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

Episode Date: May 4, 2023

Daniel and Jorge explore the question of the nature of space itself, and whether it might flow and bubble. See omnystudio.com/listener for privacy information.

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Brought to you by Novartis, founding partner of IHeart Women's Sports Network. Hey, Daniel, I have a question. about the physics of space. Oh, cool. I love those. Space is so amazing and fun to talk about. Well, not the physics of space, I mean like the office space of physics. What's the physics of office space?

You know, I remember when I visited at CERN and I walked by the office of physicists called John Ellis, and it was so messy with paper stacks so high, it looked almost impossible to walk in. Yeah, he is famously. disorganized. Now, how does that work? Do particle physicists have some kind of special trick that makes their office bigger on the inside than on the outside? You know, kind of like those Harry Potter tents? Actually, I think it might be the opposite. I think their offices are on the verge of collapsing into personal black holes. No, but that's kind of what I mean. Like, black holes might have whole universes inside of them. Do physicists offices have a whole universe

inside of him? And what are they doing inside of there? I don't know, but I suspect in John Ellis's office, there's lots of ideas lost behind his personal event horizon. Event horizon or mess horizon? The disorganization horizon. Tunis and the creator of PhD comics. Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine. And contrary to popular perception, I do try to keep my office kind of organized.

Kind of? That sounds like a little bit of a loophole there. Yeah, my office is totally kind of organized. If you said the bar really love for the definition of the word organization. I didn't want to brag too much. But yes, I do like to keep my office neat and tidy. I'm not sure that's something to brag about, is it? Don't they say genius is related to how messy your desk is?

Yeah, well, Obama said physical discipline leads to mental discipline. Yeah, well, I think Yoda said something similar also. Organization leads to hate. Hate leads to suffering, and suffering leads to the dark side. But who do you think would win in basketball, Obama or Yoda? Yoda. I mean, I love Obama, but come on, Yoda. I can do like super somersaults with a lightsaber.

Yeah, that dude could probably dunk. That's true. Anyways, welcome to our podcast, Daniel and Jorge. explain the universe a production of iHeart radio in which we do mental somersaults to try to explain the entire universe to you we go out there into the vast stretches of empty space wondering about what is actually out there what it's made out of zoom down to the very granular nature of reality itself and ask questions about what it is what it means and how we can figure it all out we zoom in we zoom out, we zoom everywhere in the universe to try to explain everything to you.

That's right, because it is a pretty amazing universe and we like to explore the force in it, the dark side of it, and also the physics of basketball sometimes as well. You know, I wonder in the Star Wars universe, you have like young Jedi, are they playing sports with each other? Do they have some version of like Jedi quidditch where they're, you know, pushing balls around with their minds? Oh, interesting question. You should write like a fan fiction novel based on is that? Harry Potter Star Wars.

Like Quigon, Quidditch, fan fiction for Star Wars, and throw in some brooms as well. But I'm asking a serious question. I think you have a deeper knowledge of these universes than I do. Do young Jedi play some sort of ball sports with their minds? I don't see why they wouldn't, I guess. I don't think it's canon. I mean, I do play with a little, like a floating ball where they try to hit it with a lightsaber.

Maybe that's a sport? I don't know. We'll have to ask George Lucas. Can we get him on the podcast? George Lucas. Oh, yeah, I totally email with George Lucas all the time. I send him all of my Star Wars ideas. Oh, good.

That would explain a lot, then. I don't get any answers, but I do email him. But it is a pretty wonderful universe. We do explore all sides of it because it's kind of a big universe. There's a lot of space in it. In fact, the universe is mostly space. The kind of thing that you're standing on and the sun that's in the sky is pretty unusual. If you're going to pick like a random spot in the universe,

you're mostly going to end up in a spot without a whole lot of stuff in it. Yeah, because as we talk about on the podcast, space is not just emptiness. It's not nothing. It is actually a thing. The thing that can stretch, that can bend, that can slow down time. It's reactive to things. It's not nothing. Exactly.

We know that space is something interesting. And it's a really fascinating step in our sort of multi-stage exploration of the universe. You know, we start just by looking at the stuff that's around us. We ask, what's that made out of? What's that made out of? What's that made out of? But we sort of never stop asking those questions. And now we're at the point where we're trying to understand, like, what is the thing that all the stuff is in? You know, if matter in the end is made of particles and those particles are oscillations in quantum fields and those quantum fields sit in space, then the next frontier of understanding really is to understand what that space itself is.

And is space sitting in some sort of like meta, super or subspace? Yeah, it's a very spacey question. there are many possibilities out there for what space can be, if you can imagine that. And it's a fundamental question at the heart of modern physics. We're trying to understand quantum theory. We're trying to understand relativity and gravitation. And at the nexus of those two is the fundamental mystery of what space actually is. Can it actually bend to make black holes?

Are black holes really black holes? Or are they something else? Why is the universe expanding what will be its ultimate fate? At their hearts, all of these questions really. are asking what is space and what are the rules of it what governs it what is it fundamentally is it in fact fundamental or is it just a frothing emergent phenomena of something even deeper yeah and do the rules of space apply to office space as well and i mean where people work not just the movie office space turns out to be mostly politics you know every time somebody retires here there's like a scramble to see who gets

their big office oh really does it go by seniority like the more senior you are the closer you're are to the snack room or the restrooms or the closer you need to be to the rest room perhaps you know academics academics always have ladder systems and ranking systems and it's no different here we have like many levels of being a professor it's not just like assistant associate and full professor within each of those is like many gradations like full professor four or associate professor seven or whatever so when a new office opens up they go down the ladder and ask people at the top of the ladder if they want it or not. And ridiculously, all the offices in my building, at least, are different sizes and shapes.

