256 - Tim Maudlin: A Masterclass on the Philosophy of Time

30:52All very kind of, okay, good. Now, go ask such a person who says that to you the next time. Hmm. Okay. Do you think the quantum wave function is complete or incomplete? This is a question that, you know, we, I think have talked about. I hope so. Einstein famously argued that the wave function is incomplete. And this is, this is a point I'm sorry for stopping you here since I brought the wave function up first, but maybe we should just say in a couple of sentences, what the wave function is. Sure. So the wave function, again, So my preferred vocabulary is to distinguish a mathematical object from a possible physical object.

31:35The mathematical object I call the wave function. Why? Because functions are mathematical objects, right? Functions just are pieces of mathematics. And I am so glad that you say this. Just because you hear people say the only real thing is the wave function. And I want to say, but that's a math thing. That doesn't make any sense. And again, my tagline a lot is the way mathematical physics works is to try to use mathematical objects to represent physical ones. Right. And if you're a philosopher, you should have thought long and hard about how any language can manage to represent any non-linguistic thing, right?

32:18The representation relation between a linguistic object, whether it's mathematical or just in English or Chinese or whatever, you know, on the one hand, you have this representational system. On the other hand, you have the thing that you're trying to represent. And then if you think, well, how is it that this thing manages to represent something about that thing, right? It's very funny to me that this episode is meant to be about the physics of time and the philosophy of time, continuous though they may be, but I think this might be the most important lesson to come out of it. I really do think it is because you can't try to think about physics if you're unclear about this distinction.

33:01So there's the wave function, okay? It's just a mathematical gadget. it in certain physical circumstances by means of pretty good rules of thumb anyway. Starting in 1920s, we kind of know how you assign wave functions to some physical systems, usually atoms and electrons and things like that. And we know how to mathematically manipulate those things in order to make certain predictions. And those predictions in many circumstances turn out to be astoundingly accurate. And so your thought is, gosh, that mathematical gadget is somehow getting at something or other, right? It's somehow representing something or other about that system.

33:46Now, the thing, it doesn't make any sense to just say the physical object has a wave function for the reasons we just gave. That's a mathematical thing. What I, my preferred locution is, if you think an individual system has a physical feature that is fairly directly, and fairly directly is something you have to think hard about, but just leave it a little vague now, fairly directly represented by this wave function, call that thing the quantum state of the system. Okay, so then you say, okay, systems have quantum states. Individual systems have quantum states. Now, Einstein didn't believe that.

34:31He thought that he didn't disagree there were wave functions, and he didn't disagree you could make pretty good predictions with them, right? I mean, he wasn't, he knew what was going on. He thought that wave functions just don't represent anything about individual systems. He thought they were kind of statistical summaries of large ensembles or large collections of systems. So the fact that the wave function was, as it were, spread out in space, as we might say, doesn't mean that anything in an individual electron is ever spread out in space. It just means that if you take a whole bunch of electrons, then they're distributed in space, right?

35:11That spreading of the wave function for Einstein was not a physical characteristic of the individual system. It was a collective characteristic of an ensemble of systems. That turns out to be a very hard doctrine to make sense of because of two-slit interference. I mean, things we can talk about. They're quantum phenomena that don't seem to be explicable if you take Einstein's view there. And I think most of us think Einstein was wrong about that. And I think it's very hard to make any sense of quantum theory without thinking there is a quantum state of individual systems. And let's add, because of entanglement, ultimately there's only one quantum state, and that's the quantum state of the entire universe.

35:59Because once two things get entangled, you can't even ascribe them individual quantum states. So, yeah, there is a – I mean, I think it's – we have every reason to believe there's a quantum state. There's ultimately one fundamental quantum state. Now we're back to fundamentality. It is the universal quantum state. That raises a real interesting question, by the way, which most physicists have never even thought about. But I never used that to make predictions. I wouldn't know how to use it. I mean, nobody knows what that is. I mean, the entire quantum state of the universe. Somehow, in certain laboratory situations, I'm able to ascribe wave functions to little subsystems.

36:49So the people who talk about this, I mean, Shelley Goldstein, a lot of the Bohmians talk about this, because it's an easy way to understand the theory, is there's a big psi, capital psi. That's the fundamental physical one. Or, you know, that mathematically represents the fundamental physical quantum state, which is the universal quantum state. Then there's little psi. That's the one we actually use to make predictions with. We attribute little psi somehow to subsystems. And that raises a very interesting question is why are we, why does that work, right? What is this little psi? Because it's not independent of the big psi.

37:30Somehow the big psi and whatever else there is has to determine the little psi. How does it do that? We're back to fundamental and derivative. The big psi is fundamental, or the big psi represents something fundamental. And the little psi that we actually use doesn't. It represents something derivative. It represents something constructed. It turns out in a kind of pilot wave approach, you can give a very clean mathematical account of how that works. In other approaches, you can't. How they explain it is a bit of a mystery, not one they've ever thought much about. So ultimately, the question of ontology, which is the question of metaphysics is what is there.

38:17And there's lots of things that exist that are not fundamental, right? This chair exists, it's here, but it's not fundamental, right? It's derivative. It's made up of atoms or something all put together in a certain way. That's why, as, I mean, David, again, David Albert has a nice example. He says, look, Look, for non-fundamental things, you don't worry about conservation laws. So his example is, look, what about fists? What's a fist? Well, there are fists. Here's a fist. Fist is just a bunch of fingers curled up. What does that mean? It means there's no conservation law that there have to be n number of fists in the world.

38:59Look, you know, now there's one. Now it's gone. Now it's here. Now it's gone. Okay, big deal. Why? Why is that not a big deal? Because it's not fundamental. It's derivative. It's just an array. A fist is just an arrangement of fingers. It would be much more disturbing if my fingers suddenly started disappearing and reappearing, right? Although they're derivative too.

39:24So the first question of ontology is what exists? Then you say, ah, yes, but what fundamentally exists? What is it that I need to postulate that doesn't get explained in terms of anything else and everything else gets explained in terms of it? one of the things there seems to need to be that physics is telling us is a universal quantum state. We need to have a space-time. That space-time has to have a structure. Newton attributed it a certain structure. Special relativity attributed it a different structure. General relativity attributed it yet a different structure. I think, as I said, the correct answer isn't any of those three, but in certain ways it may be closer to Newton than to Einstein because of non-locality, because of quantum mechanics, who explained quantum mechanical effects.

40:18Now, we started with all this. I'm going to go back. I haven't forgotten. With jittery space-time, right? Because you said, oh, they say it a microscopic, jittery, jittery, jittery. Okay. So there's this fundamental question about quantum theory, which was brought up by Einstein from the beginning and famously in the EPR paper, and the title of that paper is something like, the English isn't quite right, is quantum mechanical description of reality complete. And complete there in that title means, does the quantum mechanical description somehow describe or represent everything physical? And by the quantum mechanical description, they meant the wave function, right?

41:07That's what they meant. Does the wave function that I attribute to a system somehow or other reflect every physical fact about that system? The whole point of that paper was to argue no. That was their conclusion. They thought we need to go further with quantum understanding quantum theory that as it stood, it couldn't possibly be the final story. Now, most physicists today, if you ask them, is it complete, leave aside gravity. Okay, gravity comes with just, they would say, yes, yes, it's complete. Einstein was wrong. Einstein blew it there, right? He needed to take quantum theory more seriously.

41:53So let's suppose the quantum description, the quantum wave function is complete. Everything about the system is somehow reflected in that. and now you say, okay, so good, there's a vacuum state. So people will talk about the vacuum state in quantum field theory. I'm sure you've had people talk about the vacuum state in quantum field theory. There are other more complicated things to say about it, but let's just start here. There's a quantum state. Good. Suppose that I've got a quantum vacuum, And then they'll say, oh, in that vacuum, it's all jittery. Things are, there's all this vacuum energy.

42:34You say, really? Is that quantum state itself changing in time? Does it alter a speck in time? Nope. Static. Stationary. They can't disagree with that. It's just a fact. In quantum field theory, the vacuum state, unless you poke it, is stationary. If it's complete and it's stationary, ain't nothing changing. Right? It's complete. It somehow represents everything. It's stationary. It's not changing. Conclusion, on that basis, nothing's changing. Nothing's jittering. Nothing's jumping around. Nothing's fuzzy. nothing's buzzing around. Can't be. If you want to say the kinds of things that you've heard Brian and many other physicists say, you can say them, but the first thing you have to say is, I don't think quantum mechanics is complete.

43:36I think that there are other physical facts about systems that are not represented by the quantum state. And what's interesting, I think, in this case is that Brian's a string theorist and string theory is just fundamentally quantum mechanical. Yeah, Brian's a string theorist. But again, and let me just say this about all string. I mean, let's walk back before string theory. Before string theory, people said, okay, there are particles. They talked about particles. And a classical particle, one might easily say this is what just the word particle means in normal English is a small located object, right?

44:23It is a small thing that has a specific spatial location. And one might also say it's typically thought that that location only changes continuously, like particles don't just disappear here and then pop up over there, right? They follow continuous trajectories in some sense through space-time. and therefore you can reasonably ask of a particle at any time, where is it? And where was it a second ago? Now, if you ask a quantum, a normal physicist in quantum theory, are electrons particles in that sense? They'll say, no, they're not. No, they don't have any particular location until you measure or until you look or something like that, which you're going to say, what the hell?

45:16You mean when I look suddenly, and this is the way they talk. When you look, you force it. It didn't have a location, but you force it to make a decision about where it's going to be or something like that, which is just kind of insane, right? My eyes don't have this magical power over the world.

45:36So they're really not entitled to talk about particles. Because what entitles you to talk about particles is postulating that there are these little small located objects that move and they don't believe in them. Now, the same thing happens in spades in string theory, right? If you talk to a string, if you talk to just to put somebody who's really leans into this, like Michiko Kaku, oh, string theory is telling us the world is made up of all these vibrating strings, like violin strings, and they have harmonics and they wiggle this way and they wiggle that way. Oh, really? Does it? Are there really one-dimensional string-like objects, according to you, that are vibrating in space and time?

46:21And if you push them on that, I guarantee they'll say, no, I don't believe that, because that would be like believing in particles and particle theory. Oh, no, I don't believe that. It's a quantum theory. Of course, there aren't really any vibrating strings. They have to say that. If they don't say that, then I don't know what they're doing. Maybe they're doing a pilot wave. I mean, there would be a pilot wave version. Maybe this will help. There could be a pilot wave version of string theory, which postulates there really are one-dimensional strings and they really do vibrate. Just as in pilot wave theory, when they say there are particles, they mean there are particles.

46:58They're little located objects and they move around. and you could say they're little one-dimensional objects and they vibrate or they're little two-dimensional objects and they vibrate this way, you know, brains. You could say that, but I will guarantee you Michiko Kaku, if you push him on that point, or Brian, if you push him on that point, will say, no, no, no, of course, I don't believe that. And now the next thing, well, what is it you believe? If you believe the wave function is complete, then nothing's buzzing around, nothing's changing. And there's a whole bunch of language here about quantum fluctuations.

47:33You'll hear that a lot. Next time somebody talks about quantum fluctuations, ask them what's fluctuating. We know what a fluctuation is. A fluctuation is some physical quantity that's changing. It's fluctuating. It's changing in time. It's kind of randomly changing in time. The wave function's not fluctuating. So if you think something physical is fluctuating, you are committed to saying the wave function is incomplete. But just ask them point blank, do you believe the wave function is incomplete? There's not consistency. This stuff has not been thought through. It's cobbled together from a kind of sort of idea here and kind of a sort of idea there and a lot of appeal, interestingly, to classical physics, right?

48:19A lot of explanations that they'll basically give you a kind of explanation like Newton would give you, They kind of like to do that because you understand what Newton was saying, right? There are particles and there, you know, but then you say, are there particles? No, there aren't particles. But then all your explanations that appeal to particle motions, you're not entitled to them. So the real question is, can I articulate clearly a fundamental ontology where I say, this is the stuff I'm not going to further try to explain in terms of something else. This is the structure that it has. The only things I'm going to write down in my fundamental equations of motion are these things, right?

49:11Represent them in these things. And I'm going to try and explain what I see in terms of that. I'm going to try to explain how I can be wiggling my fingers around because at a fundamental level, say, I've got particles and my fingers are made of these particles and here's how they move and here are the forces between them and here's how they hang together, right? That's perfectly good. That's what physics and science in general is about. But you shouldn't be able to cheat at that. You shouldn't be able, when you get down to the bottom level, all of a sudden go fuzzy in your thinking and say, yes, on the one hand, the wave function is complete and it's not changing.

49:51And on the other hand, things are all wiggly and jumpy. And those don't go together. Just logically, they don't go together. So make up your mind. if the upshot of all of this is that quantum mechanics is indeed not a problem for the directionality of time then i'd like to return to where we left off we branched away from time reversal invariance right and the time reversal invariance of physical laws is often suggested to be a problem for the fundamental directionality of time. So again, this brings us back to something else you said, the distinction between representation and object. But what is time reversal invariance, and why does it not pose a problem for the fundamental directionality or fundamentality that you believe time to possess?

