Latest / Daniel and Kelly’s Extraordinary Universe / What happens to event horizons when black holes collide?

Transcript

What happens to event horizons when black holes collide? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, I have a question about smashing things together. Oh, well,
• 0:11
  Speaker 1: you came to the right place. I know you're a
• 0:14
  Speaker 1: professional smasher. I guess I'm actually wondering if it's the
• 0:17
  Speaker 1: right way to study things. I don't know, I mean,
• 0:20
  Speaker 1: what could go wrong? I mean, does it work for everything?
• 0:23
  Speaker 1: Like let's say you're trying out a new restaurants. Smashing
• 0:26
  Speaker 1: two plates together really the best way to test it?
• 0:29
  Speaker 1: I mean I would read that restaurant review, wouldn't you?
• 0:32
  Speaker 1: Or what about movies? Like you would smash Blu Ray
• 0:34
  Speaker 1: disc together. Maybe that's how they came up with awesome
• 0:38
  Speaker 1: crossover events. I mean, that's the origin of the Marvel multiverse.
• 0:43
  Speaker 1: Somebody had a stack of DVDs on their coffee table
• 0:45
  Speaker 1: and eureka, somebody smashed two comic books together, or a
• 0:48
  Speaker 1: comic book with a Blu Ray. There you go, that's
• 0:50
  Speaker 1: what happened. Smash to Hollywood actors together. Hi. I'm or Hamry,
• 1:09
  Speaker 1: cartoonists and the co author of Frequently Asked Questions about
• 1:12
  Speaker 1: the Universe. Hi, I'm Daniel. I'm a particle physicist and
• 1:15
  Speaker 1: a professor at U C Irvine, and I'm the other
• 1:17
  Speaker 1: co author of frequently asked questions about the universe. What
• 1:21
  Speaker 1: what a coincidence? What are the chances that we would
• 1:23
  Speaker 1: collide on a podcast like this? What happens when you
• 1:26
  Speaker 1: smash two co authors together? Do you get one big author?
• 1:30
  Speaker 1: You can? Do you get a voltron author? Maybe? Can
• 1:33
  Speaker 1: I be like left foot jokes aside? You get a
• 1:36
  Speaker 1: really fun book that neither of us could have written
• 1:38
  Speaker 1: on our own, filled with amazing physics insides, deep revelations
• 1:42
  Speaker 1: about the nature of the universe, and hilarious cartoons. Yeah.
• 1:47
  Speaker 1: It tackles really amazing and frequent questions about the universe,
• 1:50
  Speaker 1: like why we can't get to other stars? Or is
• 1:53
  Speaker 1: there an afterlife possible in this universe? Or why Daniel
• 1:56
  Speaker 1: doesn't believe in time travel? Wait? You don't believe in time? Terrible?
• 2:00
  Speaker 1: Didn't you read the book? Man, I'm gonna have to
• 2:05
  Speaker 1: go back in time and read it. It's too late.
• 2:07
  Speaker 1: You're out of time. I ran out of time, that's why.
• 2:11
  Speaker 1: But anyways, welcome to our podcast, Daniel and Jorge Explain
• 2:13
  Speaker 1: the Universe, a production of My Heart Radio in which
• 2:16
  Speaker 1: we smash up the two most amazing things in the universe,
• 2:19
  Speaker 1: your brain and the entire universe. We try to take
• 2:23
  Speaker 1: everything that's out there, all the craziness, the insanity, the
• 2:26
  Speaker 1: frothing quantum mess that is our reality, and squeeze all
• 2:30
  Speaker 1: of it into your brain because we believe in you.
• 2:33
  Speaker 1: We believe that your beautiful brain, even though with a
• 2:36
  Speaker 1: tiny part of the universe, can contain within it a
• 2:39
  Speaker 1: whole idea of the universe that we can look out
• 2:42
  Speaker 1: into the depths of space and actually understand what's going
• 2:46
  Speaker 1: on out there. On the podcast, we talk about everything
• 2:49
  Speaker 1: that's happening out there and explain all of it to you.
• 2:52
  Speaker 1: That's right. We smashed together scientific ideas and discoveries and
• 2:55
  Speaker 1: collide them with bad puns and a lot of conversation
• 3:00
  Speaker 1: here in order to pick up the pieces and hopefully
• 3:03
  Speaker 1: makes sense of this amazing and wonderful cosmos that we
• 3:06
  Speaker 1: live in. And you give me a hard time for
• 3:08
  Speaker 1: it sometimes, but I really do think that smashing stuff
• 3:10
  Speaker 1: together is really the best way to understand it. I mean, like,
• 3:13
  Speaker 1: who hasn't tried a sample of their neighbor's plate at
• 3:16
  Speaker 1: the table right and mixed it with their own dinner
• 3:18
  Speaker 1: to create something new? Oh? Wow? Do you ask for
• 3:22
  Speaker 1: their permission for us? Though? At least. I mean, usually
• 3:24
  Speaker 1: it's somebody in my family. So yes, I'm reaching over
• 3:27
  Speaker 1: to my wife's plate to try a French fry and
• 3:29
  Speaker 1: dip it in whatever sauces on my plate, and you
• 3:31
  Speaker 1: never know that could have been a culinary invention that
• 3:34
  Speaker 1: rocked the world. It just seems a little, you know,
• 3:36
  Speaker 1: sort of a destructive way of studying the universe. You know,
• 3:39
  Speaker 1: I'm more of an engineering type. I'd like to take
• 3:41
  Speaker 1: things apart, not smashing together. That's because you care about
• 3:44
  Speaker 1: putting them back together. I just want to know what's
• 3:46
  Speaker 1: going on inside. Well, I mean, doesn't it seem a
• 3:51
  Speaker 1: little destructive in a way, like you know, it's sort
• 3:53
  Speaker 1: of like a little kid which smashes things out of anger.
• 3:56
  Speaker 1: It is destructive, absolutely, but you know, sometimes that's all
• 3:59
  Speaker 1: you can do. Joking aside, If you have a toaster, yes,
• 4:02
  Speaker 1: you can take it apart carefully, piece by piece and
• 4:04
  Speaker 1: catalog what's inside it. And that probably is a better
• 4:07
  Speaker 1: way to understand how a toaster works than taking two
• 4:10
  Speaker 1: toasters and making a toaster collider. But sometimes the forces
• 4:13
  Speaker 1: that hold these things together are so strong and that
• 4:16
  Speaker 1: the only way to break it up to understand what's
• 4:18
  Speaker 1: going on inside is to smash it up. And that's
• 4:21
  Speaker 1: the case for example, with protons. But have you actually look.
• 4:24
  Speaker 1: Maybe there's a screwdriver for protons. You need to get
• 4:27
  Speaker 1: the right one with the right you know shape. Yeah,
• 4:29
  Speaker 1: the screw driver for protons is another proton. I guess
• 4:32
  Speaker 1: it's more like a hammer than a screw driver. But
• 4:34
  Speaker 1: then what is that screw driver made out of? Daniel? Exactly?
• 4:39
  Speaker 1: That's the only tool you have. If everything in the
• 4:41
  Speaker 1: universe is a proton, then basically you're just smashing protons together. Wait,
• 4:45
  Speaker 1: doesn't everything eventually fall apart or break apart? Can you
• 4:48
  Speaker 1: just wait for things to you know, break open? I
• 4:50
  Speaker 1: mean I have grand deadlines, and you know, I gotta
• 4:53
  Speaker 1: get stuff done. I can't just wait till the heat
• 4:55
  Speaker 1: death of the universe when everything collapses. I see, it's
• 4:57
  Speaker 1: a lack of patients, not a lack of or methods.
• 5:00
  Speaker 1: You're encouraging procrastination to the heat death of the universe. Right,
• 5:03
  Speaker 1: that's really on brand for there you go, And in
• 5:06
  Speaker 1: the meantime, the grant could support you. Right, that's right.
• 5:09
  Speaker 1: I'm going to write a grant for waiting for ten
• 5:11
  Speaker 1: to the fourteen years until the universe. Does it experiments
• 5:14
  Speaker 1: for me? We'll see how that goes. I'll cut you
• 5:17
  Speaker 1: and if it gets funded. Yeah, as long as it's
• 5:19
  Speaker 1: for ten to the fourteen dollars, I'm totally in no.
• 5:22
  Speaker 1: But the smashing things together does seem to be the
• 5:24
  Speaker 1: preferred way. Physicists like to explore things at the smallest
• 5:28
  Speaker 1: levels because there is no screwdriver for opening things like
• 5:31
  Speaker 1: protons or even courts. There is no screwdriver, there are
• 5:34
  Speaker 1: no tweezers, and it's something that we can actually do.
• 5:37
  Speaker 1: We can manipulate protons, we can tune their energy, we
• 5:40
  Speaker 1: can smash them together to see what's going on inside.
• 5:43
  Speaker 1: And the same thing is true for even bigger stuff.
• 5:45
  Speaker 1: We can't take stars apart. We don't have the machinery
• 5:48
  Speaker 1: to understand what's inside a planet, So the best way
• 5:50
  Speaker 1: to learn about it is to watch collisions of enormous
• 5:54
  Speaker 1: astronomical objects to see what's going on inside. Yeah, I
• 5:58
  Speaker 1: guess sometimes it's hard to take to apart, like you said, right,
• 6:01
  Speaker 1: Like it's hard to take a star apart. That would
• 6:03
  Speaker 1: be pretty difficult. It's pretty hard to take a star apart.
• 6:05
  Speaker 1: It's even hard to look inside a star. We had
• 6:08
  Speaker 1: the Parker Solar Probe recently, which came super close to
• 6:11
  Speaker 1: the Sun and almost fried itself but not quite. And
• 6:14
  Speaker 1: it gives us a picture of what's going on in
• 6:16
  Speaker 1: the surface and helps map a little bit of the insides.
• 6:18
  Speaker 1: But you know, we have questions about what's going on
• 6:21
  Speaker 1: deep deep in the heart of our Sun that we
• 6:23
  Speaker 1: could only really answer by smashing it into another star. Yeah.
• 6:27
  Speaker 1: I guess sometimes it's hard to look inside of the things,
• 6:29
  Speaker 1: so you kind of have to break them apart because
• 6:30
  Speaker 1: they don't open up so easily. And to be honest,
• 6:33
  Speaker 1: an engineer and we do sometimes match things together us
• 6:37
  Speaker 1: until they break. Just trust test them now, don't worry.
• 6:40
  Speaker 1: I don't know how to build a star collider, so
• 6:42
  Speaker 1: I'm not going to shoot Proximus Centauri at our star
• 6:45
  Speaker 1: anytime soon. That's a grand proposal that will never be funded.
