Speaker 1: Picture the Solar system. Likely you have put the Sun
Speaker 1: at the center, motionless in your mind, with the planets
Speaker 1: whizzing all around it. Or maybe you've seen that viral
Speaker 1: video that breaks the common view and shows the Sun
Speaker 1: in motion through the galaxy. But isn't the galaxy moving
Speaker 1: to what's the right way to think about all this
Speaker 1: to assemble a mental universe? How fast are we going?
Speaker 1: And does that question even make sense? A new study
Speaker 1: raises some interesting puzzles. Today we're going to dig into
Speaker 1: all of that and help you make sense of it.
Speaker 1: Welcome to Daniel and Kelly's Extraordinary Universe in Motion.
Speaker 2: Hello, I'm Kelley Winer Smith.
Speaker 3: I study parasites and space, and it doesn't matter what
Speaker 3: I am moving relative to, I am always moving pretty slow.
Speaker 1: Hi. I'm Daniel. I'm a particle physicist, and I'm particularly
Speaker 1: interested in our cosmic context.
Speaker 2: So, Daniel, cosmic context?
Speaker 3: Yes, what in your mind would be the coolest spot
Speaker 3: for us to be in the universe? If we could know, like,
Speaker 3: should we be in the center, should we be at
Speaker 3: the edge, if we could be anywhere you wanted us
Speaker 3: to be? Where would we be?
Speaker 1: Wow, that's a crazy question, And I can't believe nobody's
Speaker 1: ever asked me that before, and I have never thought
Speaker 1: about that before. You know, if the universe is infinite,
Speaker 1: then there are no places. Really, They're all the same.
Speaker 1: So then the question is only interesting if the universe
Speaker 1: is not infinite. And even if the universe is finite
Speaker 1: and closed, there's still no special places. So the most
Speaker 1: interesting thing would be if the universe is finite and
Speaker 1: has an edge, in which case being near the edge
Speaker 1: would be amazing because the edge would have to be
Speaker 1: different in some way from other kinds of space, and
Speaker 1: it'll be like a different kind of lego brick that
Speaker 1: makes up the universe, and different is always fascinating because
Speaker 1: like at the edge, for example, momentum wouldn't be conserved.
Speaker 1: You know, for example, like when you throw a ball
Speaker 1: against a wall, the ball bounces back, but also the
Speaker 1: wall gets pushed back a little bit, even if the
Speaker 1: wall is attached to the Earth, right, But if you
Speaker 1: throw a ball against the edge of the universe, it
Speaker 1: bounces back and the universe doesn't get pushed it can't,
Speaker 1: and so momentum is not conserved. So that would be
Speaker 1: pretty interesting to see momentum not conservation. Hey, was that
Speaker 1: the nerdiest possible answer I could have given.
Speaker 2: You pretty close.
Speaker 1: I'm trying to max out all the metrics here today.
Speaker 2: Awesome.
Speaker 3: All right, Well, let's see what other metrics Daniel can
Speaker 3: max out today as we discuss how fast we're moving
Speaker 3: through space.
Speaker 1: Yeah, this is a really fun topic because we get
Speaker 1: to talk about not just like our cosmic context, where
Speaker 1: are we in the universe? How is everything slashing around?
Speaker 1: Give you like a sense for our neighborhood and the
Speaker 1: bigger picture of view of the universe. But also it
Speaker 1: touches on some really deep and basic but hard to
Speaker 1: grapple with concepts in relativity, like what does velocity even mean?
Speaker 3: Man?
Speaker 1: So get at your banana peels. We are going to
Speaker 1: smoke them today.
Speaker 2: Oh, we're getting philosophical.
Speaker 1: I guess we always get philosophical when it's physics. Episode
Speaker 1: amazing can't be avoided. So I was wondering what people
Speaker 1: thought about this question before we dive into the physics
Speaker 1: of it. So I reached out to our amazing group
Speaker 1: of volunteers who stand at the ready to offer their
Speaker 1: ungoogled opinions on questions of the day Today. I asked
Speaker 1: them how fast are we moving through space? Think about
Speaker 1: it for a moment. What would be your answer. Here's
Speaker 1: what our group of experts had to say. Should be
Speaker 1: dependent upon the relative location and velocity of the observer.
Speaker 2: We're all going back to the same location, so effectively,
Speaker 2: we haven't gone anywhere.
Speaker 1: Ninety six thousand kilometers per second. They don't know how
Speaker 1: fast the Milky Way galaxy is moving.
Speaker 2: We're moving at thousands and thousands and thousands of kilometers
Speaker 2: per second.
Speaker 4: How fast we're going depends on our frame of reference.
Speaker 4: I'm sitting down zero miles per hour.
Speaker 2: It must be thousands of miles an hour.
Speaker 1: If the universe is infinity in size, then we're going
Speaker 1: infinity speed around something.
Speaker 4: Relative to the galaxy in the universe.
Speaker 1: I don't know, man, tough question. Speed is always relative,
Speaker 1: So the question is how fast are we moving relative
Speaker 1: to what? Velocity is relative?
Speaker 2: When it comes to space time, we're moving all at
Speaker 2: the speed of light.
Speaker 4: Relative to what's not fast enough, guys, hit the nitrous
Speaker 4: are side.
Speaker 3: But on these are great answers. And having listened to
Speaker 3: you explain physics for over a year now, my guess was,
Speaker 3: it's got to be relative to something.
Speaker 2: And then I was like, and that's all I know.
Speaker 3: But I will hear a whole hour on this topic,
Speaker 3: so soon I'll be an experts And so, yeah, what
Speaker 3: did you think of these answers?
Speaker 1: I thought they were great. They were very well informed
Speaker 1: and really funny. Also, but I have a question about
Speaker 1: your response, Kelly. Do you have a different relationship now
Speaker 1: to like the random physics question that might come up
Speaker 1: in conversation, Like if your kids ask you a random
Speaker 1: question about the universe, do you feel like more qualified
Speaker 1: to maybe answer it or dig into it with them
Speaker 1: than you did a year ago.
Speaker 3: I do, and I'm much more likely to like interject
Speaker 3: physics information. Like Hata said something about an electron the
Speaker 3: other day, and I was like, did you know that
Speaker 3: we don't know if the electron is made up of
Speaker 3: other bits.
Speaker 2: We've tried to figure it out, but we did. It
Speaker 2: doesn't look like it's made up of other stuff, but
Speaker 2: we just don't know.
Speaker 3: Because we haven't been able to, like, you know, if
Speaker 3: we had more money, we could dig in more.
Speaker 2: And she didn't. You know, I can't say she looked interested, but.
Speaker 3: I was excited and so so yes, I do feel
Speaker 3: like now that I know more about physics. I'm more
Speaker 3: excited about physics. It feels less opaque and I'm excited. Yeah,
Speaker 3: life is good.
Speaker 1: Okay, yeah, physician accomplished one person at a time.
Speaker 2: Woo. Yes, you want a biologist over.
Speaker 1: Well, then I'm one for two because I'm not sure
Speaker 1: Katrina feels the same way. Oh.
Speaker 3: Ouch, And how many years have you been working there?
Speaker 3: Is that like twenty years now? Yeah?
Speaker 1: Twenty six, twenty seven? Yeah? I know, right, Well, she
Speaker 1: definitely knows more particle physics than she did when she started,
Speaker 1: So I don't know if her enthusiasm has gone up,
Speaker 1: but her knowledge definitely has.
Speaker 3: Well, how do you feel about poop in the fridge?
Speaker 3: I guess maybe your knowledge of what's happening with the
Speaker 3: poop in the fridge has gone up, but your excitement
Speaker 3: about it has probably not.
