Short Wave - What Would It Be Like To Fall Into A Black Hole?

Episode Date: May 27, 2020

Black holes are one of the most beguiling objects in our universe. What are they exactly? How do they affect the universe? And what would it be like to fall into one? We venture beyond the point of no return with Yale astrophysicist Priyamvada Natarajan, into a fascinating world of black holes — where the laws of physics break down. Talk the mysteries of our universe with Short Wave reporter Emily Kwong on Twitter @emilykwong1234. Email the show your biggest cosmological questions at [e-mail] pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

Hey you. Yeah, you there. Thank you for listening to Shortwave. We promise to always make these episodes worth your while, if you promise, to follow and subscribe to us if you haven't already. It really helps the show. Thanks. And with that, off we go. You're listening to Shortwave from NPR. Of all the objects bopping around in our universe, few are as bizarre and enigmatic as. as black holes. Just ask Priya Natarajan. It's like the point where all known laws of physics break down. She's an astrophysicist at Yale University studying extremely cool cosmological phenomena like black holes. So for me, the personal attraction, the gravitational pull, pun intended, toward black holes, I mean, really is that they kind of represent the limits of knowledge.

Because way before black holes were mapped, studied, their picture, you may remember that famous image from last year, black holes were just an idea, a mathematical solution to Einstein's theory of general relativity. So, you know, Newton was able to tell us how gravity worked, but Newton could not tell us why gravity is that way. Einstein was able to come up with this beautiful theory that combined the shape of space, matter, and motion into one theory. The theory of general relativity?

Absolutely. The theory of general relativity does exactly that. So it was this incredible sort of deep connection that he found between the shape of space, matter and motion. And therefore, masses would distort space time, which he envisioned as a four-dimensional kind of fabric, a sheet. So picture our universe as a 4D fabric fusing space and time. And the fabric is bumpy, dotted with planets and other kinds of matter. And what matter does, it causes little potholes in these issues. You drop mass somewhere, you create a pothole. And the size of the pothole, the depth of the pothole,

depends on the mass of the object, and how tightly packed the matter is in that object. Okay, massive objects cause a distortion in space time. But astrophysicist building off this work wondered, well, what happens when you have an object whose mass is so compact that the pothole becomes a puncture in the fabric of space-time itself. And so the black hole solution is one of the simplest solutions to these very complex equations, which was the shape of space around a really concentrated kind of point mass,

and the extreme pothole that such a mass would generate around itself. And we now know the universe is filled with billions and billions of black holes. Do not worry if you are confused. Today on the show, we're going to give you some ways to finally understand what the heck black holes really are. We'll take a mind-bending journey into a black hole to a place where the laws of physics break down. Pass the point of no return. Buckle up, it's going to be awesome. I'm Emily Kwong, and this is Shortwave, the Daily Science podcast from NPR.

We're talking with Priya Natarajan, an astrophysicist at Yale and our black hole guide. First of all, right, let me just sort of clarify, right, there are different kinds of black holes. So there are black holes that are stellar mass black holes. Intermediate mass black holes, supermassive black holes, and ultramassive black holes. And each black hole, at least mathematically, has a kind of boundary called the event horizon. That is the region that encloses that puncture in space time. And this puncture is technically called a singularity. That's the black hole.

And what is special about this event? horizon is that any object that crosses the event horizon, it's the point of no return. Because that is the region within which the grip of gravity of the black hole is such that you have nowhere to go but in, you get sucked in. But you know us. We're not afraid of astrophysics. So let's dive in, starting with the first way of understanding black holes. We believe that they, stellar mass black holes in particular, are the end point of,

of the life cycle of some very big stars. So when stars form, particularly massive stars, say a star that is, you know, starts life with a birth mass that is about 10 to 15 times the mass of the sun, then it will cycle through its life. It will become a red super giant. Then it will exhaust all the fuel, become a supernova explode and then leave behind a little corpse. So that life, can I just say that life is so much more exciting than it all. Mars what you just described. And this is happening over the course of how many years? It's happening over the course of millions of years. Okay. All right. So you live for millions of years, become a

supernova. Yeah, you live fast, die young, and leave a glamorous corpse. Okay. I'm with you. I'm with you. So you have a glamorous condensed corpse. Corps of matter. That's right. So you leave behind a remnant black hole. So that's like, you know, one way to think about a black hole, like, materially, is to think about this very dense object that was left behind after a massive star has lived its life. And what if a person were to fall into a black hole? What would they see an experience? Right. So the, okay, so the first thing that one... Not that I want to do that, but as a thought experiment.

