In this episode, I chat with the author of the new book, "Quantum Mechanics: A History of Quantum Physics" about the history of quantum mechanics and quantum theory. We talk about what it means to be a quantum physicist, why it's important to understand quantum mechanics, and why we should all be asking questions about what the world is really about. And we talk about why we don't know what's going on inside a smartphone, and how we can get to the bottom of it. It's a great episode, and I hope you enjoy it as much as I did writing it. You can expect weekly episodes every available as Video, Podcast, and blogposts. Please don't forget to subscribe and comment to stay up to date with what's happening in the world of science and technology! Timestamps: 1:00:00 - Why do we know so little about quantum mechanics? 4:30 - Why does quantum mechanics exist? 6:00 Why is quantum mechanics important? 7:20 - What does it have to do with reality? 8:40 - How did quantum mechanics come about? 9:15 - What is it like? 10:15 What are we supposed to know about it? 11:40 12:10 - Is it a black box? 13:20 14:30 15:10 16:10 Why does it matter? 16 - Why is it important to us? 17:00 Is it important for us to know what is going on in the truth? 18:00 | 17:30 | What are our job? 19:10: How can we make predictions? 21:40 | Is it possible? 22:10 | What is the meaning of reality Is it real? 25:00 // Is it really? 26:30 Is quantum mechanics a blackbox? 27:30 Can we really know what we should know? ? 29:30 Are we really trying to understand it yet? 35:00 Do we know what it is? or do we need to know it yet ? 35, 36: Does it matter what it matters? 32:00 Can we know it s going on? 33:00 What do we really understand it? 35:20 | What do they really mean? & so much more? 31:00
00:00:25.000And there was a lot of backing up and trying it again and backing up and trying it again and like going over paragraphs and trying to figure out exactly what it means.
00:00:34.000But it's really excellent and really perplexing at the same time.
00:00:41.000And you know, there are different styles when it comes to writing popular books.
00:00:45.000I think there should be different styles.
00:00:46.000And my particular style is Look, it's not going to be a breezy page-turner.
00:00:53.000But if you read it carefully, like, there's not prerequisites.
00:00:56.000You don't have to come into it as an expert.
00:00:58.000What you have to come into it is someone who's willing to sit and think about every paragraph.
00:01:03.000And then hopefully it will be rewarding and you'll truly understand what's going on after doing that.
00:01:07.000Well, it is rewarding because it is fascinating.
00:01:10.000And the history of quantum physics is also pretty fascinating because I've always wondered, like, how did anybody even want to come up with this stuff?
00:01:19.000And the fact that it was so long ago, the beginnings of it were in the 19th century?
00:01:24.000Well, 1900 is the typical, literally that year, the turn of the century when Max Planck first got the first hints of it.
00:01:31.000And then, yeah, it took another 27 years to put it into final shape.
00:01:35.000Now, for regular people that don't have a background in physics, the whole idea behind it is so bizarre.
00:01:46.000It's like, why would anybody try to figure out something that – one of the things that you said that's really interesting is that you – Quantum physics is used all the time.
00:02:00.000It's used with exact calculations, but yet we don't really understand it.
00:02:08.000Yeah, no, that's the main message of the book, really, because physicists, of course, do quantum mechanics every day, whether it's, you know, straightforward quantum mechanics, quantum field theory, quantum information, quantum computing.
00:02:18.000Clearly, we're pretty good at it, you know, like transistors and lasers depend on quantum mechanics.
00:02:23.000The sun shining, figuring that out depends on quantum mechanics, the Higgs boson, etc.
00:02:28.000So to claim that we don't understand quantum mechanics is a little bit weird.
00:02:32.000But then we have quotes from people like Richard Feynman saying nobody understands quantum mechanics, right?
00:02:37.000And so if he says that, then there's some authority behind it.
00:02:40.000And the reason is what we have is sort of a black box, right?
00:02:46.000I think what I said in a New York Times article I wrote recently is physicists understand quantum mechanics in the same way that someone who owns a smartphone understands the smartphone.
00:03:44.000Yeah, and I think – and in some sense, that's fine.
00:03:48.000Like most of us don't need to know what's going on inside the smartphone to use it, but somebody should know, right?
00:03:55.000And my argument in the book is, look, 500 years from now, when historians write the history of 20th century physics, they will say two things.
00:04:05.000One is – My god, these people were so brilliant and creative to invent quantum mechanics and then they were so afraid to really take it seriously and try to understand it.
00:04:18.000Like they said, like, stop asking questions about the meaning of reality and what the world is doing.
00:04:22.000In my mind, what physics is all about is understanding reality and what the world is doing.
00:04:28.000It's not just about making predictions.
00:04:30.000Making predictions is good but we do that, you know, mostly because we're curious about what the world is doing.
00:04:36.000Well, for people outside the world of academia, when I read someone like you saying that you were discouraged from pursuing this, and you were literally told that you should be pursuing your work in cosmology and gravitation,
00:07:05.000We found gravitational waves, the microwave background, many, many things.
00:07:09.000But they were all predicted decades ago, right?
00:07:12.000So progress is driven by being surprised and it's been a long time since we've been surprised.
00:07:17.000So some people including myself say, well, One of the things to do in that situation is to take a step back and re-examine the foundations.
00:07:24.000Maybe we can take a broader look and think that we're walking down the wrong path.
00:07:29.000Now, for people that don't have any background in physics, there's a bit of an issue with public perception.
00:07:38.000And one of the things about public perception is films like What the Bleep that sort of throw this sort of cultish monkey wrench into the, you know...
