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Is time pixelated? · Daniel and Kelly’s Extraordinary Universe

• 0:01
  Speaker 1: Hey, Jorhan Daniel here, and we want to tell you
• 0:03
  Speaker 1: about our new book. It's called Frequently Asked Questions about
• 0:07
  Speaker 1: the Universe because you have questions about the universe, and
• 0:09
  Speaker 1: so we decided to write a book all about them.
• 0:12
  Speaker 1: We talk about your questions, we give some answers, we
• 0:14
  Speaker 1: make a bunch of silly jokes as usual, and we
• 0:17
  Speaker 1: tackle all kinds of questions, including what happens if I
• 0:20
  Speaker 1: fall into a black hole? Or is there another version
• 0:22
  Speaker 1: of you out there that's right? Like usual, we tackle
• 0:25
  Speaker 1: the deepest, darkest, biggest, craziest questions about this incredible cosmos.
• 0:29
  Speaker 1: If you want to support the podcast, please get the
• 0:31
  Speaker 1: book and get a copy, not just for yourself, but
• 0:34
  Speaker 1: you know, for your nieces and nephews, cousins, friends, parents, dogs, hamsters,
• 0:39
  Speaker 1: and for the aliens. So get your copy of Frequently
• 0:42
  Speaker 1: Asked Questions about the Universe is available for pre order now,
• 0:46
  Speaker 1: coming out November two. You can find more details at
• 0:49
  Speaker 1: the book's website, Universe f a Q dot com. Thanks
• 0:53
  Speaker 1: for your support, and if you have a hamster that
• 0:55
  Speaker 1: can read, please let us know. We'd love to have
• 0:57
  Speaker 1: them on the podcast. Hey Daniel, I have a question
• 1:09
  Speaker 1: for you about time? All right? I got time for that,
• 1:12
  Speaker 1: all right. So you do a lot of things, right,
• 1:14
  Speaker 1: you're a professor, you have a podcast, and you're always
• 1:17
  Speaker 1: switching between them. That's true. It's a lot of different
• 1:20
  Speaker 1: things to manage, all right. So then what do you
• 1:22
  Speaker 1: think is the shortest useful unit of time? Like, can
• 1:27
  Speaker 1: you get something done in five minutes? Or do you
• 1:30
  Speaker 1: need like an hour just to dig into something? Well,
• 1:32
  Speaker 1: you know, sort of depends on what it is. Is
• 1:34
  Speaker 1: it serious research or just like writing bad jokes for
• 1:38
  Speaker 1: the podcast? What do you mean? All right? Well, which
• 1:41
  Speaker 1: one takes more time? Oh? Bad jokes for sure? I
• 1:44
  Speaker 1: mean at some point you just can't scrape that barrel
• 1:46
  Speaker 1: any deeper. What if you just give you more time?
• 1:48
  Speaker 1: As long as you're writing jokes about time, they basically
• 1:50
  Speaker 1: just right themselves. Hi, I'm Jorge. I'm a cartoonist and
• 2:08
  Speaker 1: the creator of PhD comics. I'm Daniel. I'm a particle
• 2:11
  Speaker 1: physicist and a professor, and I never seem to have
• 2:15
  Speaker 1: enough time. Really, can't you just make time in your
• 2:18
  Speaker 1: particle collider? I mean, right, it's called space time. Can
• 2:21
  Speaker 1: you just transform some space into time? You know? What
• 2:24
  Speaker 1: I need to do is to speed up the rest
• 2:26
  Speaker 1: of the world near the speed of light, so it
• 2:28
  Speaker 1: runs slowly, and then I can just get all my
• 2:31
  Speaker 1: work done while everybody else is frozen. Oh that's a
• 2:33
  Speaker 1: good idea. But then you'd be left behind. Everyone would
• 2:35
  Speaker 1: be really far away, you'd be light years away, but
• 2:39
  Speaker 1: you would catch up and work. I would made all
• 2:41
  Speaker 1: my deadlines even though I'd be in the neighboring star system. Yeah,
• 2:45
  Speaker 1: there you go. And then how do you turn your
• 2:46
  Speaker 1: work in? You can't. I knew there was a flaw
• 2:51
  Speaker 1: on this plan. Yeah, you paradox yourself into unemployment. The
• 2:55
  Speaker 1: twin professor paradox. But welcome to our podcast. Daniel and
• 2:58
  Speaker 1: Jorge explained the Universe say production of I Heart Radio,
• 3:01
  Speaker 1: in which we take that mental journey around the universe,
• 3:05
  Speaker 1: speeding your brain up to near the speed of light,
• 3:08
  Speaker 1: so that we can try to understand the very nature
• 3:11
  Speaker 1: of the universe that we find ourselves in, this incredible,
• 3:14
  Speaker 1: glittering cosmos with all of its wonderful questions that it inspires,
• 3:18
  Speaker 1: the things that make us go, huh, why is it
• 3:20
  Speaker 1: like that? Why couldn't it be like this other thing?
• 3:23
  Speaker 1: We dig into all of that on this podcast. We
• 3:26
  Speaker 1: stare right into the abyss of our ignorance, and we
• 3:28
  Speaker 1: ask why, and we do our best to explain what
• 3:31
  Speaker 1: we do and don't know to you. Yeah, because it
• 3:34
  Speaker 1: is a pretty wonderful universe, but it's also kind of
• 3:37
  Speaker 1: a weird universe. We grow up thinking that space is
• 3:40
  Speaker 1: fixed and firm and never changes, but actually it sort
• 3:43
  Speaker 1: of does. It's it's squishy and also kind of ripley.
• 3:46
  Speaker 1: I'm glad it's a weird universe, though, What would it
• 3:49
  Speaker 1: be like if we were doing physics and discovering Yeah,
• 3:52
  Speaker 1: the universe is basically exactly as you thought it was
• 3:55
  Speaker 1: and kind of boring. After all, you would have to
• 3:57
  Speaker 1: switch careers to just writing joke. I don't think I
• 4:02
  Speaker 1: could have that as a career. But I wonder sometimes
• 4:05
  Speaker 1: about how, you know, we find the universe beautiful, We
• 4:08
  Speaker 1: find nature beautiful, and we also find it mysterious and interesting,
• 4:12
  Speaker 1: And I wonder if that's an accident or a product
• 4:15
  Speaker 1: of the way the human mind works, that we just
• 4:17
  Speaker 1: find beauty and mystery everywhere around us. Yeah, or even
• 4:20
  Speaker 1: like the word weird, like why is it weird to us? Right? Like?
• 4:24
  Speaker 1: What makes us the overall judges of what is weird,
• 4:27
  Speaker 1: and what is not? Like, maybe the universe is offended
• 4:29
  Speaker 1: by us calling it weird. Yeah, and then the word
• 4:32
  Speaker 1: weird itself is weird? Mean you say it enough times,
• 4:34
  Speaker 1: it sounds pretty weird. It's got an E and I
• 4:36
  Speaker 1: in it, like weird, weird, weird, it's a pretty weird word. Yeah. Yeah,
• 4:40
  Speaker 1: but that's the English people's fault. Blame it on the Brits.
• 4:44
  Speaker 1: So yeah, it is a pretty, let's say, interesting universe.
• 4:47
  Speaker 1: You think the universe would be offended if we called
• 4:49
  Speaker 1: it interesting, sort of like living in interesting times. No,
• 4:52
  Speaker 1: I think it's good. I think we are lucky. It's
• 4:54
  Speaker 1: one of the things that makes life worth living. You know.
• 4:56
  Speaker 1: People sometimes ask me this question, like why should we
• 4:59
  Speaker 1: fund particle physics? What good is it? And I hear
• 5:02
  Speaker 1: my colleagues making arguments like, well, you know, we might
• 5:05
  Speaker 1: have spinoff technologies or we invented the Worldwide Web. But
• 5:08
  Speaker 1: for me, the true answer is that it explores the universe.
• 5:11
  Speaker 1: It explores the nature of the human existence, sort of
• 5:13
  Speaker 1: the same way like art does you ask an artist like,
• 5:16
  Speaker 1: and why should we pay for art? Why should people
• 5:18
  Speaker 1: write books? Well, it's you know, just part of the
• 5:21
  Speaker 1: joy of life. Is unraveling the mystery of the universe
• 5:24
  Speaker 1: we find ourselves in. That's it, and that's enough. Well,
• 5:27
  Speaker 1: I'm not sure you want to be in the same
• 5:28
  Speaker 1: position that the arts are in trying to get funding
• 5:31
  Speaker 1: using that argument, So I would stick with the Worldwide
• 5:34
  Speaker 1: Web and useful technology for now. To be honest, I
• 5:37
  Speaker 1: think you just haven't asked big enough, Like why don't
• 5:39
  Speaker 1: you pitch your ten billion dollar cartoon to the government.
• 5:42
  Speaker 1: You know, the more you ask for, the more you get.
• 5:45
  Speaker 1: I'm not sure the time is right for that crazy idea,
• 5:48
  Speaker 1: the large hay drawing cartoon. Yeah, there you go. It
• 5:50
  Speaker 1: will break open the universe probably and create imaginary black
• 5:53
  Speaker 1: holes of ink that will swallow up the Earth. That's right,
• 5:56
  Speaker 1: that sounds good. I'd read that my pitching my tax
• 5:58
  Speaker 1: dollars for that. Anyway, we love for the universe is mysterious,
• 6:01
  Speaker 1: and it presents us with really fun, interesting, basic questions,
• 6:05
  Speaker 1: things that we don't understand about, you know, the very
• 6:08
  Speaker 1: like ABC's of reality. Yeah, because I guess you know,
• 6:11
  Speaker 1: we grow up experiencing the universe in one way and
• 6:14
  Speaker 1: we think it works in a certain way in our brains.
