Speaker 1: Hey or hey, I think it's time we confronted a
Speaker 1: really tricky topic. Do you think we have time for that?
Speaker 1: You know, there's no time like the present. It could
Speaker 1: be a good time. It might be a fun way
Speaker 1: to pass some time. All right, I'll make time for it.
Speaker 1: It's about time. That's so corny. How many time puns
Speaker 1: can one fit into a single podcast? That's right? How
Speaker 1: much time do you have? Um, I've got time. I
Speaker 1: think it's a timely set of puns. Well, you use
Speaker 1: that pun time after time, commending else. Now is the
Speaker 1: time to start the podcast. Now is the time to
Speaker 1: tackle this tricky topic. I am and I'm Daniel. It's
Speaker 1: time for our podcast, Daniel and Jorge Explain the Universe,
Speaker 1: a production of I Heart Radio in which we take
Speaker 1: everything about the universe, the now, the future, the past,
Speaker 1: the deep, deep, deep past and try to explain it
Speaker 1: to you. That's worry. We take the time to take
Speaker 1: a little bit of your time and maybe get you
Speaker 1: to understand a little bit more about this amazing and
Speaker 1: spacious place that we live in called the universe. That's right.
Speaker 1: And sometimes we have to grapple with topics that are
Speaker 1: sort of obvious. You know sort of things that are
Speaker 1: right in front of you and understand like does physics
Speaker 1: know how to make sense of it? Does physics have
Speaker 1: a good definition of it? Do we understand why it's
Speaker 1: this way and not that way? That's right? And so
Speaker 1: today we're tackling a topic that is probably in everybody's
Speaker 1: mind all the time. That's right. This is something you
Speaker 1: think about every day from when your alarm clock goes
Speaker 1: off to when it's time to go to bed. To
Speaker 1: stay on the podcast, we will be talking about out time.
Speaker 1: What is time anyway? Yeah? And why does it only
Speaker 1: go forwards? Why do you remember the past and not
Speaker 1: the future? Can you remember the future? That would be
Speaker 1: pretty cool. Well, that's the whole question. Right on one hand,
Speaker 1: very intuitive understanding of time. We all know what time
Speaker 1: is right, yesterday was yesterday, tomorrow's tomorrow, right now is now,
Speaker 1: But when you get down to it, we don't really
Speaker 1: understand why we have it right. Why is it like that?
Speaker 1: Why does it only go forwards? Why is the future
Speaker 1: different from the past. Yeah, it's weird to think that
Speaker 1: we are in the pressing right now and there's a
Speaker 1: past going backwards in time, and there's a future going
Speaker 1: forwards in time? But what's really the difference between those
Speaker 1: two things? Yeah? Why can't I see or feel or
Speaker 1: have any kind of memory about the future? Yeah? Exactly
Speaker 1: what makes it different? Why is the past fixed? Right,
Speaker 1: unchangeable unless you believe in crazy science fiction time travel stories,
Speaker 1: which I don't, and the future undetermined? Right? What's the difference?
Speaker 1: Can physics reveal that? Is there some understanding of time?
Speaker 1: From physics? It tells us why one is different from
Speaker 1: the other? Yeah? Why is there an arrow of time
Speaker 1: like a one way sign in the universe, in the
Speaker 1: highway of time of the universe? Yeah, this is one
Speaker 1: of those wonderful questions because on the surface of it
Speaker 1: it seems kind of dumb, Like somebody asks you what
Speaker 1: is time? You're gonna tell him, Oh, it's three o'clock.
Speaker 1: And if they dig deeper and ask you though, like
Speaker 1: what does time even mean? Man? Sometimes I say it's
Speaker 1: two o'clock. Depending on the circumstances, I always give the
Speaker 1: same answer no matter what. That way, people stop asking.
Speaker 1: My kids are aways what time is it? And they
Speaker 1: have like a watch on their hand. There's like two
Speaker 1: watches on the wall, Like why are you asking me?
