Latest / Daniel and Kelly’s Extraordinary Universe / Can we use the galaxy as a gravitational wave detector?

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Can we use the galaxy as a gravitational wave detector? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: The deepest questions about the nature of the universe have answers.
0:13
Speaker 1: Answers that are out there right now, waiting to be discovered.
0:17
Speaker 1: The nature of dark matter, the secret to quantum gravity,
0:21
Speaker 1: the mystery of dark energy. The answers lie in wait
0:24
Speaker 1: for us, but not just the answers, also the clues
0:28
Speaker 1: to reveal them. Right now, the clue to unravel these
0:32
Speaker 1: mysteries is out there. Probably the information we need to
0:36
Speaker 1: crack the code is washing over us in the form
0:40
Speaker 1: of messages from space we don't yet know how to decode.
0:44
Speaker 1: Think about how much we have learned from listening carefully
0:47
Speaker 1: to the sky answers to questions that previous generations didn't
0:52
Speaker 1: even know to ask. So that makes us wonder, of course,
0:55
Speaker 1: what answers are arriving here on Earth right now, waiting
0:59
Speaker 1: for someone clever enough to know how to listen. Hi,
1:18
Speaker 1: I'm Daniel. I'm a particle physicist, and I desperately want
1:22
Speaker 1: to hear the answers to questions about the universe. I
1:26
Speaker 1: know that these answers are out there, and I know
1:28
Speaker 1: that humans will figure them out in fifty years and
1:31
Speaker 1: a hundred years, in a thousand years, people will know
1:34
Speaker 1: the answers to deep questions about the universe that we
1:37
Speaker 1: are totally perplexed by. Little children will read books explaining
1:42
Speaker 1: to them secrets that it takes Nobel Prize winning discoveries
1:46
Speaker 1: to uncover about the universe. They will hear about them.
1:49
Speaker 1: They will be bored. They will throw a tantrum. I
1:52
Speaker 1: am desperate to read those books. I am desperate to
1:55
Speaker 1: know those things about the universe. I know that the
1:58
Speaker 1: answers are out there. I know there are are ways
2:00
Speaker 1: to figure them out. But science moves slowly and steadily,
2:04
Speaker 1: with brief flashes of insight, sometimes revealing the nature of
2:08
Speaker 1: the universe, and we just have to wait for it
2:10
Speaker 1: to happen. But not just wait, we can also push
2:13
Speaker 1: it forward. So welcome to the podcast Daniel and Jorge
2:16
Speaker 1: Explain the Universe, a production of I Heart Radio in
2:20
Speaker 1: which we do our best to push it forward by
2:22
Speaker 1: encouraging your curiosity about science, by encouraging everybody's curiosity about science,
2:28
Speaker 1: by asking the big questions about the universe and thinking
2:32
Speaker 1: about how we might possibly answer them. On this podcast,
2:35
Speaker 1: we talk about everything in the universe, the tiniest little particles,
2:39
Speaker 1: the most super massive black holes, and all the signals
2:43
Speaker 1: we are receiving from these cosmic and tiny objects that
2:47
Speaker 1: are telling us those secrets of the universe. My friend
2:50
Speaker 1: and co host Jorge can't be here today to join us,
2:53
Speaker 1: so I'm on my own telling you about all the
2:55
Speaker 1: things we can learn from the universe. If we just
2:58
Speaker 1: knew how to listen, and is no shortage of questions
3:01
Speaker 1: about the universe, we'd like answers too. Of course, there
3:04
Speaker 1: are the known unknowns, the things that we know we
3:08
Speaker 1: don't know, and we also know how to figure them out.
3:12
Speaker 1: There are so many things in science where we know
3:14
Speaker 1: exactly what it is we need to do. We know
3:17
Speaker 1: exactly what question we want to answer, and we just
3:20
Speaker 1: haven't done it yet, either because of time or expertise,
3:24
Speaker 1: or frankly, just money. Think about all we could accomplish
3:28
Speaker 1: if we poured more money into science. We know how
3:31
Speaker 1: to send rovers to other planets. We know how to
3:34
Speaker 1: send satellites to land on the moons of Jupiter. We
3:38
Speaker 1: know how to build big space telescopes. We can do
3:41
Speaker 1: these things, and we know that if we did them,
3:43
Speaker 1: we would essentially just be buying scientific knowledge. We know
3:47
Speaker 1: that the answers to some of the questions we have
3:49
Speaker 1: about whether there are life in the oceans, on those moons,
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Speaker 1: and what is going on in the deepest, darkest reaches
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Speaker 1: of the universe. Those a answers are out there waiting
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Speaker 1: for us if we just buy them. We are like
4:02
Speaker 1: children walking around in a scientific candy shop, keeping all
4:05
Speaker 1: of our money in our pockets and not purchasing those tasty, tasty,
4:10
Speaker 1: delicious scientific treats. So that's why on this program and
4:13
Speaker 1: everywhere in my life, I'm always advocating for increasing the
4:16
Speaker 1: spending to government agencies. We could buy so much knowledge
4:20
Speaker 1: about the universe. We could crack open some of these
4:23
Speaker 1: mysteries if we just spent a few more pennies. All right,
4:26
Speaker 1: maybe not pennies, maybe a few more millions of dollars,
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Speaker 1: but on the scale of government spending, it really is pennies.
4:32
Speaker 1: But in the face of those budget realities, we have
4:35
Speaker 1: to get clever. And one of my favorite things that
4:38
Speaker 1: astrophysicists do is that they don't try to build experiments themselves.
4:43
Speaker 1: They just go out and look for them. Like in
4:46
Speaker 1: particle physics, if I want to know what happens when
4:49
Speaker 1: I smash two protons together, then I say, let's go
4:51
Speaker 1: build an accelerator that does just that, that smashes the
4:55
Speaker 1: particles together and see what comes out. We are creating
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Speaker 1: the conditions that we want to The astrophysicists don't usually
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Speaker 1: have that luxury. For example, if you're curious about what
5:05
Speaker 1: happened to be a smash two galaxies together, well you
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Speaker 1: can't go out and build a galaxy sized collider. Fortunately, however,
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Speaker 1: the universe is vast, and it is crazy, and it
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Speaker 1: is filled with all sorts of amazing stuff, including, if
5:20
Speaker 1: you look hard enough, almost every experiment you would want
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Speaker 1: to do, including colliding galaxies. The same thing goes for
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Speaker 1: colliding things like black holes. Who doesn't want to shoot
5:30
Speaker 1: one black hole at another one to see what happens?
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Speaker 1: Does one black hole eat the other one? Do they
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Speaker 1: eat each other somehow? Is it some crazy cosmic dance?
