Latest / Daniel and Kelly’s Extraordinary Universe / What's the cosmic gravitational background?

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What's the cosmic gravitational background? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Hey, or Hey, I have a question for you about
0:11
Speaker 1: drawing cartoons. Hey, finally something that I'm an expert in.
0:15
Speaker 1: What's the question, Well, it's more about the backgrounds. Actually.
0:18
Speaker 1: How do you decide whether to leave the cartoon background
0:21
Speaker 1: blank or fill it in with a color, or like
0:24
Speaker 1: draw a full scene in the background. M Well, I
0:27
Speaker 1: guess it can be whatever you want the background. I mean,
0:30
Speaker 1: you just don't want to take away attention from what's
0:32
Speaker 1: happening in the panel. So the background is just like
0:35
Speaker 1: filler to be ignored. Oh, you know, it's all hard.
0:38
Speaker 1: You know. Sometimes that's where the treasures are hidden in
0:41
Speaker 1: the background. Oh, sometimes that's true in physics as well. Really,
0:45
Speaker 1: you find Waldo sometimes in the background, the cosmic Waldo background.
1:05
Speaker 1: Hi am Orhammed, cartoonists and the creator of PhD comics. Hi.
1:09
Speaker 1: I'm Daniel. I'm a particle physicist, and I have never
1:12
Speaker 1: found Waldo in one of those books. Never. I think
1:15
Speaker 1: maybe you just haven't tried, Daniel. I think that's it.
1:18
Speaker 1: I get bored after like two seconds, I'm like, why
1:20
Speaker 1: do I care about finding this guy? And yet finding
1:23
Speaker 1: the Higgs boson in a bunch of noisy data. That's
1:26
Speaker 1: somehow more interesting. Yeah, I can write a computer program
1:28
Speaker 1: that scans it for me automatically. That could write a
1:30
Speaker 1: computer program that looked for Waldo. That would be more
1:33
Speaker 1: fun do it? Yeah, I mean, what else are you doing?
1:36
Speaker 1: What else could you be doing? It's more productive than that.
1:39
Speaker 1: Welcome to our podcast Daniel and Jorge Explain the Universe,
1:42
Speaker 1: a production of I Heart Radio, in which we don't
1:44
Speaker 1: look for Waldo, but we do look for answers to
1:47
Speaker 1: the deepest questions humans have ever asked. Questions like why
1:52
Speaker 1: is the universe the way that it is? Could it
1:54
Speaker 1: have been another way? How big is it anyway? How
1:58
Speaker 1: did it start, how will it end? And what is
2:00
Speaker 1: it made out of. We don't shy away from any
2:02
Speaker 1: of these incredible questions, which inform the entire context of
2:06
Speaker 1: the human existence, and we admit ignorance. We don't pretend
2:10
Speaker 1: to know all of the answers, but we try to
2:11
Speaker 1: explain to you what science does and does not know. Yeah,
2:15
Speaker 1: we like to talk about all of those big questions
2:17
Speaker 1: that are at the forefront of science and the exploration
2:20
Speaker 1: being done by physicists and other scientists. We also like
2:24
Speaker 1: to talk about what sort of in the background of
2:25
Speaker 1: science as well. That's right. There are wonderful surprises out
2:28
Speaker 1: there in the universe. Sometimes you know what you're looking for.
2:31
Speaker 1: Sometimes you stumble across something accidentally when you were looking
2:34
Speaker 1: for something else. Sometimes you see an exciting discovery that
2:37
Speaker 1: jumps right out at you. Sometimes it's treasures hidden in
2:40
Speaker 1: the background. Yeah. And the crazy thing is that it's
2:43
Speaker 1: all there right like literally, when you look at the
2:46
Speaker 1: background of any picture that you take, and you look
2:47
Speaker 1: at the sky behind you or behind the person that
2:50
Speaker 1: you're taking the picture of, there's information there about the universe.
2:54
Speaker 1: There might be hidden secrets and interesting things to discover
2:57
Speaker 1: right there where you least expected. That's true. Even the
3:01
Speaker 1: darkest spots in the night sky have some photons coming
3:04
Speaker 1: to us from very very distant locations. If you pointed
3:08
Speaker 1: the hubble instead of your iPhone at some point in
3:10
Speaker 1: the sky, you would see millions and billions of galaxies
3:14
Speaker 1: so fat and so distant that their photons arrived like
3:17
Speaker 1: every few seconds or every few minutes, rather than all
3:19
Speaker 1: the time like the sun. But there is information in
3:23
Speaker 1: every little tiny patch of the sky about the nature
3:25
Speaker 1: of the universe and what's going on out there. Yeah.
3:28
Speaker 1: Can you detect wal dogs. Maybe in those signals standards,
3:32
Speaker 1: you know, the bosons to their waldenos, they're hard to find.
3:35
Speaker 1: I guess, yeah, if I discover particle, can I called
3:38
Speaker 1: the waldo? Like if it's in the background of the
3:40
Speaker 1: you know, the universe. I think that would disqualify you
3:43
Speaker 1: from participating in any experiment because they would not want
3:46
Speaker 1: you to give it that name. I see a pre
3:49
Speaker 1: screen for a name giving. We don't, but we should
3:52
Speaker 1: because there's been some bad choices in the past. But yeah,
3:56
Speaker 1: we like to ask all of the big questions that
3:58
Speaker 1: are out there that scientists are wondering about and that
4:00
Speaker 1: scientists are speculating about. There are interesting things that scientists
4:04
Speaker 1: think might exist and things that we have not yet detected.
4:07
Speaker 1: That's right. Every time we open up a new kind
4:10
Speaker 1: of eyeball and look out there in the universe in
4:12
Speaker 1: a new way, we find all sorts of crazy, exciting stuff,
4:15
Speaker 1: and sometimes we know what we're looking for. We think
4:18
Speaker 1: that there might be a hint a message out there
4:20
Speaker 1: in the universe we haven't detected yet that could give
4:22
Speaker 1: us fantastic clues as to the nature of the Big Bang,
4:26
Speaker 1: What happened in the first moment of the universe, or
4:28
Speaker 1: what's going on with black holes dying all across the galaxy? Yeah,
4:32
Speaker 1: because you never know where the next big answer is
4:35
Speaker 1: going to come from, or where the next big question
4:37
Speaker 1: might come from. For example, we have this great question
4:39
Speaker 1: from j J, who's five years old, who sent us
4:42
Speaker 1: a listener question through the internet. That's right, here's a
4:45
Speaker 1: question that JJ's father sent to us because he couldn't
4:48
Speaker 1: answer it himself. Here's j J as the son by
4:55
Speaker 1: that in the middle of our galaxy? Oh so ute,
5:00
Speaker 1: Wait was it a question or a statement? Is he
5:03
Speaker 1: saying he's going to make a star goes supernova? This
5:06
Speaker 1: is not the youngest supervillain listener that we have. He's
5:09
Speaker 1: asking what would happen if our star win supernova next
5:13
Speaker 1: to the supermassive black hole in the center of our galaxy. Wow,
5:17
Speaker 1: it's amazing that a five year old knows the word
5:20
Speaker 1: supernova and kind of what it means. Yeah, so thank
5:23
Speaker 1: you Lowell for encouraging the scientific curiosity in your children
5:27
Speaker 1: in the next generation. You are fueling human progress. So
5:31
Speaker 1: that's a complex question. Here, JJ is asking what if
5:34
Speaker 1: our son was somehow next to the black hole in
5:37
Speaker 1: the middle of our galaxy, and then what if it
5:40
Speaker 1: suddenly went supernova? Right, that's right, and j J doesn't
5:43
Speaker 1: have to worry. Our son is not going to go supernova.
5:46
Speaker 1: Supernova is one of the end stages of a star,
5:49
Speaker 1: when it gets so massive that it collapses gravitationally. But
5:53
Speaker 1: in order for that to happen, you have to have
5:55
Speaker 1: a lot more mass than our son does. You need
5:57
Speaker 1: like eight times the mass of our son the minimum
6:00
Speaker 1: threshold for a start to end up as a supernova. Right,
6:03
Speaker 1: But so it can go supernova on its own, but
6:06
Speaker 1: it might eat something else and then get bigger, right,
6:08
Speaker 1: and then go supernova. That's right. There is one possibility
6:11
Speaker 1: our sun will probably end its life as a white dwarf.
