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Speaker 1: Hey, Daniel, would you say you understand general relativity?

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Speaker 2: I mean i'd say I understand it better.

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Speaker 1: Every week, so that means you don't understand it.

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Speaker 2: I think it still like makes my head spin.

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Speaker 1: To be honest, what's the trickiest part of it?

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Speaker 2: I think the hardest part to get your mind around

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Speaker 2: is that spinning stuff has different gravity than stuff that

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Speaker 2: doesn't spin.

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Speaker 1: Yeah, okay, there's no way to spend that. That is

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Speaker 1: just confusing.

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Speaker 2: Sometimes I just want to like spin up extra brains

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Speaker 2: to help me figure out how space itself can spin.

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Speaker 1: That is quite a yarn you are spinning.

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Speaker 2: Maybe I'm spinning a web of physics or a web

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Speaker 2: of lies.

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Speaker 1: I'll take that for a spin.

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Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor

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Speaker 2: at uc Irdine, And those are all the spin related

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Speaker 2: jokes I could think of.

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Speaker 1: Hi, I'm Katie, and I cannot put a new spin

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Speaker 1: on those jokes. I am not a particle physicist, but

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Speaker 1: I enjoy physics in the universe and I host an

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Speaker 1: animal themed podcast.

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Speaker 2: All right, I got one more spin related joke for

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Speaker 2: you. You ready, wait?

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Speaker 1: Wait, okay, now I'm ready.

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Speaker 2: Why did scientists stop watching the Earth spin.

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Speaker 1: I don't know, Daniel why they.

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Speaker 2: Got bored and called it a day.

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Speaker 1: Oh that's my soul leaving my body.

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Speaker 2: That was a good one, and Welcome to the podcast

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Speaker 2: Daniel and Jorge explain the Universe, in which we try

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Speaker 2: to avoid your brain spinning inside your cranium as we

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Speaker 2: take a tour of how the universe works, all of

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Speaker 2: its weird and wonderful ways of operating, from the tiniest

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Speaker 2: quantum particles to the most massive of super massive black

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Speaker 2: holes spinning at the centers of galaxies. Motion and rotation

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Speaker 2: and spinning and translation, and all of these things are

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Speaker 2: essential to the way the universe works in some sense.

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Speaker 2: Understanding how things move and what they are is what

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Speaker 2: physics is all about. That's what we try to do

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Speaker 2: on this podcast, break down why things move, how they spin,

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Speaker 2: and how that affects everything around them. My friend and

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Speaker 2: co host Orge can be with us today, but we're

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Speaker 2: very happy to have Katie here with us to take

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Speaker 2: physics for a spin.

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Speaker 1: You know, I used to do ballet when I was

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Speaker 1: a kid, and one of the things you have to

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Speaker 1: learn to do in ballet is to spin without getting

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Speaker 1: dizzy and falling over and so you kind of try

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Speaker 1: to keep your head looking at a point of reference

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Speaker 1: and sort of twist your head around so that you

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Speaker 1: don't get dizzy. Are you saying that when I'm a ballerina,

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Speaker 1: I have more gravity than regular non ballerinas.

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Speaker 2: I'm saying when you do that spin, you drag the

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Speaker 2: fabric of space time along with you, like sticking a

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Speaker 2: fork in spaghetti and twisting it.

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Speaker 1: That's really cool. Now, I wonder my teacher was so

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Speaker 1: strict she didn't want us tearing holes in the fabric

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Speaker 1: of the universe with our off tempo spins.

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Speaker 2: She was really just looking out for your safety, it

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Speaker 2: sounds like. And as scientists have tried to understand the

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Speaker 2: nature of gravity, why things fall down, why things orbit

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Speaker 2: each other in the sky, we have learned so much

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Speaker 2: about the very nature of the universe around us. From

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Speaker 2: Aristotle just telling us things fall down because they like

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Speaker 2: sort of going down, to Newton telling us that gravity

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Speaker 2: is a force between objects that have mass, to Einstein

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Speaker 2: telling us that actually gravity is the bending of space,

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Speaker 2: invisibly curving in front of us and affecting the path

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Speaker 2: of everything that moves through it every time. It requires

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Speaker 2: a huge conceptual change in the way the universe works

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Speaker 2: around us, often with surprising results and strange phenomena that

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Speaker 2: really test our ability to un understand the nature of

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Speaker 2: the universe.

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Speaker 1: Do we now understand what gravity is like? Has that

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Speaker 1: answer been solved for good?

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Speaker 2: We're going to solve it today on the podcast Katie

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Speaker 2: that's right.

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Speaker 1: Oh, let me get out of notepad.

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Speaker 2: After this podcast, buy your ticket to Stockholm. No, gravity

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Speaker 2: is definitely not understood. In fact, we know that our

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Speaker 2: current understanding of gravity is limited, that there are parts

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Speaker 2: of the universe it just fails to describe, and parts

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Speaker 2: of the history of the universe that just don't make

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Speaker 2: sense if you take literally Einstein's theory of general relativity.

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Speaker 2: And one of those places is at the heart of

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Speaker 2: black holes. Black holes are famous because they're weird and

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Speaker 2: they gobble stuff up, and yet they actually exist in

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Speaker 2: the universe. But they hold within them mysteries and secrets

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Speaker 2: that might tell us how gravity actually works at the

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Speaker 2: quantum mechanical level. The thing that we don't know how

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Speaker 2: to do is merge Einstein's picture of gravity with the

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Speaker 2: way quantum mechanics tells us that reality operates at the

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Speaker 2: smallest level. Because we can't go so inside black holes.

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Speaker 2: We have to do other things to them. And one

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Speaker 2: thing we can do to black holes is to spin

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Speaker 2: them and see what happens when they stick their fork

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Speaker 2: into the spaghetti of space time.

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Speaker 1: Okay, when you say we can spin black holes, do

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Speaker 1: you mean we can just sort of twirl them around

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Speaker 1: like a giant top or something, or a huge destructive

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Speaker 1: bay blade. Are these things just out there naturally spinning

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Speaker 1: or are we shooting ping pong balls at them to

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Speaker 1: try to get them to spin both?

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Speaker 2: Actually, all the black holes we know about are too

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Speaker 2: far away for us to experiment on in the laboratory.

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Speaker 2: There aren't any very close by. But we do think

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Speaker 2: that all of the black holes that exist in the

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Speaker 2: universe do spin. Basically, everything out there is spinning. Our

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Speaker 2: planet is spinning, the Sun is spinning, Our planet spins

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Speaker 2: around the Sun. The Sun spins around the center of

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Speaker 2: the galaxy. The galaxy orbits the center of the galactic cluster. Basically,

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Speaker 2: everything out there is spinning, and because angular momentum in

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Speaker 2: the universe is conserved, we think that everything that went

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Speaker 2: into the black hole was probably spinning. So the black

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Speaker 2: holes themselves are almost certainly spinning, which means every black

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Speaker 2: hole out there is probably a spinning object. And the

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Speaker 2: fascinating thing about spinning a black hole is that it

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Speaker 2: changes its gravity. But there's a catch. Black holes can

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Speaker 2: only spin so fast before they might tear themselves open.

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Speaker 1: I mean that's also true in ballet. So the Earth

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Speaker 1: is spinning? Is that why the Earth has gravity? And

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Speaker 1: it keeps us on it?

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Speaker 2: The Earth would have gravity even if it wasn't spinning.

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Speaker 2: But the Earth's gravity is actually subtly different because it

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Speaker 2: does spin. It doesn't just pull on things, It also

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Speaker 2: twists things in orbit around it. We'll dig into all

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Speaker 2: that when we talk about frame dragging. But because spinning

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Speaker 2: of an object changes its gravity, it can also affect

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Speaker 2: the size of a black hole and puts a limit

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Speaker 2: on how fast a black hole is allowed to spin

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Speaker 2: before it cracks open and breaks the rules of physics.

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Speaker 1: Wait, so can a black hole actually crack open? Or

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Speaker 1: is the just some kind of theoretical limit.

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Speaker 2: The rules of physics actually say that there's a maximum

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Speaker 2: speed that black holes are allowed to spin before they

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Speaker 2: crack open. Nobody knows what would happen if you broke

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Speaker 2: that rule. Would it actually crack open the black hole?

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Speaker 2: Would you go to physics jail Kai's old ballet teacher

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Speaker 2: come and scold you. Let's find out.

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Speaker 1: Oh, that's the scariest option.

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Speaker 2: And so today on the podcast, we'll be answering the

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Speaker 2: question how fast can a black hole spin?

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Speaker 1: I'm gonna say fifty miles per hour? I get it.

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Speaker 2: Don't tell me that's the fastest speed you can imagine

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Speaker 2: in your mind, Kitty, you live in Italy. The drivers

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Speaker 2: there drive faster than that all the time, just when

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Speaker 2: they're going to the corner store.

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Speaker 1: I guess, but it's in kilometers per hour, and I

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Speaker 1: haven't figured that out yet.

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Speaker 2: How long you've been there already?

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Speaker 1: You know, a couple kilometers? I'm not really sure.

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Speaker 2: Right, We won't quiz you on you, but I did

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Speaker 2: go out there and ask our listeners what they thought

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Speaker 2: about how fast a black hole could spin. We're very

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Speaker 2: grateful to the listeners who participate in this segment of

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Speaker 2: the podcast, giving us a sense for what people know

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Speaker 2: and what they're confused about. If you would be willing

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Speaker 2: to add your voice to this group of volunteers, please

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Speaker 2: don't be shy. Write to me to questions at danielandthork

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Speaker 2: dot com. So think about it for a moment before

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Speaker 2: you hear these answers. Do you know how fast a

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Speaker 2: black hole can spin? Here's what people had to say.

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Speaker 1: Faster than sonic the hedgehog.

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Speaker 3: I would guess up to the speed of light. I

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Speaker 3: think nothing can go faster than that through space, so

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Speaker 3: that would be a limit. But I don't see any

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Speaker 3: reason why it couldn't get up to that speed.

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Speaker 2: I actually learned that black hole spain the other day.

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Speaker 4: I have no idea how fast they go. I believe

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Speaker 4: that the rate of rotation of a black hole has

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Speaker 4: to do with its size, so the smaller ones will

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Speaker 4: rotate faster. How fast can they go? I have no idea.

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Speaker 5: Well, I would assume that they spin very fast, because

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Speaker 5: neutron stars such as pulsars spin I believe many thousand

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Speaker 5: times per minute, and black holes are perhaps even smaller

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Speaker 5: and denser, which the contraction of their size would make

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Speaker 5: them spin even faster, just like a figure skater holding

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Speaker 5: their arms in would make them spin faster.

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Speaker 6: My instinct is that the only limit ON have asked

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Speaker 6: a black hole could spin is the speed of light. However,

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Speaker 6: I imagine there might be some kind of loophole that

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Speaker 6: may allow it to be faster than that.

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Speaker 7: Very intrigued, Well, black holes, you mean the thing that

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Speaker 7: makes the black hole or the stuff going into the

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Speaker 7: black hole, Because the stuff going into the black hole

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Speaker 7: can spin really fast, but this thing that is the

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Speaker 7: black hole is the singularity, and can a singularity even

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Speaker 7: spin I don't even know.

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Speaker 2: I don't even understand what a singularity is. Mass that's

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Speaker 2: been infinitely mashed up.

