The Joe Rogan Experience - Joe Rogan Experience #1352 - Sean Carroll

00:00:04.000 And here we go.

00:00:04.000 Hello, Sean.

00:00:05.000 Hey, Joe.

00:00:06.000 How's it going?

00:00:06.000 Thanks for being here again, man.

00:00:07.000 I really appreciate it.

00:00:08.000 So, over the weekend, I got into your book.

00:00:13.000 Yes.

00:00:14.000 Yes.

00:00:14.000 It's great.

00:00:15.000 Thank you.

00:00:16.000 I mean, I really appreciate someone like you who's trying to break down...

00:00:20.000 Quantum mechanics and quantum physics for someone like me.

00:00:23.000 It's very hard to follow.

00:00:25.000 And 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.

00:00:34.000 But it's really excellent and really perplexing at the same time.

00:00:40.000 Well, thank you.

00:00:41.000 And you know, there are different styles when it comes to writing popular books.

00:00:45.000 I think there should be different styles.

00:00:46.000 And my particular style is Look, it's not going to be a breezy page-turner.

00:00:53.000 But if you read it carefully, like, there's not prerequisites.

00:00:56.000 You don't have to come into it as an expert.

00:00:58.000 What you have to come into it is someone who's willing to sit and think about every paragraph.

00:01:03.000 And then hopefully it will be rewarding and you'll truly understand what's going on after doing that.

00:01:07.000 Well, it is rewarding because it is fascinating.

00:01:10.000 And 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?

00:01:19.000 And the fact that it was so long ago, the beginnings of it were in the 19th century?

00:01:24.000 Well, 1900 is the typical, literally that year, the turn of the century when Max Planck first got the first hints of it.

00:01:31.000 And then, yeah, it took another 27 years to put it into final shape.

00:01:35.000 Now, for regular people that don't have a background in physics, the whole idea behind it is so bizarre.

00:01:46.000 It'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.

00:02:00.000 It's used with exact calculations, but yet we don't really understand it.

00:02:07.000 Yeah.

00:02:08.000 Yeah, 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.

00:02:18.000 Clearly, we're pretty good at it, you know, like transistors and lasers depend on quantum mechanics.

00:02:23.000 The sun shining, figuring that out depends on quantum mechanics, the Higgs boson, etc.

00:02:28.000 So to claim that we don't understand quantum mechanics is a little bit weird.

00:02:32.000 But then we have quotes from people like Richard Feynman saying nobody understands quantum mechanics, right?

00:02:37.000 And so if he says that, then there's some authority behind it.

00:02:40.000 And the reason is what we have is sort of a black box, right?

00:02:46.000 I 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.

00:02:55.000 Like they know how to use the apps.

00:02:57.000 They can call people.

00:02:58.000 They can make phone calls.

00:02:59.000 They can take pictures.

00:03:00.000 They don't know what's going on inside.

00:03:03.000 Trevor Burrus And that's physicists with quantum mechanics.

00:03:05.000 They use it.

00:03:06.000 They can make very, very precise predictions.

00:03:08.000 But if you ask them, what is really going on?

00:03:11.000 Like what is actually happening?

00:03:13.000 What are all the details?

00:03:14.000 They're like, yeah, no, that's not our job.

00:03:15.000 Let's just stick to predictions.

00:03:16.000 Trevor Burrus But to someone like me, that's so terrifying because like the very nature of reality is being examined by people.

00:03:23.000 Like if it is – A smartphone.

00:03:27.000 It's being examined by people like me, who don't really understand the smartphone.

00:03:33.000 I have no idea what's going on inside a smartphone.

00:03:36.000 I know some words that you used to describe RAM and processors.

00:03:42.000 Probably electrons moving around in there, right?

00:03:44.000 Yeah.

00:03:44.000 Yeah, and I think – and in some sense, that's fine.

00:03:48.000 Like most of us don't need to know what's going on inside the smartphone to use it, but somebody should know, right?

00:03:55.000 And 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.

00:04:05.000 One 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.

00:04:18.000 Like they said, like, stop asking questions about the meaning of reality and what the world is doing.

00:04:22.000 In my mind, what physics is all about is understanding reality and what the world is doing.

00:04:28.000 It's not just about making predictions.

00:04:30.000 Making predictions is good but we do that, you know, mostly because we're curious about what the world is doing.

00:04:36.000 Well, 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,

00:04:53.000 that's where it's at.

00:04:55.000 That's serious work, yeah.

00:04:56.000 Yeah.

00:04:56.000 That seems to me to be so crazy.

00:04:59.000 It's like, if anybody should be pursuing it, it should be people like you.

00:05:03.000 I want to be fair.

00:05:05.000 So, of course, 20th century physics was incredibly successful.

00:05:09.000 And part of the attitude was, look, we have to understand nuclear physics and particle physics.

00:05:15.000 And a lot of it was the center of physics shifted from Europe to the US. And Europe is much more...

00:05:27.000 Matthew Feeney, Jr.: Yeah.

00:05:43.000 How do you do it?

00:05:44.000 Like, what experiment is it there that you can do?

00:05:46.000 As far as we know, the cookbook that we have, even though we don't understand it, works pretty well.

00:05:51.000 Like, what could you type into your smartphone that would help you understand what's going on inside?

00:05:55.000 It's kind of hard to figure out.

00:05:56.000 So I think if those attitudes were wrong, but at least, you know, they're not completely crazy.

00:06:01.000 It's not just that they were afraid of the truth or anything like that.

00:06:04.000 And I also think that it is finally changing now.

00:06:06.000 I think that there's slowly, slowly, slowly more people are appreciating that understanding quantum mechanics is important.

00:06:12.000 What do you attribute that to?

00:06:14.000 A couple of things.

00:06:16.000 One is – I mean there's good news and bad news.

00:06:18.000 Part of the good news is technology has gotten better.

00:06:21.000 So we're trying to build quantum computers for example and guess what?

00:06:26.000 Some of the ad hoc rules that we had for doing quantum mechanics might not be up to the task.

00:06:32.000 We need to understand the details a little bit better.

00:06:35.000 The other sadder thing is that so much of fundamental physics is kind of stuck right now, right?

00:06:42.000 We haven't – we literally have not been surprised by a new experimental result in fundamental physics since the 1970s.

00:06:51.000 There's one exception to that which is the universe accelerating in 1998 which was the dark energy.

00:06:57.000 We've had amazing accomplishments in experimental and observational physics.

00:07:02.000 We found the Higgs boson.

00:07:04.000 We found the top quark.

00:07:05.000 We found gravitational waves, the microwave background, many, many things.

00:07:09.000 But they were all predicted decades ago, right?

00:07:12.000 So progress is driven by being surprised and it's been a long time since we've been surprised.

00:07:17.000 So 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.

00:07:24.000 Maybe we can take a broader look and think that we're walking down the wrong path.

00:07:29.000 Now, for people that don't have any background in physics, there's a bit of an issue with public perception.

00:07:38.000 And 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...

00:07:48.000 Well, quantum physics is weird enough as it is without adding – that movie was literally created by a channeler, right?

00:07:58.000 A 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.

00:08:08.000 So David is one of many people who got a PhD in physics and then switched to philosophy because he cared about – Matthew Feeney But

00:09:06.000 anyway, he was in that film.

00:09:06.000 There's like 30-second clips of him going, yes, that is a really important question, right?

00:09:10.000 Like completely misrepresenting what he said.

00:09:13.000 And so he went public after that and complained about the film.

00:09:19.000 And he did – in a hilarious story, there was a – I think I'm going to go.

00:09:45.000 And he goes to this event in Santa Monica and he gave a talk.

00:09:49.000 He decided – he wondered like, should I just go at all?

00:09:52.000 But OK, why not?

00:09:53.000 Let's reach a different audience.

00:09:54.000 And he gave a talk and he said, look, there's two things you can do when you are faced with fundamental puzzles of reality.

00:10:02.000 One 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.

00:10:09.000 The other is you can choose to tell a flattering story about yourself.

00:10:15.000 And 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.

00:10:25.000 And the punchline is the audience loved it.

00:10:29.000 They went nuts because what they wanted was a guru of some sort and like he was just as good a guru as anybody else.

00:10:35.000 So, you know, he had a better story to tell.

00:10:36.000 A reality-based guru.

00:10:38.000 Reality guru, yeah.

00:10:38.000 Yeah, so I think you're right.

00:10:40.000 I 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.

00:10:50.000 Well, you've done an amazing job in this book of trying to boil it down for dummies like me, but it's hard!

00:10:56.000 It is a complicated and insanely nuanced subject.

00:11:01.000 Yeah.

00:11:02.000 And it's one of those things where it...

00:11:04.000 Like this many worlds theory, for one example.

00:11:10.000 Just the possibility that there's...

00:11:13.000 Like, explain that.

00:11:14.000 Sure.

00:11:14.000 Explain for people that...

00:11:18.000 Don't understand what quantum mechanics even means.

00:11:20.000 Give them just like a little bit of that and then explain many worlds theory.

00:11:24.000 Yeah.

00:11:24.000 Good.

00:11:25.000 This is what I'm here to do.

00:11:26.000 Thank you.

00:11:26.000 So, you know, an electron – take an electron.

00:11:29.000 Quantum mechanics should apply to the entire universe, but it becomes unmistakable when you look at little tiny things, right?

00:11:36.000 So we always are talking about electrons or atoms and so forth.

00:11:38.000 An electron has a position and – Well, sorry, let me not even say that.

00:11:43.000 Even that was wrong.

00:11:43.000 It's just so hard to correctly talk about quantum mechanics, right?

00:11:47.000 If you were Isaac Newton, before there was quantum mechanics, there was classical mechanics.

00:11:51.000 And basically, quantum mechanics and classical mechanics are the only two big frameworks that have ever existed in physics.