Speaker 1: So I would just say it's three o'clock no matter what,
Speaker 1: so that they stop. It sounds like it sounds like
Speaker 1: the same parenting strategy my my wife has when we
Speaker 1: going road trips to always ask how long are we
Speaker 1: do we get there? Is it? Are we there yet?
Speaker 1: And she always answers, nope, scant twenty more hours, no
Speaker 1: matter what. You're like pulling into the place, and she's like,
Speaker 1: twenty more hours, yeah, no matter what, she always says
Speaker 1: twenty It's a great strategy. You know, me and your wife,
Speaker 1: we would really get along. It seems like we see
Speaker 1: eye to eye about how to handle these approaches. How Tom,
Speaker 1: you would have some very um sarcastic kids probably exactly. Um. Anyway,
Speaker 1: I love these questions you know that are like, on
Speaker 1: the surface so simple, when you dig deep, they reveal
Speaker 1: like enormous gaps in our knowledge about the universe. Those
Speaker 1: questions are the best because those are the opportunities to
Speaker 1: reveal that the universe is different from the way we understood.
Speaker 1: Like the way we think about the universe reflects just
Speaker 1: our experience, the way we've lived and grown up, and
Speaker 1: not something fundamental, something universal, right, And that's the whole
Speaker 1: goal of physics. Yeah, it's one of those questions, like
Speaker 1: it makes you kind of look almost inwards or look
Speaker 1: in your like you one day you just wake up
Speaker 1: and you don't even know where you're standing, or how
Speaker 1: how the house that you live in was built. Who
Speaker 1: don't lose grasp of reality there? Or or hey, we're
Speaker 1: trying to dig deeper, trying to make you go crazy.
Speaker 1: Doesn't it make it kind of question at like the
Speaker 1: very nature of the universe. It does. It's sort of
Speaker 1: like if you say a word like a hundred times,
Speaker 1: like say the word marriage a hundred times, it starts
Speaker 1: to turn into a really weird word. Right, you take
Speaker 1: it apart, you look at you like, that's really strange.
Speaker 1: It's the same thing with the concept of time, Like
Speaker 1: you know, pick up your hand and rub your fingers together, right,
Speaker 1: you're feeling that right now? Right? But what does now mean?
Speaker 1: Right now? Sort of like it's always it's infinitely short,
Speaker 1: and it's slipping constantly into the past. You can never
Speaker 1: grasp onto it, you can never hold it, right, it's
Speaker 1: always you're always losing it. It's a really strange concept
Speaker 1: of concept of now. Yeah. Yeah, although I don't know
Speaker 1: if that's what makes marriage weird. But there's lots of
Speaker 1: things that make marriage weird. Um, saying it a hundred
Speaker 1: times is not it. But I remember reading a book
Speaker 1: about consciousness back when I was really interested in the
Speaker 1: science of consciousness, which we can talk about another podcast.
Speaker 1: But the basic idea in that book, as by Daniel
Speaker 1: Dennit it's called Consciousness Explained, is that there is no
Speaker 1: now that you're the consciousness is basically an illusion that
Speaker 1: all you're ever doing is remembering the immediate past. And
Speaker 1: I don't know if I believe that, but it really
Speaker 1: made me think about what now is and how you
Speaker 1: can never really grasp it. It's always just like sliding
Speaker 1: away from you and you know, whether it really exists,
Speaker 1: whether there is a now, right, whether there's a special
Speaker 1: instant that that differentiates between the past and the future
Speaker 1: right right, because sort of technically in physics of time
Speaker 1: could go both ways right like you could in time
Speaker 1: is kind of just like an arrow you can flip
Speaker 1: back and forth in the equations that you guys use, right. Yeah,
Speaker 1: time is not really very central to physics. Yeah, I mean,
Speaker 1: on one hand, it is. On one hand, it isn't.