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Speaker 1: We now know, of course, that when you do that,
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Speaker 1: you emit enormous quantities of energy in gravitational waves. We've
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Speaker 1: actually seen these things using gravitational wave detectors. So while
5:49
Speaker 1: we didn't have to build the experiment to shoot black
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Speaker 1: holes at each other, we did have to build the
5:54
Speaker 1: experiments to see the gravitational waves. But what if we
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Speaker 1: didn't have to build the experiment and we didn't have
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Speaker 1: to build the detector. What if nature said it all
6:04
Speaker 1: up for us. What if all we had to do
6:07
Speaker 1: was listen? And so today on the podcast we'll be
6:10
Speaker 1: talking about just that, a crazy new idea that might
6:14
Speaker 1: just work. So on today's program will be answering the
6:16
Speaker 1: question can we use the entire galaxy as a gravitational
6:26
Speaker 1: wave detector? I know that sounds preposterous, but astrophysicists like
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Speaker 1: to think big, and when they do, sometimes they make
6:33
Speaker 1: it work. So I was wondering how much people have
6:35
Speaker 1: heard about this topic already, if this was something everybody
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Speaker 1: was talking about or only people in the physics community. So,
6:41
Speaker 1: as usual, I asked for volunteers out there on the
6:44
Speaker 1: Internet to answer random physics questions with no preparation. It
6:48
Speaker 1: gives me an idea for what people out there already
6:50
Speaker 1: know and what they think about when they hear this question.
6:53
Speaker 1: If you'd like to participate for future episodes of the podcast,
6:57
Speaker 1: please don't be shy. It's easy, it's fun, and we
7:00
Speaker 1: love hearing from you. Please just write to me two
7:02
Speaker 1: questions at Daniel and Jorge dot com. So think for
7:06
Speaker 1: a moment, Do you have an idea for how you
7:08
Speaker 1: could use the entire galaxy to detect gravitational waves. Here's
7:14
Speaker 1: what our volunteers had to say. I don't know. I
7:19
Speaker 1: had no idea. I don't know how detectors like Ligo
7:24
Speaker 1: measure gravitational waves. I don't know the mechanism. But objects
7:27
Speaker 1: in our galaxy are quite spread out and comparted to
7:31
Speaker 1: the size of the galaxy, each of them is quite small.
7:34
Speaker 1: So I don't think our galaxy could be an effective
7:37
Speaker 1: gravitational wave detector. I don't know. The ones on Earth
7:43
Speaker 1: I believe use lasers and obviously their own distance apart.
7:46
Speaker 1: I sort of seen lectures one time about using dust
7:50
Speaker 1: or hydrogen gas or something in the universe. Whether that's
7:52
Speaker 1: gravitational waves or something else, I don't know. I'm not
7:54
Speaker 1: quite sure how you do that one. Yeah, if you
7:57
Speaker 1: think about how they measure gravity waves, uh, you're essentially
8:01
Speaker 1: like measuring the separation between two mirrors in one direction
8:05
Speaker 1: versus another direction. That's what the Liego observatory does, so
8:09
Speaker 1: you get the disoscillation signal. So I imagine you can
8:12
Speaker 1: do something similar with the entire galaxy. Um, you can
8:15
Speaker 1: just look at the Milky Way galaxy and see if
8:18
Speaker 1: if things get squished in one direction relative to another,
8:21
Speaker 1: for like supermassive gravitational waves, Like maybe you can look
8:25
Speaker 1: at the red shift at one end versus the blue
8:27
Speaker 1: shift at the other and see if there's a difference
8:30
Speaker 1: that sort of correlates as you move around. Yes, yes
8:34
Speaker 1: we can. We just have to observe how gravitational waves
8:39
Speaker 1: are affecting all the bodies in the galaxy. I don't
8:43
Speaker 1: see why you couldn't. In fact, that would be probably
8:46
Speaker 1: a good way to measure antitecht gravitational waves. So if
8:51
Speaker 1: you used an entire galaxy, and let's say you're one
8:55
Speaker 1: edge of the galaxy versus the opposite edge of the galaxy,
8:58
Speaker 1: and you were using the same principle, you should be
9:02
Speaker 1: able to pick up the movement of a gravitational wave
9:06
Speaker 1: through that galaxy. Since you're asking that question, I would say, yes,
9:10
Speaker 1: you can use the whole galaxies of gravitational wave detector.
9:15
Speaker 1: If you have a large gravitational waves traveling through the galaxy,
9:22
Speaker 1: you will impact some stars before others, and will increase
9:28
Speaker 1: and decrease the length the distance between two far apart
9:33
Speaker 1: stars quite significantly. So it's probably a very good gravitational
9:37
Speaker 1: wave detective. All right. So our listeners are smart, they
9:41
Speaker 1: know something about gravitational waves, and they have the idea
9:44
Speaker 1: that the gravitational waves must be somehow affecting things in
9:48
Speaker 1: the galaxy, and then we could see that effect somehow.
9:52
Speaker 1: But nobody quite figured out exactly how we see those effects.
9:56
Speaker 1: These ideas there about red shift and blue shift and
9:58
Speaker 1: optical lensing and ripples against things. But it's a tricky topic,
10:03
Speaker 1: and we're gonna dig to it and explain to you
10:05
Speaker 1: exactly how to use the entire galaxy as your physics experiment.
10:10
Speaker 1: But first, let's just remind ourselves what we're talking about observing,
10:14
Speaker 1: what we want to see out there, what we're trying
10:16
Speaker 1: to study, what we're using the entire galaxy as a
10:20
Speaker 1: detector of. Are these crazy things called gravitational waves? What
10:25
Speaker 1: is a gravitational wave anyway? Well, you know what a
10:28
Speaker 1: wave is. A wave is when something moves up and down,
10:31
Speaker 1: Like you put your hand in your bathtub and you
10:33
Speaker 1: slap the water and you get a wave of the water. Right,
10:36
Speaker 1: The water goes down and then goes up, and then
10:38
Speaker 1: it goes down and then goes up. Or you see
10:40
Speaker 1: waves in the ocean here in southern California and you
10:42
Speaker 1: can serve them, and you might wonder like, well, why
10:45
Speaker 1: are there waves? Right? Why does the water in the
10:47
Speaker 1: bathtub go down in waves rather than all going down
10:50
Speaker 1: at once? And that's because of a really important property
10:53
Speaker 1: in physics called locality. When your hand hits the water,
10:56
Speaker 1: it only affects the water that it touches, doesn't affect
10:59
Speaker 1: the water water on the other side of the bathtub
11:01
Speaker 1: or in bathtubs all over the universe. Right, Physics is
11:05
Speaker 1: local and information takes time to propagate, So the water
11:09
Speaker 1: on the other side of the bathtub doesn't know that
11:11
Speaker 1: you've hit the water on this side until it gets
11:14
Speaker 1: that information, until the wave arrives there. It's the same story.
