How Big is the Universe?

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Speaker 1: Inside space? Is there a place where the matter ends and it's just empty space? And then path that space? Is there something else that's not space? Can space have an edge? Right? And so that to me is the is this concept of the universe, all the matter in all the space, things beyond that space, if there is anything there I would consider not part of our universe. Oh I see, So we could like there could be through stuff and maybe at some point we run out of stuff and there, but there're still there could still be space, There could still be space. Hi. I'm Daniel and I'm Horhan, and we're here to explain the universe. Today we're going to talk about the biggest question in the universe, the biggest question you could even possibly imagine. How big is the universe? Like really, how big is it? Like? Does it go on forever? Is it just a little bit bigger than we can see? Does it wrap around on itself? Is it some other crazy thing. That's what we're going to try to tackle today. We went out in the street and we asked people what they thought about this the biggest of questions. Oh man, it's pretty big, Like I'm pretty sure it's like unmeasurable because like we don't really know much about it, so I'm pretty I wanna say, like pretty big, like it's really unmeasurable. Tend to do something article do you want, like a number or whatever you think is appropriate. Um. I remember reading someone where that's like it's always growing, so it's like infinite, right, So most people seem to feel like, wow, the universe is pretty big. Some people thought it was like infinite, and some people thought just just really big. Nobody thought it was small. Nobody's like I can see the end of it. It's just about it's only my town. It's only as far as I can see. That's right, And ask really, that's really interesting because I bet like if you ask prehistoric man how big is the universe, they would just like say, like, look around you, this is what there is, and they couldn't even really imagine. So let's break it down. There's all the stuff right as part of a right you know, this matter and energy, all that stuff feel and touch and see m But I think there's one other component which I think it a little less usual for people to think about, and that's the space. Space. I would think of the universe as all the stuff and all the space that it's in. Okay, and then like the stuff we can actually move around in, Yes, the place we can move around in the space we have at some point that space um ends. Yeah, the space could end right now. Somebody out there listening, you smart, good looking listener, you might be thinking, what how good space possibly end? He's talking about space like it's a thing, like it's water and the fish could run into the end of it or something. But briefly, we should just remind people that space is not just emptiness. It's not just a backdrop. It's not just the nothing in which stuff happens. It's stuff. It has properties that can bend and expand and ripple and do all sorts of weird crazy stuff. And so we know that it's a thing. It's a dynamic, physical thing that could do stuff. So we have to consider the possibility that it ends like That's part of the question how big is the universe? Is how much space is there? And can it end? Right? It's like for fish and we're asking how big is the ocean? Yeah, yeah, okay, exactly how big is the I wonder do you think fish? Wonder about how big is the ocean? I think fish wonder about um not getting eaten by other fish, right, and fish fish might also wonder like are there other oceans? Right? That's the all diverse for fishes. But in our universe you're saying, uh, space might have a limit to it, like there might be an end to it. Um, Yeah, but is it like a wall or is it like a what does it mean for it to be at the edge of space? Well, there could be an edge to space, and um to think about what that means, we have to think about what space is a little bit more like to think about whether space can curve or if space is flat right right, And this kind of stuff is really hard to think about in three dimensions, like what does it mean for space x y z space right x y z being one to three dimensions, the curve really hard to think about it because it's hard for us to think about that about space curving in some higher dimensions. So usually it's best if we think about it in two dimensions so we can think about it it's curving in that third dimension. So imagine that we are two dimensional scientists, were like living on a sheet of paper where we can only move in two dimensions, like x and y and then we can ask those two dimensional scientists can ask is our space curved? Is our paper universe curved? And and that changes the answer, Like say you discover that it is curved and it has a positive curvature. Positive curvature would be like on the surface of a sphere or a planet. Right, if it has positive curvature, that has consequences for its shape, because if it's positively curved, it can't go on forever, right, like the Earth. You're standing on the surface of the Earth, and you know the Earth is curved, and that means that Earth can't be infinitely big, right right, right, So you're saying, at the edge of the universe, maybe the space space is curved, and or maybe it's a possibility you have to consider that maybe space is curved everywhere. If