StarTalk Radio - Exploring Hidden Dimensions with Brian Greene

Episode Date: March 31, 2026

Is our universe an inevitable outcome of the laws of physics? Neil deGrasse Tyson and comic co-host Chuck Nice sit down with theoretical physicist Brian Greene to discuss the Many-Worlds Interpretation, the structure of the multiverse, levels of infinity, and respond to cosmic queries Neil couldn’t answer.  NOTE: StarTalk+ Patrons can listen to this entire episode commercial-free here:  https://startalkmedia.com/show/exploring-hidden-dimensions-with-brian-greene/ Thanks to our Patrons Toby Nicholls, Nick, Kevin Labranche, Mike, Sara Tunick, Ari Comart, Corey Taylor, Lance Rossie, Joe Chiarelli, Vic G, obvs, Michael Trainor, Ben Whelan, Di, Matthias Metcalfe, None Yo'Business, Kevotron, Eluivren, Vernard Ulrich jr., Paul Johnston, William Beraki, Cody Flynn, Brant Clabaugh, Eddy Stecher, Jason, Joel Watts, Luc Gareau, Thomas Fitzpatrick, Cole, Brian Flatt, Venkannareddy Yamnur, Jan Saelid, jabbbbbbbex, Al Fontaine, Alex Velasquez, Joshua Phillips, Parking Meter, neonpenny, Henry Washington, Srikar Gulukota, Marcus Aurelius, FrozenLaughs, Mr_Bman, Kevin L, Gary Matthew Spence, Big Stu, Ataka Grizzly, J, Roderick Lee Wells, Foh Chik Yong, Chris of the Green, Sensitive Knees, Laura Rivers, Darryl Harlow, Ruairidh Meyjes, Manuel Kumli, Liverpoong, Dominic, Leonard Tramiel, Cindy Brehl, Donnell Caballero, John Buck, Spyder3921, Raul Gonzales, Nick Burnett, Gints, Angelos Giannakopoulos, Igor Martens, Lucas Rayala, Randy Wing, Preston Rogers, Jason Baldwin, Julian O., Christopher Lloyd, John C, Steve Krasner, Andrea Jaramillo, spaduano, Sunny Sarraf, LINKSBYLINKS, Seoyeong LEE, typical, m m, John Latta, Mike Wyant Jr., Bhargava Kandada, Lance Wall, Will Thomas, Rick van Schijndel, Quinn Damerell, Jake Laurrell, Nefastes, Adrian R, Mike Jemison, Andrew Kell, Christopher Fahrenbach, Jiří Šebesta, Said Aspen, Tracy Thomas, and Mick & Sally for supporting us this week. Subscribe to SiriusXM Podcasts+ to listen to new episodes of StarTalk Radio ad-free and a whole week early.Start a free trial now on Apple Podcasts or by visiting siriusxm.com/podcastsplus. Hosted by Simplecast, an AdsWizz company. See pcm.adswizz.com for information about our collection and use of personal data for advertising.

in an extended version of StarTalk. That's right. I'm loving it. All things you never knew you didn't know about what's going on in the universe coming right up. Welcome to StarTalk. Your place in the universe where science and pop culture collide. StarTalk begins right now. This is StarTalk.

Neil de Grass Tyson, you're a personal astrophysicist. Got with me, Chuck. Nice, baby. What's up, Neil? All right. This is a special Cosmic Queries edition. Okay. Because half of it is not going to be Cosmic Query.

Oh, okay. Half of it, I'm just going to be talking to my man. Oh, okay. For a moment, I thought you meant you were just going to talk. Up the street. Yes. Professor of Mathematics and Physics. And physics.

At Columbia University. That's right. Let it go for Brian Green. The returning champion, Brian Green. Oh, thank you. Fan favorite, by the way. You know that. Appreciate it.

Our fans love you. That's great to hear. We love you because you're a theoretical physicist. Yeah. And while, of course, data matter, people like just thinking in an unfettered way about what could be true. Yeah. Or not true about the universe. And there's so many things being bandied about lately, especially in the quantum realm, that we thought we'd bring you in for a special recording where there's no time limits on this.

We're just going to talk universe. everything cool, weird, and wacky about the universe. Nice. And you're the man for it. By the way, when you're not here, I just sort of fumble over what I know, but when you're here, we got them. Yep, exactly. Okay?

So let's remind people, you, your specialty, I mean, historically, is particle physics specifically? Yeah, I certainly came from the particle physics side, quantum mechanics, and then moving toward gravity, which of course is the other end of the spectrum. Okay. And that's what took me to string theory, which is this a tent. to put them both together. We'll get there.

We're totally going to get there. All right, so that means there's no scale of physics that's out of your reach. Well, I wouldn't quite go that far, but. You are kind of covering it all. I'm just saying. Particles in the universe. What else is left? Well, what's left are the complicated things.

Like the brain, like the mind, like consciousness, like biology, you know, so. We stay simple. You do the easiest stuff, the physics. The easy stuff. You've written multiple bestselling books. Yeah, a lot. And the one people remember most perhaps was the elegant universe.

Was that your first? That was my first. That was your first book. And it was a runaway bestseller. Yeah. Yeah. For W.W. Norton. And your most recent book in 2020

came out just in time for COVID until the end of time. Yeah. Wow. That was very pretty pretty person of you. Yeah. Religious would be the end of days. Right.

The end of days. So what I like about you is you have a breezy way with communicating your complex physics thoughts. And in no small measure is that honed in books that are written for the public. A. B, your co-founder, I think with your wife, Tracy Day, former news correspondent. He interviewed me many years ago. I think for NBC. Good well.

ABC. ABC, yeah, yeah, yeah. And Tracy Day co-founded. the World Science Festival. Oh, wow. We did. Yeah. Now, that's just,

initially it's just being badass because it was New York. Which is the world, though. I'm not sure if you realize this. So I haven't attended as many of these as I have always wanted,

but those who I attended, I thoroughly enjoyed the juxtaposition of the science and the art and the music and just science as culture. Yeah, I mean, that's the point. I mean, much of what your work

is about the same thing. People need to see science as part of the fabric of culture. as opposed to something off there on the side that you are forced to take in school and then you leave it behind. Right, right, you leave it behind. And so I think World Science Festival

does that brilliantly. Thank you. I want to congratulate you on that. Appreciate that. Thank you. Year in and year out, it's still going strong. Yep, yep. So before we get to Cosmic queries,

because we poll our fan base, our donors, really, the Patreon members, and they all know you. So they're coming in with questions hot and heavy, straight in. And I worry that I might be asking some questions that they'd be asking. Oh, well.

Is that allowed? Yeah. So what? Okay. And for everyone that we come across that you have asked that they will ask, because they've already submitted, you will just give us $5. Because that's how much it costs to be a Patreon member. At the entry level.

At the entry level, yeah. Okay, so Brian, let's just right off the bat. We hear about the multiverse, okay? On one side of a fence. And then you cross the other side of the fence, and then we hear about the many worlds. hypothesis in quantum physics. Do these do you have anything to do with each other?

Yeah, they do. The idea of a multiverse is the umbrella concept for any variation on the theme where our world is not the entirety of reality. Oh, so that would cover all cases. All cases. Oh. Whether the multiverse or not. So the multiverse is under the many worlds.

Well, I think many worlds is under. It's under the multiverse. The multiverse is the umbrella idea. Okay. So the multiverse encompasses every single. And there are. There's something like 10 versions of many worlds that have emerged from radically different ideas. And quantum mechanics is simply one of those.

Okay. So I was mistaken to think that the more, dare I say, traditional multiverse descriptions, there's one where there's multiple bubbles within our space time. Sure. That's the inflationary. You know, I'm thinking that's the multiverse. I'm bringing it down, by the way, inflation. You're bringing it down.

Affirmability. It's a host. The universe is not really inflated. It's not really inflated. It's the best price it's ever done. There's never been a better price than the universe. So anyway. And then when I, and I'd learned many worlds when I first learned quantum physics.

Yeah. Where you needed some way to, get out of the conundrum that you're observing statistical phenomena. Yes, exactly. So catch us up on many worlds specifically, and then tell us how that plugs into the multiverse. Yeah, so when people develop quantum mechanics, this is now going back to the 1920s and 1930s. This is a tenial decade of quantum physics.

Precisely, which is why I'm writing a book on it. That will be published in this decade. Right. To catch people up on that. Yeah, yeah, exactly. Yeah, very good. And the progression of the ideas beginning in the 1920s was to note that a particle, and be specific, like an electron, it could be partly here and partly there,

50% here and 50% there. And the question was, but when you look and you measure, you always find the electron here or there, you never find it in a blended mixture being at two locations. Okay. And people scratched their head for a long time trying to figure out. How do we transition from a third? theory that describes a fuzzy haze of possibilities to the single definite reality when we make an observation or an experiment.

How much of that definite reality was a bias coming out of classical physics? Well, you could say all of it because our brains are big and we think they probably operate according to laws that are biased toward the classical, the big stuff. Yeah. And our experience. So classical physics. There's an object. It drops. There's a thing.

You move it. Right. There's just stuff that kind of makes sense. Yeah, exactly. And nothing in quantum physics makes sense. And nothing in experience suggests there's anything but one single definite reality. And that was the conundrum. Experience shows one reality.

Quantum mechanics speaks of many possibilities. And measurements in that realm. Right. That's right. So measurements in the realm of the small somehow seemed to pick out one singular definite reality. But here's the problem. When you look at the mathematics, which comes from Erwin Schrodinger, you can't transition.

Of cat fame. Yes. What a shame. The should have a Schrodinger's cat in the Broadway musical, I think. Of cats? Yeah, that would have been really cool. Well, how do you know there wasn't?

And this is the point. So, Schrodinger's mathematics forbids the transition from many possibilities to the single definite outcome of experience. And so people said, maybe the transition never happens. And this is Hugh Everett.

1957 at Princeton, he looks at the equations and says, we are imposing a classical bias on reality. We think there's a single definite reality, but according to the math, if you look at that cat, there's one universe in which the cat's alive and you see it alive and you're happy. There's another universe where you see the cat dead and you're chagrined.

And that's the true reality. Neither of you knows about the other version of you each thinks they live in a single definite reality, but the bigger picture embraces more than one world. Was that other world always there, or was it created in the moment that they had the... The realization of another world. The realization of the life or dead.

It's a really good and subtle question, and I don't think every physicist sitting in this chair would give you the same answer. As I look at the mathematics, I would say all those worlds, in a sense, are there. There's nothing really splitting, which is how we often describe, but the world splits into two.

It's more that the description of the quantum realm allows... See his body language. Let me see some of that more? I know. I love that. Give me some more of that. The mathematical description now allows us to use the language of one world or another when that language wouldn't have been applicable before your measurement.

But it's not like the world splits and splits and splits. It's all sitting there in some giant Uber realm. Gotcha. So does the realization... of the measurement. Are you saying that there's a possibility that you're not measuring a definite thing at that

moment, or instant, I'll call it, in that instant? Or are you just seeing that and everything else is just still there, but you can't see it because you're looking at this? See, it all depends on what you mean by you, and I hate to be so specific in the wording,

because if by you, you have the conventional notion of a single human being, Okay. Each version of me does see a single world, carries out a single measurement. Oh, snap! There it is. It's just that if you had a God's eye view, which we don't have, you would see many versions of me with many outcomes. Okay, that is so freaky, man. Okay, but it sounds like you just pulled that out of your ass.

