Cosmic Queries – The Complex Universe with Sean Carroll

What does Hawking radiation look like falling into a black hole? Will we ever find a theory of everything? Neil deGrasse Tyson and comedian Chuck Nice answer questions about invisible fields, many worlds, entropy, the theory of everything, and more with theoretical physicist and philosopher Sean Carroll.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Neil deGrasse Tyson?

  I love our stable of cosmologists.

• 0:01Chuck Nice?

  Yeah.

• 0:02Neil deGrasse Tyson?

  This time Sean Carroll.

• 0:03Chuck Nice?

  Yeah, Sean Carroll.

• 0:04Neil deGrasse Tyson?

  I love him.

• 0:04Chuck Nice?

  Awesome.

• 0:05Neil deGrasse Tyson?

  Cause he's brilliant and we don't have to help out his explanations.

• 0:08Chuck Nice?

  Yeah.

• 0:08Neil deGrasse Tyson?

  Cause they're better than anything we come up with.

• 0:10Chuck Nice?

  Yeah, and every time he's on, as well as Brian Cox, or Janet Levin, or Lou, or any of them, I realize I don't know Jack. Nothing.

• 0:19Neil deGrasse Tyson?

  Coming up.

• 0:21Neil deGrasse Tyson?

  Welcome to StarTalk, your place in the universe where science and pop culture collide.

• 0:30Neil deGrasse Tyson?

  StarTalk begins right now.

• 0:36Neil deGrasse Tyson?

  This is StarTalk Cosmic Queries Edition. Neil deGrasse Tyson, you're a personal astrophysicist. We got here, of course, Lord Chuck Nice.

• 0:45Chuck Nice?

  Hey, what's happening, man?

• 0:46Neil deGrasse Tyson?

  You're locked and loaded there?

• 0:48Chuck Nice?

  I'm locked and loaded, cause we got queries, man.

• 0:50Neil deGrasse Tyson?

  And they're not just queries about anything to anyone.

• 0:53Chuck Nice?

  No.

• 0:54Neil deGrasse Tyson?

  They're queries on like cosmology.

• 0:57Chuck Nice?

  Yes.

• 0:57Neil deGrasse Tyson?

  To one of our cosmologists about town.

• 1:00Chuck Nice?

  Yes.

• 1:00Neil deGrasse Tyson?

  One of our, one of our fave interviews. We've got Sean Carroll on the line. Sean, how you doing, man?

• 1:05Sean Carroll?

  Hey, how's it going? Lord Chuck, I didn't know you got a promotion.

• 1:12Neil deGrasse Tyson?

  If you try hard like he does, you might get one too.

• 1:15Sean Carroll?

  Yeah, I mean, no kings, but lords are okay. The occasional lord.

• 1:18Chuck Nice?

  There you go. That's right. No, I'm down with the no kings, but I'm still, I'm still Lord Nice.

• 1:23Neil deGrasse Tyson?

  And so let's catch people up on your trajectory through life. You spent a lot of your professional career at Caltech over in Pasadena, and now you're, you joined us back on the East Coast in Baltimore at the Johns Hopkins University, and I've got you as the Homeward Professor of Natural Philosophy.

• 1:41Sean Carroll?

  That's right. There aren't that many of those. I'm basically the only one, so it's nice.

• 1:44Neil deGrasse Tyson?

  Right. This is a very retro title.

• 1:46Chuck Nice?

  It is.

• 1:47Neil deGrasse Tyson?

  Okay. I think Newton had a title of natural philosophy.

• 1:50Chuck Nice?

  Right.

• 1:50Neil deGrasse Tyson?

  Before the word physics was a thing.

• 1:52Chuck Nice?

  Yeah.

• 1:52Neil deGrasse Tyson?

  Yeah, and, and you're one of my favorite people out there, cause not only do you bring science to the public, which is something we care deeply about here at StarTalk, but you, you have the, for me, the best combination of astrophysics fluency.

• 2:09Chuck Nice?

  Right.

• 2:09Neil deGrasse Tyson?

  Physics fluency.

• 2:10Chuck Nice?

  Right.

• 2:11Neil deGrasse Tyson?

  And philosophy fluency.

• 2:12Chuck Nice?

  Right.

• 2:13Neil deGrasse Tyson?

  You put all that together and there's no boring conversation you will ever have, ever.

• 2:19Chuck Nice?

  True. But we're gonna try to change that today.

• 2:25Sean Carroll?

  I'm gonna take this as a challenge. Yeah, I bet I can do it.

• 2:29Neil deGrasse Tyson?

  So Sean, you had a couple of books recently. I mean, you're always out there, you know, talking physics smack with the with an interested public. You have two in a row here. Space, time and motion. You know, that's, that's, you know, what's left after that, right?

• 2:46Sean Carroll?

  Right. That's a lot. Yeah.

• 2:47Neil deGrasse Tyson?

  That's pretty much everything, right? But, but no, not for Sean Carroll.

• 2:51Sean Carroll?

  Right.

• 2:51Neil deGrasse Tyson?

  He's got quanta and fields.

• 2:54Chuck Nice?

  Oh, wow. Look at that. Now it is everything.

• 2:58Chuck Nice?

  Space, time and motion, and then quantum and fields. What's left?

• 3:01Sean Carroll?

  What's left will be volume three, which is complexity and emergence. That's what I'm nearly done with writing right now. So it's a whole three-part series called The Biggest Ideas in the Universe. Yeah.

• 3:12Neil deGrasse Tyson?

  That's definitely what that is.

• 3:13Sean Carroll?

  That is.

• 3:14Neil deGrasse Tyson?

  For sure. For sure. You know, fields is a thing.

• 3:17Sean Carroll?

  Right.

• 3:18Neil deGrasse Tyson?

  That if I didn't study physics, I'd still think they were kind of imaginary. You go back to Faraday, right? Who says, well, there's a, there's magnetism there, but there's a field. Well, can I see it? No. But, but like the, the iron filings can see it, but I can't.

• 3:36Sean Carroll?

  Right.

• 3:36Neil deGrasse Tyson?

  Okay. But if you take away the iron filings, is it still there? Yeah. And so just, just to, what did it take to get everybody comfortable with the idea of a field?

• 3:46Sean Carroll?

  That's a great question because it wasn't easy. It took a while, you know? Isaac Newton worried about the fact that he didn't know about the concept of fields. He said that there was a gravitational force between the sun and the earth. And it depends on the distance, you know, the inverse square law, the bigger the distance, the less the force. But he didn't know how it got there. How does the earth know where the sun is, how far away it is, how massive it is? And he said, you know, this is over my pay grade. I'm going to leave this for future generations to decide, which is not the kind of thing that Isaac Newton said very often. So it wasn't until the 1800s.

• 4:23Neil deGrasse Tyson?

  So he knew something was up.

• 4:24Sean Carroll?

  He knew something was up.

• 4:25Neil deGrasse Tyson?

  Needed further explanation. Yeah.

• 4:27Sean Carroll?

  Wow. Action at a distance. You know, Einstein famously said spooky action at a distance for quantum mechanics, but even Newton's time, there was this weird thing. How, what is it that takes the gravitational force and moves it from the sun to the earth, et cetera?

• 4:43Neil deGrasse Tyson?

  And vice versa, yeah.

• 4:44Sean Carroll?

  And in some way, there was, you know, there was an answer there from Laplace, Pierre-Simon Laplace, but it wasn't until Faraday, like you said, that he starts moving magnets and watching electrical currents pop up in a wire next to it, like not there, not touching it, right? Through empty space, something happened. And the great thing about Faraday was he was an absolutely genius intuitive physicist. He was not the math expert that you sometimes need to be. So Maxwell, James Clark Maxwell, came along, was a huge admirer of Faraday, and basically made it all mathematically respectable and said, yeah, there's these things called the electric field and the magnetic field, and they fill all of space,

• 5:28Sean Carroll?

  and you can't see them, but we can predict what they're gonna do, and they're super duper important for explaining everything.

• 5:35Neil deGrasse Tyson?

  I think Faraday, if memory serves, in none of his published papers does an equation of any kind appear.

• 5:41Sean Carroll?

  That's possible. I didn't know quite that factoid, but it's absolutely in keeping. You know, he was thinking about, in fact, it wasn't even fields that he primarily focused on. He imagined lines of force. So like, out of an electron, there's an electric field, we would say now, but he thought they were like literally lines of force filling all of space. And Maxwell's first papers were about trying to make mathematical sense of lines of force. And he eventually said, nah, it's better to think of fields with little vectors, so like little arrows at every point, and then the lines are sort of moving in the direction of the arrows.

• 6:17Neil deGrasse Tyson?

  And that all happened in the 19th century.

• 6:18Sean Carroll?

