Speaker 1: Hey, Daniel, do you ever get frustrated by, you know,
Speaker 1: asking the biggest questions in the universe all the time? Never?
Speaker 1: I live for it. I mean, what could be more fun?
Speaker 1: How about finding the answers sometimes? Oh? There are always
Speaker 1: answers out there waiting for us to discover them. You know, really,
Speaker 1: you think all the big questions in the universe have
Speaker 1: answers to them? What if they don't. I think that
Speaker 1: even the deepest, hardest, craziest questions in the universe have answers,
Speaker 1: and one day some human will know them. Hopefully that
Speaker 1: human is you or one of our listeners. What if
Speaker 1: the big questions don't have answers? You mean, like, is
Speaker 1: white chocolate really chocolate? Can you just say? I don't know.
Speaker 1: That's what I told my kids all the time. That's
Speaker 1: an answer, right? How about ask your mother? Is that
Speaker 1: an answer to the question? Who ate all the chocolate?
Speaker 1: That one is also asked your mother? Hi? I'm poor
Speaker 1: Hammy car Tennis and the creator of PhD comics. Hi,
Speaker 1: I'm Daniel. I'm a particle of physicist and a professor
Speaker 1: at UC Irvine, and I will continue to eat chocolate
Speaker 1: until all the questions are answered. I thought you were
Speaker 1: going to say that you you ate all the chocolate,
Speaker 1: but I guess you still have answers to find. That's right.
Speaker 1: As long as they keep making chocolate, I'll keep asking
Speaker 1: questions and looking for answers. I'm not sure where this
Speaker 1: correlation between answers and chocolate came from, Daniel, Are you
Speaker 1: sure you're not just making it up? I'm not making
Speaker 1: that up. You know that there's a tight correlation between
Speaker 1: the amount of chocolate consumed per capita and the number
Speaker 1: of Nobel prizes one per capita for countries Switzerland is
Speaker 1: like knocking it out of the park. Isn't that weird? Though?
Speaker 1: Isn't the Nobel price based out of Switzerland? No, it's Sweden, man,
Speaker 1: Hello Sweden. Wrong as w country were. Clearly, Sweden just
Speaker 1: needs to be more chocolate. Clearly, everybody needs to eat
Speaker 1: more chocolate. I mean, it's good for everything. It's good
Speaker 1: for your mind, it's good for your soul. I'm not
Speaker 1: sure it's good for your waistline or your heart a
Speaker 1: little bit. That's a true correlation, right like that. If
Speaker 1: you make a plot of the countries that have Nobel
Speaker 1: Prizes and the amount of chocolate they eat per capita. Supposedly,
Speaker 1: I mean I haven't looked into the data, but supposedly
Speaker 1: there's a correlation, right, Yeah, I think we have a
Speaker 1: plot of that in the opening of one of our books.
Speaker 1: So the data is there, the correlation is true. The causality,
Speaker 1: I'm not exactly sure. It doesn't mean that you should
Speaker 1: force feed chocolate to your school children in order to
Speaker 1: get Nobel prizes in twenty years. You mean, like the
Speaker 1: causality could be the other way around, Like winning a
Speaker 1: lot of Noble prices could cause you to eat a
Speaker 1: lot of chocolate. Yeah. Maybe they're just celebrating their Noble
Speaker 1: prizes by eating chocolate, right, Or maybe there's a chemical
Speaker 1: and chocolate. It could be big chocolate, you know, just
Speaker 1: be a big conspiracy, Oh, conspiracy between big chocolate and
Speaker 1: big Nobele. Yeah, the big science and big chocolate. They're
Speaker 1: already trying to make us all bigger. I guess that's
Speaker 1: right exactly. We're asking bigger questions by making our scientists
Speaker 1: even bigger, especially around the waistline. I occupy a larger
Speaker 1: and larger fraction in the universe every year, that's right.
Speaker 1: If you occupy larger fractions of the universe. There's less
Speaker 1: of the universe to explore. Technically speaking, Yeah, well that
Speaker 1: must be what dark matter is. After all, it's just
Speaker 1: overweight physicists. I guess eating dark chocolate because white chocolate
Speaker 1: not chocolate. Maybe that's what happened out in space, like
Speaker 1: all these aliens that are more advanced, you know, sort
Speaker 1: of reach the chocolate singularity and just based out of
Speaker 1: the electronic neetic spectrum. See how much progress we've made already.
Speaker 1: I don't think anybody ever said the phrase chocolate singularity before.
Speaker 1: So that's progress right there, chocolate fuel progress. Yeah, just
Speaker 1: talking about chocolate makes even a noble price boom. But anyways,
Speaker 1: welcome to our podcast, Daniel and Horror Explain the Universe,
Speaker 1: a production of I Heart Radio in which we eat
Speaker 1: our way towards answers to some of the biggest, tastiest,
Speaker 1: most delicious question humans have ever asked. Questions about the
Speaker 1: size of the universe, the shape of the universe, the
Speaker 1: motion of the universe, the fundamental nature of the reality
Speaker 1: we find ourselves in as curious conscious beings trying desperately
Speaker 1: to understand what's going on and where is my next
Speaker 1: piece of chocolate? Coming from that's right, because the universe
Speaker 1: is full of amazing and incredible things like delicious snacks
Speaker 1: and dark matter and sometimes dark delicious snacks at all
Speaker 1: at the same time, and we're all just wondering what's
Speaker 1: going on, what's out there, and how does it work.
Speaker 1: And some of us get to do that for a living.
Speaker 1: I mean, ask questions, not each chocolate. Nobody pays me
Speaker 1: to do that yet, but it does fuel my curiosity
Speaker 1: about the fundamental nature of what things are like out there. Yeah,
Speaker 1: I guess you're a professional question asker, Daniel. Would you
Speaker 1: say that's that's how you can describe a researcher. Yeah.
Speaker 1: Everybody who have decided to spend their life doing science
Speaker 1: has done so because there's a question that drives them.
Speaker 1: Of course, I'm curious about lots of questions in science
Speaker 1: that I don't personally work on, But everybody who's a
Speaker 1: scientist has their own personal questions that drive them to
Speaker 1: spend their life asking it. You know. Maybe it's about
Speaker 1: how birds communicate and choose partners. Maybe it's about how
Speaker 1: the Earth was formed. Maybe it's about the fundamental nature
Speaker 1: of space and time. It's this personal curiosity that drives
Speaker 1: science forward. Yeah, and you forgot the very important question
Speaker 1: how do you make chocolate fat free? That would also
Speaker 1: move signs forward a lot. Apparently, you mean, how do
Speaker 1: you make chocolate chocolate free? How do you make chocolate
Speaker 1: still delicious but a little healthier? Maybe? Yeah, The answer
Speaker 1: that one is you can't. The unhealthiness is part of
Speaker 1: why it's so delicious. Oh, I say, it's the guilty
Speaker 1: pleasure of it that you like. Oh my goodness, it's
Speaker 1: just got a little extra dark. But I guess. Yeah,
Speaker 1: you're a professional question asker, which means you're also sort
Speaker 1: of a professional head spinner, right, because I mean your
Speaker 1: job is not just to answer questions that your job
Speaker 1: is to find answers to crazy questions and find crazy
Speaker 1: answers right to leave people's head spinning. That's right. Sometimes
Speaker 1: when you under these deep questions about the universe, you wonder, like,
Speaker 1: how can we even get started? How do we take
Speaker 1: that first step towards that future where some human knows
Speaker 1: the answer to those questions as like an actual fact.
Speaker 1: Sometimes it can be inconceivable to probe such big questions
Speaker 1: and know like how to get started. Yeah, and hopefully
Speaker 1: it's a future we're not just one human not the answer.