I didn't. I assure you. All right. All right. But that's an important point. Let me just emphasize that when here. Hugh Everett came up with this idea, it was the most conservative interpretation of the mathematics. Yes, it seems ridiculously uneconomical to have all these worlds.

But the math, if you just take it at face value, this is what it seems to say. Hey, this is Kevin the Somelier, and I support StarTalk on Patreon. You're listening to StarTalk with Neil deGrasse Tyson. So let's back up. You and I've chatted, we've hung out. socially, and you confided in me that when you were a kid and when you were in school, if you picked a book off the shelf and there were no equations in it, you immediately put it back. Yep. Wow.

Who does that? I got to say, that's... Who does that? A math teacher's favorite kid. That's who does that. Every math teacher's favorite student. Teacher's pet in the math class. So you have a math brain.

You have a brain. wiring where the math is clear and present to you more so than any words or descriptions that surround it. I don't have a problem with that. You are also dual professor at Columbia in physics and mathematics. What you just told me makes math the preeminent supreme account of reality because you're saying the math forces it. And I'm asking you, math is our tool. Why should math that you invented, you, anybody, humans, force anything? Why can't I say there's a different idea that's going to have different math that doesn't lead to that conundrum? So if you asked me that question 20 years ago, I would have given you one answer, which would have been very combative,

and I would have been defending mathematics as like the deep truth of the world. In the past 20 years, I've shifted closer to your perspective. I really do see math as a powerful tool for describing the external world. I don't see it necessarily as the truth of what's out there, which is why I don't support the many world's interpretation of quantum mechanics the way some of my colleagues do. I allow for it. It could be true. It's interesting. It blows your mind. But I do not say it's true because it comes out of the equations. Thank you. Wow. Okay. That's a very, I'll say, mature and advanced. That's a mature.

That's a very mature stance. You have matured in the past. I have. Because I don't, you know, I love me some math. Don't get me wrong. Not as much as you do. But when I look at Kepler, who was a mathematician, fundamentally, and he knew about the platonic solids.

Do you know about the platonic solids? I know that they're friends. Platonic friend. So you can, if you have polygons, which are flat shapes that have the same sides. on them. So a triangle would be a regular polygon. A triangle, a square, a hexagon, that sort of thing. So if you ask, can you make solid objects with these as its sides?

Right. There's only five. Five polygates that do that. Five shapes. That do exactly that. Where each side is the same polygon. Okay. Only five.

Right. And one of the obvious. One's a pyramid, definitely. One's a soccer ball. No, soccer ball has two different kinds of shapes on it. Oh, really? Yes, it does. Oh, so they're not all the same.

No, they're not. Check next time. All right. But it is a way to tile a sphere. So then you can do it. So one is a pyramid. Another one is a cube. Cube, of course.

Right. And then there's like three others given to me. Yeah, dodecahedron, and I don't even remember the rest of the name, Caihous. Yeah, so. And there's another one. Okay. So now, Kepler, a mathematician said, there must be some divine reason for this. There's five of them.

And we have six planets. There was Mercury, Venus, Earth, Mars, Jupiter, and Saturn. So he said, wait a minute, if the universe is special and math is special, obviously, they have to be connected. They must be connected. So he embedded these platonic shapes

in each other, circumscribing one around the other to see if that gave them the orbital distances of those six planets. Because if we have six planets, you have five separations between them. He thought that was a major connection. So he spent 10 years doing this. And it was like, and then it was over, he was like, I've wasted my life.

Oh, God, what have I done? But the math is what took him there. Yeah, right? The beauty of the math. Yeah. And so that was my lesson that, you know, I ain't going there. But it goes the other way, too, right? Because you go back to, say, George LaMetro.

So he's a priest, a Belgian priest. Yep. Yeah. He's studying Einstein's mathematics, finds that the equations, the math, says that the universe should be expanding or contracting. He goes to Einstein, and Einstein says, your calculations are correct, but your physics is abominable. This math is not relevant to the world.

It's like the platonic solids. You're wasting your time. And yet, in this case, Einstein was wrong. Einstein's math was relevant in the way that George Lemaich was suggesting the universe is expanding. So you have to go... Einstein didn't even know his math was relevant. So Lemaîtrek, he used calculations. of Einstein's equations to force upon him a feature of the universe that not even Einstein was imagining.

Exactly right. So that's math being bad. The math discovered that. The math discovered it. Yeah. So it's all just to say that it has to be case by case. You got me. No.

You got me there. Okay. So now if everybody's doing these quantum physics experiments all over Earth and in all alien planets, is this a countable number of worlds? Yeah. That's a tough, tough question. It's infinite in any reckoning, but exactly which kind of infinity. We kind of understand it because we don't want to go into the deep mathematics,

but there's a whole structure due to David Hilbert, a mathematician, who actually raced Einstein to the finish line in general relativity. Did not know he was on the track. Yes, in fact, he published general relativity a little bit before Einstein did. Oh. There's a little known fact. What's his name again? His name is David Hilbert.

Damn. And the thing that was... I was know Hilbert, because it's Hilbert space. Hilbert space. You have to tell me about that in a minute. Yeah. Okay. But in this particular story, Einstein had visited Hilbert in June of 1915.

Showed him everything that he'd worked out for 10 years. Then Hilbert took at the final step and published before him. In the end of the day, Hilbert said, no, no, it's your theory. It's your theory, Albert. I'm not trying to take it from you. That's very cool. But he did publish a little bit before him. Even though he would not have published had Einstein not visited him.

Yeah, he would have known. anything about this. But the point for quantum mechanics is that there is this thing that you made reference to Hilbert Space, which is the mathematical structure within which all these worlds live. And we understand the math are that pretty well. I did not know that.

So why does it need a mathematical structure in which they live? Well, if you're going to describe things with rigor mathematically, you've got to define things, you've got to have the operations, you have to be able to categorize the ingredients. And remarkably, this space,

that Hilbert introduced has just to write mathematical properties to be the space in which all these worlds live. Does it suffer from an incompleteness feature? You know, everything. Who's the dude with the incompleteness theorem? Yeah, Girdle. Girdle. Yeah. So, so, yeah, so Gertl had a very powerful result that any basically sufficiently complex

mathematical structure will have true statements that can't be proven true within the axioms of that structure itself. So it just has to be asserted. It has to be asserted or you have to somehow intuit it or feel it or, you know. In the general relativity. That sounds a little suspect. But the deep question is, are there interesting physical features of the world that would be undecidable in this girdalian sense? That's what I'm asking you.

So is there a feature of general relativity where you part the curtains enough and then there's just some assumption you had to make? Yeah. And everything issues forth from that. that you cannot deduce from anything that follows. Yeah, I mean, there certainly are axioms within these theories, for sure. But are there then deductions that are true but can't be proven within this structure itself? I don't know.

Because when you look at Girdle's proof, the kinds of things that are undecidable are very contrived. You know, with things like, you know, the set of all sets that are not subsets of themselves. You're like, well, does that ever come up in the real world? You know, or the barber of Seville, you know, nobody shaves themselves, but then, like, who shaves the barber? You know, so they're all very self-referential, and it's not obvious that they have direct relevance to things that we could measure. But it's still an important discovery that he made. Yeah. Hugely important.

And this thing about the closest I got to that barber question was I used to read brain teaser books when I was a kid. Okay. And so one of them is, you come over town and only two barbers. Yeah. And one of them is just completely messy. And the guy's unkept and his hair all. But the town looks amazing. Wait, right.

And then there's another barber where he's clean, shaven. He's, everything's neat. So which barber do you go to? I'm going to the messy one because he clearly does the other barber. Exactly. Exactly. Somebody cuts the guy. That's the guy.

That's the closest I've gotten to the barber. So with the many worlds, now connect that up to a multiverse. It's just a declaration. It's a multiverse of a kind. It's one flavor of multiverse that comes directly from the math of quantum mechanics. And the natural next question is, can you prove it? Can you demonstrate it? It feels less real to me than other multiverses I've read about.

Yeah. No, I understand that feeling because our consciousness feels singular. And this theory is saying there are many individuals in this larger realm that have your memories, that have your experiences. And they only differ from you that they saw. the cat dead and you saw the cat alive. In some universe that's up. So now let me ask you this with respect to that. Well, how to react to this?

Give me a second to like, all right. Just tear up. See, I watch a lot of Rick and Morty, so it doesn't bother me. It doesn't bother me at all. I'm just like, oh, okay. Of course it works that way. Duh. But this other me, that's me identically,

except we observed a different outcome of the experiment. Yeah, and then from there you continue to diverge, because we know that little changes right now over time can turn into major deviations in your lives later on. Because I've seen in several films, but let me pick one specifically H.D. Wells' Time Machine. I'm referenced, I didn't read the novel, but I saw the movie, When is it from the 60s?

And the guy, the main protagonist, befriends a woman who shortly after they have this encounter, she's like hit by a truck. And he says, well, I have a time machine. I can go back and fix this. He goes back and says, oh, don't exit the part this way. Go the other way. She goes the other way and something else hits her and she dies.

And the safe drops on her head. One anvil. Right. And even better. And so after two or three iterations of this, or in another one, she's mugged and killed, he concludes that it was just her time. And he can't change fate.

Can't change the outcome. Okay. But when I saw that, I said, the molecules of air that are around her are in a different place because she's displacing these molecules relative to these. That's a different universe. I'm not going to look at these as just this is the only thing that has to stay constant. Tell me about all the other little things that change relative to the big thing that you notice. Yeah.

So in that version, I think you're right. You know, if the person could really go back in time, change things, I think you would get a different universe. I don't know of any Uber law that says certain major events or minor events have to be preserved. But in the quantum mechanical version, it's completely different. If you take on board this idea, you are committing to different worlds where things are radically different. And one she would live and the other, she would die. If they are allowed, if these outcomes are compatible with laws of physics, then they will happen in one or more of the worlds in the quantum mechanical multiverse. Wow.

All things compatible with the laws of physics are realized. Wow. That's pretty wild, man. Okay, so, but, all right. I love that, though. Wait, wait, stop. I love that. Here's the only thing that I can't get with that, all right?

in that case, how do you reconcile infinity or an infinite number of worlds? Let me get there. So watch. We went from the many worlds hypothesis where it is exactly me, but I'd look at a dead cat instead of a live cat, or vice versa.

In the multiverses to which I've grown accustomed, there's possibly an infinite number of them, but maybe in one of them, I am there, mostly myself, except I have a goatee, or I'm evil Neal instead of friendly Neal. So that's not a many world's Neil. You're Neil who believes in tarot cards. So that's not a many worlds neal. That's just another statistically configured Neal out of the random molecules in that universe.

Right. But the beautiful thing about the quantum mechanical multiverse is that when you study the possible worlds that can emerge, they embrace effectively anything that would have a non-zero chance of occurring. Okay. And that's anything in effect that's allowed by the laws of physics. So if the laws of physics allow you to have a goatee, then there will be a world in the many worlds where you do have a goatee.

Right. But in that world, that's a different me looking at the cat, because the dead cat, live cat version of me, they each have a goatee. Yes. So if it's a very minor event, like doing a single observation, usually a single observation can't yield such a radical change immediately. It'll be you without a goatee in one, you without a goatee in another. But then if you wait long enough and you accumulate the huge number of ways that you could have gone left,

you could have gone right, you could have gone up, you could have said yes, you could have said no. When you put all of those possible. I could have pepperoni on that. Exactly. Exactly. Yeah. Now, one of them results in you having. a goatee because that came along for the ride in that particular world.

