Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas - 241 | Tim Maudlin on Locality, Hidden Variables, and Quantum Foundations

Episode Date: June 26, 2023

Last year's Nobel Prize for experimental tests of Bell's Theorem was the first Nobel in the foundations of quantum mechanics since Max Born in 1954. Quantum foundations is enjoying a bit of a resurgence, inspired in part by improving quantum technology but also by a realization that understanding quantum mechanics might help with other problems in physics (and be important in its own right). Tim Maudlin is a leading philosopher of physics and also a skeptic of the Everett interpretation. We discuss the logic behind hidden-variable approaches such as Bohmian mechanics, and also the broader question of the importance of the foundations of physics. Support Mindscape on Patreon. Blog post with transcript: https://www.preposterousuniverse.com/podcast/2023/06/26/241-tim-maudlin-on-locality-hidden-variables-and-quantum-foundations/ Tim Maudlin received his Ph.D. in philosophy from the University of Pittsburgh. He is currently a professor of philosophy at New York University. He is a member of the Academie Internationale de Philosophie des Sciences and the Foundational Questions Institute (FQXi). He has been a Guggenheim Fellow. He is the founder and director of the John Bell Institute for the Foundations of Physics in Croatia. Web site NYU web page Google Scholar publications PhilPeople profile Amazon author page Wikipedia Contribute to the John Bell Institute!

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Hey, everyone, it's Cal Penn. I'm inviting you to join the best-sounding book club you've ever heard with my podcast, Earsay, The Audible and I-Heart Audio Book Club. Every episode, I nerd out with amazing guests and dive into the best new audiobooks available on Audible. It's the book club for your ears. Listen to Earsay, the Audible and I-Heart Audio Book Club. On the I-Heart Radio app or wherever you get your podcast. Hello, everyone. Welcome to the Mindscape Podcast. I'm your host, Sean Carroll. Today's podcast is one of those long-awaited episodes. People have been asking for this one for a long time. You know, it's funny. Sometimes there are some possible guests who are just so obviously mindscape guests, and I haven't had them on yet, and people are like, well, what's wrong? Why doesn't he have them on yet? They must be feuding. There must be beef or something like that. That's not usually the correct answer. It's usually just that I'd like to space them out. As I've said,

many times like to have a variety, and that includes both people who I know very well and am familiar with their work, and the people I've never heard of before I got to looking for podcast guests. So Tim Maldon is someone I've known for a long time, is a leader in the philosophy of physics or what we sometimes call the foundations of physics. So studying not physics as a philosopher, but studying nature as a philosopher, but doing so in such a way that you're looking at the foundational questions of nature. You're asking the why questions, the deep questions. You're trying to be very careful. And Tim has done very important work in thinking about space time and the geometry of space time, the nature of time and the arrow of time. I will point to, I'll try to link

in the show notes, to a wonderful mock debate that was done in the Foundational Questions Institute between Tim and Julian Barber. Julian Barber famously has advocated that time does not exist, Tim has famously advocated that not only does time exist, but the arrow of time is fundamental, not just an emergent approximation because of statistical mechanics. And what FUXI does is it has the debaters flip sides. So Julian was arguing in favor of the existence of time. Tim was arguing against it. And they were both really, really good.

I got to say, they were both quite persuasive for the points of view they didn't actually agree with as well as being quite amusing. along the way. But today, we're actually going to be talking about quantum mechanics. In some sense, this can be thought of as a sequel to the podcast that did a while back with David Albert, talking about quantum mechanics. David and Tim are very good friends and have worked together for a long time. They don't agree on everything because no two philosophers agree on everything, but they are united in their skepticism about the Everett interpretation of quantum mechanics. And so with David on the podcast, even though I'm pro-Everett, I want to give the voice to sensible voices on the other side, sensible points of view.

And so David explained why he doesn't like the Everett interpretation. What we didn't get to, ran out of time, was what he does like. So today with Tim, we're going to be talking mostly about Bohmian or DeBroy-Bome versions of quantum mechanics, sometimes called hidden variable versions of quantum mechanics. I keep calling them hidden variable theories, as most people do, even though, as advocates like to point out, the variables are not hidden. The extra variables that you add to quantum mechanics to make a hidden variable theory are the ones that you observe when you actually make a measurement. And physicists have not really caught on to hidden variable theories. They're not very popular. But certain sets of people, some physicists, some mathematicians, some philosophers have kept the flame alive.

And interestingly, as we talk about in the podcast, the Nobel Prize last year was given to tests of John Bell's famous theorems, his famous inequalities, which were very much prompted. Bell's exploration of these theorems and his proof of them was prompted by David Bowman's hidden variable theory, which Bell thought was the best formulated known version of quantum mechanics. Bell thought we should be teaching it in textbooks. So it's a little weird that the people who really take these theories seriously get good results that later lead to Nobel Prizes, yet the theories themselves are not very popular within physics. Again, I could give my reasons for not being a fan of hidden variable theories, but they are, as Tim says about Everett, they are absolutely a serious attempt. It's something that you should think about if you care about these things. And so we'll give the sales pitch for why you should take these seriously. We'll talk a little bit about foundations of physics more generally and even a little bit about the arrow of time.

And the other thing that I want to mention because Tim reminded me of it at the very end of the podcast is Tim is the director, and I think his title is director, but anyway, he's the founder of something called the John Bell Institute for the foundations of physics. Tim has been very active not only in doing foundations of physics, but in advocating for the status of this subdiscipline within philosophy and physics. And the Bell Institute, which is located in Croatia and serves as a place to meet and talk about foundations of physics, is trying to raise funds to get a permanent home. So they literally have a go-fund me, and you can visit the John Bell Institute homepage at John Bell Institute.org. that will link you to a donate button. You can donate to the permanent home for the John Bell Institute. We're not there yet. We need a bunch more donations, but I think they just started.

So it's early days. Maybe Minescape listeners will kick in a little bit. And with that, let's go. Tim Maudlin, welcome to the Minescape podcast. Thank you. Good to be here. So you've been a champion for a little while of something called the Foundations of Physics. So I want to ask you two questions.

One is, what is that for the listeners out there? But also, what's your sales pitch? Like, hypothetically, if you're talking to your colleagues in a physics department or a philosophy department, how do you explain to them why foundations of physics is so important? Okay. Oddly enough, I don't have to sell it to the philosophers. It's a weird situation. You have to sell it to the physicists. But it's very simple.

Really, foundations of physics, as the name suggests, is a branch of physics, namely, the one that. that asks, what are the most fundamental items, how do we understand the most fundamental physical structures and things that there are? And that's only part of physics because you could do condensed matter physics where you say, I'm just worried about other states or the physics of stars and you take for granted a lot of the micro stuff or at least how to handle it and then you're building up from there. But if you just dig and dig and dig and say at the very bottom, what's the stuff that doesn't get explained in terms of other stuff? That's the foundations.

And so if you do that in physics, that's the foundations of physics. In philosophy, it's easy. I actually just gave a talk about this to the undergraduates at Rutgers because that is part of what philosophers call metaphysics or ontology, which is, again, just the question of what exists asked at the most generic. level. And if you're a physicalist, you think everything that exists is somehow physical. If you're not, you might think there are other things that aren't physical. But everybody pretty much agrees there's some physical stuff. Not everybody, sadly. Not everybody. Of course, every time you say something, you can think of a counter example, unfortunately. Now, the curious thing, if I describe it that way, is you say, but why should you have to sell this to the physicists?

Why isn't this just part of the physics curriculum? And that's, you know, that's, you know, has a very strange and disturbing sociological answer that really goes back to quantum mechanics because they didn't really understand when quantum mechanical formalism was first developed in a way that was very predictively successful, they really didn't understand what they were talking about. They, the physicists? They the physicists. The physicists who came up with the math.

And you can come up with math and understand how to manipulate it to get predictions, but still not look at that math and be quite sure what the physics underlying it is. And those were very good questions and they were asked very rigorously and vociferously early on by people like Einstein, people like Schrodinger, people who were very deeply involved, even in the development of the theory. But at a certain point, another crew led by Bohr and to some extent Heisenberg kind of said, well, don't ask those questions, either because for some deep philosophical reason, they're not good questions, although they sound pretty good, or eventually this morphed into what people call shut up and calculate where you don't even explain, you just say, don't ask those questions.