• 6:49
  Speaker 1: But we don't have to build these colliders ourselves. We
• 6:52
  Speaker 1: don't have to construct cosmic colliders to smash planets together,
• 6:55
  Speaker 1: because the universe is doing it for us. We just
• 6:58
  Speaker 1: have to look out there into the skies and find
• 7:01
  Speaker 1: the experiment already underway. Yeah, because it is a pretty
• 7:04
  Speaker 1: big universe. And even though it's huge and empty. It's
• 7:07
  Speaker 1: pretty big and pretty full of stuff, And so there's
• 7:10
  Speaker 1: always something going on in the universe, and some things
• 7:13
  Speaker 1: that going on is a big coalition. We have seen
• 7:15
  Speaker 1: comets slam in the planets. We have seen binary stars
• 7:18
  Speaker 1: collapse into each other. We've seen all sorts of crazy
• 7:21
  Speaker 1: stuff smash into itself and learned an incredible amount in
• 7:24
  Speaker 1: the process. Yeah, we've seen galaxy smashed together, right, that's
• 7:28
  Speaker 1: sort of how dark matter was confirmed. Yeah, we can
• 7:31
  Speaker 1: see galaxies merging in the middle of this process of
• 7:33
  Speaker 1: swirling around each other and their stars forming one new
• 7:36
  Speaker 1: elliptical galaxy. And you're right, we've even seen galaxy clusters collide.
• 7:41
  Speaker 1: The Bullet cluster is two big groups of galaxies, enormous
• 7:45
  Speaker 1: piles of galaxies smashing into each other, dark matter coming
• 7:48
  Speaker 1: out on either side, which tells us, as you said,
• 7:51
  Speaker 1: the dark matter is its own thing and not just
• 7:53
  Speaker 1: some weird twist on gravity. Yeah. I guess smashing things
• 7:57
  Speaker 1: together is a good way to explore things, especially if
• 8:00
  Speaker 1: are sort of mysterious and kind of hard to know
• 8:02
  Speaker 1: that they're there or what's going on inside of them. Right,
• 8:05
  Speaker 1: Like smashing things with dark matter in them so it
• 8:07
  Speaker 1: helps you see the dark matter. Yeah, it helps you
• 8:09
  Speaker 1: separate the dark matter from the rest of the stuff
• 8:11
  Speaker 1: because different things smash differently. Right, The gas and the
• 8:14
  Speaker 1: dust in those galaxies smashed into each other, making huge
• 8:18
  Speaker 1: explosions and bright flashes of light, but the dark matter
• 8:21
  Speaker 1: passed right through. So that tells you that dark matter
• 8:23
  Speaker 1: really is different from normal kind of matter. So yeah, absolutely,
• 8:27
  Speaker 1: smashing stuff together a great way to figure out what's
• 8:29
  Speaker 1: going on, great way to support physicists. Would like to
• 8:33
  Speaker 1: smash things as little kids. Yeah, but you know, don't
• 8:35
  Speaker 1: like smash your kids together if you're not sure what
• 8:37
  Speaker 1: they're up to. There is a limit to this idea,
• 8:41
  Speaker 1: seeing well, I think they usually smash themselves pretty good
• 8:45
  Speaker 1: without your help or direction. All right, But in no
• 8:47
  Speaker 1: way am I endorsing kids smashing on the podcast. I
• 8:50
  Speaker 1: don't even know why you would bring it up. I
• 8:53
  Speaker 1: guess you know. I guess kids are mysterious. Also, they're
• 8:55
  Speaker 1: hard to understand. Yes, absolutely, kids are hard to understand.
• 8:58
  Speaker 1: But there are better ways to understand what's going on
• 9:01
  Speaker 1: inside your children then smashing them together, right right. I
• 9:04
  Speaker 1: guess you could talk to them. I guess you could
• 9:07
  Speaker 1: just make references to them on the podcast and hope
• 9:09
  Speaker 1: they listen. Yeah, maybe like twenty years from now, when
• 9:12
  Speaker 1: they're in therapy, they'll be like, what did my father
• 9:15
  Speaker 1: think of me? Oh, it's right here on this podcast.
• 9:18
  Speaker 1: What But anyways, there is something mysterious out there in
• 9:21
  Speaker 1: the universe that we would like to know more about.
• 9:24
  Speaker 1: We would like to know what's going on inside of him,
• 9:26
  Speaker 1: But so far, they are one of the hardest things
• 9:29
  Speaker 1: to look at and figure out. A lot of people
• 9:32
  Speaker 1: write to me and ask what happens when these two
• 9:34
  Speaker 1: mysterious objects in the universe come together? Is it just
• 9:38
  Speaker 1: like other collisions or are some of the fundamental rules
• 9:41
  Speaker 1: of the universe broken? So today on the podcast, we'll
• 9:44
  Speaker 1: be tackling the question what happens when black holes collide?
• 9:53
  Speaker 1: There's a very sensationalist question, I feel, what happens when
• 9:56
  Speaker 1: black holes collide. It's sort of like shark versus shark,
• 10:00
  Speaker 1: which shark eats the other one? You know, one black
• 10:03
  Speaker 1: hole sucking in the other one, these sucking each other.
• 10:05
  Speaker 1: What does that even mean? Man? Yeah, I know, it's
• 10:08
  Speaker 1: like kind of hole fall into another hole, Like, you know,
• 10:11
  Speaker 1: holy moly, that's a complicated question that is a whole
• 10:14
  Speaker 1: lot of holes there in that theory. We need a
• 10:18
  Speaker 1: holistic understanding of how this works. But this is sort
• 10:22
  Speaker 1: of part of our I guess a recent theme we've
• 10:24
  Speaker 1: had going on in the podcast. We can almost call
• 10:26
  Speaker 1: it like Smash month or smash week exactly. We got
• 10:30
  Speaker 1: smashing on the brain over here at the podcast headquarters.
• 10:33
  Speaker 1: Hopefully will be a smashing success. But we have been
• 10:36
  Speaker 1: smashing things together. We smashed photons together last time, and
• 10:39
  Speaker 1: we smashed what else do we smash? We did a
• 10:40
  Speaker 1: whole listener episodes question about smashing stuff together. That was
• 10:44
  Speaker 1: the theme annihilation questions. And then we smash light together,
• 10:48
  Speaker 1: which turns out you can't smash together. And now we're
• 10:51
  Speaker 1: smashing black holes. What's next, Danuel smashing universes? Oh wow,
• 10:56
  Speaker 1: universe collisions. Actually, there is a theory about different bubbles
• 11:00
  Speaker 1: in the multiverse and bumping into each other and leaving
• 11:03
  Speaker 1: an imprint on the cosmic microwave background radiation. I just
• 11:06
  Speaker 1: read about this theory yet. Yeah, there was a theory
• 11:09
  Speaker 1: by Roger Penrose, and he claimed to see evidence for
• 11:12
  Speaker 1: it in the cosmic microwave background radiation, but nobody could
• 11:15
  Speaker 1: confirm it. So it's definitely not something we've seen, but
• 11:19
  Speaker 1: a pretty awesome idea. Yeah. Also it's called the Big Bounce,
• 11:22
  Speaker 1: not the Big Smash, so we can't talk about it.
• 11:25
  Speaker 1: This episode sponsored by a smash Burger. But I remember
• 11:31
  Speaker 1: the first time I heard about black holes being collided,
• 11:34
  Speaker 1: and I thought, Wow, that's incredible, like two things that
• 11:37
  Speaker 1: we definitely do not understand. And I thought to myself,
• 11:40
  Speaker 1: I want to see what happens, what comes out, what's
• 11:43
  Speaker 1: revealed in the shards of that collision, Like, show me
• 11:46
  Speaker 1: the answer, universe. Yeah, what are the shards of the
• 11:49
  Speaker 1: two sharks when they And it's sort of amazing you
• 11:53
  Speaker 1: know that it happens out there in the universe and
• 11:56
  Speaker 1: that we can see it. So to me, it feels
• 11:58
  Speaker 1: like we are peaking under the rug of nature, really
• 12:01
  Speaker 1: understanding something deep about the nature of space and time
• 12:04
  Speaker 1: by looking for these extreme collisions when nature has to
• 12:08
  Speaker 1: tell us how things were. Because black holes are pretty
• 12:11
  Speaker 1: extreme in the universe, right, there's some of the most
• 12:13
  Speaker 1: extreme conditions imaginable. Maybe they're breaking the laws of physics inside,
• 12:17
  Speaker 1: or at least the laws that we didn't know, and
• 12:19
  Speaker 1: so you can't imagine amazing things are gonna happen when
• 12:22
  Speaker 1: you smash two of them together. Yeah, they're probably gonna
• 12:24
  Speaker 1: smash the laws of physics. And I guess maybe a
• 12:27
  Speaker 1: more philosophical question is, is Daniel, kid, two holes actually collide? Like, what,
• 12:32
  Speaker 1: what's actually hitting each other? Nothing's gonna hit each other?
• 12:35
  Speaker 1: Is there just two holes? I guess you could think
• 12:37
  Speaker 1: of them as like merging, Right, if you and a
• 12:40
  Speaker 1: friend are both digging holes in the ground, you just
• 12:42
  Speaker 1: keep digging, then eventually just get one big hole, right,
• 12:44
  Speaker 1: so those two holes can sort of merge. So it's
• 12:48
  Speaker 1: more of a black hole merger, it is. But actually
• 12:51
  Speaker 1: the map doesn't quite work that way because the black
• 12:53
  Speaker 1: hole that comes out is a little bit smaller than
• 12:56
  Speaker 1: the some of the two black holes that went in,
• 12:58
  Speaker 1: which is pretty weird. Wait what, well, you just spoiled it,
• 13:02
  Speaker 1: he said, Another hole comes out. I guess the two
• 13:04
  Speaker 1: holes don't cancel each other. Yeah, they do an amazing
• 13:07
  Speaker 1: dance of relativity to form something new that comes out. Well, then,
• 13:11
  Speaker 1: as you said, this kind of thing happens all the
• 13:12
  Speaker 1: time in the years, and we get to observe it, right,
• 13:15
  Speaker 1: we certainly do, and we learn a lot about the
• 13:17
  Speaker 1: nature of space and time in the process. All right, Well,
• 13:19
  Speaker 1: as usual, we were curious how many people out there
• 13:21
  Speaker 1: had heard of black holes colliding and what maybe they
• 13:24
  Speaker 1: think happens when they do. So thank you to everybody
• 13:27
  Speaker 1: who participates in these segments for our podcast. We hope
• 13:30
  Speaker 1: you have a good time answering random questions without any
• 13:33
  Speaker 1: chance to prepare. If you like to participate and hear
• 13:36
  Speaker 1: your speculation on the podcast for everybody else to enjoy,
• 13:39
  Speaker 1: please don't be shy. Right to us two questions at
• 13:42
  Speaker 1: Daniel and Jorge dot com. So think about it for
• 13:45
  Speaker 1: a second. What do you think happens when two black
• 13:47
  Speaker 1: holes collide? Here's what people had to say. Yeah, I
• 13:50
  Speaker 1: think we know this right. So if two black holes collide, hey,
• 13:53
  Speaker 1: they make a bigger black hole? Would be I think
• 13:56
  Speaker 1: some people have discovered that they make gravitational way. Put
• 14:01
  Speaker 1: that seems like two simple and once there. So I
• 14:03
  Speaker 1: read black Hole Blues by Jane Levin, and my best
• 14:07
  Speaker 1: guess is black holes Clyde, they circle around each other
• 14:13
  Speaker 1: faster and faster, and as they get um closer to
• 14:18
  Speaker 1: each other, they're circling almost at the speed of light.
• 14:20
  Speaker 1: At the very last split second, and when they Clyde.
