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Could spacetime be a fluid? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, I have a question about the physics of space.
• 0:12
  Speaker 2: Oh cool, I love those Space is so amazing and
• 0:16
  Speaker 2: fun to talk about.
• 0:17
  Speaker 1: Well, not the physics of space space, I mean like
• 0:19
  Speaker 1: the office space of physics.
• 0:22
  Speaker 2: What's the physics of office space?
• 0:25
  Speaker 3: You know?
• 0:25
  Speaker 1: I remember when I visited at CERN and I walked
• 0:28
  Speaker 1: by the office of a physicists called John Ellis, and
• 0:32
  Speaker 1: it was so messy, with paper stacks so high it
• 0:35
  Speaker 1: looked almost impossible to walk in.
• 0:38
  Speaker 2: Yeah, he is famously disorganized.
• 0:41
  Speaker 1: Now how does that work? Do particle physicists have some
• 0:44
  Speaker 1: kind of special trick that makes their office bigger on
• 0:47
  Speaker 1: the inside than on the outside, you know, kind of
• 0:49
  Speaker 1: like those Harry Potter tents.
• 0:51
  Speaker 2: Actually, I think it might be the opposite. I think
• 0:54
  Speaker 2: their offices are on the verge of collapsing into personal
• 0:57
  Speaker 2: black holes.
• 0:59
  Speaker 1: No, but that's kind of what I mean, Like black
• 1:00
  Speaker 1: holes might have whole universes inside of him. Do physicist
• 1:03
  Speaker 1: offices have a whole universe inside of him? And what
• 1:06
  Speaker 1: are they doing inside of there?
• 1:07
  Speaker 2: I don't know, but I suspect in John Ellis's office
• 1:10
  Speaker 2: there's lots of ideas lost behind his personal event.
• 1:13
  Speaker 1: Horizon, event horizon or mess Horizon.
• 1:17
  Speaker 2: The disorganization Horizon.
• 1:34
  Speaker 1: I am Jorge May, cartoonist and the creator of PhD comments.
• 1:37
  Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor
• 1:40
  Speaker 2: at UC Irvine. And contrary to popular perception, I do
• 1:45
  Speaker 2: try to keep my office kind of organized.
• 1:47
  Speaker 1: Kinda that that sounds like a little bit of a
• 1:49
  Speaker 1: loophole there. Yeah, my office is totally kind of organized
• 1:53
  Speaker 1: if you set the bar really for the definition of
• 1:56
  Speaker 1: the word organization.
• 1:57
  Speaker 2: I didn't want to brag too much, but yes, I
• 1:59
  Speaker 2: do like to keep my office neat and tidy.
• 2:02
  Speaker 1: M I'm not sure that's something to brag about it.
• 2:05
  Speaker 1: Don't they say genius is related to how messy your
• 2:08
  Speaker 1: desk is?
• 2:09
  Speaker 2: Yeah? Well, Obama said physical discipline leads to mental discipline, So.
• 2:13
  Speaker 1: Yeah, well, I think Yoda said something similar. Also, organization
• 2:17
  Speaker 1: leads to hate. Hate leads to suffering, and suffering leads
• 2:20
  Speaker 1: to the dark side.
• 2:21
  Speaker 2: But who do you think would win in basketball? Obama
• 2:23
  Speaker 2: or Yoda?
• 2:24
  Speaker 1: Yoda? I mean, I love Obama, but come on, Yoda,
• 2:28
  Speaker 1: I can do like Super summersaults with a lightsaber.
• 2:31
  Speaker 2: Yeah, that dude could probably dunk, that's true.
• 2:33
  Speaker 1: Anyways, Welcome to our podcast Daniel and Jorge in the Universe,
• 2:36
  Speaker 1: a production of iHeartRadio in which we.
• 2:38
  Speaker 2: Do mental summersaults to try to explain the entire universe
• 2:43
  Speaker 2: to you. We go out there into the vast stretches
• 2:46
  Speaker 2: of empty space, wondering about what is actually out there,
• 2:49
  Speaker 2: what it's made out of, zoom down to the very
• 2:52
  Speaker 2: granular nature of reality itself, and ask questions about what
• 2:56
  Speaker 2: it is, what it means, and how we can figure
• 2:59
  Speaker 2: it all out. We zoom in, we zoom out, we
• 3:01
  Speaker 2: zoom everywhere in the universe to try to explain everything
• 3:05
  Speaker 2: to you.
• 3:05
  Speaker 1: That's right, because it is a pretty amazing universe, and
• 3:08
  Speaker 1: we like to explore the force in it, the dark
• 3:11
  Speaker 1: side of it, and also the physics of basketball sometimes
• 3:15
  Speaker 1: as well.
• 3:15
  Speaker 2: You know, I wonder in the Star Wars universe you
• 3:17
  Speaker 2: have like young Jedi. Are they playing sports with each other?
• 3:20
  Speaker 2: Do they have some version of like Jedi quidditch where
• 3:23
  Speaker 2: they're you know, pushing balls around with their minds?
• 3:26
  Speaker 1: Oh, interesting question. You should write like a fan fiction
• 3:29
  Speaker 1: bbble based on just that Harry Potter Star Wars like
• 3:33
  Speaker 1: qui gon quidditch fan fiction for Star Wars, and throw
• 3:38
  Speaker 1: in some brooms as well.
• 3:39
  Speaker 2: But I'm asking a serious question. I think give a
• 3:40
  Speaker 2: deeper knowledge of these universes than I do. Do young
• 3:44
  Speaker 2: Jedi play some sort of ball sports with their minds.
• 3:46
  Speaker 1: I don't see why they wouldn't. I guess I don't
• 3:49
  Speaker 1: think it's canon. I mean, I do play with a
• 3:51
  Speaker 1: little like a floating ball where they try to hit
• 3:53
  Speaker 1: it with the lightsaber. Maybe may that's a sport. I
• 3:56
  Speaker 1: don't know. We'll have to ask George Lucas. Can we
• 3:58
  Speaker 1: get them on the podcast Lucas?
• 4:00
  Speaker 2: Oh yeah, I totally email with George Lucas all the time.
• 4:03
  Speaker 2: I send him all of my Star Wars ideas.
• 4:05
  Speaker 1: Oh good, that would explain a lot.
• 4:08
  Speaker 2: I don't get any answers, but I do email him.
• 4:10
  Speaker 1: But it is a pretty wonderful universe. We do explore
• 4:13
  Speaker 1: all sides of it because it's kind of a big universe.
• 4:16
  Speaker 1: There's a lot of space in it.
• 4:17
  Speaker 2: In fact, the universe is mostly space. The kind of
• 4:21
  Speaker 2: thing that you're standing on and the sun that's in
• 4:23
  Speaker 2: the sky is pretty unusual. If you're going to pick
• 4:25
  Speaker 2: like a random spot in the universe, you're mostly going
• 4:28
  Speaker 2: to end up in a spot without a whole lot
• 4:30
  Speaker 2: of stuff in it.
• 4:31
  Speaker 1: Yeah, because, as we talked about on the podcast, space
• 4:33
  Speaker 1: it's not just emptiness, it's not nothing. It is actually
• 4:37
  Speaker 1: a thing, the thing that can stretch, that can bend,
• 4:40
  Speaker 1: that can slow down time. It's reactive to things, So
• 4:44
  Speaker 1: it's not nothing exactly.
• 4:45
  Speaker 2: We know that space is something interesting and it's a
• 4:47
  Speaker 2: really fascinating step in our sort of multi stage exploration
• 4:51
  Speaker 2: of the universe. You know, we start just by looking
• 4:54
  Speaker 2: at the stuff that's around us. We ask what's that
• 4:56
  Speaker 2: made out of? What's that made out of? What's that
• 4:58
  Speaker 2: made out of? But we sort of never stop I'm
• 5:00
  Speaker 2: asking those questions, and now we're at the point where
• 5:02
  Speaker 2: we're trying to understand, like what is the thing that
• 5:04
  Speaker 2: all the stuff is in. You know, if matter in
• 5:07
  Speaker 2: the end is made of particles, and those particles are
• 5:09
  Speaker 2: oscillations and quantum fields, and those quantum fields sit in space,
• 5:14
  Speaker 2: then the next frontier of understanding really is to understand
• 5:17
  Speaker 2: what that space itself is, and is space sitting in
• 5:21
  Speaker 2: some sort of like meta super or subspace.
• 5:24
  Speaker 1: Yeah, it's a very spacey question. There are many possibilities
• 5:27
  Speaker 1: out there for what space can be. If you can't
• 5:31
  Speaker 1: imagine that.
• 5:31
  Speaker 2: And it's a fundamental question at the heart of modern physics.
• 5:35
  Speaker 2: We're trying to understand quantum theory, were trying to understand
• 5:37
  Speaker 2: relativity and gravitation, and if the nexus of those two
• 5:41
  Speaker 2: is the fundamental mystery of what space actually is? Can
• 5:44
  Speaker 2: it actually been to make black holes? Are black holes
• 5:47
  Speaker 2: really black holes? Or are they something else? Why is
• 5:50
  Speaker 2: the universe expanding? What will be its ultimate fate? At
• 5:53
  Speaker 2: their hearts, all of these questions really are asking what
• 5:57
  Speaker 2: is space? And what are the rules of it? What
• 6:00
  Speaker 2: earns it? What is it fundamentally? Is it in fact
• 6:03
  Speaker 2: fundamental or is it just a frothing, emergent phenomena of
• 6:06
  Speaker 2: something even deeper? Yeah?
• 6:08
  Speaker 1: And do the rules of space apply to office space?
• 6:11
  Speaker 1: And I mean where people work, not just a.
• 6:13
  Speaker 2: Movie Office space turns out to be mostly politics. You know,
• 6:16
  Speaker 2: every time somebody retires here, there's like a scramble to
• 6:19
  Speaker 2: see who gets their big office.
• 6:21
  Speaker 1: Oh really, does it go by seniority? Like the more
• 6:23
  Speaker 1: senior you are, the closer you are to the snack
• 6:27
  Speaker 1: room or the restrooms, or the closer you need to
• 6:30
  Speaker 1: be to the restroom.
• 6:31
  Speaker 2: Perhaps, you know academics. Academics always have ladder systems and
• 6:35
  Speaker 2: ranking systems and it's no different here. We have like
• 6:37
  Speaker 2: many levels of being a professor. It's not just like assistant,
• 6:41
  Speaker 2: associate and full professor. Within each of those, it's like
• 6:44
  Speaker 2: many gradations, like full professor four or associate professor seven
• 6:48
  Speaker 2: or whatever. So when a new office opens up, they
• 6:50
  Speaker 2: go down the ladder and ask people at the top
• 6:53
  Speaker 2: of the ladder if they want it or not. And ridiculously,
• 6:56
  Speaker 2: all the offices in my building at least are different sizes.
