Theories of Everything with Curt Jaimungal - Sean Carroll: The Crisis in (Fundamental) Physics is Worse Than You Think...

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Starting point is 00:00:37 Meeting with friends before the show? We can book your reservation. And when you get to the main event, skip to the good bit using the card member entrance. Let's go seize the night. That's the powerful backing of American Express. Visit amex.ca slash ymx. Benefits vary by card, other conditions apply. No, I mean, I agree. What can I say? In fundamental physics, we've not had any breakthroughs that have been verified experimentally for a very long time. That's just true. Can't argue with that.

Starting point is 00:01:10 What if the past 40 years of fundamental physics research have been leading us down a dead end? What if there's something historically and structurally rotten that's holding us back from understanding the true nature of reality. In this conversation with Professor Sean Carroll, a renowned physicist, philosopher, and author who's been at the forefront of some of the most exciting and controversial developments in modern physics, he reveals the truth behind how he sees the supposed crisis in fundamental physics. In 2023, Sean stirred up the physics community with his episode on the crisis in physics, arguing that there is no crisis.

Starting point is 00:01:52 Some professors cheered him on, while other professors stated that he straw manned their views, defending physics as a whole rather than their criticisms about fundamental physics specifically. Today, Sean Carroll clears the air, all while explaining other heated topics, such as where the laws themselves come from, and what it means that our universe is a hologram. What might the next revolution in physics look like? How are you doing today, sir? Doing well, thanks for having me on. What's something you're working on that you're excited about? Oh

Starting point is 00:02:28 You know, I always tend to work on bunches of things at once We have a paper that I'm part of although the main Emphasis comes from Oliver Friedrich who is a postdoc in in Germany on Friedrich, who is a postdoc in Germany, on phenomenological consequences of holography. So holography, you know, I don't want to go too much into it, but the holographic principle is a big thing in physics and in quantum gravity. It says that, you know, there's a lot less going on in the world than you might think. The world is not really three-dimensional space. It can be thought of as a two-dimensional space with densely encoded quantum information, and we're just a projection of that into the

Starting point is 00:03:09 world. And so Oliver and a bunch of us tried to propose a way that that would actually make a difference for experimental signatures, in particular the IceCube experiment at the South Pole that is looking for high energy cosmic rays in the Antarctic ice. People say there are different forms of holography. So ADS-CFT is one form. What are other forms? Well, that's a great question.

Starting point is 00:03:35 You know, when I was your age, we had the holographic principle, but we didn't have ADS-CFT yet, right? The original idea came from Gerard de Toift, Lennard's Huskin and others thinking about black hole information. You know, since Hawking's time that the entropy of a black hole is proportional to the area of its event horizon, which on the one hand, maybe is a surprise if you think about black holes too much like a box of gas. For boxes of gas, the volume is the volume that matters when you calculate the entropy,

Starting point is 00:04:09 not the area of the boundary. But for the vacuum state of a quantum field theory, it's actually very natural for areas to be proportional to entropy. So maybe from that perspective, it's not so surprising. But anyway, to try to sort of reconcile it all, Atuf and Susskind ended up proposing their version, their early version of the holographic principle, which said that the total amount of quantum information specifying the state of a black hole

Starting point is 00:04:37 sort of can be thought of as living on its event horizon. There's no extra information hidden inside, deep inside the volume of the black hole. But it was very vague, like, okay, what are you going to do with that? What do you mean lives on? It wasn't quite clear what was going on. And when Juan Maldacena first came up with the ADS-CFT correspondence, he really wasn't thinking about in terms of holography. He was really thinking about supergravity and stacking brains on the throat of an extremal black hole and noticing that it looks like ADS and, you know, the very, you know, technically sophisticated, you know, typical Molesena brilliant way of pushing things around.

Starting point is 00:05:23 But the holographic idea was added on by Ed Whitten. You know, Whitten had known about those papers by Tufton-Suskind and he pointed out like, oh, really, we can think of this as an equivalence between a D-dimensional space time and a D plus one-dimensional space time. And it really implements holography in a very, very direct way. So these days, a lot of times when people talk about holography, they really mean the ADS-CFT correspondence. But there still is that earlier implication of it or version of it.

Starting point is 00:05:57 You know, Rafael Busso proposed some very nice covariant versions of the original holographic idea. And so we think that even though we don't live in ADS, there still should be some version of holography in our real world. But it's not at all clear exactly how it's supposed to work. And the one that you're working on is not ADS, not ADS-CFT? Yes, it's supposed to be the real world, it's supposed to be where we live. I'm still, I'm very speculative in many ways, but I still care about the world where we actually live.

Starting point is 00:06:28 Do you think that ADS-CFT gives insight into quantum gravity and universes that aren't asymptotically ADS? Well I don't know. I think as a practical matter probably it does, just because it's a good toy model. It's somewhere where people can ask questions and answer them. That's always good. You know, I am not a simple harmonic oscillator, but in some sense, a lot of what goes on in my body is successfully modeled by simple harmonic oscillators, right?

Starting point is 00:06:57 You know, you start with things you understand and you build up complications from there. So certainly questions about, you know, holography in general, entropy, the relationship between entanglement and geometry, maybe something about black hole information and how it's preserved in evaporation. Maybe all these things can be investigated in the ADS-CFT context, but I do still think that the fact that we don't live in ADS-CFT

Starting point is 00:07:25 I still think that the fact that we don't live in ADS-CFT matters in some sense. I don't think that every interesting quantum gravity question is gonna be answered by looking at ADS. There's a bit of a looking under the lamp post kind of aspect where we're hoping to answer all the quantum gravity questions looking at ADS because that's what we understand.

Starting point is 00:07:44 But I think that, you know, whether it's because there's a finite entropy for de Sitter space or whatever, I think this can be a fundamentally different set of things that we can and must discover outside of the ADS context. So what is the difficulty with a duality in de Sitter space time and CFT? I guess before I answer that, let me ask, who's the audience that I should be aiming

Starting point is 00:08:11 at? How sophisticated do we get here? I can try to be very general or very specific. Yes. Well, the audience tends to be researchers and professors in math, physics, comp sci, philosophy. So you can speak at the graduate level if you like. In fact, this podcast, just so you know,

Starting point is 00:08:28 is infamous for its technical depth. Great. People appreciate when we delve into the recondite inner workings and the abstruse mechanics. They appreciate and they crave the details on Tull. Okay, cool. So in the ADS CFD correspondence there's two kind of amazing things that happen that are crucially important to the success

Starting point is 00:08:53 of the correspondence. Probably more than just two but let me highlight two and of the two I'm going to highlight one is obvious and everyone highlights it and the other one is kind of underplayed I think. The obvious one is that if you're since the time of Roger Penrose, who figured out how to do conformal diagrams, that is to say, to take a whole big space time and to shrink it down to a finite piece of paper and look at and think about the infinity of that space time in a rigorous, careful, mathematically respectable way, one of the nice things about anti-de Sitter space

Starting point is 00:09:29 is that its boundary at infinity is a space time. It has, if you're in D plus one dimensional anti-de Sitter space, so you have D dimensions of space, one dimension of time, the boundary is a space time of dimension D, so D minus one dimensions of space and one dimension of time, the boundary is a space time of dimension D. So D minus one dimensions of space and one dimension of time. So it's this sort of naturally a hope that you can relate the dynamics in the bulk to the dynamics in the boundary. They're both dynamical theories. They both have space where you can define initial conditions

Starting point is 00:10:02 and you have time where you can evolve it. The other thing that is not as celebrated but also crucially important in anti-desider space is that anti-desider space is infinitely big. Even if you think that a finite region of space only has a finite dimensional Hilbert space which might be suggested to you by the holographic principle or by black hole entropy or whatever, in ADS there's an infinite number of finite regions of space, so the theory as a whole naturally has an infinite dimensional Hilbert space. And therefore, the boundary theory can and turns out to be, sensibly be a quantum field theory that has an infinite dimensional Hilbert space. can and turns out to be, sensibly be a quantum field theory

Starting point is 00:10:45 that has an infinite dimensional Hilbert space. So not only is it a theory, a dynamical theory at the boundary all by itself, but it's the kind of theory we know and love that we have really been working on for a long time. Now in d-sitter space, where do you have a positive cosmological constant, and let's forget for the moment,

Starting point is 00:11:01 put aside the fact that there's also a big bang and there's matter in the universe and whatever, let's just think very simply about de Sitter space. Both of those nice features no longer are true. The number one, the conformal boundary of de Sitter space is space-like, not time-like. It's partly a sphere in the future and partly a sphere in the past. And number two, you know, it depends on how you slice De Sitter space, but you can slice it so that the volume at any one spatial slice is finite. And in particular, an observer inside a horizon sees a finite dimensional horizon entropy that they want to associate with that. So for the purposes of an observer in decider, again, we don't know the answers for sure, but it's at least plausible that if there is a holographic description, it is in terms

Starting point is 00:11:55 of a finite dimensional Hilbert space. And it might not be a field theory, right? Because field theories have infinite dimensional Hilbert spaces. And it might not be a theory with any time dependence because it's not a space like, a time like boundary. So I think that there's profound differences between ADS and DS and we haven't quite wrapped our brains around them. There's very admirable attempts to think about what holography would look like in the sitter space. Celestial holography is the most popular approach right now, but none of it is anywhere nearly as advanced and reliable as what we know in anti-decider.

