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Can you be motionless in space? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Hey, we're hey. When did you get up today? How
0:11
Speaker 1: do you know I got up? I could be recording
0:12
Speaker 1: this from my bed right now. Thanks for that mental image.
0:16
Speaker 1: Now I kind of regret asking. And even if I'm
0:19
Speaker 1: in bed, I'm technically still moving. Really is your bed
0:22
Speaker 1: on wheels or something, or you have like a flying bed?
0:24
Speaker 1: That would be exciting, But no, I'm on Earth and
0:27
Speaker 1: the Earth is spinning right in space and it's also
0:29
Speaker 1: flying around the Sun. So I'm still moving right? Did
0:32
Speaker 1: that count? I mean, does your fitbit give you steps forth? Well?
0:37
Speaker 1: I don't really believe in fitbits. I believe in that bits.
0:40
Speaker 1: I have one to make one for cartoonists. Hi am
0:58
Speaker 1: rhand Ma cartoonists and the creator PhD Comics. I'm Daniel.
1:02
Speaker 1: I'm a particle physicist and a professor. You see Irvine
1:05
Speaker 1: and it feels like I'm always in motion. Oh yeah,
1:08
Speaker 1: like your mental gears are always turning or one of
1:11
Speaker 1: those people that have worked on a treadmill all the time. No,
1:14
Speaker 1: I definitely do not work on a treadmill. I work
1:16
Speaker 1: on a chair and I lean way back with a crazy,
1:19
Speaker 1: ridiculous posture that would make like any ergonomic specialist cringe.
1:23
Speaker 1: And that's what you mean by motion, that's your workout,
1:25
Speaker 1: leaning back for a nap. No, I mean that's sort
1:27
Speaker 1: of always scrambling from one thing to the other, working
1:30
Speaker 1: on this. Oops, that's late running over here. It feels
1:33
Speaker 1: like being an adult in today's modern world is always
1:36
Speaker 1: scrambling from one thing to another. You know what you mean.
1:39
Speaker 1: But you do know you have a choice there, Daniel,
1:41
Speaker 1: I could retire early, Yeah, you can. You cannot do
1:44
Speaker 1: so many things that who would I even be? Man?
1:47
Speaker 1: Who would I even be? Welcome to existential questions with
1:51
Speaker 1: Daniel and Jorge, No, but seriously, welcome to a podcast
1:53
Speaker 1: Daniel and Hojorge Explain the Universe, a production of I
1:56
Speaker 1: Heart Radio in which we do delve into the deepest
1:59
Speaker 1: of exist to questions why does the universe exist? How
2:02
Speaker 1: does it all work? What is our place in it?
2:05
Speaker 1: How long will it last? How will it end? And
2:08
Speaker 1: whose fault will it be when it finally goes poof?
2:11
Speaker 1: In which we dig deep into the very smallest, tiniest
2:14
Speaker 1: little bits of that universe, asked the basic questions about
2:17
Speaker 1: how everything works, and explain all of the answers as
2:20
Speaker 1: far as we know them to you. Yeah, because It
2:23
Speaker 1: is a confusing and vast universe, and it's a pretty
2:27
Speaker 1: restless universe. It seems to be always in motion. There's
2:30
Speaker 1: always something going on in the university because you know,
2:32
Speaker 1: it's so big, and there's always I don't know, and
2:34
Speaker 1: exploding stars somewhere. There's planet spinning everywhere, asteroids flying through
2:39
Speaker 1: the sky. It does seem to be sort of in
2:41
Speaker 1: slow motion violence. You know, you look out into the
2:44
Speaker 1: night sky and you just sort of glance at it,
2:46
Speaker 1: and it seems static. It's not like the stars are
2:48
Speaker 1: whizzing around in front of your eyes. But you know,
2:51
Speaker 1: you pay attention, you see the night sky slide by,
2:54
Speaker 1: and the longer you watch, the more you notice that,
2:56
Speaker 1: like crazy stuff is happening out there, that the explosions
3:00
Speaker 1: that take millions of years but are still very dramatic.
3:04
Speaker 1: So everything up there is actually in motion. We just
3:06
Speaker 1: sort of live in a tiny little burst of time
3:09
Speaker 1: where things seem to be stationary. Yeah, and there's not
3:12
Speaker 1: just a lot of action going on out there. There's
3:14
Speaker 1: a lot of action inside of us. And in the
3:16
Speaker 1: smallest of particles, everything is always you know, vibrating or
3:20
Speaker 1: spinning or quantum spitting or disappearing and appearing at the
3:23
Speaker 1: same time. Yeah, you're right. Quantum mechanics says that everything
3:26
Speaker 1: is in motion and has to be in motion, that
3:28
Speaker 1: nothing can actually come to rest, that nothing in the
3:32
Speaker 1: end can really have no energy. So the very nature
3:35
Speaker 1: of our existence seems to be in motion. Yeah, and
3:38
Speaker 1: it does seem like nowadays live involves a lot of
3:41
Speaker 1: moving around. You know, it seems like things are spinning
3:43
Speaker 1: and moving and changing faster than we can you know,
3:46
Speaker 1: get ahold of it. And so you know, the idea
3:49
Speaker 1: of resting or being motionless, or you know, just stopping
3:53
Speaker 1: and not doing anything is it's kind of weird, right,
3:55
Speaker 1: maybe to a lot of people. Yeah, maybe that. I
3:57
Speaker 1: think a lot of people did more of that in
3:59
Speaker 1: this life last year than they're used to. Went to
4:01
Speaker 1: fewer places, canceled traveling, didn't go to the office as much.
4:05
Speaker 1: So a lot of people were sort of stuck in
4:07
Speaker 1: a smaller orbit than they usually are by the pandemic.
4:10
Speaker 1: But still everybody is still moving. Yeah, it's been kind
4:14
Speaker 1: of a tough year for everybody, but it's still fun
4:17
Speaker 1: to kind of think about the universe and all the
4:19
Speaker 1: things that are going on inside of it, and we
4:21
Speaker 1: especially like to ask interesting questions in this podcast about
4:26
Speaker 1: you know, what's theoretically possible and what is theoretically impossible
4:30
Speaker 1: or what is theoretically nonsensical. That's right, and we're not
4:33
Speaker 1: the only ones wondering about those kinds of questions. All
4:36
Speaker 1: of our listeners are out there thinking about the nature
4:39
Speaker 1: of the universe and what's possible and what their experience
4:42
Speaker 1: is like in it. And a lot of people right
4:44
Speaker 1: in with a particular question when they notice that everything
4:47
Speaker 1: in the universe seems to be moving. Everything is sliding
4:50
Speaker 1: or spinning or orbiting or zooming through space. And I
4:53
Speaker 1: think this inspires people to ask this particular question about
4:57
Speaker 1: whether motionlessness is possible. Yeah, so to be on the podcast,
5:01
Speaker 1: we'll be tackling the question can you be motionless in space? Now? Daniel,
5:11
Speaker 1: do you think people are you know, being aspirational with
5:14
Speaker 1: this question, like how can I be motionless in space?
5:16
Speaker 1: Or are they asking you think the theoretical question is
5:19
Speaker 1: is it possible to be not moving at all in
5:23
Speaker 1: this universe? I don't think anybody is asking a practical question.
5:26
Speaker 1: I don't think they're trying to develop one of those
5:28
Speaker 1: like extreme isolation pods where you can float out in
5:31
Speaker 1: space and have nothing touch you or anything like that.
5:34
Speaker 1: I think people are pushing the envelopes because they want
5:37
Speaker 1: to know what's possible. So in that sense, I guess
5:39
Speaker 1: it's a theoretical question. Just like in our Extreme Universe
5:42
Speaker 1: podcast episodes, sometimes you learn something about the nature of
5:45
Speaker 1: space by looking at the extreme situation, asking what's the
5:50
Speaker 1: fastest you can go or what's the slowest you can go,
5:52
Speaker 1: what's the hottest something can be, what's the coldest something
5:55
Speaker 1: can be. So since everything seems to be moving, I
5:57
Speaker 1: think people are wondering is it even post the all
6:00
Speaker 1: theoretically for something to be totally at rest? What would
6:04
Speaker 1: that mean, what would it require? What does it reveal
6:06
Speaker 1: about the nature of the universe? Right? Yeah, Still I
6:09
Speaker 1: mean to think that a physicist might ask a practical question.
6:12
Speaker 1: Sorry about that, but it is a pretty interesting theoretical question,
6:16
Speaker 1: like can you be not moving? I guess, And do
6:19
Speaker 1: you think that's more about staying still or a feeling
6:22
Speaker 1: that you're not moving? Do you know what I mean? Like,
6:24
Speaker 1: do you think people are asking about is there a
6:26
Speaker 1: point in the universe that's technically not moving relative to
6:29
Speaker 1: everything else? Or do you think it means just like,
6:32
Speaker 1: how can I not have an emotion relative to anything else? Yeah,
6:36
Speaker 1: I think there's a lot of interesting stuff to unpack
6:38
Speaker 1: there about like the very nature of what it means
6:40
Speaker 1: to be in motion, that we're going to have to
6:43
Speaker 1: dig into, because I think something about this question reveals
6:46
Speaker 1: that people are thinking about speed in a way that
6:48
Speaker 1: comes naturally to them on the surface of the Earth,
6:50
Speaker 1: where it makes sense to talk about what my speed is.
