Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas - 59 | Adam Becker on the Curious History of Quantum Mechanics

Episode Date: August 12, 2019

There are many mysteries surrounding quantum mechanics. To me, the biggest mysteries are why physicists haven't yet agreed on a complete understanding of the theory, and even more why they mostly seem content not to try. This puzzling attitude has historical roots that go back to the Bohr-Einstein debates. Adam Becker, in his book What Is Real?, looks at this history, and discusses how physicists have shied away from the foundations of quantum mechanics in the subsequent years. We discuss why this has been the case, and talk about some of the stubborn iconoclasts who insisted on thinking about it anyway. Support Mindscape on Patreon. Adam Becker received his Ph.D. in physics from the University of Michigan. He is currently a science writer and a Visiting Scholar at the Center for Science, Technology, Medicine & Society at UC Berkeley. His book What Is Real? The Unfinished Quest for the Meaning of Quantum Physics comes out in paperback on Sept. 3, 2019. Web site Berkeley web page What Is Real? Talk on the history of quantum mechanics Interactive explanation of Bell's Theorem Wikipedia Twitter

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It's a simple way to add daily support to what you're already enjoying. So your wellness stays effortless wherever the day takes you. Vital Proteins. Stay vital. Visit VitalProtene's.com to get started. These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Hello, everyone, and welcome to the Mindscape Podcast. I'm your host, Sean Carroll, and today we have another episode of quantum mechanics.

I know this makes everyone very excited. Today I'm talking to Adam Becker, who is a PhD in physics, but has gone the root of becoming a freelancer. science writer. And most interestingly, for our current purposes, he's the author of a book called What Is Real. This is a really wonderful book. I've been recommending it right and left. It's about the history of quantum mechanics in the 20th century, but it's not the typical history. Most histories of quantum mechanics focus on from 1900 to 1935, and what Adam really does is look at what happens after 1935. He does a little bit of the early stuff. But the point is that as I talk about in my own book, something deeply hidden, there's this weird thing where quantum mechanics is invented.

It comes with this giant problem called the measurement problem. What really happens when you measure a quantum system? Why do the rules seem to be different, et cetera? And then after a very brief flurry of interest in talking about the measurement problem with people like Bohr and Einstein and Schrodinger going back and forth, it's forgotten. It's just dropped. It is, in fact, it becomes disreputable to even think. about the measurement problem. So Adam really digs into the history of the people who refused to

be quieted when talking about this huge problem in physics, the plucky band of rebels who really said, no, actually, this is kind of an important thing. We need to think about it. So he talks about Hugh Everett, of course, but also David Bohm, John Bell, a lot of the experimentalists like Klausur and Aspe and others, who really tackled this problem and tried to remind the physics community that despite what their advisors told them, the measurement problem in quantum mechanics is really, really important. So it's not about here solving the measurement problem. It's sort of about the history of how physicists talked about that problem,

and it's a fascinating history with colorful characters. So you'll both learn a little bit about quantum mechanics, but also learn a little bit about the history and sociology of physics, which is really much more fascinating than it has any right to be. So let's go. Adam Becker, welcome to the mind. Skinscape podcast. Well, thanks for having me. It's great to be here. Of course, this is a slightly unusual show just because they're all slightly unusual. I don't know why I keep saying that. Sure. Quantum mechanics, I should say this is a slightly usual show. It's the single topic I do the most, because I'm coming out with a book on quantum mechanics. Sure. Now, I do quantum mechanics for living, but you've written a book that's already out about quantum mechanics. So for the purposes of this interview, I'm going to pretend that I don't know much about quantum mechanics. That's okay. I'm going to try to get it out from you. Sure.

And specifically, is it okay to characterize your book as a history of quantum mechanics? Yeah, I think that's what it is. Yeah, it's definitely a history of quantum mechanics. It is, I would say, somewhat unusual history of quantum mechanics, and I think it's a good history of quantum mechanics, but I'm biased. Well, it's unusual, I guess you're going to say that in a sense that, you know, history, there's a set of things that happen, but you have an angle, right? You have a theme. I have an angle. That's one of the things that makes it unusual in that I think that the sort of dominant take on what quantum mechanics says, this thing that's called the Copenhagen interpretation, but also goes by other names like the Orthodox interpretation or whatever.

I am not a fan, to put it mildly. The other thing, though, that I think makes my book somewhat unusual as a history of quantum mechanics is there are a lot of other popular histories of quantum mechanics out there, and most of them sort of start in, say, 1900 with Max Planck, and then they say, you know, Max Planck found the black body radiation law, and that was the beginning of the quantum revolution, and then they sort of move forward from that, with Einstein and the photoelectric effect in Bohr and his model of the atom.

And then, you know, they end with, and then Heisenberg and Schrodinger developed, you know, fully-fledged modern quantum. quantum mechanics and everybody lived happily ever after. And then maybe, you know, Einstein and Bohr got into a fight, but Bor one. And then, you know, 30 years later, John Bell did a thing. And that's the end of the book. Right. My book kind of inverts that structure.

I only have a chapter or two at the beginning about the very early days of quantum mechanics. And most of the book focuses on stuff that happened, uh, from, say, 1945 onward. Which is fascinating. So just, just so there's, if there's any people out there, in the audience who think quantum mechanics is fun, but history is not, it's really, really illuminating to go through this particular kind of history

because you see where people got certain attitudes. And quantum mechanics is hardened, and it shows us a lot about physics and the physics community, right? Yeah, yeah. I mean, I think that there is general attitude or idea among some physicists and some scientists of various stripes,

that history and personalities and culture don't really matter that much in science and aren't really reflected in science. And that's just kind of wrong. It's just the objective truth, Adam. What are you talking about? We just find the truth we laid out there for people. Yeah, that's clearly true. Science is a body of facts. It's not a human process.

Yeah. But science is a human process, right? It's affected by all other human processes, right? Which is not to say that science is just, you know, bullshit that people make up. Well, we certainly make choices along the way about how to do science, right? What's important? What questions we're going to tackle and so forth? And quantum mechanics is a great example.

So why don't we, why don't we, why don't you your version of what is quantum mechanics? Oh, boy. Quantum mechanics is a phenomenally successful physical theory. It is, it is the best theory we have to account for the behavior and predict the behavior. and predict the behavior of very small objects, but also things that are constituted of very small objects, which is basically everything. Basically everything.

And so quantum mechanics, so one definition of quantum mechanics is it is, well, hold on, quantum physics, right? I don't care. Quantum theory, quantum physics, yeah, yeah, whatever you want to mean the same thing. Yeah, quantum mechanics, we usually use that for the non-relativistic theory.

But anyway, yeah. quantum physics, because it's this theory for tiny things and things made of tiny things, which is everything. It's basically our best physical theory of everything with a little asterisk on it, and the asterisk is general relativity, which is a whole other thing. But basically anything where gravity doesn't matter that much, where that much means matters less than it does, I don't know, inside of the heart of a dense star or near a black hole. Quantum mechanics is fantastic.

Okay, but what does it actually say? Let's imagine that someone is listening who just doesn't know about uncertainty or wave functions or anything like that. Yeah. Well, that's the question, right? Quantum mechanics is, so one way of answering the question is, quantum mechanics is this really good mathematical tool for predicting the outcomes of experiments and predicting, you know, how various physical phenomena will play out.

As for what it tells us is going on in the world, that's a question of interpreting the mathematical structure and the results of the experiments that we do. And that's exactly what's at stake in the story that I'm telling in my book. You know, the question of how to interpret this incredibly successful theory to figure out what it's telling us about the world is very controversial and has been since the early days of quantum mechanics back in the 1920s and even before. I mean, that's why I don't think we've actually said the name of my book yet, but that's why the title of my book is what is real question mark, right? It's not a finished story and that question is the question, you know,

at hand. Yeah, you do notice this whenever you're trying to talk about, whenever I'm trying to talk about quantum mechanics is that you can't say anything about what the theory says without choosing a formulation of it, right, without taking sides in these interpretation wars. Exactly. Yeah. I mean, you know, I could say something that would make you as a many worlds person very happy and say, well, quantum mechanics tells us that things can be in more than one place at once, in different universes, and very small systems composed of a very small number of things

can interfere with their counterparts in other universes, but then when you get large aggregate number of things, that doesn't happen as much unless you perform special tricks. That would make a lot of people very angry if I said that that was what quantum mechanics said without qualification, right? I'll lead into it, Adam. You've got to be able to make people angry. Oh, don't worry.

I have no trouble making people angry. There are a lot of people angry with me. Well, how about, I mean, why don't we just be a little bit historical? And imagine that we are there at the sole. Bay Conference, right? The Fifth International, for those of you who don't know, this was this 1927, I think. Yes. This big, like it was the moment when quantum mechanics sort of matured.

Yeah. And all the bright people in the physics world were there and they chatted it out and tempers flared. Exactly. Yeah. No, this was, I don't know, we're in L.A. It was the Oscars of quantum mechanics, right? So, yeah, there were, this was a.

this was a major, major conference in 1927 in Belgium, and all of the key players in the formulation of quantum mechanics, or almost all of them, were there. So, for example, Albert Einstein was there. Niels Bohr, the great Danish physicist, was there. Louis de Bois was there. Werner Heisenberg was there. Erwin Schrodinger was there.

