In Theory with Janna Levin

If something is possible, has the universe tried it? Are all physical possibilities inevitable? Neil deGrasse Tyson sits down with theoretical astrophysicist Janna Levin to launch “In Theory,” a new StarTalk series celebrating the weird, wacky theories of the universe and the theorists who chase them. Out on YouTube October 29, 2026!

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

• 0:00Neil deGrasse Tyson?

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• 1:10Neil deGrasse Tyson?

  Coming right up on StarTalk is a one-on-one conversation between me and my good friend and colleague, Janna Levin, theoretical physicist. Why? She's got a new series appearing on our channel called "In Theory." You're going to learn all about what makes the mind of a theorist tick and how it connects to what we know, what we don't know, and what we have yet to discover in this universe. Check it out.

• 1:40Speaker 02

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

• 1:56Janna Levin?

  Is everything that's possible in the universe inevitable if the laws of physics allow it? Will nature experiment with every possibility, no matter how improbable? I'm Janna Levin, and this is In Theory.

• 2:21Neil deGrasse Tyson?

  Neil deGrasse Tyson here, your personal astrophysicist. We've got a special version of the show today. This has got just me and Janna Levin returning to StarTalk. She is the Claire Tao Professor of Physics and Astronomy at Barnard College of Columbia University, right up the street. And she's, we have several theorists at large, she's one of them, among our favorites. And we're going to talk to her today about some recent projects she's been up to, to bring more of the universe down to earth for you. So

• 3:00Neil deGrasse Tyson?

  Janna, we're going to talk about some of the weirdest, wackiest theories of the universe because you cover them in a new series appearing in the StarTalk channel called...

• 3:17Janna Levin?

  In Theory.

• 3:18Neil deGrasse Tyson?

  In Theory. Love it. In Theory.

• 3:21Janna Levin?

  Yeah, that's where all the big ideas happen. And then we hope nature finds a way.

• 3:27Neil deGrasse Tyson?

  I spent time at Princeton, where there are a lot of theorists, not only today, but historically. And there's a sign on a door there that says, "Never trust an observation unless it's confirmed by a theory."

• 3:42Neil deGrasse Tyson?

  How do you feel about that?

• 3:43Janna Levin?

  Well, as you well know, that's inverting the usual adage where theorists are often chastised for not being experimentally verifiable. But sometimes it's just a few hundred years of patience.

• 3:59Neil deGrasse Tyson?

  I read up on the themes and I, I love it.

• 4:04Janna Levin?

  Yeah, we're out there.

• 4:06Neil deGrasse Tyson?

  You're out there because the laws of physics tell you what's possible.

• 4:11Janna Levin?

  And I think we used to imagine nature picked a specific example, but we kept learning over and over again that nature was kind of rolling the die, trying different combinations, whether it was planets, organisms, stars.

• 4:25Neil deGrasse Tyson?

  Because the laws of physics allow more than what we might see in any given moment.

• 4:31Janna Levin?

  Yeah.

• 4:32Neil deGrasse Tyson?

  To manifest in this universe.

• 4:34Janna Levin?

  We used to think the Earth was it, the Sun was it, and we realized in some sense, anything that was physically possible seemed to be attempted by nature. And if you think of the entire principle of evolution, that it's trying again and again under pressure, but nonetheless experimenting with every possibility.

• 4:54Neil deGrasse Tyson?

  And not all experiments work.

• 4:55Janna Levin?

  Not all experiments work, and not all experiments can be tried on this planet. But if we go further out, maybe all experiments are tried on other planets. And if you really want to go out there, in total, other universes, right? So I think the question is, if it's theoretically possible, maybe nature's tried it.

• 5:15Neil deGrasse Tyson?

  So is another way to say that is if it's theoretically possible, whether or not we've yet to see it or discover it, might it be inevitable?

• 5:24Janna Levin?

  Might it be inevitable?

• 5:25Neil deGrasse Tyson?

  That's my question to you. Don't ask me. I'm asking you.

• 5:29Janna Levin?

  Well, in theory, and I think that's exactly, as a theorist, what you're exploring. Sometimes you don't have a handle on what the experiment's going to be or what the observation's going to be, or if it's going to be possible to make that observation viable in your lifetime.

• 5:46Neil deGrasse Tyson?

  Either because it takes too long or costs too much money.

• 5:48Janna Levin?

  Costs too much money, takes too long, you haven't thought of a way to actually observe something that faint, that far, right? Or, or if it is another universe, does it mean that there's no communication? Will it be in principle impossible to communicate? But as a theorist, you're instead trying out all the possibilities yourself. And a lot of them die on paper. You can figure out which ones nature will say are not viable many times. But anything that really seems viable, you have to ask, has it happened?

• 6:19Neil deGrasse Tyson?

  But you just casually mentioned other universes.

• 6:22Janna Levin?

  Yeah.

• 6:23Neil deGrasse Tyson?

  Yeah, other planets, other star, other universes, right?

• 6:27Janna Levin?

  I think that conclusion has been foisted on us precisely because we kept being deposed from the center of everything. Not the only planet in the solar system. Okay, there are only, let's get this right.

• 6:39Neil deGrasse Tyson?

  Eight.

• 6:39Janna Levin?

  Eight. That's not that many. Not naming names. But then you realize...

• 6:47Neil deGrasse Tyson?

  Eight planets.

• 6:48Janna Levin?

  Probably most star systems in our galaxy, as you well know, has multiple planets. It starts to go up to the trillions. You start to imagine maybe every combination being attempted. And then you go beyond our galaxy and it starts to seem like a possibility.

• 7:04Neil deGrasse Tyson?

  We've got a trillion galaxies in our universe.

• 7:08Janna Levin?

  Yes. So if we're not at the center of the galaxy, we're not at the center of the solar system, and we're not unique in galaxies, maybe we're not unique in having had a big bang.

• 7:21Neil deGrasse Tyson?

  No! You gotta give us something.

• 7:26Janna Levin?