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Speaker 8: Black holes would not spin so fast that any given

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Speaker 8: part would have such a high angular momentum to fly

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Speaker 8: off the black hole. But being such massive bodies, they

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Speaker 8: can spin really fast.

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Speaker 1: I do enjoy the Sonic the Hedgehog answer that it

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Speaker 1: could be even faster than Sonic the Hedgehog, who probably

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Speaker 1: does spin faster than fifty miles per hour, Like, would

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Speaker 1: you say that a black hole is faster than mister

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Speaker 1: Sonic the Hedgehog.

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Speaker 2: You know, I've been asked a lot of physics questions

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Speaker 2: in my career, a lot of random questions from the public.

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Speaker 2: I've never been asked to compare a black hole to

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Speaker 2: a fictional video game character, and I just don't know

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Speaker 2: how to answer that question. Like the Sonic the Hedgehog

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Speaker 2: even follow the laws of physics. Are the two things

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Speaker 2: comparable at all? Or is it like comparing miles per

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Speaker 2: hour to kilometer per second?

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Speaker 1: Wise answer given how many Sonic the Hedgehog fans are

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Speaker 1: out there ready for blood. But yeah, I mean, it

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Speaker 1: seems like some people think it's limited by the speed

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Speaker 1: of light, and so some people think that it's got

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Speaker 1: to be faster than something like a bigger skater, or

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Speaker 1: smaller things rotate faster, or a lot of really interesting

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Speaker 1: theories from people.

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Speaker 2: Yeah, and people are definitely right that the surface of

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Speaker 2: a black hole shouldn't be able to move faster than

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Speaker 2: the speed of light. But it turns out there's another

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Speaker 2: limitation to black hole speeds that if black holes spin

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Speaker 2: too fast, they might crack open and reveal what's inside

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Speaker 2: of them. So it's a fascinating question to think about,

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Speaker 2: like what is a black hole, how do they spin,

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Speaker 2: how fast do they spin? What is the maximum speed?

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Speaker 2: And what would happen if you overspun a black hole.

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Speaker 1: It's like if you spun pizza dough too fast and

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Speaker 1: it tore itself apart. But I did think black holes

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Speaker 1: weren't so much a physical object like a pizza. I

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Speaker 1: thought it was kind of this just sort of sinkhole

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Speaker 1: in the universe of like of incredibly incredib dovidibly dense

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Speaker 1: matter that has an incredibly strong pull of gravity. I

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Speaker 1: could use a refresher on what exactly a black hole

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Speaker 1: is made out of.

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Speaker 2: Black Holes are both physical objects and that we know

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Speaker 2: there's something inside of them. There's some mass in there,

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Speaker 2: but there's also a sort of conceptual layer to them,

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Speaker 2: which is the event horizon. Then we'll talk about in

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Speaker 2: a minute, But in the beginning, it just starts with

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Speaker 2: a blob of stuff. You know, stuff has gravity, but

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Speaker 2: gravity is sort of surprisingly weak, like it's the weakest

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Speaker 2: fundamental force that's out there. Gravity is so much weaker

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Speaker 2: than like electromagnetism or the weak nuclear force or the

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Speaker 2: strong force. And you can discover this yourself. Every time

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Speaker 2: you put like a fridge magnet up on the fridge,

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Speaker 2: that tiny little magnet is holding it up. It's beating

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Speaker 2: the gravity of the entire Earth. Right, This enormous planet

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Speaker 2: with all of its rocks and magma inside of it

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Speaker 2: is pulling on that thing, defeated by a tiny fridge magnet.

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Speaker 2: That tells you how a weak gravity really is, and

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Speaker 2: yet if you accumulate enough mass, gravity can become pretty powerful.

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Speaker 2: I mean it's holding you to the surface. The Sun's

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Speaker 2: gravity is holding the entire Earth in orbit, right, the

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Speaker 2: gravity of the galaxy is holding it together. It really

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Speaker 2: is pretty impressive on a cosmic scale. So if you

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Speaker 2: build enough mass, you can get very powerful gravity. But

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Speaker 2: if you take one more step, that's when you get

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Speaker 2: to the crazy town. You take a lot of mask

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Speaker 2: and you also squeeze it down to a really small

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Speaker 2: space so you can get really close to the mass.

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Speaker 2: That's when gravity really gets bunkers.

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Speaker 1: So you have like say, the Sun could fit in

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Speaker 1: a handbag, but it still retains the gravity of the

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Speaker 1: entire Sun. And then you fit a bunch of those

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Speaker 1: little handbag sized suns into a small area, then you

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Speaker 1: have just an enormous amount of gravity.

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Speaker 2: That's right. You could turn the Sun into a black hole. First,

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Speaker 2: imagine you're standing on the surface of the Sun.

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Speaker 1: Oh hot, too hot.

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Speaker 2: I assume you're wearing appropriate foot whear, you know, not

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Speaker 2: like ballerina.

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Speaker 1: Shoes flop flops for the Sun.

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Speaker 2: Now, the gravity on the surface of the Sun is

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Speaker 2: already going to be very powerful. Because the Sun is very,

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Speaker 2: very massive, but it's not a black hole, right, it's

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Speaker 2: emitting light. Now, take the Sun and shrane get down

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Speaker 2: to an object like a few kilometers across. If you're

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Speaker 2: still at the same distance from the center, you're at

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Speaker 2: where the surface of the Sun used to be, then

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Speaker 2: you're gonna feel the same thing. Nothing has changed for you.

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Speaker 2: You're still going to feel the gravity of the Sun

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Speaker 2: in the same way because all you've done is change

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Speaker 2: the internal configuration of the stuff inside the Sun. So

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Speaker 2: nothing will change for you in terms of the gravity

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Speaker 2: you feel if you're still at the same distance. But

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Speaker 2: shrinking the Sun down to a region like the size

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Speaker 2: of Los Angeles means you can actually get much closer

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Speaker 2: to it. Right, instead of having to stand of the surface,

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Speaker 2: you can now just be a few kilometers from the

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Speaker 2: center of the Sun with all of that mass concentrated there.

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Speaker 2: So that's why the gravity gets much much stronger. It's

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Speaker 2: not just about having a lot of mass. It's about

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Speaker 2: having a lot of mass in a very small space.

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Speaker 2: And if you did that, if you shrunk the Sun

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Speaker 2: down to the size of Us Angels, it would form

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Speaker 2: a black hole.

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Speaker 1: And that black hole is called traffic in Los Angeles. Okay,

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Speaker 1: So it's really about how tightly packed this matter is

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Speaker 1: such that it has a really strong effect of gravity

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Speaker 1: and a small amount of area, and so that is

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Speaker 1: what gives a black hole such powerful sort of I

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Speaker 1: guess drainage, universal drainage, Yeah, exactly.

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Speaker 2: In Newtonian gravity, the force between two objects depends on

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Speaker 2: the distance between them, like one over the distance squared.

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Speaker 2: So as the distance gets smaller, the force gets more powerful.

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Speaker 2: And because it's one over distance squared, the force gets

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Speaker 2: much much more powerful. If you're twice as close, it's

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Speaker 2: four times as powerful. If you're a thousand times as close,

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Speaker 2: it's a million times more powerful. So this force gets

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Speaker 2: extraordinarily powerful if you can shrink the distances between the objects.

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Speaker 2: That's what compacting the sun does for you. But then

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Speaker 2: you go over this incredible threat. It's not just like

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Speaker 2: the force gets stronger and stronger and stronger. It does

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Speaker 2: something sort of incredible, which is to create this event horizon,

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Speaker 2: a region of space where anything that enters can never.

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Speaker 1: Escape, even with a really really strong rope.

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Speaker 2: Even with a really really strong rope, even light that

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Speaker 2: enters the event horizon is trapped.

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Speaker 1: What does that mean for light to be trapped?

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Speaker 2: This is where Newtonian gravity no longer works to describe

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Speaker 2: what's going on. You're imagining light moves at the speed

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Speaker 2: of light, why can't it escape the black hole? And also,

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Speaker 2: light has no mass. In the Newtonian picture, gravity is

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Speaker 2: just a force between two objects that have mass. Photons

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Speaker 2: have no mass. How can the black hole pull on

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Speaker 2: them at all? So the Newtonian picture really totally breaks

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Speaker 2: down there. Instead, the way you need to think about

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Speaker 2: it is in Einstein's view of the universe, where gravity

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Speaker 2: is not a force, it's a curving of space time.

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Speaker 2: Space itself is not always just like an evenly spaced grid.

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Speaker 2: It has wiggles and curves in it. And if you

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Speaker 2: shoot like two laser beams through space, if it's totally flat,

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Speaker 2: then those laser beams will fly forever parallel, never touching.

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Speaker 2: But if space is curved, those laser beams will bend,

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Speaker 2: sometimes they may even cross, or they can diverge away

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Speaker 2: from each other based on the curvature of space. And

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Speaker 2: that curvature is not something we can see directly right.

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Speaker 2: We can't look at a piece of space and say, oh,

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Speaker 2: I see the curvature. Instead, we just see the effect

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Speaker 2: of that curvature on the motion of stuff. And so

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Speaker 2: Einstein tells us that when you have stuff in space, mass, energy,

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Speaker 2: anything like that, it changes the shape of space. So

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Speaker 2: back to the question of the photons. What's happening when

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Speaker 2: you have a huge amount of matter in a really

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Speaker 2: tiny space is that you've curved space so much that

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Speaker 2: photons moving through that cannot escape. Photons are affected by

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Speaker 2: mass because mass changes the shape of space and photons

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Speaker 2: move through that space.

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Speaker 1: So the gravity of the black hole causes space to

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Speaker 1: sort of warp into this funnel shape through which photons

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Speaker 1: have no choice but to travel, you know, through this

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Speaker 1: funnel right exactly.

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Speaker 2: Effectively, the shape of space is changed, is so distorted

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Speaker 2: inside the black hole that every direction forward is towards

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Speaker 2: the center of the black hole. When we talk about

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Speaker 2: space being curved, we really mean like it's changing the

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Speaker 2: organization of space, the way points are connected and the

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Speaker 2: distances between them, and so inside the black hole is

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Speaker 2: really just one direction of space, which is towards the.

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Speaker 1: Center that's unnerving.

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Speaker 2: And so this region we call this the event horizon.

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Speaker 2: It's the region around the black hole where nothing can

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Speaker 2: escape anything that enters that will never escape the event horizon,

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Speaker 2: even at time equals infinity at the end of the universe.

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Speaker 2: It's actually what we mean by the event horizon. The

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Speaker 2: technical definition is that region of space which after infinite time,

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Speaker 2: particles that enter will never leave. And the size of

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Speaker 2: that event horizon depends on the parameters of the black hole,

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Speaker 2: Like the bigger the mass inside the black hole, the

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Speaker 2: more space is curved, and the larger the event horizon.

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Speaker 2: It's actually a very simple calculation. It's called the short

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Speaker 2: siled radius that tells you the radius of the black hole,

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Speaker 2: which just depends on the mass, the gravitational constant G,

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Speaker 2: and the speed of light.

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Speaker 1: All Right, so we've got this sort of space funnel

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Speaker 1: that happens that you cannot escape because you're inside of

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Speaker 1: warped space that only goes in one direction, and that

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Speaker 1: is into I guess, the tummy of the black hole.