Max Bourne. Plunk was there. Pauley, Marie Curie, Derrick. Iraq, yeah, like everybody was there. I think Rutherford was there. Like, everyone was there. And this was sort of a great coming out party for the, the version of quantum mechanics or the way of thinking about quantum mechanics that Heisenberg and Born and Bohr and Pauly had sort of cobbled together, which is not to say that those four were the only ones involved, or is it to say that those four all agreed with each other, but they agreed enough that they were able to put together a presentation that they gave, and specifically a presentation that Born and Heisenberg, I believe, gave in which they said, okay, here's the theory,

here's how it works, it's done. It's a complete theory, and you can't add anything to it, and it doesn't let you say anything about what's going on before you. you take a measurement. And this is what we call the Copenhagen interpreters. Yes, exactly. Or a version of the Copenhagen interpretation. No one agrees on what the Copenhagen interpretation is. Yeah, no one is.

That's the other thing. But it's still what we teach our students today. We teach our students something that plausibly goes by that name. That's right. Yeah. I mean, because there's, you know,

here's another way of answering your earlier question of what quantum mechanics is. And then I'll get back to the Solvay conference. Quantum mechanics is a pair of, of rules for predicting what's going to happen in the world. One of the rules is this thing called the Schrodinger equation, which is exactly the kind of thing that we love to have as a law of nature. It is deterministic. It's a beautiful partial differential equation. It's very, very pretty. It says that there are these things in the world, or that there are things, whether they're in the world, is controversial, right? It says that there are these things so hard. But they're a thing.

There are things called wave functions, and as the name sort of implies, they kind of wave. And, you know, they undulate in a way that is perfectly predictable through the beautiful mathematics of the Schrodinger equation. And then there's this other thing called the Bourne Rule. And the Bourne Rule doesn't look like a normal law of nature. doesn't look like the laws of nature that physicists were accustomed to in the 1920s, which is not in and of itself a strike against it. That's fine. Sure. We could be dramatic and new. Exactly. That's good, you know, or can be good. But the Bourne rule also...

Named after Max Born, not the concept of being born. That's true, yes, named after Max Born. The same way that the Schrodinger equation is named after Erwin Schrodinger. And to give credit where credit is due, Heisenberg came up with something sort of like the Schrodinger equation. It was something that was mathematically equivalent. But Max Bourne, he said, okay, these wave functions, there's another way that they behave. When you look at something that has a wave function associated with it, or when you take a measurement of something that has a wave function associated with it, which is supposed to be everything in quantum mechanics, that wave function collapses. It goes to zero everywhere, except in one spot or

in one spot, like in one spot or in one way. Yeah, one value. Everything, everything, everything but one value goes to zero. And which one it's going to be is probabilistic, which one is going to not be zero is probabilistic. And you can determine that by looking at the values of the wave function in the moment before you make the measurement. And the problem is that these two rules for how wave functions work contradict each other. Right. And so there's the question, when do you use one and when do you use the other one? So one rule for when you're not looking at it?

Yes. And another rule for when you are. Yes, something like that. And so the question is, which one do you use when? And the traditional answer, the Copenhagen answer, is to say, oh, you use the born rule, this collapse rule, when you're looking at things, when you're making a measurement, and use the Schrodinger equation for when you're not looking. What do we mean by looking?

What's a measurement? What counts as a measurement? Who has to do it? Right? Do you need a PhD to do a measurement? What if you just glance at it? What if you just glance at it? What if a monkey does it?

What if a bacterium does it? All these questions. So this sort of assorted host of questions that go along with this one core question of which rule do we use when, that's the measurement problem. Right, the measurement problem of quantum mechanics. Yeah. And the Copenhagen interpretation has, claims to have a solution to this,

claims to have many solutions to this because the Copenhagen interpretation isn't any one thing. But at the Solve conference, the solution that was proposed was it's not right. It's not good scientific practice to talk about what's going on when you're not looking. So the philosophical maneuver that they made? Yes, something along those lines. And not everyone was happy with this. In particular, Albert Einstein was very unhappy with this. And so he starts getting into it with Niels Bohr in particular, but really the rest of them as well.

He proposes a couple of thought experiments to try to get around this to show why this can't quite be right, or at least can't be the whole story. he is misunderstood basically right off the bat. And this goes on for years. Well, there's this popular idea that Einstein just couldn't handle or couldn't keep up with quantum mechanics. Yeah, and that's, it's such a strange myth.

It's the opposite of true. Yeah, it's the opposite of true, which usually we call that false. But it, I mean, Einstein, first of all, was one of the founders of quantum mechanics. You know, he's 1905 paper. on the photoelectric effect, postulated the existence of, you know, quantized packets of light photons. And that's hardly the only work he did on quantum mechanics throughout his

career. He did a lot of very, very important work on quantum mechanics, both before and after, though probably less after, the full modern formulation of quantum mechanics shows up in the mid-1920s. there is no evidence whatsoever that he couldn't keep up with it. He definitely understood it. He spent a lot of time thinking about it. He once said that he spent more time thinking about quantum mechanics, or I think the phrase was that he used up more brain grease on quantum mechanics than he did on relativity, which is what he's more known for.

I mean, hell, he got the Nobel Prize for his work on quantum mechanics, not for his work on relativity, which is a weird historical quirk, and Nobel Prizes aren't that important anyway. But, yeah. So he was upset, and I think it makes perfect sense if you don't know a lot about quantum mechanics, I think you should sympathize with why he was upset

at the Solve conference, both because there are these two different rules that you use under different circumstances, and just because it all seemed so ill-posed, right? Like the whole point of physics is to be precise and beautiful and exact, and this hand-wavy thing about making measurements somehow sneaked in. Yeah, yeah.

I mean, he, Einstein, Einstein had a, what was at the time, a fairly common sense view of what physics was about. He said physics is about describing what's in the world. And now you're telling me no, physics is about predicting the outcomes of experiments. What's an experiment? What, you know, if it's really only about predicting the outcomes of experiments, then how are we supposed to use it to explain things that happen in the natural world when we're not around? Which people were doing already at the time.

You know, quantum mechanics has always been used to do more than just predict the outcomes of experiments. It has also been used to explain all kinds of very, you know, interesting natural phenomena ranging from stuff as basic as, you know, why does the sunshine, to, you know, why is it that silicon behaves in this funny way where it's not really an insulator and it's not really a conductor, it's a semiconductor, right? Yeah. And that lets us build computers. You know, so everything from basic fundamental facts about the world around us, like, you know, why I can't pass my hand through the table to, you know, all sorts of strange and wonderful modern technology like LEDs or most of this recording equipment. And I thought, you know, you mentioned this very quickly, but I want to dwell on this philosophical leap made by the Copenhagen interpretation.

So if you really say that the job of your physical theory in this case is to simply predict the outcomes of experiments. And they said this, the advocates of Copenhagen, as far as I can tell, were sometimes more explicit about this than others. They were never completely on the same page. But, okay, there's a version of it which really says that. And it's almost solipsistic, idealistic, and if you really push it, you're saying it's all in the mind. You're saying like the world as something that exists external to me is irrelevant to physics. What is important to physics is the predictions that I can make and the observations that I can make. Yeah, yeah.

I mean, I think that that is definitely one way to take what they were saying. You know, I don't think that that. there is any single Copenhagen interpretation. And while Niels Bohr and Max Born and Pauley and Heisenberg and the others may have each had their own individual positions, I don't think that you can combine all of those to make something coherent. And in some cases, like with Niels Bohr, it's not even clear what each individual's position was. There's no consensus on one paper.

Exactly. Yeah, yeah. I mean, I, I, speaking of people being mad at me, this is something that some people are mad at me for. They say, but you said that Neal Spoor had this position. I didn't. I didn't say that Nealzbor had any position. I don't know what position he had, neither does anybody else. I just quoted him a few times in my book, because like if you try to translate what he says or paraphrase, people are going to be bad at you. Yeah, exactly. No, it's, it's, he's, I mean, he was a brilliant physicist and a very interesting man who did lots of wonderful things, and he just was not. a particularly clear writer or speaker. Well, David Albert, when I interviewed him for the podcast, he had a wonderful take on Niels Bohr. He said that Niels Bohr was the person in history who he would most like to have met personally.

Yeah. His reason why is because, you know, people would meet him and they would come back after talking to Niels Bohr. And number one, they would say, this was the most brilliant, wonderful, transcendently wise human being. And they would start spouting complete nonsense about the foundation. of quantum mechanics. So how can one person have this effect? Yeah, no, it's a real question. I mean, I don't know. I don't know if he's the person in history I'd most like to invite to dinner,

but I'm certainly very curious about him. When I consider potential sponsors for Mindscape, I'm naturally drawn to educational services. But policy genius can be thought of as an educational service when it comes time to search for insurance policies, whether it's life insurance, home insurance, auto insurance. You go to the website and you can find multiple quotes from the leading insurers around the country so you can pick, which is the policy that best fits you. They're at the right price. They do not add cost to the insurance policies that you'd be signing up for. They simply get a commission from the different companies that are selling them. And so you can look at all the different policies, what they involve and pick the one that is best for you. What I really like is that

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that the Copenhagen interpretation was how we think about quantum mechanics. And there were a few people who didn't like that, like Einstein, also Schrodinger. Yeah, that's right. Schrodinger did not like this. But they became increasingly marginalized, at least in terms of how we think about quantum mechanics. Yeah, that's exactly right. Yeah. They, you know, people thought Einstein and Schrodinger were kind of out of touch and kooky.