6:15
Speaker 1: So there will be a phase which becomes a red
6:17
Speaker 1: giant and blows out a lot of stuff, and then
6:19
Speaker 1: it collapses again, and then it blows out more stuff,
6:21
Speaker 1: and at the core would be left a very very
6:23
Speaker 1: dense blob, a white dwarf, which essentially just a hot
6:26
Speaker 1: rock and it's white not because this fusion going on
6:29
Speaker 1: inside it, but because it's glowing white hot. And these
6:31
Speaker 1: white dwarves usually just sit around for trillions of years
6:34
Speaker 1: and cool off but sometimes if there's another star that
6:37
Speaker 1: comes nearby, they're so dense they can eat those stars,
6:41
Speaker 1: and if they eat enough of them, that can trigger
6:43
Speaker 1: a supernova. Wow. Yeah, I sometimes feel like that. And Thanksgiving,
6:47
Speaker 1: don't bring around another pie. I'm gonna blow No more turkey, please,
6:52
Speaker 1: I'm gonna supernova. Do you gravitationally attract dessert if you
6:55
Speaker 1: eat enough turkey? No, I'm just easy electromagnetic corps for that. Nice.
7:00
Speaker 1: But I guess the question is what happens if a star,
7:02
Speaker 1: or I guess any star blows up next to a
7:04
Speaker 1: black hole? Like, does it blow away the black hole?
7:07
Speaker 1: Does it like evaporated? Does it do nothing? If you
7:10
Speaker 1: explode it next to a black hole? What happens? Well,
7:12
Speaker 1: first of all, you cannot explode a black hole, like
7:14
Speaker 1: there's nothing you can do that will destroy a black hole,
7:17
Speaker 1: because remember, a black hole is a dense blob of
7:20
Speaker 1: matter that will eat everything else, and that includes other
7:23
Speaker 1: forms of energy. So you shoot a particle beam, you
7:25
Speaker 1: shoot antimatter, you shoot dark matter into a black hole.
7:28
Speaker 1: It eats everything. It's like Jorge at Thanksgiving dinner, right,
7:31
Speaker 1: It's happy to take anything. And so anything you blow
7:35
Speaker 1: in there, including the remnants of a supernova will just
7:38
Speaker 1: make it bigger and stronger. Oh, I see, So it's
7:41
Speaker 1: not possible to like blow it away or move it,
7:43
Speaker 1: or at least maybe like push it a little bit.
7:45
Speaker 1: Is it possible to push a black hole? It is
7:47
Speaker 1: possible to push a black hole to accelerate. It is
7:49
Speaker 1: a mass, and so you can tug on it. For example,
7:51
Speaker 1: if you bring another black hole near it, those two
7:54
Speaker 1: black holes will accelerate towards each other, swirling around and
7:57
Speaker 1: creating all sorts of like gravitational radiation. And it is
8:00
Speaker 1: interesting because the supernova near a black hole, like that
8:03
Speaker 1: supernova will eject the material really really violently. It's a
8:07
Speaker 1: huge explosion. The stuff comes out like a significant fraction
8:10
Speaker 1: of the speed of light. But it won't necessarily just
8:12
Speaker 1: like get all immediately eaten by the black hole because
8:14
Speaker 1: it's moving at such high speed unless it pointed exactly
8:17
Speaker 1: at the black hole. They'll probably like miss a little
8:20
Speaker 1: bit and then swirl around the black hole and become
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Speaker 1: part of the accretion disc. That's like stuff around the
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Speaker 1: black hole that's hot and glowing. Interesting, But the explosion
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Speaker 1: itself I won't impart any like momentum on the black
8:32
Speaker 1: hole to push it a little bit, even no, it
8:34
Speaker 1: will impart some momentum on the black hole. But you know,
8:36
Speaker 1: supermassive black hole like we're talking about as a mass
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Speaker 1: that's millions of times the mass of the Sun, and
8:42
Speaker 1: the kind of supernover we're talking about comes from a
8:44
Speaker 1: white dwarf, which is like less than the mass of
8:46
Speaker 1: our Sun. So the energy from it is just going
8:48
Speaker 1: to be like a pin prick. It's like if a
8:50
Speaker 1: mosquito lands on you, does it knock you over? What
8:52
Speaker 1: depends on the mosquito, you know, it depends on what
8:56
Speaker 1: it's carrying. I mean, I've never been to Panama. I
8:59
Speaker 1: don't know how big those skeetos they get big. Yeah,
9:01
Speaker 1: not as big as the Australian ones. Everything is bigger
9:04
Speaker 1: in Australia. Well up here in the States. I've never
9:06
Speaker 1: been knocked over by a mosquito. But you know, not yet.
9:10
Speaker 1: I'm getting older and they're getting bigger. Well that's the
9:12
Speaker 1: answer for j J. Thanks for sending in the question.
9:15
Speaker 1: And so today we'll be talking about sort of what's
9:17
Speaker 1: happening in the background of the universe. We know that
9:21
Speaker 1: there's the cosmic microwave background radiation. That's light, that's electromagnetic
9:25
Speaker 1: energy that's out there hanging out from the Big Bang.
9:29
Speaker 1: But there might be other things in the background that
9:32
Speaker 1: may or may not be there that we might have
9:34
Speaker 1: information also about the universe. Right, that's right. The cosmic
9:37
Speaker 1: microwave background is a really really rich source of information
9:40
Speaker 1: about what happened in the very early universe and what's
9:43
Speaker 1: going on now. But it's just another form of light. Right,
9:46
Speaker 1: Microwaves are electromagnetic radiation. But recently we figured out other
9:50
Speaker 1: ways to look at the universe, Like we were just
9:52
Speaker 1: talking about black holes generate gravitational radiation, which is a
9:56
Speaker 1: completely different form of radiation and another way to look
9:59
Speaker 1: at the universe. And so now we're wondering about whether
10:02
Speaker 1: we can see a background to the gravitational radiation in
10:06
Speaker 1: the universe. So today on the program, we'll be asking
10:09
Speaker 1: the question what is the cosmic gravitational background and who
10:19
Speaker 1: will win the Nobel Prize for finding it? Interesting. So,
10:21
Speaker 1: it's something that we haven't found yet. It is not
10:24
Speaker 1: something that we have seen exactly. There are some hints,
10:27
Speaker 1: and we'll talk a little bit about some of the
10:28
Speaker 1: experiments that claim to maybe see it and have claimed
10:31
Speaker 1: to see it and been debunked. But so far it's
10:34
Speaker 1: not an established thing. It's like potentially a discovery in
10:36
Speaker 1: our future. It's like a treasure chest we haven't dug
10:39
Speaker 1: up yet. And it has a very similar name to
10:41
Speaker 1: the cosmic microwave background. This was the cosmic gravitational background. Now,
10:46
Speaker 1: couldn't you use a different name, like the universal Gravitational background,
10:50
Speaker 1: just to like set it apart a little bit. No,
10:52
Speaker 1: we want to use the same name to show the similarities. Like,
10:55
Speaker 1: it really is very similar in concept to the CMB,
10:58
Speaker 1: so we wanted to use a name that, you know,
11:00
Speaker 1: invade the parallelism there. That was a little bit more awkward.
11:02
Speaker 1: The CGB is harder to say than the c m B.
11:05
Speaker 1: The cg B. That sounds like a rap group maybe,
11:08
Speaker 1: or it sounds like a type of monitor. Do you
11:10
Speaker 1: have an l E ED or a c GB or
11:12
Speaker 1: maybe a Supreme Court justice? Maybe the r g B. Yeah,
11:17
Speaker 1: I'm done with c g BRBG right. Yeah. Anyways, it
11:20
Speaker 1: sounds cosmic, and we were wondering how many people out
11:23
Speaker 1: there knew what it was or had even heard of
11:26
Speaker 1: the cosmic gravitational background. So, as usual Daniel went out
11:29
Speaker 1: there into the wilds of the Internet to ask people
11:32
Speaker 1: what is the cosmic gravitational background? So thank you to
11:35
Speaker 1: all of our listeners who do live in the wilds
11:37
Speaker 1: of the Internet and allow me to visit. If you'd
11:40
Speaker 1: like to participate and send your speculation to Crazy Physics
11:44
Speaker 1: topics in the future, please don't be shy. Send me
11:46
Speaker 1: a message to questions at Daniel and Jorge dot com
11:50
Speaker 1: and you can show off to all your friends hearing
11:51
Speaker 1: your voice on the podcast. So think about it for
11:54
Speaker 1: a second. What do you think it might be. Here's
11:57
Speaker 1: what people had to say heard of the Cosmic Gravitation
12:00
Speaker 1: show background. Um, I'm going to guess that it has
12:03
Speaker 1: to do with the overall mass of the universe or
12:08
Speaker 1: density I guess of mass in the universe. It makes
12:12
Speaker 1: me think of cotton candy and when you're making it,
12:17
Speaker 1: you know, you get the big glob of cotton candy
12:19
Speaker 1: on the paper cone, but after that there's still fragments
12:23
Speaker 1: and strings of it blowing around in the machine. And
12:27
Speaker 1: that's how I picture cosmic gravitational background, just a little
12:32
Speaker 1: snippets that are left after the planets and the stars congealed.