6:53
Speaker 1: But when you go out into space, things change. Things
6:56
Speaker 1: are different the same way that like up and down
6:58
Speaker 1: have a meaning on the surface of the Earth but
7:00
Speaker 1: don't really make sense anymore out in space. I think
7:03
Speaker 1: we're going to learn that the whole concept of velocity
7:06
Speaker 1: is a little bit different than what a lot of
7:08
Speaker 1: people had in mind. And so this is a great question,
7:11
Speaker 1: not because the answer is simple and reveals the truth
7:13
Speaker 1: about the universe, but because the nature of the question
7:16
Speaker 1: makes you rethink the whole nature of motion. Yeah, and
7:19
Speaker 1: then you have to ask the follow up question, which
7:21
Speaker 1: is can you be emotionless in space? After learning the
7:24
Speaker 1: answer to the first question, I think we know the
7:26
Speaker 1: answer that it's called the movie gravity. Oh, movie criticism
7:31
Speaker 1: and physics all in one podcast. Seriously, nobody seems to
7:35
Speaker 1: have any emotions in the movie. They're all just like stoic,
7:38
Speaker 1: just trying to not die. I think in space? Can
7:42
Speaker 1: you be alive in space? That's the question they were asking,
7:44
Speaker 1: not just standing still because you're dead. But yeah, this
7:48
Speaker 1: is a pretty interesting question, and so, as usually, we
7:50
Speaker 1: were wondering how many people out there have thought about
7:52
Speaker 1: this question and whether or not they have an answer
7:55
Speaker 1: that they might have thought of. Daniel went out there
7:57
Speaker 1: into the internet to ask the question, Shan, can you
8:00
Speaker 1: be motionless in space? That's right, I go out into
8:04
Speaker 1: the web and beat the bushes for people who are
8:06
Speaker 1: interested in answering these questions for us. If you are
8:09
Speaker 1: out there on the internet and have not participated, please
8:13
Speaker 1: we want to hear your voice, especially if you're from
8:15
Speaker 1: a location we haven't heard anybody from before. We would
8:17
Speaker 1: love to hear your voice on the podcast, So please
8:20
Speaker 1: write to us two questions at Daniel and Jorge dot com.
8:24
Speaker 1: So think about it for a second. Do you think
8:25
Speaker 1: it's possible to be motionless in space? Here's what people
8:29
Speaker 1: had to say. Well, I can be motionless if I
8:33
Speaker 1: don't move a muscle, So nothing on me would move,
8:36
Speaker 1: that would qualify as motionless, I guess, But relative to
8:41
Speaker 1: something else, I would probably never be motionless because everything
8:44
Speaker 1: else is moving. The Sun is moving around the center
8:46
Speaker 1: of the galaxy, and the planets around the Sun, everything
8:49
Speaker 1: else is moving. Even space itself is expanding. So even
8:53
Speaker 1: if I'm in a point in space and the space
8:56
Speaker 1: around me is expanding, then the things around me would
9:00
Speaker 1: be moving along with it as well. So can you
9:03
Speaker 1: be motionless in space? Yes, if I don't move a muscle. No,
9:08
Speaker 1: relative to anything else, I don't think you can be
9:10
Speaker 1: motionless in space. If two bodies are passing by each
9:14
Speaker 1: other and neither is accelerating, both bodies, from their perspective
9:21
Speaker 1: would feel that they were standing still and the other
9:24
Speaker 1: one was moving. It doesn't seem like it, since your
9:27
Speaker 1: motion would be relative to whatever it was around you.
9:31
Speaker 1: So even if you're standing still on Earth, the Earth
9:34
Speaker 1: is spinning and moving around the Sun, And if you're
9:37
Speaker 1: standing still next to the Sun, it's spinning around the
9:40
Speaker 1: galaxy and the galaxy is moving. Um, but maybe it's
9:46
Speaker 1: possible to just stick still with respect to the the
9:50
Speaker 1: fabric of space. Well, if I'm not moving at all, yes,
9:56
Speaker 1: But motionless like not moving from the we really regard
10:02
Speaker 1: into something like the moon, Earth's sun, galaxy, the galaxy
10:12
Speaker 1: cluster Lannique, and so on. Probably I would be moving.
10:17
Speaker 1: Motion is relative, measured relatively to other things. So I
10:22
Speaker 1: guess you could technically you would always be motionless and
10:25
Speaker 1: always be moving in all different directions at the same time.
10:29
Speaker 1: With space expanding, I don't know if that becomes a
10:31
Speaker 1: factor too, but probably does. I don't think that you
10:34
Speaker 1: can be motionless in space. I think that there's a
10:37
Speaker 1: reason why Einstein thought up the theory of relativity, because
10:41
Speaker 1: there is no super position that we can use to
10:45
Speaker 1: compare positions in space against. You've only really got what
10:50
Speaker 1: you have, which is your own frame of reference, and
10:52
Speaker 1: then you compare that to something else. And because everybody
10:56
Speaker 1: else has a different reference, there is no set central
11:01
Speaker 1: position where something is not moving. If I somehow ended
11:06
Speaker 1: up in space and I wasn't moving for some reason, um,
11:12
Speaker 1: according to which one Newton's first law, UM, an object
11:18
Speaker 1: that is not moving, we'll stay stationary. UM. So I
11:22
Speaker 1: suppose if somehow, I don't know, if the Earth vanished
11:26
Speaker 1: and I was left suspended in space, UM, and I
11:33
Speaker 1: wasn't moving, then I would be motionless in space, all right.
11:38
Speaker 1: A lot of people there doesn't think to think it's
11:40
Speaker 1: possible to be motionless. Yeah, yeah, exactly, It's it's fascinating.
11:45
Speaker 1: I think people are just naturally reathless or they have
11:50
Speaker 1: one of those restless leg syndromes. Yeah, there are those
11:53
Speaker 1: people who are always tapping on something or got like
11:55
Speaker 1: a fidget spinner or something. Yeah, I know what my
11:59
Speaker 1: kids would say. I would say, no, it's impossible right now,
12:02
Speaker 1: what I would say about my children even if they
12:04
Speaker 1: were in space, and the kids would say, like, and
12:06
Speaker 1: why would you want to? That seems really boring, right,
12:09
Speaker 1: just lying there doing nothing. Yeah, So it's an interesting question.
12:12
Speaker 1: I guess the question sort of boils down to, like
12:14
Speaker 1: it's not about standing still, but it's more about moving, right,
12:17
Speaker 1: like your whole body moving somewhere, right, because technically we
12:20
Speaker 1: are always vibrating, right, like if we have a temperature,
12:23
Speaker 1: your our molecules are moving. This is more about, you know,
12:26
Speaker 1: whether we're as a whole dane still or translating or
12:30
Speaker 1: moving or going from one place to another, right. Yeah,
12:33
Speaker 1: I think we should sort of like approximate you as
12:35
Speaker 1: a little dot or a point particle and ignore all
12:38
Speaker 1: the motion inside you, and then ask the question, can
12:41
Speaker 1: point particle, you can spherical? You be motionless with respect
12:45
Speaker 1: to everything? Is that even possible? Right? Like cartoon Jorge,
12:50
Speaker 1: So this should be easy because I'm good at ignoring
12:52
Speaker 1: all the emotions inside of me. Right, that was a
12:56
Speaker 1: little dark. No, I'm just kidding, but yeah, it's about
12:59
Speaker 1: whether or not we're moving in relative or moving in
13:02
Speaker 1: space as a whole. Yeah, exactly. And one of the
13:04
Speaker 1: most important things to understand is that there is no
13:08
Speaker 1: absolute motion. All motion is relative. It's always defined relative
13:13
Speaker 1: to something else. You Know. People writing often and ask
13:15
Speaker 1: questions about like special relativity, and usually their questions start
13:18
Speaker 1: with something like if I was in a spaceship and
13:20
Speaker 1: I was going really really fast, and they don't say
13:23
Speaker 1: what they're going really really fast relative to? You know,
13:26
Speaker 1: they have this sense that like there's something that happens
13:29
Speaker 1: when you get up to high speeds. But the thing
13:31
Speaker 1: that's missing there is like who are you speeding by?
13:35
Speaker 1: Where are you going fast relative to? There is no
13:39
Speaker 1: sense in which you have speed other than that it's
13:42
Speaker 1: measured relative to other things or people, right, Because I
13:46
Speaker 1: guess motion is a quantity that is that can't exists
13:50
Speaker 1: on its own, right, Yeah, exactly. If you are, for example,
13:53
Speaker 1: in an empty universe, right it's just you floating in
13:57
Speaker 1: space and there's nothing else in the universe, then you
14:00
Speaker 1: or speed doesn't make any sense. You have no velocity.