50:45Good. So let's talk for a minute about the kind of invariance people mean in general before we get to time reversal invariance. So usually what's meant by a physical invariance or a physical symmetry is that if the laws of physics allow for something to happen, then there are certain systematic changes you can make, and you'll say the laws of physics, if they allow for this, they have to allow for that. Here's an obvious one, what's called rotational symmetry, at least at the level of the lab. Okay? So, you know, I do an experiment, and I'm going to assume, which might not be true, but for these purposes that the lab is kind of isolated from what's outside the lab, because I'm not going to be able to impose this symmetry over the entire universe.

51:49I can only do it in the lab. But imagine I do an experiment, and that assumption might not be true. You have to be a little careful here. Just to take a concrete example, we all know about the Nicholson-Morley experiment. We've talked about that. At one point, I said it's an interesting experiment to describe. One of the interesting things about it was they carried it out. They had an apparatus. They had an apparatus that was taking light and splitting it and sending it two different directions and recombining it to get these interference bands. But the entire apparatus was sitting on a big stone disk.

52:25And that big stone disk was floating in a pool of mercury. Why? Because they wanted to be able to take this apparatus and turn it, rotate it, right? So I'm going to set it up this way, run my experiment, take some data. Then I'm going to turn it 90 degrees, run the experiment, take the data, right? Now, in most cases, what you would expect is that the data will look the same. Now, of course, that's not always true. If I just put a compass needle there because of the ambient magnetic field of the earth, it wouldn't look the same, right? But again, we're assuming that somehow we can shield the lab.

53:14I mean, we could even put metal around it so the magnetic field of the earth doesn't penetrate into the lab or whatever. But you think the kind of, suppose I've got the laws of physics and suppose I imagine, according to the laws of physics, the situation where there's just no magnetic field, there's nothing outside the lab, the lab is sort of all there is in the universe, the rest of it's vacuum, that's empty. Do the laws of physics say that if I rotate the system, that you'll get the same data, essentially? We normally think that's what you'd expect. In fact, what we think is that if that doesn't happen, then it's your obligation as a physicist to find out what is this thing you're not taking account of, right?

54:04So this is how you might discover there is a magnetic field is because, wait, you know, I've got this little thing in my hand and I turn it like this, but the little pointy thing doesn't turn, right? It keeps pointing this way. That's just an indication that I haven't yet accounted for everything. There must be something that's, as it were, determining that it aligns this way. Of course, we think that if we were to rotate the entire Earth, the magnetic field would rotate with it. And again, now the results would show up the same in the data. So that's basically what a symmetry is, right? Symmetry is supposed to be a transformation of the physical situation that doesn't create any qualitative or observable difference.

54:55And we typically think that space is isotropic, which means if we were to rotate everything relevant, nothing would change. And homogeneous, which is that if I do the experiment here and then I pick it up and just plunk it down over there and do the experiment, I should get the same result. Again, that doesn't always happen, but when it doesn't, I think that's a failure of physics. I'm going to say, gee, if I do the experiment here and it comes out one way, and I do the experiment here and it comes out a different way, there must be something physically different between these two locations, right?

55:29There must be something going on, and I ought to figure out what that is, right? This is a kind of methodological demand, and nobody would kind of be very happy to say, no, no, no, there's just no difference at all. I mean, that would more or less be the end of physics. Okay, so there are all of these symmetries. We've got rotational symmetries. We've got translational symmetries. Galilean symmetry is fancier, right? Galilean symmetry, we've talked about, do a bunch of experiments in a boat that's at anchor in a harbor, record the outcomes. You're jumping around and you've got these flying, you know, insects and so on, dripping water.

56:09Now put the boat in motion, but on a calm sea. So it's moving in a straight line at a uniform rate, all the same, it'll look all the same. That was supposed to be a symmetry in the phenomena for Galileo. So what's time reversal symmetry? Well, it would better be called classically time derivative reversal symmetry. not time reversal symmetry, but time derivative reversal symmetry. What do I mean by a time derivative? Well, the usual time derivative, the one you're familiar with is velocity, right? I have an object moving like this, right? So it's constantly changing its position. It's got a velocity.

56:58Reverse the velocity. Okay. I mean, instead of going this way, have it go this way, right? That's a change. It's like rotating this or moving this. Try and take all of the moving pieces or changing pieces of a situation and reverse their time derivatives, reverse how they're changing. If they were going upward, now make them go downward. If they were going to the right, now make them go to the left. Now, what happens with time reversal symmetry is the following claim. Take an initial state of a system, let it evolve through time to a final state, right? And the final state could be very different from the initial state, right?

57:50All kinds of stuff going on in between. Now, take that final state, time reverse it, time derivative reverse it, and make it now the initial state and let it evolve. And the idea is that if the laws have time reversal or time derivative reversal invariance, then the final state, when I reverse the derivatives, will evolve over the same period of time to the time reverse of my original initial state. That was a little complicated, so let me say it again. I have an initial state, a final state, T-I-T-F. I have a time derivative reversal operator. I say, okay, take T-F, take the final state of my experiment, reverse the time derivatives, and make that now the initial state of a new experiment.

58:48If the laws have time reversal and variance, that will evolve forward in time. to the time reverse, to the time derivative reversal of my original initial state. So I go from here to here, plunk this down here, reverse all the time derivatives, let it evolve, and then this should be now the reversal of that. That's what the symmetry is. That you can look at some laws of nature and say they would have that symmetry. Newton's laws, f equals ma, have that symmetry. So if you say if the fundamental dynamical laws are Newton, it will have that symmetry. Does that mean time doesn't have a direction?

59:29No. Newton knew they had that symmetry. Newton thought time had a direction. I mean, it's just crazy to think the existence of that symmetry suggests that time itself doesn't have a direction, A. B, ironically, in quantum theory, it doesn't have that symmetry. Okay, so that very symmetry, which is in Newton's physics, is in Maxwellian electrodynamics, has that symmetry. It goes away in quantum mechanics. In quantum mechanics, if you're doing quantum field theory, it's believed, it's postulated that there is a fundamental symmetry of the equations that's called CPT. CPT means you don't just do one thing, like we've talked about, just twist it or move it or do this.

1:00:22CPT means you do three things. C is charge conjugation, so you replace all your particles with antiparticles. P is parity, so you replace your laboratory with a mirror image. So that's right-handed screws become left-handed screws. And T is our time derivative reversal, time reversal operator. So what is said is that in quantum field theory, it has CPT symmetry. If you do all three of those things, it will continue to obey the equations of motion, the fundamental equations. However, in the lab, you notice that CP is broken, parity violation. This is called the violation of parity. This was discovered, I mean, postulated by Yang and Li, I think, and discovered by Madame Wu.

1:01:19You do an experiment. I mean, what you would normally expect, just take P. P is parity. So I have a lab, I do some experiment. Gets a result. Now I put up a mirror. In the mirror, there's a mirror image, right, of what I just did. But now in the mirror image, the experimenter who was right-handed is now left-handed, and the screws that were right-hand screws are now left-hand screws. Now, take down that mirror and put in a pane of glass, and over here, build a second laboratory that is the mirror image, right? Replace all the right hands with left hands. That's parity. That's the parity transformation.

1:02:01It was always assumed without argument that physics was invariant under parity, that as it were, a right-handed universe and a left-handed universe would both be perfectly good physically possible universes. That's not true. That's what mattered. That's what the experiments, I mean, first, theoretically, there were some puzzles and they said, you know, we could solve this by breaking parity. This had to do with a weak interaction. We could solve this by having our fundamental equations not be invariant under a parity transformation. And then they checked, and lo and behold, you do the experiment and you try to do the mirror image experiment, but the result is not the mirror image result.

1:02:46Nobel Prize is all around. P is not a symmetry.

1:02:55Now, CP is not a symmetry, but it's said CPT is a symmetry. Now, the only way that you can recover CPT if you've broken CP is to break T. That's just mathematics. So everybody, everybody, everybody, physicists who knows quantum field theory will say, no, T is broken. And T is the thing that corresponds to what we call time reversal invariance. So that's telling you, physics itself is telling you, this is not a symmetry. So you can't appeal to physics and say it's telling us time doesn't have a direction. If you want to appeal to physics, it's telling you time does have a direction. If you needed to be reassured about that, although why in the world anybody would need to be reassured that time is a direction is beyond me.

1:03:54I mean, there's nothing more obvious in the world that the time has a direction, that we're getting older, that it goes from past to future. Now, there are lots of asymmetries in time that you'd say, okay, but merely giving time a direction doesn't explain all these asymmetries. Absolutely, 100 % correct. And there's an interesting project to account for different particular asymmetries in time, like in thermodynamics or in electromagnetic, you know, in electromagnetics. I don't want to say in electromagnetic theory, it doesn't have an asymmetry, but in everyday life it does. As they say, in everyday life, regularly radio waves come out of radio towers in expanding spherical shells, right?

1:04:48The radio, you know, like in the RKO, beep, beep, beep, beep, you know, the circles are going out. And the equations tell you they could as easily be coming in, right? They could be collapsing into the antenna. And that's true. And you can say, yeah, but we never see them do that. That's true. So you might say, why is it so easy to make outgoing things and not so easy to make incoming things. Or to use the example everybody uses, every day we see bottles fall off, or anyway, we've all seen bottles fall off of tables and shatter on the floor. The time derivative reversal of that would be a bunch of scattered pieces on the floor that, as it were, seem to spontaneously suddenly jump up and assemble themselves into a bottle and deposit themselves on the table.

1:05:44Well, we never see that, ever, ever, ever. And then they say, yeah, but if you look at the laws of physics, it says if the one can happen, the other can. That's also true. That's the time reversal and variance of the laws. They tell you they can both happen. And then you say, well, here's a puzzle. Why do we see one all the time and we never see the other if they both can happen? Now, it's a funny kind of puzzle because we all know the laws of physics allow for all kinds of things we don't see. I mean, the laws of physics allow me to win the lottery, right? My winning the lottery is not going to violate the laws of physics.

1:06:18Why don't I ever win the lottery? I mean, you say, that's a strange question. Why would you expect you're going to win the lottery? Just because the laws of physics allow it, right? I mean, it's a very strange situation if you say, I expect everything that the laws of physics say can happen to happen. We don't think that. But there is, you know, there's a good question about why some things are relatively easy and some things are not merely difficult for us to arrange, but at a practical level, impossible for us to arrange, right? I mean, I don't care how much money you give them. No scientist will ever come up with a situation where they can set up a bunch of separated pieces of glass on what look like a floor and somehow, I don't know, jiggle it.

1:07:12And all of a sudden they jump up and assemble themselves into a bottle. They're not going to be able to do it. It's too hard, too chaotic. It would require too much fine-tuning, and they'll never be able to do it. Okay, so there are reasons why they can't do it, and there are physical reasons why they can't do it, and you have to get into the physics to understand what we can control and can't control, and this and that. You know, that's all determined itself by physics. So, sure, these asymmetries are interesting, and whether you can bring them all under— I mean, you can't bring them all under the umbrella of thermodynamics.

1:07:47People often bring in thermodynamics because it is explicitly temporally asymmetric in its laws. Like the laws say that the temperature of an isolated body will tend to even out. So then you can tell if I give you two pictures which came earlier, right? Not every one of these things is thermodynamic. People often make that confusion. Then there's a much larger umbrella, which we can call statistical mechanical. So there are things – if I take a jar that's got yellow and blue particles that are otherwise the same, and the yellows are on the bottom and the blues are on the top, and I shake it, okay, it's going to look uniformly green after a while.

1:08:42If you take your microscope, you'll see the yellows and blues all mixed up. There's a perfectly good statistical mechanical explanation of that. That's not a thermodynamic. That has no thermodynamic interest. People say, oh, the entropy went up, not the thermodynamic entropy. I did because I warmed it. I mean, I warmed it up by shaking it, but that's not the point. I would warm it even if it was all yellow. People often say, oh, you know, entropy is a measure of order. That's untrue. not the entropy that appears in thermodynamics. So you've got a kind of big thermodynamic umbrella that a lot of phenomena fall under, a bigger statistical mechanical umbrella that all of thermodynamics falls under, but a bunch of other stuff as well.

1:09:28And there's a question of, okay, what asymmetries in time can I explain thermodynamically? What asymmetries in time can I explain statistical mechanically? Are there other ones that I can't explain either? Neither. Our hair going from dark to light, neither, right? Because it would not violate any law of thermodynamics or any law of statistical mechanics for us to have genes where we were born with gray hair and we'd grow up, you know, as we age, it gets darker. That's neither of those. That's just a kind of accident. It doesn't really have a deep explanation. It just worked out that way. I think you have done at this point some serious damage to the idea that time does not have a direction.

1:10:20Good. Yeah, I'm sure that we could come up with some interesting cases or possible objections, and maybe we'll do that later if there's time. But let's assume that there's a direction for now. Yeah, good assumption. I mean, maybe I've said this to you, even Descartes in Meditation One, even Descartes at his most skeptical, maybe there's no space. Maybe it's all a dream. Maybe God is trying to fool me. It never occurs to him. Maybe time isn't going on, right? He's thinking. I mean, there's a whole sequence of thoughts and beliefs and reasoning going on that he never questions that it's going on.

