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Is the Universe infinite? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, do you think there are some questions out
• 0:10
  Speaker 1: there that will never know the answer to? Deep questions
• 0:14
  Speaker 1: like when is the best time to eat a banana?
• 0:18
  Speaker 1: What do you mean is there a controversy about that? Oh? Man,
• 0:20
  Speaker 1: people argue about this stuff online, you know, slightly green
• 0:24
  Speaker 1: or wait for the brown spots. There's a lot of debate. Yeah. Well,
• 0:28
  Speaker 1: I don't discriminate. I think every banana is delicious. But
• 0:33
  Speaker 1: I was thinking, you know, a bigger questions, bigger questions
• 0:35
  Speaker 1: about the universe, like are we alone? Are there aliens
• 0:38
  Speaker 1: out there? You just went right for the alien button.
• 0:41
  Speaker 1: I have it right here on my desk for a reason.
• 0:44
  Speaker 1: But yeah, yeah, I'm talking about huge mind blowing questions,
• 0:47
  Speaker 1: you know, like is like are we alone in the universe?
• 0:52
  Speaker 1: You know, is humanity destined to wonder these questions about
• 0:55
  Speaker 1: these questions forever? Or do you think we'll find answers eventually?
• 0:59
  Speaker 1: I think as long as we were around and we're
• 1:01
  Speaker 1: putting some money in basic research, we'll keep making progress.
• 1:04
  Speaker 1: So you know, it could take a hundred years, it
• 1:06
  Speaker 1: could take a thousand years, but I think some days
• 1:09
  Speaker 1: someone will come along with a clever way to give
• 1:11
  Speaker 1: us an answer. Even for the very biggest questions, like
• 1:15
  Speaker 1: when do aliens like to eat their bananas? I think
• 1:18
  Speaker 1: aliens like to eat you while you eat a banana.
• 1:21
  Speaker 1: I got dark. I got a bunch of dark spots
• 1:23
  Speaker 1: all of a sudden. Hi am Jorge. I'm a cartoonist
• 1:42
  Speaker 1: and the creator of PhD comics. I'm Daniel. I'm a
• 1:45
  Speaker 1: particle physicist, and I love really big questions we might
• 1:49
  Speaker 1: never know the answer to. And where do you fall
• 1:52
  Speaker 1: Daniel on the bananas, Kale, green or spotty? I think
• 1:57
  Speaker 1: right in between. Green makes you just your mouth feel
• 1:59
  Speaker 1: like you're eating cardboard, but too spotty, and you're basically
• 2:02
  Speaker 1: eating a smoothie, which is not something you want. That's
• 2:05
  Speaker 1: why they invented smoothies. That's right. I actually like the
• 2:08
  Speaker 1: red bananas. If you had the red bananas, I think
• 2:11
  Speaker 1: I have. Yeah. They have them in Asia, right, yeah,
• 2:14
  Speaker 1: and also in Central America. Slightly strawberry flavored, quite delicious.
• 2:18
  Speaker 1: It's got a bouquet of strawberry and oak carbon. They
• 2:23
  Speaker 1: are sassy but unpretentious. Here we are La. Here we
• 2:30
  Speaker 1: are shilling for Big Banana. But welcome to our podcast.
• 2:32
  Speaker 1: Daniel and Jorge explain the universe and apparently bananas, in
• 2:37
  Speaker 1: which we like to explore topics that are big, bigger
• 2:40
  Speaker 1: even than questions about bananas, questions so big you can't
• 2:44
  Speaker 1: even wrap your mind around them. Yeah, it's our show
• 2:46
  Speaker 1: produced by our Hard Radio, in which we think about
• 2:49
  Speaker 1: some of the biggest questions that they're that can be
• 2:52
  Speaker 1: asked about this crazy and pretty large universe we live in,
• 2:56
  Speaker 1: that's right, and we like to take you to the
• 2:58
  Speaker 1: forefront of knowledge, what scientists are thinking about, what the
• 3:01
  Speaker 1: experts in the world have in their minds, but then
• 3:04
  Speaker 1: translated so that you out there with your kids or
• 3:08
  Speaker 1: listening on your commute or everybody who loves questions and
• 3:11
  Speaker 1: wants to understand the universe can really dig into it
• 3:14
  Speaker 1: and get something out of it more than just banana jokes.
• 3:17
  Speaker 1: Part of our what you have to do is not
• 3:18
  Speaker 1: just talk about questions for which physicists know the answer
• 3:21
  Speaker 1: and try to explain to you those answers, but we
• 3:23
  Speaker 1: also kind of like to talk about the open questions
• 3:26
  Speaker 1: out there, the questions that not even people with PhD
• 3:29
  Speaker 1: s and universities have a good answer for. Are you
• 3:32
  Speaker 1: saying PhDs don't give you all the answers? I wish
• 3:35
  Speaker 1: I had an answer for that, Danny. I remember getting
• 3:37
  Speaker 1: my PhD. It was very unceremonious moment. Did you get
• 3:40
  Speaker 1: it by default? Is that what you're saying? No? At Berkeley,
• 3:44
  Speaker 1: when you turn in your PhD, you're in some sub
• 3:46
  Speaker 1: sub basement and you give it to the margins lady
• 3:48
  Speaker 1: and she measures the margins and your PhD, and if
• 3:52
  Speaker 1: everything looks ship shape, she gives you a lollipop that
• 3:54
  Speaker 1: says PhD on it. And that's the moment you have
• 3:58
  Speaker 1: a PhD? Uh? Did they? Um? Did you do? You
• 4:02
  Speaker 1: still have that lollipop? You know, we recently cleaned out
• 4:05
  Speaker 1: our house and I found a lollipop and my daughter Hayes,
• 4:07
  Speaker 1: I was like, why does this lollipop say PhD on it?
• 4:10
  Speaker 1: You found it? You still head it around, lapping around?
• 4:14
  Speaker 1: And did you let your daughter eat it? Because it's
• 4:15
  Speaker 1: probably like twenty years old? Man, I said, eat that
• 4:19
  Speaker 1: and you will learn all the secrets of the universe.
• 4:21
  Speaker 1: It's the red deal. Take the red lollipop and you
• 4:25
  Speaker 1: will never go back. No, but it's not very satisfied.
• 4:28
  Speaker 1: You know, that moment you get a PhD, you don't
• 4:30
  Speaker 1: feel like you know that much more. It's like a
• 4:32
  Speaker 1: slow accumulation of knowledge and understanding, and in some ways
• 4:36
  Speaker 1: you learn how little you know about the universe. Right,
• 4:39
  Speaker 1: You're like grappling with the infinity of our of our ignorance. Yeah,
• 4:43
  Speaker 1: I mean, at some point you basically become the world's
• 4:45
  Speaker 1: expert in a very particular topic, and you realize that
• 4:49
  Speaker 1: if you don't know, nobody knows. Like robots that run
• 4:53
  Speaker 1: like cockroaches, for example, Yeah, that's right, nobody knows how
• 4:56
  Speaker 1: to make them practical. Nobody knows. If I don't know
• 4:59
  Speaker 1: how to make them practical, nobody knows, that's right. And
• 5:02
  Speaker 1: one of the funnest questions, one of the really crazy
• 5:06
  Speaker 1: things to think about, is just sort of the nature
• 5:08
  Speaker 1: of the universe we find ourselves in. Yeah, what what
• 5:12
  Speaker 1: is it like really? I mean from we we know
• 5:14
  Speaker 1: what we can see from this little point in the universe,
• 5:17
  Speaker 1: in the in the milky Way, from this little rock
• 5:19
  Speaker 1: that we're all floating on, but and we can see
• 5:22
  Speaker 1: some stuff out there. But what is the universe really
• 5:24
  Speaker 1: like out there? You know, what's the shape of it?
• 5:27
  Speaker 1: How how far does it go? And and what's out there?
• 5:30
  Speaker 1: And it's fascinating to me that this is a fascinating question,
• 5:34
  Speaker 1: you know, like it's fascinating that it's fascinating. Yeah, that
• 5:37
  Speaker 1: it's one of the questions that people want answers to
• 5:40
  Speaker 1: that people want to know this about the universe. You know,
• 5:43
  Speaker 1: people have all sorts of questions about how stars are
• 5:45
  Speaker 1: formed and how planets are made, and whether they're aliens
• 5:48
  Speaker 1: out there, but people are also just curious about like
• 5:51
  Speaker 1: how far does it go? How does that all work?