It would have been so much simpler if just every office was the same size. But no, they made some really big ones and some really little ones. It's almost like they wanted some drama, some political drama. Maybe that was the architect's revenge. Maybe it was. I don't know. Isn't there some kind of like office-based inertia? Like, ooh, that is a slightly bigger office, but I would have to clean my office and pack everything up to

move. So maybe I'll just get it. Yeah, I do think that a lot of people don't take a bigger office just because they're happy where they are or they don't really care or their office is such a disaster that it's impossible to imagine moving. And I think that's also why it's sometimes hard to get people out of their offices because if you've been in there for 30 years, you got a lot of stuff. You got to move out. Are you saying there is such a thing as space inertia? Like space can have inertia. Turns out space can have politics. That's even weirder. Or can a black hole have inertia? Back to actual physics, black holes definitely do have inertia, right? They have mass, which means that they have inertia. If you pushed on a black hole, then its acceleration would be

inversely proportional to its mass. But that, you wouldn't actually recommend that, right? Pushing a black hole, that would be not good. It depends. If the black hole is headed towards our solar system, then I would say, yes, let's launch something heavy to push on the black hole so that it doesn't come through our solar system. I guess what I meant is you wouldn't want to push it yourself. like send Daniel up into space having push on the black hole I don't think that would end well am I going to get a big office out of it

maybe probably yeah you might have the whole black hole to yourself that sounds great except there are no windows and I really like an office with a view well it would be all windows except I guess you couldn't stick your head out of the window

but it is interesting to think about what space could be like what is it made out of would actually make space happen. Sometimes I think about scientists, the way we think about fish, swimming around in water, probably not even really aware that they are inside some sort of fluid because that's their entire world.

It might take fish like hundreds of years or thousands of years to discover that the thing they're inside is not the fundamental nature of the universe. It doesn't exist everywhere. And it can do other kinds of things like boil and freeze and all sorts of stuff. So I wonder if we are sort of like fish, exploring the nature of space and only now discovering that it can do weird things

that might have strange properties and might not even be the fundamental layer of reality so to the end the podcast we'll be asking the question is space time a fluid what do you mean it's a fluid it's certainly a gas isn't it well time definitely seems to flow so why not space time right well it's definitely a solid thing it's always there You can rely on it. Well, back to the analogy with fish scientists, which I think probably originates with Max Tegmark, if you discover that space is more complicated than just the backdrop of the universe,

then you discover that it might have other properties. It might be able to do things like flow or bubble or have different phases. And so that's a fascinating question about the nature of space itself and sort of what it can do. Can we describe using the mathematics of fluids or do we need a completely different kind of mathematics to explain what space is up to. It is kind of a mind-blowing question to think that space time could be a fluid. It makes it seem like it's a physical thing. Like it actually has like mass to it or something or that it responds to forces and things like that.

Yeah. As we'll see, space time being a fluid would give very specific predictions for how things propagate through it, how energy is spread or dissipates. So it's a really fascinating hypothesis. And I know we've talked about in the podcast before how space time could be like a bubble, right? Or like a foam. A foam is not a fluid, is it?

No, there are many theories of what space might be down at the granular level. Is it made of little pixels which are woven together with quantum entanglement into a kind of foam? Or do those pixels operate in a different sort of way? So this is more about like at the fundamental level, what are the rules of how those pixels interact with each other? And what phenomena emerges from that? Can you describe them using the physics of foam or of liquids or of ice cream? or office space apparently or interpersonal politics or any kind of politics well as usual we were wondering how many people out there had thought about this question had thought that maybe space sign

could be a fluid so daniel went out there as usual and asked the internet what they thought thanks very much to everybody who answers these questions we love to hear your voice on the podcast and anybody out there who wants to volunteer please don't be shy just write to me to questions at danielanhorpe.com so think about it for a second do you think space time could be a fluid here's what people had to say i remember this was the argument for a theory in the big event so yeah maybe space time could be a fluid and that's the reason it only goes in one direction maybe um in previous episodes i've noticed that you say that space time it can be stretched and squashed and almost like molded in that kind of way.

So I always imagine space time being in some sort of matter state. So yes, I would say space time could be similar to a fluid. I guess that space time is fluid-ish because you can't put it in a jar or something, but it may behave like a fluid for some physics calculation. I don't know, man. It seems like, you know, there's waves in it, and we talk about it as some sort of foam. But, like, what space is the fluid occupying? That's what gets me.

I don't know. So if I think about it, what is a fluid? A fluid is, a fluid will flow, and it could flow very slow, like a glacier is ice. You'd think ice is a solid, but over long time scales, a glacier would flow like a river. And I think space time around really massive objects, like a black hole, spinning black hole in particular, will also get dragged around. I think it's called frame dragging. So space time itself will spin around the black hole. And I think as you go past the event horizon, doesn't space time itself kind of flow towards the singularity?

I'm guessing that you could consider the current chair that some point. planet and stars exert on space. Time could be considered fluid. All right. I feel like we blew people's minds with this question. Somebody's like, one of the people was like, whoa, I don't know, man. Well, that's my favorite part of this podcast is making people explore crazy ideas, is digging deep into whether the universe could really be different from the way that we imagine it. You know, so contrary to our intuition, those are the best kinds of discoveries. And I think these responses really reflect that kind of moment of exhilaration to imagine that the universe could be so different.

I like the president who said, they think it's fluid-ish. Like, hey, that's a good answer for anything. Do you think the universe is this way or that way? I think it's this way-ish. My office is organized-ish. That's right. But somebody else wrote in here that space can have ways. We know that, you know, you can feel gravitational ways.