I mean, my impression would have been that Bohr and Heisenberg were more like, we've told you the answer to those questions, and then when the Americans got hold of it, it was like, just don't even ask those questions. That's my take on it. was that it was, I mean, Boer's background was in Neocontian philosophy. He actually said very, very, very mysterious things. And I would say early on the idea of the Copenhagen School was say some incomprehensible stuff and then calculate. And then when it came to America, they cut out the first step. Good. And so, but you said sociological reasons. I mean, I can imagine why, well, don't let me

imagine. What is, in your opinion, the sociological reason why physicists would stop asking what is going on at the fundamental nature of reality? So, and I'm speculating here, when they first started, everybody's familiar with this picture of the atom as a kind of planetary system with a nucleus and then these electrons whizzing about it. We still kind of picture it that way. And that was sort of what was called the old quantum theory said that, and it said, by the way, these electron orbits are restricted. They can't just orbit anywhere where a planet can. They're restricted to these particular little orbits. And then all they can do is jump between them. And when they jump between them, they'll either give off or absorb some light. And there was a bunch of explanation that you could get

out of that basic picture. But if you pursue that picture, the natural question is, but how do they jump. I mean, what, you know, how does it get from here to there? And how does it orbit when it's in one of these orbits and questions like that? And they kind of worked beavered away at that and couldn't make much progress on it. And I think they eventually got to the point where they didn't want to say, yes, those are good questions which we can't answer. And they were satisfied that they were calculating correctly. And in order not to say there's really deep questions, we don't know the answer to, they said, no, no, no, we've got it. We just have the mathematical formalism. The only reason you're puzzled is that you're trying to push some classical picture on the microscopic

realm and it doesn't belong there and your confusion is arising from you having unjustified desires for comprehension. I have, I don't know if I've ever mentioned this to you. I have talked to fellow physicists, and I've opined that, despite everything, I personally care about more than just correctly predicting the outcomes of experiments. I actually care about talking about reality. And many of them are very open and explicit that all they want to do is predict the outcomes of experiments. Yeah. And I think it would, if somebody had a lot of funding and a lot of time, it would be interesting to figure out at what point these people started saying that. Because my experience is that young people going into physics care a lot about trying to understand. And they get

very upset. And I know this because I teach foundations of physics in the philosophy department. And I get physics students who say, this is why I went into the field. You're talking about the stuff I was interested in. And I think in most cases, I can't imagine, you know, an 18-year-old saying, I just want to calculate, right? So I think that basic curiosity, about the world gets beaten out of them. And I really think it's part of a physics education, unfortunately, to beat it out of you. So we talked about Einstein and Boris, et cetera, but it's still more or less true, you say. That's my impression.

I certainly can testify that lots of physics students will come to me and say, I get very frustrated. I raise questions to my physics professors of the form, what's really going on here? And I'm not told these are good questions, right? I really am told, don't ask them. Don't spend your time thinking about this. And slight generalization, but the philosophers, to their credit, have kept the flame alive. They've been thinking about these things. Yeah, yeah.

It's the same way that Aristotle kind of had to be squirled away in the Islamic world for a while and then eventually found his way back. Yes, I do think that that really philosophy has been a refuge. And in some cases, as you know, like David Albert got his degree in theoretical physics at Rockefeller. His background was not in philosophy, but he's in a philosophy department because these questions were welcomed in philosophy departments and not welcomed in physics departments. Now, my feeling a lot of people around us, and I have some concrete reason to believe things are getting better. I actually got an email kind of out of the blue from a chair of a physics department who said, we're thinking of trying to introduce foundations of physics into our program. Can you give me advice about, you know, what we might teach and how it might be done? This was great. And this was somebody I'd never met.

Just, you know. I was literally just yesterday talking to an undergraduate thinking about grad school. And she wasn't sure she likes the foundations of physics. So, but she's a physics undergrad. So she thought it'd be better to go to a physics department for grad school. I was asking for advice on where to go. And it was hard for me to even come up with departments who would let you do that. Right. But maybe it's changing. Yeah. And at a certain time, I guess that you could say, well, you could go here because, yes,

it's a normal physics department, but at least one or two people on the weekends and a little bit hiding from their colleagues are interested in these subjects. And we'll talk to you about them if you catch them, you know, off their clock. My best skin ever at 45? Give me a theme song and a best skincare award because it feels like this, right? That's farmhouse fresh skin, all right? I'm blowing, and everyone asks how. The best skincare is farmhouse fresh,

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David Wallace was on the show. We were mostly talking about entropy in the arrow of time. Adam Becker gave us this wonderful historical introduction. But when we were talking to David Albert, mostly we criticized the Everett interpretation of quantum mechanics. I say we being the boy. I was depending it. I always let the guest talk. So David gave his spiel.

So what we didn't get time to get into is, okay, then what instead? So if put it, let's not talk about Everett today unless it comes up. I want to be like substantive and proactive and constructive. What do we do if we're thinking about what are the, what are the mysteries we're trying to solve about quantum mechanics that got us into this trouble? And what are the avenues open to solving? Good. So that's a really good question. And there are several different dimensions to it. But let me start with a dimension, and I am going to briefly bring in Everett, but then let it go. Everybody knows there's this experiment. They say a thought experiment, although you could do it. It would be cool to do it that Schrodinger talked about with this cat that penned up in a cage with a bit of radiating.

radioactive material in a Geiger counter and this diabolical device. Actually, that turns out that Schrodinger was really just reconfiguring the same thought experiment that Einstein had written to him just before, which had to do with a keg of gunpowder that either would or would not explode in the next half hour. And you could calculate a quantum mechanical probability for it to explode and not explode. And what Schrodenger was pointing out and what Einstein was pointing out is that if you hold two views, which are very natural views you would like to hold, you got into what seemed to them to be hopeless difficulties. And the two views were, first of all, when we do quantum mechanics, we describe a system with a thing called a wave function mathematically. one of the questions is, okay, that wave function does it provide us a complete description of the system?

Meaning every physical fact about that system one way or another could be extracted if you gave me the wave function. And this was when Einstein, Podolsky, and Rosen wrote in 1935, and this is the same year as the cat paper. And the cat paper was really a response or a reaction is better to say to the EPR paper. The title of that paper is quantum mechanical description of reality complete. This is what they were looking at. And they were arguing in that paper, no. There's more to the world than wave functions. If that were true, of course, then as a physicist, again, not as a philosopher, but as a physicist, the question is, okay, what else is there?

Tell me about the other stuff. So there's one question, is the wave function complete? And then there's a question about how the wave function evolves. through time, what its dynamics is. And there's a Schrodinger wrote down this wonderful equation that has his name that has some nice mathematical properties, particularly linearity. And people certainly wanted to say at least part of the dynamics is this Schrodinger evolution. And you might say, well, why not just go whole hog and say all of it is Schrodinger evolution? That's all it ever does. Okay.

I like that idea. That sounds promising. Yeah. So if you put those two together and you say, A, the wave function is complete and B, it always evolves by Schrodinger Revolution, then you get into this problem that Schrodinger was pointing out and that Einstein was pointing out, which is that for the cat or for the gunpowder after an hour, the wave function doesn't tell you either, yes, it has exploded or no, it is not exploded, or yes, the cat is dead or no, the cat isn't dead. The wave function goes into this. we call superposition of different states, which normally you'd associate one state with the exploded gunpowder and another with the unexploded, but what the wave function gives you is not one or the other, but a kind of combination of both. And if you say, well, that's a complete description. There isn't no further fact that's left out. Then you say, but then the cat's neither alive nor dead or the gunpowder's somehow, you know, weird suspended state between exploded and not exploded. And, you know, Schrodinger's view of that was that that was ridiculous. And John Bell,

when he writes about this, I mean, the way he sums this up is he says, either the wave function as given by the Schrodenger equation is not everything or it's not correct. And Everett, now I'm just going to say the one thing about Everett is an attempt to say, no, it is both everything and correct. I king up with a way to make it both everything incorrect. Right. So I would say that's the root that leads you to the many worlds theory. And you understand the motivation. It's to keep both of those nice things. But it has this price to pay in terms of saying, you know, the idea that that one cat you

put into the cage, it either ended up alive or dead. No, that's not right. They're now, you know, and not just two cats, actually infinitely many cats. People don't point this out that there might be only one live cat, but they're going to be a whole lot of dead cats because the thing could have decayed. all these different times. Now, if you don't want to go that way, and so we won't spend our time talking about the price you have to pay and what you have to do. I suppose let's just get our cards on the table for the audience purposes. You're not a fan. I'm not, but it's a serious attempt.

I mean, you have to be very clear here. There are things I'm not a fan of, but I appreciate the honesty of people who are fans if they see what they have to confront and they, you know, straightforwardly say, yes, by making these commitments, I inherit these problems, and I'm going to work on those, right? And nobody should just turn their back, in my view, on a serious proposal. I take it to be a serious proposal. I think there are other proposals out there, which I will not name right now, which I do not think are serious. I don't think that they have any chance. I would not put many worlds in that basket. Gotcha. Okay. But if we take off the table, having the wave function be both complete and always Schrodinger, then your options are, all right,

if it's not complete, then there's something else in the world beside the wave function. And then immediately you ask, okay, what is it? And what does it do? And why am I talking about wave functions anyway and things like that? Those are the natural questions. You ought to have answers at your fingertips. Or if you say, well, I think something went wrong with the Schrodinger evolution. Then you can say, well, I think the wave function doesn't always evolve in this way.

It does this other thing that people call collapsing, right, or reducing that looks very, very, very unshrodinger-like. This was the way that when John von Neumann wrote down, his understanding of the mathematical foundations of the theory had two processes for the wave function, the Schrodinger process and a collapse process. And that's also kind of okay at a very high level. But as soon as you say that, you also now inherit an obligation to tell me, all right, well, when and how does it deviate from Schrodinger revolution? And there are lots of details that can be put in in different ways and different suggestions.