• 5:54
  Speaker 1: And to me, that says something about you know, what
• 5:56
  Speaker 1: we want to know the answers to tells me something
• 5:58
  Speaker 1: about who we are and how we think. Do you
• 6:01
  Speaker 1: think this question of um, what the universe is like
• 6:04
  Speaker 1: out there is kind of primal to us as human beings,
• 6:07
  Speaker 1: Like there's something innate in our nature that really kind
• 6:11
  Speaker 1: of wants to know kind of what what is this
• 6:13
  Speaker 1: thing that we live in? Yeah, we want to understand ourselves.
• 6:16
  Speaker 1: We also really want to understand our context. You know,
• 6:19
  Speaker 1: like if you're born in a little village, you wonder
• 6:21
  Speaker 1: what else is out there beyond the edge of the village,
• 6:24
  Speaker 1: And if you're an explorer, you wonder like what's deep
• 6:27
  Speaker 1: in that jungle and what's out beyond the oceans, And
• 6:29
  Speaker 1: it's just something in humanity that wants to know, like
• 6:31
  Speaker 1: what is the nature of their context? What defines our existence?
• 6:35
  Speaker 1: What's beyond these four walls? Yeah, you can imagine being
• 6:38
  Speaker 1: like an early explorer and thinking, you know, is this
• 6:41
  Speaker 1: the only continent or are there more continent or there
• 6:43
  Speaker 1: three continents out there if I keep going, or are
• 6:46
  Speaker 1: there an infinite number of continents? Yeah? And I love
• 6:49
  Speaker 1: some of these sort of ancient arguments, you know, from
• 6:51
  Speaker 1: like the Greeks and those folks, about like how big
• 6:54
  Speaker 1: is space and how far does it go? And it
• 6:57
  Speaker 1: really reveals something about the way they thought. To the
• 7:00
  Speaker 1: on the podcast, we'll be tackling one of these big
• 7:02
  Speaker 1: questions about the universe, probably maybe the biggest question you
• 7:06
  Speaker 1: can ask about the universe, so to the on the podcast,
• 7:10
  Speaker 1: we'll be asking the question, is the universe infinite or
• 7:19
  Speaker 1: is it just mind modeling lee enormous, right, but enormous
• 7:24
  Speaker 1: but with a limit like finite finite? Right? Does it
• 7:27
  Speaker 1: have a size or does it go on literally forever
• 7:33
  Speaker 1: and ever? Yeah, it's totally a fascinating question. And I
• 7:36
  Speaker 1: was reading about this and I came across the sort
• 7:39
  Speaker 1: of ancient argument for the universe being infinite some of
• 7:42
  Speaker 1: the ancient Greeks. They believe the argument was infinite and
• 7:45
  Speaker 1: they just needed a javelin to prove their point. Really, Wow,
• 7:50
  Speaker 1: all this time, you guys have been building telescopes and
• 7:52
  Speaker 1: space telescopes and particle colliders. All you needed was a
• 7:55
  Speaker 1: stick exactly. I like the low tech solution to some
• 7:59
  Speaker 1: of these questions. Wait, so you're saying the Greeks wondering
• 8:03
  Speaker 1: that the universe was infinite. So they knew kind of
• 8:05
  Speaker 1: generally what was going on, like we're a planet, we're
• 8:07
  Speaker 1: in a solar system, and then they were they're just
• 8:10
  Speaker 1: wondering if the Earth was infinite. No, they knew that,
• 8:12
  Speaker 1: you know, there were planets. In fact, the Babylonians knew
• 8:14
  Speaker 1: that there were other planets out there in the sky.
• 8:17
  Speaker 1: We didn't know the nature of space or you know
• 8:19
  Speaker 1: that the Sun was just an example of other stars.
• 8:21
  Speaker 1: But they had the sense that, you know, the sky
• 8:24
  Speaker 1: wasn't a ceiling. The things went on for a while
• 8:26
  Speaker 1: and the question was how far do they go? So
• 8:29
  Speaker 1: how tall is the ceiling in this bio dome we
• 8:33
  Speaker 1: live in. Yeah, and they had this fun sort of
• 8:35
  Speaker 1: thought experiment because they couldn't venture out into space and
• 8:38
  Speaker 1: involved throwing a javelin, And the argument goes something like this, like,
• 8:42
  Speaker 1: imagine the universe is finite. Okay, like it has an
• 8:46
  Speaker 1: edge to it has an edge to it. Now go
• 8:49
  Speaker 1: to that edge and throw a javelin. What happens Either
• 8:54
  Speaker 1: the javelin keep going, in which case you're not actually
• 8:57
  Speaker 1: at the edge right and repeat forever, or the javelin
• 9:01
  Speaker 1: bounces off something like hits an obstruction, in which case
• 9:05
  Speaker 1: that obstruction is past the edge. And so this is
• 9:09
  Speaker 1: sort of an argument that suggests that the universe must
• 9:11
  Speaker 1: be infinite. Oh, I see, it's kind of like um
• 9:14
  Speaker 1: testing how big your your your house is. You know,
• 9:17
  Speaker 1: if you walk and you hit a fence, throw a
• 9:19
  Speaker 1: javelin and if it hits something good, jump the fence
• 9:22
  Speaker 1: and see if there's another fence. Is that kind of
• 9:24
  Speaker 1: what you mean? Yeah, precisely. This argument is essentially trying
• 9:27
  Speaker 1: to say that it's nonsense for the universe to be finite.
• 9:30
  Speaker 1: There is no way in which an edge makes any
• 9:33
  Speaker 1: sense at all, because if you get to an edge,
• 9:36
  Speaker 1: then you know, you have to think what's past it? Uh,
• 9:39
  Speaker 1: And the javelin is sort of a way to probe it. Now,
• 9:41
  Speaker 1: that argument of course, totally flawed. It's not approved to
• 9:44
  Speaker 1: the universe into Greek. Wrong, What do you can't prove
• 9:47
  Speaker 1: that the universe is infinite with the javelin? Turns out
• 9:51
  Speaker 1: we have learned one or two things since ancient times. Yeah,
• 9:57
  Speaker 1: and we'll get into it in much more detail. But
• 9:59
  Speaker 1: the essential idea is that this is flawed because the
• 10:02
  Speaker 1: universe could be closed. It could be to the universe
• 10:05
  Speaker 1: or loops on itself, and you could keep throwing that
• 10:07
  Speaker 1: javelin and picking it up and throwing it and picking
• 10:09
  Speaker 1: it up and throwing it forever, even in a finite universe. Interesting,
• 10:13
  Speaker 1: it is possible. You're saying for the universe to have
• 10:16
  Speaker 1: a wall at the end. I actually do think that
• 10:19
  Speaker 1: that's not nonsense. It's possible for the universe to have
• 10:22
  Speaker 1: a wall. But I think the simpler idea is for
• 10:24
  Speaker 1: the universe to sort of just be closed on itself,
• 10:27
  Speaker 1: like on the surface of a sphere. You know, if
• 10:29
  Speaker 1: you're gonna throw javelin and then follow it and pick
• 10:32
  Speaker 1: it up and throw it, you could do that on
• 10:33
  Speaker 1: the surface of the Earth basically forever without hitting a wall.
• 10:37
  Speaker 1: That doesn't mean the Earth is infinite. It's not all right, Well,
• 10:40
  Speaker 1: let's get into the different scenarios for what the universe
• 10:43
  Speaker 1: can look like, whether it's infinite or not infinite or finite.
• 10:48
  Speaker 1: But it's kind of a big question, right, It's kind
• 10:49
  Speaker 1: of a deep question whether or not the universe goes
• 10:52
  Speaker 1: on forever or whether it has a limit. But we
• 10:55
  Speaker 1: were wondering, you know, we kind of would like to wonder, hear,
• 10:57
  Speaker 1: how important is this is? This question? And does it
• 11:00
  Speaker 1: really matter to people? Yeah, so I walked around campus
• 11:03
  Speaker 1: and instead of asking them if they thought the universe
• 11:05
  Speaker 1: was infinite, I asked them if it mattered to them,
• 11:09
  Speaker 1: does it make a difference in your life if the
• 11:10
  Speaker 1: universe goes on literally forever or is just really really big?
• 11:15
  Speaker 1: And then I asked them if they wanted to know
• 11:17
  Speaker 1: the answer? And I think they replies to that we're
• 11:19
  Speaker 1: quite revealing. You asked them a two part question. First,
• 11:22
  Speaker 1: you asked him the technical one, and then you asked
• 11:24
  Speaker 1: them if they wanted to know the answer. All right, well,
• 11:26
  Speaker 1: think about it. Does if you listening, think about it
• 11:28
  Speaker 1: for a second, do you think the universe is infinite
• 11:30
  Speaker 1: or just really big? And would you want to know
• 11:33
  Speaker 1: the answer either way? Here's what people have to say.