Starting point is 00:12:33 Is there a bound in the finite dimensional case? Like it tells you that the maximum dimensions of the Hilbert space is 25, or is it just you know that there exists some n? No, we actually know the number. So, you know, whenever you have two things, number one, a system with a finite entropy, a finite entanglement entropy. Let's be careful that we really need to assume that we're talking here about the von Neumann entropy, the quantum mechanical entanglement entropy of one system with the rest of the world. If you know what that entropy is, and you know that it's the maximum entropy that the system can have, that there's no way to increase the entropy by changing its quantum state or its entanglement or whatever, then you have a pretty good idea the dimensionality of its Hilbert space. It's roughly E to the entropy. I say roughly because it depends on, you know, are you on a micro-canonical or canonical ensemble or whatever, what are you keeping fixed,

Starting point is 00:13:30 etc. But, you know, that's the order of magnitude. And so we think that De Sitter space is a maximum entropy configuration. I even wrote a paper, you know, putting forward a quantitative argument to that extent. But people thought it was true for long before our paper. And the entropy of a causal patch, that is to say the entropy of a region that an observer has access to causally is, guess what? The area of its event horizon divided by, in plank units, divided by four, just like the entropy of a black hole. So if we, if you have a maximum entropy state and it has a finite entropy, that implies that you can describe that system quantum mechanically by finite dimensional Hilbert space. And the answer for our observed cosmological constant is that the entropy that the, the dimensionality of Hilbert space is of order 10 to the 10 to the 122. So that's a big number but

Starting point is 00:14:30 it's still finite. There's a big difference between infinity and just a big number and that's actually what we take advantage of in our paper. So is that a point against DSCFT or is it to be taken as a clue that this holography doesn't describe our universe? So my guess, and this is just a guess and it could be wrong and I'm not even the world's expert, is that there will be DS holography but it won't be with a CFT. It will not be with a conformal field theory. And the standard model isn't even a CFT by the way for people who are listening and wondering. That's right but I don't even think it'll be a field theory because I think it'll be

Starting point is 00:15:11 you know something more discrete something with either a finite or accountable number of dimensions of Hilbert space. So let's talk about philosophy. Good. Many people see the relationship between physics and philosophy as a marriage that should be and some people see it as a, it should be in divorce. So on the divorce side is someone like Neil deGrasse Tyson, I spoke to him about philosophy. He sees it as having recently not contributed to much,

Starting point is 00:15:47 and it would be a waste of time for physicists to learn philosophy. Where are the examples of some experimental insight that has come from a philosopher? These are the questions he posed to me. So those are questions I am posing to you. How do you see this relationship? I think that the relationship should and can be healthy. Of course, most physics or most biology or most computer science or whatever can go forward perfectly well without talking to philosophers or thinking about philosophy. You can't do science overall without thinking about philosophy. Scientists make philosophical statements all the time. They're just

Starting point is 00:16:29 usually not very good philosophical statements. You know, just ask any scientist what counts as science. Whatever their answer is, it's a philosophy claim. It's not a scientific claim and usually it's not going to be a very educated philosophy claim. And again, like I said, usually that doesn't matter. But there are some questions for which it matters a lot. I can give you a long list. The fundamental nature of quantum mechanics and the solution to the measurement problem. The fundamentals of statistical mechanics and the origin of the arrow of time.

Starting point is 00:17:03 But let me give you an example that we don't hear very often, but it is very relevant. We spent $10 billion building the Large Hadron Collider, right? We, the human race. That's a lot of money. And we found the Higgs boson, which is great. But before we built it, the motivation, the stated reason for building this,

Starting point is 00:17:22 was not just that we would find the Higgs boson. We thought that was probable, but we would find the Higgs boson. We thought that was probable, but we weren't just saying that. We said, look, there's a very good reason to also suspect that we will discover other new particles. What was that reason? Well, it's mostly based on the hierarchy problem. The hierarchy problem says that the electroweak scale, roughly speaking, think of the mass of the Higgs boson or the expectation value of the Higgs field, same order of magnitude. By all of our conventional notions of naturalness, we think that that scale should not be too

Starting point is 00:17:58 far away from the Planck scale, that quantum corrections to whatever classical value you put in tend to increase the effective electroweak scale to higher numbers until you hit some cutoff like at the Planck scale. And in fact it's much lower, it's 16 orders of magnitude lower, so this seems unnatural to us. And therefore we put a huge amount of intellectual effort into coming up with theories to explain that unnaturalness, to account for it, usually involving new particles or new phenomena like extra dimensions of space and so forth, all of which, many of which at least, had promise to be discoverable at the LHC. So in a very real sense, we built the LHC mostly because we have a naturalness problem

Starting point is 00:18:45 in the known standard model of particle physics. Okay, but when you say you have a naturalness problem, guess what? That's a philosophy question. What do you mean natural? Who's to say what is natural? Did the physicists who put forward this argument consult with philosophers?

Starting point is 00:19:03 No, they did not. And I'm not saying the philosophers would have fixed it because I don't think that I'm very happy to criticize both physicists and philosophers and I think that the philosophers missed a good chance to take this particular question seriously, and they really didn't you know, there's no very very compelling I think for for the cases I gave earlier, for the foundations of quantum mechanics, for the foundations of statistical mechanics, philosophers have done a good job. They have sort of clarified the terrain, which is what their job is, not to make new experimental predictions. But I don't think they've clarified

Starting point is 00:19:38 the terrain nearly as much as they should have when it comes to naturalness and things like that. Defining it as a problem itself, is that also assuming a philosophy? It's assuming a philosophy, yeah. So everyone always assumes a philosophy. Everyone thinks they have a feeling for like what is simple, what is natural, what is fruitful, you know, and these are all words that philosophers have used talking about the philosophy of science for a long time. But thinking it through very, very carefully is harder than you might think.

Starting point is 00:20:06 I think the real attitude of physicists is more often not that philosophy is useless, but that if they just spent 15 minutes thinking about it, they could answer all the important philosophy questions. And I think that that's not actually true. They're more subtle than that. Sabine Hosselfelder distinguishes between what she calls problems and pseudo problems. To her, a pseudo problem would be something like the strong CP problem, where it would be nice if we had an explanation as to why CP is not violated. But it's not as if there's some

Starting point is 00:20:39 inconsistency in our framework. Same with energy having an explanation. It could just be another constant. It could just be One of the 26 constants of nature what have you well, this is a very strong Philosophical claim that she is making and I would like to see You know very very careful analysis of when this is true and when it is not true I mean if I walk outside and rather than being held down to the ground by the force of gravity, I float up into the air, I could say, well, you know, I just got unlucky that time.

Starting point is 00:21:15 I flew up into the air. It doesn't really demand any deeper explanation than that. But as a matter of fact, as working people and as working scientists, we take certain features of the world to be ones that are clues to deeper explanations. Maybe there is no deeper explanation, maybe there isn't, maybe there is, but we are motivated to go look for it. And that can be very, very fruitful, that search, to look for it. Sometimes the search will not pan out. We will not find anything very different.

Starting point is 00:21:47 You know, back in the day, they would have been very, very interested in explaining why exactly there are five planets in the solar system. Today, that doesn't seem like a very pressing issue, or why the fine structure constant is 1 over 137. Today, that's not really the most pressing issue. But we only figure out what is the pressing issue by pressing on the issues that we know about and taking those clues as seriously as we can. What if Sabina would say the risk here, even though she has a book on philosophy called

Starting point is 00:22:18 Existential Physics, if I'm not mistaken, that the risk is if philosophy or physicists delve too much in philosophy, they start to introduce untestable metaphysical assumptions and maybe they prioritize elegance or philosophical elegance over empirical evidence. What would you say to that? Well, like I said, physicists can't help but do philosophy. They can only do it badly. And the problem is not that they're philosophizing, the problem is that the problems are hard.

Starting point is 00:22:49 Like if you want to understand what is the dark matter, because you're completely correct, for dark energy, we have a very good theory of what it could be. It could be the cosmological constant, maybe that's just the number, maybe there is nothing more to say. For dark matter, we're not that lucky.

Starting point is 00:23:03 We don't have an obviously correct theory. Maybe it's axions, maybe it's wimps, maybe it's, there's many, many different possible things. So you kind of have to choose what to think about, what makes the most sense to you. How are you choosing what to think about? You can't just think about everything. You literally don't have all those brain cells, right?

Starting point is 00:23:22 You have to pick and choose what you're gonna focus your efforts on. And that picking and choosing comes with ideas like simplicity, fruitfulness, fitting in with other things that we already think we know. These are fundamentally philosophical questions. The problem is not when physicists are too philosophical. It's when they lose sight of two things. There's lots of, well, there's lots of problems.

Starting point is 00:23:50 One problem is when they do philosophy badly. Another is that when they just start pushing around equations for their own sake, not trying to match up with the real world at the end of the day, I think it's a very valid criticism. But we don't know how to make progress, right? We have theories that fit the data. That's a really, really difficult position to be in. If you have

Starting point is 00:24:09 a better theory, let us know what it is by all means. And in the last case about pushing around equations, you mean theories that have been inspired by physics and the math has been inspired by physics and now they follow that map? Well, yeah, you know, the ground has shifted beneath our feet. If you grew up doing high-level theoretical physics in the 40s, 50s, 60s, there was an enormous amount of data to be accounted for, right? And the data didn't stop coming. We keep getting more and more data.

Starting point is 00:24:45 The problem is we can account for it now. It took us maybe up until the 70s to really figure out how to do it. And I'm only talking now about particle physics and fundamental physics. Obviously there's an enormous amount of effort that is going into way more than is going into particle physics.

Starting point is 00:25:02 Most physicists are doing atomic physics, condensed matter physics, plasma physics, whatever, you know, much more experimentally accessible things. But in the world of particle physics, we have the theory. It fits the data. And so it's what do you do in that situation? And I think there's different strategies that one can pursue. There is a danger when you have a theory that fits the data, you start playing around with other theories that are more speculative for their own sake.

Starting point is 00:25:32 I have no problem whatsoever with playing around with speculative theories, with trying to learn more about how the real world, about how the space of theories behaves. That's a perfectly valid thing to do. But I would strongly advocate keeping in mind that the reason we're doing it is because we ultimately care about the real world in which we live. And it is possible to forget that if you grew up in a world where you did not, no one,

Starting point is 00:25:59 neither you nor any of your friends succeeded in inventing a theory that accounted for some puzzling experimental phenomenon. Some people would say string theory may fit that. What do you say? I don't think it's string theory as a theory fits that, but maybe some string theorists fit that, that they valorize, little mathematical investigation of some particular regime of

Starting point is 00:26:26 the theory, which is maybe a tour de force intellectually, but is not actually getting us any closer to the real world. But string theory itself is certainly a very promising model for understanding quantum gravity in the real world. And I think that it's just important to remember to push it in that direction while we're doing all this more in principle, understand the nature of the theory kind of stuff. Nima Arkhani Hamed has this quote that string theory is great, it's spectacular, string theorists are wonderful, et cetera, but their track record for qualitatively correct statements about the universe is garbage.

Starting point is 00:27:07 I knew the word garbage was in there, yes. Yeah, I think that's right. I think that Neema and I both have respect for really good speculative theoretical work, but we also at the end of the day are going to judge its success by how well it fits with the real world. And I think it's perfectly fair to say string theorists have number one, not given us any great explanations for the real world that are very direct and testable.

Starting point is 00:27:33 And number two, do kind of have a track record of saying that they would. That's less often true now, but back in the 80s, they thought they were gonna be computing the mass of the muon any day. And that turns out to be Harder than we thought it would be and again, I don't necessarily blame them I get that you're excited about your theory

Starting point is 00:27:52 You're hopeful, you know, you're optimistic about how it's going to work out But then you have to be able to reconsider when things don't work out your way How do you feel about your video on the crisis in physics? I love that video. It's not really a video, it's audio, but it was a podcast episode that I did where, look, you know, you can have different opinions about the state of modern physics, but I think that a lot of people, for deep sociological reasons, end up having these opinions without being very educated about why the state of modern physics is what it is.