We detected those. So if something can have waves in it, does that mean it's like a fluid? Yeah, it's a really good, deep question. Like if you can make ripples in it, it's sort of, does that mean it is a fluid? I guess you can make ripples in a gas, too, or a solid. Yeah, liquids have special kinds of mathematics that describe them, and that's what we're going to dig into. And there are even people who have tried to build liquid analogies of space time and liquid

analogies of black holes. There's a guy in Israel who builds sonic black holes. Sonic black holes. That sounds like a good definition for our podcast. where soundways go to die I hope we're not just speaking into the void I hope there's somebody out there listening maybe we're hawking radiationing

our ideas out into the universe you mean like we're fish in a fish tank maybe and hopefully our soundways are going out there beyond the fish tank I have some evidence that there are people out there listening and we're now trapped into a sonic black hole because we get responses from listeners so if y'all are actually out there

and we're not trapped in a sonic black hole right back to us and confirm. What if we're all in your mind, Daniel. What if we're all like multiple personality aspects of you? Plot twist. It's like the plot of an M. Chimelan movie. I always wanted to be in one of his movies, so I'd be pretty happy with that outcome. But one of our respondents here also asked an interesting question. Like, if space is is a fluid, what is the fluid in? Like, what is it occupying? Is something holding it, like a jar or a fishbowl? Or some sort of super space. Like revealing the fundamental nature of

space time really just opens us up to the next level of questions like if space is a fluid or if space emerges from something else and that other thing it emerges from is more fundamental and now we can focus all of our energy on that thing it might be a never-ending cycle where we're always just digging deeper and finding deeper and deeper layers of reality we don't know if we'll ever find some sort of bedrock fundamental nature to the universe or not or we can always just ask well what's that made out of her what's that sitting in yeah goes on forever. And so let's start to dig our way through it. Daniel, let's explain what is space time. So the short version is, we just really have no idea what space is. Boom and

done. All right. Thanks for joining us. It is kind of a black hole. See, questions go to die on our podcast. One of the most confusing things about it is that we have very crisp and clear pictures of what space might be in the theories that we have built up about the universe. And as we've talked about in the podcast many times we have like two pillars of modern physics two different sets of ideas that have helped us answer questions about what's going on in the universe we have quantum mechanics and we have general relativity they're fundamentally inconsistent and they each give us a very different picture of what space might be and how it works so one of the biggest puzzles is like trying to bring these two things together to give us at least a unified picture of what space is

but as of now nobody's been able to do that yeah there are two different different views. So let's do one of them at a time. What is space time according to quantum mechanics? Or does quantum mechanics even call it space time? Or does it treat space and time differently? Yeah, quantum mechanics treats space and time very differently. It treats space as the backdrop for quantum fields. It says that space is filled with these fields that can oscillate and we have great equations to describe exactly how they oscillate and buzz. And you can use those equations to explain how electrons fly through space and how they radiate photons, which are absorbed by other particles. And so far it seems like a super-duper accurate description of what's going on in the universe.

We've done an amazing experiment to validate this description of the universe and compare it to quantum mechanics predictions, which agreed to like eight or nine decimal places. It's really super impressive. But the picture of space in quantum mechanics is just sort of like the backdrop. It's where the fields are. You know, we do the mathematics of quantum field theory. We write these fields as a function of space. We say every location in space has a value of these fields, or if it's a vector field, multiple values.

There are like these numbers embedded in space. But time is different. Time just tells us how those fields change. And one really important thing about time in quantum mechanics is that it should be infinite. Like quantum mechanics says that the universe should have always existed and should always exist because information in the universe can't be lost. It can't just go away. And so if you take the Schrodinger equation, for example, and use it to describe the

universe, you can run it backwards and forwards in time to infinity. And that actually tells you something about space itself because it says that space should have always existed throughout the whole universe. That's sort of the quantum mechanical view of space time. I feel like quantum mechanics, I feel like you're saying that quantum mechanics is still basically stuck in the same view of space as Newton was kind of, right? Like before general relativity and Einstein, we just thought space was this big emptiness. It couldn't change. It was like a judgment. It was like a giant warehouse, you know, couldn't change or move or ripple or anything like that. It was just fixed. Space was fixed. And then you had time making things move forward in time. And so quantum

mechanics sort of started from that and it didn't really kind of think about what space could be. It's sort of still stuck in that Newtonian or classical physics view of space. I think the broad strokes of that are definitely true. There's a couple sort of interesting and important caveats. One is that we have succeeded in making quantum mechanics act relativistically in some cases, like behaving with the rules of relativity. Like we can describe the motion of super duper fast quantum particles. Take an electron, accelerate to almost the speed of light or protons at almost a speed of light, and then you need like relativistic quantum mechanics.

But that's special relativity. That's just dealing mostly again with flat space. So we can bring sort of special relativity's view of space time into quantum mechanics, but you're right. Fundamentally, we're still just talking about things happening in the backdrop of space. The other important thing to understand there is that we have to add these things to quantum mechanics. Quantum mechanics doesn't naturally have the sort of symmetries and laws that we find in the universe. For example, you can build quantum mechanics without a constant speed of light

or an invariant speed of light. We know that out there in the universe, the speed of light is the speed of light, no matter who's measuring it or what the setup is. But quantum mechanics doesn't require that. It's not like built in, it doesn't fall out of quantum mechanics naturally. So it's something you have to add on to quantum mechanics. And that we've been able to do. What we haven't been able to do is make quantum mechanics consistent with curving spaces to make a quantum version of general relativity. That's the part we haven't been able to do yet. But you're right. It still sits in the sort of Newtonian backdrop where space is the stage on which things happen. So quantum mechanics maybe their view of space, its view of space, kind of matches maybe what most people think of

space or at least what, you know, anyone who's had a high school education in physics, would think of a space. Weird stuff happens in that space, according to quantum mechanics, but the space itself is just sort of like the playground on which that weird stuff happens. Yeah, like nothing weird happens to space itself. Yeah, and also that space really is Newtonian in the sense that it doesn't have a lot of the symmetries and principles that Einstein showed us that it does have, like respecting the speed of light and all sorts of relativistic invariances.

Interesting. All right, well, let's get into what general relativity says that space is. is and whether or not we could ever match it up with quantum mechanics and whether that could mean that space is a fluid. So let's get into that. But first, let's take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6,000, 6.33 p.m., everything changed. There's been a bombing at the TWA terminal.