14:03
Speaker 1: You can't have velocity because velocity is just motion relative
14:07
Speaker 1: to something else. You know. I guess this might be
14:09
Speaker 1: confusing to people because I wonder, like, you know, I
14:11
Speaker 1: think a lot of us maybe imagine that, you know,
14:14
Speaker 1: the universe maybe has an extent, like a limit, like
14:17
Speaker 1: a wall at some point. Maybe it's a big sphere,
14:20
Speaker 1: maybe it's a big blob, maybe it's a donut. But
14:22
Speaker 1: it has sort of like a shape of it. So
14:25
Speaker 1: couldn't I measure my speed or my motion relative to
14:28
Speaker 1: that shape? No, because the universe is actually symmetric. Like
14:31
Speaker 1: if you do some experiment over here and then you
14:34
Speaker 1: do the same experiment over there, you always get the
14:36
Speaker 1: same answer. There's no point in space that's different than
14:40
Speaker 1: another point in space, Like space has no texture. There's
14:43
Speaker 1: no like way to tell where you are in space.
14:47
Speaker 1: I mean, it might be that the universe is finite
14:50
Speaker 1: and has some like weird edge to it, but we
14:53
Speaker 1: haven't observed that, and the current cosmological models usually assume
14:57
Speaker 1: that the universe is infinite and that every point in
15:00
Speaker 1: it behaves the same way, Like the laws of physics
15:02
Speaker 1: are the same no matter where you are, and so
15:05
Speaker 1: you can't do an experiment determine where you are. So
15:08
Speaker 1: it's not like you can feel space moving by or
15:11
Speaker 1: measure yourself your location relative to some like absolute point
15:15
Speaker 1: in space. There is no absolute point, and so there
15:18
Speaker 1: is also no absolute velocity. Well, there's no absolute point
15:21
Speaker 1: that we know of, right, But could there be one
15:23
Speaker 1: if like the universe does have a shape or like
15:27
Speaker 1: a wall or limit in some scenarios, yes, in most scenarios, no, Like,
15:31
Speaker 1: even if the universe is not infinite, right, it might
15:34
Speaker 1: not have an edge. Like imagine the universe is closed
15:38
Speaker 1: and finite the way it like wraps around itself. That
15:41
Speaker 1: doesn't mean that there's any special point. It can be
15:44
Speaker 1: finite and still have like no special location to it.
15:47
Speaker 1: Imagine you're like on the surface of a sphere, right,
15:50
Speaker 1: then every point on that sphere is really the same,
15:52
Speaker 1: even though the service is not infinite, right, Yeah, I guess,
15:56
Speaker 1: like if the universe was like at the pag max screen.
15:58
Speaker 1: Then there's technically no real place in the pac Man's
16:02
Speaker 1: screen because it just loops around forever. But I guess
16:05
Speaker 1: I'm just trying to get to the possibly that maybe
16:07
Speaker 1: it does have an edge, in which case there would
16:09
Speaker 1: be something like an absolute position. Right. If the universe
16:12
Speaker 1: did have some sort of like strange wall as an
16:15
Speaker 1: edge to it, or some like deformity in its geometry,
16:18
Speaker 1: then yes, that would break this cosmological principle that every
16:21
Speaker 1: location is the same, and then you could measure your
16:24
Speaker 1: velocity relative to that there would be a special location
16:27
Speaker 1: in space. But still your velocity would only have meaning
16:31
Speaker 1: a relative to something. And you can define your velocity
16:34
Speaker 1: to be relative to like that weird edge of space
16:37
Speaker 1: or the Sun or the moon, or there's dust particle,
16:40
Speaker 1: but the definition of your velocity still only has meaning
16:44
Speaker 1: relative to something, right, Yeah, because I guess you know
16:47
Speaker 1: motion or velocity, it's like the change in a quantity,
16:50
Speaker 1: which is distance. So you can have distance if you
16:53
Speaker 1: don't measure relative to something else, right, yeah, exactly, And
16:56
Speaker 1: this is actually really closely connected to like all sorts
16:59
Speaker 1: of interesting deep physics of the universe. You know the
17:02
Speaker 1: fact that space seems to be the same everywhere. That
17:05
Speaker 1: if you do your experiment here and then you transport
17:07
Speaker 1: it ten light years over there and do it again,
17:10
Speaker 1: that you get the same answer. That's connected to an
17:13
Speaker 1: important law of physics, which is conservation of momentum. And
17:16
Speaker 1: we're gonna do a whole fun podcast episode about this
17:19
Speaker 1: deep theory of physics called Nuther's theorem that tells you
17:21
Speaker 1: that anytime you have a symmetry like that, something where
17:24
Speaker 1: the universe doesn't care where you are, you get some
17:27
Speaker 1: conserved quantity, something which doesn't change as you do your experiments.
17:31
Speaker 1: So in this case, the connection is the fact that
17:33
Speaker 1: you can move from one place in space to another
17:36
Speaker 1: and not have your experiment change. Is why we have
17:38
Speaker 1: conservation of momentum, which is sort of mind blowing to me.
17:42
Speaker 1: But yeah, exactly, velocity is defined relative to other things
17:46
Speaker 1: in space, not relative to space itself, right, And I
17:50
Speaker 1: think it extends not just to like your precision in
17:53
Speaker 1: the universe, right, Like you can do an experiment here
17:55
Speaker 1: or there and it should be worked out the same,
17:57
Speaker 1: but it also it comes up in doing the experiment
17:59
Speaker 1: at different velocities. Right. I can do my experiments going
18:02
Speaker 1: at a hundred moss per hour relative to the Earth,
18:04
Speaker 1: or I can do it at a hundred thousand miles
18:06
Speaker 1: per hour. I should get the same results if I'm
18:08
Speaker 1: going at a constant speed, right, Yeah, exactly. If you're
18:11
Speaker 1: in a box, you can't measure your velocity relative to
18:13
Speaker 1: stuff outside the box if you can't see that stuff
18:16
Speaker 1: at all. So if you do an experiment, it shouldn't
18:19
Speaker 1: be sensitive to your velocity relative to that stuff. So
18:22
Speaker 1: the classic scenario is like you set up some experiment.
18:24
Speaker 1: I don't know what it is. It's got you know,
18:26
Speaker 1: like balls swinging and hitting each other or whatever, and
18:28
Speaker 1: then you gently accelerate up to some higher speed, right,
18:32
Speaker 1: And the key there is gently accelerates so you don't
18:35
Speaker 1: like destroy everything. Now your speed is high relative to
18:38
Speaker 1: like the surface of the Earth or the planet you're
18:40
Speaker 1: on or whatever. You do the same experiment, you should
18:42
Speaker 1: get exactly the same result. And that's not just some
18:45
Speaker 1: like weird esoteric thing that means that you can't measure
18:49
Speaker 1: your velocity. Is no experiment you could do that would
18:51
Speaker 1: give a different answer if your velocity relative to that
18:54
Speaker 1: planet is zero or a thousand meters per second, And
18:58
Speaker 1: that means you can't build a device to measure that velocity. Right,
19:02
Speaker 1: And again this applies to just to double check, this
19:04
Speaker 1: applies to like constant velocity. Right. If I'm accelerating, then
19:08
Speaker 1: that's a whole different ball game, exactly. Acceleration is totally different,
19:11
Speaker 1: which is also really interesting. Acceleration is something you can measure.
19:15
Speaker 1: There is absolute acceleration. If you're in a box, you
19:18
Speaker 1: can measure your acceleration. Right. You can do a simple
19:20
Speaker 1: experiment toss a ball up in the air and it
19:22
Speaker 1: will move differently if you're under acceleration then if you're not.
19:26
Speaker 1: And also you'll feel it. If you're in a box
19:28
Speaker 1: and it's accelerating, it will feel just like gravity. Right.
19:32
Speaker 1: Acceleration feels just like gravity, which was the whole inside
19:35
Speaker 1: which led to general relativity and that whole revolution and
19:38
Speaker 1: understanding space and time. But position and velocity only makes
19:42
Speaker 1: sense relative to other things, right. And I think what
19:45
Speaker 1: you're saying, basically just to kind of drive this home,
19:49
Speaker 1: is that like, if you're inside of a box out
19:51
Speaker 1: in space, it's sort of impossible to know how fast
19:56
Speaker 1: that box you're in is moving relative to other things. Right.
20:00
Speaker 1: If it's moving at a constant speed, or not. It's
20:02
Speaker 1: impossible to tell that, you know, boxes floating out in
20:06
Speaker 1: space or it's like moving super fast across the galaxy. Yeah, exactly,
20:10
Speaker 1: as long as you can't look outside the box. Like
20:12
Speaker 1: if you have a window, you can look outside and
20:14
Speaker 1: you can see things moving by and measure it. But
20:16
Speaker 1: if all you can do is measure things inside the box,
20:18
Speaker 1: then yeah, you can't measure your velocity relative to anything
20:21
Speaker 1: outside the box. There's no way to tell, right, And
20:24
Speaker 1: so I think what you're getting at is that basically
20:26
Speaker 1: just the word motionless doesn't really have any meaning, right
20:30
Speaker 1: because you might think you're motionless now inside your box,
20:33
Speaker 1: but really you could be moving really fast or not
20:35
Speaker 1: at all, or moving in any kind of crazy direction
20:38
Speaker 1: outside of that box. So really the word motionless doesn't
20:41
Speaker 1: mean anything from a physics math point of view. Yeah,
20:44
Speaker 1: it's either totally meaningless or it's just totally arbitrary. Like
20:47
Speaker 1: you can pick a definition of a reference frame and say,
20:51
Speaker 1: I'm going to say that the Earth is at the
20:52
Speaker 1: center of my reference frame. Now my velocity has meaning.