00:07:48.000Well, quantum physics is weird enough as it is without adding – that movie was literally created by a channeler, right?
00:07:58.000A friend of mine, David Albert, who is one of the leading philosophers of physics – and I should also give credit to philosophers here because they have been taking quantum mechanics seriously longer than the physicists have, to be honest.
00:08:08.000So David is one of many people who got a PhD in physics and then switched to philosophy because he cared about – Matthew Feeney But
00:09:54.000And he gave a talk and he said, look, there's two things you can do when you are faced with fundamental puzzles of reality.
00:10:02.000One is you can face up to what the world is trying to tell you and you can accept it and take it as what it is no matter what you like.
00:10:09.000The other is you can choose to tell a flattering story about yourself.
00:10:15.000And the people who made this movie have decided that the mysteries of quantum mechanics are really stories about how they are powerful and have influence over reality and so forth, but it's all nonsense.
00:10:25.000And the punchline is the audience loved it.
00:10:29.000They went nuts because what they wanted was a guru of some sort and like he was just as good a guru as anybody else.
00:10:35.000So, you know, he had a better story to tell.
00:10:40.000I mean, I think that quantum mechanics, I've said before, is of all the theories in the history of science, the most easily distorted and misrepresented in the popular mind.
00:10:50.000Well, you've done an amazing job in this book of trying to boil it down for dummies like me, but it's hard!
00:10:56.000It is a complicated and insanely nuanced subject.
00:11:43.000It's just so hard to correctly talk about quantum mechanics, right?
00:11:47.000If you were Isaac Newton, before there was quantum mechanics, there was classical mechanics.
00:11:51.000And basically, quantum mechanics and classical mechanics are the only two big frameworks that have ever existed in physics.
00:11:57.000You know, classical mechanics was so good that everyone thought that was just right and it was all a matter of filling the details until quantum mechanics came along and changed things.
00:12:05.000In classical mechanics, an electron is a point.
00:12:08.000It has a position, a location in space, and it has a velocity.
00:12:41.000Just like regular physics, there's a thing, the wave function, it obeys an equation, the Schrodinger equation.
00:12:45.000You can predict what's going to happen next.
00:12:47.000But the weird thing about quantum mechanics is that there's a whole separate set of rules for what happens when you look at the thing, when you observe it, when you measure it.
00:12:56.000That's where things get squirrely with people describing it.
00:13:19.000This is what is called the measurement problem of quantum mechanics, that the rules we teach our students at Caltech or anywhere else when we teach them quantum mechanics in their sophomore year of college, the rules say when a system is observed,
00:13:35.000when it is measured – Its state, its wave function changes dramatically, suddenly, and unpredictably.
00:14:10.000It's like a little spinning top, except when you measure the spin, you can sort of send the electron through a magnetic field and it will get deflected either up or down, depending on whether it's spinning, spin up or spin down.
00:15:46.000So the act of sending it through these things where it makes it vertical or horizontal, what is happening to it when it's going through these things?
00:15:56.000So in quantum mechanics, what we say is that it's not that we don't know whether the electron is spinning clockwise or counterclockwise.
00:16:39.000Just like the cloud that you have for the electron's position, when you look at it, you see it at a location.
00:16:45.000So another way to make the same argument is Take a little piece of – I have a nice little image of this when I give talks, a little piece of uranium.
00:16:54.000So it's a radioactive little chunk of metal and you put it in a bubble chamber.
00:17:01.000So it is emitting radioactive particles and you detect the particles.
00:17:05.000You can see a little streak of motion when the particle leaves the uranium, okay?
00:17:10.000Well, like I said, when you're not looking at it, this electron is supposed to obey an equation, the Schrodinger equation.
00:17:16.000And you can ask what the prediction is.
00:17:18.000When a radioactive nucleus decays and gives off an electron, what is its wave function going to do?
00:17:25.000What is the wave function of the electron going to be?
00:17:27.000And the answer is it goes off in a spherical wave.
00:17:30.000It goes off in all directions at once.
00:17:54.000It can go out in higher energy states.
00:17:56.000But the point is, it's not going out in a straight line.
00:17:58.000But when you look at it, you see a straight line, right?
00:18:01.000That's the fundamental mystery of quantum mechanics, that how we describe the thing when we're not looking at it is different than what we see when we look at it.
00:18:09.000So when you're in pursuit of an understanding, a deeper understanding of quantum mechanics, When you're thinking about people from the 1900s that are just sort of basically getting the first steps going to understand this stuff,
00:18:27.000when you're talking about this lack of funding and the lack of encouragement for people to pursue quantum mechanics, you strongly feel like there are answers to these questions.
00:18:39.000That we just need better tools and a better understanding, better equations, more time.
00:18:45.000Yeah, me and Einstein think this, right?
00:18:47.000So Einstein is one of the secret heroes of the book because he has this reputation as someone who just couldn't quite accept quantum mechanics.
00:18:54.000The title, Something Deeply Hidden, is a quote from Einstein when he was talking about when he was a kid and he had a compass, right?
00:19:01.000And he was given his first magnetic compass and he could rotate it this way and that way.
00:20:31.000So you're secretly treating yourself as a classical thing when you make that measurement, but you really should be treating yourself quantum mechanically, right?
00:20:40.000And the other thing is something that Einstein invented, namely called entanglement.
00:20:46.000When quantum mechanics says there's a wave function for a system, it doesn't say there's a separate wave function for every particle, right?
00:20:53.000It says that there's only one wave function for the whole universe.
00:22:07.000So there is one part of the wave function that says the electron was spinning clockwise and you measured it spinning clockwise.