12:38
Speaker 1: Shure that the cosmic gravitational background is an option on Zoom. Well,
12:44
Speaker 1: this is something recent. Um, it might work like a
12:51
Speaker 1: cosmic microwave background. I think so. Never heard of the
12:58
Speaker 1: cosmic gravitational background. I guess it might be some low
13:02
Speaker 1: level gravitational way of background, or some general gravitational pool
13:11
Speaker 1: of the universe to words a specific point or from
13:16
Speaker 1: the Big Bang. I have not heard of the cosmic
13:21
Speaker 1: gravitational background, but since it has a pretty similar name
13:24
Speaker 1: to the cosmic background radiation, I'll guess it's some sort
13:28
Speaker 1: of map of the very early universe and how gravity
13:34
Speaker 1: like began to clump mass after the initial quantum fluctuations
13:41
Speaker 1: that caused the clumping, just how gravity was distributed in
13:48
Speaker 1: the very early universe right after the Big Bang and
13:51
Speaker 1: all that stuff. I have never even heard this term before,
13:55
Speaker 1: so this is a wild guess. I'm assuming it has
14:00
Speaker 1: something to do with the gravitational field of the entire cosmos.
14:06
Speaker 1: I don't know how you would measure it, but that
14:09
Speaker 1: would be my guest, all right. I like the person
14:12
Speaker 1: who say it's an option on zoom to set your
14:14
Speaker 1: background to the cosmic gravitational background. Technically that is true, maybe, right, everything.
14:22
Speaker 1: I guess everything in the background does have gravity, so
14:25
Speaker 1: and it's part of the cosmos. So really all Zoom
14:28
Speaker 1: backgrounds are cosmic gravitational backgrounds. Yeah, I wonder if astronomers
14:32
Speaker 1: even thought to look on Zoom to find the c GB.
14:35
Speaker 1: I mean, maybe it's just that easy, right, just an
14:37
Speaker 1: option on Zoom win Nobel, at least in some other
14:40
Speaker 1: noble category. Maybe. Well, there's so many options on Zoom.
14:43
Speaker 1: Who knows what's buried in some of those sub sub menus, right,
14:46
Speaker 1: there's a Waldo option? No, please no, because we know
14:52
Speaker 1: it sometimes means are not that exciting. It'd be nice
14:54
Speaker 1: to have a little a bit of a puzzle there.
14:56
Speaker 1: Find Waldo in the background of your Zoom speaker. Yeah,
14:59
Speaker 1: there you that's actually a pretty good idea to build
15:04
Speaker 1: games in a Zoom to keep people entertained. So this
15:07
Speaker 1: is pretty interesting, Daniel, I didn't even know there was
15:10
Speaker 1: a cosmic gravitational background, like most of our listeners and
15:13
Speaker 1: people who responded so step us three. I'm guessing it
15:16
Speaker 1: has something to do with gravitational waves and maybe the
15:19
Speaker 1: Lego experiment that we have to detect them exactly it
15:22
Speaker 1: does to understand what the cosmic gravitational background is, we
15:26
Speaker 1: first have to understand what gravitational messages are and with
15:29
Speaker 1: the gravitational foreground is. So let's start off with what
15:33
Speaker 1: gravitational wave is. For those of you who don't recall,
15:36
Speaker 1: space itself can ripple because mass changes the shape of space,
15:41
Speaker 1: like if you have a black hole or a heavy
15:42
Speaker 1: object or something that bends space. We know now that
15:46
Speaker 1: gravity is not just a force between two objects. It's
15:49
Speaker 1: actually space curving around masses and changing the way things move.
15:54
Speaker 1: So gravity is this like apparent force. That's just because
15:58
Speaker 1: we can't see the shape of space, the bending of space.
16:01
Speaker 1: So we know that mass can bend space. Well, what
16:03
Speaker 1: happens when mass moves or mass changes, Well, that causes
16:07
Speaker 1: ripples because if a mass moves, then it's gravitational field
16:11
Speaker 1: is going to move. So that's what causes ripples in
16:14
Speaker 1: space time, and that's what we call a gravitational wave.
16:17
Speaker 1: Right Like, gravitational signals like the effects of gravity take
16:21
Speaker 1: time and space to move. Right Like if our son
16:24
Speaker 1: suddenly disappeared or started moving or jiggling, it would take
16:28
Speaker 1: like eight minutes for us to feel those changes in
16:30
Speaker 1: its gravity. Exactly because information takes time to propagate. The
16:34
Speaker 1: gravitational fields don't change immediately. There's a ripple. There's like
16:37
Speaker 1: a wave that passes through the gravitational field, sort of
16:41
Speaker 1: updating everything, and that wave moves at the speed of light.
16:45
Speaker 1: And this is not unique to gravity, right, happens to
16:47
Speaker 1: lots of things anything in fact, where information takes time
16:50
Speaker 1: to propagate. Like think about a simple string. Maybe you're
16:52
Speaker 1: playing jump rope with your friend. You pull the string up,
16:55
Speaker 1: the whole string doesn't move at once. Right. You see,
16:58
Speaker 1: first the first bit of the string moves up, and
17:00
Speaker 1: then that pulls the next bit of the string, which
17:02
Speaker 1: pulls the next bit of the string, and which you
17:04
Speaker 1: get is a wave moving through your jump rope. Right. So,
17:08
Speaker 1: anytime you have a material where information takes time to propagate,
17:11
Speaker 1: where it's not just like instantaneous transfer, that's because everything
17:14
Speaker 1: is local, then you get a wave. And so that's
17:16
Speaker 1: true for a jump rope, and it's also true for electromagnetism. Right.
17:21
Speaker 1: We can think about photons as electromagnetic waves because if
17:25
Speaker 1: you take an electron, for example, it has an electric field.
17:29
Speaker 1: If you shake that electron, then the electric field moves
17:32
Speaker 1: with it. But again not instantaneously. It goes back and
17:36
Speaker 1: forth with the electron. And that's what a photon is.
17:39
Speaker 1: It's just an update in the electromagnetic field. Yeah, it's
17:42
Speaker 1: like a wave. It's like electromagnetic what a ripple, right,
17:45
Speaker 1: is what a photon is. Yeah, And that's how you
17:47
Speaker 1: generate photons. You have an antenna and you wiggle the
17:50
Speaker 1: electrons up and down inside the antenna changing the electromagnetic
17:54
Speaker 1: fields around the antenna in a regular pattern, and that
17:57
Speaker 1: causes waves in those fields, which are photo That's what
18:00
Speaker 1: light is. That's what light is, yes, exactly. And a
18:04
Speaker 1: gravitational wave is the same concept, except instead of wiggling
18:08
Speaker 1: a string or wiggling the electromagnetic fields, you're wiggling space itself,
18:13
Speaker 1: which is bonkers and super fun to say. Yeah, and
18:16
Speaker 1: it's a true thing, right, Like we have measurements of
18:19
Speaker 1: the house space wiggles out there in space out there
18:22
Speaker 1: in the cosmos, right, Like we've detected gravitation ways from
18:25
Speaker 1: black holes swirling around each other and things kind of exploding. Right, Yes,
18:29
Speaker 1: we have seen it, which is amazing. This is an
18:32
Speaker 1: idea that's a hundred years old. When Einstein developed general relativity,
18:36
Speaker 1: one of the big steps forward, there was this concept
18:39
Speaker 1: that information doesn't propagate instantaneously. Right in Newton's gravity, information
18:44
Speaker 1: was instantaneous, so the Sun disappeared, then gravity and Earth
18:47
Speaker 1: changed instantaneously. So when Einstein introduced this concept of the
18:51
Speaker 1: limited speed of information, which of course came from his
18:53
Speaker 1: special relativity, this was one of the big predictions that
18:57
Speaker 1: if general relativity was true, we should see gravitational waves.
19:00
Speaker 1: But everybody thought these things are tiny either gonna be
19:03
Speaker 1: really really hard to see because gravity is so weak.
19:07
Speaker 1: And then in the seventies people saw some clues about
19:10
Speaker 1: gravitational waves because they saw pulsars, and those pulsars were
19:14
Speaker 1: orbiting each other and slowly falling into each other, and
19:17
Speaker 1: the only way that happens is if they're losing energy
19:19
Speaker 1: somehow radiating gravitational waves. We didn't see the waves themselves yet,
19:24
Speaker 1: but we saw the things were radiating some kind of energy,
19:27
Speaker 1: so it must have been gravitational That won a Nobel prize.
19:31
Speaker 1: And then decades later people built machines that actually were
19:34
Speaker 1: able to measure the gravitational waves directly, like to see
19:37
Speaker 1: the waves themselves, operate on machines here on Earth to
19:41
Speaker 1: see the physical effects of these ripples of space and time. Yeah,
19:45
Speaker 1: that's the big Lego experiment a few years ago that
19:48
Speaker 1: made a big splash in the science community. And now
19:50
Speaker 1: we have other observatories to listen for these gravitational waves. Right, yeah,
19:54
Speaker 1: this is one of the Nobel Prizes I didn't win.
