Speaker 1: Hey, Daniel, do people ever send you their personal theories
Speaker 1: of the universe? Oh? Yeah, I get plenty of those.
Speaker 1: What do you think they're hoping for? A lot of
Speaker 1: them want to prove Einstein was wrong? Really, aim high?
Speaker 1: I guess after all these years, aren't we convinced Einstein
Speaker 1: was right? Actually, I'm pretty convinced Einstein was wrong. What
Speaker 1: you think you know better than Einstein? I don't have
Speaker 1: a better theory of the universe, but I'm pretty sure
Speaker 1: his theory general relativity is not a correct description of nature. Well,
Speaker 1: you should come up with your own theory then, Yeah,
Speaker 1: and then I could send it to myself and then
Speaker 1: you can answer it on the podcast. Done Nobel Prize
Speaker 1: for the two of us. Hi am more Hammad, cartoonists
Speaker 1: and the creator of PhD comics. Hi. I'm Daniel. I'm
Speaker 1: a particle physicist, and I would love if somebody out
Speaker 1: there proved Einstein wrong. Yeah, maybe even the ghost of Einstein,
Speaker 1: Einstein's grandchildren, son of Einstein or daughter of Einstein. Einstein
Speaker 1: had a pretty scandalous family situation, so I wouldn't be
Speaker 1: surprised if some of his kids or grandkids are great
Speaker 1: grandkids were a little grumpy at him. Well, they definitely
Speaker 1: heard it a nice brand name. So I mean, can
Speaker 1: you imagine going for a job and put an ice
Speaker 1: and on your resume and people are like, yeah, he's
Speaker 1: probably not or she's not, probably not smart enough, not
Speaker 1: likely to happen, right, It's a lot of pressure. What
Speaker 1: if you, like, want to be a basketball player in
Speaker 1: your name is Einstein and they're like, get off the core, Einstein,
Speaker 1: go back to your chalk board there. Yeah, exactly what
Speaker 1: do they call it when an actor can only get
Speaker 1: one kind of real type cast? Right? Like Einstein and
Speaker 1: all of his generations are all going to be forced
Speaker 1: to be doing fundamental physics. Right. I haven't seen a
Speaker 1: lot of stand up comedians, right, Or are is name Einstein?
Speaker 1: Well they probably changed their names, right, they have stage names,
Speaker 1: you know, the comedian formerly known as Einstein. I guess
Speaker 1: that would help them. But anyways, welcome to our podcast.
Speaker 1: Daniel and Jorge explain the universe in production of I
Speaker 1: Heart Radio, in which we make everybody out there and
Speaker 1: Einstein by explaining to you everything that we do know
Speaker 1: about our crazy, beautiful, hot and wet and weird universe
Speaker 1: and everything that we don't yet understand from the tiniest
Speaker 1: little bits of space and how they fit together to
Speaker 1: make this incredible, emergent, bonkers beautiful world, to the vast
Speaker 1: nature of the cosmos. How far does it go on?
Speaker 1: What's out past there? Will we ever see it? We
Speaker 1: wrap up all those questions and explain them to you. Yeah,
Speaker 1: because it is a vast universe full of intricate secrets
Speaker 1: and lots of wonders for us discover hiding and plain
Speaker 1: site sometimes right even around our own neighborhood. It is exactly.
Speaker 1: I look at the universe like the biggest murder mystery
Speaker 1: or the grandest detective novel ever written. It's like a
Speaker 1: big puzzle figuring out how does it work. We're gathering
Speaker 1: clues and trying to narrow down and figure out, like
Speaker 1: what really makes the universe tick? What does it have
Speaker 1: to be a murder mystery? Daniel, I feel like you
Speaker 1: just went kind of dark there, like like somebody had
Speaker 1: to die to make the universe. Well, you know, the
Speaker 1: universe is going to kill you, Jorge. I'm sure it's
Speaker 1: not the universe itself, but maybe my eating habits. Well,
Speaker 1: I just think it adds some drama, you know, it's
Speaker 1: always more fun to work on a mystery if there's
Speaker 1: a body involved, I suppose, I don't know. That's why
Speaker 1: there's that whole genre of murder mysteries, right, It's not like,
Speaker 1: you know, who got gently tapped on the head in
Speaker 1: the library with the candlestick. You know, it's like who
Speaker 1: got killed? So, yeah, this is a big mystery. We
Speaker 1: want to understand what is the fundamental nature of the universe,
Speaker 1: what are the rules by which it runs? How can
Speaker 1: we figure that out? And frankly, I'm amazed that we
Speaker 1: really made any progress at all. Yeah. I guess if
Speaker 1: the mystery was just word that I put my reading glasses,
Speaker 1: that wouldn't attract a lot of viewers there, or physicists,
Speaker 1: to be honest, Yeah, exactly, or true crime novelists named Einstein.
Speaker 1: All right, we like to talk about all the great
Speaker 1: mysteries out there on the universe, and also we like
Speaker 1: to talk about what scientists are doing to uncover those
Speaker 1: secrets and figure out what's really going on, because there
Speaker 1: are a lot of interesting projects and interesting science experiments
Speaker 1: going on right now as we speak, trying to peer
Speaker 1: further into the universe and closer to the very nature
Speaker 1: of matter. That's right, because even though folks like Einstein
Speaker 1: gave us a beautiful glimpse into how the universe might work,
Speaker 1: we are still figuring out whether his vision is correct
Speaker 1: or not, whether it describes the way the universe actually works,
Speaker 1: or if it's just like a very effective approximation which
Speaker 1: from some point of view seems to be successful in
Speaker 1: predicting what happens in weird situations. Yeah, and so you're
Speaker 1: convinced that Eisen is wrong, you said earlier, like you're
Speaker 1: pretty sure he's wrong, or you think he's wrong. I
Speaker 1: think he's got to be wrong. I mean, there's no
Speaker 1: way general relativity is correct. Why not, Well, it flies
Speaker 1: in the face of the nature of the universe as
Speaker 1: we know it. We know that the universe is quantum mechanical.