• 11:37
  Speaker 1: I think it does matter because it changes the scale
• 11:42
  Speaker 1: of how it's just it's just weird to think that
• 11:45
  Speaker 1: it's infinite. You can't really see that it's infinite, but
• 11:48
  Speaker 1: it's just endless to me. No, No, it's interesting, but
• 11:54
  Speaker 1: it doesn't urge me to care. Which the answer is no,
• 11:58
  Speaker 1: not really. It's interesting, but not really, not really. But
• 12:03
  Speaker 1: do you want to know? Yes, So why do you
• 12:05
  Speaker 1: want to know if it doesn't make a difference. I
• 12:08
  Speaker 1: don't know. It's a question nobody can really answer right now,
• 12:11
  Speaker 1: and I just think that's the first time I definitely
• 12:13
  Speaker 1: want to know, but it doesn't influence my everyday to life.
• 12:16
  Speaker 1: So then why do you want to know out of curiosity?
• 12:19
  Speaker 1: I don't like not knowing things. I think that's the
• 12:24
  Speaker 1: whole reason they joined physics to gain more knowledge about
• 12:28
  Speaker 1: the universe that we live in. I think it'd be
• 12:30
  Speaker 1: cool to know, but it doesn't really affect me. So
• 12:33
  Speaker 1: why is it cool to know there's a higher or
• 12:35
  Speaker 1: lower chance of like finding like a new planet, or
• 12:39
  Speaker 1: maybe like there's a higher chance of finding aliens? I'd
• 12:43
  Speaker 1: say on a day to day no, probably not. But
• 12:45
  Speaker 1: do you want to know that? The answer I think
• 12:47
  Speaker 1: I would like to know the answer. Why do you
• 12:49
  Speaker 1: want to know? Because it would be nice to be
• 12:50
  Speaker 1: able to say that I know whether or not it's
• 12:52
  Speaker 1: infinite or just unfathomedly lige alright, No, do you want
• 12:57
  Speaker 1: to know the answer? Though? Yeah? So what do you
• 12:59
  Speaker 1: want to know the answer? Just because you always want
• 13:01
  Speaker 1: to know the answers to everything? I think if it
• 13:04
  Speaker 1: is infinite, that would blow my mind. I would be
• 13:07
  Speaker 1: interested in knowing the answer to that. Yeah, alright, So
• 13:09
  Speaker 1: why do you want to know? I think I'm someone
• 13:11
  Speaker 1: who just likes to know things, and it's it's hard
• 13:14
  Speaker 1: to actually articulate the reasons for that, but because it
• 13:17
  Speaker 1: doesn't matter to me personally, but I'm intellectually curious. Al right. Well,
• 13:23
  Speaker 1: it seems like people answered both of your questions. The
• 13:26
  Speaker 1: answered whether they thought that the universe was infinite or
• 13:30
  Speaker 1: just really big, and whether or not they wanted to
• 13:32
  Speaker 1: know the answer, and they were both kind of different. Yeah,
• 13:35
  Speaker 1: most people felt like, no, of course, it doesn't make
• 13:37
  Speaker 1: a difference. You know, it doesn't change how you're going
• 13:39
  Speaker 1: to live your life. It doesn't mean you should eat
• 13:41
  Speaker 1: it in is when they're green or when they have
• 13:43
  Speaker 1: spots in them. Right, there's no practical difference. Um. But
• 13:47
  Speaker 1: then when I asked people if they wanted to know
• 13:49
  Speaker 1: the answer, they perked up and maybe they thought like
• 13:52
  Speaker 1: I had the answer and I could totally he teased
• 13:57
  Speaker 1: them and then you let them down. But the thing
• 13:59
  Speaker 1: is you should have seen the curiosity in their eyes, like,
• 14:02
  Speaker 1: imagine knowing for a moment they imagine what would be
• 14:05
  Speaker 1: like to learn that truth that could change your relationship
• 14:10
  Speaker 1: with the cosmos? Right, And I think a lot of
• 14:12
  Speaker 1: people put that really well. One of my favorite responses
• 14:16
  Speaker 1: was the guy who said that I'm someone who likes
• 14:18
  Speaker 1: to know things, and it's hard to articulate the reason why,
• 14:21
  Speaker 1: but it is something really deep, you know that you'd
• 14:24
  Speaker 1: like to know. Interesting. Yeah, I guess it. So most people,
• 14:27
  Speaker 1: it seems, acknowledge that knowing whether the universe is infinite
• 14:30
  Speaker 1: or not won't make a difference in their lives. But
• 14:32
  Speaker 1: everyone still wants to know. Everybody wants to know, and
• 14:35
  Speaker 1: I want to know. Yeah, there is sort of an
• 14:38
  Speaker 1: inherent curiosity in people. Yeah, and I think this being
• 14:42
  Speaker 1: one of the biggest of questions really touches on that because,
• 14:45
  Speaker 1: as we were saying before, I think it connects to
• 14:47
  Speaker 1: our curiosity not just about ourselves, but about this place
• 14:50
  Speaker 1: we live in. And it's sort of the biggest question
• 14:53
  Speaker 1: about the biggest topic. And so that were they disappointed
• 14:55
  Speaker 1: that you didn't know the answer to this question, that
• 14:59
  Speaker 1: you wouldn't give it to the I said, hey, you
• 15:01
  Speaker 1: got to tune into the podcast. So yeah, I did.
• 15:06
  Speaker 1: Let at a time, You're you're teasing one listener at
• 15:10
  Speaker 1: a time. I did leave these people disappointed, unfortunately, you know,
• 15:14
  Speaker 1: but hey, if they listen to podcast, maybe they can
• 15:16
  Speaker 1: understand something about what we do know about the nature
• 15:19
  Speaker 1: of this question. Well, it seems like there are only
• 15:21
  Speaker 1: two options. Either the universe is really big or the
• 15:25
  Speaker 1: universe is infinite. There's there's sort of no third option,
• 15:27
  Speaker 1: is there, I guess? So, yeah, the third option is,
• 15:31
  Speaker 1: you know, the simulation when you're actually trapped in a
• 15:33
  Speaker 1: room somewhere in the universe is about ten feet across
• 15:35
  Speaker 1: and everything you're experiencing is just bologny. But now you're right,
• 15:40
  Speaker 1: if what we're experiencing is real and it's not a simulation,
• 15:43
  Speaker 1: then at the very minimum, the universe is ginormous, but
• 15:47
  Speaker 1: it could be really really big, or it could be
• 15:50
  Speaker 1: extremely infinitely big. Yeah, and there's a lot of gradations there.
• 15:54
  Speaker 1: It could be like ridiculously big. It could be radoculously big,
• 15:59
  Speaker 1: it could be like mind blowing the unfathomably big. It
• 16:03
  Speaker 1: could be like tend to that that big, or could
• 16:06
  Speaker 1: be actually infinite about tend to the ridiculous lead duntlessly big? Yeah,
• 16:15
  Speaker 1: I mean, any of these things. These are real numbers,
• 16:17
  Speaker 1: you know. And the crazy thing for me is that
• 16:20
  Speaker 1: one of these is true. Right, there is a truth
• 16:23
  Speaker 1: out there. The universe actually does have a size. Either
• 16:26
  Speaker 1: it's finite or it's infinite, and one of those is true,
• 16:29
  Speaker 1: And one day some human might actually know that truth
• 16:33
  Speaker 1: and have that experience that all these listeners, all those
• 16:36
  Speaker 1: interviewees were hoping to have. Well, I feel really teased now.
• 16:39
  Speaker 1: I hope you have an answer for me at the
• 16:40
  Speaker 1: end here, Daniel, otherwise I'm going to be disappointed as well.
• 16:43
  Speaker 1: The answer is fund more physics research. Give Daniel more money.
• 16:52
  Speaker 1: All right, Well, let's get into this question a little
• 16:55
  Speaker 1: bit more, and let's get into how we would know
• 16:58
  Speaker 1: if the universe is infinite or fine day, and what
• 17:00
  Speaker 1: would happen if we found out. But first let's take
• 17:03
  Speaker 1: a quick break, all right, Daniel we're asking the question
• 17:19
  Speaker 1: is the universe infinite or is it finite? And I
• 17:22
  Speaker 1: guess my first question is, you know, is it possible?