Some people think early on that the collapses had to be triggered by something. So things would go nice Schrodinger-wise until X. What's the X? Oh, until a measurement is made or until an observation is made. And then that, of course, astonished. This is something Einstein was very upset about. Other people are upset about because they say, look, what do you mean an observation? I mean, who can do the observing?

You know, can a mouse observe? Can an amoeba observe? Can they, you know, trigger a collapse of the wave function? If you go that direction in a certain way, you end up with Vigner, who says, oh, we have to talk about consciousness. And now you're in the mind-body problem. And, you know, you're in a mess. Other people have said, well, no, there's a kind of trigger or something that affects collapse, but it's not measurement or observation.

It's like, say, gravity. I mean, this is something that Roger Penrose has been advocating for a long time, not with as much precision as a theory as some other things, but that somehow gravity, which is the one thing that is not well understood quantum mechanically, may come in here as triggering this non-Schrodinger revolution. And then there's another idea which is that, no, it collapses and nothing triggers it. It just happens. It happens randomly from time to time at a certain rate in a certain way.

This is called the spontaneous collapse theories. And there's a famous theory by Gerardi Romanian Weber, the GRW theory, and they just put numbers to it. I mean, this was the great thing they did. They didn't just wave their hands. They said, okay, yeah, it collapses every now and then. How often? Well, once every, you know, 10 to the 15 seconds per particle, you know, and how does it collapse? Well, you multiply by a Gaussian of this width and, you know, put some math to it.

This was what John Bell was so impressed by. I know when I talked to him about that theory was that, okay, for many years, people have had this kind of general thought, but they took the step of turning it into clean men. mathematics. And also, the mathematics, but a real theory physically, right? Yeah, not just an idea, not just the general suggestion. That's right. And it can be, in fact, experimentally tested. Yes, it does. It makes because the wave function evolution is different and because the predictions really depend on what the wave function does, it will make, it's easy to see in principle it makes different predictions. It's harder to come up with the experimental situations where you can see

those differences, although people have been working at it for some decades and making progress. The progress is mostly ruling out the theory. I mean, so far, we have not seen a signature that the theory is correct, okay? We haven't ruled it out, but you could have ruled it in. If you'd seen certain things, you could have really ruled it in. It has not been ruled in. And ruling it in, these spontaneous collapse theories, would count as falsifying these other theories. That's right.

If that were to happen, then the other things on the table that we might talk about, including Everett would, you know, a lot of the motivation for Everett would go away because one of the motivations is, but gee, this Shroden's Revolution is so nice. Yeah. So that is a motivation. I guess to a physicist, the, there's a sort of, I don't want to say intuitive, but emotional objection to these spontaneous collapse theories. Like it just looks so ad hoc that the wave function just does this. And I guess you could say, yeah, but we're fitting the data. Yeah.

And ad hoc, it's not. that I don't have some sympathy, but when you realize how difficult these questions are and the weird extremes that people have gone to say, oh, but I don't like this one because it's ad hoc, that is such weak tea, right? I mean, get over it. You know, I mean, the physical world might look a little more ad hoc than you prefer. You really shouldn't rule things out in a strong way for that reason. I guess maybe following what you said about Einstein and EPR, the one thing that you can say about quantum mechanics is that someone's going to have to give up on something that they really

want to be true. Yes, I think that's correct. I mean, yes, I'm not sure. I would say, and now I'm going to tip the hand, which you'd understand already, if you already know, I'm not that sympathetic to the many worlds because of the problem. I see there. And I also have this feeling that I can only say by saying the collapses don't smell right to me, right? I don't want to put too much weight on that, but that's just the way I feel. I'm when you're in this, you kind of make a judgment about what looks more plausible to you.

Then we have the last possibility where, okay, yeah, there are no collapses. I agree. I like the Shroden Revolution. It looks, it's clean, it's pretty, it's linear. I want to keep that, but I want my cats to just one cat goes in and one cat comes out. That means I have to have something in addition to the wave function, and now the question is what? And the amazing thing, and I think anybody, whatever you think about the theory is, at least just for the non-relativistic theory, there's some complications further on. For the non-relativistic theory, this thought occurred immediately, in 1926 already, by Louis

de Broi. and you say, what is this magical thing you're going to add to your physics? Answer, particles, point particles. Just the sort of thing you were already familiar with, the sort of thing, even Democritus, well, his were a little thick, right? They had their shapes. These can be point particles, so they're even slimmed down and more minimalistic than Democratian particles.

But the idea, okay, there are some particles, and they move around, and they constitute cats and tables and chairs. And if you want to know whether your cats alive or dead, tell me where. it's what its particles are doing and I'll give you a good idea, right? You might say that's such a simple idea. It couldn't possibly be the case that you just add some particles and write down a pretty simple looking equation for how they move and everything comes out right. But amazingly, in the non-relativistic theory, it does. I don't really see that as giving up on anything. I mean, because what you have to give up on is the completeness of the wave function, but it's not

clear what the motivation for believing that ever was, except Boer and so on saying, look, we know what to do with the wave function. If it's complete, then we're done. And we want to be done. So don't tell us there's something else, right? So in other words, the basic idea is when we invented quantum mechanics, we started saying, oh, electrons are like waves, right? They have interference patterns under the right circumstances. They spread out in the atom. they are also like particles in certain ways. We measure little dots on screens. And the brilliant breakthrough from DeBroy is that's because they're both at the same time.

Yeah. Or to put it as Bell, again, I'm always quoting John Bell. He says people were, as it were, you know, breaking their heads all the time, wave or particle, wave or particle. You'd hear waveical, right? It's a new concept you don't have. And he said, why didn't it occur to them the simple answer, wave and particle? There is a wave that is a thing that obeys a wave equation, which is why you get interference. That's the wave function or the quantum state, the thing described by the wave function.

And in addition, there is a particle, which always has a location. So if you ask, but why do these little individual spots form on my screen? It's because that's where the particle hit. No reason why you can't explain the wave-like behavior because there is a wave and the particle-like behavior because there is a particle, and their dynamics is coupled in a way that the particles are guided by a wave-like thing, and so the interference in the wave will affect where the particles go.

So this table in front of us is, in some legitimate sense, made of particles. Yeah. And the positions of those particles are, among other things, being guided by the wave function. Yes. Are they separately interacting with each other, the particles? Well, of course, the word interaction here, is one of those words that different physical theories will give you different accounts of what even

counts as an interaction. Certainly, the particles can be in a situation where what happens to one will make a difference to what happens to others, right? So the theory will just tell you, gee, you turn on a magnetic field over here and now this particle gets deflected down. And by the way, that particle, you know, will get deflected up. I mean, the example I just gave you is a little bit misleading. But now, is that an interaction between the particles? Well, it's certainly mediated by the wave function, right? The particles can't do anything to each other.

But in a way, already you have that in Newton. You say, well, how does one particle affect another gravitationally? Well, not sort of directly, but you need a gravitational field or something like that. There's a mediator. there's a physical mediator that accounts for these relations between what they do. Is that interaction? It is, but it's not quite like classical Newtonian interaction. One way to talk about this, people get a little bit, maybe this will help or maybe not, but let me say it briefly.

If you've studied any physics, if you did any Newtonian physics, you'll remember that the fundamental equation is F equals M.A where A is the acceleration. And the acceleration is the change in the velocity, and the velocity is already the change in the position. So it's a second time derivative. And what that means for Newton is that to give you the initial conditions of a system, I both have to tell you where everything is and what its momentum is. So I need both position and momentum. And then the fundamental kind of physical interaction through F-E-E-Ques-M-A is changing the momentum. Yeah. But in this theory, it's not like that. It's a first order theory. Everything is just done with one-time derivative. So the initial condition only has to be the positions. And then what

the wave function does is guide the particles. It doesn't push them around by producing Newtonian forces on them. It guides them. It, as it were, determines where they go. More in the way, this is a kind of analogy that David Bowm used to use, as if you were piloting by radio control a little boat out on the lake. And you say, yeah, as you turn the dial, you're, as it were, sending information or telling the boat where to go, but you're not pushing the boat around, right? And in fact, if the boat goes twice as far away so your radio signal is half as strong, still, as long as it's getting the signal, it's going to guide it the same way, right?

Whereas a Newtonian force, you'd sort of think, well, the further away you get, the weaker the force has to become. So it's a different fundamental picture of physical interaction. When Toyota builds an electric vehicle, we don't start with a blank slate. We start with everything we know. The BZ brings Toyota's proven engineering to electric. With impressive range, intuitive technology, and Toyota reliability, BZ reflects decades of experience. reimagined for what's next. The BZ isn't just electric.

It's Toyota Electric. We make it easy. Toyota, let's go places. And I think many physicists object to it, or you know, had this intuitive emotional response to it because the wave function is guiding the particles, but the particles don't influence the wave function at all.