00:22:14.000And there's another part of the wave function that says the electron was spinning counterclockwise and you saw it spinning counterclockwise.
00:22:22.000Like, that far, it's not controversial at all.
00:22:25.000That's clearly the prediction of the equations of quantum mechanics.
00:22:28.000But everyone else said, well, That means that I'm some weird combination of I saw it spinning one way and I saw it spinning the other way, but I've never felt that way.
00:22:37.000When I look at real electrons, I see them one way or the other.
00:22:43.000The wave function must somehow collapse.
00:22:45.000And Everett said, no, what you're missing is there's now two separate worlds.
00:22:49.000Both of those part of the wave function are real, but they're different worlds.
00:22:53.000They will never interact with each other again.
00:22:55.000What happens in one part of the wave function will not affect what happens in the other part.
00:22:59.000So now there's a version of you that saw the electron spinning clockwise, and there's another version of you that saw it spinning counterclockwise.
00:23:06.000And that's just taking seriously the prediction of quantum mechanics.
00:23:10.000It's not adding any extra stuff, any extra worlds, anything like that.
00:23:35.000Do you think of yourself as this quantum being that's existing in this super state?
00:23:41.000So, I mean, there's a couple of answers to that.
00:23:42.000One is, you know, sure, if I think about it, like, I really do believe it.
00:23:46.000You know, I have a chapter in the book, which my editor resisted at first, but then he let me get away with it, which is a dialogue.
00:23:53.000Matthew Feeney between a young philosopher and her father who is a physicist and the father is skeptical about all this philosophical nonsense and she tries to explain how many worlds works to him.
00:24:04.000At the end, his last question is, do you really believe this?
00:24:10.000Look, that's a perfectly good question.
00:24:13.000It's a very respectable question because it is Many worlds – it's not crazy or weird or bizarre, but it's certainly very, very far away from our everyday experience, right?
00:24:24.000So what it's asking you to do is to say, I have these equations.
00:24:29.000They are really, really good at fitting what I do observe in the world and making predictions.
00:24:36.000I can build the Large Hadron Collider, et cetera.
00:24:41.000I will take them seriously even for things that I can't directly observe because they're the best equations I have, right?
00:24:47.000Until a better set of equations come along, I will believe these equations.
00:24:50.000And the implication of that is, yeah, there's a whole bunch of worlds, like a huge number, like a real, you know, giant humongously, unimaginably big number, maybe an infinite number, maybe finite, we don't know.
00:26:11.000Everyone, you know, believe me, the joke about how certain political choices imply that we're living in the wrong branch of the wave function has been made many, many times, right?
00:26:21.000It's not that your choices create different universes.
00:26:24.000Different universes get created and maybe you're different in them by a little bit.
00:26:28.000In fact, I'd like to point out there is an app you can download if you have an iPhone called Universe Splitter, which will branch the wave function of the universe for you.
00:26:36.000And then if you agree ahead of time to do one thing in one branch and another thing in another branch, then there will be multiple copies of you who are living different lives.
00:26:44.000Then you can deal with that and your therapist however you like.
00:26:47.000But what is the application exactly doing?
00:26:50.000What it's doing is basically a version of measuring the spin of an electron.
00:27:05.000Yeah, and so what you can do, basically it sends a signal to a lab that coincidentally is located in Geneva, Switzerland, but has nothing to do with the Higgs boson or anything like that.
00:27:15.000They send a single photon down a pipe to what's called a beam splitter.
00:27:19.000So the wave function of the photon goes 50-50.
00:28:18.000So people will be paralyzed by analysis.
00:28:21.000That's why you should act the same as if you just lived in one universe, because you can never talk to the people in the other ones.
00:28:28.000But now, let's hit the brakes on the woo again, because people would like to believe that there are – I mean, are there an infinite number of yous existing – At the exact same time,
00:28:44.000making various choices which send you off into different directions?
00:28:48.000So, number one, we don't know if it's infinite number or just really big.
00:28:51.000But there's certainly a really, really big number.
00:28:53.000It's big enough to be, you know, big enough for whatever you want.
00:29:25.000It's a mind-bending thing, but it's a straightforward prediction of the equations and it doesn't affect our lives.
00:29:30.000There's no rule that says to be a moral person, to be a good utilitarian and make the world happy, knowing that the wave function is branching into multiple copies, I should act differently somehow.
00:29:41.000It's exactly the same as it would be in the ordinary world.
00:29:44.000Trevor Burrus And you are the ordinary world no matter how many copies of you there are or how many versions of you there are.
00:29:54.000There's no essence of you that is traveling through one of the copies, right?
00:29:58.000Like all of these people are separate people.
00:30:01.000So I use the analogy, it's like identical twins.
00:30:04.000They were the same zygote or whatever, and now they're different people, okay?
00:30:09.000Like you're you now, and if you hit the button and branch the wave function, there'll be two different people, both of whom used to be you, but they're not the same person anymore because different things happen to them.
00:30:19.000Now, when people think about the concept of quantum mechanics and the way you're talking about describing things in the micro and the macro, you think of your existence itself very similar,
00:30:34.000in a very similar manner, the way you think of electrons, the way you think of things being quantum, is that you are a combination of all these quantum things.
00:30:44.000So you don't operate in some sort of static state that's very, like here and now and carbon and you can put it on a scale and it'll never change.
00:31:19.000And like I said, you know, many worlds is one respectable version of quantum mechanics.
00:31:24.000There are other respectable versions, more respectable than the textbook presentation.
00:31:29.000But they all – all the other ones somehow lean on our classical experience.
00:31:34.000And the textbook version certainly does.
