ScienceStuffWhat's hidden inside the most mysterious object in the Universe? Jorge gets sucked in with three astrophysicists to learn the truth.
Hey, Welcome to Sign Stuff, a production of iHeartRadio or Hit Him, And today we are answering the question what's inside a black hole? There's some of the most mysterious objects in the universe. Can we even tell what's inside of them? To find out, I asked three black hole experts this question, and they each gave me a different answer. That's how mysterious black holes are. We'll talk about each of these three ideas, and I have to warn you they each get wilder and wilder. So get ready to take the ultimate dive into the unknown as we get sucked into the question what's inside a black hole? Welcome to Sign Stuff, Hi everyone. Okay, Like I said, I asked three black hole experts what's inside a black hole? And they each gave me a different answer. So on the program today we'll hear what each expert said, and it's going to get crazier and crazier, not just because our experts have wild imaginations, but because that's what the math of black holes says. Okay. The first person I talked to was Professor Julie Commerford from the University of Colorado at Boulder. Doctor Cummerford and I made a video about super massive black holes for my YouTube channel YouTube dot com slash PhD Comics. They knew she'd be a fun person to talk to about black holes. So here's my conversation with Professor Julie Commerford. All Right, doctor Comerford, thank you for joining us.
Yeah, thanks so much for having me.
Can you go into a black hole and tell us what's inside?
I know I'm having too much fun on Earth at the moment, but on my one hundredth birthday, I will vouch right now, I will volunteer to go on a rocket and you can send me into the super massive black hole.
Now, before we talked about what's inside a black hole, I asked her to tell us what exactly a black hole is. Here's what she said, for those of us that don't know what is a black hole.
A black hole is a region of space where the force of gravity is so intense that nothing can escape, no mass, no light, nothing can escape once you get too close to a black hole, and that special invisible boundary is called an event horizon, and that's the boundary across which you can no longer escape the strong gravity of a black hole, no matter how fast you go. So black hole is kind of like the Hotel California of space in that once you cross the event horizon, you can never leave, okay.
According to doctor Commerford, a black hole is basically what happens when you squish stuff, matter or energy so much that you make a hole in space, and it's a three D hole, so it basically looks like a black ball, and inside that ball, inside its event horizon, the gravity is so strong that nothing, not even light can escape. So if you're inside and you shine a laser or flashlight to the outside, that light is just going to turn around and fall right back in. And to make a black hole, according to doctor Commerford, you can squish anything, even the Earth. So how much would you have to squish the Earth for it to become a black hole?
So with the Earth, you'd have to squish it down and couppress it down all the way to the size of a marble, and at that point grabny would win and take over and pull all the Earth's mass into a black.
Hole, and the black hole would be the size of a marble.
Well, the event horizon would be the size of a marble.
And it also works with our sun. If you take our sun and squeeze it to roughly the size of Manhattan, you'd get a black hole the size of Manhattan. Okay, the next question I asked doctor Comerford was how many black holes are there out there? So, how many black holes are there that we know about? Space just full of black holes or is it something that you rarely ever run into?
Oh, spaces full of black holes. So there are two main kinds of black holes that we know about. One kind is stellar mass black holes. These are the ones that are produced at the end of a massive stars life effort it explodes in a big supernova explosion, there's a stellar mass black hole that's left behind, and they have masses similar to the masses of stars. The other kind of black hole that we know about are the super massive black holes, which have masses millions to billions of times more than the mass of a star. And typically each galaxy only has one super massive black hole and it's sitting at the center of the galaxy. But stellar mass black holes can be anywhere there are stars. So our galaxy alone, it's got one super massive black hole at the center, but it probably has around one hundred million stellar mass black holes. Sprinkled throughout the rest of the galaxy, one hundred million in our galaxy alone, and think about how many billions of galaxies are on the universe.
It seems a little dangerous to for a walk in our galaxy.
You know, black holes get a bad rap whenever someone says that they're dangerous. Black holes are like bears. If you give them enough distance, they're not going to bother you. So black holes are everywhere. The universe is littered with them.