11:18
Speaker 1: For example, you pluck a guitar string, right, which part
11:21
Speaker 1: of the string starts to vibrate at first? Well, the
11:23
Speaker 1: part that you plucked, and the rest then moves as
11:26
Speaker 1: that information moves down the string. So then why do
11:30
Speaker 1: you get a wave because the part that you pluck
11:32
Speaker 1: moves down and then it comes back up, and then
11:34
Speaker 1: it goes back down and then it comes back up
11:36
Speaker 1: and the wave are those ripples moving down the string.
11:40
Speaker 1: If information propagated instantaneously, the whole string would move at once.
11:45
Speaker 1: But the reason it doesn't, the reason you get a
11:47
Speaker 1: wave is because information doesn't propagate instantaneously. So let's get
11:51
Speaker 1: back to gravity. Gravitational waves are the waves in space itself, right,
11:57
Speaker 1: How do you make waves in space? Why does that
11:59
Speaker 1: even mean? Well, remember that we know now that space
12:03
Speaker 1: is not just like the backdrop. It's not just like
12:05
Speaker 1: where things happen in the universe. It's a thing in
12:09
Speaker 1: and of itself. It has properties. It can do things
12:12
Speaker 1: that emptiness or nothingness can do. For example, it can bend.
12:18
Speaker 1: If you put a big mass in space, what happens, Well,
12:22
Speaker 1: space bends around that mass. It changes the curvature of space.
12:27
Speaker 1: And a lot of you are probably thinking like a
12:29
Speaker 1: bowling ball on a rubber sheet, right, And that's a
12:32
Speaker 1: helpful analogy to sort of shape your mind out of
12:35
Speaker 1: the idea that space is nothingness, that it can have curvature.
12:38
Speaker 1: But it's also confusing because it's suggesting that space is
12:42
Speaker 1: curving in some other dimension. In that example, space is
12:45
Speaker 1: a two dimensional rubber sheet, and it's curving in some
12:48
Speaker 1: third dimension because the bowling ball is pulling it down right, Well,
12:52
Speaker 1: that's not what happens in our universe. Our space is
12:54
Speaker 1: already three dimensional, and when it curves, what we mean
12:58
Speaker 1: is that it changes the relative of distance between two points.
13:02
Speaker 1: Means that things that might have seemed further away are
13:04
Speaker 1: now closer because space is sort of scrunched. And that's why,
13:08
Speaker 1: for example, photons bend around massive objects, because photons always
13:12
Speaker 1: take the shortest path available to them, and that shortest
13:15
Speaker 1: path looks like a curve. If you aren't aware of
13:19
Speaker 1: the bending of space, and we have no way to
13:21
Speaker 1: detect the bending of space, we can't see it, we
13:24
Speaker 1: can't feel it other than watching things trace it out.
13:27
Speaker 1: So that's why the Earth moves in a circle around
13:30
Speaker 1: the Sun, because the space is bent in a way
13:32
Speaker 1: that makes that its most natural motion. Alright, so space
13:35
Speaker 1: can bend, But how does it ripple. How do you
13:38
Speaker 1: get a wave in space? Well, the same way you
13:40
Speaker 1: get a wave in your bathtub. Say, for example, you
13:44
Speaker 1: deleted the Sun from our solar system. What would happen. Well,
13:47
Speaker 1: you guys know that gravity doesn't move instantaneously, so we
13:50
Speaker 1: wouldn't notice for eight minutes. That's a gravitational wave. That's
13:55
Speaker 1: information about the shape of space propagating through space. It's
14:00
Speaker 1: just like when you plug a guitar string, the information
14:03
Speaker 1: that the string was plucked moves down the string. If
14:06
Speaker 1: you delete the Sun, the information that space is no
14:09
Speaker 1: longer bent moves through space, making it flat rather than curved.
14:14
Speaker 1: And if you have two black holes, for example, orbiting
14:17
Speaker 1: each other, then they are making huge gravitational waves. Because
14:21
Speaker 1: anything that has mass and accelerates makes a gravitational wave.
14:25
Speaker 1: It's changing the curvature of space through time, and that's
14:28
Speaker 1: what creates gravitational waves. And so black holes, for example,
14:32
Speaker 1: orbiting each other and eventually collapsing into a single mega
14:36
Speaker 1: black hole, they send out these ripples as they orbit
14:39
Speaker 1: each other. They're changing the shape of space around them
14:41
Speaker 1: because they're very massive, and they're bending space, and the
14:45
Speaker 1: way they're doing is changing because they are orbiting each other.
14:48
Speaker 1: So that's where those gravitational waves come from. That's where
14:51
Speaker 1: the ripples in space come from. And so how do
14:53
Speaker 1: you detect the ripples in space and time? I said earlier,
14:57
Speaker 1: And we can't see or feel the bending of space.
15:00
Speaker 1: All we can do is detect the change in relative distances.
15:04
Speaker 1: If the space between me and you contracts, then the
15:07
Speaker 1: distance between us contracts. You might think, well, whold lot
15:10
Speaker 1: of second. If we have a ruler between us and
15:12
Speaker 1: space between us contracts, won't the ruler also contract. There's
15:16
Speaker 1: a chance of that. So to avoid that, we build
15:19
Speaker 1: rulers out of light. We send light pulses back and forth,
15:22
Speaker 1: because if the space between me and you get smaller,
15:25
Speaker 1: then light will cover that distance more quickly. And if
15:28
Speaker 1: you have a mirror, I can shoot my laser at
15:30
Speaker 1: your mirror and measure how long it takes for that
15:33
Speaker 1: light to come back. And so if a gravitational wave
15:35
Speaker 1: passes between you and me, and I'm doing that all
15:37
Speaker 1: the time, I'll notice because all of a sudden, the
15:40
Speaker 1: space between us will be shorter and then longer as
15:43
Speaker 1: the gravitational wave passes. And this is not a theoretical idea,
15:47
Speaker 1: This is real. This is something we have actually seen.
15:51
Speaker 1: People have built these detectors they're called Ligo and Vitigo,
15:55
Speaker 1: and they have these mirrors underground and the mirrors are
15:58
Speaker 1: very very stable. They try not to shake them at
16:00
Speaker 1: all because any shaking those mirrors makes it impossible to
16:03
Speaker 1: see gravitational waves, which after all look a lot like
16:06
Speaker 1: the shaking of the mirrors. So they have these mirrors
16:09
Speaker 1: hyper stabilized. They're hanging from cords, and those cords are
16:12
Speaker 1: attached to something else, which is buffered, which is attached
16:15
Speaker 1: to something else, which is protected from shaking. It's like
16:17
Speaker 1: nine layers of protection against any sort of activity trucks
16:21
Speaker 1: driving by, or people slamming screen doors, or any kind
16:24
Speaker 1: of thing that would make a signal that looks like
16:26
Speaker 1: a gravitational wave. The first one we saw was in
16:28
Speaker 1: ten It won a Nobel Prize. And now we've seen
16:31
Speaker 1: more than a dozen of these things from black holes
16:33
Speaker 1: nearby that have collided and sent these pulses, and we
16:37
Speaker 1: were kind of surprised by how common these things were.
