Do black holes destroy information?

00:00:08
Speaker 1: Hey, Daniel, I've got a black hole question for you. Are you still hoping to catch and raise a black hole as a pet in your backyard? I can't confirm or deny that, But my question is what happens to the stuff I put into the black hole? Is this a question you already asked the folks at pet Smart. Yeah. You know, like, say, if I drop a banana into a black hole, what what happens to it? Is it gone forever? My advice is don't do it? Which part raise a black hole or throw a banana into it? Because I may have done both already. What's the difference? I mean, if you feed a black hole, it will grow, and a growing black hole will eat more, and eventually it will eat your house and then mine. Okay, so it's not a good idea to use a black hole to make banana's booties. Officially, no, not a good idea. Hi, I'm poor. Hey, I'm a cartoonist and the creator of PhD comics. Hi, I'm Daniel. I'm a particle physicist, and I have never created a black hole to my knowledge. How do you know, Daniel? Maybe you do it in your sleep by accident. Hey, I can't be responsible for all incidental black holes I accidentally create, right, I mean, there's got to be some legal principle there. Do you ever take homes any work by accident, you know, like you guys suddenly bring home some particles or some black holes that were created at the LHC. Yeah, sometimes I go home with a few extra protons in my pocket. Nobody even notices that doesn't sound good. But welcome to our podcast, Daniel and Jorge Explain the Universe, a production of I Heart Radio, in which we tell you all about the mysteries of the university, incredible cosmic questions that still make scientists puzzled, the things that we all wonder about this incredible, beautiful universe that we live in that we all desperately like to understand. Yeah. I take home work all the time, Daniel, because I work from home my cartoonist. So I think you take your home to work then, don't you You know the tomato tomato, it's all the same thing. But that's right. This is our podcast about the universe and all the amazing and mysterious things that are out there for us to discover. That's right, all those weird things floating in the cosmos doing strange, violent, incredible stuff and our attempts as lowly humans to understand them. Is it really possible to unravel the mysteries of the universe and lay them out inside a human mind. We will find out today and tomorrow and the next hundred episodes of our podcast. Yeah, because you know, it sometimes feels like we're building this model of the universe kind of like we're building a whole universe kind of inside of our heads and our physics theories, almost like a hologramma. That's right. It's incredible to imagine that the whole external universe, if it even exists, might be describable inside in mind, right, Like you could represent it somehow in terms of arrangements of neurons, right, and as I think the kind of idea that makes people think, like maybe the entire universe is actually just a projection of some other kind of physical arrangement. Right. Yeah, I've always wondered like maybe our brains just aren't equipped to like understand the universe. Do you ever wonder about that? Oh, I'm almost certain that we are not capable of understanding the universe at its deepest level. So are we doomed to always not know the universe. I think there's never going to be a point where we're satisfied that we think we understand and you know, imagine the kind of super intelligence that would be necessary to like fully grasp with the universe. I think about your dog. Your dog is intelligent, but it certainly doesn't understand all the physics of the universe. And so compared to some super intelligent aliens out there, we are as small as dogs, and there's no way that we could understand the universe at the level that they do. And so you essentially have to be infinitely intelligent to understand the whole university thing. And couldn't infinite intelligence exist in the universe that that would be so that would be a lot. It would create an intelligence black hole inside its mind because you can't store that much information or that much smart in a small space. Man, we've just covered dogs and black holes and like the first three minutes and including brains. But yeah, so we talked about all of the mysterious things, and one of the favorite mysterious things that we like to talk about our black holes because they're so mysterious and it seems like, you know, that there were these black pockets in almost their own universes, and it seems like anything you throw into it can never ever come out. And they're especially wonderful and fascinating because they came out of the human mind initially. It's not something we saw in the universe. It's an idea we had. We said, if the laws of physics are the way we think they are, then these things should exist. So we like mapped something inside our minds out into the universe and then went out and actually found them. I mean it's incredible, right that think that our understanding the universe could be so sophisticated and impressive that we can predict crazy new bonker stuff out there which turns out to be real. I think that's really impressive. Yeah, yeah, good jobs, physicists. Even though we are dogs compared to intelligently nothing against dogs. Of course, dogs very smart. That's why I chose them physics example, and not cats. Right, I think cats are smarter. They're not smarter than dogs. Man, you cannot train a cat. That's proof number one. That's cats are not smarter than dogs. Maybe like cats are mathematicians and dogs are physicists. Would you say that's a fair, fair comparison. Well, if you're saying that dogs are smarter than cats, that I agree with you. Masticians are just sneakier, that's right now. But black holes are a fascinating mystery and one that began inside the human brain, but one that we still don't really understand. I mean, we found them, we see them out there, but it's a continuous source of mystery and puzzlement for people everywhere and for scientists. Yeah, and it's amazing that we've seen it, like we've found one, Like they took pictures of one sort of last year, and it's like it's real, it's there, you can see it, and it looks like what we thought they looked like. That's right. The picture of the black hole shows you all the incredible gas swirling around it that's trying desperately to avoid falling into the black hole and in the process is bouncing around against all the other gas and emitting lots of radiations. So we're not seeing the black hole directly, you know, although we see a black spot there, we're seeing mostly the swirling, chaotic, crazy gas that's surrounding. Yeah. I guess you're right, because I mean, we see the black center, but there's nothing to see there because nothing can come out, or at least that's the idea of a black hole. And so the question then kind of becomes what