron. It might be passing through, you know, through some conduction band. in a metal, it's a real particle. You know, there are other interpretations where, or certainly the standard Copenhagen view, which says that that's not even a question you can ask. You know, it's quantum mechanics doesn't tell us anything about what the electron is doing when you're not looking.

What it tells you is what you are likely to find probabilities of finding the electron doing something when you do look. But it doesn't give you any information about the electron other than, well, you have its quantum state, but that doesn't tell you exactly where the electron is or how fast it's moving or whether it's spread out or localized. So there isn't an accepted answer for what is the electron doing. Some physicists will say you can't, that's a silly question, don't even ask it because it doesn't have an answer. others will say, oh, it's doing something. Or maybe it's not the electron that's real.

It's the electron's wave function that's the real thing, and the wave function is doing something physical, and that changes when you look at the electron. And that's without even getting into whether we're talking about particles and waves, or we're talking about fields, because quantum mechanics now, the modern version of describing it is in terms of quantum field theory. So what does it mean, you know, what does an electron mean?

Is it just a concentration in the electron quantum field rather than a physical mass, a little lump of matter? Right. In that second case, I imagine the question would then just be, or what is the field doing when no one's looking? Right. Now for the Copenhagen view, is it that they think the question is ill-formed, that there is no answer, or do you, they say that our axioms are silent on that. So for instance, for instance, right now we're speaking,

and if you say, according to this video call, what games are loaded on my PS5? I mean, you would just say this video call is silent on that. It doesn't answer it, but it doesn't mean that's a meaningless question per se. So what's the difference there between an axiom set being silent on something versus something not existing or being meaningless? Well, I would imagine, I mean, when we're talking about the Copenhagen view, it's a very broad church. You know, there are lots of different ways of explaining it which fall under the umbrella, we call the Copenhagen view. If it's the view as espoused by the founding fathers themselves, and particularly Niels Bohr, then I guess it's the former option, that it's a meaningless question. It's not that it's doing something

but quantum mechanics is silent about it. Quantum mechanics, or the wave function tells us everything we can know about it, everything we could ever possibly know about it. And if it doesn't tell us, you know, where precisely that electron is, that's because the electron doesn't have a precise location before we look. So don't ask where it is, because that doesn't mean anything. Rather than it's somewhere, but quantum mechanics, axioms don't tell us that thing that is definitely there. but unknowable to us. I'm extremely interested in ontology, like, what is something?

And then many physicists, they, in the first year courses, maybe second year courses, they act like that's what we're interested in. We want to know what is nature. Physics is the study of nature. In fact, the root of physics is Greek, which is synonymous with nature. Yes. Which is interesting, because we tend to separate physical nature from nature. But anyhow, that's what physics is, or that's what some people say physics is.

But then when you ask a professor, well, what exactly? exists in the world, they may give accounts that are just instrumentalists. They say, if you do this, then so-and-so occurs. Or what is length? Well, they'll say, that's what a ruler measures. Something like that. Yeah. Yeah, I hate that instrumentalist picture. You know, in very often when we talk about, you know, the struggle to understand cons and mechanics in the 1920s, encapsulated in the great Bohr-Einstein debate. that Einstein famously didn't like he felt our quantum mechanics was incomplete

it wasn't the whole story and Bohr was saying no that's it's everything and historically we say Borr has one of the argument another way of explaining that is to say Ball was the epistemologist and Einstein was the ontologist so Einstein believes in a objective reality that's out there that's knowable and the job of physics is to find out how nature is Boar's argument, the epistemological argument, is that the job of physics isn't to find out how nature is.

The job of physics is to find out what we can say about the world. On that point, I 100% subscribe to Einstein's view. I think the job of physics is to find out how the world is. And I think generations of quantum physicists going all the way back to Bohr, have somehow betrayed that principle of what the job of physics is. It's not just about what we can say. I mean, leaving aside the fact that all we can ever know is what we perceive with our eyes and interpret in our minds, you know, we're not seeing the world as it is. we're seeing it and capturing it and trying to understand it inside our heads.

Leaving that aside, there is, I think, an objective reality out there. And the job of physics is to get as close to that, I guess, ultimate truth about the nature of reality. And not to somehow chicken out and say, well, no, we can't go any further. This is the best we can do. We can't ask those questions. They're meaningless. Or we can't say what's happening when we're not looking. we may not know, but that doesn't mean there isn't something definitely happening when we're not looking.

Yeah, the 19th centuries, sorry, the 1900s, maybe 19th century, seems to be a history of people unconsciously saying, this is the best we can do, therefore any question that's outside this is meaningless. Yeah, and as far as I can tell, I mean, that attitude certainly was prevalent in the 1920s, and certainly around the circle of physicists gathered around Neil's Ball, who was, steeped in philosophy. We forget these days when physicists poo-poo philosophy as being a waste of time and they're just navel-gazing, they're not giving us anything useful, which of course is a very wrong attitude to have, very ignorant attitude to have. But certainly back in those early days, those physicists understood their philosophy. And as far as I can tell, from remembering reading all these biographies back as a student, the pervading philosophical view, point then was this idea of positivism or instrumentalism. I always think of it in my

Jim, explain it please in simple language terms. Two guys sit down and argue about something and then they realize they have no way of deciding who is right and who is wrong. If that is the case, just give up and go and have a beer and forget about it. That's sort of the positive positivist attitude or the instrumentalist attitude that, you know, all you can ever say is what you can measure. If you can't measure it, if you can't empirically show it, then it's meaningless. You know, there's no point worrying about it. And I think that was the attitude that then infected a lot of the thinkers among the early quantum pioneers. And that became the Copenhagen interpretation, it could have been very different. If Louis de Broi and Einstein and Heisenberg

had won the day, then we might have written our textbooks in a different way. It's the hegemony of the Copenhagen view, I think, that then prevailed. This is my editor's desktop untouched. There's 40 tabs. There's six drafts of a single cut. There's always a folder that's called final, inside another folder that's called final, and that mess is so much work. I appreciate very much a clean desk, a physical desk, and if my digital instantiation of a desk is messy, that also messes with my head. In other words, that mess is work. What isn't the work is what the machine made itself. System cache, broken downloads, installer leftovers, duplicate photos, etc. Clean my Mac, finds that, and removes only that. Space lens draws a map