1:10:59And that reasoning takes place in time, right? Right? So even at his most skeptical, he doesn't say maybe time doesn't have a direction. I think it's kind of crazy for anybody to think that time doesn't have a direction. I mean, they've confused themselves. Again, and people, I mean, I'll come back where I started. People often cite Augustine. Oh, I don't know what time, when you ask me, I don't know what time is. First of all, go read the passage and what he's trying to worry about there, which is not what you're thinking. But that's not a good reason. It's not a good reason to say maybe time doesn't have a direction because when you ask me what is time, I don't know what to say.

1:11:35The reason you don't is that it's not a composite thing. So you don't have the usual thing to say, which is time is made up of this and this and this. It isn't made up of anything else, right? It's fundamental and it's directed. And what I want to say is just as you don't view there to be a really substantive, interesting distinction between physics and philosophy, at least in these areas. You also view physics and metaphysics as being very closely connected. Yeah, that's an understatement, but go on. Well, after I finish, you should elaborate on that. But there are still some questions that might at least traditionally be cast in the metaphysics camp that are very close to the directionality question that are worth discussing right now.

1:12:22And there are many, but a couple I'll just start with are, does time have a rate? What does it mean to say that time flows? Yeah. I mean, so let me start. And again, I probably said this is a standard rant of mine, but okay. We love this. What is metaphysics? Because people say, is this a metaphysical question or a physical question? That is a very bad distinction that doesn't make any sense. So let's just walk back for a second. What is metaphysics? Because people, what they're reacting to is the idea is that metaphysics is super physics or beyond physics. It's the study of ghosts. After physics, right?

1:13:07Yeah. I mean, again, you go into the bookstore and if you look at the metaphysics, you'll get a bunch of stuff about Kabbalah or God knows what, you know. Exactly. Parapsychology. Exactly. That's metaphysics. Nope, nope, nope, wrong, wrong, wrong, right? Metaphysics, the term metaphysics was a title attached to something that Aristotle wrote, which the document does not contain the word metaphysics. So if you were to go up to Aristotle in the street and say, hey, Aristotle, you know, what's your metaphysics? He'd say, metaphysics? What the hell is metaphysics? Never heard of it, right? Isn't the story that one of his catalogers, like Andronicus of Rhodes, did I have the name right?

1:13:52Andronicus of Rhodes, that he just, he cataloged all of Aristotle's work. Then the physics was last and there was some leftover stuff. So he titled that Ata Meta Tafusica, which is metaphysics. Well, yeah, this is a story that goes around. I heard that story when I was a tadpole, as you did. I don't think that's true. So let's talk about the real situation. The real situation is yes, it was a later editor who was collecting together the extant manuscripts of Aristotle into volumes, right? Which we now, that's the way we now have them. And it is that later editor who stuck the name metaphysics on this set of writings of Aristotle.

1:14:39And the really kind of funny idea was, oh, he kind of had all these volumes in front of him and, okay, here's the physics. I don't know what to call that. That's sitting next to physics. I'll call it metaphysics, right? It's a thing after physics, like literally on the shelf after physics or something like that. No, that's not right, but let's get clear exactly what is right. So you have to look at this manuscript of Aristotle's and first ask, what does he call it? He doesn't call it metaphysics. And there are three main things he calls it. One thing he calls it is first philosophy, which doesn't, it doesn't give you much of a clue.

1:15:25It gives you some clue that this is about fundamental, what's really fundamental, right? What's first. But that doesn't really give you a lot of detail about the content of it. However, and this is where I'm going to say that's why this kind of silly story isn't right. Aristotle explicitly in the book we call physics calls that second philosophy. So first, second, okay. I mean, Aristotle himself saw a very close relation. Now, another rant, a new one. I haven't made this rant nearly as many times. There's this other manuscript of Aristotle, which we call Aristotle's physics. We only call that for Aristotle, okay?

1:16:16Other Greeks wrote things which have exactly the same title, and we don't call them physics. We call them on nature, right? We translate because that's what phousis in Greek means, is nature. The study of nature is the study of natural phenomena as opposed to what? artificial phenomena, for example. We make that distinction between natural and artificial.

1:16:49So if we had our heads on straight, which we don't, we would never call it Aristotle's physics, because from the way we use the word physics, that's extremely misleading from the get-go. We would say Aristotle's lectures on nature, and Aristotle tells you what he means by a nature, by something being natural. A nature is an intrinsic source of motion and rest. So this book, it can move. Right now, it's moving up. That's not natural for it, right? That's a forced motion. That's an artificial motion. It's not intrinsic to the book. You want to know what the book does naturally? Let go of it. That's natural.

1:17:37It's natural motion for Aristotle is to fall. But of course, Aristotle, when he talked about natural things, mostly what he had in mind was biology. He wrote more biology than anything else. Hell of a lot of marine biology, history of animals, parts of animals, all kinds of biological things. All of that for him was phusus, was phusus. It was natural science. So what we call Aristotle's physics is a bad name. We should call it Aristotle's natural science. A nature is an intrinsic motion of principle, a principle of motion and rest. The metaphysics first philosophy has a broader scope. It contains, it sort of contains natural science as a subpart, but it's broader.

1:18:29Why? Because there are things that exist that don't move at all, like mathematical objects. I mean, in lambda and mu of the metaphysics, he goes into mathematics. So those things don't have natures because they don't move. So what does, so he calls it first philosophy. Another thing he calls it in it is theology. but that's because he has a god-like element, the prime mover, the unmoved mover, active mind. Okay, that's part of it, but we don't think of metaphysics as just that, right? And the main thing he calls it, the thing that tells you what it really is, is the theory of being, quae being, as we said, the theory of being as such, that quae is Latin, Greek you know is hey.

1:19:25The theory of what exists merely insofar as it exists, the theory of the fundamental types of existence, that's what metaphysics is. Question, does what we call physics address some of that subject matter? Sure it does. right? When physics tells you that there are hydrogen atoms and they're made up of a proton and an electron, that's telling you part of what there is, fundamentally. Physics is a sub-part of metaphysics because it's doing ontology. I wrote a book called The Metaphysics Within Physics exactly for this reason, that physics, insofar as it contains postulates or hypotheses, about what fundamentally exists is part of metaphysics by definition.

1:20:23So to make a division there is to make a mistake. Now, you can make a division within physics between the things that are postulated that we're really pretty sure about and the things that might be postulated that are much more speculative. you can make a distinction between the things that are postulated that we have pretty direct experimental evidence for and the things that are postulated that we don't have very direct. From that point of view, strings, of course, go on the speculative side. We have no direct experimental evidence for them. So maybe you call them metaphysics. But now you're making really a distinction in confirmation theory.

1:21:05How strong is the evidence we have to believe in these things. First, you want to understand what is it you're postulating, right? Before I can even ask what's the evidence for it, the evidence for what, right? What is your theory postulating?

1:21:20So when people say, oh, that's not physics, that's metaphysics, maybe all they mean is that's not well-confirmed hypothesis tied to experimental outcomes. That's speculative. That's okay. That's a good distinction. And you should be more leery of more speculative stuff. But that's not a distinction between physics and some other spooky realm, right?

1:21:51So now that we've gotten that cleared up, I can't remember what the question was. Yeah, yeah, yeah. We start with— It was clearly a vast understatement on my part. But the question was, I said that there were many other interesting topics that are traditionally cast as metaphysical that are quite close to the question of directionality, such as rate and flow. Oh, rate and flow, right. Yeah. So, yeah, there's, again, okay, this is a long complaint. So people say, okay, if time passes, at what rate does it pass? and then you say, okay, you want a rate, you got to give me units. Like you say, how fast is the car going?

1:22:39Well, in what units? I'll give you one number if it's kilometers per second and another number if it's miles per hour and another number. Okay. Well, what kind of units could there be for the rate at which time passes? You're asking, as time goes on, how much time passes. Okay, that's pretty easy. One second per second, one minute per minute. You want a different number than one, 60 seconds per minute. That's another rate. Does it do that? Sure, it does. I mean, you're not going to literally tell me it doesn't do that. You're not going to tell me that a second from now, you won't be a second older.

1:23:18Of course you will be, right? Then people get upset, but that's a trivial answer. Okay, what do you want? Trivial is true, right? Triviality typically means nobody's going to deny that. So you wanted to know how fast time passed. Then say, shouldn't time be able to pass at two seconds per second? Well, no. I mean, of course not. What would that even mean? That would only make sense if you had two different types of seconds. You had seconds and metaseconds or hyperseconds, and then how many seconds passed per hypersecond. But there are no hyperseconds. There's just seconds. There's just time. But presumably they mean couldn't twice move twice as fast.

1:23:54And that at least seems facially plausible. I mean, a car can move twice as fast because the units are miles per hour. And you can change the number of miles and keep the same number of hours. But with time, you've got seconds, you've got seconds, right? You change one, you change the other. It just doesn't, you know. So people say, is there a rate? I mean, I've had, oh God, I'm so tired of it. You know, I keep getting, having to respond to people saying it doesn't make any sense to say time passes at one second per second. You say, well, why not? You know, it does. If I say the car, I mean, I often say this, look, if I say the car is traveling at a steady rate of one mile per hour, what do I mean?

1:24:40I mean, an hour from now, it'll be a mile down the highway, right? Right? After an hour has passed, its position will have changed by one mile. What do you mean by one second per second? I mean, after a second has passed, you will be one second older. You going to deny that? Good luck. Right? Okay, so it's a trivial answer. So what? I mean, you're asking a trivial question. You ask a trivial question, you get a trivial answer. Then they say, oh, but does time flow? This also is a mistake. It's turning a metaphor around backwards. Rivers flow because that's a spatial thing. That's a spatial change.

1:25:23A standard flow like of a river is a spatial change. This drop of water is moving through space. Rivers only flow because time passes. The flow of a river, Rivers change because time itself passes, and the water drop is different in a different location at a later time than an earlier time. That's what a flow is. So flows presuppose the passage of time. That means that the passage of time cannot itself be understood as a flow. That's, you know, question begging. What time does isn't flow. That's a metaphor. What time does is pass. That's what we say. that we use that word, time passes. If anything changes, time has to pass, because change is being different at a later time than an earlier time.

1:26:19But even if nothing changes, time passes. If the universe were to suddenly go static, it could do that, and it could do that for a period of time. Now, you know in the philosophical literature, There are examples of this where you could not only is it conceptually possible for time to pass while nothing physical changes, right? It's physically stationary. But you can even think of situations where we could have excellent empirical reason to believe that time has passed without anything changing. I mean, you probably know the paper. But anyway, so people somehow think, I mean, there are many different mistakes here.

1:27:09Here's a mistake people make. They say, oh, here's an interesting fact. They say, you know what time is? Time is what clocks measure. And maybe we've talked about this. It is true that time is what clocks are meant to measure. That's not a definition of time. That's a definition of clock. clock. That's why we think we can talk about more and less accurate clocks, because we think time itself, there is a measure of it. And a good clock is a physical device so constructed that some visible portion of it is reflecting more or less accurately how much time has passed. But if you say, no, no, time itself is just whatever clocks measure, then you're going to say, well, instantaneously clocks are perfectly accurate because they measure whatever they measure, right?

1:28:02How could they be wrong? But we think they could be wrong. We think we're making better – you make a femtosecond clock. You've done something. A femtosecond? That's a unit number? Oh, yeah, a femtosecond. That goes down below – what does femto come after? It's certainly after nanoseconds. You know, you do their nanoseconds, nanoseconds. So much more accurate than an atomic clock. The femtoseconds, yeah, it's a 10 to the 10th power. I don't know. Okay. I mean, I talk about femtosecond clocks because they actually make them now. I mean, this is part of the ongoing technological improvement in clocks.

1:28:36I mean, it was hard, as you know, to even make clocks that were accurate to a minute. I mean, this was important for navigation, for figuring out longitude. Interesting story there. And of course, there's a whole history of chronometry of people making better and better and better and better and better clocks. And then you just say, what do you mean by better? Here's what I mean. There's an actual amount of time that passed and a better clock tells you more accurately what it was. This might derail you a bit, or maybe this is where you're going, but is there some theoretical limit to how precisely time could be measured?

1:29:13Do you think time is discrete or do you think time is continuous? Good. Okay. Two different questions you just asked. Is there a limit to how accurately one can measure time? If there were a limit, it would have to arise from some fundamental physical principle, right? Which it could. You have to ask when you say, how accurately can I build a device? You say, well, what am I going to build it out of? What's it made of? How does that stuff work? work, there might or might not be limits that arise from fundamental physics on how accurate a clock could be. Do we know that? No. Why? Now, this is a very deep problem we can get into this.