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Speaker 1: So say you could go inside the space funnel without

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Speaker 1: dying horribly and sort of turning into spaghetti, what would

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Speaker 1: you find there? Just like a really dense clump of matter, Like,

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Speaker 1: what is in there?

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Speaker 2: Boy? Do I wish I knew the answer that question?

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Speaker 2: Because I would be headed to Sockholm to pick up

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Speaker 2: my Nobel Prize. It's really one of the deepest questions

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Speaker 2: in physics because we don't know what would be there.

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Speaker 2: We have a prediction from general relativity, the theory that

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Speaker 2: tells us how space bends and how matter moves through

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Speaker 2: that in space, and that theory tells us that at

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Speaker 2: the heart of a black hole is a singularity because

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Speaker 2: things that fall in a black hole have to proceed

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Speaker 2: towards the center. Eventually everything does, and the power at

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Speaker 2: the center is so incredible that it's like a runaway effect.

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Speaker 2: It just keeps compacting, compacting, and compacting, so that everything

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Speaker 2: that falls into a black hole ends up at this

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Speaker 2: one point, a point of infinite density, infinite curvature of space.

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Speaker 2: That's the prediction from general relativity. But most physicists don't

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Speaker 2: view that as a real prediction. They view that as

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Speaker 2: an indication that the theory is failing. Anytime you get

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Speaker 2: nonsense predictions from your theory, you're like, well, maybe the

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Speaker 2: theory is not being applied correctly. I look at my kids,

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Speaker 2: for example, and I say, oh, in the last fifteen years,

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Speaker 2: they've grown from basically zero to two meters high. Does

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Speaker 2: that mean in the next fifteen years they're going to

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Speaker 2: grow to four meters high and then six meters high.

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Speaker 1: Only time will tell I.

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Speaker 2: Would say that's a nonsense prediction. It tells me that

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Speaker 2: I've extrapolated beyond the region where the theory makes any sense.

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Speaker 2: You know, a simple linear extrapolation doesn't make sense there.

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Speaker 2: I need a new idea for how humans live after

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Speaker 2: age fifteen. And that's what's happening in general relativity. We

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Speaker 2: don't think there really is a point of infinite density.

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Speaker 2: We think something else is going on, and we need

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Speaker 2: a new theory to describe it, because that infinite density

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Speaker 2: also violates fundamental principles of quantum mechanics tells us we

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Speaker 2: have an incredible amount of energy concentrated in a single

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Speaker 2: point without any sort of quantum fuzz, and so quantum

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Speaker 2: mechanics tells us you need some sort of quantum fuzz

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Speaker 2: when you have that much energy. So otherwise you know

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Speaker 2: something's location and it's momentum very very precisely, and that's

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Speaker 2: just not allowed by the Heisenberg uncertainty principle. So what's

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Speaker 2: inside a black hole would tell us how space actually works.

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Speaker 2: What is gravity in the quantum sense, Is it a

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Speaker 2: quantum theory, is actually a force or is there some

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Speaker 2: sort of space foam that bubbles up from fundamental quantum mechanics.

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Speaker 2: We just don't know. But if we could look inside

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Speaker 2: a black hole, we would get an enormous clue about

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Speaker 2: how space actually works, what gravity really is, and how

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Speaker 2: to unify general relativity and quantum mechanics.

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Speaker 1: That's really interesting because like I hear about these things, like,

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Speaker 1: you know, inside a black hole, you have sort of

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Speaker 1: this infinite amount of I guess suckage. But I guess

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Speaker 1: in a way that you're right, Like, it doesn't really

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Speaker 1: make sense for there to be a single, infinitely dense point,

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Speaker 1: especially with what you were describing with sort of the

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Speaker 1: quantum fuzz the uncertainty we know exists in quantum mechanics.

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Speaker 1: But I guess, like, are there any other theories? Are

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Speaker 1: there any other leads that we have as to what

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Speaker 1: is going on there? Like, how do we even go

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Speaker 1: about figuring out what could be happening?

440
00:22:38,800 --> 00:22:41,520
Speaker 2: Yeah, great question. It's really hard because we can see

441
00:22:41,560 --> 00:22:44,520
Speaker 2: inside a black hole. We do have various other theories.

442
00:22:44,520 --> 00:22:46,240
Speaker 2: We talked about a few of them on the podcast

443
00:22:46,640 --> 00:22:50,600
Speaker 2: ideas that black holes are actually slowly collapsing stars, or

444
00:22:50,640 --> 00:22:54,160
Speaker 2: maybe they're fuzzballs made out of strings, or maybe there's

445
00:22:54,160 --> 00:22:57,080
Speaker 2: something else entirely. We do have a bunch of theories,

446
00:22:57,080 --> 00:22:59,520
Speaker 2: but testing them is difficult because all the predictions they

447
00:22:59,520 --> 00:23:03,240
Speaker 2: make a hidden behind this cosmic veil, which makes it

448
00:23:03,280 --> 00:23:05,639
Speaker 2: pretty hard to know which one is right. But there

449
00:23:05,680 --> 00:23:07,919
Speaker 2: are other features to a black hole which present a

450
00:23:07,960 --> 00:23:12,480
Speaker 2: really fascinating opportunity because, as we talked about earlier, gravity

451
00:23:12,560 --> 00:23:15,320
Speaker 2: is not just based on the amount of mass something has.

452
00:23:15,520 --> 00:23:17,680
Speaker 2: It's also based on its spin and its energy in

453
00:23:17,760 --> 00:23:21,639
Speaker 2: terms of electromagnetism. So these other features of a black hole,

454
00:23:21,760 --> 00:23:25,880
Speaker 2: the spin and the charge, might present opportunities for cracking

455
00:23:25,920 --> 00:23:28,400
Speaker 2: them open and seeing what's inside.

456
00:23:28,720 --> 00:23:32,560
Speaker 1: Okay, well, I am really excited to find out what

457
00:23:32,720 --> 00:23:36,120
Speaker 1: is inside these ballerina black holes. But first let's take

458
00:23:36,119 --> 00:23:51,600
Speaker 1: a quick break. All right, and we are back and

459
00:23:51,720 --> 00:23:56,360
Speaker 1: we were talking about the universe's deadliest ballerina, a spinning

460
00:23:56,400 --> 00:23:59,560
Speaker 1: black hole, and what might be inside of their So

461
00:24:00,080 --> 00:24:01,919
Speaker 1: we have just gotten to the part where we are

462
00:24:01,960 --> 00:24:06,679
Speaker 1: talking about how black holes spin. So I'm having a

463
00:24:06,720 --> 00:24:10,880
Speaker 1: hard time picturing what it means for a black hole

464
00:24:10,920 --> 00:24:13,879
Speaker 1: to spin, Daniel, can you let me know, is this

465
00:24:14,080 --> 00:24:16,960
Speaker 1: like a black hole doing a pure What is the

466
00:24:17,000 --> 00:24:18,280
Speaker 1: spin of the black hole?

467
00:24:19,760 --> 00:24:23,119
Speaker 2: Yeah, it's a good question, but what is spinning exactly?

468
00:24:23,280 --> 00:24:25,560
Speaker 2: But we know that black holes are made of stuff, right,

469
00:24:25,560 --> 00:24:28,320
Speaker 2: there's stuff that has fallen in, there's mass, there's energy

470
00:24:28,359 --> 00:24:31,560
Speaker 2: in there. And when stuff falls into a black hole,

471
00:24:31,720 --> 00:24:34,360
Speaker 2: it has angular momentum. Like if you drop a ping

472
00:24:34,400 --> 00:24:37,320
Speaker 2: pong ball straight in towards the center of a black hole,

473
00:24:37,480 --> 00:24:39,280
Speaker 2: then you're not making it spin at all. But if

474
00:24:39,280 --> 00:24:40,960
Speaker 2: you drop a ping pong ball and it hits the

475
00:24:40,960 --> 00:24:44,040
Speaker 2: black hole sort of far from the center, then you're

476
00:24:44,080 --> 00:24:46,359
Speaker 2: like giving it a push. The way somebody on the

477
00:24:46,359 --> 00:24:48,600
Speaker 2: Merry Go Round is spinning around and you give them

478
00:24:48,600 --> 00:24:50,640
Speaker 2: a tug near the edge of the Merry Go Round.

479
00:24:50,680 --> 00:24:53,720
Speaker 2: You're applying a torque to the Merry Go Round. Same

480
00:24:53,760 --> 00:24:55,560
Speaker 2: way you shoot a bunch of ping pong balls at

481
00:24:55,600 --> 00:24:57,800
Speaker 2: a black hole, but you do it off center. You're

482
00:24:57,840 --> 00:25:00,600
Speaker 2: going to add some spin to the black hole. So

483
00:25:00,640 --> 00:25:03,040
Speaker 2: as long as things fall into a black hole and

484
00:25:03,119 --> 00:25:06,280
Speaker 2: don't head directly for the center, if they spin around first,

485
00:25:06,359 --> 00:25:08,399
Speaker 2: then as they fall in, they're going to keep that spin.

486
00:25:08,680 --> 00:25:12,000
Speaker 2: Because in our universe, angular momentum is conserved can't just

487
00:25:12,200 --> 00:25:15,320
Speaker 2: go away, which means because the black hole is made

488
00:25:15,359 --> 00:25:18,000
Speaker 2: of stuff that was spinning around it, eventually a black

489
00:25:18,000 --> 00:25:22,119
Speaker 2: hole itself is spinning. What's actually spinning? I mean, if

490
00:25:22,119 --> 00:25:24,440
Speaker 2: you imagine like a singularity at the heart of the

491
00:25:24,480 --> 00:25:28,679
Speaker 2: black hole, it's just a point. Points themselves cannot spin.

492
00:25:29,240 --> 00:25:31,720
Speaker 2: So people imagine that what's going on inside a black

493
00:25:31,760 --> 00:25:35,359
Speaker 2: hole is not a point spinning but a ring. Instead

494
00:25:35,400 --> 00:25:37,359
Speaker 2: of having a point of infinite space, you have like

495
00:25:37,400 --> 00:25:41,600
Speaker 2: a ring of singularities, and that ring is spinning. Again,

496
00:25:41,880 --> 00:25:44,199
Speaker 2: this is the general relativity prediction, which we think is

497
00:25:44,280 --> 00:25:47,640
Speaker 2: probably wrong, but that's the more complex picture of what's

498
00:25:47,680 --> 00:25:49,840
Speaker 2: happening inside a spinning black hole.

499
00:25:49,960 --> 00:25:53,919
Speaker 1: So you have multiple singularities that form sort of a

500
00:25:54,040 --> 00:25:56,600
Speaker 1: ring inside potentially mm hmmm.

501
00:25:56,920 --> 00:25:59,840
Speaker 2: Because a ring can spin, it has some spatial extent,

502
00:26:00,359 --> 00:26:03,119
Speaker 2: it has some spatial extent at least in one dimension,

503
00:26:03,400 --> 00:26:06,719
Speaker 2: and that ring itself can spin to preserve the angular momentum.

504
00:26:06,760 --> 00:26:10,480
Speaker 2: Because again, angular menum can't just go away in our universe,

505
00:26:10,800 --> 00:26:11,960
Speaker 2: we think it's conserved.

506
00:26:12,359 --> 00:26:15,400
Speaker 1: Okay, so how do we even know that black holes

507
00:26:15,560 --> 00:26:16,080
Speaker 1: can spin?