Speaker 1: Hopefully that person gets to tell other humans yes. But
Speaker 1: there's always a first human, right. That's the joy of discovery,
Speaker 1: to be the first person to know something about the
Speaker 1: universe that nobody else knows, just like there was a
Speaker 1: first person to taste every kind of fruit on Earth,
Speaker 1: or first person to see every single mountain or to
Speaker 1: walk along a beach. There's always a first and that's
Speaker 1: the joy of discovery. You want to be the one
Speaker 1: who figures it out, not reading about it in the
Speaker 1: science times of the newspaper, right right, Although the way
Speaker 1: science works, you're never quite the first human, right because
Speaker 1: you always need things to be pu reviewed, right, like
Speaker 1: somebody needs to check your answer. You can't just like
Speaker 1: come up with an idea and have absolute certain that
Speaker 1: it's true, can you. You can't ever certain. But there
Speaker 1: are moments when you do an experiment and the results
Speaker 1: are just very conclusive. These moments of discovery where you've
Speaker 1: designed your experiment in a way to like corner the
Speaker 1: universe to revealing some truth to you. That a podcast
Speaker 1: about pulsar discovery last year in which we played audio
Speaker 1: of the astronomers watching the data come in in real
Speaker 1: time and having that moment of discovery. They almost shouted
Speaker 1: eureka live on the tape. So sometimes there really are
Speaker 1: those moments when you know something about the universe. Yeah,
Speaker 1: I guess you. Then you want to be the first
Speaker 1: human to be with like you know something. But it
Speaker 1: does leave your head spinning. This search for truth and
Speaker 1: the cosmos and searching for the idea of how things
Speaker 1: work in the explanation for why things are the way
Speaker 1: they are, including some very interesting questions about whether or
Speaker 1: not things are even spinning in the first place. That's right,
Speaker 1: because we see lots of things spinning in the universe.
Speaker 1: We know the Earth is spinning, and the Earth is
Speaker 1: spinning around the Sun, which is spinning around the center
Speaker 1: of the galaxy, which is itself spinning, which is moving
Speaker 1: around the center of the galaxy cluster. And so naturally,
Speaker 1: as a curious human being, you wonder how far does
Speaker 1: that spinning go? Yes, So to be on the program,
Speaker 1: we'll be asking the question, is the whole universe spinning? So, Daniel,
Speaker 1: how are we spinning? This question is the question it's
Speaker 1: self spinning? Is that what you're saying? This question definitely
Speaker 1: makes my head spin. And it's been one that's been
Speaker 1: debated sort of on the boundary of physics and philosophy
Speaker 1: for a few hundred years. You know, not just the
Speaker 1: question of is our universe spinning? But could it be spinning?
Speaker 1: What does it mean or the whole universe to spin
Speaker 1: spinning relative to what you know? Could you even tell
Speaker 1: if the whole universe was spinning? It's really fascinating question
Speaker 1: that tells us a lot about the nature of space
Speaker 1: itself and what is absolute and what is relative? Right,
Speaker 1: Because I guess you can, you know, ask if ace
Speaker 1: itself is spinning, right, because you know, we know sort
Speaker 1: of spaces kind of a thing that can bend and
Speaker 1: twist and ripple. What if the space itself is turning around? Well,
Speaker 1: you just blew my mind? Man? Did I make your
Speaker 1: head spin? Didn't make you want to eat more chocolate?
Speaker 1: That's always the case. That's a pretty low standard. But yeah,
Speaker 1: you can ask questions like is the stuff in space spinning?
Speaker 1: Is space itself spinning? What would space itself be spinning?
Speaker 1: Relative to? All sorts of really fun, big, mind blowing
Speaker 1: head spinning questions are involved. Well, I guess the question
Speaker 1: we're asking today is the universe spinning. So really we're
Speaker 1: we're asking about the whole shebanging like everything right. Yeah,
Speaker 1: now here's another one, Daniel, Is the multiverse spinning, It's
Speaker 1: definitely spinning money for the Marvel Universe. The Marvel Universe
Speaker 1: is spinning out cash. Yeah, they're shooting out of Spider
Speaker 1: Man's spinning web shooters. If the universe is spinning, and
Speaker 1: that spin is random, then you can imagine there might
Speaker 1: be a whole set of universes which each have their
Speaker 1: own different random spin. And then if we measured our
Speaker 1: universe to have a particular spin, we could ask like, well,
Speaker 1: why this spin not some other spin? You can add
Speaker 1: the multiverse that basically any questions, But then the multiverse
Speaker 1: would would be infinite and it would average out to
Speaker 1: nothing or not. I think this conversation is spinning out
Speaker 1: of control. Dinner, let's get back on track here. Yes, So,
Speaker 1: as usually, we were wondering how many people out there
Speaker 1: had thought about this spinning question, whether or not the
Speaker 1: whole universe is spinning or not, And so Daniel went
Speaker 1: out there into the wilds of the Internet to ask
Speaker 1: people the question, is the whole universe spinning? And thanks
Speaker 1: again to our cadre of volunteers who participate in these
Speaker 1: difficult to answer questions without any chance to do any googling.
Speaker 1: If that sounds fun to you and you'd like to
Speaker 1: hear your voice on the podcast, we would love to
Speaker 1: hear from you, So please don't be shy. It's free,
Speaker 1: it's easy, it's fun right to us. Two questions at
Speaker 1: Daniel and Joge dot com. Think about it for a second.
Speaker 1: Do you feel or think that the universe around you
Speaker 1: is spinning? Here's what people had to say. It wouldn't
Speaker 1: surprise me if the whole universe is spinning because so
Speaker 1: many things are spinning. You know, we're on a spinning
Speaker 1: Earth that, in turn is revolving around the Sun, which
Speaker 1: in turn is revolving around the galaxy, and the galaxy
Speaker 1: itself is spinning, and then our galaxy is probably spinning
Speaker 1: around other galaxies in the local group, which then uh
Speaker 1: itself probably is spinning within the bigger group. Well, I
Speaker 1: feel like we know it's expanding, but I have no
Speaker 1: idea if I've heard that it's spinning or not. Everything
Speaker 1: else in the universe is spinning, so why wouldn't the
Speaker 1: universe spin? Yes, without question, the universe is definitely spinning.
Speaker 1: There's a center of gravity, But I don't think that
Speaker 1: there is a center of gravity across the entire universe.
Speaker 1: I think there are local galactic clusters that rotate um,
Speaker 1: but yeah, because they share a center of gravity, I
Speaker 1: don't think that there's a center of gravity across the universe.
Speaker 1: So I'm going to say, no, it's not. Spin is
Speaker 1: a little relative, right, So in order for it to
Speaker 1: be spinning, it would need to be spinning relative to
Speaker 1: something outside the universe. So that's really a question. Is
Speaker 1: there anything outside the universe for which the universe could
Speaker 1: be spinning? When I think about the universe, I think
Speaker 1: of everything like it's just a word that is sort
Speaker 1: of all encompassing, and I I don't know if if
Speaker 1: we were, if the universe is all encompassing, what would
Speaker 1: it be spinning relative to? Is it that, like space
Speaker 1: itself spinning? Which doesn't make a lot of intuitive sense
Speaker 1: to me. I mean, you could probably figure out if
Speaker 1: it was spinning using I don't know, like the Michaelson
Speaker 1: Morley experiment with like the the the ether or whatever
Speaker 1: you can like test for that kind of a thing.
Speaker 1: I guess if the whole universe was spinning, then everything
Speaker 1: were be moving at the same time. So I don't
Speaker 1: know how we'd be able to tell, but maybe it is.
Speaker 1: All right, a wide range of answers. Some people said yes,
Speaker 1: no hesitation there, yes it's spinning. We got the whole
Speaker 1: range of answers here. We got from yes it's spinning
Speaker 1: to what does that even mean? To how could you
Speaker 1: even tell? It? Really pretty much represents the entire spectrum
Speaker 1: of possible answers, right, even a little bit of a
Speaker 1: maybe there, maybe it's spinning. So it's a fascinating question,
Speaker 1: is the whole universe spinning? And so let's get into
Speaker 1: the particulars of that question. I have questions about it, Daniel,
Speaker 1: could uh could the university spinning? It's a really interesting
Speaker 1: question just to ask, like what does that mean? First
Speaker 1: of all? Right, like could the university spinning? Spinning? Relative
Speaker 1: to what we've talked on this podcast for a while
Speaker 1: about real activity, you know, we talked to Carlo Rovelli,
Speaker 1: for example, about relative motion, and he made a really
Speaker 1: interesting point that we've talked about a few times that
Speaker 1: if you, for example, lived in the universe all by yourself,
Speaker 1: there's nothing else in the universe, then velocity would have
Speaker 1: no meaning. Because velocity is purely a relative quantity. You
Speaker 1: can only be moving relative to other stuff, and so
Speaker 1: in an empty universe, velocity has no meaning. Wait, what
Speaker 1: if the like the universe has a like an extent,
Speaker 1: you know what I mean, like a border or an edge,
Speaker 1: then you could be being relative to that even if
Speaker 1: you were alone in the universe. In our understanding of relativity,
Speaker 1: space is isotropic and homogeneous, meaning there are no special
Speaker 1: locations in space. The kind of cosmology you're talking about
Speaker 1: where there are special locations in space would break a
Speaker 1: lot of the rules that we think we understand, you know,
Speaker 1: like conservation of momentum. And so for now, let's operate
Speaker 1: in a universe that's essentially either infinite in extent or
Speaker 1: where every location in space is the same. So you
Speaker 1: can't be moving just relative to space. You have to
Speaker 1: be moving relative to other stuff in space. So from
Speaker 1: that point of view, you can't ask questions like is
Speaker 1: the whole universe moving? Right now, imagine the universe filled
Speaker 1: with stars and galaxies just like ours. It doesn't make
Speaker 1: sense to ask is all of that stuff moving? Because
Speaker 1: it would have nothing to move relative to if you're
Speaker 1: talking about the whole universe. So from that point of view,
Speaker 1: things like you know, velocity are purely relative. And the
Speaker 1: question then is like, is the same thing true for spin?