1:30:01We don't even know how to approach that question in quantum mechanics. Why? Because in quantum mechanics, the way it normally works is when you say you measure something, and you talked a lot about the measurement problem and you know this is very difficult terminology. But at a practical level, when you say in quantum mechanics, okay, I'm going to measure position, I'm going to measure momentum. Technically, the first thing you do is you grab this object called a Hermitian operator, right? So this is a mathematical gadget. and you use that Hermitian operator to somehow represent this, whatever you're doing, you're calling a measurement.

1:30:45For time, there is no time operator. There isn't one in quantum mechanics. Time does not appear in quantum mechanics the way position does, the way momentum does. It appears as a variable. It appears not as an operator, but as a variable. And when you talk about, say, the Heisenberg uncertainty relations, which might be part of what you have in mind when you say, how accurately can we get at time? You might say, is there an analog to the Heisenberg uncertainty relations? And the answer is there isn't. People often say there is. They say it's a time energy, but that's not right because there's no time operator.

1:31:24The uncertainty relations mathematically depend upon having two things that are operators, And then you see if they commute. That is, if I apply this operator and that one, do I get the same thing as if I do them the other way around? And that failure of commutation lies at the center of a bunch of quantum mechanical differences from classical physics. But there is no time operator. It doesn't exist. So I don't think we have any theoretical handle on the question how, in principle, how accurate could a clock be. I just don't think we have one. And I'll say something more, which is that we can't even explain data about time we can get in the lab.

1:32:14So this is another complaint. You'll hear people say, oh, the standard model explains every, it's the most successful theory in the history of the universe. It explains everything we see except maybe quantum gravity or something like that. They use us all the time. That's completely untrue. You can go into the lab and collect data now, and you don't need a large hadron collider. You don't need a big thing. You go into the lab, do a tabletop experiment, collect data on arrival times. Nobody knows how to account for them. Nobody knows how to predict them. And they're there. And we could do better because a lot of the data we have, they're not using femtosecond clocks, and they could.

1:32:54If you got interested in time, arrival time, observable time, there's a lot of work that can be done in physics that nobody knows how to explain. Anyway, you asked a different question. Let me go to the second question. It's not about clocks. Is time continuous or discrete? Good question. Nobody knows. Nobody knows. If somebody tells you quantum mechanics implies that time and space are discrete, that's untrue. Quantum mechanics does not imply that every quantity is discretized. Just standard quantum mechanics. Take energy. So you have an electron bound to a proton. You've got a hydrogen atom.

1:33:43One of the great triumphs of quantum mechanics is that it allows you to figure out different energy eigenstates, as we say, different energy shells, the orbitals, what we call the orbitals, the S orbitals, the P orbitals, and to attribute different energies to them. And that is a discrete thing, right? The S, an electron in the S orbital has this much energy, the electron in the P. And therefore, if it drops from the P to the S, it gives off light of a certain frequency. If you, to pump it up from one to the other, you hit it with light with that frequency and so on. So in some cases, quantum mechanics discretizes things.

1:34:23But if you take that electron and ionize it, if you give it enough energy so it gets kicked all the way out of your hydrogen atom, then it can have any energy you want. It has a continuous spectrum. The free electron has a continuous spectrum. It can have any energy you like. That's not discretized. That's just a fact. Anybody who knows quantum mechanics knows that fact. So if anybody says, oh, gee, space and time must be discrete because quantum mechanics, no, quantum mechanics doesn't discretize everything. But you asked a great question. Is it discrete or continuous? Answer, we don't know. Personally, and this is just me, I've been working on a theory where it's discrete, where space and time are discrete.

1:35:04Other people have worked on theories where it's discrete. All of physics that we use now, quantum field theory, general relativity, it's continuous, right? All of the big ones, the time variable appears as a continuous variable, right? You use real numbers. But of course, it could be wrong. I mean, it's like you look at a TV screen, it looks continuous, but you look close enough. It's made of pixels, it discretizes. It's everybody can see that a fundamentally discrete structure could appear continuous at macro scale. So everybody ought to make allowance for the possibility that space and time are discrete or that they're continuous.

1:35:51One could be discrete and the other could be continuous. I mean, you know, all kinds of possibilities. They have not been nearly explored enough. I think this would be an interesting time to get into something quite closely connected to something you mentioned in our last episode, which is you introduced this concept of the Xenonian observer. That's not what I have in mind right now, but you took the Xenonian observer from Xeno. And I'm wondering if you think that it might be interesting to discuss Xeno's paradoxes right now, just because they do pose problems about continuity and discreteness.

1:36:31And I wonder if they have any bearing at all, in your opinion, on this question of continuity. Sure, let's talk about that because people, let me just say, again, the story one hears, I have no reason to doubt it, the story that Plato tells in the dialogue Parmenides, is that Zeno was a student of Parmenides. and Parmenides famously argued that time and change are illusion, right? Change is an illusion. Nothing really changes. That's a hell of a postulate, right? You might say, oh yeah, really? Aren't we having a conversation now? I mean, what do you mean nothing changes? And, you know, Parmenides is one of these strange figures where, given points for the courage of his convictions, right?

1:37:22He thought he had an argument that showed that change was logically self-contradictory. And then he just drew the conclusion, well, then nothing changes. You know, most people would say, probably something's gone wrong with your argument there, Parmenides. And in fact, something did go wrong with his argument. If you look carefully into Parmenides, and we have most of his text, he just makes a mistake, okay? It's kind of a tempting mistake, but it was a mistake. Anyway, the story that Plato tells in the dialogue Parmenides is that Zeno was a student of Parmenides and was trying to support Parmenides.

1:38:00Now, Parmenides was giving you, as it were, positive arguments for his conclusion. And what Zeno was doing was saying, well, look, if you think things change, I'm going to show you that there are all kinds of absurdities that follow from the hypothesis that things change, right? I'm going to give you these paradoxes. And exactly because it's interesting here, because it wasn't known whether space was continuous or discrete, it seems as though Zeno gave you paradoxes of continuous time and paradoxes of discrete time, right? He says, if you think it's discrete, okay, you've got these problems. If you think it's continuous, you've got these problems.

1:38:42Most people focus on the ones that depend on a continuum. There are ones that don't. I mean, the stadium one is a little hard to understand. Yeah, especially without a graphic. Yeah, yeah. But everybody knows the continuous one, right? So the continuous one goes, look, if time and space are continuous, then I mean, to take the arrow, I can't possibly, as it were, shoot an arrow and have it hit the wall. Or Achilles can never catch the tortoise. I mean, these are two examples. Let's just do the wall one because it's easier. Why can't I shoot? Of course I can shoot an arrow and hit the wall. What the hell are you talking about, right?

1:39:24You know, I'll do it right now and show you I can do it. No, no, no, no, you can't. Why not? Well, because both space and time are continuous. All right. So you shoot the arrow. In order to get to the wall, you'll agree, it has to pass the halfway mark. It has to get to the halfway. Yeah, I agree. Well, and then between there and the wall, there's another halfway mark, right? Which is the three quarters way mark. It has to do that, right? And then again, and then again, and then again, and then again. I always subdivide by half, yeah? Now, if space and time are continuous, that set of divisions never ends.

1:39:58It's infinite. And I still remember hearing this in high school and it blowing my mind. Yeah. Yeah. And you say, yeah. Okay, good. So now comes the trick. Now you say, so according to you, for the arrow to get to the wall, you have to complete an infinite sequence. But you can't complete an infinite sequence. Why not? Now, pay close attention. To complete a sequence of tasks, you have to get to the last one. But in an infinite sequence, there is no last one. so you can't complete it. So that means the arrow can never get to the wall. Stop and think. And then you say, yeah, that sounds somewhat wrong there, right?

1:40:41I mean, there's something wrong with that argument. So let's put our finger on what's wrong with it. It's not true that to complete a sequence, you have to get to the last one. To complete a sequence, you have to do every one. If there's no last one, so what? As long as you do every one, you completed the sequence. And so this is Aristotle's answer, in fact, because Aristotle believed that space and time were continuous and infinitely divisible. And he said, sure, there's an infinite sequence of these spatial units, a half and then a quarter and then an eighth and then, you know, always going down by half?

1:41:25Yes. And time is equally divisible. So there's a period of time in which you will complete that task, that task, that task, that task, that task. And you complete them all, right? Because the time is just as divisible as the space. So this was Aristotle's answer to Zeno. He said, you're making a mistake there. And he is. Now, the real answer to this, as you know, to really understand this, you have to understand about summing infinite series and how an infinite series that's always getting bigger can nonetheless sum limit to a finite amount. And we all know that a half plus a quarter plus an eighth plus a sixteenth plus a 32nd forever, all that adds up to one.

1:42:13So yeah, I can shoot the arrow. It gets there in a second. It did half of it in the first half second. It did the next quarter in the next quarter second. It did the next eighth in the next eighth second, just as much as you want to divide space, I can divide time. There's no paradox. That's the answer to that. And, you know, this, of course, summing infinite series and when they even have a sum, when they converge, all of this was really only understood by data kent and stuff. You know, mathematicians finally worked this out in the 19th century rigorously, and you need to do it rigorously to explain why calculus works and so on.

1:42:51but nobody should be bothered about Zeno's paradoxes nowadays. We've answered them. And some of them you can answer, as I said. It's just the distinction between doing the last thing in a sequence and doing everything in a sequence, right? If you say to complete a sequence, you have to get to the last step, then if there is no last step, you can't complete it. But if you say to complete a sequence is to do every step, step, then even if it's infinite, you can complete it. You just need to complete an infinite number of steps. Okay, no, that was great. I haven't spoken with anybody about Zeno's paradoxes for quite some time, maybe since I first started the show, actually.

1:43:34So it's fun to get to them. Do you know, actually, I just need to mention, have you ever seen Tom Stoppard's play Travesties? No. You should see it. I mean, Stoppard's great. Stoppard is very philosophical, as you know. And he actually has a character there who's talking about Zeno's paradoxes, and he talks about the arrow and how the arrow can never arrive because of this argument. And then he says at the end, who is it? Saint Stephen died of fright, right? Saint Stephen was supposed to have been killed by arrows, but apparently they never hit him, right? He was just scared to death. Well, this might be a digression from some of the more simple common questions that I want to keep asking for a little bit.

1:44:14But if your intuitions about space, I mean, time being discrete don't come from this, which I think even though you've given a possible way of refuting the problem, a lot of people still think it's a problem today. Where does your conviction, if I can put it so strongly, that time is discrete come from? Yeah, that's too strong. It's not a conviction. The conviction is that, first of all, I think demonstrably, there are infinitely many ways you could ascribe a discrete geometry to space-time, and almost none of them have been carefully explored. Almost none. There are very few people, the causal set people, Raphael Sorkin and Faye Dauker, are among the few who are really trying to discretize, in a way, spasiotemporal structure and do physics in terms of it.

1:45:20So no, it is not a conviction that it is so. It is a conviction that it might be so, which everybody is going to agree to. Many physicists will offhandedly say, well, quantum theory tells us it is discrete, but they don't take that seriously. You know, all this stuff about quantum foam, you see these pictures, there's doesn't look discrete. It's all tangled up and fractal, God knows what.

1:45:48And I just, I mean, there's a long story about how I came up with this discrete structure that goes back to trying to understand just divergences and curls and standard vector calculus. It's a long story. I've got a manuscript I've been working on for almost a decade now, and maybe this summer I'll finish it. Oh, wow. But it's just speculative, right? It's just speculative. Now, it turns out, I will say this, and this will come back to things we've talked about. Now, if you try to discretize space-time, it's not absolutely required, but it's a very natural thing to end up with a preferred foliation.

1:46:38It's a little bit hard to avoid it. It's not that you can't avoid it, but unless you're working hard to avoid it, the natural thing to do, as soon as you start talking about discrete structures, which by a discrete structure, I just mean where you've got nearest neighbors, right? I mean, in a continuum, if I have a point and you ask, well, what's the next point over? The answer is there isn't a next point over, right? No matter how close I get, there are more points in between, right? So it's really just density here that matters in technical term, density, but continuity. In a discrete structure, there are next neighbors, right?

1:47:16You can ask what's the next one over, what's the immediately, you know, next one. And if you start doing that for space-time, so I'm trying to make a space-time structure that's discrete, it almost, just naturally, if you're not really trying to avoid it, you're going to end up putting a preferred foliation into it, temporal foliation into it. Now, I think we need one. I think we need a preferred foliation because of quantum non-locality, because of violations of Bell's inequality. So from that point of view, those chime together. You say, look, I tried to build a discrete space-time. Bang, I get a foliation.

1:47:59Hey, I need a foliation. Good. So this is not obviously going back to Newton. For Newton, space and time were continua. He's not doing anything discrete. But you do get back almost, if you do it the way I'm doing it, you get back a preferred foliation. And for me, that's not a bug, that's a feature, because I'm going to use that preferred foliation for writing down my laws of physics and accounting for quantum nonlocality. So that's the big picture of why I'm interested in that. Also, I think, I mean, if anybody's interested when the book finally comes out, I hope you find that it gives you a way of thinking even about stuff you were familiar with in continual, like vector calculus, gives you a way of thinking about it that makes it, that's enlightening.

