#468 – Janna Levin: Black Holes, Wormholes, Aliens, Paradoxes & Extra Dimensions

Janna Levin: I do believe that it wasn't a 31 third down the line because America was different. And I think that's something we have to think about right now in this particular climate. So many scientists fled here. They fled to here. Americans weren't fleeing to Nazi Germany. They came here and they were motivated by it's more than a patriotism, I mean, it was a patriotism, obviously, but it was sort of more than that. It was really understanding the threat of Europe, what was going on in Europe, and what that life, how quickly it turned, how quickly this free-spirited Berlin culture, you know, was suddenly in this repressive and terrifying regime. So I think that it was a much higher chance that it happened here in America... The world flocked here. And that won't be the case if we no longer have intellectual freedom.

Janna Levin: That weightlessness is the purest experience of gravity. And so this idea of falling is actually fundamental. It's how we talk about it all the time. The earth is in a free fall around the sun. It's actually falling. It's not firing engines, right? It's just falling all the time, but it's just cruising so fast. So actually, yeah, oh God, you said so many profound things. So one of them is really one of the ways to experience space-time is to be falling. To be falling. That is the purest experience of gravity. The experience of gravity, unfettered, uninterrupted by atoms, is weightlessness.

Janna Levin: One is to start with the equivalence principle, which he called the happiest thought of his life. And the equivalence principle comes pretty early on in his thinking. And it starts with something like this. Like right now, I think I'm feeling gravity 'cause I'm sitting in this chair and I feel the pressure of the chair and it's stopping me from falling and lie down in a bed and I feel heavy on the bed. And I think of that as gravity. And Einstein has a beautiful ability to remove all of these extraneous factors, including atoms. So let's imagine instead that you're in an elevator and you feel heavy on your feet 'cause the floor of the elevator's resisting your fall. But I want to remove the elevator. What does the elevator have to do with fundamental properties of gravity? So I cut the cable. Now I'm falling, but the elevator is falling at the same rate as me. So now I'm floating in the elevator. And if this happened to me, if I woke up in this state of falling or floating in the elevator, I might not know if I was in empty space, just floating. Or if I was falling around the earth, there would actually, they're equivalent situations. I would not be able to tell the difference. I'm actually, when I get rid of the elevator in this way by cutting the cable, I'm actually experiencing weightlessness. And that weightlessness is the purest experience of gravity. And so this idea of falling is actually fundamental. It's how we talk about it all the time. The earth is in a free fall around the sun. It's actually falling. It's not firing engines, right? It's just falling all the time, but it's just cruising so fast.

Janna Levin: The best scientists I know often ask the simplest questions. They're really, first of all, there's probably some confidence there, but also they're never going to lie to themselves that they understand something that they don't understand. So even this idea that Newton didn't understand the apple falling from the tree, had he lived another couple hundred of years, he would have invented relativity, because he never would have lied to himself that he understood it. He would have kept asking this very simple question. And I think that there is this childlike beauty to that. I know a bunch of brilliant biologists, physicists, chemists that are thinking about the origin of life. They're like, this doesn't. I know how evolution works. I know how the biological systems work, how genetic information propagates, but this part, the singularity at the beginning doesn't make sense. We don't understand, we can't create in a lab, they're bothered, every single day they're bothered by it. And that being bothered by that tension, by that gap in knowledge is, yeah, that's the catalyst. That's the fuel for the discovery. The discovery is going to come because somebody couldn't sleep at night and couldn't rest.

Janna Levin: There's something flawless about black holes that makes them fundamental, unlike anything else. So they're flawless in the sense that you can completely understand a black hole by looking at just its charge, electric charge, its mass, and its spin. And every black hole with that charge, mass, and spin is identical to every other black hole. You can't be like, oh, that one's mine, I recognize it. Has this little feature, and that's how I know it's mine. They're featureless. You try to put Mount Everest on a black hole, and it will shake it off. These gravitational waves. It will radiate away this imperfection until it settles down to be a perfect black hole again. So there's something about them that is unlike, and another reason why I don't like to call them objects in a traditional sense, unlike anything else in the universe that's macroscopic. It's kind of a little bit more like a fundamental particle. So an electron is described by a certain short list of properties, charge, mass, spin, maybe some other quantum numbers. That's what it means to be an electron. There's no electron that's a little bit different. You can't recognize your electron. They're all identical in that sense. And so in some very abstract way, black holes share something in common with microscopic fundamental particles.