00:11:57.000 You 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.

00:12:05.000 In classical mechanics, an electron is a point.

00:12:08.000 It has a position, a location in space, and it has a velocity.

00:12:11.000 It's moving somewhere.

00:12:12.000 And from that, you can predict what's going to happen.

00:12:14.000 Okay?

00:12:15.000 Quantum mechanics says, no, no, no.

00:12:17.000 The electron has a wave function.

00:12:19.000 So there's a wave.

00:12:21.000 You know, sometimes you hear this debate about are things like electrons and photons, particles, or waves.

00:12:26.000 The answer is that they are waves.

00:12:29.000 And the wave function has this weird property that when you're not looking at it, It's a wave.

00:12:35.000 It's all spread out or it's localized somewhere, but it obeys an equation, the Schrodinger equation.

00:12:39.000 So far, so good.

00:12:41.000 Just like regular physics, there's a thing, the wave function, it obeys an equation, the Schrodinger equation.

00:12:45.000 You can predict what's going to happen next.

00:12:47.000 But 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.

00:12:56.000 That's where things get squirrely with people describing it.

00:13:00.000 Yes.

00:13:00.000 And that's where they want to go woo-woo on you.

00:13:02.000 It's an opening to be woo-woo, right?

00:13:04.000 Yes.

00:13:04.000 When you say, like, what do you mean observe something?

00:13:08.000 Like, does it have to be a conscious being?

00:13:10.000 Can it be a video camera?

00:13:11.000 You know, that's just weird, right?

00:13:13.000 Is it the act of measuring that changes things?

00:13:16.000 Right.

00:13:16.000 Well, this is the puzzle, okay?

00:13:19.000 This 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,

00:13:35.000 when it is measured – Its state, its wave function changes dramatically, suddenly, and unpredictably.

00:13:42.000 Now, let me ask you this.

00:13:42.000 How do we know this based on if you're measuring it and it changes?

00:13:47.000 How do we know because we didn't measure it before?

00:13:51.000 Like, what observations are we making that we understand the state of it before it's measured without measuring it?

00:13:57.000 Good.

00:13:57.000 There's a couple of ways.

00:13:58.000 So, let me make things even simpler.

00:14:02.000 Forget about where the electron is located and think about the electron is spinning, right?

00:14:06.000 The electron is spinning just like the Earth spins.

00:14:09.000 It's really exactly like that.

00:14:10.000 It'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.

00:14:20.000 You only ever get one of two answers.

00:14:22.000 It's either going up or going down.

00:14:23.000 It's nowhere in between.

00:14:24.000 This is an empirical measured fact, okay?

00:14:28.000 So that's a part of quantum mechanics.

00:14:30.000 That's the quantum fact that there's discrete set of possible answers to this question.

00:14:36.000 Is it spinning clockwise or counterclockwise?

00:14:38.000 Yes or no.

00:14:38.000 It's just those two possibilities, nowhere in between.

00:14:41.000 So if you have a magnetic field that is oriented vertically, Send your electron through it.

00:14:47.000 It gets deflected up.

00:14:48.000 You say, oh, it's spin up.

00:14:49.000 So now I've measured its spin.

00:14:52.000 Now I know what its state is.

00:14:53.000 If I send it through another magnetic field, oriented vertically, it will always be deflected up every single time.

00:15:00.000 We know what it is.

00:15:01.000 We're going to measure it.

00:15:02.000 Measuring it in this case doesn't change it.

00:15:04.000 It's in exactly that state.

00:15:06.000 We know it, okay?

00:15:08.000 Now let's send it through a magnetic field that is oriented horizontally.

00:15:12.000 So it's going to be deflected either right or left.

00:15:14.000 We know exactly what state it's in.

00:15:16.000 It's spinning this way.

00:15:17.000 But when you send it through that magnetic field that's oriented horizontally, it gets deflected left or right 50-50, unpredictably.

00:15:25.000 There's no way we can predict it.

00:15:27.000 And then once it is, so okay, now it's been spinning up.

00:15:30.000 You measured its spin left, let's say.

00:15:32.000 Send it through another magnet that is going vertically.

00:15:35.000 And now it's 50-50 again.

00:15:36.000 It could be spin up or spin down.

00:15:38.000 So somehow, even though we knew exactly what state it was in, we couldn't predict what would happen next.

00:15:44.000 That is part of quantum mechanics.

00:15:46.000 So 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?

00:15:56.000 So in quantum mechanics, what we say is that it's not that we don't know whether the electron is spinning clockwise or counterclockwise.

00:16:04.000 It can be in a superposition of both.

00:16:08.000 That's just the spin version of the position that the electron can be spread out in a wave, right?

00:16:14.000 It's truly not just that we are lacking some knowledge.

00:16:18.000 It's that the knowledge really isn't there.

00:16:20.000 And again, this is how we teach quantum mechanics in textbooks.

00:16:23.000 And then I'm going to correct it because Many Worlds is much better.

00:16:25.000 But this is the standard textbook version.

00:16:28.000 There's a wave function.

00:16:29.000 The wave function for a spin is it's either up or down or some combination.

00:16:33.000 And then there's a rule that says when you measure the spin, you only get up or down.

00:16:37.000 You don't see the wave function.

00:16:39.000 Just like the cloud that you have for the electron's position, when you look at it, you see it at a location.

00:16:45.000 So 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.

00:16:54.000 So it's a radioactive little chunk of metal and you put it in a bubble chamber.

00:17:01.000 So it is emitting radioactive particles and you detect the particles.

00:17:05.000 You can see a little streak of motion when the particle leaves the uranium, okay?

00:17:10.000 Well, like I said, when you're not looking at it, this electron is supposed to obey an equation, the Schrodinger equation.

00:17:16.000 And you can ask what the prediction is.

00:17:18.000 When a radioactive nucleus decays and gives off an electron, what is its wave function going to do?

00:17:25.000 What is the wave function of the electron going to be?

00:17:27.000 And the answer is it goes off in a spherical wave.

00:17:30.000 It goes off in all directions at once.

00:17:32.000 Evenly.

00:17:33.000 Yeah.

00:17:34.000 All directions, evenly.

00:17:35.000 But you never see that.

00:17:36.000 Is that roughly based on the shape of the piece of uranium?

00:17:40.000 Does it vary?

00:17:40.000 No, because the electron gets from one individual nucleus of an atom, right?

00:17:46.000 So what the uranium is doing doesn't matter.

00:17:48.000 It's just that one atom matters.

00:17:50.000 And the easiest thing for the electron to do is just to go out in a sphere.

00:17:53.000 It doesn't have to.

00:17:54.000 It can go out in higher energy states.

00:17:56.000 But the point is, it's not going out in a straight line.

00:17:58.000 But when you look at it, you see a straight line, right?

00:18:01.000 That'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.

00:18:09.000 So 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,

00:18:27.000 when 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.

00:18:39.000 Yeah, that's right.

00:18:39.000 That we just need better tools and a better understanding, better equations, more time.

00:18:45.000 Yeah, me and Einstein think this, right?

00:18:47.000 So 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.

00:18:54.000 The 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?

00:19:01.000 And he was given his first magnetic compass and he could rotate it this way and that way.

00:19:05.000 It always pointed north.

00:19:06.000 And you and I would go, huh, that's cool.

00:19:08.000 But he was Einstein.

00:19:09.000 He's like, wow, this is amazing.

00:19:10.000 How does it know where north is, right?

00:19:13.000 And he said there must be something deeply hidden that explains why it's doing this mysterious thing.

00:19:18.000 And he felt the same way about quantum mechanics.

00:19:20.000 We gave these set of rules, which are called the Copenhagen interpretation of quantum mechanics.

00:19:26.000 One set of rules for when you're looking at it, one set of rules for when you're not.

00:19:29.000 And Einstein was like, oh, come on.

00:19:31.000 Clearly, this is not the final answer to the nature of reality, right?

00:19:35.000 He wanted to know God's thoughts.

00:19:36.000 He's like, I want to know everything.

00:19:38.000 We're not done yet.

00:19:39.000 There must be more going on.

00:19:41.000 And so Many Worlds is one of the proposed answers to what could be going on.

00:19:46.000 It's not the only one.

00:19:47.000 There's alternatives, but it's definitely my favorite.

00:19:50.000 It's definitely the easiest one to write down.

00:19:52.000 Let's put it that way.

00:19:53.000 Okay, so hit us with this many worlds theory.

00:19:55.000 Okay, so think about this electron.

00:19:57.000 You say that it could be either spin up or spin down.

00:20:01.000 It's a combination of both.

00:20:02.000 That's its wave function.

00:20:03.000 You measure it, you only ever see spin up or spin down.

00:20:06.000 So Copenhagen says that's because the wave function suddenly changed, snapped into place when you observed it.

00:20:12.000 Don't ask me what it means to observe something.

00:20:14.000 That's not what Copenhagen lets you ask.

00:20:17.000 Many worlds says what you're missing...

00:20:20.000 Is two things.

00:20:21.000 Number one, you're a quantum system.

00:20:25.000 You're obeying the rules of quantum mechanics.

00:20:27.000 You're made of atoms and electrons and so forth.

00:20:29.000 You have a wave function too, okay?

00:20:31.000 So you're secretly treating yourself as a classical thing when you make that measurement, but you really should be treating yourself quantum mechanically, right?

00:20:39.000 That's one thing.

00:20:40.000 And the other thing is something that Einstein invented, namely called entanglement.

00:20:46.000 When 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?

00:20:53.000 It says that there's only one wave function for the whole universe.

00:20:57.000 So the way I like to say it is...

00:20:59.000 Imagine two particles come in and bounce off of each other.

00:21:03.000 Either one has a wave function and it's unpredictable exactly what angle it's going to go off at.