Speaker 1: We know that nothing is smooth and continuous. But general
Speaker 1: relativity assumes that the universe is smooth, it's continuous, that
Speaker 1: you can like slice up space and time into infinitely
Speaker 1: small pieces, that you can know everything about the configuration
Speaker 1: of particles, for example. It just ignores the fundamental nature
Speaker 1: of the universe that's been revealed to us over the
Speaker 1: last hundred years. And that's why it breaks down. For example,
Speaker 1: we have singularities at the hearts of black holes and
Speaker 1: at the beginning of the universe. Those singularities reflect a
Speaker 1: failure of the theory. So it just can't be right,
Speaker 1: and yet it works, so darn well, well you don't
Speaker 1: think it works. But maybe there is a singularity. I
Speaker 1: don't know, isn't that possible? Well, we talked about this
Speaker 1: in our fun episode about singularities. But singularity is like
Speaker 1: a mathematical oddity. It's like an infinity. It's a failure.
Speaker 1: It's like when the theory is going I don't know,
Speaker 1: you know, it's not a real prediction, Like you can't
Speaker 1: actually have infinite density. It's nonsensical. It's like an infinite universe,
Speaker 1: which I here used to for it as a theory.
Speaker 1: That's true, and it certainly could be that weird mathematical
Speaker 1: features of the universe that we dismiss as artifacts could
Speaker 1: actually be real. Right, It wouldn't be the first time
Speaker 1: that had happened. But it seems to me like a failure.
Speaker 1: And also it seems to me impossible to reconcile general
Speaker 1: relativities view of the universe as smooth and continuous with
Speaker 1: this quantum mechanical nature of the universe. We see that
Speaker 1: it's discreet, we see that there are smallest bits. We
Speaker 1: see that there is limited information. So we're desperate to
Speaker 1: know the true story of the universe, how it actually works.
Speaker 1: But to do that we need to see Einstein's theory fail.
Speaker 1: We need to find a place where it's wrong. Yeah,
Speaker 1: and that's really hard because so far as you said,
Speaker 1: Einstein's theory, it's pretty good. It's past every test with
Speaker 1: flying colors. It's got an A plus plus plus plus
Speaker 1: plus plus. Like nobody's ever seen general relativity get anything wrong.
Speaker 1: No matter what configuration of matter or weird effects you study,
Speaker 1: or crazy intense things going on in the distance universe
Speaker 1: like black holes colliding, general activity gets its spot on. Yeah,
Speaker 1: and so there's a big question of whether or not
Speaker 1: Einstein's theories are ultimately correct or not. And there is
Speaker 1: one experiment right now, right above you will most likely
Speaker 1: trying to figure that out. That's right. We physicist her
Speaker 1: inventing more and more crazy scenarios to try to test
Speaker 1: the details of these predictions of general relativity, hoping to
Speaker 1: get it wrong, hoping to find a scenario where Einstein's
Speaker 1: theory fails and forces us to come up with another theory,
Speaker 1: or like gives us a clue as to how to
Speaker 1: formulate that next theory. So today on the podcast we'll
Speaker 1: be talking about what is frame dragging? I have to say, Daniel,
Speaker 1: it feels like the disappointing title after all that build up.
Speaker 1: I felt like we should have, you know, probing the
Speaker 1: mysteries of the nature of space and time, But no,
Speaker 1: we're going with but what is frame dragging? Well, that's
Speaker 1: because frame dragging is one of the mysteries of space
Speaker 1: and time. It's one of these bizarre effects predicted by
Speaker 1: general relativity that people go out to see, like is
Speaker 1: this actually real or is it just a mathematical artifact
Speaker 1: or was Einstein wrong? Or it could just be that
Speaker 1: you're taking a picture frame and dragging it across the floor.
Speaker 1: It could go either way. Yeah, it doesn't really conjure
Speaker 1: up the gravity of the situation if you ask me.
Speaker 1: But coincidentally does have to do with gravity, right, and
Speaker 1: I signed theory about how it all works. Yeah, and
Speaker 1: reference frames like this idea of where you put your axes,
Speaker 1: your X, Y and z, and how you measure your
Speaker 1: position and your velocity is absolutely fundamentally central to the
Speaker 1: whole concept of relativity, and so you know that gives
Speaker 1: you clues to what it might be about. And I
Speaker 1: think this is a super fun topic and I especially
Speaker 1: hope that it's being enjoyed by one particular listener out
Speaker 1: there from the Netherlands. He wrote to us last week
Speaker 1: and he said that he really liked our podcast, but
Speaker 1: that it had led to more than one occasion in
Speaker 1: which he burned dinner. Oh no, well, out of frustration
Speaker 1: or out of just not paying attention. Apparently he listened
Speaker 1: to our podcast while he's cooking, and when things get
Speaker 1: really complicated or interesting, he ignores what's on the stove
Speaker 1: and things good things go up in flames. Wow, I
Speaker 1: feel like we're destroying this person's family life here, if
Speaker 1: not his actuate home. Yeah. He also said that his
Speaker 1: kids know not to ask him anything or for anything
Speaker 1: when he's listening to the podcast, because he'll just ignore them.
Speaker 1: He or she should invite their kids to listen with
Speaker 1: him her which kid doesn't want to know about frame dragging. Yeah,
Speaker 1: so pay attention to the podcast, learn the secrets of
Speaker 1: the universe, but also don't burn your dinner. Sorry, flipped
Speaker 1: the chicken right now before it gets Yeah, let's pause
Speaker 1: so that he's can finish the dinner. All right, Well,
Speaker 1: this is an interesting question, and so as usual we
Speaker 1: were wondering how many people out there had even heard
Speaker 1: of this question and what it might mean or even
Speaker 1: have an answer. So as usual, Daniel went out there
Speaker 1: and ask people on the internet what is frame dragging?
Speaker 1: So thanks to everybody who was willing to play along.
Speaker 1: And if you have listened to the podcast and chuckle
Speaker 1: along with these answers but never contributed your own, please
Speaker 1: write to me two questions at Daniel and Jorge dot
Speaker 1: com and volunteer. I promise it's fun. Here's what people
Speaker 1: had to say. I'm going to guess that it has
Speaker 1: something to do with photography, maybe photographing of planets in
Speaker 1: a three dimensional space where we can only view them
Speaker 1: in a two dimensional aspect. We take enough pictures of
Speaker 1: the two dimensional aspects to drag them together to create
Speaker 1: a three dimensional picture. Frame dragging is when it's moving
Speaker 1: day and none of your friends show up to help. Um.
Speaker 1: Frame dragging from physics point of view, UM, I don't know.
Speaker 1: I have no idea frame dragging. UM, nothing all right.
