What's it like to fall into a black hole?

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Speaker 1: Hey, Jorge, did you pack a bag? Why do I need to back one? We're going on a field trip today. Oh nice, Where are we going? We're going on a physics field trip. Actually, does I mean I have to go to a classroom or something. It means it's a thought field trip, sort of like a thought experiment. I don't need to bring snacks. It's a thought experiment, So you can bring any snacks you can think of. Well, I can think of a lot of snacks. I am or handmade cartoonists and the creator of PhD comics. I'm Daniel. I'm a particle of physicist and I enjoy snacks from around the world. Do you just think you're a physicist, Daniel, or are you an actual physicist? What's the difference? Welcome to our philosophy podcast, folks, the philosophy of being a physicist. That's another branch of philosophy we invented on this podcast. Now is it a branch of philosophy or physics. It's a whole new field all into itself. No. On this podcast, we'd like to think that anybody who asked questions about the universe is a physicist. So anyone who claims to be a physicist is a physicist in my book, Well, welcome to our podcast Daniel and Jorge Explain the Universe, a production of I Heart Radio in which we all act like physicists and ask deep questions about the universe. How does it work, what does it look like? What are those little bits over there? How did these things even happen? And we ask those questions and try to find the answers. Sometimes we get some answers, Sometimes we just find more questions. But we hope to entertain you a little bit along the way because there are a lot of questions out there in the universe, because there are a lot of mystery still out there unresolved in the cosmos. That's right, because there are a lot of people out there asking questions. Remember that questions don't belong to the universe. They belong to us. There are our personal questions about the universe. And the way that science moves forward is people asking those questions, people thinking how does that work? Or what does it look like in there? Let's go find out. So the way we unravel secrets to the universe is first by asking those big questions. Yeah, I guess you're right. That is interesting to think about that there are like the universe doesn't have mysteries on its own. Like, I mean, the universe knows everything it knows about itself. It's just us who don't know it. And so we're asking questions and we make it a mystery. That's right, except that we are part of the universe. So maybe we are that part of the universe that's asking itself questions about itself. Universe know thyself. Man, you just give me a headache, a philosophical headache of physics tache. But yeah, there are a lot of mysteries out there, are a lot of pockets of unknown in the universe that humans we just don't know what's inside of him, that's right. And we are a curious species. We want to see what's under that what's over that hill, what's in that weird bag over there. We just want to know. So we want to see all the cool stuff in the universe. We use our telescopes to zoom in on far away stuff. We pick up rocks that fell from space. We want to see it all. Yeah, and there is no more mysterious pocket of mystery, mysterious pocket of mystery in the universe than a black hole. Black Holes are these, you know, pockets of space time that nobody really knows what's inside of them, And there might not be anything interesting inside of them, but just the fact that nobody can look inside, that nobody can go inside and tell us what comes out, makes it mysterious. It's like if I hold an empty pillow case in front of kids and say what do you think's inside? They get excited. Maybe this is a dinosaur were in there. It doesn't really matter as long as it's hidden. It's mysterious and what makes us curious. It sounds like something someone might call the cops on you, Daniel, if you started doing that random kids on the street. That was another thought experiment, not recommended that in your thought arrest. Yeah, so black holes are super weird. I mean they were theoretical up until a little while ago, until we first saw one with our own eyes, our own in tennis and cameras. I mean that we saw them gravitationally, but nobody had really sort of seen one until recently. That's right. There were a theoretical curiosity because general relativity predicted that they existed, but also predicted that they had something really really weird. At their hearts, a singularity, a place where the theory actually broke down because it predicted that space curvature went infinite. So for a long time physicist thought, well, that probably doesn't actually happen. The universe does something, there's something to prevent that from really existing in reality. But then we saw them. We see them at the center of our galaxy, these super massive black holes with stars whizzing around them, and we see stars that have collapsed into black holes. So we know they are a real thing in the universe. We just don't know it's in them. Yeah, well we got a picture of them. They do indeed look like black holes. I mean the picture that we got was it last year, I think, or a couple of years ago. It shows you a black circle basically with all the right stuff scrolling around it, but it is indeed black like there you can't see anything in the middle of it. Yeah, it's simultaneously like amazing technologically and also kind of disappointing because all you're really seeing is a sort of doughnut of accretion disc around the black hole that's glowing in just the way you'd expect, But the black hole itself just looks black, and so it's sort of hard to distinguish a black hole from nothing. Well, you can't see any stars behind it, like in we look anywhere else in space, you would see its stars behind him, right, Yeah, that's true. And next to that really bright region from the accretion disc, it is a pretty black shadow. So yeah, you're seeing a very dark shadow from the black hole. Yeah. So the question is what's inside of that dark region? What's going on in there? Because you can't see in it and there's nothing to see when you take a picture of it. Yeah, and so the explorer and us wonders what's in there? Is it possible to like send a probe or a ship or even a person to go explore? Yeah, and this is a situation that a lot of people have considered, like what would it be like to send something into the black hole? So today on