508
00:26:16,280 --> 00:26:19,320
Speaker 2: Yeah? Great question. According to the theory, they can spin

509
00:26:19,359 --> 00:26:21,600
Speaker 2: in general relativity, and also, as we talked about later

510
00:26:21,640 --> 00:26:23,920
Speaker 2: in the podcast, we've seen a bunch of black holes

511
00:26:23,960 --> 00:26:27,040
Speaker 2: and we've seen the effect of their spinning on the

512
00:26:27,119 --> 00:26:29,879
Speaker 2: stuff around them. And this is a really fascinating feature

513
00:26:29,920 --> 00:26:33,160
Speaker 2: of general relativity, that the spin of an object does

514
00:26:33,359 --> 00:26:36,600
Speaker 2: change its gravity. I mean, again, in the Newtonian picture,

515
00:26:36,600 --> 00:26:39,400
Speaker 2: which I think is pretty intuitive for most people, gravity

516
00:26:39,440 --> 00:26:42,040
Speaker 2: is just a force between two objects that half mass,

517
00:26:42,400 --> 00:26:44,760
Speaker 2: like the Earth is pulling on you. If you're a

518
00:26:44,800 --> 00:26:47,760
Speaker 2: satellite in space orbiting the Earth, you think that your

519
00:26:47,840 --> 00:26:50,160
Speaker 2: orbit is affected only by the mass of the Earth.

520
00:26:50,480 --> 00:26:54,120
Speaker 2: Why would it change the gravity if the Earth is spinning, right,

521
00:26:54,240 --> 00:26:58,560
Speaker 2: the formula is just like gmm over r square. There's

522
00:26:58,560 --> 00:27:01,040
Speaker 2: no opening in there to describe this spinning of the object.

523
00:27:01,359 --> 00:27:03,600
Speaker 2: And Newton would say it doesn't matter if the Earth spins,

524
00:27:03,640 --> 00:27:06,640
Speaker 2: it's like, got the same mass configuration everywhere. As long

525
00:27:06,640 --> 00:27:09,359
Speaker 2: as it's a perfect sphere, it should have the same gravity.

526
00:27:09,840 --> 00:27:12,880
Speaker 2: But in Einstein's picture of the universe, that spin does

527
00:27:13,080 --> 00:27:15,080
Speaker 2: change the gravity of the object.

528
00:27:15,160 --> 00:27:17,960
Speaker 1: And so we're on the Earth and so we are

529
00:27:18,080 --> 00:27:21,800
Speaker 1: experiencing a different gravity from the Earth because it is spinning.

530
00:27:22,000 --> 00:27:26,080
Speaker 1: Then if it was staying still, and so things around

531
00:27:26,119 --> 00:27:29,920
Speaker 1: a black hole would also be experiencing a different effect

532
00:27:29,920 --> 00:27:34,480
Speaker 1: from a spinning black hole versus a stationary black hole exactly.

533
00:27:34,760 --> 00:27:38,400
Speaker 2: And the crucial thing to understand is that in general relativity,

534
00:27:38,400 --> 00:27:42,320
Speaker 2: it's not just that mass bend space, but the things

535
00:27:42,320 --> 00:27:45,560
Speaker 2: that bend space come together in a complicated dance. It's

536
00:27:45,560 --> 00:27:47,800
Speaker 2: described not just by like a number, as it is

537
00:27:47,840 --> 00:27:50,840
Speaker 2: for Newton, like a single number the mass, but this

538
00:27:51,040 --> 00:27:54,359
Speaker 2: stress energy tensor tensor is just a fancy way of saying,

539
00:27:54,400 --> 00:27:57,080
Speaker 2: like a matrix, a bunch of stuff all organized. So

540
00:27:57,119 --> 00:28:00,639
Speaker 2: the mass definitely affects things, energy affects things, can energy

541
00:28:00,640 --> 00:28:05,399
Speaker 2: affects things. Also, Electromagnetic energy and spin all come together

542
00:28:05,440 --> 00:28:08,000
Speaker 2: in this complicated dance. But it's not just like you

543
00:28:08,080 --> 00:28:09,920
Speaker 2: add up all the energy and you get a number

544
00:28:09,960 --> 00:28:12,440
Speaker 2: and that's how much the curvature of space is. It

545
00:28:12,480 --> 00:28:15,240
Speaker 2: is more complicated, and spin affects the curvature of space

546
00:28:15,280 --> 00:28:18,360
Speaker 2: in a really weird way in that it spins space.

547
00:28:19,000 --> 00:28:21,199
Speaker 2: They call it frame dragging because it really is like

548
00:28:21,320 --> 00:28:23,919
Speaker 2: spinning space like a fluid. So what happens to an

549
00:28:23,960 --> 00:28:26,679
Speaker 2: object around something that's spinning is that you're not just

550
00:28:26,840 --> 00:28:30,679
Speaker 2: pulled towards it by its gravity. You're also spun. So

551
00:28:30,760 --> 00:28:33,280
Speaker 2: if you have a satellite orbiting the Earth or a

552
00:28:33,320 --> 00:28:36,040
Speaker 2: black hole and that Earth or black hole is spinning,

553
00:28:36,240 --> 00:28:38,560
Speaker 2: it's going to apply a little torque, a little twist

554
00:28:38,920 --> 00:28:42,200
Speaker 2: to the thing orbiting. We've actually measured this. We have

555
00:28:42,240 --> 00:28:45,719
Speaker 2: a satellite orbiting the Earth called gravity Probe B. It

556
00:28:45,720 --> 00:28:48,880
Speaker 2: has very very precise gyroscopes to measure its direction and

557
00:28:48,920 --> 00:28:51,560
Speaker 2: its spin. We have a whole podcast episode about this,

558
00:28:51,920 --> 00:28:54,440
Speaker 2: and they've detected this effect that the spinning of the

559
00:28:54,480 --> 00:28:57,040
Speaker 2: Earth applies like a little torque to this satellite. It's

560
00:28:57,160 --> 00:28:58,920
Speaker 2: very very subtle. In the case of the Earth, it

561
00:28:59,120 --> 00:29:02,760
Speaker 2: requires extra ordinary precision even to detect it, but it's there.

562
00:29:02,800 --> 00:29:03,600
Speaker 2: We've confirmed it.

563
00:29:04,080 --> 00:29:07,000
Speaker 1: So if you drop like a marble down a funnel,

564
00:29:07,040 --> 00:29:11,160
Speaker 1: like straight in the center down a stationary funnel, it

565
00:29:11,280 --> 00:29:13,280
Speaker 1: just goes straight down. If you drop it sort of

566
00:29:13,520 --> 00:29:16,960
Speaker 1: on the side of a stationary funnel, it rolls down

567
00:29:16,960 --> 00:29:18,880
Speaker 1: the side and then into the center. But if the

568
00:29:18,920 --> 00:29:23,000
Speaker 1: funnel like is spinning, like if you start like sort

569
00:29:23,000 --> 00:29:26,200
Speaker 1: of moving the funnel around and then put the marble

570
00:29:26,360 --> 00:29:28,840
Speaker 1: on the side of the funnel, the marble itself will

571
00:29:28,880 --> 00:29:31,960
Speaker 1: start to like sort of circle around as it goes

572
00:29:32,040 --> 00:29:34,800
Speaker 1: down into the center of the funnel. Is that kind

573
00:29:34,800 --> 00:29:35,960
Speaker 1: of what's happening.

574
00:29:36,040 --> 00:29:37,760
Speaker 2: That's sort of what's happening. There's some tricky bits there

575
00:29:37,760 --> 00:29:40,880
Speaker 2: about the funnel pushing on the marble, but in effect, yeah,

576
00:29:40,920 --> 00:29:43,200
Speaker 2: the spinning of the black hole or the spinning of

577
00:29:43,240 --> 00:29:46,400
Speaker 2: the object applies a spin to stuff near it. So

578
00:29:46,440 --> 00:29:48,600
Speaker 2: in the case of a spinning black hole, you don't

579
00:29:48,640 --> 00:29:51,320
Speaker 2: just have the event horizon, you also have this region

580
00:29:51,520 --> 00:29:55,080
Speaker 2: past the event horizon, called the ergosphere, where the black

581
00:29:55,120 --> 00:29:57,959
Speaker 2: hole is applying a certain amount of twist to stuff.

582
00:29:58,400 --> 00:30:00,920
Speaker 2: We talk once about how you can ext diract energy

583
00:30:01,000 --> 00:30:04,000
Speaker 2: from a black hole basically by dropping rocks near it.

584
00:30:04,080 --> 00:30:06,640
Speaker 2: Those rocks get spun as they go through the ergosphere,

585
00:30:06,760 --> 00:30:09,800
Speaker 2: extracting some energy from the black hole basically for free.

586
00:30:09,840 --> 00:30:12,280
Speaker 2: So I think Freeman Dyson or maybe Roger Penrose came

587
00:30:12,360 --> 00:30:14,280
Speaker 2: up with this plant to use black holes as a

588
00:30:14,320 --> 00:30:15,840
Speaker 2: power source, which.

589
00:30:15,640 --> 00:30:18,400
Speaker 1: Is pretty awesome, sounds really easy. All we need to

590
00:30:18,440 --> 00:30:20,720
Speaker 1: do is get really close to a black hole.

591
00:30:22,080 --> 00:30:24,760
Speaker 2: Exactly. So these spinning black holes have this weird effect

592
00:30:24,840 --> 00:30:28,680
Speaker 2: on space time, and it also affects their event horizon,

593
00:30:28,960 --> 00:30:31,040
Speaker 2: like how close you can get to a black hole

594
00:30:31,080 --> 00:30:34,240
Speaker 2: and still escape depends not just on the mass of

595
00:30:34,280 --> 00:30:37,560
Speaker 2: the black hole, but also on its spin and its

596
00:30:37,560 --> 00:30:41,160
Speaker 2: electric charge. Because these things enter into the stress energy

597
00:30:41,200 --> 00:30:44,880
Speaker 2: tensor that general relativity uses to do this calculation. It

598
00:30:44,920 --> 00:30:47,440
Speaker 2: can change the size of the event horizon if you

599
00:30:47,520 --> 00:30:50,480
Speaker 2: spin your black hole or if you give it electric charge.

600
00:30:50,600 --> 00:30:54,320
Speaker 1: So are we kind of getting into the limitations of

601
00:30:54,480 --> 00:30:57,840
Speaker 1: how fast a black hole can spin, because if it

602
00:30:57,880 --> 00:31:01,920
Speaker 1: is affecting the event horizon, and presumably there has to

603
00:31:01,960 --> 00:31:05,800
Speaker 1: be some characteristics to the event horizon to keep that

604
00:31:05,920 --> 00:31:10,040
Speaker 1: black hole stable. Otherwise, like if you change that event

605
00:31:10,120 --> 00:31:12,960
Speaker 1: horizon too much, what could happen to the black hole?