Right. Maybe part of that negative feeling is that they're still thinking of the wave function as a Newtonian force field? They might be thinking that this is an objection people have raised quite explicitly that this theory violates, they call it generalized Newton's third law of action and reaction, right? So they say, oh, well, in general, I think if A has an influence on B, B should have a back

influence or a reciprocal influence back on A. And that, I have to say, strikes me as just silly. I mean, in a certain way, if you say to Newton, look, doesn't the law of gravity somehow affect what particles do? He'd say, yeah, yeah, yeah. And you'd say, but what are the particles? Do they affect the law of gravity? He'd say, no, of course not, right? The law of gravity doesn't change because of what the particles do, what the way the particles behave is accounted for, as it were, by the law. So we don't usually think that if A affects B, B has to have a reciprocal back effect on A. Lots of cases where even in physics, we wouldn't say

that at all. So this seems to me to be a bit special pleading of trying to find something to complain about. I mean, certainly it sounds like a very made-up metaphysical principle. They just made up. Okay. You mentioned David Bone. Tell us his role in this story. So it's an interesting, I mean, the history of this is very interesting because, again,

people were very concerned. There was the early quantum theory by Bohr, which had this very classical-looking idea of this planetary atom and then these jumping kind of jumps, which were unusual and they didn't quite understand. And then the new quantum theory was developed in the 20s, mid-20s, and the mathematics of it came out, first matrix mechanics by Heisenberg and then wave mechanics by Schrodinger. I'm just throwing some names out, but people have heard these names. But they had the math in a way.

They kind of knew how to manipulate the math to make some predictions. But it wasn't at all clear what the physical picture was, right? What's the physical theory here? And DeBroy early on looks at this and says, well, I can just put these particles in, these point particles, and have them guided around by this quite simple equation. You need a second equation because we needed an equation to tell us what the wave function does, and we're just going to keep Schrodinger's equation for that. So we got that. No real dispute about that. Then we need a second one, which tells me what the particles do, and that's going to be a thing called the guidance equation.

And just from mathematical simplicity and other very basic physical considerations, I think I've seen claim 10 different ways that would lead you in the non-relativistic theory to a very simple obvious equation, guidance equation for this. So lots of ways to motivate it, you know, intuitively. And so DeBroy discovers this and he presents it. He was very young at the time. and some rather bad objections were made to the theory, but Dubroy on his feet couldn't answer them. And the story seems to be that he was just a bit traumatized by the whole thing because these were the big shots of physics.

I mean, he's a young guy. He's at the Solve conference with the biggest names. Einstein is there, four is there and so on. And, you know, they're probably whoever, they're beating up on him. And he just kind of seems to have abandoned the theory a bit. As far as I can tell, and I've heard people tell me this more recently who looked into it, it kind of lays fallow. Now, Einstein, who we know didn't like the Copenhagen understanding of quantum theory,

we know played around with this theory or very similar theories in the intervening years. He didn't like it, but he didn't like it because it had what he called, in a very manifest, easy-to-see way, spooky action at a distance, this non-locality. So we know why he didn't like the theory. And he could never come up with a satisfactory version to him. But it's very possible that he came up with the version that other people think is satisfactory. Exactly. He could have very well had it.

And it sort of stayed that way. And then the really interesting situation, if we get into this, is David Bohm is now a young physicist, very well regarded at Princeton. He writes a book explaining quantum theory from the kind of Copenhagen-Borien-Borri and point of view. And he's in Princeton. Einstein's over at the Institute for Advanced Study. And he's kind of saying, gosh, I would like to get my nerve to go ask Einstein what he thinks of my book, right? And he's actually trying to get other people to approach Einstein. And as this is going on, he gets a message from Einstein. And Einstein says, I read your book. I, you know, would you like to come talk about it? And the story is he goes to talk to Einstein. So it's like 1950, 51, something like that.

51, I think. Einstein has read the book, and Einstein says, I think this is the best, the clearest exposition of the Copenhagen approach that I've ever seen. I mean, he was really trying hard, but Einstein raised some objections. And the story is, and I think it was a young man who tells this story, it was Boehm's roommate at the time, that Boehm goes, meets Einstein, comes back, and he reports when he comes back, I'm back to square one. He was convinced by Einstein's objections.

He just, he couldn't answer Einstein's objections. He realized that he really didn't understand what he himself had written. And within a year, he discovers this other thing, which was the same thing DeBroy had done, and apparently independently, as far as I can tell. I mean, I was told recently, I haven't done the research myself. But again, it's not hard to find that theory if you're looking in a certain direction. Right, right. And then he publishes these papers, this two-part paper in 1952.

a theory that introduces so-called hidden variables into quantum mechanics and gives you all the right predictions. And this was something that people had believed had been proven mathematically impossible by John von Neumann when von Neumann wrote his book. So this is, of course, a shock. It's like you're not supposed to be able to do that. And then you look at the paper and you say, wait, it does look like you can do that. And we now understand that von Neumann had made not a mathematical mistake. bit of conceptual mistake, which was caught at the time by Greta Hermon. Greta Hermon, yeah.

And people pointed it out, but who's listening to Greta Herman? When Bohr and Heisenberg are saying the opposite. So in 52, the theory sort of gets reborn, it's, you know, under Boehm's name and and Bohm worked on expanding it to cover spin and some other, I mean, you know, it's a kind of very basic theory at beginning and then you start adding bells and whistles to cover more and more phenomena. And it might still have disappeared, but John Bell became a fan of it, right? Well, Bell, it's not that Bell started out as a fan of it.

Bell was a fan of this. He was a fan of saying, I understand what this theory is claiming, right? There's no mystery about it. There are these particles. There's this wave function. Here's what the wave function does. Here's what the particles do. Okay.

This is a picture of the world. Like it or lump it. When I first learned about this theory, and I was very, very skeptical about it from Shelley Goldstein. Shelly helped me a lot at one point in our discussions because I was being very obstreperous. And he said, look, surely you'll admit this is a theory of something. Okay?

It says there are these particles. There's this other thing. Here's what they do. Now, just in your mind, imagine a world as this theory describes. Wouldn't it be interesting if that world looked very much like the world we live in, which turns out to be true? This is always good advice when people have trouble thinking about new theories because they always want to fit it into their own boxes, right? And if you just ask what it would be like if it were true, we'd make progress.

Right, right. And it solved, it addressed the problem that Einstein had raised about locality by saying, yeah. Yes, so this is what I was going to say. So Bell, and Bell tells a wonderful story, right? Bell says when he first learned quantum mechanics, he was very puzzled by it. He didn't understand what was going on. And he thought you need to add something to it. You need these additional variables, the wave functions, not the whole story.

And he said he was told by his physics professors, no, no, no, no. Von Neumann has proven it can't be done, mathematically proven. You can't add any additional variables and keep the same predictions. And Bell says at the time, he didn't know any German and the book had not been translated. And so that's where it sat. He just didn't know why. He didn't understand. He couldn't read von Neumann's proof, but he was told there was a proof.

And then Bell says he just gets up in 1952 and reads this paper that's been published and says, wait, Bohm has just done what everybody's telling me Van Neumann proved couldn't be done. Something's gone wrong here. He quickly convinces himself that the mistake in that case was on von Neumann's side. but he sees that the theory has this manifest non-locality, and he asks himself, surely what Einstein must have been asking himself, can you get rid of it? Can I have a kind of theory like this,

but without the non-locality in it, that still makes the right predictions, the quantum mechanical predictions? That's the very precise thought that Bell had, and when he finally got some time off on sabbatical to sit, down. Because he couldn't do it during his regular working. Yeah, no. But the amazing thing is, of course, when you see Bell's proof, it's a few lines of

algebra. It's not like, you know, proving Fermat's last theorem, okay? It's not hard mathematically. When I first read about this stuff, which was in the Scientific American, in an article by Bernard Des Benya, back in 79, I guess, it's not, looking back on it, It's not the greatest article in the world, but it was enough was there that just with a little math, you can see, wait, wait, I see the problem, right? I really, this just stands out at you. So what happens with Bell is what Bell realizes is wait a minute. No, you can't get rid of the non-locality out of this theory. You can't get rid of the non-locality out of any theory.

I mean, throw away quantum mechanics and start from scratch from entirely different principles. Bell's proof is not about quantum mechanics. It's just about certain experiments and the correlations that you see in the outcomes. You can't have a theory that is local in a well-defined sense that will predict that. Quantum mechanics does predict it. And more importantly than quantum mechanics predicting it, the world does it. That's why the Nobel Prize went to Klauser and Aspe and Zeilinger recently for doing the experiments that showed that the violation of Bell's inequality actually occurs.

And as you and I both complained about in separate occasions, the Nobel Committee blew it in their press release. Yes, they did. They said that what they had done was what proved that Bonnoyman was right and you can't have hidden variables, which is just the irony there is so. Delicious. Yeah, because Bell became, you know, Bell then became probably the strongest advocate of this BOM's theory or DeBroyley's theory, which is a theory with additional variables.