It is not a fate. It is not a fate that you want to actually experience. So it's going to matter if you are going to fall into a stellar mass black hole or a supermassive black hole. A stellar mass black hole, the pothole is dramatically deeper because it's so much more compact. So if you are falling into a stellar mass black hole, then say you're diving in head first, right? So your hair is hanging down. So the difference in the strength of gravity between your hair and the tips of your toes, would be so strong that the gravity would rip you apart. It would stretch you out into a spaghetti. It's called spaghettification. It's a technical term. It's called spaghettification? Yes. And so you would be like stretched out, painfully stretched out, right? And of course no one can hear you scream once you cross the event horizon. So that would be your fate. Whereas in a supermassive black hole, it's a slightly gentler, um, uh, uh, horrific end. So once you fall into the event horizon, as you are approaching the event horizon,

you would be able to see the entire universe around you. You'll be able to see all the stars, the light from the stars, except you would start to see the sort of multiple copies of the universe outside, and you would see them kind of inverted. You'd see all these effects. The extreme light bending effects are called gravitational lensing. And then, it would all become black. And then you would experience something that is really weird. So one of the things that happens once you cross the event horizon is the role of space and time kind of switch.

So you will be actually falling in time rather than space. And what that really means is that every direction, any direction, back, front, right, left, you would be hurtling towards the singularity. It's a super disorienting. So when you're being spaghettified as you're falling through a black hole. Stellar mass black hole. The stellar mass black hole, you're moving through the space time, the fabric of the universe.

The fabric has now switched. So when you're falling past the event horizon and you have been spaghettified, then you are hurtling towards the singularity. which is this point where all laws of physics breakdown, that is the puncture in space time. So that's the other way of thinking about black holes. Space time would be extremely curved once you have passed the event horizon. And in fact, it won't really be space time as it is outside the event horizon

because here the nature of space and time swap. And so you're kind of falling in time, as it were. rather than space. We, of course, don't have data on this, as you can imagine. No human has fallen through time. But what would it mean to fall through time? Yeah, you know, I can think of like a different sense of what happens to time in the gravitational field of an object. So, you know, time actually slows down when you are in an intense gravitational feel. So an experience of a difference in the flow of time. Well, it's kind of a moot point, like, how are you experiencing it? Because, you know, I think by then all your cells would have

stopped functioning and you would be clinically dead. Couldn't experience anything. Yeah, that's right. But this idea, and this is kind of the second way of understanding black holes, is that... You just cannot escape the grip of the gravity. You cannot escape. And it's an infinite fall as you're falling towards the singularity. Absolutely. And this infinite fall would be experienced in the flow of time as really slowed down. Yes. So it's like a stretching out slowing down. That's right.

The other sort of peculiar way in which it would manifest is that the, you know, the friend who was waiting outside and let you sadly fall into the black hole, their clock and your clock would no longer be synchronized, right? Because your clock would have slowed down enormously. Wild. This is absolutely wild. So we've talked about black holes as glamorous star corpses. Yeah.

As punctures in the fabric of spacetime. Let's talk about the third and final framework, which has to do with what it would take to escape a black hole. So, you know, this sort of falling into the singularity and not being able to escape the intense gravity of a black hole allows you to think about black holes and their peculiar properties in another way. And that has to do with this notion of escape velocity. What is the kind of speed you would need to escape the grip of gravity of a black hole? To get released from the grip of a black hole,

this escape velocity has to exceed the speed of light, which nothing material in the universe can exceed. It's a cosmic speed limit. So that's what we mean when we say not even light can escape a black hole. So one way of thinking about black holes is having this gravitational pull that's so strong that not even light can escape that pull. Exactly. So when it comes to black holes in our own backyard, so to speak, we have one at the center of the Milky Way in our galaxy. How does that black hole interact with us if in any way? Yeah, so the Milky Way harbors a supermassive black hole that is about four million times the mass of the sun at the center. The black hole, massive as it is, is still so tiny that we in the solar system and the earth are way, way, way, way out past the region

of influence of the black hole. But the black hole has enabled the formation of the Milky Way that then enabled our solar system to form. So one could kind of poetically say that, you know, the black hole has enabled us being here. That's a really different way of thinking about black holes because, and you've written about this, we use them as tropes of death and nothingness. But what you're suggesting is there actually a force for creation in our galaxy.

Right. But, you know, I mean, it ties to the idea that at some level, right, creation and destruction, life and death are intricately related. They're part of a process. One doesn't occur without the other. They're deeply tied, right? So I think it's kind of very poetic that black holes are not just these monsters that are gobbling stuff and points of destruction,

but that the process of growing a black hole and its life history is interesting. ultimately connected to the assembly of stars. Priya Natarajan is an astrophysicist at Yale University, where she studies black holes and dark matter. Today's episode was produced by Rebecca Ramirez, edited by Viet Le and fact-checked by Emily Vaughn. I'm Emily Kwong, your host while Maddie Safaya's out. Hopefully not peering into any black holes. You hear me, Maddie? This is Shortwave, the Daily Science Podcast from NPR.

Hope you join us again tomorrow.