606
00:31:13,200 --> 00:31:16,240
Speaker 2: Exactly right, And the crucial thing to understand is that

607
00:31:16,400 --> 00:31:20,040
Speaker 2: spinning a black hole will shrink its event horizon. This

608
00:31:20,120 --> 00:31:22,880
Speaker 2: is counterintuitive because you feel like, well, you're adding energy

609
00:31:22,880 --> 00:31:25,600
Speaker 2: to the black hole. Isn't that just putting more fuel

610
00:31:25,640 --> 00:31:28,280
Speaker 2: on the fire. Remember that spin and things like electric

611
00:31:28,400 --> 00:31:30,880
Speaker 2: charge have a complicated way that they contribute to the

612
00:31:30,880 --> 00:31:33,920
Speaker 2: curvature of space. It's not really very intuitive, but adding

613
00:31:34,040 --> 00:31:37,160
Speaker 2: spin or electric charge to your black hole will shrink

614
00:31:37,280 --> 00:31:40,520
Speaker 2: the event horizon, will make it smaller. It's possible to

615
00:31:40,560 --> 00:31:42,880
Speaker 2: get closer to one of these objects if it's spinning

616
00:31:43,280 --> 00:31:47,040
Speaker 2: or has electric charge than otherwise. And as you were saying,

617
00:31:47,120 --> 00:31:50,320
Speaker 2: there's a breakdown point. If you spin the black hole enough,

618
00:31:50,480 --> 00:31:54,320
Speaker 2: the event horizon shrinks down to zero, which means there

619
00:31:54,400 --> 00:31:57,680
Speaker 2: is no event horizon, which means you've like cracked open

620
00:31:57,800 --> 00:32:02,040
Speaker 2: the black hole and revealed the brand mystery that's inside

621
00:32:02,040 --> 00:32:02,360
Speaker 2: of it.

622
00:32:02,480 --> 00:32:05,440
Speaker 1: I bet it's nugat. I bet it's filled with nugat.

623
00:32:06,680 --> 00:32:08,480
Speaker 2: I really think you should have a snack before we

624
00:32:08,520 --> 00:32:10,680
Speaker 2: do these episodes, Katie.

625
00:32:11,200 --> 00:32:15,400
Speaker 1: I'm sorry if you make space sound so delicious, Well

626
00:32:15,440 --> 00:32:18,680
Speaker 1: that's I mean. But presumably we don't know if this

627
00:32:18,720 --> 00:32:21,280
Speaker 1: has ever happened or if it could ever happen.

628
00:32:21,840 --> 00:32:24,040
Speaker 2: We don't know if this has ever happened or if

629
00:32:24,080 --> 00:32:26,480
Speaker 2: it actually could ever happen. Again, it's sort of a

630
00:32:26,520 --> 00:32:29,320
Speaker 2: prediction of general relativity, And we don't think that general

631
00:32:29,360 --> 00:32:32,560
Speaker 2: relativity is the law of the actual universe. It's just

632
00:32:32,600 --> 00:32:34,960
Speaker 2: the law of the universe we describe in our head,

633
00:32:34,960 --> 00:32:38,960
Speaker 2: which so far works perfectly to describe everything we see.

634
00:32:39,040 --> 00:32:41,440
Speaker 2: We think that it probably fails the inside of a

635
00:32:41,520 --> 00:32:44,640
Speaker 2: black hole, but we've never seen that, So this is

636
00:32:44,680 --> 00:32:48,640
Speaker 2: a prediction of general relativity that if you overspin a

637
00:32:48,800 --> 00:32:52,760
Speaker 2: black hole, you will reveal a naked singularity, you will

638
00:32:52,760 --> 00:32:56,160
Speaker 2: crack it open, you'll shrink the event horizon down to zero,

639
00:32:56,640 --> 00:32:59,440
Speaker 2: which is really fascinating because it seems like, on one hand,

640
00:32:59,480 --> 00:33:01,960
Speaker 2: an opportunity to learn this secret of the universe, like,

641
00:33:02,160 --> 00:33:04,240
Speaker 2: let's go out and overspin a black hole. I want

642
00:33:04,240 --> 00:33:06,840
Speaker 2: to see what's inside of it. Right. On the other hand,

643
00:33:06,880 --> 00:33:10,120
Speaker 2: it's like, well, is that really allowed? Is there something

644
00:33:10,120 --> 00:33:12,480
Speaker 2: in the universe that would prevent that from happening?

645
00:33:13,080 --> 00:33:17,120
Speaker 1: So do we have any calculations as to like how

646
00:33:17,400 --> 00:33:20,760
Speaker 1: fast a black hole can spin before it breaks itself apart?

647
00:33:20,880 --> 00:33:23,480
Speaker 2: Yeah, we do actually have the calculation from general relativity,

648
00:33:23,800 --> 00:33:26,200
Speaker 2: and it tells us that if there's more energy in

649
00:33:26,240 --> 00:33:29,120
Speaker 2: the spin than there is in the mass, then the

650
00:33:29,200 --> 00:33:31,880
Speaker 2: radius of the event horizon becomes a negative, which basically

651
00:33:31,920 --> 00:33:34,520
Speaker 2: means there is no event horizon. So that means the

652
00:33:34,560 --> 00:33:37,800
Speaker 2: bigger the black hole, the faster it can spin. So

653
00:33:37,840 --> 00:33:40,320
Speaker 2: it's not like there's a maximum spin rang for all

654
00:33:40,360 --> 00:33:43,480
Speaker 2: black holes, but there's like a ratio if you have

655
00:33:43,560 --> 00:33:45,800
Speaker 2: more energy in your spin than you do in your

656
00:33:45,880 --> 00:33:48,920
Speaker 2: mass than the event horizon shrinks. It's actually the same

657
00:33:48,960 --> 00:33:51,880
Speaker 2: thing for electric charge. We did a podcast episode about

658
00:33:51,920 --> 00:33:55,680
Speaker 2: that recently. If you overcharge the black hole, meaning adding

659
00:33:55,760 --> 00:33:59,719
Speaker 2: more energy to it in electromagnetism by adding like electrons

660
00:33:59,760 --> 00:34:03,240
Speaker 2: for and there's a certain ratio of mass to charge

661
00:34:03,280 --> 00:34:06,240
Speaker 2: you cannot exceed because it will shrink the event horizon

662
00:34:06,600 --> 00:34:09,560
Speaker 2: down to zero. So now there's the interesting question of like, well,

663
00:34:09,719 --> 00:34:11,480
Speaker 2: what happens if you do it? Or is there a

664
00:34:11,520 --> 00:34:13,840
Speaker 2: physical way to actually make this happen?

665
00:34:14,120 --> 00:34:16,360
Speaker 1: I mean, I think it sounds like you got to

666
00:34:16,360 --> 00:34:19,319
Speaker 1: put a sign up at the teacups ride that you

667
00:34:19,400 --> 00:34:21,680
Speaker 1: must be this big of a black hole to be

668
00:34:21,719 --> 00:34:22,960
Speaker 1: able to spin this bath.

669
00:34:25,120 --> 00:34:31,320
Speaker 2: Let's just regulate the problem away. Huh. How very progressive

670
00:34:31,320 --> 00:34:34,040
Speaker 2: of you, Katie. But there's sort of two interesting questions

671
00:34:34,040 --> 00:34:36,640
Speaker 2: here to tease apart. One is like does the universe

672
00:34:36,640 --> 00:34:39,359
Speaker 2: say this is actually impossible? And the other is could

673
00:34:39,520 --> 00:34:43,120
Speaker 2: you make it happen? Right? Some things are not against

674
00:34:43,160 --> 00:34:45,640
Speaker 2: the rules, but you have no way of making them happen,

675
00:34:45,680 --> 00:34:48,120
Speaker 2: no way of like going from our universe to creating

676
00:34:48,120 --> 00:34:51,200
Speaker 2: some configuration that you're curious about, Like, not everything is

677
00:34:51,280 --> 00:34:54,719
Speaker 2: possible to build. You have to assemble things, right. You

678
00:34:54,760 --> 00:34:56,879
Speaker 2: need a recipe for saying I'm gonna build this house,

679
00:34:56,880 --> 00:34:58,600
Speaker 2: I'm gonna put one brick and then the next brick,

680
00:34:58,600 --> 00:35:01,080
Speaker 2: and then the next brick, a way to step by

681
00:35:01,120 --> 00:35:03,960
Speaker 2: step put it together. And so while we don't think

682
00:35:04,000 --> 00:35:07,040
Speaker 2: that it's against the rules of general relativity to crack

683
00:35:07,120 --> 00:35:09,480
Speaker 2: open a black hole this way by overspinning it, we

684
00:35:09,520 --> 00:35:11,680
Speaker 2: don't think that's actually a recipe that would let you

685
00:35:11,760 --> 00:35:13,840
Speaker 2: do it. There's no way to, like, step by step

686
00:35:13,960 --> 00:35:14,480
Speaker 2: make this.

687
00:35:14,400 --> 00:35:16,800
Speaker 1: Happen, because if you got close enough to a black

688
00:35:16,840 --> 00:35:20,200
Speaker 1: hole to build something, it seems like the black hole

689
00:35:20,280 --> 00:35:22,280
Speaker 1: would just suck all your tools away.

690
00:35:22,480 --> 00:35:24,960
Speaker 2: That's one example of a practical reason why you might

691
00:35:25,000 --> 00:35:26,680
Speaker 2: not be able to do this. But people have thought

692
00:35:26,719 --> 00:35:29,080
Speaker 2: about other thought experiments, like say you have a black

693
00:35:29,160 --> 00:35:31,520
Speaker 2: hole and you want to try overspinning it. Take the

694
00:35:31,560 --> 00:35:33,520
Speaker 2: suggestion you made earlier, which is like, well, let's just

695
00:35:33,520 --> 00:35:35,839
Speaker 2: shoot ping pong balls at it, but not right at

696
00:35:35,880 --> 00:35:37,879
Speaker 2: the center. Right. Every time you shoot a ping pong

697
00:35:37,960 --> 00:35:40,080
Speaker 2: ball at a spinning black hole, you're giving it a

698
00:35:40,080 --> 00:35:42,640
Speaker 2: little push. So can't you just keep doing that forever,

699
00:35:42,800 --> 00:35:46,799
Speaker 2: eventually exceeding this ratio and cracking open the black hole. Well,

700
00:35:46,840 --> 00:35:49,560
Speaker 2: it turns out that's not actually possible. What happens when

701
00:35:49,560 --> 00:35:51,680
Speaker 2: you shoot something into a spinning black hole is that

702
00:35:51,719 --> 00:35:54,480
Speaker 2: the black hole causes it to accelerate, which gives off

703
00:35:54,640 --> 00:35:59,480
Speaker 2: some gravitational radiation, because every acceleration requires some kind of

704
00:35:59,560 --> 00:36:02,640
Speaker 2: radiation to conserve momentum. You can't just like zoom in

705
00:36:02,680 --> 00:36:06,000
Speaker 2: one direction without pushing off in the other direction. And

706
00:36:06,040 --> 00:36:09,880
Speaker 2: this gravitational radiation, it turns out, will decrease the angular

707
00:36:09,960 --> 00:36:12,920
Speaker 2: momentum of the thing you're throwing in. So basically, a

708
00:36:12,960 --> 00:36:16,000
Speaker 2: black hole that's right on the edge of being extremal

709
00:36:16,239 --> 00:36:20,560
Speaker 2: that's almost overspun will basically despin stuff that you throw

710
00:36:20,640 --> 00:36:23,800
Speaker 2: into it, so that it's impossible to overspin the black hole.

711
00:36:24,239 --> 00:36:25,959
Speaker 1: So it's self limiting in a way.