Apparently, the explosion actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System

on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Well, wait a minute, Sam, maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on. on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone.

Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to

meet. So do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. I don't write songs. God write songs. I take dictation. I didn't even know you've been a pastor for over 10 years. I think culture is any space that you live in that develops you. On a recent episode of Culture Raises Us podcast, I sat down with Warren Campbell, Grammy winning producer, pastor, and music executive to talk about the beats, the and the legacy behind some of the biggest names in gospel, R&B, and hip-hop. This is like watching Michael Jackson talk about Thurley before it happened.

Was there a particular moment where you realize just how instrumental music culture was to shaping all of our global ecosystem? I was eight years old, and the Motown 25 special came on, and all the great Motown artists, Marvin, Stevie Wonder, Temptations, Diana Raw. From Mary Mary to Jennifer Hudson, we get into the soul of the music, and the purpose that drives it. Listen to Culture raises us on the IHeart Radio app, Apple Podcasts,

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think that they could land the plane with the help of air traffic control. And they're saying like, okay, pull this, do this, pull that, turn this. I can do it my eyes closed. I'm Mani. I'm Noah. This is Devin.

And on our new show, No Such Thing, we get to the bottom of questions like these. Join us as we talk to the leading expert on overconfidence. Those who lack expertise lack the expertise they need to recognize that they lack expertise. And then, as we try the whole thing out for real. Wait, what? Oh, that's the run right.

I'm looking at this thing. See? Listen to No Such Thing on the I Heart Radio app. Apple Podcasts, or wherever you get your podcasts. All right, we're talking about the question of whether space-time is a fluid and whether that would mean that you can drink it. What kind of straw would you need? Do you need a space-time straw? What's a good mixer for space, I wonder?

Something dark. Yeah, dark vodka, dark tequila. I don't know. Maybe some Kalua. Pick your poison. I think maybe some cream because space is pretty dark. So you've got to lighten it up a little bit, you know. I'll take my space with some cream and sugar, please.

Or if it's a fluid, I guess that would that mean you can flush it? Can you flush space time? You sort of can, right? Down a black hole, maybe? Black holes are sort of the toilets of the universe. That's true. Yeah, they suck in a lot of dark matter. They actually don't, but that's a good joke.

Well, how do you know? I guess that's the topic of a different podcast. Exactly. It's a really fun question. But here we're talking about whether space time is the fluid, and we're talking about what space time is according to quantum mechanics, which is pretty much the same view that Newton had, the classical physics have about space. But then at some point, at the beginning of the 20th century,

Einstein came along and said, wait a minute, space time is not like fixed and immovable. It does things. It has properties of its own. Yeah. Einstein showed us that space. space is dynamic. It's not just a flat backdrop to the universe. It participates in the motion of the universe in everything that happens. You know, as I think John Wheeler said, mass tells space how to bend and space tells mass how to move. That means that if you have a mass in a certain part of space or a bunch of energy, then it curves space itself. And Einstein's big realization

was that what we think of as the force of gravity isn't actually a force. It's just due to our inability to directly see the curvature of space, which is affecting how things are moving. So the actions that we attribute to the force of gravity are really just inertial motions of objects through curved space. And his conception of space is this incredibly fascinating sort of curved manifold, this sort of like shape that has features to it. It's curved here. It's not curved there. But it's really totally different from the conception of space in quantum mechanics. It's not just a backdrop, right? It's not just like here's something that's happening at this location and that location. The locations themselves now have interesting

relationships. Like instead of just having a grid and every point is equally spaced, those points can have weird relative distances. Like this point is actually closer than that point on the grid. And these two points, which are super far apart in the universe normally, can actually be adjacent to each other. That's what a wormhole is. So really general relativity is telling us that space can do this weird thing about changing the relative distance. instances internally between the points that affects the motion of objects through it. And he also discovered all these fascinating symmetries like there's a maximum speed of information through the universe.

That was one of the other big revelations in Einsteinian gravity, which contradicts Newtonian gravity that said that information propagates instantly, according to Newton's gravity. So Einstein's view of space is this smooth, continuous, but dynamic thing that really plays a role in the universe. It doesn't just sort of sit in the background. and provide a frame. Yeah, it's pretty amazing. Einstein was able to kind of revolutionize that view of space.

And I wonder if you or we know how that came about like, what was the thing that set him off in that direction. Was it basically observing what happens out there in nature that the speed of light doesn't change? And if you start from there, then you can sort of put together this idea that space time can bend and ripple. Well, there are many stages in Einstein's thinking. The first is, as you describe, a special theory of relativity.

Trying to understand the Michaelson-Morley experiment. that showed that the speed of light was the same in every direction. And also trying to understand some puzzles in electromagnetic theory at the time, like why a static electron gives an electric field, but an electron in motion gives an electric and magnetic field. Like it seemed like what was happening there depended on your perspective. So Einstein was trying to resolve all of these puzzles. We have a whole podcast episode about that.

And that's what led to the special theory of relativity, the idea of the speed of light being maximum, and information propagating at a certain speed, and time not being the same everywhere in the universe, that was already a big step forward. But then it took like another 10 years for him to come up with the general theory of relativity. That's the one we're describing here,

which is about how space is curved and that curvature can explain gravity. For him, that came from puzzling over this question about like, why is gravitational mass, the mass that controls how much we get pulled on seem to be exactly the same as our inertial mass, the one that determines how much we accelerate when we get pushed.

Like the mass in F equals, M.A. versus the mass in Newton's law of gravity. Why do those two things seem to be the same? So Einstein sort of made that connection and realized that they're really all bound up in the same idea. He was able to explain all of it by changing space into a curved object. Or space time more precise. And there's a really important consequence there. If Einstein's theory of space is correct, then you can also track it backwards in time and say, look, the universe is expanding. And that means that we can go backwards. instead the universe used to be hotter and denser.