Janna Levin: One of the properties of the vacuum that is intriguing is this idea that you can never say the vacuum's actually completely empty. We talked about Heisenberg, but you know, the Heisenberg uncertainty principle really kicked off a lot of quantum mechanical thinking. It says that you can never exactly know a particle's position simultaneously with its motion, with its momentum. You can know one or the other pretty precisely, but not both precisely. And the uncertainty isn't a lack of ability that we'll technologically overcome. It's foundational. So it's that there's, in some sense, when it's in a precise location, it is fundamentally no longer in a precise motion. And that uncertainty principle means I can't precisely say a particle is exactly here, but it also means I can't say it's not. And so it led to this idea that what do I mean by a vacuum? Because I can't 100% precisely know. In fact, it's not really meaningful to say that there's zero particles here. And so what you can say, however, is you can say, well, maybe particles kind of froth around in this seething quantum sea of the vacuum. Maybe two particles come into existence and they're entangled in such a way that they cancel out each other's properties. So they have the properties of the vacuum. They don't destroy the kind of properties of vacuum because they cancel out each other's spin maybe, each other's charge maybe, things like that. But they kind of froth around. They come, they go, they come, they go. And that's what we really think is the best that empty space can do in a quantum mechanical universe. Now, if you add an event horizon, which as we said, is really fundamentally what a black hole is, that's the most important feature of a black hole. The event horizon, if the particles are created slightly on either side of that event horizon, now you have a real problem. Now, the pair has been separated by this event horizon. Now they can both fall in, that's okay. But if one falls in and the other doesn't, it's stuck. It can't go back into the vacuum because now it has a charge or it has a spin or it has something. It's no longer the property of that vacuum it came from. It needs its pair to disappear. Now it's stuck, it exists. It's like you've made it real. So in a sense, the black hole steals one of these virtual particles and forces the other to live. And if it'll escape, radiate out to infinity and look like to an observer far away that the black hole has actually radiated a particle. And the particle did not emanate from inside. It came from the vacuum. It stole it from empty space, from the nothingness that is the black hole.

Janna Levin: There's something flawless about black holes that makes them fundamental, unlike anything else. So they're flawless in the sense that you can completely understand a black hole by looking at just its charge, electric charge, its mass, and its spin. And every black hole with that charge, mass, and spin is identical to every other black hole. You can't be like, oh, that one's mine, I recognize it. Has this little feature, and that's how I know it's mine. They're featureless. You try to put Mount Everest on a black hole, and it will shake it off. These gravitational waves. It will radiate away this imperfection until it settles down to be a perfect black hole again. So there's something about them that is unlike, and another reason why I don't like to call them objects in a traditional sense, unlike anything else in the universe that's macroscopic. It's kind of a little bit more like a fundamental particle. So an electron is described by a certain short list of properties, charge, mass, spin, maybe some other quantum numbers. That's what it means to be an electron. There's no electron that's a little bit different. You can't recognize your electron. They're all identical in that sense.

Janna Levin: One of the properties of the vacuum that is intriguing is this idea that you can never say the vacuum's actually completely empty. We talked about Heisenberg, but you know, the Heisenberg uncertainty principle really kicked off a lot of quantum mechanical thinking... maybe particles kind of froth around in this seething quantum sea of the vacuum. Maybe two particles come into existence and they're entangled in such a way that they cancel out each other's properties. So they have the properties of the vacuum. They don't destroy the kind of properties of vacuum because they cancel out each other's spin maybe, each other's charge maybe, things like that. But they kind of froth around. They come, they go, they come, they go. And that's what we really think is the best that empty space can do in a quantum mechanical universe. Now, if you add an event horizon... if the particles are created slightly on either side of that event horizon, now you have a real problem. Now, the pair has been separated by this event horizon. Now they can both fall in, that's okay. But if one falls in and the other doesn't, it's stuck. It can't go back into the vacuum because now it has a charge or it has a spin or it has something. It's no longer the property of that vacuum it came from. It needs its pair to disappear. Now it's stuck, it exists. It's like you've made it real. So in a sense, the black hole steals one of these virtual particles and forces the other to live. And if it'll escape, radiate out to infinity and look like to an observer far away that the black hole has actually radiated a particle. And the particle did not emanate from inside. It came from the vacuum. It stole it from empty space, from the nothingness that is the black hole.