So here's what I want to know. Back to the infinity. Yeah. Are there a finite number of particles in this universe? There are finite number of particles in the observable universe. Ah. But the universe could go on in three far. Okay.

Then that answers my question. We don't know. Yeah. Because my point is, then that means there's a finite combination of all these particles that could create these worlds. And so how do you get to infinity? But if the universe goes on and on and on, then yeah. Yeah.

Yeah, there is no end. But even with an infinite number of universes with the same number of particles, you just configure them and keep reconfiguring. My point is this, can you reconfigure a finite number of particles to get to infinity? You can't because it's not reusing the same electron or the same proton in one world and another. Okay. It's a realization of that particle in a different configuration. Right. And that's not like a conservation of particle number.

Oh, wow. So I used to be into big numbers. I still am, but I haven't stayed with it. And one of my favorite big numbers was skews number. Do you know skews? I don't know skews number. It's 10 to the 10 to the 10 to the 34th power. Okay.

And if you play that out, you get the total number of configurations of all the particles in the observable. the observable universe. Right? So it's as though if the universe were a cosmic chessboard, it'd be the total number of possible moves. Right. Because you're not counting objects at this point.

You're counting events. Sure. You're counting things. Combinations. Yeah, I would get a different number. If I was to use the entropy of the observable universe, which we can calculate from the dark energy, I would get a 10 to the 10 to the 120.

Okay. Is that much different from 10 to the 10 to the 304? Yeah. So I think it has to do with whether you're only, only looking at material particles that, yeah, versus the energy that... Oh, no, of course. Yeah, the energy is all in there too.

Yeah, yeah. Yeah, this is just counting up the physical particles. Sure, that makes sense. Okay, okay. Cool. So do we actually know the amount of dark energy that's in the universe? Well, we measure it. We do measure it.

We do measure it by the rate at which distant galaxies are accelerating away from us. Exactly. And it's this ridiculously small number. Okay. in the units that we typically use to measure these things. And that translates into this particular number for the entropy, the number of states that the universe can possibly be found in. Right. Okay. That makes sense.

But the question you asked before, if we could return it for a second, because it is issue, this issue of infinite number of worlds. Yeah. Wait, just before you get there, I just want to remind people that when you say, if there's a chance something can happen, no matter how small,

you multiply that very, very small number by infinity and you get a you get a real number. And you get many worlds. You get many worlds. In which that could, that small probability thing could happen. Exactly. So the infinity that where you're about to go

helps bring out of the depths the statistically unlikely possibilities. And that to me is the Achilles heel or a potential Achilles heel of this approach. And again, I have to say, different people in this chair, they will say different things. But the issue that many of us have taken with the many worlds

is just that if an outcome has very small probability, right? That should mean it's very unlikely to happen. But from the analysis that you just gave, no matter how unlikely it is to happen, it will be realized in some world. So what does it mean to say something is unlikely if you're sure it's going to happen in some world?

Exactly. Yeah. Yeah. It's like having a drink. It's five o'clock somewhere. So we encounter this in astrophysics where we talk about supernovae as being an extremely rare event. Okay, not all stars will go supernovae. Even high mass stars, some go black hole. Right.

It's rare. Right. However, the galaxy has 100 billion stars in it. There's 100 billion galaxies in the universe. So when people realize if you have enough of a sample size, you could deliver every single night supernova into your camera. Right. It's a rare event that happens often. Exactly.

So that was initially kind of hard to explain to the public. Yeah. How you get that. Yeah. So we have a version of that in the quantum mechanical multiverse, but it is more of an issue because you're guaranteeing the existence of a world, a whole world filled with the observers and experimenters who are guaranteed to see the most unlikely things on a regular basis. Right.

And that is an issue. Now, there are some people who work on this who say, we've solved. that. Just read our paper, read our book, and they do some interesting mathematics. I am not convinced. And that, to me, is where the issue is. Okay. Interesting. So let me ask, I think we chatted about this over lunch a few moons back. Thanks for inviting me. Oh, it's in your inbox. Oh, I missed that. And forgive me, I might have had this conversation with Brian Cox. So I'd Sure you. Yeah.

Forgive me, because you're my favorite physicists out there. So, but so do you feel bad that I have another physicist who I... A little bad by it, isn't there? So I happened, I learned this early because I said I was into big numbers when I was a kid, that there are levels of infinity. Yeah. I think they're at least five. You can keep on going.

You buried the lead, guys. Now you've got to explain that. You can't just say that. You weren't at the lunch. So do I? Should I? That there are levels of infinity? Yeah, yeah, yeah, yeah.

But you weren't at the lunch. Do you know how counterintuitive that is? I know. You weren't at the lunch. So do I have to drag you behind us? I know, man. Listen, I'll take a doggy bag, okay? Because that's crazy what you just said.

Well, we'll explain that in a minute. All right, go ahead. So I kept thinking to myself that you can have an infinity of universes, and that would not be a big enough infinity to exactly reproduce me. and that you would maybe need it higher levels of infinity to get all the combinations that people like to talk about in the multiverse. Right, right. So does it require the higher levels of infinity?

You know, the most straightforward answer would be to say, I don't fully know because I don't know that science understands you, and by you, I mean, life well enough to say. You know what you just said? He said, I could be so simple. Right. It's trivial to copy. But-

But- under no obligation to understand you. But if you take on board the idea that you are just a collection of particles that are governed by the quantum mechanical laws, if that is something you're willing to accept,

then there is enough room inside of, you know, Hilbert space in the quantum mechanical infinity to reproduce you and to reproduce every variation on you where some of your particles... Could every variation conceivable? Yes.

Yes. Every variation allowed by the quantum laws, which simply means... Is it a reason to me that has a tooth cavity? because I've never had a cavity. If that's compatible with the laws of physics and I think it is, then yes. So non-dental plan, kneel.

Non-dental plan. This is the kneel with no dental plan. If that's within the bounds of quantum mechanics, the laws of physics don't prevent it. Then we got enough, we got enough, not matter. We have enough material to make sure that that happens. I don't need the higher levels of infinity to get there. No, right, no.

Okay. Absolutely. Okay, so now let's catch up, Chuck, because everyone else out there knows about multiple infinities. Sure. So, So these are levels of infinity. I think there's a Hebrew letter associate.

Olive. Olive. Olif zero is a traditional infinity. Aleph one, two, three. So we don't have to do all five. Just get me to like the second infinity. Yeah, so the simplest one is the one that comes to mind immediately. You just count the numbers.

One, two, three. And they just go on. And they just go on. And that's the simplest straightforward. But then if I ask you, how many numbers are there between zero, and one on the number line. Oh, wow. Now you say to yourself,

well, can I enumerate them? Can I put them into a correspondence with the counting numbers and just list them? However, but am I not... But I'm still going towards affinity. I was going to say, aren't I dividing then

when I go in between numbers? Yes. I'm kind of dividing that. You are and you could say, well, let me put a dot in the midpoint. Call that one. And then a dot in the midpoint between it and zero and call that two.

You won't cover all the numbers. the numbers. And there was a wonderful... I'll never reach one. Because there'll always be a place where I can once again put something in between one and where I am. It's another way of saying it, but Cantor had a powerful argument that's actually pretty easy to understand we'd need to write it out for me to show it to you. But he established that if you try to enumerate the numbers between zero and one, just list them,

you will fail. You will always miss some. And therefore, there are more than an infinity of numbers. between zero and one, and that next level of infinity is the version that Neil was referring. That would be Alas, give me my bag. I'm going to need my weed. Okay, so you just skipped by it, and I want to make sure we can contemplate it briefly. The one way to know which infinity is bigger than the other is you correspond them to each other. Yes, exactly.

Right, so you can say, because this is kind of a little freaky, the odd numbers is the same size, as infinity as all the counting numbers that include odd and even numbers. Of course. Now, how do you get that? Well, you know, you could take any given number and say, multiply it by two and add one to it. And in that way, you're certain to get an odd number. You get an odd number. And now you've lined up, you've lined up the numbers one, two, three upward and the list

that it corresponds to are all odd numbers. They all just go up. Yeah. Damn, that's wild. Wow, math is kind of cool. Yeah. Oh, no! Okay.

And just to taste it, if I remember correctly, al-F2, does it go into another dimension? The number of lines in three-dimensional space is a bigger infinity than the counting numbers on a number line. Yeah, that may be a way of saying it. I'm not sure. There are many ways of expressing these infinities, and there's actually a kind of almost an algorithm that allows you to start to build up this set of infinites. You can look at subsets of subsets and things of that sort. Look at power sets as it's called.

And so it's an astoundingly strange idea, which is why mathematicians who thought about this in the early days... You're all in asylums right now. I'll never get to one. I'll never get to one. I'll never get to one. I'll never get to one. That is so rude. So, and if you go to higher dimensions, in principle, does that take you to?

Not necessarily. No, I mean, if you start to look at the number of points in the plane, you know. Points of a line versus points in a plane. Yeah. So you have to be fairly sophisticated in how you build up these infinities. Okay. But for our purpose, there is this thing that we've made reference to. It's a bit abstract, this thing called Hilbert space.

And we understand it. reasonably well. It's an infinite dimensional space that David Helbert developed, but we understand it well enough to say it does have enough room to embrace all the quantum mechanical states. It has infinite dimensions. You think there's enough room?

Yeah. And within that space, in principle, there is a place that describes you. All right, so now, I am however improbable in the configuration of atoms and molecules. Even here. In this actual...

reality. Okay. So have you thought much about whether or not something can exist and whether or not it does? The likelihood of such things? Yeah, and it's a mind-blowing thing. Tell me. When you think about the sequence of steps by which you came to be, and I'm saying, let's go to your childhood, to your birth, let's keep on going further back, your grandparents, let's go all the way back to the big bank. And if you look at the sequence of steps from the big bank, I'm ancestors, go back to the big bank. You do, actually. We all do as much. We all do, right? That's how we get here.

You know, we have collections of particles that are configured in a certain way, and they have a history. And it's that history which resulted in them being in the configuration that's called Neil deGrasse Tyson. And if you look at the sequence of quantum steps, each of them are incredibly unlikely. And the collection of those sequences is innumerably huge and therefore incredibly unlikely. and yet here each of us are. So what do I do with this information? Well, I think it gives you a certain... Well, you know, if you want me to be a little bit sappy,

you know, I think it inspires a gratitude. The unlikeness of us being here at all. And therefore, is a certain kind of thankfulness that the universe turned out in a way that gave us a brief moment to stand up, look around, and appreciate everything. That's wow. So now I'm looking at that.

and immediately going back to our previous conversation about the two observers, okay? With a dead cat, live cat, and the many worlds. What you just said can negate that, meaning that also there are an infinite number of worlds where there's just no neal, and then there's an infinite number of worlds

where there is no cat, and then there's an infinite number, you know... You're absolutely right, and I think that's one of the lessons if you take the many worlds approach to quantum mechanics to heart. It is saying that clearly we are compatible with the laws of physics because we're here existence proof.

Right. And if you take the many worlds seriously, then we were guaranteed to live in some world in this grand collection of many worlds. Now, in some sense, this world is incredibly unlikely within the panoply of possibilities. But you're right. In that sense, we were an inevitable outcome of the quantum laws because we are allowed by those very laws of physics. Okay.

Right. Brian, I have a more anchored version of what you just said that I credit to Richard Dawkins. Yeah. If you look at the total possible genetic combat nations that will make a human being, a viable human being. Okay. It's a stupefyingly large number. Like four to the three billion or something, right? But 10 to the 30th power. It's high.