Speaker 1: Yeah, so that's probably fair. Yeah, okay, comparison. All right,
Speaker 1: The day I'm excited to see poop in the fridge
Speaker 1: is the day I expect Katrina to be excited to talk.
Speaker 2: About particles, all right, urriage in a nutshell.
Speaker 1: Everybody likes to talk about the interdisciplinary work, but we're
Speaker 1: living it, baby.
Speaker 2: That's right, that's right, it's messy.
Speaker 1: All right, let's get back on track and talk about
Speaker 1: our emotion through the universe, not bowel motions that ended
Speaker 1: up in Daniel's freezer.
Speaker 3: Amazing, all right, all right, so all motion, because I've
Speaker 3: been listening, motion has to be defined relative to something else. Yeah,
Speaker 3: And is there like an obvious thing to compare your
Speaker 3: motion too for this question, or do you can just
Speaker 3: pick anything?
Speaker 1: No, the obvious thing to compare your emotion to is space.
Speaker 1: And people like to think about our motion through space.
Speaker 1: They like to think about the question how fast are
Speaker 1: we moving? How fast is the Earth moving? And they
Speaker 1: imagine that we are moving through some medium. But space
Speaker 1: is really weird. Space is not something that has a
Speaker 1: frame of reference. You cannot measure your motion relative to space.
Speaker 1: You can only measure your motion relative to other stuff
Speaker 1: in space, which you know already opens the door to
Speaker 1: deep philosophical questions like well then what is space anyway?
Speaker 1: And I think that it's really hard to hold in
Speaker 1: your mind an idea of what space is because you know,
Speaker 1: on one hand, we talk about it is like having
Speaker 1: things in it like fields and matter, which is excitation
Speaker 1: of those fields, which are a property of space. Right,
Speaker 1: So it feels like there's stuff in space. I'm talking
Speaker 1: about these fields, and they're oscillating, they're doing things. But
Speaker 1: on the other hand, I'm also telling you you can't
Speaker 1: measure your velocity relative to those fields. They somehow exist,
Speaker 1: they're out there, they're part of this medium. It's a
Speaker 1: kind of an ether theory because it's not an ether
Speaker 1: that provides a frame of reference. That's really the crucial thing.
Speaker 1: And so velocity is measured between two objects, and space
Speaker 1: is not an object. It's kind of a thing, but
Speaker 1: it doesn't have this property that you can measure your
Speaker 1: velocity relative to that thing.
Speaker 3: And if you really have smoked a lot of banana pills,
Speaker 3: you should listen to one of our early episodes What
Speaker 3: is Space, where you dig into that for a whole hour,
Speaker 3: and that is some trippy stuff.
Speaker 1: And it's amazing that we don't really have a solid
Speaker 1: answer to this question. Like we have these theories and
Speaker 1: they work, and we can pull apart the philosophical implications
Speaker 1: of them. What does it mean that you can't measure
Speaker 1: your velocity relative to the thing in which light travels,
Speaker 1: for example, But we don't still really understand what it
Speaker 1: is and how it all works, and we can't pull
Speaker 1: it all together. And like quantum mechanics, view of space
Speaker 1: and general relative to view of space are very different.
Speaker 1: And so somebody please give us a theory of quantum
Speaker 1: gravity which answers all of these questions. But you know,
Speaker 1: it means something to say that velocity is relative. It
Speaker 1: means that velocity is not a property of an object.
Speaker 1: It's a property of a pair of objects. So any
Speaker 1: physics question you ask start out saying, say I'm in
Speaker 1: a ship and I'm going ninety percent of the speed
Speaker 1: of light, I'm going to ask you with respect to
Speaker 1: what it doesn't mean anything to say I'm going ninety
Speaker 1: percent of the speed of light, because you can be
Speaker 1: going ninety percent of the speed of light relative to
Speaker 1: one observer, and ten percent of the speed of light
Speaker 1: relative to another, and zero relative to another who's standing
Speaker 1: next to you on the ship, right, Your velocity only
Speaker 1: means something if you say who's measuring it? Because again,
Speaker 1: there is no absolute frame, no preferred velocity in the universe.
Speaker 3: And for those of us who have to admit that
Speaker 3: they had a little trouble remembering the difference between velocity
Speaker 3: and acceleration and motion and all of those terms when
Speaker 3: they started physics. Let's do a real quick recap motion, velocity, acceleration.
Speaker 3: What do these terms mean? Yeah, great for the purpose
Speaker 3: of this discussion.
Speaker 1: Yeah, so let's start with location, right, because that's the
Speaker 1: basic thing. You know. Location also is relative, Like I
Speaker 1: can say, like if I live in a one dimensional universe,
Speaker 1: I can say, over here location x equal zero. Then
Speaker 1: I can measure how far I am from that location
Speaker 1: from zero. So I'm at x equals five. You're at
Speaker 1: x equal zero. I can say we're five units apart. Right,
Speaker 1: But somebody else could have put x equal zero somewhere else,
Speaker 1: So my location would be different if they're measuring it
Speaker 1: or if I'm measuring it. So even location itself is
Speaker 1: relative because there's no like glowing tick marks in space.
Speaker 1: There's no like origin where the universe says this is
Speaker 1: zero or that is zero. It's just relative. So that's
Speaker 1: the basic measurement that's your location. Velocity is how your
Speaker 1: location changes with time. I was at x equals five
Speaker 1: one second later, I'm at xequal six. Then I'm at
Speaker 1: xequal seven. That's my velocity. But that's why velocity is relative,
Speaker 1: because it's a measurement of how location is changing, and
Speaker 1: location is just relative.
Speaker 2: Got it all?
Speaker 1: That's great? And what that means, for example, is that
Speaker 1: any experiment you can do can't measure your velocity relative
Speaker 1: to space. So if I build some contraption and it
Speaker 1: does something the wiz bang experiment, and I run my
Speaker 1: experiment and does a wiz in a bang, cool, and
Speaker 1: then I put it in a box. Then I speed
Speaker 1: it up and I get it going really fast relative
Speaker 1: to Earth, and I do the same experiment, it should
Speaker 1: still whiz in bang in exactly the same way. The
Speaker 1: fact that it has some velocity now relative to Earth
Speaker 1: doesn't change the physics inside the box. And it can't
Speaker 1: because if it did, then somehow I'd be measuring the
Speaker 1: velocity like within the box without measuring my distance relative
Speaker 1: to Earth. You can only measure your velocity relative to
Speaker 1: Earth by measuring your distance relative to Earth. So if
Speaker 1: the experiment just does the wiz bang experiment, if it
Speaker 1: does not like a ruler to measure the distance to Earth,
Speaker 1: then it should get the same result regardless of its
Speaker 1: location or its velocity relative to Earth. And in fact,
Speaker 1: you can promote this to a general principle. You can
Speaker 1: say you can't measure your location or your velocity. If
Speaker 1: you're like trapped in inside a box with no access
Speaker 1: to the outside universe, there's nothing you can do to
Speaker 1: measure your velocity relative to stuff in the outside universe
Speaker 1: because your velocity only has meaning relative to that stuff,
Speaker 1: and if you don't have access to that stuff, you
Speaker 1: can't measure your velocity. Does that all make sense?
Speaker 2: So you could still measure your velocity with respect to
Speaker 2: stuff in the box, right, but not? Okay, got it.
Speaker 1: But the amazing thing is that that's not true for acceleration. Right.
Speaker 1: So we talked about location, and we talked about how
Speaker 1: change in location is velocity. You can also talk about
Speaker 1: the change in velocity. So for those mathematically inclined, these
Speaker 1: are derivatives. Right. Velocity is the first derivative of location.
Speaker 1: Acceleration is the second derivative of location. It's how velocity
Speaker 1: is changing with time. Now, acceleration is something that's absolute.