Why? Because he could say, well, what's the objection? You can't object as Einstein did. I don't like it because it's non-local because now I understand, okay, the non-locality is just in the world, right? Suck it up. And it's a clear theory and so on. I mean, at one point, Bell says he's going through all these different ways of approaching quantum mechanics. And he says, well, the pilot wave approach shows the best craftsmanship. But then he says, but is that, he says then wonderfully, I mean, he always made these cutting little remarks. Is that, is that a virtue in our time? Right. Do people appreciate good craftsmanship anymore? Do they like just things that sound, woo, you know, amazing and blow your mind? Because it is, it, at some level, it's a much more

pedestrian kind of theory. You say, yeah, there's some particles. They move around. Yeah, there's wave function. That's kind of funny thing, but I'll explain how it, you know, how it plays into the architecture here. It was a rough time for the philosophy of quantum mechanics. Yeah, in certain ways. But okay, so the, I think if there are any physicists out there who are not into the foundations of quantum mechanics and they're listening, they're, they're very confused because one uses the word locality in different senses sometimes. I mean, if you ask a quantum field theorist, is there a field theory local? They would say, yes, it's very, very local. So what exactly do you mean by this word? Good. And there's even a technical, mathematical condition that's imposed

in quantum field theory that they will call locality. It has to do with commuting operators. Okay, so what's going on? Well, one thing to say is that there is, there's bell-proof there has to be some kind of influence or effect. If Alice and Bob, if I set up a pair of particles in a special state called an entangled state, and anybody who's heard about this, at least have heard the word entangled, but send the particles off way in different directions. So they're hundreds of light years apart,

one into Alice's lab and one into Bob's lab. The intuition of causal locality basically says nothing that Alice does can have any actual influence or effect on what Bob sees. Right? That doesn't mean there can't be correlation, between what they see. I mean, everybody knows, people give this example, you tear a dollar bill in half and send the two sides off in different directions. Of course, Alice seeing one half immediately informs you that Bob will see the other half. But that's not Alice doing anything that affects Bob at all. That's just trivial right. Everybody understood that. Everybody understands there could be correlations like that. But those correlations are already explained by what happened at the source. And so nothing non-local is going on in that case.

case. Bell showed, no, you can't get the kinds of correlations you see in quantum mechanics by that kind of local story. There has to be a sense in which what Alice does actually makes a difference to what Bob sees or the other way around. That's causal non-locality. Now, the next question that arises is, oh, could you implement that in some way to allow Alice to send a message to Bob, Signal Bob, right? Tell Bob whether they're going to meet for, you know, lunch today or not. And the really interesting, I mean, a very interesting thing is that at least under certain pretty clear idealizations, you can kind of look at the way quantum mechanics work and say, well, no, actually, even though you can't get rid of this connection, you also can't use it to signal.

And the person who proved that first was also Bell. People like to call it the Nobel Telephone theorem. So he was perfectly aware of it, right? You can't use the non-locality to signal. Sorry, that's a feature in Copenhagen, Everett, Bowen, whatever you want. You never use it. Well, okay. Now this is, now I'm going to, now I'm going to tread off into treacherous territory.

It's all over here. It's late in the body. Okay. If you say, and I think it's just a bad thing to say, that the fundamental postulate of, say, relativity has to do with signaling, that you can't signal faster than light. And you say, oh, well, then this is still a local theory. But that just, I think, first of all, signaling isn't even the right kind of concept that should be in the foundations of any theory, just as measurement shouldn't and just as observation shouldn't. And, and, you know, Bell proved there is this kind of non-local causation. And maybe I can't use it to signal, but so what? But then the next thought is, gosh, if there really is this real physical, non-local connection somehow, why can't I use it to signal? I mean, you sort of offhand think there must be some clever way to do it. Now, I'm going to report something.

To ask that question, of course, you really need a well-defined theory on the table in front of you, right? Because you have to ask, well, what can I do with this physics? quantum mechanics tends to use these things called her mission operators or as they call them observables and they sort of view the mathematics of that is what they look into to ask certain questions. But if you have an actual theory in front of you, you're not restricted in that way. You know, you can just say, well, can I do something?

Can I twiddle this and, you know, see something there? It looks like in the Bohmian theory with spin, there are reasons to believe you could signal faster than light. Oh. This could be the most popular podcast ever. You weren't expecting that, were you? I was not. It is, it is, I am, personally, I suspected there should be a way.

Sidhan Das, who's a young researcher, has been looking at something which amazingly people had not looked carefully at, which is in this pilot wave theory, when you add spin, okay? that's an additional physical degree of freedom. People usually just don't fiddle with it. They kind of deal with spinless particles at this level to understand things. When you add spin and when you look at, there's a very specific thing you can look at that standard quantum mechanics doesn't have an obvious way to even treat. This is the key to understanding this.

That is arrival times. So if I... This is a well- known issue. Yes, it is a well-known issue, although people just kind of put it out of their mind. So if I have an electron, as it were confined in a little box, which we kind of know how to do, and at some moment I open the box, and then I've got a screen, and at some time, a flash appears on the screen, one thing you can ask is, well, what was the transit? How long, what was the time gap between when I opened the box and when the flash occurred? And it turns out, if you ask quantum

mechanically, and in quantum mechanics, you of course have to do experiments many, many times and you get kind of statistical results. You get a distribution of results. Nobody agrees how even to make that prediction using standard quantum mechanics because there is no Hermission operator that corresponds to arrival times. Okay. In this pilot wave picture, because you have these particles and they just move, it's kind of easy, at least to ask the question according to the theory, how long did it, would it

take a particle here to get there. So you can actually do these calculations. And when you do them with spin, you start to see that there's a spin dependence of the arrival times, which you really weren't expecting, but it shows up. And if that's right, it's already a question of whether you'll see that. This is something you could check in the lab. We're trying to find people who'll do it. But you need specialized equipment and you need the motivation to do it. If there is that spin dependence of the arrival times, then there's a very quick argument, oh, you could signal. Now, the signaling would be very subtle.

I mean, it's not like you could flip a switch and a light would go on there. But it would essentially say, if Alice orients a magnet in her lab in a certain way, Bob will suddenly start seeing a slightly different distribution of arrival times than if it's oriented another way. And that would be any kind of information, right? It doesn't have to be a clean, 100% strong signal, any signal, right? Any Shannon information. Sure. And this suggests that, yeah, you actually should be able to do that.

Now, there are lots of still, there's lots of arguments within the community about whether this is right. How far do you have to carry the analysis into the observing equipment? I mean, lots of stuff. Maybe in a couple years, people will say, no, this argument breaks down for some reason. we don't quite understand yet. So I don't want to say this is nailed down. No, that's okay. But it's there.

And it's a really hot, interesting, interesting topic. And one that could be tested in a lab. Some of it you could do today. My best skin ever at 45? Give me a theme song and a best skincare award. Because it feels like this. Right. That's farmhouse fresh skin, all right?

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BZ reflects decades of experience, reimagined for what's next. The BZ isn't just electric. It's Toyota Electric. We make it easy. Toyota, let's go places. I'm not completely surprised because both you and I have written papers about energy conservation and its failure in quantum mechanics, which anyone could have done in the 1950s. I just didn't ask the question.

But is this a fact that you're talking about now? Would it be a difference between Welming mechanics and other formulations of quantum, or is it just that you can't ask the question? Yeah, it's a little hard to say because, and again, I'm now just reporting what Sid Haunt tells me, and he's done all the research. He says, if you go into the standard physics literature about arrival times, you'll find 20 different suggestions about how to do it. They tend to agree with each other in the far field. That is, if there's a long time between when you release it and when you detect it, all of these different approaches converge on the same. answers. But in the midfield, there are places where they will not converge. So what can you say? I mean, it's not clear what predictions the, quote, standard approach even makes. So you could say

if the pilot wave approach makes a clean prediction, it's clearly a different theory, because, look, it's doing something precise where the rival doesn't even have anything precise to say. The other obvious question is you've been simultaneously talking about whether you can send a signal faster in the speed of light, but also working in the context of non-relativistic quantum mechanics where there is no speed of light. So do we have to talk about relativistic quantum field theory to have this conversation? Well, we certainly don't have to talk about it to have the conversation we've had up until now because even before relativity, if you said, look, Alice is in a lab, 100 billion billion miles away from Bob. Can Alice do anything in

her lab that would make a difference to what shows up in Bob's lab, the natural thought would be no. I mean, you know, even if there were some effect, even if there were a fast effect, it would drop off with the square of the distance. It would, you know, tail off. There's, you know, so you can have the discussion about non-locality even in a non-relativistic. Now, it becomes sharper in a relativistic context because then you mean faster than light, where there is a light cone structure.