And in Einstein's theory, at least, that means that space and time can have a beginning, right? Unlike in quantum mechanics, infinite in time, Einstein's theory says that space could have had a beginning, that there could have been a moment when there was no space. So these are really very contradictory views of space. Quantum mechanics view says time is infinite and space has always existed. General relativity allows for a universe where space begins.

And so that brings us to maybe the biggest, I guess, conflict in physics. the conflict between quantum mechanics and general relativity and how they treat space. And this conflict is kind of theoretical, but also very conceptual, like you said, it's about, you know, whether time can begin or have it beginning, whether time can bend. Is the conflict here mostly theoretical? Like we can't make the theories work? Or do you think it's something maybe more fundamental that maybe the properties of space change once you get to a certain size level? Yeah, we definitely cannot make the theories work currently.

Like, people are trying from all sorts of directions to unify these things. One set of theories is saying, well, let's take quantum mechanics and try to do it in curved space. And that actually kind of works. Like, if you have space that already curves for other reasons, we do know how to do some quantum mechanics of particles moving in curved space. We don't know how to do is show how quantum mechanics can make space curved, like to get that curvature just from the particles to show how, like, having a bunch of electrons in one place will make space curved.

When people try to do that, it gets really complicated and hairy, and you get all sorts of infinities. And one of the reasons is that gravity is a real mess to do calculations with. If you emit gravitons, gravitons feel gravity, and they emit more gravitons, which emit more gravitons. So it very quickly gets out of control. Sort of like the strong nuclear force, we were talking about how gluons emit gluons,

which emit gluons, which makes it almost impossible to do those calculations. But gravity is even trickier. And so people have really failed in trying to do that. And from the other direction, people saying, well, let's take space and quantize it and say maybe instead of the force being quantum mechanical, maybe space itself is quantum mechanical. It's chopped up into little discrete bits. And this idea also hasn't quite worked yet. Nobody's really been able to bring these two things together mathematically. What you asked is like, is this a mathematical problem or a theoretical problem?

And I think the answers are connected, right? If we are able to come up with a mathematical description that explains everything we see in the universe and sort of hangs together, there doesn't give us nonsense, then we'll have a theoretical or philosophical question, like, what does that mean? You know, how far do we have to go in order to make that theory? Can we just try to bring these two theories together, or do we need to dig a level deeper and start from something else which can then explain what we're seeing on the larger level? Interesting.

I guess you'll just have a big fight about it, and then whoever wins, wins. And I think one of the deepest questions really is, like, is space itself the fundamental fabric of the universe, do we need to be building on top of space, or do we need to be tearing it apart and trying to understand what it's made out of? Like, is space itself fundamental, meaning it just is, it's like the base layer of reality? Or is space emergent? Is it just something that arises from something deeper and it's complicated interactions? That's kind of, I feel like that maybe that's a separate question than this idea of whether quantum mechanics or general relativity is right, right? It's sort of a separate question.

Like, whether either one is right, we can also ask the question, like, where does space come from? Well, it might be a path forward to giving us these two different explanations of space. Space seems to be kind of different in quantum mechanics and in relativity. And instead of harmonizing them and trying to match them together, you might be able to explain them just by saying, well, they're sort of both wrong. Neither of them are actually true descriptions of what space is. Space is something deeper and weirder that can do these two kinds of things. The way, for example, fish scientists might argue and say, look, look, ice is different from liquid water, which is different from gas.

They're just different, right? And we know, of course, they're all made out of the same thing deep down. This is just different stuff that water can do. Ice is not fundamental to the universe. Water is not fundamental to the universe. Steam is not fundamental to the universe. It's just an emergent property of water. If we can come up with like a deeper understanding of what space is,

something beyond our understanding currently, Maybe we can explain are the quantum mechanical view of space and the general relativistic view of space is like different phases of space, the way we think about different phases of water, having, you know, fundamentally inconsistent kinds of behavior. Well, that's kind of what I meant before is that like, you know, is the conflict between quantum mechanics and general relativity, could it be explained by just like having space behave differently at different scales? Like in the scale of planets and black holes, it behaves like one way where you have gravitation. waves and it bends, but maybe at the level of small particles, it behaves differently. Yeah, that's exactly the right direction. And a lot of people are pushing that way. Like, can we start at a lower level and come up with a more fundamental description of space?

And then as you say, it turns into quantum mechanics at this scale or turns into general relativity at that scale. And fundamentally, what that means is that both are wrong. Instead of trying to start from general relativity and add quantum mechanics or start from quantum mechanics and add general relativity, you sort of throw both out the window. and say let's start from something deeper and try to reproduce both of them, but neither of them fundamentally would be correct in that picture. Well, you want to throw them out.

That sounds very negative, and I feel like a lot of work has gone into those. It could just be that they're both right. They're just right at different scales, perhaps, or in different situations. Like, we still use Newtonian physics to calculate the path of baseball when you throw it or something like that. Yeah, they both work, right? They're effective theories in that they give good predictions in certain situations. But if what we're trying to do is understand the deep nature of the universe, then they're not like philosophically true. I think our final goal is to get a description of the universe that we think mirrors what's actually happening out there,

like conceptually describes the laws the universe itself is like actually following. So in that sense, general relativity in quantum mechanics wouldn't reflect what's actually happening out there in the universe, though you're totally right. They're very useful and they're very effective. The same way we use like fluid mechanics to explain what, happens when you flush your toilet and it works right it's very good it helps us avoid lots of ugly disasters doesn't mean we should stop doing it but it doesn't mean that the assumptions behind fluid mechanics are the right way to think about the reality of the universe well my toilet

seems to flush whether or not i understand the fluid dynamics unfortunately otherwise you put enough dark matter in there and i promise you it won't flush then you need dark energy to push it through. Suggest that to your plumber and see how that goes. Oh, there you go. That could be a good name for plumbing business, dark plumbers. Dark plumbers, yeah. That sounds like a CIA operation.