• 6:59
  Speaker 2: And it would have been so much simpler if just
• 7:02
  Speaker 2: every office was the same size. I know, they made
• 7:04
  Speaker 2: some really big ones and some really little ones.
• 7:07
  Speaker 3: Hmm.
• 7:07
  Speaker 1: It's almost like they wanted some drama, political drama. Maybe
• 7:11
  Speaker 1: that was the architects revenge.
• 7:12
  Speaker 2: Maybe it was I don't know.
• 7:14
  Speaker 1: Isn't there some kind of like office space inertia, Like ooh,
• 7:17
  Speaker 1: that that is a slightly bigger office, But I would
• 7:20
  Speaker 1: have to clean my office and pack everything up to move,
• 7:22
  Speaker 1: so maybe I'll just skip.
• 7:24
  Speaker 2: Yeah. I do think that a lot of people don't
• 7:26
  Speaker 2: take a bigger office just because they're happy where they are,
• 7:29
  Speaker 2: or they don't really care, or their office is such
• 7:32
  Speaker 2: a disaster that it's impossible to imagine moving. And I
• 7:36
  Speaker 2: think That's also why it's sometimes hard to get people
• 7:38
  Speaker 2: out of their offices, because if you've been in there
• 7:40
  Speaker 2: for thirty years, you got a lot of stuff you
• 7:42
  Speaker 2: got to move out.
• 7:43
  Speaker 1: Are you saying there is such a thing as space inertia?
• 7:46
  Speaker 1: Like space can have inertia.
• 7:47
  Speaker 2: Turns out space can have politics. That's even weirder.
• 7:50
  Speaker 1: Or can a black hole have inertia?
• 7:52
  Speaker 2: Back to actual physics? Black holes definitely do have inertia, right,
• 7:54
  Speaker 2: They have mass, which means that they have inertia. If
• 7:58
  Speaker 2: you pushed on a black hole, then it's acceleration be
• 8:00
  Speaker 2: inversely proportional to its mass.
• 8:02
  Speaker 1: But you wouldn't actually recommend that, right, pushing a black hole?
• 8:06
  Speaker 1: That would be not good.
• 8:07
  Speaker 2: It depends if the black hole is headed towards our
• 8:09
  Speaker 2: solar system, then I would say, yes, let's launch something
• 8:12
  Speaker 2: heavy to push on the black hole so that it
• 8:14
  Speaker 2: doesn't come through our solar system.
• 8:16
  Speaker 1: Well, I guess what I meant is you wouldn't want
• 8:18
  Speaker 1: to push it yourself, like send Daniel up into space
• 8:21
  Speaker 1: having pushed on the black hole. I don't think that
• 8:23
  Speaker 1: would end well.
• 8:24
  Speaker 2: Am I going to get a big office out of it? Maybe?
• 8:27
  Speaker 1: Probably? Yeah, you might have the whole black hole to yourself.
• 8:32
  Speaker 2: That sounds great, except there are no windows, and I
• 8:34
  Speaker 2: really like an office with a view.
• 8:35
  Speaker 1: Well, it would be all windows except except yeah, I
• 8:40
  Speaker 1: guess you couldn't stick your head out of the window. Mm.
• 8:42
  Speaker 2: Yeah.
• 8:42
  Speaker 1: But it is interesting to think about what space could
• 8:45
  Speaker 1: be like, what is it made out of, and what
• 8:48
  Speaker 1: actually makes space happen.
• 8:49
  Speaker 2: Sometimes I think about scientists the way we think about
• 8:52
  Speaker 2: fish swimming around in water, probably not even really aware
• 8:57
  Speaker 2: that they are inside some sort of fluid because that's
• 9:01
  Speaker 2: their entire world. It might take fish like hundreds of
• 9:04
  Speaker 2: years or thousands of years to discover that the thing
• 9:07
  Speaker 2: they're inside is not the fundamental nature of the universe.
• 9:09
  Speaker 2: It doesn't exist everywhere, and it can do other kinds
• 9:12
  Speaker 2: of things like boil and freeze and all sorts of stuff.
• 9:15
  Speaker 2: So I wonder if we are sort of like fish,
• 9:18
  Speaker 2: exploring the nature of space and only now discovering that
• 9:20
  Speaker 2: it can do weird things that might have strange properties
• 9:23
  Speaker 2: and might not even be the fundamental layer of reality
• 9:26
  Speaker 2: so to be.
• 9:27
  Speaker 1: On the podcast, we'll be asking the question is space
• 9:34
  Speaker 1: time a fluid? What do you mean it's a fluid?
• 9:38
  Speaker 1: It's certainly a gas isn't it.
• 9:40
  Speaker 2: Well, time definitely seems to flow, so why not space time?
• 9:44
  Speaker 1: Right, Well, it's basfinitely a solid thing. It's always there,
• 9:48
  Speaker 1: you can rely on it.
• 9:48
  Speaker 2: Well, back to the analogy with fish scientists, which I
• 9:50
  Speaker 2: think probably originates with Max Tegmark. If you discover that
• 9:54
  Speaker 2: space is more complicated than just the backdrop of the universe,
• 9:58
  Speaker 2: and you discover that it might have other properties, it
• 10:00
  Speaker 2: might be able to do things like flow or bubble
• 10:03
  Speaker 2: or have different phases. And so that's a fascinating question
• 10:07
  Speaker 2: about the nature of space itself and sort of what
• 10:09
  Speaker 2: it can do. Can we described using the mathematics of
• 10:13
  Speaker 2: fluids or do we need a completely different kind of
• 10:16
  Speaker 2: mathematics to explain what space is up to?
• 10:19
  Speaker 1: Well, it is kind of a mind blowing question to
• 10:21
  Speaker 1: think that space time could be a fluid. It makes
• 10:23
  Speaker 1: it seem like it's a physical thing, like it actually
• 10:26
  Speaker 1: has like mass to it or something, or that it
• 10:30
  Speaker 1: responds to forces and things like that.
• 10:32
  Speaker 2: Yeah, as we'll see, space time being a fluid would
• 10:35
  Speaker 2: give very specific predictions for how things propagate through it,
• 10:38
  Speaker 2: how energy is spread or dissipates. So it's a really
• 10:42
  Speaker 2: fascinating hypothesis and I know we've talked about it in
• 10:45
  Speaker 2: the podcast before, how space time could be like a bubble,
• 10:48
  Speaker 2: right or like a foam?
• 10:50
  Speaker 1: Is not a fluid is it?
• 10:51
  Speaker 4: Now?
• 10:51
  Speaker 2: There are many theories of what space might be down
• 10:54
  Speaker 2: at the granular level. Is it made of little pixels
• 10:57
  Speaker 2: which are woven together with quantum entanglement into a kind
• 10:59
  Speaker 2: of foam or do those pixels operate in a different
• 11:02
  Speaker 2: sort of way. So this is more about, like at
• 11:05
  Speaker 2: the fundamental level, what are the rules of how those
• 11:08
  Speaker 2: pixels interact with each other and what phenomena emerges from that.
• 11:12
  Speaker 2: Can you describe them using the physics of foam, or
• 11:15
  Speaker 2: of liquids, or of ice cream, or office space bright
• 11:20
  Speaker 2: or interpersonal politics.
• 11:21
  Speaker 1: Or any kind of politics. Well, as usual, we were
• 11:23
  Speaker 1: wondering how many people out there had thought about this question,
• 11:26
  Speaker 1: had thought that maybe space time could be a fluid.
• 11:29
  Speaker 1: So Daniel went out there as usual and ask the
• 11:32
  Speaker 1: internet what they thought.
• 11:33
  Speaker 2: Thanks very much to everybody who answers these questions. We
• 11:36
  Speaker 2: love to hear your voice on the podcast, and anybody
• 11:40
  Speaker 2: out there who wants to volunteer, please don't be shy,
• 11:42
  Speaker 2: just write to me. Two questions at Danielandjorge dot com.
• 11:45
  Speaker 1: So think about it for a second. Do you think
• 11:47
  Speaker 1: space time could be a fluid? Here's what people had
• 11:51
  Speaker 1: to say.
• 11:51
  Speaker 4: I remember this was the argument for a theory in
• 11:54
  Speaker 4: the Bigavon theory. So yeah, maybe spacetime could be a fluid,
• 12:00
  Speaker 4: and that's the reason it only goes in one direction.
• 12:03
  Speaker 3: Maybe in previous episodes, I've noticed that you say that
• 12:09
  Speaker 3: space time can be stretched and squashed and almost like
• 12:12
  Speaker 3: molded in that kind of way. So I always imagine
• 12:16
  Speaker 3: space time being in some sort of matter state. So yes,
• 12:23
  Speaker 3: I would say space time could be similar.
• 12:26
  Speaker 1: To a fluid. I guess that space time is fluid
• 12:29
  Speaker 1: ish because you can't put it in a jar or something,
• 12:34
  Speaker 1: but it may behave like a fluid for some physics calculation.
• 12:39
  Speaker 5: I don't know, man, it seems like, you know, there's
• 12:42
  Speaker 5: waves in it, and we talk about it as some
• 12:44
  Speaker 5: sort of foam, But like what space is the fluid occupying?
• 12:49
  Speaker 5: That's that's a That's what gets me. I don't know.
• 12:52
  Speaker 6: So if I think about it, what is a fluid?
• 12:54
  Speaker 6: A fluid is a fluid will flow and it could
• 12:59
  Speaker 6: flow very slow like a glacier is ice? You think
• 13:03
  Speaker 6: ice is a solid but over long time scares a
• 13:07
  Speaker 6: glacier would flow like a river, and I think space
• 13:12
  Speaker 6: time around really massive objects like a black hole spinning
• 13:16
  Speaker 6: black hole in particular will also get dragged around. I
• 13:21
  Speaker 6: think it's called frame dragging, so space time itself will
• 13:25
  Speaker 6: spin around the black hole. And I think as you
• 13:28
  Speaker 6: go past the event horizon, doesn't space time itself kind
• 13:33
  Speaker 6: of flow towards the singularity.