• 17:25
  Speaker 1: Which of these is possible? Are they? Are these both
• 17:27
  Speaker 1: possible possibilities for the universe? Can the universe be really infinite?
• 17:31
  Speaker 1: Or does it make sense for the universe to have
• 17:33
  Speaker 1: a wall at the end and be closed off? I
• 17:36
  Speaker 1: think unfortunately, all of these things are possible, and we
• 17:39
  Speaker 1: can go through the various scenarios. But you know, we're
• 17:42
  Speaker 1: talking about big questions here, and the questions we don't
• 17:45
  Speaker 1: have a lot of history in getting answers to. It's
• 17:48
  Speaker 1: not like we've been a lots of universes. We've seen
• 17:50
  Speaker 1: what happens, and we have a lot of experience where
• 17:53
  Speaker 1: grizzled veterans in measuring universes. Now, this is going to
• 17:56
  Speaker 1: be the first time if we ever do get an
• 17:58
  Speaker 1: answer that we would learn this about universe. So we've
• 18:00
  Speaker 1: got to be open minded. Things that seem crazy to
• 18:03
  Speaker 1: us are going to be based on our experience here, right.
• 18:08
  Speaker 1: So like if you think, oh, nobody has a PhD
• 18:10
  Speaker 1: yet on answering this question exactly, we all got to
• 18:14
  Speaker 1: be open minded. So anything that works mathematically, even if
• 18:17
  Speaker 1: it's like revolting to our physical intuition, we've got to
• 18:21
  Speaker 1: be open to it because well, we've been making progress.
• 18:23
  Speaker 1: Right before, we thought the universe was just us, and
• 18:26
  Speaker 1: then we find out that it's the size of the galaxy,
• 18:29
  Speaker 1: and then we find out there's more galaxy. So I
• 18:31
  Speaker 1: feel like our understanding of how big the universe is
• 18:35
  Speaker 1: has been getting bigger progressively. Yeah, we've been biggering and
• 18:38
  Speaker 1: biggering our imagination of the universe. But still all that is,
• 18:42
  Speaker 1: it doesn't really address the question of whether it's finite
• 18:45
  Speaker 1: or whether it's actually infinite. That just sort of increases
• 18:49
  Speaker 1: the sort of minimum distance of the universe as we
• 18:51
  Speaker 1: look further and further out. So you know, So to
• 18:54
  Speaker 1: answer your question, the universe could we finite or could
• 18:57
  Speaker 1: be infinite? Both of those things are possible. Well, let's
• 19:00
  Speaker 1: cycle each one at a time and and see what
• 19:02
  Speaker 1: each one would need. So let's say the let's let's
• 19:05
  Speaker 1: assume the universe is finite, meaning that there is a
• 19:09
  Speaker 1: limited amount of space in space um and and that
• 19:13
  Speaker 1: the universe doesn't go on forever. At some point, uh
• 19:16
  Speaker 1: it ends, it has like a volume like a set
• 19:18
  Speaker 1: number that's the volume of the universe. Is that possible?
• 19:22
  Speaker 1: Wouldn't that mean that there's like a wall at the end.
• 19:24
  Speaker 1: And if there's a wall, what's the on the other
• 19:26
  Speaker 1: side of the wall. You're gonna take your javel and
• 19:29
  Speaker 1: you're gonna go to that wall and you're gonna poke it. Right, Yeah,
• 19:33
  Speaker 1: I'm gonna spend forty billion years traveling just to throw
• 19:36
  Speaker 1: that javelin. Well, you have to remember what we're talking
• 19:39
  Speaker 1: about here is the shape of space, and space is
• 19:42
  Speaker 1: not nothing. It's not emptiness. Right. Space is a thing
• 19:46
  Speaker 1: that we are existing. It is the background on which
• 19:49
  Speaker 1: all of this physics happens. But it's not nothing. It's dynamical.
• 19:52
  Speaker 1: It can twist and bend and ripple and do all
• 19:55
  Speaker 1: sorts of crazy stuff. It's got like substance to that
• 19:58
  Speaker 1: to it, right, the space of universe. I don't know
• 20:01
  Speaker 1: if substance is the right word, but it has a
• 20:03
  Speaker 1: nature to it. It's not nothing. I see, there's there
• 20:07
  Speaker 1: is nothing, like literally nothing, and then there's space, which
• 20:10
  Speaker 1: has something we don't know if nothing is a physical possibility, right,
• 20:15
  Speaker 1: So when we're talking about like the edge of space, yes,
• 20:17
  Speaker 1: it's possible for space to be finite in different ways.
• 20:22
  Speaker 1: In one way, it could have an edge, like you
• 20:24
  Speaker 1: could just like you get to the edge of space
• 20:27
  Speaker 1: and there's and that's it. Now you might ask, well,
• 20:30
  Speaker 1: what's beyond it? Well, the answer could be that there's nothing.
• 20:32
  Speaker 1: There is not a thing beyond it. It's like when
• 20:35
  Speaker 1: you get to the north pole and you want to
• 20:37
  Speaker 1: go more north, there's just no more northiness to go.
• 20:40
  Speaker 1: Couldn't it be like like an like an island, and
• 20:43
  Speaker 1: you get to the edge of an island and beyond
• 20:44
  Speaker 1: that there's nothingness. It could be an island. The edge
• 20:48
  Speaker 1: is defined by the water, right, So what's the water
• 20:50
  Speaker 1: in this analogy, right, Well, the water could be nothing,
• 20:53
  Speaker 1: and then space could be something. Yeah, but then you've
• 20:55
  Speaker 1: sort of just redefined space to be the nothingness, and
• 20:59
  Speaker 1: then you could ask how far does that nothing go on?
• 21:01
  Speaker 1: Doesn't really answer the question, but there's a real possibility
• 21:04
  Speaker 1: that space is all there is, that there is that
• 21:06
  Speaker 1: nothing isn't an option that there's space and then there's
• 21:09
  Speaker 1: space and there's not. There's no place where there's no space.
• 21:12
  Speaker 1: Nothing is not an option by that's a confusing sentence.
• 21:17
  Speaker 1: And then you just you get to that edge and
• 21:19
  Speaker 1: you just can't go any further. Like what happens if
• 21:21
  Speaker 1: you try to keep going, you just what you would
• 21:23
  Speaker 1: not go anywhere. Maybe it's helpful to think about other
• 21:26
  Speaker 1: examples where space is not simply connected, like in a
• 21:29
  Speaker 1: black hole. If you're in a black hole, you can
• 21:32
  Speaker 1: only go in one direction. You can only go closer
• 21:35
  Speaker 1: to the center of the black hole, because that's the
• 21:36
  Speaker 1: only path the shape of space will allow. It's not
• 21:40
  Speaker 1: just that the gravity is really strong. It's the bending
• 21:42
  Speaker 1: of space that makes that means that every path points
• 21:45
  Speaker 1: towards the center of the black hole, right, and so
• 21:47
  Speaker 1: in the same way, if you've got to like the
• 21:49
  Speaker 1: edge of the universe, it just means that there's nowhere
• 21:52
  Speaker 1: to go but back or sideways. I see, like the
• 21:56
  Speaker 1: universe might redirect you. Yeah, like what happens when you
• 21:59
  Speaker 1: get to the edge of the subway system right where
• 22:02
  Speaker 1: you either you know, ride it back or you transfer
• 22:04
  Speaker 1: to another line. Like you would throw a javelin at
• 22:06
  Speaker 1: the edge of the universe and it would just get
• 22:08
  Speaker 1: deflected to the side maybe or come back at you
• 22:10
  Speaker 1: and spirit. Yeah, And that doesn't mean that there's a
• 22:13
  Speaker 1: wall they're holding it in. It just means space ends.