happens to the stuff that goes into it? Is it gone forever or cannedy recovered? Yeah? Is that stuff just like hanging out inside the black hole having a great time with all the other stuff? Does it get squeezed into some new form of matter? Is it all in a singularity in the middle. It's of the deepest questions in physics what's going on inside a black hole and what happened to the stuff that fell in? So today on the podcast we'll be asking the question those a black hole destroy information? I guess that's an interesting question because you know, it's kind of like asking what happens to stuff that goes in, Like does it get destroyed like obliterated? Does it become pure energy, unadultered, unfiltered energy that you can't make out what it is? Or does it you know, does a cork stay a cork inside of the black hole? And does it still fly around and doesn't even know it's in a black hole? Yeah? I mean, are you wondering about what happened to that banana you dropped into your black hole. I'm still wondering about my banana, Daniel. I want it back. My dog needs today. Do you like eating bananas when they're black, because that's probably what happened to your back. You mean it turned into a movie basically. Basically, But it's a fascinating question, like when something goes into a black hole. Is a black hole like a cosmic hard drive? Does it like just compress everything into some new arrangement but effectively keeping track of all the particles that came in, or is it actually deleting stuff from the universe, turning into some new configuration that doesn't have any information about what happened before it. That's a fascinating question. Yeah, and so we have a lot to impact here about black holes and information. But at first we, as usually, we were wondering how many people out there had heard of this question of whether black holes keep or destroy information? And so, as usual, Daniel went out there and ask people on the internet what they thought of this question. That's right, So thank you to everybody who have volunteered to answer random questions. If you're willing to participate and like to hear your uninformed speculation on the podcast right to us two questions at Daniel and Jorge dot com YouTube can answer these random questions. Think about it for a second, and what do you know about information and black holes and what goes into them? Here's what people had to say. I think the information diss inside a black hole. My understanding of Hawking radiation is that when a particle interacts with the black hole, information is lost. Therefore the black hole behaves like a garbage disposal. Ah, so I do know a little bit about this. So I read a book by Leonard Suskin which was talking about the black hole wars. Stephen Hawkins believe that they did disappear. Information did disappear, and the Suskin said it didn't. And I think it's started to do with holographic principle that basically all the data stays on the event arising. Yes, information disappears from black holes because they lose mass through Hawking radiation. They're more like garbage disposes than hard drives, since you can't retrieve any information that's stored in them. Um my guests would be that once an object is sucked into a black hole. It is obliterated into its most smallest particles that exist, and those things float around and mess around with other particles and probably no longer resemble whatever it is that they used to make up planets, bananas, bunnies or whatever it is. I think they like store information and then eventually, in like trillions and trillions and trillions of years, there's like hawking radiation that radiates, you know, and out in black holes go away. As far as I understand, physics falls apart inside a black hole. I've read that information doesn't disappear as such, and that all the information inside the black hole would be somehow readable on the horizon. Whatever goes in there just gets squished into a really tiny small space. So I'd probably say they're more like a garbage disposal. What goes in doesn't come out, I don't think so. I think it depends at the center of a black hole is which we don't know. If it's an infinite density single point, then it's probably more like a garbage disposal. But if it's not, then I would assume information can enter it and just gets trapped. I'm gonna equivocate on this, and so I shall leave it to my learned colleagues Daniel Watson and Hua Champ perhaps to answer that all so, I don't think that information disappears into the black hole. I think information is recorded on the edge of black hole. Information cannot disappear, like energy cannot disappear. All right, not a good outlook for what happens to stuff that goes into the black hole. Nobody nobody thinks it's hanging out happily inside. Nobody thinks that you're gonna eat that banana. I like that. There's basically every answer here. Information disappears, information doesn't disappear, information is radiated out, and they're basically garbage compactors. That's a wonderful variety of answers here. Thank you to everybody who participated, a wonderful variety of analogies here, Like is a garbage compactor? Is it a garbage disposal? Is it a recycling being? I don't think the universe recycles. I don't think it's like plastic in this black hole. Please, And you know what, if black holes are just the universe's compost, interesting they could be right. They break stuff down and maybe they store it for later for a universe garden, a star garden or story for never that's maybe the problem. Well, until the universe collapses and then everything gets too cycled. Right, that's a very optimistic view of what's going to happen to your banana. Well, this is an interesting topic, and so let's jump right into it. This might take a while because some of the things that we need to talk about include information and quantum mechanics. And so before we sort of get into the idea of what happens to information that goes into a black hole, let's talk about kind of information in general and how that works in a quantum reality. That's right, because one of the mysteries of black holes is what happens to the information that goes into them. And so first we have to understand, like what is information and what does quantum mechanics say about that information? Right? So, information is kind of like the arrangement of things, like the physicist. Information is not like ones and zeros or it's not like, yeah, you know a file or a number. It's more like the arrangement of things, right, Yeah, And it can be represented as ones or zeros or you know, things you print on a piece of paper. But fundamentally, it's the arrangement of the particles. It's really it's the quantum wave function that tells you where the particles are or where they are likely to be, and how they are interacting. Remember that everything, me and you and bananas and all that stuff are made out of particles, and we're all made out of the