712
00:36:26,120 --> 00:36:28,759
Speaker 2: Yeah, exactly, it's sort of self limiting. This is called

713
00:36:28,800 --> 00:36:31,920
Speaker 2: the back reaction. Like the black hole and the object

714
00:36:32,040 --> 00:36:35,160
Speaker 2: have effects on each other before they fall in, and

715
00:36:35,239 --> 00:36:37,319
Speaker 2: so they're pulling on each other, tugging on each other,

716
00:36:37,520 --> 00:36:41,080
Speaker 2: radiating away some gravitational energy. And it's very complicated calculation,

717
00:36:41,120 --> 00:36:43,080
Speaker 2: but people have gone through this and try to imagine

718
00:36:43,120 --> 00:36:46,200
Speaker 2: all possible ways you can throw things into a black hole,

719
00:36:46,480 --> 00:36:49,400
Speaker 2: and none of them can actually push it over the edge.

720
00:36:49,680 --> 00:36:53,400
Speaker 2: That's not saying this configuration is impossible. It's not saying

721
00:36:53,520 --> 00:36:56,200
Speaker 2: overspun black holes are not possible in the universe. It's

722
00:36:56,200 --> 00:36:59,319
Speaker 2: saying we don't know of a recipe for building one,

723
00:36:59,400 --> 00:37:02,560
Speaker 2: because as soon you get close to overspun black holes

724
00:37:02,560 --> 00:37:06,200
Speaker 2: become very very good at rejecting any more angular momentum.

725
00:37:06,400 --> 00:37:09,560
Speaker 1: I mean, it's hard to feel like this black hole

726
00:37:09,680 --> 00:37:14,240
Speaker 1: is not intentionally creating rules so that it doesn't rip apart.

727
00:37:14,560 --> 00:37:18,200
Speaker 1: But I guess that's a very homo sapient mindset that

728
00:37:18,239 --> 00:37:20,120
Speaker 1: there's some intentionality here.

729
00:37:20,400 --> 00:37:23,239
Speaker 2: No, I think you're totally onto something really fascinating, which

730
00:37:23,280 --> 00:37:26,040
Speaker 2: is like the secrets of the universe are hidden behind

731
00:37:26,080 --> 00:37:28,839
Speaker 2: this event horizon. Then as soon as we're clever enough

732
00:37:28,840 --> 00:37:30,960
Speaker 2: to think about, ooh wait, here's a loophole, maybe we

733
00:37:30,960 --> 00:37:33,360
Speaker 2: can break it open, it turns out there's like another

734
00:37:33,440 --> 00:37:35,880
Speaker 2: reason why that can't work. It does feel almost like

735
00:37:35,920 --> 00:37:39,040
Speaker 2: a conspiracy theory, like we have all the answers in

736
00:37:39,040 --> 00:37:41,840
Speaker 2: this little box, but there's no way to open the box.

737
00:37:42,280 --> 00:37:45,200
Speaker 1: We'd find the off switch to the universe in there,

738
00:37:45,480 --> 00:37:47,200
Speaker 1: and they don't want us to find it.

739
00:37:48,480 --> 00:37:50,479
Speaker 2: This is very similar to a topic we talked about

740
00:37:50,480 --> 00:37:53,759
Speaker 2: recently about overcharging the black hole. In a similar way,

741
00:37:53,760 --> 00:37:56,600
Speaker 2: if a black hole has a lot of electric charge,

742
00:37:56,760 --> 00:37:58,880
Speaker 2: then it repels stuff you try to throw in it

743
00:37:58,920 --> 00:38:01,400
Speaker 2: that has more electric charge charge, so it prevents you

744
00:38:01,480 --> 00:38:04,560
Speaker 2: from overcharging the black hole. This is the way black

745
00:38:04,560 --> 00:38:07,839
Speaker 2: holes prevent you from over spinning themselves with this back

746
00:38:07,920 --> 00:38:10,600
Speaker 2: reaction on stuff you throw in. And then people try

747
00:38:10,600 --> 00:38:13,000
Speaker 2: to be even more clever, like, well, what about internal

748
00:38:13,120 --> 00:38:16,120
Speaker 2: quantum spin? You know what if you like take something

749
00:38:16,160 --> 00:38:19,399
Speaker 2: that has internal quantum spin, like electrons, and you drop

750
00:38:19,480 --> 00:38:22,920
Speaker 2: them straight into the black hole without angular momentum, wouldn't

751
00:38:22,920 --> 00:38:25,080
Speaker 2: that add to the overall spin of the black hole?

752
00:38:25,239 --> 00:38:27,600
Speaker 2: Great idea. So people went off to do the calculations

753
00:38:27,719 --> 00:38:30,520
Speaker 2: and it turns out there are spin spin interactions like

754
00:38:30,520 --> 00:38:32,919
Speaker 2: the spinning of the black hole and the quantum spin

755
00:38:32,960 --> 00:38:36,520
Speaker 2: of this object will induce an interaction between the two things,

756
00:38:36,719 --> 00:38:40,440
Speaker 2: which again will lower the angular momentum of the falling

757
00:38:40,480 --> 00:38:44,560
Speaker 2: in object, avoiding going over the threshold. So the summary

758
00:38:44,640 --> 00:38:47,440
Speaker 2: is that we know of no way to overspin a

759
00:38:47,560 --> 00:38:51,160
Speaker 2: black hole. We currently think it might be impossible again

760
00:38:51,400 --> 00:38:54,640
Speaker 2: not impossible for it to exist as an overspun object.

761
00:38:54,760 --> 00:38:57,120
Speaker 2: To break this limit, we just don't know how to

762
00:38:57,120 --> 00:38:57,800
Speaker 2: make it happen.

763
00:38:58,120 --> 00:39:01,239
Speaker 1: Man, that really does seem like the black hole is

764
00:39:01,480 --> 00:39:06,120
Speaker 1: just trying to frustrate particle physicists like you.

765
00:39:07,560 --> 00:39:09,080
Speaker 2: It doesn't take a lot. You're just going to have

766
00:39:09,120 --> 00:39:11,440
Speaker 2: the secrets of the universe and hide them from us.

767
00:39:13,000 --> 00:39:17,160
Speaker 1: So I'm also curious to find out because we've talked

768
00:39:17,200 --> 00:39:21,399
Speaker 1: about how black holes have a maximum speed limit that

769
00:39:21,640 --> 00:39:26,399
Speaker 1: the black hole Highway patrol manages to keep in check

770
00:39:26,560 --> 00:39:31,120
Speaker 1: through these radiation, these spin spin interactions. But I'm also

771
00:39:31,239 --> 00:39:34,040
Speaker 1: curious if there is a minimum speed limit for a

772
00:39:34,040 --> 00:39:36,160
Speaker 1: black hole, if a black hole could get away with

773
00:39:36,280 --> 00:39:39,680
Speaker 1: not spinning. But maybe first we should take a quick

774
00:39:39,719 --> 00:39:42,879
Speaker 1: break to make sure that we don't get ticketed by

775
00:39:42,960 --> 00:39:58,520
Speaker 1: the black hole police. So we are back and we

776
00:39:58,560 --> 00:40:03,319
Speaker 1: are keeping this podcast under the speed limit. But as

777
00:40:03,320 --> 00:40:05,879
Speaker 1: we know, with speed limits, it's possible to go too

778
00:40:06,040 --> 00:40:09,880
Speaker 1: slow on a highway, people get mad. So is this

779
00:40:10,000 --> 00:40:13,319
Speaker 1: the same thing with black holes? Do they hack to

780
00:40:13,400 --> 00:40:17,840
Speaker 1: spin or can they just laze around and stay still.

781
00:40:18,040 --> 00:40:20,200
Speaker 2: It's a great question because most of the description of

782
00:40:20,239 --> 00:40:22,920
Speaker 2: black holes you hear about out there are these very simple,

783
00:40:23,000 --> 00:40:27,040
Speaker 2: short style black holes, just stuff in space with massive

784
00:40:27,080 --> 00:40:30,200
Speaker 2: gravity and not even talking about the spin, and that's

785
00:40:30,200 --> 00:40:32,560
Speaker 2: the sort of like generic description of a black hole.

786
00:40:32,880 --> 00:40:34,600
Speaker 2: But if you go out there and look for stuff

787
00:40:34,640 --> 00:40:38,040
Speaker 2: in space, there's basically nothing that isn't spinning. Right, Everything

788
00:40:38,160 --> 00:40:42,360
Speaker 2: in space is spinning. There was inherent angular momentum too stuff,

789
00:40:42,640 --> 00:40:45,680
Speaker 2: and that can't go away, and so stuff keeps spinning.

790
00:40:46,080 --> 00:40:48,680
Speaker 2: So it really makes no sense to imagine a huge,

791
00:40:48,840 --> 00:40:51,520
Speaker 2: massive object with all of this stuff thrown into it,

792
00:40:51,800 --> 00:40:56,600
Speaker 2: somehow perfectly balanced between positive and negative angle momentum so

793
00:40:56,640 --> 00:41:00,080
Speaker 2: that it doesn't spin. It's like flipping a billion coins

794
00:41:00,120 --> 00:41:03,799
Speaker 2: and getting exactly one half of them heads and exactly

795
00:41:03,840 --> 00:41:06,480
Speaker 2: one half of them tails. That's what you would need.

796
00:41:06,520 --> 00:41:09,200
Speaker 2: So it's not impossible for a black hole to have

797
00:41:09,239 --> 00:41:14,239
Speaker 2: no spin. It's just extraordinarily improbable. It's like an enormous

798
00:41:14,280 --> 00:41:16,480
Speaker 2: pencil balanced on its very tip forever.

799
00:41:16,800 --> 00:41:19,440
Speaker 1: I guess that's a little bit scary. The idea of

800
00:41:19,480 --> 00:41:24,640
Speaker 1: a black hole that's perfectly imbalanced, somehow defying probability and

801
00:41:24,760 --> 00:41:27,160
Speaker 1: just still kind of sucking things in it.

802
00:41:27,080 --> 00:41:29,720
Speaker 2: Is pretty weird. And black holes are weird and powerful objects.

803
00:41:29,760 --> 00:41:31,640
Speaker 2: And all the ones that we've seen out there in

804
00:41:31,719 --> 00:41:34,520
Speaker 2: space are spinning. We can tell they're spinning because the

805
00:41:34,600 --> 00:41:37,880
Speaker 2: stuff around them is spinning. Like the black hole picture

806
00:41:37,920 --> 00:41:40,160
Speaker 2: that we've seen, what we're actually looking at when we

807
00:41:40,200 --> 00:41:42,760
Speaker 2: look at that picture is not the black hole itself.

808
00:41:42,880 --> 00:41:44,759
Speaker 2: There's like a blank spot in the middle where the

809
00:41:44,800 --> 00:41:47,319
Speaker 2: black holes like not giving off any light. What we're

810
00:41:47,320 --> 00:41:50,160
Speaker 2: looking at is like the Crispy Kream donut of stuff

811
00:41:50,239 --> 00:41:53,440
Speaker 2: around the black hole that's falling in, and that stuff

812
00:41:53,520 --> 00:41:56,480
Speaker 2: is glowing. It's so hot because of the tidal forces,

813
00:41:56,520 --> 00:41:59,840
Speaker 2: the frictional gravity of the black hole, rubbing and squeezing

814
00:41:59,840 --> 00:42:02,920
Speaker 2: all that stuff as it orbits, the swishing around the

815
00:42:02,920 --> 00:42:05,760
Speaker 2: black hole before it actually gets flushed down this cosmic

816
00:42:05,800 --> 00:42:08,399
Speaker 2: toilet bowl. And every black hole that we've ever seen

817
00:42:08,719 --> 00:42:11,880
Speaker 2: has this very strong spin to the stuff around it,

818
00:42:11,920 --> 00:42:13,680
Speaker 2: which means that it is also spinning.