• 6:16
  Speaker 1: But really, when you sort of drill down into it,
• 6:18
  Speaker 1: or you scale up to bigger things. There are big
• 6:21
  Speaker 1: surprises and it doesn't work the way we think it does. Yeah,
• 6:24
  Speaker 1: I think of the universe is sort of like a ladder.
• 6:26
  Speaker 1: You know, if you look at it at one distance
• 6:29
  Speaker 1: scale and one time scale, it works a certain way.
• 6:31
  Speaker 1: If you look at another distance scale, like if you're
• 6:34
  Speaker 1: looking at particles or if you're looking at water droplets
• 6:37
  Speaker 1: or galaxies, there seem to be different rules that apply
• 6:41
  Speaker 1: at these different distance scales, and that's fascinating. It makes
• 6:44
  Speaker 1: you wonder, like, are any of these fundamental Are we
• 6:46
  Speaker 1: learning anything really deep and true about the universe? Or
• 6:49
  Speaker 1: does it all just depends on the questions you're asking?
• 6:51
  Speaker 1: And so it's not just scientists who have questions about
• 6:54
  Speaker 1: the universe and about the nature of the universe. It's
• 6:56
  Speaker 1: also our listeners and everyday people just like you. That's right,
• 7:00
  Speaker 1: because remember that science is just people asking questions, and
• 7:03
  Speaker 1: the investigations we do are motivated by the individual questions
• 7:07
  Speaker 1: of individual scientists wondering things about the universe, and that
• 7:11
  Speaker 1: includes you, because we are all out there wondering about
• 7:14
  Speaker 1: the universe and trying to figure it out. So today
• 7:17
  Speaker 1: we are tackling a question that we got from a
• 7:19
  Speaker 1: listener who comes from Sweden. It's Henrik, and Henrik is
• 7:23
  Speaker 1: a pretty interesting question about time. So here is Henrick's question. Hi,
• 7:29
  Speaker 1: I'm Henrik from Sweden and I have been wondering if
• 7:32
  Speaker 1: time could be pixelated? Is there any minimum unit of time?
• 7:37
  Speaker 1: Or could it be infinitely short? And when I listened
• 7:41
  Speaker 1: to your episode about space being pixelated or not, I
• 7:45
  Speaker 1: started wondering if time could be pixelated while space isn't,
• 7:49
  Speaker 1: or vice versa. Thank you guys. All right, it's a
• 7:52
  Speaker 1: pretty interesting question from Henry. So today on the podcast
• 7:55
  Speaker 1: will be tackling is time pixelated? That's a pretty strange question,
• 8:05
  Speaker 1: Is time pixelated? I don't usually associate pixels with time. Yeah,
• 8:10
  Speaker 1: it's a wonderful question, and I love hearing Henrik do physics.
• 8:14
  Speaker 1: You know, he is absorbing what we're talking about and
• 8:17
  Speaker 1: he's taking it to the next natural consequence. And that's
• 8:19
  Speaker 1: what you got to do with the theory. You say,
• 8:21
  Speaker 1: all right, well, this describes what I'm thinking about or
• 8:23
  Speaker 1: describes what I've seen. Can I extrapolate from it to
• 8:26
  Speaker 1: the rest of the universe or what are the consequences
• 8:29
  Speaker 1: of it? How can I test and explore this? So
• 8:32
  Speaker 1: that's exactly doing physics. So kudos to you, Henrick, for
• 8:35
  Speaker 1: doing some physics in your mind. Yeah, Daniel will be
• 8:37
  Speaker 1: sending you a check in the mill right now, right
• 8:40
  Speaker 1: after this podcast. I'm gonna email you some Swedish fish,
• 8:43
  Speaker 1: my favorite Swedish candy. All right. So then it's a
• 8:45
  Speaker 1: pretty interesting question. And Henrick was saying that he listened
• 8:48
  Speaker 1: to an episode that we had about whether or not
• 8:50
  Speaker 1: space is pixelated. So there's this idea that space could
• 8:53
  Speaker 1: be pixelated, meaning like it's not smooth and continuous, maybe
• 8:57
  Speaker 1: it's like a grid or something, or it's disc rate
• 9:00
  Speaker 1: at the very smallest level. And his question is whether
• 9:03
  Speaker 1: or not it applies to time as well. That's right,
• 9:06
  Speaker 1: because we often talk on the podcast about how space
• 9:08
  Speaker 1: and time are related, and then in relativity at least
• 9:11
  Speaker 1: we see them as parts of space time a four
• 9:15
  Speaker 1: dimensional object. So it's a very natural question. Yeah, and
• 9:18
  Speaker 1: so what did we conclude in that podcast episode about
• 9:20
  Speaker 1: space being pixelated? We concluded that we don't know, and
• 9:23
  Speaker 1: we might never know, but there are good reasons to
• 9:26
  Speaker 1: think that space might be pixelated, right, due to like
• 9:30
  Speaker 1: quantum physics and they're being like a theoretical plank scale
• 9:33
  Speaker 1: to the universe as well. Right, exactly, we don't know
• 9:36
  Speaker 1: how small the pixels of space are if they exist,
• 9:39
  Speaker 1: and we have a very simple, kind of bad estimate
• 9:42
  Speaker 1: for how small they might be, just by multiplying constants
• 9:45
  Speaker 1: of the universe together. And it's very very small number,
• 9:48
  Speaker 1: like ten to the minus thirty five meters. That's not
• 9:52
  Speaker 1: a measurement of how small the space pixels are or
• 9:54
  Speaker 1: proof that space pixels exist. But if you have no
• 9:57
  Speaker 1: other information about how to estimate it, this is all
• 10:00
  Speaker 1: you can do. It gives you a sense for like
• 10:02
  Speaker 1: what the neighborhood of the size might be, all right,
• 10:04
  Speaker 1: So then if you're curious, you can look up that
• 10:06
  Speaker 1: episode in our archive. But today we're talking about time
• 10:10
  Speaker 1: and whether it's pixelated, and so, as usually, we were
• 10:12
  Speaker 1: wondering how many people out there have thought about this
• 10:15
  Speaker 1: question or had had time to think about this question
• 10:17
  Speaker 1: at least a pixel of time and maybe had an
• 10:20
  Speaker 1: answer for it. So Daniel went out there into the
• 10:22
  Speaker 1: internet to ask listeners is time pixelated? And so if
• 10:26
  Speaker 1: you have time to donate your thoughts on random physics
• 10:30
  Speaker 1: questions for future podcast episodes. Please don't be shy, right
• 10:34
  Speaker 1: to me. Two questions at Daniel and Jorge dot com.
• 10:37
  Speaker 1: So think about it for a second. Do you think
• 10:38
  Speaker 1: there is a minimum amount of time in the universe?
• 10:42
  Speaker 1: Here's what people had to say. I guess if you
• 10:44
  Speaker 1: zoomed in far enough, time might be pixelated, like if
• 10:49
  Speaker 1: you imagined it as a film strip, if you zoomed
• 10:52
  Speaker 1: in just millions and millions and millions of times, that
• 10:59
  Speaker 1: it would beam moving sort of in frames, as if
• 11:02
  Speaker 1: like a movie kind of thing. Tom, pixelation, haven't heard
• 11:06
  Speaker 1: of it? Um, tell me about it. Sounds crazy, Yes,
• 11:14
  Speaker 1: it's a usual thing. So do you think it's pixelated
• 11:17
  Speaker 1: or continuous? Okay, it's continuous? Okay? Wow? Man, I don't
• 11:26
  Speaker 1: even know how to wrap my head around this question.
• 11:29
  Speaker 1: Is time pixelated? What does that even mean? Is it
• 11:33
  Speaker 1: just like if a second is a pixel or even
• 11:35
  Speaker 1: nano second is a pixel. I have no idea how
• 11:38
  Speaker 1: to answer this question. I really don't know what that
• 11:41
  Speaker 1: question means. Maybe like, is is time quantized in some form? Honest?
• 11:49
  Speaker 1: I have no idea time. It's very strange. A lot
• 11:53
  Speaker 1: we don't know. I'm not sure. I think that there
• 11:57
  Speaker 1: are some theories that suggest it might be, but I
• 12:00
  Speaker 1: don't know that we've measured that definitively. My understanding of
• 12:04
  Speaker 1: the measuring of time is that it's not infinitely divisible,
• 12:08
  Speaker 1: that it is hypothesized that ultimately you'll get two units
• 12:15
  Speaker 1: of time that are so short you can't get any short.
• 12:18
  Speaker 1: And I think it's referred to as plunk time pixilated
• 12:23
  Speaker 1: like all the video games. I'm not sure about. The
• 12:31
  Speaker 1: term doesn't seem right. I'm probably not. I have no
• 12:36
  Speaker 1: idea from a physics standpoint, but from a perception standpoint,
• 12:42
  Speaker 1: I feel like it is um and I think deja
• 12:46
  Speaker 1: vu has something to do with that. It's like it
• 12:49
  Speaker 1: arrives into my brain in little packets and then my
• 12:54
  Speaker 1: brain goes and smooths it all out after the fact,
• 12:58
  Speaker 1: so that it in my memories it seems like it's
• 13:01
  Speaker 1: all smooth, and I can't actually sense what's going on
• 13:05
  Speaker 1: in real time. I have no idea what that means.