Speaker 1: If you are in a box, you can measure whether
Speaker 1: that box is accelerating or not. It's very easy. You
Speaker 1: just like draw a ball. If the box is not accelerating,
Speaker 1: the ball will float in front of you. If the
Speaker 1: box is accelerating, the ball will move to the back
Speaker 1: of the box. If the box has a negative acceleration,
Speaker 1: like somebody's putting on the brakes, the ball will move
Speaker 1: to the front of the box. It's just like having
Speaker 1: a bowling ball in the back of a truck. You
Speaker 1: can use that bowling ball to tell if you're accelerating
Speaker 1: or decelerating. You can't use it to measure the velocity
Speaker 1: of the truck, but you can use it to measure
Speaker 1: the acceleration. So acceleration is absolute, but velocity is not.
Speaker 2: Okay, I get that.
Speaker 3: It still feels kind of counterintuitive because if it's the
Speaker 3: second derivative of location, it still feels like location should matter.
Speaker 3: But your box example, I understand how that works.
Speaker 1: And you know, for those philosophically inclined, you might wonder, like, well,
Speaker 1: why is that Why it's taking one more derivative make
Speaker 1: it absolute instead of relative. And that's a whole digression.
Speaker 1: But very briefly, acceleration is philosophically very similar to curvature. Right.
Speaker 1: The effect acceleration is almost exactly the same as the
Speaker 1: effect of space time curvature. In fact, acceleration can create
Speaker 1: event horizons. There are scenarios for example, where if you
Speaker 1: are constantly accelerating, you can outrun photons, effectively making like
Speaker 1: an event horizon relative to photons. That's a whole other
Speaker 1: episode we should dig into.
Speaker 2: Wait wait, wait, whoa, whoa. Did you say something can
Speaker 2: go faster than light?
Speaker 1: No, you can never go faster than light, but you
Speaker 1: can outrun a photon. So, for example, if you take
Speaker 1: off in your spaceship and you're moving slowly but you're
Speaker 1: accelerating constantly, if I then try to shoot a laser
Speaker 1: beam to catch you, it will never catch you. If
Speaker 1: you're accelerating constantly, you can outrun that photon. So it's
Speaker 1: not like if we have a race Kelly versus the photon,
Speaker 1: that you'll go faster than the photon. You'll never go
Speaker 1: faster than light, but I can't catch you with a
Speaker 1: photon if you have left earlier and are constantly exciting.
Speaker 2: Okay, all right, Yeah.
Speaker 1: So acceleration is weird. It's kind of like curvature. It's
Speaker 1: a whole thing in general relativity. But the point is
Speaker 1: that velocity is relative, and this leads to some sort
Speaker 1: of weird things like, for example, what if it's just
Speaker 1: you in the universe and nothing else, imagine an empty
Speaker 1: universe with just you. What's your velocity? There is no velocity,
Speaker 1: not that your velocity is zero. Velocity has no meaning
Speaker 1: because it's a property of pairs of objects. In an
Speaker 1: empty universe, there are no pairs of objects.
Speaker 2: It sounds very lonely.
Speaker 1: It's like being married to yourself.
Speaker 3: Oh, I can't imagine to be around for very long either,
Speaker 3: in the vastness of space. If it was just you,
Speaker 3: it would be a short, lonely existence.
Speaker 1: Always thinking about the practical aspects of weird philosophical hypotheticals,
Speaker 1: love it.
Speaker 2: Always thinking of death is pretty much where it goes to.
Speaker 1: And conversely, you can never imagine a scenario where you
Speaker 1: are at rest relative to a photon because photons always
Speaker 1: have velocity of the speed of light relative to everything.
Speaker 1: So you can never pull up alongside of photon and say, oh, look,
Speaker 1: this is what a photon looks like when it's at rest,
Speaker 1: because the photon is pure motion.
Speaker 2: If you pulled up alongside a photon, what kind of
Speaker 2: music do you think it would be?
Speaker 4: Listening to?
Speaker 1: Classic rocks?
Speaker 3: Ah?
Speaker 2: Nice, Yeah, all right, let's go with that.
Speaker 1: Yeah, or quantum punk. I'm not sure actually, so What
Speaker 1: this means is, you know, space has no texture, there's
Speaker 1: no reference frame. It feels like space is a thing,
Speaker 1: but it's not, and it's the same thing everywhere. We
Speaker 1: mentioned earlier the idea of space having a boundary and
Speaker 1: its connection to conservation and momentum, and this tells you
Speaker 1: that the idea that space has no reference frame has
Speaker 1: really important consequences. Like Nother's theorem is what tells us
Speaker 1: that space being the same everywhere leads to conservation of momentum,
Speaker 1: which is why space have an edge to it would
Speaker 1: lead to a violation of the conservation of momentum. So
Speaker 1: the fact that we never see violations of the conservation
Speaker 1: of momentum tells us space really is the same everywhere,
Speaker 1: and we've never noticed that. Like if you do an
Speaker 1: experiment here and you do an experiment there, you get
Speaker 1: different answers. Your whiz bang experiment always whizzes and bangs
Speaker 1: the same way no matter where you are. So velocity
Speaker 1: and location are purely relative, right, And this means that,
Speaker 1: for example, it doesn't mean anything to ask are you motionless?
Speaker 1: Can we be motionless with respect to space? Right? Because
Speaker 1: you can't measure your velocity relative to space.
Speaker 2: At all, because there's no space, man.
Speaker 1: Yeah, exactly. No space is a thing. It just doesn't
Speaker 1: have a velocity. So in one sense, it's like trivial
Speaker 1: to be motionless. You just say, well, I'm gonna choose
Speaker 1: my frame of reference to be me, and I'm gonna
Speaker 1: measure my velocity relative to myself. Okay, look, I'm going zero.
Speaker 3: Yay.
Speaker 1: It's also kind of trivial to have a velocity near
Speaker 1: the speed of light. Choose any of the zillions of
Speaker 1: cosmic rays that are approaching the Earth at nearly the
Speaker 1: speed of light and say that's my reference frame.
Speaker 2: I do go fast.
Speaker 1: Yes, And from the point of view of those cosmic rays, Kelly,
Speaker 1: you are moving towards them at nearly the speed of light,
Speaker 1: So buckle.
Speaker 2: Up, way to go me. I was also fast that
Speaker 2: time I jumped out of a plane that.
Speaker 1: Was fast too ooh fast, and then slow I hope.
Speaker 3: Yeah, yeah, yeah yeah yeah, and then not split not
Speaker 3: very slow, not fast and slow than very slow.
Speaker 2: But anyway, all right.
Speaker 3: So we have learned that space is confusing and you
Speaker 3: need to be careful what you're talking about your speed
Speaker 3: relative to And when we get back from the break,
Speaker 3: we're going to talk about our speed relative to lots
Speaker 3: of stuff in the universe.
Speaker 2: All right, we're back.
Speaker 3: Let's start by talking about our speed relative to let's say,
Speaker 3: my favorite planet in the Solar System.
Speaker 2: Earth.
Speaker 1: Yeah. Earth is already kind of complicated. You might think, well,
Speaker 1: I'm standing on Earth. My velocity is zero, right, but
Speaker 1: the Earth itself is spinning, right, So which part of
Speaker 1: the Earth are we talking about? Yes, if you say
Speaker 1: the part of the Earth that's under your feet, your
Speaker 1: velocity is zero, that's kind of boring. But if you
Speaker 1: say the center of the Earth, then at the surface
Speaker 1: of the Earth you're already moving quite fast. Now, at
Speaker 1: the north pole you're not moving at all due to
Speaker 1: the spin, But at the equator, the Earth is spinning
Speaker 1: at sixteen hundred kilometers per hour. Woa, Like, that's not
Speaker 1: a small amount of motion.
