Episode 31: Unsolved Problems in Physics Part 2 - Clocks, Blocks, and Eternalism

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Unofficial, reviewed transcript. It may still contain mistakes; check the podcast when wording matters.

Speakers are labeled by first name where identified. Unidentified-speaker labels may refer to different people. Bracketed question marks indicate uncertain wording.

Transcript

[00:00:10]  Bruce: Welcome back to The Theory of Anything podcast. We are continuing our discussion with Sadia about the mysteries of time and other physics-related areas of interest. So we've got Sadia and Cameo with us today. So say hello, guys.

[00:00:25]  Unidentified speaker: Hello.

[00:00:26]  Bruce: All right, Sadia, let's go ahead and just jump right back in.

[00:00:28]  Sadia: So last time we kind of talked about, we kind of wanted to talk about the laws of physics. I wanna get a little bit into what a physicist means when a physicist says laws of physics. There is actually a differentiation that we make between what are called the laws and what are called the principles. Okay? So when a physicist refers to a law of physics, it means something specific. Now, all of that is gonna tie in nicely with something called the problem of time. Okay? So I think I'm gonna try to bring all of this together because that's the best way to make sense of what I've been, what I wanna talk about in pointing out the problem of time. So I've actually divided up the problem of time into two parts. I recognize that there are two problems of time. One, I'm gonna call the first one the easy problem of time. The easy problem of time is basically about understanding what are clocks, okay?

[00:01:26]  Sadia: And then the hard problem of time that right now hardly any physicists are addressing and don't seem to be that bothered by it, I mean, they're bothered by it, but they're not doing anything about it, is about the asymmetry that rules the world. There isn't one asymmetry. Overall, there are lots of asymmetries in the world. And so the question of the hard problem is what gives the universe these asymmetries which sort of define an arrow of time, okay? And we'll talk about what we mean by arrow of time, and we're gonna identify a bunch of arrows of time that have been identified by a bunch of physicists, okay? So let's start with the easy problem, okay?

[00:02:10]  Sadia: So for the easy problem of time, before I get into it, there are certain terms that I'm gonna use, which I think I should clarify now. One of the things that actually, when I was an undergrad and I was interested in foundational issues, which I didn't pursue in the end, but what I was interested in was the idea, something called relationalism and also something that's tied to it called background independence. So let's first talk about relationalism. When you do physics, one of the things you realize is that all the measurements that we make in physics always correspond to relational data, okay? So if I measure a length, what I'm doing is I'm measuring length. When I say something is at a certain position, I am measuring relative to some reference point that I've already picked, okay?

[00:03:02]  Sadia: And luckily in the world, the world provides us with all sorts of background structure relative to which motion can be defined. And we can pick some useful reference points to say how fast something is moving, in which direction. So those things, luckily for us, we have background structures relative to which we can describe motion. But when we're trying to think of the universe as a whole, the universe is supposed to be something that is complete in itself. So we can't assume that there is anything outside of the universe, whether it be time or any type of space relative to the way which the universe expands, contracts, or whether the universe is evolving relative to some external time. All of those things just, not only that, they just don't make sense.

[00:03:55]  Sadia: It can easily be shown that how a lot of that stuff is pretty redundant. When we do physics, we have to consider when we use the word physics, I mean, sorry, the word universe, we mean something that is fully contained. So any type of measurements, any type of data we have in our theory has to refer to something that we can measure within the universe without relation to something else. Now, Newtonian theory, basically, Newton actually used absolute space and time the way he originally formulated, his laws and stuff depended on an absolute space and time to give velocity meaning. But Julian Barbour, a physicist, Julian Barbour, who's actually done a lot of work thinking about relationalism along those lines, pointed out and points out in his work that how there is no need to have this absolute structure, and Newtonian theory can be cast in a fully relational form. And it also reveals a lot of interesting things when you do that.

[00:05:05]  Sadia: So that's basically the idea behind relationalism. So I'll pause for a second. Do you have any questions or you guys have any questions about what relationalism is about?

[00:05:15]  Bruce: Yes. Let me just, I think I understand what you're saying here. So in terms of like Einstein's physics, it's all about how you are in relation to something else. So if two things are moving near the speed of light, they're going to perceive themselves differently than a point of reference that isn't moving near the speed of light. Is that what you're talking about here?

[00:05:38]  Sadia: It is sort of like that. And actually, Einstein started out instinctually, like, because he was very much, he was reading Ernst Mach, right, the philosopher Ernst Mach, who was who pushed this quite a bit, who was an empiricist. And he actually pushed that we should have everything in our theory should correspond to something that is observable, which also means that it should be relational, right? Because then if you're assuming some sort of background of something called time, which is outside our universe, then it's not, you know, I mean, it's not something we can measure if it's something that is outside that, you know, relative to which the universe evolves, it has to be part of the universe. So he pushed for that. And Einstein was inspired by that.

[00:06:24]  Sadia: And when Einstein actually came up with the principles of general relativity, and when he when he worked on, you know, worked on that, he started with that intuition. But oddly, he kind of, as Julian Barbour's pointed out, that's where I kind of learned about this, that he actually ended up settling more for an operational approach at the end. He never really fully addressed, like he never really fully addressed some of the questions, for example, how does the universe like what are clocks? You know, what defines an inertial frame of reference and stuff like that. So, but he just assumed that there were certain things that were given like clocks. And then he talked about the behavior of clocks, but he never really fully addressed the question that what, how, how a clock is defined in the universe.

[00:07:16]  Bruce: So ultimately, general relativity states that there is no privileged frame of reference. Is that the opposite of relationalism?

[00:07:27]  Sadia: No, we're actually going to, can I just say we're going to go into that? The block universe view is going to come out of that and we'll see how that works. So as we go forward, we'll talk about that. Any other questions before I move on?

[00:07:41]  Unidentified speaker: No.

[00:07:42]  Sadia: All right. So you're going to hear me talk about dynamical laws of physics, right? When we talk about physics, a lot of times we talk about, you know, in the more advanced physics, not the high school physics, but, you know, when you do the actual research level physics, you're talking about dynamical laws of physics. So just a quick differentiation, when we do kinematics, for example, we deal with, you know, descriptions of things like velocity, acceleration of a particle without considering the forces that are causing them. So we just look at how, you know, these things are related and we don't care what type of force causes it. And we don't have to include that in our picture. But when we do dynamics, dynamics is more is more complete. So the laws of physics, which are also called dynamical laws of physics.