819
00:42:13,880 --> 00:42:17,200
Speaker 1: I mean, you did scold me about needing a snack

820
00:42:17,280 --> 00:42:20,160
Speaker 1: before the show, and then you describe the stuff around

821
00:42:20,239 --> 00:42:24,359
Speaker 1: a black hole as Krispy Kreme donut getting mixed messages here,

822
00:42:24,400 --> 00:42:26,439
Speaker 1: and then you described it as like a toilet bowl,

823
00:42:26,480 --> 00:42:30,640
Speaker 1: so getting really mixed messages here. So we have measured

824
00:42:31,000 --> 00:42:33,399
Speaker 1: things around a black hole. How do we do that?

825
00:42:33,600 --> 00:42:36,080
Speaker 2: Yeah, that's a great question. One thing we can do

826
00:42:36,239 --> 00:42:39,120
Speaker 2: is look at the orbits of stars around the black

827
00:42:39,120 --> 00:42:43,440
Speaker 2: hole like in other galaxies. We can't resolve individual stars,

828
00:42:43,480 --> 00:42:46,680
Speaker 2: but we can tell how fast stars are spinning. We

829
00:42:46,680 --> 00:42:49,360
Speaker 2: can look at like the velocity of streams of stars.

830
00:42:49,360 --> 00:42:52,160
Speaker 2: We can't make out the individual ones, especially near the

831
00:42:52,200 --> 00:42:54,879
Speaker 2: centers of those other galaxies, but we can tell how

832
00:42:54,920 --> 00:42:56,799
Speaker 2: fast they're moving because of the red shift, and we

833
00:42:56,800 --> 00:42:59,120
Speaker 2: can tell the density, and so we can infer the

834
00:42:59,160 --> 00:43:02,879
Speaker 2: presence of these super massive black holes in other galaxies.

835
00:43:03,200 --> 00:43:06,080
Speaker 2: And sometimes we can directly see the effect of spin

836
00:43:06,360 --> 00:43:09,200
Speaker 2: on the stuff around it, Like if the black hole

837
00:43:09,280 --> 00:43:12,359
Speaker 2: is spinning, it changes like how close stuff can get

838
00:43:12,440 --> 00:43:14,640
Speaker 2: to the black hole, and it also changes how that

839
00:43:14,680 --> 00:43:17,680
Speaker 2: stuff is spun. There was one case where we saw

840
00:43:17,800 --> 00:43:21,280
Speaker 2: two black holes orbiting each other. So like a really

841
00:43:21,320 --> 00:43:25,080
Speaker 2: big black hole called OJ two nine seven. It has

842
00:43:25,120 --> 00:43:29,440
Speaker 2: like almost nineteen billion solar masses, one of the biggest

843
00:43:29,440 --> 00:43:32,520
Speaker 2: black holes out there that we know about. It's orbited

844
00:43:32,560 --> 00:43:35,080
Speaker 2: by another black hole that has just like one hundred

845
00:43:35,080 --> 00:43:39,200
Speaker 2: and fifty million solar masses. I mean, already a gigantic object,

846
00:43:39,200 --> 00:43:42,000
Speaker 2: but tiny in comparison to the big Mama black hole

847
00:43:42,000 --> 00:43:44,800
Speaker 2: it's orbiting, and the orbit of this smaller black hole

848
00:43:44,960 --> 00:43:48,160
Speaker 2: is processing. Imagine like an elliptical orbit, not a perfect circle,

849
00:43:48,400 --> 00:43:50,800
Speaker 2: but the smaller black hole is moving around in an ellipse,

850
00:43:50,920 --> 00:43:53,800
Speaker 2: and ellips is like an elongated circle. Well, the direction

851
00:43:53,920 --> 00:43:56,600
Speaker 2: of the elongation is changing as the little black hole

852
00:43:56,719 --> 00:43:59,200
Speaker 2: orbits the big black hole. This is like the spin

853
00:43:59,360 --> 00:44:01,960
Speaker 2: of the orbit of the little black hole around the

854
00:44:02,000 --> 00:44:05,720
Speaker 2: big black hole, and the procession of that orbit tells

855
00:44:05,800 --> 00:44:08,520
Speaker 2: us something about the spin of the big black hole

856
00:44:08,920 --> 00:44:11,840
Speaker 2: because its spin is contributing to that procession.

857
00:44:12,040 --> 00:44:15,120
Speaker 1: That's crazy. I mean first of all that a big

858
00:44:15,160 --> 00:44:18,600
Speaker 1: black hole can suck up a littler black hole, but

859
00:44:18,719 --> 00:44:22,920
Speaker 1: also just that you can see that change in movement

860
00:44:23,280 --> 00:44:26,440
Speaker 1: that would only be possible given sort of the spin

861
00:44:27,200 --> 00:44:30,439
Speaker 1: of the bigger black hole. Can we actually measure how

862
00:44:30,520 --> 00:44:34,560
Speaker 1: fast the big Mama black hole is spinning given the

863
00:44:34,760 --> 00:44:36,640
Speaker 1: procession of the smaller black hole.

864
00:44:36,880 --> 00:44:39,200
Speaker 2: Yeah, we can, Actually, we can make a calculation, and

865
00:44:39,239 --> 00:44:42,440
Speaker 2: the surface of that black hole is moving at almost

866
00:44:42,480 --> 00:44:47,880
Speaker 2: sixty thousand kilometers per second, which is like twenty percent

867
00:44:48,120 --> 00:44:51,440
Speaker 2: of the speed of light. Sort of amazing. Now, this

868
00:44:51,520 --> 00:44:54,520
Speaker 2: thing is so big though, it's radius is so huge.

869
00:44:54,640 --> 00:44:57,840
Speaker 2: It's like three hundred and sixty au it's the distance

870
00:44:57,880 --> 00:45:00,319
Speaker 2: between the Earth and the Sun. It's so large. Even

871
00:45:00,320 --> 00:45:02,120
Speaker 2: though it's moving to twenty percent of the speed of light,

872
00:45:02,160 --> 00:45:06,400
Speaker 2: it still takes five million seconds to complete one spin.

873
00:45:06,600 --> 00:45:09,400
Speaker 2: So it's such a big bear that it still takes

874
00:45:09,400 --> 00:45:11,520
Speaker 2: a huge amount of time to spin once.

875
00:45:12,040 --> 00:45:16,800
Speaker 1: Five million seconds is how many years?

876
00:45:17,120 --> 00:45:20,120
Speaker 2: Five million seconds is like sixteen percent of a year.

877
00:45:20,400 --> 00:45:24,640
Speaker 1: Okay. I can't think in seconds, so that's like two months.

878
00:45:24,719 --> 00:45:26,520
Speaker 2: So this thing is spinning at twenty percent of the

879
00:45:26,520 --> 00:45:29,840
Speaker 2: speed of light, still takes two months to complete one spin.

880
00:45:30,239 --> 00:45:34,200
Speaker 1: Okay. Because my perception of seconds are different. Like when

881
00:45:34,200 --> 00:45:37,000
Speaker 1: I'm in this podcast, they go by very fast because

882
00:45:37,040 --> 00:45:41,359
Speaker 1: I'm really interested. If I'm waiting for a bus to come,

883
00:45:41,480 --> 00:45:43,320
Speaker 1: the seconds are very long.

884
00:45:43,520 --> 00:45:46,960
Speaker 2: But there's another black hole that's spinning even faster. This

885
00:45:47,000 --> 00:45:50,120
Speaker 2: one is really small. It has only two million solar masses.

886
00:45:50,400 --> 00:45:54,439
Speaker 2: It's NNGC thirteen sixty five. But the cool thing about

887
00:45:54,440 --> 00:45:56,560
Speaker 2: this black hole is it doesn't have like a baby

888
00:45:56,600 --> 00:45:58,520
Speaker 2: black hole orbiting it, but it's close enough that we

889
00:45:58,520 --> 00:46:00,880
Speaker 2: can study the accretion disc in great detail.

890
00:46:01,120 --> 00:46:04,200
Speaker 1: Is the accretion disc the stuff that is caught up

891
00:46:04,480 --> 00:46:05,680
Speaker 1: circling the black hole.

892
00:46:06,200 --> 00:46:08,400
Speaker 2: It's the stuff that's on deck about to go into

893
00:46:08,400 --> 00:46:10,600
Speaker 2: the black hole. It's like falling in, but because it

894
00:46:10,600 --> 00:46:13,560
Speaker 2: has angular momentum, it just doesn't fall straight in the

895
00:46:13,600 --> 00:46:15,600
Speaker 2: same way like the Earth doesn't just fall into the

896
00:46:15,640 --> 00:46:18,560
Speaker 2: Sun because of the Sun's gravity it's in orbit. This

897
00:46:18,600 --> 00:46:21,279
Speaker 2: stuff also has angular momentum, which slows it down, which

898
00:46:21,280 --> 00:46:24,080
Speaker 2: prevents it from falling immediately in. It has to like

899
00:46:24,200 --> 00:46:26,759
Speaker 2: radiate away some of its energy in order to fall in.

900
00:46:27,120 --> 00:46:29,840
Speaker 2: So inside the accretion disk, this stuff is like bumping

901
00:46:29,880 --> 00:46:32,800
Speaker 2: and grinding and glowing, giving off some of its energy

902
00:46:33,200 --> 00:46:35,839
Speaker 2: just before it falls into the black hole. And so

903
00:46:35,880 --> 00:46:39,320
Speaker 2: by studying what's happening inside that accretion disc, it's like

904
00:46:39,360 --> 00:46:41,839
Speaker 2: a probe for what the gravity of the black hole

905
00:46:41,920 --> 00:46:44,000
Speaker 2: is doing to it. We can understand the tidle force

906
00:46:44,080 --> 00:46:46,760
Speaker 2: is the strength of the gravity and also the effect

907
00:46:46,880 --> 00:46:49,440
Speaker 2: of the spin, because the spin of the black hole

908
00:46:49,600 --> 00:46:52,960
Speaker 2: changes like how close the accretion disc can get to

909
00:46:53,040 --> 00:46:53,920
Speaker 2: the event horizon.

910
00:46:54,320 --> 00:46:58,359
Speaker 1: So, if it's spinning faster, can the accretion disk get

911
00:46:58,440 --> 00:47:00,040
Speaker 1: closer to the event.

912
00:47:00,640 --> 00:47:03,360
Speaker 2: Yes, exactly. If it's spinning the same way as the

913
00:47:03,400 --> 00:47:05,839
Speaker 2: accretion disc, then the accretion disc can get very very

914
00:47:05,840 --> 00:47:08,680
Speaker 2: close to the black hole without actually falling in. Whereas

915
00:47:08,719 --> 00:47:10,839
Speaker 2: if the accretion disc is spinning one way the black

916
00:47:10,840 --> 00:47:13,160
Speaker 2: hole is spinning the other way, then you end up

917
00:47:13,160 --> 00:47:15,799
Speaker 2: with this like weird gap between the black hole and

918
00:47:15,840 --> 00:47:18,279
Speaker 2: the accretion disc where stuff in that gap can't exist

919
00:47:18,320 --> 00:47:20,600
Speaker 2: because it would just fall immediately into the black hole.