Starting point is 00:28:27 So the goal of that podcast conversation, that long solo podcast, was to explain to people that the particular beliefs that modern particle physicists have aren't just handed down by some priesthood and then accepted blindly. They were, they grew up over the course of decades and huge amounts of very hard work and an enormous amount of experimental input to build this theory that is working very well for good reasons, the standard model plus general relativity. And also to understand why it is hard to go beyond that theory. It's not that we don't want to, you know, It's easy to throw stones at the lack of success of people going beyond the standard model, but until you have a successful theory of

Starting point is 00:29:12 going beyond it, I'm not gonna worry too much about your critiques. So are you aware of Peter Wojt's theories on or theories of everything he has to or Eric Weinstein's or Garrett Lisey's? I don't really follow those. No, those are not really mainstream approaches. So you know, they could be right. And then like I said before, we don't have the brain capacity to think about every theory, right?

Starting point is 00:29:41 So I'm concentrating on ones that I think have a much higher credence of eventually turning out to be right. Which are? Well, holography, you know, string theory, versions of string theory. The thing, even if string theory turns out not to be right, which is completely plausible, I am, you know, very impressed with the idea of holography. It seems like Stephen Hawking's calculation of black hole entropy and further elaborations on that idea are pushing us very strongly in the direction of saying that whatever quantum gravity is, it's not a straightforward quantum field theory.

Starting point is 00:30:18 And I think this is the problem with a lot of attempted approaches to either unification or quantum gravity in particular. They still start with space time and they take space time as a fundamental ingredient attempted approaches to either unification or quantum gravity in particular, they still start with space-time and they take space-time as a fundamental ingredient and then put things in space-time and try to let them interact. To me, the lesson of holography is that that is not the way that quantum gravity works. So even if string theory is not the correct approach to it, and I suspect that string theory is going to be at least

Starting point is 00:30:45 either correct or related to something correct in some interesting way. But at least it is compatible with this holographic idea. I mean, this is where ADS CFT fit in the game originally. It is open to the possibility that the space time that we see around us is not the fundamental ingredient. It should be stated at this point for those of you who are mathematicians wanting to learn more about the mathematics of string theory, I have a three hour deep dive called the string

Starting point is 00:31:17 theory iceberg. This behemoth YouTube video delves into the topics of dualities in string theory, the Green-Schwartz mechanism, homological mirror symmetry, and even some of the technical problems with ADS-CFT. What is specifically meant when people say, or some people say, and you can pick a person because I'm sure there are many different interpretations of this, that physics is in crisis. What's meant by that? You'll have to ask them because I don't think it's true. I guess that there's different interpretations one could have, either that we're stuck, we haven't gone very far forward in fundamental physics, or they might think that individual physicists are doing things

Starting point is 00:32:00 in the wrong way for some reason. But again and again, I'm going to keep saying the proof of the pudding is in the tasting, you know, the alternatives that I've seen offered up are not that impressive to me. In the comment section, I had a brief skim through and they were saying that when people say physics is in crisis, they don't mean physics as a whole, they mean fundamental physics and that the podcast focused on the successes of applied physics like MRIs and lasers and so on to counter the claim of stagnation. So attributing engineering feats to physics and that if we detect the Higgs boson, sure that's cool, it's wonderful, but that's a confirmation of an old theory. It's not a novel theoretical breakthrough.

Starting point is 00:32:45 How do you respond to those comments? No, I mean, I agree. What can I say? In fundamental physics, we've not had any breakthroughs that have been verified experimentally for a very long time. That's just true. Can't argue with that. Again, most physics is not fundamental physics. If you look up the membership roles of the American Physical Society and figure out what fraction of them

Starting point is 00:33:07 are doing quantum field theory or gravity or whatever, it's a small fraction. There's a lot more interesting physics out there. You might personally not be interested in it. Good for you, that's fine, but it is going on. That's what employs most physicists. Would you say that part of the distaste for the phrase, hey, fundamental physics is in

Starting point is 00:33:26 crisis stems from your love for physics, your desire to convey that adoration to other people and this whole meme of hey, physics is in crisis, bro, is typically expressed by people as you see outside the field who lack a clear understanding of the reason behind what they're saying. They're just jumping on the bandwagon of being iconoclastic. Well, I think, you know, everyone is welcome to their opinion about everything. I'm not going to gatekeep who gets to have an opinion about things. I just want people's opinion about things to be as educated as they can be.

Starting point is 00:33:56 That's why I try to offer up my own solo podcast and other efforts. I think it would make sense to say that physics was in crisis if I had a very sensible argument that physicists were working badly, were doing the wrong thing, were making mistakes. If anything, I think that in the foundations of quantum mechanics, that's an argument that you can make, that we've been ignoring the foundations of quantum mechanics for a long time. But in particle physics, quantum field theory, quantum gravity, I don't see evidence that that is the right attitude towards what physicists are actually doing.

Starting point is 00:34:34 So when I was researching this, I could see that the crisis in physics is threefold. So there's what I call the great stagnation, which we just referenced, and then there's the great schism, which I'll speak about shortly, and then the great silence. So the great stagnation is that there haven't been new discoveries that have pointed the way to physics beyond the standard model or general relativity in a way that resembles a consensus. Okay, cool. That's just one element. The other is the schism that happened approximately in the 80s or so, or especially in the 90s,

Starting point is 00:35:11 where the field is split and many people don't realize this. So there are string theorists who literally say string theory is the only game in town. I didn't know that string theorists say that. I thought that that was just a claim from people who weren't string theorists to lob at string theorists to say, hey, you all think this, but they would never say that. But I was speaking to Kuma and Vafa and he explicitly said twice in the podcast, it's the only game in town. So this also then has this element of trial by string theorists where new ideas are also evaluated by string theorists.

Starting point is 00:35:47 And I'm speaking specifically about fundamental physics. So I agree there's no crisis in physics as a whole. It's quite foolish to say that, especially just look at condensed matter physics. It's booming. And if you want to contribute something new, that's like the that's the great place to be. But it's partly this derisive and supercilious attitude by the string theorists since the 80s that have cost people jobs. And this is in part the, what Peter Wojt is talking about with his critiques, though his tend to be more mathematical about overhyping string theory. The majority of the time though. The issue is with the string culture

Starting point is 00:36:27 so that is to say that there's a history of its arrogance and its Incuriosity and its suppression of alternative ideas. That's the schism and then the Well, how about I let you comment on that? Do you see that? And then the... Well, how about I let you comment on that? Do you see that? Yeah, I mean, I would say that there absolutely are strength theorists who sincerely and honestly believe

Starting point is 00:36:51 that when it comes to quantum gravity and unification, strength theory is the only game in town. That is not necessarily true. I don't agree with them, I should say. But I get why they think that. You know, as I said, I think I explained in my podcast about this, it's not as if we fixed all the problems of physics and moved on to trying to do quantum gravity. In the mid-1980s, nobody was interested in quantum

Starting point is 00:37:19 gravity for very good reasons. The Planck scale is very large, gravity is a very weak force. We can't collide gravitons and see what happens. The prospect of getting any good theoretical handle on quantum gravity seemed unrealistic, the early 80s, I should say. String theory came along and offered an answer to some of the puzzling aspects of quantum gravity in a very unexpected way. It's a finite theory.

Starting point is 00:37:47 You can collide gravitons together in the string theory thought experiment and get a very perfectly well-defined answer. And other theories you just can't. What can you say? So that gave people very, very good optimistic reasons to push the theory forward. And then the other thing about string theory is that even though it clearly has failed in making experimental predictions we could test against data, it also clearly has

Starting point is 00:38:15 kept itself alive on the theoretical side. New ideas keep coming in. ADS CFD is a perfectly good example, but D-brains and M-theory and various versions of holography, there's lots of examples that you can give. The Swampland idea is arguably such a new idea right now. So it hasn't crashed and burned. Many theories will look promising and then they will crash and burn. String theory has remained frustrating because it doesn't connect with data, but the number of theoretical ideas is enormously rich and that's worth taking seriously. Now I do have a little bit of sympathy with the view that you just expressed, but I would express it differently. I mean I think

Starting point is 00:38:59 that the way that it often gets expressed is just clearly sour grapes, it's clearly just being curmudgeonly and people don't like my ideas, therefore I'm gonna claim that they don't have a good attitude towards science more generally. I don't think that that's a valid way of arguing, but the way that I would be able to argue it is look, precisely because experiment is not guiding us,

Starting point is 00:39:22 we should be a little humble about what theories that we like and don't, because we can always fool ourselves. We can always trick ourselves when experiment is not there to set us straight. And so, it's a very difficult thing to do, but what I would argue is that you should nevertheless, as a field, put some resources into approaches to physics that you think are probably wrong, right? Because you could be wrong

Starting point is 00:39:53 yourself. So if there is someone out there who is allocating all of the jobs and all of the grants and all of the experimental work in physics, I would argue very strongly that even in the area of fundamental physics and unification and quantum gravity, they don't just put it into string theory. They should certainly put it into other areas as well. Here's the problem with that. There is no such person.

Starting point is 00:40:17 There is no such Pope of theoretical physics who decides who gets to be in the College of Cardinals. Instead, you have physics departments, right? And physics departments hire faculty members, and they don't hire them very often in theoretical physics. Maybe, you know, if you're lucky, once every five years, you're hiring a new faculty member. So are you going to intentionally hire a faculty member

Starting point is 00:40:43 working on an idea you think is probably wrong, even if it would be good for the field because it maintains diversity and keeps ideas alive, you yourself are not gonna do that. It's probably not good for your department. So there is an academic tendency to bet too much money on the leading horse, right? To be a little bit too conventional

Starting point is 00:41:06 and conservative because you don't know what's going to turn out right. It's easier to go with what is in the mainstream. So that absolutely, I would argue, has the effect of cutting off alternatives. And so I think both that there are good substantive intellectual reasons to be skeptical of the alternatives and that we should nevertheless do a better job than we do of supporting some work on them. So practically speaking, how could we do, how could, how could that be achieved? How should one allocate resources between different research programs in a data starved

Starting point is 00:41:44 field? How could the minority? I don't know. That's a very good question, but since I'm not the Pope of Physics, I don't have to answer it. I mean, I think it's somehow, I don't know, fellowships, prizes, grant money, I really don't know. Yeah, so if I see what you're saying,

Starting point is 00:41:59 it's akin to saying trees are all born of the same birth. They're a fragile sapling at first and maybe even a flimsy seedling. And then if someone was to say there are no alternatives to string theory or at least none that are as developed, well, how do we know? Because there could be saplings, but there's the tree of string theory, which is growing its leaves and then just preventing the growth of others because of however the academic system works. So is that a fair recapitulation or am I misguided? Yeah, no, I think that's basically on the right track. Yet another way I would put it is it's a game theory kind of thing.