the podcast, we'll be asking the question, what's it like to fall into a black hole? Is this something you would wondered about? Horrid these days that have other things to wonder about the faith of humanity without a black hole. It makes me wonder like if I was standing at the edge of a black hole, would I be tempted to jump in because you might learn some of the secrets of the universe. But on the other hand, you'd probably die and at the very least would never come back to see your family. So that'd be a tough choice to have to make. Yeah, I think I would wonder what it's like to jump into it, but maybe not me jumping into it, you know what I mean? Like I would love for I don't know somebody else to do it, And for example, you'd happily send me into a black hole if I could report back what I mean, if you're standing at the edge of a black hole, would I push you? Maybe don't answer that question. Well, the good thing is the evidence would be totally gone. They could never ask you if I pushed you or not. The perfect crime. Wow, somebody has to write that science fiction novel death by black hole black hole murder. Yeah, the perfect crime because it technically it might not never happen. It might even destroy the information. Wow. Well that's that. The other next sci fi novels are criminals who use black holes to erase their evidence. Yeah. So, as usually, we were wondering how many people out there had asked themselves this question, and how many people out there. I think they have an answer for this. So, as usual, Daniel went out into the wild of the Internet to ask listeners what they think it's like to fall into a black hole. And all of these folks answered this question with knowing it in advance and no googling allowed. If you would like the answer that questions for future episodes, please write to us do questions at Daniel and Jorge dot com. We will happily put your uninformed speculation on the podcast. So I think about it for a second, what do you think it would be like to fall into a black hole. Here's what people had to say. Either you fall in a really huge, immense black hole, uh those super massive black holes, and you fall really slowly and then died at some point, or you get spaghettified in one of these smaller ones. I know that as you fall into a black hole, you will be experiencing everything in your own real time, so it's not like everything will stop or anything like that for you. As far as the rest, I would say, very painful, thank you, be very good. I think it depends on what you mean. So, like the body itself would be what they're called spaghettifier and broken into its constituent atomic particles, so you'd be pretty much ripped apart. But like the gravity is so strong, but like even the difference in your height would see a pretty significant shift in gravitational forces, So the gravity on your feet would be very much stronger, depending on restruction you're following in than the gravity you know you'd feel. And at the top of your head, well, I know that from the outside you'd never seen fallen because time would slow down so much that they love frozen. But you yourself, I think you'd probably be torn to shreds. As you know, any part of you that was ahead of some other part of you would be sucked in much faster. And I guess we don't really know the answer, but I assume it would be like torn to shreds. I don't know. I think from what I know you my body would be ripped apart. It would just be and him, you know, stretched like a spaghetti uh, stretchy, like one second you're there and the next ye're not. Obviously, no one knows what it's actually like to fall into a black hole, but from what I've read, the theory is that you would be spaghettified because you know, if you fell in the feet first, for example, your feet, the gravity at your feet would be much stronger than your head, so you get pulled apart. So I don't think it would be much fun. All right, and not good is the general message I get from. Yes, our council of Advisers recommend against pushing your podcast host into a black hole. Although that I heard a lot of mentions of pasta, so you know that could be a good snack. Yeah, exactly. I said, come prepared. You know, we're going on a field trip, so everybody packed spaghetti at something. All right, Well, there a lot of interesting answer, is there. Some people think you would survive and some people don't think you would survive. Yeah. I seem to me like these folks have about black holes and if even maybe given some thought to what it would be like to fall into it before they heard this question, so they were pretty well prepared. I was impressed. Good answers, listeners. Yeah, and nobody have to push anyone into it either that we know off and no people were tossed in the black hole for the making of this episode. Yeah, so alright, let's jump into it, Daniel. So today we're gonna sort of paint the scenario right, like, we're gonna go next to a black hole and then we're actually gonna go in. We're going to talk about what it's going to be like for somebody doing that. That's right, because a lot of people mentioned this concern that you might not even be able to go into a black hole because you would get torn up before you get too close. So I guess a question is is even possible to go into a black hole and still feel that experience or would you just die before even going in? Yeah, And it turns out that it depends. It depends on the size of the black hole. If you have a really small black hole, then the edge the event horizon, the part past which nothing thing can escape, is much closer to the singularity at the heart, and so it's actually difficult to get to the event horizon because you have to get sort of closer to the black hole. But for a bigger black hole, a massive one like the one at the center of our galaxy, the event horizon is so far from the singularity that it's safer to approach the event horizon. Wait, what what do you mean? So it is possible to go into the black hole. It is actually possible to survive going over the event horizon into the black hole as long as the black hole is big enough. That's sort of the twist. All right, Well, maybe break that down for us. What what would cause me not to survive going into the black hole. So the reason that a black hole pulls you apart this spaghettification is due to the strength of its gravitational field, but also due to how fast that gravitational field is changing the slope of the gravitational field, if you will, Because