Do we live inside an enormous black hole?
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A couple months ago, I was watching a video and I heard this question that I didn't even know was possible. Do we live inside an enormous black hole? I was like, yeah, no, it's not possible. Like, that's a strange question. So I looked up the bio of this guy, James Beecham, and he's a particle physicist at the Large Hadron Collider at CERN.

So yeah, okay. I kept watching. It turns out that the mathematics of the interior of a black hole is almost identical to the mathematics of the exterior of the black hole. At this point, I was legitimately curious. So I called him up. I find myself drawn toward all of these kinds of just the edge of our human knowledge. And I want to step just beyond it to see what's there. It's not a crazy step. It's just a very small step.

What I love about talking to James is just how sincerely he takes this question and how excited he is about the even bigger questions it opens up. Like, if we do live inside an enormous black hole. Does that mean that our universe was birthed from a black hole in another universe? And does that mean that the black holes in our universe are little seeds of baby universes in another multiverse situation?

So, I'm Noam Hassenfeld, and this week on Unexplainable, is our entire universe inside a black hole? Okay, so before we dive into the black hole, let me just give you a little heads up. James, this particle physicist at CERN, he's really good at posing fascinating questions.

He's also pretty good at not really answering them, which means there's going to be a lot more speculation than explanation coming up. Even more questions than normal for our show. Let's just say it's going to get weird, but it's going to be a lot of fun. So to start, here's a little Gravity 101. What we observe as gravity, so a ball falling toward the ground or the moon orbiting around the Earth, is

It's not that the Earth is tugging on those things. It's that the mass of Earth is warping the fabric of the universe. It's essentially creating a kind of crater in space. Gravity arises because the presence of stuff within a certain volume of space creates a kind of sinkhole in space itself. This is where we get to black holes. Because if you get enough mass in a small enough area,

Space starts to warp dramatically. The sinkhole gets so steep that nothing can escape it, even light. You can think about a black hole in space like an extremely strong water drain. If you're a fish in the water, you stay far enough away from the drain, you wouldn't even notice that it's there. But if you get close enough to the drain, at some point, the water will be flowing inward faster than you could ever possibly swim. That's like light.

If I am inside the black hole and I turn on a flashlight, that light signal is still going at light speed. But if this pocket of space is being sucked toward the center of the black hole faster than the speed of light, it's never going to be able to get outside of the black hole. And this incredibly strong gravity doesn't just affect light. It affects everything. Like, if you were falling into a small black hole and you made it past the edge, what's called the event horizon,

Space would be warped so dramatically that your feet would be pulled in faster than your head. And it would probably just start to stretch you out. You would probably get stretched into spaghetti. That's basically what I knew before speaking to James. It's the way you'll often see black holes presented in movies like Interstellar or High Life or Star Trek. Black holes suck in light. They stretch things out. They're not exactly fun places to be.

But then James went galaxy brain. For a large enough black hole, he wouldn't even notice at all. I could, in fact, just kind of sit there and I would be fine. I could hang around quite a long time, probably even indefinitely within this enormous black hole. So you're saying in a large enough black hole...

It could be potentially possible for people to just hang out and be okay? Yeah. So, you know, you can kind of just do the calculation yourself if you want to. You can calculate what the gravitational pull would be on your feet versus your head as you go into different sizes of black holes. And you can see that for smaller ones, yeah, it would be quite an extreme thing and you'd get stretched out. And for larger ones, if it's an extremely large black hole, you wouldn't even notice at all.

How large a black hole are we talking? Yeah, okay, so you can use the black hole equation. And if you want to, it'll tell you for some given amount of mass, how small of a volume you'd have to pack it in to make a black hole. That's pretty straightforward. So for example, if I wanted to make a black hole out of the entire earth, I need to pack it into a volume about the size of a blueberry.

And if you have a blueberry-sized black hole, your entire body getting sucked into that would basically just be crushed and stretched into oblivion, for sure. Right. Because, you know, just think about it, in a very, very bad way. Catastrophically, you know, I mean, honestly, from a kind of epic scientific way, that's a pretty good way to go. But, like, it would also be quite bad. Very bad. But...

If I wanted to make the black hole out of the entire sun, I would have to pack it into a volume that's around kind of the center part of London. And that's also going to be extreme curvature and extreme flow of space as you get closer to this thing. So if you happen to be in Trafalgar Square when the sun gets packed into London, you would also get sucked in and killed. But then take that to its logical conclusion. So for example, my astronomer friends are very, very good at calculating what the total mass of the observable universe is.