Speaker 3: No, you know, I realize that we don't feel that,
Speaker 3: but it is kind of amazing that we don't feel that.
Speaker 2: That is pretty quick.
Speaker 1: Yeah, And it's a little counterintuitive because this is acceleration. Right.
Speaker 1: To move in a circle at constant velocity requires acceleration
Speaker 1: because velocity is a vector, and if it's changing direction,
Speaker 1: even if its magnitude is constant. Then moving in a circle,
Speaker 1: your velocity doesn't change, but the direction of your velocity changes,
Speaker 1: and that requires acceleration. Like if you have a rock
Speaker 1: moving through space at ten meters per second and you
Speaker 1: want it to be going a different direction at ten
Speaker 1: meters per second, you've got to give it a push.
Speaker 1: That's a force, that's acceleration. You might think I should
Speaker 1: be able to measure that, and you can. Actually you
Speaker 1: can measure the rotation of the Earth because it affects
Speaker 1: how much you weigh, Like at the equator, you weigh
Speaker 1: a little bit less than you do at the north
Speaker 1: pole because you're being flung out a little bit. Like
Speaker 1: if you are on a merry go round and somebody
Speaker 1: spinning it faster and faster and faster, there's this apparent
Speaker 1: force that's pushing you away from the center. Right, that's
Speaker 1: due to the acceleration, which, as we were saying earlier,
Speaker 1: is something that you can measure. And so you can
Speaker 1: actually measure this acceleration.
Speaker 3: How long did it take for us to like figure
Speaker 3: out and accept that, because it's like that's all pretty counterintuitive.
Speaker 1: Yeah, it is counterintuitive, and it took a long time
Speaker 1: before people accepted this. When it was first proposed, people
Speaker 1: were like, what, that's crazy, And it took like having
Speaker 1: fairly precise experiments in order to be able to measure it.
Speaker 1: There are a few different effects from this kind of rotation.
Speaker 1: There is the fact that you weigh less at the equator,
Speaker 1: and there's also this Coriolis force, which is effectively like
Speaker 1: a sideways force. If, for example, you drop something from
Speaker 1: like one hundred and fifty meters, then it doesn't go
Speaker 1: straight down. It departs from straight down by like a
Speaker 1: millimeter or so, so it takes kind of a precise measurement. Actually,
Speaker 1: that was a question I was asked during my oral
Speaker 1: exam in grad school to like calculate that on the
Speaker 1: spot on a chalkboard in front of the professor's I
Speaker 1: remember that. Oh my god, that was terrible, But I
Speaker 1: think I got it right.
Speaker 2: They let you through one way or another.
Speaker 1: They did. Yes. In eighteen fifty one, the foll called pendulum,
Speaker 1: which is basically like a lead filled brass sphere suspended
Speaker 1: on a really long string, in this case sixty seven meters.
Speaker 1: You can see it rotate at a rate depending on
Speaker 1: its latitude, so it's like a pendulum that swings back
Speaker 1: and forth, but it also processes. If you ever see
Speaker 1: these pendulums in like a science museum, like a really
Speaker 1: long string, and it doesn't just go back and forth
Speaker 1: like it goes back and forth, but also the back
Speaker 1: and forth itself sort of rotates around and like leaves
Speaker 1: marks in the sand. That's because of the rotation of
Speaker 1: the Earth, and that depends on the latitude. So if
Speaker 1: you do that experiment at the equator or you do
Speaker 1: that at the North Pole, you get a different answer
Speaker 1: because of the difference in tripetal acceleration.
Speaker 3: This kind of stuff is amazing and like, so I
Speaker 3: have you know, I got to be honest, like I
Speaker 3: wouldn't want to spend my life creating precision weights or precision.
Speaker 2: Instruments and stuff. But like, so you know when you've said.
Speaker 3: If you took your weight at the equator and at
Speaker 3: the North Pole, they'd be different. But of course you
Speaker 3: don't actually mean like you weight, because the journey from
Speaker 3: the North Pole to the equator, you know, you'd probably
Speaker 3: like change your weight. You know, you'd eat a big
Speaker 3: meal in between balla.
Speaker 2: So so you're like, I'm sure what you mean.
Speaker 3: You're like you'd have like a you know, twenty kilogram
Speaker 3: weight or that you'd you know, compare at both locations
Speaker 3: and like.
Speaker 1: And you wouldn't feed any snacks to your twenty kilogram
Speaker 1: weight along the way.
Speaker 2: Yeah, exactly right.
Speaker 3: No Cheetos, No, none of those stroop waffles that they're
Speaker 3: giving on the flights now, which I am so excited
Speaker 3: that that's a new thing you can get on flights.
Speaker 1: Are you saying I couldn't go from the Equator to
Speaker 1: the North Pole without resisting a stroop waffle?
Speaker 2: I could not, But but what I'm saying is.
Speaker 1: I couldn't either.
Speaker 2: Yeah, So eighteen fifty one is one of the experiments
Speaker 2: you were talking about, And so back then it wouldn't
Speaker 2: just be.
Speaker 3: A couple hours to get from the equator to the
Speaker 3: North Pole. It would be you know, like half a
Speaker 3: year or more or something. You make that journey, so
Speaker 3: you change your weight during that time, but your twenty
Speaker 3: kilogram mass might not. But like, there's so many things
Speaker 3: we learned about the world by getting really good at
Speaker 3: making precision measurements, and like, yeah, we're such a boring
Speaker 3: and amazing species, Like, way to go us for managing
Speaker 3: to do that kind of stuff, and anyway, props to
Speaker 3: props to humans.
Speaker 1: Yeah, props to nerds, you know, people who are like,
Speaker 1: I'm super interested in this. I'm going to get really
Speaker 1: good at that, and I'm going to somehow manage to
Speaker 1: take my twenty kilogram weight from the equator to the
Speaker 1: north pole without getting caramel smeared on it or something. Yeah, right, right,
Speaker 1: thank you nerds.
Speaker 2: That's right.
Speaker 1: Yeah. And it's because of the diversity of people's interest
Speaker 1: in weird stuff that we know all these amazing things
Speaker 1: about the universe. So yay. Yeah, So that's how we
Speaker 1: know that the Earth is spinning. Of course, we can
Speaker 1: also see it from space, et cetera. So the Earth
Speaker 1: is spinning at sixteen hundred kilometers per hour at the equator.
Speaker 1: The Earth itself, of course, is moving relative to the Sun.
Speaker 1: That's thirty kilometers per second, right, So any fast again
Speaker 1: relative to the Sun. And this again is motion in
Speaker 1: a circle, and motion in a circle requires constant acceleration
Speaker 1: to maintain the same magnitude of velocity. So this is
Speaker 1: also something you could measure, like even if you were
Speaker 1: in a box, if you were orbiting a star, you
Speaker 1: could tell you were orbiting a star because that is
Speaker 1: an acceleration.
Speaker 3: Well, now I want to know when and how we
Speaker 3: figured that out, but it's not on your outline, so
Speaker 3: I'm putting you on the spot.
Speaker 1: Well, this all goes back to geocentrism and heliocentrism, right.
Speaker 1: We had these two theories of the organization of the
Speaker 1: solar system, one in which the Earth was at the
Speaker 1: center and everything moved around it, another one where the
Speaker 1: Sun was at the center and everything moved around it.