There's kind of an objective thing you mean there that's very sharp. So you can sharpen it up in the relativistic context. But I think you can still reasonably have it. It's not like all of your discussion of the non-relativistic case just falls to the floor when you notice there's relativity. My halfway informed feeling is that BOMI mechanics looks quite natural in the non-reliastic regime. and it's a little bit more of a challenge to see how we should just do quantum field theory in that picture. Yeah, there is no doubt there are both conceptual and technical challenges when you go from standard quantum mechanics, and one of the signals here for people who don't know is that in quantum mechanics,

you talk about a system having N particles and that's it, right? Unless you add some or take some away, it's going to be N particles. forever. But that's not the world. That's not the world. We now know that there is some phenomenon that we call particle creation annihilation, that particle numbers can change. And so you need to count for that. Whether, I mean, there are lots of subtleties here. One subtlety is the thing we call particle creation annihilation, is it really? And what I mean by that is when Dirac, and he's just a standard guy, was talking about this, he didn't have particles really come into. existence. He said, well, there are always infinitely many particles filling up negative energy

states. And what we call the creation of a new electron and a new anti-electron, a new positron, is really just lifting an electron that was there all along in a negative energy state, up into a positive energy state, and leaving a hole behind. And so it looks like there's a new electron, and the hole is the thing we call the positron. Now, that's a story that would account for the phenomenon without really creating any new particles. It's just moving them around in energy space, as it were. So there's certainly you have to account for the phenomenon, right? You have to account for the phenomenon. Yeah, I can take a really high energy photon and, gee, there just, you know, appears now an electron and a positron or, you know, some things that satisfy certain conservation laws.

We need to account for that phenomenon, whether it really deeply requires new particles, or do you want to give up the particle? The other thing to say is the pilot wave picture is not tied to particles. It just says there's something that the wave function is guiding. It could be particles. It could be a more field-like thing, right? There's a kind of way of doing Bohmian field theory where you replace the particles with fields,

but the same kind of architecture. And the other point to make, which at least needs to be made, is that people can say, gosh, but there's no good boeemian quantum field theory. Standard quantum field theory has been plagued by mathematical problems and, you know, runaway singularities, numbers you try to calculate and they all come out infinity. It's not as if it's all, you know, conceptual lightness and clarity in the so-called standard picture. So you don't want to hold this picture to a higher standard of mathematical precision and so on

than you're allowing for the theory that you happen to use. Okay. That's perfectly fair. But I'm just trying to get straight for the listeners out there. You know, if I'm a particle physicist and I just calculated the rate of Higgs bosons, decaying of the two photons and something like that. Yeah. Is that stuff I can do just as well in the current BOMian framework?

There are. Is that work in progress? Okay. So one of the things that people have looked at is suppose I remain, again, there are different moves you could make. You could say, I'm going to give up the particles all together and put something else more field-like in. Or you can say, no, I'm going to stick with the particles, but I am going to allow literally

the number to change. I'm going to allow particle creation and annihilation. You can do that. How you would work that out in a kind of pilot wave picture was done, has been done for 30 years ago, I guess. And what you do is you say, in the original picture, you have a fixed number of particles and all they do is move around and change their configuration. But now I say, no, no, the real space of possible states is there's a zero particle state and a one particle state and then two particle states and then three.

So this whole thing called Fox Space, which is familiar to any of the physicists you're talking about. And you say, no, that's what I'm now going to say. The thing is always in a particular location with a particular number of particles. Sometimes it just moves around in one of these sectors and the number doesn't change. And sometimes it can jump up or jump down, which corresponds to particle creation and annihilation. I now need dynamics for that. It turns out that dynamics tends, instead of being deterministic to be indeterministic, the easiest way to do it.

You say at any given time, there's a certain chance you'll jump up and create a new particle or jump down and lose particles. You can do that. And what falls out of doing that is the mathematics of standard quantum field theory. Okay. But so just so I didn't lose it, among people who are fans of BOMI mechanics right now, it's, there's a camp that thinks maybe the hidden variables are field-like, and there's another camp that thinks maybe there's just collection of particles that can change their number. So we're not sure.

That's right. There's not a leading. And there's a lot of things that are debated within it. So here's another question. People, when you start out, you're always treating electrons and gluons as particles. But, and they're all fermions, right? They're all half-a-gluons or not. Oh, sorry, I'm sorry.

I meant quarks. Then people ask, well, what about the photon? Is that a particle? Are there photon trajectories? And it turns out you can try and develop a theory in which there are and a theory in which there aren't, okay? And people work on both sides, and there's no agreement in the community. And you've asked, well, what would be the advantages, you know, of doing it this way?

what would be the advantage of doing it this way? So it's a general architecture of how to develop a theory that can be implemented, of course, in many different ways. And so even within the big house, right, there's rooms in the big mansion of people who are working in different directions. With regard to the idea of sort of stepping back from the fields and going particles as your ontology, two things come to mind, one of which is against that idea, one of which is, for it. So which one you want me to tell you first? Then you can respond. The worry I have is something like the Higgs mechanism, where it seems that the Higgs boson lurking as a field with an expectation value throughout all of space is playing a crucially

important role in explaining phenomenologically observable properties. Is that something? I mean, I think I just answered that, which is it sounds like you're the kind of person who would say, I'd rather, yeah, I'll treat my pheromions as particles and I'll treat my bosons as fields, essentially. Oh, okay. Yeah, I won't introduce particles associated with the integer spin objects. That, that I think would make you happy, right? I don't have to say there's a Higgs particle to work it into the theory.

And there is a reason to think that you're going to work bosons and fermions and different can enter into the theory in different roles. Okay, this is going to undo the good news that I had. So I don't know if you know this because I only recently learned it, but Richard Feynman, when he was inventing Feynman diagrams, part of his motivation was to get rid of quantum field theory and replace it with another theory of particles again. And we now think of Feynman diagrams as a tool for understanding quantum field theory. So he changed his mind. But his motivation, I'm told, was the cosmological constant problem. Really?

Yeah. No, I did not know that. Yeah. I mean, I was told it. I need to find the reference for it. But the idea is if you have fields, they all have these zero point energies and they add up to infinity or you cut it off and it gives you a big vacuum energy. But if you have particles, you don't have that problem. So if I were a BOMian particle ontology guy, I'd be claiming a solution to the cosmological constable.

That would be my advice. Look, that's a connection I was unaware. My understanding, and again, this is not based in anything other than what I somehow picked up on the street, was that one way, anyway, Let me put it this way. How Feynman thought about it, I'm not sure. One way to think about Feynman diagrams, which is runs contrary to way people often talk about them, is that they were just a mnemonic device, right? I have a mathematical equation that has an infinite number of terms that I need to sum up. And of course, the issue gets bad when that sum goes to infinity. But anyway, I have this, all these terms I need to add up. And that the diagrams were just easy ways

to kind of remember what the different terms looked like, right? To figure out what integral you had to do. Exactly. And now if you, the way I say people don't do that is they often pointed those things as if they are literal pictures of stuff going on. Oh, this is doing this and this is doing this and all the stuff is going on. And it's a blooming buzzing confusion of virtual particles that are running around. That talk, I don't think makes any sense on any view.

I'm on your side. Yeah. So if it's just a mnemonic technique. Then you're really, it's as if I like to say, suppose you wanted to calculate the volume of a sphere. And you just love cubes. And you say, okay, look, I'm going to first of all figure out the biggest cube I can sit inside a sphere and calculate its volume. And now I've got these other little, you know, six round pieces sticking out. Now I'm going to find the biggest cube I can get out of each of those and then add those and then more cubes and more cubes and more cubes.

And you can see, okay, there's going to be an infinite sequence of these volumes that you now need to add up to get the total volume of the sphere. But you'd say, but you shouldn't think that the sphere is this really complicated thing, right? It's actually quite simple. And in fact, here's another way to do this calculation that is straightforward and you don't do an infinite sum and G.

It's just, you know, four-thirds pyruped. No, I think that's actually an important point because lots of modern physics is motivated, beyond the standard model particle physics, searches for our next best theory is motivated by questions, naturalness, right, and fine-tuning and so forth. And I think, I don't know what the right way to think about those problems is, but I think that not only do people talk as if there really are

virtual particles popping in out of existence, which there aren't, but they also think that somehow nature starts with a classical theory and then adds quantum corrections on top of it. And nature doesn't do that. And that might change our perspective here. Right. And I think there's a, I think you're exactly right. And I think there's a methodological point here, which is that because we start out learning classical physics and it feels familiar to us and we're familiar with the math of it, there's this great temptation if someone says, oh, the way to come up with a good quantum theory is to start with a classical theory and then do this thing we call quantizing it, right?

We put the hats on. We turn certain variables into operators. And, well, most of the time, it's clear how to do that. Sometimes it's not quite clear how to do that. But you think, but this doesn't make any sense, right? The world, yes, the world behaves pretty well the way classical theory predicts at a certain scale. But that's because something emerging out of a very non-classical physics.