  All happened in the 19th century. And the great thing was, you know, if you think of the number of different apparent phenomena in the world that we now think of as electricity and magnetism in action, right? Heat, light, radio waves, X-rays, you know, the magnets, all this stuff, like very, very different things, all explained in just two Fields talking to each other, electricity and magnetism.

• 6:46Chuck Nice?

  That's amazing.

• 6:47Neil deGrasse Tyson?

  That's completely crazy.

• 6:48Chuck Nice?

  It's just crazy.

• 6:49Neil deGrasse Tyson?

  And I was just thinking, I go through this sort of existential moment, maybe once a month. I'm sitting there and I press a button on my smartphone and it changes the channel on my TV.

• 7:02Chuck Nice?

  Right.

• 7:03Neil deGrasse Tyson?

  And then I press another button, it starts my car, which is three miles away.

• 7:08Chuck Nice?

  Yeah.

• 7:09Neil deGrasse Tyson?

  You know, and I'm thinking, this is magic.

• 7:14Chuck Nice?

  Yeah, basically.

• 7:16Sean Carroll?

  Yeah, and that's, this is why writing books is good, because you write a book and you say, like, you point your remote control at your TV and a radio wave comes out and turns it on. And you get many emails saying, that's an infrared wave, not a radio wave. You don't know what you're talking about. But they're all different manifestations of electromagnetism. And so.

• 7:35Neil deGrasse Tyson?

  No, no, wait, wait, but my cellphone is not.

• 7:37Sean Carroll?

  Your cellphone is not, but your TV remote control is.

• 7:40Neil deGrasse Tyson?

  Yeah, that's for sure.

• 7:41Chuck Nice?

  Yeah.

• 7:42Sean Carroll?

  Yeah, exactly. Who knows these things? I can't keep track of these things. I'm just a theoretical physicist.

• 7:47Chuck Nice?

  It's funny, while you guys are talking, I'm sitting here with my iPad and I'm taking my finger and moving the screen up and down.

• 7:54Neil deGrasse Tyson?

  Into this void above your.

• 7:57Chuck Nice?

  Right. And it's exactly the same thing. You're like, that's, isn't that the electromagnetic field on my finger?

• 8:05Sean Carroll?

  Basically, everything is electromagnetic field. Yeah, other than gravity. It's all electromagnetism all the way down.

• 8:09Neil deGrasse Tyson?

  Yeah, we live it.

• 8:10Chuck Nice?

  We just live it.

• 8:11Sean Carroll?

  There's a hugely important philosophy of science lesson here, because like Neil said, you can't see the electric field or the magnetic field, but they're clearly everywhere. Like, we have equations that describe them exactly and make predictions and fit all the data. Therefore, we accept that they are there. You don't need to see them with your eyes to have evidence that they're part of reality.

• 8:35Chuck Nice?

  I do a whole. Stand up bit about that.

• 8:39Neil deGrasse Tyson?

  And I try to, I try to beat that into Chuck every time when I say the universe is

• 8:44Chuck Nice?

  under no obligation to make sense to you. Which, believe it or not, I can't accept. You must make sense to me because I am the center of all things.

• 8:56Neil deGrasse Tyson?

  So Sean, what's this latest paper we have you publish here, co-authored, What Hawking Radiation Looks Like As You Fall Into A Black Hole? Was that something that needed to be addressed?

• 9:07Sean Carroll?

  Uh, it's something that I've worried about for decades and honestly.

• 9:12Neil deGrasse Tyson?

  Really?

• 9:12Sean Carroll?

  Yeah, well, so here's the question. There's two things that we think are true about a black hole. One is, if you're standing very far away and you look at the black hole, Stephen Hawking says, "Black holes give off radiation." Okay, not that much radiation admittedly, especially for a big black hole, but he, again, has an equation that predicts exactly how much you should see. The second thing is, we have this feeling, no one's ever done it, but we have this belief that if you fall into a black hole, you see nothing special when you cross the boundary, when you cross the event horizon, right? It just looks like ordinary empty space everywhere. But these two statements seem a little bit contradictory because if I'm standing far away and I see radiation coming out, and then I just fall in, right?

• 9:57Sean Carroll?

  I just, I stop, you know, my rocket ship or whatever, I let myself fall in, you know, Neil, that you should see that red shift, that that radiation get blue shifted. It should look brighter and brighter and more and more energetic. So why does it turn off when you hit the event horizon? What actually happens? What is it that you see? And it turns out, this is 100% you know, implicit in all the equations that we have, but it took a lot of work to actually pull it out. And the answer, in a very short, slightly oversimplified form, is, there is high intensity radiation when you're crossing the event horizon, but you're moving so fast that you don't have time to observe it.

• 10:41Sean Carroll?

  So it looks to you like there's nothing there.

• 10:44Neil deGrasse Tyson?

  What?

• 10:45Sean Carroll?

  Yes.

• 10:47Neil deGrasse Tyson?

  You mean, in a Heisenberg Uncertainty Principle way? You don't have time to observe it?

• 10:52Sean Carroll?

  Yeah, exactly right. And by the way, before I forget, I gotta give huge credit to Chris Shalou, my co-author on this.

• 10:57Neil deGrasse Tyson?

  Your co-author, yes.

• 10:58Sean Carroll?

  He was a grad student at Harvard who just graduated, did all the heavy lifting on this and other projects, and he was fantastic. So, he, you know, he got the right answer after other people's got it wrong.

• 11:08Neil deGrasse Tyson?

  Graduate students, they have to have an exception to the slave amendment in the Constitution for graduate students.

• 11:14Chuck Nice?

  Right.

• 11:15Neil deGrasse Tyson?

  Just so you know.

• 11:16Chuck Nice?

  Why are they not, are they only three fifths of a person?

• 11:18Neil deGrasse Tyson?

  No, no!

• 11:19Sean Carroll?

  Three fifths of a scientist, yeah.

• 11:21Chuck Nice?

  Three fifths of a scientist, is that what they are?

• 11:24Neil deGrasse Tyson?

  If a graduate student did the heavy lifting, there it is.

• 11:27Chuck Nice?

  But see, that's the whole-

• 11:28Neil deGrasse Tyson?

  Shaun is in the Bahamas and his graduate student is doing it.

• 11:31Chuck Nice?

  And that's the way it should be. Shaun already did his work, okay? That's the whole idea.

• 11:35Sean Carroll?

  I would have loved to do the heavy lifting, but for his sake, I needed to let him have that experience. You know how it is.

• 11:41Chuck Nice?

  Of course, yes. I mean, listen, Leonardo da Vinci, when he painted, he had artisans that worked under him.

• 11:49Neil deGrasse Tyson?

  Yeah.

• 11:50Chuck Nice?

  And they do a bunch of the work.

• 11:51Neil deGrasse Tyson?

  Yeah.

• 11:52Chuck Nice?

  And then you come in and you sign your name.

• 11:54Neil deGrasse Tyson?

  No, but I will tell you this, that in physics and astronomy, in our journals, it is not our tradition to put our degrees after our name, the way it is in the social sciences.

• 12:08Chuck Nice?

  And why is that?

• 12:09Neil deGrasse Tyson?

  Well, I made up a reason why that's good, but I don't know if it had different origins, and Shaun, you might have some insight here. If you didn't otherwise know the people, you have no idea who is senior, who is junior, because any, a brilliant idea can come out of anybody.

• 12:23Chuck Nice?

  Gotcha.

• 12:24Neil deGrasse Tyson?

  Even your students.

• 12:25Chuck Nice?

  Right.

• 12:26Neil deGrasse Tyson?

  And so, there's no reason to segregate who's got title and who doesn't, because a brilliant idea is a brilliant idea no matter the package, and a stupid idea is a stupid idea.

• 12:36Chuck Nice?

  True, no matter who comes up with it, yeah. I like that, I like that system.

• 12:40Neil deGrasse Tyson?

  It's very egalitarian.

• 12:41Chuck Nice?

  Yeah.

• 12:42Neil deGrasse Tyson?

  I like that.

• 12:56Speaker 03

  Hi, I'm Ernie Carducci from Columbus, Ohio. I'm here with my son Ernie because we listen to StarTalk every night and support StarTalk on Patreon.

• 13:06Neil deGrasse Tyson?

  This is StarTalk with Neil deGrasse Tyson.

• 13:20Neil deGrasse Tyson?

  Sure, one other thing before we get to our Patreon questions. Something that's fascinated me for decades, ever since I could think about this question. And that's the arrow of time. Some of my earliest books in middle school are all about time and how it passes. And, and why do we know time is going forward rather than backwards? And you have some emergent thinking on that?

• 13:44Sean Carroll?