  Yeah. Well, I don't know, do I? I mean, it's possible this is the only one, but wouldn't that be breaking the whole pattern?

• 7:34Neil deGrasse Tyson?

  Trend line. All right. So if there's more than one universe, and we call that the...

• 7:40Janna Levin?

  Multiverse.

• 7:41Neil deGrasse Tyson?

  Then are there more than one multiverses?

• 7:44Janna Levin?

  Well, interesting question. I think some of that becomes a language breakdown. Are we imagining a cluster that there's a possibility that universes can interact? Can they collide, for instance? Could our big bang be a collision with another universe in our past? Or are we imagining universes that are completely disconnected in any meaningful sense? They have no relation in space or time to each other. We can't say how far away they are. We can't say how long ago they, they were. So the multiverse is right now indistinct because I think we don't understand it well enough yet, other than

• 8:27Janna Levin?

  to say, imagine there are other big bangs. It's an interesting idea, Neil. If we can classify planets, these are Earth-like planets, these are hot Jupiters, right? These are brown dwarfs. Maybe we can classify universes. I don't think that's really been done yet.

• 8:44Neil deGrasse Tyson?

  No, I don't think so. Okay.

• 8:47Janna Levin?

  Yeah. But let's, we're in this one. This one's pretty good.

• 8:49Neil deGrasse Tyson?

  I'd like this one.

• 8:50Janna Levin?

  It's like this planet's pretty good.

• 8:53Neil deGrasse Tyson?

  So as I understand it, that's the subject of your first installment.

• 8:58Janna Levin?

  Yes.

• 8:58Neil deGrasse Tyson?

  Out of how many installments?

• 9:00Janna Levin?

  We have six episodes.

• 9:01Neil deGrasse Tyson?

  Six episodes, and the first one, the multiverse.

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• 11:47Neil deGrasse Tyson?

  Hmm, space fact. There's a collision of galaxies called Stefan's Quintet. We would later learn that it's not a gathering of five galaxies. It's a gathering of only four. One of them is photobombing the collision.

• 12:06Neil deGrasse Tyson?

  If you like that fact, you can find 4,999 more in Lost in Space. 5,000 facts to help navigate the universe. Lost in Space is now available wherever you get your books.

• 12:41Janna Levin?

  I really want you to stay tuned. We're examining the exact possibility that nature experiments as much as possible, and anything viable will happen. And we contemplate what it's like, imagine the times before we realized there were other planetary systems, and we're on that cusp. So, come check it out. Drop in.

• 13:05Neil deGrasse Tyson?

  This is damn near pre-Copernican.

• 13:08Janna Levin?

  Yeah.

• 13:09Neil deGrasse Tyson?

  In our state of inquiry.

• 13:13Janna Levin?

  I mean, in a way, it's very...

• 13:15Neil deGrasse Tyson?

  Minus the religion telling us that it cannot be.

• 13:19Janna Levin?

  I mean, Copernicus really set us right on a lot of things. And honestly, everything's been, since Copernicus...

• 13:28Neil deGrasse Tyson?

  Has been Copernican.

• 13:29Janna Levin?

  Copernican. Exactly. We're not at the center of the solar system. That was the first. And ever since then, it's just kept going.

• 13:36Neil deGrasse Tyson?

  And with dark matter and dark energy driving the universe, we're not even made of the stuff that most of the universe is made of.

• 13:44Janna Levin?

  Everything anyone has ever seen.

• 13:47Neil deGrasse Tyson?

  That's emotionally wrong.

• 13:49Janna Levin?

  Right. It's a violation of your trust.

• 13:51Neil deGrasse Tyson?

  Thank you.

• 13:52Janna Levin?

  With the universe.

• 13:53Neil deGrasse Tyson?

  Thank you.

• 13:53Janna Levin?

  The dark matter, the dark energy is most of it. So imagine, oh, this is an interesting game we were playing, which was, imagine you were a dark creature. Like, the dark sector was complex enough that it had dark interactions.

• 14:07Neil deGrasse Tyson?

  I don't have to imagine that I'm a dark creature. There's no imagination necessary. Okay, go on.

• 14:12Janna Levin?

  You're gonna get us right off the air. So imagine you're looking at the galaxy, and then you see this huge halo of dark matter. And it's vast. It extends well beyond this little pancake of stars.

• 14:27Neil deGrasse Tyson?

  Hundreds of times the gravity of what you see.

• 14:30Janna Levin?

  Yeah. Imagine you're a dark astronomer, and you are arguing to your colleagues, I think there's this tiny pancake, flat little spiral of something I'm gonna call stars. In the middle there, it's less than 5% of what's in the universe. It's maybe 15% of what's in the galaxy.

• 14:52Neil deGrasse Tyson?

  Are you imagining dark matter astrophysicists?

• 14:54Janna Levin?

  Yeah.

• 14:56Neil deGrasse Tyson?

  Contemplating our existence as being so small and insignificant.

• 15:00Janna Levin?

  Imagine how long it would take them to even notice everything every human being has ever seen.

• 15:06Neil deGrasse Tyson?

  Janet, you're bumming me out.

• 15:07Janna Levin?

  I think it's kind of beautiful. We'd be like these jewels somebody discovered. This little luminosity.

• 15:15Neil deGrasse Tyson?

  Because we be luminous, in ways dark matter be not.

• 15:20Janna Levin?

  Exactly. Against all odds, you find these tiny luminous jewels buried...

• 15:26Neil deGrasse Tyson?

  So maybe they'll like us.

• 15:27Janna Levin?

  In a sea of this non-luminous...

• 15:30Neil deGrasse Tyson?

  Yes. Totally. No, they'll just take us and put us on their jewelry.

• 15:36Janna Levin?

  Wouldn't you be blown away if, in this huge galaxy, you found this little... Right, what would you call that? Centrepiece?

• 15:45Neil deGrasse Tyson?

  Yeah, I would put it on jewelry.

• 15:46Janna Levin?

  This jewel.

• 15:47Neil deGrasse Tyson?