I put it into the equation that says how tightly I would have to pack that. You'd think it's something like the size of a galaxy or something like that, right? Right. But it turns out that the amount of stuff in the universe, the observable universe, would need to be packed into a volume that is already larger than the observable universe. That's weird. If you say that's weird, it's because it is. Yeah. When I first came across this calculation, I think just like any other physicist, the first time you come across this calculation, you think,

Well, that can't be right. And so you go and start looking at it yourself and you do it yourself and it's absolutely true. So you start to think, okay, well, maybe my astronomer friends, they made an error. Maybe the mass of the universe is not really what they think it is. Maybe they got it off by half, right? I mean, that's a huge error. So maybe the total mass of the observable universe is only half of what it is. But

But it turns out you would still need to pack the entire universe into a volume that's already larger than what it is itself. So then you take this to its logical conclusion and you might ask the question, is our entire observable universe inside an enormous black hole? And that's a bit disquieting. Are you aware how that sounds? Completely aware. And so...

At first, that doesn't make much sense because, you know, again, I thought black holes were these enormous objects that are kind of voraciously sucking in things and spaghettification and stretching everything. Like if I look at the moon, it's not being voraciously sucked and pulled in one direction, right? Or being spaghettified, right? So how is it possible that I look up into space, I look around me, that I could actually be inside of a black hole? Well, think about what your experience would be like if you were inside of an enormous black hole.

You can see stuff around you. You can still exist in your kind of local patch of space. But there will be sort of a thing in the distance, a so-called horizon. What is a horizon? A horizon is something you can never get to. That's what a horizon is, right? It's something in the distance. If you ever got to the horizon, it wouldn't be the horizon anymore. Right. So you'd see this thing inside your black hole that is this horizon beyond which you can't see anything. But this event horizon is also always slowly growing.

We know that black holes are sucking things in all the time. They're getting radiation, they're getting particles and things like this. So more stuff is coming into view at all times. So this is what your experience would be like inside an enormous black hole. Now imagine you right now on Spaceship Earth. We look up into the sky. It seems fine, it seems kind of placid. Everything's kind of, you know, sitting there, you know, very serenely. But in the distance, there's an edge beyond which we cannot see.

This is the cosmological horizon beyond which there is stuff, there has to be, but it has sent a light signal to us that hasn't had time to get to us yet. And this is also slowly growing too. After a certain amount of time, stuff will start to come into this cosmological horizon and our observable universe will grow. But as it stands now, you're just kind of sitting here and with our best telescopes we're seeing this very edge of the universe slowly getting larger.

But black holes suck everything into the center, right? Like if we were in a huge black hole, there would be a center somewhere, right? Right. It is true that at the center of a black hole, there's some kind of weird little thing that we don't understand that simply doesn't make any sense, known as a singularity. Inside the black hole, you would be falling toward the center of this black hole, this kind of like point of infinite density. Right.

So if that's the case that we are in an enormous black hole, where in the universe is the singularity of our black hole? Exactly.

The closest thing that we know of in the entire history of our universe that has existed that is close to a singularity is the Big Bang. So maybe our universe as it exists now satisfies this notion that it could potentially be inside of an enormous black hole because our universe did originate from something that's very similar to a singularity, which was the Big Bang.

We had a kind of singularity-like object that was the kind of seed to our universe. And again, it's a good question where when we say the Big Bang happened 13.8 billion years ago, you could ask the question, where did the Big Bang happen? The Big Bang happened everywhere. So really the singularity in our universe, if we live inside an enormous black hole, the singularity happened everywhere at once. The singularity is all of us. It's everything. The singularity is everything. That's insane. Yeah.

Yeah. Yeah. It's so, so I get both. If I can see if I'm understanding this, it's not where is the singularity? It's like, when is the singularity almost? Yeah, that's a good way to think about it. And the answer to all of this is, again, you have to keep in mind that when we're talking about the curvature of space, we're also talking about the curvature of time because space and time are two parts of, you know, the same thing, which is space time. You can really, you have to think about them as, as related.