Speaker 1: Not a lot of people seem to have a good
Speaker 1: idea here, like the one who said it's moving day
Speaker 1: and none of your friends want to heppy move drag
Speaker 1: your art frames around. Yeah, that's a great one. Should
Speaker 1: ordered more pizza man, sorry, or you know, hired verse
Speaker 1: perhaps so. Yeah, it's a pretty interesting question because it
Speaker 1: doesn't sound physics ee, but I'm guessing it has something
Speaker 1: to do with maybe like frames of reference or coordinate
Speaker 1: systems or something like that. Exactly. It has to do
Speaker 1: with a really bizarre prediction of general relativity. Remember that
Speaker 1: general relativity is Einstein's theory of gravity, replaced Newton's theory.
Speaker 1: Newton says two objects with mass will pull on each other,
Speaker 1: that gravity is a force, but Einstein tells us that
Speaker 1: gravity shouldn't be seen as a force. It's actually just
Speaker 1: due to the fact that space and time curve around
Speaker 1: massive objects. And if you can't see those curves, like
Speaker 1: we can't detect them directly, then things will move in
Speaker 1: a surprising way, and they move as if they were
Speaker 1: under some force. And that's what gravity is. It's the
Speaker 1: effect of the curvature of space time itself. Most of
Speaker 1: the time those two things totally agree, Like you could
Speaker 1: treat gravity as a force like Newton did, or you
Speaker 1: could treat gravity is the mending of space time like
Speaker 1: Einstein does. It doesn't really change the way the Earth
Speaker 1: moves around the Sun, for example. But there are some
Speaker 1: cases where they disagree, and that lets us probe Einstein's
Speaker 1: theory as different from Newton's theory. Really, I thought it
Speaker 1: was sort of like mathematically burned in that it was
Speaker 1: the same thing. But no, there are exceptions. No, they're
Speaker 1: fundamentally different ways of seeing the universe, and they give
Speaker 1: different predictions in some cases, and almost every case they don't,
Speaker 1: which is why Newton's theory worked so well. Right, Newton
Speaker 1: got a lot of stuff right because for the most
Speaker 1: part his theory is correct, and like that's a lesson
Speaker 1: getting a bunch of experiments right. And like nailing predictions
Speaker 1: for hundreds of years in a row doesn't mean that
Speaker 1: your theory is fundamentally true. It doesn't mean that it's
Speaker 1: an actual description of nature. It just means the experimentalists
Speaker 1: having come up with a way to break your idea. Yet. Yeah,
Speaker 1: and I imagine for Einstein it was a little bit
Speaker 1: like it is now for us. With him, and that
Speaker 1: you know, at the time, Newton was like the eyesight
Speaker 1: of his day. And for him to be like I
Speaker 1: think Newton's wrong, people were like, what do you think
Speaker 1: you're smarter than Newton or for sure? And remember that
Speaker 1: Einstein is further in time from Newton than we are
Speaker 1: from Einstein. So I think Newton was probably like an
Speaker 1: even grander, you know, person in the history of science
Speaker 1: due to the passage of time, like his ideas had
Speaker 1: stood longer, and whereas Einstein, like, you know, you can
Speaker 1: see movies of the guy, you know, he's like a
Speaker 1: real person. Well, there are the effects of internet relativity,
Speaker 1: which you know makes time seem go faster, alright, So
Speaker 1: there are instances where Einstein's theory of special relativity is
Speaker 1: different than Newton's, and so we can test whether or
Speaker 1: not the theories are correct exactly. And it really comes
Speaker 1: down to things spinning. Like for Newton, it doesn't really
Speaker 1: matter if the Earth is spinning. It's gravitational pull on
Speaker 1: the Moon is the same. Like for Newton, the only
Speaker 1: thing that gravity depends on are the masses of the
Speaker 1: two objects and their relative stance. If you know Newton's
Speaker 1: equation g mm over our squared. There's no factor in
Speaker 1: there that can be influenced by the fact that the
Speaker 1: Earth is spinning. It's irrelevant because like the configuration of
Speaker 1: the mass doesn't actually change. Right, you have a perfect
Speaker 1: sphere and you spin, it doesn't change the distance between
Speaker 1: any of the objects. But for Einstein's theory it does matter. Right,
Speaker 1: But as long as the I guess the center of
Speaker 1: mass of the Earth is kind of onund the spin access, right. Yeah,
Speaker 1: if you have a perfect sphere and it's spinning around
Speaker 1: its center, then it's gravity is totally unaffected by its spin,
Speaker 1: according to Newton, because the only thing that Newton cares
Speaker 1: about is the relative distance between two little bits of mass,
Speaker 1: and so if that's not changing, then the gravity shouldn't
Speaker 1: change at all, right, and specifically like between the center
Speaker 1: of masses of the two things, Right, that's the only
Speaker 1: thing that counts for Newton. Yeah, for Newton, that's all
Speaker 1: that counts. You can treat the Earth, for example, as
Speaker 1: if it was a point particle with the same mass,
Speaker 1: and you put that point particle at the center of mass,
Speaker 1: and all the other effects of some things being closer
Speaker 1: in some things being further away cancel out which is
Speaker 1: a pretty cool, nice simplification. It makes a lot of
Speaker 1: physics much easier to do. But Einstein's special relativity is
Speaker 1: not the same. Einstein's theory of general relativity says that
Speaker 1: spin does matter, that the way an object spins affects
Speaker 1: the way that it bends space and time, and that
Speaker 1: will change the gravitational effect on objects moving around a
Speaker 1: spinning Earth versus a non spinning Earth, and we can
Speaker 1: do experiments to see if that's correct. Wait, what you
Speaker 1: mean the spinning somehow it changes the way it's bending
Speaker 1: space around it. Yes, even even for a perfect sphere.
Speaker 1: Even for a perfect sphere, what it does is it
Speaker 1: drags the space around it a little bit. It pulls
Speaker 1: the space itself, and that's why they call it frame dragging.
Speaker 1: It's sort of like if you had a ball and
Speaker 1: you dipped it in honey, and then you spun the
Speaker 1: ball a little bit, you would get the honey dragged
Speaker 1: along with the ball, right, be a little bit of friction,
Speaker 1: they would pull it along with it. Einstein says that
Speaker 1: if you have a really big mass of object and
Speaker 1: you spin it, then you drag space itself along with
Speaker 1: the object. So they should have called it like space
Speaker 1: dragging or something, but they call it frame dragging. You
Speaker 1: said it not I it should have called it a
Speaker 1: better name for sure, But what do you mean like
Speaker 1: it drag space? How can you drag space? Long? Like?