  Yeah. Janet, in your theoretical exploits, in your theoretical dalliances with the cosmos, what showed up that nobody imagined, nobody predicted, and was still kind of, really?

• 16:09Neil deGrasse Tyson?

  Really? We gotta contend with this? Nobody saw that coming.

• 16:14Janna Levin?

  Wow. I think there's a variety of possible candidates for the top, you know, the top five of those remarkable discoveries. Some might be particles that nobody imagined, that did not fit into the scheme of things. But I think...

• 16:31Neil deGrasse Tyson?

  They'll be subatomic particles.

• 16:32Janna Levin?

  Yeah, subatomic particles that, you know, famously, the Nobel Prize-winning physicist Robbie said, who ordered that? You know, he's at a particle accelerator, they're smashing things together.

• 16:43Neil deGrasse Tyson?

  It's a Robbie.

• 16:43Janna Levin?

  Yeah. Particles are coming out, and he said, who ordered that? They're making discoveries.

• 16:49Neil deGrasse Tyson?

  So if I remember, so if I remember reading, and I'm not that old, who ordered that was, you take particles that we think are just genuine particles, smash them together, they break into other particles.

• 17:02Janna Levin?

  Yeah.

• 17:03Neil deGrasse Tyson?

  That nobody saw or imagined.

• 17:04Janna Levin?

  Yes. They were not indivisible.

• 17:06Neil deGrasse Tyson?

  Not indivisible. And so we now take those particles, inventory them, and figure out what the hell the universe is trying to do.

• 17:13Janna Levin?

  I think one twist in your question, though, is when you said, nobody imagined that. And I think, over and over again, people have imagined what seemed impossible, were told it was impossible, probably themselves thought, this isn't real. But there it was. And again, in this example of nature figuring out a way to do something.

• 17:40Neil deGrasse Tyson?

  Well, these people should have known that if it didn't violate the law of physics, they're in no position to say it's impossible.

• 17:46Janna Levin?

  Well, let's take black holes. So when Carl Schwarzschild is writing a letter to his friend Einstein from the Russian front during World War I, he had mathematically solved Einstein's equations.

• 17:58Neil deGrasse Tyson?

  Did he die on the front?

• 17:59Janna Levin?

  He died from an infection contracted on the front, within six months of the letter, actually.

• 18:04Neil deGrasse Tyson?

  Oh, okay.

• 18:05Janna Levin?

  And he wrote to Einstein this beautiful solution, which we now call the black hole. They did not call it that. It took a half-century for it to get its name. But Einstein knew the math was right, was incredible.

• 18:19Neil deGrasse Tyson?

  Best name for anything ever, by the way.

• 18:20Janna Levin?

  You think? It's kind of contentious.

• 18:23Neil deGrasse Tyson?

  No. You fall and you're not coming out, it's a hole. Is light coming out? No, it's black.

• 18:30Janna Levin?

  That's the black hole calling, yeah. So let's take the example of the black hole. Exactly. Before, it was on a lunchbox. So Einstein knew the math was right. He was extremely impressed that the solution could be found so simply in the way that Schwarzschild had done this. But he thought nature would protect us from their formation. He did not believe they would be in the universe.

• 18:57Neil deGrasse Tyson?

  Even though his own theory and his own equations gave that result.

• 19:01Janna Levin?

  Right. Because the equations omitted the fact that, you know, matter doesn't like to be crushed. I really want to know what's in that thermos.

• 19:12Neil deGrasse Tyson?

  You do?

• 19:12Janna Levin?

  Yeah. And how old it is, how long it's been in there.

• 19:16Neil deGrasse Tyson?

  What, well, what's typically in the center of galaxies?

• 19:19Janna Levin?

  A black hole.

• 19:20Neil deGrasse Tyson?

  A black hole. Well, in the center of this black hole

• 19:27Neil deGrasse Tyson?

  is a Milky Way galaxy.

• 19:30Janna Levin?

  Did someone give this to you, or is this of your own design?

• 19:34Neil deGrasse Tyson?

  Someone gifted me the lunchbox.

• 19:38Janna Levin?

  That's pretty good.

• 19:39Neil deGrasse Tyson?

  From the Disney movie, which was awful.

• 19:41Janna Levin?

  Okay.

• 19:42Neil deGrasse Tyson?

  It was one of the worst movies, my 10 worst movies ever. I'm told they're remaking it, but we'll see.

• 19:46Janna Levin?

  Do you do a 10 worst movies list?

• 19:49Neil deGrasse Tyson?

  Of course. This is StarTalk. Of course we got that. I didn't mean to distract you with my lunchbox and thermos.

• 19:56Janna Levin?

  I hope the same person will send me one. I bet that was a while ago.

• 20:01Neil deGrasse Tyson?

  This is, it predates you, yes.

• 20:03Janna Levin?

  It predates me. Oh my God, is that like a character?

• 20:08Neil deGrasse Tyson?

  It's a black hole.

• 20:09Janna Levin?

  It's a character named Black Hole.

• 20:10Neil deGrasse Tyson?

  No, it's a black hole.

• 20:15Janna Levin?

  You're not putting me on.

• 20:19Janna Levin?

  I have my limits for promo.

• 20:21Neil deGrasse Tyson?

  If anyone knew how to get out, it would be you.

• 20:23Janna Levin?

  I have my promo limit. Right, exactly. I'll be consulting the survival guide.

• 20:30Neil deGrasse Tyson?

  That's the title of one of your books, isn't it?

• 20:32Janna Levin?

  Yeah.

• 20:33Neil deGrasse Tyson?

  Tell me that title again.

• 20:34Janna Levin?

  You do it better than anyone. Black Hole Survival Guide.

• 20:38Neil deGrasse Tyson?

  Oh, there's the Black Hole Blues.

• 20:40Janna Levin?

  Oh, Black Hole Blues, yes.

• 20:41Neil deGrasse Tyson?

  And then you have the Black Hole Survival Guide. And I show you this, I'm ready to put you in it, and you get tense and nervous.