Starting point is 00:42:40 In many games, it turns out that the best strategy to use is what's called a mixed strategy. So in any particular case, you might think that there's one thing to do that is certainly the best thing to do. But if you do that thing over and over again, people are going to figure out what you do and you are exploitable. So even though there is something that is the best thing to do, your best strategy is to do mostly that but also some other things as well. I think that applies to, you know, keeping different fields alive within physics or within other academic areas. It's so tricky because if you're someone like Roger Penrose and then you start to branch out in your later years, you have a Nobel Prize, then you're told you have Nobel's curse

Starting point is 00:43:24 because now you're a bit too woo. It's a tough rope to walk. Roger Penrose is a brilliant, brilliant mathematical physicist who's made absolutely central contributions to the field and as a result of that, ideas that he has that are not that promising actually get way more attention than they otherwise would. So I don't think that he gets any disadvantage from being a famous, respected Nobel Prize winning physicist. I think that he gets a little bit more respect than the idea itself would if some nobody who is a postdoc proposed exactly the same idea. I see. I see. So there's respect in the public sphere and then there's respect in the academic

Starting point is 00:44:04 sphere. And so when I speak to people on this podcast, professors and so on, there was even one in particular which I can tell you about off air because I don't want to give the person's name away. But she was saying that she and her professor friend were just cringing at Penrose speaking about orchestrated objective reduction, saying that he's lost his, he's gone off his rocker. So it seems like there's a trade-off.

Starting point is 00:44:31 You either get public respect, but if you do so, you exchange some academic cred. The orchestrated objective reduction theory, also known as ORC-OR, is a controversial theory proposed by Roger Penrose and Stuart Hameroff. It suggests that consciousness is spawned from quantum computations in microtubules within neurons, positing that these computations collapse in a specific manner guided by gravity, leading to moments of conscious experience. While ORk OR has attracted attention for its ambitious scope, and because its creator is a legend in the field, it still remains highly speculative.

Starting point is 00:45:14 Many scientists, including Scott Aronson, are skeptical. Critics argue that the brain is too wet and warm and noisy for quantum coherence to play a significant role. Interestingly, a recent paper this year does suggest that microtubules display quantum effects, specifically one called superradiance. Whether this paves the way for Penrose's theory being correct is still far from clear. How do stop losses work on Kraken? Let's say I have a birthday party on Wednesday night, but an important meeting Thursday morning. So sensible me pre-books a taxi for 10 p.m. with

Starting point is 00:45:51 alerts. Voila! I won't be getting carried away and staying out till 2. That's Stop Loss Orders on Kraken, an easy way to plan ahead. Go to kraken.com and see what crypto can be. Not investment advice. Crypto trading involves risk of loss. See kraken.com slash legal slash ca dash pru dash disclaimer for info on Kraken's undertaking to register in Canada. Physicists say that each other are off their rockers all the time. This is not exactly, you know, you don't need to win the Nobel Prize to be told that you're full of shit or off your rocker, okay? It's just more noticeable when you've won the Nobel Prize.

Starting point is 00:46:23 But, you know, there's a lot of ideas about collapse of the wave function, etc. out there. And the fact that you've heard of Penrose's versus many of them is because he's been so successful other times. And look, that's not entirely irrational. If someone is really, really brilliant, it will occasionally happen that they say things that to you seem crazy. But you should have an attitude, well, like, they've been right before, so I'm going to at least pay some attention to what they're saying here. I think that's perfectly valid. That doesn't mean you have to believe it, but you can pay some attention to it.

Starting point is 00:47:00 How do we distinguish genuine but unconventional ideas from pseudoscientific ones in such a way that we don't alienate the people who want to come into physics, who are genuinely interested in physics? that a lot of times there's bad science, which some people who don't like it want to discredit by labeling it as pseudoscience. You know, I'm perfectly happy to say that intelligent design is science. It's just crappy science. I don't have to pay any attention to it. It's like obviously wrong. So I don't need to like bend over backwards to invent philosophical ways of arguing that it's illegitimate.

Starting point is 00:47:44 I just think it's bad. Uh-huh. What would be another example of something bad, but is science? Flat earth theory. Very, very bad. All right. So there's this guy named Terrence Howard and I'm sure you've maybe seen clips. Maybe you've read about it.

Starting point is 00:48:03 What are your views on that whole situation and how it blew up? You know, look, I don't have a lot of, I don't care that much. He has zero of interest to say to any working physicist. He has some crazy ideas. Again, I get these crazy ideas in my email box every day. He gets noticed because he's a famous actor.

Starting point is 00:48:25 He's good at something else, right? It's a way more extreme version of Roger Penrose getting noticed for his theories of consciousness and quantum mechanics. But life is short. I don't have time to worry about people off the street with crazy ideas about fundamental physics. One of the ways I see that situation is that

Starting point is 00:48:42 we tell people, kids in particular, high school kids, even undergrads, like you can be a scientist, you can contribute to math, anyone can be a physicist. And remember, Feynman said that true science is about being irreverent to authority. You challenge ideas. We like to be proven wrong. That's what makes science great. And that there are no foolish remarks. And then someone comes on the scene like a Terrence Howard who's clearly interested in physics and chemistry and math and has his own ideas. And then we say, well, it turns out there are asinine comments you can make and not everyone can be a physicist. Do you see a tension? Yeah, I think that Richard Feynman

Starting point is 00:49:18 was not a very good philosopher. He was a very good physicist, but I would, you know, it's very, very hard to be right about this because his remarks there absolutely do capture something true, but they're just a little bit overly simplistic. You know, if you're a good scientist, you can't be wedded to the conventional wisdom. You can't be beholden to what everyone else thinks is true. And indeed, as any working scientist knows, the way to become super successful is to figure out why the conventional wisdom is wrong.

Starting point is 00:49:49 Right? You know, you don't become a famous scientist by proving Einstein right. You become a famous scientist by proving him wrong, by doing better than Einstein. But that's really hard to do. That's the thing that people don't get told. It's easy to be irreverent. It's

Starting point is 00:50:06 easy to be unconventional and individualistic and have your own ideas. It's really, really hard to do it well. I wrote a blog post a long time ago called Being a Heretic is Hard Work, explaining how... I'll put that on screen and then in the description as well for people to... Yeah, I don't even know what's in it because I wrote it so long ago. Maybe it's embarrassing now. But the idea is when I was an undergrad, I was very invested in the idea of overturning Einstein. And I even worked on with some professors at my institution who had data that they thought maybe was evidence against Einstein.

Starting point is 00:50:42 I thought this was very, very exciting and so forth. But I didn't understand general relativity, I didn't really understand the astrophysical data and all of its limitations, et cetera. And so to be a respected, respectable, useful, productive heretic is enormously harder and a little bit less exciting than the movies would have you believe.

Starting point is 00:51:06 And there's one other factor I think that is also super duper important here. I don't care who you are. I don't care whether you're an actor or a person on the street or a PhD in physics, that is entirely irrelevant. But I do care how much work you've done putting, put into thinking and learning about physics as it is understood.

Starting point is 00:51:30 You're asking me to put aside time in my life to read your theory and pay attention to it. Well first read my theory and pay attention to it. My theory is called the standard model of particle physics. And if you're not at the level where you've understood the reasons why that theory is so good, then look, maybe you have a brilliant idea, but probably not. And so I'm going to spend my time elsewhere. Just a tiny bit of pushback. In the case of reading the standard model, would you say that Eric Weinstein and Peter White and Lee Smolin, that they have read the Standard Model and Garrett Lisey and they understand it and they can even...

Starting point is 00:52:11 So, Lee Smolin certainly does not belong in that list of people. He is a very respected, very accomplished physicist who has some very non-conventional ideas and that's great, just like Roger Penrose, just like many people do. The others are more amateurs they're not you know people who've written a lot of physics papers people who have demonstrated that they've contributed to the field in useful ways. As I said that's fine I don't care who you are or whatever but I think that you know those I don't care about these individual people right what I care about is is, do you build on or account

Starting point is 00:52:47 for the reasons why we think the way we do already? It's, you know, here's a tip for reading papers that make outlandish claims in physics or in anything else. An outlandish claim is outlandish because the conventional wisdom doesn't accept it right away, right? It doesn't fit in. So again, the conventional wisdom doesn't accept it right away, right? It doesn't fit in. So again, the conventional wisdom is never going to be a hundred percent correct, but there are reasons why it's the conventional wisdom. And it's not

Starting point is 00:53:13 just because Ed Witten tells you that it's conventional wisdom, it's because there are good intellectual reasons. So if you're going to tell me the conventional wisdom is wildly wrong in some way, that's 100% good and fine and wonderful, but start your paper with the following phrase. We understand that you might not believe this theory for the following reasons, and now we're going to tell you why those reasons don't apply to our theory, right? Show me that you've understood why I will be skeptical, and my skepticism will be much easier to overcome. I don't mean to harp, but in Peter White's case, just to be particular, what would he say is wrong about the conventional wisdom?

Starting point is 00:53:54 I don't know. I don't think he's making that claim. I'm not familiar. Like I said, I don't read his stuff. So, part of earlier when I talked about the crisis in physics, I mentioned there's the great stagnation, the great schism, and then the great silence. So the great silence is that it's difficult to have a conversation like this, but inside academia. Now, you may say, hey, behind closed doors, but I'm unaware of any conference that's dedicated to questioning the direction of fundamental

Starting point is 00:54:28 physics itself. And even when talking about, look, we don't have the time to read other people's ideas. David Gross was speaking to Carla Rovelli about loop quantum gravity versus string theory. And David was saying something about loop quantum gravity has a problem with matter, with fermions. And Carla Rovelli was like, what are you talking about? We saw that at least a decade or two ago. And David Gross was like, oh, that's news to me.

Starting point is 00:54:59 And I'm there watching, many other people are watching, thinking you don't have many competitors. Like string theory is 50% of the people in fundamental physics. You don't have many competitors. It's loop quantum gravity, maybe some asymptotic safe gravity, maybe some causal dynamical triangulations. But there's not much. And so you should be aware of the latest developments of your competitors.

Starting point is 00:55:26 So I don't know if it, yeah, anyway, what do you say to that, sir? Well I think what I said before in a similar way, I don't think that David Gross has any responsibility for being up to date in the latest developments in competitors to string theory. I think the field has a responsibility to take those developments seriously, but an individual 80-year-old Nobel Prize-winning physicist has earned the right to think about the ideas that he thinks are the most promising. And there's, again, very good reasons for him to believe that loop quantum gravity is not promising. I think that nevertheless, despite those reasons, it's good that as a field we give some resources to loop quantum gravity. And what you have to understand is that the whole field is in constant conversation about

Starting point is 00:56:19 these things. And much of the conversation does happen behind closed doors, not because it's super secret, but because you have a faculty meeting. And at the faculty meeting in your physics department, the theoretical physics group comes up and says, we would like to hire another string theorist. And the audience they're pitching to is not a bunch of string theorists, right?

Starting point is 00:56:40 It's a bunch of condensed matter physicists and astrophysicists and atomic physicists. They have to make the case that a string theorist is what should be hired. They have to offer some reason. And likewise, someone who says, well, no, we should hire a loop quantum gravity theorist. They have to give some reason. They have to, what is the result? What is the breakthrough that you've made in loop quantum gravity?

