Daniel and Kelly’s Extraordinary Universe - Can the Universe exist without space?

Episode Date: May 4, 2021

Daniel and Jorge break down the Universe to its most basic level and ask if space is necessary Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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Wow. What does your family get you for your birthday then? Empty space? Actually, my wife rents a dumpster and says I can throw out anything I want. That's like a negative present. Hey, space is precious. You know, you can't have too much of it. You can't have too much, nothing. Said nobody never. Nothing is better than nothing. This is the best nothing I ever got.

Hi, I'm Horham, a cartoonist and the creator of PhD comics. Hi, I'm Daniel. I'm a particle physicist, and I really do love space. And welcome to our podcast, Daniel and Jorge, Explain the Universe, a production of IHeartRadio. In which we explore all the stuff in space. Empty space, not so empty space, space filled with really crazy bonkers stuff that's hard to understand. And sometimes even the very nature of space. We talk about all of these things in this podcast and we break them down.

And our goal is to deliver them to you in a way that actually makes sense. So you go away thinking, huh, I get it. Or at least I get it as much as scientists. at it, which sometimes isn't that much. And sometimes it feels like we're talking about a whole lot of nothing. And sometimes we are literally talking about nothing. And sometimes we're trying to figure out what is nothing exactly. Right.

Yeah. Deep questions. Now, Daniel, when you say you love space, do you mean like you love, you know, just space travel, like where the planets are? Or did you just like, you know, having the idea of space in your life? I love all of it. I love outer space. I love deep space.

I live near space. I also love having space in my living. room. Like, it's not unusual for me to toss out a piece of furniture and go, you know what? The room is just better with nothing there. You like everything about space. There's nothing negative about space for you. I'm pretty pro-space. Yeah, absolutely. You would live in an empty box if you could. Exactly. I'm like a cat that way. Are you looking forward to your children leaving the house then? Because that's just more space. That is more space. I'm not looking forward to them leaving, but if they do, I'm looking forward to throwing all their stuff away.

Oh, man. That's going to come back. to haunt you. They're like, why did you throw away my comic book collection? That's worth $3 million now. Yeah, exactly. But this space is priceless. Right. Well, we like to talk about space in this podcast and also about what it represents and what

it means because it's kind of a topic that businesses don't have a super clear idea about. That's right. And it's one of these really fun questions in physics because only recently did we figure out that it's a question that sort of has an answer. It's a question that's worth asking. It's one of these questions that's so basic that we just sort of assumed we knew the answer. You know, space is space. It's the nothing.

It's the emptiness. And only recently have we realized, wow, space could be much more than that. And it really deserves our attention. Right. Even more important is this sort of idea that maybe we don't need space. Like maybe it's just sort of like an add-on to the universe. Yeah. Is it at the foundation of reality or is it just something that fills up something else?

You know, imagine what it would have been like to be a person. 10,000 years ago. You never would have experienced reality without air, for example. So the concept of like a vacuum, a place where there was no air, would have been totally alien to you. So now, of course, we know that that's possible. It seems obvious that air is not a fundamental property of the universe. But we're at the next level and wondering like, well, is space fundamental?

Can you take it apart? Do you really need it? Yeah. In fact, most of the universe doesn't have any air in it, right? Most of the universe is pretty empty. Yeah, from that point of view, exactly. We were dealing with a very unrepresentative example. And we do this all the time in science.

We assume that the things we experience are universal. And we can generalize from these examples to the whole universe. We're doing this all the time left and right without even realizing it. So now we're asking a similar question about space. You know, are our assumptions about space valid? Can we break it apart? Do we even need it? Is it possible for it to have bubbled up from something else?

Yeah, it's a spacey topic. But space is pretty empty. I think we have a whole podcast episode about that, right? Like, what's the average density of the universe? Or, like, how much stuff is there really on a, like, cubic foot? Yeah, we do have a whole podcast about how empty space is. And we take you on a journey from the top of the atmosphere into the solar system and then out into interstellar space and then finally into intergalactic space.

And mostly space is intergalactic space, right? Like, there are these huge streams of galactic clusters of galaxies swinging around each other. but between them there are these vast bubbles and voids that don't have galaxies in them. So most of the universe sort of by volume is this intergalactic space, which is not totally empty. There's still stuff in there. There's a little bit of dark matter. There's definitely dark energy, but it's most of the universe.

And it's pretty empty, but not down to zero. Yeah. And there's a lot of it space, I mean, in the universe. There's a whole bunch of it. Like, if you were going at the speed of light, it would still take you as far as we know right now. you know, tens of billions of years just to go from one side to the other. That's a lot of time. Absolutely.