Right. Yeah. What matters is not even how big it is, but it's vastly larger than the total number of people who have ever been. Born. Right. Yeah. Which plus or minus, it's about 100 billion. Yeah. Okay. So, Dawkins's point is, we should cherish life because most people who could ever exist will never even be born. That's right. Yeah. Yeah. So we can be sad that you die, but he describes those people who die as the lucky ones. Who got to live in the first place. Because you can only die if you got to live. Right. And for me, that's a little more anchored than. Yeah, but to take the point we're saying before, if the multiverse version of quantum mechanics is the right way of thinking about it, then they did. Then they did live if their genetic sequence was compatible with the law of physics. So, you know, so don't feel bad for all those little swimmers that didn't quite make it to the egg. The sperm you're talking about?

Yes, exactly. So, Brian, I get this question often. Surely you do as well. if we live in a multiverse, and we're just one of an infinitude, where are the other universes? Yeah. And you're going to cop out and say, oh, they're in the infinite dimensional Hilbert space? Well, it's easier to answer that question for other flavors of multiverse, like the inflationary multiverse that you made reference to before because... That's the simplest.

That's the simplest one to picture. So those are other places in our own... We're in a bubble. Right. And there's another bubble over there in the same sort of space-time. The same construct. Construct. Yeah.

Because according to inflation at cosmology, as you're making reference to, there was an energy field that gave rise to repulsive gravity that drove our big bang, but the math shows that it would not have used up all of that energy

in the process. Some would be left over. The leftover energy would yield another big bang, and it would not be fully used up yielding another big bang. And so these distinct big bangs, as you say,

would give rise to these sort of bubbles in a big cosmic bubble bag. So that's in one construct. Yeah. Okay. But now there are other variants of multiverses where it's sort of separate. Yeah. When you talk about the quantum mechanical multiverse, it's much harder to think about where those other worlds are.

They're not kind of adjacent to our space. It's a more abstract place that they inhabit. And I'm going to try to avoid using the word Hilbert space. But that's the mathematical architecture. within which we can see these worlds existing. I can't picture. I can't picture where these other worlds are. If you ask me, do I have a mental image of them?

Not really. Okay, so that's a mathematical architecture. Can I divine an experiment that would show that they exist? Can I wormhole to them? Yeah. Do I even want to wormhole to them? Because quantum physics might give you slightly different laws of physics. It's unlikely the laws of physics are different,

but the properties of ingredients might be different. principle, if there are sufficient quantum mechanical processes that could yield worlds with those distinctions. But I don't know of an experiment. I don't think anybody does, where when you can say, if we could get this and this result, we would establish that the multiverse is true. You tell me that other universes, gravity can leak out of them? Yes, so that's another variation on the multiverse that comes from string theory, which we can talk about. Oh, we get there, yeah, okay. But just to presage what we might talk about, in this version, universe is sort of like one piece of bread in a big cosmic loaf. And the other slices of bread

would be the other universes. So they would really be hovering next to us just displaced in an actual additional dimension of space. And then you're right, gravity can influence, permeate that space. So when I was having my little ayahuasca trip, I met these beings that were in-betweeners and they were in between dimensions. That's where they occupied. Okay, I feel so silly. We're listening. Okay, they explained that...

They talked to you. They did. They talked to me. And they were two-dimensional beings that I could see in 3D. Sounds creepy, but that's the only way I can explain it. Okay? And they explained to think of it like an infinite number,

and they call them dimensions, going out and going up and going out, but to think of them as a deck of cards slaffed up the way we see a deck of cards, we see it as one deck of cards, but it's not. It's however many cards are in that deck. And until you separate them,

that's when you can see the different things. That's how it was explained to me. So this is almost the reverse of that. It's as if we only see one card in the deck. That's our world. Right. But a God's Eye view would see the entire deck, which would have the other cards. And that's where they see.

Right. I see it as the one card. And they were explaining that they see it as the deck. But anyway, I'm just, I had shared that with Jan 11. And she was like, that's pretty interesting because. And then she gave me some speak that I didn't understand. Yeah, it must be the same basic idea. Actually, we just wrote a paper on these so-called brain worlds in string theory.

So this is something. Brain isn't short for membrane. Memory. Yeah. Sorry. Yeah. I should have said that. Thank you. You know, so these ideas, these are universes that are like a membrane, and there can be multiple membranes, which would be multiple worlds.

Right. And in principle, as Neil was mentioned, they can influence each other. Gravity from one can influence things in the other. So I never took, I'm saddened by this. In graduate school, I'm taking astrophysics classes, but I wanted to take more physics. And a physics class I never took was field theory. Yeah. A whole course on field theory.

You can come to my class one of these. One of these, yeah, I've taught field theory a number of times, yeah. I'll let you know next time. Excellent. I sit in the back. Boy, that's not intimidating. I'm going to fail. I'm going to fail.

I'm going to fail. No, but I'm not in a position to calculate or even really know why. Gravity can escape, but not the electromagnetic forces. Well, I can give you a quick mnemonic sort of to think about that, which is so in string theory. gravity is communicated by a string that has no ends. It's a closed loop. The electromagnetic force is communicated by photons, which in string theory are strings that have two open ends,

and those ends are anchored to the membrane. They can't escape the membrane, but because the gravity particle, the graviton, has no ends, just a loop, it's not anchored. It can get off and travel between those worlds. Is that a description that would be in the book, string theory for dummies? It's there, no doubt.

Okay, so if that's the case, why isn't what we measure as dark matter just gravity leakage from another slice of breath? People have made proposals like that. If you're dark matter is meant to explain the gravity that we know is there. It's really dark gravity. It's dark gravity. Yeah, so if you can have some source of gravity that you don't literally see, it's a candidate. And so people have put forward, it's hard to make this idea really work. but in terms of its general possibility, sure.

Because the betting persons, you know, if you're into betting what an outcome would be, an exotic particle is sort of the betting man's solution to. Yeah. But that's put forth by particle physicists. Right. You know, if you're a hammer, you're... A little bit of bias, right?

A little bit of bias, right? So I'm liking me the, you know, the gravity spillage. No, I like the idea. It's in detail, it's only when you get down to brass tacks. It's hard to make this really work. All right. Let's pick up the baton here on strength theory. Yeah.

Okay. Where I'm a little older than you, but we came of age with enough overlap. So I can speak of the 1980s as a time where strength theory was birthed and started taking off with some vigor. Yeah. All right. Everybody I spoke to at the time. And at the time, I was at the University of Texas, which had its share of strength

theorists. Yes. And Steve Weinberg was serious. for sure. A graduate of my high school. That's true. That's true. Not your high school.

Yeah, I agree. Okay. So Steve Weinberg, a Nobel laureate in physics, cosmologist, you know, all the way back. Anyhow. So I asked people, so when are you guys going to figure this out? Because you're trying to unify quantum physics and the large and the small. And it's, oh, we're almost there five years. In five years, we think we'll do it.

So, you know, 10 years later, well, when are you going to do it? five years, 20 years later. Oh, and five years? The problem is hard. It's a hard problem, but we're on the, and so I've never heard convergence. Yeah.

In any conversation about strength theory landing where it had intended. Yeah. A, B, could it be, and I think I've said this on stage to you, and you didn't jump up and try to hurt me, could it be that all of you are just too stupid to figure out the solution? And let me say that more charitably. Are we awaiting the birth of some 21st century Einstein to see the solution here that none of the rest of you are?

Yeah, yeah, it's all possible. First off, I would never have said five years back then. It's a very dangerous thing to make a prognostication of that. There was a huge enthusiasm. But look, string theory has done miraculous things since the 1980s, and I'm happy to sort of list the achievements, but you're right, it's not done the one thing that ultimately matters,

which is make a prediction that we can test, you know, at a particle collider and determine whether these ideas are correct. And it could well be that we just don't have the brainpower to get there. And it may not be that we're awaiting the birth of the next Einstein. Maybe we're just awaiting the next configuration of AI that may be able to do what we as individuals have not been, able to do. I do think there's a real

possibility of the nature of research changing the next five to ten years. If I said five years in the next five years, do you hear that? I did hear that. This one I'm willing to stick with, though, because, you know, I give you an example. I mentioned this paper that I wrote with

Jana Levin that you may reference to. Is just the loaf of bread paper? No, we wrote a handful of papers together. This is a more recent one. And I wondered, could Chad get the answer that took us a long time to get? Chat GBT.T. If I treated it as sort of a good graduate student. So I just gave it a few prompts the way you would to a graduate student, did not give it the answer. And it couldn't look up the answer. We hadn't yet published the paper.

And within a half an hour, it was able to reproduce the results that took us months to get. Oh, my gosh. And so it's as if you have the greatest graduate student known to humankind, even an army of them at your disposal. And that's now. This is a hologram right now. It's an AI. I'm not even here. So what is it going to be like in five years? You know, it's both exciting and scary at the same time. I have a colleague who has a similar story regarding his research where he was prompting chat to think about a problem. Yeah. And it solved a problem that he could, he had not been able to solve. And actually solved it. Yeah, actually solved it. Wow. In the, in the sort of you prompt a really good graduate student

in just the way you're describing. Right. But catch us up just on why the whole field is called string theory. Well, the basic ingredient is a filament that looks like a tiny piece of string. The idea is that it can vibrate in different patterns.

And the different particles that we know and love, electrons, quarks, neutrinos, and so forth. The fundamental particles. Fundamental particles would each correspond to different vibrational patterns of this new entity called the string. So the string becomes the fundamental

particle. Yes. And it's a unity because it's one thing that can manifest as many different things, depending on how it's vibrating. Which is for people who like unity, this is a beautiful thing. It's a beautiful thing, and it goes even further. When you look at the math of this, you find that not only does it unify all the particles, but it unifies quantum mechanics and general relativity.

Laws of the small and the laws of the big. Does it do that for free? It does that for free. It just comes out. I'm telling you, you look at the math. That's a nice fact. That's really. Let me, you know, you look at the math, right?

You stare at the equations and out pops Einstein's equations from general relativity. Wait, to whom does it pop? Who do you have to be for it to pop out? So I had not fully embraced that reality of string theory. So I'm delighted to hear that. So that was part of the enthusiasm that people would have then had. That was really the heart of it all. The major obstacle.

The major obstacle is that the theory is mathematically complex. and the pathway from the fundamental equations to physics we can see in the laboratory is fraught. It's difficult. It's tough terrain to cover. And so we've been developing

mathematical tools to do that for now 30 years. We've made progress on black holes. The 80s was 40 years ago. I guess you're right. Oh my God. Strength there hasn't answered that question yet. It's 40 years ago.

40 years ago. 40 years before that was the 1940s. Yeah. Just to put this in contact. with you on that. All right. You know, so we've been for 40 years, you know, and so we've understood things about space and time and gravity and black holes, which I didn't think we'd ever understand in my lifetime. Yeah.

On the flip side, though, we've not understood the things that I thought we would have understood by now, which would be make a prediction for what's going to happen at the large Hadron Collider, and let's check it. And so it's an interesting thing that we've made headway in the very things I thought would be too hard. And we've not made headway in the things that I thought we would be able to reach by now. Right. So I don't like making arguments that other people make just for the sake of bringing the argument to you. But just let me just do that. Let me do it anyway. Let me do it anyway.