00:31:36.000It says like you're a classical person observing a quantum mechanical system and so forth.
00:31:40.000And Everett, when he was a graduate student, he had arguments across the ocean with people in Copenhagen who tried to push their way forward.
00:31:49.000And he's like – Matthew Feeney Obeying the rules of quantum mechanics and the
00:32:19.000conventional Copenhagen theory is just not up to it.
00:32:23.000When I was reading it, I was thinking, a thought came across my mind that it's almost like the human brain is a radio that's picking up a distant signal but getting better and better at tuning into it all the time.
00:32:38.000And that we are thinking of ourselves in this very limited, primitive, biological way, because that's how we evolve.
00:32:45.000But slowly but surely, through people like you, and through work on this stuff, we're gaining this more comprehensive view of what reality is itself, and that we're experiencing these stages of comprehension.
00:33:00.000And that's why, again, going off of what you're saying about your being...
00:33:34.000Yeah, but no, I like the analogy very much because the human brain did not evolve to understand quantum mechanics.
00:33:40.000It didn't evolve to understand science at all.
00:33:45.000Some of my best friends are human beings, but we are wonderful bundles of impulses and heuristics and shortcuts and ways to rationalize our behavior and stuff like that.
00:33:56.000And the idea that we can aspire to be logical, And to develop theories and reject them and to develop theories that are very, very far away from our everyday experience is a relative latecomer on the evolutionary scene and we're still not really good at it.
00:34:13.000We're getting better at it and this is part of it.
00:34:15.000You know, quantum mechanics is the biggest challenge that we have in physics to our intuitive understanding of the world and so there's a question How should we try to understand it?
00:34:26.000How much of it should we lean on our intuitive understanding?
00:34:28.000And how much should we just accept that the world is fundamentally super-duper different?
00:34:32.000I think that's a perfectly good question.
00:34:34.000I'm not trying to prejudice the answer one way or the other.
00:34:36.000I mean, our experience is limited, but it's all we have, right?
00:35:31.000The human understanding of the world we live in has obviously radically changed over the last 500 years.
00:35:37.000And if we continue to exist in this current state or a slightly better state as things move on, it's going to get better.
00:35:45.000But quantum mechanics and quantum theory to me almost seems like an ant trying to understand the choices on Netflix.
00:35:53.000It's like those choices exist, but the ant really lacks all tools.
00:36:00.000I mean, without people like you especially describing the computations and what's been done and what we currently understand, for a regular person with no background or even no knowledge of it, no one's ever explained it to them at all, it's almost outside of the realm of our capacity for reasoning.
00:36:39.000So a Turing machine, Alan Turing, the great – A computer scientist who broke codes and things like that.
00:37:02.000Like, anything you can ask, if you can do this problem, then you can also do that problem, and there's sort of a maximal hardness to problems, and so a Turing machine can do that problem, if you give it enough time.
00:37:11.000And there's some problems that are undoable, so no machine can do those, but the doable ones can be done on a Turing-complete machine.
00:37:17.000So in some sense, this is not a rigorous fact by any stretch, but I think there's an analogy with human reasoning.
00:37:24.000Like at some point, we're a little bit smarter than dogs and cats.
00:37:29.000But it's not just we're a little bit smarter, we're a different kind of smart.
00:37:35.000We can reason symbolically and abstractly.
00:37:38.000We can write things down and pass them down through generations.
00:37:41.000We can imagine futures in ways that they can't.
00:37:44.000So even though the number of neurons or the number of connections in our brain might not be that different between a human being and a chimpanzee, it's a different kind of reasoning that has been opened up.
00:37:54.000We've become capable of this kind of thought and I think that's enough.
00:37:59.000My idea is that we are smart enough to understand the laws of physics, whatever they turn out to be, quantum mechanics or something beyond quantum mechanics.
00:38:07.000And to the person on the street who's never learned anything about quantum mechanics, it is so different from how you experience the world that it seems bizarre and you do have to like read the same paragraph over and over again sometimes.
00:38:20.000But I think it is absolutely understandable if people make the effort.
00:38:24.000I don't think there's any person who can balance their checkbook but not understand quantum mechanics.
00:39:24.000When we talk about the Earth going around the Sun, forget about quantum mechanics, just do classical mechanics, Isaac Newton, Earth orbiting the Sun, okay?
00:39:42.000The Earth is made of something like 10 to the 50th atoms, okay?
00:39:47.000In principle, to tell you what the Earth is doing, I should tell you what every one of those atoms is doing, right?
00:39:52.000But I have no idea what every one of those atoms is doing.
00:39:55.000All I actually in the real world need to tell you to predict what the Earth is doing is to tell you the center of mass of the Earth, where it is and where it's moving.
00:40:04.000So, only using an incredibly tiny amount of information, I can make incredibly precise and accurate predictions.
00:40:11.000I have this enormous handle over what the world's doing, ignoring almost all the data that there is about the specific state of the world.
00:40:20.000So, that's emergence when you don't need to know almost anything about a system.
00:40:25.000You have certain very, very special high leverage pieces of information I think we're good to go.
00:40:46.000It's because Newton's laws of physics are a really, really good approximation that let you make predictions without knowing the quantum wave function of the car you're driving, right?
00:40:54.000And if you needed to know the quantum wave function of the car you were driving, it would be hopeless.
00:40:58.000It's just computationally intractable.
00:41:00.000So the world appears to us in a way that is very convenient in some ways.
00:41:06.000We need to know so little about the world to yet understand quite a bit of it.
00:41:11.000Otherwise, we couldn't get through the day.