Speaker 1: If you were alone in a universe, all by yourself,
Speaker 1: an empty space, could you tell if you were spinning? Right?
Speaker 1: Because velocity, like you're saying, is relative, but acceleration is
Speaker 1: not relative. Right, Like, you could also ask the question
Speaker 1: is the universe accelerating? And that one would have meaning
Speaker 1: right because moving could also apply to acceleration. Yes, velocity
Speaker 1: is purely relative, but acceleration is absolute. Some you can
Speaker 1: measure the acceleration of an object. If you were alone
Speaker 1: in the universe, you could build a little device that
Speaker 1: would tell you whether or not you were accelerating. And
Speaker 1: it's not a complicated device. You could just like have
Speaker 1: a ball in a box and hold it steady. If
Speaker 1: the ball moves towards one side, it means you are
Speaker 1: accelerating in the other direction. That's just how an accelerometer works.
Speaker 1: Or if you're inside a box, you can tell whether
Speaker 1: you're accelerating because you would feel an effective gravity against
Speaker 1: one side or the box. Right, So you can build
Speaker 1: an accelerometer. You don't have to be accelerating relative to
Speaker 1: any other thing. You can be accelerating relative to absolute
Speaker 1: space time. It's interesting the history of how we came
Speaker 1: to these realizations. The first person to think about this
Speaker 1: question whether spin is absolute or relative? You know, can
Speaker 1: you be spinning relative to space or do you have
Speaker 1: to spin relative to other stuff? Was actually Isaac Newton, Right, yeah,
Speaker 1: because where I guess the question is whether or not
Speaker 1: we're spinning or not, and that one can be relative, right,
Speaker 1: or not relative. So that was a question, if you're spinning,
Speaker 1: what are you spinning relative to Are you spinning relative
Speaker 1: to space or are you only spinning relative to other
Speaker 1: stuff out there in the universe? Right, So it's spin
Speaker 1: sort of like acceleration or is it more like velocity?
Speaker 1: And at the time, of course of Newton, Newton thought
Speaker 1: that velocity was absolute, that you were moving relative to
Speaker 1: space itself. But he proposed a really fun thought experiment
Speaker 1: as a way to sort of like measure whether or
Speaker 1: not you're spinning and basically, like you know, a spinometer
Speaker 1: in the same way you can build an accelerometer to
Speaker 1: see if you're accelerating. He thought, let's build an experiment
Speaker 1: that measures whether or not you're spinning. And it's pretty simple.
Speaker 1: You take a bucket of water, and you know the
Speaker 1: surface of the water is flat, and then you start
Speaker 1: spinning the bucket and you spin it sort of along
Speaker 1: its access You could like twist a rope on the
Speaker 1: handle or something like that. Now, what happens, of course,
Speaker 1: is that the bucket starts spinning, and then eventually the
Speaker 1: water gets dragged along by the buckets, and now the
Speaker 1: water is also spinning. And what happens is that the
Speaker 1: water gets pushed up against the sides of the buckets.
Speaker 1: So the surface of the water is no longer flat.
Speaker 1: It's now concave. And so this, he says, is a
Speaker 1: way to measure whether or not you're spinning, because even
Speaker 1: if you're like on the bucket, if you're like an
Speaker 1: ant on the bucket, you can still tell that it's concave.
Speaker 1: Right every it you will agree that the surface of
Speaker 1: the water is now concave. So it's like a way
Speaker 1: to measure the fact that you are spinning, right, It's
Speaker 1: sort of like it's trying to measure whether or not
Speaker 1: there are centripetal acceleration or forces on you because like,
Speaker 1: if you're spinning, something must be causing you to to
Speaker 1: spin to change directions all the time, and that's what
Speaker 1: the centripetal acceleration is. Yes, centripe tol acceleration is pulling
Speaker 1: you towards the center's changing your velocity vector so you're
Speaker 1: moving in a circle. For example, centrifugal acceleration is the
Speaker 1: fictional force that you feel because you're in a non
Speaker 1: inertial reference frame, so that the ant, for example, or
Speaker 1: the water feels that force pushing them outwards. You know,
Speaker 1: the same way. For example, if you are on a
Speaker 1: spaceship out in deep space and it was spinning, you
Speaker 1: would feel an effective gravity. You'd be able to walk
Speaker 1: along the inside of that spinning can as if there
Speaker 1: was gravity. This is one plan for having effective gravity
Speaker 1: and deep spaces. Make your spaceships spin, right. So Newton thought, well, obviously,
Speaker 1: then spin is absolute right that you're spinning relative to
Speaker 1: spa ace, because you can build this thing that measures it.
Speaker 1: And even if you were in the frame of the bucket,
Speaker 1: if you were spinning with the bucket, you could still
Speaker 1: tell that the bucket was spinning. So now imagine that
Speaker 1: bucket in deep and empty space. You should be able
Speaker 1: to tell whether you're spinning or not based on whether
Speaker 1: the water is concave or whether it's flat. So Newton
Speaker 1: was like, I'm very sure that spin is absolute, meaning
Speaker 1: that you could tell maybe if the universe, the whole universe,
Speaker 1: was spinning, right, like if we were just sitting here
Speaker 1: and we felt this in tripital exceloration um, even though
Speaker 1: nothing seemed to be moving, then maybe you could tell
Speaker 1: that the everything was spinning exactly. And if spin is absolute,
Speaker 1: then you could measure the spin of the universe, right,
Speaker 1: because the whole universe could be spinning in space, and
Speaker 1: if that was happening, according to Newton, you could measure it.
Speaker 1: But not everybody agreed with Newton. There was a guy
Speaker 1: named Ernst Mock who came along and said, no, no, no,
Speaker 1: that's not true at all. Spin is purely relative. Motion
Speaker 1: is relative, after all, right, like if you're moving through space,
Speaker 1: that's purely relative. So Mark said, maybe everything is relative,
Speaker 1: maybe all motion in the universe, acceleration and velocity, and
Speaker 1: this is before relativity, right before Einstein said maybe everything
Speaker 1: is relative. And then people said, well, what about the bucket, right,
Speaker 1: the bucket can tell if you're rotating, and Mark said, well,
Speaker 1: the bucket is rotating relative to the stars out there.
Speaker 1: That's why the surface of the bucket gets concave, because
Speaker 1: it's rotating not relative to space, but to the stars
Speaker 1: out there in the universe. That doesn't make a lot
Speaker 1: of sense. It doesn't make a lot of sense to
Speaker 1: me either. But remember, at the time, people didn't really
Speaker 1: understand the notion of space and time and relativity, and
Speaker 1: these questions were sort of up in the air, you know.
Speaker 1: People wanted to know, for example, if velocity is relative,
Speaker 1: as we all accept, then why isn't acceleration relative? Like
Speaker 1: you said it earlier that velocity is relative but acceleration
Speaker 1: is not. But why not? And at the time people
Speaker 1: didn't understand, and so this was sort of a beautiful
Speaker 1: idea to say, well, maybe everything is actually relative, and
Speaker 1: the reason that the surface of the bucket gets concave
Speaker 1: is somehow because of the distant stars. And on the
Speaker 1: other side, people say, well, that's ridiculous, Like, are you
Speaker 1: saying that if you spun a bucket in empty space
Speaker 1: that it would stay flat? Right? He said, absolutely, If
Speaker 1: you spin your bucket and then you start removing the
Speaker 1: stars out there in the universe that the surface of
Speaker 1: the bucket would go from concave to flat, that somehow
Speaker 1: those distant, distant stars are telling the bucket surface what
Speaker 1: to do. I feel like MOK should have stuck to
Speaker 1: like sound research, maybe not trying to do astronomy here.