  I absolutely do. You know, this is something that was hugely important for me in my career. The arrow of time is just the fact that the past and future are different from each other, right? Like, I can have photographs of the past. I cannot have photographs that are truly representing what happens in the future.

• 14:00Neil deGrasse Tyson?

  AI's got your future.

• 14:01Sean Carroll?

  Lord Chuck can do it, but I can't do it. So, you know, why is this true? And Aristotle wouldn't even have had the question. Like, there are, there's different things. Like, why is an elephant not in orange? Like, what are you even asking? But once Isaac Newton comes along with his theory of physics, suddenly the distinction between the past and future disappears. Like, these equations don't treat the past and future differently. So, it turns out, long story short, that it's a cosmology question. The early universe, 14 billion years ago, near the Big Bang, was in a very special, organized state. And it's becoming more disorganized and higher entropy, as we say, ever since then. That's where the arrow of time comes from. But, okay, why was the early universe like that? And that, we don't know.

• 14:46Sean Carroll?

  So, I wrote a paper about this 20 years ago. And I'm re-visiting that now to try to improve upon it. We still don't know, but I do think we're making progress in that direction.

• 14:54Neil deGrasse Tyson?

  Well, I'd hope so after 20 years.

• 14:56Sean Carroll?

  That's not very long in the history of the universe. Yeah, I was gonna say.

• 15:00Neil deGrasse Tyson?

  Oh, excuse me, oh, universe on me. It's a fourth of your life, a fifth of your life.

• 15:06Sean Carroll?

  The universe will wait.

• 15:08Neil deGrasse Tyson?

  We know which direction time moves because certain phenomena we would never see in reverse. Like some famous ones are that you drop a blob of ink in water. The ink will disperse. You never see that happen in reverse. Right. So if you if you're just eavesdropping on a scene.

• 15:26Chuck Nice?

  Right.

• 15:27Neil deGrasse Tyson?

  And no one told you which way time was pointing. Just by phenomena that occur, you should be able to know. You should be able to figure it out.

• 15:34Chuck Nice?

  Yeah. Like you never see an orange fall up from the ground back onto a branch.

• 15:39Neil deGrasse Tyson?

  Right.

• 15:39Sean Carroll?

  But these are, you know, you're picking good examples, but let's admit you're picking the easy examples. We understand those examples, but I can make a choice about what to do right now. Like I could make a choice right now. This is the most boring podcast ever. I'm going to storm off and not do it.

• 15:55Chuck Nice?

  You won't be the first.

• 15:59Sean Carroll?

  But I can't make a choice now not to have come on the podcast in the first place. I can't make a choice that affects the past.

• 16:08Chuck Nice?

  Oh, look at that.

• 16:09Sean Carroll?

  And so that's right there at the boundary of physics and philosophy. Both the physicists and the philosophers need to think about this. And again, we have good ideas, but there's still work to be done.

• 16:18Chuck Nice?

  Wow. And now, now you got me thinking about the multiple timelines and uh, parallel universes and every single, like if we are on a, call it a trajectory. Every choice that we make, all those other possible trajectories from this point of decision still continue forward just without me. So what the hell is happening there?

• 16:51Sean Carroll?

  Not sure if I'm quite on board with your um, explanation there about what's going on.

• 16:56Chuck Nice?

  Well, no, what I'm saying is I'm being way too literal, Sean. What I'm saying is the possibilities of all those trajectories.

• 17:04Neil deGrasse Tyson?

  Well, to the many worlds hypothesis.

• 17:06Chuck Nice?

  Is that what that is?

• 17:06Neil deGrasse Tyson?

  I think that's what you're describing there.

• 17:08Sean Carroll?

  Okay. Well, it's pretty close. I mean, many worlds is like really down to earth and, and equation based. There's the Schrodinger equation of quantum mechanics tells you what set of things happen in. The future and which don't. And it's a it's not because you're making a decision that creates a difference between one world and another. It's because of entanglement in the underlying quantum structure of reality. But but we do have reason to believe that there are other copies of the universe where things turned out a little bit different. And it's it's you can all if you have an iPhone, you can download an app called Universe Splitter. And I'm a big I'm a big salesman for this app here. And I don't get any commission or anything, but I think everyone should get it because when you're torn between two decisions.

• 17:54Sean Carroll?

  You know, should I take this job or should I, you know, just continue living a life of leisure? You can ask the phone and it will, you know, you can plug in these two options and it will send a photon down a beam splitter that has a 50 50 chance of saying, you should take the job. Or you should just stay sitting around and then there'll be if you do it, if you obey the instructions, you know, there will be a world in which you did the other thing.

• 18:19Chuck Nice?

  That brings me to my question.

• 18:22Neil deGrasse Tyson?

  You got a question before we start.

• 18:24Chuck Nice?

  Before we even start. And specifically.

• 18:27Neil deGrasse Tyson?

  Did you pay your $5 a month?

• 18:28Chuck Nice?

  I'm I owe you.

• 18:31Sean Carroll?

  In another world, he did.

• 18:32Chuck Nice?

  In another world.

• 18:38Chuck Nice?

  That's funny. All right, Sean, this is specifically for you. Okay, I this question.

• 18:45Neil deGrasse Tyson?

  That is your question.

• 18:45Chuck Nice?

  It's my question. First of all, you have to be familiar with this experiment. And the double slit delayed choice quantum eraser experiment. Okay.

• 18:54Sean Carroll?

  I know you've been worried about that one. Yeah.

• 18:56Chuck Nice?

  No, I really am, Sean. I'm dead serious.

• 18:58Neil deGrasse Tyson?

  So Sean.

• 18:59Chuck Nice?

  I told Neil, this is keeping me up at night.

• 19:01Neil deGrasse Tyson?

  Sean, that's a thing.

• 19:02Sean Carroll?

  It's a thing. Yeah, it's a thing. Right.

• 19:03Chuck Nice?

  It's the double slit delayed choice quantum eraser experiment.

• 19:06Neil deGrasse Tyson?

  Okay, I'd never heard of this. Okay, go.

• 19:08Chuck Nice?

  Okay, and and maybe it's all I don't know, maybe it's I read about it and I'm just like, this is crazy. Maybe it's BS. I don't know.

• 19:14Neil deGrasse Tyson?

  Give it to me.

• 19:15Chuck Nice?

  So it appears that the photons know they're being measured, like they actually know. All right, so the signal photons and the Idler photons show a constructive wave interference pattern when they're not measured by a detector. But there's four detectors and they can't know because of the way the detectors are set up, because the photons are split and some go on not to be measured and some go on to be measured. Okay, now, here's the deal. There is no wave interference pattern when they are measured. So this makes it look like they know when they're being observed. I can understand the whole explanation of entanglement.

• 20:00Chuck Nice?

  I don't know why, I should say I can accept it. I don't know why it's easy for me to accept that, but I can just accept it. What I can't know or understand is a particle knowing that it's being watched. So are there any hypotheses that would explain why this thing would know?

• 20:24Neil deGrasse Tyson?

  So that's just that your query there, sounds like you just need the double slit experiment.

• 20:30Chuck Nice?

  No.

• 20:30Neil deGrasse Tyson?

  I'm still distracted by the rest of what it's called.

• 20:33Chuck Nice?

  No, this is beyond the double slit experiment. Because, well, maybe I'll let Sean explain it, because I can explain it, but I'm probably not going to do, explain it as eloquently as Sean, the way the experiment is set up.

• 20:45Sean Carroll?

  It's a, yeah, the double slit experiment is of course, a famous thought experiment originally. They wrote down what it should do long before they ever did it, to illustrate the magic of quantum mechanics. You have a single electron going through two slits. It's detected somewhere on the other side. And it's just a dot, you know, you can't figure out that much from the dot, but you do that many, many, many times and what you see is an interference pattern. It's like a wave went through the two slits and waves go up and down depending on how far away they are from the target. And so a wave going through one slit can interfere with the wave going through the other slit and that's what you see in the distribution of dots on the detector screen.

• 21:25Sean Carroll?

  So the miracle occurs when you observe which slit the electron goes through, right? Because in the Copenhagen usual way of thinking about quantum mechanics, when you observe the electron, you collapse its wave function. It's no longer going through both slits. You saw it go through one or the other. And magically, the interference pattern goes away. Because indeed, you changed the electron dramatically by observing which one it goes through. So that's all, that's all standard stuff. Everyone, you know, and their mom learns that in kindergarten when they're learning about quantum mechanics. The delayed choice quantum eraser experiment is a hilariously convoluted elaboration of that,

• 22:09Sean Carroll?

  which makes people feel bad for no good reason at all.

• 22:13Chuck Nice?

  Oh, thank God.

• 22:14Sean Carroll?