1:48:55It was enlightening to me. anyway. If time is discrete and then it seems like we should look at time as a collection of instances, instance, one after another, then what prevents you from, this goes back to the beginning of our conversation, of looking at time as something that is composite. It's something like an ordered set of these instants? Sure. I mean, there's the temporal structure. So when you talk about time, maybe a better word is temporal structure.

1:49:38And of course, time, I mean, look, there are lots of different moments of time. I mean, I don't want to say time doesn't have a multiplicity in it. What I said at the beginning was that it's fundamental. It's not made of anything else. The parts of it are temporal parts, right? And the question is, what is the structure in which all of those parts are organized? And that is giving an account of time, of temporal structure. What is it that's organized, and how is it organized? Now, let's, again, make a distinction here. For Newton, as we saw when I read it, what gets organized are these spatially global instance.

1:50:23And they get organized by being put in a time order of earlier to later. And there's also an amount of time, right? There's a distance, there's a metric, how much time passes between here and there. In relativity, the fundamental temporal objects are not global. They're local. They're like space-time events. They're localized in both space and time. But then they have a structure put on them, a relativistic structure, and that gives you space-time structure. So sure, I didn't mean to say, of course, the ultimate temporal structure is a structure of something that has many parts, but they're all temporal or spatiotemporal parts, and they're organized by a temporal or spatiotemporal structure, which itself does not arise from anything else.

1:51:10Is that? Yeah, yeah. Okay, and now I have another, I think that this question is quite fascinating. I guess we might want to call it cosmological, but it's about whether time has a beginning. And over the course of this show where I'm, I don't know, past, when this comes out, I'll be past 250 episodes. I've spoken to a lot of physicists and gotten a lot of ideas. You mentioned David Albert already many times. He, of course, as you know, we did an episode that I titled A Masterclass on the Arrow of Time or Direction of Time. I don't know what I'll call this one, a masterclass on something about time.

1:51:51But anyway, he has what's famously known as the past hypothesis. So there is this initial condition. But then another member of the JBI, the John Bell Institute, you were wearing a pin before, but it's gone. And maybe we'll talk about it a little bit at the end. Julian Barber, he was on the show a long time ago. And he has this idea of the Janus point in time where there is a point if you go back far enough. but then it branches and there are i don't know how he would want to describe it but perhaps different timelines stemming out of this yeah sean carroll has a similar kind of idea and then i know that i don't want to i want to don't want to go so far as to say that i know because i don't fully understand it but for stephen hawking i mean you go back far enough and then it just kind of becomes fuzzy there isn't a beginning point of time so anyway i just wanted this was just to say that there are many possible options.

1:52:51So I'm wondering where you fit in here on the beginning of time. Good. Right. You just gave a bunch of different possible options. I certainly do not agree with Dave, with Julian. Okay. Or Sean. Again, Sean has a similar thing. It's like for Sean, there's a kind of, I don't know what to say, mother of all time region. And then coming out of it in opposite directions, as it were, are baby universes or progeny universes. Does this have anything to do with the many worlds theory? It's not really, no, this is not, this is a cosmological thing. It's not really a quantum mechanical thing. And he would say, and this is going to follow on from stuff David would say, he would say that time proceeds from past to future this way along this group and that way along that group.

1:54:04And if you ask, but what's the direction of time at the central region, at this central mother region, there isn't one. Now, that happens if you say stuff like, oh, the direction of time just is the direction of increasing entropy. So this is something people say. To me, it's as bad as saying a definition of time is time is what clocks measure. You say, no, you got that backwards, right? Clocks are what measure time. It's not that time is what clocks measure. Yes, entropy increases generally. It doesn't have to. We all agree it need not increase. We all agree in classical statistical mechanics, if the universe is closed, eventually it will decrease.

1:54:50That's Planck-Rae's theorem. I don't think the direction of entropy increase is the direction of time. The direction of time is just given by the fundamental earlier-later structure. It's because time has a direction that you can correctly say that generally entropy increases, right? Increases means is larger at a later time than at an earlier time, but now I need earlier or later to even define what increase means. I mean, as I like to say, if someone says, you know, at two different times, I had two different weights. At one, it was larger than the other. You'd say, well, it's kind of important to understand which was lower and which was later, because if you're trying to lose weight, if it goes one way, you're going the wrong direction, right?

1:55:39So increase is a word that has the direction of time built into it. So you can't say, right, for people who want to say, oh, the direction of time just is, by definition, the direction in which entropy gets larger, I want to say, A, that's not what physics says. That's certainly not what standard statistical mechanics says, just the opposite. It says, it is possible and eventually will happen, and at a small scale happens all the time, that entropy decreases. But to say entropy decreases is to say that the direction of the forward direction of time is not the direction in which entropy is getting larger.

1:56:18Okay? So now what happens with the beginning of time, is there a beginning of time? There are two questions here, actually. Let's separate them. Is there a beginning of time the past hypothesis, okay? Different questions. I think everybody would agree they're different questions. Is there a beginning of time? Let's be now a little careful about that. It could mean, was there a first moment of time, a literally initial condition of the universe, literally a moment of time that counts as the first moment of time? Could be. Nobody knows. Second question. Now, does time go back infinitely? Now, it could be that time doesn't go back infinitely, but there's no first moment.

1:57:15That's like take the number line and remove zero. Then you can't keep going in that direction, but there's no first one either because there's always an earlier one because it's dense, right? There's literally no first positive number on the number line, real number line, right? There's no first positive number, but you can't go back forever and stay in the positive numbers. So that's a second question. Does the physical universe, is it limited in its time extent? Now, if you have a discrete thing, if it's limited, there's a first one, right? In a discrete structure, if it doesn't go on forever, then there's a first one.

1:57:56In a continuous structure, it might not, as it were, go on metrically infinitely, but there still might not be a first one, as the example of the number line illustrates. So does the physical universe, A, have an initial time? B, does it go back indefinitely, metrically in time? Answer, nobody knows. Nobody knows. Nobody has a good reason to believe one thing or the other. Roger Penrose has developed what he calls a cyclical cosmology where there is no first. There's always an earlier period. The period we would call a Big Bang, which was an interesting event. It was preceded by another epic, which was preceded by another epic, which, well, as far as he knows, was preceded indefinitely.

1:58:51Now, the idea that time could go to the past infinitely, people get queasy about that because they say, how could we have... There hasn't been enough time to get from now. Get back to Zeno. Yeah, this is like Zeno, but now not just with division infinite, it's with infinite extent, right? There are two kinds of infinity, infinity in extent and infinity in divisibility. Zeno was more about infinity in divisibility. This is about could an infinite amount of time have passed to get us here? And many people get queasy about that. Personally, I get kind of queasy about that. I can't say it's logically impossible because it isn't.

1:59:29I get queasy about continuity. Yeah, I mean, I prefer discrete structure because I think it's easier. It's cleaner, right? It's really clean. It's like I can get down to the bottom and here at the bottom, this is next to that.

1:59:46Anyway, so was there a literally initial period or moment of the existence of the physical universe? Was there an initial period or moment in the temporal structure? Does it go on in terms of metric indefinitely, or is there only so much of it, like 13.8 billion years of it? Great questions. Nobody knows. And different hypotheses, people have different hypotheses. Penrose has these epics that preceded the Big Bang. And then people say, well, do we have any empirical evidence of that? And he's thought about it and he thinks we do. I mean, he literally thinks some features of the cosmic background radiation are indications are, as it were, the effects of stuff that happened in the previous epoch.

2:00:43Other people, of course, disagree. You can trace out what general relativity says, and people often do. And again, general relativity not as a quantum theory, as plain vanilla general relativity. We know that the universe, as it were, the matter is all moving away from each other. You know, the universe is expanding, if you will. And then if we say, well, how did we get here? And now you run the story backward in time. Okay, then it all comes together. And if it all comes together, we talked about this stress energy tensor that shows up in general relativity. As it comes back together, the stress energy tensor gets larger and larger because you have more and more concentrated density of energy.

2:01:38And eventually it goes infinite. I mean, and then you get a singularity. You get a mathematical singularity. The equations break down. What does that indicate? Well, some people think that indicates that's where time itself began. Some people think, no, that indicates that's where physics, present physics doesn't work, right? That's where general relativity doesn't work anymore. And if you were, again, we had this quote from Einstein when he said one side of the field equation was fine marble and the other was low-grade wood, I'm sure Einstein would say that's where the low-grade wood is breaking, right?

2:02:13It's because you're using the stress-energy tensor, which I always knew was just an approximation. A better theory shouldn't do that.

2:02:24So people who take general relativity a bit too seriously, as if it's the final word, tend to say, oh, space and time must be finite because when you trace back using those principles, you end up at this singularity.

2:02:43Then there's this, I'll say a word about this. So then there's this Hawking stuff, the no boundary condition, boundary condition. You said things for Hawking get fuzzy. That's not right. Nothing gets fuzzy. Hawking does a trick that many physicists do. So we've talked about in general relativity, you have a pseudo-Romanian metric. It's got this light cone structure. It's not like Euclidean geometry. It's not even like the geometry of the surface of a sphere because those don't have anything like a light cone structure in them.

2:03:24So what they do is they do what's called a wick rotation and replace time with imaginary time. This is all math. It sounds fancy, right? It's just math. It's like I take something, I put I times that something in it. And then all of a sudden, they're not working in a pseudo Ramanian metric anymore. They're working in a regular Ramanian metric. And then the idea is there's just no edge to it. I mean, if you trace it back in time, you don't get to an edge. It's not that it gets fuzzy. It's not that it disappears. It just kind of smoothly goes on. The way, I mean, here's a kind of analogy. Take the surface of the Earth, right?

2:04:04Interesting question. Let me just ask you, is the surface of the Earth infinite or finite? Finite. Okay. Is there an edge to it? No. Right. So it's unbounded. It's finite, but unbounded. You don't, you can keep, wherever you are on earth, you can keep going in, you know, we're thinking of it as a two-dimensional thing. We can go in any direction, right? We don't ever run into an edge, but it's finite. And so Hawking sort of wanted something like that, where if you go back in time, it's not that you ever reach a singularity or an obstruction or you get stopped or things break down. It all continues to be nice and smooth, but there's only finitely much of it.

2:04:53Something like that. That's, I mean, I'm not saying enough to make exact sense out of the proposal, but the idea was that, you know, again, they say there's an, it's a no boundary condition, boundary condition, because there is no boundary. There's because you can always keep going, but they do it through this wick rotation, a funny kind of thing they do. Okay, you know, fine. All kinds of speculations people can have. I have no problems with speculations. Just be upfront about what you need to get your speculations to work. I don't think that one works because I think although there's this mathematical procedure of replacing time with imaginary time and going from a pseudo-Romanian metric to a Romanian one.

2:05:34It's a mathematical position. It doesn't make any sense physically. It's just math, just ungrounded math. Now, that's about time itself. What about the past hypothesis? Well, the past hypothesis is an observation. I don't like the term past hypothesis. I call it the past conclusion. Why? You look around at the world and you know a lot about the physics of how the world works and you know a lot about thermodynamics and statistical mechanics. And you say, it follows from what I see now that earlier on the entropy of the universe in some sense, if you can define it, must have been lower. The only way you can explain what you see now and all the stars and what they're doing is that the entropy was lower.

2:06:34That's a conclusion, right? It's not a hypothesis. It's a conclusion. That raises the question, but why was it lower? And now you get into a big, big, big philosophical issue. Maybe you've seen, And Roger Penrose, again, has written a lot about this. And if you read some of Penrose's books, he actually has a picture, and it's a picture of this big space and God, and God has a little pointer, and God is pointing out the initial condition of the universe. And the idea is that it's a very, very, very atypical initial condition, that most of the physical states the universe can be in are in thermodynamic equilibrium.

2:07:28And in thermodynamic equilibrium, you don't got stars, you don't have planets, you don't have people, you don't have nothing because nothing like that. Because at equilibrium, you're at equilibrium. It's just like a gas. I mean, it's just nothing, you know. And it's not like that, right? And we are very, very, very, very, very far, thank goodness, from thermodynamic equilibrium. And we always have been. The entire history of the universe up until now, as far as we know, has not been at equilibrium. So the earlier states of the universe were certainly not equilibrium states. They were low entropy states.

2:08:04Now the question is, hmm, can I explain that? First, I observe that that's the case. True. Nobody can deny it. Second question, can I explain it? Now, here are a couple different models. So I said Penrose has a model, the cyclic cosmology, where before what we call the Big Bang there was an earlier epoch. And our Big Bang arose. This all has time going forward. Our Big Bang is a causal consequence. It arose out of this earlier epoch by means of laws that he's trying to write down. And what he wants to show is that there's a kind of phase transition that takes you from one epoch to the other, that when you get to the other side of that phase transition, you're in a low entropy state.

2:09:02So that would be an explanation. Why is our Big Bang a low entropy state? Because it arose out of this earlier state, and the means by which it arose guaranteed that it was going to come out as a low entropy state. That would be an explanation for the fact that entropy was lower. There are people, of course, who think, no, there was nothing before the Big Bang, right? There is no previous state, so you can't explain it by arising from anything earlier. You just have to postulate there was an earlier state.