And remember, the speed of light is like mind-bogglingly fast, right? It's incredibly fast. And yet these distances, even inside our solar system, are incredible. Like, it takes minutes for light to get from here just to Mars, which is our neighbor and hours to get out to the outer solar system. And when we communicate with probes and rovers and stuff on other planets, the reason you can't drive them is because they are so far, away. You can't do real time driving because the lag is too long and that's just inside our solar system. So the distances to other galaxies, millions of light years and deeper into space billions of light years, they're hard for us to get our mind around. So yeah, space is pretty

spacious. I guess I hadn't thought about it before. Like even if you're Superman or Superwoman and you're traveling, you're able to fly at the speed of light, it would still take you like a billion years just to, you know, go to the other galaxies out there in the universe. Yeah, well, that's an interesting question, does Superman have to travel at the speed of light? Can he be superluminal? I mean, how far away is his home planet anyway? I don't know. You're the physicist. I just read the comic books. I don't dissect them scientifically. I'll go find out exactly where his home planet is and figure out if he broke the law on the way here. And if so, I'll issue him a physics ticket. Well, he can just burn it up with his heat vision, Daniel. And also, how are you going to arrest him?

Good luck with that. Citizens arrest, Mr. Superman. But yeah, there's a lot of space. out there, it's definitely not a small part of the universe, but I guess the question is, is it a necessary part of the universe? So today on the podcast, we'll be asking the question Can the universe exist without space?

Space, space, space, space. That question is so profound, it needs an echo. It echoes through the vacuum of infinity. Through the vacuum of our understanding of the universe, absolutely. through the empty space in my head. But it's a fun question.

It sort of mirrors the way I treat furniture. You know, I look around my house and I ask myself, do we need that chair? Nobody ever sits there. And we get rid of it. We're like, ah, it's better off. And now we're cycling through modern physics and we're like, hmm, do we really need the whole concept of space? Like, is it really have to be included in the sort of fundamental list of things you need

to build the universe? Or is it like, you know, ice cubes or atoms or hurricanes, something that, you know, comes from your more basic ingredients. I would hate to be a furniture in your house. I feel like I would live in constant fear. Yes, absolutely. You must constantly justify your existence in my house or you're on the trashy.

It's like Huff Post reporters, you know. Hopefully that's just for your furniture, not your family as well, or pets. Absolutely. Living creatures definitely belong to the family. Chairs, not so much. So if you could have a bigger house, would you have a bigger house?

No, no, I don't need a bigger house. In fact, I had some friends who once moved to a bigger house and almost ruined their marriage because they ended up shouting in each other from different rooms across the house and they did better when they had to, you know,

share a small apartment. Yeah, we talked about this and I offered the better solution of just getting an intercom system. You are going to engineer everybody's marriage, huh? I want to go to your couples counseling. There's a solution for everything in engineering. Marital engineering.

Wow, that's a better name for therapist. But anyways, yeah, it's a big question whether or not we need space in the university. It seems pretty fundamental, you know, Like, how can you have a universe without space? Like, isn't space the universe? Yeah, but just because it's hard to imagine doesn't mean it's not reality, right? A lot of what reality is was difficult for us to wrap our minds around.

So when you do this kind of exploration, you've got to sort of be willing to give up something you thought was fundamental, something you assumed was inherent, and ask your question of whether it can come from something else. All right, well, as usual, we were wondering how many people out there had thought about this spacious question, whether or not. but we need space. So Daniel went out there into the wilds of the internet

to ask people, is it possible to have a universe without space? Here's what they had to say. Oh, that's a good question. I don't think so. Okay. No.

Why? I don't know. I don't know. I don't know. I don't know. I don't know why. I just know. I think space is only one of the dimensions, right? You could probably have a universe

that's just time and maybe not space. I'm going to say yes Well my understanding is that Yeah I guess you can I mean was there space when the Big Bang occurred In the moments after that Or was it all dense matter with zero space But my understanding is that

If you have a different universe It could operate off a completely different set of physical laws So I guess never say never in that regard You can have a universe without space our situation with matter having out-competed anti-matter I think is actually pretty unique I think there are little universe blips all over where universe pops into existence and annihilates

and no spaces created I guess you can have universe without just this dimension space and you can have all the other dimensions possible but it will be crowded i guess it would mean what you mean by universe because before the big bang all the universe was there it was just compressed and to my knowledge there's no space so if you can't that was the universe then yeah all right some mixed reactions here some people could live without it some people could really want it yeah it basically wraps up the whole question of what space is and where it comes from and all of these answers. I see echoes of general relativity and quantum mechanical perspectives on this question.

So good job, listeners. And to those of you who would like to participate in future rounds of answer random questions for the podcast, please write to us to questions at danielanhorpe.com. There's a lot of reference here in the answers to the Big Bang too, right? That's something I hadn't thought about before. Was there space before the Big Bang at the Big Bang? or was space created at some point in the history of the universe? Yeah, space and time, right?

All right, well, let's dig into it, Daniel. Let's start with maybe the basic stuff. Like, what is space? How do physicists think about what space is? Yeah, this is a great question. And we have sort of two answers for what space is based on whether you're thinking about it from the point of view of quantum mechanics or whether you're thinking about it from the point of view of general relativity.

And remember that these are the same. two pillars of thinking in modern physics, two great ways to describe parts of the experiments we've done. Quantum mechanics describes basically everything that has to do with little particles at small scales and all the forces that we're familiar with except for gravity. And general relativity talks about how space is curved and it's bent. And that's really what gravity is. And so the answer to the question, what is space? Sort of depends on whose perspective you want to take first. What do you mean? How can something depend on your perspective? Aren't you looking for like one answer?