• 13:36
  Speaker 1: I'm guessing that you could consider the curvature that some
• 13:40
  Speaker 1: kind of and start to exert on space time could
• 13:44
  Speaker 1: be considered blue. All right. I feel like we blew
• 13:47
  Speaker 1: people's minds with this question. Somebody's like one of the
• 13:50
  Speaker 1: people is like, WHOA, I don't know, man.
• 13:55
  Speaker 2: Well, that's my favorite part of this podcast is making
• 13:57
  Speaker 2: people explore crazy ideas, is dig deep into whether the
• 14:02
  Speaker 2: universe could really be different from the way that we
• 14:04
  Speaker 2: imagine it, you know, so contrary to our intuition. Those
• 14:08
  Speaker 2: are the best kinds of discoveries. And I think these
• 14:10
  Speaker 2: responses really reflect that kind of moment of exhilaration to
• 14:15
  Speaker 2: imagine that the universe could be so different.
• 14:17
  Speaker 1: I like the person to say they think it's fluid ish. Hey,
• 14:22
  Speaker 1: that's a good answer for anything. Do you think the unerus.
• 14:25
  Speaker 1: Is this there that way? I think it's this way ish.
• 14:28
  Speaker 2: Hmmm, my office is organized ish.
• 14:31
  Speaker 1: That's right. Yeah. But somebody else wrote in here that
• 14:35
  Speaker 1: space can have ways. We know that. You know you
• 14:37
  Speaker 1: can feel gravitational ways. We detected those. So if something
• 14:40
  Speaker 1: can have ways in it, does that mean it's like
• 14:42
  Speaker 1: a fluid?
• 14:43
  Speaker 2: Yeah, it's a really good deep question.
• 14:45
  Speaker 1: Like if you can make ripples in it, it's sort
• 14:47
  Speaker 1: of does that mean it is a fluid? I guess
• 14:48
  Speaker 1: you can make ripples in a gas too, or a solid.
• 14:51
  Speaker 2: Yeah. Liquids have special kinds of mathematics that describe them,
• 14:53
  Speaker 2: and that's what we're going to dig into. And there
• 14:55
  Speaker 2: are even people who have tried to build liquid analogies
• 14:58
  Speaker 2: of space time and liquid and analogies of black holes.
• 15:02
  Speaker 2: Is a guy in Israel who builds sonic black holes.
• 15:05
  Speaker 2: Sonic black holes. That sounds like a good definition for
• 15:09
  Speaker 2: our podcast. We're soundways good to die. I hope we're
• 15:13
  Speaker 2: not just speaking into the void. I hope there's somebody
• 15:15
  Speaker 2: out there listening. Maybe we're hawking radiationing our ideas into
• 15:19
  Speaker 2: the universe.
• 15:20
  Speaker 1: M you mean like we're fish in a fish tank. Maybe,
• 15:24
  Speaker 1: hopefully our soundways, are you going out there beyond the
• 15:27
  Speaker 1: fish tank?
• 15:28
  Speaker 2: I have some evidence that there are people out there
• 15:30
  Speaker 2: listening and we're not trapped into a sonic black hole
• 15:32
  Speaker 2: because we get responses from listeners. So if y'all are
• 15:35
  Speaker 2: actually out there and we're not trapped in a sonic
• 15:37
  Speaker 2: black hole, right back to us and confirm.
• 15:39
  Speaker 1: What if we're all in your mind, Daniel, what if
• 15:41
  Speaker 1: we're all like multiple personality aspects of you plot twist?
• 15:47
  Speaker 1: It's like the plot of an m. Jamelon movie.
• 15:50
  Speaker 2: I always wanted to be in one of his movies,
• 15:52
  Speaker 2: so I'd be pretty happy with that outcome.
• 15:53
  Speaker 1: But one of our responders here also asked an interesting
• 15:56
  Speaker 1: question like if space is a fluid, what is the
• 15:59
  Speaker 1: fluid in, Like what is it occupying? Is something holding
• 16:03
  Speaker 1: it like a jar or a fissible.
• 16:05
  Speaker 2: Or some sort of super space Like revealing the fundamental
• 16:08
  Speaker 2: nature of space time really just opens us up to
• 16:11
  Speaker 2: the next level of questions, like if space is a fluid,
• 16:15
  Speaker 2: or if space emerges from something else, and that other
• 16:17
  Speaker 2: thing and emerges from is more fundamental, and now we
• 16:20
  Speaker 2: can focus all of our energy on that thing. It
• 16:22
  Speaker 2: might be a never ending cycle where were always just
• 16:25
  Speaker 2: digging deeper and finding deeper and deeper layers of reality.
• 16:29
  Speaker 2: We don't know if we'll ever find some sort of
• 16:31
  Speaker 2: bedrock fundamental nature to the universe or not, or we
• 16:34
  Speaker 2: can always just ask, well, what's that made out of
• 16:37
  Speaker 2: or what's that sitting in?
• 16:38
  Speaker 1: Yeap goes on forever, and so let's start to dig
• 16:42
  Speaker 1: our way through it. Daniel, let's explain what is space time?
• 16:45
  Speaker 2: So the short version is we just really have no
• 16:48
  Speaker 2: idea what space is.
• 16:50
  Speaker 1: Boom and done, all right, thanks for joining us. It
• 16:54
  Speaker 1: is kind of a black hole. See question Yeah, good
• 16:56
  Speaker 1: diet on our podcast.
• 16:58
  Speaker 2: One of the most confusing things about it is that
• 17:00
  Speaker 2: we have very crisp and clear pictures of what space
• 17:04
  Speaker 2: might be in the theories that we have built up
• 17:06
  Speaker 2: about the universe, and as we've talked about in the
• 17:08
  Speaker 2: podcast many times, we have like two pillars of modern physics,
• 17:12
  Speaker 2: two different sets of ideas that have helped us answer
• 17:14
  Speaker 2: questions about what's going on in the universe. We have
• 17:16
  Speaker 2: quantum mechanics and we have general relativity. They're fundamentally inconsistent,
• 17:21
  Speaker 2: and they each give us a very different picture of
• 17:24
  Speaker 2: what space might be and how it works. So one
• 17:27
  Speaker 2: of the biggest puzzles is like trying to bring these
• 17:29
  Speaker 2: two things together to give us at least a unified
• 17:32
  Speaker 2: picture of what space is. But as of now, nobody's
• 17:35
  Speaker 2: been able to do that.
• 17:37
  Speaker 1: Yeah, there are two different views, so let's do one
• 17:39
  Speaker 1: of them at a time. What is space time according
• 17:42
  Speaker 1: to quantum mechanics or does quantum mechanics even call it
• 17:45
  Speaker 1: space time or does it treat space and time differently?
• 17:48
  Speaker 2: Yeah, quantum mechanics treat space and time very differently. It
• 17:52
  Speaker 2: treats space as the backdrop for quantum fields. It says
• 17:56
  Speaker 2: that space is filled with these fields that can oscillate,
• 18:00
  Speaker 2: and we have great equations that describe exactly how they
• 18:03
  Speaker 2: oscillate and buzz, and you can use those equations to
• 18:06
  Speaker 2: explain how electrons fly through space and how they radiate
• 18:10
  Speaker 2: photons which are absorbed by other particles. And so far
• 18:12
  Speaker 2: it seems like a super duper accurate description of what's
• 18:16
  Speaker 2: going on in the universe. We've done amazing experiments to
• 18:18
  Speaker 2: validate this description of the universe and compare it to
• 18:20
  Speaker 2: quantum mechanics predictions, which agreed to like eight or nine
• 18:23
  Speaker 2: decimal places. It's really super impressive. But the picture of
• 18:26
  Speaker 2: space and quantum mechanics is just sort of like the backdrop.
• 18:29
  Speaker 2: It's where the fields are. You know, we do the
• 18:31
  Speaker 2: mathematics of quantum field theory. We write these fields as
• 18:34
  Speaker 2: a function of space. We say every location in space
• 18:38
  Speaker 2: has a value of these fields, or if it's a
• 18:40
  Speaker 2: vector field, multiple values. There are like these numbers embedded
• 18:44
  Speaker 2: in space. The time is different. Time just tells us
• 18:47
  Speaker 2: how those fields change. And one really important thing about
• 18:50
  Speaker 2: time in quantum mechanics is that it should be infinite.
• 18:53
  Speaker 2: Like quantum mechanics says that the universe should have always
• 18:56
  Speaker 2: existed and should always exist because information in the universe
• 19:00
  Speaker 2: can't be lost, it can't just go away. And so
• 19:03
  Speaker 2: if you take the shorten your equation, for example, and
• 19:05
  Speaker 2: use it to describe the universe, you can run it
• 19:07
  Speaker 2: backwards and forwards in time to infinity. And that actually
• 19:10
  Speaker 2: tells you something about space itself, because it says that
• 19:13
  Speaker 2: space should have always existed throughout the whole universe. That's
• 19:17
  Speaker 2: sort of the quantum mechanical view of space time.
• 19:20
  Speaker 1: I feel like quantum mechanics. I feel like you're saying
• 19:22
  Speaker 1: that quantum mechanics is still basically stuck in the same
• 19:26
  Speaker 1: view of space as Newton was kind of right, like
• 19:30
  Speaker 1: before general relativity and Einstein, we just thought space was
• 19:33
  Speaker 1: this big emptiness. It couldn't change. It was like a
• 19:36
  Speaker 1: giant warehouse, you know, couldn't change or move or ripple
• 19:39
  Speaker 1: or anything like that. It was just fixed. Space was fixed.
• 19:41
  Speaker 1: And then you had time making things move forward in time.
• 19:44
  Speaker 1: And so quantum mechanics sort of started from that, and
• 19:47
  Speaker 1: it didn't really kind of think about what space could be.
• 19:50
  Speaker 1: It's sort of still stuck in that Newtonian or classical
• 19:53
  Speaker 1: physics view of space.
• 19:54
  Speaker 2: I think the broad strokes of that are definitely true.
• 19:56
  Speaker 2: There's a couple of sort of interesting and important caveats.
• 20:00
  Speaker 2: One is that we have succeeded in making quantum mechanics
• 20:04
  Speaker 2: act relativistically in some cases, like behaving with the rules
• 20:08
  Speaker 2: of relativity. Like we can describe the motion of super
• 20:11
  Speaker 2: duper fast quantum particles. Take an electron accelerate to almost
• 20:15
  Speaker 2: the speed of light, or protons at almost the speed
• 20:17
  Speaker 2: of light, and then you need like relativistic quantum mechanics.