you are not a tiny point, you are an actual physical thing. You have a front and a back and two sides. And if the black holes pulling on for example, you're head at a different strength than is pulling on your feet, then effectively it's pulling your head off of your body. It's tearing you apart. That's what we call tidal forces. When gravitational forces are different on one side of an object and on the other, that's the same as having a force pull that thing apart. And that's happening like right now. It's not something that just happens near a black hole. Is like if I stand up here on Earth, the Earth is pulling my feet more than it's pulling my head. That's right. The Earth is trying to pull your head off your body right now. But the slope of the Earth's gravitation of field, how much different it is at your feet and at your head, is very, very small, and your body is strong enough to resist that tension. You can resist the tidal force of the Earth. So here on Earth it's weak. Post gravity is relatively weak pasta compared to a black hole. But in a black hole gravity is stronger, and so the difference between the gravity and my head and my legs is stronger. So that could pull me apart. That's right, because these tidal forces, the thing that pulls you apart depends on the forces being different at your foot and at your head. And as you get closer to a black hole, closer to the center of the black hole, the curvature increases, the difference of the gravitational force at your head and your foot increases. Now the Earth, you can't get that much closer to the Earth than its surface. If you dug into the Earth, the gravitational forces actually start to weaken because you have a lot of the mass on the outside of you. The cool thing about a black hole is that it has so much mass in a tiny little area, so you can get really close to it without losing any of the gravitational force. It just gets stronger and stronger and stronger. So that's why for a black hole, you can get close enough to it that it has an event horizon, and that the tidal forces, these things pulling you apart, can be stronger than your body can withstand. Now, I think that usually people talk about that happening before you enter the black hole. But you're telling me that it's not necessarily Like I won't get spaghettified necessarily outside of the black hole. I could get spaghettified inside of the black hole, in which case I could technically go into a black hole. Yeah, exactly. The threshold of which you get spaghettified depends on the mass of the black hole. Now, so it is the size of the black hole. But there's this point where they cross. If a black hole is big enough, then the sort of spaghettification point is inside the event horizon. If the black hole is small enough, then the spaghetification point is outside the event horizon. You get torn apart before you go inside to a small black hole you get torn apart after you go inside. For a really big black hole, that's because the size of the black hole where the edge of the event horizon is depends differently on the mass than the spaghettification point. Right, And when you say event horizon, you mean like the actual like what this is considered the edge of the black hole, Like that's the point where light can't escape exactly. And that's just an arbitrary definition. We say the black hole begins at the event horizon, the place where a ray of light, even if pointed exactly away from the black hole, still would not be able to escape. All right, So then I guess then technically, if I wanted to go into a black hole like pass the event horizon, I need to pick a big black hole, right, because the little one would turn me apart before I go into it. Yeah, that's right. You need to pick a black hole about a thousand times bigger than the mass of our sun before it's safe to enter, before coming to the event horizon will not tear you apart from the tidal forces. That doesn't sound like a lot like I would expect to, you know, decent sized black hole to be more than a thousand times the mass. Yeah, and there are big black holes out there that are much bigger than that. In fact, there's a bit of a gap. There are a few black holes out there that are like ten or fifty or eighty times the mass of our sun. These come from stars just collapsing into a black hole. And then there are black holes in this sort of million sun range, and these are the black holes at the centers of galaxies, these super massive black holes. There actually aren't a lot of black holes in that intermediate range because there isn't a process to form them, unless there, of course, are primordial black holes that nobody's seen those. So your options are black holes that are sort of small like the mass of our sun, which would be too dangerous to get close to, or really really big ones which are pretty safe to approach. There's no medium option, like you can only buy a compact car or a giant suv. Yeah, but the giant SUVs are safer, and the bigger they get, the safer they are, because the bigger they get, the further from the singularity the event horizon is, and so the safer it is to go across that event horizon, right, And the bigger black holes are also harder to park, so there's a trade off. Yeah, well you're going to the black hole. Nobody's gonna bring the black hole to you. What do you mean, no matter how important you are. Well, technically everyone near a black hole pools on the black hole. So the technically the black hole moves a little bit towards you tube. Yeah, exactly, just like blowing in the wind. You know, it has almost no impact. But you're right, You and the black hole are a system, and together you're orbiting the center of mass, which is basically the black hole. You're basically negligible when it comes to black holes. Well, it sounds like if you're curious to see what's inside of a black hole and you want to get inside past the event horizon, you need to pick a big one, otherwise you'll be torn apart before you even get there. Right, Well, let's get into what you would actually see as you go into the black hole, and let's talk about what's inside of it. But first let's take a quick break. All right. I know, we are taking the probably the worst field trip anyone can take, which is to go inside of a black hole. He probably wouldn't come back in time for races or the school bell. But we're talking about what it would be like to go into into it, Like what would you experience, what would you see, what would you hear or