Speaker 1: But I guess you're saying that's kind of the thinking
Speaker 1: at the time, like maybe if you sort of like
Speaker 1: removed a reference frame, and maybe that's kind of what
Speaker 1: he was getting at. It's like, if you remove the
Speaker 1: reference frame of the stars, then somehow, um, maybe you
Speaker 1: lose all relativity. Yeah. Max said that spinning is relative.
Speaker 1: If you're not spinning relative to something else, then you're
Speaker 1: not spinning. Spinning in an empty universe has no meaning
Speaker 1: that you could never tell. You know that if you
Speaker 1: were in an empty universe and I started to spin you,
Speaker 1: you wouldn't feel your arms get pushed out towards the side.
Speaker 1: If you build a spaceship and spun it in an
Speaker 1: empty universe, you wouldn't feel effective gravity that comes somehow
Speaker 1: from the distant stars that are defining a reference frame.
Speaker 1: And this was a beautiful idea, and even Einstein liked that.
Speaker 1: Einstein thought Oh, this sounds really nice, and he tried
Speaker 1: really hard to work it into his theory of relativity,
Speaker 1: because I think the idea was that motion is relative, right,
Speaker 1: like everything is relative. So Einstein basically came up later
Speaker 1: and said, actually, turns out Newton is wrong and also
Speaker 1: Mock is wrong. They're both wrong in slightly different ways.
Speaker 1: All right, Well, let's get into how Einstein proved them
Speaker 1: wrong and whether or not the whole universe is spinning,
Speaker 1: because my head is spinning a little bit right now,
Speaker 1: and I kind of made a little break, so we'll
Speaker 1: be right back. All right, we're asking the question is
Speaker 1: the whole universe spinning? I am getting a little dizzy
Speaker 1: just thinking about and talking about this question. And where
Speaker 1: we left off was that Einstein looked at Newton and
Speaker 1: then he looked at another researcher back in the day,
Speaker 1: and he said, um, you're both wrong. Actually, maybe spinning
Speaker 1: is also relative. So Einstein said, definitely, Newton is wrong,
Speaker 1: because Newton said that all motion is absolute, that space
Speaker 1: is like its own absolute frame, and velocity is absolute,
Speaker 1: that in an empty universe and object moving in his
Speaker 1: train line, you could somehow measure its velocity relative to
Speaker 1: absolute space. So Einstein said, no, that's ridiculous. There is
Speaker 1: no preferred location in space, There is no preferred velocity
Speaker 1: in space. That doesn't make any sense. And he built
Speaker 1: that into his theory of relativity. But he also said
Speaker 1: that Mack was wrong because Mak wanted to go even
Speaker 1: further and say, well, even acceleration is relative, and Einstein
Speaker 1: liked that idea, but he found that it didn't actually work.
Speaker 1: And so what Einstein says is that space is relative.
Speaker 1: And we've talked up on the podcast a few times
Speaker 1: about how time is relative. Also different observers in the
Speaker 1: universe feel timed differently. But when you put the two together,
Speaker 1: space time, you actually do get something absolute. Einstein didn't
Speaker 1: actually like calling his theory relativity theory because he thought
Speaker 1: it oversawled the relativity aspect of it. He wanted to
Speaker 1: call it invariance theory. But anyway, what he found was
Speaker 1: that space is relative and time is relative, but that
Speaker 1: space time together had some absolutes in it that lets
Speaker 1: you measure whether something is accelerating, and spinning counts as accelerating.
Speaker 1: So acceleration and spin are absolute, but velocity is relative.
Speaker 1: I guess it sort of maybe depends on your definition, right,
Speaker 1: Like is spinning motion also motion, or is spinning motion
Speaker 1: like something that's not motioned, you know what I mean?
Speaker 1: Like maybe you're saying, you know, spinning involves acceleration, and
Speaker 1: therefore it's not sort of the same as moving with
Speaker 1: a constant velocity exactly. Spinning is definitely a kind of acceleration.
Speaker 1: So then the question really is is acceleration absolute. If
Speaker 1: acceleration is absolut if you can measure acceleration out in
Speaker 1: deep space, that means that spinning is absolute, that you
Speaker 1: could also measure spin in deep space. And so Einstein's
Speaker 1: theory of relativity shows us that velocity is relative, but
Speaker 1: that acceleration is absolute. That you can tell if an
Speaker 1: object is accelerating, which also means you can tell if
Speaker 1: it's spinning, right, which means that if you even if
Speaker 1: you were alone in the universe, you can still get dizzy.
Speaker 1: You can get dizzy in an empty universe. And we've
Speaker 1: seen this other times when we've talked about Einstein's theory
Speaker 1: of relativity and spin. Because Einstein's theory, for example, predicts
Speaker 1: a difference between the gravity of an object that's spinning
Speaker 1: a gravity of an object that's not spinning. A spinning
Speaker 1: object has this weird effect frame dragging, where like drags
Speaker 1: space along behind it a little bit. And Newton doesn't
Speaker 1: predict that because Newton says there's no difference between the
Speaker 1: gravity of a spinning object and a non spinning object,
Speaker 1: and that wouldn't make any sense if spinning was purely relative. Right,
Speaker 1: So spinning objects have a different gravitational effect, and therefore
Speaker 1: you must be able to tell the difference between spinning
Speaker 1: and non spinning objects, right, But I wonder if that
Speaker 1: is that something. I guess that's just kind of built
Speaker 1: into the laws of the universe that we that we
Speaker 1: can tell, Like why does the universe draw the line
Speaker 1: between velocity and acceleration, because you know, mathematically, it's just
Speaker 1: like one derivative over. It is just one derivative like
Speaker 1: it could have been acceleration is also invariant, but then
Speaker 1: the derivative of acceleration the next one over, is not relative.
Speaker 1: It does seem sort of arbitrary to like draw the
Speaker 1: line at the first derivative and not the second derivative.
Speaker 1: And there are a lot of really deep ideas here.
Speaker 1: One of them has to do with symmetry and conservation laws.
Speaker 1: We'll talk about that in an episode coming up soon
Speaker 1: on Nuther's Theorem. I think the best way to think
Speaker 1: about it is to think about what is invariant, what
Speaker 1: is preserved in the universe. The reason, for example, that
Speaker 1: you can tell that something is accelerating versus something is
Speaker 1: not is because of their path through space time. You know,
Speaker 1: this has to do with things like free fall. Right,
Speaker 1: if you are just moving through space without accelerating, you
Speaker 1: don't feel any forces, which you're effectively doing is making
Speaker 1: a straight line through space time. Like your path through
Speaker 1: space time is just a straight line. If you're accelerating,
Speaker 1: you like burn your rocket. If you're being pushed by something,
Speaker 1: then you make a curve in spacetime. So the reason
Speaker 1: that you can tell whether something is accelerating or not
Speaker 1: is because everybody agrees. All observers agree whether or not
Speaker 1: you're making a straight line in space time or a
Speaker 1: curve in spacetime. That's what it means to say that
Speaker 1: spacetime itself is absolute, that the universe can tell the
Speaker 1: difference between straight paths and spacetime and curved paths in spacetime. Well,
Speaker 1: I guess that's kind of what I mean, like, you know,
Speaker 1: you said, it's all sort of depends or it's all
Speaker 1: because of some symmetry in the universe. But then like,
Speaker 1: what if the universe they didn't have those symmetries, or
Speaker 1: what if we lived in another universe without those symmetries,
Speaker 1: would those RULs be different? Or is that invariant about
Speaker 1: the velocity and acceleration kind of baked into math itself.
Speaker 1: It's not baked in the math. You could construct cosmologies
Speaker 1: where things were different. This is the universe that we
Speaker 1: find ourselves in. These are the rule that we discover.
Speaker 1: You know. It's sort of like asking the question and
Speaker 1: why is momentum conserved? And the answer is space is
Speaker 1: the same everywhere? All right, well, why is this space
Speaker 1: the same everywhere? It's not required by mathematics. You could
Speaker 1: have a universe where the rules of physics vary from
Speaker 1: place to place. We just don't seem to have that universe.