16:40
Speaker 1: So now you might be thinking, great, we have a
16:42
Speaker 1: gravitational wave detector. We've seen these things. Why would we
16:45
Speaker 1: need to build a gravitational wave detector at the size
16:49
Speaker 1: of the galaxy. Well, gravitational waves come in lots of
16:52
Speaker 1: different colors, basically, just the same way light has lots
16:55
Speaker 1: of different frequencies. Light is electromagnetic radiation, and it can
17:00
Speaker 1: have a frequency that puts it in the visible so
17:02
Speaker 1: it has different colors, or it can have very long
17:04
Speaker 1: frequencies like down in the radio, or it can have
17:07
Speaker 1: very short frequencies and be an X ray or a
17:09
Speaker 1: gamma ray. So all of these are different kinds of
17:12
Speaker 1: electromagnetic radiation and we need different kind of instruments to
17:16
Speaker 1: see them. You can't see the same thing with an
17:18
Speaker 1: optical telescope that you can see whether radio antenna or
17:21
Speaker 1: an X ray telescope. Well, the same thing is true
17:24
Speaker 1: for gravitational waves. Gravitational waves come in all different frequencies.
17:30
Speaker 1: Space can ripple it lots of different frequencies, and very
17:33
Speaker 1: high frequency ripples are different from very low frequency ripples,
17:37
Speaker 1: and the kind of things that we can see with
17:38
Speaker 1: LIGO are in a sort of narrow range of gravitational waves.
17:43
Speaker 1: It was designed to see gravitational waves from solar mass
17:47
Speaker 1: black holes that were colliding with each other, and so
17:50
Speaker 1: it's sort of only sensitive to that little spectrum. Imagine
17:53
Speaker 1: if we had only ever built optical telescopes and we
17:55
Speaker 1: couldn't look at the sky in the UV or in
17:58
Speaker 1: the X ray or in the IDEO, we would be
18:01
Speaker 1: missing a huge slice of the picture. So what we
18:04
Speaker 1: need to do our build gravitational wave detectors that can
18:07
Speaker 1: detect various different frequencies of gravitational waves so we can
18:12
Speaker 1: listen to the messages from the universe and learn all
18:15
Speaker 1: of its crazy secrets. So we'll talk about how to
18:17
Speaker 1: build gravitational wave detectors that can detect very very low
18:21
Speaker 1: frequency gravitational waves and tell us all about what's going
18:24
Speaker 1: on in the early universe and the collisions of supermassive
18:28
Speaker 1: black holes. But first, let's take a quick break. All right,
18:44
Speaker 1: we're back and we are talking about building a gravitational
18:48
Speaker 1: wave detector the size of the galaxy actually made out
18:52
Speaker 1: of the galaxy, and we reminded ourselves what gravitational waves
18:56
Speaker 1: are and how they have been seen so far by
18:59
Speaker 1: gravity aational wave observatories on Earth that use delicate mirrors
19:04
Speaker 1: balanced underground miles apart to detect very very small deviations
19:09
Speaker 1: in the distances between those mirrors. These deviations are like
19:13
Speaker 1: one part in ten to the twenty into the extraordinary
19:16
Speaker 1: experimental accomplishment that they can do these things. It took
19:19
Speaker 1: a huge amount of work to make those mirrors insensitive
19:23
Speaker 1: to all sorts of things that would shake them, that
19:25
Speaker 1: would look like the gravitational waves, and when they finally
19:28
Speaker 1: did see them, it was a really nice, very clear
19:31
Speaker 1: signature because they knew exactly what they were looking for.
19:34
Speaker 1: They knew what kind of gravitational waves black holes should
19:37
Speaker 1: make as they fall into each other. What happens is
19:40
Speaker 1: that the black holes start slowly moving towards each other
19:44
Speaker 1: as they get closer and closer, and they start spiraling
19:47
Speaker 1: faster and faster. So the frequency of the gravitational wave
19:50
Speaker 1: increases as the black holes get closer together. And so
19:54
Speaker 1: they call this like a chirp because it goes faster, faster, faster, faster,
19:57
Speaker 1: faster and higher entire and hire and higher and high,
19:59
Speaker 1: and that's a hi, as my voice will go. So
20:01
Speaker 1: they knew sort of what they were looking for. They
20:03
Speaker 1: did all these numerical relativity calculations to figure out just
20:07
Speaker 1: what it looks for. But you know, those black holes
20:09
Speaker 1: were generating gravitational waves long before we saw them. It
20:13
Speaker 1: took years for these black holes to actually merge. What
20:16
Speaker 1: we saw was just the last little bit as the
20:20
Speaker 1: frequency moved into a range that Ligo could see it.
20:23
Speaker 1: Ligo was designed to see gravitational waves from black hole mergers,
20:27
Speaker 1: but only the last few seconds of them. Right there
20:30
Speaker 1: were years, probably a gravitational waves that we couldn't see.
20:33
Speaker 1: So why can LIGO not see gravitational waves that are longer?
20:37
Speaker 1: The problem is seismic noise. The Earth itself is shaking.
20:42
Speaker 1: We live on the surface of the Earth, which is
20:43
Speaker 1: part of the crust, and the crust is always sliding,
20:46
Speaker 1: and that makes it very difficult to see little ripples
20:50
Speaker 1: in space and time. We can see them if the
20:52
Speaker 1: ripples are fast enough, sort of faster than the Earth
20:55
Speaker 1: typically shakes, but anything at a lower frequency, the sizemic vways,
21:00
Speaker 1: the shaking of the Earth itself makes basically impossible to
21:04
Speaker 1: see those things. The Earth is shaking more loudly than
21:07
Speaker 1: those gravitational waves, and it's not just the frequency, it's
21:10
Speaker 1: because of the amplitude. Also, the intensity of the gravitational
21:14
Speaker 1: wave signal gets stronger as you get near the end
21:17
Speaker 1: of the black hole merger. As the black holes are
21:19
Speaker 1: getting close and closer together, the gravitational waves get stronger.
21:22
Speaker 1: So the gravitational waves from the early part of the
21:24
Speaker 1: story we're missing because they're longer frequencies that our detectors
21:29
Speaker 1: can't see over the seis mc noise of the Earth,
21:32
Speaker 1: and they're much quieter, which makes it harder for us
21:35
Speaker 1: to see them. So how do you see these longer
21:38
Speaker 1: frequency gravitational waves. Then, well, the problem is that you're
21:42
Speaker 1: buried in the Earth. One idea is, don't be buried
21:45
Speaker 1: in the Earth. Take it to space. Right. So one
21:49
Speaker 1: science fiction sounding project that's actually very real is a
21:53
Speaker 1: project called LISA, which is a laser interferometer in space. Right.