feel as you go in? Yeah, it would be pretty fun. I think it would be an awesome field trip. I mean, it's not when you could return from and so the permission slip would be pretty crazy. But yeah, I think you might learn something deep and true about the universe. You might reveal a secret, an answer nobody knows, and so I think it'd be pretty someome. I would definitely sign myself up for this field trip really, like tomorrow, if somebody said, hey, Daniel, would you like to go into a black hole and learn the secrets of the universe? You would jump in? You know, I might. I don't think I would take a trip to Mars just for like planting a flag on Mars, but to know the answer to one of the deepest questions in the universe. I might, just because remember that black holes are where general relativity breaks down, is where we know that our theory of how space and mass bend and dance with each other doesn't work anymore. And something quantum, something new, something weird is going on in there, and the only place we think general relativity does break down is inside these black holes, and so they literally hold secrets to really deep questions about the universe that physicists are struggling over. So it's sort of like asking, if I had an answer to a deep question about the universe in this envelope, would you tear it open? Yeah? Of course I would. I would shred it instantly, right, even if the envelope tells you apart they never come back. Well that's really interesting, because I mean, you would give up knowing everything else about dear life just to get this one secret. I think you'd be really tempting. Yeah. I mean, fortunately, nobody's going to actually ever offer me this, so I can bluff as much as i'd like. Oh I see, I see, we can have any opinion really doesn't matter, all right, So what would it be like? So I picked the big black hole because those are safer to approach than little black holes, which is kind of weird, but I guess that's how the math works. So now I picked a really big one and I'm approaching it. What do I see? Well, the first thing you see is the thing around the doughnut around the black hole. Because most black holes are active, they're still sucking stuff into them. But stuff doesn't fall directly into the black hole because it still has some angular momentum, which means it's spinning the way that we're spinning around the Sun for example, without just falling in. So the black hole has this stuff in orbit around it. Also, that's called the accretion disc. It's the swirling mass of gas and dust and doing all sorts of crazy stuff, and some of it is falling in. But to all end, it has to like lose some energy, has to give up some angular momentum, and it does that by like getting squeezed and glowing and giving off light. I guess. In technically, a black hole is not that different than like a sun, for example, so it would have stuff orbiting around it. Yeah, it has hot gas orbiting around it, and that hot gas is glowing. It's not having fusion necessarily, but it's a very bright emitter. These are some of the brightest things in the galaxy, these disks of gas around a black hole. When they get really intense, you call them quasars or even blaze ours, and they are super duper crazy bright, So it's sort of ironic that some of the brightest things in the universe are next to some of the blackest things in the universe. Right, But it's also not true that every black hole has a bright accretion this like, some black holes could just be like sitting there, right. Yeah, they certainly could be, and it just depends on what's around it. If you have a primordial black hole that was created during the Big Bang and it's just like floating out around there and there's nothing to eat, then it could just be silently stealthily sitting there, totally black. The creation disc just comes from stuff that's sort of on deck about to fall into the black hole. But you're right, it's not necessary that there's anything like that there. But if we're choosing a supermassive black hole, the only way that happened is if it's at the center of a galaxy, which means it's been sucking in gas and dust and it's surrounded by stuff. So you're pretty likely to find an accretion disk around a supermassive black hole. Okay, right, that's right, because we picked a big one to go into, so it's it probably has that disk, and so as you approach it, you probably want to avoid that disc, right, and it's going to be a flat disc, so it it's not that hard to avoid because it's pretty hot, that's right. It's pretty hot and pretty nasty. And say you want to avoid that, you want to come in from the top or from the side, unless it's one of these quasars, in which case it also has a crazy, you know, spinning magnetic field that's beaming a huge beam of light along the north and south axis, So you want to come in a bit of an angle. But yeah, there's an opening there. I mean, this is a black hole field trip, but we still want to keep safety in mount right, Yeah. And so the acretion disc is at about three and a half times the width of the black hole, right. Yeah. If you say the event horizon is the radius of the black hole, then the accretion disc sort of ends around three and a half times that. Anything less than that and the stuff is going to fall into the black hole. So everything at that point and a little bit further out can sort of stably orbit the black hole for a while until it loses its energy through collision or radiation or whatever, and then eventually falls in. But you don't find much gas and dust less than three and a half because that stuff has already falling in. I see, it's kind of like the rings of Saturn. Like the rings of Saturn are a ring, they don't go all the way to the surface of the planet because stuff that's closer to the planet falls in. So it is like it's hanging out there in space. Yeah, exactly. So that's sort of the inner edge of the accretion disc of the black holes three and a half times of radius for just that same reason. Yeah, alright, so I'm going into the black hole, I move past the acreation disk. What am I seeing now? So now what you're looking at is the shadow of the black hole. And we have to keep in mind as we get closer and closer to the black hole, that space around the black hole is bent. Remember that space is not just the backdrop, is not just the emptiness. There's a dance between space and mass. Mass tells space how to bend, and space tells mass and light how to move. So that means that photons don't