2:09:33Is there some way to understand why that would be a low-entropy state? Well, now another Roger Penrose, a different one, an earlier one, he had a hypothesis about that too. It was a pretty pretty one. And he said, oh, the basic hypothesis is that the space-time, initial space-time structure, I mean really initial, had a feature called zero vial curvature. Now, you know, there's a lot of math in this, but basically we talked about the curvature of space-time. You can divide that curvature into different pieces. One piece is called the vial curvature. And what Penrose pointed out is that the Big Bang, as we understand it, had almost zero and maybe exactly zero vial curvature.

2:10:15And that the reason why it had such low entropy was that, because a typical state will not have zero vial curvature. And as time goes on and all these black holes form, the vial curvature goes up, up, up, up, up, up, up. And at the end, it'll have very large vial curvature. So then you might say, well, that's a kind of interesting hypothesis. The hypothesis is the initial state had zero vial curvature. Okay, that would explain it. Now, you could, of course, say, but why did it have zero vial curvature? But now we're in this game of when do you want to stop, right? No matter what I give you as an explanation, you can always say, but why that?

2:10:57But why that? Why that? That's the three-year-old version of doing philosophy. No matter what you ask me a question, no matter what I give you to explain it, you then further ask the question again, again, again. Now, everybody can see that's a mugs game, right? You got to stop somewhere. Where do you stop? You stop where it's simple. You stop where it looks kind of compelling. I mean, actually, Parfit has some interesting writings, philosophical writings about this, which are basically the question, what are reasonable-looking foundational postulates, ones where you say, I don't think I need to go deeper than that.

2:11:39Now, you never know you've gotten to the bottom. You can't know you've gotten to the bottom. But if there is a bottom, sometime you might get to the bottom, and then you're going to waste a lot of time trying to dig a sub-basement where there isn't one. And zero vile curvature, okay, that's a real simple thing to say. In the context of general relativity, it has a precise content. That would be a version of David's past hypothesis. Now, David and Barry, lower, are Humeans. So they're in a, what to me is funny situation of saying, well, a law of nature just is some kind of informative generality.

2:12:20So from their point of view, just saying the initial condition was low entropy, that automatically becomes a law if it's easy to say and a lot follows from it. I don't buy that. I'm not a Humean. I'm a non-Humean. I think the fundamental laws are laws of temporal evolution. They do not have Humean accounts. This thing could not be a law of temporal evolution because it's a claim about what happens at a certain time. So yeah, for me, if there's an explanatory principle there, I like a one like Penrose's, if it turned out to be right. If you could explain everything by having space and time be finite and that the initial state had zero vial curvature, I wouldn't lose any more sleep over it.

2:13:10I just couldn't see there's any prospect of getting anything better as fundamental principles from which I can explain everything. But I wouldn't call that a law. Because if you ask me, couldn't, in some sense of couldn't, couldn't the universe have started out in some other state, I'd say, yeah, I mean, because I think the laws are laws of temporal evolution. They wouldn't stop it from starting out somewhere else. But okay, it started out with vile curvature zero. That's good. Someone says, I can explain why it started with vile curvature zero, because it arose out of something else by a process which gives rise to vile curvature zero.

2:13:43Okay, fine. I'll listen to that. That sounds good. You never know where to stop, but you know you better stop somewhere. Tim, I want to make sure that we get to time of flight and arrival time experiments, because I know that that's what you've been working on. But at the same time, I also think it's really important that we're going over these basic, long-lived questions that people have been puzzling over for eons. So there are a couple more that I want to talk about. One brings us back to this idea of time being a collection of instants, perhaps. And it's this debate between presentism and eternalism, a debate maybe about the reality, however nebulously defined that is, of these instants.

2:14:32So first, maybe I should ask just for context for our listeners what this debate is between presentism and eternalism and how your theory of time falls into it. Okay, so I'm going to give you a characterization of this debate, which is going to sound very unfair because it's going to make one side look kind of silly. I think this is accurate. Okay. And we can start with what you just said. Reality, however nebulously that's defined. Okay. Reality should not be defined nebulously. There's reality. They're facts. Okay. And question, Are there facts about the past? Sure. Of course there are. I was born in Washington, D.C., blah, blah, blah.

2:15:20Okay, lots of facts about the past. Are there facts about the future? Now, the are there may throw you a little, so don't worry about that. Will there be facts about the future, if you want to say, or, you know, yes, right? Just as stuff happened in the past, stuff will happen in the future. As I say, the deep philosophical principle here was best articulated by Doris Day. Que sera, sera, right? Stuff is going to happen. Just as there was one past, there will be one future. Next question. How much do we know about the past? Well, a little bit. A lot of stuff we don't know, a lot of stuff we never will know.

2:16:11Anybody who starts to tell you what actually happened in the past is a function of what we know or can know about the past, they've gone way with it. No, that's entirely false. Here's an everyday fact about the past, which we do not know and will never know. What was Socrates' blood type? He had one. We don't know what it is. We will never know what it is. There's no decent sense of could know that we could know what it is. But he had one. If you somehow jump to saying if we don't know whether he was A, B, or O, or some weird sub, then he wasn't any of them, then you've just gone way off the rails, right?

2:16:57I mean, ontology is not constrained by epistemology, right? What there is is not constrained in that way by what we can know. So that's just a huge error. So, there was a past, there is a present, there will be a future. If you're in relativity, you can't quite say that because that's a very Newtonian thing to say. You've got this absolute time marching on. There's all the stuff that happened before now, there's now, and all the stuff that will happen after now. In relativity, there's the stuff in my past light cone, the stuff in my future light cone, and the stuff in space-like separation. It's a big other chunk.

2:17:33But it's all, there's all facts. It just goes one way. Okay? That's all eternalism says. It's obviously true. What does a presentist want to say? The words that'll come out of their mouth is something like, no, all that exists is what there is now. And first of all, you want to say, well, unless you're rejecting relativity, which most of you don't want to do, there is no such thing as now because that requires absolute simultaneity. So already your thesis doesn't make any sense. But even if you put in a slice, even if you, you know, put in an absolute slice and I say now, globally, is that all there is?

2:18:17No, there's all the stuff that happened in the past, all the stuff that's going to happen in the future. I mean, Quine introduced a technical usage of the word is, which by definition means is, was, or will be. That's okay. That's good. You know what it means. Are there dinosaurs in quine sense? Sure. Are there manned colonies on Mars? Nobody knows yet. That's just to ask, will there be manned colonies on Mars? Nobody knows yet. Were there dinosaurs? Sure. We know that. Again, the epistemology of it is a different issue. Is determinism relevant in this at all? Determinism is completely irrelevant to this.

2:19:03Determinism is a matter of the fundamental dynamical laws of physics. Even if the fundamental dynamical laws are indeterministic, like in a collapse theory, so the present state could evolve in different ways, right? Right? Determinism is basically the claim that the present state, and by which you mean the global state, again, it really helps to have a foliation here. The global state, the global physical state of the universe at a moment, plus the laws of physics, determine uniquely the future and usually uniquely the past. I mean, you can come up with cases that are only deterministic to the future, but not the past, or the past but not the future.

2:19:45Those are weird, but normally it goes both ways. Okay. In a collapse theory is usually an indeterministic theory. So the present state of the universe is consistent with different ways it goes on, and also consistent with different ways it went in the past. This is also a mistake that Suskind makes. Okay, forget that. Um, so suppose the laws of the universe are indeterministic. Does that mean there wasn't a unique past and won't be a unique future? No. It means we won't, we certainly don't know what either of them, can't presently know what either of them will be or were because our database is what we have now.

2:20:31And you're telling me the laws of physics are consistent with everything there is now, and therefore everything we have now, which is a small subset of that, evolving in different ways and having gotten here in different ways. So in an indeterministic theory, there are, again, epistemic constraints, but it's perfectly eternal. An eternalist would say, still, there was one past, there will be one future. Why is it indeterministic? Because the laws of physics allow those to go differently. You know, conditioned on any given moment, it could evolve differently. In a deterministic universe, once you condition on everything going on at a moment, everything usually to the future and to the past is fixed.

2:21:17There's only one way it could go consistent with the fundamental dynamical laws. So eternalism has nothing, nothing, nothing to do with determinism. And eternalism, as I understand it, is just the triviality that there was one past, there will be one future. The entire universe from beginning to end is some four-dimensional structure with stuff in it that happens. Happened, is happening, will happen. I don't know how anybody can deny that. There's nothing. And time goes and end. I mean, for me, time is going this way, right? It has a direction to it. The presentist somehow doesn't like that. The presentist wants to say, no, all there really is is what there is now.

2:22:03Lee Smolin is somebody who also affiliated with the JBI who I've spoken with and identifies himself as an extremely radical presentist. Yeah, well, Lee, I don't think he means presentism in the sense I just defined it. Lee doesn't think the laws of nature are fixed. I mean, an assumption I just made is that there are just the laws of nature. They don't change. Maybe they're deterministic. Maybe they're indeterministic, right? Maybe it's a collapse theory. I don't know. But the laws of nature themselves are not evolving. And are you referring here to his idea that black holes are connected to baby universes where there's sort of natural selection with the laws.

2:22:55No, that's an earlier idea of Lee's. I mean, you have to separate Lee into periods. Yeah, yeah, yeah. So there was this idea that, and this is a little bit like we said with Penrose. With Penrose's cyclical cosmology, we have a big bang, but there was stuff happening before that that gave rise to it, right? But for Penrose, it's like there's one universe, it goes through an epoch, there's a big bang, another epoch, another epoch. They're just sequentially like this. We had this idea a long time ago that maybe when just a regular black hole forms, when a star collapses, and if you just are following out plain vanilla general relativistic field equations, you get down to a singularity.

2:23:39Maybe somehow by quantum effects, you tunnel through the, as they say, you tunnel through the singularity and then that gives rise on the other side to a new universe with a big bangy kind of beginning. And then he had this idea, well, then a universe that has more collapsing stars will have more progeny. You think of these successor universes as progeny, and then you try and play some kind of evolutionary game. It doesn't quite work because there's no selection principle. Okay, doesn't matter. But then this was supposed to, he was supposed to say, oh, that's why we see the physics we see because physics has, as it were, become fine-tuned to make black holes by this.

2:24:24That was early. That was early. And all of that, you're just always using, you tend to always be using the same laws. Now, maybe you allow through this crunch and new thing to change what we call the constants of nature. So maybe through that, as it were, in this epoch, electrons have a certain mass ratio to protons, and in the next one, it's a different one. If that's true, then you could kind of see how the idea is you could see how, well, it would prefer ones that gave you a mass ratio that gave rise to more black holes. And then there'd be a kind of quasi-evolutionary explanation for some of the constants, you know, fine-tuning problem?

2:25:12That's early Lee.

2:25:17Lately, what Lee has been arguing is entirely different. It's the laws themselves, not the constants. The laws themselves evolve in some sense and keep track of what they did in the past and stuff. I don't, I'm not a fan of that myself. But anyway, you need to separate those two. They're very different hypotheses. Well, now without any further ado, we get to get to what for you is probably the dessert of this episode. And that's talking about the arrival time and time of flight experiments. So what are those even to begin with before we launched into... Good. And let me also correct what might be a misapprehension from something you said earlier.

2:26:03You said, that's what I'm working on. It's not what I'm working on. It's what Siddhunt Das and Will Cavendish particularly are working on, these young guys who are doing, to me, fantastic, fantastic, fantastic work. Well, essentially, you're working on some philosophical aspect of them. Well, yeah. I mean, I'm backing up some of what they're doing methodologically. You're working on it. I'm going to write a little, I wrote a little introduction to one of their papers. They're doing the hard lifting here. Okay. I mean, I really, they're doing the hard lifting and they can do it. I just actually, we were just at a workshop with Sid Hunt and Will and David was there and some other people.

2:26:41In New York? No, it was up in Lake Placid and Daniel Sudarski. Oh, I have to mention this. In the last episode, I said you should have Daniel on or Bob Wald on to check what I said about general relativity. Okay. I actually asked Daniel to listen to the whole damn four and a half hour episode. And he said, there's no major mistakes. He's little things that he would have said differently, but he said, there are no major mistakes. That's good. Okay. Congratulations. Yeah. Well, I was happy to hear him say that. Yeah. Anyway. Yeah. So they're doing the heavy, I mean, they have the amount that they've done and the amount of detail they can give you is just astonishing to me.

2:27:22That's not me. But let's easily talk about what the question is. Go into a lab. Here's something you can do nowadays. You couldn't do it 20 years ago. You take an electron or take a single atom and you put it in a magnetic trap. There are different types of traps. There are magnetic traps. I mean, there are pole traps. They actually matter, which they are. I didn't know any of the this a week ago, two weeks ago. Okay, you put it in a trap, you can hold it here. And nowadays, they can hold it for a pretty good amount of time, individual, single particle, individual, single atom. And you've got a wave guide, which is going to kind of, it's just something that bounds it on this side.