• 14:24
  Speaker 1: The force has enough energy to overpower the energy that
• 14:29
  Speaker 1: an entire galaxy might put out, and that's why we
• 14:31
  Speaker 1: can sense the gravitational waves galaxies away UM here on
• 14:36
  Speaker 1: Earth with the new instruments we have. In general, I
• 14:40
  Speaker 1: don't think there's a direct collision of a black hole,
• 14:44
  Speaker 1: but rather they orbit each other closer and closer and closer,
• 14:48
  Speaker 1: with probably the stronger one feeding off of the weaker one. Ultimately,
• 14:56
  Speaker 1: after all the fireworks are done, I would assume that
• 15:00
  Speaker 1: the smaller one would be eventually absorbed into the larger one,
• 15:08
  Speaker 1: and you have one substantially larger black hole. When two
• 15:12
  Speaker 1: black holes collide, I think they just merged into a
• 15:16
  Speaker 1: larger one. We can observe gravitational waves happening while this occurs,
• 15:23
  Speaker 1: but other than that, I think they just merge. When
• 15:27
  Speaker 1: black holes collide, gravity waves make their way to our
• 15:33
  Speaker 1: clever listening devices here on Earth and UM I think
• 15:38
  Speaker 1: probably is a lot of energy released and they become
• 15:42
  Speaker 1: one black hole. When black holes collide, I mean you
• 15:46
  Speaker 1: have very very heavy, heavily dense, and very strong gravity
• 15:52
  Speaker 1: come from these things. So when they collide, it's got
• 15:56
  Speaker 1: a kind of one window which everyone is a more
• 16:00
  Speaker 1: dense and be strongly have stronger gravitational forces, and then
• 16:06
  Speaker 1: it's kind of absorbs. They make a lot of gravity
• 16:11
  Speaker 1: waves and then they make one big all right, A
• 16:17
  Speaker 1: lot of fun answers here. I like the one that
• 16:20
  Speaker 1: said when they collide they eat each other kind of
• 16:23
  Speaker 1: like sharks. But who is eating who? Man, that doesn't really.
• 16:27
  Speaker 1: But if one shark starts eating the tail of the
• 16:29
  Speaker 1: other shark, and then the other shark starts eating tail
• 16:32
  Speaker 1: the other shark, what's going to happen? It's like a
• 16:34
  Speaker 1: yin yang shark somehow, Yeah, ying shark. Yeah, maybe the
• 16:37
  Speaker 1: shark ends up eating itself when you get a sharknado
• 16:41
  Speaker 1: because they're spinning around so fast. That's probably how that
• 16:43
  Speaker 1: crossover event happened, right, A Shark DVD and a Tornado DVD. Boom?
• 16:47
  Speaker 1: That's right. Yeah, one bad idea smashed another bad idea. Yeah,
• 16:52
  Speaker 1: why not? Right? Who knows what happens when you collide
• 16:54
  Speaker 1: the craziest things in the universe. So I love the
• 16:56
  Speaker 1: creativity there, thank you? Yeah, why not? Maybe that should
• 16:59
  Speaker 1: be the hell of the podcast. Why not, let's get smashing. Well,
• 17:05
  Speaker 1: let's break it down for people here. Daniel maybe let's
• 17:08
  Speaker 1: start with the basics. What is a black hole. Black hole,
• 17:11
  Speaker 1: as you said, is a hole in space and time,
• 17:13
  Speaker 1: but it is a really strange hole, you know. Really,
• 17:16
  Speaker 1: what it is is a location where there's so much
• 17:19
  Speaker 1: mass and energy in one spot that's it's dense enough
• 17:22
  Speaker 1: that particles that are near it are doomed to fall in.
• 17:25
  Speaker 1: You know, mass and energy hells space how to bend,
• 17:29
  Speaker 1: and then space tells and particles and mass and other
• 17:31
  Speaker 1: things how to move. So the more mass and energy
• 17:34
  Speaker 1: you have somewhere, the more space curve, which is why,
• 17:37
  Speaker 1: for example satellites or with the Earth instead of just
• 17:39
  Speaker 1: flying away, you could think of all of gravity in
• 17:42
  Speaker 1: fact as the invisible curvature of space rather than like
• 17:46
  Speaker 1: a Newtonian tugging. And so black holes are where space
• 17:49
  Speaker 1: is curved so much that there are particles that can
• 17:52
  Speaker 1: never escape. So there's sort of holes in space, and
• 17:55
  Speaker 1: there's sort of holes caused by gravity, right, Like that's
• 17:58
  Speaker 1: another way to do sort of think about at it, right,
• 18:00
  Speaker 1: And it's it's like there's there's so much stuff and
• 18:03
  Speaker 1: energy in them that it just sucks everything in and
• 18:05
  Speaker 1: and it sucks them so much you can never get
• 18:08
  Speaker 1: up Yeah. Mostly you can think about gravity in two
• 18:10
  Speaker 1: different ways. You can think about like a force something
• 18:13
  Speaker 1: is pulling on you, and like the Earth is tugging
• 18:15
  Speaker 1: on you. That sort of Newton's idea of gravity. But
• 18:18
  Speaker 1: black holes come out of general relativity, which encouras you
• 18:21
  Speaker 1: to think about gravity in a very different way, since
• 18:24
  Speaker 1: the gravity isn't a force, it's just that space is curved.
• 18:26
  Speaker 1: But you can't see that curvature. The only thing you
• 18:29
  Speaker 1: can see is the effect of that curvature on the
• 18:31
  Speaker 1: motion of objects. So you shine a flashlight, for example,
• 18:34
  Speaker 1: through curved space, then it seems to you to bend,
• 18:38
  Speaker 1: but that bending is just because it's moving in a
• 18:39
  Speaker 1: straight line through curved space you can't see. So when
• 18:43
  Speaker 1: you apply that to black holes, you don't get like
• 18:45
  Speaker 1: a really strong force of gravity. You at a place
• 18:48
  Speaker 1: where space has ben so much that now it's just
• 18:50
  Speaker 1: one directional Things inside the event of horizon of a
• 18:54
  Speaker 1: black hole always end up at the singularity, according to
• 18:57
  Speaker 1: general relativity, because that's the only direction left in space.
• 19:02
  Speaker 1: Right Yeah, But general relativity might be wrong to right, Like,
• 19:06
  Speaker 1: there's this possibility that maybe gravity is a forcedome. There
• 19:08
  Speaker 1: are forests, gravity particles, and everything right. General relativity almost
• 19:12
  Speaker 1: certainly wrong at some level, not in the sense that
• 19:15
  Speaker 1: it's making mistakes about GPS or that we're getting the
• 19:18
  Speaker 1: numbers wrong, but it can't really be the true description
• 19:21
  Speaker 1: of nature, as you said, because, for example, it predicts
• 19:23
  Speaker 1: singularities at the hearts of black hole, and you know
• 19:26
  Speaker 1: that's not as much a physical prediction like general relativity is,
• 19:29
  Speaker 1: and say there is a point of infinite density as
• 19:32
  Speaker 1: much as it's a breakdown of the theory. It says, well,
• 19:35
  Speaker 1: here's what I predict, and that seems sort of nonsense,
• 19:37
  Speaker 1: so at this point, replace me with a better theory.
• 19:40
  Speaker 1: So we don't know what's going on at the heart
• 19:41
  Speaker 1: of black holes. It could be that the right picture
• 19:43
  Speaker 1: of gravity is as a sort of quantum field. The
• 19:46
  Speaker 1: way we have all the other forces. You can think
• 19:48
  Speaker 1: about gravity is the exchange of gravitons. So yeah, you're right,
• 19:52
  Speaker 1: general relativity almost certainly wrong. On the other hand, it
• 19:55
  Speaker 1: predicts black holes and we see them, so it's right
• 19:57
  Speaker 1: about a lot of stuff. Well, black holes are really strange,
• 20:01
  Speaker 1: and there are a couple of really strange things about them, Like,
• 20:03
  Speaker 1: first of all, I like can't escape, so they just
• 20:05
  Speaker 1: look like a giant whole and space, but it also
• 20:09
  Speaker 1: does interesting things like slow down time. Yeah, there are
• 20:11
  Speaker 1: two different kinds of time dilation in our universe from relativity.
• 20:16
  Speaker 1: One is much more commonly talked about, which is velocity
• 20:18
  Speaker 1: based time dilation. If you see somebody moving fast through
• 20:21
  Speaker 1: the universe relative to you, you see their clocks slowing down,
• 20:25
  Speaker 1: And that kind of time dilation is relative because if
• 20:27
  Speaker 1: they look back at you, they see your clocks slowing down.
• 20:31
  Speaker 1: So you too, disagree about whose clock is slowing down,
• 20:34
  Speaker 1: which is really weird and confusing makes you doubt like
• 20:37
  Speaker 1: you know, truth and the existence of reality. But the
• 20:40
  Speaker 1: kind of time dilation that happens to a black hole
• 20:42
  Speaker 1: is different. The more space is curved where you are,
• 20:45
  Speaker 1: the more your clock will slow down. And that's not
• 20:47
  Speaker 1: a relative effect, is absolute. So if your friend gets
• 20:51
  Speaker 1: near a black hole where space is curved more, you
• 20:53
  Speaker 1: will see their clocks slow down because they're in more
• 20:56
  Speaker 1: curved space. They will see your clock going faster. Right,
• 21:00
  Speaker 1: it's the opposite of the relative time dilation that happens
• 21:03
  Speaker 1: due to velocity. Here is absolutely because everybody agrees. So
• 21:07
  Speaker 1: if you are falling near a black hole, your friend
• 21:09
  Speaker 1: will see you slow down, and you will see them
• 21:11
  Speaker 1: sped up. Yet it's pretty cool effect. And like you
• 21:14
  Speaker 1: will literally see them moving slow motion, right, and they
• 21:16
  Speaker 1: will literally see the entire rest of the universe moving
• 21:20
  Speaker 1: in fast forward. Yeah. And so if you see somebody
• 21:23
  Speaker 1: falling towards the black hole, the closer they get, the
• 21:25
  Speaker 1: more their time slows down. And so it actually takes
• 21:28
  Speaker 1: an infinite amount of time for the last thing to
• 21:31
  Speaker 1: fall into a black hole. Like you toss the banana
• 21:34
  Speaker 1: into a black hole, you don't actually see it enter
• 21:36
  Speaker 1: the black hole past the event horizon until time equals infinity. Right.
• 21:41
  Speaker 1: We've had I think whole podcast about this because it's
• 21:43
  Speaker 1: it's sort of a little bit mind bending because you
• 21:46
  Speaker 1: do sort of see black holes growing over time, right,
• 21:49
  Speaker 1: and at some point that they're going to overtake the banana. Right. Yeah,
• 21:52
  Speaker 1: that seems confusing because it suggests the black holes could
• 21:54
  Speaker 1: never grow because nothing could actually fall into them. That's
• 21:57
  Speaker 1: why I said it's only true for the last thing
• 21:59
  Speaker 1: to fall into a black hole because as the banana
• 22:01
  Speaker 1: falls towards the black hole, the event horizon actually grows
• 22:05
  Speaker 1: before the banana crosses over. A black hole isn't like
• 22:07
  Speaker 1: a pet where you need to put something in it
• 22:09
  Speaker 1: for it to get bigger, doesn't have to like eat
• 22:11
  Speaker 1: the banana the sides. The event horizon reflects the total
• 22:14
  Speaker 1: gravitational energy of the system. So as the banana falls
• 22:17
  Speaker 1: into the black hole, the event horizon actually grows out
• 22:19
  Speaker 1: to meet it. And then if you throw something else
• 22:21
  Speaker 1: like an apple after the banana, that also pulls out
• 22:25
  Speaker 1: the event horizon, so it will come and encompass the banana.