Speaker 1: How can you pull on space? Yeah? How can you
Speaker 1: pull on space? Right? Like? Well, what is you in space?
Speaker 1: We don't know? But space can do a bunch of
Speaker 1: weird things, right. It can bend, and it can ripple,
Speaker 1: and it can twist. So what we talk about when
Speaker 1: we say space is curved, really what we mean there.
Speaker 1: It's not that it's like curved like a big sheet
Speaker 1: relatives to some other direction, but that we're changing the
Speaker 1: relative distances between points in space, so that, for example,
Speaker 1: the shortest path from A to B is no longer
Speaker 1: what you would imagine to be a straight line, but
Speaker 1: a different path because the distances between the points along
Speaker 1: the way have been shrunk. So in the same way,
Speaker 1: you can talk about dragging space with you as this
Speaker 1: weird effect and additional sort of curvature of space, Like
Speaker 1: when an object is spinning, it curves space differently around
Speaker 1: it than if it isn't spinning. Does that due to
Speaker 1: the fact that you know, maybe the particles or the
Speaker 1: masses at the surface of the sphere are have some
Speaker 1: kind of velocity, and so there's some sort of you know,
Speaker 1: sort of lagging its effect to the things around it.
Speaker 1: Or how would you explain what what's causing that dragging
Speaker 1: of space. You're right that Newton assumes that gravity is instantaneous.
Speaker 1: Like in Newton's world, if an object disappears, then it's
Speaker 1: gravity disappears instantaneously, even for objects really far away. But
Speaker 1: in Einstein's world, gravity takes time for information to propagate.
Speaker 1: So if the sun disappears, we don't notice that for
Speaker 1: eight minutes in this situation, I don't think that's the
Speaker 1: explanation for frame dragging, because frame jagging exists even in
Speaker 1: a object that's been spinning for like a long long
Speaker 1: time and there's no change, no update, no like information
Speaker 1: needs to propagate, So it can be like a steady
Speaker 1: state situation. It's not like a transient effect. A better
Speaker 1: way to think about it is as the gravitational version
Speaker 1: of electromagnetic induction. If you're familiar with that concept. All right, well,
Speaker 1: let's get a little bit deeper into this frame dragging,
Speaker 1: and most importantly, how could we measure it and potentially
Speaker 1: prove Einstein wrong. But first, let's take a quick break. Alright,
Speaker 1: we're talking about proving Einstein wrong, and there's a bunch
Speaker 1: of people out there trying to do this. Right, there's
Speaker 1: an official government funded experiment trying to prove his theories wrong. Yeah,
Speaker 1: there's lots of ways that we've been testing Einstein's theories. One,
Speaker 1: of course, we're just like looking for black holes. That
Speaker 1: was a prediction of Einstein's theory, which turned out, of
Speaker 1: course to be correct. Another is gravitational waves. People were
Speaker 1: looking to see if space itself would ripple when two
Speaker 1: black holes orbit around each other and then finally gobble
Speaker 1: each other up. And you know, we saw those that's
Speaker 1: pretty awesome. And so all of these things are tests
Speaker 1: of Einstein's relativity. But there's a series of folks developing
Speaker 1: like hyper sensitive tests to look for like these like
Speaker 1: small little deviations because we can't like organize our own
Speaker 1: black hole experiment where were like shoot one black hole
Speaker 1: at another, so we have to do the experiments here
Speaker 1: on Earth. And because gravity is so weak, the effects
Speaker 1: are really really small effects that are like really dramatic
Speaker 1: when black holes are involved, are really not very dramatic
Speaker 1: when ping pong balls are involved. What about black pink bubballs?
Speaker 1: Oh my god, we didn't try that. Hold on a second,
Speaker 1: noble price please. Alright, So one of these effects that
Speaker 1: you're trying to test is called frame dragging, which is
Speaker 1: how a spinning object kind of drag space around at
Speaker 1: the edges. But there's another effect that that has to
Speaker 1: do with gyroscopes, right, Yeah, all these effects can be
Speaker 1: well measured by gyroscopes because what they do, in effect
Speaker 1: is make something spin. Like the Earth has its gravity,
Speaker 1: it's pulling on you, but if it's spinning, it's gravity
Speaker 1: will also give you a little bit of a twist.
Speaker 1: And so we measure these things by using gyroscopes. And
Speaker 1: you're right, there are two different effects that can happen
Speaker 1: to a gyroscope here. One is this frame dragging effect,
Speaker 1: and the other is this really awesome effect, this geodetic effect.
Speaker 1: It's called that lets you measure the curvature of space directly.
Speaker 1: You can like exactly measure whether or not space is
Speaker 1: curved by putting a gyroscope in orbit around a planet. Now, gyroscope, again,
Speaker 1: it's just like a spinning mass, right exactly. You take
Speaker 1: something and you spin it and you try to make
Speaker 1: you really precise so it doesn't wobble, and because of
Speaker 1: conservation of angular momentum, if nothing touches it, it should
Speaker 1: keep spinning. Right, So there are no external forces on
Speaker 1: a spinning object. It should keep spinning the way like
Speaker 1: if you push something in outer space, it should keep
Speaker 1: going forever unless something stops it. Because of angular momentum,
Speaker 1: if you spin something like the Earth, and the Earth
Speaker 1: is a gyroscope, it should keep spinning. And so you
Speaker 1: can measure if there's any force on a gyroscope by
Speaker 1: seeing if the angle of its spin changes or if
Speaker 1: it's spin rate changes, and also like if it starts
Speaker 1: tilting to right m exactly, they called that precession. So
Speaker 1: if you put some force on a gyroscope, you could
Speaker 1: slow it down, or you could change the angle of
Speaker 1: its spin if it tilts a little bit. And so
Speaker 1: that's what these experiments are. The one in particularly called
Speaker 1: the gravity probe B experiment. Yeah, these are really fun experiments. Basically,
Speaker 1: somebody said, what if we take a gyroscope and we
Speaker 1: put it out in space and we orbit the Earth. Now,
Speaker 1: Newton says that if the gyroscope is perfect, then the
Speaker 1: Earth is the spirit, etcetera, etcetera. That gyroscope, once you
Speaker 1: started spinning, will spin forever the same way, and orbiting
Speaker 1: the Earth will have no effect on it, right, because
Speaker 1: orbiting the Earth just pulls on it and it has gravity.