  I actually wrote a blog post about it called "The Notorious Delayed Choice Quantum Eraser", where I make fun of people who are trying to make you lose sleep because of this.

• 22:25Chuck Nice?

  Well, they got to me.

• 22:26Sean Carroll?

  They got it, I know, yeah. We're all victims here, I think. So the way that that works is, rather than just observe whether the electron goes through the left slit or the right slit, what do you mean by observe? You mean like, maybe you with your eyeball or with some measuring apparatus have detected it. But what if you just entangle it a little bit? Like, you entangle it with one little particle, okay? Then, unlike if you personally had observed it, you could imagine unentangling it. You could imagine not letting it get the interference pattern destroyed, or you could imagine having it be destroyed. And you can make that decision after the electron's been detected. That's the slightly spooky part, right?

• 23:09Chuck Nice?

  That's, that's the spooky part, right.

• 23:10Sean Carroll?

  If you were the kind of person who spoke a language of, "The electron goes through one slit or the other slit and it's making a decision", then what Chuck says, like, "It sounds like the electron's decision was affected by what I did after it was detected. Oh my God, how could that be?" But if you just talk the language of a wave going through and becoming entangled and taking quantum mechanics seriously, all of this is 100% what is predicted by the Schrodinger equation of quantum mechanics, without anything knowing anything, anything making any choices, or anything going backward in time.

• 23:48Chuck Nice?

  Okay.

• 23:49Neil deGrasse Tyson?

  So there.

• 23:49Chuck Nice?

  So there you have it.

• 23:51Sean Carroll?

  It's hard to explain, but I encourage people to Google notorious delayed choice quantum eraser, and they will find my blog post and they will hear it all. And this is literally the chapter I wrote for my book, Something Deeply Hidden, which is all about quantum mechanics. And I read the chapter and said, this is too much. Like, they don't need this. Like, this is too complicated and specific. So I just made it a blog post instead.

• 24:14Neil deGrasse Tyson?

  Excellent. And where do we find that blog post?

• 24:16Sean Carroll?

  On my blog, preposterousuniverse.com/blog. But again, if you just Google delayed choice quantum eraser with the word notorious in front, my blog post will come up first, I promise you.

• 24:27Neil deGrasse Tyson?

  Preposterous universe.

• 24:28Chuck Nice?

  Preposterous universe. That's preposterous.

• 24:31Sean Carroll?

  Exactly.

• 24:34Neil deGrasse Tyson?

  All right.

• 24:34Chuck Nice?

  All right. Well, that was good, man.

• 24:35Neil deGrasse Tyson?

  All right.

• 24:36Chuck Nice?

  Well, thanks for that.

• 24:36Neil deGrasse Tyson?

  You got your $0 worth out of that one.

• 24:38Chuck Nice?

  Yeah, I got my $0 worth of it.

• 24:39Sean Carroll?

  It's a perfect example of, rather than trying to demystify quantum mechanics, sometimes people try to mystify it. They try to make it sound even more confusing than it is.

• 24:50Chuck Nice?

  Even more.

• 24:50Sean Carroll?

  Quantum mechanics really is confusing. You don't need to make it sound more confusing than it is. And that's what this is doing.

• 24:56Chuck Nice?

  That's, and you're absolutely right. Well, that's cool, man. I'm, well, I appreciate that. Okay, here we go. This is from our buddy Kevin the Semmelier. And he says, if dark matter were a wine varietal,

• 25:14Chuck Nice?

  would we be at the, I know it exists, but I can't quite describe it, stage? Or the, I swear I taste something, but everyone thinks I'm making it up stage?

• 25:27Chuck Nice?

  That's funny. On a more grounded note for the holidays, Gaia Promis.

• 25:33Neil deGrasse Tyson?

  Gaia.

• 25:33Chuck Nice?

  Gaia.

• 25:34Neil deGrasse Tyson?

  Gaia.

• 25:35Chuck Nice?

  Gaia. Oh, Gaia, like Gaia.

• 25:36Neil deGrasse Tyson?

  G, no, G A.

• 25:38Chuck Nice?

  G A J A. Gaia.

• 25:39Neil deGrasse Tyson?

  It's Italian.

• 25:39Chuck Nice?

  Okay. Gaia Promis, which is a beautiful super Tuscan, will pair incredibly well with any roast that you are planning.

• 25:47Neil deGrasse Tyson?

  Oh.

• 25:47Chuck Nice?

  And you're familiar with this Gaia Promis.

• 25:50Neil deGrasse Tyson?

  It's expensive, but it's good.

• 25:51Chuck Nice?

  Okay.

• 25:52Neil deGrasse Tyson?

  Yeah, yeah.

• 25:52Chuck Nice?

  All right. And you say, you say that like, Chuck, you can't afford it. That's what you just said.

• 25:57Sean Carroll?

  That's what I was hearing.

• 25:58Chuck Nice?

  That's all I heard. You were like, Gaia, yeah, Chuck, you cannot afford it. Okay. So maybe one day I'll pour it for you at my house. In the meantime, keep dreaming.

• 26:06Sean Carroll?

  But the yellowtail's good, Chuck. Don't worry, you'll love it.

• 26:10Neil deGrasse Tyson?

  Two Buck Chuck.

• 26:11Chuck Nice?

  Two Buck Chuck, I'm down.

• 26:13Neil deGrasse Tyson?

  So, so in that question, I guess he tried to, using his wine expertise, trying to probe, what's really going on with the dark matter, dark energy or both?

• 26:23Chuck Nice?

  No, he said, dark matter.

• 26:25Neil deGrasse Tyson?

  Just dark matter.

• 26:25Chuck Nice?

  Yeah.

• 26:26Neil deGrasse Tyson?

  Yeah, could you just put some, some anchoring on to, because a lot of people think we're just making it up.

• 26:33Chuck Nice?

  Yeah, making it up.

• 26:34Neil deGrasse Tyson?

  Yeah.

• 26:34Chuck Nice?

  And does it have to be a particle?

• 26:36Sean Carroll?

  Ooh, ooh, that's a tougher one. You made it tough. I had an easy question. You threw me a softball there.

• 26:40Chuck Nice?

  See, this is what I do, man. You just saw what I did with that stupid delayed double slit thing. I can't help, and Neil, we just did this earlier. We were together earlier before you got on, and he was just like, Chuck, you overthink everything. Just calm down, bro.

• 26:58Sean Carroll?

  Look, you know, back in my day, when, when Neil and I were young, it was perfectly okay to think that maybe dark matter didn't exist. In other words, there were absolutely things going on in galaxies and clusters of galaxies, things like that, that looked like dark matter, looked like there's more matter in a galaxy than we could attribute, account for just by counting the stars and the gas and the dust. But maybe there was something weird going on with gravity, you know, maybe Isaac Newton and Albert Einstein didn't have the last word. We've long since passed that phase of the development of cosmology. And I think a lot of people haven't caught up because we've learned so much more from the leftover radiation from the big bang, the cosmic microwave background, from gravitational

• 27:42Sean Carroll?

  lensing with clusters of galaxies, from the growth of structure of galaxies and clusters and things like that. Dark matter exists. It's really there in some form or another. Now, maybe gravity's also modified. That's, that's perfectly okay. But yeah, there's something called dark matter. Is it a particle? Well, we got to admit, we don't know what it is. The range of possibilities goes from, you know, some tiny fraction of the mass of an electron to the mass of the moon or something like that, right? I mean, there's a very, very large range of possible masses that dark matter could have. If it's a particle, could it be something beyond a particle?

• 28:20Sean Carroll?

  It always could be like anything is possible, but boy, it really acts like particle like like we know a lot about where the dark matter is, how much of it there is, how fast it's moving. It looks exactly like some massive slowly moving particle that was sort of still stationary in the early universe. And started moving ever since then. So it's our job to go actually find it, then we'll know.

• 28:46Neil deGrasse Tyson?

  So two small points. The I I whenever given the occasion, I don't describe it as dark matter because we don't know it's matter. But it is definitely dark gravity. That's what it is. Right? Because we're tracking gravity at every turn that we say we're measuring the dark matter. So I think that's the the most honest way to describe it because because Sean, you've seen this there there there. Clickbait. There's a news article that says, you know, scientists may be wrong about dark matter.

• 29:18Sean Carroll?

  Of course.

• 29:19Neil deGrasse Tyson?

  It might not be matter.

• 29:20Sean Carroll?

  Yeah.

• 29:20Neil deGrasse Tyson?

  But you're right, but we can't be wrong about dark gravity because we don't know what it is. Right? I'm just trying to distinguish that.

• 29:26Sean Carroll?

  No, I think that's a perfectly good and fair distinction, but I think that I would just be more conclusive about what we do know, you know, like I said.

• 29:34Neil deGrasse Tyson?