21:58
Speaker 1: It takes the same concept of having mirrors where you're
22:01
Speaker 1: bouncing lasers back and forth, and it puts it out
22:04
Speaker 1: there in space. That's much more technologically difficult and expensive,
22:07
Speaker 1: of course, but it does solve this problem of the
22:10
Speaker 1: Earth background noise. There is no seismic noise out there
22:14
Speaker 1: in space. So LISA would be much more powerful, much
22:17
Speaker 1: more sensitive, and able to hear gravitational waves at longer frequencies.
22:23
Speaker 1: But again that's expensive and that's far off in the future,
22:26
Speaker 1: and so until then people are thinking, do we need
22:28
Speaker 1: to build our own gravitational wave detectors or can we
22:32
Speaker 1: find one already existing in the galaxy? Can we use
22:36
Speaker 1: the galaxy itself as a gravitational wave detector? And the answer,
22:40
Speaker 1: of course, obviously is yes, because if we're doing an
22:43
Speaker 1: whole episode about it, I wouldn't get to this point
22:45
Speaker 1: of the episode and then just say no goodbye, see
22:48
Speaker 1: you later. The way we do it is us an
22:49
Speaker 1: ocean of very precise clocks that naturally exist in the galaxy.
22:54
Speaker 1: Of course, I'm talking about pulsars. Pulsars are the end
22:59
Speaker 1: point of a stall are you know. The star forms
23:01
Speaker 1: when gas and dust swirl together and compactify and eventually
23:05
Speaker 1: get dense enough that fusion happens. Then hangs out for
23:08
Speaker 1: a few billion years, burning all of that fuel, pushing
23:11
Speaker 1: back against gravity, preventing it from a collapse. But eventually
23:15
Speaker 1: that fuel gives out and it can no longer provide
23:18
Speaker 1: the heat and the radiation to prevent gravity from compacting
23:21
Speaker 1: it even further. And depending on the mass of the star,
23:25
Speaker 1: it can end up in various scenarios. It might turn
23:27
Speaker 1: into a black hole if it's very massive, might turn
23:29
Speaker 1: into a white dwarf basically a hot lump of stuff
23:33
Speaker 1: if it's not that massive. In the middle is a
23:36
Speaker 1: category of object called neutron stars. Here there's enough gravity
23:40
Speaker 1: to compact ify it to squeeze it down really really dense.
23:44
Speaker 1: We're talking about a significant fraction of the mass of
23:46
Speaker 1: the Sun in an area like the size of Los Angeles.
23:50
Speaker 1: It's incredibly dense, it's incredibly weird matter. Also, it's called
23:53
Speaker 1: a neutron star because it's been taken and squeezed so
23:57
Speaker 1: much that the electrons and the protons and he had
24:00
Speaker 1: ms are squeezed together and turn into neutrons. Usually it
24:04
Speaker 1: goes the other way. You have a neutron hanging out,
24:06
Speaker 1: it turns into a proton and an electron. But here
24:09
Speaker 1: because the pressure that's basically been reversed, and you've got
24:12
Speaker 1: an object which is mostly neutrons and in some really
24:15
Speaker 1: weird intense state. In addition, these things are spinning really
24:19
Speaker 1: really fast because they have all the angular momentum of
24:21
Speaker 1: the original stuff that made them. But now they're a
24:24
Speaker 1: really small space. And because angular momentum is conserved, you
24:27
Speaker 1: can't just get rid of it. It doesn't just disappear.
24:30
Speaker 1: Then it has to spin faster as it gets smaller,
24:33
Speaker 1: just like a figure skater pulling in her arms and
24:36
Speaker 1: you get more compact, you need to higher velocity to
24:39
Speaker 1: match the smaller radius to have exactly the same angular momentum.
24:44
Speaker 1: All right, So we have a spinning object, the neutron star,
24:47
Speaker 1: some fraction of these have also really powerful magnetic fields,
24:51
Speaker 1: and those magnetic fields operate on the particles on the
24:54
Speaker 1: surface of the neutron star and can generate beams of energy.
24:57
Speaker 1: They push the protons and the neutrons and they generate
25:00
Speaker 1: these massive beams of energy which follow the magnetic fields.
25:04
Speaker 1: So you have this spinning object with a very powerful
25:07
Speaker 1: magnetic field, with a beam of energy coming out the
25:09
Speaker 1: top and the bottom, the magnetic north and the magnetic south.
25:13
Speaker 1: What happens to the spin of this object is not
25:16
Speaker 1: aligned with the magnetic axis. What if the beam is
25:19
Speaker 1: not shooting straight up, so it's always going in the
25:21
Speaker 1: same direction, but sort of off to the side a
25:23
Speaker 1: little bit, then what happens is that that beam sweeps
25:26
Speaker 1: around it points in a different direction. Right. Imagine holding
25:29
Speaker 1: a flashlight and spinning around. If you're holding it straight up,
25:32
Speaker 1: the flashlight doesn't change as you spin, But if you're
25:35
Speaker 1: holding it to the side, then you're gonna be blinding
25:38
Speaker 1: different people as you spin around. Right. That's what a
25:41
Speaker 1: pulsar is a very intense beam of light pointing outside ways,
25:44
Speaker 1: so that as it sweeps around, that beam passes over
25:48
Speaker 1: different things. And from Earth we see these things when
25:50
Speaker 1: that beam passes us. So there's a lot of pulsars
25:53
Speaker 1: out there in the galaxy that we can't see because
25:55
Speaker 1: their beam never passes us. But the ones where the
25:58
Speaker 1: beam does sweep over the Earth, we see that as pulses.
26:02
Speaker 1: We got a pulse every time it sweeps by. The
26:04
Speaker 1: incredible thing is that they're very very regular. Here you
26:07
Speaker 1: have an object of incredible mass, trillions of tons of
26:11
Speaker 1: stuff spinning at very high speeds up to like hundreds
26:15
Speaker 1: of hurts, right like an incredible amount of stuff, spending
26:18
Speaker 1: many times per second, and doing it very regularly. It's
26:22
Speaker 1: not like every point two seconds and then every point
26:24
Speaker 1: three seconds and every point four seconds. These things are
26:27
Speaker 1: more precise than some atomic clocks. They're like the most
26:31
Speaker 1: precise natural clocks out there we have found, and the
26:33
Speaker 1: universe is filled with them. They are all over the galaxy.