2:28:09And at some moment, which you define, you have some very good clocks. We You need now, again, these femtosecond clocks, very accurate clocks. Some defined moment, you drop the confinement on this side, and you let the wave function, the quantum state, and the particle, if you think there is a particle, evolve and drift down this wave guide. There's a screen here. And eventually, a spot forms on that screen. And it forms both at a place, which you can just, if it's a photographic emulsion, but at a time. So you need a really accurate clock here to mark out not only where, but when did that screen fire, marking the arrival, as we would say, of the particle.

2:29:03And if you want to get really fancy, between here and here, you can put a two-slit kind of barrier so that you get these interference bands that you always talk about in quantum mechanics. But the point is, don't just look at where, look at when. That's data. You can collect that data. Some people, 30 years ago, they collected it. You could do much better nowadays. And you would think it should be a task of physics to be able to predict, even if only statistically, not only where but when will those spots appear. Nobody knows how to do it. Nobody knows. If you talk to Will and Sidon, who've looked at this, they say they can find you two dozen different proposals in the literature about how to even calculate.

2:30:03Now, you can see, I mean, let's just make some conceptual points. A, most physicists, as I said already, they say there are particles, but they don't believe there are particles, right? They don't believe there are actually located electrons, say, or located individual atoms that follow trajectories through space-time from the trap to the screen. So as soon as you say that, you say, well, what do you mean, you know, what you call this is the arrival time or the transit time, right? How much time elapsed between dropping this barrier here and the spot forming on the screen? But if you don't believe there are particles, then it can't be the time the particle arrived because no particle arrived.

2:30:51So now you're really in a conceptual mess. How do you even explain spots forming on screens? Now, I was unaware of this two weeks ago. There is a whole literature on the problem of screens in quantum theory, and it's unsolved. Nobody knows how to make a proper physical model of how a spot forms on a screen in standard quantum mechanics, much less when a spot. Now, the when problem's worse because, as I said, in standard quantum mechanics, you associate what are called observables with Hermitian operators. And there is an operator, a position operator, but there's no time operator. So you don't even know what you're doing.

2:31:35You don't even know how to approach it. Dozens of different proposals in the literature. They tend to agree in the scattering regime. So the scattering regime is where I have a target. I send something in and then I measure way, way, way, way back there what comes out. And it turns out, I guess, all of these or most of them agree in these limits because when you take these limits, then certain terms wash out, right? And they tend to agree in the limits in the long scattering regime. But they do not agree in the – if I start bringing the screen in and I don't do – I'm not doing scattering theory.

2:32:20They don't agree. And nobody knows even what the data is. and the point of it is again you talk to physicists and it's like oh we've worked every damn thing out that you can check in the lab until we build a super super super collider you know to go another step up from the large hadron collider and that's completely untrue These are tabletop experiments that can be done where you could collect data, if nothing else, about where and when dots appear on screens. That should be data that everybody needs to account for and nobody knows how to. Now, the next point is, I said a standard physicist is absolutely handcuffed on this because they don't believe there are particles anyway.

2:33:18If you have a pilot wave theory like Bohmian mechanics or something in that area, there's a big dispute about what to call Bohmian mechanics I don't want to go into. But take any theory that says, yeah, I think there are particles. I think electrons really are particles or, you know, they really do move. It really does get to the screen, right? It really was somewhere in the trap. And when you dropped it, it moved out of the trap and it went down this waveguide and eventually it hit the screen. It should be obvious that such a theory has an immediate conceptual advantage in trying to account for this data.

2:33:59Because if a particle really does arrive at the screen, then you can say what accounts for where and when it arrives has something to do with where and when it arrives. But if you don't think there are particles that arrive, you can't say that. And it is not clear what you do say. Not at all. To me, this is the most exciting avenue of way to go forward, of physics. And I'm just not, you know, I'm giving you my honest opinion, the most exciting thing I've seen in my lifetime. because when they say the standard model explains everything, what do they mean? All they mean is the standard model gives you a collection of particles that account for scattering theory as we have it.

2:34:50That's it. But most of the world is not scattering theory. Scattering theory is a very, very tiny little part of physics. it originally was done by what's called S matrix theory, where basically you say, all I really care about is I have an input and I have an output, right? The input is say two particles or whatever that are coming in. The output is whatever's going out. And all I want to do is account for this input output relation. And then you would write down what was called an S matrix, a scattering matrix that just takes, but then you say, but what's going on in the middle, right? I mean, in detail, how is this scattering occurring?

2:35:31You say, I don't care. I just want the scattering to come out right. Okay, that's something you can do. And I guess you can say the standard model looks like it's given you all the fundamental particles you need, those of you who don't believe in particles at all. But anyway, all the fundamental particles you need to do scattering theory, as far as we know, to the energies we can do it. But that's not all of physics. It's not even all of what's easily accessible physics. And these experiments are not being done. I mean, Siddhant has been trying for years to get experimentalists. Now, it's kind of specialized experimental apparatus you need.

2:36:13You need to be able to trap these particles. You need these high-precision clocks. And you need to, you know, when you really get into, and most theorists don't get into this kind of detail of experimental constraints. You know, how do I make the wave guide? What do I make the screen out of? What kind of problems are those going to, you know, give me?

2:36:39But it can be done. It has been done. These time of flight or arrival time data are used all the time. In fact, when physicists say I've measured the momentum of a particle, they've never measured the momentum directly. They've basically measured a time of flight and then used classical mechanics, not quantum mechanics, classical mechanics to calculate a momentum. It's a very shady kind of thing to do. right? The amount that people who proclaim to believe in quantum physics appeal to classical physics when they're trying to explain things to you, track that. Because often those are checks they cannot cash.

2:37:27They might say, oh yeah, I'm kind of talking classically here, but of course I don't mean that. Then you say, okay, then do it from beginning to end quantum mechanically and see what happens. There's a lot of appeal to classical physics in what they offer as physical explanations that they are not entitled to and that they could not really eliminate and still give you a coherent story. So you can try that for fun someday. You're not confrontational enough, you'll never do that, but anyway. No, I'm not confrontational in particular, as you've noticed. Yeah, let me run on like this. Well, there have been lots of times in the podcast history where I should have been confrontational, but it's just not the way that I am.

2:38:12It's not your style. Anyway, you said a lot of things there that I want to jump on and not in a confrontational way. But one is you said that this is the most exciting thing that's happened in physics in your lifetime for moving forward with physics. I'd like to get to that in a second. But first, do these experiments lend any sort of confirmation or insight into how you answered or would answer or have been answering these more traditionally metaphysical questions about fundamentality, flow, rate, direction, presentism, eternalism, anything like that? I mean, the only – the one – not there. There is one place where these experiments could, to everybody's satisfaction, nail something down.

2:39:11As you know, I've been – I more or less got into this business because I was worried about Bell's theorem and violations of Bell's inequality and non-locality. Okay? And I've been arguing for most of my career, please pay attention to Bell. I mean, I haven't been arguing it like a, you know, original thesis. Please read Bell. Please understand what he proved. What he proved is that you have these non-local, somehow there's some non-locality. Somehow, even though I've isolated Alice over here in her lab and Bob over here in his lab, and I put them very far apart, even such that if she does an experiment, there's not enough time for a light to carry news of that experiment, how it was done and how it came out over to Bob or vice versa, okay?

2:40:04That there still has to be some physical influence connecting those two labs, okay that's what belt proof

2:40:15now if you accept that this is now not a theorem but it's suggestive I think you'd say gosh I you're telling me there's this physical non-locality you're telling me it has to go faster than light maybe I can somehow make use of that to signal maybe I can use that for Alice to send Bob a signal faster than light. There's a causal connection there, some kind of real physical connection there. Can I use it? Now, this is not a theorem, but it's suggestive. You'd say, yeah, you'd think maybe if you're clever. It's there, right? It's there. Most physicists by far think, no, you can't do that. You can't signal with it.

2:41:08There can't be superluminal signals. And you say, why do you believe that? And they'll say, well, that's according to relativity. And you say, yeah, but relativity can't explain this, right? No relativistic theory, because relativity is local, it's relativistic locality. No relativistic theory can predict violations of Bell's inequality, but they occur, okay? If there's this non-locality offhand, I would think if I was clever, I could use it to send superluminal signals. Now, that's not a theorem. You can write down, you could write down a theory with this non-local influence, but for some reason, you're blocked, right?

2:41:52The physics itself steps in and says, you cannot use me to signal. That, it's not impossible. It'd be a little weird, right to me it's not what i would expect i'd really want to understand but why i mean what you know what how is this being blocked what's where the physics is using has this connection what what else is coming in and saying you can't use this to send signals right so my immediate intuition is i bet you can and then you say oh yeah you think so how now you say ah now i need a theory. Now, in order to understand exactly in which experimental conditions you might be able to prove that you might be able to send these signals, now I need a precise theory.

2:42:39I can't begin to answer that question in the abstract. I need a really specific theory. Now, it turns out, Now, this is what Will Cavendish will tell you. And if you want to have Will Cavendish on, have Will Cavendish on. Will Cavendish will tell you he's looked again at over a dozen proposals in the literature, in the standard literature, and he keeps finding superluminal signaling in those proposals. That if you think them through, you'll say, ah, if you're right, yes, you can send signals. Sidant Das came up in a kind of pilot wave setting. here's a way you could send signals.

2:43:26If you can send superluminal signals, that kills relativity, dead. Then there's no longer a dispute. Because if you can send these superluminal signals, then you need a preferred foliation. And you can even tell what it is. You could even determine what the foliation is empirically. And then it's all over for relativity. I think that's the way it has to go, right? I think it has to go because you need a preferred foliation to account for the violations of Bell's inequality, and we know those occur. I think that non-locality is built into quantum mechanics from step one, because you start out looking at configuration space for the universe.

2:44:09What do you mean by the configuration of the universe? You mean where are all the particles at a certain time? What do you mean by at a certain time. Well, I need a foliation. So to me, all this stuff is pointing in the same direction, and all this stuff is making sense to me that at the end of the day, in this conflict between quantum theory, the non-locality and quantum theory, the violations of Bell's inequality, let's just say that because you can take quantum theory out of it, the observed violations of Bell's inequality, are in conceptual conflict with relativity, that it's relativity that's going to have to be changed.

2:44:50It's going to be changed by putting in a preferred foliation. And unless something really weird happens, if you know the right experiments, you can actually determine that foliation. And probably if you know the right experiments, you can send superluminal signals. That's the way I think it's going to turn out. And nobody's looking in that direction. If you go to a normal physicist and you say, I have a theory that allows you to send superluminal signals, they will then stop listening to you. I reject your theory. They think they've built into quantum field theory that you can't do that, but they haven't.

2:45:26And there's a whole story about that. They're making a mistake when they say that. All they've done is impose a condition that means you can't do it one certain way. It doesn't mean you can't do it at all. So to me, as opposed to people, you know, worrying about black hole thermodynamics and information loss paradox and all this stuff where they're saying, gosh, you know, we're stuck because the standard theory explains everything we can see. We have to go way out on some limb to make any progress. I think, no, go into the lab, do arrival time experiments, get some really clean data there, Try and explain it.

2:46:04See what happens when you do. There's a bunch of stuff to be done that can be done. And it doesn't involve, you know, kalabayow manifolds and God knows what, right? It's funny that you mention black holes and information loss because that's exactly what was occurring to me as a place that it might be logical to go next or in that direction, just because as you held your two fists out, which were conserved, they stayed there for a little while. They're gone now, I guess. You had relativity on one side, Bell's inequalities. You replaced quantum with Bell's inequalities on the other. The conflict between relativity and quantum, the quantum is a big area in, I mean, there's a lot going on there.

2:46:56So black holes, one place, quantum gravity, another. And what I was going to ask is whether you find these time flight, arrival time experiments to be particularly exciting because they point in the direction of figuring out quantum gravity. And also I was curious just – I mean you made me think of black holes and the information loss issue and whether or not that has anything to do – and we can learn anything from those debates and dialogues about what time is. Okay, so in principle, because general relativity has to do with space-time structure, these kinds of arrival time experiments could shed light on gravitational effects and putting together a theory that accounts for everything, including gravity.

2:48:02I mean, you have to account for gravity. But the first iterations of them that can be done, you would hope that gravity is negligible. It's not playing any important role. It's really important to see that this is not a problem that arises from trying to put together quantum theory and gravity. This is a problem that arises in trying to get an explanation for phenomena that really should have nothing to do with gravity. It shouldn't matter if you were doing some of these experiments in interstellar space where everybody would say the gravitational effects are negligible. Of course, at the end of the day, if you add allowing particles to drop through gravitational fields or all kinds of stuff that you would normally bring in general relativity, it could have bearing.

2:48:55But that's way far in the future, and that also needs tremendous amount of even more accuracy in your clocks. I mean, I think I mentioned last time, we're at the point of accuracy in clocks where if you take two atomic clocks and place them on the floor and synchronize them and lift one up just this high and then put it back down, they're out of sync. And that's a space-time effect that is explained and predicted by general relativity. right? But yeah, I would not look at these arrival time things in the first raft of what you could do to be looking for gravitational effects. And if you ask, what are they saying?