00:21:08.000 So both of the particles that go off, you don't know where they're going.

00:21:13.000 But because momentum is conserved, if they came in at equal velocities, they'll go out at equal velocities in opposite directions.

00:21:40.000 Matthew Feeney What happens physically?

00:21:45.000 Like, forget about you're a person, you're conscious, all that BS. Like, you're a physical system, you obey the Schrodinger equation.

00:21:51.000 You are a quantum mechanical system, you obey the laws of physics.

00:21:55.000 So you look at the electron, your wave function changes.

00:22:00.000 It used to be you're just a person doing whatever you do, but then after you look at the electron, you become entangled with it.

00:22:06.000 And it splits.

00:22:07.000 So there is one part of the wave function that says the electron was spinning clockwise and you measured it spinning clockwise.

00:22:14.000 And there's another part of the wave function that says the electron was spinning counterclockwise and you saw it spinning counterclockwise.

00:22:20.000 Now, everybody knows this.

00:22:22.000 Like, that far, it's not controversial at all.

00:22:25.000 That's clearly the prediction of the equations of quantum mechanics.

00:22:28.000 But 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.

00:22:37.000 When I look at real electrons, I see them one way or the other.

00:22:40.000 That can't be right.

00:22:41.000 That can't be the final answer.

00:22:43.000 The wave function must somehow collapse.

00:22:45.000 And Everett said, no, what you're missing is there's now two separate worlds.

00:22:49.000 Both of those part of the wave function are real, but they're different worlds.

00:22:53.000 They will never interact with each other again.

00:22:55.000 What happens in one part of the wave function will not affect what happens in the other part.

00:22:59.000 So 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.

00:23:06.000 And that's just taking seriously the prediction of quantum mechanics.

00:23:10.000 It's not adding any extra stuff, any extra worlds, anything like that.

00:23:14.000 I think?

00:23:20.000 I think?

00:23:35.000 Do you think of yourself as this quantum being that's existing in this super state?

00:23:41.000 So, I mean, there's a couple of answers to that.

00:23:42.000 One is, you know, sure, if I think about it, like, I really do believe it.

00:23:46.000 You 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.

00:23:53.000 Matthew 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.

00:24:04.000 At the end, his last question is, do you really believe this?

00:24:08.000 Are you really taking this seriously?

00:24:10.000 Look, that's a perfectly good question.

00:24:13.000 It'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?

00:24:24.000 So what it's asking you to do is to say, I have these equations.

00:24:29.000 They are really, really good at fitting what I do observe in the world and making predictions.

00:24:36.000 I can build the Large Hadron Collider, et cetera.

00:24:41.000 I will take them seriously even for things that I can't directly observe because they're the best equations I have, right?

00:24:47.000 Until a better set of equations come along, I will believe these equations.

00:24:50.000 And 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.

00:25:01.000 I think?

00:25:16.000 Do you think of each choice that you make possibly changing everything about the world that you exist in?

00:25:25.000 How are you looking at it?

00:25:27.000 You know what I'm saying?

00:25:28.000 Because you are a guy who probably understands it as good as anybody that's alive.

00:25:33.000 So as weird as this stuff sounds...

00:25:35.000 To me, it sounds like...

00:25:37.000 I mean, it's almost impossible for me to comprehend.

00:25:40.000 So I'm trying to filter it through your understanding of it.

00:25:43.000 Well, I think that...

00:25:44.000 Just taking this jacket off.

00:25:45.000 We're getting serious.

00:25:46.000 I know.

00:25:46.000 It's getting hot in here.

00:25:47.000 Physics is heating us up.

00:25:54.000 Yeah, I'm not exactly sure how to say it the best.

00:25:56.000 You know, it doesn't change who you are.

00:26:01.000 It's certainly not true that you making a decision is what branches the wave function of the universe.

00:26:07.000 I guess that's the right thing to say.

00:26:08.000 Good, because I want to stop all woo.

00:26:09.000 Yeah, you can't do that.

00:26:10.000 Before it happens.

00:26:11.000 Everyone, 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?

00:26:19.000 Oh, okay.

00:26:21.000 It's not that your choices create different universes.

00:26:24.000 Different universes get created and maybe you're different in them by a little bit.

00:26:28.000 In 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.

00:26:36.000 And 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.

00:26:44.000 Then you can deal with that and your therapist however you like.

00:26:47.000 But what is the application exactly doing?

00:26:50.000 What it's doing is basically a version of measuring the spin of an electron.

00:26:54.000 It's called Universe Splitter?

00:26:55.000 Universe Splitter.

00:26:56.000 It's only for iPhones.

00:26:57.000 I'm going to grab this right now.

00:26:58.000 Sorry, Android people.

00:26:59.000 Yeah, sorry.

00:27:00.000 It's not even a webpage.

00:27:02.000 It's only an app.

00:27:03.000 There's equivalent webpages.

00:27:04.000 Okay, I'm pulling it up right now.

00:27:05.000 Yeah, 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.

00:27:15.000 They send a single photon down a pipe to what's called a beam splitter.

00:27:19.000 So the wave function of the photon goes 50-50.

00:27:22.000 It gets sent left.

00:27:23.000 It gets sent right.

00:27:24.000 And if you agree, and so then it sends back whether you ended up in the branch of the wave function where it went left or where it went.

00:27:31.000 There you go.

00:27:32.000 199. Come on.

00:27:33.000 The power of changing the universe is in your hands.

00:27:36.000 I downloaded it.

00:27:37.000 I got it.

00:27:37.000 I paid for it.

00:27:38.000 I got it right here.

00:27:39.000 All right.

00:27:39.000 Whew.

00:27:40.000 So if you have any tough choices, you can type in, like, you know, I want to have pizza or I want to have Chinese food for dinner tonight.

00:27:47.000 Well, it says in one universe I will take a chance, in the other one I will play and save.

00:27:51.000 Yeah, but you can correct those.

00:27:53.000 You can fill in whatever you want.

00:27:55.000 Really?

00:27:55.000 Yeah, that's the good part.

00:27:57.000 What is happening with this?

00:27:58.000 I will ask her to marry me.

00:28:00.000 I will not ask her to marry me.

00:28:01.000 I will accept this job.

00:28:03.000 I will go somewhere else.

00:28:04.000 Is this the equivalent of a quantum fortune cookie?

00:28:06.000 Yeah.

00:28:07.000 But accept that all possible fortunes are obtained in different universes.

00:28:12.000 The bad news is you can't ever find out how things went in the other universe.

00:28:16.000 You can't talk to the different universes.

00:28:18.000 That's the problem, right?

00:28:18.000 So people will be paralyzed by analysis.

00:28:21.000 That'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.

00:28:28.000 But 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,

00:28:44.000 making various choices which send you off into different directions?

00:28:48.000 So, number one, we don't know if it's infinite number or just really big.

00:28:51.000 But there's certainly a really, really big number.

00:28:53.000 It's big enough to be, you know, big enough for whatever you want.

00:28:56.000 But it's not everything.

00:28:58.000 It's not – the theory does not say everything happens somewhere, right?

00:29:01.000 The theory says the Schrodinger equation is obeyed.

00:29:03.000 There's an equation that is obeyed.

00:29:05.000 So – Electrons will never convert into protons because electrons are negatively charged and protons are positively charged.

00:29:12.000 And nowhere in the Schrodinger equation can you violate the conservation of charge, right?

00:29:16.000 So there's plenty of things that don't happen, but then there are plenty of things that do happen.

00:29:19.000 And some things are more likely than others for you to experience.

00:29:22.000 So again, it's sort of a...

00:29:25.000 It's a mind-bending thing, but it's a straightforward prediction of the equations and it doesn't affect our lives.

00:29:30.000 There'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.

00:29:41.000 It's exactly the same as it would be in the ordinary world.

00:29:44.000 Trevor Burrus And you are the ordinary world no matter how many copies of you there are or how many versions of you there are.

00:29:54.000 There's no essence of you that is traveling through one of the copies, right?

00:29:58.000 Like all of these people are separate people.

00:30:01.000 So I use the analogy, it's like identical twins.

00:30:04.000 They were the same zygote or whatever, and now they're different people, okay?

00:30:08.000 So that's the same thing.

00:30:09.000 Like 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.

00:30:19.000 Now, 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,

00:30:34.000 in 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.

00:30:44.000 So 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.

00:30:55.000 There's constant versions of you.

00:30:58.000 Yeah, it's kind of like a whooshing where more and more versions of you are being created all the time.

00:31:03.000 And it's an interesting thing because even the best trained physicists sort of think intuitively classically.

00:31:11.000 Like, look, here's a table, there's a bottle, right?

00:31:14.000 You have to.

00:31:14.000 Red light comes, hit the brakes.

00:31:16.000 And this is how we evolved, right?

00:31:18.000 This is how our brains work, right?

00:31:19.000 And like I said, you know, many worlds is one respectable version of quantum mechanics.

00:31:24.000 There are other respectable versions, more respectable than the textbook presentation.

00:31:29.000 But they all – all the other ones somehow lean on our classical experience.

00:31:34.000 And the textbook version certainly does.

00:31:36.000 It says like you're a classical person observing a quantum mechanical system and so forth.

00:31:40.000 And Everett, when he was a graduate student, he had arguments across the ocean with people in Copenhagen who tried to push their way forward.

00:31:49.000 And he's like – Matthew Feeney Obeying the rules of quantum mechanics and the

00:32:19.000 conventional Copenhagen theory is just not up to it.

00:32:23.000 When 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.

00:32:38.000 And that we are thinking of ourselves in this very limited, primitive, biological way, because that's how we evolve.

00:32:45.000 But 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.

00:33:00.000 And that's why, again, going off of what you're saying about your being...