Speaker 1: It makes it orbit, but it shouldn't change the direction
Speaker 1: of the gyroscope. That's what Newton says, that the gyroscope
Speaker 1: will forever point the same direction, but the geodetic effect
Speaker 1: and the frame dragging effect, both of them will twist
Speaker 1: this gyroscope a little bit. So they came up with
Speaker 1: this experiment, gravity Probe B, which is basically nothing but
Speaker 1: like a really super duper precise gyroscope in space in
Speaker 1: orbit around the Earth like a satellite. Right, Yeah, it's
Speaker 1: its own spacecraft. It's its own satellite, just dedicated to
Speaker 1: actually these four spinning balls moving around the Earth. So
Speaker 1: it's a probe because it's an experiment and it's probing gravity,
Speaker 1: and it's B because it's the second one. Right. Gravity
Speaker 1: Probe A was another experiment. Yeah, that's right. Gravity Probe
Speaker 1: A was a different space based experiment to probe gravity,
Speaker 1: but it was probing a different feature of gravity and
Speaker 1: it used like a totally separate setup. It had like
Speaker 1: a hydrogen maser on it, and it was measuring the
Speaker 1: equivalence principle whether gravity is really the same as the acceleration.
Speaker 1: You know, the whole idea of Einstein's general relativity is
Speaker 1: that gravity, this force we feel, is just the curvature
Speaker 1: of space. And so they're out there to measure whether
Speaker 1: you could tell the difference between like the curvature or
Speaker 1: space and other accelerations. And of course they found that
Speaker 1: you couldn't. Yeah, so the gravity probe a confirm Einstein's theory,
Speaker 1: so it didn't prove him wrong. And now we have
Speaker 1: launched this probe B to further test then, and that
Speaker 1: was launched a while ago, right almost fifteen years ago.
Speaker 1: It was launched in two thousand four, and they were
Speaker 1: sent it up there and they studied these gyroscopes for
Speaker 1: a couple of years before they got the results. But
Speaker 1: this is a really really hard experiment, Like, not only
Speaker 1: is it really complicated, because like even understanding the general
Speaker 1: relativity of what they're testing is complicated, but building a
Speaker 1: gyroscope that's sensitive enough to see these effects, which are
Speaker 1: really really tiny effects, is just like a huge technical
Speaker 1: challenge because I guess these effects of gravity are not
Speaker 1: that strong around us like here and on Earth, because
Speaker 1: Earth Earth, it's not that massive, you know, astronomically speaking,
Speaker 1: like if you were in a black hole. Around a
Speaker 1: black hole, would be easier to measure these things. Yeah,
Speaker 1: if you had stronger gravity experiments, these things would be obvious.
Speaker 1: And also if these things were obvious in our environment,
Speaker 1: we would have noticed them, right. Newton would have had
Speaker 1: to incorporate them into his theories just to get like
Speaker 1: the orbits of the planets right and stuff. And so
Speaker 1: these are very very small effects, which is why you
Speaker 1: need very very sensitive experiments because remember gravity is actually
Speaker 1: a very very weak force, like it dominates the universe
Speaker 1: in the end, controlling its structure, but it's a very
Speaker 1: weak force compared to everything else. You know, you can
Speaker 1: overcome gravity with a simple kitchen magnet. Every bolt of
Speaker 1: lightning has a lot more energy than the gravitational field
Speaker 1: of the Earth, and so it's hard to see a
Speaker 1: very small effect gravitationally because you have to isolate it
Speaker 1: from everything else. I guess maybe it wouldn' would have
Speaker 1: been easier to send these pros like orbit Jupiter or
Speaker 1: something just something heavier. It's so easy to orbit Jupiter
Speaker 1: or the Sun, right, why don't just send it into
Speaker 1: the Sun. Why don't they put me in charge here? No,
Speaker 1: you're right, it's definitely would have been an advantage to
Speaker 1: have more massive object, but it's also just harder to
Speaker 1: control and communicate with a satellite that's much further away,
Speaker 1: and it's just it takes years to get there, and
Speaker 1: you need propellant and you can't repair it and all
Speaker 1: this kind of stuff. So it's just easier to work
Speaker 1: and your Earth orbit. All right, So let's just maybe
Speaker 1: describe for folks how this experiment works. I mean, we
Speaker 1: know it's got a little tiny gyroscope inside of it,
Speaker 1: but what is how does that work? What does the
Speaker 1: gyroscope it look like? So the gyroscope has to be
Speaker 1: super super accurate. What you really would love to do
Speaker 1: is just have a spinning ball in space and nothing
Speaker 1: around it, just like totally isolated. Have a ball spinning
Speaker 1: in space and measure as it goes around the Earth
Speaker 1: whether it's direction of spin is changing. But of course
Speaker 1: you can't just put a ball in space. You have
Speaker 1: to measure it somehow, and you have to protect it
Speaker 1: so they built this whole spacecraft around this spinning ball,
Speaker 1: and they want this ball to be spinning, but they
Speaker 1: don't want the spacecraft to touch it. So what they
Speaker 1: do is they have this ping pong ball size sphere
Speaker 1: of quartz and it has to be really super spherical
Speaker 1: because if it's lopsided in any way at all, then
Speaker 1: it would like develop a wobble and then you won't
Speaker 1: be able to measure these really small effects. So they
Speaker 1: spent like a decade perfecting how to make the roundest
Speaker 1: object in the history of humanity. What they spent ten
Speaker 1: years just polishing this little ball. Yeah, they'd mind this
Speaker 1: perfect courts in Brazil, and then they have this factory
Speaker 1: in Germany which can like polish them and melt them
Speaker 1: and get them in exactly the right configuration. And this
Speaker 1: thing is, I'm not joking, the most spherical object ever manufactured.
Speaker 1: Like it has its own entry in the Guinness Book
Speaker 1: of World Records. Wow. Well, so first of all, it's
Speaker 1: a perfect crystal like it's one perfect lattice of courts atoms,
Speaker 1: and then it's been polished and shaped to be this
Speaker 1: the roundest thing ever, the roundest thing ever. It's three
Speaker 1: ten millions of an inch from perfect spiracity. Like the
Speaker 1: difference between you know, the radius at one point and
Speaker 1: the radius anywhere else is this infinitesimal amount. It's amazingly smooth. Wow,
Speaker 1: I'm imagine. Ain't some you know, old German person with
Speaker 1: a little polishing cloth going rub for ten years? How
Speaker 1: they did it? Yeah, that's basically that's basically it um.