same particles. So the thing that's different between you and lava and hamsters and bananas is not the stuff you're made out of. That's really the same stuff that everything is made out of. It's how that stuff is put together. It's like if you had a book of recipes and they all had exactly the same ingredients, just had different arrangements like where you put the stuff. That's literally how things in the universe are built. And so what we mean by information from a physics point of view is just that is how the particles are put together to make this versus that, right, And it's also kind of the history of them a little bit, right, Like you can make a banana cake and I can make a banana caig, but they're going to be different bana caggs depending on you know, what the size of the pan I use, or whether I put in a little bit more of this, or a little bit more of that, or how I poured it. They're bothing that tastes like banana aig, but they're gonna be different banana caigs because they were arranged kind of with a different history. And that's right. So our two banana cream pies both have information about what happened to those bananas, how they got there, how they originally were developed and grown and blended up and and turned into the banana cream pies. Because our two banana cream pies are not identical, they contain information about how they got there. Their arrangements are unique because only one way to create that particular banana cream pie. And so you could run the clock backwards and figure out where everything came from in your pie. Yeah, So I think that kind of what you're saying is that it's like, it's kind of like if you're playing billiards or some thing, if you see all the balls kind of arranged in a particular way on the table, you can sort of backtrack how they all got to how billiard balls usually start. That's right, And that's what we mean when we say quantum mechanics does not destroy information. It says that you can tell how you got to where you are. So, just like you said in the billiard balls example, if you see balls moving on the table, you can tell how you got there. You said, well, this must have happened in a certain way. You know, Bob must have hit Alice's ball and it bounced off this wall, etcetera, etcetera. There's only one way to get to this exact particular arrangement. And so because information is not destroyed, it's all the information you need to figure out how you got here is present in this configuration. You could run the clock backwards, you can run a physics simulation backwards and figure out exactly how you got to hear or run it forward. Right like that, I think you're saying that there's no ambiguity in the universe, Like if you you come upon a crime scene, you can tell exactly what happened, like a physicist could. If you sort of rewind the universe and play the laws of physics backwards, you can sort of reconstruct what happens every time precisely. And it's really weird that this comes up in quantum mechanics because you might think, yeah, quantum mechanics is not something that's going to give you certainty that tells you you can know everything about the universe, right, because quantum mechanics is something that feels like it has a lot of built in uncertainty. And so what quantum mechanics tells you is you can always know the wave function. That's the thing that tells you where the particles are likely to be, not that you could actually know where the particles are. In the same way, you can backtrack the wave function. You can say if the particles have a certain way function that says that they're more likely to be on the left side of the table. Now you can backtrack that and tell where they were likely to be in the past, not where they actually were. It's all about the wave function. It's all about this evolving probabilities. The way so looking back into the past is also there's also probabilities or do you know for sure where the party like if like if I see an electron and I measure, you know where it is and where it's going to the best degree that I can can, I tell you where it was before and how fast it was going. No, you can only know the probabilities. You can't collapse the wave function into the past because that would have changed where it is today. But if you know the way function today right, then you can backtrack it into the past and you can propagate it into the future. Any idea is that if you look at any configuration of matter, you should be able to tell where it came from. That's the core idea that you have to understand. I see. So when you talk about information, you don't mean like where things are and where they're going, but you also kind of include these quantum probabilities as information, Like that's also information to physics, Yes, that's the actual quantum information, because they don't know where the particles are. We really just know these probabilities. And so like when we talk about like quantum teleportation copying things, we're talking about copying not the where the particles actually are, but their probabilities, because that's really what the quantum information is. It kind of feels a little unsatisfying on physicists because I feel I feel like you're telling me that information includes not knowing kind of in a way, you know what I mean, Like information includes also non information. Yeah, what's the most information that you can have about the universe is information about the probabilities, and that information cannot be destroyed. Like we don't know where the electron is. It's not like there's a fact there that's not accessible to us. It just isn't determined. But the way function is the thing that tells you that it's more probable to find it on the left side or the right side. That is totally determined. And that's the level of quantum information we can have. That's the most information that the universe allows you to have almost right, Like you know you can know the position and the velocity of a particle to a perfect degree because of the uncertainty principle, because and that's just the rule of the universe. The universe is like, nope, you can't know everything all of the time everywhere. That's right, And that's why quantum information cannot be destroyed, because the probabilities cannot be destroyed. Like if an electron is somewhere in your box now, then it is somewhere in your box in the future. You're like, out of all the probabilities in the future, they still have to add up to one. And that's why if you run the clock backwards, you should still get probabilities adding up to one in the past, and if you run it back even further, you should still get probabilities added up to one because information is not destroyed can't just disappear, because your particles don't just disappear, you don't know where they are. But the probabilities can't disappear. The probabilities can slash around, but they can't just go away. And so that's why we're so fascinated about