Speaker 1: So this is sort of like a discovery of ours.
Speaker 1: The universe seems to obey this principle, and these are
Speaker 1: the consequences of that principle. Why does it obey this principle?
Speaker 1: We don't know, But we've discovered it. It's sort of
Speaker 1: like saying, okay, the speed of light is invariant for everybody.
Speaker 1: Everybody measures the speed of light to be the same. Why,
Speaker 1: we don't know, but here are the consequences of it.
Speaker 1: This is the invariance that Einstein discovered that space is
Speaker 1: not invariant, but space time is. You know. Another way
Speaker 1: to think about these paths is to think about like,
Speaker 1: you know, imagine how you get from your house to
Speaker 1: your work. Somebody could draw like a set of axes X,
Speaker 1: y Z and say Joge gets from his house to
Speaker 1: his work and from this coordinate to that coordinate. And
Speaker 1: somebody else could come along and say, well, I have
Speaker 1: a totally different set of coordinates for Jorges path from
Speaker 1: him to work, and those are totally different coordinates, but
Speaker 1: doesn't matter. And it doesn't matter because the path itself
Speaker 1: is the same. The two observers would look at the
Speaker 1: path and say, oh, it's a straight line or no,
Speaker 1: it's a wiggle because he stops at the fridge on
Speaker 1: the way from his bed to his cartooning studio. Right,
Speaker 1: So people agree about the shape of the path even
Speaker 1: if they don't agree about the actual coordinates. That's what
Speaker 1: it means that space time, your path through space time
Speaker 1: is absolute, even if your coordinates are arbitrary. Well sometimes
Speaker 1: I work from bed. Even everyone would agree that it's
Speaker 1: a short community. Yeah, exactly. If your path is a point,
Speaker 1: then everybody would agree. Yeah, that's the whole point of
Speaker 1: being a cartoonist is to live in a point. But
Speaker 1: I think what you're saying is that you know, it's
Speaker 1: sort of baked into the laws of at least this
Speaker 1: universe that we live in, that you can't tell if
Speaker 1: something is spinning, Like it's not something that you can hid,
Speaker 1: or it's not something that you can like maybe never tell.
Speaker 1: But the question we're asking today is whether the whole
Speaker 1: universe is spinning, which kind of makes me wonder, like
Speaker 1: feel like, now it could go either way, because yes,
Speaker 1: you can tell if something is spinning in the universe,
Speaker 1: but what if the universe itself is spinning? Could you tell? Here?
Speaker 1: I think we have to be careful about what we
Speaker 1: mean by the universe. And I'm talking now about the
Speaker 1: matter in the universe. Like I take all the stuff,
Speaker 1: the galaxies, the dust, the gas, the dark matter, is
Speaker 1: all of that stuff spinning and that here it's spinning
Speaker 1: relative to space time. Spacetime itself can that spin? Like, well,
Speaker 1: what would that be spinning relative too? There's no external
Speaker 1: metric for spacetime itself to spin. So we're talking about, like,
Speaker 1: you know, the Earth is spinning, is it possible that
Speaker 1: everything else is also spinning in that same way that
Speaker 1: the Earth is spinning? Oh? I see You're you've been
Speaker 1: spinning this question the whole time, Daniel. You're really asking
Speaker 1: is the whole stuff in the universe spinning? You're not
Speaker 1: asking if the universe is spinning. Well, it depends on
Speaker 1: whether you're including space time in that spin. And I
Speaker 1: would say it doesn't make sense for space time itself
Speaker 1: to spin, but stuff in space time can spin relative
Speaker 1: to space time. Well, I guess maybe let's explore that
Speaker 1: a little bit. Like we've talked about space being a thing,
Speaker 1: How do you know it's not spinning? It could be
Speaker 1: spinning even if it's not relative to anything. Right, the
Speaker 1: same way that we talked about expansion of spacetime, we
Speaker 1: don't say that spacetime is expanding into something else. We
Speaker 1: only have intrinsic measurements. We are in spacetime. There's nothing
Speaker 1: outside of space time to measure, so we can only
Speaker 1: measure internally. Right, So we say spaces expanding, people ask
Speaker 1: what is it expanding into? Well, it's not expanding into anything.
Speaker 1: It's just increasing the relative distances between stuff in space.
Speaker 1: So in the same way, you can't really ask what
Speaker 1: is spacetime rotating in It's not in anything. It just
Speaker 1: sort of is. And so there's no sense in which
Speaker 1: space time could spin. But I thought you were going
Speaker 1: the other way, because you know, you can say that
Speaker 1: space is expanding, but it's not expanding relative to anything.
Speaker 1: Couldn't I just say spacetime is spinning, but it's just
Speaker 1: not spinning relative to anything. Then what does that mean
Speaker 1: for it to be spinning? What does it mean for
Speaker 1: its expanding nothingness? It means that the distances between stuff
Speaker 1: are getting larger, right, But what does it mean for
Speaker 1: space time itself as a whole to spin? You can
Speaker 1: tell whether's something is spinning relative to space time same
Speaker 1: way you can tell whether you know distances are growing,
Speaker 1: but you can't tell whether spacetime itself is spinning. You
Speaker 1: could maybe, like maybe if I was alone in the
Speaker 1: universe and I got dizzy, you know what I mean?
Speaker 1: Like I guess what I'm wondering is, could there be
Speaker 1: like an inherent centripital acceleration to the universe. I think
Speaker 1: it's possible. Mathematically, there is always an ambiguity there, even
Speaker 1: in the case of expansion, because general relativity has this
Speaker 1: weird difficulty by talking about the velocities of things that
Speaker 1: are very far away, you always define either relative velocities
Speaker 1: or velocities relative to space. And so probably there's a
Speaker 1: way you could construct a universe that had a rotating
Speaker 1: space time that had an inherent built in centrifugal acceleration.
Speaker 1: You know, for example, a curvature of space would give
Speaker 1: you that effect if space was curved in such a
Speaker 1: way that you effectively felt a negative gravity. And there
Speaker 1: are some folks out there argue that dark energy may
Speaker 1: partially be due to some like inherent and trifugal force
Speaker 1: due to the rotation of space time itself, rather than
Speaker 1: some expansion of space. WHOA wait, so like the space
Speaker 1: and could be spinning and it might be the answer
Speaker 1: to dark energy. That's one thing people were probably and
Speaker 1: we'll talk about how people use type one a supernova
Speaker 1: to try to answer that question. You a little bit
Speaker 1: when we talk about how to measure whether space is spinning.
Speaker 1: All right, we'll leave that for another episode, but I
Speaker 1: guess in this episode we are now shifting the question too.
Speaker 1: Is everything in the universe in spacetime it's self spinning,
Speaker 1: because you know, it could be spinning, right Like, like
Speaker 1: you said earlier, the Earth is spinning, and we're spinning
Speaker 1: around the Sun, and the Sun is spinning around the
Speaker 1: gaxy and the GALSSI. It's probably spinning around some larger
Speaker 1: cluster of galaxies, and that could also be spinning relative
Speaker 1: to other clusters. You know, is everything may be spinning.
Speaker 1: It's a really fun question, and what we expect, what
Speaker 1: physics predicts, is sort of counterintuitive because on one hand,
Speaker 1: we see that everything is spinning, as you say, the
Speaker 1: Earth is spinning, of the galaxy is spinning, but we
Speaker 1: don't actually expect, on very very large scales for all
Speaker 1: the stuff in the universe to be spinning. That if
Speaker 1: you added up all the stuff in the universe, we
Speaker 1: actually predict that it should have zero spin, right because
Speaker 1: it seems kind of implausible almost that everything would not
Speaker 1: to be spinning, that it would be sort of standing still.
Speaker 1: It doesn't. It's actually a very specific prediction of inflation. Remember,
Speaker 1: inflation is this prediction that the universe started out much
Speaker 1: much denser, much much more compact, and then spread out
Speaker 1: and expanded and blew out, and that all the structure
Speaker 1: we see in the universe comes from like the little
Speaker 1: quantum fluctuations in density from the early universe. And it's
Speaker 1: that expansion itself that we think would have killed effectively
Speaker 1: any rotation. Remember what happens when you're spinning. If you're
Speaker 1: like on ice in your figure skater, if you pull
Speaker 1: your arms towards yourself, then you start to spin faster.