• 13:09
  Speaker 1: I guess not because I think it's continuous with the
• 13:14
  Speaker 1: way that Madam moves in space. All right. Not a
• 13:19
  Speaker 1: lot of ideas here. Maybe people didn't spend enough time
• 13:22
  Speaker 1: thinking about it. They only thought one or two units
• 13:25
  Speaker 1: of time on this and they should have at least
• 13:26
  Speaker 1: been ten or two. Yeah, it's a tough question. It
• 13:29
  Speaker 1: seems to have puzzled people. Most people just throw their
• 13:31
  Speaker 1: hands up in the air and said, I don't know. Yeah,
• 13:33
  Speaker 1: it seems a little bit more foreign to people than
• 13:36
  Speaker 1: the idea that space is pixelated, like you're familiar with
• 13:39
  Speaker 1: looking at a screen, the idea of locations being a
• 13:43
  Speaker 1: grid that makes some sense. But the idea of time
• 13:46
  Speaker 1: being pixelated, that you know that there are discrete units
• 13:49
  Speaker 1: of time as we move forward, that we're stepping forward
• 13:53
  Speaker 1: instead of sliding forward, that seems to be a little
• 13:55
  Speaker 1: bit more alien. Yeah, so let's maybe tackle this one
• 14:00
  Speaker 1: kind of idea at a time. So, first of all,
• 14:01
  Speaker 1: what would it mean for time to be pixelated? Would
• 14:04
  Speaker 1: it mean like you can cut up time or you
• 14:06
  Speaker 1: can step through time in small increments, but at some
• 14:09
  Speaker 1: point there comes a point where you can take smaller
• 14:12
  Speaker 1: steps in time. There's sort of two very different but
• 14:16
  Speaker 1: closely related ways for time to be discreet, for there
• 14:20
  Speaker 1: to be like a minimal, sensible unit of time. The
• 14:23
  Speaker 1: first is what you were just talking about. This idea
• 14:26
  Speaker 1: of pixelization, and pixelization is something we think about for space, right,
• 14:30
  Speaker 1: like pixels on the screen. You can either be at
• 14:33
  Speaker 1: x equals seven or x equals eight, but you can't
• 14:36
  Speaker 1: be at x equals seven and a half. So that's
• 14:39
  Speaker 1: very natural sense for space and for time. The idea
• 14:43
  Speaker 1: would be that things step forwards in time, that you
• 14:47
  Speaker 1: could be like time equals one point seven or time
• 14:50
  Speaker 1: equals one point eight, but there is no time equals
• 14:52
  Speaker 1: one point seven and a half. That the universe just
• 14:55
  Speaker 1: goes from one point seven boom to one point eight.
• 14:58
  Speaker 1: It's like ticks on a clock, but there's no moment
• 15:01
  Speaker 1: in between the ticks, Like you can't have a half
• 15:03
  Speaker 1: of a second or something like that. Yeah, and you know,
• 15:06
  Speaker 1: obviously seconds aren't the minimum immunity of time. You can't
• 15:09
  Speaker 1: have half of a second. If time units exist, but
• 15:11
  Speaker 1: there's a minimum discrete chunk of time, it would be
• 15:14
  Speaker 1: super duper small. So that to us it seems continuous, right,
• 15:18
  Speaker 1: and you think it doesn't exist or like what happens
• 15:21
  Speaker 1: in between those two times? Yeah, well what does it
• 15:24
  Speaker 1: mean for the universe to be in between those times?
• 15:27
  Speaker 1: It's like it doesn't have a meaning, Like time is
• 15:31
  Speaker 1: here and time is there, but in between there isn't anything.
• 15:34
  Speaker 1: It just doesn't exist. This is something that's sort of
• 15:36
  Speaker 1: familiar to us from learning quantum mechanics, that not everything
• 15:41
  Speaker 1: has like a smooth classical path, you know, like an electron.
• 15:44
  Speaker 1: You measure it here and then you later you measure
• 15:47
  Speaker 1: it over there. Does that mean that it went from
• 15:49
  Speaker 1: here to there? No, it just means it was here
• 15:52
  Speaker 1: and then it was there. It doesn't have to have
• 15:54
  Speaker 1: a location in between. We think of everything as smooth
• 15:59
  Speaker 1: and continuous because that's the way it seems to us,
• 16:01
  Speaker 1: because we're kind of big and slow. But the universe,
• 16:05
  Speaker 1: as you were saying earlier, could be drastically different from
• 16:07
  Speaker 1: the way we experience it, all right, So that's one
• 16:10
  Speaker 1: possibility that time just doesn't exist in between time pixels,
• 16:14
  Speaker 1: like there's a grade of the time in the universe.
• 16:17
  Speaker 1: And that's actually something that makes sense to us sort
• 16:19
  Speaker 1: of numerically, like when we simulate things in the computer.
• 16:23
  Speaker 1: You want to describe, for example, how a hurricane moves
• 16:26
  Speaker 1: or how galaxies form, and we want to simulate them.
• 16:29
  Speaker 1: That's exactly how we do it. We make a grid
• 16:31
  Speaker 1: in time, and we step our simulated universe forward. We say,
• 16:35
  Speaker 1: something's happening right now, what's going to happen at the
• 16:37
  Speaker 1: next time step, and you can decide is it going
• 16:39
  Speaker 1: to be a nanosecond in the future or ten minutes
• 16:41
  Speaker 1: in the future. Depends on how much computing time you have.
• 16:45
  Speaker 1: But it's very natural to step things forward in time
• 16:47
  Speaker 1: in simulations, right, You do simulations with time steps. But
• 16:51
  Speaker 1: simulations are not perfect, right, and that that's one of
• 16:53
  Speaker 1: the main reasons is that they do have sort of
• 16:55
  Speaker 1: a resolution. It doesn't do it continuously like the universe
• 16:58
  Speaker 1: sort of seems to be. Yeah, exactly, they're not continuous,
• 17:01
  Speaker 1: they're discreet. And you're right that you want really small
• 17:03
  Speaker 1: time steps so that you're extrapolating in a reasonable way.
• 17:07
  Speaker 1: But it might be that the universe actually does have
• 17:09
  Speaker 1: the same sort of time steps, and if you did
• 17:11
  Speaker 1: your simulation with a time step equal to that of
• 17:13
  Speaker 1: the universe, then it would be perfect. But wow, that
• 17:17
  Speaker 1: would be weird, right, Like the universe would be operating
• 17:19
  Speaker 1: at the minimum possible time step because but the computer
• 17:23
  Speaker 1: is in the universe, so that would blows my mind
• 17:26
  Speaker 1: a little bit. But all right, So that's the first
• 17:28
  Speaker 1: kind of time pixelization. What's the second. The second is
• 17:31
  Speaker 1: that time isn't actually pixelized in the sense that you
• 17:35
  Speaker 1: could have any value of time. It's not like values
• 17:39
  Speaker 1: in between one point seven and one point eight are disallowed.
• 17:42
  Speaker 1: If you try to measure like when did something happen?
• 17:45
  Speaker 1: You could get any number between one point seven and
• 17:47
  Speaker 1: one point eight. All those values are real and possible.
• 17:51
  Speaker 1: In this idea, though, there's a minimum resolution, like you
• 17:54
  Speaker 1: can't measure differences in time that are smaller than a
• 17:57
  Speaker 1: certain number, Like if you measure something twice, you can't
• 18:00
  Speaker 1: get two measurements that are closer than a certain minimum distance,
• 18:04
  Speaker 1: but you can get any value. So it's sort of
• 18:06
  Speaker 1: like you have this minimum resolution, but it can slide
• 18:09
  Speaker 1: up and down the time scale where and land wherever. Okay,
• 18:13
  Speaker 1: I think I know what you're saying. You're saying that
• 18:14
  Speaker 1: maybe like every possible time step exists or is possible,
• 18:18
  Speaker 1: like you can have one point oh three seconds and
• 18:21
  Speaker 1: up one point two four seven seconds, but maybe at
• 18:26
  Speaker 1: some point, at some scale of smallness and time, it
• 18:29
  Speaker 1: just kind of becomes random or fuzzy or sort of unknowable. Yeah, exactly,
• 18:34
  Speaker 1: And we can think about that because we think about
• 18:36
  Speaker 1: quantum particles in exactly that way. Like an electron is quantized, right,
• 18:41
  Speaker 1: it's a single object quantized of the electron field. So
• 18:45
  Speaker 1: it's got a certain like natural width to it, below
• 18:49
  Speaker 1: which you can't really probe where its location is, but
• 18:52
  Speaker 1: it could be anywhere. It can live in continuous space.
• 18:56
  Speaker 1: If space is continuous, you can still have discrete objects
• 18:59
  Speaker 1: in side of it. And in that same way, time
• 19:01
  Speaker 1: might be like fundamentally continuous, but there might be a
• 19:05
  Speaker 1: minimum basic resolution of time below which the time difference
• 19:08
  Speaker 1: between two events has no meaning, no meaning, but it exists,
• 19:12
  Speaker 1: but it's sort of random. And because it's random, you're
• 19:15
  Speaker 1: saying it doesn't have any meaning. But is that really
• 19:17
  Speaker 1: pixelated though? Like it's so it doesn't fit our idea
• 19:20
  Speaker 1: of a pixel, right, It's more like there's no pixel,
• 19:23
  Speaker 1: but it's sort of fuzzy at a certain scale. Yeah, exactly.