• 20:21
  Speaker 2: But that's special relativity. That's just dealing mostly again with
• 20:24
  Speaker 2: flat space. So we can bring sort of special relativity's
• 20:28
  Speaker 2: view of space time into quantum mechanics. But you're right, fundamentally,
• 20:32
  Speaker 2: we're still just talking about things happening in the backdrop
• 20:35
  Speaker 2: of space. The other important thing to understand there is
• 20:37
  Speaker 2: that we have to add these things to quantum mechanics.
• 20:40
  Speaker 2: Quantum mechanics doesn't naturally have the sort of symmetries and
• 20:44
  Speaker 2: laws that we find in the universe. For example, you
• 20:47
  Speaker 2: can build quantum mechanics without a constant speed of light
• 20:50
  Speaker 2: or an invariant speed of light. We know that out
• 20:52
  Speaker 2: there in the universe the speed of light is the
• 20:54
  Speaker 2: speed of light is the speed of light, no matter
• 20:56
  Speaker 2: who's measuring it or what the setup is. But quantu
• 20:59
  Speaker 2: mechanics doesn't require that. It's not like built in. It
• 21:02
  Speaker 2: doesn't fall out of quantum mechanics naturally. So something you
• 21:04
  Speaker 2: have to add on to quantum mechanics, and that we've
• 21:07
  Speaker 2: been able to do we haven't been able to do
• 21:09
  Speaker 2: is make quantum mechanics consistent with curving spaces, to make
• 21:12
  Speaker 2: a quantum version of general relativity. That's the part we
• 21:16
  Speaker 2: haven't been able to do yet. But you're right, it
• 21:18
  Speaker 2: still sits in the sort of Newtonian backdrop where space
• 21:21
  Speaker 2: is the stage on which things happen.
• 21:23
  Speaker 1: So quantum mechanics maybe their view of space, it's viewo
• 21:27
  Speaker 1: space kind of matches maybe what most people think of
• 21:30
  Speaker 1: as space, or at least what you know, anyone who's
• 21:32
  Speaker 1: had a high school education in physics would think of
• 21:36
  Speaker 1: a space.
• 21:36
  Speaker 2: Weird stuff happens in that space, according to quantum mechanics,
• 21:39
  Speaker 2: but the space itself is just sort of like the
• 21:42
  Speaker 2: playground on which that weird stuff happens.
• 21:44
  Speaker 1: Yeah, Like nothing weird happens to space itself.
• 21:48
  Speaker 2: Yeah. And also that space really is Newtonian in the
• 21:51
  Speaker 2: sense that it doesn't have a lot of the symmetries
• 21:53
  Speaker 2: and principles that Einstein showed us that it does have,
• 21:56
  Speaker 2: like respecting the speed of light and all sorts of relativistic.
• 21:59
  Speaker 1: And varying interesting. All right, well, let's get into what
• 22:03
  Speaker 1: general relativity says that space is and whether or not
• 22:07
  Speaker 1: we could ever match it up with quantum mechanics, and
• 22:10
  Speaker 1: whether that could mean that space is a fluid. So
• 22:12
  Speaker 1: let's get into that, but first let's take a quick break.
• 22:27
  Speaker 1: All right, we're talking about the question of whether space
• 22:30
  Speaker 1: time is a fluid and whether that would mean that
• 22:33
  Speaker 1: you can drink it. And what kind of straw what
• 22:35
  Speaker 1: you need? Do you need a space time straw?
• 22:39
  Speaker 2: What's a good mixer for space? I wonder something dark?
• 22:42
  Speaker 1: Yeah, dark dark vodka, dark tequila. I don't know, maybe
• 22:46
  Speaker 1: some kalua pick your poison.
• 22:48
  Speaker 2: I think maybe some cream because space is pretty dark,
• 22:50
  Speaker 2: so you got to lighten it up a little bit,
• 22:51
  Speaker 2: you know. I'll take my space with some cream and
• 22:53
  Speaker 2: sugar please.
• 22:54
  Speaker 1: Or if it's a fluid, I guess that means you
• 22:56
  Speaker 1: can flush it? Can you flush space space time? You
• 22:59
  Speaker 1: sort of can, right, a black hole?
• 23:00
  Speaker 2: Maybe black holes are a sort of the toilets of
• 23:04
  Speaker 2: the universe. That's true.
• 23:05
  Speaker 1: Yeah, they suck in a lot of dark matter.
• 23:09
  Speaker 2: They actually don't, but it's a good joke.
• 23:12
  Speaker 1: Well, do you know, I guess that's the topic of
• 23:16
  Speaker 1: a different podcast.
• 23:17
  Speaker 2: Yeah, exactly. It's a really fun question.
• 23:19
  Speaker 1: You were talking about whether space time is the fluid,
• 23:21
  Speaker 1: and we talked about what space time is according to
• 23:24
  Speaker 1: quantum mechanics, which is pretty much the same view that
• 23:27
  Speaker 1: Newton had the classical physics have about space. But then
• 23:30
  Speaker 1: at some point at the beginning of the twentieth century,
• 23:33
  Speaker 1: Einstein came along and said, wait, dam minute. Space time
• 23:36
  Speaker 1: is not like fixed and immovable. It it does things,
• 23:39
  Speaker 1: It has properties of its own.
• 23:41
  Speaker 2: Yeah, Einstein showed us that space is dynamic. It's not
• 23:45
  Speaker 2: just a flat backdrop to the universe. It participates in
• 23:48
  Speaker 2: the motion of the universe in everything that happens. You know,
• 23:52
  Speaker 2: as I think John Wheeler said, mass tells space how
• 23:54
  Speaker 2: to mend, and space tells mass how to move. That
• 23:58
  Speaker 2: means that if you have a mass and certain part
• 24:00
  Speaker 2: of space, or a bunch of energy, then it curves
• 24:02
  Speaker 2: space itself. And Einstein's big realization was that what we
• 24:07
  Speaker 2: think of as the force of gravity isn't actually a force.
• 24:10
  Speaker 2: It's just due to our inability to directly see the
• 24:13
  Speaker 2: curvature of space, which is affecting how things are moving.
• 24:17
  Speaker 2: So the actions that we attribute to the force of
• 24:19
  Speaker 2: gravity are really just inertial motions of objects through curved space.
• 24:24
  Speaker 2: And his conception of space is this incredibly fascinating sort
• 24:28
  Speaker 2: of curved manifold, this sort of like shape that has
• 24:31
  Speaker 2: features to it. It's curved here, it's not curved there.
• 24:34
  Speaker 2: But it's really totally different from the conception of space
• 24:38
  Speaker 2: in quantum mechanics. It's not just a backdrop right, it's
• 24:41
  Speaker 2: not just like here's something that's happening at this location
• 24:43
  Speaker 2: and that location. The locations themselves now have interesting relationships,
• 24:48
  Speaker 2: like instead of just having a grid and every point
• 24:50
  Speaker 2: is equally spaced, those points can have weird relative distances,
• 24:53
  Speaker 2: like this point is actually closer than that point on
• 24:56
  Speaker 2: the grid, and these two points, which are super far
• 24:58
  Speaker 2: apart in the universe normally, can actually be adjacent to
• 25:01
  Speaker 2: each other. That's what a wormhole is. So really general
• 25:04
  Speaker 2: relativity is telling us that space can do this weird
• 25:06
  Speaker 2: thing about changing the relative distances internally between the points
• 25:10
  Speaker 2: that affects the motion of objects through it. And they
• 25:13
  Speaker 2: also discovered all these fascinating symmetries, like there's a maximum
• 25:17
  Speaker 2: speed of information through the universe. That was one of
• 25:19
  Speaker 2: the other big revelations in Einsteinian gravity, which contradicts Newtonian gravity.
• 25:25
  Speaker 2: That said that information propagates instantly according to Newton's gravity.
• 25:29
  Speaker 2: So Einstein's view of space is this smooth, continuous, but
• 25:33
  Speaker 2: dynamic thing that really plays a role in the universe.
• 25:36
  Speaker 2: It doesn't just sort of sit in the background and
• 25:38
  Speaker 2: provide a frame.
• 25:39
  Speaker 1: Yeah, it's pretty amazing. Eislin was able to kind of
• 25:42
  Speaker 1: revolutionize that video space. And I wonder if you or
• 25:47
  Speaker 1: we know how that came about, Like what was the
• 25:49
  Speaker 1: thing that set them off in that direction? Was it
• 25:51
  Speaker 1: basically observing what happens out there in nature that the
• 25:54
  Speaker 1: speed of light doesn't change. And if you start from there,
• 25:57
  Speaker 1: then you can sort of put together this idea that's
• 25:59
  Speaker 1: based on and bend and ripple.
• 26:01
  Speaker 2: Well, there are many stages in Einstein's thinking. The first is,
• 26:04
  Speaker 2: as you describe special theory of relativity, trying to understand
• 26:07
  Speaker 2: the Michaelson Morley experiment that showed that the speed of
• 26:09
  Speaker 2: light was the same in every direction, and also trying
• 26:11
  Speaker 2: to understand some puzzles in electromagnetic theory at the time,
• 26:15
  Speaker 2: like why a static electron gives an electric field, but
• 26:18
  Speaker 2: an electron in motion gives an electric and magnetic field.
• 26:22
  Speaker 2: Like it seemed like what was happening there dependent on
• 26:25
  Speaker 2: your perspective. So Einstein was trying to resolve all of
• 26:27
  Speaker 2: these puzzles. We have a whole podcast episode about that,
• 26:30
  Speaker 2: and that's what led to the special theory of relativity,
• 26:33
  Speaker 2: the idea of the speed of light being maximum and
• 26:36
  Speaker 2: information propagating at a certain speed and time not being
• 26:40
  Speaker 2: the same everywhere in the universe. That was already a
• 26:42
  Speaker 2: big step forward, But then it took like another ten
• 26:44
  Speaker 2: years for him to come up with the general theory
• 26:46
  Speaker 2: of relativity that's the one we're describing here, which is
• 26:49
  Speaker 2: about how space is curved and that curvature can explain
• 26:52
  Speaker 2: gravity for him, that came from puzzling over this question
• 26:55
  Speaker 2: about like, why is gravitational mass the massive controls how
• 26:59
  Speaker 2: much we get pulled on one seem to be exactly
• 27:01
  Speaker 2: the same as our inertial mass, the one that determines
• 27:04
  Speaker 2: how much we accelerate when we get pushed, Like the
• 27:07
  Speaker 2: mass in f equals M versus the mass in Newton's
• 27:11
  Speaker 2: law of gravity. Why do those two things seem to
• 27:13
  Speaker 2: be the same. So Einstein's sort of made that connection
• 27:16
  Speaker 2: and realized that they're really all bound up in the
• 27:18
  Speaker 2: same idea. Able to explain all of it by changing
• 27:21
  Speaker 2: space into a curved object or space time or space time. Yeah,
• 27:27
  Speaker 2: and there's a really important consequence there, right, If Einstein's
• 27:31
  Speaker 2: theory of space is correct, then you can also track
• 27:34
  Speaker 2: it backwards in time and say, look, the universe is expanding,
• 27:37
  Speaker 2: and that means that we can go backwards instead. The
• 27:39
  Speaker 2: universe used to be hotter and denser, and in Einstein's
• 27:42
  Speaker 2: theory at least that means that space and time can
• 27:44
  Speaker 2: have a beginning, right Unlike in quantum mechanics infinite in time,
• 27:48
  Speaker 2: Einstein's theory says that space could have had a beginning,
• 27:51
  Speaker 2: that there could have been a moment when there was
• 27:53
  Speaker 2: no space. So these are really very contradictory views of space.