[00:08:31]  Sadia: So when I say dynamical laws of physics, that's going to mean the same thing as when I'm going to say laws of physics. They're about correlations that fully contain what it takes to describe the evolution of the system, whether it's your clock, the time parameter, whatever, you know, whether there are interactions in the system. All of that should be fully contained. In that view, when we're looking at a dynamical law that should be fully contained relation in that sense, you know, kind of we're saying relational and nothing should be left outside of it. So the interactions or the so-called forces are part of the dynamics. So these dynamical laws or the laws of physics are expressed in the form of differential equations.

[00:09:15]  Sadia: And in a fully relational theory, the emergence of these dynamical laws with time. So we'll see that time actually, what we call time or clocks, you know, it has to emerge with the dynamical... it has to emerge with these dynamical laws. And it can be realized as a result of solving a sort of extremization problem, like a variational principle by which we say, OK, we'll get into this in a minute, but it comes about through and solving an extremization problem. So any questions at this point? So like I said, that there is a difference between laws and principles. Principles in physics are more like meta laws, and sometimes they're just expressed as a statement.

[00:10:04]  Sadia: They are sort of taken for granted and come from the intuition of a physicist. They are not directly testable, but because of the models that incorporate the wisdom or whatever you want to call it. I don't want to use the word wisdom, but that incorporates the sensibilities of that principle basically indirectly tests the principle. So what we really test are our models, but the principles, like, for example, law of conservation of energy, that is more like a principle. Then there is another principle of Einstein. I don't want to get in too detail.

[00:10:42]  Sadia: Like, there is general relativity is based on some principles, like the equivalence principles. So to think of these, these are kind of more like meta laws that kind of talk about the behavior, you know, that kind of constraint laws in a sense. OK, so so but when I use the word laws of physics, when a physicist says a law of physics, usually we mean dynamical laws, which are kind of like differential equations, are put in the form of a differential equations, whether it be the Schrödinger equation. In classical mechanics, it would be your equation. Newton's, there's a, you know, like a differential equation that can help you solve the problem of the evolution of a particle under a certain force. So stuff like that are what we call the laws of physics.

[00:11:30]  Bruce: Okay. So just to maybe relate it to our interview with Chiara, principles are like in constructor theory, they're things that are forbidden or science of can and can't type things, correct?

[00:11:45]  Sadia: Exactly. So yeah, so we see that there are a lot of principles right now in constructor theory. And yeah, that's right. Okay. So anyways, as I said earlier, a fully relational dynamical theory should emerge with its own clocks. In other words, once you take the idea of relationalism seriously, and then you see how... [unclear phrase] In a minute, I'm going to show you how laws emerge in a theory, you'll see that they will emerge with something that you can use as a clock. They kind of go hand in hand. They're pretty much just intimately kind of connected to each other, the concept of a clock. So I wanted to throw out something that John Wheeler had said. Just yesterday, I ended up actually going back and looking at his thick book called Gravitation, which he wrote with two other people. But he talks about time. He says time is so defined that motion looks simple.

[00:12:44]  Sadia: So time is so defined, and this is kind of really subtle, and he kind of goes into it. So I'm sort of going to go into this and hopefully explain that. But interestingly, you know, you pick up all sorts of books on general relativity and stuff, and they talk about time, but you never really fully are satisfied with what time really is. And, you know, I kind of had that feeling when I took general relativity, and I kept asking, no, but what is, okay, you're saying this is something, and you know how Einstein goes into talking about the behavior of clocks and stuff. But I still never, I'm like, but what am I supposed to make of time? What is a clock? What defines a clock? And I wasn't even sure, like, what was it that was bothering me, till I actually read Julian Barbour's book, the first book he wrote was called The End of Time. And that is a question that I haven't heard anybody else address but Julian Barbour.

[00:13:40]  Sadia: So it was fascinating, like that opened me up to looking at physics in a deeper way, and then I think a lot of operational approaches. That's one of the things about operation, like even quantum mechanics, quantum mechanics started out with a very operational approach too. And that can kind of blur your vision of what the reality is like. So anyways, let's go forward and hopefully that will make a little bit more sense.

[00:14:14]  Bruce: Can you explain what you mean by operational approach?

[00:14:17]  Sadia: Operational approach means that you take certain things. So you assume that the universe gives you clocks, right? That you can have a good clock. In a minute, I'll tell you what I mean by a good versus a bad clock, right? So once you assume that the universe provides you with good clocks, an operationalist is interested in how the behavior of the clocks, different clocks relative to each other changes, when somebody is moving, accelerating relative to another observer and so forth. So if you are... So the opposite of that, so what I'm saying is that when you are purely stuck in operationalism, you may not care how the clock actually comes about in the universe. What gives rise to a clock? What is it about the universe that provides us with clocks?

[00:15:03]  Bruce: It treats a clock as an atomic thing. We're not questioning how it works. We're just saying this is something the universe has as clocks, and this is how they happen to function.

[00:15:15]  Sadia: Yeah, like for example, even Einstein, there was some place I can't remember the exact quote that he kind of looked at a clock as if it's something that works, kind of has a periodicity to it and so forth. Even though he kind of, you know, so Julian Barbour's actually pointed out that, no, you don't really need any periodicity for a clock. And as a matter of fact, astronomers, I have a background in astronomy too, so I kind of appreciate that, that astronomers knew more about time than physicists did a long time ago. You know, the ancient astronomers were doing timekeeping, so and then some other people have kind of highlighted what a clock really is. Maybe as we go forward, I think you'll probably get a better idea of what I'm kind of talking about. It's kind of hard to, and then you'll see what I mean that then we can go back, if you like, to the question of what operationalism is and what it misses out.

[00:16:11]  Sadia: Okay. So now I'm going to show you the approach of how Julian Barbour has addressed this question of what is a clock.