00:33:07.000 We're good to go.

00:33:34.000 Yeah, but no, I like the analogy very much because the human brain did not evolve to understand quantum mechanics.

00:33:40.000 It didn't evolve to understand science at all.

00:33:45.000 Some 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.

00:33:56.000 And 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.

00:34:13.000 We're getting better at it and this is part of it.

00:34:15.000 You 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?

00:34:26.000 How much of it should we lean on our intuitive understanding?

00:34:28.000 And how much should we just accept that the world is fundamentally super-duper different?

00:34:32.000 I think that's a perfectly good question.

00:34:34.000 I'm not trying to prejudice the answer one way or the other.

00:34:36.000 I mean, our experience is limited, but it's all we have, right?

00:34:40.000 We have to be based on that.

00:34:41.000 And so some people wonder, is quantum mechanics just impossible to understand?

00:34:48.000 Like, is the human brain not up to the task?

00:34:50.000 The current human brain.

00:34:51.000 The current human brain, sure.

00:34:52.000 But I think that – no, I think that that's totally wrong.

00:34:55.000 I think that number one, quantum mechanics certainly is very understandable.

00:34:59.000 And number two, I don't think that anything about nature is impossible to understand for the current human brain.

00:35:04.000 I mean maybe it is.

00:35:05.000 There's no way of knowing for sure.

00:35:06.000 But there's zero evidence that we will fail in our ambition to try to understand the universe.

00:35:11.000 It's just – It's hard and it takes time.

00:35:13.000 Look, a hundred years ago, we didn't have quantum mechanics at all.

00:35:17.000 Like, we've made enormous progress and a hundred years is nothing, even in human history, much less cosmological history.

00:35:24.000 So, don't be impatient.

00:35:26.000 Take time.

00:35:28.000 But it just seems to me that...

00:35:31.000 The human understanding of the world we live in has obviously radically changed over the last 500 years.

00:35:37.000 And if we continue to exist in this current state or a slightly better state as things move on, it's going to get better.

00:35:45.000 But quantum mechanics and quantum theory to me almost seems like an ant trying to understand the choices on Netflix.

00:35:53.000 It's like those choices exist, but the ant really lacks all tools.

00:36:00.000 I 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.

00:36:19.000 Nope.

00:36:19.000 I got to disagree.

00:36:20.000 I think it's just hard.

00:36:21.000 I think there's a difference.

00:36:22.000 I think that – and I could be wrong about this, but I think that there was a phase transition.

00:36:28.000 There was some – you know how we talk in computer science about a certain kind of computational machine being Turing complete?

00:36:36.000 I mean maybe you don't know this, but this is something we say.

00:36:38.000 Please explain that.

00:36:39.000 So a Turing machine, Alan Turing, the great – A computer scientist who broke codes and things like that.

00:37:02.000 Like, 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.

00:37:11.000 And 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.

00:37:17.000 So in some sense, this is not a rigorous fact by any stretch, but I think there's an analogy with human reasoning.

00:37:24.000 Like at some point, we're a little bit smarter than dogs and cats.

00:37:29.000 But it's not just we're a little bit smarter, we're a different kind of smart.

00:37:32.000 Like we did pass a threshold.

00:37:34.000 We can use language.

00:37:35.000 We can reason symbolically and abstractly.

00:37:38.000 We can write things down and pass them down through generations.

00:37:41.000 We can imagine futures in ways that they can't.

00:37:44.000 So 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.

00:37:54.000 We've become capable of this kind of thought and I think that's enough.

00:37:59.000 My 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.

00:38:07.000 And 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.

00:38:20.000 But I think it is absolutely understandable if people make the effort.

00:38:24.000 I don't think there's any person who can balance their checkbook but not understand quantum mechanics.

00:38:30.000 They just need to put the time in.

00:39:02.000 Yeah, if I was thinking about quantum mechanics when I was driving my car, things would be much worse than they are.

00:39:08.000 And that's because the classical world is a really good approximation.

00:39:13.000 I mean, this is something I'm also interested in.

00:39:15.000 Yeah, you know, this is important.

00:39:19.000 Emergence, right?

00:39:19.000 I talked about this in the last book, in The Big Picture.

00:39:23.000 Think about this.

00:39:24.000 When we talk about the Earth going around the Sun, forget about quantum mechanics, just do classical mechanics, Isaac Newton, Earth orbiting the Sun, okay?

00:39:32.000 We can predict that.

00:39:33.000 We can write down the equations.

00:39:35.000 We can tell you where the Earth was a million years ago or a million years in the future, right?

00:39:40.000 But think about how amazing that is.

00:39:42.000 The Earth is made of something like 10 to the 50th atoms, okay?

00:39:47.000 In principle, to tell you what the Earth is doing, I should tell you what every one of those atoms is doing, right?

00:39:52.000 But I have no idea what every one of those atoms is doing.

00:39:55.000 All 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.

00:40:04.000 So, only using an incredibly tiny amount of information, I can make incredibly precise and accurate predictions.

00:40:11.000 I 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.

00:40:20.000 So, that's emergence when you don't need to know almost anything about a system.

00:40:25.000 You have certain very, very special high leverage pieces of information I think we're good to go.

00:40:46.000 It'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?

00:40:54.000 And if you needed to know the quantum wave function of the car you were driving, it would be hopeless.

00:40:58.000 It's just computationally intractable.

00:41:00.000 So the world appears to us in a way that is very convenient in some ways.

00:41:06.000 We need to know so little about the world to yet understand quite a bit of it.

00:41:11.000 Otherwise, we couldn't get through the day.

00:41:13.000 The idea that everything is in motion is also very difficult for people to wrap their brain around.

00:41:18.000 You see a stationary rock on the ground, you think that rock is still.

00:41:24.000 But it is not.

00:41:26.000 Nothing is still.

00:41:27.000 You know, it's pretty still.

00:41:28.000 But it's a part of the Earth.

00:41:29.000 It's pretty still.

00:41:30.000 The Earth is spinning.

00:41:31.000 Sure, the Earth is spinning.

00:41:31.000 So relatively, in terms of the universe, everything is in motion in some way, shape, or form.

00:41:37.000 Well, 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?

00:41:50.000 Right, right.

00:41:50.000 Right?

00:41:51.000 So if you're standing next to the rock, it's not moving with respect to you, right?

00:41:54.000 If you're just stationary there.

00:41:56.000 There's also what I try to squelch in the book.

00:41:59.000 One of the misunderstandings about quantum mechanics is the idea of quantum fluctuations, right?

00:42:03.000 The 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.

00:42:10.000 That's not what quantum mechanics says.

00:42:12.000 Like, 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.

00:42:20.000 It's really not changing appreciably over time.

00:42:23.000 If 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.

00:42:31.000 But when you're not looking at it, it's not jiggling.

00:42:34.000 It's just sitting there quietly, according to quantum mechanics.

00:42:36.000 So is this confusing description based on our limited ability to perceive?

00:42:41.000 It's actually based on the fact that we inevitably attach a notion of reality to what we do perceive, right?

00:42:49.000 So in quantum mechanics, what we perceive is different than what really is.

00:42:53.000 And that really bugs people.

00:42:55.000 Because I just saw it.

00:42:57.000 I mean, how much more real could it be, right?

00:42:59.000 The 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.

00:43:11.000 You can't know both of them at the same time.

00:43:13.000 It's not that you can't know both of them at the same time.

00:43:16.000 It's that neither one of them exists.

00:43:18.000 Position and velocity are things you measure.

00:43:21.000 They're not the elements of reality that quantum mechanics uses.

00:43:24.000 And there's a difference there and people don't like that.

00:43:27.000 But by the way, I wanted to bring up a whole other aspect of the not moving thing, which I think is fascinating.

00:43:32.000 And it's nothing to do with quantum mechanics, but it is a future frontier for physics, I think.

00:43:38.000 You know, we can look at the bottle of water and say, like, it looks pretty stationary.

00:43:42.000 It's not really changing.

00:43:44.000 I can also look at you, and you're sitting there pretty quietly.

00:43:47.000 You're not really changing.

00:43:48.000 But there's a tremendous difference because this is stationary, not moving, because all of its pieces are stationary and not moving.

00:43:57.000 I mean, this is liquid, so it's not the best example.

00:43:59.000 The table would be a better example.

00:44:00.000 But you and I are sort of macroscopically stationary, trying to sit here more or less quietly.

00:44:06.000 But inside, there's a lot of churn going on, right?

00:44:09.000 There's, you know, a lot of cellular biology.

00:44:11.000 There's ATP is being created and destroyed.

00:44:14.000 And, you know, signals are going from our brain and back and forth.

00:44:17.000 And someone like Antonio Damasio, the neuroscientist, emphasizes this idea of homeostasis, that there is stuff going on beneath the surface, but it regulates our...

00:44:33.000 I think we're good to go.

00:44:38.000 I think we're good to go.

00:44:54.000 I think we're good to go.

00:45:08.000 The idea that there's an enormous number of you making various choices.

00:45:15.000 Yeah.

00:45:16.000 And that these various choices will ultimately affect how long you exist.

00:45:21.000 In some branches.

00:45:23.000 So there is a weird thing called quantum immortality.

00:45:27.000 I don't like to talk about it, but people hear about it, so I sometimes need to mention it.

00:45:32.000 Max Tegmark, who is a friend of mine, a very smart guy, popularized this idea.

00:45:35.000 He 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.

00:45:45.000 So you have your universe splitter, okay?

00:45:47.000 You have your app on your iPhone and you split the universe.

00:45:49.000 And if it goes one way, you don't do anything.

00:45:52.000 If it goes the other way, faster than you can react, a machine is activated that kills you instantly.

00:45:59.000 Okay?

00:46:00.000 So you don't even know it.

00:46:01.000 You don't even perceive it.