We are absolutely looking for one answer, but we don't have one answer. We have two theories, quantum mechanics and general relativity. They treat space very differently and we haven't been able to unify them. So the short answer is we don't know what space is because we don't have a single coherent theory for the whole universe. And the two theories we do have disagree about what space is. All right. So what are the two theories about space?

And is there enough space between them to tell the difference? Well, you know, let's start with quantum mechanics. Quantum mechanics is the theory that tells us how electromagnetism works, how the weak force works, you know, how photons move, and it tells us that space is fundamental. It assumes that space exists and it adds stuff to it. So if you're going to build the universe using at least our current theory of quantum mechanics, then you start from space. You say, let's assume there's a space.

And then at every point in that space, I'm going to say whether or not there's a quantum field and how much energy it has. but it's sort of like at the bedrock of the whole theory, just like assuming that space and time are things that you can put fields in them. Right, because that's kind of baked into the definition of a field, right? Like you can't have a field without space. Like a field is by definition, like how things vary in a space.

That's right, exactly. And we'll talk later about whether you can generalize that to like abstract spaces rather than physical spaces and what that means. But you're right, for the physical fields that we're talking about, you know, like the photon field, it's just a value all through space. But as you say, space is fundamental to that. You need to know, like, there's a certain value of the field here. And over there at a different location in space, it has a different value.

And for example, the Schrodinger equation tells us how a wave function exists across space and how that wave function evolves through time. It spreads out through space, for example. So it's pretty deeply baked in. So quantum field theory, sort of the modern version of it, as we think about it, doesn't really have an answer to the question of what is space. It just sort of like assumes it exists and starts from there. It's like the basic list of ingredients.

Would you say then that maybe quantum fields define space or do you think space could exist without quantum fields? Well, that's a great question. In our current theory, you can't have space without quantum fields like quantum fields fill the entire universe. There's no sense in which you could have space without them. That's just sort of according to the theory. But do they define space? I think they're deeply coupled to it. Yeah, absolutely.

So I think it's definitely part of the inherent nature of space in quantum field theory that you have these fields that live on top of it. But remember that quantum field theory can also have stuff in it that doesn't sort of come in at the very beginning, right? Like we can talk about the very basic ingredients of the universe, space and quantum fields, but we don't add to that things like, you know, the atom, right? The atom is not a required. element of the definition of the universe, it comes from that other stuff. So the atom, we think it

exists, but it's not like fundamental. And remember the goal of physics, as you say, is to come to one theory, one explanation, one most basic list of ingredients and the rules for combining them that then explains everything else. So we're constantly trying to throw stuff out on purpose so we can get like the minimal list of fundamental things that can then explain everything else as emergent. We want to explain ice cream and atoms and hurricanes in terms of the simpler, more basic elements. Do you guys rent the dumpster then, too, so you can throw out theories? I definitely want to throw space out on the physics dumpster. I would love to explain space in terms of something more basic and fundamental and say,

man, remember when we had space cramming in here, we had no space because we had so much space. But then if there's no space, then there's no space in the dumpster either, Daniel. Where would you throw it out? Oh, man, I'll get a bigger dumpster. All right. So then that's quantum mechanics, but then general relativity has a different view of space. Yeah, general relativity tells us that space is not something which is just like inherent and that you can assume. General relativity tells us that space is really different.

It's dynamical. It's not like the backdrop for everything. Instead, it's in this dance with matter, right? When you have matter and energy around, space bends and it curves. and it can do weird things like it can ripple, right, and it can expand. And this is things that we see, like we see ripples in space. We know that this general relativity picture is at least approximately correct. It might not be the fundamental theory of the universe, but it's really accurate.

It predicts these gravitational waves and we see them. It can accommodate at least the accelerated expansion of the universe in terms of a cosmological constant. We don't understand why that's there, what's happening, et cetera, but it can be accommodated in general relativity. So it's a very successful description of how matter and space interact and it suggests that space is not fundamental that it sort of sits at the same level

as matter and energy because the two sort of have this feedback loop between each other. It basically says that space is a thing, right? Like it's not static. It doesn't exist. It doesn't ignore matter. You know, like it responds to matter.

And, you know, it's not independent of matter. Exactly. And you can do these weird things that we never imagined that it could do, which means it might be able to do other weird things we also hadn't yet had the imagination to do anytime we're limited by our imagination I'm always skeptical that we've thought of everything I know the theorists are very smart even our science fiction authors are always pushing the boundaries of creativity when it comes to like you know intellectual

concepts but there's always the possibility that there's always something else out there we just haven't thought of that could be happening in our universe so space could have really weird properties that we never imagined. Imagine, for example, being a scientist that's a fish, swimming through water all the time and not realizing, you know, that space could end or that your water wasn't actually fundamental and they could do other weird things like boil and turn into a gas. You know, space like that could have other phases, other weird properties we just haven't observed yet. And so we assume are impossible. Because I guess once you can get space to bend or ripple or expand, then who knows what you can make it do. Who knows what you can make it do, exactly. And the solutions to