Starting point is 00:57:01 If you do, you will have a much higher chance of succeeding in convincing people to hire people like you. Like I said, there's not enough support for the more quirky minority perspectives, but it's not zero because there isn't a top-down hierarchy. There's always the chance for you to make your case. So even if the system is not perfect, the system does allow you to try to convince other people that what you're doing is promising in some way. So earlier, we talked about how do we practically speaking divvy up the funds, or if that's even the correct approach to minority approaches, at least currently minority approaches. And, and then the answer was, well, we don't know because neither of us are popes. Are there discussions that you're aware of in physics thinking about this, but in a public way, not just behind closed doors? Sure.

Starting point is 00:58:00 I mean, look, I've been to plenty of conferences where people have panel discussions on the crisis in physics or the state of string theory or the future of physics in various ways. I mean, you can literally Google the future of physics conference and there's plenty of those. They're not the most relevant conversations. I think those faculty meetings are more relevant. I think that funding agencies have meetings. How much money are you going to allocate to these different things? And empirically different approaches to physics do die

Starting point is 00:58:33 off. You know in the 60s there was a big boom in S-matrix theory and it was sort of an alternative to quantum field theory. But it didn't pay out and quantum field theory did. And so quantum field theory won and people stopped doing S-matrix theory and people stopped giving funding to S-matrix theorists. That of course was in the heyday where you had all this wonderful experimental data guiding you as to which approaches worked and which ones didn't. And today we're not that lucky. So, you know, I think that, like I said, I'm not, my focus is not in fixing the academic system. I don't think the academic system is perfect in any way, but I'm much more interested in understanding the universe.

Starting point is 00:59:17 It's useful to have a summary of the situation thus far. After speaking with people like Neil Turok of the University of Edinburgh, Lee Smolin of the Perimeter Institute, Gregory Chaitin of the Institute for Advanced Studies, among others, who all believe there is a crisis in fundamental physics, I've identified their claim down to three elements. Number one, the great stagnation. So this is the claim that since the 1980s, there haven't been experimentally verified theoretical innovations in fundamental physics.

Starting point is 00:59:47 Now this is a different claim than quote unquote physics is in crisis. It's a specific claim. Indeed, you can do this exercise yourself. For fun, last week I went through every single Nobel Prize in physics since the 1980s and asked myself whether the award is being given for work based on a theory fomented after the 1980s, or if this was just confirmation of a theory cemented prior to the 1980s. How many instances do you think there were? Zero. Number two is the Great Schism. This refers to the split that occurred in the physics community, particularly in the 1990s. Super string theory emerged as a dominant paradigm, with some proponents claiming it's

Starting point is 01:00:29 the only game in town. This led to a divide between string theorists and those pursuing alternative approaches. The schism is not just about scientific disagreement, it's about academic positions and general direction. How should one allocate resources between different research programs in a data-starved field? And number three, the great silence. This refers to the difficulty in having an open, constructive dialogue about the state

Starting point is 01:00:57 of fundamental physics in academia. There's a perceived trial by string theorists, where new ideas are evaluated primarily by them. A string theorist may say that criticisms without offering an alternative is not useful. Put up or shut up. This sentiment was also levied against Peter Wojt in 2007, when he wrote Not Even Wrong. However, when someone does have a theory, they're also criticized for trying to promote their own theory, as happened again with Wojt in 2022. Now both of these statements can't be true at the same time. From speaking with those aforementioned professors, as well

Starting point is 01:01:34 as others who do believe there to be a crisis in fundamental physics, they keep reiterating that they're not being listened to and they're misrepresented. For instance, string theorists claim that alternative theorists are resentful because the string theorists aren't working on their theories. However, the people that I speak to, both on air, and there are links in the description, and off air, suggest that the issue is more that string theorists won't listen to their theories. And that's a different claim.

Starting point is 01:02:03 It's a claim of silence. The question becomes, if there is no global authority in physics to mandate change like a pope, and simultaneously that dominant paradigms like string theory persist due to self-reinforcing mechanisms, then at what point does it indeed become the moral onus of individual researchers, like a David Gross, for instance, to stay informed about competing theories? Just as peer review is seen as an obligation to give back to the field, what about staying aware of alternative developments as a duty to keep the field healthy. Now the great stagnation may be changing as there's now evidence such as the Muon G2 anomaly and also DESI's new data on dark energy.

Starting point is 01:02:54 You can read the Economist's article called The Dominant Model of the Universe is Creaking which discusses these developments. So which of the two camps do you fall on? Is it the responsibility of the theorist for coming up with great new methods for testing their ideas, so the phenomenologists? Or is it with the experimentalists who aren't creative enough and they're proposing constantly new particle colliders? That's the meme that Sabina tends to promulgate, but of course, that doesn't characterize all particle physicists or experimental particle physicists or let alone experimental physicists in general. Either way, which of those two lanes do you subscribe to?

Starting point is 01:03:34 It is entirely not the experimenter's job to do that. It is a theorist's job to do that. The experimenters are guided by theory. You don't do experiments randomly. You don't just like throw instruments together and see what happens, right? You build very, very precise machinery for what you think is a good reason, right? You couldn't just build the Large Hadron Collider without knowing that there was going to be new particles there that would have certain signatures. You would have to control for your noise in certain ways. You have to be sensitive to certain particles coming out, etc. etc. etc. If the experimenters don't know what to look for, it is not their fault that they have not found data that overturns the theories that we already have. It's the theorists who have to tell them what to look for. This is why I wrote this paper

Starting point is 01:04:21 that we started with, because we need to ask questions about, okay, if ideas like holography are true, what would be the experimental signatures? I mean, Lee Smolin is entirely correct. It's absolutely possible that the data are already there. And I think that's very, very worth doing, but I'm not going to blame the experimenters for not having done it yet. Yeah. I don't mean to blame Brian Keating or any of the experimenters who may be watching.

Starting point is 01:04:48 Now, in 2018, you had a paper called Beyond Falsifiability. I found that title super interesting. Please, can you tell myself and the audience what the crux of that paper is? Sure. There was this famous idea from Karl Popper, a philosopher, about demarcating science from non-science. And you have to understand, Popper had very clear examples in his mind. His idea of a good scientific theory was Einstein's general theory of relativity.

Starting point is 01:05:20 His idea of a bad scientific theory was Freudian psychoanalysis. He had other examples of bad scientific theories, but those are two good paradigms that people will be familiar with. And he came up with the idea that the difference between these two theories is that general relativity stuck its neck out. It said, if I, general relativity, am correct, then light will be deflected by a certain angle during a solar eclipse. And he says Freudian psychoanalysis does not do that. Freud does the opposite. You come up with some story that your patient has told you and a good psychoanalyst will always be able to explain it using psychoanalysis.

Starting point is 01:05:55 So there's no way to show you that psychoanalysis is not right, okay? So that was the falsifiability criterion that was supposed to demarcate science from non-science. So it doesn't work. It's not at all. You can read the paper. I encourage people to actually read the paper, not just the title. But the argument is not that we don't need evidence or we don't need data or anything like that. That is the opposite of the argument. The argument is that the relationship between theory and data is way more complicated and nuanced than this simple idea that Popper had.

Starting point is 01:06:35 For one thing, you can have a theory, it makes a prediction, you do the experiment, it does not come in line with the theory, and you realize, actually, I made the prediction badly. Or you realize, oh, my experiment was wrong. Like, there's a million different ways that you actually need to get into the nitty gritty of the experimental

Starting point is 01:06:55 process to understand that relationship. The other is that you have to think about, are you saying that things are unfalsifiable in principle or in practice? You know a classic example of a theory that people say is not falsifiable is the many worlds interpretation of quantum mechanics because it says there are all these other worlds. Popper was a fan of the many worlds interpretation of quantum mechanics because it made definite statements. of the many worlds interpretation of quantum mechanics because it made definite statements. You cannot in principle see the other worlds,

Starting point is 01:07:29 sorry, I should say you cannot in practice see the other worlds, but in principle, there's a different world, there's a different reality if the worlds are there than if the worlds are not. So as far as Popper was concerned, that was fine. He hated the Copenhagen interpretation of quantum mechanics. He didn't love to be very, very, he didn't love the many worlds interpretation because

Starting point is 01:07:47 he had his own interpretation he thought was even better. But he did not say that it was not legit because of falsifiability reasons. And the hilarious thing, of course, is that physicists who will go around poo-pooing philosophy love the falsifiability criterion because they understand it, right? It fits on a bumper sticker. they think it solves all the problems. Philosophers of science know perfectly well that it has all these problems, the reality is much richer than that. And so in the paper you will see some pretty damning quotes

Starting point is 01:08:17 about the falsifiability criterion by professional philosophers of science. And again, not, you know, any criticism of Karl Popper as a philosopher. He's one of the great philosophers of science of the 20th century. Isaac Newton was wrong about gravity because we know better now. Karl Popper was wrong about the demarcation problem because we know better now. So what was his interpretation of quantum mechanics? Oh, I don't even know. It never got very far. It didn't get very popular. What you mentioned about the in beyond falsifiability in the first part of your explanation, that if you have a theory, you make a prediction. The prediction turns out the data

Starting point is 01:08:56 doesn't match the prediction. There's something called the bundle of hypotheses by Quine. Have you heard of that? What was it called? Bundle of hypotheses by Quine. Oh, heard of that what was it called bundle of hypotheses by oh yeah yeah yeah yes okay they were reminding me of that so well yeah sorry let me let me just butt in very quickly like sure this is part of why falsifiability is not put in central importance by philosophers of science because all of your experimental data is ultimately interpreted through the lens

Starting point is 01:09:26 of a theory. As we've already said, which experiments you do is interpreted through the lens of a theory. There can be a whole bunch of extra hypotheses, as what Quine was getting on about, that feed into the actual experimental prediction you make that might be wrong, even though the fundamental theory that you thought you were testing was, is completely okay. So that's why it's just much harder than, it's much harder in the real world

Starting point is 01:09:53 than Popper's cartoon would make it out to be. And I specifically, in the paper I tried, again, this was completely ignored because people don't like to read papers, they like to read titles. I tried to make very clear in the paper. I apologize, sir. No, it's not about you, I'm sorry. I didn't like to read papers. They like to read titles. I tried to make very clear in the paper. I apologize, sir. No, it's not about you.

Starting point is 01:10:07 I'm sorry. I didn't mean about you. By the way, you are going to continue that point, but I'm going to start a series on this channel called The Daily Archive, where I'll go over a different paper from the archive in five to 10 minutes and outline it to people. So Beyond Falsifiability will be one of them. Good. So yeah, the point I'm just trying to make very quickly

Starting point is 01:10:26 is that the actual Karl Popper, the human being who was a philosopher of science had a much more nuanced view of the philosophy of science than this little cartoon Popper that physicists sometimes invoke without ever having read what he says. And it's the cartoon Popper that I was actually arguing against in that paper.