• 22:28
  Speaker 1: So that's how we see black holes actually grow out
• 22:30
  Speaker 1: there in the universe is a continuous stream of stuff
• 22:33
  Speaker 1: falling into it and pulling out the event horizon. Right,
• 22:36
  Speaker 1: But you don't have to feed them, but it's it's
• 22:37
  Speaker 1: nice to feed them, right. You don't want a black
• 22:39
  Speaker 1: hole to starve. I don't know. It depends where the
• 22:42
  Speaker 1: black hole lives. If it lives in your basement, I
• 22:44
  Speaker 1: don't think it's a good idea to feed it. I
• 22:46
  Speaker 1: think if it lives up in your basement, it's game
• 22:48
  Speaker 1: over for you for here house. You know, there is
• 22:52
  Speaker 1: some size of a black hole where it's radiating away energy,
• 22:56
  Speaker 1: and you could feed it at the same rate, so
• 22:57
  Speaker 1: you could have a stable black hole that you keep
• 23:00
  Speaker 1: pet You can't have a pet then you just contradicted yourself.
• 23:03
  Speaker 1: Just don't pet it. I guess you don't touch it.
• 23:06
  Speaker 1: I wouldn't recommend it. But theoretically it's possible to keep
• 23:09
  Speaker 1: a black hole stable. I see. And so something else
• 23:11
  Speaker 1: that's interesting about a black hole is that there are
• 23:13
  Speaker 1: only a few things we can know about them, right,
• 23:15
  Speaker 1: I mean, they're a black hole. Stuff falls in and
• 23:17
  Speaker 1: we never see it again, but there are a few
• 23:19
  Speaker 1: things that you can tell about them. Everything that falls
• 23:22
  Speaker 1: into the event horizon is lost to us and what
• 23:24
  Speaker 1: happens to it, and we cannot know information about what's
• 23:27
  Speaker 1: inside the event horizon. Can't escape. But that doesn't mean
• 23:30
  Speaker 1: we can't measure things about the global black hole. Like
• 23:33
  Speaker 1: a black hole has mass, It tugs on you even
• 23:36
  Speaker 1: though you're outside the event horizon, and so you can
• 23:39
  Speaker 1: use that to measure how much stuff is inside the
• 23:42
  Speaker 1: event horizon. How much mass does this black hole have.
• 23:45
  Speaker 1: So there are a few things you can measure from
• 23:47
  Speaker 1: outside the event horizon, and that's the mass of the
• 23:50
  Speaker 1: black hole. Also the electric charge of the black hole,
• 23:53
  Speaker 1: because charge is conserved in the universe. You drop an
• 23:56
  Speaker 1: electron into a black hole that changes its charge and
• 23:59
  Speaker 1: its electric yield. The same thing for its spin. Black
• 24:02
  Speaker 1: holes can spin. So there's this theorem called the no
• 24:05
  Speaker 1: hair theorem that says those the only three things you
• 24:08
  Speaker 1: can know about a stable black hole, mass, spin, and charge. Wait,
• 24:12
  Speaker 1: what is it called the no hair theorem? How does
• 24:15
  Speaker 1: hair falling get fit into this? I think it's a
• 24:18
  Speaker 1: joke that says that you can't know whether black holes
• 24:20
  Speaker 1: are hairy, Like you can't know what's going on inside
• 24:23
  Speaker 1: the black hole that have blonde hairs, have a mohawk.
• 24:26
  Speaker 1: It's like, you know, just an example of something you
• 24:28
  Speaker 1: can't know about a black hole. M it could have
• 24:31
  Speaker 1: been called the no tattoos theorem. Also, yeah, that makes
• 24:34
  Speaker 1: no sense to me, but that's the official name. All right,
• 24:38
  Speaker 1: Well that's a black hole. And so now the big
• 24:40
  Speaker 1: question is what happens if I take two black holes
• 24:43
  Speaker 1: and I smushed them or smashed them or merged them together.
• 24:47
  Speaker 1: Apparently a lot of things happen. So let's get into that.
• 24:50
  Speaker 1: But first let's take a quick break. Alright, we're talking
• 25:05
  Speaker 1: about smashing black holes together, and Daniel, this happens all
• 25:09
  Speaker 1: the time, right, Like we've recently been able to listen
• 25:12
  Speaker 1: to black holes colliding, and a lot of they had.
• 25:14
  Speaker 1: They happened more often than we thought in black hole
• 25:16
  Speaker 1: collisions were first observed in two thousand and fifteen, but
• 25:20
  Speaker 1: it was a very, very long search for black holes.
• 25:23
  Speaker 1: People started decades and decades before that trying to invent
• 25:26
  Speaker 1: systems that were sensitive enough to the radiation emitted from
• 25:30
  Speaker 1: black hole collisions so that we could see it here
• 25:33
  Speaker 1: on Earth. This is something predicted by Albert Einstein, though
• 25:36
  Speaker 1: he thought we could never actually observe it, that this
• 25:38
  Speaker 1: is a cool effect. Too bad, it's too tiny for
• 25:41
  Speaker 1: us to ever see. Oh I see, so before we
• 25:43
  Speaker 1: could listen to them with gravitational waves. People were trying
• 25:47
  Speaker 1: to see them, but they never found any right, Yeah,
• 25:49
  Speaker 1: people were trying to listen to them with gravitational waves
• 25:51
  Speaker 1: for a long time. That was Einstein's prediction that they
• 25:54
  Speaker 1: would create from gravitational waves, but it would be impossible
• 25:57
  Speaker 1: for us to see these gravitational waves to observe them.
• 26:00
  Speaker 1: And you know, I'm in the company who agreed with
• 26:01
  Speaker 1: Einstein for a long time. When I was thinking about
• 26:03
  Speaker 1: grad school, I had a few different choices, and one
• 26:06
  Speaker 1: was going to university that was deep into ligo, that
• 26:09
  Speaker 1: was developing the technology and trying to observe gravitational waves,
• 26:13
  Speaker 1: and I remember thinking, that's cool, but they're never going
• 26:15
  Speaker 1: to make that happen, and so I'm gonna go do
• 26:17
  Speaker 1: particle because instead. Yeah, yeah, I'm in the company of
• 26:20
  Speaker 1: Einstein as well. I have crazy hair as well. But
• 26:24
  Speaker 1: Einstein was wrong and so was I, because they did
• 26:27
  Speaker 1: see gravitational waves. They did see this crazy pattern of
• 26:30
  Speaker 1: radiation emitted from the collisions of black holes. Yeah, I
• 26:34
  Speaker 1: think what I was asking is, like, could you see
• 26:37
  Speaker 1: two black holes merging together? I mean, we can sort
• 26:40
  Speaker 1: of see black holes out there in the universe, and
• 26:42
  Speaker 1: we can definitely see their effect on the stars or
• 26:45
  Speaker 1: the galaxy around them. Could you ever hope to, you know,
• 26:48
  Speaker 1: detect the black hole collision without the gravitational waves tection, Like,
• 26:52
  Speaker 1: could you ever see two black holes actually colliding? You
• 26:55
  Speaker 1: can't actually see them, but you're right, you don't see
• 26:57
  Speaker 1: the black holes themselves colliding. Black holes are surrounded by
• 27:01
  Speaker 1: accretion disks, all sorts of matter that sort of on
• 27:03
  Speaker 1: deck for falling into the black holes, and so sometimes
• 27:07
  Speaker 1: when two black holes collide, there are creation discs also
• 27:10
  Speaker 1: collide and create light. They've seen as a couple of
• 27:13
  Speaker 1: times where they've seen flashes of bright light at the
• 27:16
  Speaker 1: same time and in the same direction as they've observed
• 27:19
  Speaker 1: gravitational waves. So they have seen in a couple of
• 27:22
  Speaker 1: occasions bright flashes of light emitted from black hole collisions. Right,
• 27:27
  Speaker 1: but before like maybe you would see the bright flash
• 27:30
  Speaker 1: of light, but you wouldn't be able to know if
• 27:32
  Speaker 1: it was a black hole collision. Yeah, exactly, it just
• 27:35
  Speaker 1: seemed like a flash of light. And there's lots of
• 27:37
  Speaker 1: weird flashes of light in the universe and you can't
• 27:40
  Speaker 1: necessarily tell that one is from a black hole or
• 27:43
  Speaker 1: from something else, or just from two stars colliding or
• 27:45
  Speaker 1: two blobs of gas colliding. So really, the unique signature
• 27:48
  Speaker 1: and the thing that told us that black holes were
• 27:50
  Speaker 1: colliding where these patterns of gravitational waves, which are like
• 27:53
  Speaker 1: ripples in space and time itself. And so far since
• 27:58
  Speaker 1: we've seen a whole bunch of I've heard a but
• 28:01
  Speaker 1: a whole bunch of these black hole collisions, like maybe
• 28:03
  Speaker 1: like ten a year or something. Right, it's incredible we
• 28:06
  Speaker 1: have like fifty examples now and to appreciate how amazing
• 28:08
  Speaker 1: that is, realized that we didn't know how often black
• 28:11
  Speaker 1: holes collided. When Lego turned on, it was like a
• 28:15
  Speaker 1: new kind of instrument, and we're listening to something new
• 28:17
  Speaker 1: in the universe, or a new kind of eyeball. We're
• 28:19
  Speaker 1: looking for things in the universe. It's all just an
• 28:21
  Speaker 1: analogy because gravitational radiation is not something you can see
• 28:25
  Speaker 1: or here. We're just trying to translated into sort of
• 28:27
  Speaker 1: human experience. But we didn't know if this kind of
• 28:29
  Speaker 1: thing happened once in a century, once in a millennium,
• 28:33
  Speaker 1: or like ten times a second. So when they turned
• 28:35
  Speaker 1: this thing on, it could have been that they were
• 28:37
  Speaker 1: waiting for years to hear the first one, or that
• 28:40
  Speaker 1: they came fast and hard and amazingly. We were lucky,
• 28:43
  Speaker 1: and they're pretty common. And they saw a gravitational wave
• 28:46
  Speaker 1: in the first test run, Like they turned this thing
• 28:49
  Speaker 1: on and they were just like doing calibration runs just
• 28:51
  Speaker 1: to make sure everything was working, and boom, they saw
• 28:54
  Speaker 1: a signal in the first calibration run. So they were
• 28:57
  Speaker 1: like off to the races, writing a paper and week two.
• 29:00
  Speaker 1: It's pretty amazing, pretty cool, And they happen pretty often,
• 29:03
  Speaker 1: maybe like once a month, once every month and a half.
• 29:05
  Speaker 1: And do they happen here in our galaxy, or are
• 29:07
  Speaker 1: we listening to these collisions from all over the universe.