• 22:17
  Speaker 1: That's a total possibility. Space gets spacey or wonky at
• 22:21
  Speaker 1: the edges. Yeah, it gets because space is about it's
• 22:24
  Speaker 1: about the relative connections of these pieces, right, It's not
• 22:27
  Speaker 1: an emptiness. It's a thing where it's like this fluid
• 22:30
  Speaker 1: we're moving through. And what we're talking about is the
• 22:34
  Speaker 1: curvature space, the connectedness of space, the topology of it,
• 22:37
  Speaker 1: if you want to get technical, how it's connected to
• 22:39
  Speaker 1: other bits, and and that changes, right, that changes when
• 22:43
  Speaker 1: you put mass in something, it changes how that stuff
• 22:46
  Speaker 1: is connected. All right. So that's one possibility is that
• 22:48
  Speaker 1: the universe is finite with an edge that is kind
• 22:51
  Speaker 1: of wonking doesn't let you poke through it. Yeah, that
• 22:54
  Speaker 1: would be really weird and awesome to discover. But it
• 22:57
  Speaker 1: could also be finite in the way the surface of
• 22:59
  Speaker 1: the Earth is finite but doesn't have an edge. And
• 23:02
  Speaker 1: then it could be we call that closed. It could
• 23:04
  Speaker 1: be essentially be curved. And we know that that space
• 23:08
  Speaker 1: could be curved, right, gravity and energy bends it, and
• 23:11
  Speaker 1: so it could just be that you keep going and
• 23:13
  Speaker 1: you just sort of loop back to where you started. Right.
• 23:15
  Speaker 1: It's like asking what is the length of a circle,
• 23:18
  Speaker 1: Like if you take a leg the string string and
• 23:20
  Speaker 1: you tie it to itself into a circle, like, what's
• 23:23
  Speaker 1: the length of it. It's finite, but it's not um
• 23:26
  Speaker 1: like a set number because it just goes around and around. Yeah,
• 23:29
  Speaker 1: and it doesn't have an edge, right, there's no wonky
• 23:31
  Speaker 1: bit there. You just keep going. And so that's totally
• 23:34
  Speaker 1: possible and that is consistent. If space curves in a
• 23:38
  Speaker 1: certain way, then it can loop back on itself. And
• 23:42
  Speaker 1: so we're talking about now, is this curvature of space
• 23:45
  Speaker 1: is really important in understanding the possible shapes of the universe,
• 23:48
  Speaker 1: which determine the possible sizes, right, because if, for example,
• 23:53
  Speaker 1: space is curved in that way it's like the surface
• 23:55
  Speaker 1: of a sphere, then it can't be infinite. It cannot
• 23:59
  Speaker 1: if space is curve, right, If space is curved like
• 24:01
  Speaker 1: the surface of the sphere, then it cannot be infinite. Yeah,
• 24:03
  Speaker 1: then it would have to be closed and therefore finite.
• 24:06
  Speaker 1: Really couldn't it be like a spiral like it's curved,
• 24:09
  Speaker 1: but it just keeps spiraling outwards forever, like fucilit pasta
• 24:13
  Speaker 1: or something. Yeah, Like just take a string and keep
• 24:17
  Speaker 1: spiraling it up. It's interesting. Um, you can have topologies
• 24:22
  Speaker 1: that are like a donut, you know, a bagel or
• 24:26
  Speaker 1: something that have positive curvature, but that's still like a
• 24:29
  Speaker 1: like a like a like a seashell, you know, like
• 24:32
  Speaker 1: it just keep sparling out folding outwards. Isn't it possible
• 24:36
  Speaker 1: to Yeah, I wonder about that, you know, or like
• 24:39
  Speaker 1: the surface of a cylinder, surface of a cylinder is
• 24:42
  Speaker 1: also um curved, but could go on forever, But then
• 24:48
  Speaker 1: the curvature would only be in one dimension. So I
• 24:50
  Speaker 1: think if the curvature is sort of even in every direction,
• 24:54
  Speaker 1: then then the sphere is the only a sphere or
• 24:57
  Speaker 1: a toroid is the only shape that's consistent with that curvature.
• 25:00
  Speaker 1: What if it looks like a slinky, you know, like
• 25:02
  Speaker 1: a like a spring, then it could be finite, infinite
• 25:05
  Speaker 1: and curved. Well, but I think the slinky is essentially
• 25:08
  Speaker 1: the same topologically as a straight cylinder. It's just sort
• 25:11
  Speaker 1: of bent in another space, and that doesn't have curature
• 25:14
  Speaker 1: in every direction. But we're when we're talking about measuring
• 25:18
  Speaker 1: the curvature of space, it's something innate and it would
• 25:20
  Speaker 1: be the same in every direction. Oh, I see. If
• 25:22
  Speaker 1: it's if it's curved inwards in all directions, then you
• 25:25
  Speaker 1: sort of have to fold in on itself. And so
• 25:27
  Speaker 1: that's another possibility, right, the universe could be finite and
• 25:30
  Speaker 1: have a wonky edge, or it could be finite and
• 25:32
  Speaker 1: be closed on itself. Um and like the surface of
• 25:35
  Speaker 1: a sphere without any edges. So that that's how a
• 25:38
  Speaker 1: finite universe can make sense without imagining like a giant
• 25:42
  Speaker 1: brick wall at the end, which doesn't make sense. Yeah. Yeah,
• 25:45
  Speaker 1: And but and you say you always like to say
• 25:47
  Speaker 1: that this possibility that the universe is finite, it's sort
• 25:50
  Speaker 1: of maybe comforting to human brains, but it is kind
• 25:54
  Speaker 1: of a crazy idea, the idea that the universe ends
• 25:58
  Speaker 1: at some point, or that there there's it doesn't go
• 26:00
  Speaker 1: on forever. Yeah. Do you think it's comforting to think
• 26:02
  Speaker 1: that the universe is finite because because infinity is hard
• 26:05
  Speaker 1: to imagine? Yeah, I mean infinity is kind of scary, right,
• 26:09
  Speaker 1: It's like it's like living in an infinite house. It's
• 26:11
  Speaker 1: like a nightmare. The electricity bill, yeah, the cleaning bill,
• 26:17
  Speaker 1: and the how many beds you have to buy, how
• 26:21
  Speaker 1: many I kea furniture a dress as you have to build.
• 26:25
  Speaker 1: I mean, it's a it's the stuff nightmares are made up.
• 26:28
  Speaker 1: You could literally be building furniture forever. Yeah, and once
• 26:31
  Speaker 1: you lose your keys, they're just gone. Man, They're gone.
• 26:34
  Speaker 1: That's true. I'm not sure which is more comforting, But
• 26:37
  Speaker 1: I think the idea of a finite universe is really
• 26:39
  Speaker 1: odd because then there's a number, right, the universe would
• 26:43
  Speaker 1: have a size, And then you have to ask, like
• 26:45
  Speaker 1: why that number? Why not seven times that number or
• 26:49
  Speaker 1: half that number? What is important about that number? And
• 26:52
  Speaker 1: you wonder like is it random or is it fixed?
• 26:54
  Speaker 1: Is it determined by something? Right? It would there would
• 26:57
  Speaker 1: be like a fixed number of uh, you know, electrons
• 27:01
  Speaker 1: in it. You know, like there would be uh seven
• 27:04
  Speaker 1: point three trillion point one and not one electron more
• 27:10
  Speaker 1: or less, right is there? Yeah? That's what makes a
• 27:14
  Speaker 1: physicist worry. It's just hard to grapple with. But that's
• 27:18
  Speaker 1: why we're doing physics, right. We're asking these really basic
• 27:20
  Speaker 1: questions about the universe so that then we can do
• 27:23
  Speaker 1: the philosophy. Is so that then we can like do
• 27:25
  Speaker 1: the therapy. Were like, all right, turns out this is
• 27:28
  Speaker 1: the universe we live in. What does that mean? How
• 27:31
  Speaker 1: do I live my life in that kind of universe?
• 27:34
  Speaker 1: And does that mean that when you go to a
• 27:35
  Speaker 1: restaurant and you look at the menu, like the many
• 27:38
  Speaker 1: makes you uncomfortable, like why are there only thirteen dishes here?
• 27:41
  Speaker 1: Why aren't there fourteen dishes or twelve? I know that
• 27:45
  Speaker 1: that doesn't arise from some de fundamental principle of the universe.
• 27:49
  Speaker 1: That arises from some argument you know, between the managers
• 27:52
  Speaker 1: um when they were founding the restaurants, and not every
• 27:54
  Speaker 1: number you spot reveal something deep about the universe. Alright, alright, alright,
• 27:59
  Speaker 1: so then that's the finite possibility. So step me through
• 28:03
  Speaker 1: the infinite possibility, because to me, this one is the
• 28:05
  Speaker 1: one that seems impossible, like how can something be infinite?
• 28:08
  Speaker 1: But you're saying the universe could be infinite. The universe
• 28:12
  Speaker 1: could totally be infinite. Yeah, I mean if space is
• 28:15
  Speaker 1: very simple and flat, you know, like the surface of
• 28:19
  Speaker 1: a of a flat plane, then it could just keep
• 28:22
  Speaker 1: going on. It could just go on and on and on.