19:58
Speaker 1: Do you keep track of all the Nobel Prize if
20:00
Speaker 1: you don't win. I mean there's a lot more Noble prices.
20:02
Speaker 1: I haven't one than I have one, so it's more
20:05
Speaker 1: work to keep track of. But I interviewed at cal
20:08
Speaker 1: Tech and was thinking about going to grad school there
20:10
Speaker 1: to work on this project. But I remember thinking to myself,
20:12
Speaker 1: they're never going to see these things. Oh my gosh,
20:14
Speaker 1: this seems too hard, and I decided to go to
20:16
Speaker 1: particle physics instead. And you know, they won the Nobel Prize.
20:20
Speaker 1: Congrats to them. They proved me wrong. So one more
20:22
Speaker 1: mistake I've made in my career. Well, you were involved
20:25
Speaker 1: in the discovering the Higgs boson that won a Noble Prize, right, Yeah,
20:29
Speaker 1: I didn't win a Nobel Prize for that, but that
20:30
Speaker 1: went to the theorist. But yeah, I was involved there. Anyway,
20:33
Speaker 1: we have the Lego and the Virgo experiments. These are
20:36
Speaker 1: observatories around the world that use interferometers to see these wiggles.
20:41
Speaker 1: And these wiggles come from really big events, dramatic events
20:44
Speaker 1: out there in the universe that generate gravitational waves. Like
20:47
Speaker 1: any time any object with mass accelerates, it generates a
20:51
Speaker 1: little gravitational wave. But you know, gravity is so weak
20:54
Speaker 1: that in order to see these things you need a
20:56
Speaker 1: big gravitational wave. Things like two black holes swirling around
21:01
Speaker 1: each other and then merging and eating each other generates
21:04
Speaker 1: a lot of gravitational wave energy. That's the kind of
21:07
Speaker 1: thing that we can see here on Earth. But even
21:09
Speaker 1: if it's that big, even if it's a huge, dramatic
21:11
Speaker 1: cataclysmic event, we can just barely see it here on
21:14
Speaker 1: Earth because the ripples in space and time are very
21:17
Speaker 1: very small. For example, if you took a rod, then
21:19
Speaker 1: when a gravitation wave passed, it would get shorter by
21:23
Speaker 1: one part in ten to the twenty and then we
21:26
Speaker 1: get longer as the wave passed by one part in
21:28
Speaker 1: tens of the twenties. So to see these things you
21:30
Speaker 1: need really really accurate measurements of distance. Yeah, it's a
21:34
Speaker 1: crazy amount of engineering to be able to measure things
21:37
Speaker 1: so small and it works. And they've seen a lot
21:41
Speaker 1: of these crazy events like black holes colliding with each
21:44
Speaker 1: other or black holes with neutron stars, and we've seen
21:47
Speaker 1: like maybe a dozen of them, and so they're common
21:50
Speaker 1: and they sort of form, as you say, the foreground
21:53
Speaker 1: of the gravitational universe, right, the gravitational field in the universe.
21:58
Speaker 1: And so there's the question of whether or not there's
22:01
Speaker 1: also kind of a background in gravitational waves, and whether
22:04
Speaker 1: or not that has some interesting signals that might tell
22:07
Speaker 1: us about the origins of the universe. So let's get
22:10
Speaker 1: into that. But first let's take a quick break. All right,
22:25
Speaker 1: we're talking about the cosmic gravitational background now, Daniel, we
22:28
Speaker 1: talked about gravitational waves. That's when like big things like
22:31
Speaker 1: black holes and neutron stars swirl around each other and collide.
22:35
Speaker 1: They generate these ripples in space that we can detect here.
22:38
Speaker 1: That's what you call the foreground of the gravitational universe, right,
22:42
Speaker 1: that's right. Those are like big shouts in the gravitational spectrum,
22:46
Speaker 1: huge events that we're listening for specifically in their short
22:50
Speaker 1: their localizes, they come from one direction, right, then they're
22:53
Speaker 1: big events were like things happening, but there might be
22:56
Speaker 1: things happening in the background as well, that's right. Just
22:58
Speaker 1: like when you look up at the sky you see
23:00
Speaker 1: photons from stars. Those are like little localized events. You
23:04
Speaker 1: can see them. But then in between all the stars
23:06
Speaker 1: is the background, right, is the thing that you're not
23:09
Speaker 1: looking for usually, And what we're interested in here is like,
23:12
Speaker 1: is there a background to gravitational radiation? Are there things
23:16
Speaker 1: between these big events, these big gravitational shouts that we
23:20
Speaker 1: can listen to and we can hear and maybe learn something.
23:24
Speaker 1: The concept of a background is something everybody should be
23:26
Speaker 1: familiar with. Like if you're at a party and you're
23:28
Speaker 1: trying to talk to your friend, there's sometimes a lot
23:30
Speaker 1: of background noise, or at a restaurant or a bar,
23:33
Speaker 1: there can be a lot of background noise, which you know,
23:35
Speaker 1: isn't the information you're looking for. You're trying to listen
23:37
Speaker 1: to your friends story, trying to seem interested in it,
23:39
Speaker 1: but there's always other noise around you, which sometimes makes
23:42
Speaker 1: it hard to listen to it. Right, that's the background. Yeah,
23:45
Speaker 1: there's might be stuff that you don't maybe want to
23:47
Speaker 1: pay attention to, but maybe you do. Maybe there's some
23:50
Speaker 1: interesting conversations behind your friends. Yeah, that's right. I like
23:52
Speaker 1: eavesdropping in bars, listen to other people's conversations. In this case,
23:56
Speaker 1: it's interesting because we only recently became able to serve
24:00
Speaker 1: the cosmic gravitational four ground. Right, we were listening for
24:03
Speaker 1: gravitational radiation and didn't hear anything for years and years
24:07
Speaker 1: and years because we were making our instruments more and
24:09
Speaker 1: more sensitive. It's only recently we've been able to hear
24:12
Speaker 1: the loud shouts. Right, Only recently we've been able to
24:14
Speaker 1: hear your friend at the bar talking in gravitational radiation.
24:18
Speaker 1: Now we're getting ambitious. We're like, can we hear what's
24:20
Speaker 1: going on between the shouts? Is there anything there? Also?
24:23
Speaker 1: And it's interesting that you call it gravitational radiation? Can
24:27
Speaker 1: I use it? Is it a technical term? Gravitational radiation? Yeah? Absolutely,
24:31
Speaker 1: it's radiation. It's transmission of energy. And when two black
24:34
Speaker 1: holes collide, the new black hole that's formed has less
24:37
Speaker 1: mass than the masses of the two black holes that
24:40
Speaker 1: formed it combined. And the reason is a lot of
24:42
Speaker 1: the energy is lost. And it's not lost to light,
24:45
Speaker 1: it's not lost the particles. It's lost through gravitational waves.
24:49
Speaker 1: And sometimes it's like, you know, five times the mass
24:52
Speaker 1: of the Sun is lost in gravitational radiation. So yes,
24:55
Speaker 1: it's absolutely the radiation of huge amounts of energy. Interesting. Yeah,
25:00
Speaker 1: like it's quantifiable, like it carries energy. It's not just information.
25:03
Speaker 1: It has some sort of substance to it, It has
25:06
Speaker 1: some energy to it. For example, you could take a
25:08
Speaker 1: seventy solar mass black hole, combine it with a thirty
25:12
Speaker 1: solar mass black hole, and end up with a ninety
25:14
Speaker 1: solar mass black hole, which means that ten masses of
25:18
Speaker 1: the Sun's worth of energy was dumped out into the
25:21
Speaker 1: universe in gravitational radiation. Now, don't be confused, we're talking
25:24
Speaker 1: about gravitational waves, not gravitons. Right. Gravitons are not a
25:30
Speaker 1: thing we know exists. It's the theoretical quantization of the
25:34
Speaker 1: gravitational field. So we know the gravitational waves exist. Those
25:39
Speaker 1: are waves in the gravitational field, but we don't know
25:42
Speaker 1: if that field is quantized into like the smallest piece,
25:45
Speaker 1: which would be gravitons. So gravitational waves exist, we don't
25:49
Speaker 1: know yet if they're made of gravitons. Interesting, So then
25:51
Speaker 1: how would you define as the cosmic gravitational background. Is
25:55
Speaker 1: it like fainter signals or is it like a hum or?
25:59
Speaker 1: Is it like actually always in the gravity of the universe. Yeah,
26:02
Speaker 1: it's all of those things. It wouldn't be localized in
26:04
Speaker 1: any particular direction. It's not something that comes from one
26:07
Speaker 1: particular event, like one of these cataclysmic mergers, and it
26:11
Speaker 1: should be an overall hum And I think it's useful
26:14
Speaker 1: to go back to the cosmic microwave background radiation as
26:18
Speaker 1: a sort of comparison because it's very similar in concept.