• 29:10
  Speaker 1: They happen all over the universe, and we can see
• 29:12
  Speaker 1: these things really far away, like billions of light years. Now,
• 29:15
  Speaker 1: the further you are away from these things, of course,
• 29:18
  Speaker 1: the fainter they are, and so they're closer, is easier
• 29:21
  Speaker 1: for us to see them there, further away than the
• 29:23
  Speaker 1: head needs to be more dramatic, more powerful for us
• 29:27
  Speaker 1: to observe them. But we've detected these collisions from black
• 29:30
  Speaker 1: holes that are billions of light years away, But are
• 29:33
  Speaker 1: they happening here in our milk away galaxy? We see
• 29:36
  Speaker 1: black hole collisions fairly commonly, but we can see them
• 29:39
  Speaker 1: from really really far away, and they don't happen actually
• 29:42
  Speaker 1: that often in any individual galaxy, so we haven't actually
• 29:45
  Speaker 1: seen one happen yet in the Milky Way. Remember, the
• 29:48
  Speaker 1: black holes are not that common. We have really big
• 29:50
  Speaker 1: ones in the center of the galaxy, the black holes
• 29:53
  Speaker 1: created from stellar collapse. But they get two black holes
• 29:56
  Speaker 1: to collide. You really need like two black holes in
• 29:58
  Speaker 1: a binary system, because I guess it fifty seems like
• 30:01
  Speaker 1: a lot of black holes colliding. But it's a big universe, right,
• 30:04
  Speaker 1: there are trillions of galaxies out there, so the fact
• 30:06
  Speaker 1: that we're only seeing you know, maybe one year, it
• 30:10
  Speaker 1: means that maybe they're not that common. Yeah, they're not
• 30:13
  Speaker 1: that common sort of per galaxy, but they happen often
• 30:16
  Speaker 1: enough for us to have a pretty nice data sample,
• 30:18
  Speaker 1: which means that we can really study these things. It's
• 30:20
  Speaker 1: not just like we saw one and then we're wondering
• 30:23
  Speaker 1: if that was typical or not. We have like dozens
• 30:25
  Speaker 1: of these things, so we can start to ask statistical
• 30:28
  Speaker 1: questions about what's likely and what's common. We can see
• 30:30
  Speaker 1: which ones are weird, which ones are normal. It's really
• 30:33
  Speaker 1: an awesome moment when you can start to do like
• 30:34
  Speaker 1: population science on black hole collisions. Yeah, like statistical you
• 30:40
  Speaker 1: know surveys. All right, Well, maybe step us through here.
• 30:43
  Speaker 1: What happens? What's like, step by step, what's going on
• 30:46
  Speaker 1: when two black holes collide? Because you know, I think
• 30:49
  Speaker 1: one thing that a lot of people might not know
• 30:51
  Speaker 1: is that black holes can move, right, Like it's fair
• 30:53
  Speaker 1: to think of a whole moving like a hole in
• 30:54
  Speaker 1: the ground doesn't move, but black holes can move when
• 30:57
  Speaker 1: they can sort of like fly through space and and
• 31:00
  Speaker 1: run into other black holes. You know, black holes have
• 31:02
  Speaker 1: bass just like everything else, and so they have inertia
• 31:05
  Speaker 1: and they can have momentum. Black hole can move in
• 31:07
  Speaker 1: the same way that you can move past a black hole.
• 31:10
  Speaker 1: Remember that velocity is just relative in our universe. So
• 31:13
  Speaker 1: if you're flying past the black hole from its point
• 31:15
  Speaker 1: of view, then from your point of view, the black
• 31:17
  Speaker 1: hole is flying past you, right, And so these things
• 31:20
  Speaker 1: definitely can move. And a lot of people probably think
• 31:23
  Speaker 1: about black hole collisions like two black holes just flying
• 31:26
  Speaker 1: through space and bumping into each other like two dogs
• 31:28
  Speaker 1: in the park smashing into each other or something, because
• 31:31
  Speaker 1: they weren't looking where they were going. Instead, these two
• 31:33
  Speaker 1: things have sort of been faded to collide since their birth.
• 31:38
  Speaker 1: Remember that a lot of stars are born as binary systems.
• 31:41
  Speaker 1: They were made near each other and gravitationally bound from
• 31:44
  Speaker 1: the beginning, orbiting each other in a long dance, and
• 31:47
  Speaker 1: that's how most black hole collisions happen. They start as
• 31:50
  Speaker 1: a binary star system, then each one collapses into a
• 31:53
  Speaker 1: black hole. Then you get black holes orbiting each other.
• 31:55
  Speaker 1: So they've always been neighbors. It's not like they're just
• 31:58
  Speaker 1: two strangers that smash into each other and they're obitting
• 32:00
  Speaker 1: each other and they're slowly losing that energy, radiating away
• 32:05
  Speaker 1: their orbital energy until eventually they collide. WHOA, yeah, because
• 32:10
  Speaker 1: I guess most black holes come from stars. And so
• 32:13
  Speaker 1: if you have a binary system and both stars turn
• 32:16
  Speaker 1: into a black hole, then you have a binary black
• 32:18
  Speaker 1: hole system. Right, But isn't that sort of rare? I mean,
• 32:20
  Speaker 1: it's a little rare first start to turn into a
• 32:22
  Speaker 1: black hole. But now yet you need to have both
• 32:25
  Speaker 1: of them in the binary star system turned into black
• 32:27
  Speaker 1: holes exactly. And so those are the conditions you need.
• 32:30
  Speaker 1: And we're still understanding your black hole formation. But it
• 32:33
  Speaker 1: depends on how much mass there was in each individual star.
• 32:37
  Speaker 1: If it's a massive enough, then eventually it will collapse
• 32:40
  Speaker 1: into a black hole. There's like no way to avoid
• 32:42
  Speaker 1: it when it burns up its fuel. And the thing
• 32:44
  Speaker 1: I think is interesting is understanding why these things are inevitable,
• 32:47
  Speaker 1: Like why can't two black holes just orbit each other
• 32:50
  Speaker 1: happily forever until the end of the universe. Why do
• 32:52
  Speaker 1: they have to fall into each other? Right? Like in
• 32:55
  Speaker 1: our solar system, you know, are the planets are orbiting
• 32:58
  Speaker 1: the Sun pretty stably, pretty stable, e that's true, We're
• 33:02
  Speaker 1: not falling to the Sun yet, not today and not tomorrow.
• 33:05
  Speaker 1: But you know, these orbits are not technically stable because
• 33:08
  Speaker 1: every time you're in orbit around something, you're accelerating, and
• 33:11
  Speaker 1: anything that's accelerating in our universe, it's changing its velocity,
• 33:15
  Speaker 1: is generating gravitational waves. You know what is a gravitational wave.
• 33:20
  Speaker 1: It's just when your gravitational field changes. If you have
• 33:24
  Speaker 1: an object in space, it has a gravitational field, it's
• 33:27
  Speaker 1: changing the shape the curvature of space. Is that object accelerates,
• 33:31
  Speaker 1: then the curvature of space changes, but it doesn't change instantaneously.
• 33:35
  Speaker 1: Just like if the Sun disappeared, we wouldn't notice for
• 33:37
  Speaker 1: eight minutes or whatever. It would take time for that
• 33:39
  Speaker 1: gravitational information to propagate. And so when something accelerates, it's
• 33:44
  Speaker 1: changing the curvature of space, and that's what's happening when
• 33:47
  Speaker 1: the Earth is going around the Sun. It's accelerating and
• 33:50
  Speaker 1: so that radiates away some energy in terms of the
• 33:53
  Speaker 1: information about updating the curvature, right right, So we're slowly
• 33:57
  Speaker 1: losing a little bit of energy in our orbit and
• 33:59
  Speaker 1: so eventually, I guess in the very very very very
• 34:03
  Speaker 1: far future, the Earth is gonna fall into the Sun.
• 34:06
  Speaker 1: That's right, although other things will happen before the Earth
• 34:09
  Speaker 1: falls into the Sun due to radiating gravitational energy because
• 34:12
  Speaker 1: the Earth is not that massive. But if you have
• 34:14
  Speaker 1: two black holes that are really really massive, they're going
• 34:17
  Speaker 1: to radiate a lot more gravitational energy, and so as
• 34:20
  Speaker 1: they lose energy, they fall into each other. Right. They
• 34:23
  Speaker 1: can't maintain their orbit if they don't have that energy,
• 34:26
  Speaker 1: so they're very orbit The thing that's accelerating them around
• 34:28
  Speaker 1: each other is shaking the curvature of space around them,
• 34:32
  Speaker 1: creating these gravitational waves and forcing them to get closer
• 34:35
  Speaker 1: and closer and faster and faster, so it's more like
• 34:39
  Speaker 1: a swirl in than a collision. Right. It's sort of
• 34:42
  Speaker 1: like if you have a still lake or a still
• 34:45
  Speaker 1: body of water and you take two fingers and you
• 34:47
  Speaker 1: sort of rotate them or spin them around each other,
• 34:49
  Speaker 1: they're gonna be generating waves on the water. That's sort
• 34:53
  Speaker 1: of how people see the two black holes, kind of
• 34:55
  Speaker 1: radiating out energy as waves exactly. And it's a deep
• 34:59
  Speaker 1: concept that's really applicable to lots of different physical phenomena, right,
• 35:03
  Speaker 1: Like how do you generate radio transmissions? You take electrons,
• 35:06
  Speaker 1: which have an electric field, and you accelerate them up
• 35:09
  Speaker 1: and now you shake them and that wiggles the electric field.
• 35:12
  Speaker 1: That wiggle in the electric field is nothing more than
• 35:15
  Speaker 1: a photon. It's passing of information and energy through that field.