what happens inside a black hole, because we're wondering, like, does the information inside a black hole? Does it get deleted or is it still stored in there, Like it's a black hole that has a banana versus an apple, have something different inside it that tells you that one has a banana, one has an apple, or the actually deleting stuff. Interesting? Interesting, Yeah, I get. The question is if I throw a banana and one black hole, and I throw the equivalent apple the copy of that black hole, are the two black holes different at the end or are they basically the same? That's kind of the question exactly, And quantum mechanics says they have to be different because if they're not different, then you've destroyed the information about which one got the banana and which one got the apple in a corner. Quantum mechanics, and this is a very deep, very bedrock principle. Information cannot be destroyed. Like you go to a particle theorist and you say, what if I prove the quantum mechanics doesn't preserve information, that you can delete information from the universe, then basically they just throw all their books away and we have to start everything from scratch. It's that deeply ingrained into physics. I guess it's like comparing apple black holes to banana black holes. All Right, I'm starting to feel a bit a little bit like a dog here, uh, and not fully able to grasp all this stuff. But that's kind of the nature of quantum mechanics. So let's get into whether or not black holes can destroy this quantum information, and if they can, then how do we explain it? But first let's take a quick break. All right, we're talking about weather. Black holes can destroy quantum information. And so Danny, you were telling me that quantum information includes like the probability of all the particles in the universe, or at least a bunch of particles that you're looking at, and you're telling me that quantum mechanics says that you can't destroy this information, Like you can't just forget about it, Like it's always kind of encoded in how the particles are arranged or what they're doing. That's right. It's sort of like the central premise of that TV show Devs, where they try to reconstruct details about what happened two thousand years ago by getting really fine data about the molecules in the air and the earth and just backtracking it two thousands of years. The ideas that the evidence for the past is still with us here in the president, that if you had incredible computing power and enough data, you could reconstruct any event. It's like the perfect crime novel. Wow, and so yeah, Like can you look at a banana and tell what the plant the griod looked like? Kind of, that's right, the ideas that no two bananas are identical, but somewhere in that banana there's a clue about where it came from and what it was like and whether it got sun on a certain day, and all that information is somehow encoded in the banana. They're making me feel guilty about eating a banana. You're like you're destroying a perfect, unique gem in the univers just becomes part of who you are. Right, if I took you apart, I could figure out exactly how many bananas you had last week and what happened to them, and the stars that burn the potassium that's in that banana, Like all that history is encoded in that banana and then in you. Well, and also when I flushed down the toilet, technically you would have to go down the toilet. That's a whole different maybe podcast episode. That's a different kind of black hole. We're not going to dive into different um. So let's get into now. Quantum mechanics says that you can destroy quantum information. And so what happens when you throw it into a black hole? Like does it get destroyed or does it stay around inside of the black hole? That's the big question. Yeah, and so on the surface you imagine, well, black holes suck in information. Right, you put something into a black hole, it can never leave, So therefore it's information is stuck inside the black hole. That doesn't mean necessarily that it's destroyed. Right, Like you put a banana inside a black hole, you could still be in there. The particles that made it up could be like squished and whatever, but they just got quantum mechanics aified into a new arrangement. And just like when you ate the banana or when it grew, it's information could still be preserved, but be stuck inside the black hole, you know, like a like a neutron star kind of breaks everything down to the cork level, but all the courts are still kind they're bunched together precisely, and if the information is still in there, it's stuck inside the black hole. Right, nothing can ever leave the black hole. But also you can't get any information from the outside about what's in the black hole. The only things you can know about a black hole are its mass, whether it's spinning, and whether as electric charge. There's this crazy theorem in physics called the no hair theorem that says that's all you can know about a black hole. You mean, like the overall charge of it, Like the black hole can have a charge to it. Yeah, if you have a black hole with no charge, it's neutral, and you throw an electron into it, then it has a charge and you can measure that charge. You can know whether there are charged particles inside a black hole. Oh, I guess you can measure how much it pulls proton through or something like that, just like you can measure it's mass. You throw a banana into a black hole, it got heavier. You should be able to measure its mass by measuring the gravitational field around a black hole. Can also measure whether it's spinning. But that's the extent of the information you can have, right. You can't tell what's inside. You can't tell the detailed history of the banana from the outside, so you can never get that information back out, right. So that's step number one. Is the information, if it still exists, is inside the black hole and can never leave, right. But that's not the same as destroying it. It's just kind of storing it. It's like inside if somewhere I can never that's right. And if black holes live forever, this wouldn't really be an issue. Would be a question of, like, well, what happens inside the black hole? It's fascinating, but we believe that probably information is just in there, sort of cut off from us forever, but still existing. Right, it's still having its own little happy life inside of the black hole. That's right. The banana party, that's where bananas go so that you don't eat them. Right, it's the only safe space in the universe. They don't have to worry about training black because everything is black inside of a black hole. That's right. But then Stephen Hawking came along and he showed us that black holes actually they can disappear, right, Yes, you can make it black hole disappear. It can evaporate. Yeah, black holes they evaporate. They give off very small amounts of radiation, little particles here there. For very big black holes, this happens