20:55
Speaker 1: I'm talking about velocity relative to the Earth. But you
20:58
Speaker 1: could also pick anything else. You could pick the sun,
21:00
Speaker 1: you could pick that grain of dust. You could pick
21:02
Speaker 1: a distant comment. Your answer depends on your choice, and
21:05
Speaker 1: your choice is totally arbitrary, and no choice is better
21:08
Speaker 1: than any other. So you can either say velocity is meaningless, right,
21:12
Speaker 1: or you can say it only has meaning when you
21:14
Speaker 1: make an arbitrary choice of what you're measuring it relative to. Right.
21:18
Speaker 1: So basically, when you try to answer the question can
21:20
Speaker 1: you be motionless in space, you're saying that's kind of
21:23
Speaker 1: a nonsensical question, or like an impossible question to ask
21:27
Speaker 1: in terms of the math and in the physics, because
21:29
Speaker 1: there's no way to tell if you are motionless, because
21:32
Speaker 1: it depends on what you measure your motion relative to
21:34
Speaker 1: and it could be anything. It could be anything, and
21:36
Speaker 1: even if you pick something, it would be totally different
21:39
Speaker 1: according to somebody else. Yeah, exactly, Like in some sense
21:42
Speaker 1: the answer is trivial, like, yes, you can be motionless
21:44
Speaker 1: in space if you measure your motion relative to yourself.
21:48
Speaker 1: So by definition, your velocity is zero relative to yourself. Boom,
21:52
Speaker 1: your motionless in space. So that's what I meant when
21:54
Speaker 1: I said, like, this question is interesting because this whole
21:56
Speaker 1: question of velocity, I think people have an intuitive sense
21:59
Speaker 1: of like motion is something that you can measure, but
22:02
Speaker 1: you can't actually measure it in a pure sense. You
22:04
Speaker 1: can only measure relative to other things, and so it
22:07
Speaker 1: becomes kind of arbitrary and unfortunately meaningless. All right, well,
22:11
Speaker 1: I think that's a little counterintuitive because our daily experience
22:14
Speaker 1: is that we are moving on Earth, and the Earth
22:16
Speaker 1: is moving around the Sun, and then the Sun is
22:18
Speaker 1: moving around the galaxy. So let's dig a little bit
22:20
Speaker 1: deeper into these types of motions and then let's try
22:23
Speaker 1: to answer whether or not it is actually possible to
22:26
Speaker 1: get around that loophole. But first let's take a quick break.
22:42
Speaker 1: All right, we're trying to answer the question can you
22:44
Speaker 1: be motionless in space? And the answer is um, yes
22:50
Speaker 1: and no, or or ask a better question? Is the
22:52
Speaker 1: answer it's yes according to our legal department, as long
22:56
Speaker 1: as you define a reference brain right, because idea is
23:00
Speaker 1: that you know, I can always say emotionless relative to
23:02
Speaker 1: whatever box I'm in, but you know who knows what
23:05
Speaker 1: this box is moving relative to? Yeah, And that's sort
23:09
Speaker 1: of like the abstract theoretical answer, and it's unsatisfying because
23:13
Speaker 1: there are some reasonable choices you can make, right in theory,
23:17
Speaker 1: what reference frame you pick to measure your motion is
23:19
Speaker 1: totally arbitrary and and there's no one preferred over others.
23:23
Speaker 1: But there are things around us that it makes sense
23:25
Speaker 1: to define your motion relative to. Right, you know, we
23:28
Speaker 1: have the Earth, we have the Sun, we have the galaxy,
23:30
Speaker 1: and it's fascinating how we are moving relative to those things. Yeah,
23:34
Speaker 1: and it's not a little bit of motion. We're going
23:37
Speaker 1: pretty fast right here on Earth. So what like, let's
23:40
Speaker 1: maybe take it one step at a time. What if
23:43
Speaker 1: I define our emotion as relative to the Earth or
23:46
Speaker 1: the center of the Earth, how fast are we moving? Yeah? Right,
23:48
Speaker 1: relative to the Earth or the center of the Earth.
23:50
Speaker 1: Those are two different things. If you say, what's my
23:53
Speaker 1: motion relative to this patch of earth underneath my feet, Well,
23:56
Speaker 1: if you're just standing on it, then it's obviously zero.
23:59
Speaker 1: But if you say, what's my motion relative to the
24:01
Speaker 1: very center of the Earth, then you have to measure
24:04
Speaker 1: the spinning of the Earth, right, Because the Earth is
24:06
Speaker 1: not just a ball of rock moving through space. It's
24:09
Speaker 1: also spinning, spinning pretty quickly like it's a big rock,
24:13
Speaker 1: and it spins once every twenty four hours, so that's
24:17
Speaker 1: pretty high speed. You know, at the equator, for example,
24:20
Speaker 1: the surface of the Earth is moving at six kilometers
24:24
Speaker 1: per hour relative to the center of the Earth, And
24:27
Speaker 1: of course that depends on your latitude, because at the
24:30
Speaker 1: north pole it's not moving at all, and at the
24:32
Speaker 1: south pole is not moving at all, and at the
24:34
Speaker 1: equator it has that maximum speed. Right, Although I wonder
24:38
Speaker 1: if you're committing the same error that we were pointing
24:39
Speaker 1: out earlier, because you just said the Earth is spinning
24:42
Speaker 1: really fast, But don't you have to say what it's
24:44
Speaker 1: spinning fast relative to? Yeah, exactly, like, couldn't the whole universe,
24:48
Speaker 1: like strange coincidence, be spinning kind of at the same
24:51
Speaker 1: rate the Earth is, in which case we're not really spinning. Yes,
24:55
Speaker 1: And here we're talking about spinning relative to the center
24:58
Speaker 1: of the Earth. Right, when you talk about spin, you
25:01
Speaker 1: have to pick an axis around which you're spinning. And
25:04
Speaker 1: so you're right that there's no like preferred access there.
25:07
Speaker 1: And that's actually a really interesting question I want to
25:09
Speaker 1: get into in a future episode. But whether or not
25:12
Speaker 1: the whole universe is spinning, or whether the Earth is spinning,
25:15
Speaker 1: it's a deep question called mocks principle that we should
25:17
Speaker 1: dig into. But you're right, you need to pick a
25:20
Speaker 1: reference frame there. So here we've picked the center of
25:22
Speaker 1: the Earth, or more specifically, if we're talking about spinning,
25:25
Speaker 1: an access that goes from the north to the south
25:27
Speaker 1: pole right, So we're spinning really fast relative to that access,
25:31
Speaker 1: and maybe a common question might be like, why don't
25:34
Speaker 1: we feel that motion? Like you know, if I sit
25:37
Speaker 1: in a Merry Go round or one of those state
25:40
Speaker 1: fair rights that spin your round, I definitely feel that,
25:42
Speaker 1: But we don't feel this crazy spinning of the earth
25:45
Speaker 1: right now. Yeah, it's really interesting. And if you dig
25:47
Speaker 1: back into history, as science was sort of like figuring
25:51
Speaker 1: out that the Earth was spinning, that it was moving
25:54
Speaker 1: in this way, people realize this and they're like, well,
25:56
Speaker 1: that's ridiculous, Like if the Earth was spinning that fast,
26:00
Speaker 1: you would definitely feel it, wouldn't we And so it
26:02
Speaker 1: was counted to people's impressions like when don't we fly
26:05
Speaker 1: off into space? Right? And the answer is yes, we
26:08
Speaker 1: would fly off into space if the Earth was spinning faster,
26:11
Speaker 1: you know, like if you speed up a Merry Go
26:12
Speaker 1: round and you can't hold on anymore, then you fly
26:15
Speaker 1: off the Merry go round. Well, what's happening here on
26:17
Speaker 1: Earth is that we are spinning, like gravity is holding
26:20
Speaker 1: us down to the surface of the Earth, and gravity
26:23
Speaker 1: is more powerful than that's tripetal force. And also the
26:26
Speaker 1: Earth's spin is very very smooth and doesn't change. Like
26:30
Speaker 1: the Earth was spinning up and slowing down all the time,
26:33
Speaker 1: then you would definitely notice that. But because it's very
26:36
Speaker 1: nearly constant, it just sort of gets like subtracted out
26:39
Speaker 1: from the gravity that you feel. Like you feel gravity, right,
26:42
Speaker 1: it's holding you to the Earth. You notice it. If
26:44
Speaker 1: the Earth wasn't spinning, there would be more effective gravity,
26:48
Speaker 1: Like gravity would feel stronger if the Earth wasn't spinning.
