Can the Universe exist without space?

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Speaker 1: Hey, Jorge, are you a hoarder or do you like to throw things away? We keep everything, we have, every drawing, my kids ever made. Man, not me. I value space more than stuff. I love to throw things away. Wow, what does your family give you for your birthday? Then? Empty space? Actually, my wife rent a dumpster and says I can throw out anything I want. It'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 more handmade cartoonists 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 university production of I Heart Radio, in which we explore all the stuff in space, empty space, not so empty space, space builled with really crazy bonk, or 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 get 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 and to your children leaving the house then, because that's just more space, is more space. I'm not looking for 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 want you. They're like, why did you throw away my comic book collection that's worth three million dollars? 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, what it means, because it's kind of a topic that businesses don't have a super clear idea about. That's right. It's one of these really fun quite 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 ten thousand 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? Could you take it apart? Do you really need it? Yeah? In fact, so the universe, it 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 our 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, our 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 space 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 spaces 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. That'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 are 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 boggling lee 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. You know, 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 if even if you're Superman or Superwoman and you're traveling, you can 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 bring it up with his heat visioned 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 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, and it sort of mirrors the way I treat furniture. You know, I look around my house and I asked 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, m, 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 a 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 I almost ruin their marriage because they ended up shouting 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'm gonna go to your your couple's 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 universe. 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 got to sort of be willing to give up something you thought was fundamental, something you assumed was inherent, and ask your question whether it can come from something else. All right, Well, as usual, we were wondering how many people out there have thought about this spacious question, whether or not we need space. So Daniel went out there into the well to 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, why, Well, 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 can probably have a universe. It's just time and maybe not space. I'm gonna say yes. Well, my understanding is that, yeah, I guess you can. Um. I mean, was this space when the Big Bang occurred in the moments after that, or was it all dense metal with zero space? But my understanding is that if you have a different universe that 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 antimatter, I think is actually pretty unique. Um there, and I would I think they're a little universe blips all over where universe pops into existence and annihilates and no spaces created. I guess you can have universe with out 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 was no space. So if you can't that just 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 spaces and where it comes from and all 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 two questions at Daniel and Jorge dot com. There's a lot of reference here and the answers to the Big Bang to write that's something I hadn't thought about before. Was their 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 like quantum mechanics or whether you're thinking about it from the point of view of general relativity. And remember that these are the two pillars of thinking in modern physics, too 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 were 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 gonna build a 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 gonna 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 field here and over there at a different location in space, it has a different value. And for example, the shrouding your 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 basical list of ingredients. Would you say then that maybe quantum fields defined 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 filled 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 into 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 ad and 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 want 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 criming in here and 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 the 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, etcetera, but it can be accommodated in general relativity. So it's very successful description of how matter and space interact. And it suggests that space is not fundamental, that it sort of states at the same level as matter our energy, because the too sort of have this feedback loop between each other. 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, and 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 know, 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 that 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. You know, space is how we treat it. Some people might say space is just like a mathematical construct in our minds. You know, that'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 spaces 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 through it in the dumpster or not. Please please please, please, please please please. 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. 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 know 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 of 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 the sense that you could, in principle, calculated all from fundamental particles. But that's not like a smart way to do biology. Nobody would anybody 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 add your bets and not offend your spouse's biologist. I have the deepest of respects for my spouse and also for biology, which is 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 a sort of a fundamental conflict about them? Like 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, do we have spaces the list of fundamental ingredients in our new theory of quantum gravity or not. And there's a couple of 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 a discreet 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 has 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. Member gravity so much weaker than all the other forces, like ten to the thirty times weaker. So we can't really test these things because all the other forces dominate. Two protons, for example, coming together, the large Hage and 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 then 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 plantum 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. Wave function 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 has 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 thing that we can sort of let go of these concepts of position and based the whole existence of the universe just on those sort of abstract spaces than 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 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, in 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 on it just because it doesn't mean that it has more energy to it or more matter to it, or you know, sits closer to you, or you can do more things with it. It's just so happens that this thing has a labeled with a big price on it, and that that one has a labeled with a lower price on it. Is that kind of what you mean, Like, maybe space is really just like the economy of the 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 well, and then people who are distant, and then people who are basically super impossibly far away. Well, it might be that that sort of like the fundamental definition of who you are and what your spaces 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 and 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 way 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 probably for that particle, and then link them together and say, well, this one is entangled 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 and more general, like it can be infinite dimensional. You can have complex values, you know, imaginary numbers, all sorts of things. So this is 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. It's 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 can have like our chunk of space which is all woven together, and you could 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. 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 without space. It's not necessarily clear that you need space to have the universe. And you can have parts of the universe with space, parts of the universe without space, and other parts of the universe you know 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 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 the whole genre for that. But that's sort of the quantum mechanical view. If you say quantum mechanics is primary and the way function for the universe is the most basic thing, then can you build up a universe without spaces? 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 gonna do a whole podcast about that sometime in the future. Well all right, well then, and 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 further and 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 and 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 quantum 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 do 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 and there's there's no space, if there's no space being created exactly, and it might be that you can have a universe before space is created. Might be the 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 quests, and so we just really don't have a notion and understanding of what space is even in general relativity. But it's certainly is possible that it can be created. And 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. Alright, 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, 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 ask them if space was fundamental or emergent, if it came from something else more fundamental, I bet you get like saying that it's an emergent, that it's not fundamental, that it's 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 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 they 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 This is just 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 gotta 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 like does everything it has to do, meaning it can describe everything that gravity can do, and they 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 of 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 measure it. 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. It 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 can 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 like gravity is as powerful as the other forces, that 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 inside from the theory to tell us, well, look, here's how the universe is put together. Here's our theory of what spaces, 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, some experiment we can predict the outcome of that can tell you whether or not this is right. It's like if only you can break the loss of physics so that you could figure out the laws of exactly. And there's maybe one more hint of something that we can do, which is 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 trying to find some gravitational radiation from the Big Bang itself. But what do you mean, like a shock wave, or like actual radiation, or like gravitons. Yes, exactly all of those things. You know that we have microwave background radiation from about four hundred thousand 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 as from you know, four hundred thousand 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 have to look further back to the actual creation of the universe, whatever happened there, And so it might be Passe will 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 spaces 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 didn't experiment where they thought they measured those waves. It was called BICEP two. 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 glimmour as to whether space was created or whether it had always been there. And there's another possibility right us to whether or not we can confirm this existence or the tendency of space, and that is that maybe in the future there might not be any space. Right exactly, are we going to run out of space or are we just gonna, you know, get a victim 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? But 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 were space 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 any time, you know, unless we observe something incredible or we make a breakthrough in one of these theories that let us look or you know, kinks that we can use this 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 on 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 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 I Heart Radio or more podcast from my heart Radio visit the I heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.