[00:16:20]  Sadia: So first of all, going back a little bit to the John Wheeler's statement about time is so defined that motion looks simple. Now this is going to get really subtle. So it's really, I was thinking about what's the best way of talking about this. This can get really confusing. So let's say that you're studying the evolution of a system. All right. You're looking at a system and it behaves some, it's behavior exhibits some sort of an anomaly that doesn't fit in your worldview, like in the sense of like, in the same sense that when Newton, in Newton's time, we had the Newtonian theory, but Mercury's orbit showed that kind of anomaly that didn't really fit. There was a little bit of, I forget what exactly was it about the Mercury's orbit that just didn't fit in well with his theory. So, you know, so you can almost, you can say that there is this presence of this fictitious force, right, that is not explained from within your worldview.

[00:17:19]  Sadia: When I say worldview, I mean from the lens of your known physics. OK, so we could say that in that case, Mercury's behavior would be something that didn't look simple. All right. But we know that Einstein's general relativity came and showed that in his theory, the everything about Mercury's orbit is fully understood. So then that motion no longer looks complicated. So do you see what I'm trying to say when I say simple versus complicated?

[00:17:46]  Bruce: Yeah. So, well, you're talking about the perihelion, if I pronounce that correctly, of Mercury, which can only be—can't be explained under Newtonian physics, and it requires general relativity to be able to explain Mercury's motion. So in this case, it sounds like when you're saying it's complicated, that almost is more like it's an anomaly, to use the Kuhnian term. It's a problem, to use the Deutschian term. It's something that doesn't match our expectations with the current theory that we believe we have.

[00:18:19]  Sadia: Yes. And then that anomaly disappears when you're looking through the lens of general relativity. So there's no problem there. And then time, what is time, is tied to that idea. And the time in any theory should be defined so that the motion from the lens of that theory looks simple. Does that make sort of some sense? Because time is used to, like time for a theory, like when you have a clock that is based on a certain theory or from a certain understanding, let's see, what am I trying to say here that from within a theory it has, well, let's go forward. I think I need to make that point a little bit more. Because I'll probably end up going into the whole thing. So the other thing we have to consider is that a clock can't really, a single clock can't really, is kind of can't be defined on its own. It's always, you know, when we talk about clock, we really should be talking about clocks. Because what do we use clocks for, right?

[00:19:18]  Sadia: In day-to-day life, you want to keep appointments in the olden days, you know, when the astronomers or this, you know, who were at one point astrologers, they were interested in all sorts of events such as eclipses, they want to keep up with the seasons. So the idea is that, you know, to do that, like you're, and I'm going to show you in a minute what I mean by this, that the clocks have to march in step in order for them to help you keep your appointments. By marching in step, what I mean is that if you have a clock with, let's say, you know, the old fashioned ones with a dial where it turns.

[00:20:02]  Unidentified speaker: Yeah.

[00:20:02]  Sadia: So you're looking at what, when you look at it, you can think of that as the hand of a clock turns a certain angle every time. Right. So let's say that we measure that angle and maybe it's certain number of degrees or so. And then we compare it to some other clock where maybe it's a digital clock. So when you have a second goes by on the digital clock versus an angle turns on your mechanical clock, the ratio of the two should remain constant if they are to be good. Like, you know, for those two clocks for somebody with one clock versus the other to be able to keep appointments. So this idea that they should march in step is important to the concept of clocks. So that's why you can't really first of all, you know, it's meaningless to talk about a single clock.

[00:20:52]  Sadia: What does that mean? OK, the other thing I'm going to talk about is let's talk about a good versus bad clock. So a bad clock is something that again kind of using what Wheeler said using that it will make a motion look complicated. So let's say that I'm using a bad clock. In other words, that the intervals on that clock are somehow not moving, you know, like changing in a uniform way, right? Obviously, now, can you see there's a bit of a circularity here because just to even make that statement requires another clock, right?

[00:21:24]  Unidentified speaker: Right, right.

[00:21:25]  Sadia: Because and just to clarify that point even further, here's the thing. So let's say that I think that, you know, just to kind of start off, I said that I have a bad clock, a bad clock will make a simple motion look complicated. So let's think of a simple motion, simplest motion being an object moving at constant speed in a certain direction in a straight line. So an object moving at constant speed in a straight line. Now, if you measure, if you actually try to calculate the speed of an object using a bad clock, you're going to think that that object is accelerating or decelerating.

[00:22:02]  Bruce: If the clock is like slowing down or speeding up, then it's going to make it look like the object that's actually moving at a constant speed is speeding up or slowing down.

[00:22:12]  Sadia: Exactly. Now, let's imagine that if there's no independent way for us to know whether an object is actually moving at a constant speed in the same like in a straight line, how do you know that it's not the clock that's bad, but it's actually the particle that's actually accelerating or decelerating? Right? It is possible that maybe if you had no other independent mean of determining that the object is actually accelerating or decelerating, then you're going to have a problem at hand. You're going to say, is my clock a good clock and just the object is accelerating? Or if the clock is bad, making it look like a simple motion is more complicated. See, this is what I mean when I say an operationalist gets stuck. These are the type of questions you want to ask yourself. Like, how does the universe create good clocks? Are there such things as good clocks? What constitutes a good clock? Right?

[00:23:10]  Sadia: So these are the sort of questions that take us deep into the heart of relationalism. And we have to agree.

[00:23:17]  Bruce: Okay, I'm with you. And that makes sense. Can I take a stab at how you would solve that problem? So I'm not a physicist, and I've never given this any thought at all prior to this moment. But it seems like you would want to try to set up an experiment where you knew something was moving at a constant motion and wasn't accelerating. And then because there were no known other forces acting on it. And then you could use that to determine if the clock is good or bad.

[00:23:47]  Sadia: So that's exactly right. But again, it goes down to our assumption that how sure can we be that that is an isolated system? Because in reality, all isolated systems in a universe are always approximate. And as a matter of fact, I'm going to start to go into how the very first clocks were realized, which was the ancient astronomers. So that is a standing question, right? That we are making the assumption that we can be sure that our system is isolated. And in a way, I mean, I will say that we are lucky that the universe does provide us with approximately isolated systems. So for example, our solar system, the entire solar system, is decently isolated from the rest of the universe to give us decent clocks. At the end, it really depends on what sort of accuracy you're looking for, what sort of precision you're looking for.

[00:24:40]  Sadia: Like when, you know, if I'm doing an experiment where I am worried about nanoseconds or whatever, then, you know, I mean, I'm not going to use the solar system as a clock. You know, I would go to the atomic clocks. But we have to address that question that in the end, and you are on the right track, of course. That's how we know what a good clock is. It has to be kind of like an isolated system. And it also ties in with what a dynamical law is, because an isolated system... Well, let's go forward, actually. Let me give you an example, and then we will kind of talk about that. Any other questions or any comments before I go on?