travel in straight line. So what you're looking at, what you see isn't necessarily what's there and the environment of Earth where light mostly travels in straight lines. You can assume that you're seeing things as they are, but if there are lenses and distortion happening, then you expect to see an image which doesn't necessarily correspond exactly to what's literally there. But what you see in front of you is this big black circle, this shadow of the black hole that's like two and a half times the size of the actual event horizon, and you'll see it be all black. And why is that? Why is the black circle that I see bigger than the actual black circle of the black hole Because anywhere in that black shadow there's no path for light to get to your eye. Is like if you traced it backwards, if you started from your eyeball and trace the path of light, that light would always end up in the black hole. So, for example, what you're looking at when you look straight at the heart of the black hole is the black hole, and no light comes from there, obviously, so you see black. But if you look above the edge of the black hole, like larger than the rays the black hole, then the light would come from the back of the black hole and then curve around the black hole to your eye. So what you're actually seeing there is sort of the path light would take to get to the back of the black hole, but again, no light is emitted from the back of the black hole. Yeah, so that means that I'm actually seeing kind of the back of the black hole right like above the actual black hole. I'm actually seeing the back of it because it's sort of the light gets distorted from the back around the black hole and onto my eye. It's sort of like a lens like it's being magnified in three D exactly. Another way to think about it is put a star on the other side of the black hole, like a really bright star. Would you see it's light creeping over the edge of the event horizon. The answer is no, because those photons would get bent down and then sucked into the black hole. Even if they don't hit the event horizon. As they pass over it, the black hole curves their path, It slurps them down, and they get sucked into the black hole eventually, so you don't see that light. So the first light that you could see, the light that would survive being passed to your eyes is about two and a half times the event horizon. That's why we talked about seeing an image of the black hole. It's not the literal black hole itself. It's a distortion of the space that makes it look bigger. It's like a mirrage, like it's the black hole is pretending to be bigger than it is. That's right. It's like a black cat that's gotten really mad, and it's like and it posts up and post itself up. Yeah, there you go. Black cats black holes both are bad luck if they cross your path, that's right. And so maybe the black hole is more scared of us than we are of it. The black hole is full of black cats, which case, they will tear you apart. Also, I think we just figured out we just answered the deepest question about quantum gravity right there. All right, So I see the shadow and now but now I'm getting closer, even closer than the shadow, or can I enter the shadow? Well, as you get closer this shadow, this circle of black that you see in front of you, it starts out like two and a half times the rays of the black hole, it just gets bigger and bigger in your field of view. And not just because you're getting closer to it, but because the distortion of space is magnifying it more and more. Right, So as you get closer and closer to it, it sort of grows and takes up more and more of your field of view, and it gets bigger and bigger and bigger. But there is awesome stuff that happens even before you get to the event horizon. Yeah, what happened. Well, once you get to like one and a half times the event horizon, this is the last point where light can orbit the black hole stably. Remember the event horizon is where light pointed outwards can't escape the black hole. But even before that, light pointed inwards won't just gave the black hole. Right, If you're two times the size of the event horizon and you shine a flashlight into the black hole, boom, it's going to get slurped in. Now, if you're one and a half times the event horizon and you shine a flashlight sideways so that it's not going towards or away from the black hole, and that light has just enough power to bend all the way around the black hole and come back and hit you in the back of the head. What light can orbit a black hole? But light has no mass. Light has no mass. But remember space is curved, and light doesn't move in straight lines. It moves in the shortest path. And what gravity is is the bending of space, which changes effectively what is the shortest path between two things? Like the reason that the Earth is going around the Sun is not because the Earth has mass, but because the Sun has bent the shape of space. So it's more natural for this Earth to go in this circle. And so light also can follow these curved paths when space is bent. We see that all the time in gravitational lensing, etcetera. And so what how upens here is light essentially is orbiting the black hole. So if you shine a flashlight, it will illuminate the back of your own head, or if you don't have a flashlight, you look out and you'll see photons from the back of your own head. Whoa I've always wanted to know at the back of my head looks like And you can't just ask somebody around you. You have to take a field chip to the black hole. That's the most efficient way just to find that. It's easier than putting you a couple of mirrors. And so at that point, any light that's pointed at all towards the black hole will fall in. Any light that's pointed perfectly tangent to the black hole will orbit, and any light that is pointed at all out will still escape. It needs some angle away from the black hole to escape, but it's still possible. So this is the point of no return for almost like for for light in a way, Yeah, as you get closer, light can still escape if it's pointed further and further out, And as you get closer and closer, the event horizon is a point at which even light pointed straight out from the black hole can no longer get out. But the angle for light to escape gets smaller and smaller as you get closer and closer to the event horizon, until eventually it disappears. All right, So then I've satisfied my curiosity. I know what the back of my head looks like, finally, And then