And there's no reason to think that the right way into that physics is to start with the approximation and then twiddle with it, right? It's got to go the other way around, right? You need the fundamental physics and then hopefully you can understand why the classical approximations work as well as they do. But I think people are tempted, you know, because you have this kind of kind of algorithmic thing of, oh, just take a variable and put a hat on it and turn it into an operator. But conceptually, that's just not the right way to think about it. Yeah, reality doesn't work that way. Yeah, reality doesn't work that way. So good. I'm glad we can find like all of our

points of agreement against the consensus, despite the fact that we have some disagreements. But this question of the speed of light I'm going to go back to the experiment, that the possible signaling because I do not know about that work. I don't know whether it's right. So that's okay. We're putting it on, yeah, right there. But the idea of looking hard for possible experiments to do, I think is a crucially important one. I mean, my impression is that your typical boe mien on the street thinks there's no experiment to do to test bone versus conventional quantum mechanics, whatever that is. Do you have a feeling about that? I do, and I, This is a discussion I am in right now arising out of this work that is a lot of people in the

Bohmian camp will kind of say, oh, but we know that it won't make different predictions than, quote, standard quantum mechanics. Now, I think that's just wrong. I think there are, you know, kind of toy cases that make it obviously wrong, but leave those aside. I just tried to understand what the argument was, and I can't get it, right? And so I think that. and I think some of this is defensive, right? Because there's this, and you stop back a second, and you see this is so unfair. You have standard quantum mechanics, whatever it is. Anyway, you can make lots of good predictions with it. Then somebody comes up with a new theory, and then they say, oh, does your theory make any new predictions? If not, why should I pay any

attention to it? Now, the first thing you notice is, but wait, if these two theories had been discovered in the opposite order, right, you know, you would be going the other way around. So this can't be, from a logical point of view, a good objection that, you know, why should I take your theory seriously? Because it makes all the same predictions as my theory, because that's, you know, that doesn't make any sense. But I think that is an objection that physicists often made. And so, you know, there were certain kind of defensive procedures that were put up to say, oh, no, we're not saying they're new predictions, right? But, and then you'd have to go on. My view is a sharp theory, again, standard quantum mechanics has certain vaguenesses in it.

If you have to talk about measurement, if you have to talk about observation, because those are vague terms. These are the objections that we had. And so you'd expect a sharp theory will certainly ought to differ in some ways. And you should be looking hard at where those differences might be. So the unfair question, what fraction of the BOMians out there agree with you about that? It's not an unfair question, but it's a sociological question which I just can't answer. I don't know. I don't know.

And even the, as it were, the BOMian camp is divided into subcamps and probably the statistics and the different ones are different. And probably my guess is weirdly enough, it probably correlates with age. Oh, that's not weird at all. I think younger people are more open to certain things than people who've been through a lot of battles. But I really don't know. Where are these BOMians of which you speak? Are they in philosophy departments or physics departments or Europe? Well, a lot of them, yeah.

So there were a lot of students in Europe. And I'm sorry, this is going to be just a little hard for me. Um, Detloff der, who was at the LM in, in Munich, had always a dozen graduate students. Unbelievable what he did that nobody else I know has ever done to promote young people and bring them into this. And he was in a physics department. He was in, he was in the physics, he was in the math department. Oh, math, math department. And he was just the most wonderful, caring,

Dr. Fata and looked after these students. He could not get many of them jobs in academia. A lot of them have gone into

other industry, whatever. They did their work. But there are a lot of young people who came through that program

who know it, who know the theory and work on it. Sidhan Das, who I mentioned, was one of Detleff's last students. And some of his

students, a couple of them are in Tubaigan So there are more of them in Europe who've come through LMU and through his influence. Then the other thing that's happened is a lot of physicists who realize they're interested in foundations notice that if you have credentials as a philosopher, you can literally more easily have an academic career in a philosophy department as a philosopher of physics than you can in the physics department.

Still true, yes. So some of them have switched over. Also, Detlefs do. I mean, Dustin Lazarevich, who's now in the Technion in Israel, there are people who are around. And it's more than there used to be. I mean, the total number is up. What the effect of losing Detloff, because Detloff died during COVID, I don't know. I mean, nobody right now is doing what he was able to do.

And we have to hope that some, you know, dedicated. person with the right, the right psychology and, and so on can, can kind of take his place and help people along. Do you think we started by talking about why you don't need to make the sales pitch to philosophers? They get it. Yeah. How deeply do they get it? How much has quantum mechanics changed what philosophers think about metaphysics? So this is an interesting question. In philosophy, I would say there are three camps of people who do what goes under the name metaphysics. I just gave this talk at Rutgers, the undergraduates about metaphysics and science. Are metaphysics and science enemies or friends or what?

Or the same thing. Yeah, exactly. That was my conclusion at the end. So you jumped right to the end. But no, there's an interesting history because really there's a certain point where they're clearly considered to be enemies. I mean, Carnap. And anyway, I would say that in metaphysicians, people would self-identify as metaphysicians in philosophy now fall into kind of three camps.

There's a camp that's sometimes called analytic metaphysics, which tends to be doing things which don't seem to care much about science. They're asking questions that don't, it's not obvious that any scientific theory would bear one way or the other on the question. Could you give us an example? Oh, are there, I mean, these is not just going to be words. Are there universals or tropes? Okay, so this is the kind of thing that a philosopher of a certain kind will understand

and they'll be fighting with each other forever about universal and tropes. And it's very hard if you say, well, you know, did Newton believe in universal tropes? You'd say, well, the Newton didn't care. I mean, you know, this is not, it's just not an issue that that is built into the guts of that theory in any obvious way. then there are, then there's another camp that goes by the name scientific metaphysics for the reason of saying what I think is obviously correct. Metaphysics is about describing what exists at the most general scales.

And if you're interested in what exists in the physical world, you better pay attention to science. Not to say that the scientists can just answer those questions, but they do have relevant things to say to offer. but then that group kind of subdivides into two the ones who then specialize, say, to do philosophy of physics. Now that really requires learning some math and some physics. And at a reasonably good scale, some people have full PhDs in physics, you know, but you

certainly have to devote some time to just studying math and physics to do this in a kind of specialized way. And then there's another group of people who clearly acknowledge the relevance of the physics, but they're not experts. And so they like to listen to the experts and try and figure what they can draw out of it, right, without themselves delving so deeply into it. I would say that's how the landscape goes. But do they talk to each other these people? Or do they go to the same conferences? Yeah, I mean, they're certainly, they do talk.

Well, they're in each other's presence. I mean, there are a lot of specialized conferences. Words happen. But there are conferences. I mean, I was just invited to be on a panel at the metaphysics society of America. And I'll tell you, the people in that society are not people you'll ever run into. And, you know, they were doing a very different kind of metaphysics, but they were happy. I talked about what I do and the way I think about it.

And they didn't throw bricks at me. It wasn't the way they thought about it. They were interested. They were interested. Yeah, they were interested. And they appreciated having the conversation. And I mean, philosophers tend to be pretty open to talking about weird stuff because that's more of us comes with the territory. Whatever strikes them as weird, you still don't just reject it.

I guess what I'm getting at, and I'm not trying to presume the right answer because I honestly don't know. But to what extent can we imagine smoothing over the conceptual differences between thinking about physics and thinking about metaphysics? Like it really should be thinking about reality is what we're doing, right? Yeah. I mean, we do, you know, I do need to mention here that, again, you can be interested in metaphysics and not be a physicalist. So you'd say, part of what I do really is not going to be informed by physics. If I'm a mathematical platonist and I'm worried about mathematical reality and I say,

that's just not part of physical reality. So I don't care how your physics comes out. That's a fair, you know, that's a fair thing. So not all of metaphysics has to be hostage. Sure. You know, or all that interest. It depends on, you know, where you're, where you're focusing your attention. Okay. We actually, you know, Barry Lower was another person we had on recently. And Barry, he said something not on the podcast, sadly, but in informal conversation that was even stronger than something I would say. I think he was being humorous about it. But he said he remembers very vividly being struck the day he realized that most problems of philosophy could be cured or solved by statistics. statistical mechanics. And I think that he has a different view about you than that do. So we're running out of time a little bit, but I wanted you to have a chance to give a little bit of your view of the arrow of time and things like that, which is the other giant thing, the people who care about foundations of physics spend their time worrying about.

Right. So let me actually start with the last thing first and just get it out in the open so people ought to at least be aware of it. I would say it is kind of everybody has this idea. There's space and it's kind of three-dimensional, at least at large scales. And if I talked about, say, the north-south direction at a certain point, if I went on to say, by the way, space goes north to south, it doesn't go south to north. You'd look at me funny and say, what in the world are you talking about, right? The spatial thing, it just, there are two directions and they're oppositely directed, but space

itself doesn't go more one way than the other. I don't even know what you mean. On the other hand, the person in the street, you say, you know, time goes from past to future. It doesn't go from future to past. They, again, nod at you and say, yeah, you know, tell me something new. Now, I happen to agree with that, that as I think time is fundamentally different from space, temporal structure is fundamentally different from spatial structure in the temporal structure. have a fundamental directionality to it and spatial structure doesn't. This turns out to be a very

contentious view among philosophers and physicists for funny reasons, I would say, I don't know that we have the time to go into, but it surely is the minority view. And it's a little bit view. Just to clarify, it's a little bit different than there are physicists out there and philosophers who will question whether or not time exists or whether it's fundamental. But here we're talking about the direction the direction of time. Not time. Yes, that's right. That's right.