Speaker 1: And that's why, for example, the Earth is spinning because
Speaker 1: it started out from a cloud of stuff that was
Speaker 1: very gently spinning and then collapsed, and the is now
Speaker 1: spinning faster. But expansion has the opposite effect. So as
Speaker 1: the universe expands, we expected to spin less and less.
Speaker 1: Because inflation expanded the universe by like ten to the
Speaker 1: thirty than any tiny random rotation of that initial blob
Speaker 1: of stuff, we would expect that to be effectively zeroed
Speaker 1: out by inflation. Right, I guess maybe I'm getting a
Speaker 1: little confused here because of what we're actually asking, Like,
Speaker 1: I guess, are we asking whether all this stuff in
Speaker 1: the universe has a zero or non zero average spin?
Speaker 1: Do you know what I mean? Like, for sure I
Speaker 1: can spin in my chair here, and the Earth is
Speaker 1: for sure spinning, and the Sun is definitely spinning, and
Speaker 1: the galaxy and the galaxy clusters are definitely moving relative
Speaker 1: to other things. I guess is the question, like, if
Speaker 1: you average out everything, all the stuff in the universe,
Speaker 1: does it have a spin to it or does it
Speaker 1: all cancel out to exactly zero? Is that kind of
Speaker 1: what we're really asking here? Yeah, draw line through space
Speaker 1: and measure the spin relative to that line, and then
Speaker 1: ask is that overall spinning all the stuff in the universe?
Speaker 1: Is that zero or not? Right? Sort of like if
Speaker 1: you have a snow globe, maybe I'm thinking, you know,
Speaker 1: you can have all the snowflakes inside moving and twirling
Speaker 1: and looking chaotic, but overall you can sort of tell
Speaker 1: whether or not this stuff in it is spinning relative
Speaker 1: to the globe. What you're saying is that it maybe
Speaker 1: has to do with the beginning of the unse like
Speaker 1: if this stuff at the beginning of the universe had
Speaker 1: a little bit of a spin, that's the only way
Speaker 1: it could still have spin today, Yeah, because angular momentum
Speaker 1: is conserved. Right, If you are spinning, you will always
Speaker 1: be spinning. There's no way to stop something from spinning
Speaker 1: unless you're coming in from the outside with some other
Speaker 1: spin to cancel it out. If you're talking about the
Speaker 1: whole universe, then there is nothing outside and so if
Speaker 1: the whole universe somehow started out spinning, it should still
Speaker 1: be spinning today, although that spin would get dampened out
Speaker 1: and go to very very small values because of the
Speaker 1: expansion of the universe, like a figure skater shooting her
Speaker 1: arms out for like millions and millions of miles or spin,
Speaker 1: but then go to the to the zero. So that's
Speaker 1: what we're talking about, is is there spin to this
Speaker 1: stuff in the universe and it should persist if it's there, right,
Speaker 1: Because I think what you're saying is that the universe
Speaker 1: had no spin at the Big Bang when it was
Speaker 1: super super tiny small, and thence if it had no spin,
Speaker 1: there's no way for it to gain spin since then
Speaker 1: like it can't like push off against anything right to
Speaker 1: get spin. There's no way to spin the entire universe.
Speaker 1: There's nothing to like push against. Right. If you're talking
Speaker 1: about the whole universe is nothing that you can push against,
Speaker 1: because that would mean something outside the universe and the
Speaker 1: universe is everything, right, unless maybe, like spacetime itself has
Speaker 1: a like a lean, like a lean to it, right,
Speaker 1: or something, you know, like it has a preference for
Speaker 1: a matter and not antimatter. It has a preference for
Speaker 1: certain things, you know, four wards some time and not
Speaker 1: backwards some time. Could it also have like a little
Speaker 1: bit of a spin preference. Yeah, we usually ask this
Speaker 1: question under the assumption that spacetime is homogeneous, meaning it's
Speaker 1: the same everywhere and in every direction. But it's certainly
Speaker 1: possible if we discovered an overall spin to the universe
Speaker 1: to wonder that comes from and you know, could be
Speaker 1: generated by like some features in spacetime that aren't the
Speaker 1: same everywhere I see. But your your basic answer is
Speaker 1: that the stuff in the universe has any spin. Now,
Speaker 1: it must be due to any kind of spin it
Speaker 1: has at the beginning of the universe. But even if
Speaker 1: it had a little bit of a rotation at the
Speaker 1: beginning of the universe, that would have all sort of
Speaker 1: gone to almost zero by now. Yes, So we would
Speaker 1: be very surprised if we look out into the universe,
Speaker 1: measure its overall spin, and find it to be spinning
Speaker 1: at any significant rate. That would be a big shock.
Speaker 1: It would make all your head spin for sure, relative
Speaker 1: to all the chocolate you're eating. It would be a
Speaker 1: fantastic and delicious discovery because it would be a clue
Speaker 1: that's something we think is true, is not that there's
Speaker 1: something else going on that we don't understand, and like
Speaker 1: the biggest, most delicious scales. All right, well, let's get
Speaker 1: into how we could tell if the universe, or at
Speaker 1: least the stuff in the universe, is spinning at any
Speaker 1: significant rate, because I think Daniel is hungry, so let's
Speaker 1: get that answer asap. But first let's stick another quick break. Alright,
Speaker 1: we're talking about whether or not all this stuff in
Speaker 1: the universe is spinning, Dan, and you said it's unlikely
Speaker 1: for it to have any kind of spin, because expanding
Speaker 1: the universe would have killed any sort of momentum. But
Speaker 1: what if I'm thinking, what if the universe was spinning
Speaker 1: a lot at the beginning, couldn't it also have some
Speaker 1: sort of remnant spin twit at this point? Yeah, it would,
Speaker 1: and we might be able to measure that if we
Speaker 1: devise tests that are very very sensitive, and so you're
Speaker 1: right that the current theories of physics suggests that spin
Speaker 1: is dampened by expansion. But we don't have an idea
Speaker 1: for why the universe would or would not be spinning originally.
Speaker 1: So if the universe was somehow born spinning super duper fast,
Speaker 1: we could still measure that today, and that would be
Speaker 1: interesting because our cosmology allows for the universe to spin.
Speaker 1: It's possible for the whole universe to have been born spinning,
Speaker 1: for it to have been a spinning baby shot out
Speaker 1: of the universe womb and doing a triple lets. And
Speaker 1: remember we don't really know much about that birth. We
Speaker 1: talked about possible theories of like infloton fields decaying into
Speaker 1: normal matter. There's are really displaceholders for like where to
Speaker 1: have future ideas the shape of those ideas, but we
Speaker 1: definitely don't have ideas firm enough to where we can say, like,
Speaker 1: the universe should not have been born with any spin.
Speaker 1: For sure, there's a huge opening there for ways the
Speaker 1: universe could have been born and allowing for it to spin,
Speaker 1: And definitely Einstein's ther relativity says it is possible. It's
Speaker 1: meaningful for the stuff in the universe to be spinning, right,
Speaker 1: So I guess that means that if you do discover
Speaker 1: that all the stuff in the universe is spinning right now,
Speaker 1: it maybe shouldn't be that surprising. You'll just tell you
Speaker 1: if it was spinning at the beginning or not. It
Speaker 1: would tell you that it was spinning a lot at
Speaker 1: the beginning, and then you'd have to go into your
Speaker 1: theories and say, like, well, how do I make that happen?
Speaker 1: You know? Is it a diverse where the spin is
Speaker 1: somehow random and we just got a big serving of
Speaker 1: it is necessary because of some property of the universe beforehand,
Speaker 1: the universe is inherently always spinning. It would be a
Speaker 1: lot of really fun questions. Yeah, or maybe the universe
Speaker 1: mom just hit a lot of chocolate before the baby
Speaker 1: universe was born and made the baby universe spin out
Speaker 1: of control. All right, So then what are some of
Speaker 1: the ways that we could maybe test today, like where
Speaker 1: we are now in this spinning or not spinning universe,
Speaker 1: whether or not things are spinning everything, whether or not
Speaker 1: everything is spinning. So people have been thinking about this
Speaker 1: for decades, and remember Einstein's theory of relativity is only
Speaker 1: about a hundred years old. To this concept that the
Speaker 1: universe can spin absolutely relative to space time. He's only
Speaker 1: about a hundred years old, and it took a while
Speaker 1: for people to understand what it means. You know, Einstein
Speaker 1: actually believed Mark for decades until later in his life
Speaker 1: when he was like, no, beautiful, but I think he's wrong.