26:51
Speaker 1: So you are feeling the spinning of the Earth as
26:53
Speaker 1: a sort of like slight lessening of the gravity you feel,
26:56
Speaker 1: but it doesn't change very much you don't notice, right,
26:58
Speaker 1: which you just made me think that like if the
27:00
Speaker 1: Earth wasn't spinning, we would all weigh a little bit more, yeah,
27:04
Speaker 1: like we would feel gravity, we would be heavier. Yes,
27:06
Speaker 1: and you do weigh more at the north pole than
27:09
Speaker 1: you do at the equator, but only by a very
27:11
Speaker 1: small amount. And that's why you don't typically notice these things.
27:14
Speaker 1: And that's why the whole sense that the Earth is
27:16
Speaker 1: spinning underneath us feels weird because it's not something you
27:19
Speaker 1: can intuitively grasp, right. But I think, you know, I
27:22
Speaker 1: think you sort of hit on it when you said
27:24
Speaker 1: that the Earth is spinning really smoothly, like like that's
27:26
Speaker 1: I think that's one reason why we don't feel this
27:29
Speaker 1: crazy spinning. But I think maybe the other part of
27:33
Speaker 1: it is that it's it's not kind of like a
27:35
Speaker 1: perfect motion system, right, Like we still do technically feel
27:40
Speaker 1: things like koreolitis acceloration, right, and and things that would
27:43
Speaker 1: happen if you were kind of in a merry go
27:44
Speaker 1: around trying to get to the center or trying to
27:47
Speaker 1: move around and merry go around. We technically still feel
27:50
Speaker 1: those weird forces that they're just kind of small relative
27:53
Speaker 1: to the size of the Earth. Absolutely, you can do
27:55
Speaker 1: experiments to prove that the Earth is spinning because a
27:58
Speaker 1: rotating reference frame is not inertial reference frame for you
28:01
Speaker 1: special relativity wonks out there, and so you can definitely
28:04
Speaker 1: detect that what happens when you have a reference frame
28:07
Speaker 1: that's accelerating and when you're spinning that's acceleration because you
28:11
Speaker 1: need a force towards the center of the spinning What
28:14
Speaker 1: happens when your reference frame is spinning is that you
28:16
Speaker 1: get some apparent force. It feels like there's some force
28:19
Speaker 1: doing something, even though it's just duty your spinning. And
28:22
Speaker 1: here on Earth that's the Coriolis force. And so, for example,
28:25
Speaker 1: if you drop a rock from the top of a
28:27
Speaker 1: very tall tower, you can measure how far it moves
28:30
Speaker 1: sort of sideways in a way that it wouldn't if
28:32
Speaker 1: the Earth wasn't spinning. You know, it moves like a
28:34
Speaker 1: couple of centimeters when it falls like a hundred and
28:36
Speaker 1: fifty meters. So it's a small and subtle effect, but
28:39
Speaker 1: you definitely can measure it, and it would be more
28:41
Speaker 1: dramatic if the Earth sped up. Interesting, So, like if
28:44
Speaker 1: you went up to the top of the tall tower
28:46
Speaker 1: and you drop the rock, it wouldn't fall straight down.
28:48
Speaker 1: It would sort of curve in this weird way because
28:51
Speaker 1: the Earth is spinning. Yeah, exactly. Like imagine you're back
28:53
Speaker 1: on that Merry Go Round and you want to throw
28:55
Speaker 1: a ball to your friend who's in a different spot
28:58
Speaker 1: on the Merry go Round. You can't act you just
29:00
Speaker 1: throw it in a straight line towards your friend, because
29:03
Speaker 1: by the time the ball gets there, your friend will
29:05
Speaker 1: have like rotated away. So if you want to throw
29:08
Speaker 1: the ball so that it gets to your friend, you
29:09
Speaker 1: gotta throw it like a little bit to the left,
29:11
Speaker 1: because if you throw a ball straight while you're spinning
29:13
Speaker 1: on a merry go round in your view, the ball
29:15
Speaker 1: doesn't move straight, it'll like curve to the right. So
29:18
Speaker 1: you've gotta account for all these things when you're throwing
29:20
Speaker 1: the ball. And so because the earth is spinning, the
29:23
Speaker 1: same effect happens when you like drop a rock from
29:25
Speaker 1: the top of a tower, or if you've ever been
29:27
Speaker 1: to one of those cool science museums where they have
29:29
Speaker 1: one of those really tall pendulum, it's called the foe
29:31
Speaker 1: called pendulum, but you have to say with the French
29:33
Speaker 1: accent it's called a pendulum. Focal is an experiment done
29:38
Speaker 1: in the eighteen fifties originally that proved that the Earth
29:41
Speaker 1: was spinning because you can feel this effect on this pendulum, right.
29:44
Speaker 1: The pendulum is like a heavy weight on a very
29:47
Speaker 1: long string, and so it's sensitive to small pushes in
29:50
Speaker 1: various directions. You set the pendulum going back and forth,
29:53
Speaker 1: and then it eventually just starts spinning on its own.
29:56
Speaker 1: And that spinning of course, is coming from the Coriola's force.
29:58
Speaker 1: It's coming from the in of the Earth. Right. So
30:01
Speaker 1: I think all these things kind of add up to
30:04
Speaker 1: that conclusion that we might feel like we're motionless here
30:07
Speaker 1: on Earth, and that even though motionless doesn't mean anything,
30:10
Speaker 1: we still sort of feel motionless. But really there are
30:12
Speaker 1: these strange forces going on, right because the Earth is
30:15
Speaker 1: spinning and the reference frames are accelerating right, m exactly.
30:19
Speaker 1: And if the Earth was not spinning, if there was
30:21
Speaker 1: no like acceleration, because remember, spin is acceleration, then there
30:25
Speaker 1: be no way to measure the Earth's velocity relative to
30:28
Speaker 1: other stuff. So we can measure the Earth's spin only
30:31
Speaker 1: because it is acceleration. It's not just constant velocity. That's
30:35
Speaker 1: a bit counterintuitive because it feels like it's constant because
30:38
Speaker 1: it's a constant rate of spin. But constant spin requires
30:41
Speaker 1: acceleration because requires a force to move you towards the
30:44
Speaker 1: center of the spin. All right, well, what about relative
30:48
Speaker 1: to the Sun. That's a pretty stable and almost stationary
30:52
Speaker 1: big thing. Can we can we be motionless relative to
30:55
Speaker 1: the Sun. Yeah, that's actually a really interesting question. And
30:58
Speaker 1: you know, the Earth, of course is moving pretty fast
31:01
Speaker 1: relative to the Sun, and we should be glad that
31:03
Speaker 1: we are, because it's the reason that we don't just
31:05
Speaker 1: like plunge headfirst into the Sun. Right. People think about like,
31:09
Speaker 1: if you're near a black hole, would you just get
31:11
Speaker 1: automatically sucked up, when the answer is no, if you
31:15
Speaker 1: can get into orbit around the black hole, And the
31:17
Speaker 1: same thing is true for orbiting around any gravitational object.
31:21
Speaker 1: Like the reason the Earth doesn't fall into the Sun
31:23
Speaker 1: is because we have high speed relative to the Sun.
31:26
Speaker 1: You know, this is the kind of stuff people are
31:28
Speaker 1: talking about with these like New Shepherd and Virgin galactic
31:31
Speaker 1: launches into space. You know, people are saying that's really
31:34
Speaker 1: super cool and awesome, but you know, all they did
31:36
Speaker 1: was sort of like go up into space. The much
31:39
Speaker 1: more difficult thing is to get up into space and
31:41
Speaker 1: then get into orbit because that requires a super fast
31:44
Speaker 1: velocity relative to the Earth. So the Earth is moving
31:47
Speaker 1: relative to the Sun at like thirty kilometers per second,
31:50
Speaker 1: and we should be glad that it is, because otherwise
31:52
Speaker 1: we would fall headfirst into that huge burning ball of plasma.
31:57
Speaker 1: You mean, those commercial flights that just kind of dip
31:59
Speaker 1: into space. They don't like, staying in space is a
32:02
Speaker 1: lot harder. Yeah, staying in space is a lot harder
32:05
Speaker 1: than dipping your toes and then coming back to Earth.