26:21
Speaker 1: Like when you look at in the night sky you
26:22
Speaker 1: see stars and galaxies, but also between those stars and galaxies,
26:26
Speaker 1: we are getting light from the very early universe. That's
26:29
Speaker 1: the cosmic microwave background radiation, and it's in every direction,
26:32
Speaker 1: no matter where you look. And it first appeared as
26:35
Speaker 1: a hiss in a radio telescope. We had a whole
26:37
Speaker 1: fun episode about how that was discovered. And it's left
26:40
Speaker 1: over light from the very early universe from four hundred
26:43
Speaker 1: thousand years after the Big Bang. The reason we call
26:46
Speaker 1: that the background radiation is again because it's sort of
26:48
Speaker 1: everywhere the universe was filled with this plasma and admitted
26:52
Speaker 1: this light which was going in all direction. It's like
26:54
Speaker 1: it's not coming from a particular thing like a sun
26:57
Speaker 1: or a pulsar or something like that. It's like it's
27:00
Speaker 1: coming from everywhere, like you hear this his his in
27:03
Speaker 1: the signal of the universe everywhere you look. Yeah, and
27:06
Speaker 1: it's sort of a funny naming thing because it's called
27:08
Speaker 1: the background radiation for that reason that it doesn't come
27:11
Speaker 1: from any particular direction. But you know, now we have
27:13
Speaker 1: experiments dedicated to just looking for this. So it's like
27:17
Speaker 1: you're looking for the background. Is it really still the background?
27:20
Speaker 1: It's sort of like your target, it's your signal, right,
27:22
Speaker 1: no longer the background. Right, if the background becomes a foreground,
27:25
Speaker 1: then what's in the background the background background. We have
27:28
Speaker 1: multiple Nobel Prizes awarded, specifically four experiments measuring and analyzing
27:33
Speaker 1: ripples and wiggles in the cosmic microwave background. So it's
27:37
Speaker 1: definitely you know, worth calling it a foreground something. But anyway,
27:40
Speaker 1: you have to call it a background Nobel Prize, like
27:43
Speaker 1: a noisy you know, static qui Nobel Prize. Maybe it's
27:47
Speaker 1: like an off the record Nobel Prize, you know, like
27:49
Speaker 1: this is on background only. Yeah, there you go unofficial.
27:53
Speaker 1: The universe doesn't want to speak up about its secrets.
27:56
Speaker 1: It just wants to like slip it to us on background.
27:58
Speaker 1: I think that would conveniently reduce the number of noble
28:00
Speaker 1: prices you haven't want, Daniel. That would be difficult. I
28:03
Speaker 1: could be like, look, I have this secret about the universe,
28:05
Speaker 1: but I can't tell you how I know it because
28:07
Speaker 1: I got it on background from a source. I would
28:09
Speaker 1: be pretty disappointing. And of course you gotta protect your sources,
28:12
Speaker 1: right absolutely, even if it's the universe. Yeah, So then
28:16
Speaker 1: the cosmic microwave background is this sort of leftover light
28:20
Speaker 1: from the early universe. What would be the cosmic gravitational background.
28:24
Speaker 1: So we don't know exactly because we haven't seen it.
28:27
Speaker 1: We only have theoretical ideas for what could be creating it,
28:31
Speaker 1: what it might look like, but we're excited to see
28:33
Speaker 1: if it's there. The limitation on seeing this thing is
28:36
Speaker 1: making our experiments sensitive enough to listen to these very
28:40
Speaker 1: very quiet signals, And the challenge there is making your
28:44
Speaker 1: experiment insensitive to other things that look like gravitational waves, right,
28:48
Speaker 1: that look like this hum or, this hiss. Because the
28:51
Speaker 1: way these experiments work. For examples, you have like two
28:54
Speaker 1: mirrors hanging miles apart in a tunnel underground, shooting lasers
28:59
Speaker 1: back and forth to me sure the distance between them,
29:01
Speaker 1: and it's very easy to get wiggles in that distance.
29:04
Speaker 1: It's like the mirrors shake a little bit for a
29:06
Speaker 1: breeze flows through and moves the mirror. You know, the
29:09
Speaker 1: size of a gravitational signal is a tiny, tiny fraction,
29:13
Speaker 1: much smaller than the width of a human hair, and
29:16
Speaker 1: so it's very hard to isolate these things and just
29:18
Speaker 1: sort of like experimentally to make these systems work so
29:21
Speaker 1: you can see these signals, and so the challenge is
29:23
Speaker 1: making them work even better, making them even more sensitive.
29:26
Speaker 1: So now we could pick up like a low level
29:29
Speaker 1: omnidirectional hum if it exists, right, And I guess the
29:33
Speaker 1: tricky thing is that you know, you have your instrument,
29:35
Speaker 1: it's listening to the universe, and it's picking up noise
29:38
Speaker 1: from its environment, from the Earth, from the circuits in
29:42
Speaker 1: your instruments, but it's also maybe picking up noise from
29:45
Speaker 1: the universe itself in gravity right in the gravitational spectrum
29:49
Speaker 1: of the universe. And so you want to be able
29:51
Speaker 1: to say like Okay, this crazy random noise here that's
29:55
Speaker 1: from my experiment, and this crazy random noise here is
29:58
Speaker 1: actually from the universe. Is gravity exactly. It will be
30:01
Speaker 1: a much more difficult thing to demonstrate we've seen than
30:05
Speaker 1: the gravitational waves we've seen so far, because it's easier
30:08
Speaker 1: to see things that are like individual cate exclismic events.
30:11
Speaker 1: First of all, they're isolated, so you can say it
30:14
Speaker 1: happened and then it stopped, whereas the gravitational background is
30:17
Speaker 1: going to be like all the time, so you can't
30:19
Speaker 1: say like, oh, we turned it on and off. And
30:21
Speaker 1: here's the difference. And also, the gravitational waves that we
30:24
Speaker 1: have seen have a very particular signature, like when black
30:27
Speaker 1: holes swish around each other and create these gravitational waves,
30:31
Speaker 1: it's not just like a big screen. We know exactly
30:33
Speaker 1: what it should look like. You should start small, and
30:35
Speaker 1: should get bigger and bigger and faster and faster as
30:38
Speaker 1: they swore a closer and closer. So the gravitational waves
30:40
Speaker 1: we're looking for in the foreground have a very particular
30:43
Speaker 1: pattern when we first saw them. That's what convinced us
30:46
Speaker 1: that we had actually seen them right, that they look
30:48
Speaker 1: just like what we expected. If you do these numerical
30:51
Speaker 1: relativity calculations that predict the signature of the fingerprint of
30:55
Speaker 1: these gravitational waves, that makes it much easier to see
30:58
Speaker 1: they come from particular direction, they're very where it lived,
31:01
Speaker 1: and they look different from everything else. But as you say,
31:04
Speaker 1: we're just looking for a hiss, it's much harder to
31:06
Speaker 1: know if that his is coming from gravitational waves or
31:09
Speaker 1: from wiggles in your detector. So experimentally it's much much
31:13
Speaker 1: more challenging. And I think the idea is that this
31:15
Speaker 1: noise in the gravity of the universe and the gravitational
31:18
Speaker 1: spectrum of the universe, again, it's not coming from anywhere
31:21
Speaker 1: in particular, It's coming from everywhere, and it's maybe made
31:25
Speaker 1: up of you know, what would it be made out of.
31:28
Speaker 1: Is it made out of like big explosions somewhere else
31:31
Speaker 1: that have sort of propagated and diffused throughout the universe?
31:34
Speaker 1: Is there any idea? We don't know exactly what it
31:35
Speaker 1: might look like, and we can dig in a minute
31:38
Speaker 1: about the possibilities what could be generating it and what
31:40
Speaker 1: it would look like. But you know, one possibility is
31:43
Speaker 1: that it looks sort of like a hiss. Another possibility
31:46
Speaker 1: is that it's like very slowly changing, you know, like
31:49
Speaker 1: instead of having a wave that changes over seconds the
31:52
Speaker 1: way gravitational waves from black holes do, it might be
31:55
Speaker 1: like a very gradually changing tide, like we're seeing a
31:58
Speaker 1: gravitational wave that slates over like years or decades or centuries.
32:04
Speaker 1: And that again, it would be much harder to see
32:06
Speaker 1: because we like to look for the pattern that tells
32:08
Speaker 1: us that there was actually something there. But again I
32:10
Speaker 1: think it is that you would be looking for like
32:12
Speaker 1: a hum in the distortion of gravity in the universe, right.
32:18
Speaker 1: We have to make sure that you know you're measuring
32:20
Speaker 1: the wiggles in gravity really well, and then you'd be
32:24
Speaker 1: looking for some sort of activity there that wasn't like coherent.