00:41:13.000The idea that everything is in motion is also very difficult for people to wrap their brain around.
00:41:18.000You see a stationary rock on the ground, you think that rock is still.
00:41:31.000So relatively, in terms of the universe, everything is in motion in some way, shape, or form.
00:41:37.000Well, you know, there's a lot going on here, actually, because on the one hand, Einstein teaches us, you know, when you say something is moving, you have to say, with respect to what?
00:41:56.000There's also what I try to squelch in the book.
00:41:59.000One of the misunderstandings about quantum mechanics is the idea of quantum fluctuations, right?
00:42:03.000The idea that an electron sitting in the orbit of an atom is really jiggling around there and you don't know exactly where it is.
00:42:10.000That's not what quantum mechanics says.
00:42:12.000Like, if you're a good Everettian anyway, a good many-worlds person, there's a wave function to the electron and the wave function is sitting there not moving.
00:42:20.000It's really not changing appreciably over time.
00:42:23.000If you were to observe the electron, you would see it somewhere, and if you were to observe it multiple times, it would be in different places, so it looks to you like it's jiggling around.
00:42:31.000But when you're not looking at it, it's not jiggling.
00:42:34.000It's just sitting there quietly, according to quantum mechanics.
00:42:36.000So is this confusing description based on our limited ability to perceive?
00:42:41.000It's actually based on the fact that we inevitably attach a notion of reality to what we do perceive, right?
00:42:49.000So in quantum mechanics, what we perceive is different than what really is.
00:42:57.000I mean, how much more real could it be, right?
00:42:59.000The way that we describe, you know, I go on a rant in a whole chapter of the book, like, The Heisenberg uncertainty principle, that there's uncertainty to either your position or your velocity.
00:43:11.000You can't know both of them at the same time.
00:43:13.000It's not that you can't know both of them at the same time.
00:44:00.000But you and I are sort of macroscopically stationary, trying to sit here more or less quietly.
00:44:06.000But inside, there's a lot of churn going on, right?
00:44:09.000There's, you know, a lot of cellular biology.
00:44:11.000There's ATP is being created and destroyed.
00:44:14.000And, you know, signals are going from our brain and back and forth.
00:44:17.000And someone like Antonio Damasio, the neuroscientist, emphasizes this idea of homeostasis, that there is stuff going on beneath the surface, but it regulates our...
00:45:23.000So there is a weird thing called quantum immortality.
00:45:27.000I don't like to talk about it, but people hear about it, so I sometimes need to mention it.
00:45:32.000Max Tegmark, who is a friend of mine, a very smart guy, popularized this idea.
00:45:35.000He said, look, and it's a little bit macabre, sorry about this, a little bit weird, the experiment, but imagine you're playing quantum Russian roulette.
00:45:45.000So you have your universe splitter, okay?
00:45:47.000You have your app on your iPhone and you split the universe.
00:45:49.000And if it goes one way, you don't do anything.
00:45:52.000If it goes the other way, faster than you can react, a machine is activated that kills you instantly.
00:46:17.000The only version of you that survives is the one that was lucky enough to be in the branch where you didn't die every single time.
00:46:24.000So Tegmark's argument was that if you do this over and over again and you survive, You should take that as good evidence that the many worlds interpretation of quantum mechanics is correct because in other versions you probably just died, right?
00:46:40.000I don't think it's a good way to go through your life.
00:46:42.000I think that the reason why we don't want to die is not just that we will experience pain but that sort of But prospectively, right now, the idea of being dead in the future bothers me, right?
00:46:55.000Like if someone said, you know, you're going to die in that date, might be useful information, but I'd be sad, right, if that date was soon.
00:47:03.000And I think the same thing is true in the quantum immortality experiment.
00:47:06.000I don't buy the move that says – Well, in all the branches where you're dead, it doesn't matter because you're dead.
00:48:33.000It's therapeutic if you don't like all the other worlds.
00:48:35.000It's basically, you know, the equations are the same as many worlds except there's new equations and new stuff.
00:48:39.000So it complicates the theory by adding new variables.
00:48:42.000But the good news is it says only one of the branches of the wave function is real.
00:48:46.000I don't need to worry about the other ones.
00:48:48.000The problem is it's very hard – my particular problem is it's very hard to reconcile these ideas with modern physics.
00:48:55.000Like if you thought the world was made of individual particles, it would do okay.
00:48:59.000But these days we use quantum field theory and quantum gravity and things like that.
00:49:03.000And those more modern ideas are harder to attach hidden variables to.
00:49:07.000So hidden variables are an old idea, but I think that they're hard to make work.
00:49:12.000The other idea, which is more dramatic, a little bit more fun, is – Every single electron has a wave function, and it seems to you that when you observe it, it collapses.
00:49:22.000But maybe what's really going on is the following, that there's a random probability every second that every electron will just spontaneously collapse.
00:49:30.000So it's all spread out, but its wave function just randomly collapses.
00:49:47.000There's way more than 100 million electrons in this table.
00:49:50.000There's, you know, billions and billions and billions of electrons.
00:49:53.000So somewhere in the table, all the time, an electron is localizing at one particular position, and because that electron is entangled with all the other electrons, the table maintains a location in space.
00:50:05.000And this is called spontaneous collapse or GRW theory after the initials of the people who invented the theory.
00:50:12.000And the great thing about GRW theory is that it's experimentally distinguishable from many worlds because it says that if I have a collection of atoms, even if I'm not observing it, even if I'm not entangling it, one of the wave functions should spontaneously localize occasionally and that will heat it up.
00:50:27.000Energy is not conserved in this theory.