the universe had curved space and it was positively curved, that would mean that it could be um sort of looped on itself very naturally, the same way the surface of a planet is, and you could travel around it through space and not really get to the edge, right, Like where is the edge of the Earth? Well, the Earth, the surface of the Earth, the two dimensional surface doesn't have it like people in historic times. Maybe they saw the earth around them and they thought, oh man, this is pretty big. It probably goes on forever, but they didn't know that actually land curved. That's right, And and it turns out that we're actually kind of on this sphere. And if you keep going in one direction and you kind of loop back around, that's right. Yeah. And it's not like you get to the edge and you get magically transported back to where you started or something. There's no you know, shortcut or magic there on the surface of the earth. You to keep walking, you come back to where you started, connected back onto itself exactly. That's the key. So that's a big curvature space like space that we're in. Could kind of like if you keep going in one direction and a spaceship, you'll come back around to the same spot exactly. And the way you said it was perfect. It's the connection. So we like to talk about space by using this analogy of living in two dimensions and thinking about it being curved in a third dimension. Now pop that up to three dimensions, right, because we know our space is at least three dimensions, and popping an aspirin because it's now I'm getting it. Did we work on getting addibility to support this podcast because we're sending them a lot of customers. My god, that could be a great um sponsor. That's right, um, So pop that up into your three dimensional space, right, and then you can ask, well, what does it mean for three dimensional space to be curved? Well, it's not that we imagine that it's curved in some other fourth dimension. It's not that it's hanging in four dimensional space and has a curvature in it. It's how space is connected. We call it intrinsic curvature because it reflects how one part of space is connected to another part of space. So without hanging in four dimensions, you can be connected in a way that space is curved and you look back on yourself without ever really noticing. So when we talk about the size of the universe, we mean that it has made some kind of edge, but made that edge is not like how we think of a nedge, is like a stub or a wall. Maybe it's just kind of looped around, and so the size of it is kind of like this blob of space, right, yeah, exactly. And the possible answers for the size of the universe depend on how it's curved. Right, If it's positively curved, then it can only really be like a big sphere, which means it's finite. Right if it would negative? What if it's not right? Um, if it's flat. If space is flat like it's um, doesn't curve intrinsically, then it could potentially go on forever. If space is negatively curved, that's like the shape of a of a saddle, the negative curvature, then it could have all sorts of really weird shapes, but it could still be infinite. Okay, so the options are infinite or not infinite. That pretty much categorizes the options for everything. How big is your house? Where? Hey? Is it infinite or not infinite? I want to see that option actually on Zillo from Yeah, I would love to have infinite square feeda house, would you really? Because then all and you have to look forever for your kids shoes? Right, where'd you put them? I put them in room numbers somewhere between here and infinity. Yeah. So let's talk about the possibilities of what could be beyond the observable universe. I mean, we talked a little bit about before about maybe it's infinite, Maybe it's not infinite. Um. Do we really have no idea whether the actual universe is just a little bit bigger than the observable universe, much bigger than the observable universe, or it could be infinite. We really have sort of no indication of which possibility it is. We have a few clues, they're kind of indirect, and I want to talk about that some more, but first let's take a quick break. One clue comes from the curvature of space. We talked earlier about how the curvature space affects the how the size of the universe could be. And if the space is curved positively or negative or flat, that limits the options, right, So that's something we can measure. We can measure it here. We can look around us and measure how curved is space in our universe? Um. And that might be a bit of a puzzler, right, like, how does that mean? How could space be curved? How could you possibly measure it? Um? And to think about that, it's best to go back to the two dimensional example. You're living on the surface of a planet. For example, if you were a two dimensional scientist living on the surface of a planet or or some surface and you want to know is this surface curved. What you could do is make a triangle, because triangles are very sensitive to curvature. For example, you draw triangle on a sheet of paper, you add up the angles, then you get a degrees every triangle, every flat surface, no matter what. Beautiful results basic geometry. That's right. Yeah, Now imagine that triangle sitting on the surface of a tennis ball. You can draw triangle on the surface of a tennis ball that has three right angles on it, because triangles behave differently