00:46:02.000 You don't have any pain.

00:46:03.000 You're just instantly dead.

00:46:05.000 And you do this over and over and over and over and over again.

00:46:08.000 So in most branches of the wave function, you're dead.

00:46:11.000 But in those, you're dead.

00:46:13.000 You don't know anything.

00:46:14.000 You don't feel like you're dead.

00:46:15.000 There's no regret after the fact.

00:46:17.000 The 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.

00:46:24.000 So 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?

00:46:38.000 I don't think that's quite right.

00:46:40.000 I don't think it's a good way to go through your life.

00:46:42.000 I 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?

00:46:55.000 Like 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.

00:47:03.000 And I think the same thing is true in the quantum immortality experiment.

00:47:06.000 I don't buy the move that says – Well, in all the branches where you're dead, it doesn't matter because you're dead.

00:47:12.000 You don't feel anything.

00:47:13.000 Like I think that right now it's okay for me to be bothered by the prospect that in many future worlds I will not be there.

00:47:19.000 So I think that at the end of the day, once again, you should act in quantum mechanics just like you act in the regular world.

00:47:24.000 Are there competing theories to this many-worlds theory that you've embraced and then discarded?

00:47:32.000 Yeah, there's two big ones that are quite popular.

00:47:36.000 One is more or less what Einstein had in mind, which are called hidden variable theories.

00:47:41.000 So basically, you know, if you have an electron and you say, look, when I'm not looking at it, it's wave-like.

00:47:47.000 When I look at it, it's like particle-like.

00:47:50.000 Maybe it's both.

00:47:51.000 Maybe there is a wave and there is a particle.

00:47:54.000 So in a hidden variable theory, there's a wave function, just like there is in many worlds.

00:47:58.000 But there's also another set of variables saying there's really a location of the electron, right?

00:48:03.000 Maybe I don't know where it is, but there really is an electron located somewhere.

00:48:06.000 And that location of the electron is pushed around by the wave function, but it's a whole new part of reality.

00:48:14.000 So there's separate branching of the wave function and all that stuff, but none of that is reality.

00:48:19.000 Where reality is is where the particles are.

00:48:21.000 And this is now called Bohmian Mechanics.

00:48:25.000 David Bohm in the 1950s developed the most respectable version of this.

00:48:30.000 It's sort of...

00:48:33.000 It's therapeutic if you don't like all the other worlds.

00:48:35.000 It's basically, you know, the equations are the same as many worlds except there's new equations and new stuff.

00:48:39.000 So it complicates the theory by adding new variables.

00:48:42.000 But the good news is it says only one of the branches of the wave function is real.

00:48:46.000 I don't need to worry about the other ones.

00:48:48.000 The problem is it's very hard – my particular problem is it's very hard to reconcile these ideas with modern physics.

00:48:55.000 Like if you thought the world was made of individual particles, it would do okay.

00:48:59.000 But these days we use quantum field theory and quantum gravity and things like that.

00:49:03.000 And those more modern ideas are harder to attach hidden variables to.

00:49:07.000 So hidden variables are an old idea, but I think that they're hard to make work.

00:49:12.000 The 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.

00:49:22.000 But maybe what's really going on is the following, that there's a random probability every second that every electron will just spontaneously collapse.

00:49:30.000 So it's all spread out, but its wave function just randomly collapses.

00:49:37.000 I think we're good to go.

00:49:47.000 There's way more than 100 million electrons in this table.

00:49:50.000 There's, you know, billions and billions and billions of electrons.

00:49:53.000 So 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.

00:50:05.000 And this is called spontaneous collapse or GRW theory after the initials of the people who invented the theory.

00:50:12.000 And 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.

00:50:27.000 Energy is not conserved in this theory.

00:50:29.000 So people are doing experiments to test this.

00:50:32.000 So it's really, you know, legit experimental science.

00:50:36.000 Atoms.

00:50:37.000 The current perception by the general public of atoms is that it's mostly empty space.

00:50:45.000 Yeah, that's a bad idea.

00:50:46.000 This is not true.

00:50:47.000 Or not correct, or not...

00:50:50.000 It's certainly not what many worlds says.

00:50:52.000 Right.

00:50:52.000 So this is, you know, there are two enormous problems with our current way of presenting quantum mechanics.

00:50:58.000 One is the measurement problem, which is this question, like, what do you mean look at it?

00:51:02.000 What do you mean observe?

00:51:03.000 Like, what actually happens?

00:51:04.000 When does that happen?

00:51:05.000 That's the measurement problem.

00:51:06.000 But the other problem is...

00:51:09.000 I don't know.

00:51:29.000 In hidden variable theories, there's a wave function and there's also particles.

00:51:34.000 So there's extra ontology, extra pieces of reality.

00:51:37.000 So the question of, is the atom mostly empty space, depends on what you think is real.

00:51:45.000 So the wave function of the electron fills the atom.

00:51:49.000 So if you're a many-worlds person like me, You think what is real is the wave function.

00:51:54.000 It fills up the atom, and the atom is not mostly empty space.

00:51:58.000 The atom is the wave function.

00:51:59.000 It has that size, right?

00:52:00.000 You 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.

00:52:10.000 When you measure it.

00:52:11.000 Well, yes.

00:52:12.000 So many worlds says there's no such thing as where it is.

00:52:16.000 There's only a probability of seeing it.

00:52:18.000 Everyone knows that, but people kind of deny it.

00:52:21.000 They talk as if there really is a location of the electron, even if they should know better.

00:52:24.000 So generally, people who say that atoms are mostly empty space are just being sloppy.

00:52:30.000 They're just really thinking of the electron as a little tiny dot rather than a wave function.

00:52:35.000 There is an exception to that because there is a fourth version of quantum mechanics that is somewhat popular.

00:52:41.000 I said three.

00:52:42.000 I said many worlds, hidden variables, and spontaneous collapse.

00:52:46.000 There's another version that just says, look, the wave function has nothing to do with reality.

00:52:51.000 In many worlds, it's all of reality.

00:52:53.000 In spontaneous collapse, it's all of reality but it obeys different equations.

00:52:57.000 In hidden variables, the wave function is part of reality but there's also particles.

00:53:02.000 In 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.

00:53:15.000 So your wave function is just a tool you use to make a prediction for what the experimental outcome is going to be, right?

00:53:22.000 And that's more or less what we teach our students.

00:53:25.000 And this approach says, don't bother about reality.

00:53:30.000 What we should concern ourselves with is the experiences of agents who make predictions and update their probability expectations of the world.

00:53:41.000 And 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?

00:53:51.000 I think if they're honest, they would say, don't ask those questions.

00:53:55.000 We don't ask reality questions.

00:53:56.000 We just ask, what are you going to see kinds of questions.

00:53:59.000 But I think that some of the less honest ones will say, sure, an atom is mostly empty space because an electron has a location somewhere.

00:54:04.000 We just don't know what it is.

00:54:06.000 Why do they approach it in this, the way you're describing it, a sloppy way?

00:54:12.000 Why do you think that is so common?

00:54:15.000 Well, 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.

00:54:28.000 So, 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.

00:54:36.000 And I think that's terrible, but they will say it.

00:54:39.000 And so when you press them too much on questions like, you know, is the atom mostly empty space?

00:54:45.000 You know, what happens when we make an observation?

00:54:46.000 They just kind of get uncomfortable and say, no, you're asking the wrong questions.

00:54:50.000 Let's ask questions about what will we see at the Large Hadron Collider if we smash protons together, right?

00:54:56.000 And those are perfectly good questions, too.

00:54:57.000 But I think that the what's really going on questions are also interesting.

00:55:01.000 So because they don't care about these questions, they will often be sloppy in answering them, right?

00:55:06.000 It is hard.

00:55:07.000 Like you said, it's hard when you read the book.

00:55:10.000 It's hard when you write the book.

00:55:11.000 It's hard when you think about these things as a professional physicist.

00:55:14.000 It's not natural.

00:55:15.000 It's not easy.

00:55:17.000 It's not intuitive.

00:55:18.000 So 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.

00:55:30.000 Trevor Burrus Now, how was all this stuff verified or argued?

00:55:35.000 Like, say, if you're sitting down, you're having a conversation with someone who espouses a competing theory.

00:55:41.000 How are you guys working this out?

00:55:44.000 Good.

00:55:45.000 I think that if everything were going along really, really well, we would be making experimental predictions and testing them.

00:55:54.000 But 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.

00:56:09.000 But we really haven't.

00:56:10.000 They were neglected.

00:56:11.000 They were backwaters.

00:56:21.000 But that's what we need to do.

00:56:22.000 We need to like catch up on the last 70 years of lost time and work out what the implications are of these ideas.

00:56:30.000 So the ball I think is in the theorist's court.

00:56:32.000 The experimenters are working hard.

00:56:33.000 The experimenters are doing amazing things with lasers and atoms and learning about how to manipulate quantum systems at a delicate level.

00:56:42.000 But the theorists have not given them sharp experimental questions that would really illuminate the foundations of quantum mechanics.

00:56:50.000 So honestly, what it is, is a bunch of people get around a table and talk to each other.

00:56:54.000 They're like, all right, I think that what happens when the wave function branches is this.

00:56:58.000 So a typical question we'll try to address is...

00:57:02.000 In 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.

00:57:12.000 And someone says, what do you mean 50-50 chance?

00:57:15.000 Especially 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.

00:57:22.000 What is the meaning of the phrase, there's a 50-50 chance?

00:57:26.000 What is the nature of probability in this game where everything is perfectly deterministic, right?

00:57:30.000 So that's not the kind of question that you answer very easily by doing an experiment.

00:57:34.000 You have to think about it.

00:57:35.000 So that's the kind of thing that we argue about.