920
00:47:20,680 --> 00:47:22,560
Speaker 2: But if they're spinning together, then the spin of the

921
00:47:22,560 --> 00:47:25,520
Speaker 2: black hole like accentuates the spin of the accretion disc

922
00:47:25,840 --> 00:47:27,960
Speaker 2: and it helps it spin faster. It can actually get

923
00:47:27,960 --> 00:47:30,759
Speaker 2: closer in before falling into the black hole. So by

924
00:47:30,760 --> 00:47:32,719
Speaker 2: looking at like the size of the gap between the

925
00:47:32,719 --> 00:47:35,359
Speaker 2: event horizon and the start of the accretion disk, they

926
00:47:35,400 --> 00:47:38,880
Speaker 2: can measure the rate of spin of the black hole itself.

927
00:47:38,920 --> 00:47:41,840
Speaker 2: And this guy is spinning at eighty five percent of

928
00:47:41,920 --> 00:47:45,400
Speaker 2: the maximum rate allowed for this mass black hole.

929
00:47:45,760 --> 00:47:49,839
Speaker 1: Man, he's got like the universe police kind of following him.

930
00:47:49,840 --> 00:47:52,160
Speaker 1: They haven't put their lights on yet, but they're keeping

931
00:47:52,160 --> 00:47:53,399
Speaker 1: an eye on them.

932
00:47:53,800 --> 00:47:56,360
Speaker 2: Exactly, And so this is fascinating, Like, Wow, this guy's

933
00:47:56,600 --> 00:48:00,480
Speaker 2: close to an overspun black hole. Be really interesting to

934
00:48:00,520 --> 00:48:02,680
Speaker 2: watch as that stuff falls in, to see like, is

935
00:48:02,719 --> 00:48:05,560
Speaker 2: it's beating up? Does it gradually approach ninety nine point

936
00:48:05,680 --> 00:48:08,560
Speaker 2: nine nine nine percent? Or are we wrong about how

937
00:48:08,560 --> 00:48:11,399
Speaker 2: black holes can't be overspun and maybe this one will

938
00:48:11,440 --> 00:48:14,560
Speaker 2: actually get cracked open, maybe that stuff will fall in

939
00:48:14,760 --> 00:48:16,520
Speaker 2: and erase the event horizon.

940
00:48:16,719 --> 00:48:20,080
Speaker 1: We better keep an eye on it also, because the

941
00:48:20,360 --> 00:48:23,239
Speaker 1: faster it spins, the closer you can get to the

942
00:48:23,280 --> 00:48:26,680
Speaker 1: event horizon without falling in, Daniel, is this the kind

943
00:48:26,680 --> 00:48:28,799
Speaker 1: of black hole that you would want to travel to

944
00:48:29,080 --> 00:48:32,040
Speaker 1: and try to sort of drop some sonar into the

945
00:48:32,040 --> 00:48:33,160
Speaker 1: middle of the black hole?

946
00:48:33,320 --> 00:48:35,520
Speaker 2: I mean, I don't even travel the conferences anymore. There's

947
00:48:35,600 --> 00:48:37,640
Speaker 2: no way that I'm going to visit a black hole.

948
00:48:37,760 --> 00:48:40,759
Speaker 2: Absolutely not. I am too old for that. But I'm

949
00:48:40,840 --> 00:48:44,799
Speaker 2: very happy to send up you know, co hosts, guest hosts,

950
00:48:44,880 --> 00:48:46,800
Speaker 2: all these kind of people who would happily volunteer.

951
00:48:47,000 --> 00:48:50,800
Speaker 1: It's an interesting pool of people. You'd be okay sending

952
00:48:50,880 --> 00:48:53,000
Speaker 1: to a black hole as long as you bring.

953
00:48:52,840 --> 00:48:54,560
Speaker 2: Your travel mike and tell us what you're learning as

954
00:48:54,560 --> 00:48:55,040
Speaker 2: you fall in.

955
00:48:55,280 --> 00:48:57,440
Speaker 1: Yeah. I do have a good wind screen on it,

956
00:48:57,520 --> 00:48:59,000
Speaker 1: so it should still come through clear.

957
00:48:59,120 --> 00:49:00,680
Speaker 2: But you know, I think the less to take away

958
00:49:00,680 --> 00:49:04,600
Speaker 2: from this is that space is so much weirder than

959
00:49:04,640 --> 00:49:07,560
Speaker 2: we thought it was. Even the idea of space being

960
00:49:07,640 --> 00:49:12,000
Speaker 2: bent into curves by mass is weirder than Newton thought of.

961
00:49:12,400 --> 00:49:14,839
Speaker 2: But there's so much more to it than just that

962
00:49:15,239 --> 00:49:18,320
Speaker 2: space is not just bent into curves. It's also spun.

963
00:49:18,560 --> 00:49:23,160
Speaker 2: It's flowing like a fluid around very massive objects, dragged

964
00:49:23,200 --> 00:49:26,880
Speaker 2: along with them like a fork twirling that spaghetti. And

965
00:49:26,920 --> 00:49:29,680
Speaker 2: that changes the way that black holes operate. The event

966
00:49:29,719 --> 00:49:32,240
Speaker 2: horizon of a black hole is not just a function

967
00:49:32,360 --> 00:49:34,920
Speaker 2: of its mass. It's also a function of its spin

968
00:49:35,360 --> 00:49:36,920
Speaker 2: and its electric charge.

969
00:49:37,120 --> 00:49:40,959
Speaker 1: I feel like this is a great personality test of

970
00:49:41,239 --> 00:49:44,680
Speaker 1: who wants to see the black hole over spin and

971
00:49:44,719 --> 00:49:48,400
Speaker 1: break apart and maybe break the universe? And who would

972
00:49:48,440 --> 00:49:51,640
Speaker 1: like the black hole to not break apart and keep

973
00:49:51,680 --> 00:49:52,320
Speaker 1: things safe?

974
00:49:52,440 --> 00:49:54,640
Speaker 2: Oh my god, who would be in that second category?

975
00:49:54,640 --> 00:49:56,640
Speaker 2: Who would not want the black hole to wreak the

976
00:49:56,680 --> 00:50:02,880
Speaker 2: rules the universe? Who we've been talking about here, not me?

977
00:50:04,400 --> 00:50:07,200
Speaker 2: Remember that seeing the universe break the rules, it's not

978
00:50:07,239 --> 00:50:10,840
Speaker 2: a failure, it's not a problem, it's an opportunity. Those

979
00:50:10,880 --> 00:50:12,880
Speaker 2: are the moments when we learn what the real rules

980
00:50:12,880 --> 00:50:14,799
Speaker 2: of the universe are. The universe is out there, we

981
00:50:14,840 --> 00:50:17,160
Speaker 2: think following some set of rules, and we have in

982
00:50:17,200 --> 00:50:20,560
Speaker 2: our heads some internal description of that, a model of

983
00:50:20,600 --> 00:50:23,440
Speaker 2: how we think the universe works, and when those two

984
00:50:23,520 --> 00:50:26,200
Speaker 2: things clash, that's when we get to update our list.

985
00:50:26,239 --> 00:50:28,520
Speaker 2: Were like, oh, turns out we were wrong about what's

986
00:50:28,520 --> 00:50:31,480
Speaker 2: going on over here. Let's fix things. But we need

987
00:50:31,520 --> 00:50:34,040
Speaker 2: those clues sometimes, we need the universe to show us

988
00:50:34,080 --> 00:50:37,000
Speaker 2: what's wrong with our understanding of how it works by

989
00:50:37,040 --> 00:50:40,920
Speaker 2: contradicting our predictions. And so if we see the universe

990
00:50:41,000 --> 00:50:43,480
Speaker 2: breaking the rules that we thought, it's not a failure.

991
00:50:43,560 --> 00:50:46,759
Speaker 2: It's a huge leap forward. It's an open door to

992
00:50:46,800 --> 00:50:49,840
Speaker 2: a deeper understanding of how the universe actually works.

993
00:50:50,080 --> 00:50:53,080
Speaker 1: Well, kids, you heard Daniel. You gotta break rules to

994
00:50:53,160 --> 00:50:55,000
Speaker 1: learn exactly.

995
00:50:55,080 --> 00:50:58,840
Speaker 2: Unfortunately, it seems like black holes are fortresses of knowledge.

996
00:50:59,040 --> 00:51:01,480
Speaker 2: Not only do they have these event horizons that keep

997
00:51:01,560 --> 00:51:05,560
Speaker 2: us from seeing what happens at extraordinarily extreme circumstances, but

998
00:51:05,640 --> 00:51:09,080
Speaker 2: also there very wildly at protecting those event horizons. You

999
00:51:09,120 --> 00:51:12,280
Speaker 2: thought you could overcharge a black hole, it repels your idea.

1000
00:51:12,520 --> 00:51:15,040
Speaker 2: You thought you could overspin a black hole. It's got

1001
00:51:15,080 --> 00:51:17,680
Speaker 2: its own spin doctors to keep you from doing it. So,

1002
00:51:17,800 --> 00:51:19,879
Speaker 2: for now, at least, we don't know how to crack

1003
00:51:19,960 --> 00:51:21,040
Speaker 2: open a black hole.

1004
00:51:21,200 --> 00:51:23,360
Speaker 1: We need a rogue black hole, a maverick.

1005
00:51:23,520 --> 00:51:25,520
Speaker 2: We need to put a black hole in witness protection.

1006
00:51:27,960 --> 00:51:29,120
Speaker 1: What would that even look like?

1007
00:51:29,560 --> 00:51:32,319
Speaker 2: Put a black hole inside another black hole? I don't know,

1008
00:51:32,440 --> 00:51:35,600
Speaker 2: we'll ask the SBI. Well, thanks very much everybody for

1009
00:51:35,640 --> 00:51:39,240
Speaker 2: going on this journey inside the mysteries of the universe,

1010
00:51:39,320 --> 00:51:41,759
Speaker 2: wondering what's going on inside a black hole and how

1011
00:51:41,800 --> 00:51:45,080
Speaker 2: we could ever know and whether we ever will. And

1012
00:51:45,120 --> 00:51:48,000
Speaker 2: thanks very much Katie for taking this crazy physics tour

1013
00:51:48,080 --> 00:51:49,520
Speaker 2: and breaking all the rules with us.

1014
00:51:49,760 --> 00:51:52,360
Speaker 1: Thank you for not shooting me into the center of

1015
00:51:52,400 --> 00:51:52,960
Speaker 1: a black.

1016
00:51:52,719 --> 00:51:56,959
Speaker 2: Hole, not yet, at least stay tuned. Thanks everyone, tune

1017
00:51:57,000 --> 00:52:07,360
Speaker 2: in next time. Thanks for listening, and remember that Daniel

1018
00:52:07,400 --> 00:52:10,840
Speaker 2: and Jorge Explain the Universe is a production of iHeartRadio.

1019
00:52:11,120 --> 00:52:16,239
Speaker 2: For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,

1020
00:52:16,400 --> 00:52:18,760
Speaker 2: or wherever you listen to your favorite shows.