Speaker 1: And they have to make four of these things because
Speaker 1: they wanted independent measurements. So they have four of these things,
Speaker 1: and like to give you a sense of how smooth
Speaker 1: this is, if you took one of these things and
Speaker 1: you blew it up to be the size of the Earth,
Speaker 1: then the difference between like the highest mountain and the
Speaker 1: deepest trench would only be eight feet. So it's like
Speaker 1: it's it's smooth at the atomic level. Yeah, there's forty
Speaker 1: layers of atoms. Difference between the highest peak on this
Speaker 1: thing and the deepest, like scratch on it, forty atoms.
Speaker 1: So that German lady over there polishing it, you know,
Speaker 1: she's doing it atom by atom, right, So then you
Speaker 1: take these small quartz balls and then you spin them up.
Speaker 1: Then that's your gyroscope. Do you put four of them,
Speaker 1: and you spin them up before you launch them, or
Speaker 1: do you spin them up and once you get the
Speaker 1: space you spin them up down here on Earth, right,
Speaker 1: because you got to test them. But then you also
Speaker 1: spin them up and get them started up there in space.
Speaker 1: But you can't just like touch them. You can't like
Speaker 1: if you touch this thing, then you'll ruin it, right,
Speaker 1: And so they spin them up first. They levitate them
Speaker 1: electrostatically by you know, having this like actric field, and
Speaker 1: then they spin them up by shooting a stream of
Speaker 1: helium at them. They get them going four thousand revolutions
Speaker 1: per minute, like it's got little jets of helium, you know,
Speaker 1: hitting it kind of on the sides. Yeah, exactly provides
Speaker 1: a little torque by shooting this stream of helium at it,
Speaker 1: and then it evacuates the chamber, so there's no helium left.
Speaker 1: So you have this whole spacecraft and it's sort of
Speaker 1: surrounding this levitating ball of spinning quartz, but it's not
Speaker 1: touching it. Oh I see, it's just floating in space.
Speaker 1: But it doesn't drift to the size or anything. They
Speaker 1: have these electrostatics to try to keep it from drifting
Speaker 1: to the size because the spacecraft can drift a little
Speaker 1: bit right, or something hits the spacecraft, then it might
Speaker 1: bump into the ball. So they have these little like
Speaker 1: electrostatic controls to try to like push it along with
Speaker 1: the spacecraft. It's sort of like that game operation. You know,
Speaker 1: you gotta like not touch the sides ever, or you
Speaker 1: got a big buzz. Yeah, And I guess if Newton
Speaker 1: was right and Einstein was wrong, then this little quartz
Speaker 1: ball would keep spinning for are a really long time, like,
Speaker 1: you know, just be spinning in space, no friction, no
Speaker 1: air resistance, so it just spin for a really long time. Right, Yeah,
Speaker 1: if we've done it perfectly, it would spin forever. Right.
Speaker 1: They have not done it exactly perfectly, but they estimate
Speaker 1: that once they spin this thing up, it shouldn't slow
Speaker 1: down due to friction or impurities for fifteen thousand years,
Speaker 1: which is pretty awesome feat of engineering. And then you
Speaker 1: said they put up four lease, there's like four different
Speaker 1: spacecraft or like one spacecraft with four little quarts balls.
Speaker 1: It's one spacecraft with four little quartz balls in them.
Speaker 1: And that way they get like not totally independent measurements,
Speaker 1: because four totally separate spacecraft would have cost a lot more.
Speaker 1: This way, if one of the balls goes wonky or
Speaker 1: has an impurity in it, they have like three backups.
Speaker 1: But they ended up all four of them working and
Speaker 1: giving them measurements. And then they combine the information from
Speaker 1: all the balls in that one spacecraft to give them
Speaker 1: a measurement of this these procession effects. Okay, so I
Speaker 1: guess then the question is, once you get these little
Speaker 1: balls spinning, do they spin that for fifteen years or
Speaker 1: do they start wobbling and wiggling due to general relativity.
Speaker 1: So let's get into how they measured that wobble and
Speaker 1: what does it all mean Daniel, But first let's take
Speaker 1: another quick break. All right, we're talking about frame dragging
Speaker 1: and the gravity probe B experiment and how it's trying
Speaker 1: to prove Einstein wrong. All right, so it's so far
Speaker 1: we put these four perfect quartz balls up into space,
Speaker 1: we spun them up, and now we're trying to see
Speaker 1: if somehow the dragging of space by a spinning Earth
Speaker 1: will somehow make these balls wobble exactly. So there's two
Speaker 1: effects we're looking for here. One is the geodetic effect,
Speaker 1: which measures the curvature of space itself, because the gyroscope
Speaker 1: going around the Earth direction it's spinning will actually twist
Speaker 1: a little bit because the space in the vicinity is
Speaker 1: a tiny bit curved, and that applies basically a little
Speaker 1: force different from the actual just force of gravity pulling
Speaker 1: it towards the center of the Earth and gives it
Speaker 1: a little twist. Right, the force of gravity just pulls
Speaker 1: towards the center of the Earth. This geodetic effect gives
Speaker 1: it a little spin, and the frame dragging is a
Speaker 1: separate effect that's pulling space along with it, and it
Speaker 1: gives it a different kind of spin. So we're looking
Speaker 1: for two different sort of spin changes in these gyroscopes.