And maybe they were kooky, but they were not wrong, I think, to have doubts about this. but their work was increasingly outside of the mainstream of the work that the rest of the physics community was engaging in, not in the sense that, oh, it was wrong or fringe, but in that the rest of the physics community was just not thinking about these things. They were working on other things. And part of that was for, you know, really obvious historical reasons, right? This debate was going on in the early to make. mid-1930s, mostly in Europe.

There were some things also going on in the 1930s in Europe into the 40s that were somewhat distracting to a lot of people. And physicists in particular had other things to worry about. Yes, they did. Yeah. So, you know, by the 1940s, people were working on other things, such as the Manhattan Project. And so, and then after the Manhattan Project, after the war, suddenly there was this realization due to, you know, the, I hesitate to use the word success for the Manhattan

project, but due to the achievements of the Manhattan project, there was recognition by governments and industry and the military that there was a lot of value to be had in funding massive amounts of applied physics. And so rather than worrying about the foundations of quantum mechanics, this influx of money. and the people who came along with that were concerned with working out implications of quantum physics, which is a good thing to do.

There was a lot of really, really great science done in that period. And I do think that if the attitude had been, okay, you know what, there's a problem here at the foundations, we'll come back to it later. There's something that we need to figure out, but in the meantime,

we have a lot of really interesting work to do, and maybe that'll help us understand, the theory better and that will shed more light on things. If that had been the attitude, I wouldn't have had a book to write. Yeah. Because that, and I think that's a very sensible attitude, there have been many other theories in the history of science that have worked that way. You know, Newton himself, right, talked about his own theories in this way sometimes.

But that's not what happened. Sorry, that's not what happened. Instead, it was, oh, those problems are solved. we don't have to worry about the foundations. Now we can work on these applications of the theory. And the foundations we mean, is the correct attitude towards this measurement problem really just to only ask about measurement outcomes? Or is there some other version of quantum mechanics, some other way of thinking about things that is more traditionally physically scientific? Exactly.

Yeah. I mean, with this influx of money and people that came after World War II, questions like, but what does the theory mean were kind of swept under the rug? And there's been a lot of really good work on how the changes in physics after World War II led to changes in the way that quantum mechanics was taught. That's been done by the historian of science, David Kaiser at MIT. who, you know, has gone back through physics curricula and textbooks from the time and found that the larger the classroom, the less time spent on, you know, the meaning and foundations of the theory

and the more time spent on applications. And I think that makes sense. You know, it's easier to teach people how to solve a partial differential equation than it is to, you know, talk about these thorny philosophical issues at the heart of the theory. I do think that we're going to get, we'll get to the, you know, plucky band of rebels who did want to keep thinking about the foundations. And blew up the death start. I mean, let me try, since my usual spiel is what a huge mistake it was to ignore the foundations. Yeah. Let's try to be charitable.

Sure. To the people who did ignore the foundation. Absolutely. So as you said, there's a lot of applied physics to do. There was even non-applied physics. Sure. I mean, when Murray-Gel-Mond is working out, you know, the SU3 symmetry group, the eight-fold way, There's no applications of this to the military or anything like that.

But so what would someone back then have said if you said, why aren't you thinking about quantum mechanics as a foundational theory? Well, I think that answers would have varied, right? One answer that someone could have given was, but we are. Take a look at, I think this is the late 1940s, early 1950s, early 1950s. Speaking of non-applied foundational work of a different kind, take a look at what happened with, how do I describe this without using jargon?

There was this little shift in the way that atoms emitted light called the lamb shift. So a slight miscalibration between what you predicted and what you saw. Exactly, yeah. And at first people just thought it would, go away. And then as experimental techniques and theory got better and better, the mismatch got more and more obvious until it became clear, there was a real problem. And this led to the development of a new foundational theory of quantum physics called quantum electrodynamics. And this is, you know,

what the single piece of work that Richard Feynman is most well known for, as well as Julian Schwinger, Tobinaga, Tobinaga, and Freeman Dyson. Yeah, exactly. But okay, I mean, to be fair, that could be classified as a particular theory within the quantum mechanical umbrella rather than the foundations of quantum mechanics. Sure, that's true, but if you were to ask these people... It had nothing to do with the measurement. That's right. It had nothing to do with measurement problem, but it certainly wasn't really applied. Sure. Right.

So if you ask those people, you know, why aren't you paying attention to the measurement problem? They might have said something like, the theory works very well. This has all been worked out. And we're focusing on real problems, not chasing phantoms. So that's one possible answer. Another possible answer would be to say, well, what do you mean? they're, you know, rather than to say the problem's been solved, they would say, no, there was

never a problem there, right? It's not a problem. You know, they might take some version of the Copenhagen interpretation and really swallow it entirely and say, no, it really is all about these, uh, these observations that we make. That's really all that matters. Uh, you know, we're, we're very good at doing physics. Physicists are very good at doing physics. We're not always, is good at describing how we're doing. Oh, we're doing physics. Yeah, exactly. That's okay. Those who cannot do teach. Yeah. Sometimes those who can do don't know how to teach. Right. Exactly. But, but yeah, I mean, you know, just the same way that we deny, oh, you know,

things outside of the realm of science have no influence on science itself. You can sort of see somebody saying, oh, no, no, no, no. Physics is definitely all about the outcomes of measurements. and then, you know, they go off and do something that's clearly not about the others. But no one ever said that before quantum mechanics, right? I mean, I guess Mock might have said that. Yeah, Mock said things kind of like that. There were philosophers, yeah. And Mock was both a philosopher and a physicist sort of, yeah.

So, yeah, people definitely did say things kind of like that beforehand. In fact, some people thought that that's what Einstein had been saying in 1905 when he came up with special relativity, and that was a big inspiration for them. Though if you then go back and take a look at Einstein's other work from 1905, it's very clear that actually that's not really the kind of thing that he thought. Okay, speaking of which, Einstein and also Schrodinger, who was sort of on his side, they didn't give up, you know, post-Solvey conference. And so they're not giving up was a huge boon to humankind in the sense that they basically invented entanglement, right?

Yeah, I mean, yeah, it forced. the rest of the physics community to understand that entanglement was maybe the defining trait of quantum mechanics. You should tell us what entanglement is. Yes, that, well, so that's another thing where no matter how I describe it, it's going to be picking some interpretation. So let me see what I can do. So pick the right one.

Yeah, pick the right one, clearly, yeah. The joke here, of course, is that you have a preferred interpretation of quantum mechanics, and I just have an anti-preferred interpretation of quantum mechanics. But yeah, so entanglement, quantum mechanics makes it very clear that under really a wide variety of circumstances, you can have two things that are widely separated. Particles or whatever. Particles or whatever, really. That, you know, despite the fact that they are very far apart, you know, they could be on the other side. of the solar system.

And despite the fact that there's no obvious connection between them, there are instantaneous correlations in experiments that you conduct on each of the two of them. And you can account for that in several different ways. And that's another one of the things that's at stake in this interpretation debate. Right. So the reason why Einstein, so, yeah, you see, two particles far away, quantum mechanic says that when we measure them,

all we do is predictive probability for getting certain outcomes. But what Einstein and Podolsky and Rosen say that the probability of getting one thing is deeply affected by doing a measurement on the other one, even if they're really far away. Exactly. And sort of, this seems to

violate at least the spirit of Einstein's theory of special relativity. Yes. You could see why he'd be upset about it, but it doesn't actually let you send signals fast from the speed of light or anything like that. Yeah, yeah. You can prove that you can't use it to send signals like that. It's, it looks like an instantaneous influence. It doesn't look like something that you could use for instantaneous communication.

And so why did Einstein think this was a big deal? Einstein thought this was a big deal because he saw no reason to believe in any kind of instantaneous influence. He said, well, if we really want to say that we can't talk about what's going on before we make measurements, then we have to say it's an instantaneous influence. because you make a measurement way over here and you make a measurement way over there, and they have correlated outcomes all the time. So if it really, you know, if there was really no fact of the matter before you made the measurement, then they must have been conspiring immediately across great distances.

Or, he said, you could do the reasonable thing and say that, no, when you first sent them off in different directions, they already had a sort of agreed upon set of properties. and so that lets you get around this without saying that, you know, the two objects have this sort of long-distance conspiracy going on. So even though we couldn't predict what our measurement outcomes were, the particles knew what their measurement outcomes were going to be. Exactly. So Einstein says, given that the two options are something totally normal like that, or this long-distance, you know, what he called spooky action at a distance, he chose door number one. And given that those were apparently the two options on the table at the time, that seemed like a reasonable thing for him to do.

And the response that he received was not great. Niels Bohr wrote a sort of famously impenetrable response, which he later apologized for how poorly written it was, but then didn't really proceed to elaborate on what he had meant. I was told that part of it was even printed in the wrong order. Is that the history? Okay, so, right, so the printing in the wrong order, this is really inside baseball. So it was not originally printed in the wrong order.