So string theory has not been without some criticism as something that has consumed the ambitions of graduate students and faculty and promotion. And so it's a field without a prediction that can be tested, yet it had such a presence on the landscape of physics departments that it might have smothered some other branches of physics that might have been a little more promising. You just comment on that. I sound like jealousy to me. Well, it's an interesting argument

because the very graduate students and junior faculty and senior faculty who this person who's making this argument fears may have wasted their time, not looking at something more promising. You got to assume they're really smart people because of the very people you think who could have pushed the frontier of another field. And if they're that smart,

allow them to make the choice for where they think the greatest promise is. Yeah, who are you to say that they're not going to... Yeah, who are you to say? So it's not as if somebody was like putting a bag over their head or, you know, putting a gun to... They were looking at the ideas that were out there, found the string theoretic idea so compelling that they were willing to take a chance.

And that chance may not pay off in our lifetime. And tell me about the 10 or 11 dimensions? Yeah. Because that sounded very cop-outy. Well, you know, it's like, I can't explain this, let me throw in a dimension. Ah, good, good, good, good. But I need another dimension. But why do you need the dimensions?

Good, good, good. And I think if I articulate this correctly, I think you'll have the same epiphany that you did about gravity coming out of string theory a moment ago. Because, again, you wondered, do you have to put general relativity into string theory? I said, no, no, it just comes out for free, which is a beautiful thing. How about the extra dimensions? They come out for free, too. They're forced upon you by the equations.

Oh, you don't put it in. Not at all. The math does it for you. Literally, this is not a joke. There's an equation in string theory that basically looks like D, the number of dimensions, minus 10 times as complicated factor must be equal to zero for this theory to be self-consistent. The complicated thing is never zero, therefore D minus 10 must be zero. Therefore, D must equal 10.

That is where the extra dimensions are forced upon you by the equations. That's insane. That's pretty cool, though. Yeah. I mean, that's... So 10 dimensions. Wow. So we don't experience them.

Why? Because we believe that they're probably too small. for us to see with the naked eye. I don't know what a small dimension means. It means that if you head off in a given direction, you kind of return to your starting place so quickly. You can think about a straw, right? A straw has a long dimension that we can easily see,

but it has a curled up circular dimension. And if that circle, of course, we can see that with the naked eye. But if you made that circles... You sucky liquid through it. Yes, but if you made that circle smaller and smaller and smaller, at some point, you won't see it at all, and you'll think it's just a line. Line.

you've hidden the extra dimension. So all the other dimensions are hidden? We think that is one explanation for why we don't see them. Can anything exist in those hidden dimensions? In fact, I was going to call the elegant universe hidden dimensions. That was the title I was playing with back, you know, 25 years ago. But anyway, yes, exactly. All right, so you're hiding the dimensions from us.

Yes. Okay. Now, that is by hand. So when we look at the math, the equations don't tell us these extra dimensions are really, tiny. Instead, we're doing what you accuse me of perhaps on other things. We're saying, how can we make this theory compatible with what we see?

Let's envision that the extra dimensions are really small. Got it. Okay. So a string is 10 dimensions. A string is living in a 10-dimensional space. Right. Okay. Now, why would a string be fundamental and not, because a string is one-dimensional? Yeah. And dimensions are just dimensions.

Why can't there be another reality maybe in which we're embedded with the string is not fundamental, but a plane is what's fun about it. Yes, and that's one of the developments in string theory itself. So when we talk about these membranes, the piece of bread or the card in

the deck. So the string theory up by a dimension. And string theory takes you there. It's not something again that you put in by hand. He goes wherever his equations want to tell. I got to say, it's pretty fascinating. I need to say, this is a purely mathematical undertaking. Totally. But the beauty of it is

you don't put things in from the outside. You study the equations and it takes decades sometimes, but you extract what the equations are trying to tell you. So before to go to queries, what is the current state of string theory? Current state is... It's healthy. It's funny. I asked this question in a program to three string theorists,

a world science festival program. I asked them, guys, grade string theory. How, you know, if string theory was a student, you know, how would you grade it? And the grades went from B plus. I think that may have been Nobel laureate David Gross. I could be getting their grades wrong to an A plus, which was Andy Strominger, who's a string theorist at Harvard. And if you look at its theoretical insight into black holes, the mathematical insights that it's given started whole fields of mathematics.

If you have any interest in the nature of space and time and what it might be made of, these are the things. the kinds of insights of string theory is giving. So I'd say it's very healthy, but it has not made a prediction, allowing to determine whether it's correct. Wow. And that's almost a violation of one of the most important tenets of a viable theory. Yes. And that's why maybe you shouldn't call it string theory.

Oh, what should we call it? Yeah, maybe call it the string hypothesis. Okay. Theory really should be reserved. That's a more humble. Yeah. But the math makes it a theory. Well, the theory, yeah.

The theory, you, for a theory to be a bona fide theory, it's got to not only account for what you see, right, or in an organized, coherent way, it's got to make predictions that you have verified. Right. You've got to be able to, you have to be able to measure it. If you have not predicted, then it's only one half of what's going on. And then it does. Yeah. So we're using the word wrong. And I agree with people who are sticklers on that. Got it. But is that because, and I don't want to sound like a, you know, a jackass, but what you just explained. I got to say, like, Einstein had it easy. I'm serious. Yeah, right. Einstein had it easy compared to what you're just talking about.

I agree. He wrote down his equations, and within a handful of years, you could test it. Right, because it's like, it's here. Right. It's right. It's around us. It's everywhere. Like, you're talking about stuff that is, I mean, how do you get to it?

Right. We've had problems, unsolved problems that have lasted much longer than these 40 years in the history of science. Okay. So it took a long time to understand heat. and energy. That's very funny what you just said. It took us a very long time to understand heat. No, we didn't know what it was.

The fundamental basis of it. That's hilarious. No, no, we didn't know. Is it some fluid? A fluid? Caloric? They called it caloric. That could flow. Yeah.

And you know where we did most of it looks? Well, no, that's the air looking like. The air is a fluid. The air is a fluid, though. That's not the heat. But go ahead. One of the main centers of experiments for this were cannons. Because you'd fire cannons,

the metal gets hot. So as it got hotter, they weigh it to see if it had more heat. If the heat was a thing. Right. If it was like possessing heat. Possessing heat. So, yeah, so we went decades and decades

with other, so maybe I shouldn't be so hard on string theory. Yeah, this is a pretty good place to have gotten. Let's wrap it up right here, folks. Thank you, good night. Okay, and one last thing. I want to hear it again, because it was so beautiful.

All right. So beautiful. Just tell me, speak to me, Brian. Because it's sweetness to my ears. When I heard you say, I think it was you, that the virtual particles in the vacuum of space coming in and out of existence, as predicted by quantum physics,

they are quantum entangled with each other, and that quantum entanglement are wormholes. And those wormholes represent the literal fabric that stitches together the universe itself. Yeah, we were definitely talking about this at some point. Where are we on that? Well, it's a beautiful idea. Beautiful.

It really comes from Lenny Suscon and Juan Maldesana and a whole army of string theorists who developed these ideas. He came here, gave a talk, one of our evening talks at the point. Yeah, he's a wonderful book. Very innovative guy. Yeah, I mean, he's driven physics for decades. So he and Juan Maldesana realized that these quantum entangled particles, which Einstein really in a sense predicted in his EPR paper, Einstein, Podolsky, and Rosen in 1935, may be connected to another Einsteinian idea, which he came up with the two months distinct from that first paper.

and Einstein rose in paper on wormholes. That is, two particles that are far apart can have a subtle quantum link. And that quantum link may be nothing but a wormhole yielding a shortcut through the fabric of space that in some sense makes them very close to each other. And those wormholes themselves are what space time is comprised of.

So the substrate of space itself would be wormholes. Yes. That's right. So Mark von Romsdoch, the British Columbia, Canadian physicist, realize that these wormholes may be the fiber stitching together the fabric of space itself.

Because he could show mathematically, if you cut the quantum entanglement, the fabric of space pulverizes. It falls apart because you no longer have the wormholes connecting pieces of space together. That is wild. Okay. So I'm going to keep watching that space.

That's great. It's time for Cosmic Queries. Oh. We should have some jingle or something that's, that, or some animation. Some animation would be good. You know, cosmic queries. Right.

Questions asked by you, if you're a Patreon member, knowing that our guest today is Brian Green, the one and only. So, we have a starter question. Yes. From one of our own producers. Yeah, Tamson, our producer. Yeah. Our taskmaster.

Yeah. Tamson wants to know this, Brian. if spacetime had consciousness and could have a favorite movie. What do you think that movie would be? I think it would be a Planet of the Apes. Really? That scene at the end, you know,

with a half submerged or sunk in statue. You blew it out. Damn you're a lot of hell. Damn you. That's it. Wow. Because that played loosey-goosey with space time. Yeah.

To go into the future is another Earth and it was a different evolutionary path. It was the first time that time travel really meant something to me as a kid. I was like, oh, man, this is crazy. Yeah. That's a good one, man. Planet of the Earth, the original. The original. Forget about the other 75,000 follow-ups.

Exactly. Return to anybody. Escape from the plane. A bride of the planet of the apes. Manality of the planet of the apes. You know, when I went back and saw that film, it's actually quite deep because the different species of apes had different roles. It's a caste system. It's a caste system, for sure.

Right. So the chimpanzees were the academic class. Right. Because they're close. Why not? Of course. They're our closest cousins. And the baboons were like the police, right?

Or the guerrillas were the police. The orangutans are the elders. No, the orangutans were the diplomats. Diplomats, that's correct. Right. The politicians. It was a caste system. Yeah.

That's right. It's pretty wild. So our first few questions have been previously asked by our Patreon's supporters. But you said, I'm going to have to see what Brian says about this. Oh. Right. So they were elevated. So they were elevated.

Okay. It was above my pay grain right there. Okay. They wrote in with a question. And you were like, let me get my supervisor. I punted it. I punted it. Okay.

I went you to go. So this is Brian Berg. He says, Hey, Dr. Tyson, Lord Nice. Chuck, you should be able to nail this one. It's Brian from Portugal. Brian, shut up. He says, can you help explain the information paradox with black holes?

My understanding is that quantum mechanics and hawking radiation are at odds about this. One says, Information is forever. The other says information disappears when a black hole evaporates. Are we any closer to understanding how this can be? Thanks, and please keep doing what you're doing.

We need real science to carry on, live long and prosper. Oh, nice. Let me preface that a little more here. So I was delighted to learn that the evaporation of black holes, the hawking radiation, is the exact inventory of fundamental particles

that went in, even though it's being conjured out of the gravitational field of the black hole itself, the energy density of the field. So I said, oh, so that's a total reckoning of ingredients. But if I went in as a DNA molecule and I come out as the various fundamental particles, the information that I was DNA is gone. So no, there's no preservation of information there. And that's what Stephen Hawking said.

So when Stephen Hawking did his initial calculation, in the 1970s, he came up with this idea that black holes could actually radiate through quantum processes, the production of particles just outside the edge of a black hole, one falls in and the other races away. And the question was, do the particles race away have the information content about everything that fell in or don't they? He said they don't. My calculations show it's a thermal bath of particles, a vanilla featureless bath of particles, no information. inside of it. We particle physicists said,

come on. Quantum mechanics doesn't allow information to be lost or destroyed. So if you're saying that, you're saying quantum mechanics is wrong. Okay. And we're not willing to go there. Yeah, quantum is so, it's so successful.