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Get tidy today. Try Clean My Mac for free for seven days and use my code theories for 20% off. That's code theories, T-H-E-O-R-I-E-S at Clean My Mac.com. Yeah, my view is if someone says this is the best that we could do, to me, you shouldn't let your ontological learned helplessness

bleed outward to other people. I mean, some of the questions that I want to answer, that you want answered, that the audience wants answer, are meaningless questions that have no answer. I mean, interestingly, there is a tie between epistemology, so what we can know, and then ontology, which led to special relativity, the block universe in particular. So why don't you tell us about that? So it's an idea that grew out of Einstein's special theory of relativity, which he completed in 19, But it wasn't a view that he, Einstein himself, first stumbled upon. It came out of the thinking of Herman Minkowski, another physicist, of fact, one of Einstein's old tutors, who was the first person to say that time and space somehow, you know, they're no longer absolute, they have to be

combined into four-dimensional space time. That going all the way back to Newton and Galileo, there was this obvious idea, it seems obvious because it's common sense, that space is where stuff happens and time is time. It's that cosmic clock ticking by independently measuring the seconds, minutes, hours, years, absolutely everywhere in the universe. Because of relativity theory, Minkowski realized that that can no longer be true, that Newtonian-Galalayan picture of absolute space independent from absolute time doesn't work. You have to combine them, to get into four-dimensional space time. Why? Because of special relativity.

Because the notion that you have a principle of relativity, you can't tell if you're in a reference frame, if you're not undergoing acceleration, then you can't tell whether you're standing still or moving at a constant velocity. So everyone has the right to say they are at rest and everyone else is moving. The problem, of course, is that if I think I'm at rest and you're moving past me and you say you're at rest and I'm moving past you, well, we won't agree on things like how long an object is, distances in space or durations, intervals in time.

And so how do you reconcile that? I say, well, the time gap between these two events, these two flashes of light was 10 seconds and you say, no. it was only five seconds and we both use our clocks and we both think we're measuring it accurately. The notion of space time, which led to the idea of the block universe, is that, well, there is a way of reconciling our views, which is to say that within four dimensions, combined distances and time, space and time, the three dimensions of space with the one of time, now you have this new construct, which is hard for us to imagine, but it's four, because our brains are only three dimensions. dimension, or we can't think in four dimensions. But within that mathematical construct, we will

agree on distances between two events. But those distances are now, connect both distances and time intervals. And that's something that we all agree on, regardless of how fast we're moving relative to each other. So it became obvious that because of special relativity and what happens when things move close to the speed of light, Newton and Galileo couldn't be right. That was just an approximation. And the only way to make sense of everything was to say, we live in four-dimensional space time. Well, four-dimensional space time is everything and, you know, is everywhere and all times. In it, time becomes another axis. So we think of the three dimensions of space, you know, the X, Y, and I'll call it Z for your American audience axes.

I'm Canadian, but I think it still applies. Canadians still say Z, right? Or do Canadians say Z? I think so. Oh, gosh. I'm from Toronto. It's so close to what American say that. Okay, well, I was going to say,

I thought maybe because you're close to the UK. I mean, we think Canadians aren't. Yeah, we're the mix. You're the mix, exactly. So these three axes are mutually perpendicular, so they're right angles to each other. One axis is perpendicular to the other two. And then you say, well, time is the fourth dimension.

that has to be perpendicular to all three spatial axes. But where do you draw that fourth axis so it's at right angles to the other three? You can't. And that's because I'm wiggling my finger around, but I'm wiggling around within 3D space. Time is beyond outside of 3D space. By definition, it's the fourth dimension. Nevertheless, when we talk about the block universe, when we say, we want a picture of 4D space time. How can we get an image or what it means?

Well, we cheat. What we do is we say, well, space we know is three dimensions. It's a volume. But imagine space was just two-dimensional. Imagine we throw away one of the three axes and we just have cardboard cutout flat universe. Because then we have that third dimension free to give to the time axis. And so the block universe is a useful simplification of four.

D space time that allows us to picture some sort of 3D block in which two of the axes give a surface, which is space, and the third axis is time running at right angles to that surface. So you can think of slices, I think of like a loaf of bread. Slices of the loaf are all of space at a particular moment in time. And the idea of a block universe allows us then to think about events, distances, time intervals happening in space time, where we've sort of done away with one of the spatial axes just so that we can quite literally wrap our heads around it. I see. Okay, so I had a misconception about what the block universe is. I thought what you described was just space time, 3D space time instead of 4D space time. And the block universe was

that plus the idea that time is frozen. And so you just have... have the space time where there's no flow of time, privileged flow of time. Well, I think of the block universe as being, as habit, one of it, the axes is the time axis. And therefore, all times exist in the block universe, but they're there. You can pinpoint a point on the time axis and say, at that moment in time. So it gives us what we call the eternalist. picture, that all, you know, past, present and future are all equally real. We sit on a particular slice of space, of 2D space, because we've thrown away one of the dimensions, which cuts the

time axis at a certain point, and that's what we call our now. And we're conscious of that, now moving along the time axis. So that's why, you know, we perceive of time flowing. But that's us, that's our perception. As far as relativity is concerned, if you're looking at the block universe, all times coexist. So now is no more special than a moment last week or a moment a million years in the future. Any more than where I am now is any more special than where you are or where the centre of the Andromeda Galaxy is. All points in space are equally real. We may regard where we are as special because that's where we are. The same with the time axis.