• 20:48Janna Levin?

  I do.

• 20:49Neil deGrasse Tyson?

  This is bad PR for your book.

• 20:53Janna Levin?

  Yeah, I mean, the book doesn't end well. I mean, you know, you can bide your time, is all I'm saying. I think what's interesting is not something nobody imagined. I think that's exactly what's interesting about this premise, is that it's all imagined. You can conceive of it. And then, over and over again, nature finds a way to do it. So with the case of black holes, Einstein could not foresee a way in which mass could overcome its repulsion, the forces, the internal forces, the nuclear forces.

• 21:34Neil deGrasse Tyson?

  That idiot.

• 21:35Janna Levin?

  And nature thought of a way to do it.

• 21:36Neil deGrasse Tyson?

  That idiot.

• 21:38Janna Levin?

  Yeah, that guy. You know, nature thought of a way by killing off-

• 21:42Neil deGrasse Tyson?

  So nature was smarter than Einstein.

• 21:44Janna Levin?

  Yeah, I mean, nature's smarter than all of us. That's why we're an homage to nature.

• 21:51Neil deGrasse Tyson?

  Our very existence is an homage to nature.

• 21:54Janna Levin?

  What an experiment. What a bunch of ideas in play. What's amazing about scientific discovery is precisely how astoundingly clever nature is. And we're just catching up, right? We're trying to formalize it, describe it, understand it, but nature's the real genius.

• 22:16Neil deGrasse Tyson?

  That's a soundbite right there. Yeah, who ordered dark energy?

• 22:22Janna Levin?

  Yeah, Einstein.

• 22:23Neil deGrasse Tyson?

  What's up with that? It's in his equation.

• 22:25Janna Levin?

  Yeah.

• 22:26Neil deGrasse Tyson?

  But he didn't even like it.

• 22:27Janna Levin?

  He didn't like it.

• 22:28Neil deGrasse Tyson?

  My boy did not like his own damn equation.

• 22:30Janna Levin?

  He could not make a mistake.

• 22:32Neil deGrasse Tyson?

  That idiot.

• 22:33Janna Levin?

  That guy. That guy could not make a mistake, as hard as he tried to be a buffoon. You know the story where somebody was saying to him, Einstein, you have to be more careful. Your name is on these papers, your important name. And he's like, my name is on plenty of wrong papers. It was not a concern to him. He would sometimes contradict himself. There's allegedly a story where he wrote some paper about the existence of gravitational waves, the non-existence. And then, when it was accepted for publication, it was in page proofs, it was just supposed to be copy editing, he submitted an entirely different manuscript that 100% contradicted the original paper.

• 23:11Neil deGrasse Tyson?

  So that way, you're right.

• 23:12Janna Levin?

  Yeah, you could always point to one of the-

• 23:14Neil deGrasse Tyson?

  People will remember if you're right, and they're not gonna remember if you're wrong. That idiot. So if I were to pick one, I would say that the universe is knowable. Earth is knowable. You have tabletop experiments. But why should that apply across the universe?

• 23:37Janna Levin?

  That's why you love Isaac.

• 23:39Neil deGrasse Tyson?

  My man.

• 23:40Janna Levin?

  Because he was kind of the first to map that.

• 23:44Neil deGrasse Tyson?

  My man. His equations of gravity, with the moon going around Earth and Earth going around the sun, they also applied to Jupiter's moons going around Jupiter. And Jupiter's not a star, and the moons are not planets.

• 24:00Janna Levin?

  Yeah.

• 24:00Neil deGrasse Tyson?

  So this was the first hint that laws of physics as established here on Earth may be that way also in the heavens.

• 24:11Janna Levin?

  Well, and also that he thought mass was this deep thing, charge, this kind of gravitational charge that big celestial bodies felt against each other, their mass. It's a crazy idea to map that all the way to the sky.

• 24:31Neil deGrasse Tyson?

  Let's take this exercise to the present, not the past.

• 24:34Janna Levin?

  Yeah.

• 24:36Neil deGrasse Tyson?

  What's going on today that might be true, but is completely out there?

• 24:44Janna Levin?

  Well, you love Isaac Newton.

• 24:46Neil deGrasse Tyson?

  Me and I.

• 24:47Janna Levin?

  You realized, yeah, that this heft that we feel makes it tough to push us around, right?

• 24:56Neil deGrasse Tyson?

  It's a middle-aged man belly, right here. Hard-earned.

• 25:00Janna Levin?

  Hard-earned man.

• 25:01Neil deGrasse Tyson?

  I have six-pack abs. It's just under the fat. Yeah, but they're there.

• 25:06Janna Levin?

  That's another episode. When we show our six-pack abs, when we're like doing an exercise video.

• 25:11Neil deGrasse Tyson?

  We can totally do that.

• 25:12Janna Levin?

  You should do an exercise video.

• 25:13Neil deGrasse Tyson?

  Well, I kind of did. I kind of did.

• 25:15Janna Levin?

  Was it a dance video?

• 25:16Neil deGrasse Tyson?

  No, I was in Terry Crews's exercise facility.

• 25:20Janna Levin?

  Oh, my God, that's hilarious.

• 25:21Neil deGrasse Tyson?

  And we would like-

• 25:22Janna Levin?

  Can I find this?

• 25:23Neil deGrasse Tyson?

  We were pumping iron. And we were just talking about pumping iron.

• 25:26Janna Levin?

  Oh, my God, I see a whole bunch of promo ideas here. Yeah.

• 25:30Neil deGrasse Tyson?

  So what today

• 25:32Janna Levin?

  Yeah.

• 25:33Neil deGrasse Tyson?

  satisfies these criteria of centuries past?

• 25:38Janna Levin?

  So if we look at your big hero, Newton's discovery that gravity could be mathematized.

• 25:47Neil deGrasse Tyson?

  Yes.

• 25:47Janna Levin?

  It could be described as a very simple system of equations.

• 25:51Neil deGrasse Tyson?

  And indeed, it was.