Speaker 1: One tells us about the geodetic effect and the other
Speaker 1: one orthogonal to it, tells us about frame dragging. And
Speaker 1: so we're trying to measure really small wobbles and these
Speaker 1: spinning balls, and so how do we measure these things? Yeah,
Speaker 1: that's a real challenge, right, You've got these spinning balls,
Speaker 1: you don't ever want to touch them. So how do
Speaker 1: you tell how a perfect sphere is spinning if you
Speaker 1: can't even touch it? Right? So what they do is
Speaker 1: they coat these spheres with super conducting niobium. It's this
Speaker 1: weird element and if you get niobium really really cold,
Speaker 1: and when it spins, then the charges nio bum generate
Speaker 1: a magnetic field, and so you can measure the direction
Speaker 1: of the magnetic field, which tells you exactly how this
Speaker 1: sphere is spinning without touching the sphere itself. Oh interesting,
Speaker 1: it's like you coated with sort of like a magnet
Speaker 1: type of thing, and then since it's spinning, it generates
Speaker 1: a magnetic field that you can measure if it wobbles
Speaker 1: or not. But it's a very very slight magnetic field
Speaker 1: because it's a very thin layer of niobium, and you
Speaker 1: want to put a very thin, perfect layer on it
Speaker 1: so you don't ruin, you know, the polishing job that
Speaker 1: you're German Bubba has done. And so they have to
Speaker 1: use these really cool magnetometers called squids that are these
Speaker 1: fun quantum magnetomic devices that we should do a whole
Speaker 1: other podcast about. But they're very very sensitive to very
Speaker 1: small magnetic fields. These are the magnetic fields are like
Speaker 1: one ten billionth of the Earth's magnetic field. So you
Speaker 1: can't just put up any compass up there. You've got
Speaker 1: to have a really sensitive magnetometer, but doesn't mean like
Speaker 1: probing this magnetic field also affect the spinning ball, Like,
Speaker 1: isn't there like a danger of like accidentally pushing it
Speaker 1: when you're when you're trying to poke it? Absolutely, And
Speaker 1: that's why you don't want to have like another magnet
Speaker 1: up there. So you have this squid device which is
Speaker 1: very very sensitive and minimally feeds back to the spinning sphere,
Speaker 1: which you're right, You can't measure anything in this universe
Speaker 1: without affecting it, and that includes magnets, right, Using magnetic
Speaker 1: probe to probe magnets, it's going to have a little
Speaker 1: bit of feedback effect, but here they think that that
Speaker 1: feedback effect is negligible compared to the magnetic field that's
Speaker 1: being generated. All right, So then these magnetometers are super sensitive.
Speaker 1: If the little balls wobble by even a one tenth
Speaker 1: of a milliarc second, which is like like a billions
Speaker 1: of a couple of billions of a degree, right, then
Speaker 1: they would notice, Yeah, that's right. And so it's just
Speaker 1: super incredible that they even built this thing, and you know,
Speaker 1: it took decades and decades. People have been thinking about
Speaker 1: this for a long time, But they're all these engineering
Speaker 1: problems like how do you get a gyroscope this smooth,
Speaker 1: how do you measure it, how do you keep it
Speaker 1: from bumping in of the spacecraft? How do you develop
Speaker 1: a magnetomata or this sensitive? So all of these different
Speaker 1: problems were like total roadblocks for a long time, and
Speaker 1: then one by one they were able to overcome them
Speaker 1: and actually put this thing together and actually build it
Speaker 1: and send it into space and make it work. So
Speaker 1: it's it's a real tourtive force of engineering and physics together.
Speaker 1: So and it well went up into two thousand and four,
Speaker 1: and they got to results in two thousand seven, so
Speaker 1: we we know what happened. We do know what happened,
Speaker 1: And because Einstein is still taught in school, then you'll
Speaker 1: know the answer are already, which is that they confirmed
Speaker 1: Einstein's prediction. So Einstein theory can be used to predict
Speaker 1: exactly the curvature of space as you go around the
Speaker 1: Earth and the geodetic effect this twist on the gyroscope.
Speaker 1: It can also be used to predict how much space
Speaker 1: is being dragged along by the Earth, and this gives
Speaker 1: a smaller effect in a different direction and so they
Speaker 1: saw both of these and both effects are totally consistent
Speaker 1: with what Einstein predicted. So like, we send these things
Speaker 1: up there, and they did exactly what Einstein predicted. Like
Speaker 1: you can see how do these things wobble due to
Speaker 1: the bending of space? Exactly? You can see these things
Speaker 1: get twisted by space itself. It's hard to think about
Speaker 1: how gravity can make something twist, right, Like, we're familiar
Speaker 1: with gravity making something move in a circle, but actually,
Speaker 1: like also give it a twist. It's because it's twisting
Speaker 1: space as well, right Like, when space gets dragged along
Speaker 1: by the Earth, it makes these weird, sort of sheer
Speaker 1: effects in the fabric of space itself, and those come
Speaker 1: out to be like a little twist. I think it's
Speaker 1: also maybe helpful to try to visualize what's going on
Speaker 1: with the geodetic effect. You're probably familiar with, Like how
Speaker 1: you can measure the curvature of space if you take
Speaker 1: like a triangle and you add up all the angles.
Speaker 1: And on flat space, if you're add of all the angles,
Speaker 1: then they all add up to a hundred eighty degrees,
Speaker 1: but on a curve surface you might get different angles. Well,
Speaker 1: there's another even cooler way to think about how space
Speaker 1: is curved, and that's by thinking about a circle. You
Speaker 1: take a circle that on a flat space and you
Speaker 1: compare its radius to its circumference, and the relationship is
Speaker 1: too pie right. That's famous, of course, But if space
Speaker 1: is curved, then that no longer holds because, for example,
Speaker 1: the radius can get longer if space is curved. So imagine,
Speaker 1: for example, a circle around the Earth, and if the
Speaker 1: Earth wasn't there, you could measure the radius of that circle.
Speaker 1: You know, where the center of the circle would be
Speaker 1: sitting nominally at the center of the Earth, and that
Speaker 1: would be the radius of the Earth, and the circumstance
Speaker 1: of the circle would be the circumference of the Earth.
Speaker 1: But because space is bent, and that path actually gets
Speaker 1: a little bit longer, right, because like imagine, for example,
Speaker 1: you have like a circle with a bubble in it.
Speaker 1: If you move along the bubble, then you're going to
Speaker 1: measure larger radius than if you're just moving exactly towards
Speaker 1: the center. Right. It's like trying to measure the equator
Speaker 1: from the north pole. You'd have to sort of go
Speaker 1: around the coverature of the Earth. Yeah, and so what
Speaker 1: we're doing here is we're sort of measuring, you know,
Speaker 1: pie in some sense, we're measuring whether moving around the
Speaker 1: Earth sort of lines up with the radius of the Earth.
Speaker 1: So that's one thing that the geodetic effect is measuring,
Speaker 1: is the local curvature. And if there was no curvature
Speaker 1: in that space, then moving around the Earth a gyroscope
Speaker 1: wouldn't process at all. But because there is that little
Speaker 1: bit of curvature, then things don't quite line up. You know,
Speaker 1: the radius and the circumference don't have the right relationship.