extremely slowly. But as black holes get smaller, they evaporate more quickly, and then they can actually disappear. They can poof out of existence as they give away their last little bit of energy. Even like giant black holes will eventually disappear, like once all black holes suck everything in the universe, Eventually they will evaporate. Right, that's right. A black hole, if you do not feed, it will give off Hawking radiation and get smaller. Right. It gives off its energy, and that energy comes from its mass, and so therefore it gets smaller, and the smaller it gets, the more radiates. So giant, massive black holes they might have lifetimes of trillions of years. But yes, eventually they will radiate away all of their mass in terms of this hawking radiation and disappear, right, And so then the question is what happened to the information you put into it? That's right, what happened to the information inside the black hole? Like you put this banana inside the black hole. You trust the black hole is going to keep your banana information safe. But then you come back a billion years later and the black holes gone. You're like, what what happened to my You deleted my banana from the universe. You know you can't do that. Quantum mechanics says that's impossible. So the question is what happened to the information? And you might be tempted to think, oh, well, maybe it's somehow stored in that hawking radiation, right, because the hawking radiation came out of the black hole. But hawking radiation is very special. It comes from the temperature of the black hole. It comes from treating a black hole, like everything else in the universe, is a thing that has a non zero temperature which glows. And what's very important to understand is that the hawking radiation depends only on the mass of the black hole. Like how much hawking radiation you get and which particles you get are determined by the mass of the black hole and literally zero else, So none of the information that's inside the black hole can possibly leak out in hawking radiation. Well, I guess it's kind of like if you have a glass of water, if you leave it out, it's gonna evaporate, but you can sort of trace what happened to the water. You can trace the like the vapor of what molly kills as it least the glass of water. Like that's okay, Like that's preserving the information. That's right. But a black hole doesn't evaporate by having the stuff inside of it leak out. It evaporates by almost like having the stuff at the surface destroyed itself. Kind of that's right. And remember the no hair theorem tells us that you can't get any information out of a black hole. That none of the configuration of particles inside a black hole, or the swirling or non swirling, or the singularity or non singularity can affect what's produced on the outside of the black hole. So the Hawking relation cannot have any information about what's going on inside the black hole. It's not like that water vapor example. It's a good contrast because it doesn't tell you anything about what happened inside the black holes. This amazing sort of mysterious way to delete a black hole without knowing anything about what's inside of it, right, because the reason is not because of the theorem. The theorem is sort of because of what's happening in the physics of it, right, And it's yeah, the theorem describes the physics of it right, right, And and what's happening is that, like at the surface of a black hole, you get this pair of particle and antiparticles kind of appearing, and one of them goes into the black hole, the other one goes out of the black hole, and that's kind of how it evaporates. Happening at the surface of it. It's not happening because of anything that's inside of the black hole exactly, and it comes just from the mass the black hole. As you say, virtual particles like positron anti positron pairs are created near the black hole's edge where there's a lot of gravitational energy, and then one of them is given a boost from that gravitational energy while the other one maybe gets sucked in, and because it's given a boost from that gravitational energy, that energy comes from the mass of the black holes. The black hole itself is decreased a tiny little bit in mass, and so it's stealing some of the energy from the black hole without apparently taking any information from it. And so that's the weird thing is that, like you put information in a black hole, you can never get it out, but then the black hole can disappear. So where did the information go? Really, there's no information in that suckings radiation. I mean, like, wouldn't it like where it happens where there's these particles and antiparticles form and where the one of them goes right and the other one goes left. Wouldn't that sort of depend on exactly what's going on inside of the black hole. Well, the where the particles are created is just quantum randomness around the black hole, so that happens totally randomly, not depending on what's inside the black hole. And then they're boosted from the gravitational field, which is the mass of the black hole. So you can know the mass of the black hole, and that's what determines how these particles get boosted and whether they go in the right direction, etcetera. But that doesn't contain all the information. Like if you threw an apple or an equivalently masked banana into a black hole, that would give you black holes of the same mass, so they would affect talking radiation in exactly the same way. So the fact that one used to be an apple and one used to be a banana is now irrelevant, which means quantum information has been deleted all right, which is kind of bad news for quantum physics, because you're telling me that this idea that you can't destroy information is fund mental to quantum mechanics. Maybe I really quickly, can you tell me why it's so fundamental. I mean, remember what we talked about earlier. The reason you can't destroy information in quantum mechanics is because particles should always exist somewhere. I mean, if you have a particle now, as you exist somewhere in the future, it's quantum information cannot be destroyed, like you don't know exactly where it is, but you know what it's probability distribution looks like, and it should have a probability distribution in the future also, and so that can change as the universe moves forward, but the information about should not be deleted anywhere. Right, Well, I guess my question is, you know why not? Like why why? Why would we quantum mechanics breakdown if I just suddenly took some particles and deleted their quantum information? Like why would the universe complain or with the universe care if I had destroyed that information? All? Right? Well, mathematically we look at the equations that describe a wave functions. We have a wave function that tells us where particles are likely to be you, and that moves forward in time. There's an equation that describes how that happens. It's