However, in, you know, the dark days before the internet, if you wanted to find Boer's reply to the EPR paper, you, you know, the Einstein-Podolsky-Rosen paper, you had to go find it in a book. and the book where it was sort of most famously and widely available was a book from the early 1980s called, I think, quantum theory and measurement. It's a big red book. And in the first, I think in all of the first edition printings of that book, two pages of Boar's reply were swapped. And it's only like a four or five page reply. So that's a pretty big difference. And the story, which is, I think impossible. to verify is that nobody noticed for years. Yeah, because they couldn't understand it anyway. Yeah. What difference does make what order the pages are in. And also, you know, there's, Boar's replies sort of serve this very important social function just by existing.

Because people could say, oh, you're not, you know, you don't have to worry about that EPR thing. Boer worked it out. It's on that page. And so people didn't actually read it. It was just there. But yeah, you can now, of course, download it online and whatnot. But a story that I know is true, because, you know, I don't know if nobody noticed it.

It definitely was printed in the wrong order. When I first read it, I first read Boar's reply, I guess it was 2005. So I did not have to get it from that book. I did get it from the internet. I had the pages in the right order. I printed them out. I read it. And then I went to the professor that I was working with at the time.

And I said, you know, this is a really bad translation. Is there a better translation available into English? English because, you know, I thought, oh, well, you know, Boer wasn't a native English speaker. Maybe this was written in Danish. I see where this is going. Yeah. And then the professor told me, no, no, Adam. He wrote this in English. Yeah, this is the original. Yeah. So, yeah, it's just a fabulously impenetrable reply. But like you say, it let the rest of the community say, oh, yeah, Einstein's objection. And by the way, Einstein's objection was not quantum mechanics is wrong. Right. It was just that it was just a stepping stone toward a bigger theory that we would someday have.

Yeah, he said that it was simply incomplete. And in fact, I think that was the title of the paper. You know, can quantum mechanical description of reality be considered complete? Not correct. So, yeah, no, people thought that Einstein was wrong. Einstein actually wrote a letter to Schrodinger shortly after the EPR paper came out, saying that he had gotten letters from, you know, a couple dozen different physicists from around the world explaining why he was wrong, and none of them agreed with each other.

So, yeah, Einstein and Schrodinger sort of laughing at everybody else behind their backs. Schrodinger, meanwhile, writes a paper in support of the EPR position saying, look, you know, this is this, this long-distance connection, this is a fundamental property of quantum mechanics, it's everywhere, and you can't really get around it. And to show you another kind of example of the same thing, let's talk about a cat in a box. with radiation and a vial of cyanide. And so this is where the famous Schrodinger's cat thought experiment comes from. That's fair. And so Schrodinger points this out as, you know, he comes up with this thought experiment to explain why there must be some,

you know, deeper fact about the world. Or so he thought that quantum mechanics doesn't capture because otherwise, you know, maybe you can have a particle that's not in any particular state before you look, but the Schrodinger's cat thought experiment says, well, if you have a particle in that state, you can set up an experiment where a cat is neither dead nor alive before you look. And saying that a particle is in, you know, a subatomic particle that we have no direct experience with is in, you know, neither one state nor the other.

That's one thing. But cats are either dead or alive. You know, there are cats in this apartment right now. I haven't seen them. I am sure that they are either dead or alive. Yes. In fact, they're alive. Yes.

Okay, yes. But, okay, but just to get the philosophy on the table here. Yeah. Einstein and Podelsky and Rosen make this point about spooky action at a distance, but they didn't just say, and that's obviously crazy. Like Schrodinger with his cat, his argument was really at the level of, that's obviously crazy. That's true.

That's true. No, the EPR thought experiment in that respect is more rigorous. EPR was a little bit more rigorous. They wanted to make the case that if you believe that there really is something actually happening at every location in space in ways that they tried to make carefully defined and so forth, then quantum mechanics couldn't be complete. And this is going to skip ahead a little bit, but then John Bell comes along and says that, okay, Einstein is basically sketching out an aspiration. Someday will have a better theory that explains all this without spooky action at a distance. and Bell basically proved that no such theory can ever reproduce the predictions of quantum mechanics. Yeah, Bell, people have called Bell the person who proved Einstein wrong.

People have also called Bell the person who proved Einstein right. I think that neither of those are really correct, though I'm more sympathetic to the second one, because what Bell proved was that Einstein was right to be worried, but that his proposed solution couldn't work because you can, can modify the EPR thought experiment in this very subtle and, you know, brilliant way, that will basically give you a real experiment that you could build. And the results of that experiment, if they conform with the predictions of quantum mechanics, can't be accounted for with this sort of pre-existing answers that Einstein.

had in mind for how these particles were, you know, arranging to have these long-distance correlations. Right. And Bell, so is an example of how it was to try to do foundations of quantum mechanics. So we're talking about like 60s and 70s now. And he was a perfectly respectable particle theorist at CERN at the big laboratory where we discovered the Higgs Bose on a few years ago. And correct me if I'm wrong, but he basically hid the fact that he was working on the foundations of quantum mechanics from his colleagues at CERN? He didn't, I don't know, Hyde is a little bit strong. He didn't advertise it. He certainly didn't advertise it. Yeah. You know, there is, there is this nasty, well, nasty is probably a little strong.

There was certainly whispers about John Bell at CERN that, you know, oh, he did something important in quantum foundations, but don't worry about it because quantum mechanics works anyway. Yeah. Don't hold it against me. Yeah, exactly. Yeah. One of Bell, Bell's good friends, who he worked with on the other work he did, not quantum foundations. Bell's sort of everyday physics work was in quantum field theory. And one of Bell's good friends was Martinez-Veltman. And the story is that Veltman one day said to Bell, you know, you did this thing in the, in quantum foundations, do I need to worry about this?

Will it affect my work in quantum field theory at all? And Veltman is a very good quantum field theorist. He won the Nobel Prize. Yes, he did win the Nobel Prize, yes. And so, you know, Veltman asks Bell this question and Bell says, no, don't worry about it. It's not going to affect your work at all, which is true. Yeah. And so Bell, yeah, he certainly didn't advertise that he was working on this stuff.

He also didn't work on it in a serious way, you know, great length until well after his career was established and safe. You know, he thought about this stuff in college and then he thought about it a little bit in his early graduate work. and then he was dissuaded from working on it, and so he put it off to the side and came back to it later. Free is great, but only if it's useful. Free credit scores from some apps can differ by as much as 100 points from your actual FICO score that 90% of top lenders use when you apply for a credit card, personal loan, car loan, or mortgage.

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That you can't have secret new values, secret new parameters of physics that as Einstein had hoped would, you know, fix the outcomes of future experiments, even if we human beings don't know. about it. But that's not what Bell proved. In fact, we have to talk about David Bome, who is certainly one of the more interesting characters in the story. Yes, he is. Yeah. So, no, Bell certainly didn't prove that you can't have these hidden variables like Einstein wanted. Bell proved that you can't have a particular kind of hidden variables. Um, ones without spooky action at a distance. And really, what he proved was not really about hidden variables at all. It was really saying that you can't have a theory without spooky action and a distance of some kind

unless you break something even more fundamental. Which we'll get to later. Which we'll get to later. Yeah, exactly. My man Hugh Everett broke all the thing. Yeah, no, I think the way I describe it in my book is, he showed that you either have to have spooky action at a distance or something even weirder.

Yeah. But yeah, so David Bome, right? So David Bome was in a lot of ways the inspiration for Bell's work and someone who's work Bell admired very clearly. David Bome was a student of Robert Oppenheimer, the guy who was in charge of the Manhattan project, though he himself only he didn't. follow Oppenheimer to Los Alamos. Why is that?

Well, he didn't follow Oppenheimer to Los Alamos because David Bohm had been briefly a member of the Communist Party in Berkeley where he was doing his PhD work. And so when he applied for security clearance to go to Los Alamos, he was denied that clearance. They did not tell him that this is why they denied him the clearance. They lied to him and told him it was because he had relatives in Europe who could be held as hostage against him, which, while true in theory, was definitely not the real reason, as, as, you know, documents uncovered well after Bohm died, proved. But, but yeah,

Bome did do some important work that was relevant to the Manhattan Project for his PhD, which was promptly classified and thus removed from his apartment, forcibly by military police, because he didn't have clearance to have his own work. And so... It was a crazy time. We're talking about the early 40s. Yeah, yeah. This is like 41 or 42, something like that.

Maybe more like 43. It doesn't matter. The point is it's during World War II. It was a crazy time, like you said. And yeah, no, he didn't have any of his research notes. Oppenheimer had to go to the UC Berkeley administration and say, you have to give him a Ph.D. anyway. Just trust me, which they did, which was good.