Okay, here's where I asked her what's inside a black hole? Like what happens to all the stuff that falls into them? But let's get to the main question of the episode. I would say this is it the biggest question when I go around to schools talking to kids. That's kind of what they want to know.
That is a great question that is really hard to answer because the whole point of a black holes we can't peer inside, We can't peer over the event horizon and see what's going on inside there. So we have physics, We have our understanding of how the universe works, and we can try to apply that physics to understand what's going on inside a black hole. And people do that, write papers about that, but we don't actually know.
Okay, Like doctor Comerford said, it's very hard to see inside a black hole because that's the whole point of a black hole. Even if you were to send in a robot to look inside a the robot would be stuck in there forever and B the robot wouldn't be able to send any signals out because the signals would also be stuck in there. Remember, not even light can get out of a black hole. But as doctor Commerford says, we can use science to look inside. We can use our theories about how the universe works to reconstruct what's going on inside a black hole. Here's how doctor Cumberford describes it.
So what we do know is inside the black hole, the force of gravity pulls everything together to one point. So all that mass, all that light is going to end up at that one infinitely dense point that we call the singularity. And there the curvature space time is infinite, there's infinite energy density, and so all the known laws of physics breakdown. We don't have any existing understanding of physics that explains if and it courveragsu're an infinite density.
Okay, here's what's happening. We have a theory about how the universe works called general relativity. You might have heard of it. It's one of the things Einstein is famous for, and it's a theory that tells us how gravity works and how it bends space and time. And the theory predicts that when you first go into a black hole, when you cross the event horizon, uh, nothing much happens. You just keep falling towards the center. So part of the answer to what's inside a black hole is that it's mostly just space. It's super duper warped space because of all the gravity, but it's still just space. So most of the time you're inside a black hole, you just spend it falling to the center. Are you saying that inside a black hole is just more space.
It's face, but it's space that's really curved. So think of like a really steep water slide. You know, it's pretty frictionless because there's not a lot of stuff in the way to slow down your fall. You'd be falling fast, but there wouldn't be much to bump into because everything that's fallen in before you has ended up at the singularity.
What you're calling this singularity, which is where all the stuff that's in a black hole accumulates. That's right, all right, This is where it gets really interesting. At the center of a black hole is what scientists call the singularity, and this is where the really crazy stuff happens. As you'll hear from our experts in that singularity could be the end of time, or a portal to another universe, or maybe even a universe factory. So when we come back, we'll talk to our next expert and hear what he thinks is inside the inside of a black hole. Stay with us, you're listening to sign stuff. Welcome back, Okay. Like I said, I talked to three black hole experts, and they each gave me a different answer about what's inside a black hole. The next person I talked to was someone who specializes in the interior of black holes.
So I'm doctor Tyler McMackin, and I'm a professor of physics at the University of Mary So I teach physics and I research the interiors of black holes.
Fantastic, that is the perfect specialty for episode today. And you've written several papers on this topic. Actually, what are we going to find inside of a black hole?
Well, it's a good question. There's essentially three different theories of what happens inside black holes. First is a portal to another universe, the second is some exotic ball of matter, and then the third is something we call a singularity, which is basically a brick wall where space and time itself comes to an unavoidable end.
Okay, WHOA, that's a lot to digest. Doctor McMackin has three ideas for what could be at the center of a black hole, so we'll take them one at a time. The first one is that at the center of a black hole is a portal to another universe.
Yeah, so for this first idea, there is a portal to a new universe. This goes back to the early days of when people were first discovering the equations that describe black holes. The scientist named Roy Patrick Kerr, he was a New Zealander in the nineteen sixties, came up with a model that allows for both a black hole and a white hole to exist simultaneously. The idea would basically be, we fall into the black hole. Once we get to the center, then we just go through the drain or whatever analogy want to use, and then pop up the other side.
Okay, what doctor mcmackinn is saying is that the equations for a black hole also predict something called a white hole, which is the opposite of a black hole. So if a black hole is a place where stuff falls in and can never get out, a white hole is a place that constantly throws out stuff and nothing can ever go in. It's like a three D cosmic fountain, which is the opposite of a hole. So if you fall into a black hole and you get to the middle and somewhat made it through the singularity, you would come out of a white hole somewhere else where.