Speaker 1: And it's really only like fifty or so years that
Speaker 1: people have been are thinking about this in a way
Speaker 1: that they test it. And one of the simplest ideas
Speaker 1: is just like, well, let's just look and see if
Speaker 1: the universe appears to be spinning relative to some fixed point.
Speaker 1: You mean looking at all the stuff in the universe,
Speaker 1: not the universe itself. Yeah, all the stuff in the universe.
Speaker 1: And so, for example, are the galaxies, the distant galaxies?
Speaker 1: Are they spinning relative to the Milky Way or relative
Speaker 1: to the Solar System? And the cool thing is that
Speaker 1: you can treat the Solar System, because itself is spinning,
Speaker 1: as a sort of gyroscope. That the Solar System is spinning,
Speaker 1: and it's going to continue to spin, and because of
Speaker 1: conservation of Anglo momentum, it has to keep spinning and
Speaker 1: basically the same direction, so it like defines an access
Speaker 1: and then you can ask, well, is the rest of
Speaker 1: the universe sort of spinning around us relative to the
Speaker 1: Milky Way? What do you mean? I would that tell
Speaker 1: you if the universe was spinning, I mean the stuff
Speaker 1: in the universe was spinning. Well, it would tell you
Speaker 1: whether the universe was spinning relative to the Milky Way.
Speaker 1: At least we can measure the Milky Way spin, right,
Speaker 1: because we can tell whether an individual object needs spinning,
Speaker 1: and so that gives us like a reference point, and
Speaker 1: then we can ask whether the rest of the universe
Speaker 1: is spinning relative to us. So we can measure our
Speaker 1: spin relative to spacetime, and then we can measure the
Speaker 1: rest of the universe is spin relative to the Milky Way,
Speaker 1: just by looking at the galaxies and saying, like, are
Speaker 1: they moving relative to us? Oh? I see, But isn't
Speaker 1: that sort of a given, Like don't we expect the
Speaker 1: Milky Way to be, you know, spinning in some weird
Speaker 1: direction relative to everything else, all the stuff in the universe.
Speaker 1: We can measure the Milky Way spin relative to spacetime
Speaker 1: because it's absolute, and then we can measure the motion
Speaker 1: of the distance galaxies relative to the Milky Way, and
Speaker 1: if that's exactly the opposite, then that suggests that the
Speaker 1: whole rest of the universe is essentially not spinning. Oh,
Speaker 1: I see, Because you're saying that you can measure the
Speaker 1: spinning of stuff relatives to spacetime. There is sort of
Speaker 1: like a reference frame in the universe, and that's called
Speaker 1: space time. And you're saying, because the Milky Way is
Speaker 1: close to us, we can measure that pretty accurately. It
Speaker 1: gives us sort of a compass of how we're spinning
Speaker 1: relative to spacetime. And then you're saying, let's look at
Speaker 1: everything else and see if it's rotating relative to that exactly. So,
Speaker 1: say you're spinning around inside of a room, you can
Speaker 1: have a way to measure your own spin. You have
Speaker 1: like a gyroscope that tells you your own spin, and
Speaker 1: you can also measure your spin relative to the walls.
Speaker 1: So those two numbers agree, that tells you the walls
Speaker 1: are not spinning. Those two numbers disagree. That tells you, Oh, well,
Speaker 1: I guess the walls are also spinning. So that's what
Speaker 1: we can do. We can measure our spin of the
Speaker 1: Milky Way and then we can measure the spin of
Speaker 1: the Milky Way relative to the distant galaxies, and then
Speaker 1: we can ask are the distant galaxies spinning in absolute sense?
Speaker 1: But I guess my question is why do even need
Speaker 1: to go that far? Like, couldn't I just use the
Speaker 1: gyroscope here on Earth and then measure the galaxies relative
Speaker 1: to my little gyroscope. Yeah, but the Milky Way is
Speaker 1: a better gyroscope than your little gyroscope. The Milky Way
Speaker 1: and the Solar System provide pretty nice gyroscope because it's
Speaker 1: a huge amount of mass and a very long lever arm,
Speaker 1: and so they're very precise. But there are lots of
Speaker 1: ways you can construct this experiment. The real limitation, though,
Speaker 1: is that it's very hard to observe the motion of
Speaker 1: those distant galaxies because they're really really far away, and
Speaker 1: so they hardly move at all. And we've only been
Speaker 1: looking at them for like a hundred years. It's only
Speaker 1: Hubble a hundred years ago they even discover that there
Speaker 1: were other galaxies out there. So if they are moving,
Speaker 1: they're moving very very slow, not in a way that
Speaker 1: we can tell relative to spacetime, right, They're moving super slow.
Speaker 1: They're moving they're expanding, right, they're moving away from us.
Speaker 1: But now we're talking about not radial motion away from us,
Speaker 1: the rotational motion right perpendicular to the line between us
Speaker 1: and them, and we haven't seen that kind of rotation.
Speaker 1: Like I think you're saying, like, if you correct for
Speaker 1: the motion of the Earth and correct for the motion
Speaker 1: of the Earth around the Solar System and the milk
Speaker 1: away and all that, it would be hard to tell
Speaker 1: because they're so far away, Like for us to see
Speaker 1: them spinning around and around the cosmos, it would have
Speaker 1: to be moving like ridiculously fast, right, Because we can
Speaker 1: measure their velocity in a radial direction pretty well because
Speaker 1: of Doppler effect. Measuring their velocity in the other direction,
Speaker 1: you know, requires seeing their change in their own relative
Speaker 1: to the Milky Way, which requires like you know, seeing
Speaker 1: them actually move, and that's really hard to do for
Speaker 1: stars and even harder to do for galaxies. They need
Speaker 1: to be either moving really really fast, or you have
Speaker 1: to observe for like a billion years and we're only
Speaker 1: a hundred years in. Yeah, that's the real limitation. Like
Speaker 1: it's possible, and you just need a lot of time,
Speaker 1: or they need to be moving really really fast in
Speaker 1: an obvious way that we can see it, and that's
Speaker 1: not happening. Can you just to ask him? Call him
Speaker 1: all right? So that that one has its limitations. You're
Speaker 1: not gonna gonna get a Nobel prize anytime soon with
Speaker 1: that method. What are some other ways we can measure?
Speaker 1: Other things we can do is to look at the
Speaker 1: expansion of the universe. So we know that things that
Speaker 1: are far away from us are moving away from us,
Speaker 1: and we know that that expansion is accelerating. So this
Speaker 1: is the discovery of dark energy. That something is stretching out.
Speaker 1: The universe seems to be creating new space between points
Speaker 1: all of the time. And the interesting thing is that
Speaker 1: cosmologists say that if the whole universe was rotating, if
Speaker 1: everything was spinning, then that would look a little different.
Speaker 1: That expansion would look different than it would if the
Speaker 1: universe was not spinning. And so the way that we
Speaker 1: measure that the universe is expanding is a couple of ways.
Speaker 1: One is that we look at type one A supernova,
Speaker 1: these standard candles that we know exactly how bright they
Speaker 1: should be, and so when we see one, we can
Speaker 1: tell how far away it is because of how bright
Speaker 1: we see it. We have these like tracer points in
Speaker 1: the universe, so we can see their expansion over time,
Speaker 1: and we can see the history of the expansion of
Speaker 1: the universe. And if there was a swirl in that expansion,
Speaker 1: if the universe was rotating at the same time as expanding,
Speaker 1: then that would look a little different than if it
Speaker 1: was just expanding in a purely radial way. What do
Speaker 1: you mean, because I would mess with the I guess
Speaker 1: the basic motion of things, right, because it suddenly has
Speaker 1: an extra component of velocity and it's feeling an extra
Speaker 1: component of exploration. Yeah. Imagine you're like on a Merry
Speaker 1: Go Round and you have a bunch of friends and
Speaker 1: you all throw ping pong balls out. If you're spinning,
Speaker 1: or if you're not spinning, then those ping pong balls
Speaker 1: have a different path, right, They would curve if you're spinning.