32:07
Speaker 1: Like they were just up in space for a few
32:09
Speaker 1: minutes and they just came right back. But you know,
32:11
Speaker 1: what NASA has done, and even SpaceX is done, is
32:14
Speaker 1: much more difficult because you need a much higher velocity
32:17
Speaker 1: to stay in space. Right, Staying in space basically means
32:20
Speaker 1: falling towards the Earth and missing it, sort of like
32:22
Speaker 1: in the Hitchhiker's Guide to the Galaxy. And to do that,
32:25
Speaker 1: you need to be moving fast enough that when you
32:27
Speaker 1: fall towards the Earth, it's sort of not there anymore,
32:30
Speaker 1: just like the motion on the Merry Go Round. Yeah
32:32
Speaker 1: you like overshoot it? Yeah, exactly, overshoot it. And so
32:35
Speaker 1: that's what the Earth is doing around the Sun. We're
32:36
Speaker 1: moving at thirty kilometers per second, which is pretty fast,
32:40
Speaker 1: but that's the velocity we need because the Sun's gravity
32:43
Speaker 1: is so strong. That's the velocity we need to overshoot
32:46
Speaker 1: it every time we fall in towards it. Wow, Well,
32:49
Speaker 1: what about relative to the galaxy? Um? Can we how
32:53
Speaker 1: fast is the Sun moving relative to the galaxy? The
32:55
Speaker 1: Sun is really zipping around right here, we're talking about
32:58
Speaker 1: gravitational system. And at the core of the galaxy is
33:02
Speaker 1: an enormous mass of stuff. Right. We are sort of
33:05
Speaker 1: like out in the suburbs, where there's like one star
33:09
Speaker 1: every few cubic light years, But in the center of
33:12
Speaker 1: the galaxy, things are much dense or much crazier, right,
33:15
Speaker 1: and they're hot, throbbing urban center. There's an enormous black
33:18
Speaker 1: hole with millions and millions of stars worth of mass
33:21
Speaker 1: and then just lots of stars, and so there's an
33:24
Speaker 1: extraordinarily strong gravitational force on the Sun from the center
33:28
Speaker 1: of the galaxy, and so the Sun is orbiting the
33:31
Speaker 1: center of the galaxy. But to avoid falling into that
33:34
Speaker 1: black hole, it has to move really fast. It moves
33:37
Speaker 1: at eight hundred thousand kilometers per hour relative to the
33:40
Speaker 1: center of the galaxy. Wow, that's crazy. Like if you
33:43
Speaker 1: plant the flag in the middle of the galaxy, that's
33:45
Speaker 1: how fast we're moving relative to that. Yeah, relative to
33:48
Speaker 1: that black hole, we are moving at eight hundred thousand
33:51
Speaker 1: kilometers per hour. It's pretty impressive. But you know, the
33:53
Speaker 1: galaxy is so big that it still takes like two
33:56
Speaker 1: hundred million years for the Sun to go around the
34:00
Speaker 1: center of the galaxy, Like a galactic year is two
34:03
Speaker 1: million earth years. Wow, that's a long time to wait
34:07
Speaker 1: for your birthday every time. But I think the point
34:11
Speaker 1: is that, you know, you might think that you're motionless here,
34:13
Speaker 1: but actually you're moving relative to the Sun of the Earth.
34:16
Speaker 1: And actually you might think that the Earth is not moving,
34:19
Speaker 1: but then it's moving relative to the Sun, and the
34:21
Speaker 1: Sun is moving relative to the galaxy by a lot um.
34:25
Speaker 1: But then I guess the question is is the galaxy
34:27
Speaker 1: moving relative to anything else? Right? I think this sort
34:30
Speaker 1: of goes back to the heart of the original question,
34:32
Speaker 1: which is like can you be motionless in space? Can
34:34
Speaker 1: you like get away from all of this stuff? Or
34:37
Speaker 1: like the other question is like the galaxy itself can
34:39
Speaker 1: it just be hanging out in space? So this is
34:42
Speaker 1: a really interesting question. But again you have to measure
34:44
Speaker 1: the motion of the galaxy relative to other stuff. And
34:48
Speaker 1: so now what's the other stuff when you can look
34:50
Speaker 1: at other nearby galaxies and measure like our velocity relative
34:54
Speaker 1: to Andromeda or relative to other galaxies that are nearby,
34:58
Speaker 1: but that's just sort of seems arbitrary. Is just you know,
35:00
Speaker 1: a random galaxy nearby? What you can do, though, which
35:03
Speaker 1: I think is pretty cool, is you can find the
35:05
Speaker 1: motion of our galaxy relative to like all of the
35:09
Speaker 1: stuff in the universe, like the average of all of
35:12
Speaker 1: the things in the universe. Interesting I mean in terms
35:15
Speaker 1: of mass or energy or just like to think that
35:18
Speaker 1: it has some sort of like aggregate that's not moving exactly.
35:22
Speaker 1: We talked earlier about how you can't measure your velocity
35:25
Speaker 1: relative to space itself, right, but you can measure your
35:28
Speaker 1: velocity relative to stuff. And even though there's no preferred
35:31
Speaker 1: location in space, there is stuff in space, right, you
35:35
Speaker 1: can ask, like, is there a velocity where you're not
35:37
Speaker 1: moving relative to like all of the average stuff. And
35:40
Speaker 1: so the way cosmologists do this is they look at
35:43
Speaker 1: the cosmic microwave background radiation. This is the radiation that's
35:46
Speaker 1: left over from the very very early universe, that plasma
35:50
Speaker 1: that was hot and glowing. Around three eighty thousand years
35:53
Speaker 1: after the beginning of the universe, the universe became transparent,
35:57
Speaker 1: and that light has been bouncing around ever since. In
36:00
Speaker 1: so that light sort of tells us about where the
36:02
Speaker 1: stuff was in the very early universe, and we can
36:05
Speaker 1: measure our velocity relative to this radiation which is sort
36:08
Speaker 1: of like measuring your velocity relative to the stuff in
36:12
Speaker 1: the early universe. So while you can't measure your velocity
36:15
Speaker 1: relative to like empty space, space is not empty. It's
36:18
Speaker 1: filled with stuff, and you can actually find a preferred
36:21
Speaker 1: reference frame in which the cosmic microwave background radiation or
36:25
Speaker 1: the plasma that generated it is at rest. WHOA, I
36:29
Speaker 1: feel like you just kind of pulled a fast one
36:31
Speaker 1: on me, Like at first, you can convince me at
36:33
Speaker 1: first that there's no way to have an absolutely velocity,
36:36
Speaker 1: But now and you're sort of telling me that there
36:37
Speaker 1: is kind of a way to do it if you
36:40
Speaker 1: depending on how you define what the universe is right exactly,
36:44
Speaker 1: imagine an empty universe. You can't have any velocity in
36:47
Speaker 1: that empty universe. Now put ten galaxies in that universe.
36:51
Speaker 1: You can say, well, I could have a velocity relative
36:53
Speaker 1: to one galaxy or another one, or I could just say,
36:56
Speaker 1: what's my velocity relative to all the stuff, Like find
36:59
Speaker 1: the ridge motion of all the stuff in the universe,
37:02
Speaker 1: and you could say that's my velocity, and it's a
37:04
Speaker 1: reasonable definition. It's sort of arbitrary, but it's also sort
37:08
Speaker 1: of not arbitrary because like there's only one way to
37:10
Speaker 1: choose the average velocity of all the stuff in the universe, right,
37:15
Speaker 1: because that is the universe, right, Like, who cares? So
37:17
Speaker 1: that space is slippery and undefinable, and you can't, you know,
37:22
Speaker 1: measure a relative to it. What matters is this stuff
37:24
Speaker 1: in it? Maybe? I guess that you know, it depends
37:26
Speaker 1: philosophically if you think space is fundamental or mass is
37:29
Speaker 1: fundamental or whatever. I mean. You could also define a
37:31
Speaker 1: frame in which those ten galaxies, your whole universe in
37:34
Speaker 1: this example, is moving right at a billion miles per
37:37
Speaker 1: hour to the left. You know, you could define that
37:39
Speaker 1: reference frame also the universe theoretical physics says their equivalent,
37:43
Speaker 1: But yeah, I think it makes sense to define a
37:45
Speaker 1: reference frame relative to all the stuff in the universe.
37:47
Speaker 1: And the crazy thing is we can kind of do that.
37:50
Speaker 1: And we can do that by looking at the cosmic
37:52
Speaker 1: microwave background radiation and asking are we moving through that
37:55
Speaker 1: radiation at some speed in some direction? All right, well,
37:58
Speaker 1: let's get into how we can actually to hell that
38:01
Speaker 1: velocity relative to the background radiation, and maybe there are
38:04
Speaker 1: other ways to be motionless in the universe. But first
38:07
Speaker 1: let's take another quick break all right, So it is
38:22
Speaker 1: sort of possible to define motion relative to all the
38:27
Speaker 1: stuff in the universe, not to space, but to all
38:29
Speaker 1: the stuff in the universe. You're saying you can do
38:32
Speaker 1: that through the cosmic microwave background radiation. Now that's the
38:36
Speaker 1: like the leftover light from the Big Bang. Are you
38:38
Speaker 1: saying that we can tell which way we're moving relative
38:40
Speaker 1: to that kind of glow? We can, absolutely, because like
38:44
Speaker 1: everything else, we can measure our velocity relative to the
38:47
Speaker 1: stuff that emitted it by using red shifts and blue shifts.
38:51
Speaker 1: Like if a star is moving away from us, then
38:53
Speaker 1: the light that it sends us is red shifted. It's
38:56
Speaker 1: wavelength is lengthen it's stretched out because that's is moving
39:00
Speaker 1: away from us. And if it starts moving towards us,
39:02
Speaker 1: then its wavelength is shrunk. It's like squeezed down. It's
39:06
Speaker 1: blue shifted. And when we measure the cosmic bacrowave background radiation,
39:10
Speaker 1: we notice a very very strong effect that one side
39:13
Speaker 1: of the sky is red shifted and the other side
39:15
Speaker 1: of the sky is blue shifted. So that very clearly
39:17
Speaker 1: gives you a measurement for like our motion through the
39:20
Speaker 1: cosmic microwave background radiation. M M. Interesting. It's sort of
39:24
Speaker 1: like if you stick your head out this side of
39:26
Speaker 1: a moving car. You know, one side of your head
39:28
Speaker 1: would feel the air hitting one side of your face
39:32
Speaker 1: harder than it would on the other side, and then
39:34
Speaker 1: that's how you know that you're moving in a particular
39:36
Speaker 1: direction relative to the air you're moving in. Yeah, exactly.