• 25:52Janna Levin?

  And indeed, it was. It predicted Kepler's laws, post-dicted Kepler's laws, and we could understand-

• 25:59Neil deGrasse Tyson?

  Kepler predates Newton.

• 26:00Janna Levin?

  Yes.

• 26:01Neil deGrasse Tyson?

  Yes.

• 26:01Janna Levin?

  Then comes my guy.

• 26:03Neil deGrasse Tyson?

  Who's your guy?

• 26:04Janna Levin?

  Einstein.

• 26:05Neil deGrasse Tyson?

  Okay.

• 26:05Janna Levin?

  Who replaces this simple system of just equations with this really elegant description of a curved spacetime. He kind of supplants gravity. He says, it's not really a force. Really, we live in this beautiful curved spacetime. Relativity is stunning.

• 26:21Neil deGrasse Tyson?

  We have the right to ask. Are these just different interpretations of something that they both described completely accurately? The problem is-

• 26:33Janna Levin?

  I think it's a great question. It's not exactly right. Einstein struggled to make sure he could reproduce what Newton could do at the low velocities and the low energies, where Newtonian gravity was valid and uncontested. And Einstein really struggled to reproduce Newton. And if he couldn't reproduce Newton, he knew he was wrong. So it's not that they're different or incompatible. One is kind of larger than the other. So Einstein's envelops Newtonian gravity, but then it goes beyond. And there are predictions that are strictly relativistic that were not consistent with Newtonian gravity, which proved Einstein was on to something.

• 27:18Janna Levin?

  We had taken more steps, genuinely. The bending of the path of light around an eclipse that Eddington famously saw in 1919, which verified Einstein's theory of general relativity. I like to say it was as though humanity was in the shadow of the war and stepped into the shadow of the moon and then emerged, you know, citizens of the same Earth.

• 27:42Neil deGrasse Tyson?

  Methinks the light would have bent under Newtonian rules. So I don't think it was just that the light bent at all.

• 27:53Janna Levin?

  It's true.

• 27:53Neil deGrasse Tyson?

  It was by how much it bent.

• 27:54Janna Levin?

  It was by how much it bent.

• 27:55Neil deGrasse Tyson?

  It bent by twice the amount that Newton would have predicted.

• 28:01Janna Levin?

  Yes, absolutely.

• 28:02Neil deGrasse Tyson?

  Right, okay.

• 28:02Janna Levin?

  And Einstein had already, by himself, when he first wrote down what was ultimately the theory that began to work for him, in pen and paper had confirmed the procession of the perihelion of Mercury. So as Mercury's slightly, slightly elliptical orbit approaches, closest approach to the sun, instead of forming a closed ellipse on its way out and coming back in to the exact same point, it actually overshoots a little. And so it makes one of those beautiful figures. You know, so you were a kid with one of those pen figures. This tiny procession-

• 28:34Neil deGrasse Tyson?

  Spirograph machine.

• 28:35Janna Levin?

  Spirographs, yeah. Was considered, maybe there's another big Jupiter out there somewhere, but nobody thought you had to rewrite Newton's laws.

• 28:43Neil deGrasse Tyson?

  Astronomers already had that figured out.

• 28:46Janna Levin?

  Yeah, there was another body.

• 28:47Neil deGrasse Tyson?

  There was another body that we hadn't seen yet, and we called it Vulcan.

• 28:51Janna Levin?

  Oh, Vulcan. I couldn't remember what it was called.

• 28:53Neil deGrasse Tyson?

  We were out of our Vulcan minds. No, it was quite natural to assume there's something perturbing it, and it's near the sun. Maybe it's a planet so close to the sun-

• 29:04Janna Levin?

  It's a lot more reasonable.

• 29:05Neil deGrasse Tyson?

  It's lost in the glare.

• 29:06Janna Levin?

  Right.

• 29:06Neil deGrasse Tyson?

  It's more reasonable that we need a completely freaking new law of gravitational physics-

• 29:11Janna Levin?

  Spacetime is geometry.

• 29:12Neil deGrasse Tyson?

  That transcends Newton.

• 29:14Janna Levin?

  Totally.

• 29:14Neil deGrasse Tyson?

  Who's gonna say that?

• 29:16Janna Levin?

  Einstein.

• 29:16Neil deGrasse Tyson?

  Except your boy.

• 29:17Janna Levin?

  So the crazy, he said he had heart palpitations. He was so excited to be able to match. So he was very much devout in terms of his adherence to Newtonian gravity. He just wanted to take a step beyond.

• 29:31Neil deGrasse Tyson?

  Didn't he apologize to Newton at some point?

• 29:34Janna Levin?

  I don't know. I mean, I-

• 29:35Neil deGrasse Tyson?

  I heard rumor.

• 29:36Janna Levin?

  They certainly weren't contemporaries, so.

• 29:39Neil deGrasse Tyson?

  I think he did it in his autobiography.

• 29:42Janna Levin?

  What was he apologizing for?

• 29:44Neil deGrasse Tyson?

  The towering intellect of Newton?

• 29:49Neil deGrasse Tyson?

  Deducing the nature of the universe? You're gonna find a crack in the armor? That was the universal law of gravitation? You gotta apologize for that.

• 30:00Janna Levin?

  Did he ever disrespect Newton?

• 30:03Neil deGrasse Tyson?

  No, I don't think so.

• 30:03Janna Levin?

  Yeah, I don't think so either.

• 30:06Janna Levin?

  I think he was being gracious. So, what's interesting about where we are now, a hundred years more after Einstein, we might be superseding both of them. We might be in a moment where, yes, Newton's laws have to be reproduced by any theory beyond Newton, like relativity. Now, relativity has to be reproduced by any theory beyond Einstein's.

• 30:32Neil deGrasse Tyson?

  Only because they've been experimentally verified.

• 30:34Janna Levin?

  They've been experimentally verified, stunning.

• 30:36Neil deGrasse Tyson?

  So, there's a misconception that physics just goes here and then there, and whatever is true.