It would be even harder to deny the existence of time altogether. But certainly the directionality is hotly contested. I think time itself has a direction. Now, it is clearly the case that there are temporal, manifest temporal asymmetries on any view. If you give me two pictures of somebody 10 years apart, usually I can look at them and figure, oh, this was the younger and this is the older, right? Because people tend to wrinkle up. Now, that's not, maybe they had, you know, cosmetic surgery.

I could get that wrong, you know, but there are certainly lots of very reliable temporal asymmetries. And those need an explanation. Simply saying time has a direction would not explain all by itself any of those observable temporal asymmetries are what people sometimes called arrows of time. So I think all of that is a perfectly good objective study, even if you believe as I do, that one of the things you can invoke is that time is itself directed, right? That doesn't give me these observable asymmetries like that, but it might be part of the explanation. How does it help?

Since people like David Albert and Barry and myself think that you don't need an intrinsic arrow if you just have an initial condition that is doing all the work. Well, because a lot of the explanation, I mean, we can do this in different levels, but let me do the first level. What do I mean by explaining something? Well, often I think it's a kind of causal explanation. I talk about cause and effect. And now you say, okay, but what distinguishes cause and effect? Offhand, in many cases, causes precede the effects.

I mean, if people often talk about running a movie backward or imagining that, which, of course, you can literally run a movie backward, but then the end sequence comes before the title sequence. You still have a direction of time. If you took that seriously as a movie of something in the normal direction, also all the causal structure would be reversed, right? What were causes would become effects. And therefore, the structure of causal explanation would be different, right? And so you have to get a bit deep, and statistical mechanics does come into this here in a way that we couldn't get on the table clearly in a short period of time where, you know,

You not only have causal explanations where you say this particular precise physical state gives rise to this later one, but other kinds of statistical explanations where you say this kind of physical state, not, I haven't precisely, but I'm going to constrain it in certain ways. There's a class of various. Gives rise to this kind of state. I mean, this is the sort of thing that you take a box of gas and you say if you wait a while, it'll eventually relax to an equilibrium. And that, of course, shows a directionality to it because from this initial state, you can say in five minutes, it'll be equilibrium. If you look at the equilibrium state at a generic level, a kind of fuzzed out level, you couldn't say, oh, five minutes ago it was in this non-equilibrium state. So the kind of asymmetry there, and that's connected to certain asymmetries in statistical explanation, probabilistic explanation. It's very interesting and deep, hard topic.

A bit different than worrying about, say, relativity, which you might say is about space-time structure. Quantum mechanics is about material structure. Statistical explanation is about a kind of explanatory project and what goes into it and what succeeds as giving statistical explanations of things. But I do think that reversing the direction of time, you might have a very good, what you consider to be a very good statistical explanation of something as seen, as it were, in one direction of time. And if you look at the other direction and say, wait, there's no explanation at all.

The explanatory part went away. All I can say is a massive coincidence or else to be teleological and say the future is somehow, but, you know, the future is somehow affecting the present. But I take it to be one of the great discoveries of the scientific revolution to get rid of that kind of teleology. Does your view that time has an intrinsic direction affect what we would call microfysics, the standard model of particle physics, for example, or could it? Sure, it could. I mean, I think that it plays into your fundamental picture of space-time structure. And of course, one needs an account of space-time structure to even begin to write down what you think of his laws of physics. And I think there are very specific ways in which having a direction,

well, certainly having a direction, let me just give you a very concrete thing, one could say. Suppose I have a kind of grid, like a street grid, and I have two points on it, and you ask me, okay, how many continuous paths are that it will take me from A to B? And typically the answer, if the grid goes on forever, it's infinitely many, because they can kind of go short way or around or far around, go way out and come back. Now, suppose I put some arrows on that grid, right? So they're one-way streets. Now it's not at all clear that this number will always be infinite. Now it might be quite tightly constrained. The directionality gives me a resource there that a lack of directionality doesn't have. And I think that's actually

quite important and plays out in trying to understand the laws of physics, but it's much more complicated. It's much more complicated. But that's what you're thinking about these days. That's one of the things I'm thinking about very hard. I mean, I've been working on thinking about what space at time could be like if they were actually not continuous but discrete at fundamental scale. I worked a long time and did six chapters just on space and now I have to bring in time. And the time part really has to have a direction. Just for it to work, it has to have a direction. And you have to understand how the directionality comes in. Sorry, what do you say for it to work? For this, for this scheme I have to to be a kind of thing where you could do a plausible looking sort of physics with.

Do you have a catchy name for your scheme? Yeah, full discrete geometry. Full discrete geometry. Okay, good. And the time directedness has to be part of the story. It's fundamental in it. Okay. All right, good.

Well, we're looking forward to that. So am I. Yeah, I know. You said chapters. Yeah, I mean, well, I'm up on chapter eight now. I mean, the spatial part went real well. And then it was like, okay, part two. Let's bring in time.

and then you realize it's a tricky business. Is it quantum we're talking or classical? This is all classical geometry. But quantum field theory, there is a connection to quantum field theory, which I'll just state briefly. We talked about problems just in doing quantum field theory, just mathematical problems. One way that this kind of bo-mean or pilot wave approach for quantum field theory was done, was done by Bell.

It's called Bell-type quantum field theory. And one thing he does is he puts it on a lattice. That is he doesn't do it in continuous space. He does it on a kind of discrete lattice, and you have these jumps from lattice points to lattice points. That turns out to be very important to have a structure where you can do the math in a clean way. Okay. Looking forward to the book coming out. We'll pre-advertise it here.

So here's the last, I'm not even call it a question, thing to respond to. When we talk about quantum mechanics, and as we say, you had to give up something maybe that was hopeful or intuitive or whatever. and even in relativity, it seems like maybe the world is a little bit different. Is there hope for fundamentally understanding why the world is this way? Like in retrospect, can you say, oh, yes, it had to be quantum mechanics, or are we just stuck with it? Yeah, I think people like to say that why the quantum, you know, you'll get this thing. I think, oh, come on, just, you know, grow up. No, I mean, there's going to be foundations.

It's going to be the, and one of the really hard questions, in this whole topic is the question, where do I stop digging? Right? Where is my spade turned? Where do I say, okay, I've hit a foundation here. It looks like this is a plausible place to stop. And all you can say is, yeah, this is the way it is. Could it have been some other way?

Yeah, it could have been some other way. It isn't. This looks like a plausible place to stop. If you think, if you're never going to be satisfied, okay, then you're never going to be satisfied. And the problem is there are dangers in both direction. If you're too easily satisfied, you'll stop digging when, in fact, you could discover a lot of interesting structure lying underneath where you've stopped. But if you're too pig-headed, you're going to get to the bottom and still be banging your head against it forever because there is nothing underneath it, right? So there's a kind of, you know, connoisseurs feel for where's a reasonable place to stop.

But I don't think you're going to be stopped by some master principle that says it could only have been this way. how could you expect that? The world is kind of contingent. Well, that seems like a reasonable place to stop. So, Tim Walden, thanks very much for being on the Mindscape podcast. Can I actually, before you do that, because I'm here and I have many voices, many years than I ever kind of normally will have, and I'm going to just take advantage of you and say, one of the things I'm doing is trying to promote foundations of physics and whether I'm doing it is I've founded this thing called the John Bell Institute for the foundations of physics. And we are at the very moment, a kind of critical moment where we're trying to buy a

physical place for us to live. And if anybody out there likes people who talk about this stuff and thinks they should have a place to go where they can meet and talk to each other, we have a go-fund meet. Or you could go to www.w.w.johnbell Institute.org. if anybody would like to help us out in any way, it's our moment of need, and we would appreciate it greatly. Good to be reminded of that. I will also mention that in the intro and put links on the web page. I can mention it because it's an audio podcast. Tim is wearing a very fetching John Bell Institute polo shirt right now. So that could be swag. I don't know. Is that a go fund me?

This, to get the shirt, you've got to come to the place. The only, the only exceptions to that are my parents. who are 95. And I said, you can have shirts without actually going. But this is, this, you can only wear the shirt if you've been there and you've seen this beautiful island in Croatia and enjoyed it. And then you get a shirt. But it is, it is actually an important thing. I'm glad you mentioned it, because it's a reminder that ideas are great and conversations about them are great, but institutions also matter for getting these ideas. And this is the problem is this field is an academic orphan. Yeah. Right. Foundations of physics doesn't fit

it means it kind of doesn't fit in physics departments and it doesn't really fit in philosophy departments. Tell me. And so, you know, if it's going to live, a place has to be made for it. All right. Let's look it up on the internet. So in that case, Tim Mawson, thanks very much for being on the Weinscape podcast. Thank you. What if you could have even more and more and more help to pursue your goals? At LPL Financial, we offer more ways for advisors and their clients to thrive. So what if you could? Paid advertisement. Investing involves risk, including potential asset principal, LPL,

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