Speaker 1: And I think it's fascinating that the Greeks actually had
Speaker 1: the idea for heliocentrism. People often say, oh, the Greeks
Speaker 1: just assumed that the Earth is at the center. They
Speaker 1: considered heliocentrism. They considered the idea that the Sun was
Speaker 1: at the center, and they even had an idea for
Speaker 1: how to check. They thought that they could look at
Speaker 1: the stars and if the Earth was moving around the Sun,
Speaker 1: they would see the stars wiggle in the sky. And
Speaker 1: they were right, they should be seeing that. That's called parallax.
Speaker 1: But they were wrong about the distance to the stars.
Speaker 1: They thought the stars were pretty close so that they
Speaker 1: should be able to see the parallax. And when they
Speaker 1: didn't see the parallax, they concluded incorrectly that the Earth
Speaker 1: wasn't moving. If they had known the stars were so
Speaker 1: far away, they would have realized that you can't use
Speaker 1: parallax to discover the motion of the Earth unless you
Speaker 1: have really fine telescopes. And we weren't able to do
Speaker 1: that until like the eighteen hundreds.
Speaker 2: Oh man, how frustrating. They were so close.
Speaker 1: I know, they really on the edge of this. They
Speaker 1: made the wrong assumption, led them down the wrong path. Anyway,
Speaker 1: a couple thousand years later people figured out that the
Speaker 1: Earth is moving around the Sun, but not by measuring
Speaker 1: the acceleration the local acceleration of the Earth, but by
Speaker 1: seeing the phases of Venus and then also getting more
Speaker 1: precise measurements of the motion of the planets, so we
Speaker 1: could see the geocentrism didn't really work, though it worked
Speaker 1: surprisingly well even with cycles and epicycles.
Speaker 3: But then how did we figure out the thirty kilometers
Speaker 3: per second figure?
Speaker 1: Oh? There, you could just use Kepler's laws, like if
Speaker 1: you know the period of the planet and the distance
Speaker 1: to the Sun, then you can figure out our local velocity.
Speaker 1: It's just basic kinematics. So we've known that for hundreds
Speaker 1: of years.
Speaker 3: Folks, you should all know that Daniel didn't write that
Speaker 3: down in his notes. He just has the soul in
Speaker 3: his head. He's a smart guy, all right, keep going.
Speaker 2: This is basic stuff, Kelly. You didn't have to be
Speaker 2: a jerk face.
Speaker 4: I was just something nice.
Speaker 1: I'm just trying to deflect your compliment. Thank you very much,
Speaker 1: all right.
Speaker 2: Yeah, that's what you're supposed to say, Daniel.
Speaker 1: And so there are these videos out there that try
Speaker 1: to break people out of the mental image of the
Speaker 1: Earth moving around the Sun and the Sun being stationary.
Speaker 1: And I think that's cool, because it's true that the
Speaker 1: Sun is not stationary with respect to the galaxy. But
Speaker 1: it doesn't really mean anything to say the Sun is
Speaker 1: moving through space, right, It's always relative to something. So
Speaker 1: even if you have like a stationary image of the
Speaker 1: Solar System, if you're approaching the Solar System with the velocity,
Speaker 1: then the Sun is in motion relative to you. Like
Speaker 1: if you are on three I at lists the Interstellar Visitor,
Speaker 1: then the Sun is in motion. Or if you put
Speaker 1: yourself at the center of the galaxy, then the Sun
Speaker 1: is in motion. So it's true that you can move
Speaker 1: to a frame where the Sun is in motion instead
Speaker 1: of a frame where the Sun is at rest. But
Speaker 1: it's a little misleading to suggest that, like, oh, really,
Speaker 1: the Sun is moving through space. It's moving relative to something,
Speaker 1: and the most interesting thing it's moving with respect to
Speaker 1: is the center of the galaxy.
Speaker 2: And how fast is it moving with respect to the
Speaker 2: center of the galaxy.
Speaker 1: It's moving eight hundred thousand kilometers per hour around the
Speaker 1: center of the galaxy, which is like a big number,
Speaker 1: but you know, it doesn't really affect your life because
Speaker 1: think about it the other way. It means that the
Speaker 1: center of the galaxy is moving eight hundred thousand kilometers
Speaker 1: per hour relative to us, but it's really far away,
Speaker 1: so like, who cares how fast it's moving relative does
Speaker 1: doesn't mean anything for us here on Earth, though it
Speaker 1: is fun to think about, like how long it takes
Speaker 1: the Sun to go around the center of the galaxy.
Speaker 1: It takes like a couple hundred million years for the
Speaker 1: Sun to do one orbit. So if you think about
Speaker 1: that as like a galaxy year, the way that like
Speaker 1: the Earth takes one Earth year to go around the Sun,
Speaker 1: the Sun takes one like galaxy year to go around
Speaker 1: the center of the galaxy, then our solar system is
Speaker 1: about twenty galaxy years old.
Speaker 2: She's almost old enough to drink. I wonder what her
Speaker 2: preferred drink's going to be. It might be tea, maybe
Speaker 2: she's not into alcohol.
Speaker 1: Cosmopolitan maybe, oh, cute love it, that's probably what it's
Speaker 1: going to be.
Speaker 4: Yeah.
Speaker 1: I think that's pretty cool because it means the galaxy
Speaker 1: has not had that many rotations. It's already formed all
Speaker 1: of the structure and the spiral arms and all that
Speaker 1: stuff without spinning more than fifty times. Right, that's kind
Speaker 1: of mind blowing.
Speaker 2: That is kind of mind blowing. How many turns around
Speaker 2: the galaxy is it going to have? Do you know?
Speaker 1: Well, that's a great question. Well, we're scheduled for a
Speaker 1: collision with Andromeda in a few billion years, and that's
Speaker 1: only another like ten ish or fifteen ish rotations.
Speaker 3: Change the subject all messed up again? No, no, I
Speaker 3: don't want to hear this all right, moving on, And.
Speaker 1: Of course you can ask, well is the galaxy in motion?
Speaker 1: And you have to ask is it motion relative to what?
Speaker 1: And so there's a bunch of different choices you can
Speaker 1: make here. You could choose the local galaxy cluster and
Speaker 1: say we're orbiting around the center of mass and the
Speaker 1: galaxy cluster. But I think here we should like skip
Speaker 1: forward to the biggest picture question and say, like, is
Speaker 1: there any kind of frame out there you could use
Speaker 1: that's like the center of stuff? Because on one hand,
Speaker 1: there is no preferred frame in the universe for space.
Speaker 1: You can't say I'm moving through space with respect to anything,
Speaker 1: But there is a bunch of stuff in the universe,
Speaker 1: and you can ask like how fast am I moving
Speaker 1: relative to all the stuff in the universe. So this
Speaker 1: feels like a weird kind of card trick. You have
Speaker 1: no velocity relative to space, but I can then fill
Speaker 1: space with a bunch of stuff like space was filled
Speaker 1: with the hot dense plasma a few billion years ago,
Speaker 1: and that stuff has no velocity relative to space either, right,
Speaker 1: Because you can't have velocity relative to space, but it
Speaker 1: doesn't mean that Now I can ask like, how fast
Speaker 1: on going relative to that stuff? Right? So it's sort
Speaker 1: of like I put wallpaper on the wall and I said,
Speaker 1: you can't ask your velocity relative to the wall, but
Speaker 1: you can ask your velocity relative to the wall paper. Right.
Speaker 2: Yeah, it feels like cheating.
Speaker 1: It does feel like cheating, but in this case.
Speaker 3: The wallpaper isn't there, right, or because the plasma's not
Speaker 3: there right, or it was a long time ago, but
Speaker 3: it's not there now.
Speaker 1: Yeah, so the plasma's not there anymore. And really, you know,
Speaker 1: the wallpaper has no velocity relative to the wall. It's
Speaker 1: just like there's something else in the room with us. Now,
Speaker 1: so we can finally ask do we have a velocity
Speaker 1: relative to something? It's like, go back to that empty universe.