• 30:41Janna Levin?

  You throw away the old thing.

• 30:43Neil deGrasse Tyson?

  No, you don't throw away the old. The old still works.

• 30:44Janna Levin?

  Right.

• 30:45Neil deGrasse Tyson?

  Because it was experimentally verified.

• 30:47Janna Levin?

  You don't throw away a bicycle, a pedal bike, because you invented the electric bike.

• 30:52Janna Levin?

  So, we're on the cusp now where, it's not that Newton was wrong and Einstein was wrong or that kind of, exactly what you're saying, but...

• 30:59Neil deGrasse Tyson?

  They were incomplete.

• 31:00Janna Levin?

  They're incomplete to the extent that we know there must be a quantum theory of gravity. There must be, there has to be, because the universe collides at the smallest scales, highest energies with curved spacetimes. There's a paradigm there we can't get our hands on. People have been wrestling with since Einstein.

• 31:19Neil deGrasse Tyson?

  It's a shotgun marriage.

• 31:21Janna Levin?

  Yeah, and Einstein wanted to throw away quantum mechanics. And yet, quantum mechanics seems to be the one that might be enduring.

• 31:31Neil deGrasse Tyson?

  Did he really say God doesn't play dice with the universe?

• 31:35Janna Levin?

  I mean, I don't know if that's an apocryphal story or not. I believe he indeed said that, but I don't think he meant it in the religious sense.

• 31:44Neil deGrasse Tyson?

  How does he know? Why does he believe he knows how God would make the universe?

• 31:50Janna Levin?

  You were describing how the most miraculous thing about the universe is that it's comprehensible.

• 31:54Neil deGrasse Tyson?

  Yes.

• 31:55Janna Levin?

  I think that's what he means. Why would the universe become incomprehensible? This universe who had promised to be knowable through mathematics. As much of our marvel as it was, as great a mystery as it was, that it was comprehensible. Why would it suddenly fail us?

• 32:13Neil deGrasse Tyson?

  Okay, so, I once wrote on this subject.

• 32:16Janna Levin?

  Yeah.

• 32:16Neil deGrasse Tyson?

  And I came up with a sentence I really like, and I'm gonna say it again.

• 32:18Janna Levin?

  Okay.

• 32:19Neil deGrasse Tyson?

  Okay? That with quantum physics, the uncertainties are precise. We are certain about the uncertainties.

• 32:32Janna Levin?

  Yeah.

• 32:32Neil deGrasse Tyson?

  It's not just willy-nilly, who knows what's coming next?

• 32:35Janna Levin?

  No, we formalize it.

• 32:37Neil deGrasse Tyson?

  We have precise knowledge

• 32:41Janna Levin?

  Yeah.

• 32:42Neil deGrasse Tyson?

  of those uncertainties.

• 32:43Janna Levin?

  It defines the entire mathematics. Non-commutative variables, all of these Grossman numbers, all of these things are designed to encode and formalize and make precise uncertainty.

• 32:58Neil deGrasse Tyson?

  So, maybe the idea that some parts of nature can only be described statistically, but we know precisely those statistics. So, he wasn't happy with that?

• 33:09Janna Levin?

  No, he wasn't happy because it really was weird, is weird.

• 33:13Neil deGrasse Tyson?

  It's stuck in his craw.

• 33:14Janna Levin?

  It remains weird.

• 33:16Neil deGrasse Tyson?

  Are we one day gonna find out that quantum mechanics, oh, it's just simply this thing, and now everything is understandable in a classical brain way?

• 33:26Janna Levin?

  I think that there have been really brilliant attempts to say, hey, if we hide a bunch of extra variables, then this becomes completely deterministic in the normal way, just really complicated.

• 33:37Neil deGrasse Tyson?

  So, hidden variables?

• 33:38Janna Levin?

  Hidden variables, yeah.

• 33:39Neil deGrasse Tyson?

  They're operating in a deterministic way. We just can't see them.

• 33:43Janna Levin?

  We just can't see them.

• 33:43Neil deGrasse Tyson?

  So, therefore, they're beyond our ability to calculate.

• 33:45Janna Levin?

  Right, but you can actually prove that those do not explain the results of observations. The bizarre thing about quantum mechanics, as poorly as we understand it philosophically, we're great at it computationally.

• 33:59Neil deGrasse Tyson?

  Shut up and calculate.

• 34:00Janna Levin?

  Shut up and calculate.

• 34:01Neil deGrasse Tyson?

  I'm in that camp.

• 34:02Janna Levin?

  And to 14 decimal points.

• 34:04Neil deGrasse Tyson?

  Shut up and calculate.

• 34:05Janna Levin?

  That's gonna be confirmed at an accelerator experiment.

• 34:08Neil deGrasse Tyson?

  Right.

• 34:08Janna Levin?

  Like, that is stunning.

• 34:10Neil deGrasse Tyson?

  As far as we good there.

• 34:11Janna Levin?

  Yeah.

• 34:12Neil deGrasse Tyson?

  If you wanna worry about what it means, go to the bar.

• 34:15Janna Levin?

  Yeah, right. Bar talk.

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• 39:49Neil deGrasse Tyson?

  What's up with wormholes?

• 39:50Janna Levin?

  Yeah.

• 39:50Neil deGrasse Tyson?

  I think we can make it on paper, right?

• 39:52Janna Levin?

  Yeah, we can make wormholes on paper.

• 39:54Neil deGrasse Tyson?

  On paper?

• 39:54Janna Levin?

  Yeah.

• 39:55Neil deGrasse Tyson?

  So, so...

• 39:56Janna Levin?

  We can't do them in the lab yet.

• 39:58Neil deGrasse Tyson?

  Why not?

• 39:58Janna Levin?

  Because we don't know of energy sources that behave like that. We know of energy sources that kind of do.

• 40:04Neil deGrasse Tyson?

  Could they behave that way in another universe?

• 40:06Janna Levin?