  And you sounded very good there. You've sounded really good.

• 29:37Sean Carroll?

  In the 80s, what we were discovering was there's more gravity at the edges of galaxies than there is that you would predict from the stars, et cetera, inside. So, okay, maybe gravity is different, but nowadays we see gravity where there is no ordinary matter to cause it. So it's not just that the strength of gravity is different, but it's just pointing at something which we're not seeing. So that's dark matter.

• 30:06Neil deGrasse Tyson?

  You said a moment ago that we might one day need to modify gravity, but that's not what we need to do to explain dark matter.

• 30:15Sean Carroll?

  It is not sufficient to explain dark matter. We need extra stuff out there and just to be super duper clear, because again, much like the notorious delayed choice quantum eraser experiments. Sometimes people like to make things harder to understand rather than easier to understand. There are people who have theories of modified gravity. Where they've changed Einstein's theory of gravity and they say, I can explain away the dark matter. But when you look at their theory of gravity, in addition to changing gravity, they've also put new sources of gravity in there, which are just dark matter.

• 30:49Chuck Nice?

  Right. They break the universe in the process. Okay. All right. Well, that's Okay. Kevin, kudos for the Thank you, Kevin. Creative posing of the question. This is Rachel Ambrose. And Rachel says, hey, Rachel here from Austin, Texas. I'm a big fan of Sean and his Mindscape podcast.

• 31:09Sean Carroll?

  Thank you, Rachel.

• 31:10Chuck Nice?

  I've been thinking.

• 31:11Sean Carroll?

  Product placement.

• 31:14Chuck Nice?

  Rachel says, I've been thinking about the spinning universe hypothesis, which says the entire universe may be rotating very slowly as a whole. This was hypothesized to help resolve the Hubble tension. But I was thinking, if it's true, could this also help us explain dark energy as a kind of centrifugal force, or centrifugal, depending upon how you want to say it?

• 31:40Sean Carroll?

  Yeah, look, I'll be super honest. And my honest answer is, I don't know. That sounds like a research program. Rachel should write a paper about this and submit it to the Physical Review. I don't, I doubt it, is the slightly longer answer, because if the universe is rotating, then that tends to break the isotropy of the universe.

• 32:05Chuck Nice?

  Okay. God bless you for that.

• 32:07Sean Carroll?

  I'm gonna, I'm gonna fill you in. Isotropy just means things look the same in every direction.

• 32:13Chuck Nice?

  Okay. Statistically the same. Statistically the same. Not exactly the same. Of course.

• 32:18Sean Carroll?

  That's right. So there's not like a big hotspot in one side of the universe and cold spot on the other side. It's more or less the same average everywhere with little fluctuations around it.

• 32:27Chuck Nice?

  And we have that right now.

• 32:29Sean Carroll?

  That's exactly what we have. And so, once you start messing with that, can you mess with it like just a little bit and maybe no one has noticed yet? Sure, you absolutely always can. But it's hard to do that. And the theory that we have for dark energy With Einstein's cosmological constant, just does a really good job at fitting the data in a sort of a simple, direct, blatant kind of, here I go kind of way. So I'm absolutely open to creative new things like the rotation of the universe, but where would that come from? I'm not sure. And what other effects would it have on observable quantities? I'm also not sure. So that sounds like a work.

• 33:10Chuck Nice?

  Okay, very cool.

• 33:12Neil deGrasse Tyson?

  I think we still need verification that that net angular momentum is manifest everywhere. I think it was just one pocket of the universe where they made this measurement. And, and so you would need to do more of the universe to reveal this.

• 33:26Sean Carroll?

  Right.

• 33:26Neil deGrasse Tyson?

  If it's really true. So it was just, it was the, it's which way spiral galaxies are rotating.

• 33:31Sean Carroll?

  Right.

• 33:31Neil deGrasse Tyson?

  If there's a net rotation in one direction over here, that says there's something going on in the whole universe.

• 33:37Sean Carroll?

  Gotcha.

• 33:37Neil deGrasse Tyson?

  Right. Because these galaxies wouldn't know about each other necessarily. There's something.

• 33:42Sean Carroll?

  So they would be, they're responding to the same thing.

• 33:44Neil deGrasse Tyson?

  Exactly.

• 33:44Sean Carroll?

  That's the case.

• 33:45Chuck Nice?

  Correct.

• 33:45Sean Carroll?

  I got you.

• 33:45Chuck Nice?

  Correct.

• 33:46Sean Carroll?

  By the way, there's just, just to, so people know that you got to be careful about these things. There was one study that had the brilliant idea, it was a while back, so we didn't have, you know, the computers weren't there. They had volunteers. It was like citizen science. They said, here are some pictures of spiral galaxies. You go through them, you citizen scientists, and tell us, are they counterclockwise spirals or are they clockwise spirals? Okay. And you would expect it to be 50 50, but it was like 70 30. Like there were a lot more clockwise spirals than counterclockwise spiral. And astronomer was like, oh my God, what is going on? And someone had the brilliant idea, okay, let's give the same galaxies to the same people, but let's take the mirror image of them. Let's flip them.

• 34:30Chuck Nice?

  Ah, what a smart idea.

• 34:32Sean Carroll?

  And guess what? It was still 70% clockwise galaxies. It was, people were seeing things. People are not unobjective.

• 34:41Neil deGrasse Tyson?

  Get people out of the equation.

• 34:43Chuck Nice?

  Yeah, there you go.

• 34:45Sean Carroll?

  So you just, just got to be careful about all of these things.

• 34:47Chuck Nice?

  Sean Browning says, hello, this is Sean Browning from Hood River, Oregon. In a previous episode, Neil stated that if you were to fall into a black hole, that would see the future in, of the universe unfold. Or you would see the future of the universe unfold.

• 35:04Neil deGrasse Tyson?

  Behind you.

• 35:05Chuck Nice?

  Right.

• 35:05Neil deGrasse Tyson?

  Yeah, yeah.

• 35:06Chuck Nice?

  If that's true, then what would happen if the black hole finished evaporating before the universe ended?

• 35:15Sean Carroll?

  So I think that the details matter here. You know, there's a way that we have of thinking about black holes that is sort of idealized. Like, I wrote a textbook on general relativity, and you can learn about black holes in there. But the real world black holes are messy, and you know, they're made of stuff and things like that. So I don't actually think it's true that you see an enormous amount of the past of the universe in a real black hole. In a real black hole, you would, as you know, get spaghettified and die very quickly, right? So if you're in a real evaporating black hole, you would first get spaghettified, and then you would be released as a stream of black body radiation. And none of you is experiencing anything here. So, you know, I think that you don't need to worry.

• 35:58Sean Carroll?

  Like, you would see more, maybe, than you would if you were outside the black hole. But there's no apparent paradox that you're gonna see the whole thing.

• 36:05Chuck Nice?

  Got you. Okay. You're very literal, Sean.

• 36:09Neil deGrasse Tyson?

  But the point is, if your time is slowing down as you near the black hole, then the time for the rest of the universe is speeding up, right? I mean, you see, sorry, you're normal, and the rest of the universe is speeding up. So I think that's the foundation of this question.

• 36:27Chuck Nice?

  That is.

• 36:28Neil deGrasse Tyson?

  However long it takes you to fall into the black hole, will the universe, or vice versa, will one of them live out their days before the other one finishes what it's doing?

• 36:36Sean Carroll?

  I think that you should always think about, I mean, what I would like is that everyone in the world thought about spacetime diagrams and light cones. You know, your past light cone, which is the set of all things that can send light signals to you without moving faster than the speed of light, it never covers the whole universe. It never sees the future. It never sees things that are further away from you than the speed of light can get. That's true whether you're inside a black hole or not. So there's some quantitative question about how much you see, but there's no worry you're seeing things that didn't happen yet before the black hole evaporated.

• 37:11Chuck Nice?

  Wow, that, well, that's a bummer.

• 37:16Sean Carroll?

  You're the one falling into a black hole. There's other bummer's you have to worry about. Let me tell you.

• 37:20Chuck Nice?

  This is true.

• 37:21Neil deGrasse Tyson?

  It's not your biggest bummer.

• 37:22Chuck Nice?

  It's not the biggest bummer.

• 37:25Chuck Nice?

  All right, this is Shadow Dominic, and he says.

• 37:28Neil deGrasse Tyson?

  That's the name, Shadow Dominic?

• 37:30Chuck Nice?

  Yeah.

• 37:30Neil deGrasse Tyson?

  All right.

• 37:31Chuck Nice?

  He says, hi, this is Dominic from Madison, Wisconsin. If you could instantly know the answer to one currently unsolved physics problem, no strings attached. Was that a pun?

• 37:43Neil deGrasse Tyson?