• 27:57
  Speaker 2: Quantum mechanics view says time is infinite and space has
• 28:00
  Speaker 2: always existed. General relativity allows for a universe where space begins.
• 28:04
  Speaker 1: And so that brings us to maybe the biggest I
• 28:07
  Speaker 1: guess conflict in physics, the conflict between quantum mechanics and
• 28:10
  Speaker 1: general relativity and how they treat space. And this conflict
• 28:14
  Speaker 1: is kind of theoretical but also very conceptual. Like you said,
• 28:17
  Speaker 1: it's about, you know, whether time can begin or how
• 28:20
  Speaker 1: a beginning, whether time can bend? Is the conflict here
• 28:24
  Speaker 1: mostly theoretical, like we can make the theories work or
• 28:29
  Speaker 1: do you think it's something maybe more fundamental, that maybe
• 28:31
  Speaker 1: the properties of space change once you get to a
• 28:34
  Speaker 1: certain size level.
• 28:35
  Speaker 2: Yeah, we definitely cannot make the theories work currently, Like
• 28:39
  Speaker 2: people are trying from all sorts of directions to unify
• 28:41
  Speaker 2: these things. One set of theories is saying, well, let's
• 28:44
  Speaker 2: take quantum mechanics and try to do it in curved space,
• 28:47
  Speaker 2: and that actually kind of works, like if you have
• 28:50
  Speaker 2: space that already curves. For other reasons, we do know
• 28:53
  Speaker 2: how to do some quantum mechanics of particles moving in
• 28:56
  Speaker 2: curved space. We don't know how to do is show
• 28:58
  Speaker 2: how quantum mechanics can make space curved, like to get
• 29:02
  Speaker 2: that curvature just from the particles, to show how like
• 29:05
  Speaker 2: having a bunch of electrons in one place will make
• 29:08
  Speaker 2: space curved. When people try to do that, it gets
• 29:10
  Speaker 2: really complicated and hairy, and you get all sorts of infinities.
• 29:13
  Speaker 2: And one of the reasons is that gravity is are
• 29:15
  Speaker 2: real nest to do calculations with. If you emit gravitons,
• 29:18
  Speaker 2: gravitons feel gravity, and they emit more gravitons, which emit
• 29:21
  Speaker 2: more gravitons, so it very quickly gets out of control,
• 29:24
  Speaker 2: sort of like the strong nuclear force. We were talking about
• 29:26
  Speaker 2: how gluons emit gluons, which emit gluons, which makes it
• 29:30
  Speaker 2: almost impossible to do those calculations. But gravity is even trickier.
• 29:33
  Speaker 2: And so people have really failed in trying to do that.
• 29:37
  Speaker 2: And from the other direction, people are saying, well, let's
• 29:39
  Speaker 2: take space and quantize it and say maybe instead of
• 29:42
  Speaker 2: the force being quantum mechanical, maybe space itself is quantum mechanical.
• 29:46
  Speaker 2: It's chopped up into little discrete bits. And this idea
• 29:49
  Speaker 2: also hasn't quite worked yet. Nobody's really been able to
• 29:52
  Speaker 2: bring these two things together mathematically. What you asked is like,
• 29:55
  Speaker 2: is this a mathematical problem or a theoretical problem? And
• 29:58
  Speaker 2: I think the answers are connected. If we are able
• 30:01
  Speaker 2: to come up with a mathematical description that explains everything
• 30:04
  Speaker 2: we see in the universe and sort of hangs together,
• 30:06
  Speaker 2: doesn't give us nonsense, then we'll have a theoretical or
• 30:09
  Speaker 2: philosophical question like what does that mean? You know, how
• 30:12
  Speaker 2: far do we have to go in order to make
• 30:14
  Speaker 2: that theory? Can we just try to bring these two
• 30:16
  Speaker 2: theories together, or do we need to dig a level
• 30:18
  Speaker 2: deeper and start from something else which can then explain
• 30:22
  Speaker 2: what we're seeing on the larger level?
• 30:24
  Speaker 1: Interesting, I guess you'll just have a big fight about it.
• 30:28
  Speaker 1: And then wherever win in spins.
• 30:29
  Speaker 2: And I think one of the deepest questions really is
• 30:32
  Speaker 2: like is space itself the fundamental fabric of the universe?
• 30:36
  Speaker 2: Do we need to be building on top of space
• 30:38
  Speaker 2: or do we need to be tearing it apart and
• 30:40
  Speaker 2: trying to understand what it's made out of? Like is
• 30:44
  Speaker 2: space itself fundamental? Meaning it just is, it's like the
• 30:48
  Speaker 2: base layer of reality. Or is space emergent it's just
• 30:52
  Speaker 2: something that arises from something deeper and it's complicated interactions.
• 30:56
  Speaker 1: That's kind of I feel like that maybe that's a
• 30:58
  Speaker 1: separate question. Then this idea whether quantum mechanics or general
• 31:02
  Speaker 1: relativity is right, right, it's sort of a separate question,
• 31:05
  Speaker 1: like whether either one is right. We can also ask
• 31:07
  Speaker 1: the question like where does space come from?
• 31:10
  Speaker 2: Well, it might be a path forward to giving us
• 31:13
  Speaker 2: these two different explanations of space. Space seems to be
• 31:15
  Speaker 2: kind of different in quantum mechanics and in relativity, And
• 31:19
  Speaker 2: instead of harmonizing them and of trying to mash them together,
• 31:22
  Speaker 2: you might be able to explain them just by saying, well,
• 31:24
  Speaker 2: they're sort of both wrong. Neither of them are actually
• 31:27
  Speaker 2: true descriptions of what space is. Space is something deeper
• 31:30
  Speaker 2: and weirder that can do these two kinds of things
• 31:33
  Speaker 2: the way for example, fish scientists might argue and say, look, look,
• 31:36
  Speaker 2: ice is different from liquid water, which is different from gas.
• 31:39
  Speaker 2: They're just different, right, And we know of course they're
• 31:42
  Speaker 2: all made out of the same thing deep down. This
• 31:44
  Speaker 2: is just different stuff that water can do. Ice is
• 31:47
  Speaker 2: not fundamental to the universe. Water is not fundamental to
• 31:50
  Speaker 2: the universe. Steam is not fundamental to the universe. It's
• 31:52
  Speaker 2: just an emergent property of water. If we can come
• 31:55
  Speaker 2: up with like a deeper understanding of what space is,
• 31:59
  Speaker 2: something beyond our understanding currently, maybe we can explain are
• 32:03
  Speaker 2: the quantum mechanical view of space and the general relativistic
• 32:06
  Speaker 2: view of space is like different phases of space the
• 32:10
  Speaker 2: way we think about different phases of water having you know,
• 32:13
  Speaker 2: fundamentally inconsistent kinds of behavior.
• 32:16
  Speaker 1: Well, that's kind of what I meant before, is that,
• 32:18
  Speaker 1: like you know, it's the conflict between quantum mechanics and
• 32:20
  Speaker 1: general relativity. Could it be explained by just like having
• 32:24
  Speaker 1: space behave differently at different scales, like in the scale
• 32:27
  Speaker 1: of planets and black holes, it behaves like one way
• 32:30
  Speaker 1: where you have grampetition waves and it bends. But maybe
• 32:33
  Speaker 1: at the level of small particles, it behaves differently.
• 32:36
  Speaker 2: Yeah, that's exactly the right direction, and a lot of
• 32:38
  Speaker 2: people are pushing that way, like can we start at
• 32:41
  Speaker 2: a lower level and come up with a more fundamental
• 32:44
  Speaker 2: description of space and then as you say, it turns
• 32:47
  Speaker 2: into quantum mechanics at this scale, or turns into general
• 32:49
  Speaker 2: relativity at that scale, and fundamentally, what that means is
• 32:52
  Speaker 2: that both are wrong. Instead of trying to start from
• 32:55
  Speaker 2: general relativity and at quantum mechanics, or start from quantum
• 32:58
  Speaker 2: mechanics and ad general relativity, of throw both out the
• 33:01
  Speaker 2: window and say let's start from something deeper and try
• 33:03
  Speaker 2: to reproduce both of them, but neither of them fundamentally
• 33:06
  Speaker 2: would be correct in that picture.
• 33:08
  Speaker 1: Well you want to throw them out? That sounds very
• 33:10
  Speaker 1: negative and I feel like a lot of work has
• 33:13
  Speaker 1: gone into those It could just be that they're both right.
• 33:16
  Speaker 1: They're just right at different scales perhaps or in different situations,
• 33:19
  Speaker 1: like we still use Newtonian physics to calculate the path
• 33:22
  Speaker 1: of baseball when you throw it or something like that.
• 33:24
  Speaker 2: Yeah, they both work right. They're effective theories in that
• 33:28
  Speaker 2: they give good predictions in certain situations. But if what
• 33:31
  Speaker 2: we're trying to do is understand the deep nature of
• 33:34
  Speaker 2: the universe. Then they're not like philosophically true. I think
• 33:38
  Speaker 2: our final goal is to get a description of the
• 33:41
  Speaker 2: universe that we think mirrors what's actually happening out there.
• 33:45
  Speaker 2: Like conceptually describes the laws the universe itself is like
• 33:48
  Speaker 2: actually following. So in that sense, general relativity and quantum
• 33:51
  Speaker 2: mechanics wouldn't reflect what's actually happening out there in the universe.