Starting point is 01:10:46 Did you just point out the problems with traditional falsifiability or did you propose, hey, here's the demarcation? Because earlier you said you don't care too much about that demarcation, although you care about good versus bad. Yeah, I do not claim to have the once and for all correct philosophy of science. So I do try to be humble about that. And what I try to say is, look, let's think about why Popper's idea about falsifiability is so compelling. It's because he's trying to emphasize two things. Number one, that a good theory is

Starting point is 01:11:17 definite. It doesn't explain every possible reality. It says some realities are okay and some are not. And number two, we judge the success of theories empirically. The reason why I'm a fan of the many worlds interpretation of quantum mechanics is because it fits the data that we actually have. And its opponents say, but there's this other data we can never get that would make it even more obviously true, namely looking at the other worlds and you can't get that would make it even more obviously true, namely looking at the other worlds and you can't get that data. Why do I care about that? Why do I care about the data we can't get?

Starting point is 01:11:51 I care about fitting the data we can get and Popper was on that side. What would Popper say about the different ways that we can compactify in string theory and saying that there's this landscape and sure we have a Swamp Land program but there are conjectures there. It's not complete yet. What do you say that that it sounds akin to there's many variants, so people may interpret that as many worlds or, or many possibilities? So certainly I don't know what Karl Popper himself would say.

Starting point is 01:12:20 I'm not going to put words in his mouth. I think that the relevant point is that in any one particular compactification, that is a definite theory of the world. And that theory can be right or wrong. There can be many, many, many compactifications. That's absolutely true. But that makes our life hard.

Starting point is 01:12:40 And that doesn't make the theory intellectually disreputable. It just means that we might not ever figure out which one, if any, is the right one. Is this good versus bad science the same as religion versus science? Or would you see religion as something different, not pseudoscience, not bad science, it's something different? Religion is too broad a category to say much specific about. There is natural theology. There is the attempt to learn about the nature of God

Starting point is 01:13:08 through observing the natural world. But there's also plenty of aspects of religion that number one, have nothing to do with the natural world. And number two, don't proclaim to be scientific in any way. So I don't think it's an apples to apples comparison. Speaking of naturalism, what is poetic naturalism? Poetic naturalism is an idea I explored in my book, The Big Picture, which tries to, you know,

Starting point is 01:13:33 in the spirit of people like Daniel Dennett, the philosopher who recently passed away, say that there is a base reality, there is the world, that in principle could be described perfectly well, but there's also all these sort of more coarse-grained higher-level descriptions of the world, what what Dene called the real patterns in the world, and they deserve to be thought of as real aspects of the world also. So you can be naturalist, you think there's only one world, the natural world, but poetic

Starting point is 01:14:02 because there are many different ways of talking about the natural world, but poetic because there are many different ways of talking about the natural world. Some of those ways will be purely scientific, you know, the theory of tables and chairs is based on the theory of atoms and molecules at the end of the day, but I don't need to know about atoms and molecules to talk about tables and chairs. Other theories might not be based in science, theories of of ethics or aesthetics where there's no experiment you can do to figure out whether or not your claim is true or false, but nevertheless they serve a purpose to us in our everyday lives. Ah, okay.

Starting point is 01:14:35 So would it be akin to saying the standard model is an effective field theory and chemistry is akin to an effective model of that. And then biology, an effective model of chemistry. I know I'm abusing the terminology, but there is a reality to the different levels, even though in principle, quote unquote, they can be reduced down to physics. Yeah, I think that's most of it, but there's also this extra thing

Starting point is 01:14:59 that some things cannot be reduced down to physics, even in principle, things like morals and aesthetics. Ah, so, look, it's so cool that you think about morals and aesthetics and philosophy, and I'm curious, when did that start? I think it's probably safe to say that it started when I was an undergraduate. I was an undergraduate at Villanova University, a good Catholic school where they forced you to take a whole bunch of classes far outside your major.

Starting point is 01:15:32 Every liberal arts undergraduate, liberal arts and sciences undergraduate, had to take three semesters of philosophy in addition to three semesters of religious studies and three semesters of history and three semesters of English all down the line. So that's where I first took a formal philosophy course, and I did fall in love with it right away. I didn't, and ended up being a philosophy minor, I didn't ever think that it would have something to do with my work in physics.

Starting point is 01:16:00 That wasn't until much later, till I was a professor, a junior faculty member, that I realized that some of my work in cosmology had a very direct overlap with people in philosophy departments who worked on what they called foundations of physics. So rather than arguing about Karl Popper type stuff, what's a theory, what's not a theory, they were really doing physics, but they were just doing physics in a way that would only get them hired in philosophy departments. Oh, that's super interesting. Yeah, so those are my people.

Starting point is 01:16:31 You have to explain more. What is meant by that? They're doing foundations of physics, but if for some reason would only be the job placement was only in the philosophy department. Well, think about the arrow of time, which is where I was actually working on this particular thing. So I didn't get into quantum mechanics until somewhat later. So thinking about

Starting point is 01:16:50 why the past is different from the future, it goes back to Boltzmann and Maxwell and other people, you know, because they're the ones who invented the problem. The problem didn't exist before them because there just was an arrow of time. The past was different from the future. It only became a problem when you invented these mechanistic kinetic theories where you said that heat is the kinetic energy of molecules and entropy is the number of ways you can arrange them, etc. So basically you're reducing everything to particles obeying Newton's laws. And Newton's laws don't have an arrow of time in them. And so if you're reducing everything to particles obeying Newton's laws,

Starting point is 01:17:31 now you have a problem that you didn't have before. Why is there an arrow of time? And there's a long tradition in physics, going back to Boltzmann, of claiming that you have derived the arrow of time when you really haven't. You've cheated, you put it in your assumptions and you derived time asymmetric conclusions from time asymmetric assumptions, which is not very difficult to do. And it was the philosophers who really figured this out and got it straight.

Starting point is 01:17:58 And I think that in the philosophy of physics community, foundations of physics community, David Albert at Columbia is given the most credit for really sort of establishing what is thought of as the conventional picture, where you give equal credit to the dynamical laws and to the initial conditions. And again, plenty of people had sort of said words like this. Richard Feynman, Arthur Addington, plenty of people, you know, have thought about this, but it was the philosophers who really said it clearly and rigorously and so forth. Meanwhile, in physics classes around the world, we're still told that you can derive the second law from some equations without putting in an initial condition explicitly.

Starting point is 01:18:41 And that's just wrong. We just lied to, but that's okay because you get the right answer and physicists at the end of the day just want to get the right answer which is that entropy increases. What was wrong with Boltzmann's argument and what's meant exactly when you say people should give or or that David Albert showed that people should give equal credit to initial conditions and evolution laws. So the idea that Boltzmann had was that you could start with, and again not only Boltzmann but others, you could start with this idea that a gas is actually a bunch of, let's say atoms bumping into each other, okay? And then you can just use probability and statistics to derive the idea that

Starting point is 01:19:23 entropy increases. And he indeed did prove a theorem, the H theorem, that kind of sounds like that. But it makes an assumption, the assumption of what is called molecular chaos. In German, the Stosszahl Ansatz. And the molecular chaos assumption says that if I have a bunch of molecules going to bump into each other, they are uncorrelated with each other, which makes sense. They're moving around randomly in the box of gas, etc. But it turns out at the technical level, you can make that assumption once.

Starting point is 01:19:57 But as soon as you make that assumption at one moment of time, then when the molecules bump into each other, now they're correlated. Now they're coming in opposite directions from where they were before, right? So you can't remake that assumption again and again. So either there's two, you have a choice of two possible mistakes. One mistake is you remake that assumption again and again, and that's usually what people do because it gets them the right answer.

Starting point is 01:20:26 Or you just apply it at the beginning of your problem and not the end. The reason why that's a mistake is because you're trying to derive the fact that there is a difference between the past and future. And if you assume there's a difference between the past and the future, then you haven't really succeeded, right?

Starting point is 01:20:40 And look, again, people are smart. Lo Schmitt pointed this out to Boltzmann. Lo Schmitt had been Boltzmann's professor and Boltzmann kind of filibustered. He never came up with a good answer to this so-called reversibility paradox. And ultimately the answer is, you have to explicitly break time reversal symmetry

Starting point is 01:21:03 by putting an initial condition that is low entropy. So what do you make of approaches that do away with initial conditions or boundary conditions like Hawking and Hartle? And for people who are listening, when they hear Hawking and Hartle, no boundary, and they think in terms of you have an equation and you input something in the equations of the black box and the output, it sounds like there is no input. How can you even have an output? What does that look like? Help people understand that. Well, so there's two things. Number one, Hartle and Hawking have what is called the no boundary proposal for the wave function of the universe, but it's certainly an initial condition. They

Starting point is 01:21:40 certainly apply it at the beginning and not the end. It's called the no boundary condition for technical reasons in quantum gravity. So let me let's indulge our readers with some technicalities for 30 seconds and then we'll pull back. Feynman told us that we can do quantum mechanics by doing a path integral. That is to say by summing up contributions from every different possible trajectory the system can take. in this case because we're doing gravity The trajectories a system can take are geometries of space-time Okay, so you would like to sum over every geometry of space-time. That's hard

Starting point is 01:22:17 So the first move that Hawking makes is let's Instead of summing over every space-time Let's sum over every space time, let's sum over every space. So let's just imagine that there was no time dimension and just treat everything in a Euclidean way, as we say, but we let it be curved. And then if you have some state of the universe at one moment of time,

Starting point is 01:22:39 you can sum over all of the Euclidean continuations of that to the past that don't have another boundary. They have the boundary that is the moment of time you're looking at, but no previous boundary and that's the no boundary wave function of the universe. Now if that's all you ever did, that would be cheating just as much as Boltzmann did. You're putting in an arrow of time. In later years, Hartle and Hawking and also Thomas Hurtog, who wrote a book about this not too long ago, who was their collaborator, they talked to people like me and David Albert and other people who cared about the arrow of time, and they realized that they need to be a little bit more careful about what their assumptions were. And it actually goes back to an even earlier

Starting point is 01:23:25 debate between Stephen Hawking and Don Page in the pages of Nature and so forth. But the result is that they now would like to claim that the set of all solutions to their equation is completely time symmetric. But we live in a solution that is not, and that's actually a very sort of plausible, clever possibility to think about. I think it's very alive, but I think that again, quantum gravity is too hard for us to say anything definitive about it one way or the other. Others, like myself, have other theories

Starting point is 01:23:59 where you don't really focus on the quantum state of the universe, you have a universe that is largely classical, but is also symmetric between the past and future. And the real difference is that we don't see the whole universe. So in our picture, what you and I think of as the Big Bang is not the beginning of the universe. It is the emergence of our little bit of universe out of some pre-existing thing.