2:49:38The answer right now is we don't have the data. We just don't have the data. This is the amazing thing. We could get all this data and then put it in front of anybody and say, okay, here's the data. Here's arrival time data that gives you not only when but where these spots formed on the screen. Go to your theory and try and account for that. That's a challenge for everybody. We don't have the data and we could get it. And it's a big challenge because people don't know how to do it. They do not know how to do it.

2:50:09So now the information loss paradox. All right, let me say a word about that. I have a paper. it's up on the archive. I never published it. I mean, I hope to put it in a book one day called Paradox Lost, if anybody wants to look it up, saying there is no information lost paradox. Again, it's just a mistake. And it's a mistake that comes from not understanding general relativity, quite honestly. So this question of information, is information conserved? Well, now I'm going to go back to Suskin. Suskin says such silly things. what do they mean by conserving information? Kind of a weird thing to even talk about.

2:50:50Information is a funny kind of abstract thing. Shannon defines it fine, but it doesn't, you know, why should fundamental physics even be in the game of talking about information? When they say things like, well, according to quantum theory, information is conserved. What do they mean? They just mean simply they think that it's a deterministic theory, right? In any deterministic theory that's deterministic in both directions, if you know the entire physical state at one time, you can figure out the entire physical state in any other time, whether earlier or later. In that sense, information is not lost.

2:51:21Now, that information is never accessible to anybody. Why? Because it's got to be the entire physical state of the universe. And one thing nobody will ever know is the entire physical state of the universe. And even if they did know it, they couldn't calculate with it. But anyway, they couldn't know it because you're only a little part, you don't have access to it, right? But you can ask, are the laws of physics fundamentally deterministic. Now, what they do is they say, oh, in quantum theory, if it's always Schrodinger evolution of the universal quantum state, that's deterministic. Sure is. Sure is.

2:51:53Schrodinger evolution is deterministic. And then they say, so information is never lost. But then somebody like Susskind says, oh, that guy tuffed, he's so silly. He thinks that fundamentally physics is deterministic. I mean, go and check your own interviews with Susskind. He kind of pooh-poohs looking for deterministic. He thinks, obviously, quantum theory is indeterministic. But in an indeterministic theory, information is not conserved. Because you're saying this state is consistent with different future states and with different past states. So you lose information. I mean, they're completely confused about what they're arguing.

2:52:32Right. That is interesting. Now, in order to even talk about this, you have to talk about the state of the entire universe at a moment. For that, you need one of these slicings, these Cauchy surfaces. And in this paper, I argue that if you take into account the Cauchy surfaces, you never had a problem in the first place. It is true that in the case of black hole… Tim, can I actually interrupt you for a moment? Just because I think that this is a really interesting point, and I want to make it sure that it's clear to both me and the audience. If you're saying that in an indeterministic version of quantum mechanics, information can't be conserved because the present is compatible with multiple different pasts.

2:53:14So we can't recover the information from the actual past. Yes. Okay. And I think that's very profoundly interesting to note here. Look, it's kind of, I don't want to say it's trivial. It's obvious when people talk about quantum mechanics being indeterministic, they mean the present situation is compatible with different possible futures. You could manage to find a theory that's indeterministic to the future but not to the past, but quantum mechanics isn't like that. If it's indeterministic to the future, it's equally indeterministic to the past. It means the present could have arisen from different pasts, but that means information is lost.

2:53:53There was one actual past. We don't know what it is. You couldn't know, even if you could know the entire physical state of the universe now, which you can't know, but even if you could, you couldn't figure out what the past was because different paths are compatible with it, just as different futures are compatible with it, right? Now, if you look at this stuff about black hole information loss paradox, you have to go into the stuff about Cauchy's research. I'm just going to say this. I can't explain it. If anybody's interested, you can look up this paper, Paradox Lost. Great title. In order to – the easy way to resolve that paradox is to be careful about your Cauchy surfaces and to notice that if black holes evaporate as Hawking claimed they did, and there's a whole story we could go into why he thinks that and the gaps in that argument.

2:54:46But if they do, and you represent that evaporation in a Penrose diagram, which we did last time, I showed you some Penrose diagrams, you can see that the information isn't lost. It resides inside, as it were, the black hole, if you will, even after it's evaporated. Now, that sounds funny, but I could show you in a diagram how that works. It requires a certain technical observation about this not being a continuous evolution in a continuum. Okay, there are theorems that Garrosh proved that Cauchy surfaces can't change their topology, but in this circumstance, they do. Okay, and you can understand why that happens.

2:55:32Anyway, all that stuff's in that paper for anybody interested. So there never was a problem. And, you know, we could have a whole session about how Hawking got to his radiation and what he inferred from the radiation and Page and all these other people. There's, you know, another eight hours on that or whatever. But, yeah, let me say I don't think – and I think people thinking that was the key to making progress were profoundly confused. And especially if you're someone who says the fundamental problem is that information is never lost and by the way, I think quantum mechanics is indeterministic.

2:56:14I mean, this is just flatly, basically flatly contradictory. You know, you're just, you're double thinking. It's Orwellian. And it's wasted a lot of people's time. Well, this conversation could not be complete if, even though we have discussed this issue many times, I did not ask at least a couple of things about time travel. Okay. So here's just a simple one. Is it at all possible, physically speaking, for us to get back to the dinosaurs and observe them? My answer, and I've given it before, nope. I see no reason from any piece of physics ever that suggests that's possible. You can take some mathematical expressions of the laws and make some really weird mathematical models because you haven't put constraints on the topology of the models, which would say you can do that, but I think there's no reason to believe those are physically realistic.

2:57:08I think time is intrinsically directed. It goes from past to future, and it doesn't go back. So there's no way you are going to having a continuous conscious life, remembering your past and getting into a rocket or getting into a weird, you know, time tunnel-y thing, will suddenly find yourself among the dinosaurs. Nope, sorry, out of luck. A recent conversation that I had on the podcast involves a guest suggesting that aliens could be time-traveling humans from the future. and it sounds like I just saw a very long blink. It sounds like you're ruling that out. Yep. And I would like to just get the strength with which you're ruling this out.

2:57:59How unlikely does it seem to you that our physics at this point could be so profoundly wrong that this sort of time travel could be possible? I mean, look, am I allowed to use infinitesimals? I mean, I don't even know that I could come up with a real number small enough. I don't want to – look, I'm a philosopher. I don't want to rule anything out 100%. Get as close to 100 % as you like. That's how confident I am that's not going on and it never – no, that's just a mistake. I think, of course, you have to ask, why in the world would somebody say something like that? I mean, why in the world? I mean, aliens to begin with, I'll just make this short comment.

2:58:47Please. From all of these sci-fi movies that we've had forever, what do aliens do? They have hyper technology, they come here, and then what do they do? They kidnap people and probe their anuses? They, you know, play tricks on people. I mean, how silly is that? They come down so you can see them and then they zip off. How silly is that? Why would they do that? If they have such high technology, they would never be seen. Why would they want to go peek around and then let us see a little bit of them and then disappear? I mean, it's just silly. It's just nonsensical. It's like, you know, no serious person should be considering such a thing.

2:59:32doesn't, you know, what a waste of time. I don't want to say it's a waste of time because I, I find it very interesting, entertaining more than, I mean, I, I'm, I don't believe that there are aliens here. I mean, yeah, aliens here. There's a perfectly good question. Is there life elsewhere in the universe? You have something like the Drake equation you can criticize this way. And that way seems to suggest there might ought to be life somewhere else, right? Did it evolve into higher forms of life? Next question. Next question. Let me actually point out something here that everybody misses. So I think, yeah, if there are enough planets, blah, blah, blah, probably life has evolved elsewhere because it evolved here.

3:00:19What about higher forms of life, right? Things that could swim and crawl. Sure, eyes. Yeah, absolutely eyes. They're gonna have eyes, right? Evolution will give them eyes. Question, will evolution lead to high intelligence that can make technology like spaceships? Answer, on Earth, there have been billions of species for billions of years. Think of all the dinosaurs over the entire period that dinosaurs existed. All that time, evolution was operating and not a single one of them could even make a hammer. It is not, in general, an evolutionary advantage to have high intelligence. Cockroaches will long outlast us.

3:01:11They're evolutionarily better adapted to survive than we are. So the question is, in all the history of life on Earth, only one species has evolved enough intelligence to make technology of any serious amount. If he's, oh, you know, a monkey can take a stick and take off the leaves and get ants. Yes. But I mean, serious technology. Only one. Out of all those billions and billions and billions, what does that tell you? 100 % for sure there is not a big evolutionary push for high intelligence. That raises the question, why us? And I think the answer is probably a combination, as people have said, opposable digits, right?

3:01:56I mean, what are you going to do with this intelligence that's going to be so useful? If you have pause, you know, probably opposable digits, fine motor control, probably voices and being able to produce language. So you need voice boxes that can produce language, you know, probably a combination of those. There was something unique in the evolutionary history of Homo sapiens that gave small increments of extra intelligence such a big survival advantage that it blew up our heads as big as they could go. It blew up our heads to the point where if they got any bigger, women would all die giving birth.

3:02:41That's also why we are neonates, right? We're born helpless, as everybody says. unlike a cult, unlike a puppy that's up and running around. We are helpless for years, and we have to be looked after. Why? Because we're basically way premature. Why? Because our heads are so big that if they waited any longer, the mother would die. It's only humans where intelligence gave that kind of advantage evolutionarily. So if you ask me, hey, we just found a planet. We have all sorts of reasons to believe it's got plants, it's got, you know, organic molecules. Do you think it has intelligent life to the point that it could make technology?

3:03:24I'd say probably not. Very unlikely. If that were a common thing, there'd be more than one intelligent species on Earth. Well, I wasn't planning on it, but I'm very glad I managed to shoehorn a question about aliens in here. That was really wonderful to listen to. But now just a brief note on which to end. I know I've asked you this question many times, but I think it is the way to finish our episodes. And that is, what is the John Bell Institute and how's it doing right now? It's doing great. Really? Yes. That's awesome. Big news. Big news since the last time we talked. Great. Right. So the John Bell Institute is a collection of people who are interested in the foundations of physics.

3:04:08It is the John Bell Institute for the foundations of physics. It exists because foundations of physics is not a recognized anything. Pretty much nobody in the world has a position in the foundations of physics. Maybe Sean Carroll does now, sort of. You know, some of us hang out in philosophy departments, but we're not identified. It's not a department of, you know, there's no department of foundations of physics anywhere. So I'm trying to, been trying to create an institution devoted to these questions. And we have lots of, we have a faculty, we have a bunch of honorary fellows, we have a bunch of regular fellows.

3:04:49Anybody can go to our website and see who's involved. And what I've been doing since I created it is trying to find a home for it. My hope was to buy a place that we had on the island of Var in Croatia, and that's what I was aiming for. And that, for various logistical reasons, became impossible as of last year. So then the question is, what is plan B? Okay, we have now, I had before on paper, but now we have joined with the University of Split. The University of Split has just acquired a beautiful, beautiful location with a large lecture room and a small lecture room and housing for 40 students.

3:05:33Amazing. That they are making available to us to kind of have a permanent association between the John Bell Institute and this location. It's a little bit outside of Split, if anybody's ever been there, on the Mariana Peninsula. Beautiful location, right on the water. There's a beautiful public beach, five-minute walk away. It's spectacular. And so I got permission to use that location within the last three weeks. Amazing. And we are hoping now Anjel Obasi has proposed to actually even at the end of August put on a summer school on foundations of physics. We are just trying to get that organized.

3:06:27It's short in time. So, you know, we hope we can get that organized. If anybody's interested, we'll put up information as soon as we have it on the website about students who might want to apply for it. I mean, we've got a, you know, we've got a lot of details to work out quickly. but I'm doing my best on that. So as far as that goes right now, we have a place for summer schools and workshops. I hope sometime now in the distant future, and anybody who gave money, we much appreciate it. And we still, although we are not going to use it to buy this one location, we still need it. We're trying to recover as much as we can from that location.

3:07:07We have moving costs and any other money we're going to use to put on these summer schools. So if anybody wants to give us money, we still need it. And the GoFundMe is still there. I mean, I need to change it, but anyway, it would still go to us and we would greatly appreciate it. I hope eventually actually to have a physical location that's just us for, not for summer schools and workshops, but for individuals who work to come where they can just stay with other people and just hang out and work, do their work and talk to other people. So if this eventually in, you know, another few years, there might be a second location for that.

3:07:50We can't do that in this university of split location, but we can put on workshops in summer schools. So we should start the first one this summer and then And hopefully by next summer, kind of be up and running and have some things going on there. So fingers crossed. Yeah. Well, this is news to me. So I'm really so happy to hear this for you and for the JBI. I have truly lost count of the number of conversations we've had on the show now. But my mind is already worrying as I think about, and I want to stress, I said worrying, not worrying about what we're going to do for the next one. But thanks, Tim.

3:08:31This has been excellent. Thank you.