• 35:20
  Speaker 1: So you take a mass, Now it has a curvature
• 35:23
  Speaker 1: in space. You wiggle that mass, you accelerate it. That
• 35:26
  Speaker 1: wiggling of space time is gravitational radiation. It carries away energy,
• 35:32
  Speaker 1: all right. So they're not sort of, you know, aimed
• 35:34
  Speaker 1: at each other. They're more like swirling together. But then
• 35:37
  Speaker 1: at some point they lose energy and they swirl faster
• 35:40
  Speaker 1: and faster and closer and closer, and at some point
• 35:42
  Speaker 1: they start to touch, I guess right, or yeah, they
• 35:46
  Speaker 1: start to touch. And to think about that, you have
• 35:48
  Speaker 1: to think about what you mean by two black holes touching, right, Like,
• 35:52
  Speaker 1: what is the edge of a black hole? What's the
• 35:54
  Speaker 1: surface of it? Often we talk about it in terms
• 35:57
  Speaker 1: of the event horizon. We talked about the event horizon
• 35:59
  Speaker 1: as if it's like something physical, you know, like a
• 36:02
  Speaker 1: surface or a boundary or something. It's really just sort
• 36:05
  Speaker 1: of like a location past which you can never escape
• 36:08
  Speaker 1: the black hole. But it's not like there's anything there
• 36:11
  Speaker 1: at the event horizon. There's no physical surface. It's just
• 36:14
  Speaker 1: like past this point you will never escape. Like the
• 36:17
  Speaker 1: edge of a hole is not really a barrier, it's
• 36:19
  Speaker 1: just where you fall in. Yeah, it's just where you
• 36:21
  Speaker 1: fall in. The subtle point also is that you can't
• 36:24
  Speaker 1: measure the event horizon technically. To calculate where the event
• 36:27
  Speaker 1: horizon is, you need to know like what happens to
• 36:30
  Speaker 1: every particle that comes near it. Then you find sort
• 36:32
  Speaker 1: of like the surface in which if a particle passed
• 36:34
  Speaker 1: through it, nothing ever escaped, So you sort of need
• 36:37
  Speaker 1: to know the fate of every particle to figure out
• 36:39
  Speaker 1: exactly where the event horizon is. Wait, wait, what what
• 36:43
  Speaker 1: do you mean we can't tell where it is? Like,
• 36:45
  Speaker 1: can we do? We just take a picture of a
• 36:47
  Speaker 1: black hole recently? Doesn't that give us a pretty good
• 36:50
  Speaker 1: idea by the way that the light bends around it
• 36:53
  Speaker 1: where the event horizon is. We did take a picture
• 36:56
  Speaker 1: of black hole, and that does give us clues about
• 36:58
  Speaker 1: the size of the event horizon uson because actually what
• 37:01
  Speaker 1: we're seeing there is the shadow of the black hole,
• 37:03
  Speaker 1: which is larger than the event horizon because you know,
• 37:06
  Speaker 1: some light, for example, will pass near it and get
• 37:08
  Speaker 1: bent around it, so the shadow actually looks a little
• 37:11
  Speaker 1: bit bigger than the event horizon. But check out our
• 37:13
  Speaker 1: whole episode about the black hole image for details about that.
• 37:16
  Speaker 1: But in principle, even that picture doesn't tell you exactly
• 37:19
  Speaker 1: where the event horizon is. Like it could be that
• 37:21
  Speaker 1: there's a particle that could pass a little bit closer
• 37:23
  Speaker 1: to the black hole that we're seeing in that picture
• 37:25
  Speaker 1: and then escape. You don't know for sure. Now we
• 37:29
  Speaker 1: can calculate it, right. General relativity lets you calculate the
• 37:31
  Speaker 1: size of the event horizon, so we have this short
• 37:34
  Speaker 1: styled radius. But it's not like something you can locally measure.
• 37:37
  Speaker 1: You can't say I'm in or I'm out at any
• 37:40
  Speaker 1: given moment in the universe. It's not like some device
• 37:42
  Speaker 1: you could build that could tell you I'm inside a
• 37:44
  Speaker 1: black hole or I'm outside a black hole. You can
• 37:47
  Speaker 1: either calculate from general relativity where you can shoot a
• 37:49
  Speaker 1: bunch of particles at it and wait till the end
• 37:51
  Speaker 1: of the universe and see which one's escaped and which
• 37:53
  Speaker 1: ones didn't. So it's sort of a fuzzy boundary, I think,
• 37:57
  Speaker 1: is what you're saying exactly, And we're gonna have to
• 37:59
  Speaker 1: keep that definitely in mind as we think about what
• 38:01
  Speaker 1: happens when the event horizons get close to each other.
• 38:04
  Speaker 1: All right, yeah, so what happens? So I have a
• 38:06
  Speaker 1: one black hole and I have another black hole and
• 38:08
  Speaker 1: meat in my hands, and I'm swirling them and I'm
• 38:10
  Speaker 1: bringing them together, and they're swirling and swirling, and at
• 38:13
  Speaker 1: some point where the event horizon would be, or where
• 38:17
  Speaker 1: we think it is, or fuzzily where it should be,
• 38:19
  Speaker 1: they start to overlap, and they start to overlap. And
• 38:22
  Speaker 1: when people write to me about this, something they're confused
• 38:24
  Speaker 1: about is like a black hole's event horizon is a sphere, right,
• 38:27
  Speaker 1: It's like centered around the singularity. Now you have two
• 38:30
  Speaker 1: black holes, both of rich or spheres. What happens when
• 38:33
  Speaker 1: they touched? You suddenly get a sphere at the center
• 38:37
  Speaker 1: of the two? You know, does that mean the event
• 38:39
  Speaker 1: horizon is like shrinking a little bit? What happens there?
• 38:42
  Speaker 1: And so the answer is you can't have like discontinuities
• 38:44
  Speaker 1: with the event horizon is in one place and then
• 38:47
  Speaker 1: one instant later it's totally different. It's a smooth transformation
• 38:52
  Speaker 1: from happing two blobs to one blob, and a little
• 38:55
  Speaker 1: bit surprisingly that means that the event horizon is not
• 38:58
  Speaker 1: always spherical. The transition between two black holes and one
• 39:02
  Speaker 1: black hole that results it's a weird sort of peanut shape. Yeah,
• 39:06
  Speaker 1: I'm imagining. I guess. You know, like if you if
• 39:08
  Speaker 1: you take two ink plots, like two blobs of ink
• 39:11
  Speaker 1: and you sort of bring them together, they're gonna sort
• 39:13
  Speaker 1: of like touch maybe at the boundary and then sort
• 39:16
  Speaker 1: of merge and but just a little bit first, and
• 39:19
  Speaker 1: then the blobs sort of merges together, the two blobs
• 39:22
  Speaker 1: become a peanut shape, and then they sort of blob
• 39:24
  Speaker 1: block together. Is that sort of what happens. That's sort
• 39:26
  Speaker 1: of what happens. And to figure out exactly what the
• 39:29
  Speaker 1: shape of the event horizon is, people do these numerical
• 39:31
  Speaker 1: relativity calculations where basically they shoot a bunch of particles
• 39:35
  Speaker 1: near these two masses and they figure out where the
• 39:37
  Speaker 1: no go zones are, where if a particle passed through
• 39:40
  Speaker 1: it it ends up in the singularity no matter what.
• 39:43
  Speaker 1: They have to calculate the event horizon in this way
• 39:45
  Speaker 1: to like figure out where the no go zones are,
• 39:48
  Speaker 1: and they do these incredible simulations and you can find
• 39:50
  Speaker 1: these images online if you want. To look at the video.
• 39:53
  Speaker 1: We'll put a link into the show notes. And what
• 39:55
  Speaker 1: happens is you have like two blobs, and as they
• 39:57
  Speaker 1: get closer to each other, there's like a film mint
• 40:00
  Speaker 1: that forms between them. Now, the event horizon looks sort
• 40:02
  Speaker 1: of like a dumbbells, like two big blocks with a
• 40:04
  Speaker 1: very thin line between them. Then as they get closer
• 40:08
  Speaker 1: and closer, that line grows and grows and grows. Eventually
• 40:11
  Speaker 1: you have like a peanut, and then a tic tac
• 40:13
  Speaker 1: and finally a sphere. Wait we skip past the peanut
• 40:16
  Speaker 1: m and m or of a whole bunch of other candies.
• 40:20
  Speaker 1: All right, well let's get into what actually is happening
• 40:22
  Speaker 1: with that event horizon and where do all the gravitational
• 40:27
  Speaker 1: waves come from. But first let's take another quick break.
• 40:43
  Speaker 1: All right, we're talking about smashing two black holes together.
• 40:46
  Speaker 1: And the scenario we're picturing is two black holes that
• 40:50
  Speaker 1: came from a set of binary stars and each start
• 40:53
  Speaker 1: became a black hole. Now the black holes are swirling
• 40:55
  Speaker 1: around each other, getting closer and closer and closer, and
• 40:57
  Speaker 1: just as they're about to touch, they actually sort of
• 41:00
  Speaker 1: reach out and touch each other kind of in a way. Right, Yeah,
• 41:02
  Speaker 1: they become regions in space between the two black holes
• 41:06
  Speaker 1: that are now effectively inside their event horizon. They're combined
• 41:10
  Speaker 1: event horizon because if you're in that place, you will
• 41:13
  Speaker 1: not escape. So you could have been outside the event
• 41:15
  Speaker 1: horizon just before, but now this filament has formed where
• 41:19
  Speaker 1: if you were right between them, you no longer have
• 41:21
  Speaker 1: any chance to escape the black hole. And to me,
• 41:24
  Speaker 1: it's really fascinating this moment when the event horizon is
• 41:27
  Speaker 1: no longer a sphere, because it's an opportunity to learn something,
• 41:31
  Speaker 1: to know something about the history of the black hole.
• 41:34
  Speaker 1: What's going on inside even from the outside. What do
• 41:38
  Speaker 1: you mean, what what can you learn? What could you
• 41:40
  Speaker 1: hope to learn? Well, if you come along a black
• 41:42
  Speaker 1: hole and it's a perfect sphere, you have no idea
• 41:44
  Speaker 1: what's inside? Is it bananas? Is it apples? Is it
• 41:47
  Speaker 1: the result of a star collapsing or two stars collapsing?
• 41:50
  Speaker 1: You have no idea about like the merger history of
• 41:52
  Speaker 1: that black hole. But if you come along at the
• 41:55
  Speaker 1: moment when the black holes are still merging, then you
• 41:57
  Speaker 1: know this must have come from too. You know that
• 42:00
  Speaker 1: there are two singularities inside that event horizon, or you
• 42:04
  Speaker 1: know something about the history of it more so than
• 42:07
  Speaker 1: if you just come along to a spear, Right, so
• 42:09
  Speaker 1: you know a little bit about what's going on inside
• 42:12
  Speaker 1: the event horizon. I see you're saying. It tells you
• 42:15
  Speaker 1: a little bit about what happens when you change a
• 42:18
  Speaker 1: black hole, right, because a non changing black hole is
• 42:21
  Speaker 1: sort of mysterious and impenetrable. But the black holes that's changing,
• 42:25
  Speaker 1: maybe you can tell something about whether you know all
• 42:27
  Speaker 1: the stuff inside of it is concentrated in the middle
• 42:29
  Speaker 1: or spread out evenly, things like that. Yeah, it's fascinating
• 42:32
  Speaker 1: to me because black holes are like the most identical
• 42:35
  Speaker 1: thing in the universe. Remember this, in theory, only three
• 42:38
  Speaker 1: things to know about a black hole the only three
• 42:40
  Speaker 1: numbers that totally determine it, and two black holes that
• 42:43
  Speaker 1: have the same mass, spin, and charge are totally equivalent.
• 42:46
  Speaker 1: There's no way you can do experiments to tell them
• 42:49
  Speaker 1: apart except unless and this is the crack in the
• 42:52
  Speaker 1: no hair theorem. If you have a black hole with
• 42:55
  Speaker 1: that mass and that's been that charge, but it's still
• 42:58
  Speaker 1: finishing its last merger, you can know one little clue
• 43:01
  Speaker 1: about that black hole. You can know that it came
• 43:03
  Speaker 1: from this merger, and that must mean that the inners
• 43:05
  Speaker 1: of the black hole haven't quite settled down yet. They
• 43:08
  Speaker 1: haven't like formed the singularity or the quantum fuzz of
• 43:11
  Speaker 1: all or whatever is going on inside. Because the event
• 43:14
  Speaker 1: horizon has a different shape. It's the same mass, the
• 43:17
  Speaker 1: same spin, and the same charge, but a different shape.