Well, it can be basically wherever you want it to be, so it'll be a whole new universe. And some people have imagined that it could lead to somewhere else in our current universe or some when else in our current universe.
Yes, that's right. This wormhole could not just take you to another part of the universe. It could also take you to another top I'm in the universe. You could time travel, or it could even take you to a whole other universe. But it could be a different universe. What does that even mean? Another universe?
Yeah, I guess it really means that there's no way of getting back to where you were originally. So it's completely causally disconnected from the current universe that we have. We can't communicate by sending light signals from one to the other.
Huh, like a whole different reality.
Yeah, anything is possible, I suppose. Yeah.
So then the other universe does it exist somewhere else and we're just kind of using the black hole as a tunnel.
Yeah, I guess it would be better to think of it as we're using the black hole as a bridge between the two universes. So that's why it's often called a wormhole.
Would this other universe be like the opposite of our universe?
It doesn't have to be. It's just not necessarily like, oh, there's this parallel universe where you have an evil twin or something.
Like that, Doctor McMackin. Assuming I'm not the evil twin.
Yes, we are all the evil twins. The other universe is the normal one.
Right, So that's one thing that the laws of physics predict could be inside a black hole. And here I should mention this is for a perfectly still black hole. We'll get more into that later. But the second thing doctor Meke Becken said could be at the center of a black hole is a ball of exotic matter, a ball.
Of y, a ball of exotic matter. The more likely outcome is that instead of this infinitely long, dense drain at the center, this is replaced by some currently unknown process that will stop the collapse and just form a ball. Maybe it's some sort of quantum star or something like that.
A quantum star that sounds like a great name for superhero franchise. I agree, what is a quantum star? All right, here's doctor Backin's second idea. At the center of a black hole, where all the stuff that fell into the black hole is coming together and scrunching together, there is something that is keeping all that stuff from becoming an infinitely dense point. There's some kind of quantum force that's preventing all that stuff from collapsing, and so it creates a ball that just sits there in the middle of the black hole. So it'd just be sort of like pure matter or energy. It just as pure as you can get it, because it wouldn't be in the form of electrons or quarks or anything.
Right, Yeah, something strings squanto phoam. There are tons of different theories.
And this would be like at the very center, or as soon as we go into the black hole, we would run into this ball.
So it would be at the very center.
Yes, okay, this gets into one of the ultimate frontiers of science, and that is mixing together the two most successful theories in the history of our understanding of the physical world. On the one hand, we have general relativity, Einstein's theory that predicted black holes, that predicts that at the center of a perfectly still black hole is a point of infinite density that could be a wormhole to another universe. And on the other hand, we have quantum mechanics, the theory that tells you that when you get down to the level of super small atoms and particles, things are kind of fuzzy and you can't really have points with infinite density. So, depending on whose right, at the center of a black hole could be a point of infinite density, or there could be some sort of strange or exotic quantum force that keeps all that stuff from collapsing and forms. And I still love this name, a quantum star at the center of a black hole. Scientists don't really know which is true.
We don't currently have a theory for how those two theories combined together to make one consistent model. And so people are searching for this and that it goes under the general name of quantum gravity, and so you need a full theory of quantum gravity to figure out what's happening.
All right.
The third idea doctor Magneckin had is something he calls a wall or time and space end. And this is something that comes up when you think about what black holes are actually like out there in nature. Remember, I said, a lot of the ideas we talked about assume the black hole was perfectly still and not moving. It turns out that's rarely the case.
I would say, all of the objects that we see in the universe have spin. So everything from planets to stars to galaxies has at least some amount of rotation, and so we expect that black holes will also have some sort of spin to them as well. Then, because it's spinning, the Singularity doesn't look like a point anymore. It looks like a ring, which is really weird to think about.
Okay, here's what's happening. Nothing in space is really standing still. Almost everything out there is spinning. Planet spin, stars and sun spin moons, asteroids, even clouds of gas and galaxies. They're all turning to some degree. And the same is true for black holes. And if a black hole is spinning, that means that everything inside of it is spinning, and that makes the center of the black hole act like a merry go round.