• 28:24
  Speaker 1: And in some ways, that's sort of the simplest idea
• 28:27
  Speaker 1: because it doesn't require an edge or complicated topology. I mean,
• 28:31
  Speaker 1: it requires you to somehow invent an infinite number of electrons,
• 28:34
  Speaker 1: which is you know, a whole other problem you have
• 28:36
  Speaker 1: to tackle at something like an infinite amount of energy, right,
• 28:40
  Speaker 1: and matter and possibilities like there's it means that there
• 28:45
  Speaker 1: are versions of this Earth somewhere out there in the
• 28:48
  Speaker 1: same universe as us. And if you had a lot
• 28:51
  Speaker 1: of experience measuring universes and finding them to be finite,
• 28:54
  Speaker 1: I would understand your skepticism. Right, But you have exactly
• 28:58
  Speaker 1: the same experience that everybody else has, which is you
• 29:00
  Speaker 1: have no idea how big a universe should be or
• 29:03
  Speaker 1: whether it's weird to have an infinite universe, And so
• 29:06
  Speaker 1: it could totally be and it could be very natural.
• 29:09
  Speaker 1: You're saying that that I don't have a PhD in universizing.
• 29:14
  Speaker 1: You have an incredible array of talents, but that is
• 29:16
  Speaker 1: not one of them. Well, um, all right, so I
• 29:21
  Speaker 1: guess as a physicist you kind of have to treat
• 29:24
  Speaker 1: all possibilities. Is possible? You know, if it's possible, then
• 29:28
  Speaker 1: it's a possibility. Yeah, And so all you can do
• 29:30
  Speaker 1: is say, what's possible, what would make sense from the
• 29:33
  Speaker 1: physics point of view, what can we make work, you know,
• 29:36
  Speaker 1: mathematically and theoretically, And then you go out and you
• 29:39
  Speaker 1: confront those theories with the data, and you say well,
• 29:41
  Speaker 1: do they predict something we can measure it is there's
• 29:44
  Speaker 1: something in the universe out there that can give us
• 29:46
  Speaker 1: a clue as to which of these scenarios we are
• 29:49
  Speaker 1: actually living in, right, because there might be clues out
• 29:52
  Speaker 1: there that tell you whether the universe is finite or
• 29:55
  Speaker 1: infinite without having to go to the edge to check
• 29:58
  Speaker 1: that's right. We certainly can learn think about this question
• 30:00
  Speaker 1: by doing actual measurements that don't involve javelins. Well, what
• 30:04
  Speaker 1: do we know right now about the universe? Like, how
• 30:07
  Speaker 1: how big do we think it is? As as we
• 30:09
  Speaker 1: know it right now? How big do you do we
• 30:10
  Speaker 1: think it is? Well, we've been looking out into space
• 30:13
  Speaker 1: for a while and we have these really clever tools
• 30:15
  Speaker 1: now for measuring how far away stuff is. You know,
• 30:18
  Speaker 1: we can we talked about this on the podcast, measuring
• 30:21
  Speaker 1: the distance to nearby stars by basically looking at them
• 30:24
  Speaker 1: in two ways like binocular vision, and then using supernovas
• 30:28
  Speaker 1: and stuff to measure the distance to even further stuff.
• 30:31
  Speaker 1: So basically what we can do is we can ask,
• 30:33
  Speaker 1: like how far out can we see? That sets a
• 30:36
  Speaker 1: minimum size for the universe, just like you know, what's
• 30:38
  Speaker 1: the observable universe? Right? Like what's the furthest thing that
• 30:43
  Speaker 1: we can see with our eyes or telescopes, And that
• 30:45
  Speaker 1: tells us at least the universe has to be that big.
• 30:48
  Speaker 1: That's right, And your naive calculation might be, well, it
• 30:51
  Speaker 1: must be the speed of light times the age of
• 30:54
  Speaker 1: the universe, which is almost fourteen billion years, and so
• 30:57
  Speaker 1: you might think, oh, it's a sphere for billion light
• 31:01
  Speaker 1: years in radius, but that's actually an underestimate. The universe
• 31:04
  Speaker 1: that we can see is much much bigger than that. Right,
• 31:08
  Speaker 1: that is so naive, Daniel, That's like what a third
• 31:13
  Speaker 1: year gradu stude in physics might think. But no, I
• 31:16
  Speaker 1: don't mean to be kind of saying at all. I
• 31:18
  Speaker 1: mean like that would make a lot of sense that
• 31:20
  Speaker 1: that's all we can see because light has to travel
• 31:22
  Speaker 1: here from those places. And we talk a lot in
• 31:24
  Speaker 1: the podcast about how you know, the further away you look,
• 31:27
  Speaker 1: the further back in time you're looking at, eventually you
• 31:30
  Speaker 1: run out of time. The universe is not infinitely old,
• 31:33
  Speaker 1: so stuff that's really far away just hasn't had a
• 31:35
  Speaker 1: chance to get here. Yeah, well that's how how how
• 31:38
  Speaker 1: many we would think it would be. But you're saying
• 31:41
  Speaker 1: that we can tell the size by how far the
• 31:44
  Speaker 1: then the furthest thing we can see is yeah, and
• 31:47
  Speaker 1: it turns out that stuff is further away than the
• 31:50
  Speaker 1: age of the universe times the speed of light. Because
• 31:52
  Speaker 1: the universe is not static, it's expanding. Stuff is moving
• 31:56
  Speaker 1: away from us. So light has gotten to us from
• 31:59
  Speaker 1: stuff that is how further away than the speed of
• 32:03
  Speaker 1: light times the age of the universe Because we know that, right,
• 32:05
  Speaker 1: whether it's finite or infinite, we know it's getting bigger.
• 32:08
  Speaker 1: We know it's stretching, it's expanding, it's getting more spread out.
• 32:11
  Speaker 1: So the furthest we can see is about forty three
• 32:15
  Speaker 1: billion light years away or or I guess twenty one
• 32:19
  Speaker 1: billion light years each way, No, it's forty three billion
• 32:22
  Speaker 1: light years in radius. So it's a diameter of more
• 32:25
  Speaker 1: than ninety billion light years across, which is I mean,
• 32:28
  Speaker 1: it's a huge number. Like why anybody even need more
• 32:31
  Speaker 1: universe than that? Well, depends on how many Daniel and
• 32:37
  Speaker 1: jorgees you want? You want. We've got big plans here.
• 32:40
  Speaker 1: Folks need a more room. We need we need more
• 32:43
  Speaker 1: of us obviously, all right, So our current estimate of
• 32:47
  Speaker 1: how big the universe is is ninety six billion light years.
• 32:51
  Speaker 1: What meaning it would take you right now ninety six
• 32:55
  Speaker 1: billion years to go from one end to the other
• 32:57
  Speaker 1: or more, I guess since it's growing. It's growing. Yeah,
• 33:00
  Speaker 1: so you couldn't actually go from one edge of the
• 33:02
  Speaker 1: observed universe to the other because it's growing in space
• 33:05
  Speaker 1: is expanding faster than like can move through it. So
• 33:08
  Speaker 1: a photon on one edge of the of the universe
• 33:11
  Speaker 1: will never reach the other side of the observable universe.