Yeah, or a Sith operation, more like that. Yeah, if that van is parked outside your house, I would suggest moving. If your plumber brings out a lightsaber. First of all, super cool. You should totally take a selfie with your plumber, but they might damage the plumbing. Yeah, but also see. if he can dunk. I hear those Jedi are really good at basketball. Well, would they be dunking with a toilet?

I don't know. This analogy has gone off the rails. All right, well, let's tackle maybe the question that we started off with, which is, is space time a fluid? Like, can space time flow, I guess, and swirl or get flushed down a toilet? Daniel, where does this idea come from? This comes from an attempt to try to explain the nature of space, as we talked about as not fundamental, but something that emerges from a lower level. of reality. And it says essentially that maybe space is like water. It's made out of some smaller pieces that follow very, very different rules. And that our experience of it is sort of like the

experience of water. We really are like the fish scientists. That space itself is made out of some smaller bits we have yet to discover. And those bits interact with each other in a way that follows the laws of fluid mechanics that our understanding of fluids and water actually might be able to be applied to space itself. Space emerges from some weird quantum bits, and those bits come together in a way that can be described by fluid mechanics. Yeah, it's kind of like the idea that maybe there's like a super space, and inside of that super space is what we call space, and that it's actually made up of like little bits of space,

meaning like when I think I'm moving through space or when a particle thinks it's moving through space, it's actually like maybe hopping between bits of space. is that that's kind of the idea right that's kind of the idea and it's also attractive from the point of view of explaining some of the symmetries and the invariances that we see like we don't understand where for example this law of the speed of light comes from why is there a maximum speed of information in our universe in quantum mechanics we just don't see that right it doesn't exist in the theory of quantum mechanics something we have to add to quantum mechanics sort of by hand but a space is an emergent phenomenon if it comes from the weaving together of these

weird quantum bits, they might be able to have the maximum speed of information sort of emerge from those laws. The way that like water as a liquid can do things that water as an individual particle doesn't do, or that water as a crystal can do things, has properties that water as an individual particle doesn't do. Maybe these invariances and these symmetries sort of emerge with space. They're the properties that come when space comes together to form these liquids. And fundamentally, you're right it's like these little bits of space sort of woven together and it's fascinating to think about like how you weave space together to make it a liquid it says that you start from a universe where all you have are like weird little quantum bits you have these locations but they don't sort of exist in space yet they just are like are there and then they get quantum entangled with each other which sort of connects them then things that are really tightly quantum entangled with each other we call those things close to each other things that are loosely quantum entangled, we call those things further from each other. Things that are not entangled at all are like out of your light cone completely.

So you sort of like build space up by quantum entangling all these weird little sort of non-space bits and space itself comes out of all those things working together. Yeah. And I think maybe the idea is like maybe as you're moving around these space bits, there are rules about moving through these space bits that maybe explain things like the speed of light limit in our universe, right? Like maybe if I'm switching between space bits, there's a certain cost to that. And then that would explain the limit of the speed of light.

And that's kind of what you're saying is that maybe these things that we think of as fundamental phenomena or properties of the universe could just be like the little tiny rules between space bits that make up space. Exactly. So that picture, which is more like a sort of quantum space foam, says you build space out of these little bits and the rules that we observe sort of come out of the arrangement of those things. They're not fundamental to the bits themselves or sort of how you put them together. This new theory says, well, maybe space isn't like a foam. It's kind of like a foam, but it's a little bit different. You don't use the mathematics of foam instead use the mathematics of liquids. Say space isn't like a grid that's woven together with quantum entanglements.

Maybe there's a little bit of a different physics there. And what's happening is that these little bits of space can sort of like slide past each other. They can like flow around each other. They can do things that foam or crystal can't do. This actually leads to slightly different predictions for the behavior of space. And one of them is that the limit on the speed of light is not actually absolute. It's like approximate that light doesn't always travel at the speed of light. There might be like very small variations there.

I see. The idea is that maybe these bits of space that space is made out of aren't connected to each other. Like they're not linked together. Like you might link like a chain mail or a chain link fence. Maybe they're just kind of like floating out. there in some super meta space and they can actually kind of slosh around and move relative to each other. Is that the idea? That's sort of the idea, though. What you described sounds more like a space gas. Think about like a crystal where the bonds between the atoms are really, really strong,

right? That's sort of like our idea of a space foam. Now relax those bonds a little bit and you have like a space liquid. Your right, things can slide past each other, but they're not totally ignoring each other. There's still interactions between those space bits, which is how fluid effects emerge. If they were totally disconnected, you have like a collisionless, non-interacting gas of space bits, then you would expect very, very different kinds of behavior. This theory says, instead of having space like a rigid crystal of locations that are fixed to each other, loosen it up a little bit and let those flow. Not completely where they're ignoring each other, there's still sort of some bonds between them, but let them flow a little bit. And it leads to different

predictions for how light moves through this sort of liquidy space. Well, I guess what does that mean? Does that mean that as I'm moving through space, if the space liquid happens to be moving, then I'm going to move differently through it? Or would I even notice if the liquid around me is flowing? When things move through a liquid, they move in a different way than when they move through a solid, right? And a solid is more rigid and so it's sort of better at propagating waves, right? Which is why like sound moves faster through your table than it does through the air. In denser materials, things are more tightly bound, sound moves faster. And so things in space time liquid would move differently than things in sort of a space time foam or

space time crystal and specifically it would mean that it sloshes a little bit so there'd be like a dissipation that if you shoot a super high energy photon across the universe instead of it getting to the other side of the universe with the same amount of energy it would lose some of that energy to like this sloshing of space itself sounds like we're all in a hut tub is that I feel like you're saying the universe is just a nice bubbly hot tub that we're all relaxing it. All right, well, let's talk about what makes us think that the universe or that space time can be a fluid and whether we have any evidence of it. And if we do, what would that mean about our understanding of how everything works?

So let's get into that. But first, let's take another quick break. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently the explosion actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay.