what happens as I go in further than one and a half times the radius of the black hole. Well, it's pretty cool because this shadow, which has become bigger and bigger, grows and grows and grows, and eventually it's even taking up more than half of your vision. All right. If you imagine yourself sort of at the center of a sphere, you can look all around you. The black hole starts out at one point of it, and as you get closer and closer, it fills up more of that sphere, and then it takes up even more than half of that sphere. So you're not yet inside the event horizon, but the distortion of light makes it look like it's sort of eating you. It's like all around you, behind you, you can still see out to the universe, but a head of you and sort of around you you see just the black hole shadow and it's completely pitch black, right, like there's you're seeing the black hole, which is completely black. There's no stars or anything that's right. It's there's no stars, there's nothing there because everything that has fallen into the black hole is ahead of you and cannot radiate towards you. Right, Nothing that's inside the black hole can shoot anything in your direction. The thing that remember is that black holes change the shape of space, and inside the black hole, space is sort of one directional. Every direction points towards the center. And that's sort of beginning to happen now as you approach the event horizon. So things that are closer to the event horizon than you, they could still send you a photon, like if a friend had jumped in before you and he was sending flashlight pins back to you. You could still see your friend, but the black hole itself is not radiating anything else. But if you turn around and you look at sort of the shrinking window out to the rest of the universe, you do see something pretty awesome. Yeah, I guess if it's eating you up the blackness, it would be like going into a tunnel and the entrance to the tunnel gets smaller and smaller. Yes, it's exactly like going into a tunnel and that engines gets smaller and smaller. Except when you look at from a tunnel, you can only see sort of light that shoots straight into the tunnel. But here, if you look back where you came from, you can see every direction. You can see the whole universe. Advantage point from the black hole. You can see from the other side of the black hole. Right, it'd be like a super powerful fish eye lens that let's you see everything in a small view. That's right, because things like that are on the other side of the black hole. Their light can bend around the black hole and then come back and hit your eyeball. So the black hole while it's about to eat you, is also still giving you like a three hundred and sixty degree view of the universe because of all this distortion. You wow. And so it's a shrinking view two, right, Like, as I moved towards the black hole, the actual radius of the actual edge of the black hole, that view is going to be shrinking and shrinking and shrinking, and then eventually what it disappears and becomes a dot. Yeah, And as you move further and further in your window to the universe shrinks and eventually becomes a tiny dot. Right, Because think about it. If you're at the event horizon and you're looking out, the only way for light to escape is to go straight out from the event horizon any other angle and it's gone, which means if you invert that, like coming at any other angle has to have come from the black hole. So you're gonna see all black except for one dot. And in that dot is a picture of the entire universe compressed into a tiny little image. Oh man, And then you're inside the black hole. And then you're inside the black hole, and take careful notes, because I want to hear all about it. All right, let's talk about what is actually happening to you as you go into the event horizon. But first let's take another quick break. All right, Daniel, we are answering the deepest questions of the universe right now, which is that inside of the event horizon of a black hole, the universe has disappeared behind me into a dot. Now I am inside of a black hole. What's happening to me? So we don't know. We don't know what's inside a black hole. We don't know like the structure of matter. Is there really a singularity at its core? Is there something else weird going on? We're pretty sure a singularity can't be right because it's an infinity, and we don't think that those things actually exist in nature. That's what general relativity predicts. Though general relativity also breaks down at the singularity, can't make any real predictions. So we don't know. But we could just sort of like assume that general relativity is right and talk about what it would be like to go into a general relativistic black hole. Well, it only breaks down at the very center, right, That's right, we think, So you know, up until you get to the center, we you can sort of predict what's going to happen. Yeah, if general relativity just needs like a small modification, if it means like, okay, general relativity is right about most of the black holes, just at the core. It doesn't quite get the singularity right, and it gets like fuzzed out by quantum mechanics. Maybe, but it could be that we're totally wrong and that what's inside a black hole is completely different and a huge surprise, and quantum gravity is something totally unexpected. We just don't know, we can't see, which is frustrating. But yeah, we can imagine that there's some sort of singularity the core, and then we could talk about what it's like then to cross the event horizon and dive in. Right, we can just assume e signs right. I mean a guy, he's gotten some things, right, He had a couple of big hits. He's got a pretty good track record. Yeah, so let's go with Einstein is right and think about what would be like to fall into the black hole. And again, the most important thing to remember is that once you're inside the black hole, space is now one directional. That means it's not just like gravity is pulling you really hard and you can't manage to escape. If you could just go faster than the speed of light, it means that every path moves towards the center of the black hole. It's weird to think about space being one directional, but think about the way you think about time time very naturally think of as one directional. Outside a black hole, time is one directional, moves forwards. Inside a black hole, space is one directional and moves towards the center. Right, But that's the