Speaker 1: So you get this very small effect that's the geodetic effect. Cool,
Speaker 1: and so the gravity probe be confirmed is like these
Speaker 1: are super tiny, subtle effects, but this instrument actually wasn't
Speaker 1: able to measure this bending of space. I feel like
Speaker 1: it brings it all to the really home, you know,
Speaker 1: it's not just something that's happening around the edges of
Speaker 1: black holes. It's like, you can measure the bending of
Speaker 1: space around Earth like a few a few miles from
Speaker 1: where you are right now. Yeah, if you have thirty years,
Speaker 1: eight hundred million dollars, you two can measure the curvature days.
Speaker 1: Bezos could do this a couple of times a day.
Speaker 1: You can do it before lunch. But you're right, it's
Speaker 1: a real tutor force. It's amazing. It's a big effect
Speaker 1: at black Hole, and it's a really almost negligible effect here. Like,
Speaker 1: nobody needs to include these calculations even in their satellite
Speaker 1: navigation problems. You know, nobody needs to worry about these
Speaker 1: things now. But they're included in the GPS calculations, right,
Speaker 1: Like the GPS and your phone takes into account the
Speaker 1: curricture of space or the effects of relativity. They the
Speaker 1: GPS on your phone definitely takes into account the effects
Speaker 1: of relativity, but that's mostly the time dilation, the fact
Speaker 1: that down here on Earth were closer to the Earth's
Speaker 1: gravitational well, and so time moves a little bit slower.
Speaker 1: So relativity is all sorts of effects. These effects, the
Speaker 1: geodetic effect and the frame dragging effect, don't need to
Speaker 1: be included in GPS. If they did, then we could
Speaker 1: just use GPS directly to measure them. But you need
Speaker 1: like a special super isolated, complicated experiment just to prove
Speaker 1: that these effects even exist, so we can safely ignore
Speaker 1: them in GPS calculations. But you definitely right, GPS uses
Speaker 1: other effects of relativity right, Yeah, I guess. I mean,
Speaker 1: you know, like the basically the bending of spacetime that
Speaker 1: Einstein figure it out. It is, it's in our everyday lives.
Speaker 1: It is, it affects our lives. It determines whether or
Speaker 1: not we get where we're going. All right, So then
Speaker 1: Einstein was right. No surprise there, I guess. I guess
Speaker 1: where people expecting him to be wrong? They were they
Speaker 1: hoping he was wrong? Or are they happy to confirm it.
Speaker 1: I think that the guys who built this satellite wanted
Speaker 1: him to be right because they were set out to
Speaker 1: measure it, and you know, to prove that this effect
Speaker 1: is real. So I suspect they wanted him to be right.
Speaker 1: But I was rooting against Einstein. I definitely wanted him
Speaker 1: to be wrong. Oh man, I got nothing against the guy.
Speaker 1: I mean, I don't know him at all, But it
Speaker 1: would be super cool to measure a different effect, right,
Speaker 1: to go up there and have these super sensitive devices
Speaker 1: that can measure the curvature space and you see something weird,
Speaker 1: something non Einsteinian, something that gives us a clue about
Speaker 1: how the future theory of gravity needs to look. So
Speaker 1: you always want everyone to be wrong. Daniel that seems
Speaker 1: like a difficult perspective to have as a collaborator, But
Speaker 1: together we all want to discover flaws in our theory
Speaker 1: because those are the potential learning moments. Right when our
Speaker 1: theory predicts something that doesn't happen, or fails to predict
Speaker 1: something that does happen, that's a time when we can
Speaker 1: pull on that threat and unravel the mystery and reveal
Speaker 1: something deep about the universe. So it's cool that Einstein
Speaker 1: was right. It's awesome. It's need kudos to these folks
Speaker 1: who built this experiment, But I think it would be
Speaker 1: much more cool if they saw something weird and new
Speaker 1: that gives us a clue about how to build a
Speaker 1: theory of quantum gravity, right, or at least maybe like
Speaker 1: a clue as to how to put together you know,
Speaker 1: general relativity and quantum mechanics, right, because that's still the
Speaker 1: big mystery, and probably confirming this further, it just makes
Speaker 1: it harder to figure out what's going on. Yeah, we're
Speaker 1: sort of stuck, right. I deeply believe that Einstein's theory
Speaker 1: can't be a real description of nature, But until it fails,
Speaker 1: we don't really know what to replace it with. We
Speaker 1: don't really have a better idea, and people are working
Speaker 1: on all sorts of stuff string theory and loop quantum gravity,
Speaker 1: and we have podcast episodes on that you can check out.
Speaker 1: But so far, none of those really work, none of
Speaker 1: those succeed in unifying quantum mechanics and gravity, and so
Speaker 1: we're still at a loss. And you know, we could
Speaker 1: continue to work theoretically, just like waiting to have a
Speaker 1: good idea, but I'm hoping to get a clue experimentally.
Speaker 1: I'm hoping to break one of these things to see
Speaker 1: some new weird effect that requires us, that inspires us
Speaker 1: to come up with a new theory. Right, and you're
Speaker 1: a quantum physicist, so I'm going to assume that you're
Speaker 1: just gonna buy default route for the other team to
Speaker 1: be wrong. That's what experimentalists try to do, right. We're
Speaker 1: not out to just confirm people's theories is correct. We're
Speaker 1: rather to discover new stuff, to see weird things in
Speaker 1: the universe that give you clues just about how things
Speaker 1: really work. Well, in this case, they confirm Einstein's theories.
Speaker 1: And it's pretty cool that you can go out there
Speaker 1: and see the bending of space or at least measure
Speaker 1: it with really accurate evolves made out of course, but
Speaker 1: you know, it's the thing you can measure and test
Speaker 1: and probe and get data on and know that it's
Speaker 1: actually happening in this universe. Weird stuff like that predicted
Speaker 1: by this beautiful mathematical theory is real. Like space really
Speaker 1: is getting twisted around the Earth. This is not just
Speaker 1: a calculation. This is our universe. All right. Well, we
Speaker 1: hope you enjoyed that, and please remember to turn your
Speaker 1: chicken or turn off the stove as you listen to
Speaker 1: this podcast. We don't want to cause any accidents out there,
Speaker 1: at least not here on Earth, maybe in space. It's
Speaker 1: all right, and pay attention to your kids. Well, thanks
Speaker 1: for joining us, see you next time. Thanks for listening,
Speaker 1: and remember that Daniel and Jorge Explain the Universe is
Speaker 1: a production of I Heart Radio. Or more podcast from
Speaker 1: my Heart Radio. Visit the I Heart Radio, Apple Apple Podcasts,
Speaker 1: or wherever you listen to your favorite shows.