Bome had no problem with the Copenhagen interpretation at this time. You know, Oppenheimer was a great admirer of Boer. Bome was a great admirer of Oppenheimer. And so he didn't really think too critically about it, and it seemed to work for him. Then he started teaching quantum mechanics classes. So teaching is what's going to get you in trouble, clearly. Well, clearly not usually, since most businesses seem to have no trouble.

ignoring the foundations even when they teach quantum again. That's fair. That's fair. Bowen was a thoughtful guy. Yes, Bowen was a thoughtful guy. He was teaching quantum mechanics classes at Berkeley out of Oppenheimer's research notes, or sorry, lecture notes. And then he got a position at Princeton and continued to teach out of a mix of his own notes

and Oppenheimer's notes and started turning that into a textbook. And that textbook he wrote was trying to give the best version of the Copenhagen interpretation that he could and make it as clear as he could make it. And in the process of trying to do that, Boe's faith in the Copenhagen interpretation just plummeted until by the end of the process, he was just completely plagued with doubt. The more you think about it, the less sense of me. Yes, which I certainly agree. So then Boehm went and met with Einstein, who had, who had,

looked at Boe's textbook once it came out and sort of called Boehm into his office and said, look, you wrote this book and, you know, how do you feel about it? And Boehm said, I'm plagued with doubt. And Einstein said, look, that's because you're trying to defend an indefensible position. You did the best job that you could do, but no one can do it because it doesn't work. And so Bohm walked out of that meaning thinking, can I find another way to look at this? Can I find another way to think about quantum mechanics? And he did. He independently rediscovered a set of ideas that Louis DeBroy, one of the other founders of

quantum mechanics had come up with back in the late 1920s, and then sort of finished the work that DeBrois started and put together this theory, which goes by a bunch of different names, BOMian mechanics, DeBoi-Bomb theory, pilot wave theory. I like calling it pilot-wave theory because that's descriptive of the content of the theory. Also, by the way, when DeBroy actually tried to present his theory at the Solve conference, and he was just hectored out of his own theory. Exactly. No good reason. Yeah, basically, yeah. I mean, it is true that the job wasn't done, but he could have finished it and he didn't. Yeah. So, Bome, okay, Bome finished that. took up that mantle.

Exactly. Boehm took up that mantle, puts this thing together relatively quickly, and sends it off for publication. The problem is that at the same time that all of this was happening, Boehm's past was catching up with him. He got called up in front of the House on American Activities Committee

and testified in front of it to committee, including Richard Nixon, who was a congressman at the time. And he was asked to name names and tell people, you know, who the other people in the Communist Party in Berkeley during World War II were. He wouldn't do it. He was held in contempt of Congress. He was arrested in his office in Princeton.

And by the time he got back to campus after his friends posted bail, he had been suspended and banned from the Princeton campus. And he was working on all of these. ideas during that suspension. And this is 1951. Yeah. Yeah, yeah. This is 1951.

So while he's suspended, he works on these ideas about quantum mechanics. And then has his day in court. He's cleared on all charges because it turns out that, you know, you don't have to name names. He had pled the first and the Fifth Amendments. There is a first and a fifth amendment. Yeah, exactly. Yeah. So he's cleared on all counts, but Princeton effectively fired him after that.

And he couldn't get a job anywhere else, even though he had recommendation letters from Einstein and Oppenheimer. He couldn't get work, you know, doing academic physics anywhere in the U.S. or Europe, much to his, you know, disappointment. finally he gets a position in Brazil. And so toward the end of 1951, he goes down to Brazil. And shortly after arriving, he's summoned to the U.S. consulate where they illegally confiscate his passport and tell him that he can only have it back if he goes back to the United States, which he doesn't want to do because he's worried that he's going to be arrested again and, you know, maybe, you know, brought up on false charges or something.

So he's trapped. By now it's the height of the Red Scare. Exactly. It's the height of the Red Scare and the McCarthy era. So Bome is trapped in Brazil. He can't get out. He was planning to go give a bunch of talks in support of his ideas because his papers were due to be published imminently just a couple months later. So when they are finally published in very early 1952,

Bome can't defend his ideas through anything other than writing letters to people. And so mostly he's just ridiculed. You know, someone, I, one of the quotes that I found in my research for my book, which I like the best, was someone said that Bome had, you know, something to the effect of, had a very illustrious set of people sticking knives in his back all year long. in 1952, which, yeah, it's absolutely true. You know, Wolfgang Pauley, Werner Heisenberg.

Yeah, these are not the political knives of being a communist. These are physics knives of like, you're a crazy person who doesn't understand quantum mechanics. Exactly, yeah. But the fact that he was a communist also didn't help, not only because he couldn't leave Brazil, but because at that time, most physics funding was coming from the military.

And it was the height of the Red So. scare. And so if, you know, someone in your physics department was suspected of being a communist, that could turn off the faucet of funding. And that's a scary thing. So, yeah. And basically, to make it very, very brief, his theory, the pilot wave theory, was the kind of hidden variable theory that Einstein wanted, except, rather than avoiding spooky action at a distance, it reifies. It's all like, the spooky action is doing all the work here. Yeah, it's riddled with spooky action at a distance. There's a great quote from Bell saying that, you know, he resolved the EPR paradox in the way that Einstein would have liked the least. Yeah, something like that. Yeah,

it's, it's really, um, another quote from Bell, actually, about, uh, about BOMS, uh, theory was that, um, if you shook a magnet right here, it would instantaneously affect the position of every single electron anywhere in the universe, which is not a pleasant thing to consider as a physicist. Doesn't mean it's wrong. Well, Isaac Newton would have been perfectly happy. Exactly, yeah. Newton would have been fine with it.

And obviously, the influence is very, very small. And by the way, this hasn't gone away. Yeah. This is this Bohemian mechanics, pilot wave theory, is still one of the leading contenders for a sensible interpretation of quantum mechanics. Not so much among physicists, but among philosophers and people who work on foundations.

And how would you characterize the state of play with reconciling these kinds of ideas with quantum field theory and relativity? Yeah, I mean, the fundamental problem with pilot wave theory, BOMian mechanics, whatever you want to call it, is that it doesn't seem to play nice with relativity for exactly these reasons. You know, relativity doesn't have a preferred frame of reference.

It doesn't let you have things go faster than light. Bomean mechanics seems to violate that. I would have a much better answer to your question about the state of play in about three hours. I'm getting dinner with Chip. Oh, Stevens. My collaborator. Yeah.

But we rule out retro causality here in this podcast. Yeah, sure. That's not a version of quantum mechanics we like. So the information you will get in the future can not probably get back to us here. be used here. So the way that I like to put it, I'm just trying to check, reality check myself. I'm not an expert on Bomi mechanics. People have tried to make it compatible with relativity and quantum field theory. There have been yeoman-like efforts. I don't think there's been anything completely convincing. I think that's correct. If you ask them why the problem is there,

they will say something like, or at least some of them will say something like, well, Quantum field theory actually has its own foundational issues independently of the measurement problem in quantum mechanics, which is true. And that makes it very, very difficult to come up with a, you know, Bohemian formulation of quantum field theory because it's not clear what kind of quantum field theory you want that can account for all the different phenomena

that quantum field theory, you know, accounts for. I don't quite know what to make of that. Well, you know, I think it's a great example of how non-alorithmic physics really is. Yes. Not the results you get from physics, but the process of doing it, right? You have all of these sorts of puzzles, things we don't yet know the answer to, and some of them you have to say, oh, don't worry. That'll be figured out.

Whereas others you have to say, this is really important. We should really focus on solving this. different people are going to make different choices. Exactly. Yeah. No, physics is definitely subject to contingency and personality and, you know, random fate. For 50 years, the physics as a field made the choice that the foundations were not worth worrying about. Exactly. And even now, I'd say the standard position is, eh, don't worry about it. You know, it's not as rabid as it was before. It's not you shouldn't worry about it. It's, eh, don't worry about it.

As I'm recording this, I literally this week just recorded the audiobook for my upcoming book something deeply hidden on quantum mechanics. So it seems appropriate that I'm going to talk about Audible, one of the leading services for audiobooks, magazines, and more. When you become a member of Audible, you get one audiobook every month and two Audible originals, as well as 30% off regularly priced

audiobooks. There's also, of course, an app so you can listen to your audiobooks at any time. We have a special offer for Mindscape listeners. You can join Audible with a 30-day free trial. You'll get your first audiobook and two Audible Originals for free. Just go to audible.com slash mindscape. That's A-U-D-I-B-L-E dot com slash mindscape, or text Minescape to 500-500-500-50-50-50. Something deeply hidden will be coming out, hopefully, September or October on Audible. And you can have my previous books from Eternity to Hear,

the big picture and so forth. They're all available on audiobooks. So happy listening. We don't need to talk too much about Everett because it's my podcast. Sure. The audience will get plenty of Everett over the years.

But interestingly, he was there at Princeton in the early 50s. Did they overlap? Ever was a student and Bohm was an assistant professor. Yes, that's correct. They didn't overlap. They just missed each other by something like two years.

Okay. Because I think Everett shows up at Princeton as a grad student, and I want to say 53 or 54, and Bohm is gone by the end of 51. Okay. So I wonder if, you know, all of this influence, all of this work on quantum foundations at Princeton in the early 50s wasn't ultimately Einstein's fault.

I mean, Einstein certainly influenced Bome. Yes. He apparently taught a class? He gave a lecture that Everett was at, though Everett doesn't... Didn't remember? Yeah, he didn't remember later in life. On the other hand, other people say that Everett was there. It makes sense that Everett was there.