00:57:37.000 How often do you guys get together?

00:57:40.000 Yeah, it happens.

00:57:42.000 There's conferences.

00:57:43.000 It's a small community.

00:57:44.000 Someone asked me just the other day because the book came out, Something Deeply Hidden, last week and I've been on book tour.

00:57:49.000 So 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?

00:58:01.000 Maybe a hundred, something like that.

00:58:03.000 Not a very large number.

00:58:04.000 Like, if you say how many people would classify themselves as particle physicists, it would be tens of thousands of people.

00:58:09.000 I remember there's a woman who came to the comedy store after the last podcast that we did, and she apparently is also working on it.

00:58:27.000 Ah, okay.

00:58:36.000 The 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.

00:58:51.000 And she wanted to talk to me about it to say, you know, please have more people on.

00:58:56.000 Please talk about this more.

00:58:57.000 You know, we need support.

00:58:59.000 It does baffle me a little bit how difficult it is swimming uphill to get more support for this kind of thing.

00:59:10.000 It is just an enormous privilege to be able to call your job thinking about the fundamental nature of reality, right?

00:59:19.000 Like, 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.

00:59:29.000 And, 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.

00:59:39.000 Is 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?

00:59:47.000 In part, yeah.

00:59:49.000 I mean, there's no one else in the physics department at Caltech who cares about these issues.

00:59:53.000 I mean, some of them care in the sense that they are happy that I'm doing it, but no one does it really to themselves.

00:59:59.000 Yeah.

00:59:59.000 Well, there's a couple other people in the philosophy department who care about these.

01:00:03.000 And a lot of folks, you were saying, get pushed into philosophy.

01:00:06.000 Why is that?

01:00:08.000 I mean, is it just because it's so complex that it's so esoteric?

01:00:11.000 There's so many people that just – the support for it's not there, but the support for philosophy is more common and mainstream?

01:00:19.000 Yeah, you know, there's different kinds of support.

01:00:21.000 One kind of support in academia is who do you hire, right?

01:00:25.000 What areas do you want?

01:00:26.000 Like 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.

01:00:37.000 Do we need people doing biophysics?

01:00:39.000 Do we need people doing this?

01:00:40.000 And by the time they get to the foundations of quantum mechanics, there's usually very little support.

01:00:45.000 I think we're good to go.

01:00:53.000 I think we're good to go.

01:01:04.000 Many of the questions that they're asking cannot be tested experimentally, right?

01:01:09.000 What is infinity?

01:01:11.000 Well, you know, okay, it's hard to do an experiment there, but it's an important question, right?

01:01:16.000 And so you need patience, but also it's harder to make progress because it's easy to be trapped by your intuition, right?

01:01:24.000 Like 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.

01:01:31.000 And quantum mechanics doesn't look reasonable to anybody.

01:01:33.000 So it's a wonderful corrective.

01:01:36.000 It's a wonderful reality check when you think, well, reality has to be this way.

01:01:39.000 And then someone can say, well, look at quantum mechanics.

01:01:41.000 That's different than what you said.

01:01:43.000 So philosophy and quantum mechanics, they sort of – they share some sort of a border.

01:01:50.000 Yeah.

01:01:50.000 Oh, yeah, absolutely.

01:01:51.000 I 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.

01:01:59.000 But when I was an undergraduate, my favorite philosophy classes were like the philosophy of morality or political philosophy, right?

01:02:06.000 I 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.

01:02:15.000 You know, the structure of scientific revolutions is the famous book that everyone reads.

01:02:19.000 People like Thomas Kuhn and Paul Feyerabend and so forth.

01:02:22.000 Okay, that's interesting, but it's sort of meta-science, right?

01:02:27.000 It's like how science is done, not how the world works.

01:02:29.000 And it wasn't until, you know, circa 2000 that I discovered that there are philosophers of physics who are kind of really doing physics.

01:02:38.000 You 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.

01:02:49.000 There was a part of the book that shocked me because I had a ridiculous idea once and this idea was not my idea.

01:02:58.000 Apparently LaPaz had a very similar idea as a thought experiment.

01:03:02.000 I 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.

01:03:16.000 And 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.

01:03:30.000 That's right.

01:03:31.000 So this is called LaPaz's demon, although he never called it that.

01:03:35.000 Pierre-Simon Laplace was a brilliant guy.

01:03:37.000 He deserves to be much more well-known.

01:03:39.000 So I think I've mentioned his name in every book that I've ever written for totally different reasons.

01:03:44.000 He helped invent probability as we currently understand it, for example.

01:03:48.000 But yeah, so Isaac Newton came up with the rules of classical mechanics in the 1600s.

01:03:54.000 But it wasn't until Laplace around the year 1800 that this implication of classical mechanics was realized.

01:04:00.000 It'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.

01:04:13.000 And you knew the laws of physics and you had arbitrarily large computational capacity.

01:04:18.000 Laplace said a vast intelligence, okay?

01:04:21.000 Then to that vast intelligence, the past and future would be as determined and known as the present was because that's the clockwork universe.

01:04:30.000 It's deterministic.

01:04:31.000 Everything is fixed once you know the present moment.

01:04:33.000 Now, quantum mechanics comes along and throws a spanner into the works a little bit.

01:04:38.000 If you're a many-worlds person, Laplace's daemon is still possible.

01:04:43.000 So 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.

01:04:53.000 But what you're predicting is all of the branches of the wave function.

01:04:57.000 So any individual person inside the wave function still experiences apparently random events, right?

01:05:04.000 So you can't predict what will happen to you even if you can predict what will happen to the entire universe.

01:05:11.000 Woo! 0.99

01:05:11.000 Sean Carroll. 0.99

01:05:13.000 My goodness.

01:05:14.000 There's a lot of people pausing this podcast right now, just shaking their head like...

01:05:18.000 You 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.

01:05:28.000 They have really, really good high-level articles about all sorts of things.

01:05:32.000 And so I wrote an article called, What is Probability?

01:05:36.000 Because, you know, again, this is a philosopher's kind of question.

01:05:39.000 Like, you know, physicists will just put it to use and get on with their lives.

01:05:42.000 Philosophers will say, well, what do you really mean by probability?

01:05:46.000 The 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.

01:05:57.000 That's what you mean.

01:05:58.000 It's called the frequentist idea of probability.

01:06:02.000 But then what do you say like, well, what is the probability that Donald Trump wins re-election?

01:06:08.000 That's not going to happen an infinite number of times.

01:06:10.000 You're not going to do the experiment.

01:06:11.000 Or even better, what was the probability that Lee Harvey Oswald actually was the lone shooter of JFK? That already happened.

01:06:18.000 That's in the past, right?

01:06:20.000 But we can easily say, well, I think it was an 80% chance that that's true, right?

01:06:23.000 So 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?

01:06:34.000 Like, 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.

01:06:41.000 And 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.

01:06:53.000 So, in quantum mechanics, is probability more like frequentist probability or is it more like Bayesian probability?

01:07:00.000 The answer is it depends on what your favorite version of quantum mechanics is.

01:07:03.000 In one of these spontaneous collapse theories, it's very much like a frequency.

01:07:08.000 Like, you know, you just – things happen randomly and it's purely objective.

01:07:11.000 In something like many worlds – well, sorry, I should say in something like hidden variables – It's Laplace's demon all over again.

01:07:19.000 So Laplace's demon doesn't work in a spontaneous collapse theory because the laws of physics are not deterministic.

01:07:25.000 You don't know when things are going to collapse all by themselves.

01:07:29.000 In a hidden variable theory, The hidden variables and the wave function evolve deterministically, but you don't know what the hidden variables are.

01:07:38.000 So you can assign some probability to having them be different things.

01:07:40.000 So there's some ignorance involved.

01:07:43.000 Many worlds is the coolest idea because it's kind of – and this is what is kind of hard to wrap your mind around.

01:07:50.000 On the one hand, there is only the wave function.

01:07:53.000 It describes the universe exactly.

01:07:55.000 But imagine that I measure the spin of an electron, okay?

01:07:58.000 So I actually do know what the wave function is going to evolve into.

01:08:02.000 It's going to evolve into a 50-50 split of I observed it spinning up and I observed it spinning down.

01:08:08.000 But I only ever find myself in one side or the other.

01:08:13.000 So...

01:08:14.000 There is always a moment in between when the wave function splits and when I know about it.

01:08:21.000 It splits much faster than I can know about it.

01:08:23.000 The rate, the speed of a wave function branching is some incredibly tiny number, 10 to the minus 20 seconds or something like that.

01:08:30.000 And the time scale of things happening in my brain is like 10 to the minus 3 seconds at best, okay?

01:08:36.000 So there will always be a time when there are two copies of me.

01:08:42.000 One on the branch where the spin was up, one on the branch where the spin was down.

01:08:45.000 But they're both identical.

01:08:47.000 They don't know which branch they're on yet.

01:08:49.000 So they need to be good Bayesians and say, well, what probability should I assign that I'm on one branch or the other?

01:08:55.000 And it turns out that the probabilities work exactly like the textbook quantum mechanics tells you the probability should work out.

01:09:01.000 Trevor Burrus The wave function squared is the probabilities.

01:09:04.000 Trevor Burrus The wave function squared.

01:09:05.000 Trevor Burrus Yeah.

01:09:06.000 This is a rule called the Born rule after Max Born who was the physicist who invented it.

01:09:11.000 So 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.

01:09:20.000 Schrodinger, Erwin Schrodinger of Schrodinger's cat fame – I think we're good to go.

01:09:45.000 That was his hope.

01:09:46.000 What actually happens when you solve the equation is that the electron spreads out all throughout the universe.

01:09:50.000 So his hope was dashed.

01:09:52.000 And then he's like, all right, I have this equation.

01:09:54.000 What is it?