• 33:55
  Speaker 2: Though you're totally right, they're very useful and they're very
• 33:57
  Speaker 2: effective the same way we use like fluid mechanics to
• 34:00
  Speaker 2: explain what happens when you flush your toilet, and it
• 34:03
  Speaker 2: works right, it's very good. It helps us avoid lots
• 34:06
  Speaker 2: of ugly disasters. Doesn't mean we should stop doing it,
• 34:09
  Speaker 2: but it doesn't mean that the assumptions behind fluid mechanics
• 34:11
  Speaker 2: are the right way to think about the reality of
• 34:14
  Speaker 2: the universe.
• 34:15
  Speaker 1: Well, my toilet seems to flush, whether or not I
• 34:17
  Speaker 1: understand the fluid dynamics. Fortunately, otherwise, you enough and you put.
• 34:23
  Speaker 2: Enough dark matter in there, and I promise you won't flush.
• 34:28
  Speaker 1: Then you need dark energy to push it through.
• 34:32
  Speaker 2: Suggest that to your plumber and see how that goes.
• 34:35
  Speaker 1: Oh, there you go, that could be a good name
• 34:36
  Speaker 1: for plumbing business dark plumbers.
• 34:40
  Speaker 2: Dark plumbers. That sounds like a CIA operation.
• 34:43
  Speaker 1: Yeah, or SITH operation.
• 34:45
  Speaker 2: Were like, Yeah, if that van is parked outside your house,
• 34:48
  Speaker 2: I would suggest moving.
• 34:49
  Speaker 1: If your plumber brings out a lightsaber. First of all,
• 34:53
  Speaker 1: super cool, you totally take a selfie with your plumber,
• 34:56
  Speaker 1: but they might damage the plumbing.
• 34:58
  Speaker 2: Yeah, but also see if you can dune. I hear
• 35:00
  Speaker 2: those Jedi are really good at.
• 35:01
  Speaker 1: Basketball, Well, would they be dunking with a toilet? I
• 35:06
  Speaker 1: don't know.
• 35:06
  Speaker 2: This analogy has gone off the rails.
• 35:08
  Speaker 1: All right, Well, let's tackle maybe the question that we
• 35:10
  Speaker 1: started off with, which is is space time a fluid
• 35:14
  Speaker 1: like space time flow? I guess and swirl or get
• 35:17
  Speaker 1: flushed down a toilet? Daniel, Where does this idea come from?
• 35:21
  Speaker 2: This comes from an attempt to try to explain the
• 35:23
  Speaker 2: nature of space, as we talked about, as not fundamental
• 35:26
  Speaker 2: but something that emerges from a lower level of reality.
• 35:30
  Speaker 2: And it says essentially that maybe space is like water.
• 35:35
  Speaker 2: It's made out of some smaller pieces that follow very
• 35:38
  Speaker 2: very different rules, and that our experience of it is
• 35:41
  Speaker 2: sort of like the experience of water. We really are
• 35:44
  Speaker 2: like the fish. Scientists that space itself is made out
• 35:47
  Speaker 2: of some smaller bits we have yet to discover, and
• 35:49
  Speaker 2: those bits interact with each other in a way that
• 35:51
  Speaker 2: follows the laws of fluid mechanics, that our understanding of
• 35:56
  Speaker 2: fluids and water actually might be able to be applied
• 35:59
  Speaker 2: to space self. Space emerges from some weird quantum bits
• 36:03
  Speaker 2: and those bits come together in a way that can
• 36:06
  Speaker 2: be described by fluid mechanics.
• 36:08
  Speaker 1: Yeah, it's kind of like the idea. Then maybe there's
• 36:11
  Speaker 1: like a superspace and inside of that superspace is what
• 36:15
  Speaker 1: we call space, and that it's actually made up of
• 36:18
  Speaker 1: like little bits of space, meaning like when I think
• 36:20
  Speaker 1: I'm moving through space, or when a particle thinks it's
• 36:23
  Speaker 1: moving through space, it's actually like maybe hopping between bits
• 36:27
  Speaker 1: of space. Is that's kind of the idea, right.
• 36:29
  Speaker 2: That's kind of the idea, And it's also attractive from
• 36:31
  Speaker 2: the point of view of explaining some of the symmetries
• 36:34
  Speaker 2: and the invariances that we see, Like we don't understand where,
• 36:38
  Speaker 2: for example, this law of the speed of light comes from.
• 36:41
  Speaker 2: Why is there a maximum speed of information in our universe?
• 36:45
  Speaker 2: In quantum mechanics, we just don't see that right, it
• 36:47
  Speaker 2: doesn't exist in the theory of quant mechanics. Something we
• 36:50
  Speaker 2: had to add two quantum mechanics sort of by hand.
• 36:53
  Speaker 2: But if space is an emergent phenomena, if it comes
• 36:55
  Speaker 2: from the weaving together of these weird quantum bits, they
• 36:58
  Speaker 2: might be able to have the maximum speed of information
• 37:01
  Speaker 2: sort of emerge from those laws. The way that like
• 37:05
  Speaker 2: water as a liquid can do things that water as
• 37:07
  Speaker 2: an individual particle doesn't do, or that water as a
• 37:10
  Speaker 2: crystal can do things has properties that water as an
• 37:13
  Speaker 2: individual particle doesn't do. Maybe these invariances in these symmetries
• 37:17
  Speaker 2: sort of emerge with space. They're the properties that come
• 37:21
  Speaker 2: when space comes together to form these liquids. And fundamentally,
• 37:25
  Speaker 2: you're right, it's like these little bits of space sort
• 37:27
  Speaker 2: of woven together, and it's fascinating to think about, like
• 37:31
  Speaker 2: how you weave space together to make it a liquid.
• 37:34
  Speaker 2: It says that you start from a universe where all
• 37:36
  Speaker 2: you have are like weird little quantum bits. You have
• 37:39
  Speaker 2: these locations, but they don't sort of exist in space yet.
• 37:43
  Speaker 2: They just sort of like are there, and then they
• 37:45
  Speaker 2: get quantum entangled with each other, which sort of connects them.
• 37:49
  Speaker 2: Then things that are really tightly quantum entangled with each other.
• 37:52
  Speaker 2: We call those things close to each other. Things that
• 37:55
  Speaker 2: are loosely quantum entangled. We call those things further from
• 37:58
  Speaker 2: each other, things that are not intense at all, or
• 38:00
  Speaker 2: like out of your light cone completely. So you sort
• 38:03
  Speaker 2: of like build space up by quantum entangling all these
• 38:07
  Speaker 2: weird little sort of non space bits, and space itself
• 38:10
  Speaker 2: comes out of all those things working together.
• 38:13
  Speaker 1: Yeah, And I think maybe the idea is, like, maybe
• 38:16
  Speaker 1: as you're moving around these space bits, there are rules
• 38:19
  Speaker 1: about moving through these space bits that maybe explain things
• 38:22
  Speaker 1: like the speed of light limit in our universe. Right, Like,
• 38:24
  Speaker 1: maybe if I'm switching between space bits, there's a certain
• 38:27
  Speaker 1: cost to that, and then that would explain the limit
• 38:30
  Speaker 1: of the speed of light. And that's kind of what
• 38:32
  Speaker 1: you're saying, is that maybe these things that we think
• 38:34
  Speaker 1: of as fundamental phenomenas or properties of the unverse could
• 38:37
  Speaker 1: just be like the little tiny rules between space bits
• 38:41
  Speaker 1: that make up space exactly.
• 38:43
  Speaker 2: So that picture, which is more like a sort of
• 38:45
  Speaker 2: quantum space foam, says you build space out of these
• 38:48
  Speaker 2: little bits, and the rules that we observe sort of
• 38:50
  Speaker 2: come out of the arrangement of those things. They're not
• 38:52
  Speaker 2: fundamental to the bits themselves or sort of how you
• 38:54
  Speaker 2: put them together. This new theory says, well, maybe space
• 38:57
  Speaker 2: isn't like a foam. It's kind of like a but
• 39:00
  Speaker 2: it's a little bit different. You don't use the mathematics
• 39:03
  Speaker 2: of foam. Instead use the mathematics of liquids. Say, space
• 39:06
  Speaker 2: isn't like a grid that's woven together with quantum entanglements.
• 39:10
  Speaker 2: Maybe there's a little bit of a different physics there.
• 39:12
  Speaker 2: And what's happening is that these little bits of space
• 39:14
  Speaker 2: can sort of like slide past each other, they can
• 39:17
  Speaker 2: like flow around each other. They can do things that
• 39:20
  Speaker 2: foam or crystal can't do. This actually leads to slightly
• 39:23
  Speaker 2: different predictions for the behavior of space, and one of
• 39:26
  Speaker 2: them is that the limit on the speed of light
• 39:29
  Speaker 2: is not actually absolute. It's like approximate. That light doesn't
• 39:33
  Speaker 2: always travel at the speed of light. There might be
• 39:35
  Speaker 2: like very small variations there.
• 39:37
  Speaker 1: I see. The idea is and maybe these bits of
• 39:39
  Speaker 1: space that space is made out of aren't connected to
• 39:42
  Speaker 1: each other, Like they're not linked together like you might
• 39:45
  Speaker 1: link like a chain mail or a chain link fence.
• 39:49
  Speaker 1: Maybe they're just kind of like floating out there in
• 39:52
  Speaker 1: some super meta space, and they can actually kind of
• 39:55
  Speaker 1: slosh around and move relative to each other. Is that
• 39:57
  Speaker 1: the idea?
• 39:57
  Speaker 2: That's sort of the idea, though what you described sounds
• 40:00
  Speaker 2: more like a space gas. Think about like a crystal
• 40:02
  Speaker 2: where the bonds between the atoms are really really strong. Right,
• 40:05
  Speaker 2: that's sort of like our idea of a space foam. Now,
• 40:08
  Speaker 2: relax those bonds a little bit, and you have like
• 40:10
  Speaker 2: a space liquid you're write, things can slide past each other,
• 40:13
  Speaker 2: but they're not totally ignoring each other. There's still interactions
• 40:16
  Speaker 2: between those space bits, which is how fluid effects emerge.
• 40:20
  Speaker 2: If they were totally disconnected, you have like a collisionless,
• 40:23
  Speaker 2: non interacting gas of space bits, then you would expect
• 40:26
  Speaker 2: very very different kinds of behavior. This theory says, instead
• 40:29
  Speaker 2: of having space like a rigid crystal of locations that
• 40:33
  Speaker 2: are fixed to each other, loosen it up a little
• 40:36
  Speaker 2: bit and let those flow, not completely where they're ignoring
• 40:39
  Speaker 2: each other. There's still sort of some bonds between them,
• 40:41
  Speaker 2: but let them flow a little bit, and it leads
• 40:44
  Speaker 2: to different predictions for how light moves through this sort
• 40:47
  Speaker 2: of liquidity space.