So if your black hole is spinning a little bit, then you get this thing, which we could call a centric fugal for us, things that are spinning tend to get flung outwards, and so that provides this outward force that pushes against the flow of space. So that must mean there's some point where the speed of the thing that you threw outward matches the inflowing speed of the space itself. That's going to happen a special spot called the ener horizon.
Okay, this gets a little complicated, but it's like if a thousand people were all trying to ride a merry go round, but the merry go round was spinning really fast, the merry go round would be flinging people out at the same time that people were trying to get on it, So you'd get this ring around the merry go round where people would just pile up. The same thing happens in a rotating black hole, but with space.
All of this debrie that ever fell into the black hole gets caught up in this one part, and eventually we might imagine that it blocks up the flow of the space itself. And if you then were to try to fall into the black hole after that, you would just hit this brick wall where all of this mass stuff has just built up and accumulated. So this is what we call a singularity, where we have basically an infant amount of energy that signals the end of space itself and the end of time itself.
So this singularity is not singular.
It's a whole surface.
Yeah, maybe you should pick another name for it.
That is a good point. Do you have any suggestions? I'm open, I'm all.
Ears, okay to recap Here are the three possibilities for what's at the center of a black hole, according to doctor mcmackinn Number one. If it's a perfect black hole, there could be a point of infinite density at the center of the black hole, which could potentially be the entrance to a wormhole that connects to a white hole somewhere else in another time or maybe even in another universe. Possibility Number two. If quantum mechanics wins at the smallest levels, then some kind of quantum force which we don't know about yet, could keep all this stuff inside a black hole from collapsing into an infinite point. And then you'd have a ball of exotic quantum matter or a quantum star just sitting in the middle of a black hole, shining a light that will never get out. And possibility number three. If it's a realistic black hole, which means it's spinning, then that spinning could also prevent the black hole from collapsing into an infinite dot, and you'd get a ring where stuff accumulates and where time and space just stop. Phe I told you this got crazier and crazier. And we haven't even gotten to our third expert. So when we come back, we'll talk to another theoretical astrophysicist who has an even wilder prediction for what could be at the center of a black hole. So don't go anywhere. Keep spinning with us as we go deeper and deeper into black holes.
We'll be right back.
Okay, we've now reached the deepest level of black hole mystery. We've talked about several wild but still theoretically possible ideas about what could be at the center of a black hole, from quantum stars to wormholes, to other universes, to walls of infinite density where time and space end. But this next idea might take the cake as being the craziest, and it came up during my chat with Professor Andrew Hamilton. Doctor Hamilton is also a professor at the University of Colorado at Boulder who studies theoretical astrophysics and in particular, the insides of black holes. Thank you, doctor Hamilton for joining us today, No problem, Thank you.
Hey.
Today we're answering the question what is inside of a black hole? What can you tell us about what's inside?
Oh, this is the most interesting place in the entire universe. Uh huh, there's a challenging statement to make.
Yeah.
Well, first of all, I have to give you a little bit of background on this. Even today, there's certain amount of debate as to what happens. So I'm going to give you a version which I think is probably the most realistic view of what happens.
Okay, okay, In the scenario that doctor Hamilton is about to describe, we're assuming that at the center of the black hole is the singularity ring we talked about before. That's the point where the centerfical force of the spinning black hole pushes stuff out and meets with all the stuff that's falling in because of gravity. You know, the point where time and space end. And doctor Hamilton then imagines what happens if you throw two rocks into the black hole, one going with the spin of the black hole and one going against the spin of the black hole.
Let's take a rock, Okay, something tangible. I'm throwed in prograde. Okay, that means with the spin of the black hole. Because it's throw grade, it has extra spin compared to the black hole, and as a result of that, it turns around inside the black hole and tries to go outwards at the inner horizon.
All right, that's the first rock. You throw it in in the same direction as the spin of the black hole. That means it's going extra fast. So when it gets to the center, it actually overshoots the singularity ring and it tries to come out of the black hole.