• 19:25
  Speaker 1: It sets a scale which I think that the physicist
• 19:28
  Speaker 1: is interesting because it means that you can't infinitely divide time.
• 19:32
  Speaker 1: That was the other part of Hendrick's question, like can
• 19:34
  Speaker 1: you have infinitely small slices in time? Does it make
• 19:37
  Speaker 1: sense to think about things happening at one moment and
• 19:40
  Speaker 1: then tend to the minus one thousand seconds later, Like
• 19:44
  Speaker 1: does their universe really evolve things step by step at
• 19:48
  Speaker 1: that granularity. And what this would tell you is not
• 19:51
  Speaker 1: that things are locked into specific numbers, but that it
• 19:54
  Speaker 1: makes no sense to think about steps in time that
• 19:57
  Speaker 1: are that small. You can just make stuff u It's
• 20:01
  Speaker 1: unknown and it's undetermined, right in the same way that like,
• 20:05
  Speaker 1: not all the information about an electron is knowable, not
• 20:08
  Speaker 1: just because we can't measure it, but because it's not
• 20:11
  Speaker 1: specified as undetermined. In that same way, pieces of time
• 20:15
  Speaker 1: smaller than like whatever is the minimum resolution and time
• 20:18
  Speaker 1: are not known or knowable. All right, Well, those are
• 20:21
  Speaker 1: the two ways in which time could be pixelated, and
• 20:23
  Speaker 1: so let's get into why we think it might be
• 20:26
  Speaker 1: pixelated and whether or not we'll ever know if it
• 20:29
  Speaker 1: is or not. But first let's take a quick break.
• 20:44
  Speaker 1: All right, we're asking the question is time pixelated? And
• 20:48
  Speaker 1: so we had a whole episode about whether space was pixelated,
• 20:51
  Speaker 1: and we had all those reasons there. But now we're
• 20:54
  Speaker 1: asking if time is pixelated, And so the question is
• 20:57
  Speaker 1: why do we think time might be pixelated? It seems
• 20:59
  Speaker 1: pretty continuous and smooth to me. It does seem continuous
• 21:03
  Speaker 1: and smooth, but you know, our intuition breaks down when
• 21:06
  Speaker 1: we try to apply it to things that are much
• 21:08
  Speaker 1: much faster or much much smaller, and they reveal that
• 21:12
  Speaker 1: the rules of the universe are really pretty different. Of course,
• 21:14
  Speaker 1: when you zoom out to things like our skill, those
• 21:17
  Speaker 1: rules do sort of coalesce to recover our experience. So
• 21:21
  Speaker 1: it's amazing that you can have like one set of
• 21:23
  Speaker 1: rules for the very tiny particles and it can all
• 21:26
  Speaker 1: sort of work together to conspire to give a very
• 21:29
  Speaker 1: different kind of universe at the human scale. Right, So
• 21:31
  Speaker 1: then maybe step us through. What are some of the
• 21:33
  Speaker 1: arguments for saying that time is pixelated and what are
• 21:36
  Speaker 1: maybe some of the arguments against it being pixelated? Well,
• 21:39
  Speaker 1: I think there's a few elements here. One is, you know,
• 21:42
  Speaker 1: what is more natural? Like what do we expect to
• 21:45
  Speaker 1: be the truth? Like, is continuity of time really the
• 21:49
  Speaker 1: most natural thing? Or in the end, is discreete this
• 21:53
  Speaker 1: more natural? What would make more sense to us was
• 21:56
  Speaker 1: the sort of default position. And I think a lot
• 21:58
  Speaker 1: of people out there would assume, well, continuousness, right, like
• 22:01
  Speaker 1: time should flow smoothly. It seems to flow smoothly to me,
• 22:05
  Speaker 1: But you know that doesn't mean that that's the case.
• 22:08
  Speaker 1: You know, you watch TV and it seems to flow continuously,
• 22:11
  Speaker 1: but you know deep down that it is actually discreete.
• 22:13
  Speaker 1: Your television is not updating infinitely many times per second.
• 22:18
  Speaker 1: And that's the key, is that continuity, having continuous time,
• 22:22
  Speaker 1: implies a sort of infinity, and we just don't see
• 22:25
  Speaker 1: infinities in nature very often, right, Yeah, I guess like
• 22:28
  Speaker 1: if you showed it a four K, you know, high
• 22:31
  Speaker 1: resolution television to somebody from the you know, a tenth century,
• 22:35
  Speaker 1: they would probably be fooled into thinking like there's actually
• 22:38
  Speaker 1: something magical, real going on inside of it to be
• 22:40
  Speaker 1: but really it's you know, flashing, you know, twenty nine
• 22:43
  Speaker 1: times a second, and it's really only like two thousand
• 22:46
  Speaker 1: by two thousand pixels exactly. And continuity is really strange,
• 22:50
  Speaker 1: Like to imagine an infinite amount of information as the
• 22:53
  Speaker 1: universe evolves forwards, it's sort of like Zeno's paradox, Like
• 22:57
  Speaker 1: how do you even get from one second to two
• 22:59
  Speaker 1: seconds if you have to go through an infinite number
• 23:02
  Speaker 1: of sub seconds to get there? You know, it feels
• 23:05
  Speaker 1: like at some point you've got to take an actual
• 23:07
  Speaker 1: step forward, and to do that, you can imagine a
• 23:10
  Speaker 1: minimum unit of time where the universe is finally like
• 23:14
  Speaker 1: ticking over Otherwise, how does it even leave the one
• 23:17
  Speaker 1: second mark if it's always taking a smaller and smaller
• 23:19
  Speaker 1: and smaller and infinitely smaller step forwards. So you're saying
• 23:22
  Speaker 1: that a continuous universe sort of makes sense to us
• 23:25
  Speaker 1: from our experience, but it starts to break down when
• 23:27
  Speaker 1: you really drill into it, because you come up with infinities.
• 23:30
  Speaker 1: You do, you come up into infinities. And what we've
• 23:33
  Speaker 1: discovered is we look around us in the universe, is
• 23:35
  Speaker 1: that discreetness is actually much more natural. Like the things
• 23:39
  Speaker 1: that we see around us that seem continuous are actually discreet.
• 23:43
  Speaker 1: Like that chair you're sitting on right now. It seems
• 23:45
  Speaker 1: like it has a smooth surface, right, but it doesn't.
• 23:48
  Speaker 1: It's actually a lattice. A lattice is a network of
• 23:51
  Speaker 1: points that are tied together to approximate a smooth surface.
• 23:56
  Speaker 1: And if you zoom out, of course it looks smooth,
• 23:58
  Speaker 1: but if you zoom in far enough, it looks like
• 24:00
  Speaker 1: a chain link fence, you know, and a beam of
• 24:03
  Speaker 1: light that is shining on your plants, it's actually a
• 24:06
  Speaker 1: bunch of packets of photons. So the world around you,
• 24:09
  Speaker 1: though it seemed continuous, almost everything about it is actually discreet.
• 24:14
  Speaker 1: I see you're saying, because maybe the space and physical
• 24:17
  Speaker 1: things around this are sort of pixelated in a way
• 24:20
  Speaker 1: through discrete, then it would sort of make sense for
• 24:23
  Speaker 1: time to also be pixelated, exactly. And that's sort of
• 24:25
  Speaker 1: a natural intuitive argument, right, And it doesn't really hold
• 24:28
  Speaker 1: that much water. It's just sort of to get you
• 24:30
  Speaker 1: in the mindset of thinking, maybe discreete is the more
• 24:33
  Speaker 1: natural outcome instead of continuous. Right, then you need to
• 24:36
  Speaker 1: be persuaded against being discrete instead of being persuaded against
• 24:40
  Speaker 1: it being continuous. Right. But I guess the universe doesn't
• 24:42
  Speaker 1: care about what we think are our opinion of it.
• 24:45
  Speaker 1: So what are sibility I guess more of physically robust
• 24:48
  Speaker 1: arguments for or against time pixelation. Right. And so it
• 24:51
  Speaker 1: turns out that when you drill down into the very
• 24:54
  Speaker 1: small time and the very small space, what you do
• 24:57
  Speaker 1: is you run into questions about how gravity works. You know,
• 25:01
  Speaker 1: in very very small spaces. Now you have things like
• 25:04
  Speaker 1: particles moving around, and you get into questions of like
• 25:07
  Speaker 1: what are the forces between those particles? And if you
• 25:10
  Speaker 1: have very very short time, then you're talking about very
• 25:12
  Speaker 1: very high energy gravity kicks in and in the end
• 25:15
  Speaker 1: you need to know something about how quantum gravity works,
• 25:19
  Speaker 1: like what are the gravitational effects for very high energies
• 25:23
  Speaker 1: and very short distances, And people who are working on
• 25:26
  Speaker 1: quantum gravity these theories of like, you know, what is
• 25:29
  Speaker 1: the fundamental nature of space? Is it sliced up into
• 25:32
  Speaker 1: pieces or not? Are there gravitons? All these fun questions.
