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