[00:25:17]  Unidentified speaker: No.

[00:25:18]  Sadia: All right. So the question is, how do we know a clock is a good clock? Or how do we know a good from a bad clock without there being some sort of a perfect master clock? So a perfect master clock could be something that refers to a fully closed system. You know, [unclear] an isolated system somewhere. Or in the case of Newton, he assumed that there was some master clock outside the universe. And he assumed an absolute time. So and he gave up on relationalism. And Poincaré, Physicist Poincaré actually kind of, you know, pushed on the relational approach himself. And then Julian Barbour fully took it on as a challenge and actually contributed a decent amount to this whole issue in classical physics. I was actually on one of his workshops on time when he solved something called somewhat of related issue of called the Scholium problem. And it was it was kind of it was really neat.

[00:26:18]  Sadia: It was kind of it's a memorable moment for me when I went there. He actually lives close to Cambridge and Oxford. And he's worked with a lot of people like Lee Smolin who says that, you know, like Barbour actually mentored him. And he's kind of a little bit of like a sage, a physicist sage. He's actually an independent physicist. He kind of he left academia and kind of worked on issues that he was interested in and did his research. What he did was he was translating papers from Russian into English. That's how he made his living and he lived on a farm, which is roughly kind of somewhere about the same equidistant from Oxford and Cambridge University. So he hangs out with a lot of people there. And just to kind of give you an idea, since I'm mentioning Julian Barbour quite a bit. OK, so so let's address the question. And Julian Barbour gave me an appreciation. He asked this question that what is the duration, right? What is duration? So let's start by building a simple clock.

[00:27:17]  Sadia: Let's go to classical mechanics. Let's not worry about quantum theory, general relativity. Let's think of a simple universe based purely on classical mechanics. And so Julian Barbour beautifully addresses this question that what is the bare minimum we need in the universe to construct a clock where we could have, where the system could evolve relative to some clock parameter. OK, so he's beautifully in his book and papers and stuff has beautifully shown that to define a clock parameter, you basically need a minimum of three objects with correlated motions. So those three objects could be imagine a very simplistic, like a simple solar system without any other planets other than sun, maybe two other planets. It could be a binary star system where two stars go around and another planet that goes around them. So there are three objects. We don't really have to assume that there is some sort of a periodic motion taking place where every planet has to trace out a set path.

[00:28:20]  Sadia: No assumption like that is needed. All we need is three-particle system with correlated motions. All right. So now think of taking snapshots. Imagine that we are like God, like figure, and we can take pictures of this simple universe governed by classical mechanics. And we take pictures of the three objects. All we are given, even though I'm saying, we are assuming that we are God-like figures, which pretty much makes you think that there is an outside world and space. But that is only so I can talk to you about this. When I'm talking to you, it's kind of really hard to talk in a fully relational way. It's just a useful way to communicate the idea. But all that exists for the universe is those three particles. So what are the things that one can meaningfully talk about, right?

[00:29:11]  Sadia: Let's say that if the three-particle system, imagine a snapshot. If that whole thing expanded or contracted, do you think it would even be meaningful to say that there has been an expansion or contraction if all that actually happened was everything scaled up or down? Yeah, you won't know, right? Similarly, what if one particle, now think about how the configuration has changed. If the configuration changes, all we can really say is that maybe one length has gotten longer relative to the other length. You can just use one of the relative, you can describe a unit of length as the distance between two objects. You can use that to measure the other objects, the distance to the other objects. But there is this problem that if all these lengths are changing, how do we even meaningfully talk about length? We can only ever talk about things in relation to each other.

[00:30:10]  Sadia: But Barbour has pointed out that there is one thing that holds a little more meaning in a relational universe like that. For example, the angle, the overall shape, because the three objects make a triangle, right? The angle between the two objects is a meaningful relational parameter. So he says, now going forward, and how do we get a clock out of that? And why I'm saying that you just need a bare minimum of three particles and their configurations as they change through time. And you can actually do that with just two snapshots of the system at two different times. Now, of course, I'm using the word time, and obviously there is something to be said about that. But imagine that all that exists were those configurations, like just snapshots. So now let's plot a graph, which we are going to call the configuration space.

[00:31:02]  Sadia: Regular, normally when we plot graphs at a high school level, we're plotting position against time or something like that to show the evolution of the system. In this case, we're plotting a graph where each point represents the configuration, the entire configuration of that three particle system. Now imagine all possible configurations plotted in this configuration space, or configurational graph if you want to call it. The next thing we're going to do is we're going to pick two points, just two points on the graph, and we're going to think of all possible paths through which the system could go from one point to the next. So imagine connecting the two paths through all these different configurations using different graphs. And then the next thing we do is we define something called an action.

[00:31:56]  Sadia: I'm not going to go too much into it, but we're about to solve an extremization problem. We're going to apply a variational principle. And we're going to say that there is this quantity called action in physics, which is well known by all the physics people and students. And the path with the smallest, or with the, I should say, extremal action turns out to be the one which shows the configurations that actually obey Newtonian physics. And not just that.

[00:32:26]  Bruce: Say that again. I don't think I quite got it.

[00:32:29]  Sadia: So the extremal paths, so all the different paths, if you actually picked those and looked at the different configurations, most of them pretty much are not going to show you any correlation, right? It's just going to be like, oh, well, the configuration changed like this, like that, whatever. But there is one particular path that's going to pick up a correlation, and that's the one which is an extremal path, you know, where this thing called action is extremized.

[00:32:59]  Sadia: That's the path whereby the evolution follows a law. That's the only path where you're going to see that the evolution actually follows what can be recognized as a law, and where you can, from that path, and this is what we do in physics, we actually solve these problems and we get equations out of, like we get equations of motion out of that, to that extremization problem. So not just that, typically we kind of don't worry about it, and we just call, you know, look at the evolution in time, but there's nothing really, you don't really have to assume any time parameter.