And also, I don't know, Everett was a funny guy. And people forget things. But yeah, and it certainly... Apparently, there was a lot of sherry consumed. Yes, there was a lot of alcohol of various kinds. It's absolutely true. But, yeah, Everett certainly read a great deal of Einstein. Everett also talked with Eugene Vigner, who was someone who was at Princeton at the time,

who harbored his own kinds of doubts about the Copenhagen interpretation. And so I think he was definitely an influence on Everett and probably vice versa. And, yeah, Einstein was there. and, you know, the other thing is, Princeton at the time was one of the best places to be doing physics in the world. Smart people would end up there. Exactly, yeah.

And I think that smart people are more likely to, more likely to question these truths that they've just sort of been handed on a platter, which is not to say that if you question those truths, that makes you a smart person. Okay, I mean, we're, there's a lot of physics to get through here, So I don't want to dwell too much on Everett because we'll get there otherwise. But, you know, Bome suggested an answer to the measurement problem, namely there were hidden variables.

We just don't know their values. Yeah. And so measuring is revealing some truth about nature that we hadn't known before. Yeah, yeah. And Everett suggests a completely different one. He gives up on, and so what Bome gives up on is locality. Yeah. He allows for spooky action at a distance.

That's right. Yeah, I mean, it's certainly a little bit more complicated than, measurements simply reveal things that were already there because measurements can still influence things. But it's, it's, it's like, it's a much less mysterious process. And Bummey Mechanics is, you know, harkens back to the classical paradigm, right? Where there are definite values of things and we measure them. Yeah, in some ways. There's some hearkening.

Yes. There's definitely some hearkening. Yeah, it's true. Whereas Everett takes completely the opposite point of view. He says there's no hidden variables. There's just this wave function. We should take it seriously. There's not two different ways of evolving.

There's only one way of evolving. And the price he pays is that when you measure something, the universe branches into multiple copies. Yes. Yeah. Which is this radical and deeply strange solution to the problem. But again, deeply strange is not a strike against things. Exactly.

Yeah. And Bohm was chased out of the country and then stabbed in the back. Yes. Everett sort of took his golden parachute, right? He didn't even try to get a job as a physics professor. Yeah, I mean, he was certainly not happy with the way that his work was received. I mean, Everett's mentor and advisor at Princeton was the great physicist John Wheeler. And Wheeler was, you know, one of Boer's most devoted students. And so when he saw Everett's work, He really liked Everett's work at first, but he wanted it to get the blessing from the master, right? To get the blessing from Boer. And Boer and...

That was never going to happen. Yeah, that was never going to happen. Borr in his inner circle never gave it that blessing because of course they didn't. And the whole experience was definitely, you know, a traumatizing one for Everett. But on the other hand, Everett was never going to stay in academia. That was my impression. Yeah, it wasn't where his passions were. He wasn't chased out.

Yeah, he wasn't chased out. If he had wanted to stay, he might have had problems. I don't know. I mean, Wheeler was still willing to go to bat for him. But Wheeler made Everett make a lot of revisions to his ideas in his PhD thesis to try to make more happy. It didn't work, of course. And then Everett did what he was always going to do, which is he finished his PhD and went and got a job working for the military industrial complex, you know, doing essentially war. gaming. Simulations. Yeah, exactly.

Bomb falling. Exactly, yeah. And, okay, so there was this sort of brief moment in the 1950s when a couple people at Princeton thought deeply about the foundations of quantum mechanics. Yeah. And it's fairly safe to say that their efforts had zero impact for the next few decades. Didn't have big impacts for a decade or two. Yeah, that's true. I mean, and I'm also, you know, these are not the only people who thought deeply about the foundations

of quantum mechanics. They're just the one whose work ended up being the most influential in the coming years. But yeah, no, people didn't, there wasn't a lot of widespread, you know, open talking about the foundations of quantum mechanics. There wasn't a lot of research done on it. You know, the work that Bohm did and that Everett did was probably the most notable work done in the quantum foundations at the time. And then Bell shows up.

Yeah. Um, Bell is one of these people who had never been happy with the story that he'd been presented with about quantum mechanics. And then, you know, he, he got into fights with his college professors about it. And then shortly before finishing his university studies in, uh, in 1949, shortly before finishing college, um, and he's in Northern Ireland. He's at, uh, uh, Queens College and, uh, Queens College in Belfast, I think. The point is, he's at college, he's almost done, and then he comes across a book by Max Bourne, in which Bourne describes a, among other things, a proof from the great and mighty physicist John von Neumann. And John von Neumann is one of the giants of 20th century math and

physics. And so if there's a proof of something by John von Neumann, it's almost certainly correct. And Bourne says that von Neumann proved that this way of understanding quantum physics as fundamentally driven by, you know, chance that happens, you know, like these weird random chance events that happen when you make measurements is the only way to think about quantum physics. Yeah, so it can't really be deterministic hidden variables. Right, exactly. There's no other way to think about it. And so Bell is very impressed by this, and he wants to go look at the proof, but he can't,

because at the time it's only available in German, Bell doesn't speak German, but he thinks, okay, I'd better put this down because von Neumann is right. And if I keep thinking about this, I'm just going to fall down a well, and I'm never going to come out. So he goes off and does some work in accelerator physics. and then while he's working that job in 1952, he sees the papers from David Bome. And he reads these papers, and he immediately realizes there's nothing wrong

with what Bome said. Bome may not be right, but it's certainly a perfectly legitimate way of looking at quantum mechanics. And so then Belle realizes, well, von Neumann must have been wrong. How can you prove something can't exist when here's an example of it exists?

Right, exactly. So here's a counter example. So he, again, wants to go look at the proof. It's still only available in German. So he goes off and works in other things for a few years. He goes to graduate school. He suggests to his PhD advisor that he could either, you know, one day give a talk about either, you know, BOM's work and the quantum measurement problem or about accelerator physics.

And his PhD advisor, I've never done. gonna i never pronounce this name correctly rudolph pyrol yeah yeah it doesn't matter the point is well-known physicist another student of bore um or or colleague of bore a student of heisenberg uh said you know it basically gave him a look and said why don't you give a talk about accelerator physics and so he just he sort of left yeah quantum foundations aside for a while and then finally in the mid-1960s he gets a chance to think about these things. And he sits down and looks at von Neumann's proof, which is finally available in English,

along with a couple of other proofs that are sort of related. And he said, you know, I looked at von Neumann's proof and it fell apart in my hands. It's not just wrong, it's silly. It clearly doesn't work. And so he writes... But was it that he didn't... He made a mistake in the proof

for just didn't prove the thing that people were saying. He didn't prove the thing that people said who proved. And he also didn't prove the thing that he thought he'd proven, right? You know, this proof shows up in Von Neumann's textbook, quantum mechanics textbook, which is a really, you know, incredible intellectual work with this one flaw in it. But in that book, Von Neumann makes it clear that this is how he's thinking about it. And it's not correct.

He hasn't proven what he said. My impression was, again, I forget where. from your book that Einstein, who did speak German, had seen von Neumann's book and was at least skeptical of this claimed proof. You know, I didn't... And he talked about it to Bohn. Yeah. There are stories about that, and I'm not sure, like, the stories about Einstein's awareness

of von Neumann's proof are not particularly well-sourced. Okay. So I didn't put them in my book because I didn't want to get... Yeah, exactly good. Yeah. And then, of course, people attacked me from not putting them in my book. because no one's ever happy. But the point is, yes, Einstein may have been aware of it.

He may not have been aware of it. But even if he was aware of it, he was skeptical of it. But the point is, Von Neumann's proof didn't prove what von Neumann, and especially a lot of other people, thought it proved. And so Bell works on it and looks at that proof and these other proofs that are sort of like it and shows, no, they don't rule out hidden variables. That's not what they do.

they do this other thing. And Greta Herman knew it. Yes, that's right. Greta Herman, a mathematician and philosopher and student of Emmy Noter, pointed out the problem with von Neumann's proof just a few years after he published it in 1935. And nobody listened to her. Yeah, nobody got. Yeah.

A variety of reasons, probably including the fact that she was a woman. There you go. But Bell independently rediscoveres these problems, also discovers the problems in similar proofs that have been published since, publishes a paper basically saying, look, these proofs don't do what you think they do. Hidden variables are still on the table. They just need to meet these requirements. And then at the end of the paper, he says, but there's still the question about, you know,

theories, hidden variable theories, whether they need to be a little. like booms in that they need to have this non-locality. That's an open question which somebody should answer. And so then he starts working on that immediately afterward. Right. And then he answers it. And he says, no, this non-locality, it's a fundamental feature not just of hidden variables, but of any theory that's going to reproduce the results of quantum mechanics with the

exception of theories that break something even more fundamental. Like many worlds. Like many worlds. Yeah. So basically, if, Experiments have definite outcomes. Yes. If experiments have definite outcomes and there's not some vast conspiracy going back to the beginning of time.

Super determinism. Yes, exactly. Just in case the audience does know the buzzwords. Yes. Let them in on that. Exactly. So those are pretty much the only two ways out. Now, people are definitely not going to be happy with me for saying that.