  No. Stay away from string theory.

• 37:46Chuck Nice?

  Was that a pun? What are you doing, bro? He says, which one would you pick and why?

• 37:51Sean Carroll?

  I mean, the cheating answer is, yes, tell me the theory of everything.

• 37:56Sean Carroll?

  Then I could like work out everything else from that.

• 37:58Neil deGrasse Tyson?

  Let me, let me double up behind you. What gives you the confidence that a theory of everything even exists?

• 38:06Sean Carroll?

  Because the universe exists.

• 38:08Neil deGrasse Tyson?

  No, no, no, I'm not accepting that. No, don't tell me. No.

• 38:11Sean Carroll?

  You should accept the universe, Neil.

• 38:16Neil deGrasse Tyson?

  It could be that quantum physics and general relativity in this universe never come together and there's nothing that would ever bring them together. That's just how the universe is. We're invoking a philosophical bias of beauty to even assert that there is one theory of everything.

• 38:38Sean Carroll?

  Nope, that's not true.

• 38:39Neil deGrasse Tyson?

  Oh, tell me.

• 38:40Sean Carroll?

  The universe exists. There is something that happens, right? We don't know the best way of summarizing what happens. The best way of summarizing what happens in the universe might just be to literally list everything that happens. That'd be a terribly uninformatory theory of the world. We think we can do much better than that. I'm not saying that the theory of everything is simple or elegant or fits on a napkin or a T-shirt or anything like that. But there is some full and complete description of the universe.

• 39:08Neil deGrasse Tyson?

  The fact that you said it could be a very long account of everything that happens. But if it's everything that, that happens, then that's.

• 39:16Chuck Nice?

  And it's everything that happens.

• 39:17Neil deGrasse Tyson?

  Then it's everything that happens.

• 39:18Chuck Nice?

  Yeah, okay.

• 39:18Neil deGrasse Tyson?

  So that could be just a really messy, ugly, not philosophically beautiful theory of everything. Because there's a page in the book for everything that happens.

• 39:25Chuck Nice?

  Right.

• 39:27Sean Carroll?

  Because I'm very much in agreement with the philosophy that we should not be going around telling the universe how to behave. Like, we can't decide ahead of time what the universe is like. It's absolutely possible that the ultimate explanations are not that simple. I actually don't believe that. I think the ultimate explanation probably will be really, really simple, but I don't know. Yeah.

• 39:46Chuck Nice?

  What if you can't access that information? Like, it is non-accessible on this plane of existence, but the answer is there.

• 39:58Neil deGrasse Tyson?

  Or you're saying, are we just too stupid as humans?

• 40:02Neil deGrasse Tyson?

  That's another way to ask your question.

• 40:04Chuck Nice?

  Yeah, I guess it is.

• 40:06Neil deGrasse Tyson?

  Do you think that we have sufficient intellect to even get there?

• 40:10Sean Carroll?

  Yes.

• 40:10Chuck Nice?

  Okay.

• 40:11Neil deGrasse Tyson?

  Oh, alright. That's encouraging. Loving him some Homo sapiens there. Okay.

• 40:16Sean Carroll?

  I mean, again, we don't know, but what I like to do is just think about how far we've already come, you know? A hundred years ago, we had just finished getting quantum mechanics. We didn't know about the expansion of the universe. We certainly didn't know about quantum fields and the standard model and all these things.

• 40:34Neil deGrasse Tyson?

  We didn't know about other galaxies yet. It happened in 1926.

• 40:38Chuck Nice?

  Holy moly.

• 40:39Neil deGrasse Tyson?

  Yeah.

• 40:39Sean Carroll?

  Of course, it's possible we'll never get there, but the rate at which we've been learning things, and this is just the past hundred years. Think about the past thousand years, and 10,000 years from now, we're gonna know a lot.

• 40:54Chuck Nice?

  If we're here.

• 40:55Neil deGrasse Tyson?

  Yeah. If we are here. One of the hypotheses that I thought was intriguing was that as we measure the limits of whatever the limits are of what we're measuring, we might reach a cutoff like in a Truman Show example where he goes to the horizon, but the horizon is a painted...

• 41:17Neil deGrasse Tyson?

  Sky. So we, we, we look at like the energy levels of gamma rays or the, we find a cutoff that would have no natural explanation, other than that somebody programmed this and they had to put in a limit because they couldn't put infinity into their software.

• 41:36Sean Carroll?

  Yeah. Yeah. So I think that's, it's fascinating to imagine at a slightly more detailed, careful level, what are the ways that we could become convinced that we're not ever going to find a simple theory of, of everything?

• 41:51Neil deGrasse Tyson?

  That's another way to think about it.

• 41:52Sean Carroll?

  Yeah. And things like that are, you know, maybe we get evidence that we live in a simulation or the, you know, that, that, that, that the laws of physics are different from place to place and time to time. And so even if we get them figured out here, we won't know them some other way. But again, what's amazing to me is how rock solid and reliable the laws of physics are. Like we're able to extrapolate them way past the environments in which we invent them and they still work. Just, I just gotta put one example on the table, which is big bang nucleosynthesis. This is my favorite example of exactly this, you know, a bunch of scientists, mostly in the 20th century, figured out the rules of nuclear physics, the rules of gravity,

• 42:35Sean Carroll?

  the rules of cosmology, and they realized the universe is 14 billion years old and they extrapolate these rules back to when the universe was one minute old. And they make a prediction for how much hydrogen and helium they should be, and they got it right. Like, what in the world? That's the impressive thing to me. Like, we can figure this stuff out.

• 42:57Chuck Nice?

  Fantastic. Oh, that is, well, that's, that's, that's very encouraging.

• 43:02Neil deGrasse Tyson?

  And there's another, uh, there's an example I got from Rich Gott. George Gamow makes a prediction based on this early nucleosynthesis of the universe, that there should be a residual

• 43:16Neil deGrasse Tyson?

  Temperature.

• 43:17Chuck Nice?

  Okay.

• 43:17Neil deGrasse Tyson?

  Of the universe.

• 43:19Chuck Nice?

  And that would be the temperature, pretty much, not pretty much, that would be the temperature everywhere.

• 43:22Neil deGrasse Tyson?

  Everywhere, everywhere. So, so, so he, so think of the, the level of extrapolation this required. And he said the temperature would be 10 degrees. Okay.

• 43:33Chuck Nice?

  Okay.

• 43:33Neil deGrasse Tyson?

  So then we finally measure it. It's three degrees.

• 43:37Chuck Nice?

  Wow.

• 43:38Neil deGrasse Tyson?

  Okay, so you can say.

• 43:39Chuck Nice?

  He was an idiot. He really crapped the bed.

• 43:46Sean Carroll?

  The standards were lower back then, Chuck. It was a very different time.

• 43:50Neil deGrasse Tyson?

  But Rich Gott said, that's like predicting that a 10 foot flying saucer would land on the lawn of the White House. But it was a three foot flying saucer.

• 44:01Chuck Nice?

  Right, yeah. That's pretty wild.

• 44:03Neil deGrasse Tyson?

  Oh, my gosh, it's a flying saucer.

• 44:06Chuck Nice?

  No, that's super impressive.

• 44:07Neil deGrasse Tyson?

  Yeah.

• 44:08Chuck Nice?

  Yeah. All right, very cool.

• 44:09Neil deGrasse Tyson?

  So you, you, you helped me, talked me off the ledge there. You know, every now and then I just wake up skeptical.

• 44:14Chuck Nice?

  Yeah.

• 44:15Neil deGrasse Tyson?

  That we're gonna ever figure anything out.

• 44:16Chuck Nice?

  Mm hmm.

• 44:17Neil deGrasse Tyson?

  And what we have figured out, I need to be more impressed with that.

• 44:20Chuck Nice?

  People are impatient. Yeah, I know. Like, it'll, it'll take some time.

• 44:23Neil deGrasse Tyson?

  Thank you.

• 44:47Neil deGrasse Tyson?

  So what, what else you got?

• 44:49Chuck Nice?

  All right, this is Shota. I'll say Zidzy Gurry. Zidzy Gurry.

• 44:56Neil deGrasse Tyson?

  I'm betting that is so not right, but go on.

• 44:58Sean Carroll?

  Easy for you to say.

• 45:01Chuck Nice?

  All right, Shota Zidzy Gurry. Anyway, hello, this is Shota from Georgia. What a name like that. Anyway.

• 45:10Chuck Nice?

  Maybe it's Soviet Georgia. I mean, Georgia. Yeah, it's not Soviet anymore. But yeah, I know what you're saying. He said, or Shota says, regarding the many worlds interpretation, is it simply a mathematical framework we use to describe quantum behavior and apparent wave function collapse? Or do you think it represents an actual physical process in which the universe truly branches into separate real worlds? Yeah, how real are these, these other worlds? These many worlds?