What we regard as now is special because that's what we perceive as a present moment, but all times coexist in the block universe. Okay, so forgive me. Please dispel my misunderstanding. No, you've got me worried now. Have I been teaching the block universe wrong all these years? No, no, no. Let me tell you the way I understand it.

Yeah. We don't have a time in the block universe. universe because, I mean, this is the way I understand it, but I'm most likely incorrect. Please, please. So forgive me. Okay. Okay. We don't have a time in the block universe. We have space time without a hyphen. Many people put a hyphen between space time. I know. Yeah, I hate that. It's one word. Yeah. Right. Because it's a putty that's not exactly space, not exactly time, until you are an observer and your trajectory then traces out of time. Okay. So now you can have a time and a space when you're an observer. But then to visualize what the block universe

is, we can only visualize it from one observer's perspective, but the block universe is technically that plus the invariant structure that allows you to interpolate between different observers. So you can't exactly visualize it. Good. So that's what I thought the block universe was. No, you're right. I think you're right. When I think of the block universe and slices of space at the moment's time, that is indeed

from the perspective of some observer, some reference frame. And so, you know, all points on a particular slice for that observer, you know, if that's your, if that's their present moment there now, then all points on that slice are happening simultaneously at that moment. But another observer moving relative to the first, their slice of now will be at an angle. So there'll be events that I see as simultaneous that you see as separated in time. And so we don't, you're right. We don't. You're right. We don't. don't all see the same block universe. Maybe I'm being a bit too free and easy with the idea of a time axis. You're right. It is exactly that. It's not something that you can crystallize into a space axis and time axis unless you pick an observer. But of course, what observer are we talking about? This has to be someone embedded within the universe. The whole point of the block universe is the God's eye view that you can stand outside the universe. So it's not observer dependent. So there's that issue. Right. Right. I think the issue, not with what you've said, but what people visualize,

including myself, say, 10 years ago, is an isolated, it's an ice block. I mean, the easiest way to visualize it as an ice block, but it's some ice block of some observer, but then at the same time, there's not the observer, there's multiple observers. And so it's quite tricky to just visualize it at once. You've given me a challenge now to try and think of how to explain it more accurately. No, it's good. I like it, actually. Well, okay, so what is your view then on the block universe and the flow of time? And the arrow of time, which are distinct. Yeah, absolutely. So the flow of time is something that we psychologically think is a thing that's happening.

You know, we're aware of an ever-changing present moment. And this goes all the way back to the ancient Greeks, the idea of a river of time. It's, take your pick whether it's tight, you're standing on the riverbank and time is flowing past you, or you're on a boat being carried downstream by the river and reality is unfolding on the riverbanks. But the fact that time is flowing, things are changing is something that is absent in physics. You know, there's nothing in the dynamical equations of physics, the physics that describe how systems change over time

that has any notion of time flowing. Equations, they have the parameter, what's called coordinate time, little letter T that appears in the equation, and you put in a value for that, that tells you the state of the system at that time. You can evolve the equation forwards in time or backwards in time

and work out what the state of the system is at another value of T. of coordinate time, but time itself doesn't in and of itself flow in any meaningful sense according to physics. The arrow of time is different. The hour of time is something much more tangible and worthy of discussion within physics, whereas the flow of time is something that may be wrong, but we sort of dismiss it as being part of what in the book I call manifest time. It's the psychological time. It's very distinct from physical time and how time enters the laws of physics. How do those two connect? The manifest image of time and then the manifest,

sorry, and then the scientific one. That was the challenge I set myself in my book. Well, that's a huge challenge. But it's also a challenge that I failed to meet. Oh, I should say that while you're speaking, if for those who are listening, there are visuals on screen. For instance, in your book you have as one of the first images, a flowing diagram, which I'll show because Princeton University Press allows that to be shown. I actually checked. So that particular image will be shown. Great. And I'm very pleased with all those images, all the diagrams of the book I drew.

Oh, great. Obviously, Princeton University Press have artists who make it neat. with nice aligns and things, but they're basically all my artwork, you're very, very, very, very pleased with. Yes, so I think manifest time or psychological time is how we perceive it. And it has its issues.

You know, the philosophical problems of time, does time flow, is now special, why is the past before the future, those sort of things are part of how we perceive time. there are quite separate issues and problems regarding physical time, like how do you reconcile the different ways time enters our equations? Is it a dimension in space time? Is it simply a coordinate in dynamical equations?

Is this an arrow coming from thermodynamics? Those are real physical problems quite distinct from the problems of manifest time. But the overarching challenge, of course, is can you combine them? Not just solve those problems, but is manifest time just an illusion or can we reconcile it with physical time? And, you know, I have to be honest and say that that is, you know, after thousands of years of deep thinkers trying to come across here, I'd be arrogant and saying, but finally, in my book, I have come to the answer.

It's still a problem. That's what makes time such a fascinating subject. We understand what the problems are, we can debate them and discuss them, but we haven't come to a satisfactory solution yet. Maybe we never will. So let's suppose we just stipulate the arrow of time. Okay.

So we say there exists an arrow of time. Okay. Which I don't find that, in fact, space time requires an arrow of time. We can talk about it later. Okay. Okay. So anyhow, what I want to know is suppose you impose

you impose a structure of an arrow of time onto physics. That's not there, but you just say, okay, this is going to be the privileged arrow of time. Do we then have a reason to think this arrow of time of physics will coincide with our flow of time phenomenal experience? Well... Or do you imagine they could be separate or maybe... No, I don't think they can be separate. I mean, the fact is we have different mechanisms or ways of saying how an arrow of time could appear. There are different arrows of time. I'll say later why I think there is one

master arrow of time, one ring to whatever it is from the Lord of the Rings, one ring to bind them all or whatever. But, you know, so there is the arrow of time due to thermodynamics that coming from the second law of thermodynamics, which says that, you know, entropy can never decrease. It always increases or if it reaches a maximum, it stays at a maximum. So there's a an arrow of time from thermodynamics pointing in the direction of increasing entropy, increasing disorder. There's the causal arrow of time which says causes must come before their effects and not the other way around. You can't violate causality. There's the arrow of time from quantum mechanics through measurement. Decoherence is a system leaking away its quantumness into its surrounding

