Daniel and Jorge Explain the UniverseTake a cosmic field trip with Daniel and Jorge, as they guide you on a thought experiment into the heart of the most mysterious objects in the Universe.
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Terms apply. 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.
They still need to bring snacks.
It's a thought experiment, so you can bring any snacks you can think of.
Oh well, I can think of a lot of snacks. I am poor handmade cartoonist and the creator of PhD comics.
Hi.
I'm Daniel. I'm a particle 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 asks 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 iHeartRadio 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 the little bits over there? How do 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 mysteries 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. They are our personal questions about the universe. And the way that science moves forward is people asking those questions. People thinking hmm, how does that work? Or oh, what does it look like in there, let's go find out. So the way we unravel secrets of 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. We are that part of the universe that's asking itself questions about itself. Universe know thyself.
Oh man, you just give me a headache, a philosophical headache, a physics take. 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 them.
That's right. And we are a curious species. We want to see what's under that rock, 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 pillowcase in front of kids and say what he thinks inside, they get excited. Ooh, maybe this is a dynasta we're 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 to random kids on the street.
That was another thought experiment, not recommended.
That didn't 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 antennas and cameras. I mean 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 with the theory actually broke down because it predicted that space's curvature went infinite. So for a long time, physicists 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 what'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 this right stuff swirling around it, but it is indeed black, like 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 the sort of donut of accretion disk 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 if you look anywhere else in space, you would see the stars behind them.
Right, Yeah, that's true. And next to that really bright region from the accretion disk, 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 we 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 wonder about?
Jehe These days I have other things to wonder about, like the faith of humanity without a black hole.
Well, 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 then what is for example, you'd happily send me into a black hole? If I could report that?
What I mean, if you are standing at the est 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 might not never happen.
It might even destroy the information.
Hmm. Wow, well that's that. The other next sci fi novel are criminals who use black holes to erase their evidence. Yes, So, as usual, we were wondering how many people out there had asked themselves this question, and how many people out there think they have an answer for this. So, as usual, Daniel went out into the wilds 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 without knowing it in advance and no googling allowed. If you would like to answer such questions for future episodes, please write to us two questions at Danielanjorge dot com. We will happily put your uninformed speculation on the podcast.
So 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, 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.
ILL think you'll be very good. I think it depends on what you mean. So, like, the body itself would be what they call spaghettified and broken into its constituent atomic particles, so you'd be pretty much ripped apart. But like, the gravity is so strong that, 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 whistrauction you're falling in, than the gravity you know you'd feel at the top of your head.
Well, I know that from the outside you'd never see it fall in because time would slow down so much that they'd look frozen. But you, yourself, I think, probably 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'd be like torn to shreds.
I don't know. I think from what I know, my body will be ripped apart. It will just be spread, you know, stretched like a spaghetti.
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 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'd be much fun.
All right, and not good is the general message I get from the books.
Yes, our Council of Advisors recommend against pushing your podcast host into a black hole.
Although 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 soundtime.
All right, Well, there's a lot of interesting answers there. Some people think you would survive, and some people don't think you would survive.
Yeah, it seems to me like these folks have thought about black holes and have 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 of.
And no people were tossed in the black hole for the making of this episode.
Yeah, so all right, let's jump into it, Daniel. So today we're going to sort of paint a scenario, right, like, we're going to go next to a black hole and then we're actually going to 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 it 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 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 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 hole is pulling on, for example, your head, at a different strength than it's 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 in 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 gravitational 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. Past 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 in my head and my legs is stronger. So that could pull me apart.
That's right, because these tidal forces, a 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, with 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 spaghetified necessarily outside of the black hole. I could get spagetified 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 spaghetification 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 spaghetification point.
Right, And when you say event horizon, you mean like the actual like what physins 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 past the event horizon, I need to pick a big black hole, right, because a 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.
Oh, that doesn't sound like a lot like I would expect the you know, decent sized black hole to be more than a thousand times the mass or signing.
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 the 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 offs.
Yeah, well, you're going to the black hole. Nobody's going to bring the black hole to you know. What do you mean, does no matter how important you are.
Well, technically everyone near a black hole pools on the black hole. So technically the black hole moves a little bit towards you too.
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 get there.
That's my advice.
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.
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All right, Daniel, we are taking the probably the worst field trip anyone can take, which is to go inside of a black hole. He probably would have come back in time for reess or the school bell, but we're talking about what it would be like to go into it, Like, what would you experience, what would you see? What would you hear or feel? As you go in.
Yeah, it'd 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. Bud. Yeah, I think you might learn something deep and true about the universe. You might reveal a secret and answer nobody knows, and so I think it'd be pretty awesome. 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? Yes, of course I would. I would shred it instantly.
Right, Even if the envelope tears to you apart, they never come back. Well that's really interesting because I mean, you would give up knowing everything else about your life just to get this one secret.
I think it'd be really tending. 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, it doesn't matter, all right, So what would it be like? So I picked a 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, there are 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 disk. It's this swirling mass of gas and dust and doing all sorts of crazy stuff, and some of it is falling in. But to fall in, 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 blazars, 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 disk. 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 accretion 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 necessar that there's anything like that there. But if we're choosing a super massive 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 super massive black hole.