Speaker 1: You have no velocity. It means nothing to have a velocity.
Speaker 1: Then I fill that universe with stuff. Now you have
Speaker 1: a velocity relative to all of that stuff. And that
Speaker 1: stuff has no velocity relative to anything else in the
Speaker 1: universe except for you or itself. It has no velocity
Speaker 1: relative to space. Right, But there is a preferred frame
Speaker 1: in the universe. That frame is the frame of all
Speaker 1: the stuff in the universe. And so you can't ask
Speaker 1: about your velocity relative to space, but you can ask
Speaker 1: about your velocity relative to the stuff in the universe.
Speaker 3: And why is that the preferred Why is the frame
Speaker 3: that doesn't actually exist and is a mind trick the
Speaker 3: preferred frame.
Speaker 1: Because it's the only one we can think of.
Speaker 3: Okay, all right, there's no other option, right, digging the honesty,
Speaker 3: you can either.
Speaker 1: Give up or you can choose this one, and neither
Speaker 1: a satisfactory.
Speaker 3: And how fast are we going relative to the space wallpaper?
Speaker 1: The answer is, we don't know. We actually have two
Speaker 1: different measurements, and they disagree by a lot.
Speaker 2: What All right, let's take a break, and when we
Speaker 2: come back, boy, things even more confusing.
Speaker 1: You thought this was going to be a simple episode,
Speaker 1: didn't you.
Speaker 4: I hope so.
Speaker 3: And we're back, and we should have saved this episode
Speaker 3: for Halloween because we're going to talk about this spooky
Speaker 3: radio dipole anomaly.
Speaker 1: So we're interested in the question of how fast are
Speaker 1: we moving relative to all the stuff in the universe.
Speaker 1: Because you take an empty universe and you PLoP a
Speaker 1: bunch of stuff into it. Now there's a frame, right,
Speaker 1: the frame in which that stuff is at rest, and
Speaker 1: how do you measure that? Well, we're going to talk
Speaker 1: about two different ways of measuring it. One tries to
Speaker 1: measure our velocity relative to the stuff in the early universe.
Speaker 1: So brief history of the universe, A bunch of stuff
Speaker 1: happened that we don't understand at all, but somehow led
Speaker 1: to a universe filled with a very hot dense plasma.
Speaker 1: That plasma is a and then it's cooling as the
Speaker 1: universe expands. Suddenly it cools enough for the protons and
Speaker 1: electrons to get together and make neutral hydrogen, and the
Speaker 1: universe suddenly becomes transparent, which means all the light that
Speaker 1: previously was being absorbed just after it was emitted now
Speaker 1: flies free, free lights, and the universe has been transparent
Speaker 1: ever since then, which means we can still see that light.
Speaker 1: We can see evidence of that hot dense plasma, and
Speaker 1: that's what's called the cosmic microwave background radiation. It's microwave
Speaker 1: because that's the frequency we see it at. It was
Speaker 1: a very very high frequency because very hot plasma's emit
Speaker 1: a very high frequency light, but it's been stretched out
Speaker 1: by the expansion of the universe to very long wavelengths
Speaker 1: and low frequency. So we can still see that light
Speaker 1: and we can see Doppler shifts in that light. Okay,
Speaker 1: so we can still see that light, which means basically
Speaker 1: we can look around and see that plasma right And
Speaker 1: you know, it's a little bit confusing to think about
Speaker 1: what part of the plasma we're seeing. If you look
Speaker 1: in one direction from Earth, you're seeing light that's been
Speaker 1: traveling basically fourteen billion years since it was emitted and
Speaker 1: just got to Earth. If you look in the other
Speaker 1: direction from Earth, you're seeing light that traveled to fourteen
Speaker 1: billion years since it was admitted and just got to Earth.
Speaker 1: So you're looking at bits of plasma that were like
Speaker 1: across the universe from each other. If you look all
Speaker 1: around the Earth, you're seeing light from a shell of
Speaker 1: plasma that emitted light in the direction where Earth was
Speaker 1: going to be and just arrived here now. And as
Speaker 1: time goes on, we see light from a different shell
Speaker 1: of plasma, a larger and larger shell, further and further
Speaker 1: away from us. But we're always going to see CMB
Speaker 1: light because the universe was filled with this plasma. So
Speaker 1: it's a great way to measure our velocity relative to
Speaker 1: the stuff in the universe back when the universe was
Speaker 1: filled with this plasma that conveniently all gave off this light.
Speaker 2: But so everything you just said made sense, but we're
Speaker 2: talking about in an anoma, So I feel like I
Speaker 2: wasn't supposed to understand all of it.
Speaker 1: No, you're still supposed to understand it, And the way
Speaker 1: we measure our velocity relative to that light is pretty simple.
Speaker 1: We just look to see if the light is blue
Speaker 1: shifted or red shifted. Because if you're moving towards something,
Speaker 1: frequency goes up. If you're moving away from something, frequency
Speaker 1: goes down. Wavelengths to get longer. And most of the time,
Speaker 1: when you look at a picture of the CMB, like
Speaker 1: on the internet, it looks like all these little red
Speaker 1: and blue dots, and what you're looking at there is
Speaker 1: not the raw CMB light. What you're looking at is
Speaker 1: that when they remove our velocity effect, if you look
Speaker 1: at the raw CMB, it's like blue on one side
Speaker 1: and red on the other. Because we are moving relative
Speaker 1: to the CMB, we're not at rest relative to it,
Speaker 1: so they usually subtract this part out. Because we're moving
Speaker 1: at three hundred and seventy kilometers per second through the CMB,
Speaker 1: so pretty fast.
Speaker 2: Yeah, look at us go.
Speaker 1: So that's sort of the closest we can come to
Speaker 1: saying how fast are we moving through this stuff in
Speaker 1: the universe. That's a big number, and people would like
Speaker 1: to know is that really correct? Are we making a mistake?
Speaker 1: And you know, what we're measuring there is our velocity
Speaker 1: relative to the stuff that used to be in the
Speaker 1: universe fourteen billion years ago. We can do a cross
Speaker 1: check by looking at the stuff in the universe now
Speaker 1: and asking, well, how fast are we moving relative to
Speaker 1: like distant galaxies for example, and all that stuff, And
Speaker 1: so we can make the same measurement. We can look
Speaker 1: for galaxies and we can ask, like, is there like
Speaker 1: blue shifted or red shifted and that should make a
Speaker 1: map across the sky of like blue shifted versus red
Speaker 1: shifted galaxies and tell us which direction are we going
Speaker 1: and how fast relative to all the galaxies out there
Speaker 1: in the universe. Not relative to space again, but relative
Speaker 1: to the stuff in the universe. And we should get
Speaker 1: the same answer because the galaxies out there in the universe,
Speaker 1: they came from this CMB stuff, right, that's stuff clumped
Speaker 1: together and made structure and eventually formed galaxies which spun
Speaker 1: for a few times before they collided with other galaxies,
Speaker 1: et cetera. So we should get the same answer, right.
Speaker 3: Well, so then why did we need to do all
Speaker 3: this CMB stuff if we could have just done it
Speaker 3: with the galaxies or it's just nice to double check.
Speaker 2: Replication is good.
Speaker 1: It's nice to double check, and you think you should
Speaker 1: get the same answer in two different ways, so you
Speaker 1: always got to do it both ways, right, got it?
Speaker 1: That's the worrier in you, like, h what have we
Speaker 1: got it wrong? Let's double check?
Speaker 2: Yeah, anxiety.
Speaker 1: And so they recently made this measurement. It's tough to do.