32:26
Speaker 1: There wasn't like a spike or a particular shape. You
32:30
Speaker 1: need to establish that you're seeing a signal that is
32:32
Speaker 1: louder than the noise in your device, that your device
32:36
Speaker 1: is less noise than the signal you are seeing, which
32:38
Speaker 1: is tricky. And then what it would look like is,
32:40
Speaker 1: as you say, it would be like sort of random
32:42
Speaker 1: ripples in space and time, the way the cosmic microwave
32:45
Speaker 1: background radiation sort of has like little ripples in it.
32:48
Speaker 1: You get like a little distortion this direction, a little
32:50
Speaker 1: distortion not direction, a little distortion the other direction. And
32:52
Speaker 1: all these distortions would be much much smaller than the
32:55
Speaker 1: signals we've already seen. It would be even fainter. Right.
32:58
Speaker 1: And what's cool is that with our instrument snow like
33:00
Speaker 1: Lego and Virgo, we can tell which way gravitational waves
33:05
Speaker 1: are coming from. Right, so this would also tell you
33:08
Speaker 1: that they're coming from everywhere, not just in a particular direction.
33:11
Speaker 1: That's right. We can tell the direction of gravitational waves
33:14
Speaker 1: mostly because they take time to propagate, and so we
33:16
Speaker 1: can see them in different observatories around the world. There's
33:20
Speaker 1: one in Louisiana, one in Washington State, and one in
33:23
Speaker 1: Italy does Virgo, and as the gravitational waves sort of
33:26
Speaker 1: washes over the Earth, it arrives at one place before
33:29
Speaker 1: another place, and that timing information allows us to figure
33:32
Speaker 1: out so where in the sky it might have been
33:34
Speaker 1: coming from. But as you say, is cosmic gravitational background
33:37
Speaker 1: would be coming from all directions. Cool. Well, let's get
33:40
Speaker 1: into now whether or not this gravitational background really does
33:44
Speaker 1: exist and what could be making it and what he
33:47
Speaker 1: can tell us about the universe. But first, let's take
33:49
Speaker 1: another quick break. All right, we're talking about finding wads
34:06
Speaker 1: in the cosmic gravitational background of the universe. Then you know, like,
34:10
Speaker 1: is there something interesting in the background noise of gravity
34:14
Speaker 1: in the universe. Yeah, we don't know yet whether it's
34:17
Speaker 1: out there, right, This is like an idea people have had.
34:20
Speaker 1: There are theories that suggest it might be out there
34:23
Speaker 1: and could contain like treasures of the universe, and people
34:25
Speaker 1: have looked for it, but we don't really have a
34:28
Speaker 1: conclusive evidence for it so far. Like Lego and Virgo
34:32
Speaker 1: are best gravitational wave detectors have looked for us very specifically.
34:36
Speaker 1: But what they see sort of in between the loud
34:38
Speaker 1: shouts from black holes, looks to them just like noise
34:41
Speaker 1: in their detector. Like they can estimate how much noise
34:44
Speaker 1: they expect to have in their detector, and that's what
34:46
Speaker 1: they see, and their estimate for their noise is above
34:50
Speaker 1: anything that anybody predicts for cosmic gravitational background. So sort
34:53
Speaker 1: of like you go into a library and you're listening
34:55
Speaker 1: for whispers, but you know you can't hear the whispers yet.
34:58
Speaker 1: All you can hear is like electronic noise in your device,
35:01
Speaker 1: and that's what you hear, so you don't see anything.
35:03
Speaker 1: We also haven't really learned anything yet. You just learned
35:06
Speaker 1: that you need a better listening device. Oh, I see.
35:08
Speaker 1: It's like, we know we have kind of a crappy microphone,
35:11
Speaker 1: so we know that with our current set up, we
35:14
Speaker 1: can't listen to this background radiation, which means that we
35:17
Speaker 1: maybe don't know if it exists or not. Like this
35:20
Speaker 1: is a theoretical concept, then this cosmic gravitational background or
35:24
Speaker 1: does the theory pretty much predict that it exists, we
35:26
Speaker 1: just can't measure it. Yeah, but first I gotta stand
35:29
Speaker 1: up for Lego and Virgo, because you just called them
35:30
Speaker 1: crappy microphones are like the world's most amazing supersensitive microphones,
35:35
Speaker 1: just not quite supersensitive enough to listen to this incredibly
35:39
Speaker 1: faint signal. But you're you're absolutely right. So this is
35:42
Speaker 1: something people have theorized, and you know, there were moments
35:45
Speaker 1: when people thought they might have seen it. Lego hasn't
35:47
Speaker 1: seen it yet, but there was a moment people might
35:49
Speaker 1: remember this experiment BICEP two something on the South Pole,
35:53
Speaker 1: which thought they saw the effect of this radiation on
35:57
Speaker 1: the cosmic microwave background radiation they can measure, and they
36:01
Speaker 1: had this whole claim that they had discovered it and
36:03
Speaker 1: it was evidence that there was cosmic gravitational background radiation
36:06
Speaker 1: which was tweaking the cosmic microwave background radiation. But it
36:10
Speaker 1: turns out it was wrong. It was just that they
36:12
Speaker 1: didn't understand how much dust there was in the university
36:14
Speaker 1: caused a fake signal. So there was a real excitement
36:17
Speaker 1: there for a while, and then that faded. And now
36:19
Speaker 1: recently there's another experiment which is super cool, which it
36:23
Speaker 1: uses a galaxy size measuring device and they think they've
36:27
Speaker 1: seen evidence for this cosmic gravitational background. Why you mean
36:30
Speaker 1: we have something that big that we can use to
36:33
Speaker 1: measure the gravitational ways of the universe. We have something
36:36
Speaker 1: the size of a galaxy. Yeah, well, we have our
36:38
Speaker 1: galaxy and people have figured out how to use the
36:41
Speaker 1: galaxy as a gravitational way of observatory. We're gonna do
36:44
Speaker 1: a whole episode on this because it's super awesome. But
36:47
Speaker 1: very briefly, if you look at pulsars out there in
36:50
Speaker 1: the universe, these are fast rotating neutron stars that send
36:53
Speaker 1: us super super regular pulses of light, and you can
36:56
Speaker 1: tell if those things get pushed away from us or
36:58
Speaker 1: pulled towards us when a gravitational wave passes, because it
37:02
Speaker 1: changes when those light pulses arrive. And there's an experiment
37:05
Speaker 1: that's looked at some of these very regular pulses. It's
37:07
Speaker 1: called nano grab and they see a signal which looks
37:11
Speaker 1: like cosmic gravitational background radiation. But you know, it's early
37:14
Speaker 1: days and there have been false claims before, so nobody's
37:17
Speaker 1: really accepted this yet. It's just sort of like an
37:20
Speaker 1: exciting possibility, all right. So we're actively listening for this
37:23
Speaker 1: background or trying to listen to it. And it's sort
37:26
Speaker 1: of a funny thing, right, It's like trying to see
37:29
Speaker 1: if you can listen to the background noise and in
37:31
Speaker 1: a noisy bar, right or in a quiet library, it's
37:35
Speaker 1: sort of like you're trying to get everyone to quiet
37:37
Speaker 1: down so you can see if there is sort of
37:40
Speaker 1: a his there or not exactly. If you're curious about
37:43
Speaker 1: what's going on outside your house, for example, you turn
37:45
Speaker 1: off the TV and Telbrady shut up and listen to
37:48
Speaker 1: see if it's just crickets or something else going on. Outside.
37:51
Speaker 1: Did you turn this into a scary movie? Like what's
37:54
Speaker 1: out there? What's out there that we we can't hear? Yeah,
37:57
Speaker 1: And there's a whole range of reasons why we think
37:59
Speaker 1: the cosmic a gravitational background might exist, and there's some
38:02
Speaker 1: like kind of boring possibilities to explain it, and then
38:05
Speaker 1: there's some crazy, exciting, bonkers possibilities. I guess, you know,
38:08
Speaker 1: maybe as many of our listeners might be wondering, like
38:12
Speaker 1: does it make sense that there wouldn't be a cosmic
38:15
Speaker 1: gravitational background? Like things are everything causes gravitational ripples, so
38:20
Speaker 1: why wouldn't there be a background exactly? And that's the
38:22
Speaker 1: sort of most boring explanation is everything causes gravitational waves,
38:27
Speaker 1: Like every time you accelerate in your car, you cause
38:30
Speaker 1: a little gravitational wave. As the Earth moves around the Sun,
38:33
Speaker 1: it's generating gravitational waves, and there's a lot of that
38:35
Speaker 1: stuff going on in the universe. Most of that is
38:38
Speaker 1: really really small, but the idea is that it sort
38:40
Speaker 1: of adds up to this like overall stochastic background, and
38:44
Speaker 1: in particular, black holes that are too far away for
38:47
Speaker 1: us to like make out individually should add up to
38:51
Speaker 1: like an overall sort of noise level in the background.