• 43:20
  Speaker 1: Event horizon hasn't yet collapsed into a sphere. Oh. I
• 43:23
  Speaker 1: see you're saying, we can learn about the resulting black holes,
• 43:26
  Speaker 1: but we don't really wouldn't know anything about the holes.
• 43:29
  Speaker 1: The two holes that went into it right like they would,
• 43:32
  Speaker 1: Those would still be a mystery. Those would be a
• 43:34
  Speaker 1: little bit of a mystery. But you can know something
• 43:36
  Speaker 1: about their relative masses. For example, if two black holes
• 43:39
  Speaker 1: that are equal in mass merge, then as they're merging,
• 43:42
  Speaker 1: they look different than a black hole where one was
• 43:44
  Speaker 1: like of the final mass and the other one was
• 43:47
  Speaker 1: one because it's more asymmetric. So you know something about
• 43:50
  Speaker 1: what went into the black hole from the shape of
• 43:52
  Speaker 1: the sort of peanut before it collapses into a sphere.
• 43:56
  Speaker 1: I just think that's fascinating because it's a tiny little crack,
• 43:59
  Speaker 1: and any crack to say, like, I know something about
• 44:01
  Speaker 1: what's going on past the event horizon. That's tantalizing because
• 44:05
  Speaker 1: I mean, it was so little about what's inside. I
• 44:07
  Speaker 1: see you're saying, like a regular black hole by itself,
• 44:10
  Speaker 1: it's inscrutable. But if you see what two of them
• 44:12
  Speaker 1: joining together, you're like, hey, I know a little bit
• 44:14
  Speaker 1: about what happens in these extreme conditions. Yeah, you know
• 44:18
  Speaker 1: a little bit about the history of this black hole,
• 44:20
  Speaker 1: whereas for an other normal black hole, you know literally
• 44:23
  Speaker 1: zilch except for the mass, spin and the charge. And
• 44:26
  Speaker 1: here you have like a little bit more information. Plus
• 44:29
  Speaker 1: you get to describe these things in terms of a
• 44:31
  Speaker 1: diagram the physicists called a pair of pants diagram, which
• 44:34
  Speaker 1: is a lot of fun. Yeah. I guess if you
• 44:37
  Speaker 1: google pants and black holes, you'll get a whole bunch
• 44:40
  Speaker 1: of interesting images. I haven't tried it to make we
• 44:45
  Speaker 1: should maybe should have. The adults in the audience checked
• 44:49
  Speaker 1: that first. The ideas that you have two patches of
• 44:51
  Speaker 1: space time, which is sort of like the legs of
• 44:53
  Speaker 1: the pants, and then they're merging and they form like
• 44:56
  Speaker 1: the waist eventually. So if you draw that out with
• 44:59
  Speaker 1: like two of space time connecting each other, you start
• 45:02
  Speaker 1: with two, you end with one. It's sort of like
• 45:04
  Speaker 1: a pair of pants. Yeah, I think it's very hard
• 45:07
  Speaker 1: to paint that picture. But I think the main point
• 45:08
  Speaker 1: is that when the two black holes get together, they
• 45:11
  Speaker 1: sort of reach out in the middle, they start merging
• 45:13
  Speaker 1: that sort of I guess whether you're in scene would
• 45:15
  Speaker 1: be in the pants. And then they blocked together, right,
• 45:19
  Speaker 1: Is that sort of what happens? Like? Is that what this?
• 45:20
  Speaker 1: At least that's what the simulations say, that they just
• 45:23
  Speaker 1: blocked together and become one big hole. Yeah, they blocked
• 45:26
  Speaker 1: together and become one big hole and in the process
• 45:29
  Speaker 1: released an incredible amount of gravitational radiation. And we can
• 45:32
  Speaker 1: learn something about that process from looking at the details
• 45:35
  Speaker 1: of the wiggles of that radiation, right, And a lot
• 45:38
  Speaker 1: of this energy comes from the angular momentum, right, Like
• 45:42
  Speaker 1: maybe they're spinning around each other slowly when they're far apart,
• 45:46
  Speaker 1: But then when as the two black holes get together,
• 45:48
  Speaker 1: they have to preserve the same angular momentum as other.
• 45:51
  Speaker 1: By the time they get really really close each other,
• 45:53
  Speaker 1: they're spinning at incredible speeds, right, which makes for huge accelerations,
• 45:57
  Speaker 1: which make for a huge gravitational way. And that's why
• 46:00
  Speaker 1: probably every black hole out there is spinning the simplest
• 46:04
  Speaker 1: idea we have of a black hole, the short stile
• 46:06
  Speaker 1: black hole of a sphere is in the event that
• 46:09
  Speaker 1: the mass is not spinning, is just sitting there. But
• 46:12
  Speaker 1: because things fall into a black hole, and they will
• 46:14
  Speaker 1: always swirl around before they fall in, because otherwise they
• 46:18
  Speaker 1: have to fall in directly to the center of like
• 46:20
  Speaker 1: perfectly online with the singularity. Any deviation from that, they're
• 46:24
  Speaker 1: gonna fall in with a little bit of angular velocity
• 46:27
  Speaker 1: and so with momentum, and so they're gonna end up spinning.
• 46:30
  Speaker 1: So the final black hole has to be spinning. Every
• 46:32
  Speaker 1: black hole out there in the universe is almost certainly
• 46:35
  Speaker 1: spinning for that reason. And two black hole spinning around
• 46:39
  Speaker 1: each other, you're absolutely right, how a lot of angular momentum,
• 46:42
  Speaker 1: and they're going to generate a lot of gravitational radiation.
• 46:44
  Speaker 1: But the end result, what ends up happening at the
• 46:48
  Speaker 1: end is the emerge into one bigger black hole that's
• 46:50
  Speaker 1: bigger than the two individual black holes, but maybe like
• 46:54
  Speaker 1: not as big as if you just added the mass
• 46:56
  Speaker 1: of the two black holes exactly. They lose some of
• 46:59
  Speaker 1: that map ass, right, what happens when you lose energy
• 47:02
  Speaker 1: as a black hole, you lose mass, just like if
• 47:05
  Speaker 1: a black hole is radiating Hawking radiation, it's shooting out particles,
• 47:09
  Speaker 1: it's losing mass, and so if therefore it's shrinking, right,
• 47:12
  Speaker 1: So black holes can evaporate. They can lose their mass
• 47:15
  Speaker 1: through hawking radiation and get smaller and smaller. If they
• 47:18
  Speaker 1: also lose energy by gravitational radiation, they are also getting smaller.
• 47:24
  Speaker 1: And so there's so much energy released in these collisions
• 47:27
  Speaker 1: that sometimes they can lose a lot of mass, like
• 47:30
  Speaker 1: as much mass is our sun, right, and this energy
• 47:33
  Speaker 1: goes out as gravitational ways. But also I imagine a
• 47:36
  Speaker 1: whole bunch of like light to write like quasars have
• 47:40
  Speaker 1: you know, all that gas that was around each of
• 47:42
  Speaker 1: them is you know, going through these extreme velocities and
• 47:46
  Speaker 1: smashing against each other. A lot of that must go
• 47:48
  Speaker 1: out as basically light as well. Most of the energy
• 47:51
  Speaker 1: is radiated as gravitational radiation. It can be like five
• 47:55
  Speaker 1: of the mass of the system is lost due to
• 47:58
  Speaker 1: gravitational radiation. Can also be light emitted, and this is
• 48:01
  Speaker 1: sort of an open question. People have only seen a
• 48:04
  Speaker 1: couple examples where they have seen flashes of light perfectly
• 48:07
  Speaker 1: coincident with black hole collisions, and so something they're excited
• 48:11
  Speaker 1: to study. This is an era of multi messenger astronomy
• 48:14
  Speaker 1: when you can see the same thing you know, electromagnetic
• 48:16
  Speaker 1: radiation light as you can in gravitational radiation, and so
• 48:19
  Speaker 1: you can study it much more deeply. It's not something
• 48:22
  Speaker 1: we've seen many examples of, so it's not something that's
• 48:25
  Speaker 1: very well understood yet. All right, so stay tuned as
• 48:27
  Speaker 1: we get more samples of these collisions. But I guess, well,
• 48:30
  Speaker 1: one big question. It kind of goes back to what
• 48:32
  Speaker 1: you were saying before, which is that you know, time
• 48:35
  Speaker 1: slows down near a black hole. So if you're if
• 48:37
  Speaker 1: I'm near a black hole, my time is frozen basically
• 48:41
  Speaker 1: or it's super slow motion. So how do these But
• 48:43
  Speaker 1: but now, if you get a black hole nextly the
• 48:46
  Speaker 1: other one, isn't one of them slowing time down for
• 48:49
  Speaker 1: the other one? And wouldn't they just look to us
• 48:51
  Speaker 1: like they're frozen in time? Yeah, you might wonder, like
• 48:54
  Speaker 1: why do black holes ever collide? Don't they slow each
• 48:56
  Speaker 1: other's time down so much that they basically just get
• 49:00
  Speaker 1: rozen before they merge? Right, Remember that a black hole
• 49:03
  Speaker 1: is not a single point in space, So really, what
• 49:06
  Speaker 1: we're talking about is the merger of their event horizons.
• 49:10
  Speaker 1: And so while the two singularities may orbit each other
• 49:13
  Speaker 1: for a long time, slowing down because of the time dilation,
• 49:16
  Speaker 1: their event horizons can merge before the singularities come together. Right,
• 49:21
  Speaker 1: but still, like the time should be slowing down almost
• 49:25
  Speaker 1: to a stand still near the edge of each black hole,
• 49:28
  Speaker 1: so as they start to merge, when things kind of
• 49:32
  Speaker 1: freezing time. So things sort of do freezing time in
• 49:35
  Speaker 1: the sense that they get slowed down. Like what are
• 49:38
  Speaker 1: we seeing when we see black holes merge? We see
• 49:40
  Speaker 1: a pattern of gravitational radiation that comes from the black hole.
• 49:44
  Speaker 1: We see its speed up and go faster and faster
• 49:46
  Speaker 1: and faster. Now, when you look at that, you might wonder, like,
• 49:49
  Speaker 1: why isn't that slowed down? Why isn't it get like
• 49:52
  Speaker 1: spread out and slowed down. Why don't we see the
• 49:54
  Speaker 1: gravitational radiation gets slower and slower. The answer is that
• 49:57
  Speaker 1: we are. We are seeing the effects of that time
• 49:59
  Speaker 1: down lation already. Like if there wasn't time dilation, then
• 50:03
  Speaker 1: that gravitational radiation just for the collision would be going
• 50:06
  Speaker 1: insanely fast. So we are seeing the effects of time
• 50:09
  Speaker 1: dilation already. Sort of build in. When we see black
• 50:12
  Speaker 1: holes collide, it would look different without the time dilation. Oh,
• 50:16
  Speaker 1: I see, you're saying, like things are so extreme. Things
• 50:19
  Speaker 1: are moving so fast around these collisions, and gravitational ways
• 50:24
  Speaker 1: are being emitted so quickly and so intensely that even
• 50:28
  Speaker 1: with almost freezing time, they still come out and they
• 50:31
  Speaker 1: seem at a sort of a certain frequency for us exactly.