Hmm, okay, right, that's right, because we picked a big one to go into, so 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 disk, so it's not that hard to avoid because it's pretty hot.
That's right, it's pretty hot and pretty nasty, and so 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 money.
Right, yeah, And so the accretion disk 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 stablely 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 fallen 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 disk of the black holes three and a half times of radius for just that same reason.
Yeah, all right, so I'm going into the black hole, I move past the accretion 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. It's 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 eyes. 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 raise of the black hole, then 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, yeah, 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. So that's why we talk about seeing an image of the black hole. It's not the literal black hole itself. It's the distortion of the space that makes it look bigger.
It's like a mirage 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 and it puffs 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.
Maybe the black hole is full of black cats, which case they would till tear you apart.
Also, I think we just figured it out. We just answered the deepest question about quantum grap 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 to raise 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's some 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 escape 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 sideway so that it's not going towards or away from the black hole, then 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.
Wait, 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, et cetera. And so what happens 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'll look out and you'll see photons from the back of your own head.
WHOA, I've always wanted to know what the back of my head looks like.
And you can't just ask somebody around you. You have to take a field trip to the black hole. That's the most efficient way. Yeah, it's easier than putting a couple of nerves, for sure. 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 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, till 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 is 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. Right, if you imagine yourself sort of at the center of a sphere, you can look all around you. The black hole starts out in 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 ahead of you and sort of around you you see just the black hole shadow.
Whoah, and it's completely pitch black, right, like you're seeing the black hole, which is completely black. There's no stars or anything.
That's right, there's no stars, is 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 you 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 pings 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'd 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 out from a tunnel, you can only see sort of light that shoots straight in to the tunnel. But here, if you look back where you came from, you can see every direction. You can see the whole universe. A vantage 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. So 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 each you, is also still giving you like a three hundred and sixty degree view of the universe because of all this distortion. Yeah.
Wow, And so it's a shrinking view too, Right, Like, as I move towards the black hole, the actual ratis of the actual edge of the black hole, that view is going to be shrinking and shrinking and shricking, and then eventually what it disappears, it 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 trade 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 going to 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.
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All right, Daniel, we are answering the deepest questions of the universe right now. We just stepped inside of the event horizon of a black hole. The universe 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, 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 super frustrating. But yeah, we can imagine that there's some sort of singularity at 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 Eyestein's right. I mean, that 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 to 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's 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 you 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. It moves towards the center.
Right, But that the thing 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. Ooh, man, It's like relativity says you can't escape a black hole and that you can't go faster than 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 fundamentals of relativity, you.
Would break intodin 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 firewall, 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 of 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.
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 in a paramidial kind of space talking to his daughter.
Depends on if you believe in the power of.
Love forehead, Yeah, the fifth dimension. Yeah, So like according to general alativity, what would I see if anything? Would I just see stuff continuing to fall into the black hole or what?
Well, 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 see a little dot otherwise all around you is just blackness, a view of the singularity. But that's assuming that your brain still works. Right, we talked about spaghetification, and the tidle force is 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 in all around And if 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.
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 it could function very well. I mean, 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 the blunt go from your heart to the back of your head still if your head moves faster than the blood, Like, 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 totally dominated by the gravitational forces of the black hole, which would swamp everything else. And so I think practically it be impossible to counter to that and be like, you know, taking a jump on a super super massive 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 it giant planet, you could still jump off of the inside of your spaceship.
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 in just the right direction, then you could continue.
To pre you go. Is 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. All right, So 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 would I need to like bringing 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 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, the tidal 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'd 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 Heisenberger and certainty 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 that could get even closer, then, because the quantum singularity might have some actual spatial extent, there might be a small window in there for you to do some experiments and actually measure it. But I think even before then it'd be fascinating just to map out the gravity as a function of the radis, to see, like how does the gravitational intensity change or the curvature of 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 in your feet, and that might tell you whether or not general relativity is working not.
Yeah, they're doing lots of really cool tests of general relativity 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, then you could understand something about what's happening at the center just from the gravitational twisting and the tweaking of the gravitational forces inside the black hole, you can see like is it spinning? Maybe the singularity is a ring and it's actually spinning, or maybe it's just a 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 us all. You would just sort of confirm this one part of general relativity. Would that be worth it for you?
Or there could be a surprise? Right, this is just two as 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's 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 intellectually 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 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 gonna 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 distracting some piece of information about the universe and just knowing it. Because remember, science is about people's individual curiosity and this is mine.
Hmmm, 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, And I think that's something that surprises a lot of people is that as you fall into the black hole, there's sort of like nothing there. I mean, you get torn apart by the gravity, but there's no threshold at the event horizon. Theres 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 turns your part inside of.
It Yes, it'd be a pretty smooth fall until you get torn into shredded.
Better eat do 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, I think it's, you know, part of a great exercise of human evolution to imagine and to wonder what it 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 like. 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.
Yes, and by somebody, we mean you, Daniel. You're going to be the first one. Because you 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.
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 iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from a new into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.
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