• 25:35
  Speaker 1: They make a lot of arguments about space being discreete
• 25:38
  Speaker 1: and we can dig into those in a minute. And
• 25:40
  Speaker 1: almost all of those arguments also apply to time because
• 25:44
  Speaker 1: space and time are very closely related. So the physical
• 25:48
  Speaker 1: arguments that there might be a minimum unity to space,
• 25:51
  Speaker 1: a lot of those same arguments you can use to
• 25:54
  Speaker 1: make minimum unit of time. Yeah, because I guess in
• 25:58
  Speaker 1: physics there is this idea that time is just another
• 26:02
  Speaker 1: dimension maybe or it's like you know the fourth leg
• 26:05
  Speaker 1: and the table that is space time, and that it's
• 26:08
  Speaker 1: somehow like the same thing, right, you sort of think
• 26:10
  Speaker 1: about it that way in physics. Yeah, and it's even
• 26:13
  Speaker 1: more closely connected. Let me give you an example. You
• 26:15
  Speaker 1: can make a pretty simple argument that there should be
• 26:18
  Speaker 1: a minimum unit of space, and then you can take
• 26:21
  Speaker 1: the same argument and use it for time. So it
• 26:23
  Speaker 1: goes like this. You say, let's, for example, try to
• 26:26
  Speaker 1: measure a particle. What happens if you try to measure
• 26:28
  Speaker 1: a particle really really precisely, so you know it's position,
• 26:32
  Speaker 1: like basically exactly well. Quantum mechanics says, if you know
• 26:36
  Speaker 1: something's position really really well, then you don't know it's
• 26:39
  Speaker 1: momentum very very well. Right that the more precisely you
• 26:42
  Speaker 1: measure the position, the less you know about the momentum.
• 26:45
  Speaker 1: That means that this particle now has a huge uncertainty
• 26:48
  Speaker 1: on its momentum, so much so that it might have
• 26:52
  Speaker 1: enough momentum basically enough energy to create a black hole.
• 26:57
  Speaker 1: And once you create a black hole, well, then you
• 26:59
  Speaker 1: can no longer measure something about this particle because it's
• 27:01
  Speaker 1: inside a black hole. So, like, these very simple arguments
• 27:05
  Speaker 1: suggest that there's a minimum distance below which you can't
• 27:09
  Speaker 1: measure something because if you did, it would turn into
• 27:11
  Speaker 1: a black hole and prevent you from measuring it. So
• 27:14
  Speaker 1: that's the argument about space, And you can make a
• 27:16
  Speaker 1: very similar argument about time. WHOA, you just kind of
• 27:22
  Speaker 1: skipped through a few time steps there. You're saying the argument,
• 27:24
  Speaker 1: like one argument for space being pixelated is that you know,
• 27:28
  Speaker 1: if you don't have a pixel to the universe. Then
• 27:30
  Speaker 1: basically kind of like um, things can be anything at
• 27:34
  Speaker 1: a certain level, and one of those things could be
• 27:36
  Speaker 1: a black hole, and that's that's impossible or is that's
• 27:38
  Speaker 1: weird or are you saying that we don't see that.
• 27:40
  Speaker 1: I'm saying that the universe has a mechanism to prevent
• 27:43
  Speaker 1: you from knowing something very precisely, because if you knew
• 27:47
  Speaker 1: it that precisely, it would turn into a black hole,
• 27:49
  Speaker 1: and then censored that information. So it's sort of like
• 27:52
  Speaker 1: a fundamental limit there, because if you ask questions deeply enough,
• 27:56
  Speaker 1: basically the universe responds by covering things up with black holes.
• 27:59
  Speaker 1: And we don't see that, thankfully, which means that the
• 28:02
  Speaker 1: universe does have sort of like a fundamental maybe a
• 28:06
  Speaker 1: pixelation of space. Yeah, although we can't really do this experiment,
• 28:09
  Speaker 1: like how could you measure a particle with such precision
• 28:12
  Speaker 1: that it's momentum would be so uncertain that it might
• 28:14
  Speaker 1: turn into like a microscopic black hole. So that's not
• 28:17
  Speaker 1: an experiment we could do. We'd love to do that
• 28:19
  Speaker 1: experiment and observe microscopic quantum black holes. Wow, we would
• 28:22
  Speaker 1: learn so much. It's just really sort of a thought
• 28:24
  Speaker 1: experiment that demonstrates how if you ask precise enough a question,
• 28:28
  Speaker 1: the universe sort of counters with a black hole to
• 28:31
  Speaker 1: prevent you from learning about it. But how do you
• 28:33
  Speaker 1: know those black holes aren't there? Maybe they are there,
• 28:34
  Speaker 1: but they're so small you can't see them. Yeah, maybe
• 28:37
  Speaker 1: they are there, but it still means that you can't
• 28:39
  Speaker 1: know the position of this particle to a certain resolution
• 28:43
  Speaker 1: because it turns into a black hole, and you can't
• 28:45
  Speaker 1: measure what's inside a black hole. Okay, so that's an
• 28:48
  Speaker 1: argument for space being pixelated. So then how do you
• 28:50
  Speaker 1: translate that into time? Well, the relationship and quantum mechanics
• 28:54
  Speaker 1: between position and momentum, there's exactly the same relationship between
• 28:58
  Speaker 1: energy and time. And if you want to make a
• 29:00
  Speaker 1: bunch of measurements of a particle at very very small
• 29:03
  Speaker 1: time steps like now, and then tend to the mind
• 29:06
  Speaker 1: is one hundred seconds later, that introduces uncertainty in the
• 29:10
  Speaker 1: particle's energy. So time and energy have the same relationship
• 29:14
  Speaker 1: and quantum mechanics as position and momentum. It's another of
• 29:17
  Speaker 1: the Heisenberg and certainty principles. And so if you measure
• 29:20
  Speaker 1: a particle trajectory in time very very precisely. Then you
• 29:24
  Speaker 1: create the same uncertainty in its energy, which allows it
• 29:27
  Speaker 1: to potentially have enough energy to create a black hole,
• 29:29
  Speaker 1: and boom, cosmic censorship rises again. I see, But isn't
• 29:34
  Speaker 1: it maybe even the same argument, right, because I feel
• 29:37
  Speaker 1: like momentum is sort of related to velocity and velocities
• 29:40
  Speaker 1: like distance divided by time, So it really aren't you
• 29:43
  Speaker 1: just making the same argument twice, except that you know
• 29:46
  Speaker 1: you're using the fact that time and space and velocity
• 29:50
  Speaker 1: are related to each other to carry over the argument, right, Like,
• 29:54
  Speaker 1: couldn't maybe space be pixelated but time not pixelated. But
• 29:58
  Speaker 1: because they're related when you're trying to measure velocities, then
• 30:02
  Speaker 1: it implies that time is pixelated. That's exactly the argument. Yeah,
• 30:06
  Speaker 1: it says that space and time are very closely connected,
• 30:09
  Speaker 1: and therefore an argument you can use to pixelate space
• 30:12
  Speaker 1: is going to also give you pixelization of time. Right,
• 30:15
  Speaker 1: But maybe time is fundamentally not pixelated. It just appears
• 30:18
  Speaker 1: pixelated because spaces or maybe space is not fundamentally pixelated,
• 30:23
  Speaker 1: but time is. Right, Yeah, that's what I mean. I
• 30:26
  Speaker 1: feel like, Yeah, I feel like that's not really an
• 30:28
  Speaker 1: argument four time being pixelated, right, I see that's interesting.
• 30:31
  Speaker 1: That's a philosophical question. I think that it shows you
• 30:34
  Speaker 1: that the two things have the same relationship, so it
• 30:37
  Speaker 1: makes the most ends for them to both be pixelated
• 30:40
  Speaker 1: or not. In this case, quantum mechanics suggests that they
• 30:43
  Speaker 1: both are. But I see that other interpretation. Yeah, all right,
• 30:45
  Speaker 1: So there is an argument for time being pixelated, and
• 30:49
  Speaker 1: it has to do with quantum mechanics, and so that
• 30:52
  Speaker 1: sort of the uncertainty principle. So then, but do you
• 30:54
  Speaker 1: have then have a reason of why space and time
• 30:56
  Speaker 1: are pixelated like that? And it all comes down to
• 31:00
  Speaker 1: what happens at these very very small distance scales when
• 31:02
  Speaker 1: you have a lot of energy, and this is the
• 31:04
  Speaker 1: province of quantum gravity. And unfortunately, we don't have a
• 31:08
  Speaker 1: strong theory of quantum gravity, Like we don't have a
• 31:11
  Speaker 1: theory that works that describes what happens when gravity comes
• 31:15
  Speaker 1: into play with quantum objects and that gravity is strong.
• 31:19
  Speaker 1: If we did, then it would lay out for us
• 31:21
  Speaker 1: what is the minimum unit of time, what is the
• 31:23
  Speaker 1: minimum unity of space if there is one at all,
• 31:26
  Speaker 1: And the different flavors of quantum gravity that we're considering,
• 31:30
  Speaker 1: the different ideas people are working on for what's going
• 31:32
  Speaker 1: on at the very smallest scale and how this all works.
• 31:35
  Speaker 1: Have sort of different approaches to dealing with minimum distance
• 31:39
  Speaker 1: and minimum time. But I guess, couldn't you take the
• 31:43
  Speaker 1: sort of theoretical size of the space pixel and then
• 31:47
  Speaker 1: convert that to a time pixel because you're saying they're
• 31:50
  Speaker 1: sort of related or tied together. Yes, exactly, and that's
• 31:53
  Speaker 1: what's done, for example, in loop quantum gravity. Loop quantum
• 31:57
  Speaker 1: gravity says maybe the universe is not continuous in space.