• 50:35
  Speaker 1: That's built into those calculations, and we do the numerical
• 50:38
  Speaker 1: relativity to figure out like what's happening, and where is
• 50:40
  Speaker 1: the event horizon, how much gravitational radiation is emitted. That's
• 50:43
  Speaker 1: of course taken into account, and so we're seeing just
• 50:46
  Speaker 1: what we expect time dilated, slowed down collision, but still
• 50:50
  Speaker 1: generating these gravitational waves, so it's not slowed down to zero.
• 50:55
  Speaker 1: I see. So if you are like near one of
• 50:56
  Speaker 1: these black holes as an observer, like it would be
• 50:59
  Speaker 1: like insane, right, It wouild just like happen in a flash. Yes, exactly,
• 51:03
  Speaker 1: would happened much more quickly. If you were very close
• 51:05
  Speaker 1: to the event horizons of these black holes as they
• 51:07
  Speaker 1: were happening, so you had sort of the same clock
• 51:10
  Speaker 1: as they would, you would see something very different. Just
• 51:12
  Speaker 1: the same way if you see somebody fall into a
• 51:14
  Speaker 1: black hole from far away, you see their time getting
• 51:17
  Speaker 1: slowed down, but they don't see that, right, they experienced
• 51:20
  Speaker 1: time normally. They just fall in and end up hitting
• 51:22
  Speaker 1: the singularity if you look very very different, if you
• 51:24
  Speaker 1: were in the neighborhood of the black hole. Mm. So
• 51:26
  Speaker 1: that's pretty convenient, right, Like, usually when you want to
• 51:29
  Speaker 1: observe something colliding really fast, you have to use a
• 51:32
  Speaker 1: high speed camera or you have to somehow slow down
• 51:35
  Speaker 1: time or sampled super fast that you get a good
• 51:38
  Speaker 1: picture of what's going up. This one has sort of
• 51:39
  Speaker 1: like a built in slow mo setting. Exactly when the
• 51:43
  Speaker 1: most interesting thing happens in the universe, it automatically goes slow,
• 51:47
  Speaker 1: just like in special effects in the movies, right, just
• 51:49
  Speaker 1: like in Marvel movies, where like the bad guy shoots
• 51:52
  Speaker 1: at the good guy and it's like time slows down
• 51:56
  Speaker 1: so they can dodge it. Yeah, exactly, just like in
• 51:59
  Speaker 1: the matrix they can make those crazy bends and dodge
• 52:01
  Speaker 1: those bullets. All right, Well, I guess then that's what
• 52:04
  Speaker 1: happens when you collide to black holes. They sort of
• 52:07
  Speaker 1: slowly reach out to each other. They start to merge,
• 52:10
  Speaker 1: you get a peanut shaped black hole, I guess, and
• 52:13
  Speaker 1: then that eventually blogs into a bigger black hole. And
• 52:16
  Speaker 1: some folks write and ask questions like, is it possible
• 52:19
  Speaker 1: for particles to escape the black hole during the merger
• 52:23
  Speaker 1: because they've heard the black holes shrink a little bit
• 52:25
  Speaker 1: they radiate this energy away, and so like, maybe when
• 52:29
  Speaker 1: the black holes are combining, something can like sneak out
• 52:31
  Speaker 1: the back, right, which is a fun idea, But unfortunately no,
• 52:35
  Speaker 1: black holes do not leak out any of this information
• 52:38
  Speaker 1: when they emerge. And the key thing to understand is
• 52:41
  Speaker 1: that even though the mass of the two black holes
• 52:43
  Speaker 1: is smaller than there's some the volume of a black
• 52:46
  Speaker 1: hole grows very quickly with its mass. So even though
• 52:50
  Speaker 1: the final mass is not just the sum of the
• 52:51
  Speaker 1: incoming mass, the final volume can be like eight times
• 52:55
  Speaker 1: the original black hole volume. So the event horizon is
• 52:58
  Speaker 1: smaller than it would have been if it hadn't radiated
• 53:01
  Speaker 1: gravitational radiation, but it's still bigger than either of the
• 53:04
  Speaker 1: two black holes combined. But you're saying, I think some
• 53:09
  Speaker 1: things do sort of escape, right, Some information escapes, right,
• 53:13
  Speaker 1: like even if it's in a different form in the
• 53:15
  Speaker 1: form of gravitational waves. I think you're saying earlier that
• 53:19
  Speaker 1: you know, you can learn a little bit of the
• 53:21
  Speaker 1: its history as stuff escapes, right, that's information, right, Yeah,
• 53:24
  Speaker 1: the gravitational waves contain information about the mass of the
• 53:27
  Speaker 1: black hole and its location and its velocity. Doesn't tell
• 53:30
  Speaker 1: you anything about what's going on inside. But you're right,
• 53:33
  Speaker 1: from the shape of the event horizon, you can tell
• 53:35
  Speaker 1: a little bit about the history of this black hole.
• 53:39
  Speaker 1: And you're right, that's also encoded in the gravitational waves.
• 53:42
  Speaker 1: But if something was just like at the edge of
• 53:43
  Speaker 1: the black hole as it was merging, could somehow, you know,
• 53:48
  Speaker 1: get lucky and somehow, you know, as these things are merging,
• 53:50
  Speaker 1: it maybe pools on the event horizon in such a
• 53:53
  Speaker 1: way that somehow it gives you a little bit of
• 53:55
  Speaker 1: a window for like one particle to like shoot out. No,
• 53:59
  Speaker 1: unfortunately not, that's what the event horizon means. The event
• 54:02
  Speaker 1: horizon is not a physical surface, is just like the
• 54:05
  Speaker 1: location past which no information ever actually gets out, so
• 54:09
  Speaker 1: you can't ask, like, is it possible for something to
• 54:11
  Speaker 1: get out? Well, that's like by definition, that's what the
• 54:13
  Speaker 1: event horizon is. It's the point where nothing ever escapes,
• 54:16
  Speaker 1: no information leaks out. That's how we figure out where
• 54:19
  Speaker 1: the event horizon is for these things at any given moment.
• 54:23
  Speaker 1: We look into the future history of these black holes
• 54:25
  Speaker 1: in our simulation and say, where's the point pass which
• 54:28
  Speaker 1: nothing ever escapes? Right right? I guess I'm thinking, like,
• 54:31
  Speaker 1: you know, like, if you're accelerating the black hole really fast,
• 54:34
  Speaker 1: isn't it possible for something to escape? You know, like
• 54:37
  Speaker 1: if I accelerated the Earth really fast, the things on
• 54:40
  Speaker 1: one side would be squished against the Earth, but maybe
• 54:42
  Speaker 1: the things on the other side of the Earth might
• 54:45
  Speaker 1: fly off and get left behind. It's certainly true that
• 54:48
  Speaker 1: if you did that to the Earth you would cause
• 54:50
  Speaker 1: incredible damage. And I like the way you're thinking about
• 54:53
  Speaker 1: really destructive experiments just to learn about the nature of
• 54:55
  Speaker 1: the universe. Kudos they're you're the becoming a physicist. But
• 54:59
  Speaker 1: if you did that to black hole, you with nothing
• 55:01
  Speaker 1: would leak out of the event horizon. That black hole
• 55:03
  Speaker 1: is enough curvature that even photons moving at the speed
• 55:06
  Speaker 1: of light can't escape, and by accelerating the black hole
• 55:08
  Speaker 1: can't make anything travel faster than the speed of one.
• 55:11
  Speaker 1: All right, it seems like it's plausible well, but I
• 55:14
  Speaker 1: think the main question is what happens when two black
• 55:17
  Speaker 1: holes collide, And they sort of don't collide, right, they
• 55:20
  Speaker 1: sort of smushed together. I guess it's the simple answer.
• 55:23
  Speaker 1: They sort of grow to meet each other and for
• 55:25
  Speaker 1: a few moments there you have a black hole that
• 55:28
  Speaker 1: doesn't have a spherical event horizon, which is kind of
• 55:31
  Speaker 1: an incredible revealing moment for the black hole. Yeah, you
• 55:35
  Speaker 1: get a peanut, I guess, peanut black hole. All right, Well,
• 55:39
  Speaker 1: I think this really kind of points to some of
• 55:41
  Speaker 1: the amazing things that can happen out there in the universe.
• 55:44
  Speaker 1: You know, the situations with that are not just extreme,
• 55:48
  Speaker 1: but it's like you take two extreme situations and you
• 55:50
  Speaker 1: smash them together, you get like extra extreme. The thing
• 55:53
  Speaker 1: that amazes me is that we can do these calculations.
• 55:56
  Speaker 1: People perform these simulations using numerical relativity tools. They described
• 56:00
  Speaker 1: these incredible bonkers things that's happening, and then we can
• 56:03
  Speaker 1: actually look out there in the universe and we see them.
• 56:06
  Speaker 1: It really happens, and it makes you wonder, like, is
• 56:09
  Speaker 1: this what's really going on out there? If I could
• 56:11
  Speaker 1: fly out to the black hole and like watch it
• 56:13
  Speaker 1: with my eyeballs. Is this what I would see? You know?
• 56:16
  Speaker 1: And I hope that one day, eventually we can't travel
• 56:18
  Speaker 1: the universe and we don't have to just see these
• 56:20
  Speaker 1: black holes from billions of light years away. We could
• 56:23
  Speaker 1: see these collisions close up. Yeah, just make sure you
• 56:25
  Speaker 1: bring some peanuts to snack on while you watch, and
• 56:29
  Speaker 1: smash your peanuts together with a chocolate bar and boom,
• 56:31
  Speaker 1: you invented chocolate. Eminem's that's too extreme, Daniel extreme snacking
• 56:37
  Speaker 1: with Daniel and Jorge. All right, well, we hope you
• 56:39
  Speaker 1: enjoyed that. And think about all the amazing things that
• 56:42
  Speaker 1: are happening right now in the universe. Who's you know
• 56:44
  Speaker 1: echoes we're hearing right now that are washing through right
• 56:47
  Speaker 1: now and maybe telling you about what happened in that collision.
• 56:51
  Speaker 1: Think about all the things that are happening in the
• 56:53
  Speaker 1: universe and sending us information that we don't even know
• 56:55
  Speaker 1: about that we're ignoring that future generations of scientists will
• 56:59
  Speaker 1: just cover and we'll use to learn incredible things about
• 57:02
  Speaker 1: the universe. Yeah. I mean, there must have been hundreds
• 57:05
  Speaker 1: or thousands or hundreds of thousands of black hole collisions.
• 57:09
  Speaker 1: Who's crash, whose mush sounds washed over humanity, but we
• 57:13
  Speaker 1: never even knew. We see a tiny, tiny fraction of
• 57:17
  Speaker 1: the universe, and we understand even lesson. Thanks for joining us,
• 57:21
  Speaker 1: see you next time. Thanks for listening, and remember that
• 57:31
  Speaker 1: Daniel and Jorge explain the Universe is a production of
• 57:34
  Speaker 1: I Heart Radio. Or more podcast from my heart Radio,
• 57:37
  Speaker 1: visit the I heart Radio app, Apple Podcasts, or wherever
• 57:41
  Speaker 1: you listen to your favorite shows.