called the shrouding your equation, and the shrouding your equation says you can move information from here to there, but it's unitary, doesn't ever destroy information. And if information is destroyed, that means that wave functions can disappear. And that just doesn't happen in the shorten your equation, and so we would have to totally rethink the way quantum mechanics works if that was to happen. It's like a bedrock assumption that we've built into quantum mechanics. I see, it's like I guess in quantum mechanics and wave functions, you know, these functions don't don't just exist in the present and in the past. They're all sort of tied together mathematically to where they're going to be in the future. That's right, So like if you destroy it in the future, then you're really destroying it through all history. You don't have a term for that in the equation. Yeah, And the equations work the same way forwards and backwards in time, and so if the wave function is ever destroyed, that means that you couldn't go from a non existent wave function backwards in time into the wave function you have now. So this sort of this time and variance built into quantum mechanics. You can run the clock forward, you can run the clock backwards. You should be able to move backwards and forwards at all points. But if the information is ever deleted, that means you can't move backwards and forwards at all points. And the shrunning equation, the basic assumptions on which it's built are totally wrong, and quantum mechanics doesn't work, and we'd have to come up with a new theory. It's not like the universe would puff out of existence. Right, This is all human ideas about how the universe might work. This is a basic assumption we've built into quantum mechanics that we're pretty sure is right. But black holes are telling us that they're doing something that we thought was impossible. Man, there's such troublemakers, all right, So we have a big unknown here. How can both things be true? How could information never be destroyed according to quantum mechanics and how can information be destroyed according to black holes and hawking radiation? So let's get into what could possibly explain this can prediction. But first let's take a quick break, all right, Daniel, can information be destroyed inside of a black hole? So quantum mechanics says no, but kind of a black hole say yes. So what's going on? Is quantum mechanics wrong or do black holes just kind of destroy our conception of how the universe works. This is a big puzzle in physics for a long time, and it's such a big puzzle that like big folks on both sides, like great brains on both sides of the argument, had like public debates about it and even made bets about the resolution of this. Right. Yeah, there's a famous bed by between Hawking and Kip Thorne and John Preskill. Right, that's right. John Prescille believed that somehow the information was sneaking out of the black hole back into the universe, that it was leaking out essentially where Stephen Hawking and Kip Thorn they thought, know, the information can't ever leave the black hole, and therefore it must be lost from the universe, and quantum mechanics is wrong. So they made a very public sort of bet about this. All right, So they made this bed and did they was one of im proven right? Well, they did come to what they think is a resolution to this, and so Hawking and Thorn actually capitulated on the bet in public and said, all right, Prescott, we think you're right. We think that the information somehow leaks out of the black hole. So wait, physicists think that black holes don't destroy information. That's right. So the idea now is probably black holes don't destroy information. I mean, the general categories of solutions are one, maybe quantum mechanics is just wrong and we have to toss it all out and rethink everything about our idea of the universe at the smallest scales, like that's an option and hey, that wouldn't be so bad. It's not like everything unravels and we all go living in caves or something. Just a bunch of physicist careers unraveled. No, those are the best moments for physicist careers because like, wow, that cracks open something deep that we thought was true. Those are the revolutions in physics we live for. That's why we're here to figure out what in the firm and turns out to be wrong, because those are the times when you can get a new glimpse onto a new insight into the universe. I mean, wow, that would be amazing. Right, So that's one possibility maybe quantum mechanics is wrong um, And what are other possibilities black holes are wrong? Another one is that like black holes, you can think of them as storing this information, but that they're also like connected to another universe. We've talked about how maybe black holes are like doors to wormholes that are connected on the other side to other places in the universe. They could also be connected to like separate distinct universes that we don't otherwise have access to. It's a possibility. I mean, we're it's like a what if on top of a wood if. But the idea is that therefore the information could be in that universe, like maybe the banana got sucked into the black hole and then slur belong to the wormhole and it's living off it's banana like days in that other universe. Now, even when our black hole disappears, I see like somehow there's a white hole on the other side that's spewing out bananas. That's right, a banana hole. I think it's what the people in that universe we call it like that. I think they call it the magic banana fountain. They're like whole cult surrounding it about how generous this banana fountain is. You're like a god in that universe. You're like the giver of bananas in that universe. I'm a legend. I'm a legend in another universe. They're like, but please stop throwing bananas in there with a bite taken out already, I mean please. So that's one idea, Yes, that it's information is not disappearing, it's just going somewhere else. Yeah, but that's hard to really understand because then you can't still really do quantum mechanics, like the information is effectively lost to us, and so then we can't do quantum mechanics of our universe, so it's not really Essentially, if it's lost to us, it's a bummer. It's a bummer because you know, is our wave function entangled with their wave function if they're in another universe? Then no, And so really quantum mechanics says, you can't lose any information from your wave functions. So if you lose it to a totally incoherent wave function, it's effectively lost anyway. So quantum mechanics says no to that. Very clever, I think, awesome idea, which would be a great basis for science fiction. Interesting like we're entangled with other universe. Yeah, but we wouldn't actually be entangled, right, That's the problem is that our wave function isn't connected to theirs because it goes through the wormhole. All right, So then what's the third The third possibility