38:54
Speaker 1: There should be black holes merging and neutron stars colliding
38:57
Speaker 1: with black holes all over the galaxy. Some of them
39:00
Speaker 1: are too far away for us to like pick out individually,
39:02
Speaker 1: but they should turn into like a hum, the way
39:05
Speaker 1: like a whole crowd in a baseball stadium. You can't
39:07
Speaker 1: make out their conversations, but you can tell the people
39:09
Speaker 1: are talking. You hear this like overall hum. So people
39:12
Speaker 1: expect that that can tell us something about like the
39:15
Speaker 1: overall rate at which gravitational waves are generated by distant objects. Right,
39:20
Speaker 1: But I guess is it possible that maybe you know,
39:22
Speaker 1: I'm just thinking, like maybe the universe could be quantized
39:25
Speaker 1: enough so that at some point there is no noise,
39:29
Speaker 1: do you know what I mean? Like, maybe at some
39:30
Speaker 1: point there's a minimum size to these irritation and ways
39:33
Speaker 1: at which point and since everything is so faint, everything
39:35
Speaker 1: just flattens out. Is that possible? It's possible. But you know,
39:39
Speaker 1: take an analogy to photons coming from distant galaxies. You
39:43
Speaker 1: look up in the night sky. You can't tell that
39:44
Speaker 1: there are galaxies there because they're so distant, Because the
39:47
Speaker 1: photons aren't arriving very frequently because they're quantized, right, It's
39:51
Speaker 1: not like you can get point o one photon. Every
39:53
Speaker 1: second you get one and then a minute later you
39:55
Speaker 1: get another one. But they are still coming, and so
39:58
Speaker 1: there is a non zero rate there. It's not like
40:00
Speaker 1: it goes exactly to zero. They just get less and
40:02
Speaker 1: less frequent. And so if gravitational waves are made of
40:06
Speaker 1: gravitons and they're super duper distant and faint, we should
40:09
Speaker 1: still be getting gravitons every once in a while, even
40:12
Speaker 1: from the most distant sources of gravitational radiation. But yeah,
40:15
Speaker 1: that would be really challenging to pick up, right. But
40:18
Speaker 1: I guess you know, photons are sort of discretized in direction,
40:21
Speaker 1: but gravitational waves kind of goes out in all directions, right,
40:25
Speaker 1: like a ripple in a pond. Yeah, but you know,
40:27
Speaker 1: a star sends out photons in all directions. It's really
40:29
Speaker 1: equivalent when a black hole merger event happens. It sends
40:32
Speaker 1: out gravitational waves in every direction. We just only pick
40:35
Speaker 1: them up from one direction, and so we would be
40:38
Speaker 1: picking up the gravitons from those events. And if these
40:41
Speaker 1: things are happening everywhere, we should be getting gravitons and
40:43
Speaker 1: gravitational waves in every direction from all these distant events.
40:47
Speaker 1: And so this is, you know, what people expect at
40:49
Speaker 1: a very bare minimum. Because we know the black holes
40:51
Speaker 1: are generating gravitational waves, we should be able to pick
40:55
Speaker 1: out at least the gravitational background from these distant events. Interesting,
40:59
Speaker 1: so we think there's definitely a cosmic gravitational background from
41:03
Speaker 1: just because we know there's things happening in the universe
41:05
Speaker 1: that are making them. So it makes sense that we
41:07
Speaker 1: would be sort of inundated with the faint ripples from
41:11
Speaker 1: all of these events, even things other than you know,
41:13
Speaker 1: black hole mergers. Even for example, when a star collapses
41:16
Speaker 1: into a black hole, you get gravitational waves. When a
41:18
Speaker 1: supernova goes off, you get gravitational waves. If a supernova
41:22
Speaker 1: goes off near a black hole, like JJ was suggesting,
41:25
Speaker 1: you get gravitational waves. So we should be able to
41:27
Speaker 1: see all these things sort of like added up all together, right,
41:30
Speaker 1: but it might be so faint that we can't see
41:31
Speaker 1: them or hear them. They are definitely too faint for
41:34
Speaker 1: us to see them now. But you know, with future
41:36
Speaker 1: observatories and improvements in our technology, we should in principle
41:40
Speaker 1: be able to see it if it's there, right, all right.
41:42
Speaker 1: So that's one possible source of cosmic gravitational background. What
41:46
Speaker 1: are some of the more bonkers sources that might be
41:48
Speaker 1: out there? One really exciting one is a mission of gravitons.
41:52
Speaker 1: You know, in some theories, gravitons are the quantization of gravity.
41:57
Speaker 1: Remember that our theory of gravity general real activity is
42:00
Speaker 1: a classical theory. It says that you can have any
42:03
Speaker 1: arbitrarily small distance, or any arbitrarilly small amount of energy,
42:07
Speaker 1: or any arbitrarily small slice of time. The quantum mechanics
42:10
Speaker 1: says that's probably not true, and the theory of quantum
42:13
Speaker 1: gravity would have gravitons in it, as we've said before,
42:16
Speaker 1: like the basic element of gravity, and these things should
42:19
Speaker 1: be emitted basically any time anything happens, you know, when
42:22
Speaker 1: a particle gets accelerated, it should emit a graviton, When
42:26
Speaker 1: an electron jumps down an energy level, it should emit
42:29
Speaker 1: a graviton. And so in principle the universe is filled
42:33
Speaker 1: with these gravitons, and they would be very very high frequency.
42:37
Speaker 1: Like the gravitons we've seen so far, have an oscillation
42:40
Speaker 1: time of like you know, a few seconds, these would
42:42
Speaker 1: be much much higher frequency, like you know, mega hurts
42:45
Speaker 1: sort of gravitons, and so that's exciting because it would
42:48
Speaker 1: be like a signal of quantum gravity, right, But do
42:51
Speaker 1: they need to be gravitons, Like when a adom relaxed
42:54
Speaker 1: us from an excited state doesn't also generate a gravitational
42:58
Speaker 1: wave like a regular wave. It does, But now we're
43:00
Speaker 1: talking about a quantum particle, and a quantum particle should
43:03
Speaker 1: emit quantized bits of radiation, right, it can't admit classical radiation,
43:09
Speaker 1: And so this is something we don't understand. We don't
43:11
Speaker 1: know how to do gravitational calculations for a particle, for
43:14
Speaker 1: a quantum object that requires the theory of quantum gravity.
43:17
Speaker 1: We just don't have, so general relativity like can't tell
43:20
Speaker 1: you what happens to the gravity of a particle. And
43:22
Speaker 1: we can't really do those experiments very easily because particles
43:25
Speaker 1: have almost no detectable gravity because there's so light in
43:29
Speaker 1: mass and gravity is so weak. So we just don't know.
43:32
Speaker 1: But you know, maybe all those particles out there are
43:34
Speaker 1: sort of like humming in gravity and we can pick
43:37
Speaker 1: up like the some of them like, maybe all the
43:39
Speaker 1: particles in the universe sending us gravitons simultaneously would be
43:43
Speaker 1: something we might be able to detect. Interesting. I think
43:45
Speaker 1: they're saying that, maybe, like the gravitational background of the
43:48
Speaker 1: universe is not coming from these giant events and supernovas
43:52
Speaker 1: and black holes gliding, and it might be being generated
43:55
Speaker 1: by everything like you and I just sitting here. It
43:57
Speaker 1: could be generating gravitational noise. Yeah, we should be in theory,
44:01
Speaker 1: and we should be able to measure it. And if
44:02
Speaker 1: we see it and we measure its frequency, we can
44:05
Speaker 1: use that to understand how they're being generated, the same
44:08
Speaker 1: way we look at the frequency of everything else, and
44:10
Speaker 1: we see emission from hydrogen, for example, at a particular frequency.
44:13
Speaker 1: We see transitions in lithium gas at a particular frequency.
44:17
Speaker 1: So these would be like a fingerprint for what's generating
44:20
Speaker 1: gravitational waves in the universe. Who tells something about gravity
44:23
Speaker 1: and the composition of the universe. It would be amazing
44:26
Speaker 1: to see gravitons emitted as the cosmic gravitational background. And
44:30
Speaker 1: what about some of the other bonkers possibilities that are
44:33
Speaker 1: making this cosmic gravitational background. One that gets me really
44:36
Speaker 1: excited are gravitational waves emitted from the very very early universe.