But yeah, you know, you'll sometimes hear people say, no, you can say. save locality if you get rid of the hidden variables. That's not true because then you're still left with Einstein's EPR argument. Then you'll hear people... Like you already said, Bell's theorem and his argument wasn't really about hidden variables. That's right. It was about there's no way to reproduce quantum mechanics without spooky action at a distance. Yeah, exactly.

That's exactly right. And, you know, you'll hear people say, well, you can save locality if you give up realism. I have yet to hear a definition of realism that satisfies that, unless you're giving up the idea of things. In which case, sure, you can have locality. People do. People do. But then, you know, what does locality even mean?

Yeah. Yeah. So, yeah. So let's put ourselves where we are now. So it's like the 60s or 70s, most of the physics community has been ignoring the measurement problem of quantum mechanics. was Bome and Everett in the 50s, but even Bome sort of didn't keep talking about it a lot. He did other things.

I remember there's this quote from Yakir Ahronov, who was one of his students. And together they invented the Aronov-Bome effect, which is really, really important. Yes, it is. And someone asked him, you know, Aronov, did you ever talk to Bome about his theory? And Naharanov says, no, we only ever talked about physics. I hadn't heard that quote, but that seems pretty plausible to me. Yeah, I mean, he definitely, he told me that when he started working with Bohm, they had an agreement to not work on that stuff. I think in part because Bohm was worried about what impact that would have on Aronov's career and quite understandably.

Well, and there was even this infamous memo from the editor of the physical review saying, we won't even look at papers in foundations of quantum mechanics. Yeah, yeah, which someone later pointed out. Yeah, he said, we're not going to look at paper. and the foundations of quantum mechanics unless they propose a new experimental result or a new experiment that you can do. And someone pointed out, well, you know, if we had that policy 30 years ago, that would have forced you to reject Boer's reply to EPR. Yeah. Yeah. But yeah. It's a sign of the times, though. Exactly. Yeah. No, it was really bad. So yeah, in the 50s, we had Bowman Everett. In the 60s, we had Bell. Bell's paper is published. He doesn't hear anything about it for years.

part of this is because there's this weird story about where that paper and the other paper he did before that were published, which is a whole thing that we're not going to get into. But yeah, people just weren't paying attention. And then at the very end of the 1960s, Bell gets correspondence about this paper for the very first time from a graduate student named John Klauser at Columbia University who wants to conduct an experiment to test this particular set of outcomes. of quantum mechanics to see if Bell's proof holds about the world. Because basically what Bell showed was you can do an experiment, and if the experiment agrees, if the outcome of the experiment agrees with quantum mechanics, then you don't have locality. And if it doesn't agree with quantum mechanics,

then you can have locality, but also you've broken quantum mechanics, which is important. The experiment couldn't show that Bell was. as wrong, Bell gave us horns of a dilemma. Exactly, yes. Either there's spooky action at a distance, or quantum mechanics is wrong, or even worse things, like many worlds. Yeah, yeah. So you can experimentally figure out which horn were wrong. Yeah, either quantum mechanics is correct in this outcome, or we can have locality.

So you have to actually do that experiment, and Klauser wanted to do it. And so did a couple of other people. And so Klauser got together with a guy named Abner Shimoni at Boston University and a couple of other guys named Horn and Holt. And they wrote a paper, you know, sort of massaging Bell's result into a form that could actually be tested called the C-H-S-H-H paper after their initials. This is always an underappreciated part of the process of physics, turning the crazy things that they're. years do into something that can be experimentally probed. Or at least something that can be computed, right? But yeah, yeah, exactly.

So they do this. And then in the very early 70s, I think 71 or 72, Klauser, who at this point is a postdoc at Berkeley, along with another guy named Stuart Friedman, actually do an experiment to test, to test the predictions of quantum. Mechanics in this, in this situation, and they find that quantum mechanics works. Surprise.

Yeah, surprise. Exactly. Yeah. Pretty much everybody thought that it would. Klauser was not sure. Klauser really thought that it might turn out the other way. And if it had, he, you know, he would be even more well known than he already is. But, yeah.

But no, quantum mechanics survived, which meant that we couldn't. have locality with, you know, again, not in one world. Yes, not in one world, yes. And that's been, that idea of testing these things has been upgraded and carried forward to the present day, all sorts of more elaborate tests of Bell's inequalities. Exactly, yeah. So Klauser was first, and then in the late 70s, this guy named Alain Aspe, did a more, did a more detailed experiment testing, again, the predictions of quantum mechanics in these conditions

and found again that quantum mechanics worked. And Klausor and Aspe really had very different career trajectories from that point on. Klauser, when he did this, he was a postdoc. He didn't have a permanent position. And he had a lot of trouble getting a permanent position and ultimately never really did, even though he'd done, you know, this really impressive experimental work. So his career sort of suffered as a result of doing this work. Aspe had a permanent position before he did the work. Wise. Yes. And in fact, when he'd gone to John Bell to talk with him about doing this work, you know, Aspe met with Bell before setting out on the this experimental journey.

Bell wouldn't even talk to him about it until Aspe assured him that he had a permanent position because Bell was so worried about damaging the careers of young physicists. But Aspe did this experiment and then went out and gave a lot of talks about it. And Aspe is very good at giving talks. It makes a very big difference.

Yeah, it makes a very big difference. So he's very good at giving... Neil's Boer was very good at convincing people of his point of view. And Einstein, you know, know, for all his genius, kind of just expected people to go along with him. He was not that good at the sales pitches. No, he really wasn't. He was not a people person. Yeah, he was. Yeah, and, whereas Boer almost had to work with people to do his work. Einstein almost never worked with

people, or he worked with a very small group of people. He worked with people on the EPR paper, but then afterward he never talked to Podolsky again. Yeah, he did not like, he did not like how that paper turned out. And I really think that that the clearest versions of the EPR paradoxes Einstein thought about are in Einstein's later writing, where he really explained it much more clearly. But yeah. So Aspe was a big force in changing how the field thought about the foundations of quantum mechanics. Exactly, because he showed, hey, he made people aware that there was, you know,

at least one really nice experiment to be done in quantum foundations. and that in turn caused people to take a look at Bell's work, and then when they did that, all sorts of interesting things happened. Not only was there a renewed interest in quantum foundations, but this also drove the new field of quantum information and quantum computing. And to be fair, I do give people a hard time. The physics community, I give them a hard time for ignoring quantum foundations, but there is not only a feeling that there's more interesting things to be done,

but there was a feeling that it's impossible to make progress on that kind of question because it's more a philosophy question there's no experimental input, et cetera, et cetera. And that is one way of changing that is to do an experiment that has a big impact on this field. Exactly, yeah. Exactly, yeah, that's exactly right.

I mean, I think, you know, as I was saying before, if the attitude of the physics community was, it's very hard to make progress, and so I'm not going to work on it because it's really hard, that'd be one thing, that'd be fine. The problem is when you change that to this normative statement, when you say, oh, it's very hard and you shouldn't work on it. It's a bad idea to work on it, not just because you'll suffer professionally, but because that's not the kind of thing that we do as physicists.

And that's certainly endemic. Yes. So, in fact, let's, I guess there's two big things I still have to, I still want to ask you about. Sure. One is, despite all the bad mouthing we've done at the Copenhagen interpretation, It's sort of come back, or at least versions of it have come back in the form of these epistemic approaches to quantum mechanics. There's a whole subset of people who really, you know, get behind the idea that all we're supposed to be doing, all quantum mechanics purports to do, is to make predictions for experimental outcomes. Well, there are definitely people who believe that, and there are definitely people who support these epistemic interpretations.

epistemic meaning that the wave function is about our knowledge about the world rather than a thing in the world. But I wouldn't say that the people who support these epistemic interpretations are all people who say, no, we really, quantum mechanics is really only about the outcomes of experiments, and we shouldn't be doing more than that as physicists. I mean, someone we both know, Matt Lefer at Chapman University, he is certainly a supporter of these epistemic interpretations, but he is a scientific realist. He thinks that there is a world and there's stuff in the world,

and the job of physics is to go after that stuff. He just thinks that the quantum wave function isn't one of the things in the world. It's a statement about our knowledge. That's right. That's a very good clarification. Yeah. So we have this quantum wave function.

It's the thing that you can't get away without having in any version of quantum mechanics. Yes. And I think that's one of the few things everyone, There's a weight function. Yes. Schrodinger's equation talks about the evolution

of something. Yeah. But at least there's a quantum state. Right. There's a quantum state. Well, right. But then,

but amazingly we can't say in our best understanding of the world whether that thing is real or just a tool. Yeah. And so the epistemic folks want to say, it's just a tool.

It's just like a probability distribution. When you say that I've flipped a coin and I haven't looked at it yet. Yeah. So there's a 50-50 chance it's heads or tails. I can give a probability.

distribution to that, but there is a reality beneath it. And they want to make the wave function like that. Yeah. Yeah, I think that's right. There are people who think that, I don't know, there are positions that I, I don't know, now we're getting back to the subject of people being angry with me. There are people who hold positions that are extremely Copenhagen-like, who will say, no, the wave function is a statement of our knowledge. and there isn't a thing underneath it. Well, and proudly so, right?