environment. The opposite doesn't happen. You know, there are arrows of time, pointing the direction of the expansion of the universe, the cosmological arrow of time. So there are lots of different ways of describing how and why time should be irreversible, move in one direction. The way we perceive time psychologically, how it manifests arrow of time, most would argue that emerges from the thermodynamic arrow, that increasing entropy, or, you know, a system that's off equilibrium is moving towards all. always try to move towards equilibrium. That increase in entropy, an hour of time, we can

trace it all the way up to what we call the psychological hour of time, why we, in our brains, why are we perceived time to move in a certain direction? So I'm not so interested in why we perceive there to be an hour of time psychologically. I think that's a lot of of as part of manifest time and it's sort of obvious. Of course, we get older and of course balls roll down hills and of course, you know, charge batteries go flat, go dead. You take a pack of cards that is unshuffled and you shuffle them, they become more shuffled.

Well, all of that is what we perceive to be a directionality to time. What's more interesting for me is, is the physical arrow of time, if indeed there is a master arrow of time, is that baked into the universe from the start, or is it simply just a subjective matter of how we look at the universe? And I would argue that there is a time is real

and the directionality of time is real. Of course, the big problem here is that all the dynamical equations of things, physics or the laws of fundamental laws of physics, say there is no hour of time. They work equally well forwards in time and backwards in time. They say they're time reversely a variant. So for over a century now, no, not quite. Yeah, yeah, over a century, nearly two centuries. Physicists have argued about how does an hour of time, the irreversible time that we perceive, emerge from time symmetric underlying laws?

And I argue very strongly in the book that that's the wrong way around of thinking about it. There is a directionality to time. There is an hour of time, regardless of humans, it's not subjective. You know, there was a direction to time before life existed on Earth. That arrow of time is the fundamental thing. The dynamical equations of physics, the equations of physics that tell us time is symmetric, they're not the full story. They are idealizations because they only apply to isolated systems. You know, you have particles of, you know, molecules of air in a box. If that box could be

perfectly isolated from its surroundings, then you might think with all the molecules gathered in one corner, over time they will spread out and fill the box. And you might say, well, look, there's entropy is increasing, there's an hour of time. But if you zoom into the molecular motion of individual molecules and run that movie backwards, you can't tell any difference. So the dynamical equations work equally well forwards and backwards in time. It's only when you zoom out, you coarse grain, you know, you look at the macroscopic details, that you see an emergent arrow of time.

But more fundamental is the time symmetry. but that only applies to isolated systems, the box of gas that's isolated from its surroundings. Nothing is truly isolated from its surroundings in our universe. For those molecules of gas to have been put in the corner of the box in the first place to move the molecules away from equilibrium, required the box to be interacting with its external environment. A piston. Someone came in and pushed those molecules into the corner. So everything is interacting with everything else. Nothing is truly isolated.

And because nothing is truly isolated, that always gives us an arrow of time. It's only when, you know, it's an approximation and idealization to say that a system is isolated, therefore we can use our time symmetric equations. They're a special case. The only system where you really could have time symmetric, time symmetry is the entire universe

because the entire universe is the only thing that is truly isolated because it doesn't have an outside. And so, yeah, we worry about how does a time's arrow emerge in a universe that may be timeless or maybe time symmetric, but that's a separate question.

For us, embedded within the universe, there is always a real arrow of time from the star. Ah, interesting. Okay, I thought you were going to say, at the level of the whole universe, we don't have time symmetry because of the big bang, because there's something special. Well, no, we do have time symmetry. So the idea there is that we say, look, today entropy of the universe is a certain value, and tomorrow entropy of the universe will be slightly higher. The time symmetric equations, if we're talking about the entire universe describing it with, time symmetric unitary evolutionary evolution, that should say that if you switch the direction of time

over and go to the past, then yesterday should have higher entropy than today, right? You know, entropy should increase in both directions if there's time symmetry. But there's nothing special about today. I could go back to last week and say, well, universe had a certain entropy then, move forward in time, I'll find that yesterday has lower entropy than. than today, today has lower entropy than tomorrow, and so on. But what's so special about a point last week? Time symmetry should say that a week before then entropy should have increased. So whatever you, whatever moment in time you pick, time symmetric dynamics suggests that you could

reverse time and things would work equally well in tribute increases of birth direction. So here's the trick that people do. They say, well, if we move that special moment all the way back to the Big Bang, since there's no time before the Big Bang, we don't have to worry about time symmetry. We're only ever worrying about all moments after the Big Bang in which entropy is increasing. So it's a cheat. It's called the past hypothesis. Right. Yeah. So the past hypothesis works, but it is a cheat because it breaks time translation invariants. And we've solved one problem, but we've arrived us another. But it's sort of a cosmological In the biologists in particular don't mind it, because, you know, if that special moment is the moment of the Big Bang, then fine. The Big Bang was a special moment. The universe is the beginning of the universe. In fact, I talk in the book about how, when we talk about how could the universe become the way it is today, well, we need two ingredients. We need those initial conditions, very special edition conditions, but we also need entropy to be very, very low. And I try and explain in the book that,

The entropy very, very low, a highly ordered universe is part of the special conditions. Just the nature of the forces, the nuclear forces, gravity, and the fundamental constants and the coupling, all those fundamental ingredients that the universe needed to have, the fine tuning, they give us a low entropy universe. So there is something special about the Big Bang and thereafter, you know, we have an arrow pointing into the future in the direction of the expansion of space and so on. Most skin care is built to react, so some wrinkle line shows up, for instance, and your cream is meant to smooth it over.