44:40
Speaker 1: Our theory of what happened in the very beginning of
44:43
Speaker 1: the universe is called inflation. It suggests that space was
44:46
Speaker 1: stretched by a ridiculous amount, by like a factor of
44:49
Speaker 1: ten to the thirty in a short amount of time,
44:52
Speaker 1: like tend to the minus thirty. When you do that,
44:54
Speaker 1: you've got to generate gravitational waves because that's like the
44:57
Speaker 1: biggest ripple in space has ever seen, right, So there
45:00
Speaker 1: should be huge gravitational waves left over from that, because,
45:04
Speaker 1: like the CMB, it happened everywhere all at once, so
45:08
Speaker 1: it should be like a cacophony of gravitational waves. But
45:11
Speaker 1: over the fourteen billion years since, they've probably gotten stretched
45:14
Speaker 1: out and smoothed over. And so this would be exciting
45:17
Speaker 1: to detect because it would probe the very very very
45:20
Speaker 1: very early universe. Like people talk about how the CMB
45:23
Speaker 1: tells us about the Big Bang, it doesn't really. It
45:26
Speaker 1: tells us about a plasma that's formed four hundred thousand
45:30
Speaker 1: years later. It's like reading about the birth of Jesus
45:32
Speaker 1: from somebody who wasn't there, who wrote like hundreds of
45:35
Speaker 1: years later. Gravitational waves from inflation would come from like
45:38
Speaker 1: ten to the minus thirty two seconds after the beginning
45:41
Speaker 1: of the universe. So it's like really a first hand
45:43
Speaker 1: account of the beginning of the universe. If we could
45:46
Speaker 1: see it, it would tell us a huge amount about
45:48
Speaker 1: how the universe actually began. All right, Yeah, interesting, I
45:51
Speaker 1: guess you know, anything with mass and energy affects gravity, right,
45:55
Speaker 1: or it creates gravity or and so anytime you have
45:58
Speaker 1: a change in the universe, or anything really happening in
46:00
Speaker 1: the universe, it's going to generate a gravitation a ripple, right, Yeah,
46:04
Speaker 1: even like the beginning of the universe, that must have
46:06
Speaker 1: generated a bunch of ripples. Yeah, huge ribbles exactly. Tsunamis
46:10
Speaker 1: of gravitational waves. You could probably serve them. Yeah, with
46:14
Speaker 1: your friend Walda on a surfboard. Look, I know you
46:17
Speaker 1: keep trying to include him. I just don't like the guy. Okay,
46:21
Speaker 1: what do you have against Walda? I don't know. He
46:24
Speaker 1: just won't let me find him. You know, he's just elusive.
46:28
Speaker 1: He's a sneaky guy. But sneaky particles are totally cool
46:32
Speaker 1: with sneaky particles, all right, So then what's the last
46:34
Speaker 1: possibility here that might be causing a background in the universe.
46:38
Speaker 1: The last possibility is the most bonkers, and these are
46:41
Speaker 1: cosmic strings. We talked about this one in the podcast
46:45
Speaker 1: Now a couple of years ago. They're like cracks in
46:48
Speaker 1: space and time. We are used as spacetime being sort
46:50
Speaker 1: of smooth. If you go from here to there, you
46:53
Speaker 1: can sort of just like slide through space. But we
46:55
Speaker 1: don't really understand how space was formed, and as the
46:57
Speaker 1: universe cooled, it might have like formed differently in different regions,
47:01
Speaker 1: leading to like weird discontinuities, like parts of space are
47:05
Speaker 1: a little different here and a little different there, and
47:07
Speaker 1: at the boundaries there can be these cracks where like
47:10
Speaker 1: space changes from one state to another, And so these
47:13
Speaker 1: would be like long filaments, maybe even you know, like
47:16
Speaker 1: thousands of light years long, that have like cracks in
47:20
Speaker 1: space and time, and as they wiggle, they would generate
47:23
Speaker 1: gravitational waves. And there's some theories that like the ends
47:26
Speaker 1: of the wiggle really fast like a whip, causing these
47:29
Speaker 1: crazy gravitational waves. So if that's happening all over the universe,
47:33
Speaker 1: we might be able to pick up some of those
47:35
Speaker 1: signals and detect the existence of these cosmic strings. Whoa,
47:39
Speaker 1: it's like the universe was a giant guitar, and like
47:42
Speaker 1: there's giant light years long strings that are you know,
47:45
Speaker 1: basically making no it's music, right, Yeah, we don't know
47:48
Speaker 1: if they exist. It's a super cool theory. If we
47:51
Speaker 1: do find them, we would tell us that we understand
47:53
Speaker 1: something deep about how space and time sort of formed
47:56
Speaker 1: in the early universe. You can think about them sort
47:58
Speaker 1: of like the way ice isn't as clear. If you
48:01
Speaker 1: take water and you cool it down, you get these
48:03
Speaker 1: cracks sometimes because it doesn't all crystallize in exactly the
48:06
Speaker 1: same way. And so this would really tell us something
48:09
Speaker 1: about how space itself formed in the very early universe.
48:12
Speaker 1: Would be super awesome. That's my new theory of the
48:15
Speaker 1: origin of the universe. Dandium. When new religion, it's that
48:17
Speaker 1: the universe it's she's a giant guitar played by a
48:21
Speaker 1: giant rock star named Waldo. Waldo is um we just
48:27
Speaker 1: found it a new religion, all right, So I guess
48:29
Speaker 1: when one final question is, how would we know which
48:32
Speaker 1: of these origins of the background might be, Like do
48:34
Speaker 1: we have any hope at all of ever knowing like, oh,
48:37
Speaker 1: this noise is coming from inflation or gravitons or cosmic strings,
48:41
Speaker 1: they would look different, right. Gravitational waves have frequencies, just
48:44
Speaker 1: like light does. Different frequencies of light look different. You've
48:47
Speaker 1: got radio, you've got infrared, you've got X rays, you've
48:50
Speaker 1: got gamma. Raised in the same way, gravitational waves have frequencies.
48:54
Speaker 1: The ones we've seen have frequencies of about a second,
48:57
Speaker 1: and we have sensitivities due to our detectors to a
49:00
Speaker 1: range of frequencies. So they come at very very high frequencies,
49:03
Speaker 1: we think they might be gravitons. If they come at
49:05
Speaker 1: lower frequencies, they might be from inflation. If they're sort
49:08
Speaker 1: of periodic and spastic, then they might be from cosmic strings.
49:11
Speaker 1: So each one of these has like a different fingerprint.
49:14
Speaker 1: If there's just nothing there except for like the low
49:16
Speaker 1: level hum that that should be pretty flat and lots
49:19
Speaker 1: of frequencies represented. So the sort of spectrum of the
49:23
Speaker 1: frequencies there is a fingerprint that tells you what generated it.
49:26
Speaker 1: We just gotta, I guess, tune up those microphones and
49:28
Speaker 1: turn up the amplifiers and reduce the noise just to
49:31
Speaker 1: be able to maybe listen to these signals. And be
49:33
Speaker 1: able to tell which one is which. Yeah, and we
49:35
Speaker 1: have some exciting plans. The Ligo Observatory is based here
49:39
Speaker 1: on Earth, and what they'd like to do is build
49:42
Speaker 1: a much bigger version out in space. They want to
49:45
Speaker 1: put three satellites out there that managed to somehow keep
49:49
Speaker 1: a very precise distance from each other and then shoot
49:51
Speaker 1: lasers back and forth to detect the passing of gravitational
49:54
Speaker 1: waves or the cosmic gravitational background. It's not science fiction.
49:58
Speaker 1: There's a real experiment might really happen sometime in the
50:01
Speaker 1: next ten or fifteen years, and it can really teach
50:04
Speaker 1: us something deep about the universe. It's Lego in space.
50:08
Speaker 1: It's called Lisa, all right. Well, that's what the cosmic
50:11
Speaker 1: gravitational background is. It might be there, it might not
50:14
Speaker 1: be there. We think it's there, but we don't know
50:17
Speaker 1: quite what's causing it, right, and we don't know if
50:19
Speaker 1: it's there, We don't know what's causing it. But we're
50:22
Speaker 1: desperate to listen to these signals that might contain new
50:25
Speaker 1: treasures about the early universe. So stay tuned once again,
50:30
Speaker 1: and maybe think about that when you look up at
50:31
Speaker 1: the night sky once again, and how much information is
50:34
Speaker 1: bathing over us as we speak, and that might tell
50:38
Speaker 1: us about the very origin of the universe. And think
50:41
Speaker 1: about all the gravitational radiation that you are generating. Every
50:44
Speaker 1: time you go out there and get exercise or hit
50:46
Speaker 1: the accelerator in your car. You are contributing to the
50:49
Speaker 1: cosmic gravitational background, some of us more than others. Like
50:52
Speaker 1: if you're a couch potato, technically you're just creating less
50:55
Speaker 1: noise for the universe, right, that's true, But you're getting
50:57
Speaker 1: more and more massive, So if you ever do get
50:59
Speaker 1: off the couch, you're gonna be pretty noisy, right, there's
51:01
Speaker 1: a trade off there, all right. Well, thanks for joining us.
51:04
Speaker 1: We hope you enjoyed that. See you next time. Thanks
51:14
Speaker 1: for listening, and remember that Daniel and Jorge Explain the
51:17
Speaker 1: Universe is a production of I Heart Radio. For More
51:20
Speaker 1: podcast For my Heart Radio, visit the I Heart Radio app,
51:24
Speaker 1: Apple Podcasts, or wherever you listen to your favorite shows. Yeah,