general relativity are so complicated and difficult and that it's not possible to conceive of all the possible configurations that are consistent with it. Those are the two views of space. One says that it's something that you can't touch or that you live on top of. And the other one says that it's something

that it's more of a thing. Like it's dynamic and you can manipulate it and it can change. So those are the two basic views about space, right? But it doesn't sort of explain what space is. It's just sort of like how you regard space. Yeah, but that's sort of what space is. space is how we treat it. Some people might say space is just like a mathematical construct in our

minds. You know, it's not actually something that's physical. For example, in quantum mechanics, we never deal with space itself directly, right? All we ever do is deal with the fields in space. We never, like, interact with space itself. And so it's sort of like just an abstraction. It's just like a way of thinking about organizing these fields. Whereas in general relativity, like space is the thing. It's the thing that's keeping us on the earth. It explains gravity, which is pretty important. So, you know, how we represent them in our theories goes a long way to telling you what we think they are. All right.

Well, I think that sets the space for a deeper discussion about space and whether or not Daniel can throw it in the dumpster or not. Please, please, please, please, please, please, please, please, please. Oh, man. I would be so offended if I was space right now. I would limit your space, Daniel. But let's get into that question. and also whether or not we will ever be able to know what the answer is. 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 6.33 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.

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mental health, and the ways we heal. Because I think hair is a complex language system, right, in terms of it can tell how old you are, your marital status, where you're from, you're a spiritual belief. But I think with social media, there's like a hyperfixation and observation of our hair, right? That this is sometimes the first thing someone sees when we make a post or a reel is how our hair is styled. We talk about the important role hairstylists play in our community, the pressure to always look put together, and how breaking up with perfection, can actually free us. Plus, if you're someone who gets anxious about flying, don't miss Session 418 with Dr. Angela Neil Barnett,

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The guest list is absolutely stacked for season two. And, you know, we're always going to keep you up to speed on all the news and happenings around the women's sports world as well. So make sure you listen to Good Game with Sarah Spain on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Presented by Capital One, founding partner of IHeart Women's Sports. I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about exploring

human potential. I was going to schools to try to teach kids these skills and I get eye rolling from teachers or I get students who would be like, it's easier to punch someone in the face. When you think about emotion regulation, like you're not going to choose an adaptive strategy which is more effortful to use unless you think there's a good outcome as a result of it if it's going to be beneficial to you. Because it's easy to say like go you go blank yourself, right? It's easy. It's easy to just drink the extra beer. It's easy to ignore to suppress seeing your colleague who's bothering you and just like walk the other way avoidance is easier ignoring is easier denial is easier drinking is easier yelling screaming is easy complex problem solving

meditating you know takes effort listen to the psychology podcast on the iheart radio app apple podcasts or wherever you get your podcasts All right, we're talking about space and whether or not we can just toss it out, Daniel. I feel like that's so unappreciative. How can you just throw the thing out that you grew up in? Well, you know, let's make a distinction here. We are, of course, searching to explain space to figure out whether it's the basic ingredient to the universe or whether it emerges from something else. But that's not to say the things that emerge are uninteresting or unimportant, right?

Like the entire field of biology is emergent in this. sense that you could in principle calculate it all from fundamental particles. But that's not like a smart way to do biology. Nobody would and nobody does do biology from the particle perspective. I just want to make sure people don't think that we're being negative about emergent phenomena. They're fascinating. They're amazing. They're incredible. We are emergent phenomena. It's just, you know, part of this question of getting down, drilling down to the deepest nature of reality is to ask what's fundamental and what's emergent. Not necessarily to judge them. You just want to head your bets and not offend your spouse who's a biologist.

I have the deepest of respects for my spouse and also for biology. Just not your furniture. Just not my furniture, absolutely. All right, so there are two perspectives about space. It seems like quantum mechanics doesn't say anything about space other than it's there and you can't mess with it. And general relativity says that it's something that you can sort of mess with and change and bend. And I guess the question is, are those two things incompatible or is there sort of a fun conflict about them. Couldn't you have quantum mechanics sit on top of general relativity?

Yeah, exactly. And people are working on exactly that, trying to unify general relativity and quantum mechanics in several different ways. And in doing so, they're giving us hints about answers to this question, about whether space is fundamental or not. Like when they put these two things together, they basically have to make a decision. Like, well, did we have space as the list of fundamental ingredients in our new theory of quantum gravity or not? And there's, a couple different approaches. One is sort of like make gravity a quantum theory thinking about it as like just another quantum force that exchanges particles, the gravitons in order to make gravity happen and sort of making quantum mechanics primary. And the other is to try to quantize gravity itself.

You know, either make the universe into little pixels or take the gravitational field and make it discrete. And so that would make a general relativity sort of at the primary foundational level of these new theories of quantum gravity and which direction you go sort of dictates the fate of the idea of space and whether it's fundamental or emergent. I guess maybe one difference is that like in general relativity,

if you have a speck of dust, it's technically bending the space around it. But in quantum mechanics, if you have like a proton or an electron, it's not really bending space around it, right? In quantum mechanics, we have no description of the curvature of space that works, right? So yeah, absolutely.