26:37
Speaker 1: So you might imagine then how we might be able
26:39
Speaker 1: to use them to measure the distortion of space. If
26:43
Speaker 1: you are on Earth and you're surrounded by a bunch
26:45
Speaker 1: of pulsars, and even watching these pulsars for a while
26:48
Speaker 1: so you know them. You know how long it takes
26:51
Speaker 1: between pulses for a given pulsar then what you can
26:54
Speaker 1: do is see if that changes. Think about what happens
26:57
Speaker 1: as a gravitational wave passes over the Earth. It changes
27:01
Speaker 1: the distance between us and those pulsars. What that means
27:05
Speaker 1: is that the pulses would take longer or shorter amounts
27:09
Speaker 1: of time to arrive here on Earth. So if you
27:12
Speaker 1: know how often the pulses should be arriving and you
27:14
Speaker 1: see a deviation, you see your residual from what you expect,
27:18
Speaker 1: then that means something happened. The distance between you and
27:21
Speaker 1: that pulsar has changed. And so a while ago people
27:25
Speaker 1: figured out how to use all of these pulsars, these
27:28
Speaker 1: precise clocks to calculate what would happen if a gravitational
27:32
Speaker 1: wave past us, and it wouldn't affect all pulsars the
27:35
Speaker 1: same way, right, because gravitational waves have this sort of
27:38
Speaker 1: quadruple effect. They squeeze in one direction at the same
27:42
Speaker 1: time they're pulling in another direction. So we can't look
27:45
Speaker 1: at an individual pulsar and say, oh, there was a
27:48
Speaker 1: gravitation wave. What we need to do is have a
27:51
Speaker 1: whole network of pulsars, have them all around us in
27:54
Speaker 1: every direction, so that a gravitational wave has a very
27:57
Speaker 1: distinct signature, so it looks different from other random weird
28:01
Speaker 1: blips we might see, or changes in our instrument or
28:04
Speaker 1: anything else that might affect the timing but isn't due
28:08
Speaker 1: to gravitational waves. Is a classic trick and experimental physics
28:12
Speaker 1: is to make the thing you're looking for look unique,
28:14
Speaker 1: so that when you see it, you know you saw it.
28:17
Speaker 1: And so there were a couple of folks named Hellings
28:19
Speaker 1: and Downs, and they did this analysis and they showed
28:22
Speaker 1: what would happen if a gravitational wave passed over the
28:25
Speaker 1: Earth and between us and a whole network of pulsars,
28:30
Speaker 1: And what would happen is a predictable pattern in the
28:33
Speaker 1: way that the pulses arrive on Earth. You can google
28:37
Speaker 1: this and check it out if you're interested in learning
28:39
Speaker 1: more details. But there's a particular signature we would expect
28:42
Speaker 1: to see in the pulses from pulsars and the timing
28:46
Speaker 1: of those pulsars arriving here on Earth if a gravitational
28:50
Speaker 1: wave passed. And remember that we're not targeting fast gravitational
28:54
Speaker 1: waves the ones that liego can see. Those are things
28:57
Speaker 1: where it's like a hundred hurts in the frequency. There
29:00
Speaker 1: is fast ripples in space and time. We're interested in
29:03
Speaker 1: slow ripples in space and time. We're interested in very
29:06
Speaker 1: long gravitational waves. Were interested in like the beginnings of
29:10
Speaker 1: black holes coming together, and not just little itty bitty
29:13
Speaker 1: black holes like the ones that Lego has seen. We're
29:16
Speaker 1: interested in super massive black holes right because we think
29:21
Speaker 1: that those black holes also combined. We talked earlier about
29:24
Speaker 1: galaxy colliders shooting one galaxy at another. Well, that actually
29:28
Speaker 1: happens in the universe. I don't know who's controlling it,
29:31
Speaker 1: or if anybody ever is, but galaxies do merge. We
29:35
Speaker 1: see evidence for this in lots of galaxies. We can
29:37
Speaker 1: tell that some galaxies have recently undergone a merger because
29:40
Speaker 1: they're sort of chaotic, and we can see other galaxies
29:43
Speaker 1: that have had mergers billions of years ago. We think
29:46
Speaker 1: that the Milky Way, for example, has remnants of other
29:48
Speaker 1: galaxies that it's eaten. So if galaxies have supermassive black
29:53
Speaker 1: holes at their center, then what happens when two galaxies merge?
29:57
Speaker 1: What happens when one eats another one, which you get
30:00
Speaker 1: is the merger of super massive black holes. These things
30:04
Speaker 1: are black holes, not like just a little bit bigger
30:06
Speaker 1: than our Sun. These things have masses like ten million
30:09
Speaker 1: or sometimes billions of times the mass of our Sun.
30:13
Speaker 1: It's staggering. It's hard to even get your mind around. Now,
30:16
Speaker 1: imagine two of them and they're coming together, and they're
30:19
Speaker 1: eating each other. They're forming one huge Grandma black hole right. Well,
30:25
Speaker 1: that is going to admit a lot of gravitational waves,
30:27
Speaker 1: and in the very beginning, very early part of that,
30:31
Speaker 1: while the galaxies are still merging, while those black holes
30:34
Speaker 1: are just beginning their dance, there's going to be very
30:38
Speaker 1: low frequency, long gravitational waves that take a long time
30:42
Speaker 1: to propagate, in a long time to measure as they
30:46
Speaker 1: move through the universe. And so that's what a pulsar
30:49
Speaker 1: array could be sensitive to. It could see gravitational waves
30:54
Speaker 1: from the collisions of super massive black holes from the
30:58
Speaker 1: beginning stages of those collisions while the two galaxies are
31:01
Speaker 1: still beginning to form together. And we also don't understand
31:04
Speaker 1: that the size of supermassive black holes. We know that
31:08
Speaker 1: there's a relationship between galaxies and supermassive black holes that
31:12
Speaker 1: typically the larger the black hole, the larger the galaxy,
31:16
Speaker 1: But we don't understand how these supermassive black holes got
31:19
Speaker 1: so big. We look back in the very early universe
31:22
Speaker 1: and we see that there are already black holes like
31:25
Speaker 1: a billion times the mass of the Sun, only a
31:28
Speaker 1: billion years into the history of the universe, and in
31:31
Speaker 1: our calculations, that's just not enough time to make that
31:35
Speaker 1: bigger black holes. The deep mystery how these supermassive black
31:38
Speaker 1: holes got so supermassive, and so one way to figure
31:42
Speaker 1: this out is to see them merging. Is to understand
31:44
Speaker 1: what happens when these two things combine. Is to look
31:47
Speaker 1: at the early parts and say, oh, okay, this came
31:50
Speaker 1: from too slightly smaller black holes, or maybe three, or
31:53
Speaker 1: maybe something else entirely is going on. That's why we
31:56
Speaker 1: are desperate to listen to these messages and to understand
32:00
Speaker 1: what's going on with these very low frequency black holes.
32:04
Speaker 1: So we talked about how to listen through low frequency
32:06
Speaker 1: black holes by building a system of pulsars all across
32:10
Speaker 1: the galaxy and watching as the signals from those pulsars
32:14
Speaker 1: shift in frequency as a gravitational wave passes, and we
32:17
Speaker 1: talked about what might be generating those gravitational waves. I
32:20
Speaker 1: want to tell you all about an experiment that claims
32:22
Speaker 1: to maybe have seen some of these low frequency gravitational
32:26
Speaker 1: waves by using a pulsar array. But first, let's take
32:30
Speaker 1: another break. All right, we're back and we are talking
32:45
Speaker 1: about using the entire galaxy as a gravitational wave detector.