are a curved surface, Yeah, it could imagine that it could be ninety degrees, meaning that it adds up to two seventy degrees. Yeah, exactly. So let's take a break, so everyone can go get a tennis ball and sharp. You try this at home, and we'll be right back when you have your tennis ball. Alright, assuming you're holding a tennis ball and you've annoyed your partner or your spouse or your child by drawing triangles on it, you can see the triangles behave differently on a curved surface. It looks kind of bloated. Yeah, yeah, it looks distorted. And so if you just make a triangle and add up the angles you can see whether or not the space you're in is curved or flat? Is that kind of crud to think about the curvature space. It's kind of like a distortion of space. Yes, Yes, it's a distortion and how the pieces of space are connected to each other, which changes how you move through space. Changes like how you can get from one spot in space to another spot in space. Yeah, like I think I'm going straight, but I'm actually kind of being distorted one way or the other. Yeah, it changes what straight means. Okay, So so then the curvature might give some clues as to whether, like we wrap around in ourselves or whether, um we don't. I mean, that's all it can tell us, right, it's whether we're on a sphere or we're not on a sphere. Well, there's one other option, which is that we're on a sort of a saddle. Space is negatively curved. Imagine you have a sheet of paper that's forms sort of like a bowl or the opposite of a sphere, and you're in the middle of that bowl. You can draw a triangle in that and it will have angles of less than eight degrees. Can really measure the chunky had distortion. Yeah, yeah, not quite a bowl because that's just the inside of a sphere, but something that has a sort of saddle shape. Um. And so you draw triangle, you make a measurement, and that tells you. And so we've done that. We've made those triangles and we've measured them to very high precision in three dimensional space. Like any answers on this the the sheet of the universe, Yes, exactly. We've done it in two different ways, at least that I can think of at the top of my head. One is that we looked at giant cosmic triangles in space. You know, we've looked at the cosmic microwave background radiation, this leftover photons from the birth of the universe, and drawn these triangles and measured the angles and and they come out to degrees. It seems like space is flat. Flat were flat? Yeah, And that's a puzzle. It's really interesting. There a lot of people wonder like, why is space flat? We've measured to be flat to within you know, like point one percent, and for a long time that was a mystery. But some people don't think that space could be curved, like what would why would what would that be weird. Yeah, and well that that leads perfectly into the second way we've measured the curvature of space, which is you might ask what causes space to curve? Right, why would you expect space to be curved or flat or negatively curved. And the answer is that the thing that curves space is matter. Right. You put stuff, matter and energy into space, and it curves it. That's what general relativity tells us that that gravity is in fact the curvature of space. So we know that space gets curved. Like you put the Sun in the center of the Solar System, it curves space so that the Earth very naturally moves in a circle around it. Right, that's an impact of the curvature of space. There, nobody's turning the Earth. Nobody's like driving the Earth around the Sun, right, but constantly turning. It's moving in what it considers to be a straight line. But space is curved, so it's it's just moving constantly in an orbit, not like a force pulling the Earth towards the Sun. But gravity is more like it's distorting the space around the Sun so that the Earth just can naturally goes around it. That's right, that's that's a great way to think about it. And so matter distorts space and causes curvature of space, and so you can ask is there enough matter and energy in the universe to curve space or to make it negatively curved or positively curved? Right? And um, if space is totally empty, if there's no matter in it at all, and then it's negatively curved, you have to add energy and matter to make space zero have zero curvature. And so we've measured this. We've measured the total energy naturally wants to be negatively curved, but if you add stuff to it, then it gets a straighter. That's right, Um, Space with no energy density in it at all would have negative curvature, and so you add stuff to it. In fact, if you add I think it's six hydrogen atoms worth of energy per square meter, then space has zero curvature between five and six. And so we've measured the amount of stuff that's in the universe and it all adds up to be just about the right number to make space be not curved, which is seems like a weird coincidence, right, It seems like an important clue, like why does all the stuff in the univer has happened to add up to the number that's just right to make space not be curved. Would that let's take a break. We'll be back in just a short minute. Space seems to be flat, at least space in our part of the universe seems to be flat. It could be that other parts of the universe it's curved, right, But in our part of the universe it seems to be flat. And we think that's sort of that it maybe extends out to as far as