• 32:01
  Speaker 1: It quantizes space itself, right, instead of trying to quantize
• 32:04
  Speaker 1: gravity is a maybe gravity is a quantum theory and
• 32:08
  Speaker 1: you're exchanging gravitons. It says, takes space itself and imagine
• 32:12
  Speaker 1: it not to be smooth and continuous, but like a
• 32:15
  Speaker 1: big foam, like a bunch of tiny little bubbles that
• 32:17
  Speaker 1: are all linked together as these loops. And so it's
• 32:21
  Speaker 1: very natural to think about space as having a minimum
• 32:23
  Speaker 1: distance in loop quantum gravity. It's actually essential because in
• 32:27
  Speaker 1: loop quantum gravity, if space has no minimum distance, then
• 32:31
  Speaker 1: a bunch of the calculations they do give nonsense results.
• 32:34
  Speaker 1: You get like infinities and craziness. So it sort of
• 32:36
  Speaker 1: saves the whole theory to have these minimum values, so
• 32:40
  Speaker 1: they rely on that, and the same arguments can be
• 32:43
  Speaker 1: used in loop quantum gravity to argue for minimum steps
• 32:46
  Speaker 1: in time, so like maybe space is pixelated or foamy,
• 32:50
  Speaker 1: but gravity is maybe continuous. But this would sort of
• 32:53
  Speaker 1: merge quantum mechanics and relativity together exactly. And I actually
• 32:57
  Speaker 1: asked Carlo Ravelli about this yesterday. He's an expert in
• 33:00
  Speaker 1: loop quantum gravity, and I asked him if in looke
• 33:03
  Speaker 1: quantum gravity you could have a theory that is patilated
• 33:07
  Speaker 1: in space but continuous in time, or if you absolutely
• 33:11
  Speaker 1: had to have discrete time as well, And he said
• 33:15
  Speaker 1: that he thinks that the theory is on solid footing
• 33:18
  Speaker 1: from the point of view of space pixels that you
• 33:21
  Speaker 1: can represent areas having discrete units. So that's very solid
• 33:25
  Speaker 1: and very confident about that. And he says that you
• 33:27
  Speaker 1: can do something similar with time, but there are some
• 33:29
  Speaker 1: complicated jumps you have to make in the argument, and
• 33:32
  Speaker 1: he wasn't a confident in it. But he also said
• 33:36
  Speaker 1: that he would be very surprised if anything that included
• 33:40
  Speaker 1: time and it's a measurement could really have a continuous
• 33:42
  Speaker 1: spectrum because from his point of view, the world is quantum,
• 33:46
  Speaker 1: everything about the universe is discrete, and then he would
• 33:49
  Speaker 1: be very surprised if time was any different. It seems
• 33:51
  Speaker 1: like the theorists don't think time is continues, that it's
• 33:56
  Speaker 1: maybe more likely or would make more sense, that it's
• 33:59
  Speaker 1: pixelated exactly in loop quantum gravity, it makes most sense
• 34:02
  Speaker 1: for time to be pixelated in the same way that
• 34:05
  Speaker 1: space is. Now there are other theories of quantum gravity,
• 34:09
  Speaker 1: theories like string theory, that have a different approach on
• 34:12
  Speaker 1: minimum units of time. Well, I guess maybe the question
• 34:16
  Speaker 1: that a lot of people might be thinking at this
• 34:18
  Speaker 1: point is that would it makes sense for time to
• 34:20
  Speaker 1: be pixelated or could it still be continuous? And one hand,
• 34:23
  Speaker 1: it makes perfect sense for time to be chopped up
• 34:26
  Speaker 1: in the minimum units, because, as we say, quantum mechanics
• 34:30
  Speaker 1: tells us that the universe is discrete, right, But there's
• 34:33
  Speaker 1: a problem when you do that. Introducing like a minimum
• 34:36
  Speaker 1: time scale or a minimum length scale is tricky because
• 34:40
  Speaker 1: we know from the other great theory of the universe relativity,
• 34:44
  Speaker 1: that things like distances and times are not universal. So like,
• 34:48
  Speaker 1: for example, if we're in the laboratory and we're measuring
• 34:51
  Speaker 1: the universe down to its minimum distance. We have some
• 34:54
  Speaker 1: pair of tweezers that can work at the plank length.
• 34:57
  Speaker 1: For example, what happens if somebody is zooming by the
• 35:00
  Speaker 1: spaceship and they're watching our experiment, They see us like
• 35:03
  Speaker 1: length contracted. They see everything shortened because they're moving at
• 35:07
  Speaker 1: a fast speed relative to us. So then they would
• 35:10
  Speaker 1: be seeing things at smaller than the minimum distance. So like,
• 35:13
  Speaker 1: having a minimum distance breaks special relativity in a really
• 35:17
  Speaker 1: important way. Right, what do you mean It doesn't break
• 35:21
  Speaker 1: relativity in a way. It just means that it's it's
• 35:24
  Speaker 1: all sort of relative. Right, Like to someone moving at
• 35:26
  Speaker 1: a certain speed, the minimum distance in the universe would
• 35:29
  Speaker 1: be this much, and to someone not moving at that speed,
• 35:32
  Speaker 1: it would be this much, but it would still have
• 35:33
  Speaker 1: a minimum distance. Yeah, if you assert the primacy of relativity,
• 35:37
  Speaker 1: then you're giving up an absolute minimum distance. You're saying
• 35:39
  Speaker 1: minimum distance is not really minimum, it's relative. But if
• 35:42
  Speaker 1: you start from the other direction, you say, no, there's
• 35:44
  Speaker 1: an absolute minimum distance anybody can measure, no matter how
• 35:48
  Speaker 1: their speed. Then that would break relativity. If you can't
• 35:51
  Speaker 1: have the two things at the same time, you can
• 35:53
  Speaker 1: have one, but then it breaks the other one. So
• 35:55
  Speaker 1: you're saying that a pixelated universe, even a space pixelated universe,
• 36:00
  Speaker 1: would break relativity or it's not consistent with relativity exactly.
• 36:04
  Speaker 1: It's inconsistent with special relativity, which we thought until now
• 36:07
  Speaker 1: was like pretty well established, Like we have measured it
• 36:10
  Speaker 1: out the wazoo and it works pretty well. But you know,
• 36:13
  Speaker 1: these directions in quantum gravity really do suggest that there
• 36:16
  Speaker 1: might be space pixels. But that's fundamentally inconsistent with special relativity.
• 36:21
  Speaker 1: So that's a big puzzle to work out. I see,
• 36:23
  Speaker 1: safe relativity is true, as Einstein said, then the universe
• 36:28
  Speaker 1: is not pixelated, or it can't be pixelated, or it
• 36:30
  Speaker 1: doesn't make sense for it to be pixelated. Yeah, and
• 36:32
  Speaker 1: you know we're focusing today on pixels in time. There's
• 36:35
  Speaker 1: another consequence of having pixels in time. You know, if
• 36:38
  Speaker 1: the universe is not continuous, if it's discreet, right, if
• 36:42
  Speaker 1: you can have like time equals one point five seconds
• 36:45
  Speaker 1: and one point six seconds but not time equals one
• 36:47
  Speaker 1: point five five seconds, that means the time is not
• 36:50
  Speaker 1: smooth and the universe sort of cares what time you're
• 36:53
  Speaker 1: at that you can't like do the same experiment halfway
• 36:56
  Speaker 1: between time pixels, and that actually has a really important consequence.
• 37:00
  Speaker 1: As we've talked about once on the podcast before. This
• 37:02
  Speaker 1: basic concept that energy in the universe is conserved that
• 37:06
  Speaker 1: relies on an assumption, and that assumption is that space
• 37:09
  Speaker 1: has a symmetry in time, that space always looks the same,
• 37:13
  Speaker 1: that the universe doesn't care when you do an experiment.