32:50
Speaker 1: We reminded ourselves that gravitational waves are these ripples in
32:54
Speaker 1: space and time. Sometimes they are generated when two small
32:57
Speaker 1: black holes merged become a larger black hole, but they
33:00
Speaker 1: can also be generated by super massive black holes as
33:04
Speaker 1: galaxies merge and their central masses do a dance to
33:08
Speaker 1: find out who's going to be in charge of the
33:10
Speaker 1: new galaxy, and you can use pulsars to watch these
33:13
Speaker 1: things happen. Pulsars are very regular clocks that send us
33:17
Speaker 1: pulses at a very precise intervals, and as a gravitational
33:20
Speaker 1: wave passes between us and them, shortening or extending the
33:24
Speaker 1: distance between us and them, it can change the frequency
33:27
Speaker 1: which those pulses arrive and give us a clue that
33:29
Speaker 1: gravitational wave may have passed us. And this is not
33:32
Speaker 1: a brand new idea, which means people have been doing
33:35
Speaker 1: this for a while now. There's a group called Nano
33:38
Speaker 1: grab that's been doing it for the last fifteen years.
33:41
Speaker 1: They have a set of about forty five pulsars that
33:44
Speaker 1: they've been listening to very regularly. They picked them and
33:47
Speaker 1: they watch them with radio telescopes, and they observe the
33:50
Speaker 1: frequency at which these pulses arrive here on Earth. And
33:53
Speaker 1: after twelve and a half years they think they see
33:56
Speaker 1: something interesting. They see something which they can't explain. They
34:00
Speaker 1: see deviations in the patterns of these pulsars, right, And
34:05
Speaker 1: that's exactly what you would expect to see if there
34:07
Speaker 1: was a gravitational wave. You would expect that the pulsars
34:11
Speaker 1: wouldn't be sending you their pulses at the very precise
34:14
Speaker 1: atomic clock level, calibrated pulses that we're used to, but
34:17
Speaker 1: that there would be these deviations. Now, nanogravi is not
34:20
Speaker 1: his own experiment. It's of course using pulsars that are
34:24
Speaker 1: already out there in the universe, and it uses telescopes
34:26
Speaker 1: that already exist on Earth. For example, the Green Bank
34:29
Speaker 1: Observatory that we always talked about in the center of
34:32
Speaker 1: the radio quiet zone in the United States where you're
34:35
Speaker 1: not allowed to own a telephone or turn on your microwave,
34:38
Speaker 1: they used the Aristobo radio telescope before it's unfortunate collapse,
34:42
Speaker 1: and they use all of these things together to try
34:44
Speaker 1: to monitor all of these pulsars. Now, in January of
34:48
Speaker 1: one they release their preliminary results, and what they see
34:51
Speaker 1: is not consistent with no gravitational waves. Right, it's not
34:55
Speaker 1: what you would expect if everything was normal. Unfortunately, it's
34:59
Speaker 1: also not it's consistent with gravitational waves. We talked about
35:03
Speaker 1: how if there were gravitational waves, you would expect to
35:05
Speaker 1: see sort of a regular pattern. You would see pulsars
35:08
Speaker 1: in one direction from Earth looking closer to you, and
35:11
Speaker 1: pulsars in another direction, looking further because gravitational waves squeeze
35:16
Speaker 1: space in one direction and lengthen it in another direction.
35:19
Speaker 1: So that's not what they see. What they see can't
35:22
Speaker 1: be explained by gravitational waves, but it also can't be
35:25
Speaker 1: explained by anything we know. And that's exciting, right, because
35:29
Speaker 1: every time you open up a new kind of eyeball
35:32
Speaker 1: or build a new kind of ear to listen to
35:34
Speaker 1: the universe's messages, we hear a surprise. Because sometimes we
35:38
Speaker 1: go out there trying to answer one question and we
35:41
Speaker 1: get evidence to answer another one, one we didn't even
35:44
Speaker 1: know existed. We all remember stories of accidental discoveries. In fact,
35:48
Speaker 1: pulsars themselves were an accidental discovery. Somebody was out there
35:52
Speaker 1: looking to study quasars in the distant universe and hear
35:55
Speaker 1: their radio messages and accidentally discovered pulsars. So it would
35:59
Speaker 1: be pretty funny if pulsars then in turn gave us
36:01
Speaker 1: clues about something else in the universe and we didn't
36:04
Speaker 1: even know to look for. There are several of these
36:07
Speaker 1: groups doing these studies watching pulsars. It takes a while
36:11
Speaker 1: because we're talking about very low frequency events. We're talking
36:14
Speaker 1: about gravitational waves. They could take years, decades, centuries to
36:19
Speaker 1: propagate across the universe. Not that they're moving slowly, but
36:23
Speaker 1: that their frequency is very very long, So the information
36:26
Speaker 1: moves quickly, but the ripples in space themselves are moving
36:30
Speaker 1: at a very slow speed, just like you can have
36:32
Speaker 1: light traveling at the speed of light. Having very low
36:35
Speaker 1: frequency waves like radio, and the kind of things they
36:38
Speaker 1: can look for are not just super massive black hole collisions,
36:42
Speaker 1: although that is super fascinating. We're also interested in general,
36:46
Speaker 1: in what is the gravitational signal out there. We recently
36:50
Speaker 1: did an episode about the cosmic gravitational background because we
36:54
Speaker 1: suspect that the universe is filled with these low frequency
36:57
Speaker 1: gravitational waves. We know that every thing that has mass
37:00
Speaker 1: and accelerates creates gravitational waves. That means that as the
37:04
Speaker 1: Earth goes around the Sun, it generates gravitational waves. It
37:07
Speaker 1: means that every time you run to the store to
37:10
Speaker 1: get a pint of ice cream, you generate gravitational waves.
37:13
Speaker 1: And so there should be gravitational waves everywhere. There should
37:15
Speaker 1: be sort of hard to make out. It's not like
37:17
Speaker 1: we can pick out individual things unless they are very
37:20
Speaker 1: dramatic events, like to nearby black holes colliding. But in general,
37:24
Speaker 1: there should be sort of like a low level hum
37:27
Speaker 1: of gravitational waves in the universe, some of them from
37:30
Speaker 1: inspiring supermassive black holes and some of them from neutron
37:34
Speaker 1: stars being formed or other black holes being created, or
37:37
Speaker 1: supernovas should be generating gravitational waves. It should be everywhere.
37:41
Speaker 1: So we should be able to sort of pick up
37:43
Speaker 1: this low frequency gravitational waves as it sort of slashes
37:47
Speaker 1: through the universe. And if we see something in those
37:50
Speaker 1: low frequency gravitational waves that we don't expect, we might
37:54
Speaker 1: learn something new about the universe. For example, we said
37:58
Speaker 1: that one way to generate frequency gravitational waves that you
38:02
Speaker 1: could detect with a galaxy size pulsar array come from
38:06
Speaker 1: inspiraling black holes. Well, that might be true. What it
38:10
Speaker 1: might be that the way these black holes merge, these
38:13
Speaker 1: supermassive black holes merge, is different from what we expect.