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while my wife opening it. Born from over 10 years of longevity research, One Skin is helping you unlock your healthiest skin now and as you age. For a limited time, try one skin with 15% off using code TOE at oneskin.co.com slash TOE. That's 15% off at one skin.com with code TOE. After your purchase, they'll ask you where you heard about them. Please support our show and tell them that we sent you. So something just happened recently. The economist sat down with Elon Musk, who told them that AI will surpass human intelligence within five years. And then in 10, humans won't. be running the world. It went viral, and I recommend you check it out. See, the Economist is more than a magazine. Actually, I subscribe to the Economist's annual subscription. Their science and AI coverage is among

the best that I found anywhere. And I say that as someone who reads plenty of it, they even covered how dark energy may be weakening with time. If that holds up, it completely changes our understanding of the universe's fate. Those are exactly the kinds of questions that we explore every week on this channel. Now, the Economist is, of course, known for global affairs, both political and economic reporting. Interestingly and flatteringly, Toe is one of the only podcasts that the Economist partners with. Quick note this just in. The Economist has a 60% off flash sale until the next couple days, only until September 23rd Wednesday. That's not a deal they have just anywhere. Head to Economist.com

slash toe, T-O-E, to subscribe. That's Economist.com slash T-O-E for 50% off the annual subscription. Is the low entropy of the Big Bang? Is that an empirical finding? In other words, do you look out with the telescope and say, okay, I write down the entropy of the Big Bang?

Or is this something we have to stipulate, put into our equations, and then the rest work? Well, it's something that, you know, the laws of physics as we understand them, tell us about the early universe. You know, we can trace back, you know, going all the way back, you know, beyond the cosmic microwave background to when the universe starts expanding, when it was hot and dense, and we can go through those different epochs in the evolution of the universe. So we know when it was very early, it was very hot and dense. We know that it was,

you know, apart from a few sort of tiny irregularities in, in, in, uh, uh, uh, uh, uh, uh, uh, the density and temperature of the universe, it was pretty evenly distributed. It was in thermal equilibrium. We also know that gravity didn't kick in straight away. So gravity was swaying in the wings. Gravity is what gives us the low entropy or part of the story of what gives us low entropy of the universe. So you don't have to measure something to know that if the universe was hot and dense and in thermal equilibrium and lots of particles buzzing around, they hadn't clumped together. So the universe was too hot for gravity to start clumping matter into denser regions.

So we know that. We also know from how the atoms were formed, how elements were synthesized from nuclear synthesis. The fusion gives us another, way of reason for believing how the entropy is low. The reason the sun is shining now is because it's a source of low entropy, because it's undergoing nuclear fusion, it's turning hydrogen into helium and other elements by fusing subatomic particles together. That is giving an increase in entropy. And so from everything we understand about the laws of physics and the forces that

govern how far particles behave, tell us quite clearly how and why the entropy of the universe near the Big Bang was so low. We don't need more than that, I would argue, empirically. Gosh, maybe this question is ill-formed. So please try to make sense of it. Okay. The statistical arguments you gave are time symmetric. And entropy, if it's low at some time here, actually will increase in the future, but also increase in the past. Right. Okay. So that's why they move the endropic, the low entropy condition all the way down to the Big Bang.

But then, how do we know that we're evolving into the future or that this is the past and the Big Bang is the future and we're just switching the arrow? Well, we don't. I mean, well, okay, let me rephrase that. if we believe there is a master arrow of time pointing in a certain direction, as I do, then I think, you know, it's not that increase in entropy due to the Second Law of Thermodynamics is what gives us an arrow. We have an arrow of time pointing on past the future, and entropy increases in that direction. It's sort of, it's a subtle switch of the argument. The universe expands in the direction of that arrow. Psychologically, we believe that time is pointing in that direction.

There was an idea, is it Thomas Gold, the Gold Universe hypothesis, which is that the universe is a big bang, it expands, and then it recalapses in a big crunch, and everything is symmetric. So if it starts off the big bang and time is moving forward and it reaches maximum entropy, then if it starts to recalapse again, if it's symmetric, entropy has to start decreasing again, right, to get back to a point of low entropy. Well, if entropy is decreasing in the collapsing phase, but psychologically we always think our future is in the direction of higher entropy, then the universe now may be collapsing, but, you know, as seen from outside, but we still think it's expanding because our arrow of time has switched over.

Now, there are reasons for dismissing that argument which I talk about in the book. But I think we're okay, as long as we say, look, there's an arrow of time baked in to the universe from the Big Bang Yang into the future. The one interesting idea that probably may rescue what you're saying is this notion of what's called the Mirrori. universe because we talk about, you know, is the Big Bang really the beginning of time? Well, maybe it's beginning of time for us. It's the beginning of our arrow pointing into our future. But there may be a universe heading back in time for whom time is pointing the other direction. So we think they're in our past pre the Big Bang. They think we're in their past pre the Big Bang. And of course, what's nice about that is now you've got back to time

symmetry. Right. With the Big Bang being a special moment, but there is a past as the same as the future. It's an idea. It's a theory that we have no empirical evidence for, but, you know, cosmologists do this all the time. They come up with these really clever ideas that are fun, but then they struggle to say how they're going to test those ideas empirically. Carlo Rovelli blurbed about your book. Yeah. And again, links on screen and in the description. but he doesn't believe in the fundamentality of time. Yeah. And you believe in the fundamentality of the arrow of time.