  Yeah, and they could behave that way in this universe if we just figured out how to make it. So, for instance, sometimes it requires something called a negative energy density, which sounds terribly unstable and like a violation of all that is holy and good. But it's not impossible. We know of strange ways...

• 40:22Neil deGrasse Tyson?

  All that is sacred.

• 40:23Janna Levin?

  Yes, all that is sacred. We know of strange ways to temporarily trap energies that look effectively like they have somewhat a negative capacity. So, none of it's impossible. We just don't, in the lab, know how to go mine something and put it together and make it make a wormhole.

• 40:40Neil deGrasse Tyson?

  Laws of physics do not prevent it.

• 40:42Janna Levin?

  They do not prevent it. There are conjectures, right? There are conjectures, energy conjectures, that no such energy can exist, but they're conjectures.

• 40:53Neil deGrasse Tyson?

  Remind me what a conjecture is.

• 40:55Janna Levin?

  So, a conjecture is a supposition that we haven't discovered the law yet, but that when we do, it will adhere to this principle.

• 41:04Neil deGrasse Tyson?

  So, people are pulling it out of their ass?

• 41:06Janna Levin?

  Right, pulling it... So, like, a conjecture might be that negative energies are forbidden. A chronology protection conjecture is a very interesting one.

• 41:16Neil deGrasse Tyson?

  Oh, that was Stephen Hawking.

• 41:17Janna Levin?

  Yes.

• 41:18Neil deGrasse Tyson?

  Tell me that one.

• 41:19Janna Levin?

  So, he realized that, in the context of relativity, time travel was not forbidden, that if you're just doing... You're not doing quantum mechanics, you're not doing nuclear physics, you're just doing relativity on paper.

• 41:29Neil deGrasse Tyson?

  Planal relativity.

• 41:30Janna Levin?

  You absolutely can find solutions that involve time travel, traveling backwards in time. They exist.

• 41:38Neil deGrasse Tyson?

  That doesn't mean the actual universe will do it.

• 41:40Janna Levin?

  That's the conjecture. So, Hawking stated what he called the chronology protection conjecture, the idea that, once I add quantum mechanics, or once I understand quantum gravity, it will protect us from chronology violating paths. We cannot go back to before we were born.

• 42:01Neil deGrasse Tyson?

  This sounds a lot like Einstein saying, "I have a conjecture that you can't have a black hole."

• 42:05Janna Levin?

  Right, that's right.

• 42:06Neil deGrasse Tyson?

  "Nature will find some way to prevent it."

• 42:08Janna Levin?

  A conjecture is not a law.

• 42:09Neil deGrasse Tyson?

  Okay.

• 42:10Janna Levin?

  Or a proof.

• 42:11Neil deGrasse Tyson?

  Okay.

• 42:12Janna Levin?

  And many conjectures lie at the side of the road as we have...

• 42:17Neil deGrasse Tyson?

  Litterbug.

• 42:18Janna Levin?

  Right, made unbelievable discoveries that have left them behind. We don't know that you cannot time travel.

• 42:25Neil deGrasse Tyson?

  And it's all done?

• 42:27Janna Levin?

  Yes, it's all filmed. It's so exciting.

• 42:29Neil deGrasse Tyson?

  Cool.

• 42:30Janna Levin?

  I want to get back in, do it again. Well, maybe I can.

• 42:34Neil deGrasse Tyson?

  We'll see if anybody watches it, that would be enough reason to do it again. But if no one watches it, we're done here.

• 42:42Janna Levin?

  If the tree falls in the forest. You know, Moby Dick was a bomb.

• 42:47Neil deGrasse Tyson?

  Was that true?

• 42:48Janna Levin?

  Oh, my God, it bombed.

• 42:50Neil deGrasse Tyson?

  Really?

• 42:51Janna Levin?

  It had the most vicious reviews.

• 42:52Neil deGrasse Tyson?

  Wow.

• 42:53Janna Levin?

  Melville died thinking his great work...

• 42:57Neil deGrasse Tyson?

  Call me Israel.

• 42:59Janna Levin?

  Ah, it's so terrible.

• 43:01Neil deGrasse Tyson?

  Oh, okay.

• 43:02Janna Levin?

  "With hate's heart I stab at thee." That is a book, too.

• 43:07Neil deGrasse Tyson?

  Okay.

• 43:08Janna Levin?

  Oh, we discuss whether the universe genuinely has three spatial dimensions in one time, or if there are more spatial dimensions. I particularly love this topic. That's my research topic.

• 43:20Neil deGrasse Tyson?

  Love me some dimensions, too.

• 43:21Janna Levin?

  Love me some dimensions.

• 43:22Neil deGrasse Tyson?

  Dimensions, good. And you also talk about black holes?

• 43:24Janna Levin?

  Black holes.

• 43:25Neil deGrasse Tyson?

  You have to. You've written two books on it.

• 43:27Janna Levin?

  Yes, I spent a lot of my life in that whole arena.

• 43:30Neil deGrasse Tyson?

  I have to say your titles again. The Black Hole Blues.

• 43:32Janna Levin?

  That's the best.

• 43:34Neil deGrasse Tyson?

  And The Black Hole Survival Guide. You have to go there, have to touch that.

• 43:38Janna Levin?

  Yes. I suggest everyone carry it around, just in case.

• 43:42Neil deGrasse Tyson?

  Because you never know.

• 43:43Janna Levin?

  You never know.

• 43:44Neil deGrasse Tyson?

  You never know. Topology is a thing.

• 43:47Janna Levin?

  Well, we talk about space not being taken for granted, not this infinite stage, just with events of the universe, stars exploding and things happening, playing out against this infinite stage. The stage itself can be quite organic, evolves, and quite complex. I call it origami. The space can be wrapped up...

• 44:08Neil deGrasse Tyson?

  I love origami.

• 44:09Janna Levin?

  ...a crazy little origami, and small parts and larger parts.

• 44:13Neil deGrasse Tyson?

  I was an origami maniac as a kid.

• 44:15Janna Levin?

  Were you?

• 44:16Neil deGrasse Tyson?