[00:33:34]  Sadia: You can pick any other parameter, suitable parameter, relative to which the system evolves, and you can just call it time if you like, but there is no really good reason to call it time. It's just one variable, so that variable could be something like, imagine your triangle, right? Imagine an angle, one of the angle that you pick in the triangle, and when that angle changes, how the other angles change relative to that and how everything else evolves as this angle changes. So that angle could just be used as that time parameter. So you pick some sort of suitable parameter, suitable being relational variable, and you just use that as your clock parameter.

[00:34:17]  Bruce: Okay, so basically in this triangle, you've got three angles, you pick one of them, one of the angles, and it becomes the clock, and then the other two you measure in terms of that first angle.

[00:34:29]  Sadia: Exactly. So you basically picked a clock parameter relative to which you can meaningfully talk about the evolution of the system. And guess what? Time has disappeared, right? I mean, of course, time has disappeared if you ignore that there is actually an evolution of the system. So in Barbour's universe, which originally he called Platonia, he actually changed it. You can see where that word is coming from, right? His website is actually called platonia.com, by the way, still, although his idea has changed and now he no longer calls it Platonia. It's a different type of a space, a shape space. But so in his universe, all that exists are configurations of the universe. So here I'm just talking about a three particle, the bare minimum that you need for a clock, but you can add more and more particles. And then, you know, as long as you have an isolated, approximately isolated system in a universe, within the universe, you can use that to get a clock, right?

[00:35:28]  Sadia: You define a clock, and that will be enough to give you, to meaningfully define the evolution of that system. So the system could be the entire solar system now. So you see time has started to vanish, right? Yeah. So the more seriously you start taking these dynamical equations, whether it be in classical mechanics, whether you go now to general relativity, whether you go to quantum theory, people having looked at this type of problem like that have started to, when I say people, I mean physicists, are now starting to become more and more convinced that time really, if that's all there is to clocks and time, then time really doesn't exist, or the better way of saying that it is an emergent property, right? So, it's kind of taking physicists towards that type of thinking, where more and more people are like, yeah, you know, that's all there is to time.

[00:36:27]  Sadia: Okay, so time is emergent. See how the clocks emerged out of our theory, so time is emergent. Okay, so anyway, so our solar system actually, you know, within our solar system, we can pick clocks and they show remarkable correlations. So for example, in astronomy, there's something called ephemeris time. I'm not going to go into too much of the detail, but there are different times, types of clock measures. One is to do with the mean solar time. There's another one called sidereal time, ephemeris time. So the ancient astronomers were familiar with, you know, this type of stuff. The ephemeris time came much later, but the sidereal time where you take into account the background of the stars, you know, you can define clocks in that way.

[00:37:21]  Sadia: And this allowed the ancient astronomers or astrologers to keep up, to do their timekeeping, to make predictions of the solar eclipses and stuff like that. And you can see how the predictions would go hand in hand with that, right? Because the whole definition of a clock is based on the idea that there are these laws, all of that emerges together, so you can make predictions as well.

[00:37:42]  Sadia: So you could even use the area, for example, kind of based on Kepler's laws, where the planets sweep out equal area and equal intervals of time, you could actually have clocks that march in step in this way, where you, when you look at the area swept by a planet, some planet, and maybe you pick a certain amount of area that when a planet sweeps, and you compare that to some, you know, and maybe when Earth makes its full rotation, and those two seem to decently march in step. So there you have good clocks provided by the solar system, where you can do timekeeping. And then you can even make mechanical clocks on Earth, which keep up with these clocks. So that's the whole game of timekeeping here for you. All right. So this type of a thing that I talked about pretty much has been like approached in general relativity as well.

[00:38:38]  Sadia: I kind of started with classical mechanics, but Julian Barbour has actually done work, a lot of work in general relativity as well. And so now let's go back to this whole thing of block universe view. What is that about? So Julian Barbour took this idea of relationalism really seriously. And he asked himself that how relational or how sometimes the way he puts it, how Machian, as in Ernst Mach, who was the big relationalist, how Machian is general relativity. So looking at the way general relativity is formulated, which gives us that block universe view, it seems to be that the general relativity doesn't appear to be fully Machian, as he's expressed.

[00:39:23]  Sadia: So in the standard formulation of general relativity, time is fully spatialized, kind of like how I've talked to you about it. In other words, you reduce everything in general relativity to basically a geometric theory of spacetime. So you have this geometric theory, which corresponds to this block universe view, and the different slices of this block universe would correspond to different, like where you can see that a slice would have all the clocks that appear simultaneously, or are in, what's the word, where the clocks are synchronized, and you can talk about absolute simultaneity in that plane. But there is no special slice of that universe, right? You can keep slicing in a different way. There is no one slice that sticks out and says, hey, this might represent some sort of a present moment, the now in the universe.

[00:40:20]  Sadia: So you see, interestingly, this is the view which goes with the philosophy of eternalism, which is pretty much what's believed by, I would say, majority of the physicists, although I don't know. I've never seen a poll, but that's kind of like, you know, if you buy into the block universe view, you are, you can't escape eternalism, is what I'm trying to say.

[00:40:36]  Bruce: So if you think of time as simply another dimension, which is the way we sometimes try to describe Einstein's physics, because he, I can't remember exactly how this works, but mathematically, you look at the space and time just becomes one of the dimensions, and it actually traces out movement through that for whatever dimensional space. But one of the implications there is that time—past to present, and it's deterministic. So this may be tied very directly to determinism. It's deterministic, so past, present, and future all already exist, essentially, in this way of looking at physics. Is that what we're talking about here?

[00:41:16]  Sadia: Yeah, but it isn't necessarily, determinism does give another view, too, as I'll show you in Julian Barbour's formulation of general relativity. But the idea is in this way of formulating general relativity, where you take spacetime on equal footing, the space and time can actually mix together. That's the thing that when you first take a special relativity course, it's kind of weird, like, you know how when you go from a point A to B, right? You can take alternative routes. You could go, say, you know, it's kind of hard to do that without drawing a diagram, but you could go left and then you could go forward and you reach that point. But you may also go in a slightly different, two different angles and reach that point. And you can break down your main journey using two other alternative journeys. So that's how we do, like, when we're looking at purely space, but you can also put time in the picture. And it seems like the space and time can now mix together, too.