And so if we live inside of a black hole, and if these are big ifs, if we live inside of a black hole, and if this is a meaningful statement to make, then where is the singularity inside of our enormous universe-sized black hole? And the answer is that it's either nowhere or everywhere. And these are kind of the same statement.

Because our Big Bang happened everywhere at once. Oh, man. But there's an interesting corollary to this. Hit me. Somebody out there right now is thinking, James, you're a crazy person because we have black holes inside our universe right now. How is it possible that you can have black holes inside of a black hole?

Yes, how? That's a very good question. Is it possible, and again, this is where we start to go from the kind of edges of science and starting to step over into the kind of like speculative part, not in a crazy way, but just stepping that way. Is it possible that our universe was birthed from a singularity of a black hole in another universe? And does that mean that the black holes in our universe are little seeds of other universes in a multiverse itself? Wow.

So the idea there is that in our universe, there could be infinite other universes that are the black holes in our universe. Correct. Okay. And when I say correct, I mean, it's a hypothetical possibility. You know, I mean...

At the end of the day, I might sound like a theorist, but in fact, I'm an experimentalist. And so I need an experiment to be able to demonstrate to me whether or not these things are true. Okay. And right now, we don't actually have any way to possibly test these hypotheses. I would never be so hubristic to foreclose the idea that somebody in the future might come up with a way to test this. But right now, we can't. Dang. No one's ever gone to a black hole. And if you did go inside of a black hole, like we know, it's a one-way trip.

However, we should start with what we know, what we don't know. What is it we don't know? We have no idea what's actually going on inside of a black hole. So the first thing we should do is we should try to maybe study a black hole up close. So either we wait for a very long time to have, you know, interstellar space travel. But another way is if we could make black holes in a laboratory. You can make them? Well, if we were able to make miniature black holes in a laboratory, that would teach us a lot.

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Okay, we've been on this long, spaghettified journey together, so let's just get our bearings for a second. It's possible we might be living in an enormous black hole, because in a black hole there'd be this edge we can't see past that would always be getting further away. Which sounds a lot like what we see from Earth right now. We just tend to see it as our universe getting bigger. But we can't prove this one way or the other, because we don't really know that much about black holes to begin with.

And we can't go out and study one up close because the closest confirmed black hole is just way too far away. So James Beauchamp, this particle physicist at CERN, he's got a different idea. If we want to study a black hole, we might be able to make one. Which leads me to a question I admit I never thought I'd be asking a physicist.

Wait, wait, how do you make a black hole? Yeah, okay, so to make a black hole, normally you need a pretty violent event, like an enormous star exploding and collapsing. So you need a pretty violent event to make a black hole. But what if we wanted to make miniature black holes that technically satisfy the equations of black holes, but they're so small and tiny that they would never do anything. In fact, they would evaporate immediately. We know that over long enough timescales, black holes should evaporate.

This is something called Hawking radiation. Eventually, the universe will run out of stuff for black holes to suck in, and they will eventually have to evaporate. And over enormous timescales, they should evaporate all this stuff. So we know the black holes will evaporate. And if I made a tiny, tiny, tiny black hole, that should evaporate too. So if I were able to make these under controlled conditions, this would teach us a lot about black holes. And in principle, it would be the first step toward understanding better what might be inside of a black hole.

And you said we might be able to make black holes in a lab?

Well, this is where it gets complicated because keep in mind what I said it takes to make a black hole. You need a kind of a violent event. But really what you need is you need to pack a large enough amount of stuff, either mass or energy density within a certain amount of space. And this would naturally make a black hole. So if I have two protons and I get them close enough together and smack them together, in principle, I can make a black hole. The problem, though, is that I would have to reach an energy, you know,

a collision energy that is so high that it's outside of the realm of our civilization at this moment. However, there's this idea that this energy at which you would make black holes, it could in fact be much, much lower because there could be extra dimensions of space that are everywhere around us all the time and tiny and curled up. Now this is a bit strange. - Extra dimensions?

that would somehow allow us to make black holes? Oh, yeah. So at first, that doesn't make much sense. But you can think about it like, for example, imagine you're watching your friend on a tightrope. Maybe your friend's a tightrope walker. She's walking on a tightrope between two buildings. And you're down below, like in Manhattan. You're looking up and watching. You're like, oh, I hope you're okay. But from your perspective, she only has one dimension that she can go in, right? One direction, back and forth. That's it. She goes side to side. She falls, jumps up and down. She's going to jostle herself and fall too.