00:50:29.000So people are doing experiments to test this.
00:50:32.000So it's really, you know, legit experimental science.
00:52:00.000You get the feeling that atoms are mostly empty space because you think that really the electron is a point, and the wave function is just telling you where you might see it.
00:52:53.000In spontaneous collapse, it's all of reality but it obeys different equations.
00:52:57.000In hidden variables, the wave function is part of reality but there's also particles.
00:53:02.000In the other approach, which is called an epistemic approach to quantum mechanics, the wave function is just a way of talking about your personal knowledge of the world, your knowledge or lack of knowledge, your ignorance of the world.
00:53:15.000So your wave function is just a tool you use to make a prediction for what the experimental outcome is going to be, right?
00:53:22.000And that's more or less what we teach our students.
00:53:25.000And this approach says, don't bother about reality.
00:53:30.000What we should concern ourselves with is the experiences of agents who make predictions and update their probability expectations of the world.
00:53:41.000And so someone like that, if you ask them, you know, how is an electron located in an atom or how is an atom mostly empty space?
00:53:51.000I think if they're honest, they would say, don't ask those questions.
00:54:15.000Well, you know, it is part of the attitude that physicists have adopted that we use quantum mechanics but we don't try very hard to understand it.
00:54:28.000So, you can talk to plenty of physicists on the street and they will tell you to your face that understanding reality is not their job.
00:54:36.000And I think that's terrible, but they will say it.
00:54:39.000And so when you press them too much on questions like, you know, is the atom mostly empty space?
00:54:45.000You know, what happens when we make an observation?
00:54:46.000They just kind of get uncomfortable and say, no, you're asking the wrong questions.
00:54:50.000Let's ask questions about what will we see at the Large Hadron Collider if we smash protons together, right?
00:54:56.000And those are perfectly good questions, too.
00:54:57.000But I think that the what's really going on questions are also interesting.
00:55:01.000So because they don't care about these questions, they will often be sloppy in answering them, right?
00:55:18.000So even if you're a super-duper expert at solving the equations and making predictions, But understanding what's going on is a whole other activity that a lot of physicists don't try very hard to do.
00:55:30.000Trevor Burrus Now, how was all this stuff verified or argued?
00:55:35.000Like, say, if you're sitting down, you're having a conversation with someone who espouses a competing theory.
00:55:45.000I think that if everything were going along really, really well, we would be making experimental predictions and testing them.
00:55:54.000But I think the theorists have sort of dropped the ball here in the sense that the theoretical physicists should have, since the 1930s, been developing these alternatives like many worlds, hidden variables, whatever, and using them to make predictions.
00:56:33.000The experimenters are doing amazing things with lasers and atoms and learning about how to manipulate quantum systems at a delicate level.
00:56:42.000But the theorists have not given them sharp experimental questions that would really illuminate the foundations of quantum mechanics.
00:56:50.000So honestly, what it is, is a bunch of people get around a table and talk to each other.
00:56:54.000They're like, all right, I think that what happens when the wave function branches is this.
00:56:58.000So a typical question we'll try to address is...
00:57:02.000In ordinary quantum mechanics, we say, if I send the electron through one way or I send it through the other way, there's a 50-50 chance that I will see it go left or go right.
00:57:12.000And someone says, what do you mean 50-50 chance?
00:57:15.000Especially in many worlds where there's a 100% chance there'll be a world where it goes left and a world where it goes right.
00:57:22.000What is the meaning of the phrase, there's a 50-50 chance?
00:57:26.000What is the nature of probability in this game where everything is perfectly deterministic, right?
00:57:30.000So that's not the kind of question that you answer very easily by doing an experiment.
00:57:44.000Someone asked me just the other day because the book came out, Something Deeply Hidden, last week and I've been on book tour.
00:57:49.000So I was being interviewed and someone said, how many people do you think in the world would classify themselves as working on the foundations of quantum mechanics?
00:58:36.000The limited number of how many of you guys there are and gals there are out there, I mean, whatever the number is, when that spark gets ignited and other people start tuning into it, she was so excited that this was being discussed on a podcast.
00:58:51.000And she wanted to talk to me about it to say, you know, please have more people on.
00:58:59.000It does baffle me a little bit how difficult it is swimming uphill to get more support for this kind of thing.
00:59:10.000It is just an enormous privilege to be able to call your job thinking about the fundamental nature of reality, right?
00:59:19.000Like, you know, I gave my first book tour talk was last Tuesday, and I had dinner the night before with, you know, several philosophers of physics in the New York area, you know, from Columbia and NYU and Everett.
00:59:29.000And, you know, we're all friends, and we could talk about, you know, our cats and our cars, but every single word discussed at the table all night long was about the philosophy of physics.
00:59:39.000Is it because you guys work in isolation, essentially, and then when you get together, you're so pumped up to be discussing these things with like-minded souls?
01:00:26.000Like a physics department will generally say, yeah, we should have some people doing particle physics, some people doing astrophysics, some people doing condensed matter and solid-state physics, and then it becomes hard.
01:01:11.000Well, you know, okay, it's hard to do an experiment there, but it's an important question, right?
01:01:16.000And so you need patience, but also it's harder to make progress because it's easy to be trapped by your intuition, right?
01:01:24.000Like when it's just you thinking and trying to think hard and be rational and so forth, it's easy to fall into a trap of, well, this looks reasonable to me.
01:01:31.000And quantum mechanics doesn't look reasonable to anybody.
01:01:51.000I mean the things – so I was always a big fan of philosophy ever since I was an undergraduate and I discovered it for the first time.