[00:42:19]  Sadia: And which also again kind of goes with the whole thing that, it may sound weird to somebody who's thinking of time as this something other mysterious thing. But as I've shown you, time could just be picked as some other, any type of other useful parameter in the evolution of when you express your dynamical laws. So there's no mystery there when you actually understand that. You're not like, why, you know, what is this time then? So but the thing that happens in this view, in this block universe view, is that there is no, like the, you can't really meaningfully talk about a present moment, because you can't really say that there is a present moment that permeates the entire universe, as if there is a now that exists for everything, everywhere, right? So now I'm going to actually talk about what Julian Barbour did.

[00:43:16]  Sadia: So Julian Barbour realized, if I'm not mistaken in this, that, you know, one of the things that he realized was that this formulation of general relativity is not fully relational, because there is the size actually turns out to have more absolute meaning. So even though time kind of becomes relative, you know, like what I mean is that there is no absolute simultaneity, there is an element that is not relational and that has to do with the size of the universe, which also kind of gives meaning to the expansion of the universe and stuff like that. But he actually reformulated general relativity by picking some other elements as primitive to his formulation. So in the standard formulation, you take space-time, right? But he actually focused more on the spatial part. He didn't mix, he didn't take a space-time view.

[00:44:10]  Sadia: The more primitive stuff in his theory are basically shapes. As I said, you know how that angle, you know, now you can see where he, why he might have picked that, because he's seen the angle as a more relational parameter. Then he, then he actually formulated general relativity rather than in some sort of a configuration space. He actually formulated in something called a shape space where size really doesn't matter. Like size is not, you know, anything universal. There's no universal size in that theory. Now, when he solved that, solved that problem using the same sort of variational principle we talked about, then he gets something interesting out of that. In his theory, there is actually an absolute simultaneity. So, so in his theory, there is a now.

[00:45:01]  Sadia: Okay, so that's the difference between the two. And there are some problems, I think, that they haven't resolved yet, how that fits in interpreting the redshift that we see because the cosmological redshift is expanding. So there is an issue there. So I don't know this.

[00:45:17]  Bruce: Can you describe that quickly? I don't know if everyone would know what you're talking about when you talk about the cosmological redshift. That might be gobbledygook to many people.

[00:45:26]  Sadia: Okay, so the universe is expanding, as we know. And so if you look at a distant galaxy, as it goes farther away, we know that from the basic physics that if you have an object that's emitting light and it starts to go away from you, its light tends to shift toward the red part or the lower frequency.

[00:45:48]  Bruce: Because of the Doppler effect.

[00:45:51]  Sadia: So now the expansion of the universe also gives us a Doppler effect. It's a little bit different in nature because here we're saying that the fabric of reality is somehow, it's the space itself that's expanding. It's not because something is moving away from us in space. The space itself is expanding, right?

[00:46:09]  Unidentified speaker: Right.

[00:46:09]  Sadia: So there is some sort of a meaning. I'm not sure about this. This is a little bit fuzzy here, but somehow the scale seems to have some sort of a meaning there that Barbour seems to not be happy about in the standard formulation. And he thinks it's not fully relational. So he, in an attempt to make a fully relational formulation of general relativity, he actually realized that, well, in his theory, it's actually, there is an absolute simultaneity. So in other words, there is a special slice. I mean, I don't want to use the block universe view because we're not doing that anymore. But as if there are some special privileged observers whose clocks will all meaningfully define a now, a present moment, which is absent in the block universe view.

[00:47:01]  Bruce: So one thing that you're kind of assuming here is that I suspect a lot of people don't even know is that in general relativity, there's no such thing as simultaneity. It depends on your reference. So it's typically and they do that because of the way we do science fiction for Cameo's benefit and she's really into science fiction books. We always assume the existence of simultaneity. So we imagine in Star Trek that they got subspace messages that can move faster than the speed of light. And so they can call Earth and then they can talk with Earth about what's going on at that same moment as what's happening in the other part of the galaxy that the Enterprise is in. Under general relativity, that simultaneity does not exist. It literally just does not exist. The physics does not allow for it.

[00:47:55]  Bruce: There is no sense in which something's happening here on Earth. And at the same time, something is happening on the other galaxy away from us. That would actually be determined by factors such as how fast you're moving and which direction you're moving in and a number of other things that seem very counterintuitive to us. So Penrose talks about this. He actually makes a claim, and I'm still not sure I understand this. He claims that the invasion that's starting in another galaxy, that two people walking along the street going in opposite directions, that to one of them, the invasion has already started and to one of them, the invasion hasn't started yet.

[00:48:38]  Bruce: And I'm not even sure how to work the math out for that. But that is what he claims in his book to try to make the point that there's no such thing as simultaneity under Einstein's physics. So this is what Sadia is talking about, is that this is an alternate theory, Julian Barbour's alternate theory, which I've never had hadn't heard of until she just brought it up right now, where there actually is simultaneity, where there is a sense in which you can say, hey, while this is happening on Earth, this is what was happening on Mars or in the other galaxy or something along those lines.

[00:49:08]  Unidentified speaker: Right.

[00:49:08]  Cameo: Meanwhile, at the exact same time.

[00:49:11]  Bruce: Right.

[00:49:11]  Unidentified speaker: Right.

[00:49:12]  Sadia: Yeah. So so actually, I mean, I would be a little bit hesitant in saying that's an alternate theory. Maybe there is because one could ask the question, you know, how even in quantum mechanics, there are two different formulations. That's another interesting question in itself, that when we have two different mathematical formulations of the same theory, are they the same theory or are they different? Because if you're an instrumentalist, all that matters is that it gives you the same predictions. Right. But when you actually take the theory seriously and see what it tells you about the ontology of the world, then I think one can ask this question more meaningfully. In a lot of time, you know, an instrumentalist would say, oh, these are just two different formulations of the same theory. So, but using that, I would still say that what Barbour is claiming is that he's not really presenting a new theory.

[00:50:02]  Sadia: He's really just taking general relativity and reformulating in a fully relational way. So it's a reformulation, just like you have the Heisenberg versus Schrödinger picture. He's saying that he's going to reformulate and he's done that. And in his theory, it turns out that there is. So the original formulation of general relativity gives you what you just described, right? That there is no absolute simultaneity. But his formulation shows that there are a privileged set of observers where you can say that there is such a thing as absolute simultaneity throughout the universe.