Now imagine you zoom in to the rope itself. Suddenly, if you were an ant on the rope, there's an extra dimension that you did not see from a distance. The ant can go side to side, but the ant can also go around the rope. It has a different dimension. This, in fact, is entirely possible about our universe now.

There could be extra dimensions of space everywhere all around us at all times, except they're imperceptible to you and me. You don't feel them, but maybe your particles and forces do. And if that's the case, we would help explain why gravity is so weak compared to the other forces of nature. And maybe the reason why we measure gravity as being so weak compared to these other ones is because you and I are only experiencing a tiny three-dimensional slice of gravity that actually exists in multi-dimensions. Like gravity is like...

leaking into these other places and we're only getting a bit of it? Exactly. And it has the consequence that that would then lower the energy at which we would need to run a collider to make miniature objects that would be these little black holes. Just to make sure I'm following here. Yeah. If there are these extra dimensions we can't see, that would make it possible to make a black hole. We just need...

kind of a big enough collider? Yeah, I mean, okay, so this is why, you know, for several years, I'd used this concept of building a collider around the moon. The moon? Yeah, just as a kind of like, you know, inspirational tool. Think big, kids. Okay. But then a few years ago, I'm like, huh, I should put this down into real paper. It'd be fun to do the exercise to see if there's any showstoppers to build an enormous collider on the moon. Turns out there's no showstoppers. We could totally do this. And just to be clear, like, there is a conceivable situation in which...

We could build a collider on the moon and make miniature black holes. There is that conceivable situation, yes. If...

There are extra dimensions of space, which are very small and curled up in everywhere around us. And if these are on the scale of something that can be accessed at a collider that reaches the energies that we would reach on a circular collider around the moon, which would be something like a thousand times the energy of the current Large Hadron Collider, then yes, we could use the moon collider as a black hole machine. There's a lot of ifs there. Okay.

But it's entirely possible. Like, again, this is the stuff that really keeps me up at night and really kind of like, you know, drives a lot of us, right? It's like we talked about before. This is the very edges of our knowledge. It's the very edges of science, right? Where then we step just beyond it just to see what's there. It's not a crazy step. It's just a very small step. It's totally logical, right? Again, it follows completely logically from all the scientific stuff we know about space, about black holes, about general relativity, about, you know, particle colliders. It's entirely possible. There's a lot of ifs there, but it's entirely possible, yes.

Do you think we live in a black hole? Yes, 100%. Okay. No, it's something that, again, I can't say yes or no. I have to gloriously claim the experimentalist, the empiricist mantle and say it is not possible to say yes or no right now with current understanding. It is a possibility that we live inside of an enormous black hole, but it is not currently testable. And also, I cannot say yes or no. So then why are we bothering with any of this?

I don't know. These questions to me are interesting because you sometimes get dismissive responses from other physicists too, where it's like, oh, well, you know, yeah, we don't really live in a black hole and it's kind of silly to think about. But when we posit questions like this, it in principle can spur us to the new idea that stretches us beyond our current understanding. And that is worth it in and of itself.

I think about the fact that it's like, I have a tiny, tiny, tiny amount of time in this universe, right? And the fact that I have this tiny amount of time to even ask questions about the universe is precious and wonderful.

The fact that we get a chance to even ask these questions is remarkable. You know, when you and I ask questions about the universe, honestly, it's the way by which the universe asks questions about itself. Yeah. And that should lead us to understand, you know, at a very deep fundamental core level, I am just one tiny, both insignificant and totally significant piece of this glorious universe.

This episode was produced by me, Noam Hassenfeld. We had editing from Jorge Just, with help from Meredith Hodnot, who runs our team. Mixing and sound design from Christian Ayala, scoring from me, and fact checking from Melissa Hirsch. Manding Nguyen is dreaming about Alaska, and Bird Pinkerton made it to the Galapagos Islands with her beak beeper. She started to hear a faint beep when the ground beneath her feet gave out, and she started to fall.

If you have questions or thoughts about this episode, you can email us at unexplainable at Vox.com. You can also support the show and all of Vox's journalism by joining our membership program today. You can go to Vox.com slash members to sign up. And if you really love supporting us, leave us a nice rating or review wherever you listen. It really helps us out a lot. Unexplainable is part of the Vox Media Podcast Network, and we'll be back next week.

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