Right. That's, you've got to be ready for okay. You got to be somebody more than Stephen Hawking. And this led Lenny Susskin again, and Gerard de Tuf, who won the Nobel Prize, and various other people to spend 25 years. trying to answer this question. And we believe, largely from string theory, that we do understand that the information does, in a very subtle way, come out of the black hole. S subtle quantum

correlations between the particles that emerge from the black hole do carry all the information of, say, the DNA molecule that fell in. So you can recover all the information we believe. Now, there are still mysteries that we're still figuring out, but just about every single. everybody, including Hawking before he passed away, agrees that we believe the information does come out. Preservation. He had a gap with somebody, wasn't it? Was it with Preschool?

John Presco. Yeah, great. He was a postdoc when I was a graduate student at the University of Texas. Okay. Yeah. So Presco won the bet then. So Prescott won the bet, but Kip Thorne was also part of this. And Kip Thorne was unwilling to concede.

Kipp Thorne is in our archives. Check him out. Yeah, absolutely. We interviewed him in his office in Pasadena. So, so Hawkinson. Hawking conceded the bet that John Prescol said the information does come out, and he gave him an encyclopedia of baseball. A lot of information he provided him as the way to... Baseball already has too much information.

Now you have an encyclopedia of it. It made good on his bet. I don't know where Kip Thorne stands on this. I don't know if he has conceded. Okay. Okay. What's the business about the information being stored in the event horizon? Have you?

Yes. Oh, what do you call that? That's the holographic. photographic idea, and that's part of the solution for why we believe the information comes out. And it's Susskind again. Susskind again. This guy is incredible. Things fall into a black hole, and we believe that they leave on the surface in some sense a copy, a residue of their information, and that's how we can come back out.

It never actually goes in. They never went in. The imprint was left on the event horizon. Very cool, man. Super cool, man. Yeah, so we have an explainer on whether or not we are living in a black hole. We could be. properties, yeah, we could be.

If it's big enough, yeah, okay. All right, here we go, this is Rachel. Rachel says... And we're still in questions that I had to call my boss. Rachel says, what's up, Dr. T, Rachel here from Austin, Texas. I've been thinking about the spinning universe hypothesis, which suggests our cosmos might be rotating as a whole. This idea has been proposed as a potential way to resolve the Hubble tension. But it got me wondering, if the universe is indeed spinning,

Could the force we attribute to dark energy, which is causing the accelerated expansion, actually be explained by a kind of cosmic centripical force? So she's saying that we just on a whirling bird, whirling dervus. We're in a whirling dervice. We're in a teacup ride. It's hard to see how you'd make that work. When we see the evidence for dark energy, it seems to be so-called isotropic. It's the same in every direction in which you look.

whereas if the universe is spinning, there's an axis. There's an angular momentum that picks out some directions as different from others. That's right. So it's hard to see how that will work. There's no centrifugal force. Yes, but if you look off the axis, we study the motion of distant galaxies. We look across the entire sky. And so we have sufficient data, I think, to rule that possibility out.

But who knows? Write a paper and we'll see whether it works. Yeah, that was all right. What a great question. Okay. We're going to move into regular questions now. Wait, wait. Let me pull out one that was there, and I forgot who asked it,

and it was about whether we'd have a quark catastrophe. So we had a Patreon member right in. The questioner knew that if you have two quarks in some kind of nucleon, then you try to pull them apart. There's a point where that snaps, but you've invested so much energy in it. The two new quarks show up in that instant. Now you have two pairs of quarks.

Right? We good with that? Yeah. Okay. So, in a black hole, or maybe in the big rip, either, let's look at the, you're descending to the singularity, the two quark particle falls, tidal forces get greater and greater, and then it splits the two quarks. So now we come two pairs of quarks as they fall in. then it becomes four pairs and then eight pairs. And it'll just be this unlimited increase in the number of quarks as it descends to the singularity.

Why doesn't that happen? Well, you do feel tidal forces as you get ever closer to the center for sure. But I'm not a quark. And it's a finite time scale between when you cross the event or eyes and then you hit the singularity. And I can well imagine that particle pairs are created in the last. moments of this, but whether all of the energy gets transformed in this way, that seems unlikely. After I rethought about it, it occurred to me, it's pulling that energy out of the black hole. So it would evaporate the whole black hole.

Oh, if they're thinking that in infinite energy transfer, then, yeah, absolutely. Everything is finite timescales, finite energies. And so, yeah, exotic processes can certainly happen when the gravitational force is that powerful. Now, of course, when you get to the singularity, we have no idea what actually happens. Because you street theorists haven't figured it out yet. We have not, but that's actually a real point. That's one of the goals that we've not yet achieved. And the big rip would be the same thing.

There's a point where the accelerating expansion of the universe. If it was sufficiently high. Would get on the scale of nucleons and split apart the quarks. And they make another pair and would just keep doing that. Yep, yep, yep. I mean, there are many other processes that can happen in the world. So I wouldn't just focus on this. There are all sorts of ways that enter.

can transfer from the big rip or the gravitational energy of a black hole into particle production, into various kind of processes. I'm just like creates a whole universe of quarks. You'd have to sort of calculate the rate at which those processes happen versus other things. The entire dark energy universe. Inside you, but we're still inside the black hole? No, no, now we're just looking at the big rig. I'm just wondering if this keeps happening, it's using up the energy of...

But then, of course, if that's... were the case, it would no longer undergo the accelerated expansion. Exactly. It would halt expansion. Right. Exactly. Okay. Okay.

All right. This is Michael de la Morena, who says, is time a dimension or a field? It seems more like a field because it can be affected by gravity. That was another one that I punted to Brian. Mm-hmm. Is time a dimension or a field? Well, I'd say the deep lesson of Einstein was that, that space and time can be affected by their environment.

And they, in turn, create the very environment that then back reacts on their own shape and structure. And so we usually think about time as a coordinate, a label, telling us when things happen, just like coordinates in space tell us where things happen. And the unexpected thing is that label, the amount of time between two different locations, can be influenced by the force of gravity. Right. But that doesn't require that it be a field. Yes, it doesn't require it be a field.

Right. To be influenced by a force. But I understand the intuition because we used to think that the labels, the locations of where and when things happen, in a Newtonian perspective, they're just inert. They just sit there.

They don't do anything. Einstein elevated them to be dynamical qualities of the world. And that's the deep lesson. Very cool. Great question, Michael. All right, this is Cody Rosenberg, who says, Hello, Doctors and Chuck. I'm Cody Rosenberg from Eugene, Oregon.

Please know that y'all are goaded for us armchair astrophysics. Physicist or physics enthusiasts. All right, very nice. Anyway, do you guys think that life is inevitable? Do you think it would be weird for a universe to exist that can't be experienced or observed? Do you think we are the physical manifestations of the universe yearning to experience itself? So it's a very John Wheeler-like way of looking at the world.

Wheeler would love to say that we are the way that the universe becomes cognizant of itself. It's a poetic. In a eyeball. Yeah, a U, a serifed U. And on one of the upwards of the U, there's an eyeball looking at the other line of the U. So the universe. Looking at itself. So it's a, you know, narcissistic or beautiful, depending on your perspective, that we're here so the universe can think about itself.

I don't know of any law that makes life inevitable. It seems it was a lot of happenstance between the Big Bang and today. But, you know, we don't understand a lot about the world and maybe one day we'll find there's this law, this inevitability of the existence of galaxies and stars and planets and people, at least on one such planet. I don't know of any such law today. Let me ask you about this. But there's some thinking that, and this is wishful thinking, not because someone has researched this,

that you go to a different planet, you can take a geologist there. They'll be comfortable there because they'll know what a rock, you know, there's an igneous rock. Because they see their crap everywhere. Yeah, that's right. So the rocks and the minerals, there might be some more exotic ones.

Exactly. But they have a sense of how, what elements do when they're heated for a certain amount of time under pressure. Right. And that repeats. depending on the planet. So there are general rules of geology

that apply to all planets. So let's go to biology. Okay. Could the DNA molecule be a natural consequence of complex chemistry operating on planetary surfaces? Could it be as natural on a planet as rock tar? To the geologists. And that's what I was about to ask,

and both of you can chime in on this, how cheap is life? So forget if it's inevitable, how cheap is life? I don't know what they're right. Well, in the sense that it formed relatively quickly on the planet Earth, so it didn't take an enormous amount of time.

If it took billions of years, you'd say, whoa, that was some hard stuff. Yeah, it formed in just, in fact, we used to, how long do you think it took? Half a billion, I'd say? Okay, that's what we used to say. Oh, okay. What would you say now?

Okay, we used to say that because you'd start the clock at when Earth formed, right? Right, four and a billion years. Yeah, yeah, and then the early, early signs of life were like 3.8, 3.9. So you say 600, million years, we used to say.

And then we said, no, no, that's unfair. That's unfair. When Earth formed, there was periods of heavy bombardment where the surface of the Earth could not have sustained complex chemistry. Of course. Because the energy is so high, it breaks apart. Let the Earth cool, for goodness sake. So the cooling, you let it cool at about four billion years.

It's half a billion years. At four billion years, now you start the clock. And you have life 200 million years later. Wow. that's really great. Right. In the grand scheme. In the grand scheme. So that's what I'm saying.

So life is pretty cheap then. Yeah, it's 5% of the total time Earth has been around. Again, however, I think that's likely the way to talk about it, but there are so many detailed physical chemical processes that maybe they just so happen to come together in this one planet of the trillion that are out there. So when we understand it better, that cheapness may explain. by a coincidence of a whole lot of factors that just happened to align on our planet. I don't think that's how it's going to turn out, but it's a possibility.

It's a possibility, yeah. Well, except that, you know, there are amino acids on meteorites. Yeah, we've found them already. Right, yeah. An interesting question, though, is the way that proteins are coated by amino acids is uniform across all life. It's the same code. Three base pairs on the genetic code give rise to a particular amino acid.

That is the code that works for you, me in all life. On another planet, if there is other form of life, the deep question will be, is it the same code? Or is it different? It doesn't need DNA at all. Right. Right. And so if it's different, that would be wonderful. That would suggest that life in a whole variety of different forms can exist throughout the end of it.

We're not fully explored all the ways of being alive. Yeah. Wow. All right. Well, great question. Way to go. Cody. All right.

This is Aaron Bailey, who says. Hey, StarTalk, I am Aaron from Florida, and we're sorry. Stop! Florida's trying. They're trying. Yeah, so Aaron says, long-time viewer, first-time subscriber. Thank you, Aaron. We appreciate that.

According to Einstein's equations, is time travel still possible if you are traveling to a black hole, and why can't we use gravitational detectors to measure the properties of dark matter? So in the first question, yeah, I mean, Einstein's special and general activity both embrace a certain kind of time travel. And the black hole provides the mechanism for one kind. If you go hang out near a black hole, time for you elapses more slowly compared to someone who's far away. Famously portrayed in interstellar. And so if you go to the edge of a black hole and you hang out and then you come back, everyone that you meet is going to be much older. Their clock was going much faster than your clock.

And that is, some people say, well, that's not time travel. That is time travel. You've traveled into their future, which would have been your future if you stayed there. Exactly. And you know who they left up in the ship. The black dude. He came back like, oh, God, damn. 23 years.

Yeah. You know why serious. Now, you know, I'm on Social Security. Don't get it. You go down there, you tell me you'll come right back. You're worse than that. You're worse than my kids. You're worse than my kids.

I don't get it, Matthew McConaughey. All right. What was the second half to that question? Yeah, what was the other half? And so the second half, he says, why can't we use gravitational detectors to measure the properties of dark matter? Well, we do. The way we know dark matter exists is by the gravitational influence that it has on its environment.

What we're unable to do is identify what the dark matter is made of. Right. And so we have these detectors all over the planet trying to capture little particles of dark matter. If that's the right explanation, we haven't been able to find any yet. You know what are doing that? What? Okay, you know, they're pulsars. Yes.