01:01:59.000But when I was an undergraduate, my favorite philosophy classes were like the philosophy of morality or political philosophy, right?
01:02:06.000I took philosophy of science classes, but they seemed to be kind of dry to me because they were all about how scientific theories are constructed and chosen.
01:02:15.000You know, the structure of scientific revolutions is the famous book that everyone reads.
01:02:19.000People like Thomas Kuhn and Paul Feyerabend and so forth.
01:02:22.000Okay, that's interesting, but it's sort of meta-science, right?
01:02:27.000It's like how science is done, not how the world works.
01:02:29.000And it wasn't until, you know, circa 2000 that I discovered that there are philosophers of physics who are kind of really doing physics.
01:02:38.000You know, they're not asking how physics works, they're asking how the world works, but they're asking in a way that is comfortably located in philosophy departments and right now not so much in physics departments.
01:02:49.000There was a part of the book that shocked me because I had a ridiculous idea once and this idea was not my idea.
01:02:58.000Apparently LaPaz had a very similar idea as a thought experiment.
01:03:02.000I had an idea once that if one day there was a computer that was so powerful that it could accurately describe every single object on earth that we would be able to figure out the past.
01:03:16.000And LaPaz was saying that not only that, he proposed for the entire universe, like every single object, electron, everything in the atom in the entire universe, that you would not only be able to show the past, but also predict the future.
01:03:31.000So this is called LaPaz's demon, although he never called it that.
01:03:35.000Pierre-Simon Laplace was a brilliant guy.
01:03:37.000He deserves to be much more well-known.
01:03:39.000So I think I've mentioned his name in every book that I've ever written for totally different reasons.
01:03:44.000He helped invent probability as we currently understand it, for example.
01:03:48.000But yeah, so Isaac Newton came up with the rules of classical mechanics in the 1600s.
01:03:54.000But it wasn't until Laplace around the year 1800 that this implication of classical mechanics was realized.
01:04:00.000It's a clockwork universe, that the way classical mechanics works is if you tell me the state of a system right now at one moment, by which in classical mechanics you would mean the position and the velocity of every part.
01:04:13.000And you knew the laws of physics and you had arbitrarily large computational capacity.
01:04:18.000Laplace said a vast intelligence, okay?
01:04:21.000Then to that vast intelligence, the past and future would be as determined and known as the present was because that's the clockwork universe.
01:04:31.000Everything is fixed once you know the present moment.
01:04:33.000Now, quantum mechanics comes along and throws a spanner into the works a little bit.
01:04:38.000If you're a many-worlds person, Laplace's daemon is still possible.
01:04:43.000So if you know the wave function of the universe exactly, and you have infinite calculational capacity, you could predict the past and the future with perfect accuracy.
01:04:53.000But what you're predicting is all of the branches of the wave function.
01:04:57.000So any individual person inside the wave function still experiences apparently random events, right?
01:05:04.000So you can't predict what will happen to you even if you can predict what will happen to the entire universe.
01:05:14.000There's a lot of people pausing this podcast right now, just shaking their head like...
01:05:18.000You know, I wrote a little article that just appeared in Quantum Magazine, which, by the way, if anyone here is a science fan, Quantum Magazine is the best online magazine for science these days.
01:05:28.000They have really, really good high-level articles about all sorts of things.
01:05:32.000And so I wrote an article called, What is Probability?
01:05:36.000Because, you know, again, this is a philosopher's kind of question.
01:05:39.000Like, you know, physicists will just put it to use and get on with their lives.
01:05:42.000Philosophers will say, well, what do you really mean by probability?
01:05:46.000The traditional answer is if you're flipping a coin and you say it's 50-50, what you mean by that is that if you flipped it an infinite number of times, half the time it would be heads, half the time it would be tails.
01:06:20.000But we can easily say, well, I think it was an 80% chance that that's true, right?
01:06:23.000So this is called Bayesian probability, where rather than thinking of an infinite number of things going on, you're assigning a degree of confidence to your lack of perfect knowledge, right?
01:06:34.000Like, I don't know exactly, there's something, yeah, there's something going on, I don't know what it is, so I assign a probability.
01:06:41.000And just like the frequency that, you know, the credence, as we say, that you assign to these different ideas is a positive number, then all the credences add up to one, because something happened.
01:06:53.000So, in quantum mechanics, is probability more like frequentist probability or is it more like Bayesian probability?
01:07:00.000The answer is it depends on what your favorite version of quantum mechanics is.
01:07:03.000In one of these spontaneous collapse theories, it's very much like a frequency.
01:07:08.000Like, you know, you just – things happen randomly and it's purely objective.
01:07:11.000In something like many worlds – well, sorry, I should say in something like hidden variables – It's Laplace's demon all over again.
01:07:19.000So Laplace's demon doesn't work in a spontaneous collapse theory because the laws of physics are not deterministic.
01:07:25.000You don't know when things are going to collapse all by themselves.
01:07:29.000In a hidden variable theory, The hidden variables and the wave function evolve deterministically, but you don't know what the hidden variables are.
01:07:38.000So you can assign some probability to having them be different things.
01:09:06.000This is a rule called the Born rule after Max Born who was the physicist who invented it.
01:09:11.000So I mean read the book of course but like you said at the very start, the history of quantum mechanics is just so fascinating and hilarious.
01:09:20.000Schrodinger, Erwin Schrodinger of Schrodinger's cat fame – I think we're good to go.
01:09:57.000And it was Max Born, a whole other guy, who said, what the wave function does is you square it, and that's the probability of seeing something somewhere.