ending is only because you can't go faster than the speed of light. If you could go faster than the speed of light, you could sort of come out of that space. Right. Oh man, It's like relativity says you can't escape a black hole and that you can't go fast in the speed of light. So what would happen if you believed relativity about one thing but ignored it about the other thing. I'm not sure that would sort of break the fundamental assumption of relativity. You would break into thine. All right, Well, I guess one thing that's interesting to note is what happens when you actually cross the event horizon, Like when you step through that point where light can escape. You know, what actually happens to me as I go in. Yeah, And the surprising thing is if you've picked a large black hole where the tidal forces are not going to pull you apart, the event horizon is not a special place. It's not like there's a fire our wall, or there's a gate, or there's dragons or anything right there. It's just the point at which light can no longer escape. And so your view the universe continues to shrink, and you see more and more blackness around you. And that's because every path for you, every future direction of yours, is towards the center of the black hole, which of course isn't emitting anything and looks black. So that's the only thing that happens as you cross the event horizon. No fireworks, no craziness, just sort of a ceiling of your fate. And so then what I would experience is just pure darkness. Right according to general relativity, I wouldn't see any flashes of light or Matthew McConaughey and a you know, premidal kind of space talking to his daughter. Depends on if you believe in the power of love rhead, Yeah, the fifth dimension. Yeah, to like, what according to general alativity, what would I see if anything, would I just see stuff continuing to fall into the black hole or what? You can't see anything that's in front of you, right, because even if stuff has fallen into the black hole before you, it's ahead of you and it can't emit light in your direction, so you just see blackness ahead of you. The only light you could see while you're inside the black hole is from things behind you. If you're not traveling at the speed of light, then someone outside the black hole can still be shooting a laser at you that could catch up to you in that remaining little tunnel from the outside universe, so you still can't see a little dot. Otherwise, all around you is just the blackness, a view of the singularity. But that's assuming that your brain still works. Right. We talked about spaghetification and the tidal forces tearing you apart, but we don't even know if your mind, if your brain could work, if space becomes one directional, because you know, your brain relies on nervous signals, which go forwards and backwards and sideways and all around, and the space is one directional, could your blood even pump, could your nerves even fire? Right? You couldn't have a thought that goes from the front of your head to the back of your head, right, exactly, exactly, Nothing can move further from the center of the black hole because space is just one directional and so it's hard to imagine how your body could be configured in a way that you would actually even survive. What would my body hold together? Even? Technically, yes, right, technically, yes, the gravitational title forces near the edge of the event horizon, a big black hole would not be enough to tear you apart, so it wouldn't pull you into pieces. But I don't think you could function very well. I mean, your body would have to be reorganized in a way so that things just flow in one direction. And so you know, like if your blood is getting pumped away from your heart, it's never returning to your heart, And that doesn't sound like the recipe for a long life. Well what if I was just thinking, like, could be blood go from your heart to the back of your head? Still if your head moves faster than the blood, like you could you still have circulation that way? Like? Could parts of my body accelerate more than the other parts, which means they do go to the back of my head? I think that your motion here would be ondly dominated by the gravitational forces of the black hole, which would swamp everything else. And so I think practically it would be impossible to counter that and be like, you know, taking a jump on a super supermassive planet is basically impossible. And here we're talking about gravitational forces, which, even though they're not strong enough to pull you apart yet, are still very very strong. And you have nothing to push against, right, so how are you going to accelerate your head relative to the rest of your body. Well, it'd be like, you know, in a super heavy planet, it's hard to jump from the surface, But if I'm falling towards a giant planet, you could still jump off of the inside of your spacehip. Yeah. I suppose if you brought something along to push against, then you could relatively change your acceleration compared to that object. So you bring like a huge bag of bananas and you start throwing them into the center of the black hole, then you would change your acceleration relative to those things. Yeah, so you could maybe still have thoughts as you go in if each of your little blood molecules throws tiny bananas and just the right direction, then they could continue to park because that the idea. Then you'd be glad you ate a bunch of bananas before you went in. We've just proved it, folks. Bananas will save you inside a black hole. They do help you think. Alright, So, um, I would not see a lot of interesting things, but maybe I would experience something different, you know, like how would you you said I might discover the secrets of the universe inside? Would I see them, feel them or what I need to like bring in an experiment with me. Yeah, well, we don't know, because we don't know what you would see. You can imagine, you know, what would it be like under various scenarios, like if the singularity is real? Well, unfortunately, there's no way you survive getting that close. I mean, we talked about picking a black hole that's big enough to cross the event horizon. But definitely, at some point if you get close enough to a singularity, that title forces will shred you and so you just cannot survive. But imagine then you had some like super duper strong probe that was strong enough to resist that sort of crushing force and it could get closer. Well, it doesn't really matter