we can see. Yeah, it seems to follow the same rules, and so you're absolutely right. That rules out, you know, the potato universe that we're living on the surface of its huge cosmic potato or bubble universe, whatever, and rules out the saddle universe. With the universe is negative curvature. Seems like space is flat, which is going on direction forever? Um, I'll just keep going. Not necessarily right, we know space is flat. That doesn't necessarily mean that it's infinite. It's a natural idea, right. If space is flat, then it doesn't curve on itself. And so it seems like you could be able to go on forever, but earlier that you can't just have a wall. You can't just have a wall. But since we don't know what space is, we don't really know how it works. We don't really know how it's connected. It's still possible that it could be flat but connected in a weird way. So where one edge is connected to the other edge, like you go flat you're moving through flat space, but it just loops on back on itself. It's like it is connected in that way like an asteroids game, you know, you go at the edge of the screen, you appear on the other side, but like a teleport to the other side. Yeah, yeah, and not necessarily teleport, Like that could just be the way space is connected. So that's weird that that wouldn't feel u you mean, like an asteroid games are like pac Man where you walk off one side of the screen and suddenly appear on the other side like that. It's possibility. Physicies are like, hey, that could be true. That certainly could be true, yes, absolutely, But the other possibility is also true, which is maybe it just goes on forever. Right. It could be that the that space goes on forever um. And that's also kind of weird because that's infinite space, right, yeah, yeah, and it could be the space is flat, but it just ends because we can't see past the observable universe, and so we have intuition and ideas and speculation and we think, oh, this would be more natural, or that would be more natural, or I wish the universe looked that way, but at this point that's all we can do. Um. Yeah, So it's a it's a fascinating concept infinity because, as you say, if things go on forever and then you get infinite number of tribes at everything, then that means that, given quantum randomness, you really do get every possibility out there. So that means it's somewhere out there, there's a universe where we're recording podcast and I'm named Jorge and your name Daniel, and you know, another universe where every possible thing you can imagine happens. That's really true, I mean, it's actually happening. If there is an infinite universe with infinite space, it means it could be really far away and we could never get there and prove it. But if that is reality, then it's really happening right now, which is crazy to think about. Right right, we just will never see it we'll never see it, yeah, or if we wait long enough, maybe we would. But but it's also so it's on one hand, like really crazy to imagine infinite universe with infinite stuff in it. On the other hand, it's sort of natural, right, like what's the simplest explanation? Is it simpler to imagine an edge? Right, like a limited amount of stuff? Um. I find those ideas to be sort of weird, and they sort of call back to, you know, geocentrism, the idea that we're the center, we're an important place in the universe. It's much more natural for me to think the universe just goes on forever and we're just at one dot in a random spot in it. Um. Otherwise they have to explain, like why the universe began here, Like imagine the scenario the infinite space but finite stuff scenario. Then you have to ask, why did the Big Bang happen here and not fifty billion light years to the left or to the right in that infinite space? Why is that clump matter here where we are? Yeah? So my personal preference, based on no science at all, is the infinite space infinite stuff universe because it sort of puts to rest some of those questions, right, It doesn't raise weird questions or inconsistencies. Yeah. Yeah, it just asks you to imagine creation of an infinite stuff in a moment. I mean that's not too much currently. I don't know if anybody who has such clever ideas for ways to determine whether the universe is infinite or finite by just looking at stuff around us. So the only way we could do it is direct by looking at the universe, which of course we can't. So currently it feels impossible. But you know, we always have to leave a little bit of an open door there for some future physicist more clever than us comes up with a clever way to probe whether the universe is find out or infinite just by looking at clues around us. You might say that, um, there's plenty of room to grow there. Certainly is there? Certainly is cool. Well, I hope you guys enjoyed that discussion. Um. Yeah, And maybe when you look out at night into the stars, you think about the idea that maybe the universe is infinite or maybe we're seeing all that there is, and regardless, it's a beautiful, gorgeous universe out there. And if you're into views, the best view out there is the night sky on the top of a mountain, where you can see billions of light years across. Amazing business. So however big the universe is, go out and enjoy it. Do you have a question you wish we would cover, Send it to us. We'd love to hear from you. 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