We don't have a quantum mechanical description. of gravity or the bending of space, so we can't describe how space is bent around of dust particle. We know that it is, though, right? We think that that's true. One of the difficulties is that we can't test these things very well because particles have very, very small amounts of gravity. Remember, gravity is so much weaker than all the other forces, like 10 to the 30 times weaker. So we can't really test these things because all the other forces dominate.

Two protons, for example, coming together, the Large Hadron Collider, feel almost no gravity. in comparison to the strong and the weak and the electromagnetic forces. So it's very hard to do an experiment at the particle level that tests gravity. I guess maybe to get back to our question then, what do these two theories say about the idea of having no space? Like, could you have no space in quantum mechanics or general relativity? Or is that impossible according to the theories? So there are now really fun ideas about how space might not be fundamental,

how you could have a universe without space in quantum mechanics. And I think these ideas are really cool because they make us think about quantum mechanics sort of at a more basic level. You know, we think about the wave function, for example. Wayfunction is like this basic element of quantum mechanics. It tells you what's going to happen to a particle.

Or, for example, where a particle might be. If you have a question about the outcome of your experiment, the wave function tells you this outcome is a certain probability and that outcome has another probability. And typically, we think about the wave function as distributed across space, like is the electron here or is the electron there? But in principle, it can be distributed across abstract states also, you know, like the electron spin or the outcome of your experiment or all sorts of other kinds of things.

And so it's not hard for us to sort of augment the current concept of space with these like abstract spaces. We call them Hilbert spaces in which the wave function lives. And it might be that those Hilbert spaces are the actual primary things. that we can sort of let go of these concepts of position and base the whole existence of the universe just on those sort of abstract spaces, the ones that are not physical, that don't represent actual locations,

that are not anywhere. I think what you're saying is that, like maybe space, according to the theory, is not like a physical thing or a physical space, but it's rather just sort of like a mathematical concept or set of relationships. Is that what you mean? Yeah, we know that it's a set of relationships.

As we said earlier, quantum mechanics, we never actually interact with space. All we do is we see sort of the propagation of information through fields as that information moves through space. But really, that information is moving through the field. And so you can think about it in terms of like pieces of space that are sort of woven together. So it's like the relationships between different elements of the field. And the space itself is really just like the relationship between those elements. So this one is far away from that one or this one is close to that one. So you don't have to have those bits of the field like hanging in an absolute actually

existing space. It might just be that they have those relationships in another way and woven together that gives the same effect as if they were actually in a space. I wonder if it's sort of like the concept of money, you know, like something is worth more or has a bigger price tag on it just because it doesn't mean that it has more energy to it or more matter to it or, you know, sits close. closer to you or you can do more things with it, it just so happens that this thing has a label with a big price on it and that one has a label with a lower price on it. Is that kind of what you

mean? Like maybe space is really just like the economy of the universe. Yeah, exactly. And you can also think about it in terms of like your networks. Think about your relationships with your family. Who are you close to? We even use that word close, right? Even if you're physically far away from somebody else, you have a network of people that you interact with who know you very, very well and then people who are distant and then people who are basically super impossibly far away. Well, it might be that that's sort of like the fundamental definition of who you are and what your space is rather than like where you actually are sitting in your bedroom or in Los Angeles or in Germany or wherever.

Maybe space is just an emotional space. You know what I mean? Like space is really just the emotional currency of your relationships. Yeah. And these are just analogies we're using to try to get your mind away from this primacy of space that we've been assuming in thinking about the universe as built out of things that don't hang in space but still have relationships with each other. And then those relationships are what space emerges from. And we can actually do this not just by doing analogies to social media,

but actually mathematically. And people have taken the wave function of the universe, for example. Think about like, what is a quantum mechanical description of the whole universe? Can you describe everything in the universe? And you don't have to necessarily put them in a location. You know, just say there's a probability for this particle and probability for that particle and then link them together and say, well, this one is entangled with that one. This concept of quantum entanglement of particles having like their fates connected to each other because they have a common past. This entanglement might provide that weave. It might provide the connection between like the bits of the universe that when you weave them together, some things are more entangled than others.

And so they seem closer together and other things are less entangled. And so they seem more distant. It might be that this quantum entanglement are those same relationships that connect these bits of the wave function that make it seem as if it is hanging in some space. And this sort of set of relationships or currency or valuations, that's what you call these Hilbert spaces. Or is that different? The Hilbert space is the set of possible wave functions that you can have. And then the relationships between the different wave functions that are disconnected, those are the entanglements, those come together to make this sort of like grand weave that we call space. And if this is true, it doesn't mean that space is not like real. It just means that it

comes from something else, you know, that it bubbles up from something more primary. Just like air is real, even if it's not fundamental to the universe. You can still breathe it. It's still very nice on a nice, fresh, windy day. In Los Angeles, come on. Never happens. But I guess maybe a question is, what's the difference? You know, like the word Hilbert space still has the word space in it. So, like, what would be the difference between a Hilbert space or these abstract connection space and maybe a more regular definition of space? Well, our four-dimensional space has certain properties, you know, information transforms through it in a certain way. It follows the speed of light. There are four dimensions, including time. An abstract Hilbert space is much broader

or more general. Like, it can be infinite dimensional. You can have complex values, you know, imaginary numbers, all sorts of things. So this was sort of like a subset of all the possible Hilbert spaces. It's like it turns out that the relationship between all these quantum wave functions can be described in this sort of simpler subspace, this four-dimensional subspace in which all that information can be mapped onto. The whole hill of beans. The whole hill of beans.