Speaker 1: You got to look at galaxies in the radio you
Speaker 1: have to subtract all sorts of other effects. Galaxies are
Speaker 1: not as spread out evenly as the CMB is, and
Speaker 1: so fascinatingly what they find is they measure the same
Speaker 1: direction of motion. So they agree. The CMB measurement and
Speaker 1: this radio galaxy measurement agree in the direction. But the
Speaker 1: radio galaxy suggests that we're moving two to five times
Speaker 1: faster than the CMB measurement.
Speaker 2: Says, oh, that's the anomaly.
Speaker 1: That's the anomally. It's called the radio dipole anomaly. A
Speaker 1: pretty recent measurement, and it's not understood like either. It
Speaker 1: means there's something very wrong with our understanding of the
Speaker 1: universe and how it's evolved over time. But that would
Speaker 1: be pretty surprising, because you know, we really think the
Speaker 1: CMB was there and it filled the universe and it
Speaker 1: was mostly smooth, and the universe has expanded isotropically, so
Speaker 1: it'd be pretty hard to explain how this happened. Most
Speaker 1: likely this is due to something boring like these radio
Speaker 1: galaxies have to be seen through a telescope. They're all
Speaker 1: in different locations, and the telescope isn't as good at
Speaker 1: spotting them in different locations, or the measurements of their
Speaker 1: velocity are not quite as accurate, or the calibration changes
Speaker 1: over the sky and maybe drifts as you move the telescope.
Speaker 1: So people are hunting for an explanation, and you know,
Speaker 1: usually what you do is like look for a boring explanation,
Speaker 1: like oh, every time somebody made ramen in the microwave
Speaker 1: in the breakroom, or data shifted by two points, right,
Speaker 1: that was an actual explanation for an astrophysical anology in Australia. Yeah,
Speaker 1: it was burritos in the microwave. So you always look
Speaker 1: for those kind of things before you conclude everything we
Speaker 1: know about the universe is, which is how the clickbait
Speaker 1: of many of these articles started out.
Speaker 2: Yeah.
Speaker 3: Well, also, you know, I think what we should conclude
Speaker 3: is that we need more money for better telescope. So
Speaker 3: that we can make all of these measurements more accurately.
Speaker 1: Exactly, And you should look at not just radio galaxies,
Speaker 1: but other kinds of galaxies and other stuff in the universe,
Speaker 1: and we should measure this kind of stuff in lots
Speaker 1: of different ways, because this is how you make discoveries. Folks.
Speaker 1: You think you understand something, you double check it, you
Speaker 1: get an answer that's not what you expected, and that
Speaker 1: forces you to reconsider your ideas about the universe. And
Speaker 1: you sometimes hear out there on the internet that, like,
Speaker 1: scientists will protect the narrative because they don't want to
Speaker 1: upend the apple cart in order to get grants, and like, no,
Speaker 1: absolutely not. Scientists love to upend the narrative. I know.
Speaker 1: That's why you see these crazy clickbait articles. It's a
Speaker 1: scientist trying to upend the narrative with their latest study
Speaker 1: which blows up our understanding of the universe.
Speaker 2: That's how you get the awards.
Speaker 1: Exactly. Scientists are not working together to protect some narrative.
Speaker 1: They're all working against each other, desperately using every trick
Speaker 1: they can to prove their friends and rivals wrong.
Speaker 2: Yeah, they're varying degrees of cutthroat.
Speaker 3: I don't want to make everybody sound like a jerk,
Speaker 3: but yes, I agree. If you can prove the dominant
Speaker 3: narrative wrong, that's when you get all the awards. All right, Well, Daniel,
Speaker 3: I am exhausted from all of this moving. Can we
Speaker 3: talk about Are there ways to not move? Ways to
Speaker 3: stay motionless in space?
Speaker 1: Yeah? So it doesn't mean anything to be motionless with
Speaker 1: respect to space, right, And people sometimes write to me
Speaker 1: about this question when they read time travel fiction and
Speaker 1: they're like, if I went back in time to fourteen
Speaker 1: ninety two, wouldn't the Earth be in a different place?
Speaker 1: And how come this science fiction novel I read didn't
Speaker 1: account for that? And you're giving me a funny look.
Speaker 1: This is a very common question. People think that they gotcha,
Speaker 1: and like, well, number one, time travel breaks a lot
Speaker 1: of physics anyway, and so maybe you should give the
Speaker 1: author a little bit of leeway on this detail. Also,
Speaker 1: it's question doesn't have any meaning, Like the Earth's location
Speaker 1: over time only means something relative to some axis, to
Speaker 1: some frame. So if you choose the frame of the Earth,
Speaker 1: then like you go back in time and you're still
Speaker 1: on the Earth. So yes, if you choose the frame
Speaker 1: of the Sun, the Earth would be in a different
Speaker 1: location in fourteen ninety two than it is now. But
Speaker 1: the question doesn't really have meaning.
Speaker 2: Oh, I see what they were getting at. Now, you
Speaker 2: would your time machine would dump you in the vastness
Speaker 2: of space instead of on Earth, then that.
Speaker 1: Would be bad.
Speaker 2: Okay, okay, all right, okay, But we've decided let it go.
Speaker 2: Enjoy your fiction.
Speaker 1: Number one, let it go, which is my approach when
Speaker 1: I read time travel fiction, as I rarely do for
Speaker 1: that reason. And number two, the question assumes some absolute
Speaker 1: reference frame, right, which just doesn't exist. And you might think, well,
Speaker 1: what is the right reference frame? And there is none, right,
Speaker 1: And the problem here is that time travel doesn't make
Speaker 1: any sense anyway, and so there's no like hard physics
Speaker 1: way to ask that question. But you can be motionless
Speaker 1: with respect to other stuff, which can be cool, like,
Speaker 1: for example, you can be motionless with respect to a
Speaker 1: point on the Earth's surface, right, like.
Speaker 2: A point on the Earth's surface.
Speaker 1: If, for example, you want to build a space elevator,
Speaker 1: you want that space elevator to be connected to the
Speaker 1: Earth by a cable, and so you'd like it to
Speaker 1: be effectively in geosynchronous orbit above someplace, hopefully on the
Speaker 1: equator that you built this thing, and so that's geosynchronous orbit.
Speaker 1: We have no motion relative to the Earth's surface. You're
Speaker 1: still in orbit, and it's still acceleration your velocity relative
Speaker 1: to the center of the Earth. But you can have
Speaker 1: no motion relative to the Earth's surface.
Speaker 3: Can I tell you a fun story about Yes, you
Speaker 3: can space elevators.
Speaker 2: I'll try I'll keep it. I'll try to keep it short.
Speaker 2: No do so.
Speaker 3: The bit the hard thing about making a space elevator
Speaker 3: is trying to come up with a material for the
Speaker 3: cable that is strong enough to hold the elevator, but
Speaker 3: also isn't so heavy that you're just like lifting the
Speaker 3: cable a whole time, right, And so carbon nanotubes might
Speaker 3: one day maybe work. What we have it made a
Speaker 3: continuous one that's long enough. But even if you did,
Speaker 3: what you'd really have to worry about is if it
Speaker 3: ever got struck by lightning, that could, like you the
Speaker 3: game over, Like it could destroy the cable. And so
Speaker 3: I was talking to somebody about what to do about that,
Speaker 3: and their answer was, well, you know, there's this part
Speaker 3: of the ocean that's never recorded.
Speaker 2: A lightning strike got to be kidding me.
Speaker 1: You know that meme where they have the airplane and
Speaker 1: like airplanes that return only have hits in these locations,
Speaker 1: like the survivor effect meme.
Speaker 4: Yeah, it's basically that one.
Speaker 1: Wow.