• 37:16
  Speaker 1: It's just could happen now or later or yesterday. You know,
• 37:20
  Speaker 1: it doesn't care about your deadlines. And discrete time breaks
• 37:23
  Speaker 1: that it says there are special values of time that
• 37:26
  Speaker 1: makes sense, and so that would throw conservation of energy
• 37:29
  Speaker 1: out the window. So if you have discrete units of time,
• 37:33
  Speaker 1: then basically you break conservation of energy. That seems like
• 37:37
  Speaker 1: an important rule in the universe. Yeah, so we're breaking
• 37:39
  Speaker 1: all the rules today. All right, Well, I guess what
• 37:42
  Speaker 1: I'm getting is that it makes sense for time to
• 37:45
  Speaker 1: be pixelated by some arguments like loop quantum theory and
• 37:49
  Speaker 1: thinking about space being pixelated, but it doesn't make any
• 37:51
  Speaker 1: sense for it to be pixelated from other points of
• 37:54
  Speaker 1: view like relativity or conservation of energy. All right, well,
• 37:57
  Speaker 1: let's get into our last question, which is how would
• 37:59
  Speaker 1: we even know if time is pixelated. Could we device
• 38:03
  Speaker 1: an experiment to tell us whether or not it's true
• 38:05
  Speaker 1: or whether it will be a mystery until the end
• 38:08
  Speaker 1: of time? But first, let's take another quick break. All right,
• 38:24
  Speaker 1: is time pixelated? I guess Daniel, The biggest question is
• 38:27
  Speaker 1: how would we know? Like, are we trapped in the
• 38:30
  Speaker 1: matrix and we think times smooth and continuous, and are
• 38:33
  Speaker 1: we always gonna be trapped in this matrix thinking that
• 38:36
  Speaker 1: it's continuous or will we ever be able to step
• 38:38
  Speaker 1: outside of time and see that it's actually you know, discrete. Unfortunately,
• 38:42
  Speaker 1: we might never know. You know, it might be that
• 38:46
  Speaker 1: time is continuous and we are hunting forever for the
• 38:49
  Speaker 1: minimum unit and not finding it, but not finding it
• 38:52
  Speaker 1: doesn't mean it doesn't exist. So there's a possibility that
• 38:55
  Speaker 1: we could always be frustrated, sort of like you know,
• 38:58
  Speaker 1: finding the smallest particle. You never really know if it's
• 39:01
  Speaker 1: the smallest particle or if there's a smaller particle inside
• 39:04
  Speaker 1: that that's so small you can't see it. But that
• 39:07
  Speaker 1: would be sort of a limitation of our technology, right
• 39:10
  Speaker 1: or is that always gonna be true because you know,
• 39:13
  Speaker 1: you're sort of like you can't prove a negative kind
• 39:16
  Speaker 1: of or you know, since infinity is forever, there's no
• 39:19
  Speaker 1: way we can never get down to the small enough
• 39:22
  Speaker 1: level to be sure that it's not pixelated. You know,
• 39:24
  Speaker 1: I think there are ways that we could like convince
• 39:26
  Speaker 1: ourselves that it probably is pixelated, but it'd be pretty
• 39:30
  Speaker 1: hard to prove that it's not, you know, pretty hard
• 39:33
  Speaker 1: to prove that it's infinitely continuous. I think you need
• 39:36
  Speaker 1: some pretty elaborate theory of physics that requires that that
• 39:39
  Speaker 1: has some other consequences somehow that I can't even imagine
• 39:42
  Speaker 1: that you could then confirm. So I think it's easier
• 39:44
  Speaker 1: to prove that it is discrete than to prove that
• 39:47
  Speaker 1: it's continuous. But you just gave me some arguments for
• 39:50
  Speaker 1: why space might be pixelated, right with the whole infinitely
• 39:53
  Speaker 1: small black holes. Couldn't we come up with a theory
• 39:55
  Speaker 1: or some sort of way or some sort of consequence
• 39:58
  Speaker 1: over the theory of the equation to say that, look it,
• 40:01
  Speaker 1: time has to be pixelated. Yeah, exactly. I think that's
• 40:03
  Speaker 1: the best way forward. If we come up with a
• 40:06
  Speaker 1: rigorous theory of quantum gravity and it requires, because of
• 40:10
  Speaker 1: its very nature, you know, for time to be pixelated,
• 40:13
  Speaker 1: and then that theory holds together and makes a bunch
• 40:15
  Speaker 1: of predictions. You know, maybe not directly showing us the
• 40:18
  Speaker 1: clock ticks of the universe, but having other consequences of
• 40:23
  Speaker 1: that it's inherent nature. Then we can be pretty confident
• 40:26
  Speaker 1: that the universe is pixelated when it comes to time.
• 40:29
  Speaker 1: All right, Well, then how could we hope to prove
• 40:32
  Speaker 1: that it is pixelated? Then? What kinds of experiments can
• 40:34
  Speaker 1: we make or what experiments have been made so so far?
• 40:37
  Speaker 1: The edge of our knowledge is basically particle colliders. Particle
• 40:42
  Speaker 1: colliders smash particles together at very very high energy, which
• 40:46
  Speaker 1: is the same thing as saying that they're studying things
• 40:48
  Speaker 1: at very very small distance scales. Remember that the energy
• 40:52
  Speaker 1: of an object controls its effective wave function right at
• 40:56
  Speaker 1: the width of its wave function, and really really high
• 40:58
  Speaker 1: energy object is one with very high frequency, which means
• 41:02
  Speaker 1: that you can localize it to very specific place. And
• 41:05
  Speaker 1: so with very high energy particles you can probe things
• 41:08
  Speaker 1: really small distances. Or think about it another way, the
• 41:11
  Speaker 1: more you crank of the energy of your particle colliders,
• 41:14
  Speaker 1: the smaller the particles you can discover, because you can
• 41:17
  Speaker 1: break them open and see small things inside them. So
• 41:20
  Speaker 1: we've made a lot of progress there, and we are
• 41:22
  Speaker 1: studying things that are like tend the minus twenty meters wide,
• 41:27
  Speaker 1: you know, quarks that are inside the proton. So that
• 41:29
  Speaker 1: sounds pretty small, right, It's like ten to the minus
• 41:32
  Speaker 1: twenty meters is a very small slice of the universe.
• 41:36
  Speaker 1: But you know it's ten to the fifteen times bigger
• 41:39
  Speaker 1: than what we think is the Plank scale, which is
• 41:41
  Speaker 1: tend of the minus thirty five meters. And that's a
• 41:44
  Speaker 1: big ratio, right, Yeah, you just need more money, tenie,
• 41:48
  Speaker 1: just as the taxpayers for more money. Yeah, we should
• 41:51
  Speaker 1: siphon funds out of your ten billion dollar comics project.
• 41:55
  Speaker 1: You can't touch that. Some some things are more important
• 41:57
  Speaker 1: than understanding the nature of the universe, that's right. But
• 42:00
  Speaker 1: that's a limited distance, right, that's not quite the limited
• 42:03
  Speaker 1: time or is it the equivalent you're saying. I'm saying
• 42:06
  Speaker 1: their equivalent because these experiments also happened really really fast,
• 42:09
  Speaker 1: and to be really really fast you have to have
• 42:12
  Speaker 1: really really high energy also, and so fundamentally, these high
• 42:15
  Speaker 1: energy experiments are probing short times and small distances at
• 42:20
  Speaker 1: the same time. But unfortunately they're like way too weak
• 42:24
  Speaker 1: to probe really the fundamental nature of the universe and
• 42:27
  Speaker 1: to make them big enough and powerful enough to probe
• 42:30
  Speaker 1: that distance scale you need like a collider the size
• 42:33
  Speaker 1: of the Solar System or maybe even the galaxy. So
• 42:36
  Speaker 1: it's not even something we even imagine asking for a
• 42:39
  Speaker 1: little too expensive to make a collider of the size
• 42:41
  Speaker 1: of the Solar system. So then what can we do? What?
• 42:44
  Speaker 1: What are alternatives to break in the bank here to
• 42:46
  Speaker 1: find the answer? So people are trying to come up
• 42:48
  Speaker 1: with tabletop experiments, things you can do in a single
• 42:51
  Speaker 1: laboratory to probe either directly, like the discrete nature of
• 42:56
  Speaker 1: space and time, or to try to like do really
• 42:58
  Speaker 1: subtle experiments to understand quantum gravity. There's some really cool
• 43:02
  Speaker 1: ideas developing experiments that might really work and could actually
• 43:06
  Speaker 1: help us understand how things work at the smallest scale.
• 43:09
  Speaker 1: The first idea was proposed about ten years ago by Bekenstein.
• 43:12
  Speaker 1: He's a guy who worked closely with Stephen Hawking to
• 43:15
  Speaker 1: develop the understanding of black holes that we have today,
• 43:18
  Speaker 1: so definitely a smart person. And he had this crazy
• 43:21
  Speaker 1: idea of shooting a single photon at a crystal. And
• 43:25
  Speaker 1: the idea is that what happens when you shoot a
• 43:27
  Speaker 1: photon at a crystal. It's a quantum object. Either it
• 43:30
  Speaker 1: gets absorbed or it doesn't. And if it gets absorbed,
• 43:33
  Speaker 1: then you know where does its momentum go like pushes
• 43:36
  Speaker 1: the crystal a little bit, the same way we talk about,
• 43:39
  Speaker 1: you know, like solar sales, shooting photons from the sun
• 43:43
  Speaker 1: and hitting a sale of pushing a spacecraft forward. This
• 43:46
  Speaker 1: is like a mini version of that, where you shoot
• 43:48
  Speaker 1: a single photon at a crystal and if it gets absorbed,
• 43:51
  Speaker 1: it needs to like move forward a little bit. And
• 43:54
  Speaker 1: so the idea is to like tune the energy of
• 43:56
  Speaker 1: the photon so it matches like the basic minimum distance
• 44:01
  Speaker 1: of the universe, so you can measure somehow if this
• 44:05
  Speaker 1: crystal like slides forward a tiny bit. All right, So
• 44:09
  Speaker 1: you're shooting a photon, and I guess you make the
• 44:11
  Speaker 1: photon small enough that maybe you'll see that jump between
• 44:14
  Speaker 1: like oh it hit the crystal and oh it didn't
• 44:17
  Speaker 1: hit the crystal, which would sort of tell you that
• 44:19
  Speaker 1: the universe is not continuous. Is that kind of what
• 44:22
  Speaker 1: the experiment would be doing. Yeah, that's the idea that
• 44:25
  Speaker 1: you have like lots of these little photons and they're
• 44:27
  Speaker 1: interacting with elements of the crystal. If you tune in
• 44:30
  Speaker 1: just right, they have like just enough energy to move
• 44:33
  Speaker 1: it one like quantum universe step forwards. And so this
• 44:37
  Speaker 1: is an idea that beckn Seem proposed about ten years ago,
• 44:41
  Speaker 1: and some people thought it was very exciting, like, oh wow,
• 44:43
  Speaker 1: maybe we could measure quantum gravity on a tabletop. Other
• 44:46
  Speaker 1: folks I've asked have frankly said it's probably bullcrap and
• 44:48
  Speaker 1: would never work. I see, all right, so that's a
• 44:51
  Speaker 1: no no. What are other ways in which we could
• 44:53
  Speaker 1: maybe figure out if time is pixelated? Well, the really,
• 44:56
  Speaker 1: I think the most promising way to figure out if
• 44:58
  Speaker 1: time is pixelated is to try to get it these
• 45:01
  Speaker 1: theories of quantum gravity, to understand, you know, basically the
• 45:04
  Speaker 1: nature of space and time itself, and to do it
• 45:07
  Speaker 1: all at once. So these aren't experiments where you can
• 45:09
  Speaker 1: like see the universe take forward in time, but they
• 45:12
  Speaker 1: are experiments that might help reveal the very nature of
• 45:15
  Speaker 1: space and time, which we give us clues about whether
• 45:18
  Speaker 1: space and time are pixelated. And the way to make
• 45:21
  Speaker 1: progress there is to try to see gravity having influence
• 45:24
  Speaker 1: on individual particles, because we don't know how gravity works
• 45:28
  Speaker 1: when it comes to little particles like we know how
• 45:30
  Speaker 1: gravity works when it comes to the Earth and the Moon,
• 45:33
  Speaker 1: or the Earth and the Sun for example, or even
• 45:36
  Speaker 1: black holes. But we don't know what happens between two particles.