But it also means other interesting things. If this is true, it means that, for example, you could have different spaces inside this like larger Hilbert space. You could have like our chunk of space, which is all woven together. And you can have another one somewhere else was also emerged and is totally disconnected from ours. And you could have maybe parts of it without these relationships, right? Like you could have a whole bunch of people with no friends on Facebook. Exactly. Or even parts of the world where there is no Facebook. What? Hard to imagine, right? But it might be true. And so if this picture is accurate, then the answer is absolutely you can have the universe with

space. It's not necessarily clear that you need space to have the universe and you can have parts of the universe with space and parts of the universe without space and other parts of the universe that have different kinds of spaces. And you might be thinking, hold on, he's saying the word parts. What does he mean? If there's no space, what parts is he talking about? And again, you know, these parts don't necessarily have like a spatial relationship. You can't say this one is here and that one is there in the sense of like, where is your family? You know, you guys might be physically somewhere, but the actual relationships between you, those connections that tie you together. Like, where is that? It isn't really anywhere. It's just sort of in your emotional space.

Yes, if you can't find your family, that's a whole different problem there. And a whole different type of podcast. There's a whole genre for that. But that's sort of the quantum mechanical view. If you say quantum mechanics is primary and the wave function for the universe is the most basic thing, then can you build up a universe without space? Is space necessary? That's the quantum mechanical path. Right. And it sounds like the answer is sort of, yes. Like if quantum mechanics is all there is, then it might be possible to see how you could not have space. Absolutely. And there's some really fun recent ideas, things called like condensate cosmology, where space condenses in these like steam-like droplets from these weird fun spin networks that are more fundamental.

But we're going to do a whole podcast about that sometime in the future. Cool. All right. Well, then now what does general relativity say about not having any space? Is that possible according to that view? General relativity really has no problem with space not existing because in our general relativistic understanding of the universe, think about what happens in the history, right? We have the current universe. We look back in time and we see the universe getting more and more compact. And we propagate

back and further and further and it approaches this special moment, this singularity, this time before which space does not exist. And, you know, there are various ideas for how to tackle that. what that means and if it's a breakdown of the theory and if it needs to be replaced by something else. But in our current, albeit imperfect, non-quant mechanical general relativity, there is this concept that there is no space before the Big Bang. There's no space or it was just super compressed? It's super compressed in the very first moments of the universe. But before that, before the singularity itself, right, this moment of infinite density that space did not exist, that it doesn't make sense to ask where is something or when is something because the whole notion

of space and time came into existence then like there is no space and time before then and this is not something that's very easy to think about because we don't think about space and definitely not time beginning right but a whole other podcast episode about whether you need time and if time is an emergent phenomena it's a whole even more difficult question to grapple with because you have to think about like could there be a time before which there was no time? But putting that aside for the time being, at least, it's hard still to think about a universe existing without space. But if you can still have time, right,

if you say time exists, but maybe space is not fundamental, it might make sense to you to think about like space itself is this weird thing we talked about, this weird goo that does stuff. And it can bubble and it can expand. It's being created right now. If it's being created, then, you know, maybe there was a moment before it was created.

Or, you know, you can think, about what is there when it's not being created, right? There's no space if there's no space being created. Exactly. And it might be that you could have a universe before space is created. It might be that time existed before the Big Bang, but just not space. And there's some like conditions required for space to be created for it to expand. Like you might think it's a weird concept for space to be created. But remember that it's happening right now. You know, the expansion of the universe is not the motion of stuff through the universe. It's the creation of new space between us and other galaxies, between you and your couch, between everything and everything else. So it's happening right now.

And it's just that we have only recently realized that space is this bizarre fabric that can do these things like be created spontaneously, everywhere simultaneously, that we've come to ask these questions. So we just really don't have a notion and understanding of what space is, even in general relativity. But it certainly is possible that it can be created in So, yeah, you can imagine there being a pre-Big Bang moment when there was a universe but just no space. All right. Well, it sounds like both theories are pretty cool with the idea of not having space. They can both take it or leave it.

Yeah, absolutely. Variations of quantum mechanics can accommodate space not being fundamental. Even though our current quantum field theory sort of assumes that it's there, you can build these extensions that sort of make it possible for space to be emergent for it to bubble up rather than just being an assumed. property of the universe. All right. So space, take it or leave it? Leave it. All right. Let's get into how we would ever know if space is or not disposable or dispensable. But speaking of time, it's time to take another quick break. 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 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. I'm Dr. Joy Harden Bradford, and in session 421 of therapy for black girls, I sit down with Dr. Ophia and Billy Shaka to explore how our hair connects to our identity, mental health, and the ways we heal. Because I think hair is a complex language system, right, in terms of it can tell how old you are, your marital status, where you're from, you're a spiritual belief. But I think with social media, there's like a hyperfixation and observation of our hair, right? That this is sometimes the first thing someone sees when we make a post or a reel is how our hair is styled.