Speaker 1: That's one way to measure or rotation. And so we're
Speaker 1: trying to measure the rotation of all the stuff in
Speaker 1: the universe by looking at the path of these tracers,
Speaker 1: these type one a supernova to see is it consistent
Speaker 1: which is flying straight out or is it consistent with curving.
Speaker 1: We can't observe them for very long. But we have
Speaker 1: these momentary tracers, then you can do some sort of
Speaker 1: like back calculation to say, like are they consistent with
Speaker 1: rotation or are they consistent with pure expansion? Oh? I see.
Speaker 1: I think what you're saying is like, like if everything
Speaker 1: in the universe was in a Merry Go round, we
Speaker 1: would see the stars, the supernova or at least the
Speaker 1: stuff around like the equator. That stuff would be maybe
Speaker 1: expanding faster, maybe or moving differently than the stuff like
Speaker 1: above and below us on the Merry Go round. Yeah,
Speaker 1: if there's an overall rotation, that implies that there's a
Speaker 1: rotation in some plane, right, some access around which you
Speaker 1: are rotating, and that essentially defines a north and a
Speaker 1: south just the same way like the Earth's rotation defines
Speaker 1: a north pole and a south pole, and the Solar
Speaker 1: system has a north and the south defined by its rotation.
Speaker 1: So that would create different directions in the sky where
Speaker 1: things look different, basically a huge anisotropy. We actually talked
Speaker 1: about on the podcast once about this access of evil,
Speaker 1: this idea that maybe things in the universe do look
Speaker 1: a little bit different north to south if depending on
Speaker 1: how you define it. That's exactly the kind of thing
Speaker 1: you would expect to see if the universe was rotating.
Speaker 1: You'd expect to see some difference in one half of
Speaker 1: the sky versus the other half of the sky. Right,
Speaker 1: you would expect it to be a little wider in
Speaker 1: the middle around the waistline. The universe is either rotating
Speaker 1: or been eating too much chocolate, you know, one of
Speaker 1: those two. There's only two posibilities. You can use similar
Speaker 1: tests with another very sensitive probe of the universe's expansion.
Speaker 1: That's the cosmic microwave background radiation. That's this light from
Speaker 1: the very very early universe. And we were talking about
Speaker 1: how if this rotation exists, it should have existed a
Speaker 1: long time ago. It's actually much more powerful to see
Speaker 1: it earlier on, before the universe expanded so much, because
Speaker 1: the rotation would be more dramatic and so in the
Speaker 1: same way that if the universe is rotating, it would
Speaker 1: affect the way things are expanding, it would also affect
Speaker 1: that plasma that generates did that CNB light The plasma
Speaker 1: is very sensitive to like how much dark matter there
Speaker 1: is and how it's moving, and how the normal matter
Speaker 1: is sloshing around into and out of those dark matter
Speaker 1: gravitational wells, and if there was an overall spin, it
Speaker 1: would affect those patterns in very subtle ways, and people
Speaker 1: have studied those and not seeing any evidence for universal rotation.
Speaker 1: M M. It's kind of like you we talked about
Speaker 1: it before, how the cosmic microwave background is like a
Speaker 1: picture of the baby universe, like an early picture of
Speaker 1: the universe, and so you you don't see any Basically,
Speaker 1: what you're saying is you don't see any spin in
Speaker 1: that picture, nor do you see it being uh, like
Speaker 1: the baby's not extra wide around the middle. Yeah, And
Speaker 1: it's a little subtle because it's not like you're looking
Speaker 1: at the actual universe and seeing it's spin. You're looking
Speaker 1: at like the patterns that spin would cause in the
Speaker 1: clumpiness of the universe. It would make very distinctive patterns.
Speaker 1: And this is actually the most sensitive test we have
Speaker 1: for the universe's rotation, is this cosmic microwave background light.
Speaker 1: In their early eighties, people saw some weird stuff in
Speaker 1: the sky from radio signals that led them to believe
Speaker 1: maybe the universe was rotating. There's a paper in two
Speaker 1: I read from a guy in Manchester in Birch who
Speaker 1: claimed to be measuring the rotation of the universe that
Speaker 1: attended the minus thirteen radiants per year. But this measurement
Speaker 1: in the CNB is more powerful and is not consistent
Speaker 1: with any rotation, So people think Burchess measurement was probably wrong. Well,
Speaker 1: I'm getting this sort of the picture that if you're
Speaker 1: asking the question, is the stuff in the universe spinning?
Speaker 1: If it was spinning, then you would see some sort
Speaker 1: of like you said, an isotriptropy, meaning like it would
Speaker 1: the universe would look differently whether you're looking at the
Speaker 1: spinning direction or whether you're looking at the its waistline
Speaker 1: or the equator of the spinning stuff in the universe.
Speaker 1: And it seems like for for all accounts looking at
Speaker 1: galaxies and looking at the baby picture of the universe,
Speaker 1: there is no different or like preferred direction that you
Speaker 1: can see as far as we can tell. Here's a
Speaker 1: study we talked about on the Access of Evil episode
Speaker 1: where people looked at the spin of Alexis and they
Speaker 1: found that galaxies in one direction of sky tend to
Speaker 1: be spinning left more than any other direction of the sky.
Speaker 1: And they claim this is maybe evidence for the universe
Speaker 1: to be rotating. But a lot of people criticize that
Speaker 1: paper and think that it probably underestimates systematic effects that
Speaker 1: could cause that, you know, local gravitational effects or or
Speaker 1: other uncertainties that they didn't take into account. So overall,
Speaker 1: there's no evidence for universal rotation, although our cosmology allows it. Right,
Speaker 1: it is possible our universe to rotate, it just doesn't
Speaker 1: seem to be doing that right, or at least not
Speaker 1: to tend to the negative nine radiance per year, which
Speaker 1: sounds like a small number. It's like point zero zero
Speaker 1: zero zero nine zeros and then a one. But if you,
Speaker 1: like you said before, like you know, the universe expanded
Speaker 1: tend to the what like thirties sixty two times since
Speaker 1: the Big Bang, And so it could just be that
Speaker 1: are these instruments this way of knowing, it's not accurate
Speaker 1: enough yet, Like there could be a little bit of
Speaker 1: spin down there still underneath the what we can measure.
Speaker 1: You will never have infinite precision, and so either the
Speaker 1: universe is not spinning or spinning very very gently. Yeah,
Speaker 1: it's a kitty merry go around. You know, nobody wants
Speaker 1: us to throw up all that chocolate. Yeah, nobody wants
Speaker 1: the six flags crazy roller coaster eversion of the universe.
Speaker 1: So I guess the answer is, is the stuff in
Speaker 1: the universe spinning? Not that we can tell, but it
Speaker 1: could still be spinning a little bit. We just don't
Speaker 1: know for sure yet. And fascinatingly, we could tell if
Speaker 1: the stuff in the universe was spinning. Spin itself is absolute,
Speaker 1: and that tells you something really deep about the nature
Speaker 1: of space and time and motion. That velocity is relative,
Speaker 1: but acceleration is not. Acceleration is absolute relative to space
Speaker 1: time itself. Yeah, and it would also sort of tell
Speaker 1: you that the universe kind of has a direction, right,
Speaker 1: It kind of would have a north and a south,
Speaker 1: and a tropical zone. It prefers dark chocolate to white chocolate.
Speaker 1: All right, Well, um, we hope your head is not
Speaker 1: spinning from all that discussion about spinning. Well, we hope
Speaker 1: that it does sort of make you think about whether
Speaker 1: or not the things around you are moving the way
Speaker 1: you think they are, and whether or not the universe
Speaker 1: was maybe born a pretty chill baby or a crazy
Speaker 1: spinning baby. And I hope you come away a little
Speaker 1: bit in awe of the fact that we can ask
Speaker 1: such amazing enormous questions about the nature of the cosmos,
Speaker 1: and that we have ways just from this tiny spinning
Speaker 1: rock finding initial answers to these questions. Yeah, and that
Speaker 1: we can talk about it in an hour and only
Speaker 1: make forty seven chocolate references. That's right, only make the
Speaker 1: forty seven bad chocolate plants. All right, Well, we hope
Speaker 1: you enjoyed that. Thanks for joining us, see you next time.
Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain
Speaker 1: the Universe is a production of I heart Radio. For
Speaker 1: more podcast from my heart Radio, visit the i heart
Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your
Speaker 1: favorite shows. H