[00:50:40]  Bruce: Yeah, okay. By the way, in my interview of Sam Kuypers where we talked about the Heisenberg versus the Schrödinger picture of quantum physics, one of the main things that he is pointing out in his paper is that there is a difference in the way we would conceive the world, depending on which of those formulations we take more seriously. So in one of them, there is this idea of locality. In the other one, there's this idea of non-locality. And so he was working out which of those he felt was the more accurate picture of reality, even though they're in some sense the same theory.

[00:51:16]  Sadia: No, I could have totally guessed that. That's why I kind of made that differentiation that if you're an instrumentalist, then you're not going to see any difference. All you care about is really the predictions, right? So if both theories give the same, both formulations are giving the same predictions, then you're like, oh, this is the same theory. But obviously Sam Kuypers is a deep thinker. He's not an instrumentalist. So it's totally understood. And he's actually, I kind of attended recently this conference on shoulders of Everett, and it was a pleasure listening to his talk. It seems like he's paid attention to Barbour's work as well. And I just totally got a kick out of him. Part of me is like, Sam Kuypers, you're doing exactly what I wanted to do actually a little while back. Now I'm thinking in a different direction, but you're exactly taking on that challenge that I actually was interested in.

[00:52:02]  Sadia: So, but anyways, long story short, he actually did ask that question that what are clocks in quantum theory? And people seemed a little puzzled about his question actually, but I think he's thinking along the right lines. That's why instrumentalism is bad. There you go. Simple thing, all the stuff that I'm talking about, some of the stuff that I'm talking about, this is kind of outside of the reach of an instrumentalist. So if you're just going to focus on your predictions, then you might miss out on the opportunity. Maybe if you have two formulations, you're not really even going to have much to say about anything, where one formulation might be the step towards the next successful theory, right? Taking that forward. Okay, that was a nice tie, actually.

[00:52:50]  Sadia: That's good. So anyways, so in his formulation, there turns out to be a global notion, some sort of a global notion of simultaneity, at least, even if you don't want to call it time, right? Because he still thinks that it's, you know, obviously it's an emergent phenomena. Okay, so that's general relativity for you. Now, same type of stuff, as I said, with, you know, even Sam Kuypers kind of mentioned it last time, and I've been interested in for a while, physicists such as Wootters and Page wrote a paper about this long time ago. I don't fully understand the stuff in quantum mechanics, but supposedly, at least I know this, that even in quantum mechanics, even though in Schrödinger picture, you seem to think that time is not part of the physics and that there is some, you know, time as an absolute sense that exists in quantum theory.

[00:53:43]  Sadia: But Wootters and Page, and I think if I, I may be wrong in this, but I think they used the Heisenberg picture to show that no, even in quantum theory, the time can emerge with the dynamics in that theory. But here's the view you get from the quantum theory done in this way. This is the crux of this now. In that picture, you get, the picture you get is, and this is kind of, this follows from something called the Wheeler-DeWitt equation. The solution of that is actually a wave function of an entire universe. And it's static. It's timeless. It's stationary. Time, as well as dynamics, emerges in the subsystems of the universe that are entangled with some suitably chosen clock, endowed with some sort of an appropriate observable, observable that we can call a clock observable.

[00:54:34]  Sadia: This has been pointed out, you know, like I said, there are two physicists that I just mentioned, and even Chiara and Vedral, they actually, I hope I'm not mispronouncing his name, they actually wrote a paper on that clarifying that too. But I'm still, my knowledge, I mean, of this subject, I'm not an expert, so I'm not really sure how successfully the clocks have been, you know, how this issue of clocks has been settled. It seemed like, I mean, again, I don't want to put words in anybody's mouth.

[00:55:07]  Sadia: It seemed like even Sam Kuypers seemed to have some worries that we haven't really fully addressed this issue well. But anyways, so the idea that I want to stick to is that even in quantum mechanics, not only in general relativity, even in quantum mechanics, as we have seen it also in classical mechanics, there has been push towards banishing time, where time is looked upon as an emergent thing, not as some mysterious thing that flows, whereby the universe is evolving in time. So since I've given you pretty much a little bit of a thing on our best theories, if those are the best theories and that's what they're showing you, that's a good reason for majority of the physicists who take these theories seriously to think that time is not real in the sense that we used to think, that it's some emergent property of the universe and that what we really live in.

[00:55:58]  Sadia: So if I'm going to just conclude this part from that one, if one is a physicist and takes this view seriously and just gets fixated on this and the success and counting the success of the theories such as general relativity and quantum mechanics, one can, one arrives at the conclusion that we live in a static, timeless universe because clocks are only ever defined within a universe. They're like the notion of a clock for an entire universe really starts to become meaningless. So if you imagine that you have a finite universe, I mean, first of all, we don't know whether it's finite or not. But if you assume like, like there's some sort of a finite universe, then you can't really then the whole universe cannot be, you know, if you can define, I mean, you could try to say, well, I can define a clock. But remember, I said that clocks only make sense. It has to be clocks, not a clock for it to be meaningful in any way.

[00:56:53]  Sadia: So clocks exist in the universe. And so that thing doesn't really make sense for the entire universe. You could call the entire universe having its own clock. But imagine if the clock of the universe suddenly accelerated. Would that make any difference to anything in the universe? We wouldn't really notice anything, right? Because clock is so deeply tied to the idea of dynamical laws that it really shouldn't make any difference. So why should we even take this idea of time and extend it to the whole universe? That's basically the whole thought behind saying that we live in a timeless universe. And the universe maybe it's some sort of a wave function, it's some static state. If you think quantum theory is the most fundamental theory, then you're going to imagine that that's kind of like what it is, a static wave function. All change, motion, experience of a now or the present moment are basically then thought of as some illusions that mind has created.

[00:57:52]  Sadia: That's kind of what Julian Barbour believes. And that's what I believed till about last year, I think.

[00:58:01]  Bruce: And I guess that makes sense. What you're really saying is that strange as this idea may sound, it kind of just follows from the theories, the best theories available to us that you've just mentioned up to this point.

[00:58:14]  Sadia: Exactly. So if you are a physicist, and there is a tendency for us physicists to keep, for us to look at the world through the lens of our theories, and we're always open to saying, yeah, of course, we don't understand everything in this universe, but these are our best theories. These are so well tested. We've had clocks for a long, long time. Since the astronomers, these theories have also allowed us to make predictions, even though the predictions always work for simple isolated systems with very basic kind of, you know, like, which don't have a lot of complexity. But still, these theories have been so successful. You know, look at the modern technology that depends on them, that looking through that lens makes you think that that's what the universe is about. You know, let's extend it to the entire universe. And that's it. There's no time. There's no room for novelty. It is strictly deterministic from the point of view of an observer.