• 45:41Sean Carroll?

  Yeah, it's a great question. So the way I like to think about it is, we have an equation, the Schrödinger equation. You can read about it in my book, Quanta and Fields, by the way. And the equation makes predictions for what's going to happen. And the, the simplest reading of the prediction is that the universe branches into these many copies, slightly changed because in one, the electron is spinning clockwise and the other it's counterclockwise, but otherwise the universe is the same. And we live in one of those possibilities. We don't see the other ones and it seems to fit the data. So then you say, okay, what about all those other possibilities? Should we take them seriously as real? And the answer is, if you take our possibility as real, then you have two choices.

• 46:26Sean Carroll?

  Number one, either you take the other possibilities as also real, you know, you treat them equal. They're all there in the equation. I'm going to take them seriously. Or you tell me why I shouldn't treat the other ones as real. And there's a long history of people trying to come up with reasons why the other worlds aren't there, disappearing worlds, theories of quantum mechanics, as Ted Bundy has called them. It turns out to be hard. It turns out to be awkward and doesn't fit in well with modern physics. You can try to do it. It's a free country, you know, go, go nuts, like invent all the theories of quantum mechanics you want. Or you can just say, yeah, they're there. I don't care. Like they don't bother me. They don't, they don't, you know, like take up the resources we have in our world or anything.

• 47:10Neil deGrasse Tyson?

  It's not grabbing a beer in the middle of the night from your fridge.

• 47:18Neil deGrasse Tyson?

  And just, uh, correct me if I'm wrong. When we think of what's called the Copenhagen interpretation, that's the many worlds hypothesis, correct?

• 47:24Sean Carroll?

  No, that's the opposite.

• 47:25Neil deGrasse Tyson?

  The opposite. So to describe the opposite.

• 47:27Sean Carroll?

  Copenhagen is the one that was invented by Bohr and Heisenberg back in the day.

• 47:31Neil deGrasse Tyson?

  And Bohr is the only one who's Danish in that pair.

• 47:34Sean Carroll?

  Yes, that is correct.

• 47:35Neil deGrasse Tyson?

  So why does he get the name? Why does his hometown get the name of the, the idea?

• 47:39Sean Carroll?

  He was slightly older than everybody else and he founded the Institute for Theoretical Physics in Copenhagen where all this work was done. So.

• 47:46Neil deGrasse Tyson?

  Well, there you go.

• 47:47Chuck Nice?

  He had the money.

• 47:49Sean Carroll?

  Heisenberg was a, was a postdoc when, you know, at this time and Bohr was a famous physicist. So, um, the Copenhagen puts in the laws of physics, the notion of measurement. It says that when you make a measurement of something, a dramatic effect occurs where the wave function that describes the system, uh, completely changes. The, the real hardcore Copenhagen philosophy is that there is no such thing as what the system is doing before you measure it. There, the whole of reality consists of nothing but measurement outcomes. That's what Copenhagen actually says.

• 48:30Neil deGrasse Tyson?

  Okay. I, I had learned, I, I remembered learning that, but I didn't connect it with the Copenhagen interpretation. And that's if I, if we were to divide into camps, that's my camp. I, I, it took me a while to grow accustomed. It took, let me restate what you just said. It's, it doesn't even make sense to talk about it unless there's a measurement of it. You, to talk about a state of a system unless you can measure it. And then the measurement is the reality of what things are. Is that, is that, am I, did I oversimplify that?

• 49:00Sean Carroll?

  No, that's actually, that's actually quite good. And, and I'm, I'm all about like, the universe doesn't care about you and your measurements. The universe is just out there and I'm just going to believe in it. Why not? It's, you know, the universe is, is impersonal and the word measurement should not appear in the fundamental laws of physics.

• 49:15Chuck Nice?

  Wow, that's cool. I like that. I like that. All right, this is Rory L. who says, hello, Dr. Tyson, Lord Nice, Dr. Carol, Rory from Colorado here, the happy recipient of a gift subscription. Wow, somebody gave him a Patreon gift subscription. Hey, guess what? You guys can do that, too. Give a gift subscription to somebody else. Buy them a year of Patreon.

• 49:38Neil deGrasse Tyson?

  And by the way, that's a cheap ass subscription.

• 49:40Chuck Nice?

  It really is. But you can make somebody really happy for not so much money.

• 49:45Neil deGrasse Tyson?

  Right.

• 49:45Chuck Nice?

  Okay, Dr. Carol, which science discipline do you rely upon the most when studying a possible multiverse? Or is it a combination? Thanks.

• 49:57Neil deGrasse Tyson?

  And throw philosophy in there as well, as a branch of thought.

• 50:00Chuck Nice?

  Why not? Yes.

• 50:01Sean Carroll?

  I presume that the question is referring to like, is it mostly a philosophical question? Or is it mostly a physics question?

• 50:07Neil deGrasse Tyson?

  Or is it mostly quantum physics or relativity physics? How about that? Add that in there.

• 50:13Sean Carroll?

  There's also, right, different parts of physics are also very relevant here. But this is exactly why I chose to title myself a professor of natural philosophy, because I don't think that there's a boundary or a dividing line between the philosophy of it all and the physics of it all. You are never going to invent quantum mechanics by sitting around in your armchair, thinking about how the universe would be, right? You needed experiments that gave you, giving you data that you couldn't otherwise account for. And that's what led us to quantum mechanics. But then quantum mechanics leads us to this idea of many worlds happening every time you make a quantum measurement. And philosophy becomes super important for accounting for that, for understanding that. The physicists, bless their hearts, have done a terrible job. Most of

• 50:57Sean Carroll?

  them just live in denial and don't even want to think about this. And it's kind of an embarrassment, but the philosophers have at least taken up the challenge. I don't think that we're done yet. I don't think we have a perfect understanding of everything. That's good. That's good for me. Full employment for me and my graduate students. We still have things left to do. But I think you need them all. There's no one answer there.

• 51:17Neil deGrasse Tyson?

  As everyone from the South knows, if you say bless his heart, the next thing is going to be a nasty insult.

• 51:23Chuck Nice?

  Well, yeah, and the South blesses. Heart means F you.

• 51:29Chuck Nice?

  They're just, they got it down to a science. The most polite F you possible.

• 51:34Neil deGrasse Tyson?

  Bless his heart.

• 51:35Chuck Nice?

  Bless his heart. This is John Mayer. He says, hi, I'm John from San Diego and listen. Every episode I listen to, it's my jam. Thank you, dear Dr. Tyson and Dr. Carol.

• 51:46Neil deGrasse Tyson?

  Can we, can we, can we advertise that?

• 51:49Chuck Nice?

  What?

• 51:49Neil deGrasse Tyson?

  Star Talk.

• 51:50Chuck Nice?

  It's my jam.

• 51:54Chuck Nice?

  He says, Dr. Tyson, Dr. Carol, and the energetic Lord Nice, please help me understand how a photon traveling between stars experiences no time, yet also has a wavelength pattern and changes over space and time. Is the wavelength a function of the photon? Or is it a display function of the spacetime medium within which it is traveling within? Or is it even something else?

• 52:18Neil deGrasse Tyson?

  Ooh.

• 52:19Chuck Nice?

  What a great question.

• 52:21Sean Carroll?

  People love this question. I get this question. It's, uh, and they don't like the answer, which is that photons don't experience things. They're just single particles. Electrons don't experience things either. I think that we get in trouble because we are complicated creatures, right? With senses and memories and things like that. And so we have a feeling for what it is like for time to pass. And that wouldn't apply if we were moving at the speed of light, because then no time would pass. But when we talk about the wavelength of a photon or its path through the universe, we're not talking about its inner experience. We're not talking about its first person point of view. We're talking about what it looks like to us. The photon passes us by. It has a wavelength. It has a path.

• 53:05Chuck Nice?

  So it's all about us.

• 53:07Sean Carroll?

  It's all about us. In that case.

• 53:09Chuck Nice?

  It's all about us.

• 53:10Sean Carroll?

  Well, even better. It's all relative, as Einstein would have said. It's relative from what the observer sees of the photon.

• 53:16Chuck Nice?

  Relative to the observer. Yeah. And it's also about the math, because that's the thing that people, that the photon is a particle, but the math is why it doesn't experience time. It has no mass and it's traveling at the speed of light. So there is no time. There just isn't.

• 53:31Sean Carroll?

  That's right. It travels through a path in spacetime that takes it no time from its point of view.

• 53:38Chuck Nice?

  Right.

• 53:38Neil deGrasse Tyson?

  Okay. However, if you look at muons. A muon knows when to decay.