01:10:04.000Like, if the wave function looks like this, it's some spread out thing, there's very small probability over here and large probability over there because the probability is the wave function squared.
01:10:14.000And Schrodinger said like, oh my god, that's awful.
01:11:11.000Be a good advisor in the sense that, you know, challenge them intellectually and get them to do interesting things, but in a way that will lead to a productive career.
01:13:06.000And the same David Albert who appeared in What the Bleep, and we talked about quantum mechanics and the measurement problem.
01:13:12.000And, you know, he said – he put it really well.
01:13:15.000He said, like, if there's a figure from history who I would like to have dinner with, it would be Niels Bohr.
01:13:20.000And because, like, he was certainly an amazingly good physicist, very, very influential.
01:13:26.000But over and over again, super-duper smart people would get together and talk to Niels Bohr and come away spouting nonsense about the foundations of quantum mechanics.
01:13:37.000So somehow he had this magic charisma that worked in a bad direction to like make people just become crazy about quantum mechanics in a bad way.
01:13:46.000And that's part of the reason why we haven't dug into the foundations of quantum theory for so long.
01:13:52.000He was just incredibly charismatic in a weird way because he was a terrible writer.
01:13:58.000You know, there's this story where Einstein wrote this paper about entanglement and spooky action at a distance and Bohr responded to it.
01:14:06.000And everyone said – because by this time, 1935, people were already bored with the foundations of quantum mechanics and they didn't want to think about it.
01:14:13.000So if anyone said, well, what about Einstein's worries?
01:14:16.000They would just say, oh, Bohr wrote a paper.
01:14:46.000Like John Wheeler, who was Hugh Everett's advisor, was sort of an acolyte of Bohr.
01:14:52.000And he – there's sentences he said like, I never knew what people meant when they talked about people like Jesus or Socrates or Buddha until I met Niels Bohr.
01:15:25.000So, you know, part of the reason I wanted to write this book is it's very much like, you know, another thing I do is go around and talk about science and religion.
01:16:38.000Let's, you know, be embarrassed that the field of physics has not put its effort into it and make an effort here.
01:16:45.000And so maybe that will – so that's what my, you know, most ambitious hope for a book like this is that 20 years from now, there'll be a flood of young physicists who think this is really interesting.
01:16:55.000Yeah, well, the number, what would you estimate it would be currently?
01:16:59.000Like, how many people do you think worldwide?
01:17:00.000Yeah, it's certainly of order 100. That's it?
01:17:24.000Yeah, I guess, but still, that's stunning when you hear that it's somewhere around 100. Yeah, I mean, we have, here in California, we have CEQIN, the California Quantum Interpretation Network, which is a group of us, you know, the people we know in California who care about these issues and we need to talk about them,
01:18:26.000That's bad for physics in a big way because it's great that we had a theory that came true with the Higgs boson, but in some sense we learned from the Large Hadron Collider the smallest amount it was possible for us to learn.
01:19:14.000So we had good reason to think that there should be a bunch of other particles that you would discover at the Large Hadron Collider, and they weren't there.
01:19:22.000Meanwhile, we have very good reason to think that 25% of the matter in the universe is dark matter, 25% of the energy in the universe, and we had very good reason to hope that we could detect it by now in an underground laboratory, and we haven't.
01:19:35.000And it's there, but it's beyond our reach somehow.
01:19:38.000So it's just so hard to make progress under these circumstances.
01:19:42.000And meanwhile, we have big, cool ideas like string theory that are hard to connect to the real world.
01:19:48.000So this is the last third of the book to me is, you know, again, like I have my favorite ideas, but there's a bigger picture about what kinds of ideas we should pursue and how we should pursue them.
01:19:59.000So the last third of the book is Maybe we need to understand quantum mechanics to better understand quantum gravity and the theory of everything, you know?
01:20:07.000Like, how should we expect to understand quantum gravity if we don't understand quantum mechanics?
01:20:41.000So it's not only physics, but also philosophy and neuroscience and biology and math and computer science.
01:20:47.000There's a whole bunch of things in there that I'm not an expert on.
01:20:49.000I'm a big believer that people should talk about things they're not an expert on, but they should talk about them in some I don't understand everything here, so I will talk to some experts, right?
01:22:39.000There's a whole journey to saying, oh, this is important enough.
01:22:43.000I should dedicate myself to a week of my time to reading this book.
01:22:47.000And hearing people talk about it in an informal setting is both illuminating but also like, oh, yeah, there's ideas in there I really need to get to.
01:22:55.000So I'm a big believer in diverse ecosystems.
01:23:03.000There's all sorts of ways to get this information.
01:23:05.000Yeah, I think it's opened up the interest in a far broader group of human beings, too, because in having conversations like this with you or with, you know, the hundreds of people that I get to talk to on a regular basis, it sparks ideas in people that,
01:23:21.000you know, in their seemingly mundane existence maybe just would never get in there.
01:23:26.000And it allows these new areas of inquiry and new areas for them personally to go look into.
01:23:34.000And I get messages and I meet people all the time that tell me how much it's changed the way they view things because they've now been exposed to interesting information that's sort of sparked their Absolutely.
01:25:34.000Like where did I get that idea, right?
01:25:36.000And I think that despite all of the misinformation, et cetera, that's out there, if you are intellectually responsible and want to get things right, putting your ideas out there in public to be critiqued is a wonderful tool.
01:25:52.000So like it helps you figure out like what I do understand and know and what just were kind of vague ideas that somehow got into my brain for no good reason.
01:30:08.000I lug my little portable podcast studio around, so if I'm going to Boston in a few weeks, I'm going to try to get 10 people on the podcast.