We talk about the important role hairstylists play in our community, the pressure to always look put together, and how breaking up with perfection can actually free us. Plus, if you're someone who gets anxious about flying, don't miss session 418 with Dr. Angela Neil Barnett, where we dive into managing flight anxiety. Listen to therapy for black girls on the IHeart Radio app,

Apple Podcasts, or wherever you get your podcast. Get fired up, y'all. Season two of Good Game with Sarah Spain is underway. We just welcomed one of my favorite people and an incomparable soccer icon, Megan Rapino, to the show, and we had a blast. We talked about her recent 40th birthday celebrations, co-hosting a podcast with her fiancé Sue Bird, watching former teammates retire and more.

Never a dull moment with Pino. Take a listen. What do you miss the most about being a pro athlete? The final. The final. And the locker room. I really, really, like, you just can't replicate, you can't get back. showing up to locker room every morning just to shi-talk. We've got more incredible guests like the legendary Candace Parker

and college superstar AZ Fudd. I mean, seriously, y'all. The guest list is absolutely stacked for season two. And, you know, we're always going to keep you up to speed on all the news and happenings around the women's sports world as well. So make sure you listen to Good Game with Sarah Spain on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

Presented by Capital One, founding partner of IHeart Women's Sports. I'm Dr. Scott Barry Kaufman, host of the psychology podcast. Here's a clip from an upcoming conversation about exploring human potential. I was going to schools to try to teach kids these skills, and I get eye rolling from teachers or I get students who would be like, it's easier to punch someone in the face. When you think about emotion regulation, like you're not going to choose an adapted strategy which is more effortful to use unless you think there's a good outcome as a result of it, if it's going to be beneficial to you.

Because it's easy to say, like, go blank yourself, right? It's easy. It's easy to just drink the extra beer. It's easy to ignore, to suppress, seeing a colleague who's bothering you and just, like, walk the other way. Avoidance is easier. Ignoring is easier. Denials is easier. Drinking is easier.

Yelling, screaming is easy. Complex problem solving. Meditating. You know, takes effort. Listen to the psychology podcast on the IHeartRadio app, Apple Podcasts, or wherever you get your podcast. All right, Daniel, it sounds like physicists could take space or leave it. It sounds like both theories about the universe would be okay. They wouldn't break down if you suddenly got rid of space.

Yeah. And I think if you took a survey of physicists right now and you asked them if space was fundamental or emergent, if it came from something else more fundamental, I bet you'd get like 90% saying that it's emergent, that it's not fundamental, that it comes up from something else, which means that you could have a universe without it or portions of the universe without it. I think that's the current mainstream thinking. And as we all know, the universe works democratically. So whatever the majority says must be true. No, we're definitely capable of being misled and having the wrong idea. But I think it's sort of exciting that it's widespread.

It means that lots of people are working on it. People are developing new ways of thinking about these really, really basic questions. And people out there also should be excited. It means that, like, we're just in the beginning of asking questions about the universe and tackling them. If you are excited about questions like, you know, what is the universe and where did it come from and what's it really made out of? Remember that there are huge tracts of questions that are just really being explored

by physicists now. And so there's plenty of room to make, like, really fundamental Einstein-level discoveries about the nature of the universe. Right. I think what you're saying is that there's an electoral college in the universe, and who knows? Who knows what the rules are for that? That's right. Fortunately, physics is easier to calculate than the electoral college. All right. I guess maybe now the big question is, how would we know or not whether space is fundamental or whether or not it's like an add-on or like an optional preference in the universe you could live in? Is there a way for us to test it because we live in this space that we're trying to test? Is it possible to, I don't know, create an experiment where you have no space?

Yeah, there's really two steps to that. First is we've got to make more theoretical progress and then we got to do some experiments. So on the theoretical side, what we really need is a unification of quantum mechanics and general relativity. We need a theory of quantum gravity that tells us how the universe works so that we can think about like what is. space. And this theory, if it all hangs together and does everything it has to do, meaning it can describe everything that gravity can do and it can describe all the tiny fundamental particles and it brings those together in a way that makes sense that, you know, they don't disagree with each other like the current quantum mechanics and general relativity

do. Then we can ask questions of that theory. So first we've got to make progress theoretically. We need like an actual theory that totally works. Before the break, we talked about a few possibilities, like directions people are going. These are like half-formed ideas. People are like building scaffolding. You can see the outlines of a structure. People are trying to make work. But nobody has an actual functioning theory of quantum gravity where we can ask these kind of questions and get answers. I guess you need some sort of theory first, right? Like you can't just take out space and measure it and not measured. How do you measure not space? Well, we have done a lot of really cool experiments about space, right? Like seeing gravitational waves is incredible.

tells us that space really is sort of fungible and dynamic and measuring the expansion of the universe. That's also kind of an experiment that tells us what's going on with space. And a lot of times, experiment informs us. Remember that we didn't expect the universe to be expanding in an accelerating manner until we saw it. And it totally shocked us and surprised us. So sometimes experiments can inform us. I think in this case, we really need theory to tell us like how we can do experiments to answer this question because currently, the only experiments I can think of are ones that are like at the center of a black hole or requires super colliders the size of a solar system. Not things we can get done tomorrow.