39:38
Speaker 1: It's like if you said, well, let's fill the whole
39:41
Speaker 1: universe with air, then all of a sudden, there is
39:43
Speaker 1: any reference frame that makes sense, like your air speed
39:46
Speaker 1: through this universe, right, and it kind of is sort
39:49
Speaker 1: of filled with air. I mean, it's not actually air molecules,
39:52
Speaker 1: of course, but it's radiation from the early universe, and
39:55
Speaker 1: we can measure our speed relative to it, like the
39:58
Speaker 1: speed of the cosmic microwave back under radiation wind m m.
40:03
Speaker 1: So like if we look in one direction, this micro
40:05
Speaker 1: background radiation looks a little bluer, and then we looked
40:08
Speaker 1: on the other side, it looks a little redder, and
40:10
Speaker 1: that doesn't change I guess, right, it's it's sort of
40:13
Speaker 1: relative to what frame of motion. I guess you can
40:16
Speaker 1: measure relative to our galaxy, right, Yeah, our galaxy is
40:19
Speaker 1: moving through this now Earth of course, is moving around
40:23
Speaker 1: the Sun, which is moving around the center of the galaxy,
40:25
Speaker 1: so you have to subtract that out. But we measure
40:27
Speaker 1: this as the motion of our galaxy through the c MB,
40:31
Speaker 1: and it's pretty cool. And it's also not that small,
40:34
Speaker 1: like we're kind of clipping along through the c NB
40:37
Speaker 1: at a pretty healthy rate. Yeah, it's like millions of
40:39
Speaker 1: kilometers per hour. Yeah, exactly two point one million kilometers
40:43
Speaker 1: per hour through the c MB. And for those of
40:46
Speaker 1: you who are enthusiasts about the c MP, you might
40:48
Speaker 1: know that we talk a lot about the details of
40:50
Speaker 1: the scene, being like the wiggles in it, how it's
40:52
Speaker 1: a little hotter here and a little colder there, and
40:55
Speaker 1: that corresponds to fascinating information about the nature of the
40:57
Speaker 1: early universe. That's after we sup tracked out this big
41:01
Speaker 1: red shift and blue shift effect. We sort of like
41:03
Speaker 1: neutralize that so we can just look at the relative
41:06
Speaker 1: variations here, we're talking about a velocity relative to the CNB.
41:10
Speaker 1: We subtract that out and then we look for these
41:12
Speaker 1: wiggles to extract all sorts of cool physics juice about
41:15
Speaker 1: the universe, and it has a lot of items c
41:19
Speaker 1: I imagine for Cosmos. It's probably toxic. You know, everything
41:23
Speaker 1: out there in space will kill you. I'll give you
41:25
Speaker 1: a good sumber. You just made me think that. You know,
41:28
Speaker 1: the CMB comes from the Big Bang, which is the
41:31
Speaker 1: beginning of the universe. Right, So if there was a
41:34
Speaker 1: relative velocity between the CNB, which represents the stuff in
41:39
Speaker 1: the universe, and actual space, then it would have to
41:43
Speaker 1: come from the Big Bang, right, Like it would mean
41:45
Speaker 1: that the Big Bang was sort of moving relative to
41:48
Speaker 1: space when it happened. But that's arbitrary, right. The motion
41:51
Speaker 1: of the CNB relative to space depends on defining a
41:54
Speaker 1: reference frame for space, which doesn't exist. So you can
41:58
Speaker 1: imagine the CNB as stay scenary in space, or you
42:01
Speaker 1: can imagine the CNB and the Big Bang is like
42:03
Speaker 1: moving through space at a zillion miles per hour. They're
42:06
Speaker 1: totally equivalent, and you can't tell the difference because you
42:08
Speaker 1: can't define a reference frame for space. Right. But it's
42:11
Speaker 1: kind of weird to think that the Big Bang happened
42:13
Speaker 1: at a zillion miles per hour. Yeah, it is weird,
42:16
Speaker 1: and it is more natural to define a reference frame
42:18
Speaker 1: for like the stuff. And it's also kind of cool
42:21
Speaker 1: because it feels like a choice was made. Right. It
42:22
Speaker 1: feels like, well, the stuff is here and it's not
42:26
Speaker 1: over there, and it's not moving at this speed. But
42:28
Speaker 1: really it's all relative, right. It feels unnatural to imagine
42:32
Speaker 1: the stuff moving in a million miles per hour. It
42:33
Speaker 1: feels more natural to say, let's choose a reference frame
42:36
Speaker 1: with the stuff is zero. But that's sort of our intuition.
42:40
Speaker 1: It's not like physically meaningful. But so I guess then,
42:44
Speaker 1: you know, if we are moving relative to the CNB,
42:46
Speaker 1: do you know which way we're going, Like, are we
42:49
Speaker 1: moving up? Like relative to California? Are we moving up
42:51
Speaker 1: down that? Right? Relative to the universe? Like can you
42:54
Speaker 1: compute that? We can compute that, and there is a vector.
42:57
Speaker 1: It doesn't make sense to talk about it relative to
42:59
Speaker 1: California because California is directed through the CMB changes all
43:02
Speaker 1: the time, because you know, the Earth is spinning and
43:04
Speaker 1: the Earth is moving around the Sun, and yeah, it's
43:06
Speaker 1: always moving. But at any given time you could compete like, oh,
43:09
Speaker 1: right now we are technically moving through the stuff in
43:11
Speaker 1: the universe in this direction. Yeah, yeah, you can do
43:14
Speaker 1: that calculation. In fact, maybe we should make a website
43:16
Speaker 1: for that. That would be pretty fun for people to
43:18
Speaker 1: see where we're moving through the universe and half past
43:20
Speaker 1: we're going at any particular time. Yeah, Now, is it
43:23
Speaker 1: possible then to be sort of motionless relative to the CNB,
43:27
Speaker 1: Like are there spots in the universe or could we
43:29
Speaker 1: you know, as we're moving and spinning and moving through
43:32
Speaker 1: the galaxy and the Solar System, could we at some
43:34
Speaker 1: for an instant be not moving relative to the CMB. Yeah,
43:37
Speaker 1: that is totally possible. And astronomers and astrophysicists called this
43:41
Speaker 1: peculiar velocity because you know, like on average all the
43:45
Speaker 1: stuff is stationary relative to the CNB, but you know,
43:48
Speaker 1: nothing is stationary. Everything is like switching around and moving
43:51
Speaker 1: relative to each other, like our galaxy and the next
43:54
Speaker 1: galaxy over Andromeda are moving towards each other, for example.
43:58
Speaker 1: But it is possible we just don't have and to
44:00
Speaker 1: be stationary relative to the CNB. But you could like
44:03
Speaker 1: get in a spaceship fly out between galaxies, measure your
44:07
Speaker 1: velocity relative to the CNB and like perfectly adjusted so
44:11
Speaker 1: that you're not moving. So it is sort of technically
44:13
Speaker 1: possible to be motionless relative to the the stuff in
44:16
Speaker 1: the universe, Yes, but not to space. But to the
44:19
Speaker 1: stuff that the in the in the universe. You could
44:22
Speaker 1: you know, fly out there and go too point one
44:24
Speaker 1: million kilometers per hour in the right direction, and you
44:27
Speaker 1: might achieve velocity that makes you still relative to the
44:31
Speaker 1: entire universe. Yeah, exactly, you would have no average velocity
44:35
Speaker 1: relative to all the stuff in the universe. You know,
44:38
Speaker 1: that wouldn't change like special relativity effects because those things
44:41
Speaker 1: are still relative to other observers and stuff like that.