is that maybe somehow that information is actually imprinted on the Hawking radiation. So go back, that's what I was saying, wasn't it that you were saying? He shot me down? But now it seems like Stephen Hawking agrees with me. That's right. This is known as the Hawking thorn cham theory of the universe should be. No, you're right, and you know, our understanding before this was that it's impossible for the information to be in the Hawking radiation for the very reasonable arguments that I gave you five minutes ago, which I will now undermine. It made me feel bad, Daniel, No, nor yeah, alright, So here's why your idea was a good one. And you know, whenever you have an apparent contradiction, you have a string of logical arguments that leads you to something nonsensical, you have to go back and read examined, like well what about this one? Is this one? Are we really sure about this? And try to find a hole in it. And so the idea is that maybe somehow the information about the banana you threw in is imprinted on the hawking radiation. Well, how could that happen because once it goes inside the black hole, the only information we can get about it is how much mass it has, which is essentially destroying the banana nous of the information. So the idea is maybe it never really goes inside the black hole, like maybe a banana when you throw it into a black hole, spends eternity sort of on the surface of the black hole. One. And this is actually what what happens when you throw something into a black hole. You never actually see it go in because remember, when near a black hole, there's incredible gravity, and that slows down time. Like you threw a clock into a black hole and you watched it with a telescope, please from very far away, you would see that clock ticks slow down because the presence of mass slows downtime. Right. Yeah, So to the banana, you're seeing, the banana gets frozen at the surface kind of. Yeah. As it gets closer and closer to this event horizon, time slows down more and more, to the point where it slows down essentially infinitely. And you can watch this banana for the whole time, the lifetime of the universe. You will never see it cross the event horizon. Oh uh. It's not like it goes in and then the particles the photons can come out. It's like it never goes in. Kind of from our point of view, From our perspective, you never see anything actually go into a black hole. Now it gets closer and closer, and it gets redder and redder because the light from that banana, which can still get to you. Because the banana is not actually in the black hole, it gets stretched also by the gravity and gets redder and redd or longer and longer wavelengths. So what happens if you have trillions of years to hang out and watch, is that banana falls in more and more slowly, gets darker and darker, and eventually goes out past the visible spectrum. You can't see it, and then you have to use your infrared telescope to watch your very gently glowing banana. Right. But I guess I thought I thought time was became a singularity, only only at the center of the black hole. You're saying that time actually stops at the edge of it. Yeah, at the edge of the black hole, time slows down essentially infinitely, like and that's for you. You're from the outside point of view. You're watching the banana go in. That's not the same thing as the banana experiences. Banana can fall into a black hole, and it can totally experience going past the event horizon, right, because time always goes at one second per second for the person experiencing it. We have a different story about what happens in banana watching from the outside. So for us, the banana never actually goes into the black hole for us. Interesting for us. Wait, so it gets frozen at the surface forever. Yes, but it gets stretched out right, It's not like just happy, you can't go back and pick up your banana. It gets stretched out and reddened and smeared over the surface of the black hole. And essentially it distorts the event horizon. It like changes the shape of the event horizon in some way. And the ideas that maybe the banana changes the shape of the event horizon differently than an apple wood, or differently than another banana in a way that we can see, or in a way that we will never see, in a way that in principle preserves the quantum information of that banana and can influence the hawking radiation produced at that point instead of the event rise and being a perfectly smooth sphere and now has little quantum wiggles in it, and those quantum wiggles tell you about what's been thrown into the black hole, meaning that you could measure the hawking radiation and reconstruct whether you threw a banana or an apple in exactly that the black hole. You threw banana in would give you different hawking radiation than the banana you threw an apple into, and that it's encoded somehow and now in the surface of this black hole, which contains all the information but everything that's been thrown into the black hole. So you're not breaking general relativity because you're not getting information but what's inside the black hole, because in principle, all of this is now encoded on the surface of the black hole. Right, But the courts in the banana dude disappear or you don't see them. You don't see them going into the black hole. Like they're going to survive crazy experiences being near a black hole and get torn apart and smash and other stuff. So who knows what's going to happen, But their quantum information should still be there. Everything that happened to them is describable by quantum mechanics, and just like being eaten or being turned into banana smoothie, their history is still carried with me. And that's okay with quantum mechanics, Like as long as the quantum history information and information is somehow carried on, even if it's like passed between the banana cork it passes on that information to the hawking radiation. That's still okay, that's right. Did you just create a new kind of cork, the banana cork. We've got up cork, charm cork, banana cork. I thought they already existed. No, but you're exactly right. Somehow, the information about that cork that was inside your banana is encoded on the surface of the black hole and influences the hawking radiation that's produced. And therefore, if you like gathered all the hawking radiation that came out of a black hole, you could tell exactly what had gone into the black hole in the whole lifetime of the black hole. And this is weird because this is what they call like the holographic principle, meaning like you know, you can describe, like if the whole universe falls into a black hole, you could at some point technically everything would be described on the surface of the black hole, right, which is like a two D surface. It's like a flat surface. Yeah, it's sort of mysterious to say you can describe everything that's happening in a three D space, like the inside of a black hole, just by