So tell me about that. Right. Well, because for me, you know, the big problem is what's called Loshmits Paradox, the idea from the 19th century that, you know, how do you reconcile time symmetry in our dynamical equations with a directionality and irreversibility, irreversibility of time coming from the second law thermodynamics, how does irreversible time

come from time symmetry? And I argue in the books the other way around, within the universe, because systems are not isolated, there is always a direction to time moving from off equilibrium towards equilibrium. The arrow of time is fundamental. Time symmetry is only true when you're dealing with an isolated system. And so, for me, the arrow of time is baked into the universe. And if the arrow of time is baked into the universe, then time itself must be real. You can't have time an illusion, but an arrow that's real. The arrow of time, the directionality of time requires time's reality at a more

fundamental level. So in that sense, yeah, I would disagree with Carlo Rovelli. who regards everything is, you know, all about relations between things and time itself isn't real. But that's the lovely thing about, you know, working the foundations of physics, you know, Carlo Rovelli might disagree with Brian Green about string theory because Carlo Rovelli is an advocate of loop quantum gravity. He doesn't like many worlds interpretation, so we'll disagree with the likes of Sean Carroll. We disagree. It's almost philosophical disagreements because it's really, you know, if there was physical evidence for one argument over the other, then we'd have to give up on the argument that is wrong.

So for me, time is real and it's fundamental. Although there is this issue of whether time is emergent, you know, is it really baked in from the very start or does it, is. emerge from something more fundamental. There I'm open-minded on. It may well be the case. We don't have a theory of quantum gravity yet that we can all agree on. It may be some form of string theory. It may be some form of loop quantum gravity. It may be causal set theory. There's also these candidates of unifying the laws of physics together to this so-called theory of everything. And I think until then, we're not going to have an answer about what time is. And so it may be that time emerges in the same way that, you know, temperature emerges from more fundamental

particle vibrations, you know, there's no such thing as temperature when you're looking at just the movements of individual molecules. You zoom out and suddenly temperature appears. Or there's no notion of the wetness of water when you're looking at individual H2O molecules. That's something that emerges when you zoom out. more complex ideas are things like consciousness. Consciousness doesn't exist at the level of individual neurons firing and talking to each other. It emerges when you zoom out and you have tens of billions of neurons all interconnected. So it may be that time is a feature of reality that emerges out of some fundamental quantum domain,

from quantum entanglement, for example. But for me, that doesn't make it less real. It's still there. and the reason I think it's real is because I think the arrow of time itself is real. As I say, to have an arrow, you first need time for that, to have something to make the arrow out of. Why is it that time has a special arrow, but then space doesn't? Because time isn't like space.

I mean, I guess one might also argue, why do we perceive, there may be more, but why do we perceive of several dimensions of space, three dimensions for us, maybe other hidden dimensions, who knows if string theory or M theory is correct, but we only have one dimension of time. So time isn't the same. When we talk about time as the fourth dimension, that doesn't mean it's democratically at the same level as the dimensions of space. It is different.

And so I guess, I mean, I hadn't really given this too much thought, I guess the directionality, the error of time is unique to time in a way that there is no directionality to space because there's more than one dimension of space. Time, we perceive time as changing as well. You know, we don't perceive spaces. Well, okay, the word change requires time, right? And philosophers have argued, you know, what is more fundamental is, do you need time for there to be change? Or is change what gives us the concept of time? We don't have that same philosophical problem when we're talking about the dimensions of space. They just are. I mean, a foolish question, which is foolish, so forgive me, that I asked Simon Saunders, is that, look, if in special relativity you can always boost and trade your time dimensions for a space dimension,

then why can't we trade some of the... these time paradoxes by boosting into a spatial one where there is no paradox. Okay, what does Simon Saunders tell you? Yeah, I mean, relativity works and space time diagrams are useful tools, but I don't know how literally one should take. them. Certainly, yes, you're right. You know, you can, you know, the space time interval between two events, according to one observer has a little, has a bit of space and a bit of time.

Another observer will measure the same space time interval, but their distances and time intervals will be different if you separate them. We can't measure space time intervals directly. We always have to measure distances in space using rulers, measuring sticks, tape measures, and we need to measure intervals and time using clocks. So inevitably, you know, we have to separate 4D space time into three dimensions of space plus one dimension of time. And the boost, the switching over a bit of time becomes space or space becomes time is what we do when we carry out transformations between reference frames. But I don't know if that how literal, we should take that.

The question you asked Simon was what? Supposing, there are no paradoxes of space. Not in the same way we have paradoxes of time. Oh, I see. Okay, okay. I see. So, yeah, if we transform and boost to convert time into space, do we lose those paradoxes? Do we dissolve some paradoxes? Yes.

Or furthermore, do we gain spatial paradoxes, if you boost from space to time. I'm going to have to think about that. I mean, what I don't want, I don't want to give you some off the top of my head B.S. exploitation without thinking. It's an interesting point, and I have to say I haven't considered that yet,

but you've got me thinking. But now, last question. Suppose we believe in the block universe, okay? Yeah. So we're eternalists in a sense. And then we believe in the non-local. of quantum mechanics as being somehow more than just correlational, then why can't we use that to send information back in the past?

Because if you have faster than light and special relativity, you can send information to the past. Well, I think advocates of DeBroy-Bome, pilot wave theory, would say that that's because relativity itself is wrong. The block universe picture is wrong. In principle, you should be able to send signals instant. If the universe is truly physically non-local, and if two entangled particles on either side of the galaxy

can literally instantaneously talk to each other, then you're sending signals way beyond the speed of light, which means relativity is wrong. You can synchronize clocks. All clocks in the universe could be synchronized because you can tell it. Each clock can tell all other clocks instantaneously how to synchronize their time. I guess, so I guess that, you know, if relativity then has to fall, then the block universe itself is no longer a valid picture. It's a big price to pay, but it can't be ruled out.

You know, the reason why relativity seems to hold for us is because we haven't been able to work our way through the quantum fog of maintaining local connections in reality, even if at the quantum level, things are truly non-local. Now, this is more an English question than it is a physics question. But Einstein said quantum mechanics was incomplete. And then just a moment ago, you said, if BOMians are correct and special relativity is wrong. Now, when I spoke to Roger Penrose, he said Einstein said quantum mechanics is incomplete, but Roger believes, Sir Roger, believed Einstein to have been too polite. Roger's like, no, I think quantum mechanics is wrong because it needs a major modification. If your theory needs a major modification, it's just wrong. It's not incomplete.