• 40:48
  Speaker 1: Well, I guess what does that mean? Does that mean
• 40:50
  Speaker 1: that as I'm moving through space, if the space liquid
• 40:53
  Speaker 1: happens to be moving, then I'm going to move differently
• 40:57
  Speaker 1: through it? Or would I even notice if the liquid
• 41:00
  Speaker 1: around me is flowing.
• 41:01
  Speaker 2: When things move through liquid, they move in a different
• 41:03
  Speaker 2: way than when they move through a solid, right, And
• 41:06
  Speaker 2: a solid is more rigid, and so it's sort of
• 41:08
  Speaker 2: better at propagating waves, right, which is why, like sound
• 41:12
  Speaker 2: moves faster through your table than it does through the air.
• 41:15
  Speaker 2: In denser materials, things are more tightly bound, sound moves faster,
• 41:18
  Speaker 2: and so things in space time liquid would move differently
• 41:22
  Speaker 2: than things in sort of a space time foam or
• 41:24
  Speaker 2: space time crystal. And specifically, it would mean that it
• 41:27
  Speaker 2: slashes a little bit, so there'd be like a dissipation
• 41:31
  Speaker 2: that if you shoot a super high energy photon across
• 41:34
  Speaker 2: the universe, instead of it getting to the other side
• 41:36
  Speaker 2: of the universe with the same amount of energy, it
• 41:37
  Speaker 2: would lose some of that energy to like this slashing
• 41:40
  Speaker 2: of space itself.
• 41:42
  Speaker 1: Mmm, sounds like we're all in a hut tub. I
• 41:48
  Speaker 1: feel like you're saying the universe just a nice bubbly
• 41:51
  Speaker 1: huttub that we're all relaxing it all right, Well, let's
• 41:54
  Speaker 1: talk about what makes us think that the universe or
• 41:57
  Speaker 1: that space time can be a fluid, and whether we
• 42:00
  Speaker 1: have any evidence of it, and if we do, what
• 42:02
  Speaker 1: would that mean about our understanding of how everything works.
• 42:06
  Speaker 1: So let's get into that, but first let's take another
• 42:08
  Speaker 1: quick break. Right we're asking the question can space time
• 42:23
  Speaker 1: be a fluid? And it sounds like this is the
• 42:26
  Speaker 1: idea that we're all just sitting in a hot tub somewhere.
• 42:30
  Speaker 1: This is a hot tub time machine Universion of dealers.
• 42:33
  Speaker 1: We started out with an office space as a comedy
• 42:36
  Speaker 1: and now we're in space. Time Machine could be the sequel.
• 42:40
  Speaker 2: Me you, Barack, Obama, and Yoda all sitting in a
• 42:43
  Speaker 2: hot tub understanding in the nature of space time.
• 42:47
  Speaker 1: That's an awesome picture. And I can't wait for our
• 42:49
  Speaker 1: listeners to draw and draw on this fan art.
• 42:53
  Speaker 2: Or maybe if Obama is a listener to the podcast
• 42:55
  Speaker 2: Chill Ride In and you know, come and join us
• 42:57
  Speaker 2: on our acoustic hot tub that is this podcast.
• 43:00
  Speaker 1: And also we can finally answer the question what happens
• 43:03
  Speaker 1: if you turn a lightsaber on inside of a hot tub?
• 43:07
  Speaker 2: Or maybe he's got an opinion about whether he could
• 43:09
  Speaker 2: beat Yoda in one on one basketball.
• 43:11
  Speaker 1: Mm, well, Obama seems like a humble guy. I don't
• 43:14
  Speaker 1: think he would try to take on Yoda.
• 43:17
  Speaker 2: He is respectful, that's true.
• 43:19
  Speaker 1: All right. Well, I guess this is an interesting idea
• 43:22
  Speaker 1: that space time can be fluid, that maybe it's not
• 43:25
  Speaker 1: fixed out there in the universe. Maybe it's a thing
• 43:27
  Speaker 1: that can slash around, that it's made up of little
• 43:29
  Speaker 1: bits that kind of move relative to each other. And now,
• 43:33
  Speaker 1: Daniel Dewey have any inclination that this theory is true.
• 43:38
  Speaker 1: Does it match up well with some observations that we
• 43:40
  Speaker 1: have in experiments or is it just an idea out
• 43:42
  Speaker 1: there that we think that maybe one day could possibly
• 43:46
  Speaker 1: explain things.
• 43:47
  Speaker 2: At this stage, it's really just an idea, but there
• 43:49
  Speaker 2: are some fun experiments we can do to try to
• 43:52
  Speaker 2: test it, so it's not just an idea people are
• 43:55
  Speaker 2: having a hot tubs. It's something people are out there
• 43:57
  Speaker 2: really working on trying to verify because it does makes
• 44:00
  Speaker 2: some very cool predictions. And the's sort of two categories
• 44:03
  Speaker 2: of experiments. There's experiments we're doing up in the sky,
• 44:06
  Speaker 2: like looking at things out in the universe, and also
• 44:08
  Speaker 2: things people are doing in the lab to try to
• 44:10
  Speaker 2: make like sonic black holes to study them. The first
• 44:13
  Speaker 2: one has to do with like how light propagates through
• 44:16
  Speaker 2: the universe. As we said earlier, there are rules about
• 44:19
  Speaker 2: how fluid behaves, and if you shoot something through fluid,
• 44:23
  Speaker 2: it will lose energy, will dissipate its energy. Fluids have
• 44:27
  Speaker 2: these two properties. That's called dissipation where you lose energy
• 44:30
  Speaker 2: over time, and dispersion where things that different energies travel
• 44:34
  Speaker 2: at different speeds. And so that's not something we've seen
• 44:37
  Speaker 2: in space. Like if you shoot photons across the universe currently,
• 44:40
  Speaker 2: we think they arrive with the same energy as when
• 44:43
  Speaker 2: they left, like they never get tired. We've also seen
• 44:45
  Speaker 2: that photons at all different energies, red photons, blue photons,
• 44:49
  Speaker 2: green photons, infrared photons all travel at the same speed.
• 44:53
  Speaker 2: So people are trying to understand if this is really true,
• 44:56
  Speaker 2: because if space time was a liquid, then those would
• 44:59
  Speaker 2: be broken little bit. Photons would lose a little bit
• 45:02
  Speaker 2: of energy as they move through the universe, and red, green,
• 45:04
  Speaker 2: and blue photons would travel at slightly different speeds. So
• 45:08
  Speaker 2: they're trying to do this experiment, though it's tricky because
• 45:10
  Speaker 2: we don't have like a huge laser pointed at the
• 45:13
  Speaker 2: Earth to let us do this experiment.
• 45:15
  Speaker 1: Sounds like a dastardly plot for a supervillain slash experiment.
• 45:19
  Speaker 2: Though we almost do have a huge laser. There's this
• 45:21
  Speaker 2: thing up in the sky called the crab Nebula, which
• 45:23
  Speaker 2: is an excellent source of really really high energy photons.
• 45:28
  Speaker 2: It's shooting photons at us up to like eighty terra
• 45:31
  Speaker 2: electron bolts. Remember the Large Hadron Collider, the most powerful
• 45:35
  Speaker 2: human accelerator on Earth, only gets things up to like
• 45:38
  Speaker 2: six and a half or seven terra electronvolts. So this
• 45:42
  Speaker 2: thing is shooting photons at us more than ten times
• 45:45
  Speaker 2: the energy of the LAC, which makes it a great
• 45:47
  Speaker 2: way to study how photons propagate through the universe.
• 45:52
  Speaker 1: It sounds like you have a lot of ideas for
• 45:54
  Speaker 1: disproving this crazy theory, but I guess my question was
• 45:57
  Speaker 1: more like what makes us think that this crazy theory
• 46:00
  Speaker 1: could be true? Like? Is there something that it predicts
• 46:03
  Speaker 1: that maybe matches up with some unexplained phenomenon in space.
• 46:07
  Speaker 2: We don't need this theory to explain anything that we see.
• 46:10
  Speaker 2: It's just an attempt theoretically to try to harmonize our
• 46:14
  Speaker 2: idea of the universe to come up with a new
• 46:16
  Speaker 2: explanation for what's out there, sort of from the bottom
• 46:19
  Speaker 2: level up to explain how we end up with general
• 46:22
  Speaker 2: relativity and how we end up with quantum mechanics. But
• 46:25
  Speaker 2: you know, you can't just describe something theoretically and say
• 46:28
  Speaker 2: here's my description of the universe. You also have to
• 46:30
  Speaker 2: make predictions that can be verified and tested to see
• 46:32
  Speaker 2: if this is what's really happening out there. So we
• 46:36
  Speaker 2: don't need this to explain any results of experiments, and
• 46:39
  Speaker 2: we don't have any experiments where quantum mechanics and general
• 46:41
  Speaker 2: relativity disagree because those experiments are essentially impossible to do.
• 46:45
  Speaker 2: But it does make predictions that we can test so
• 46:48
  Speaker 2: that we can prove or disprove this theory.
• 46:51
  Speaker 1: I guess what I mean is like, does this crazy
• 46:53
  Speaker 1: theory actually make quantum mechanics in general relativity play well
• 46:57
  Speaker 1: together or we just think it might, or does it
• 47:01
  Speaker 1: actually harmonize everything.
• 47:02
  Speaker 2: If it's true, then it does allow for us to
• 47:05
  Speaker 2: derive sort of general relativity and quantum mechanics from one source.
• 47:09
  Speaker 2: All the math is not completely worked out, like there
• 47:12
  Speaker 2: is no completely well worked out theory of quantum gravity
• 47:16
  Speaker 2: from which you can get the effects of general relativity
• 47:18
  Speaker 2: and quantum mechanics. This is sort of like one direction
• 47:21
  Speaker 2: people are working in, and there's a series of recent
• 47:24
  Speaker 2: papers sort of thinking about the consequences of it, Like,
• 47:26
  Speaker 2: we don't have all the details worked out yet, but
• 47:29
  Speaker 2: if this theory is true, it would have these consequences.
• 47:32
  Speaker 2: Let's go check and see if we can see those
• 47:34
  Speaker 2: things happening in the universe, because if we can, that
• 47:37
  Speaker 2: means we're on the right track.