  Oh, yeah.

• 44:17Janna Levin?

  Yeah, yeah. You still got some skills?

• 44:19Neil deGrasse Tyson?

  I can do, like, five things.

• 44:21Janna Levin?

  Yeah. Well, the universe has countable ways it can be folded up. So, if the universe is really three-dimensional, we know all of the possible ways it can be wrapped up into a kind of origami. And there are...

• 44:36Neil deGrasse Tyson?

  But as you go to higher dimensions, all bets are off.

• 44:38Janna Levin?

  Way more complicated, all bets are off. But even with just three dimensions, if we imagine the universe is born and it is not infinite, or it is infinite, and we ask, is nature trying every possibility? As it happens mathematically, factually, there are an infinite number of ways for the universe to be finite. But there are very few number of ways for the universe to be infinite. So, where are we? Where do we live?

• 45:07Neil deGrasse Tyson?

  Can I even repeat that? Okay, there's an infinite number of ways a finite universe can be configured topologically.

• 45:20Janna Levin?

  Yeah, glued up into origami, all the unique ways it can be folded together.

• 45:24Neil deGrasse Tyson?

  But there's only a finite number of ways...

• 45:26Janna Levin?

  Very few.

• 45:27Neil deGrasse Tyson?

  ...an infinite universe can be configured.

• 45:29Janna Levin?

  Exactly. So, if we really imagine nature's trying everything, trying over and over again, there's one way for all the dimensions to be infinite. There's a couple of ways for some of the dimensions to be finite and the rest infinite. The infinity of other possibilities are all finite and glued together in some complex origami.

• 45:52Neil deGrasse Tyson?

  This is right around where Chuck Nice would say, "I need some weed."

• 45:57Janna Levin?

  I feel like Chuck would stand up and walk out right now.

• 46:00Neil deGrasse Tyson?

  Right about now.

• 46:01Janna Levin?

  Right now.

• 46:02Neil deGrasse Tyson?

  Chuck exits stage left. One last question. What's your opinion of ambulance-chasing theorists?

• 46:10Janna Levin?

  Oh, that's so interesting. By ambulance-chasing theorists, you mean there's a tiny observation that people aren't even sure about, and then there's 15 papers by theorists trying to fit this one tiny little... Not my favorite, not my favorite.

• 46:23Neil deGrasse Tyson?

  And then we later find out that there was something wrong with the observation, yet we have 15 theories to explain the wrong observation.

• 46:30Janna Levin?

  Yeah, that's ambulance-chasing.

• 46:31Neil deGrasse Tyson?

  That's ambulance-chasing.

• 46:32Janna Levin?

  Yeah, but the great theorists are out there, and I think that's what we're paying respect to in this series, which is we're honoring the deeper ideas. We don't know if they're right, we don't, and we don't know if they're observable or verifiable. But we are very much curious if this is an experiment, this whole thing, this whole universe lark, and if it's being tried over and over again, and every idea that we have that's internally consistent, that's consistent with the laws of physics, if that might be realized somehow, somewhere, sometime.

• 47:08Neil deGrasse Tyson?

  What does it mean if I come up with a theory, and it explains a whole bunch of stuff, and then I make another prediction out of that same theory, and it's nowhere to be found in the universe? Should I keep looking for it, or is the theory overstepping?

• 47:22Janna Levin?

  Hmm, it's a really interesting question. You could say we're there now, because the dominant components of the universe that are driving the evolution of the universe are not things we've discovered. We've not found dark matter or dark energy. There are ideas of where it might be, the experiments aren't finding them there. Does that mean we abandon the attempt to look for a neutrino-like particle that might be the dark matter? Or do we keep pressing? I think this is a quandary every experimental physicist runs against if the first experiments aren't successful. And if the first 20 years aren't successful, then what do we do?

• 48:05Neil deGrasse Tyson?

  So, in the end, your series is a love letter to theorists.

• 48:10Janna Levin?

  That's beautiful. I love that. Yes, it is a love letter to theorists.

• 48:18Neil deGrasse Tyson?

  So, well, good luck with this series.

• 48:20Janna Levin?

  Thank you, man.

• 48:21Neil deGrasse Tyson?

  Yeah.

• 48:22Janna Levin?

  Thanks so much.

• 48:23Neil deGrasse Tyson?

  I haven't seen any of them. We had other producers do this.

• 48:25Janna Levin?

  I know.

• 48:26Neil deGrasse Tyson?

  But I wasn't even looking.

• 48:27Janna Levin?

  I know, but I was texting you. I was, I was texting you, asking your advice.

• 48:31Neil deGrasse Tyson?

  So, we look forward to this, and it was so deserving of your own thing.

• 48:36Janna Levin?

  Thanks so much, man. It's really been fun.

• 48:38Neil deGrasse Tyson?

  Online there, and you're one of our favorite guests, so...

• 48:42Janna Levin?

  Appreciate it.

• 48:43Neil deGrasse Tyson?

  We have no reason to think that won't...

• 48:44Janna Levin?

  It's my favorite show.

• 48:45Neil deGrasse Tyson?

  ...continue into the fanbase.

• 48:48Janna Levin?

  Yes, love it.

• 48:49Neil deGrasse Tyson?

  The Janna fanbase. All right. This has been another installment of StarTalk. This edition, in theory, with the one and only Janna Levin. Until next time, keep looking up.

• 49:23Speaker 05

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• 49:52Speaker 06

  Welcome to Science of Perception Box.

• 49:54Speaker 07

  Perception Box. Perception Box. One's own perception of consciousness.

• 49:58Speaker 06

  The Perception Box. Hi, I'm Elizabeth Koch. What's a Perception Box? You could think of it as a kind of reality filter that's constantly shaping how we see ourselves, other people, and the world around us. Yet we often don't even recognize it's there.

• 50:12Speaker 07

  Your face is a mask, and you're behind this mask.

• 50:15Janna Levin?

  Science of Perception Box. Listen and subscribe wherever you get your podcasts.