01:09:55.000 Like, what does the wave function do?

01:09:57.000 And 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.

01:10:04.000 Like, 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.

01:10:14.000 And Schrodinger said like, oh my god, that's awful.

01:10:16.000 I'm sad I had anything to do with it.

01:10:18.000 He regretted being involved with this whole idea of probabilities and collapses and all that stuff.

01:10:24.000 Do you see an increased interest in this subject among students?

01:10:28.000 I mean, is this – this seems like a very – yeah?

01:10:32.000 I do, but, you know, with things like that, it's always hard to, you know, protect against my own biases, right?

01:10:40.000 Like I see the people who are interested come to me because I keep talking about it, right?

01:10:45.000 And maybe I'm, you know, ruining their lives by getting them interested in it.

01:10:49.000 You know, when I have real graduate students, I try – That's interesting.

01:11:01.000 So you're protecting them?

01:11:11.000 Be 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.

01:11:19.000 And part of that is get a job, right?

01:11:21.000 Like, you know, I'm not a believer in being such an idealist that you stop doing physics by the time you're out of graduate school.

01:11:27.000 You know, keep going.

01:11:28.000 Do you think it's possible to boil this down to a documentary that isn't filled with woo?

01:11:33.000 Like just a response to something like What the Bleep?

01:11:38.000 Some sort of entertaining yet clear version of what you're saying?

01:11:46.000 I think so, yeah.

01:11:47.000 If there's any producers out there who want to option my book...

01:11:50.000 Jump in, kids.

01:11:51.000 You know, I think it's...

01:11:52.000 Especially these days when computer graphics are really good, right?

01:11:57.000 And we can visualize things that we couldn't visualize before.

01:12:00.000 That would help.

01:12:00.000 Yeah, and that was...

01:12:01.000 In fact, I think that you got a copy of my book that didn't have any figures in it, right?

01:12:05.000 Didn't you get the ARC? I believe so, yeah.

01:12:07.000 That makes it much harder.

01:12:08.000 The real book has pictures in it.

01:12:10.000 Oh, okay.

01:12:10.000 That does make things hard.

01:12:11.000 Is that out?

01:12:12.000 Yeah, I'm sorry.

01:12:13.000 I should have brought a copy.

01:12:14.000 It came out last week.

01:12:43.000 Last week.

01:12:44.000 Oh, okay.

01:12:46.000 We're good to go.

01:13:06.000 And the same David Albert who appeared in What the Bleep, and we talked about quantum mechanics and the measurement problem.

01:13:12.000 And, you know, he said – he put it really well.

01:13:15.000 He said, like, if there's a figure from history who I would like to have dinner with, it would be Niels Bohr.

01:13:20.000 And because, like, he was certainly an amazingly good physicist, very, very influential.

01:13:26.000 But 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.

01:13:37.000 So 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.

01:13:46.000 And that's part of the reason why we haven't dug into the foundations of quantum theory for so long.

01:13:51.000 What was it about him?

01:13:52.000 He was just incredibly charismatic in a weird way because he was a terrible writer.

01:13:58.000 You know, there's this story where Einstein wrote this paper about entanglement and spooky action at a distance and Bohr responded to it.

01:14:06.000 And 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.

01:14:13.000 So if anyone said, well, what about Einstein's worries?

01:14:16.000 They would just say, oh, Bohr wrote a paper.

01:14:18.000 Don't worry about it.

01:14:19.000 And Bohr's paper was reprinted in this book you could buy and then you could read it.

01:14:24.000 And the pages were printed in the wrong order and no one noticed.

01:14:31.000 And it's just hard to make sense of what he said.

01:14:34.000 So – Did people pretend to understand what it was saying even though it was in the wrong order?

01:14:39.000 That's how weird it is.

01:14:40.000 Yeah, and that's how bad a communicator he was.

01:14:43.000 But in person, everyone loved him.

01:14:46.000 Like John Wheeler, who was Hugh Everett's advisor, was sort of an acolyte of Bohr.

01:14:52.000 And 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.

01:15:03.000 So he had some magnetism.

01:15:05.000 That's why David Albert wanted to meet him.

01:15:07.000 He's like, what did that guy have?

01:15:09.000 What was it like to talk to him that people loved him so much even though he was kind of wrong about the foundations of quantum mechanics?

01:15:15.000 But it's at least someone who's charismatic, who has that sort of enigmatic personality.

01:15:23.000 Trevor Burrus Yeah, that's right.

01:15:25.000 So, 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.

01:15:34.000 And I'm an atheist myself.

01:15:35.000 So I say that, you know, science leads us to not believe in God.

01:15:38.000 And I talk about this to very different audiences, churches and things like that sometimes.

01:15:44.000 Trevor Burrus How's that go?

01:15:45.000 Well, it depends very much on the age of the person in the audience is the thing.

01:15:50.000 Older people, like, they made up their minds. 1.00

01:15:52.000 They're not going to change.

01:15:53.000 But young people, even very, very religious young people, are fascinated by what I have to say.

01:15:59.000 It's not that they change their mind right away, but it's like, I've never heard someone put it that way before, right?

01:16:05.000 And maybe they do change their mind later, maybe not, but at least they've heard a perspective that they were not exposed to earlier.

01:16:11.000 I think the same thing is true with quantum mechanics.

01:16:13.000 Like, there's a buttload of books about quantum mechanics on the market.

01:16:16.000 There's no shortage of books about quantum mechanics, but they're mostly with this spirit of, isn't this bizarre?

01:16:22.000 Isn't this weird?

01:16:23.000 We'll never understand it.

01:16:24.000 And I think that that Many, many people who grew up to be physicists, this is what they're doing when they're 12 years old.

01:16:30.000 They're reading these books, right?

01:16:31.000 And so I wanted to write a book which said, like, actually, we could maybe understand this if we just tried.

01:16:36.000 It's not ineffably mysterious.

01:16:38.000 Let's, you know, be embarrassed that the field of physics has not put its effort into it and make an effort here.

01:16:45.000 And 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.

01:16:55.000 Yeah, well, the number, what would you estimate it would be currently?

01:16:59.000 Like, how many people do you think worldwide?

01:17:00.000 Yeah, it's certainly of order 100. That's it?

01:17:04.000 I think so, yeah.

01:17:05.000 Like, you know, when we have conferences, there's often 12 people there or 20 people. 0.99

01:17:08.000 Holy shit. 0.94

01:17:09.000 I mean, maybe there's more because I haven't met them all, but it always depends on how you draw the boundaries also. 0.98

01:17:14.000 Whereas, yeah, there's thousands or tens of thousands of people in most subfields of physics.

01:17:18.000 So, I mean, why would you go into the subfield where there's no money or promotion chances?

01:17:23.000 It's...

01:17:24.000 Yeah, 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,

01:17:43.000 and it's like 15 people.

01:17:45.000 Wow.

01:17:46.000 And again, it depends on where you draw the boundaries and so forth.

01:17:50.000 But if one of you guys kicks the bucket...

01:17:52.000 I know, that's how we get to get new blood in there, you know?

01:17:55.000 But like I said, I do think it's growing, it's expanding, and I'm optimistic.

01:18:01.000 I tend to be optimistic.

01:18:02.000 You know, there is this...

01:18:03.000 I alluded to it before, but let's emphasize it.

01:18:08.000 We turned on the Large Hadron Collider in 2009. We turned it on in 2008, and then it exploded.

01:18:15.000 We fixed it and turned it on again in 2009. And it found the Higgs boson in 2012. And it didn't find anything else.

01:18:24.000 And that's bad.

01:18:26.000 That'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.

01:18:41.000 There's a Higgs boson and that's it.

01:18:43.000 What about quark gluon plasma?

01:18:45.000 Yeah, that's great, but we knew it was there.

01:18:48.000 I mean, we'll learn details about it, but the fundamental underlying laws that give rise to that, we've known since the 70s.

01:18:54.000 So there's a million things we learn about, you know, like for the gravitational waves, for measuring the Higgs boson.

01:19:00.000 We pin down numbers.

01:19:02.000 We measure the cosmic microwave background, the leftover radiation from the Big Bang.

01:19:05.000 But you would like something more that you could bring to people saying that this is very valuable and tangible stuff.

01:19:11.000 Well, not just that.

01:19:12.000 I wanted to make progress, right?

01:19:14.000 So 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.

01:19:22.000 Meanwhile, 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.

01:19:35.000 And it's there, but it's beyond our reach somehow.

01:19:38.000 So it's just so hard to make progress under these circumstances.

01:19:42.000 And meanwhile, we have big, cool ideas like string theory that are hard to connect to the real world.

01:19:48.000 So 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.

01:19:59.000 So 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?

01:20:07.000 Like, how should we expect to understand quantum gravity if we don't understand quantum mechanics?

01:20:12.000 Come on.

01:20:13.000 Right.

01:20:13.000 And what was the motivation behind starting your podcast?

01:20:16.000 It's called Mindscape?

01:20:17.000 Mindscape, yeah.

01:20:18.000 Mindscape.

01:20:19.000 Yeah, I've been having lots of fun with the podcast.

01:20:22.000 It's been great.

01:20:23.000 And several episodes about...

01:20:33.000 I'll tell you the motivation was when I wrote my previous book, The Big Picture.

01:20:39.000 It was a sprawling book.

01:20:41.000 So it's not only physics, but also philosophy and neuroscience and biology and math and computer science.

01:20:47.000 There's a whole bunch of things in there that I'm not an expert on.

01:20:49.000 I'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?

01:20:59.000 So I went around talking to experts.

01:21:00.000 I interviewed people.

01:21:01.000 I had so much fun because I was writing a book.

01:21:04.000 I could literally just email a Nobel Prize winning biologist and say, could I drop by and talk to you for an hour?