Incomplete is a synonym for wrong to him. So I want to know, would you say that special relativity in the BOMI, case is wrong or needs to be modified because incomplete, at what point do you say a theory is wrong versus incomplete is the question? Yeah, okay. Well, that's probably, I mean, I don't agree with Roger that it's quantum mechanics that has to give way. But he's probably right in this idea that incomplete is the wrong term to use.

Incomplete might mean, approximate, right, in the same way that Newtonian gravity is approximate. It's wrong in terms of the picture you used to describe it, you know, instantaneous, invisible force between masses rather than what we regard as the more correct way of curvature of space type and general relativity. So we wouldn't say Newtonian mechanics is incomplete. nor would I say it's wrong. I would just say it's approximate. So maybe Einstein should have said quantum mechanics is approximate and there is something better beyond it. And equally well, it may be that relativity, special relativity or general relativity is also approximate and there is something better beyond it. You know, which one has to give way is the big. challenge of modern physics. How do you unify quantum mechanics, quantum field theory with general relativity? How do you bring them together when they're two very different pictures of reality?

Or does one have to change? Does the other have to change? Or do they both have to change? We don't know. And that's in a sense the argument between various candidate theories of quantum gravity, whether it's string theory or loop quantum gravity. So yeah, I think Rogers correct that incomplete is too polite but I wouldn't say wrong I would say

approximate in the same way you desire Bohmian mechanics to be correct do you have a certain preference for which quantum

gravity approach is correct um I don't have a dog in the fight I mean that that's I guess the truth you know I am I'm I don't work in quantum gravity

um Jim what does your heart tell you well my heart tells me that to have the correct theory of quantum gravity, it's not simply a matter of reconciling quantum field theory with relativity. There are two things. One is that we should not forget about thermodynamics. There are three pillars of physics. There's quantum mechanics. There's relativity and there's thermodynamics. We have quantum thermodynamics, which is a new hot topic at the moment. We have relativity and thermodynamics, ideas about things like the Black Hole paradox and so on, the information.

theory. And we have quantum gravity, quantum mechanics. So like, there are pushes to bring two of those three pillars, any two together, but I think we need to bring all three together at once. And the reason for that is because that's the only way we're going to understand the nature of time. Time enters quantum mechanics differently from the way it enters relativity and differently from the way it enters thermodynamics. In one it's a coordinate, in another it's a dimension of space time, in another it's an arrow, and I think we need to bring all three together.

We need to understand the nature of time. So my hope or view is that the correct theory of quantum gravity is the one that gives us the most sensible picture notion of time itself. And I don't think string theory or loop quantum gravity cut the mustard, as they say. I don't think they do the job. Certainly ideas like causal set theory is a sort of a lesser known candidate for theory of quantum gravity treats time in a way that I find more comfortable, that time is real. and then there's a directionality to time, you know, for cause following effect, sorry, cause coming before effect.

Right. I'd reverse the arrow suddenly. So, yeah, I have sympathy for people working in causal set theory in a way that I don't have, followed by loop quantum gravity, because I like Carla Rovelli and Lee Smolin, you know, because then, last guys, I have nothing against string theory. I'm just one of those nor am I one of those physicists who says string theory isn't even science and what a waste of time and effort but it has

I feel it's sort of had not had its day it hasn't given us anything after decades of so much effort and so many smart people working on it it's very powerful mathematics

but it hasn't led to the success that we might have hoped after so many years. So for that reason, I'm sort of not as big a fan as I may have been when it first started off. Right, right. I mean, it's always tricky. You have to say what you said so carefully because there are successes that have come from string theory, but the difference is there were some major promises or at least major hopes that came from string theory early on. Some of them have not been realized, although there are some important advances that have come from string theory.

Absolutely, there have been, you know, holography and ideas like that that I think are very important. And we'll prove to be correct, you know, if we're talking about the ontology, about the nature of reality, they'll prove to be correct. But at the moment, string theory is very much very clever and powerful mathematics, rather necessarily the way nature is. To come full circle, speaking about ontology, when we talk about what is time, see, when we say what is a quark, we have an idea of what a quark could be. It's a particle. I mean, that's one potential answer to what is a quark.

Another is that it's potentially a string if you look close enough. Another is that it's, I don't know, whatever. It's actually a field and then you have to excite. Okay. And maybe there's fourth and fits. But when it comes to what is time, I mean, that's a bit trickier to think about

what the heck would a satisfying answer look like. Because it's not as if we're looking for this. This is what time is ultimately, that you can just hold and it's right here. Yeah. Yeah. I think inevitably we're never going to be able to say what time is because unlike any other physical concept, even space, you know, we are embedded in time. You might say, well, we're also embedded in space. But we're still able to talk about what space is in a way that we can't talk about time. Time, maybe because of manifest time, our psychological view,

but the fact is we are embedded within it and you can't describe it from the inside and you can't step outside of time to talk about it objectively. We can't conceptualize and talk about things like the block universe and so on, or we can do equations and very clever equations and time. And so, you know, very early pioneers of quantum gravity came up with, you know, the Wheeler-Dewitt equations, an equation that sort of describes quantum mechanics and gravity together, and it doesn't contain time at all. Therefore, people talk about, well, maybe the correct theory of quantum gravity is indeed timeless. Time doesn't exist in the entire universe. So there are ways of abstracting how time enters the laws of physics. But ultimately, I don't think we'll ever

be able to say objectively what time is, because we can never pull ourselves outside of it and look at it from the outside. We're carried along that river of time, you know, and we can't stop it. That's the best we can do, maybe. Why does Embedinus put a limitation for us knowing it, Well, I hope that's true. I hope it doesn't. I hope that despite being embedded within it, if I'm a true ontologist, then yeah, I should subscribe to that philosophy, that physics is about finding how nature is, not what we can say about nature. And that should include the nature of time itself. We should be able to say what time is. It's hard to see how we would do that. What is time doing when no one's looking? It's carrying on as, you know, it doesn't care that no one's looking. It's carrying on, you know, time existed before there was life on earth. Time started the big bang.