They're rapidly rotating neutron stars. In a very precise way. Extremely precise. Right. And they're across the galaxy. They're not all that many of them. Right. But there's enough to map out the galaxy.

So if you precisely know and measure the pulses of these pulsars, Okay. You can track a gravitational wave moving across the galaxy. Yeah. So you kind of use them like buoys in the ocean. Ooh, good analogy there. Beautiful idea. And you don't even need LIGO for that.

Yeah. You just need high-sensitive, high-precision time. Yeah, for gravitational waves of a certain wavelength, this is a beautiful way of detecting their influence. Super cool, man. Yeah. All right. Let's move on to Alex Friass, who says,

says, hey, Dr. Tyson, Lord Nice. Alex here from Mexico. Oh, I should say Alex. No, Alejandro. Alexander from Mexico. Isn't that racist that you assume? I can be racist. I'm black.

I don't know if you realize. Okay. The world invented racism for me. Okay. Okay, here we go. From Mexico. He says. Did I tell you?

Did I tell you? It was, I was giving a public talk, and I thought I'd say something funny. Right. I was talking about the dinosaurs. And they went extinct by an asteroid that hit the Yucatan Peninsula, the Yucatan Peninsula of Mexico. And I said, but that's not what the dinosaurs called it. Okay.

Okay. That's funny. I thought it'd be funny. Right. And then someone in the front road said, they called it Mexico. That's funny, too. Spanish fluid dinosaurs. Yeah.

Okay. All right. And then you had Trumposaurus. It was just like, give them out. Anyway, I've always been intrigued and confused by the idea of super symmetry. Ooh, nice. If the standard model of particle physics is one of the most successful theories we have, what is telling us that it needs doubling up?

What would supersymmetry fix in our understanding of the universe? and what problems might it create? Thank you both and greetings from your neighbors in the beautiful Upper West Side. Oh, nice. Oh, look at that. Where to go, Alex, from right of the street. So let me sharpen that even further.

Sure. So the standard model is quite an organizational map of our particles and our forces and the like. In its current state, now that we've got the Higgs, the Higgs, is it missing anything? is it a closed box right now? And if we do anything to it, does it simply make it more powerful? Or do we know we need things to explain other things that we don't yet understand?

Good, good. So the main motivation for supersymmetry is to address exactly the way you frame the question, which is when we study this Higgs particle, this newest edition that we found on July 4th, 2012, at least that's where the announcement was, When you look at the mathematics, it says that the mass of the Higgs particle should be much, much bigger than the mass that we find. And when we try to keep the mass at the value measured, we have to stand on our mathematical heads to do so. We have to tune and tune and tune. If supersymmetry were true, the terms that would push the Higgs mass up, they cancel out from those pairings.

That's why we need the pairings. That's why we need the doubling. And if you can cancel out the new contributions, you can rest easy. The Higgs mass will stay at a small value. Look at that. So how many more particles come along? It doubles it.

It really does. For every known particle, there is a partner. Electrons have super symmetric. Yeah, super symmetric election. Do we have words for all these particles? Yes, so the electron has the selectron. Quarks, squarks, neutrinos. No.

Yes. No. Yes. I don't name them. The snootrino, no. Yeah. You know why? because somebody, when they found it, they're like,

no, neutrino, neutrinos, no, okay. And so the big hope, if you would have spoken to me as a graduate student in the 1980s, the big hope and the reason we believe that string theory might be five years away was we expected supersymmetry, which is the super in super string theory. We thought it would be found.

Those particles would be found at the large Hadron Collider. And they were not found. Wow. And so this did not. And they will never be found. Well, that's probably true because the collider has a limited energy reach. Nothing in our theories tells us how massive the partner particles would be. If they're sufficiently massive, they'll be beyond the reach of the large Hadron Collider.

So there's a natural explanation for why we didn't find the particles, but we were certain that we would. He wants another collider. Yeah, there you go. You're going to need one. Look at that. Wow, that is fascinating, though. Okay. And does the Higgs have the, do we have a name for the other particle?

Higgsino. Higgsino. Yeah. I prefer squigs. You won't go with squarks. You might as well go with squids. The photon? What's the symbol?

Fotino. Really? Really. Okay. And the W and Z bosons, those are harder, Zenos or weinos. Winoes. They get a little bit, yeah. Yeah, that's getting a little funky.

The graviton? Well, you see, the supersymmetry that we're talking about doesn't have gravity in it when you're just talking about the standard model. Oh, standard model doesn't have gravity. Yeah. Yeah. But if you include gravity, then there is a version. It's called supergravity. And it comes out of string theory as well.

And it's the gravitino. Right. All right. It's from the graviton. Yeah. Right. Okay. All right.

Well, way to go there, Alex. So we're still looking for him. Yeah. You're still looking for him. There's no evidence for them. Okay. Is this just a matter of a lack of detectors? Could you build enough detectors where we could get all this, capture all this stuff?

Not so much detectors, it's a matter of the energy. So how big the collider is. And that's, you know, colliders are expensive. And the bigger they are, the more money they cost. And we had a big one going in our side of the pond. The superconducting supercollider in Texas funded in the 1980s under Reagan. and dug the hole got all ready, Waxahatchee, Texas.

It would be three times as powerful, I think. Yeah, about 50 TV, and we have 14 TV. Yeah, yeah, so three times the power of the one that was built in Switzerland. And then early 90s, they zeroed the budget. And they said, oh, those cost overruns and this sort of thing. But, but... Oh, some kind of defense thing. We no longer were fighting for our lives.

Peace broke out in Europe. The fall of those. Yes. Peace breaks out and all of a sudden, it's like, we don't need physicists. We need this. What do we need physicists for? And they're little toys.

You never heard of cost overruns and any other particle accelerator for the whole 20th century. Right. Interesting. This is Blake who says, Hey, it's Blake. Greetings from warm, sunny,

Columbia, South Carolina. Way to rub it in there, Blake. He says, there are quite a few theories. radical particles that have been discussed on this show, the graviton, the tachian strings, etc. But we don't seem close to actually finding any of them. Are there any experiments proposed that might help us capture and learn about these elusive particles if they exist?

And slightly more an engineering question, if we did find them, how might we use them for the benefit of humanity? Yeah. Do they have a use if we find them? I mean, well, if dark matter is actually found and it is a particle, look, it's, deepen our confidence, our understanding. Can I imagine applying dark matter particles to build something? The whole point is they're incredibly elusive.

They only interact gravitationally. How do we even capture them if they don't interact with anything? They don't even interact with themselves. They interact with themselves. Yes, but anything that has energy interacts gravitationally. And these dark matter particles through indirect quantum processes do interact with ordinary matter. And that's how these detectives are set up. Or is that the energy?

Well, yes. Well, that's the dark energy. Yeah, but it's the same basic idea. And so, yes, you can detect these things, but that's different from gathering them together and engineering with them. So I don't see any direct benefit that comes out. There's no bricks and mortar.

Right. You know, but again, it's the same argument what we made before. The deeper your understanding, that's step one. And then someone figures out where that goes. That's going to take it. That's going to take you someplace else, right. Okay, gotcha.

All right, this is Luke Sr. who says, best regards from Joliet. He says, Dr. Luke Lipporte, Ph.D. Translation Scholar and Synologist. He says, could it be the entanglement phenomenon is simply a matter of absence of the time dimension at the scale of the particles and that we see two particles interacting instantaneously at a distance in some, you know, his word, magical way. In their own three dimensions only universe, they're just unaware that a change of state has occurred, that for them there's no before entanglement slash after entanglement. Thank you

very much. It's a very well thought out question. Does it make sense? It does. And I think we can interpret it more or less along this wormhole idea that we were describing before. the wormhole notion, again, this is still very much at the forefront. We're still working out the details. But if it is the case that two distant particles are connected by a wormhole, if they're entangled quantum mechanically, then it would be as if they're right next to each other. To them, they don't know the difference. To them, they don't know that they're far apart.

And so that's a variation on the same thing. I don't think you can say they live in a world without time because the conundrum is to us beings that do have time. you do something here and it instantaneously, according to us, affect something over there. And that would still be a puzzle no matter what. And one explanation would be, well, they're actually closer together than you think by looking at them because they have this secret shortcut connection,

which could be the wormhole. So I think for so many years, people were imagining wormholes as some kind of ride in a water park. Exactly. You know, even in the movie Contact. Jodie Foster is going through. And so, but no, you just stepped through. No, you step through in your...

I think it depends on the nature of the wormhole, but yeah, there can be versions where it's effectively stepping from one place to another. Scott Trek did it right, though. They had a portal where it looked like a doorway threshold. Sitting on the edge of forever. Sitting on the edge of forever. And that's a wormhole. You step through it and you're already there.

There's no ride. There's no... You just step through it and you're already there. And that's another one where they were going to save someone's life. And they decided not to. And they realized... What they're going to change the future. Yes.

In fact, I was talking with Bill. and he said that was his favorite episode. Really? It's my favorite watching as a viewer. Yeah, just because it dealt with time travel in a very emotional and unorthodox way. Yeah. And causality is actually addressed. All right, Zachary E says, hello, Dr. Tyson, Lord and Ice, Dr. Green.

Is it possible that through the many worlds interpretation, quantum immortality can become macroscopic If every single possible state of every single particle in existence is equally real, I feel like the superposition of a single particle in quantum immortality theory can be expanded to incorporate the superposition of every single particle in existence. Yeah. And look, you know, another way of saying it is, we said before that the many worlds allows a world in which anything compatible with physics is realized, us living to,

100, 200, 500, a thousand. I don't know that there's a law of physics that prevents that can happen. Now, there is a law of Jesus. I'm bored that will allow that. The bored of, the board of, who can you imagine living a thousand years? Ugh.

Who, I'm, oh, kill me. Just thinking about it, I want to die. So wait, here's something that we did not raise, which was if there's another identical me, yeah, is it me? That's the deep question. That is the question. Now, that's a consciousness question.

And I think the answer to that is yes. No, I think the answer is no. Why? Because we've already kind of done that experiment. They're called twins. No, I'm saying that person has literally your memories, literally your self of sense of self until something measurement that causes you to be different. Yeah. Yeah.

So it's truly you. That's wild. I mean, if I spoke to that version of you, you would adamantly claim, yes, I'm the same guy. That's me. It's me. It's me, damn it. That's funny. Yeah.

I don't know what to say. I've never heard you say that before. Stop. So that means we are living forever. The reincarnation. Yeah. Yeah. Are all over this.

That's right. Right. Why? Or at least extraordinarily long. You know, maybe there is some physical law about maybe the proton decay. 10 to the 38 years. Is that 10 to 38? Yeah.

Or the call 10 to whatever. More than 10 to the 32. Yeah. 32. Wow. All right. This is Marcus Ruzon. And Marcus Rizan says,

Hello, Neil and Brian. Love the show. I've been wondering something about time and light. If nothing can travel faster than light and the speed of light is a universal constant, could it be that time itself is actually an emergent, property of light. Is it possible that what we perceive as time is actually just a consequence of us traveling through space time at a finite speed below the speed of light? Is that not confirmed

by the fact that from the point of view of a photon there is no time, thanks, and keep looking up from Singapore. Yeah. Nice. Okay. And in some poetic sense, I agree with what the questioner asks. They're saying that if a photon had consciousness, from its perspective, it would not know that time is elapsing. Now, I think it's really important to recognize that you're extrapolating Einstein's result to a particle for whom the equations don't literally apply

in the way that we're using them. Correct. So if you apply Einstein's ideas to any massive body, you find that they can't travel at the speed of light. And therefore they will always have this conception of time. Exactly. But if you want to push it to the absolute limit, which I call poetry, not quite mathematics, then yes. Right.