Starting point is 01:24:24 And the whole shebang is actually symmetric in time So again not cheating the way that Boltzmann did that's a great wordplay The whole shebang versus the big bang. Yep. So can you explain what? How is one supposed to think of the whole shebang compared to the big bang and are you saying that our experience of the arrow? Of time is somehow some local phenomenon? It's absolutely in my picture some local phenomenon. The whole shebang is just a casual word for the multiverse, right? The idea in cosmology of the multiverse is that there are regions of space and space-time that are

Starting point is 01:25:03 just far away in either space or in time, so we can't see them, where conditions are very, very different. And so in our picture, that includes not just far away in space, but even before the Big Bang as well. And again, plenty of other people have theories of things that happened before the Big Bang,

Starting point is 01:25:22 but except for our model, I think this is still true, they do one of two things. Either they put in an arrow of time forever so that there is some directionality to the time evolution of the universe. For example, Penrose's conformal cyclic cosmology does that. Or they treat our Big Bang as a special moment, as a moment of special conditions, low entropy for whatever reason, because it fits the data or whatever, which is also perfectly fine.

Starting point is 01:25:52 But in both cases, you're not explaining the special condition of our early universe, you're putting it in in some way. Our ambition is to not make any assumptions about the speciality of the state of the universe at any one moment of time, and to argue that in almost any initial condition, you can go both forward and backward in time, and get a universe that ultimately looks like ours. So that's an explanation, whereas sometimes people would say, we explain the fact of fine-tuning because everything happens and then there's the anthropic argument. So what you're saying is not the anthropic argument.

Starting point is 01:26:29 Ours is anthropic only in the following sense. In our whole shebang, the vast, vast majority of places to live have no matter in them, have no matter or energy, just empty space. So of course we're not going to find ourselves there. We're going to find ourselves in hospitable regions of space-time. So that's anthropic in exactly the same way that we explain why we live on the surface of the Earth rather than on the surface of the Sun. There's a lot more surface to the Sun than the Earth, but it's not a hospitable place to live, so we're not surprised that we find ourselves here.

Starting point is 01:27:04 Your recent work on holography, do you consider that to be work in place to live so we're not surprised that we find ourselves here. Your recent work on holography, do you consider that to be work in quantum gravity or do you consider that to be work in reconciling GR with the standard model, which is different? It is work in quantum gravity but it is not proposing a new theory of quantum gravity. It is taking a purported feature of quantum gravity, namely holography, which again is descended from Hawking and Bekenstein, et cetera, and asking is it possible that that feature in a very robust model independent way

Starting point is 01:27:39 has potentially experimentally observable consequences. So it's not a theory of quantum gravity, it's a theory of how quantum fields behave in the presence of gravity. The definition of quantum gravity is that you sum over metrics or possible geometries or that you second quantize, so-called second quantize, Einstein's equations. Does this ring true to you as a definition of quantum gravity because that would be distinct from the more broader reconciliation between General relativity and the standard model. I don't know

Starting point is 01:28:12 That's it. That's a definition that you're welcome to or not for for me Whatever the correct quantum theory is that gives rise to gravity is quantum gravity. I see Okay gives rise to gravity is quantum gravity. I see. Okay, so when someone says we need to marry general relativity with the standard model and it could be through some novel mechanism that doesn't involve a path integral over geometries, then that would still be a quantum theory of gravity. A theory of quantum gravity.

Starting point is 01:28:39 For me it would be, yeah. But again, I'm not gonna insist that everyone stick with my definitions. I see, I see. Well, the reason is because I know that the string theorists have the concept of string universality I don't know if you've heard of that Have you heard of string universality, I mean, yeah, I've heard of it, but I'm not an expert So I couldn't I couldn't give you the definition

Starting point is 01:29:02 it just says that any theory of any consistent theory of quantum gravity is, can be gotten to by some low energy limit of a string theory. So, sure there may be other quantum gravities out there, but they will all end up being string theories anyhow. That's a good thing to conjecture. We'll have to figure out whether it's true. Exactly. Hard to prove. It's a braggadocious claim. Right. Because the, sometimes I ask a, I ask string theorists what's the definition of string theory and then I thought it would just be you have a theory where your fundamental ontology

Starting point is 01:29:35 is an extended object or at least that's where it came from or maybe it's one of the five flavors or something akin to that. But then they would say, well, it's, we're studying quantum gravity. It's any consistent theory of quantum gravity. I think before the second super string revolution, so before the mid 1990s, it was pretty clear what string theory was. But it was a fundamentally perturbative theory.

Starting point is 01:29:59 You had strings and you would scatter them, and you would calculate the Feynman diagrams and get an amplitude and so forth. But when we started to understand dualities in the mid 90s, these were non-perturbative phenomena that were not based on scattering strings off of each other. And for better for worse, the field became much richer. You know, people were trying to understand these dualities and holography and special new kinds of field theories that you could get to by taking limits of these string theories

Starting point is 01:30:28 and so forth. And so these days, if you ask almost any person who you think is a string theorist, are you a string theorist? They will say, no, I am thinking about theoretical physics, you know, and I get it because they're thinking more broadly than just the old fashioned 1980s style strength theory. What's meant when the term publish or perish is echoed? Publish or perish is somewhat of a supposed to be a dark joke, right?

Starting point is 01:30:56 But it basically is the idea that in academia, you are judged at the end of the day by what you publish, you know, not by being smart or being personable or being friends with anyone. What have you done? What have you accomplished out there in the literature whether it's scientific literature or humanities or arts or whatever? So if you want to succeed in academia and getting a job and keeping the job you have to publish things There's a physicist and he was saying look the second question after what is my name is how many citations do I have?

Starting point is 01:31:28 And that this just incurred in some job application for a post-doc or could be an assistant professor, I don't know. And he was saying that this encourages people to just keep publishing trivial or just what barely makes the mark instead of monumental achievements. And then also citing your friends I those are citation cliques and I believe that's what was referenced in publish or perish What do you make of this in the modern era where you have preprints and everything is electronic You can figure out not only that someone has a bunch of site a bunch of publications

Starting point is 01:32:01 but whether those publications had an impact on the scientific literature and by how many times they are cited. And that is not a perfect proxy for whether their work is good or not, but it's better than just counting how many publications they have, right? I've never seen any application for any job or anything that asks you how many citations you have, but

Starting point is 01:32:25 you wouldn't need to because anyone can go online and figure it out in 30 seconds. Go to Google Scholar and you'll plug in somebody's name and you'll be told. It is, there are ways to try to exploit the system strategically, right? Like you say, get all your friends to cite your papers or whatever those ways are not super effective, you know once I would I'd like to think that at a decent university Which I like to think that I'm at now at Johns Hopkins when you hire someone doesn't matter Only how many citations you have you want to look at their papers? Like are they interesting or do they say good things, you know at the end of the day?

Starting point is 01:33:10 if you, you know, at the end of the day? If, you know, it's a big world out there and I can't say that all places work like that, but I cannot imagine hiring somebody just because they have a lot of citations and I don't know what work they've actually done. What papers are you most proud of? Yeah, the papers I'm most proud of are uncorrelated with how many citations they have actually. I think the paper that I explained about the arrow of time is probably one of the ones I'm most proud of, even though there's some mistakes in there, some calculational things that I think

Starting point is 01:33:41 I could improve upon now, but I think the idea was very interesting and might even be right, you know, ideally being right is interesting. Interesting. I wrote a paper with Chip Sabins about deriving the Born Rule in the many worlds interpretation of quantum mechanics,

Starting point is 01:34:03 which was like my first philosophy of quantum mechanics paper. So I'm personally proud of that, just because it's the first one in that direction. And I have one called Quintessence and the Rest of the World, which was an early intervention in theories of dark energy when they became interesting in 1998, when we just discovered dark energy. And I pointed out some issues of naturalness with many people's theories of dark energy,

Starting point is 01:34:32 and I pointed out how to get around them. And on the basis of that, I made an experimental prediction, which they're still trying to test these days. People like Brian Keating and others. So that always makes you feel good when you make an experimental prediction that people are trying to test. And where do your ideas, what you consider to be the best ideas of yours, where do they come from? When do they occur to you? Is there a pattern to them? Honestly, the best ideas come out of annoyance because you read other people's papers, you hear what they're talking about and you think to yourself like, that doesn't quite work, that doesn't quite fit together like the quintessence paper

Starting point is 01:35:06 There were all these people writing writing models of dark energy with scalar fields that were very low mass and for some reason Weren't interacting with anything else. I thought that was very unlikely So I explained that it was unlikely for the arrow of time paper There are a lot of cosmologists writing papers about what they consider to be natural conditions for the early universe. And I think that they were not actually natural, they were just cheating, just like Boltzmann did back in the day. So I got annoyed with that and I tried to do better. So what would you say is the correct model in your present deliberation of dark matter? Oh, dark matter I'm quite open about. You know, I was completely of the opinion 20 years ago that there were good arguments

Starting point is 01:35:51 for weakly interacting massive particle, dark matter. But those arguments went hand in hand with other arguments that would have led you to believe that the Large Hadron Collider would discover a lot of new particles when it turned on. And so that hasn't happened. So I've updated my credences about that. Like I said, there's plenty of other options on the market. I think axions are probably the most plausible right now.

Starting point is 01:36:15 Axions are also good for other reasons. So but we'll have to wait and see. That's an empirical question. Neil Turok and Latham Boyle have a joint model and they believe that dark matter is right-handed neutrinos. Now, I shouldn't say belief, I should say that they just proposed that, although Neil himself may have said he believes that to be the case. You know, I think you gotta be careful when you say someone believes something.

Starting point is 01:36:41 It is the job of theoretical physicists to propose ideas they may or may not believe. My first ever published paper was a model that violated Lorentz invariance, that picked out a preferred rest frame of the universe. Not because I believe that Lorentz invariance is violated in that way, but it goes back to what we were talking about before. The experimenters can't do an experiment

Starting point is 01:37:03 until the theorists tell them what to look for. And so we were, you know, pioneering the idea that you would violate the Renssen variance and then ask the question, how would you know what would be the experimental outcome that you could go look for? So I don't know whether Neil and Nathan actually believe that the dark matter is right-handed neutrinos, but they're very very very sensible in exploring that possibility. Myself, yeah I don't know I think that their model is one of the ones that I briefly alluded to before where you pick some special initial conditions at the Big Bang and I think that I want to do better than that somehow. Maybe we can't like like we said Maybe the universe is just like that, but I'm holding out hope that we can do better

Starting point is 01:37:50 Is there something like a no-go theorem that you see them violating or something that comes to mind when? Someone proposes that dark matter could be right-handed neutrinos. No, I don't know that need it very well could be I think that dark matter is something where we should be very pluralistic, very open-minded, thinking about lots of different possibilities. I asked Latham Boyle for a question for you and he said, can Sean tell me, he said, I'm a boring person, Kurt. So here's my question. What's something new that will blow my mind?