• 45:39
  Speaker 1: Are they like passing little gravitons back and forth? Are
• 45:42
  Speaker 1: they bending space? Is space discrete? There? Like? What we
• 45:46
  Speaker 1: need to do is see really strong gravitational effects on particles.
• 45:50
  Speaker 1: The problem, of course, is that particles have almost no
• 45:53
  Speaker 1: mass and so they have almost no gravity. But we've
• 45:56
  Speaker 1: gotten pretty good recently at building larger quantum of objects,
• 46:00
  Speaker 1: like getting a whole bunch of particles and getting them
• 46:03
  Speaker 1: like in sync together into one quantum state like a
• 46:07
  Speaker 1: Bose Einstein condensate or something similar, where you can make
• 46:10
  Speaker 1: like larger and larger objects that have quantum properties, and
• 46:14
  Speaker 1: maybe we can make them large enough that we can
• 46:17
  Speaker 1: start to see the gravitational effects between like clumps of
• 46:20
  Speaker 1: quantum objects. I see, like if you make a big
• 46:23
  Speaker 1: enough quantum object, you would see how anything quantum interacts
• 46:26
  Speaker 1: with gravity. Because right now we don't really know, right
• 46:29
  Speaker 1: like our theories breakdown when you try to make quantum
• 46:33
  Speaker 1: particles interact with gravity. We just don't know what happens
• 46:36
  Speaker 1: when quantum particles are feeling gravity. And so what we've
• 46:40
  Speaker 1: done so far is made things like Bose Einstein condensates
• 46:44
  Speaker 1: that have like, you know, maybe up to a thousand
• 46:47
  Speaker 1: atoms in them, these tiny little blobs of stuff. And
• 46:50
  Speaker 1: that's really not big enough to observe any gravity, because remember,
• 46:53
  Speaker 1: gravity is the weakest force out there. But we're making progress,
• 46:57
  Speaker 1: and it's the kind of thing where like in ten
• 46:58
  Speaker 1: years undergrads will be doing that in their freshman physics lab.
• 47:02
  Speaker 1: It'll be very easy or be like on a computer
• 47:04
  Speaker 1: chip kind of thing, And in the basements of research
• 47:07
  Speaker 1: facilities they will be like having quantum diamonds and superpositions
• 47:11
  Speaker 1: and doing crazy experiments. But I guess maybe the question is,
• 47:14
  Speaker 1: you know, that might help us figure out if gravities quantized,
• 47:17
  Speaker 1: but how does that help us know if time is
• 47:19
  Speaker 1: quantized or pixelated. Yeah, it will tell us if gravity
• 47:22
  Speaker 1: is a quantum theory or not, you know, or if
• 47:25
  Speaker 1: space is quantized or not. So it will sort of
• 47:27
  Speaker 1: help us get direction theoretically for how to tackle this
• 47:32
  Speaker 1: very question about the nature of space and time. So
• 47:34
  Speaker 1: it won't directly tell us if time is pixelated, it
• 47:37
  Speaker 1: will give us a lot of clues about how to
• 47:39
  Speaker 1: build a theory of quantum gravity, and gravity of course
• 47:42
  Speaker 1: very closely connected to space and time, so it'll sort
• 47:45
  Speaker 1: of like help us lay the foundations to maybe eventually
• 47:48
  Speaker 1: get there. But it's you know, it's nice to know
• 47:51
  Speaker 1: that we might be able to do some experiments that
• 47:53
  Speaker 1: can help us figure out if gravity is quantum or not,
• 47:57
  Speaker 1: so that we can try to get our heads around
• 47:59
  Speaker 1: these basic questions. Is about the nature of space and time, right,
• 48:02
  Speaker 1: But even if you find out the gravity is quantized
• 48:04
  Speaker 1: and spaces quantized, you still wouldn't technically right. Maybe possibly
• 48:07
  Speaker 1: now if time itself is also quantized, like we said earlier,
• 48:11
  Speaker 1: it could be the one of the is quantized on
• 48:12
  Speaker 1: the other one is not. But it depends on the
• 48:14
  Speaker 1: details of your quantum theory. Right, So if you discover,
• 48:17
  Speaker 1: for example, string theory is right, then string theory says, well,
• 48:20
  Speaker 1: time is sort of continuous, but there are is a
• 48:22
  Speaker 1: minimum resolution below which it doesn't make sense to ask questions.
• 48:26
  Speaker 1: Or if you discover oh no, it looks like loop.
• 48:28
  Speaker 1: Quantum gravity is correct and Carlo Revelli was right and
• 48:31
  Speaker 1: time is also quantized, So it might help you because
• 48:34
  Speaker 1: it would reveal the quantum theory that describes space and time,
• 48:38
  Speaker 1: which might require time to be continuous or smooth, or
• 48:42
  Speaker 1: it might show us that none of our ideas are
• 48:44
  Speaker 1: correct in something else totally weird and new is required,
• 48:47
  Speaker 1: and time might not be quantized. It might be something
• 48:49
  Speaker 1: else totally different than we haven't even imagined. It might
• 48:52
  Speaker 1: be a different time. It would be time for a
• 48:55
  Speaker 1: new idea. It will be a timely discovery. Yeah, so
• 48:58
  Speaker 1: I would say that in summary. You know, it's not
• 49:00
  Speaker 1: something that we're gonna be able to directly probe very easily,
• 49:03
  Speaker 1: but we can get around to it's sort of at
• 49:04
  Speaker 1: the back by trying to build a consistent theory of
• 49:07
  Speaker 1: space and time, which requires understanding quantum gravity. Because you
• 49:11
  Speaker 1: don't think there is there could ever be an experiment
• 49:13
  Speaker 1: that could test it directly. I think those experiments require
• 49:17
  Speaker 1: such enormous energy they're effectively like creating black holes, and
• 49:22
  Speaker 1: so it's hard to imagine you ever doing experiments at
• 49:24
  Speaker 1: that scale, right, Who would ever make a black hole
• 49:27
  Speaker 1: on purpose? I would. I totally would sign me up.
• 49:32
  Speaker 1: I'm not saying I wouldn't want to. I'm just saying
• 49:34
  Speaker 1: I don't think it's possible. I think maybe it's time
• 49:36
  Speaker 1: to cut short this episode now before we introduce too
• 49:40
  Speaker 1: many bad ideas into a physicist brain. All right, well,
• 49:43
  Speaker 1: I guess the question is yet to be determines. There
• 49:45
  Speaker 1: are their arguments for time being pixelated and arguments against
• 49:48
  Speaker 1: time being pixelated. It sounds like we might never know.
• 49:51
  Speaker 1: But if we make enough progress just in basic, you know,
• 49:54
  Speaker 1: fundamental theories of the universe, maybe it'll come up. Hopefully
• 49:57
  Speaker 1: it will come up. Is that kind of the planned there,
• 50:00
  Speaker 1: Let's focus on something else and let's procrastinate, and maybe
• 50:04
  Speaker 1: we'll come up on its own. Let's figure out the
• 50:06
  Speaker 1: foundations of everything, and maybe along the way we'll solve
• 50:09
  Speaker 1: this other problem. All right, and maybe we'll find more
• 50:12
  Speaker 1: time for you, Daniel, to do all the things we
• 50:14
  Speaker 1: wanted to all right, Well again, I think it's an
• 50:16
  Speaker 1: interesting reminder of how much we don't know about the universe,
• 50:19
  Speaker 1: about basic things like space and time, and it's time
• 50:22
  Speaker 1: that we figure them out. It's always a good time
• 50:24
  Speaker 1: for for physics, right, It's always a good time, and
• 50:27
  Speaker 1: there's always a good time for physics, and physicists are
• 50:30
  Speaker 1: always a good time and that's the But that's a
• 50:32
  Speaker 1: theoretical conjecture there, Daniel that's never been proven in the lab.
• 50:36
  Speaker 1: No experiments have proven that. I think unfortunately that's true.
• 50:40
  Speaker 1: Maybe we should collige physicist together and just see what
• 50:42
  Speaker 1: happens that. Now, that sounds like fun. That sounds like
• 50:44
  Speaker 1: a good time to you. All right, Well, we hope
• 50:46
  Speaker 1: you enjoyed that. Thanks for giving us your time, See
• 50:49
  Speaker 1: you next time. Thanks for listening, and remember that Daniel
• 50:59
  Speaker 1: and or Hey Explain the Universe is a production of
• 51:02
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• 51:05
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• 51:09
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