There was no one looking and time was moving and it had a direction and events were happening and there was change and all the time there's change, you know there's time. Even when there's no change, there's still time. Wait, but do you believe there's change? change? Yeah. Yeah. I believe, well, okay. Sorry. Yeah, yeah, yeah, no, no, see, this is where, this is where, you know, the philosophy comes in in the same way that do you believe there's a flow of time, you know, is change synonymous with time flowing, and our equations of physics don't say there is. Allow me to paint the picture just so that we can be clear, and also I can show something on screen. So, remember this hairy ball, there's this theorem about, you can't, Coma Harryball. Okay.

Right. And then there's a vector field on a sphere. But in the block universe, supposing we're taking one person's perspective and we just have this this 3D universe,

then the flow of time also becomes like vectors in this block of ice. They're just vectors. It's a vector field. Right. But there's not flowing. You can have a vector field

without flowing per se. So that's what I'm viewing as what you mean when you say there's an arrow of time. And that's why I was asking about, does anything actually change or is it just that

right there with arrows embedded but there's no changing arrows or prefer foliation from which everything is just moving up or ad upward yeah I mean if I'm arguing

that time's arrow is baked in to the universe pointing in a certain direction then and if the causal arrow of time points in that direction

then I guess if the block universe is coming out of relativity and relativity says you can't violate causality, then, right, your arrows might be not exactly parallel, but there's a limit to how off parallel they can be. They still have to be broadly pointing in a particular direction, the direction of the expansion of the units, the direction that started from the Big Bang outwards, the direction of cause coming before its effect, the direction of increasing entropy,

all those different arrows are following this master arrow. And yes, when we're moving relative to each other, we will have different perceptions of the relativity of simultaneity, we will have different notions of time, but we're not going to see cause and effect switching over. So in that sense, for me, the arrows of time can't be too far away from being,

they won't point exactly in the same direction, but broadly, they always, they can't be opposite to each other. They can't, on a sphere, they can't, you can't have arrows of time pointing in opposite directions because no observers would see that. Speaking of time, thank you for spending so much of it with me and with the audience. Again, links to on time are going to be on screen as well as any other relevant links and gosh I want to know because I'm writing a book right now for Penguin Press called the edge of everything about modern physics and then the various other subjects which I won't get

into here but it's it's killing me it's so much work it's so extremely difficult it's extremely difficult to write yeah yeah yeah and and you know for me I'm at a different stage because I've written my book it's it's about to be published and and you'd think that ah I can just sit back and enjoy the acclaim. You know, great ideas. But no, I'm doing podcasts with other smart people, and I'm having to think really hard and realize, damn it, there's still stuff I don't understand.

There's so much stuff I don't understand. So, yeah, the struggle doesn't end when you've got the final products, when you've poured all your passion and your thoughts, your ideas into a book, and it's now in print. You can't sit back and enjoy, reap the reward. You're still, in a sense, people want to quiz you about why you think this and why did you write that? So, yeah, I'm going to have to go and lie down now anyway. I just wrote on Substack that they say writing is in the rewriting.

That's where the true writing is. But for me, writing is in when you put it on the page and you realize how humdrum and foolish you are. That's when the real birth of writing begins. Well, as long as that doesn't put you off, as long as you don't get disillusion to think I will stop. You just keep going. No, no, no. Not for me. Okay, well, thank you.

Where can the audience find out more about you? Well, I have a Wikipedia page that's very, very out of date, but I do have a website, Jamalcolili.com, without the hyphen, which I try and keep up to date. So, you know, I point to my new YouTube channel. I'm baffled where, you know, I'm doing some. I've done a lot of TV documentaries over the years of the BBC. Some of them are now on various streaming. platforms like Prime and Netflix.

And a lot of them on YouTube. I didn't put them on YouTube, but someone else has done and is getting a lot of commercial revenue from them. So you can find a lot of my stuff on YouTube. My books are sold in all good bookshops. But yeah, I think let's see how on time performs and what people think of what people think of it. There's some hard topics in there. You did say, in the Princeton University Press released,

you did say this book exemplifies who you are as a physicist. Something like that. Can you tell me why? Because, you know, other books I've written, this I think book number 15. Congrats, by the way, whole in the world. Thank you. It's killing yourself 15 times. Well, I mean, I've been around the block a few times. But, you know, there are either been things that, you know, I've taught or that

interesting subjects that I know about and I'm an expert in quantum mechanics or relativity or whatever or there could be things on the history of science which I've had to research. But this is the first book where I've really struggled to try and get clear in my head what I think about the subject before I can put it down on the page. It didn't come automatically. You know, endless nights on the edge of sleep, trying to think of a new metaphor or analogy, and how do I explain about the isolated systems interacting with the environment? What sort of example? Yes, and I very much like that. I very much appreciate that. That to me is what makes a good book. Partly is why I hate myself, because I'm trying to do something similar. I don't want to,

I want to invent ideas as I'm creating the book. I don't want to pre-think it and then just write down what I've already thought onto the page. And I find, so Gertil Asher, was like that, where you see a playfulness and an invention. Absolutely. It's hard to do that, but it's also the most satisfying way of writing, rather than regurgitating other people's ideas. If you can find an original way of explaining something or thinking about something, that's extremely rewarding. It says as rewarding as rewarding as doing fundamental research. Well, again, thank you so much. And I hope to speak with you again. I hope we get to meet someday. Thank you. I hope so too. Thanks very much. It's been

good fun. Hi there, Kurt here. If you'd like more content from theories of everything and the very best listening experience, then be sure to check out my substack at kurtjymongle.org. Some of the top perks are that every week you get brand new episodes ahead of time.

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