• 33:14
  Speaker 1: So we know at least it right now, as far
• 33:17
  Speaker 1: as we know, is eight six billion light years y. Yeah,
• 33:20
  Speaker 1: and that's the minimum, right, So that's an at least
• 33:22
  Speaker 1: and that's already a really big number. But we know
• 33:25
  Speaker 1: something else about the universe, which is really important. We
• 33:28
  Speaker 1: know not just how far we can see. We know
• 33:30
  Speaker 1: something about the shape of space. We know like how
• 33:33
  Speaker 1: things are curving. All right, let's get into the shape
• 33:36
  Speaker 1: of space and how shapely it is and whether or
• 33:40
  Speaker 1: not it is actually infinite or just crazy big. But
• 33:43
  Speaker 1: first let's take another quick break, all right, Daniel, So
• 33:58
  Speaker 1: we know that the universe right now, or at least
• 34:00
  Speaker 1: at some point is at least eighty six billion light
• 34:04
  Speaker 1: years wide, but we don't know if it if it
• 34:06
  Speaker 1: keeps going on much more than that, or a little
• 34:10
  Speaker 1: bit after that, or maybe that it's actually infinite and
• 34:14
  Speaker 1: it goes on forever beyond eighty six billion light years
• 34:18
  Speaker 1: that we can see. And so I guess the question is,
• 34:21
  Speaker 1: how could we even tell, you know, we're sitting here
• 34:23
  Speaker 1: in this little rock and this tiny galaxy, how could
• 34:27
  Speaker 1: we possibly tell whether the universe goes on forever or not,
• 34:31
  Speaker 1: because we can't really get travel is far, you know,
• 34:34
  Speaker 1: forever to check. Yeah, you're right, in some sense, we
• 34:37
  Speaker 1: know literally nothing about what's passed there. Like there could
• 34:41
  Speaker 1: be crazy blue dragons the size of galaxies out there
• 34:45
  Speaker 1: and we would have no information about it because photons
• 34:48
  Speaker 1: from those dragons haven't reached our eyeballs, and so almost
• 34:52
  Speaker 1: anything could be happening outside the observable universe. So any
• 34:56
  Speaker 1: argument we're gonna make, it's gonna be sort of frustratingly
• 34:59
  Speaker 1: in direc act because we can't go out there. And
• 35:01
  Speaker 1: even if you wait another billion years the observable universe grows,
• 35:06
  Speaker 1: we can see more of it, will never literally never
• 35:09
  Speaker 1: see all of it. Right, It's not like we will
• 35:11
  Speaker 1: could ever prove directly that the universe is infinite. So
• 35:14
  Speaker 1: it's going to rely on some sort of more indirect argument, right,
• 35:18
  Speaker 1: because you could send a probe out there to see
• 35:20
  Speaker 1: if you hit a wall or if it curves around,
• 35:22
  Speaker 1: but you would have to check forever to make sure
• 35:24
  Speaker 1: that the universe doesn't go on forever. So you could
• 35:27
  Speaker 1: prove that the universe is finite, but you can't prove directly,
• 35:31
  Speaker 1: at least that it's infinite. Like you could send a
• 35:33
  Speaker 1: probe out there and it does hit a wall, or
• 35:36
  Speaker 1: it loops back around itself and comes back to Earth
• 35:38
  Speaker 1: and it's very surprised. Right, You could you could make
• 35:41
  Speaker 1: that kind of demonstration, and people have looked, you know,
• 35:43
  Speaker 1: they've looked out of the space to see like our
• 35:45
  Speaker 1: stars repeating, do you see the same pattern over and
• 35:48
  Speaker 1: over again, which would suggest that the universe is sort
• 35:51
  Speaker 1: of small and finite and that light is zoomed through
• 35:54
  Speaker 1: it a few times in the history of the universe.
• 35:57
  Speaker 1: So you could prove that it's finite, but direct that
• 36:00
  Speaker 1: it's infinite is actually impossible. Wow, that's a little disturbing.
• 36:04
  Speaker 1: But we can make some interesting arguments, right. You know
• 36:07
  Speaker 1: you said before you were making arguments before about how
• 36:10
  Speaker 1: unusual or unnatural infinity is we can make sort of
• 36:13
  Speaker 1: the opposite set of arguments. We could argue that infinity
• 36:16
  Speaker 1: is actually the most natural explanation. You can find some
• 36:21
  Speaker 1: mathematical proof that the universe is infinite. You mean, like,
• 36:25
  Speaker 1: from what we can tell about the nature of the universe,
• 36:27
  Speaker 1: it says our formulas say that the universe should be
• 36:30
  Speaker 1: infinite or finite. Yeah, you can make that kind of argument.
• 36:34
  Speaker 1: And while that argument will never be like a satisfactory
• 36:38
  Speaker 1: because you can't ever prove that something is infinite, it
• 36:41
  Speaker 1: could still be pretty satisfactory. And a lot of other
• 36:44
  Speaker 1: things in physics or in science at least we accept
• 36:47
  Speaker 1: with the same level of proof. For example, we think
• 36:51
  Speaker 1: that momentum is conserved everywhere in the universe. You know,
• 36:53
  Speaker 1: we think that every time things bump into each other,
• 36:56
  Speaker 1: that the momentum is the same before and after. We
• 36:58
  Speaker 1: haven't checked every and all time rocks bump into each other,
• 37:02
  Speaker 1: the momentum didn't leak out of the universe somewhere, right,
• 37:05
  Speaker 1: We have a fundamental principle. There's a symmetry about translational
• 37:09
  Speaker 1: invariance that we invoke that we believe, and that momentum conservation,
• 37:13
  Speaker 1: momentum is a consequence of it. So in a similar way,
• 37:16
  Speaker 1: we make some argument that implies the universe has to
• 37:19
  Speaker 1: be infinite, then maybe we could believe it. I see, like,
• 37:23
  Speaker 1: maybe if a conservation of momentum uh necessitates like it
• 37:28
  Speaker 1: needs for the universe to be infinite for it to
• 37:30
  Speaker 1: be true, then we might as well say that, yes,
• 37:32
  Speaker 1: the universe is infinite, because if you believe conservation of momentum,
• 37:35
  Speaker 1: then you have to believe that the universe is infinite. Yes,
• 37:37
  Speaker 1: and I have to necessitate that, right, So you need
• 37:40
  Speaker 1: some theory of how the universe works that requires the
• 37:44
  Speaker 1: universe to be infinite. That so the theory only works
• 37:46
  Speaker 1: if the universe is infinite. And then you need to
• 37:50
  Speaker 1: rule out all other possible theories um and show that
• 37:53
  Speaker 1: the data are consistent with your theory that requires an
• 37:56
  Speaker 1: infinite universe. And in that case you could convince yourself
• 38:00
  Speaker 1: that the universe is infinite. If you had the right
• 38:02
  Speaker 1: pH D thesis, you could make the you could convince
• 38:05
  Speaker 1: yourself of anything. Yeah, And so I went around and
• 38:08
  Speaker 1: I actually asked cosmologists this question, you know, said, can
• 38:11
  Speaker 1: you imagine a theory of inflation or of the early
• 38:14
  Speaker 1: universe or cosmology that only works if the universe is infinite,
• 38:19
  Speaker 1: and that stumped all of them. Really, they couldn't imagine it. Well,
• 38:24
  Speaker 1: we have a theory of the universe. It's inflation. That's
• 38:26
  Speaker 1: most natural if the universe is infinite, but it could
• 38:30
  Speaker 1: probably work in a finite universe also, it can work
• 38:33
  Speaker 1: either way. It doesn't assume an edge. It doesn't assume
• 38:37
  Speaker 1: an edge or curvature. And you know, we've measured the
• 38:39
  Speaker 1: curvature of the universe and we've measured to be really flat,
• 38:43
  Speaker 1: like very very very very flat, and that's consistent with
• 38:46
  Speaker 1: what we think happened the very beginning of the universe.
• 38:48
  Speaker 1: We think the universe expanded really really quickly and that
• 38:51
  Speaker 1: stretched everything out um. But to cosmologists, the universe is
• 38:54
  Speaker 1: either infinite or like ridiculously big, like we're on the
• 38:59
  Speaker 1: surface of a huge sphere. And to them, it doesn't
• 39:02
  Speaker 1: really make that much difference for their calculations because theologists.
• 39:06
  Speaker 1: For the cosmologists, oh man, so everyday people care more
• 39:10
  Speaker 1: about whether the universe is fine it are infinite than cosmologist.
• 39:13
  Speaker 1: Well that's funny because I asked them, like, does it
• 39:15
  Speaker 1: make a difference to your theory whether the universe is
• 39:17
  Speaker 1: actually infinite or just really vast, like you know, like
• 39:20
  Speaker 1: it seems flat because we're on the surface of a
• 39:22
  Speaker 1: huge sphere, but it's actually not and it is. No,
• 39:25
  Speaker 1: it doesn't make any difference. And then I said, well,
• 39:27
  Speaker 1: would you like to know the answer? And then they
• 39:29
  Speaker 1: were like, oh, of course I'm curious, you know, And
• 39:32
  Speaker 1: so in that way they share this wondering curiosity, right,
• 39:36
  Speaker 1: even though it doesn't affect their job either, even as cosmologist.