No, exactly. Because for example, general relativity and quantum mechanics, they disagree about what's at the center of a black hole. You know, general relativity says, oh, there's a singularity there. But quantum mechanics says you can't have a singularity because that's too much information isolated in one little spot. and it violates the Heisenberg uncertainty principle. And so if you could see what was going on inside the black hole,

you could get great clues as to how to build your theory of quantum gravity. Or if you could somehow do tests of particles feeling gravitational forces by building a super huge collider and smashing those particles together at crazy high energies, enough energy where gravity is as powerful as the other forces, then maybe you could get a clue as to how to build your theory of quantum gravity. But we can't do either of those experiments today. And so I think what we need is some insight from the theory to tell us, well, look, here's how the universe is put together. Here's our theory of what space is.

And this theory gives us a clue about how to look for evidence that the theory is correct. You know, there's some like wrinkles and experiment we can predict the outcome of that can tell you whether or not this is right. It's like if only you could break the loss of physics so that you can figure out the loss of physics. Exactly. And there's maybe one more hint of something that we can do, which is that. that we can look for more evidence of this creation of space. We can look for evidence of those first moments just after the Big Bang and try to find some gravitational radiation from the Big Bang itself.

But what do you mean? Like a shockwave or like actual radiation or like gravitons? Yes, exactly. All of those things. You know that we have microwave background radiation from about 400,000 years after the Big Bang when this hot plasma cooled and became transparent. We see those photons. And people often say that that radiation is like from the Big Bang itself.

It's not quite. It's from, you know, 400,000 years after the Big Bang when the universe became transparent and that light is now still propagating around. We'd love to see earlier. We'd love to look further back to the actual creation of the universe, whatever happened there. And so it might be possible to do that by looking for gravitational waves that were created in those very first moments when the universe was expanding so rapidly.

we think that gravitational waves were made. So there's another kind of radiation called the cosmic gravitational background that might have clues as to what the nature of space is and whether it was created in those first moments if we could see it. Like the echoes of the creation of space. Yes, exactly. And so we have theories about what that might look like under various configurations. And you might remember several years ago,

people did an experiment where they thought they measured those waves. It was called Bicep 2. But then it turns out that they were mistaken. And they were actually just measuring dust between galaxies. So that was disappointing, but it might still be possible with a better round of experiments, more precision and control of that dust to see the actual radiation from the early universe and get a glimmer as to whether space was created or whether it had always been there. And there's another possibility, right, as to whether or not we can confirm this existence or dependency of space.

And that is that maybe in the future there might not be any space, right? Yeah, exactly. Are we going to run out of space or are we just going to, you know, get evicted from our house? No, you're absolutely right. And some of these theories of loop quantum gravity, for example, they predict that the universe's expansion will stop and it will turn around and it will compactify so that space is like being destroyed instead of being created and we'll have like a reverse big bang, this big crunch. And it's not clear what would happen after that. Would we get another big bang? Would we just have no space for a while?

Does time even exist anymore? We don't know. So, yeah, stick around another few trillion years and the question might just answer itself. Yeah, things might get a little bit more crowded. Or spacey. And cluttered. All right, well, it sounds like it is possible for the universe to not have any space, but we may not find out anytime soon unless we observe something incredible

or we make a breakthrough in one of these theories that let us look for, you know, kinks that we can use as evidence that space cannot exist. Yes, and I think that there will be theoretical progress. People are working really hard on this stuff. Black hole information paradox is giving us some clues. So there's a lot of really smart people working really hard in these questions. And I think in the next five or ten years, we'll see some really clever, fascinating, mind-blowing theories coming out to explain our bunkers universe. They just need a little of space, you know, no pressure.

All right. Well, we hope you enjoyed that discussion. Thanks for joining us. See you next time. Thanks for listening and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio. For more podcasts from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys.

Then, everything changed. 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 my boyfriend's professor is way too friendly and now i'm seriously suspicious wait a minute sam maybe her boyfriend's just looking for extra credit well dakota luckily it's back to school week on the okay story time podcast so we'll find out soon this person writes my boyfriend's 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 oh hold up it's Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast and the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Get fired up, y'all. Season two of Good Game with Sarah Spain is underway.

We just welcomed one of my favorite people, an incomparable soccer icon, Megan Rapino, to the show. And we had a blast. Take a listen. Sue and I were like riding the lime bikes the other day. And we're like, we're like, we're like, we're like, people, We got more incredible guests like Megan in store, plus news of the day and more. So make sure you listen to Good Game with Sarah Spain on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

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