Now, if you then throw a rock in retrograde against the flow of the black hole, then it doesn't have extra centrifugal force, and it just goes down, kind of goes with the flow, and those two rocks, one trying to get out was the other one going inwards, will bang together at very high energy. And the closer they get to the inner horizon before they bang together, the higher the energy with which they will collide.
So that's the scenario. If you throw a second rock against the spin of the black hole, it's just going to fall to the center, and you can imagine that at some point it's going to hit the other rock you threw in before, the one that overshot the center and is trying to get out, And those two rocks would have an enormous amount of energy because remember they're at the bottom of a black hole, so they're going super fast.
This is not a speculation with animating. This is a prediction of general relativity. I'm not pulling you a fast one.
Okay, okay.
So it's a very remarkable instability because the closer they get to the inner horizon, the faster they go through each other, the larger the energy they and if they could reach the inner horizon, they would actually have infinite energy relative to each other. So let me explain how high the energy can get. Are you listening. Okay, let me throw in a rock and I'll throw it into the supermassive black hole at the center of our galaxy and is having docks thrown at it all the time. Right, It's like times square Central when New York got something. Everything is happening down at the centers. So you imagine a rock falling in throw it in prograde, so it becomes trying to go out with the inner horizon and then wait a while. And for example, the black hole at the center of eye galaxy Sagittarius, a star weighs in it four million times the mass of our Sun, and it takes about twenty seconds to fall from the horizon to the singularities. So wait twenty seconds. Each twenty seconds that you wait before throwing in a retrograde rock, the energy which they collide doubles. Doubles. Do you get there doubles, So if you wait twenty seconds, the energy doubles. If you wait a minute, that's three doublings. If you wait an hour, it's ten to the sixty. That is a huge energy that vastly exceeds the energy that the large hadron Collida can do by a huge amount, and it easily reaches energies culparable to those of the Big Bang. WHOA, Okay, so this is the other place in the universe where Big Bang energies are at tanked. And I think that is one of the most interesting things that one could know about black holes.
All right, What doctor Hamilton is saying is that any black hole, like the big one in the middle of our galaxy, there are rocks crashing into each other all the time inside the black hole, and they're doing it according to current theories, with energies that are as high as the energy of the Big Bang. The Big Bang, of course, is the big expansion that happened when our universe was born. So what happens when you have that kind of explosion inside of a black hole?
I don't know what happens when you're just talk to what happens when you bang rocks together at energy use which approach and possibly even exceed the quantum limited energy ten to the nineteen GV it's more than a trillion times. The largest energy that is achievable is the large hadron collide. What happens at those very high energies?
Could new universes be born from that energy?
I want to say yes because I can't say no.
In other words, according to doctor Hamilton, inside of a black hole, there could be new universes being born. And remember, there are millions, if not trillions, of black holes in the universe, according to doctor Cummerford, and each of them could be having little baby universes being born inside of them all the time.
I mean, if you hypothesize that universe can reproduce, make babies, right, that's what we're talking about. Can our university reproduce It's not a totally crazy idea because there was a Big Bang. What happened at the Big Bang? We just don't know. There are curious that somehow the universe spontaneously came into existence. All of these ideas are possible, right, There's something called eternal inflation. The hypothesis that our university produces is something that potentially could be testable. Right.
So yeah, inside of a black hole there could be new universes being born. And that means that our universe, the one we live in, could be inside of a black hole created inside another universe, and each universe could be making trillions of other universes. This hypothesis that universes can reproduce. It's something that the Hamilton thinks could even be testable, but that's going to have to be the subject of another episode for now. The answer to what's inside a black hole seems to be we don't know. It could be a wormhole to another universe, a ball of mysterious quantum matter, a wall at the end of time and space, or, with enough imagination and math, a source of infinite universes. In other words, reality could be black holes all the way down. Thanks for joining us, see you next Wednesday, and if you like this podcast, please leave us a review. You've been listening to Science Stuff production of iHeartRadio, written and produced by me or yham credited by Rose Seguda, executive producer Jerry Rowland, and audio engineer and mixer Ksey Pegrom. And you can follow me on social media. Just search for PhD Comics and the name of your favorite platform. Be sure to subscribe to Sign Stuff on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts, and please tell your friends we'll be back next Wednesday with another episode.