• 39:40
  Speaker 1: That's right. But I did get an estimate, an estimate
• 39:43
  Speaker 1: of of how crazy the idea his or or what
• 39:46
  Speaker 1: this theory would look like. No, an estimate for sort
• 39:48
  Speaker 1: of the minimum size of the universe, given that what
• 39:51
  Speaker 1: we've measured is that the universe seems flat, than either
• 39:55
  Speaker 1: the universe is infinite or it's at least ten to
• 39:59
  Speaker 1: the ten to the ten to the hundred and twenty
• 40:03
  Speaker 1: two megaparsex wide. What And that's an that's an argument
• 40:10
  Speaker 1: from like looking at the quantum fluctuations in the early
• 40:13
  Speaker 1: universe and asking how did those blow up to give
• 40:17
  Speaker 1: us the universe that we have now, and if so,
• 40:19
  Speaker 1: how much must it have blown up? And that's the
• 40:22
  Speaker 1: number they come up with so if you ask its cosmologies,
• 40:27
  Speaker 1: people who think about the universe and the beginning of it,
• 40:29
  Speaker 1: they have a minimum size of the universe. Some of
• 40:33
  Speaker 1: them do. This is not like a widely believed numbers,
• 40:35
  Speaker 1: just like an estimate some of them, I see. But
• 40:39
  Speaker 1: so some of them, based on what they know about
• 40:41
  Speaker 1: the universe, they think that the universe has to be
• 40:44
  Speaker 1: at least that humongous number big. That's right. But but
• 40:48
  Speaker 1: I think another interesting thing to understand is that to cosmologists,
• 40:51
  Speaker 1: the universe being infinite is sort of the default. It's
• 40:54
  Speaker 1: the idea that makes the most sense to them. They
• 40:56
  Speaker 1: have no trouble with that at all. And the reason
• 40:59
  Speaker 1: is that they invoke a very basic argument. They say, look,
• 41:02
  Speaker 1: the universe should be the same everywhere, and if the
• 41:05
  Speaker 1: universe is finite, then you ask questions like why is
• 41:08
  Speaker 1: it finite? Why is it here? Why is it not
• 41:10
  Speaker 1: over there? And so this sort of like universal principle
• 41:14
  Speaker 1: the universe should look the same everywhere, makes it very
• 41:17
  Speaker 1: natural for them to think of the universe as being infinite. Right,
• 41:20
  Speaker 1: I'm a little suspicious, Daniel. I feel like you asked
• 41:22
  Speaker 1: this because those becausemologies and they they they believe the
• 41:26
  Speaker 1: universe is infinite. But when you pro them to give
• 41:28
  Speaker 1: you a minimum number, they just gave you a ridiculous,
• 41:31
  Speaker 1: made up, fake number. I mean, what kind of numbers
• 41:35
  Speaker 1: like ten to the tent to the tent to the tent.
• 41:37
  Speaker 1: That's that sounds like they just pull that out of
• 41:39
  Speaker 1: their pocket. Well, you know, you can read the paper
• 41:42
  Speaker 1: will link to it from this episode, and there actually
• 41:46
  Speaker 1: is a calculation there, you know, and you start from
• 41:48
  Speaker 1: small quantum fluctuations and what we know about the expansion
• 41:50
  Speaker 1: of the universe, and if you want to get a
• 41:53
  Speaker 1: universe that's this flat where space really does seem flat
• 41:56
  Speaker 1: than either it's infinite or you're on the surface of
• 41:59
  Speaker 1: a doncillous the big sphere of radius. I don't even
• 42:03
  Speaker 1: know what you name that. Oh, I see what you're saying.
• 42:05
  Speaker 1: You're saying that if the universe is finite, then we
• 42:07
  Speaker 1: would see more curvature in it, because that's the only
• 42:11
  Speaker 1: way to explain the finite universes is kind of the
• 42:14
  Speaker 1: sphere or tourist type of thing. Oh I see, nice,
• 42:18
  Speaker 1: but the only so, the only way to explain the
• 42:20
  Speaker 1: flatness that we see is by either assuming the universe
• 42:24
  Speaker 1: is infinite or it's a ridiculous number. Yes, And I
• 42:28
  Speaker 1: hold that hope that you know, someday these cosmologists will
• 42:32
  Speaker 1: think of a reason and will think of a way
• 42:34
  Speaker 1: to actually test the infinitude of the universe. Infinitude that
• 42:39
  Speaker 1: sounds like like a I don't know, like a brand
• 42:42
  Speaker 1: of of of a sound equipment or something. It sounds
• 42:47
  Speaker 1: like sneakers that Bill and Teddible were in their next
• 42:49
  Speaker 1: great adventure. But you know, we're in the early days
• 42:52
  Speaker 1: of understanding this question. You know, we don't understand how
• 42:55
  Speaker 1: the universe came to be. There as a lot of
• 42:57
  Speaker 1: possible constraints there. If we understood the mechanism that created
• 43:00
  Speaker 1: the universe and started inflation, then we can answer questions
• 43:04
  Speaker 1: like is it reasonable to have an infinite number of
• 43:06
  Speaker 1: electrons or just ten to the seventy jillion? And so
• 43:10
  Speaker 1: there's a lot more information coming down the pike, and
• 43:12
  Speaker 1: so I'm optimistic that one day we will know the
• 43:14
  Speaker 1: answer to this question. All right, Well, it sounds kind
• 43:17
  Speaker 1: of like you guys are leaning towards infinite, you know,
• 43:20
  Speaker 1: it definitely sounds like we should all be preparing our
• 43:22
  Speaker 1: brains for the fact that this is an infinite universe
• 43:26
  Speaker 1: and there there's an infinite number of mees out there
• 43:28
  Speaker 1: in other earths, repeating itself after a while. I hope,
• 43:33
  Speaker 1: so you know, I hope the universe goes on forever.
• 43:35
  Speaker 1: It'd be sort of claustrophobic mentally to imagine that there's
• 43:39
  Speaker 1: a limited amount of stuff. You know, that if we
• 43:41
  Speaker 1: somehow we're able to travel the stars, that there's like
• 43:44
  Speaker 1: a full list of all the stars you could visit,
• 43:46
  Speaker 1: and of course it'd be a big number. But it's
• 43:49
  Speaker 1: not that comfortable to imagine that there's an end to
• 43:52
  Speaker 1: that list, that at some point you'd be like, well,
• 43:54
  Speaker 1: I've done them all, kind of like this episode, which
• 43:56
  Speaker 1: we have to wrap up soon because it's not infinite
• 44:00
  Speaker 1: amount of time we have and too bad, right, wouldn't
• 44:02
  Speaker 1: you just like to talk forever? Well? Are you sure?
• 44:08
  Speaker 1: But what people like to listen to us forever? A
• 44:11
  Speaker 1: couple of dudes talking friend infinitude. Daniel and Jorgey Talk Forever,
• 44:18
  Speaker 1: the longest podcast ever. It's just a continuous stream that
• 44:23
  Speaker 1: and you'll never get to the end of it because
• 44:24
  Speaker 1: we keep talking. If you started after we already began talking,
• 44:28
  Speaker 1: you'll never catch up, right right, And after a while
• 44:31
  Speaker 1: we just keep repeating the same jokes, although I don't
• 44:34
  Speaker 1: think you need an infinite universe for that thing, or
• 44:36
  Speaker 1: a podcast. We've already we already closed the curvature of that.
• 44:41
  Speaker 1: I think we've measured the curvature of this podcast. Yeah,
• 44:44
  Speaker 1: it's fairly round. It's about fifty podcasts episodes before we
• 44:48
  Speaker 1: start repeating the jokes. But I think this is one
• 44:50
  Speaker 1: of my funnest questions because it really does touch on
• 44:53
  Speaker 1: our innate curiosity, our desire to understand the way the
• 44:56
  Speaker 1: world works and our place in it, you know, And
• 44:59
  Speaker 1: are we totally insignificant or are we just very insignificant?
• 45:04
  Speaker 1: And that's an important question. All right, Well, but in
• 45:06
  Speaker 1: this universe, we want to thank you for joining us,
• 45:08
  Speaker 1: and we hope you enjoyed that. Thanks to everyone for
• 45:10
  Speaker 1: tuning in and for lending us a non infinite slice
• 45:12
  Speaker 1: of your day. Before you still have a question after
• 45:22
  Speaker 1: listening to all these explanations, please drop us a line.
• 45:26
  Speaker 1: We'd love to hear from you. You can find us
• 45:28
  Speaker 1: on Facebook, Twitter, and Instagram at Daniel and Jorge that's
• 45:32
  Speaker 1: one word, or email us at Feedback at Daniel and
• 45:35
  Speaker 1: Jorge dot com. Thanks for listening, and remember that Daniel
• 45:39
  Speaker 1: and Jorge Explain the Universe is a production of I
• 45:41
  Speaker 1: Heart Radio. For more podcast from my heart Radio, visit
• 45:45
  Speaker 1: the i heart Radio Apple Podcasts, or wherever you listen
• 45:49
  Speaker 1: to your favorite shows. Yeah.