Speaker 3: I think that wasn't just a meme. I think that
Speaker 3: was actually like a study during World War one or two. Yeah, yeah, yeah, yeah, okay, anyway, yeah, yes.
Speaker 2: Yes, that cracked me up.
Speaker 3: I'm like, all right, fingers crossed, there's never any lightning
Speaker 3: here again. And then I think you also wanted the
Speaker 3: ability to be able to move it a little bit
Speaker 3: in case a storm came through.
Speaker 1: Well, I think the terrifying thing is you guys pointed
Speaker 1: out in your book soon is is what happens when
Speaker 1: the cable snaps, because basically, now you have this like
Speaker 1: kill wire moving at high velocity like somehow or us
Speaker 1: the Earth's surface, and like yikes.
Speaker 3: Yeah right, or if somebody decides to snip your wire,
Speaker 3: forget if there's lightning, just like a terrorist cutting your wire. Okay, anyway,
Speaker 3: no more doomsday scenarios relative to space elevators. Let's talk
Speaker 3: about lagrange points because I always found these slightly confusing,
Speaker 3: but you can clear it up for me.
Speaker 1: Well, what I'm confused because I call them lagrange points.
Speaker 3: Look at you, nobody. Nobody expects me to say it right.
Speaker 3: They expect you to say it right. That's your responsibility,
Speaker 3: not mine.
Speaker 1: Well, it depends. Are they named after, you know, Jean
Speaker 1: Louis Lagrange or are they named after the city in
Speaker 1: Texas or the Zzy Top song or you know, I.
Speaker 2: Think the zz Top song probably.
Speaker 1: Nice.
Speaker 3: Now that we've both done that together, I think we've
Speaker 3: made this joke before and we'll probably make it.
Speaker 1: Again, probably because that's how our memories work.
Speaker 2: I look for.
Speaker 1: Yeah, there are these fun points where you can be
Speaker 1: at rest relative to the Earth Sun system. Like, for example,
Speaker 1: if you are the James Webb Space Telescope and you
Speaker 1: don't want to be in orbit or on the Earth
Speaker 1: because you need to be super duper cold, you can
Speaker 1: choose to be at lagrange point two, which is on
Speaker 1: the other side of the Earth from the Sun, where
Speaker 1: all the gravitational effects of the Earth and the Sun
Speaker 1: cancel out, and so you could just sort of like
Speaker 1: hang out there.
Speaker 3: Yeah, so I guess so when I look, all right,
Speaker 3: so I'm looking at the diagram that you provided, and
Speaker 3: so you've got this spot that's on the far side
Speaker 3: of the Earth and on the far side of the Sun.
Speaker 2: And I guess I always kind of feel like, why doesn't.
Speaker 3: It just drift away? But I guess you still have
Speaker 3: the gravity pulling it in. I'm not sure I have
Speaker 3: a really great question to ask here, just kind.
Speaker 1: Of Well, so imagine that you wanted to be in
Speaker 1: the Earth's orbit. Right, So you have Earth and it's
Speaker 1: orbiting the Sun, and you're like, hey, I want to
Speaker 1: join the Earth's orbit. Where could you be in Earth's orbit? Well,
Speaker 1: if you're right next to the Earth, then you and
Speaker 1: the Earth would pull on each other and you would
Speaker 1: smash into the Earth. So try to get a little
Speaker 1: bit further from the Earth. Well, how far away from
Speaker 1: the Earth you have to be? Well, one solution is
Speaker 1: to be on the other side of the Sun from
Speaker 1: the Earth. So that's the lagrange point three. If you
Speaker 1: and the Earth are on opposite sides of the Sun,
Speaker 1: then you won't pull on each other and you can
Speaker 1: share an orbit with the Earth, right, Okay, So you
Speaker 1: can both hang out in the same orbit without crashing
Speaker 1: into each other. So that's what you want. It turns
Speaker 1: out there are two more points there's a leagarnge point
Speaker 1: four and five, which are like thirty degrees ahead or
Speaker 1: behind the Earth. It can also be in those points
Speaker 1: where everything balances out and you can both be in
Speaker 1: orbit together. And this is why Jupiter, for example, has
Speaker 1: a big cluster of asteroids ahead of it and behind
Speaker 1: it in its orbit. Right. I think they're called the
Speaker 1: Trojans and the Greeks.
Speaker 2: Cool love it. I hope they get along.
Speaker 1: Ironic foreshadowy. And another one is to be between the
Speaker 1: Earth and the Sun, so closer to the Earth because
Speaker 1: the Earth has less gravity, but between the Earth and
Speaker 1: the Sun, that's the lagrange point one. Lagarage point two
Speaker 1: is on the outside past the Earth's orbit, and it's
Speaker 1: basically in a line from the Sun to the Earth
Speaker 1: and then past it. And so you can be out
Speaker 1: there where your orbit is not disturbed by the Earth.
Speaker 1: You could also just be in lagrange point two in
Speaker 1: orbit around the Sun and be fine. But then if
Speaker 1: you're not synced up with the Earth, the Earth is
Speaker 1: going to disturb your orbit every time it passes you.
Speaker 1: But if you're synced up with the Earth, so you're
Speaker 1: always keeping the Earth, Sun and your telescope in a line,
Speaker 1: then everything is stable, and that's where the James web
Speaker 1: Space Telescope hangs out because the Earth provides a shade
Speaker 1: from the Sun and the telescope needs to be super
Speaker 1: duper cold so that it doesn't emit radiation in the
Speaker 1: same wavelengths that it's observing.
Speaker 3: Okay, so it's constantly in motion relative to the Sun,
Speaker 3: but not the Earth. But not the Earth, and have
Speaker 3: humans put things in all of these lagrange points.
Speaker 1: So we've used lagrange points one and two. One is
Speaker 1: the one that's closer to the Sun, and two is
Speaker 1: the one that's further from the Sun. And two, for example,
Speaker 1: we have the James Webs Space Telescope, and it's not
Speaker 1: actually at too, it's orbiting too, so you can put
Speaker 1: other stuff there. And there are things that one which
Speaker 1: is pretty clear to Earth. For example, there's like the
Speaker 1: Solar and Heliospheric Observatory is there, and other stuff likes
Speaker 1: to be there, and we haven't put anything at four
Speaker 1: and five. They're kind of a little bit far away.
Speaker 1: That James Wes Space Telescope is already like kind of
Speaker 1: far away for an observatory, and four and five are even.
Speaker 2: Further and three is super far, so we have we
Speaker 2: put anything at three.
Speaker 4: Yet No.
Speaker 1: Three is super duper far away. It's on the other
Speaker 1: side of the Earth. And that wouldn't be terribly convenient
Speaker 1: because we couldn't communicate with it very easily because the
Speaker 1: Sun would be in the way. Yeah, and so that's
Speaker 1: basically all you can do to be like motionless in
Speaker 1: the universe. You could try to be like motionless with
Speaker 1: respect to the CMB frame if you'd like that wouldn't
Speaker 1: like feel very special. You could try to be motionless
Speaker 1: with respect to the Earth and hang out in space
Speaker 1: at one of the lagrange points, and that's kind of
Speaker 1: special and you can see things about the universe. That's cool.
Speaker 1: But in general, motion is something kind of slippery because
Speaker 1: it requires you to measure your velocity with respect to
Speaker 1: something else in the universe. A lonely concepts requires you
Speaker 1: to be paired up with something out there in the universe.
Speaker 1: So there is no solo motion or solo location in
Speaker 1: the universe. If you want to be in motion, you
Speaker 1: gotta find a friend.
Speaker 2: Ah.
Speaker 3: That's a nice note to end on, all right, extraordinaries,
Speaker 3: thank you for moving through the universe with us.
Speaker 2: We appreciate you. Spending time with us.
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