Terrorism. Law and Order Criminal Justice System is back. In Season 2, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Oh, wait a minute, Sam.

Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate.

Well, according to this person, this is her boyfriend's former professional. and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not?

To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. I don't write songs. I take dictation. I didn't even know you've been a pastor for over 10 years. I think culture is any space that you live in that develops you. On a recent episode of Culture Raises Us podcast, I sat down with Warren Campbell, Grammy-winning producer, pastor, and music executive to talk about the beats, the business, and the legacy behind some of the biggest names in gospel, R&B, and hip-hop.

This is like watching Michael Jackson talk about Thurley before it happened. Was there a particular moment where you realized just how instrumental music culture was to shaping all of our global ecosystem? I was eight years old. And the Motown 25 special came on. And all the great Motown artists, Marvin, Stevie Wonder, Temptations, Diana Ross. From Mary Mary to Jennifer Hudson, we get into the soul of the music and the purpose that drives it. Listen to Culture raises us on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

Imagine that you're on an airplane and all of a sudden you hear this. Attention passengers. The pilot is having an emergency and we need someone, anyone, to listen. land this plane. Think you could do it? It turns out that nearly 50% of men think that they could land the plane with the help of air traffic control. And they're saying like, okay, pull this, pull that, turn this. It's just, I can do it my eyes close. I'm Manny. I'm Noah. This is Devon. And on our new show, no such thing. We get to the bottom of questions like these. Join us as we talk to the leading expert on overconfidence. Those who lack expertise, lack the expertise they need

to recognize that they lack expertise. And then, as we try the whole thing out for real. Wait, what? Oh, that's the run right. I'm looking at this thing. Listen to no such thing on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. All right, we're asking the question,

can space time be a fluid? And it sounds like this is the idea that we're all just sitting in a hot tub somewhere. This is the hot tub time machine version of the universe. We started out within office space as a comedy and now we're in hot tub space time machine. Could be the sequel. Me, you, Barack Obama and Yoda,

all sitting in a hot tub, understanding the nature of space time. That's an awesome picture. And I can't wait for our listeners to draw and draw this fan art. Or maybe if Obama is a listener the podcast, he'll write in and, you know, come and join us on our acoustic hot tub that is this podcast. And also we can finally answer the question. What happens if you turn a lightsaber on

inside of a hot tub? Or maybe he's got an opinion about whether he could beat Yoda in one-on-one basketball. Well, Obama seems like a humble guy. I don't think he would try to take on Yoda. He is respectful. That's true. All right. Well, I guess this is an interesting idea that space time can be fluid that maybe it's not fixed out there in the universe, maybe to think that can slosh around, that it's made up with little bits that kind of move relative to each other. And now, Daniel, do we have any inclination that this theory is true? Does it match up well with some observations that we have in experiments? Or is it just an idea out there that we think that maybe one day could possibly explain things? At this stage, it's really just an idea, but there are

some of fun experiments we can do to try to test it. So it's not just an idea people are having in hot tubs. It's something people are out there really working on trying to verify because it does make some very cool predictions. And there's sort of two categories of experiments. There's experiments we're doing up in the sky, like looking at things out in the universe and also things people are doing in the lab to try to make like sonic black holes to study them. The first one has to do with like how light propagates through the universe. As we said earlier, there are rules about how fluid behaves. And if you shoot something through a fluid, it will lose energy, it will dissipate its energy.

Fluids have these two properties that's called dissipation where you lose energy over time and dispersion where things at different energies travel at different speeds. And so that's not something we've seen in space. Like if you shoot photons across the universe, currently we think they arrive with the same energy as when they left, like they never get tired. We've also seen that photons at all different energies, red photons, blue photons, green photons, infrared photons, all travel at the same speed. So people are trying to understand if this is really true,

because if space time was a liquid, then those would be broken a little bit. Photons would lose a little bit of energy as they move to the universe, and red, green, and blue photons would travel at slightly different speeds. So they're trying to do this experiment, though it's tricky because we don't have like a huge laser

pointed at the earth to let us do this experiment. Sounds like a dastardly plot for a supervillain slash experiment. Though we almost do have a huge laser, there's this thing up in the sky called the Crab Nebula, which is an excellent source of really, really high energy photons. It's shooting photons at us up to like 80 terra electron volts. Remember, the large Hajon Collider, the most powerful human accelerator on Earth, only gets things up to like six and a half or seven terra electron volts. So this thing is shooting photons at us more than 10 times the energy of the LHC,

which makes it a great way to study how photons propagate through the universe. It sounds like you have a lot of ideas for disproving this crazy theory, but I guess my question was more like, what makes us think that this crazy theory could be true? Like, is there something that it predicts that maybe matches up with some unexplained phenomenon in space? We don't need this theory to explain anything that we see. It's just an attempt theoretically to try to harmonize our idea of the universe,

to come up with a new explanation for what's out there sort of from the bottom level up to explain how we end up with general relativity and how we end up with quantum mechanics. But you know, you can't just describe something theoretically and say, here's my description of the universe. You also have to make predictions that can be verified and tested to see if this is what's really happening out there. So we don't need this to explain any results of experiments. We don't have any experiments where quantum mechanics and general relativity disagree because those experiments are essentially impossible to do. But it does make predictions that we can test so that we can prove or disprove this theory.

I guess what I mean is, like, does this crazy theory actually make quantum mechanics and general relativity play well together? Or we just think it might? Or does it actually harmonize everything? If it's true, then it does allow for us to derive sort of general relativity and quantum mechanics from one source. All the math is not completely worked out. like there is no completely well-worked-out theory of quantum gravity from which you can get the effects of general relativity and quantum mechanics. This is sort of like one direction people are working in and there's a series of recent papers sort of thinking about the consequences of it.