01:21:09.000 And they would say yes.

01:21:10.000 And when the book was done, that went away.

01:21:12.000 I don't have the license to just call people up randomly and say, can I talk to you for an hour?

01:21:18.000 But if you have a podcast, then suddenly, yeah, people want to talk to you.

01:21:22.000 So I've gotten – I talked to Wynton Marsalis, the trumpet player, the Grammy-winning trumpet player.

01:21:31.000 I talked to Seth MacFarlane the other day.

01:21:35.000 I've talked to Nobel Prize winners, MacArthur Prize winners, philosophers, biologists, documentary filmmakers.

01:21:42.000 I just really have a blast.

01:21:43.000 So yeah, this podcasting thing, I think it's going to take off.

01:21:47.000 You should look into it.

01:21:48.000 Yeah.

01:21:49.000 Well, for me, I mean, there's no way I would be able to get someone like you to sit down and explain things like this without a podcast.

01:21:56.000 Well, it's taking advantage, I think, right?

01:21:59.000 I mean, I'm not telling you this.

01:22:01.000 Let's say we're telling the audience this, but it's...

01:22:06.000 We can talk as long as we want, right?

01:22:07.000 You take advantage of this better than anybody.

01:22:10.000 And it's different.

01:22:13.000 It doesn't replace things like books, okay?

01:22:16.000 Books are always where you can get into the weeds a little bit more specific, a little bit more careful.

01:22:21.000 But there's a long road.

01:22:23.000 There's a lot of books out there.

01:22:25.000 I'm not going to read all of them.

01:22:26.000 That was the other motivation behind starting my own podcast is that I had a stack of books I wanted to read.

01:22:30.000 And to force myself to read them, I would invite the author onto the podcast.

01:22:34.000 But...

01:22:37.000 I can't read all those books.

01:22:38.000 Which books should I read?

01:22:39.000 There's a whole journey to saying, oh, this is important enough.

01:22:43.000 I should dedicate myself to a week of my time to reading this book.

01:22:47.000 And 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.

01:22:55.000 So I'm a big believer in diverse ecosystems.

01:22:58.000 I like Twitter.

01:22:59.000 I like little YouTube videos.

01:23:01.000 I like podcasts.

01:23:01.000 I like books.

01:23:02.000 I like talks.

01:23:03.000 There's all sorts of ways to get this information.

01:23:05.000 Yeah, 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,

01:23:21.000 you know, in their seemingly mundane existence maybe just would never get in there.

01:23:26.000 And it allows these new areas of inquiry and new areas for them personally to go look into.

01:23:34.000 And 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.

01:23:53.000 And including me.

01:23:55.000 Like, literally yesterday, one of the areas that I had hoped to get onto Mindscape podcast is economics.

01:24:03.000 I'm very interested in economics. 0.93

01:24:04.000 But I realized, I don't know crap about economics.

01:24:07.000 Like, I'm not interested in, you know... 0.70

01:24:10.000 The trade deal or what interest rate the Fed should set.

01:24:15.000 And the problem with economics is it's too relevant to the real world.

01:24:17.000 So people want to talk about monetary policy and things like that.

01:24:20.000 But I want to talk about the underlying theoretical ideas, right?

01:24:23.000 And I realized it's hard to get those.

01:24:25.000 So I downloaded some economics podcasts and I started listening to them.

01:24:30.000 And this happens to me all the time.

01:24:32.000 I'm listening to a good podcast.

01:24:33.000 I'm in the car and I have to stop it to think about what just happened because they said something and it gave me an idea.

01:24:40.000 And the great thing about being a physicist is there's some relationship between what I do for a living and almost everything else, right?

01:24:46.000 Like whether it's economics or biology or philosophy.

01:24:50.000 So I can always say like, hmm, that's an interesting idea.

01:24:52.000 I wonder if I should write a paper about that.

01:24:55.000 And I wouldn't have done that very easily without the podcast format, yeah.

01:24:59.000 No, it's a really interesting time.

01:25:00.000 It's a really exciting time to spread information.

01:25:03.000 It's a really exciting time to find things that you're interested in.

01:25:07.000 And also, you know, I've always noticed this about the internet in general, which is that...

01:25:13.000 Trevor Burrus I have to sit back and think like, 1.00

01:25:33.000 oh, maybe I am full of shit. 1.00

01:25:34.000 Like where did I get that idea, right? 0.98

01:25:36.000 And 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.

01:25:51.000 It really does go like, oh, yeah.

01:25:52.000 So 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.

01:26:00.000 Yeah.

01:26:00.000 Yeah, if you're open to the floodgates, that's the problem is there's so much feedback.

01:26:07.000 It's really hard to separate the wheat from the chaff.

01:26:11.000 It is, yeah.

01:26:12.000 And, you know, different people have different strategies.

01:26:14.000 Like when I talked to Seth MacFarlane, it was interesting.

01:26:18.000 He reads the comments.

01:26:19.000 Like he wants to know.

01:26:20.000 Doesn't he have like 12 million Twitter followers or something crazy?

01:26:23.000 And he hates it.

01:26:24.000 He's like, it's poisonous and toxic.

01:26:26.000 But he reads them.

01:26:29.000 And, you know, for good reasons.

01:26:31.000 He's like, look, I'm creating entertainment.

01:26:33.000 Like, if I don't know what the people I'm trying to reach think about it, what is the point?

01:26:38.000 It's like much like me in physics, like the kind of physics I do is not building a better machine or curing cancer, right?

01:26:44.000 It's only because human curiosity leads us there.

01:26:47.000 So if I don't tell other people about it, what's the point?

01:26:50.000 And...

01:26:56.000 Yeah.

01:27:02.000 Yeah.

01:27:03.000 Yeah.

01:27:05.000 Yeah.

01:27:14.000 Yeah, I read a lot of other people's things.

01:27:16.000 I don't read any of my stuff, like any of the stuff that's coming at me.

01:27:19.000 It just got too overwhelming after a while.

01:27:22.000 And it also interferes with...

01:27:33.000 Yeah, I mean, that's the secret.

01:27:38.000 Like, people ask, like, you know, how can I spend so much time on Twitter?

01:27:41.000 And I'm like, what are you talking about?

01:27:42.000 Like, I spend five minutes a day on Twitter.

01:27:44.000 Yeah.

01:27:45.000 Tweeting and maybe another 15 minutes reading other people's tweets and zero time responding to tweets.

01:27:50.000 That's the secret.

01:27:51.000 Twitter is a terrible medium for conversing.

01:27:54.000 You just can't be precise. 0.99

01:27:55.000 You can easily misunderstand and people easily become aggressive jerks, right? 0.97

01:28:00.000 It's the worst possible way to have a back and forth unless you already know somebody and are just trying to clarify something. 0.97

01:28:06.000 Yeah.

01:28:07.000 I use it for linking to things.

01:28:08.000 Like I say, Twitter is for linking, not for thinking.

01:28:10.000 Yeah, it's like the hierarchy of communication.

01:28:13.000 Top of the food chain is one-on-one talking.

01:28:16.000 Just two people having a conversation, and especially without any sort of heightened...

01:28:22.000 Sense of importance or anger or frustration with that other person.

01:28:26.000 Just two people talking.

01:28:27.000 That's number one.

01:28:28.000 Like with no gravity, right?

01:28:30.000 Number two is probably phone calls.

01:28:33.000 Like calling someone.

01:28:35.000 You don't see them.

01:28:36.000 It's not as good.

01:28:38.000 But being in front of someone physically, one-to-one, is the best way to do it.

01:28:43.000 Which is one of the reasons why I love podcasts as well, is because you get a chance to put that energy out there.

01:28:50.000 The energy of a one-on-one, actual conversation with people.

01:28:54.000 As opposed to writing an article.

01:28:58.000 I'm sure you've had snarky articles written about you.

01:29:01.000 It's weird.

01:29:02.000 It's like, well, I wouldn't say that.

01:29:04.000 Why are you saying that?

01:29:05.000 Well, you're determining my thoughts.

01:29:08.000 And I've almost gotten to the point where I never respond to those.

01:29:12.000 But I get a lot of them.

01:29:13.000 I mean, I get a lot of them.

01:29:14.000 I'm sure.

01:29:14.000 When you started the podcast, was it always in a studio or did you do things remotely remotely?

01:29:19.000 Back in the day.

01:29:20.000 It's always...

01:29:21.000 We've only had a few conversations remotely through Skype.

01:29:26.000 And one of them was with this Egyptologist, John Anthony West, who was in poor health.

01:29:30.000 He's since passed away.

01:29:31.000 And then we eventually did get him into the podcast studio.

01:29:34.000 But I started doing it in my house.

01:29:38.000 And just with friends.

01:29:39.000 There was no...

01:29:42.000 We're good to go.

01:30:04.000 But I totally think that it's much better if you're in person.

01:30:07.000 So whenever I can do that.

01:30:08.000 I 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.

01:30:17.000 No, that's great, man.

01:30:18.000 I'm excited you're doing it.

01:30:20.000 And thank you for writing the book, and thank you for coming in here and talking about it.

01:30:24.000 And if people want to get your podcast, it's available on iTunes, it's everywhere.

01:30:27.000 Wherever podcasts are sold, yeah.

01:30:29.000 Anything else?

01:30:31.000 Many things, but you know, this is good, yeah.

01:30:33.000 Okay.

01:30:34.000 The podcast and the book are the things I'm hearing.

01:30:36.000 All right.

01:30:37.000 Well, always a pleasure, Sean.

01:30:38.000 Thank you very much.

01:30:39.000 Thanks a lot, Joe.

01:30:39.000 Thanks for being here.

01:30:40.000 Bye, everybody.

The Joe Rogan Experience - September 15, 2019

Joe Rogan Experience #1352 - Sean Carroll

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