• 53:46Chuck Nice?

  Oh, that's right.

• 53:47Neil deGrasse Tyson?

  So it must have an internal clock for you to just say a particle, and you even mentioned electrons, doesn't care about time. If I'm a decaying particle, I do care about time.

• 53:56Chuck Nice?

  Ooh.

• 53:57Neil deGrasse Tyson?

  So there.

• 53:58Chuck Nice?

  Ooh.

• 53:59Sean Carroll?

  You guys gotta stop anthropomorphizing elementary particles.

• 54:06Neil deGrasse Tyson?

  Muon say, you ready to go? You ready to jump out of this one?

• 54:08Chuck Nice?

  That's right.

• 54:10Neil deGrasse Tyson?

  Let's go together, hold hands.

• 54:12Chuck Nice?

  Uh, that's great. That's great.

• 54:15Sean Carroll?

  Yeah, there is time that the extent of a muon's path through the universe does include a passage of time. But the muon as an elementary particle has no hopes or desires. Sorry.

• 54:28Chuck Nice?

  Poor muon.

• 54:31Neil deGrasse Tyson?

  All right, time for one last question.

• 54:32Chuck Nice?

  All right, this is Ben Grund or Grooned. He says, hello, smart people. Ben from Novi, Michigan. I think Sean helped me understand entropy best in his books and lectures. Charles Lu made an interesting, uh, comment recently that time can be measured by entropy.

• 54:49Neil deGrasse Tyson?

  Ooh.

• 54:50Chuck Nice?

  I was wondering, is entropy creating time in some strange way? Thanks for all the blown gaskets.

• 55:00Neil deGrasse Tyson?

  Brain gaskets.

• 55:01Chuck Nice?

  Exactly, exactly.

• 55:03Neil deGrasse Tyson?

  Let me, let me add some extra punctuation in that question. If entropy goes up with the passage of time, allowing us to deduce the arrow of time by seeing systems left to themselves as we watch entropy rise within them. Could it be that entropy goes up no matter what the universe is doing, even if it were recollapsing? Or is the entropy intricately connected to an expanding universe? So that even if we, so even if we recollapsed, the entropy would continue to go up?

• 55:40Sean Carroll?

  As far as we know, there's no connection between whether entropy goes up and down and whether the universe is expanding or contracting. You could have it anyway. There's an empirical fact about our universe that entropy was low when the universe was relatively tiny and has been going ever since. But if it started collapsing, we expect that entropy would still be going up toward the future. But, and that's part of the actual answer to the question, which is that you have to distinguish between time and the arrow of time. Time could exist without an arrow, and the fact that entropy provides time with an arrow doesn't mean that it explains or accounts for time itself. Like, here in this room where I am, if I take my coffee mug and I let it go, it falls to the ground.

• 56:25Sean Carroll?

  It falls down. It doesn't fall up. There's an arrow of space here in the room. There's a clear distinction between up and down. But it's because the Earth is beneath my feet. It's not because the Earth is creating space. The Earth is just distinguishing between two different directions in space, up and down. That's what entropy does for the universe.

• 56:45Neil deGrasse Tyson?

  I like that. That's great. That was really good, man. But wait, but if we recolaps and the whole universe then occupies a small volume, isn't that necessarily a lower entropy universe?

• 56:57Sean Carroll?

  Nope.

• 56:58Neil deGrasse Tyson?

  What? What? No, don't, don't, don't leave me hanging. We, we have to end now, okay? You can't leave me hanging like with a nope.

• 57:06Sean Carroll?

  We gotta go. All right. Bye, everyone.

• 57:09Neil deGrasse Tyson?

  It was like a ticking easy.

• 57:10Sean Carroll?

  Bye, have a beautiful time.

• 57:16Neil deGrasse Tyson?

  We learned from statistical mechanics where you have this like blob of gas and you just let it go and then it will expand and its entropy will go up because there's more places the particles can occupy and it's not contained within a volume. If the universe is shrinking... The whole universe is in a smaller and smaller and smaller volume. How could you tell me that that universe can also have an increase in entropy?

• 57:43Sean Carroll?

  Do you think eggs are gonna start unscrambling just because the universe starts shrinking?

• 57:47Neil deGrasse Tyson?

  Yes.

• 57:51Sean Carroll?

  Please don't think that Neil deGrasse Tyson.

• 57:52Chuck Nice?

  Okay.

• 57:53Sean Carroll?

  No, that makes sense.

• 57:54Chuck Nice?

  All right.

• 57:55Sean Carroll?

  Right.

• 57:55Chuck Nice?

  Yeah.

• 57:56Sean Carroll?

  All right.

• 57:56Chuck Nice?

  The eggs are broken, they're in, they're in the Bane-Marie and that's it. Yeah, you've scrambled them up.

• 58:01Sean Carroll?

  All right. Just in case there's anyone who really wants it out there, I mean, Neil's given a very good reason to think that entropy should go down. And the secret to, you know, for a little bit more technicality, because it's the end of the podcast, we should care about phase space, not space. That is to say, we should think about both the positions of particles and also their velocities. So the positions of particles are indeed gonna get squeezed together if the universe collapses, but the velocities are gonna spread all out and do crazy things and increase the entropy of the whole configuration. And in fact, it's gonna look wildly inhomogeneous with black holes and empty regions and it's gonna look nothing like our early universe looked. Wow.

• 58:46Sean Carroll?

  Man, you're good.

• 58:49Sean Carroll?

  I'm old, I've done this before, not my first rodeo.

• 58:54Neil deGrasse Tyson?

  So Sean, Quantum and Fields, that was 2024?

• 58:56Sean Carroll?

  That was 2024, and the one I'm supposed to be finishing up right now is called Complexity and Emergence 2026.

• 59:03Neil deGrasse Tyson?

  Nice.

• 59:04Chuck Nice?

  All right.

• 59:05Neil deGrasse Tyson?

  Nice.

• 59:05Chuck Nice?

  Look at that.

• 59:06Neil deGrasse Tyson?

  And after that, that's the trinity of the universe, you're done.

• 59:09Chuck Nice?

  Yeah.

• 59:09Neil deGrasse Tyson?

  You go to Bahamas.

• 59:10Sean Carroll?

  I figure like the trilogy format worked well for JR R. Tolkien, it should work well for me too, so.

• 59:18Sean Carroll?

  I'm waiting for the adaptation.

• 59:20Neil deGrasse Tyson?

  And then you escaped to Middle Earth and all as well.

• 59:22Sean Carroll?

  Right.

• 59:23Neil deGrasse Tyson?

  We find you online with The Preposterous Universe?

• 59:26Sean Carroll?

  That's right, and a lot of my work these days, you know, talking out there is in the podcast format with the Mindscape Podcast, yeah.

• 59:32Neil deGrasse Tyson?

  Mindscape. And how often do you, do you drop those?

• 59:35Sean Carroll?

  Every single week.

• 59:37Chuck Nice?

  Wow.

• 59:37Neil deGrasse Tyson?

  Once a week.

• 59:37Chuck Nice?

  Very nice. Very nice.

• 59:38Neil deGrasse Tyson?

  Very nice. And at least some of your fans came through us to get back to you again.

• 59:43Sean Carroll?

  Absolutely.

• 59:43Neil deGrasse Tyson?

  We were delighted by that.

• 59:44Sean Carroll?

  Podcast pros, yeah.

• 59:46Neil deGrasse Tyson?

  Well, Sean, delighted to see you again. Next time I'm in Baltimore, I'll give you a call. I was there actually a few months ago, I just forgot to call you.

• 59:52Sean Carroll?

  Ah.

• 59:53Neil deGrasse Tyson?

  Don't.

• 59:55Sean Carroll?

  It's going in your permanent record.

• 59:56Chuck Nice?

  He's like, you know, you don't really have to tell me that.

• 1:00:00Chuck Nice?

  You know, that's something you can keep to yourself. You know what I mean?

• 1:00:05Sean Carroll?

  Hundred percent. Next time we're on the podcast, he's going to be saying, yeah, I went back to Baltimore again. I forgot.

• 1:00:12Sean Carroll?

  Strange how I forget every single time.

• 1:00:14Neil deGrasse Tyson?

  Sean, delight to see you once again.

• 1:00:16Sean Carroll?

  All right.

• 1:00:16Neil deGrasse Tyson?

  Yeah. All right.

• 1:00:17Sean Carroll?

  Good stuff.

• 1:00:18Neil deGrasse Tyson?

  This has been StarTalk Cosmic Queries, yet another cosmology edition. I love these. No end to people's curiosity. Chuck, you doing good? Always a pleasure, man. This was so much fun. All right. Neil deGrasse Tyson, your personal astrophysicist. Until next time, keep looking up.