knowing information on a two D space the surface of the black hole. So like, how can everything inside a three D space be described by the surface of that space. Well, that's what we call a hologram. A hologram is a two D image that's projected into a three D space, so it looks three D. The entire hologram is determined actually by what's happening on the surface. So the ideas maybe black holes, the interiors of them are just holograms of their surfaces that you can build a sort of a theory of physics that works in three D. That's actually the theory of physics in two D on a surface, like you don't need three dimensions. Maybe you can describe everything on on a surface exactly. And so the idea is like, well, maybe that's also true like for our universe, Like maybe our three D universe is just a projection, is a two D hologram of what's happening at the edge of our universe. We think we live in this three D world and we're all moving around three dimensions. But if you can print all the information of a three D world onto a two D surface, then it's possible that we actually live on the two D surface at the edge of the universe somewhere and that what we experience is that three D world is really just a two D surface. But okay, so I guess it's like if this can happen on a black hole, then maybe it's happening everywhere. And maybe if we don't really need three dimensions, maybe like we have a redundant dimensions, right, And then there was this incredible result in string theory which backed this up. This guy at the Institute for Advanced Science, Jue Malda Sena, he came up with this theory that showed that string theory in you know, three dimensions that we experience, it can actually be described by a quantum theory in two dimensions. So he showed how you could reconstruct a theory of our universe in three dimensions only on a two dimensional surface. So it sort of showed mathematically that this might be possible. So what does that mean? That means that we're really living an illusion, like the three dimensions that we think we're living in are actually just an illusion. Kind of It could be, right, Yeah, it certainly could be. It could be that we actually live in a two D space Like I mean, it doesn't make any difference like feeling like you live in three D and actually living in three D, Like what's the difference? Uh? Nothing, But mathematically it might be that our three D universe can be described as just a two D surface, which is sort of fascinating because you feel like there's too much information here, right that that everything that's happening to us is somehow too much to squeeze down to two dimensions. But mathematically it can be equivalent. It could be that it's just that we don't have the full freedom of the three dimensions, that we're just a projection of two D spit. But I guess maybe the way you explain it maybe is that you also have time and maybe like somehow time is also giving you that extra feeling of a three or third dimension. Right, Well, here we're just talking about spatial dimensions, and so that two D space would also have time in it, so it's allowed to evolve that things can move on the two D surface, and that changes what happens inside the three D space, But we don't know right that. Yeah, I guess that's what I mean. It's like, because you have time, then you can maybe store more things into that to the information than then you might think. But you know, it's a big leap, Like we say, maybe information is stored on the surface of black holes, which means that maybe you can determine their interior to maybe the whole universe is a holomeram. Like, there's a lot of big leaps there, But again they're also fascinating there, Like, you know, maybe trying to solve this mystery about what's happening inside of a black hole tells us about what's possible for ideas we could have about the universe, and and reveals to us sort of shocking new mathematical connections that show us that the richness of our universe might actually be representable in terms of a smaller set of dimensions. Right, Yeah, like maybe we're all living in a video game. Kind of it just seems like we're in a three D world, but really we're we're just in this kind of reconstruction of a three D world, that's right. And if we are living in a video game, I want to know what are the cheat codes? How do I reset? How do I get extra lives? Exactly? All right? Well, um, it sounds like maybe black holes are not destroying information. Maybe that that seems to be kind of the current physics thinking is that maybe it is sort of recorded on the surfaces of black holes. Yeah, and you know, this stuff is pretty hand wavy. It's not like people have really worked out the mathematical details of it. It's sort of like an idea for idea we might have. It's like a crack a way to explore it that might be able to reveal what's happening with black holes and information. It's not like a very totally solid worked out idea. I see, these are just kind of like directions in which that might have playing these things exactly exactly, and we we we might be getting closer to knowing the answer, right, I mean, we just took a picture of a black hole. Maybe in the future we might get closer to it and figure these things out. Or is this closed off to us forever. That's a great question. And you know, we could send somebody into a black hole and maybe they could learn something about it. The problem is we'd never know the answer because they couldn't tell us. We might as well send dogs in, right, Well, we're going to get a letter from the cat. Our cats depending it. You know, Well, if you're a dog lover, you can, we can send cats to we should just send robots. And let's just send robots. No, there's no society protecting the life of robots, right, that's right, the dog robots, dog robots. There, that's a perfect compromise, all right. But again, it just tells you that there's a lot we don't know about the universe, and that even like our experience of it, this three dimensional experience of it, might be not real or not what we think it is. Yeah, and that deep insights into the very nature of the universe can come from these little odds and ends, these things that all we thought we understood, and then there's a little detail that doesn't quite make sense, and when you tug on that thread, it could unravel literally everything we think we understand about the universe. This is how lots of great discoveries were made relativity, quantum mechanics, and hopefully future crazy bonkers discoveries that people will have a hard time accepting is the true nature of the anivers Until then, I guess I'll stay to a blender to make my fans. I think that's a good idea. All right, Well, we hope you enjoyed that Thanks for joining us. Let's see you next time. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of I heart Radio. For more podcast for my heart Radio, visit the i heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows. M