Like we don't have all the details worked out yet, but if this theory is true, it would have these consequences. Let's go check and see if we can see those things happening in the universe. Because if we can, that means we're on the right track. I mean, I don't mean to tell you how to do your business. But before you point a giant laser to Earth, wouldn't we want to make sure that this is a theory that is going to be worth doing that? Do you know what I mean?

Like, I would see how it would be important to verify this theory, but only if it made things work. But it sounds like we don't even know if it's going to make things work. We don't know if this theory of a space-time fluid actually works theoretically. You're right. In the same way that we don't know

as string theory works fundamentally. People are still working on it. But we'd also love to have ways to test string theory to verify its predictions to understand if we're on the right track or not. And also sometimes getting experimental verification provides clues. It, like says, oh, you have a whole different set of ideas about this theory. Well, the experiment prefers this one or that one. So we can give you some guidance sometimes.

So it's nice when theory and experiment can sort of work hand in hand. I mean, we don't develop a complete theory of the standard model before we build our first particle detector, right? We sort of do it in increments. And we get clues from experiment and then ideas from theory. and it's sort of like a tag team. Well, at least with the Higgs-Bosin, I feel like that theory was saying it kind of worked out

and there were predictions of it, and then you went off and built a giant thing. Yeah, that is one example of success from having a theoretical idea. But of course, that theoretical idea came from experimental observations that we didn't understand at that time, right? Seeing the W and the Z were massive

and the photon wasn't and not understanding that. And so what we've got to do is go out there and do a bunch of experiments and look for weird stuff. Sometimes you get a confirmation of the idea you had and sometimes you don't. Wait, are you trying to say, that when it comes to space time being a fluid, you just got to go with the flow.

You don't want to flush it all down. Well, I do think that these results from the Crab Nebula are super awesome. I mean, they look to these photons and they try to measure whether there's any, like, change in the energy spectrum, the kind that you would expect if space time was a fluid.

And they didn't see any, which means that, you know, space time might still be a fluid, but if it is, it's a fluid that's like super duper slippery. Like the fluid effects, these like frictiony effects where you're losing energy as you're moving through space time.

are very, very small. So, like, maybe space time isn't a fluid. Maybe it's a super fluid. Ooh, it has superpowers kind of. Meaning, like, it doesn't behave. It's not like a thick, gooey fluid. It's almost like supernatural fluid. Yeah, superfluids are like superconductors.

They have almost no friction. They flow very, very smoothly. So if space time is a fluid, then it has to have, like, very, very slight fluid effects. So we do have an experiment or an observation, at least it says that space time, is not a fluid then it might still be a super fluid but it's definitely not a fluid is that what the observation says yeah it's not like thick chunky soup that's for sure that we can rule that out if it is a fluid if spacetime does follow these properties and bubbles up from something deeper and has fluid like effects they would be very very very subtle but it doesn't mean they're not right

you can always rule it out to some level but there's sort of another direction we can approach this which is to try to do experiments on earth to understand whether this theory even holds together. And there's a guy in Israel, the Technion, who builds these sonic black holes, try to understand, like, how gravity might emerge from a fluid theory of space time. He's noticed a lot of similarity mathematically between how waves propagating fluids and how waves propagate in curved space time. So what he's done is he's experimentally built a weird kind of fluid that has strange behaviors that are very similar to the behavior of gravity, to the point where he's even built a fluid with what he calls an acoustic horizon, meaning it generates sound waves that cannot escape

this weird little blob inside his fluid. Whoa. So wait, he's like building fluids out of real atoms, like real materials, and using that like a Lego model of what space might actually be? Is that what you're saying? Yeah, exactly. He's doing what they call analog gravity. He's like, if the mathematics of this works for space time, it should also work when you

put other things together. So instead of doing experiments using spacetime bits, which we don't know how to manipulate, it's like let me do it with other kind of bits. So he does it with rubidium atoms and he builds these Bose-Einstein condensates and he gives them all sorts of weird properties so that the sound waves moving through those rubidium atom fluids should operate the same way photons move through the space-time liquid. So he's actually successfully built what they call an analog black hole. It's not an literal black hole. But But it has similar properties in that fluid to photons moving through space time. That feels like a little bit of a stretch, but I guess I trust you that it's an interesting way to study the...

I feel like you're building a model and trying to say that like if it works for my Legos, it works for quarks. Yeah, he's definitely made some very bold claims and there's a lot of controversy about what it means, but it's definitely fascinating. So the fascinating thing about this is that they're not black holes. Black holes don't emit light. These are like silent holes because they don't emit sound. right there's like quiet holes they're like the uncomfortable silence in social situations it's like what would you even say you're in a hot tub with yoda and obama it would be a sonic black hole as well it might be a little awkward yeah all right well it sounds like this is a super fascinating theory

and kind of challenges our views of space time itself like maybe the fundamental platform of the universe isn't what we think it is maybe it's something that sits inside of an even bigger meta or super space platform or environment. And these are interesting ideas that might bring together quantum mechanics and general relativity, but stay tuned. Experiments so far say that maybe space isn't a fluid, but that maybe the hot tub of the universe is actually a super hot tub of the universe. Yeah, and these ideas take a while to bubble up and to percolate through the brains

of humans. And it might be that one day we look back at our understanding of space time and think, wow, we were so foolish. We didn't even understand the liquid we were. swimming in. Yeah, it sounds like we need to soak on it for a little bit longer. I always prefer to soak rather than scrub. Just don't do it with a lightsaber, I guess.

All right, well, we hope you enjoyed that. Thanks for joining us. See you next time. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of IHeart Radio. For more podcasts from IHeart Radio, visit the IHeart Radio app. Apple Podcasts, or wherever you listen to your favorite shows. There's been a bombing at the TWA terminal, just a chaotic, chaotic scene.

In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Every case that is a cold case that has DNA. Right now in a backlog will be identified in our lifetime. On the new podcast, America's Crime Lab, Every case has a story to tell, and the DNA holds the truth. He never thought he was going to get caught, and I just looked at my computer screen.

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