because the closer you get to singularity, there's always more singularity ahead of you, or the singularity is a point of infinite density, so you can't be like in it. You can't be past some of it. There's always space between you and it, and that space gets smaller and smaller and smaller, sort of like Zeno's paradox, and the gravitational force gets greater and greater and greater until it grows to infinity. But you can't like be inside of it or in part of it. It's a tiny infinitesimal dot. You'ld only just see blackness ahead of you unless quantum mechanics is right, and that singularity isn't actually infinite. If it exists in some sort of finite space it's like fuzzed over by the Heisenberg uncertainty principle, and it's a little bit larger, then it might be possible to like interact with that in some way, or to see it like talking to other parts of the singularity. Well, but even if it was fuzzy in the middle, it would still tear you apart at some point, right, it would tear you apart before you got anywhere close enough to do any physics experiments. But you know, if you had some really powerful probe, they could get even closer than because the quantum singularity might have some actual spatial extent. There might be as small window in there for you to do some experiments and actually measure it. But I think even before then, it would be fascinating just to map out the gravity as a function of the radius. See like how does the gravitational intensity change or the curvature space change as you get closer and closer to the black hole center. That could have some surprises. You could like measure the gravity in your hands as opposed to the gravity your feet, and that might tell you whether or not general relativity is working. Yeah, they're doing lots of really cool tests of general relativity, and right now, from the outside of black holes, they're watching gas swirl and they're asking, does it swirl at the velocity we expect? And they're using that essentially to measure the gravitational force just past the edge of the black hole, because they can't measure it on the inside, which is what they would actually love to do. So if you're inside the black hole, you can measure those forces of gravity, and then you could understand something about what's happening at the center just from the gravitational twisting and the tweaking of the gravitation forces inside the black hole, you can see like, is its spinning? Maybe the singularity is a ring and it's actually spinning, or maybe it's just the dot. So you could learn something about its structure by taking more detailed measurements of the gravitational force as a function of the distance from the center. Now, Daniel, would that be worth it for you to learn that and never come back, because I mean it doesn't sound like you know, the universe would reveal, so you would just sort of confirmed this one part of general relativity. Would that be worth it for you? Or there could be a surprise. Right, this is just two ideas humans have had, and we don't think either of them is right. Was waiting inside a black hole could be something totally different. It could be a portal to another place in the universe, right, a wormhole? It could be something completely surprising that unexpected. I mean, think about how much of a surprise relativity was or quantum mechanics, and now we're talking about something which fuses and changes both of them, and so that could be a surprise on the same scale or even grander than the intellectual leap required to absorb those and so yeah, I'm thirsty for that kind of realization. Sign me up right. Well, but you wouldn't be able to tell anyone, right because you're inside of the black hole. But I would know you would be the only human not to know this information and you wouldn't be able to tell anyone. Would you still want to know if you couldn't tell anyone, Well, since nobody's ever going to call my bluff, I can confidently say yes, I would want to know, because for me, physics isn't about like finding it out and writing the paper. It's about knowing. It's about that moment when you're asking nature a question and forcing nature to reveal the answer, to extracting some piece of information about the universe and just knowing it because remember, science is about people's individual curiosity and this is mine. All right, Well, it sounds like it's possible to go into a black hole and discover some secrets of the universe and actually survive, and it would be pretty interesting and pretty mind and light bending to do it. Yeah, I think that's something that surprises a lot of people is that as you fall into the black hole is sort of like nothing there. I mean, you get torn apart by the ay, but there's no like threshold of the event horizons, no trumpets that play, and you just sort of fall right on in. Now, it's a different story for people who are watching you jump into a black hole. There's all sorts of weird relativistic effects there as they see your time slowing down, even though for you you can just fall right into the black hole without noticing any effects on your clock. Wow, so it would be a pretty smooth fall until it tears your part inside of it. Yes, it would be pretty smooth fall until you get torn into shreds. Better at your spaghetti before you get to that point, then that's right. How do you review that on Yelp? Would have been five stars but got shredded and got turned into dinner for the black hole? All right? Well, um, I think it's you know, a part of a great exercise of human evolution to imagine and to wonder what would be like to do these crazy things in the universe. Absolutely, and these are fun mind experiments because they sharpen our ideas. They make us think what would it actually be. Let's do the calculation. Let's think about what would happen to somebody who jumped into a black hole. And hey, maybe someday somebody's bluff will be called and they will actually be transported to the edge of the event horizon and encouraged to dive in to learn the answers some of these deep questions about physics of the universe. And by somebody, we mean you, Daniel, You're going to be the first one. Because he said it on the record, We're throwing you in. That's right. This is a legal statement right here. I am bound by these statements. All right, Well, we hope you enjoyed that little field trip inside of a black hole. I hope you packed enough snacks. Thanks for joining us, 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. No