Starting point is 01:38:24 Any new great ideas that Sean has heard about recently? This is not a terribly great question, Kurt, something like that, but this is my question. What I want to, the sort of scenario slash hypothesis that I'm thinking about very, very gradually because it's a little bit half-baked, is how the laws of physics themselves could emerge out of the quantum evolution of the wave function of the universe. We have this idea in many worlds

Starting point is 01:38:55 that you have a wave function, it evolves. In the traditional understanding, when you measure a spin of a particle that is in a superposition of spin up and spin down, you have two worlds in the traditional understanding of many worlds, one of which you measured spin up, one of which you measured spin down, but those worlds are exactly identical except for the spin is up or the spin is down. In particular, the laws of physics are exactly identical in those two worlds. But I think we can be more open-minded. We can be more general than that.

Starting point is 01:39:27 We can explore possibilities where you start with a wave function evolving under a Hamiltonian where you wouldn't recognize the Hamiltonian as, oh, it's three-dimensional space with the standard model of particle physics and things like that, right? It looks like some mess. And out of this same kind of process of decoherence that you end up in the late universe measuring spin up or spin down, it could be the case that what you and I recognize as the dimensionality of space-time, the field content of quantum field theory,

Starting point is 01:40:00 maybe even the existence of Lorentz invariance, and Gage invariance and things like that, they emerge out of the branching of the wave function and the decoherence process. I don't know if that's true or not, but that's what I'm thinking about right now. Yeah, have you thought much about how did the laws themselves come about?

Starting point is 01:40:18 Well, this would be trying to do that. I mean, at some point you would have to argue that there is some feature that our current laws have that makes them, and perhaps, you know, look, it's many worlds. There could be many other branches of the wave function where things look very different, but maybe, you know, the individual branches like it when things look local and Lorentz invariant. I really don't know. What keeps you up at night? I sleep pretty well.

Starting point is 01:40:54 I'm not kept up by that much. Politics is much more likely to keep me up than physics is. Physics is much more likely to have me dream about it. I don't have political dreams, but I do have physics dreams. If I'm deep into a paper and I'm writing in any one moment, I start dreaming about it and that's a little disconcerting, but I do sleep through it. Well, some people get profound ideas from dreams. Have you?

Starting point is 01:41:15 I think that's overrated, to be honest. Profound fruitful ideas. Yeah. Now, most of my dream ideas are pretty nonsensical. They're very unhelpful to me. So earlier you seemed a bit skeptical of loop quantum gravity, and I'm wondering what do you see as its shortcomings as compared to, say, string theory? Well, loop quantum gravity has its beginnings as a field theory. It has its beginning as trying to quantize general relativity. Ash Ticard invented these variables using holonomies and so forth and Smolin and Revelli figured out ways to quantize them and you know solve the Hamiltonian constraint things like that. That just seems to me to be the wrong approach. Like I don't think that quantum gravity is going to come out of quantizing general relativity. I think it's gonna be more subtle than that

Starting point is 01:42:07 Uh-huh. So there's nothing in you think it's just wrong from the approach not some lack of results or Well, I think because of the approach it is fundamentally not a holographic theory It is hard to get that kind of holographic behavior or the Bekenstein bound and other things that we know from semi-classical quantum gravity. Maybe it's possible? Like, people are very, very clever. I thought that they had the entropy of a black hole and its equivalent to Bekenstein-Hawking entropy.

Starting point is 01:42:42 Well, they say they do, but they knew what answer they wanted to get, and they got it. And it is not clear to me they're not cheating when they get it. Yes, okay. Well, that's always going to be a problem because we have all this data. So any new theory will have that as an issue, even string theory. Yeah, that's right, but string theory has more impressive accomplishments to its name, such as calculating the, not just calculating that the area is equal to the entropy, but taking a limit where you turn gravity off, and the thing that made your black hole is now just a set of fluctuating brains, where you just do conventional statistical mechanics to it, and still get the right entropy calculation.

Starting point is 01:43:22 And that's, you know, a non-trivial check that they're on the right path. Yeah, so when people say that string theory has all of these mathematical results or all of these interesting physical results and alternative approaches don't have that, I'm always thinking, doesn't one have to weight that, like W-E-I-G-H-T, have to weight that by how much manpower and time was spent on string theory versus an alternate approach. So for instance, it's not quite fair to compare a whole program that's been around for 10 years, let's say, that has 100 people working on it with another one that has a thousand people working on it for 30 years. Something akin to that. Absolutely. I think that's true. But what are you going to do? The community finds string

Starting point is 01:44:14 theory much more promising, so they put more resources into it. I don't mean to say that there's something that has to, well, there should be something that's done. As for what, neither of us have a great answer to that. But I mean to say that we can't say that some other approach isn't as rigorous or isn't as well developed as a critique against that approach without taking into account this weighting system. Yeah, that's completely fair. Everyone has to use their own best judgments because we don't know what the right answer

Starting point is 01:44:43 is. I put a lot of weight on the fact that I don't think that quantum gravity comes from quantizing general relativity. The other thing that string theorists put a lot of weight on is if you just think as a particle physicist thinks and you scatter two particles off of each other, in that ultraviolet regime when you get up near the Planck scale, every field matters. It's not just gravity. There's no regime in which you can think about gravity and not think about the other forces.

Starting point is 01:45:10 And quantum, loop quantum gravity starts from a theory of gravity more than anything else. It doesn't rely on a specific matter content in the way that string theory unifies those things. Maybe those considerations are not relevant to the end of the day, but that's all we got to go on, so people are going to vote with their feet and decide what they think is more worth investigating. What advice do you have to the young person who's listening, who's watching, who would like to become a physicist or a mathematician? Maybe those are different

Starting point is 01:45:42 pieces of advice there. They are different people. I can't give advice to mathematicians because mathematics is great, but it's not my own passion. Mathematics is about proving theorems and conjuring up possible worlds that are not real. And like we said at the beginning, I'm interested in the real world more than anything else. For physicists, I would think very, very carefully about the, and I always say this to my students, what is the intersection of what you care about, what you're good at, and what the rest of the world cares about?

Starting point is 01:46:15 If there is no intersection of those three things, maybe rethink the area that you are in. But we all know, we've been talking, that progress is slow now in fundamental physics. The questions are amazingly important and fascinating, but the answers are slow in coming right now. So I think it's completely valid for a young physicist to say, you know, I think that studying complexity or artificial intelligence or biophysics is more up my alley than studying string theory or quantum gravity is. Even though the questions are super important, I'm not sure I know how to make progress on

Starting point is 01:46:54 them. What about advice for a philosophy student? Well, philosophy is very broad, right? There's very different kinds of philosophers. You can be a very well-respected philosopher studying Immanuel Kant, who was the works of Kant. He's a very specific 19th century philosopher, and that's okay. That's something that you can do, and it's very interesting and difficult to do, but it's completely different than being a philosopher of physics who is trying to do foundations of physics and try to understand the quantum measurement problem or something like that. So I can't give advice to the vast majority of philosophers. The little bit of advice I would give is you know, try to keep in touch with same advice I'm giving with physicists, the real world.

Starting point is 01:47:44 What we know about how the world works. There is such a thing as quantum mechanics, there are equations, the laws of physics underlying our everyday lives are very well known. Don't invent a philosophical system that is incompatible with what we know about fundamental physics. And lastly, I know you don't like the word belief, so let's say bet. If you were to place a bet on something that's held sacred currently, maybe it's supersymmetry, maybe it's the arrow of time, you mentioned that in physics today, just by your colleagues, you have an

Starting point is 01:48:16 understanding of the fervor of the field. So what's something that is almost taken as an assumption that you think is false, that will be overturned or what have you. Two of them. Because I imagine one of them will be one that we've covered already. I think that's very hard to give an honest answer to because if I really thought,

Starting point is 01:48:41 the way that I think is not that assumptions that everyone shares are false. I don't have many beliefs along those lines. My beliefs are more along the lines of, we're not paying enough attention to this problem, right? So in the case of like the foundations of quantum mechanics, it's not that people have strong beliefs about it that are false, it's that they don't care.

Starting point is 01:49:01 It's that they're not paying attention to it, right? So I think that physicists should pay more attention to that. And I think the same thing could be said about, you know, the anthropic principle or statistical mechanics or a whole bunch of things. You know, it's very, very hard. Physics is also a very big broad field right now. I think there's very exciting areas like stochastic thermodynamics, which looks at the thermodynamics of small but not too small numbers of particles where you can actually see the fluctuations happening. I think this is an amazing field that is just beginning to grow and will be revolutionary

Starting point is 01:49:38 in the next 50 years and very, very few people are working on it. So there's plenty of interesting things out there in physics, but my favorites do not always line up with the favorites of the field more broadly. We've gone this whole conversation without, I think even mentioning once consciousness. And this is theories of everything. So, okay, you say good. So maybe you don't want to end on that,

Starting point is 01:50:03 but what is your take, sir, on the hard problem of consciousness or consciousness in general? I already gave it away when I was giving advice to young philosophers, which is, uh, make sure your theories of philosophy are compatible with what we know about physics. My, I don't have any strong opinions about consciousness other than whatever it is, it's compatible with what we know about physics. You're not going to fix the puzzles of consciousness by changing what we know about physics. As I say in a paper that I wrote called, you know, consciousness and the laws of

Starting point is 01:50:38 physics or something like that, physics was very easy to understand. We know a lot about it. Consciousness is very hard to understand. We know a lot about it. Consciousness is very hard to understand. We know next to nothing about it. The fact that consciousness is a puzzle should not lead you to change the good things we know about physics. It's like losing your car keys and solving the problem by buying a new car. That's usually not the best way to do it.

Starting point is 01:50:59 Maybe it's right, but there's got to be a better way to bet. What would be examples of these people who are, or these theories that are throwing away physics? Oh, plenty of people. Roger Penrose tries to do it, right? In his case, it's still compatible at low energies, no? True. Well, many people who have non-physicalist views of consciousness, either directly dualist

Starting point is 01:51:24 theories or maybe like panpsychist or property dualist theories. All of these theories say that the experience of consciousness is more than a sort of reductionist way of talking about the collective behavior of atoms and particles. And I think that it's not more than that. Sir, thank you for spending two hours with me or one hour 45 minutes or so. Thank you for spending so long with myself and with the Theories of Everything audience. It's an honor to speak with you. It's a long time coming and it's, well, it's something I'll remember.

Starting point is 01:52:01 So thank you, sir. Great. My pleasure. Good luck with it. Looking forward to seeing it. Some brief channel updates. Stick around for the next minute as they may concern you. Firstly, thank you for watching. Thank you for listening.

Starting point is 01:52:15 There's now a website, curtjymungle.org, and that has a mailing list. The reason being that large platforms like YouTube, like Patreon, they can disable you for whatever reason whenever they like. That's just part of the terms of service. Now a direct mailing list ensures that I have an untrammeled communication with you. Plus, soon I'll be releasing a one-page PDF of my top 10 toes. It's not as Quentin Tarantino as it sounds like. Secondly, if you haven't subscribed or clicked that like button, now is the time to do so. Why? Because each subscribe, each like helps YouTube push this content to more

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Theories of Everything with Curt Jaimungal - Sean Carroll: The Crisis in (Fundamental) Physics is Worse Than You Think...

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