38:16
Speaker 1: There might be something else going on, and that might
38:19
Speaker 1: help us understand how they get so big and how
38:22
Speaker 1: galaxies form. Because when black holes pull each other together,
38:25
Speaker 1: mostly what's going on is the force of gravity that
38:28
Speaker 1: dominates everything. But black holes have other properties as well. Right,
38:32
Speaker 1: black holes can spin because when something falls into a
38:35
Speaker 1: black hole doesn't lose its angular momentum. So if something
38:38
Speaker 1: falls into a black hole with angular momentum, then the
38:40
Speaker 1: black hole itself has to spin. Anglo momentum doesn't go away,
38:44
Speaker 1: same way electric charge doesn't go away. If you have
38:48
Speaker 1: a black hole which is electrically neutral and you throw
38:50
Speaker 1: an electron into it, what happens, Well, now you have
38:53
Speaker 1: a black hole with a charge. So there's a famous
38:55
Speaker 1: theorem called me no hair theorem that tells us that
38:59
Speaker 1: black holes can have only those properties mass, spin, and charge,
39:04
Speaker 1: and any other information about what's going on inside the
39:06
Speaker 1: black hole is hidden from you, and that's not because
39:09
Speaker 1: you can't give it a charge. It's because it's sort
39:11
Speaker 1: of unstable that the process is going on there will
39:14
Speaker 1: seek to balance it out. If, for example, you throw
39:17
Speaker 1: a cork into a black hole, well, a cork feels
39:19
Speaker 1: the strong nuclear force. It's a colored object, where color
39:23
Speaker 1: is the equivalent of electric charge for the strong nuclear force.
39:26
Speaker 1: What happens if you throw that into a black hole,
39:29
Speaker 1: but there's so much energy there that it will pull
39:31
Speaker 1: other corks out of the vacuum and eventually balance itself out.
39:35
Speaker 1: That's why most things around us don't have a strong
39:37
Speaker 1: nuclear charge, because those charges are inherently unstable. So that's
39:41
Speaker 1: something that's going on with black holes, and black holes
39:44
Speaker 1: are able to neutralize all those forces except for spin,
39:47
Speaker 1: charge and mass. But what if there are other forces
39:51
Speaker 1: out there? We know that there's a lot we don't
39:53
Speaker 1: know yet about the universe. We know that there are
39:56
Speaker 1: huge questions that are unanswered. There might be entirely new
40:00
Speaker 1: forces out there. What if, for example, dark matter feels
40:03
Speaker 1: a force, not a force that we're familiar with, but
40:06
Speaker 1: a force that only dark matter can feel with itself.
40:09
Speaker 1: Imagine if there was like a dark photon out there
40:11
Speaker 1: that interacted with dark matter particles that had a dark charge.
40:15
Speaker 1: In that case, it might be that supermassive black holes
40:19
Speaker 1: have more than just spin and mass and electric charge.
40:22
Speaker 1: They might also have a dark charge, in which case
40:26
Speaker 1: that could affect the way that these supermassive black holes
40:29
Speaker 1: fall into each other. It could have a powerful force
40:32
Speaker 1: that changes the way they're interacting and how fast they're
40:36
Speaker 1: falling into each other, and that could change the way
40:38
Speaker 1: these gravitational waves look. These very low frequency gravitational waves
40:42
Speaker 1: as they're beginning their dance would look different if there
40:45
Speaker 1: are different forces in play, because it would change the frequency.
40:49
Speaker 1: Remember that the frequency of the gravitational wave is determined
40:52
Speaker 1: by how fast the black holes are moving around each other,
40:55
Speaker 1: which depends entirely on the forces between them. So we
40:58
Speaker 1: could use these gravitational waves as a probe to look
41:01
Speaker 1: for new physics, new beyond the standard model, things that
41:05
Speaker 1: we do not yet understand. So, while it would be
41:07
Speaker 1: exciting to see gravitational waves and have them be exactly
41:11
Speaker 1: what we expect, have them be just the kind of
41:13
Speaker 1: gravitational waves we expect from neutron stars and supernovas and
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Speaker 1: inspiring supermassive black holes. It might be even more exciting
41:21
Speaker 1: if these pulse are arraysed detect gravitational waves that we
41:24
Speaker 1: don't understand that need new explanations, they need new ideas,
41:29
Speaker 1: because they are clues that there are things going on
41:32
Speaker 1: out there in the universe that we don't know about.
41:34
Speaker 1: And in the end, that's the biggest goal. That's the
41:37
Speaker 1: reason we listen to the nights guy, That's the reason
41:40
Speaker 1: we do science because we want to find something new.
41:43
Speaker 1: We want to gain a broader understanding of what's out
41:46
Speaker 1: there in the universe. We want to break the cognitive
41:48
Speaker 1: shackles of being here on Earth and be creatures of
41:52
Speaker 1: the universe. We want to understand everything that's out there,
41:55
Speaker 1: and we want to use all of our tools to
41:57
Speaker 1: find it. Unfortunately, we are trapped here on the Earth
41:59
Speaker 1: and we can only use the signals that get here.
42:02
Speaker 1: But at the very least we should pay careful attention
42:04
Speaker 1: to those signals. So even if they are little hints
42:07
Speaker 1: from pulsear timings, that's something weird is going on in
42:10
Speaker 1: the space between us and the pulsears, revealing that something
42:13
Speaker 1: else weird is going on between super massive black holes
42:16
Speaker 1: as they dance. These are the kind of clues that
42:19
Speaker 1: we need to unravel, these subtle little stories that tell
42:22
Speaker 1: us the deepest secrets of the universe. So write to
42:25
Speaker 1: your politicians and tell them we should fund more science
42:28
Speaker 1: because we want to learn more about the universe. But
42:30
Speaker 1: until then, we will come up with clever and cheaper
42:33
Speaker 1: ways to listen to those signals from the universe and
42:37
Speaker 1: hope to unravel those mysteries. Thanks for listening to this
42:40
Speaker 1: crazy story of ingenuity and creativity in astrophysics. Stay tuned,
42:45
Speaker 1: and if you have a topic you would like to
42:47
Speaker 1: hear us talk about, please don't be shy. Or if
42:49
Speaker 1: you have any question at all about physics or something
42:52
Speaker 1: you read, I answer all my emails, so right to
42:55
Speaker 1: us two questions at Daniel and Jorge dot com. Can't
42:58
Speaker 1: wait to hear from you. Thanks everybody, Yeah, thanks for listening,
43:08
Speaker 1: and remember that Daniel and Jorge explained. The Universe is
43:11
Speaker 1: a production of I Heart Radio or more podcast For
43:14
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