There are people who identify themselves as Copenhagen supporters, not just because there's nothing better, but because that's the right answer. Exactly, yeah. And when you push them on, what do you mean by Copenhagen, you get a variety of interesting answers,

and one of the things that happens is you get them sort of jumping between mutually contradictory positions, which if you can pull that off, is a really effective rhetorical move because it turns out that anything follows from a contradiction. So you can always answer any question that you've been given.

You just have to contradict yourself. So cubism is an example of an epistemic theory. It is. Do you understand cubism well enough to talk about it? For the audience, this is capital Q, capital B, ism. So quantum basianism.

Yeah, although they now say that that's not what it stands for and it's not clear what it does stand for. It's just a name. Yeah. So I think that this is where I'm going to get people mad at me for my book, because I tried to be, you know, I'm very pro-everate, pro-many worlds. I tried, as I said in the book, to be fair but not balanced.

Yes. So I certainly gave all of the good lines to Everettian quantum mechanics, but I tried to say correct things about the other interpretations. And cubism or epistemic approaches more generally are where the chances are greatest that the proponents of those theories will not think I'm being fair. to be fair, but I just can't figure out what they're saying. So, speaking of people being mad, I was originally planning to have a chapter in my book about epistemic theories and then my editor started yelling at me for being way over word count,

which I was. And I ultimately decided, you know, this is a book about the history of quantum foundations and how we got from where we were to where we are. And these epistemic interpretations, or as I call them in my book, information-based interpretations, because I try to use less jargon. No, that's good.

You're probably smart choice. Yeah. I don't know that they like it, but whatever. They're newish, right? They certainly have Copenhagen-ish DNA, but they are mostly things from the 1990s and later. They're young and being developed. Exactly.

And so... Yeah, exactly. And so I decided, oh, that means that I can get away with not discussing them a great deal because we haven't seen how they're going to play out yet. And, you know, if you're writing a history book that tries to go up to the present day, the hardest part is always going to be the last 15 to 20 years. And so I just kind of... We haven't yet decided what history says. Exactly, yeah. So I do mention them in my book, but I don't go into it in a great deal of detail.

And I talked with Matt about this and he said, yeah, that seems like a perfectly reasonable move. However, some other sci-epistemic people and some cubists or cubists, whatever, I'm bad at pronouncing things, are not happy about that and are also not happy with how I present bore in my book and, you know, whatever. But I have to say, I don't think that I really understand their position terribly well either. And that could be me, but I'm not sure that it is. I have tried quite a bit to understand it, although once I realized that I wasn't going to be going over it in great detail on my book, I stopped trying quite as hard. Yeah, because I was working on the book. But I have since tried some more. and and I'm actually, I'm going to have a chance, I hope, later this year, to sit down and talk with David Merman, one of the Cubists again.

Yeah. But I did talk with him. I had two long conversations with him while working on my book. He's someone I know from when I was in college, because he's at Cornell and that's where I went for college. And he's the aforementioned professor who told me, you know, gave me the bad news that, no, there's not a different translation of Boers paper. So yeah, David Merman is a lovely guy. He and I disagree about quantum mechanics, and I'm not sure that I understand his position. I am not sure what to make of cubism. Okay. That's fine. Yeah.

That's perfectly fair. Probably the most prudent thing you can say. I think that's right. Yeah. Yeah. But is it a, the other big point I wanted to give us a chance to talk about is, is the very fact of the existence, the resurgence, the renaissance of people trying to make something like Copenhagen respectable. Is it a reflection of the fact that quantum foundations more broadly are becoming slightly more respectable in physics? I mean, you still don't see, look, Caltech and Harvard and Princeton,

you're not going to hire physicists who study the foundations of quantum mechanics as, you know, senior faculty members. But maybe with not only the experiments in quantum optics and so forth, but also interest in quantum computing, quantum information, it's become a little bit less objectionable to worry about the foundations of quantum mechanics. Yeah. I mean, it definitely has become less objectionable. I mean, you know, you've talked with David Albert about this. things are certainly not the way that they were when he was in graduate school, right? You know, when I was in undergrad, I was curious about these things, and I had some professors saying, why are you asking these questions? But there was also David Merman who said, yes, ask these questions. And, you know, my PhD advisor is certainly not someone who spends time

thinking about these things, even though he's a very, very, very good physicist and a very smart man. but he doesn't mind that I think about these things. He just would have minded if I had spent time doing that rather than doing my research when I was in graduate school, and I didn't do that. So, yeah, I think that part of it is just, you know, people look for new options, right? People come into a new field or come into a newly resurgent field

and want to do something new, which is completely understandable. I also think some of it comes from an understanding on the part of people who are sympathetic to the Copenhagen interpretation that if they want it to survive, they can no longer ignore the competition. So for many, many years, the strategy was, what all? alternatives, right? There are no alternatives. I did at one point. I'm on the Colloquium Committee, Caltech, and I suggested getting a talk on BOMian mechanics. And I was swiftly slept down with a withering gaze, if that's a mixed metaphor that I can get away with.

So we're not quite there yet. Yeah. Situation might be improving a little bit. Yeah, yeah. I think, I think that's right. I mean, on the one hand, sure, that's true. On the other hand, people have been inviting me to give physics colloquia at, you know, some pretty good places. Like I gave talks, it wasn't a colloquium, but it was a public talk sponsored by the Harvard Physics Department. Cornell's invited me back.

Michigan's invited me back. Granted, that's because I went to both of those places. Michigan for my PhD. But still, those are good schools. They're good physics departments. And other departments that I have no affiliation with have also invited me. And you did not get tomatoes thrown at?

I did not get tomatoes thrown at me. I thought I was going to get tomatoes thrown at me, and I didn't. You know, I gave a talk at Berkeley Lab, which is, you know, almost in my backyard and nothing bad happened. And they knew what I was coming to give a talk about. You know, I made it very, very clear in the title and abstract. You know, I was not saying, you know, I'm not a partisan for any particular interpretation. I was just saying, hey, the measurement problem is a thing. And it's an important open problem in physics. That doesn't mean that everybody has to work on it any more than anybody, then everybody has to work on any other open problem, right?

We wouldn't want that. But you should be aware that it's an open problem. The same way that everyone's aware that we don't have a theory, you know, we don't have a definite, well-accepted theory of quantum gravity, right? That's a well-known open problem, even if you don't work on that. And relatedly, maybe, in fact, part of the reason why people have not been too much in favor of thinking about quantum foundations, is it has the aura of philosophy about it. Yes.

And for those of us who think it's an important problem, that's a good thing. Yeah. I mean, it's been probably that in statistical mechanics, arrow of time type stuff, the foundations of quantum mechanics are the area in which the philosophers have in some sense carried the torch for a while as physicists have been ignoring things. Yeah, yeah, I think that's right. I mean, the whole disciplinary split between physics and philosophy is a pretty modern invention. Um, you know, we used to call scientists natural philosophers, right? Einstein and Bohr would not have understood it.

Exactly. Yeah. I, you know, it used to be that that physicists generally had a pretty good schooling in philosophy and certainly didn't have outright contempt for it. And in less than a century, we've gotten to a point where many well-known scientists and physicists do have open public contempt for philosophy. And, you know, I do talk about that a little bit toward the end of my book. I'm really not quite sure why that happens. I mean, I've heard it suggested that it coincided with the shift in the center of physics from Europe to the United States. I think that that's correct. And I think that there's certainly... Americans have always been more down-to-earth, practical folk. Yes.

None of this abstract nonsense for us. We're going to build things. That is absolutely true. But it's also not true that, you know, there are no American physicists who have, you know, philosophical inclinations. There always have been some, right? It's, I think there's a lot of different sociological things that went into it. World War II not only shift at the center of physics to the U.S. It also, you know, created the era of big science. And that certainly had something to do with it. But I'm still sort of puzzled.

you know, you get, you get physicists saying these things about philosophy. And I don't think, you know, sure, we physicists have a deserved reputation for being arrogant when it comes to looking at other fields. But I don't think that you would get a physicist, you know, just saying, I don't understand why anybody does, I don't know, sheet metal production, right? that just seems like a silly thing. And anybody who studies best practices and that is just wasting their time, right?

I don't know anything about sheet metal production, but I do know that it's probably good to do it in a way that people don't get hurt, right? Because when you're manufacturing anything, people can get hurt. That's why I'm not an experimental physicist. But... Well, I think you said, I forget whether it was in your voice,

in your book, or whether you were quoting someone, but there was this wonderful idea that part of the reason might even Bell, who said part of the reason for the rejection of philosophy and foundational questions more generally was that most physicists think that if they would just spend 20 minutes thinking about it, they could figure it all out, they just haven't found the time yet. That is indeed Bell. Yes. Yeah, that's exactly right. Yeah, no, he was a really, really good writer and speaker. Well, I hope that things are getting better. Well, you know, we're on the same side in terms of

what would qualify as better, but I do think that slowly, gradually, it's getting there. Your book, I think, definitely had a salutatory effect. Hopefully, mine does. And we're looking forward to whatever book you end up writing next. Thank you. Yeah, so am I. Adam Becker, thanks so much for being on the podcast. Thanks for having me.