• 47:39
  Speaker 1: I mean not I mean to tell you how to
• 47:40
  Speaker 1: do your business, but like before you point a giant
• 47:43
  Speaker 1: laser of the Earth, wouldn't we want to make sure
• 47:45
  Speaker 1: that this is a theory that is going to be
• 47:48
  Speaker 1: worth doing that, do you know what I mean? Like,
• 47:50
  Speaker 1: I would see how it would be important to verify
• 47:54
  Speaker 1: this theory, but only if it made things work. But
• 47:57
  Speaker 1: it sounds like we don't even know if it's going
• 47:58
  Speaker 1: to make things work.
• 47:59
  Speaker 2: We don't know if the theory of a space time
• 48:01
  Speaker 2: fluid actually works theoretically right, and the same way that
• 48:04
  Speaker 2: we don't know as string theory works fundamentally. People are
• 48:07
  Speaker 2: still working on it, but we'd also love to have
• 48:09
  Speaker 2: ways to test string theory to verify its predictions to
• 48:13
  Speaker 2: understand if we're on the right track or not. And
• 48:16
  Speaker 2: also sometimes getting experimental verification provides clues it like says, oh,
• 48:20
  Speaker 2: you have a whole different set of ideas about this theory, Well,
• 48:23
  Speaker 2: the experiment prefers this one or that one, so it
• 48:25
  Speaker 2: can give you some guidance sometimes. So it's nice when
• 48:28
  Speaker 2: theory and experiment can sort of work hand in hand.
• 48:31
  Speaker 2: I mean, we don't develop a complete theory of the
• 48:33
  Speaker 2: standard model before we build our first particle detector, right,
• 48:36
  Speaker 2: We sort of do it in increments, and we get
• 48:38
  Speaker 2: clues from experiment and then ideas from theory, and it's
• 48:41
  Speaker 2: sort of like a tag team.
• 48:42
  Speaker 1: Well, at least with the Higgs boson, I feel like
• 48:44
  Speaker 1: that theory was sent and kind of worked out, and
• 48:46
  Speaker 1: there were predictions of it, and then you went off
• 48:48
  Speaker 1: and built the giant thing.
• 48:49
  Speaker 2: Yeah, that is one example of success from having a
• 48:52
  Speaker 2: theoretical idea. But of course that theoretical idea came from
• 48:55
  Speaker 2: experimental observations that we didn't understand at that time, right,
• 48:58
  Speaker 2: seeing the W and the Z were massive and the
• 49:00
  Speaker 2: photon wasn't, and not understanding that, and so we got
• 49:03
  Speaker 2: to do is go out there and do a bunch
• 49:04
  Speaker 2: of experiments and look for weird stuff. Sometimes you get
• 49:07
  Speaker 2: a confirmation of the idea you had, and sometimes you don't.
• 49:10
  Speaker 1: Are you trying to say that when it comes to
• 49:11
  Speaker 1: space time being a fluid, you just got to go
• 49:13
  Speaker 1: with the float. You don't want to flush it all down.
• 49:15
  Speaker 2: Well, I do think that these results from the crab
• 49:17
  Speaker 2: nebula are super awesome. I mean, they look at these
• 49:20
  Speaker 2: photons and they try to measure whether there's any like
• 49:23
  Speaker 2: change in the energy spectrum, the kind that you would
• 49:25
  Speaker 2: expect if space time was a fluid, and they didn't
• 49:28
  Speaker 2: see any, which means that you know, space time might
• 49:31
  Speaker 2: still be a fluid. But if it is, it's a fluid,
• 49:33
  Speaker 2: it's like super duper slippery. Like the fluid effects, these
• 49:37
  Speaker 2: like friction, the effects where you're losing energy as you're
• 49:39
  Speaker 2: moving through space time are very very small. So like,
• 49:42
  Speaker 2: maybe space time isn't a fluid, maybe it's say superfluid.
• 49:46
  Speaker 1: Ooh, it has superpowers kind of meani like it doesn't.
• 49:51
  Speaker 1: It's not like a thick, gooey fluid. It's almost like
• 49:54
  Speaker 1: supernatural fluid.
• 49:55
  Speaker 2: Yeah, superfluids are like superconductors. They have almost no friction.
• 49:59
  Speaker 2: They flow very very smoothly. So if space time is
• 50:02
  Speaker 2: a fluid, then it has to have like very very
• 50:04
  Speaker 2: slight fluid effects.
• 50:06
  Speaker 1: So we do have an experiment or an observation at
• 50:08
  Speaker 1: least it says that space time is not a fluid.
• 50:11
  Speaker 1: Then it might still be a superfluid, but it's definitely
• 50:15
  Speaker 1: not a fluid. Is that what the observation says.
• 50:17
  Speaker 2: Yeah, it's not like thick, chunky soup. That's for sure
• 50:20
  Speaker 2: that we can rule that out. If it is a fluid.
• 50:23
  Speaker 2: If space time does follow these properties and bubbles up
• 50:26
  Speaker 2: from something deeper and has fluid like effects, they would
• 50:28
  Speaker 2: be very very very subtle. But it doesn't mean they're
• 50:31
  Speaker 2: not right. You can always rule it out to some level.
• 50:33
  Speaker 2: But there's sort of another direction we can approach this,
• 50:35
  Speaker 2: which is to try to do experiments on Earth to
• 50:39
  Speaker 2: understand whether this theory even holds together. And there's a
• 50:41
  Speaker 2: guy in Israel, the Technion who builds these sonic black
• 50:45
  Speaker 2: holes try to understand like how gravity might emerge from
• 50:49
  Speaker 2: a fluid theory of space time. He's notices a lot
• 50:52
  Speaker 2: of similarity mathematically between how waves propagate in fluids and
• 50:56
  Speaker 2: how waves propagate in curved space time. So what he's done,
• 51:00
  Speaker 2: he's experimentally built a weird kind of fluid that has
• 51:03
  Speaker 2: strange behaviors that are very similar to the behavior of gravity,
• 51:07
  Speaker 2: to the point where he's even built a fluid with
• 51:10
  Speaker 2: what he calls an acoustic horizon. I mean, he generates
• 51:13
  Speaker 2: sound waves that cannot escape this weird little blob inside
• 51:17
  Speaker 2: his fluid.
• 51:18
  Speaker 1: WHOA, So wait, he's like building fluids out of real atoms,
• 51:23
  Speaker 1: like real materials, and using that like a lego model
• 51:26
  Speaker 1: of what space might actually be.
• 51:28
  Speaker 2: Is that what you're saying, Yeah, exactly, He's doing what
• 51:30
  Speaker 2: they call analog gravity. He's like, if the mathematics of
• 51:34
  Speaker 2: this works for space time, it should also work when
• 51:38
  Speaker 2: you put other things together. So instead of doing experiments
• 51:40
  Speaker 2: using space time bits, which we don't know how to manipulate,
• 51:43
  Speaker 2: it's like, let me do it with other kind of bits.
• 51:45
  Speaker 2: So he does it with rubidium atoms, and he builds
• 51:48
  Speaker 2: these Bose Einstein condensates, and he gives them all sorts
• 51:51
  Speaker 2: of weird properties so that the sound waves moving through
• 51:54
  Speaker 2: those rubidium atom fluids should operate the same way photons
• 51:59
  Speaker 2: move through the space time liquid. So he's actually successfully
• 52:03
  Speaker 2: built what they call an analog black hole. It's not
• 52:06
  Speaker 2: a literal black hole, but it has similar properties in
• 52:10
  Speaker 2: that fluid to photons moving through space time.
• 52:14
  Speaker 1: That feels like a little bit of a stretch, but
• 52:15
  Speaker 1: I guess I trust see that. It's an interesting way
• 52:18
  Speaker 1: to study the I feel like you're building a model,
• 52:20
  Speaker 1: but in trying to say that, like, if it works
• 52:23
  Speaker 1: for my legos, it works for quarks.
• 52:25
  Speaker 2: Yeah. He's definitely made some very bold claims and there's
• 52:27
  Speaker 2: a lot of controversy about what it means, but it's
• 52:29
  Speaker 2: definitely fascinating. So the fascinating thing about this is that
• 52:32
  Speaker 2: they're not black holes. Black holes don't emit light. These
• 52:35
  Speaker 2: are like silent holes because they don't emit sound right,
• 52:38
  Speaker 2: there's like quiet holes.
• 52:40
  Speaker 1: They're like the uncomfortable silence in social situations. It's like,
• 52:44
  Speaker 1: what would you even say, you're the hot up with
• 52:46
  Speaker 1: Yoda and Obama. It would be a sonic black hole
• 52:49
  Speaker 1: as well.
• 52:50
  Speaker 2: It might be a little awkward.
• 52:51
  Speaker 1: Yeah, all right, Well, it sounds like this is a
• 52:54
  Speaker 1: super fascinating theory and kind of challenges our views of
• 52:58
  Speaker 1: space time itself, like maybe the fundamental platform of the
• 53:02
  Speaker 1: universe isn't what we think it is. Maybe it's something
• 53:05
  Speaker 1: that sits inside of an even bigger meta or super
• 53:08
  Speaker 1: space platform or environment. And these are interesting ideas that
• 53:12
  Speaker 1: might bring together quantum mechanics and general relativity. But stay tuned.
• 53:16
  Speaker 1: Experiments so far say that maybe space isn't a fluid,
• 53:20
  Speaker 1: but that maybe the hut tub of the universe is
• 53:22
  Speaker 1: actually a super hot tub of the universe.
• 53:25
  Speaker 2: Yeah, and these ideas take a while to bubble up
• 53:28
  Speaker 2: and too perkoly through the brains of humans. And it
• 53:30
  Speaker 2: might be that one day we look back at our
• 53:32
  Speaker 2: understanding of space time and think, Wow, we were so foolish.
• 53:35
  Speaker 2: We didn't even understand the liquid we were swimming in.
• 53:38
  Speaker 1: Yeah, it sounds like we need to soak on it
• 53:40
  Speaker 1: for a little bit longer.
• 53:43
  Speaker 2: I always prefer to soak rather than scrub.
• 53:45
  Speaker 1: Just don't do it with a lightsaber. I guess all right. Well,
• 53:47
  Speaker 1: we hope you enjoyed that. Thanks for joining us, See
• 53:49
  Speaker 1: you next time.
• 53:58
  Speaker 2: Thanks for listening, and remember that Annel and Jorge Explain
• 54:01
  Speaker 2: the Universe is a production of iHeartRadio. For more podcasts
• 54:05
  Speaker 2: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever
• 54:09
  Speaker 2: you listen to your favorite shows.