44:45
Speaker 1: But yeah, you could be motionless relative to the stuff
44:48
Speaker 1: in the universe. That's pretty cool to think that there
44:52
Speaker 1: is it is possible to achieve that, And I wonder
44:55
Speaker 1: if we sort of sometimes sort of achieve it, right
44:58
Speaker 1: like as we're spinning around the Earth and as the
45:00
Speaker 1: Earth is spinning around the Sun, or do you think
45:03
Speaker 1: that because the galaxy is moving so fast that there's
45:05
Speaker 1: no way we can sort of cancel out that motion. Yeah,
45:08
Speaker 1: our motion relative to the CMB as the galaxy is
45:11
Speaker 1: much greater than even the Sun's motion through the galaxy. Right, Like,
45:15
Speaker 1: the galaxy is moving at two point one million kilometers
45:18
Speaker 1: per hour through the CMB. The Sun is moving in
45:21
Speaker 1: eight hundred thousand kilometers per hour. So even if the
45:24
Speaker 1: Sun was moving in just the right direction, Like opposing
45:27
Speaker 1: the galaxy's motion to the CMB, it would still only
45:30
Speaker 1: reduce it down to like, you know, one point three
45:33
Speaker 1: million kilometers per hour, or it can make it even
45:36
Speaker 1: faster up to like, you know, almost three million kilometers
45:38
Speaker 1: per hour. But we don't ever actually achieve zero velocity
45:41
Speaker 1: relative to the c MB. Interesting, but it is possible,
45:44
Speaker 1: which I think is pretty cool. But there is one
45:48
Speaker 1: last sort of confounding factor, which is the fact that
45:50
Speaker 1: space is expanding. Now, how does that affect this possibility
45:53
Speaker 1: of being motionless relative to the universe. Yeah, it confuses everything,
45:58
Speaker 1: you know, because we're not just talking about objects being
46:00
Speaker 1: static in space. Right. Space is expanding, which means new
46:04
Speaker 1: space is being made between things. Right, so you have
46:07
Speaker 1: a bunch of different things happening at once. You have
46:10
Speaker 1: like the universe expanding, so that even if nothing was
46:13
Speaker 1: moving relative to any of the other stuff, still distances
46:17
Speaker 1: between things would be growing because space is being created
46:20
Speaker 1: between us and other galaxies, which is like whole mind
46:24
Speaker 1: bending concept of its own right. But then we're also
46:27
Speaker 1: interested in that motion, like are we moving relative to
46:30
Speaker 1: Andromeda whereas our galaxy going So cosmologists separate this out
46:34
Speaker 1: and the two pieces as they are. Right, there's the
46:36
Speaker 1: expansion of the whole universe, which is like happens that
46:39
Speaker 1: in the same level, the same way everywhere between us
46:42
Speaker 1: and other galaxies, between me and you, between the Earth
46:44
Speaker 1: and the Sun, all this stuff. And then there's this
46:47
Speaker 1: sort of local motion, like we call this peculiar velocity
46:51
Speaker 1: relative to that expansion, and so astronomers define these things
46:55
Speaker 1: called co moving coordinates, where we basically subtract out the
46:59
Speaker 1: expansion of the universe and say, let's just isolate the
47:01
Speaker 1: peculiar velocity, the stuff that's like only due to like
47:04
Speaker 1: local gravity. I guess I'm not sure probably what that means.
47:08
Speaker 1: Does that mean that it is not possible to find
47:10
Speaker 1: that spot where you're not moving relative to the universe
47:13
Speaker 1: because the universe is also expanding, so things will be
47:16
Speaker 1: sort of moving relative to you even if you find
47:18
Speaker 1: that spot. No, I think it still makes sense. I mean,
47:21
Speaker 1: find that spot where you're not moving relative to the CMB. Now,
47:24
Speaker 1: everything is expanding away from you, but that's true wherever
47:27
Speaker 1: you are, so that doesn't change your average velocity relative
47:31
Speaker 1: to the CMB because things are moving away from you.
47:34
Speaker 1: Always in every direction, so the average velocity still would
47:37
Speaker 1: be zero. It does mean that everything is moving away
47:41
Speaker 1: from you always, and so nothing is really ever at rest.
47:44
Speaker 1: But you can still have average velocity of zero relative
47:47
Speaker 1: to all the stuff in the universe, even though that
47:49
Speaker 1: stuff is expanding. Like imagine you're standing on the surface
47:52
Speaker 1: of a sphere and you find a spot where you're
47:55
Speaker 1: not moving relative to like all the average stuff in
47:58
Speaker 1: the universe. Now that spheres exp banding, so everything is
48:01
Speaker 1: getting bigger, but you're sort of still at the center
48:03
Speaker 1: of all those velocities, right. I see, like the universe
48:07
Speaker 1: could be getting bigger, but you'd still be still relative
48:10
Speaker 1: to all of it. Yes, even though it's growing. Yes,
48:12
Speaker 1: as long as you're defining your reference for him to
48:14
Speaker 1: be like the average motion of all the stuff in
48:16
Speaker 1: the universe, right, and as long as the universe is
48:19
Speaker 1: not finite, because if it is finite, then you kind
48:22
Speaker 1: of have to find the center of mass, or you
48:24
Speaker 1: have to kind of find the sweet spot center in
48:26
Speaker 1: order for really to be motionless. All right, Well, there
48:30
Speaker 1: is another interesting scenario, which is this idea that you
48:34
Speaker 1: can move through time or not move through time. I'm
48:37
Speaker 1: not sure, so Daniel, How does time fit into this
48:40
Speaker 1: idea of being motionless in space? Yeah, I think a
48:42
Speaker 1: lot of people think about our motion through space when
48:45
Speaker 1: they read time chapel novels, because sometimes you have, like
48:48
Speaker 1: your protagonists creates a time travel device and they go
48:51
Speaker 1: back in time, and then the astute reader things, hold
48:53
Speaker 1: on a second. If you're going back in time, aren't
48:56
Speaker 1: you going to miss the Earth? Like the Earth is
48:58
Speaker 1: moving around the Sun. If you go back in time
49:00
Speaker 1: of month, you should be in deep space, right? Don't
49:03
Speaker 1: you need to move through time and space in order
49:05
Speaker 1: to catch up with the Earth. So a lot of
49:07
Speaker 1: readers write into me with this quibble about the science
49:10
Speaker 1: fiction novels they read, right, because like a million years ago,
49:14
Speaker 1: the Earth was not in the same spot at all, right,
49:16
Speaker 1: because the galaxy is technically moving a couple of million
49:19
Speaker 1: miles per hour. Yeah, sort of. And it's a fair
49:21
Speaker 1: point because things are in motion, and so you need
49:24
Speaker 1: to move sort of through time and through space. But again,
49:27
Speaker 1: it sort of depends on your reference frame. If your
49:29
Speaker 1: reference frame is like the center of the Earth, then
49:32
Speaker 1: you know, none of that motion is really relevant and
49:34
Speaker 1: it doesn't affect like how time works or how space works.
49:38
Speaker 1: If your reference frame is the center of the galaxy,
49:40
Speaker 1: then it does kind of matter. And so it sort
49:42
Speaker 1: of depends on like when you're programming your time machine,
49:46
Speaker 1: what coordinates does it take? You know, is it taking
49:49
Speaker 1: its coordinates relative to this center of the galaxy, in
49:51
Speaker 1: which case you better be careful about how you type
49:53
Speaker 1: them in, or is it taking its coordinates relative to
49:56
Speaker 1: the Earth for example, Right, But the problem is that
49:58
Speaker 1: the Earth is accelerating, and the UH and the galaxies
50:01
Speaker 1: and the Solar System is accelerating, So it would probably
50:04
Speaker 1: be really really complicated, right to sort of keep that
50:07
Speaker 1: same reference frame exactly, And so if you're going to
50:09
Speaker 1: move through time, you need to also be moving through
50:12
Speaker 1: space to make sure you land in the right spot.
50:15
Speaker 1: Some good advice for when we when I build that
50:18
Speaker 1: time machine, or at least good advice for science fiction
50:21
Speaker 1: authors when you write time travel into your novel, at
50:23
Speaker 1: least make sure to include this so that our listeners
50:25
Speaker 1: don't get annoyed. Right, right, you know, you have to
50:28
Speaker 1: add the caveat that it's a space time machine, not
50:30
Speaker 1: just a time machine, exactly, exactly, every working time travel
50:34
Speaker 1: machine is actually a space time travel machine. There you
50:37
Speaker 1: go h G. Wells got it totally wrong. We should
50:40
Speaker 1: have been its titles. Too bad. We can't have him
50:42
Speaker 1: on the podcast. If we had a time machine, we
50:44
Speaker 1: could have him on the podcast. Yeah, but he would
50:46
Speaker 1: be in a totally different prison. You're right, we'd be
50:50
Speaker 1: interviewing him from two million miles away. All right, Well,
50:53
Speaker 1: I think that answers the question pretty well. Can you
50:55
Speaker 1: be motionless in space? The answer is no, but you
50:59
Speaker 1: could be most and list relative to the stuff in
51:02
Speaker 1: the universe, which is pretty much the universe, right, Like
51:05
Speaker 1: you could You could technically be motionless relative to the
51:08
Speaker 1: stuff in the universe, just not relative to space. WHOA,
51:11
Speaker 1: you just demoted space to not be like an important
51:14
Speaker 1: part of the nature of the universe. That's kind of
51:15
Speaker 1: a big deal. I think I demoted relative to the
51:19
Speaker 1: question in the podcast episode, but no disrespect to space.
51:22
Speaker 1: I like space. I like my space. But yeah, we
51:26
Speaker 1: hope you enjoyed Dad. Thanks for joining us, See you
51:29
Speaker 1: next time. Thanks for listening, and remember that Daniel and
51:40
Speaker 1: Jorge explained. The Universe is a production of I Heart
51:43
Speaker 1: Radio or more podcast For my heart Radio, visit the
51:46
Speaker 1: I Heart Radio app, Apple Podcasts, or wherever you listen
51:50
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