[00:59:10]  Sadia: And all that you are doing is uncovering [what] already exists. And so now you're into the realm, basically you're an eternalist now. That's called eternalism. All right. So there you go. So now we've reached, we've talked about so far what the current physics reveals to us.

[00:59:29]  Unidentified speaker: Okay.

[00:59:30]  Sadia: Yeah, I guess next time what I'm going to go back to first, a quick thing about what are laws. And then, you know, now I'm going to, I think next time I'm going to focus on how laws are time symmetric. And I'm going to go into where that fails, the failure of physics, the current physics, and how physicists are ignoring that and still adamant in thinking that somehow we have to take our best theories in physics, and they should have the final say. And then we'll talk about the hard problem of time.

[01:00:01]  Bruce: Okay. All right. This has been very interesting, Sadia. I definitely have never given this any real thought before. So you're raising a lot of things I hadn't thought about.

[01:00:12]  Sadia: Sometimes it's almost like saying, hey, let's talk, let's for a second analyze the lens through which I view the world. To me, this was a realization that I had. I really had not really seriously analyzed the lens through which I viewed the world. Because, you know, it was always about, you know, the good explanations, the good explanations, and hey, look how beautifully explains. And yeah, of course, there's a lot of stuff we [can/can’t—unclear] explain. But eventually we will explain that. But then you, when you take that seriously, and you really take your ideas seriously, your lens, that's when you, I mean, this is kind of like what happened to me even when I was religious too. I actually had to just take my idea really seriously and dive into it. And then suddenly compare it to other things that are around in the world.

[01:01:01]  Bruce: And then this is one of the great secrets of critical rationalism that even most people I know that consider themselves critical rationalists don't seem to get, which is you're not trying to typically defeat the other theory. You're trying to take it seriously and let it defeat itself. You basically can take any theory seriously. A theory that is wrong should be taken seriously too. You always take every theory seriously. You look at it and you see what the consequences are. One of the things that is difficult in conversations is when people use ad hoc arguments. And usually don't realize that's what they're doing. What they really need to do is they need to take each of their ad hoc arguments that they're usually just trying to defeat some point.

[01:01:48]  Bruce: You need to then take that ad hoc argument and say, okay, let's pretend it's actually true. What are the consequences of that ad hoc argument? And when you start doing that, you start to realize how bad ad hoc arguments actually are and why you don't want to use them. As long as you're not actually taking them seriously, which typically people don't take them seriously, then they kind of feel like they're good arguments and they emotionally feel like good arguments. And so this is something that I can applaud you on this front. This is really what critical rationalism is. So one of the pillars of critical rationalism is that you take every theory seriously and you really try to work out what are the consequences of this theory if we take it seriously.

[01:02:30]  Sadia: Actually, you know, interestingly, I actually realized I actually discovered critical rationalism before I actually studied critical rationalism in a weird way or Popper's theory. Like I had read Deutsch's book and kind of the first time I read a lot of it, you know, there were things that I got more fixated on and some of it went over my head. But through my own, like when I started thinking about religion, interestingly, there was a time in my life, I would say roughly two to three years of my life, something happened. It was after I had finished the grad school. I could not pick up a physics or science book. I got totally immersed. You know, that was the time when I said, you know, I was born and raised a Muslim. I'm going to take my religion seriously. I really want to know.

[01:03:11]  Sadia: And I was, you know, at that time, I remember like I was totally in love with God, but it wasn't any type of anthropomorphized type of, it was more of an intellectual thing, but that was an idea that I was in love with. But at the same time, I think truth always mattered to me more than anything. And I always used to, I mean, since my childhood, I actually used to pray. In my prayer, I literally, there was one prayer that I prayed pretty much every day, which goes like Rabbe Zidni Ilma, that, you know, it's more, it's basically like, oh, Lord, you know, increase my knowledge or, you know. So that is something I was after. And I, when I started taking it seriously, I came to a realization that I was only just viewing my religion through the, through its own lens.

[01:03:55]  Sadia: And how was I going to ever discover anything if all I'm saying is taking the Word of God and just analyzing it, you know, through that lens. And then I'm like, you know what, I need to look at other things. And I didn't know what I was looking for. I'm like, I need to find some connections. Maybe there's some commonalities, maybe there's some paradoxes. And I started looking into other religions. And then the more I went out like this in my comparative studies, and every time I would have an idea, I would take it more seriously. But taking the idea seriously didn't mean that I just looked at it within my worldview. I had to compare it to other views. And I actually, at one point in my life, I realized that I was holding on to the idea of a God that I could have just called Universe. And I'm like, what am I even doing here? Like, what type of game am I trying to play here with myself?

[01:04:43]  Sadia: And literally, for me, becoming an atheist was actually natural. Like, I never felt like it was like, oh, my God, how... what an idiot—I can't... you know, like, do I really believe in God? Nothing like that. It was just a natural progression. And one day for me, like, God was gone. And I think the same approach, it's not it's just knowledge in general. I mean, like, it's whether it's morality, whether it's physics. And I when I came across Popper's ideas through Deutsch, one day I actually kind of realized that, you know, and that day when that was a natural step, I think it was almost like it just needed a little nudge. And I think Deutsch did it for me. Like, I was almost there. But then one day, something just popped in my head. I'm like, what am I? What am I holding on to here? What am I doing? So, yeah, yeah, no, I'm with you.

[01:05:32]  Sadia: I think and I always tell a lot of times that I've never expected anybody to ever become an atheist or anything like that. All I ever tell people is, look, I don't know. I'm on a journey. I mean, you just need to take your ideas seriously and see where they take them. I don't know where I'm going to go next. I mean,

[01:05:46]  Bruce: but interesting, interesting. That's some interesting background there, by the way. Thank you.

[01:05:51]  Unidentified speaker: Yes.

[01:05:53]  Bruce: All right. Well, thank you, everybody.

[01:05:55]  Unidentified speaker: Thank you so much for this [unclear].

[01:05:57]  Bruce: Yeah, we will continue this on the next episode.

[01:06:00]  Sadia: Yeah, sounds good.

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