Because the key is the photon has no mass. Yes. That's the key. Yes. That's it. Yep. So once you have mass, you can't be a photon and you can't, you'll never experience with that photon experience. Precisely.

All right. Okay. Well, there you go, Marcus. But thanks for the, you know. I had nothing to add to that. Okay. All right. This is Patrick Dietz.

And Patrick says, hello, Dr. Tyson, Dr. Green, Lord Nice. Pat Dietz from Ravenna, Michigan. Could the reason we cannot see dark matter also account for the expansion of the universe due to dark matter moves faster than light? Let me read that again. Could the reason we cannot see dark matter also account for the expansion of the universe due? to dark matter moving faster than light. Okay. That's a tough one to parse for me.

It's really rough, but I see what he's saying. How can you see the thing that's faster than the thing that allows you to see the thing? Right. I get this sort of collection of words, but the problem is... Okay, by the way, people... It's a satchel award. This is why I love scientists, because they know how to call you a dumb ass. Without ever...

saying those words. See? The important point is that for a particle to be a particle of dark matter, it has to have mass. Once it has mass,

it can't travel fast in the speed of light. So the ideas don't meld together in a consistent way. There you go. All right. I like the question

just for the fun of it. All right. Thank you, Patrick. This is Mr. Zoot. And Mr. Zoot says, Dear Star Talkers, Jeffrey here pronounce Jeffrey Chuck

Screw you Mr. Zoot He says I understand electron orbitals are really probability clouds but still exist in discrete energy levels around the nucleus. What then happens during ionization?

Do they stay as a probability cloud? Just untethered from their anchor so to speak? Do they still have discrete energy levels? hey, what gives and thanks? So if that... It's a great question.

Somebody's thinking. And so it certainly does stay as a probability cloud or probability wave. Right. If an electron is ionized, say, from hydrogen. But if that electron is living in a universe that is not a box, that's infinitely big, then we don't believe its energy levels will be quantized. You think it'll be continuous? Yes.

So if you have a particle in a box, if you have a particle in a box, if you have a particle in a box, then the energy levels are quantized, but they are dependent upon the size of the box. Because you're solving the wave equation. You're saving the wave equation in a box. You're expanding the, what's it called? The harmonics. The harmonics.

Yes. And the monics have to die. They have to fit inside the box. But if there's no box, then they could have any wavelength at all, any energy at all. What you're saying is that the energy of a free electron is not quantized. Correct. I did not know that.

That's, I've never heard that before. Now you explained that it's obvious that it could only be that way. That's wild. Wow. That's absolutely wild. Very cool, man. Wow, great question, Jeffrey. And just to highlight, because he said something important here.

So we'll call it a box, but let's look at a tube. Let's look at an organ tube. Okay. Like a pipe organ. Right. And you can ask, what kind of wave can you set up inside that tube? And it can only hold a wave where the complete wave is there. Right.

You can't hold like a half a wave. Right, right. So it sets what the wavelength is, the frequency of the sound, that's the wavelength, you get that from the wavelength, in each tube. So different tubes have different frequencies that resonate inside of those tubes. Right. And so when I think of atoms, I think of you've got the nucleus with the protons sets up a box. And so you then you do the math and you get a set of wavelengths, so I'll call them that, that fit inside this box. And it's unique for every atom. And that's what gives you the spectra of each atom. That's so each atom has a unique spectrum. Right.

Yeah. It's really cool. That is excellent. Wow. I learned stuff on this show. It's so great. So did I. I just never thought about free electrons in their energies.

Yeah. Okay. This is Brian Nadu, who says, Hey, Dr. Tyson, Dr. Green, Lord Nice. Brian from upstate New York here. With the discovery and verification of the gravity. assist at all in reconciling general relativity and quantum. I love that.

I'm a huge. Isn't it just assumed that there's a graviton? And that assumption needs to be verified, hopefully. And what's the energy of a graviton relative to the waves that we just detected? Well, the energy, the mass of a graviton, we believe, is zero because gravity also travels at the speed of light. So it's much like a photon. in that particular way. And yes, if we could ever really detect a graviton,

do experiments with gravitons, scatter gravitons off of each other, then yes, we would learn an enormous amount about general relativity and quantum mechanics. Yeah, but we'll help you merge them. Well, our... Because that's a quantum expression of gravity. That's right.

In fact, the very existence of a graviton would be the first evidence that gravity is quantized. And so we're assuming that there is... is a graviton, but verifying it would be a huge step. Who was the first to presume that? The idea of the graviton? I don't historically know. So, but my understanding was the gravitational wave.

Yeah. Well, he was a reluctant gravitational wave person. He was really uncertain in 1916 and 1918 about whether they were real. Okay. Amazing. Yeah. Yeah. So I'm just saying the quantum assumption is that where you have a

wave, you also have a particle. Yeah. And like the photon is a wave and a particle. Yep. Okay. Wow. Okay. That's super cool, man.

That's a good question. Who first introduced the very idea of a graviton? I don't know the answer. It feels kind of natural if you're going to... I'm going to look that one up. Quantum. Yeah. Quantum quantify.

Yeah. All right, this is Tash Shaw. And Tash says, Dear Dr. Tyson, Dr. Dr. Green, Lord Nice. I'm Tosh from Orange. Australia. I'm a long-time listener, so my boyfriend bought me a subscription to Patreon for Christmas. Oh, nice. Very nice. What a nice boyfriend. Very nice gift. Yeah. That's a smart man.

I have read that other dimensions could potentially be detected through gravitational and other anomalies. I was wondering how we would be able to distinguish these from any effects of dark matter. So would there be dimensional differentiations? Yeah. In fact, a proposal that was made a while ago is that at a collider, like the Large Hadron Collider, when you slam protons together, you can calculate and measure how much energy you have before the collision.

You can measure how much energy you have after the collision. And if you have less energy after the collision, that energy must have gone somewhere. somewhere. That is so cool. And the possibility is the energy went into the other dimensions. Oh. And so this was a missing energy signature of extra dimensions that we were again hoping we would see.

Why would you presume that and not as what occurred in the first neutrino experiment? That's right. So it could be some other particle, mysterious particle carrying away. Right. Because the first neutrino, they didn't experiment and there was an imbalance. Yeah, there was an imbalance. There was like you start with this much energy and they have less. Right.

And you accounted for all the particles. Right. So what's up with that? Well, maybe there's another particle. What's up with that? And they say, if there is a particle, it has to be neutral and it has to be very low mass. And the guy who proposed it was Italian. So little neutral one, neutrino.

Oh. Like Bambino, little baby. Like Bambino, neutrino. What you got? Check. Let's go to Cosmic Moss. Says, hello, everyone. Love the show and every star you've had.

had on it. You guys are great. I love the way you teach. Please keep the education up. Dr. Tyson, Dr. Green, could theoretically a frequency be matched at two points in space by a micro particle uninhibited by resistance only to be met by its astrophysical counterpart. Neil, I think you should take it this. I don't know that I understand the question. I know. Kind of like matter, anti-matter, but the particle is already in existence.

and then it's a counterpart that impedes, I guess, the entanglement. It's kind of like... Read the first sentence again. All right, he goes, could theoretically a frequency, all right? So that's the, I guess, his version of the string. Be matched at two points in space by a micro particle. So that's the entanglement. Maybe.

Uninhibited by a resistance only to be met by its astrophysical counterpart. The only counterpart particle is. are anti-matter. That's it. Yeah, there's no other thing. That's what I'm saying. And there's not much antimatter in the universe. Right.

In fact, well, other than the centers of stars, we probably make all the antimatter there is in the universe on Earth, would you say? I haven't done the calculation, but I could imagine that. I mean, just think about that, right? There's plenty of antimatter made in the center of somebody. Most antimatter in the universe will get annihilated finding matter. Immediately in the centers of the sun, right? Yeah.

The cool part was in one of the Dan Brown stories. The Catholic Church had a vial of antimatter that they carried. That's so funny. Dominus's spirit. Oh, he's gone. Physics jokes, people. All right. So, yeah, I don't, it's not quite clear.

If it met it's actually the counterpart, it would annihilate, no matter what else is going on here. Right, no matter what else is going on here. All right. So here we go. Kenny Watts says this. Hey, Dr. Tyson, Dr. Green. So, Lord Nice.

Kenny from Dothan, Alabama. Is the reason why we can't reach the absolute zero degrees in temperature because of the CMB? Is it due to the act of time using energy to move forward, creating heat? And if we were to reach absolute zero degrees, would space time move forward in that region? Yeah. Yeah. I'm a few pieces of this, Brian. So my understanding of absolute zero is that,

you know, all particle motion stops, except it doesn't because you have quantum fluctuations, even that absolute zero. That's the key point right there. Okay. That's the real barrier. Okay, so, but why isn't the cosmic microwave background a barrier? Well, if you didn't shield yourself from 2.7 degree photons,

they would influence. But presumably, if you're able to shield your environment... Yeah, but the shielding would have to be temporary because the heat transfers. Yeah, sure. But an experiment takes place over a period of time. So as long as your time scales are set, right? That's what a thermos works.

Yeah, exactly. So I think it's really the uncertainty principle is a true barrier against truly having particles at a definite location, not moving. That would mean position and speed were both nailed down at the same time. Which is not happening. Right. You're not going to do that. Not happening. Wow.

So the wave function would cease to exist if you were ever to get to the place where you could get the particle to stay. exactly frozen, like still and definable in one point. Okay, so what is the temperature of that state of matter? Well, it depends on the details. You can calculate the quantum fluctuations of a field, and if you tell me how it interacts and its mass, you can calculate its quantum fluctuations, and indeed that's how you make predictions about the Casimir effect,

where you have two metal plates, and there's empty space between them. Evacuated completely. And yet those plates can pull together, because the fluctuations of the field inside are a little bit less than the fluctuations outside. And that imbalance, you can actually calculate it and you can determine how the plates come together.

That is so freaky, man. It's all freaky. That is so freaky. I love it. It's all freaky. Oh, my goodness. And then they attract. Yeah.

Yeah. Brian, you freaky dude. So we should do this every week. What do you say? No, Brian, you have a life? Thank you, Brian. My pleasure. This is great.

You're working on a quantum physics book. Yep, yeah. This is the decade, the centennial decade of the discovery of quantum physics. Exactly. We can't have too much quantum physics out there. And this is for the general public? Yeah, so we're finishing it up now in 2027. It should be out.

Get it out in this decade. Yeah, that's the key thing. Okay. All right. And this year we're recording this in 2026. This is the centennial of Edwin Hubble discovering that the Milkyway is not the only galaxy. in the universe. Wow.

He discovers that Andromeda is not just a fuzzy spiral sitting within our stars. Right. It's a whole other island universe out there. That's, I love that. That was 100 years ago. So, this has been a special edition because it's an extended conversation with my friend and colleague, Brian Green, right up the street at Columbia University. And delight, thanks for spending the afternoon in my office.

My pleasure. It was great fun. All right. And Chuck. Always a pleasure. Baby. Yes. And catching you on YouTube.

Were you just smart enough? That's right. On the StarTalk YouTube channel. Were you just smart enough for this conversation? Today I was the dumb ass and happy to be so. All right. Until next time, Neil deGrasse Tyson. Keep looking up.