Speaker 1: Tom you could write a lot of physics down without
Speaker 1: ever thinking about time. On the other hand, time is
Speaker 1: essential property physics because we're trying to use physics to
Speaker 1: predict the future. So um, this time is both like
Speaker 1: not part of physics and deeply entwined in it at
Speaker 1: the same time. So it's, uh, it's an important topic. Yeah, no,
Speaker 1: And it's a topic that everybody experiences right at every
Speaker 1: second of the day, every day of the year, every
Speaker 1: year their lives. They're experiencing time, and they're moving forwards
Speaker 1: in it, and they feel it, right. Yeah, they think
Speaker 1: about it, they think about the future, they remember the past,
Speaker 1: and so it kind of makes you wonder how many
Speaker 1: people actually think about or know what time actually is. Yeah, exactly.
Speaker 1: So I was wondering do people know why time goes forward? Like,
Speaker 1: I mean, physicists don't really, but it's always fun to
Speaker 1: ask general public questions that scientists don't know the answer to,
Speaker 1: just to see what they come up with. So I
Speaker 1: walked around the US of Irvine campus and I asked
Speaker 1: people why does time only go forwards? Here's what people
Speaker 1: had to say. Do you know why time only goes forwards? Um?
Speaker 1: Not really, honestly, I have like some sort of like
Speaker 1: intuition why it only goes forward? But I don't think
Speaker 1: we can't explain that. Yeah, okay, cool, I have no idea. No,
Speaker 1: I don't any guess. If I had to go, I
Speaker 1: just said gravity or something. Okay, No, I don't any idea,
Speaker 1: best guess. Sorry. I think time is lack of force
Speaker 1: dimensional right, So actually I don't know, creaky right, Okay,
Speaker 1: I'm not sure. Okay, Well, when I think of time,
Speaker 1: I think of it kind of almost as a linear progression,
Speaker 1: meaning that it's a constant in the universe, and it's
Speaker 1: always kind of moving forward, and that's something that we
Speaker 1: accept as being a fact of the universe, at least
Speaker 1: as we understand it now. So in that regards, I
Speaker 1: think that's why we can only see it as moving forwards,
Speaker 1: because it doesn't kind of make sense to us or
Speaker 1: it's not even physically possible currently for us to move
Speaker 1: backwards in time, so we don't consider it in that way.
Speaker 1: I think it might be a matter of observation. So
Speaker 1: relative to us, time moves forward, and the way that
Speaker 1: you experienced the world biologically is designed to be in
Speaker 1: a manner that is sort of one dimentional and a
Speaker 1: forward mind all the time. But in reality it might
Speaker 1: be that the fourth dimension of time in space time
Speaker 1: might just be a way of describing the universe that
Speaker 1: the math predicts a from physics and my option perhaps
Speaker 1: other related science fills. Okay, cool, Yeah, so I got
Speaker 1: a pretty good mix of answers there, right from the
Speaker 1: standard physics, like gravity, which is you know, that's a
Speaker 1: good answer. You never know, it might be, right, gravity.
Speaker 1: Somebody actually said gravity. I don't know gravity, It could
Speaker 1: be it could be. Yeah, well, gravity is like the
Speaker 1: answer to half the questions in physics, the way like
Speaker 1: pie is the answer to half the questions in math. Right,
Speaker 1: so if you have no idea, you could just say
Speaker 1: gravity and have the time. You'll be right. Not the
Speaker 1: movie the fourth right, yeah, the fabric of space time itself.
Speaker 1: That's right, it's gravity. Yeah. And then you know, some
Speaker 1: other folks had some more elaborate discussions, But people had opinions.
Speaker 1: People did have opinions. Yeah, some of them were sort
Speaker 1: of longer word salad. Right, you know, some of them
Speaker 1: hit on some of the scientific concepts time being a
Speaker 1: fourth dimension, etcetera. Um, but um, yeah, a lot of
Speaker 1: people want to ask them this question. You could just
Speaker 1: see in their faces that they had not ever considered this.
Speaker 1: They're not even question they had imagined, but as soon
Speaker 1: as they thought about it, they realized they didn't know.
Speaker 1: And that's my favorite part of this this topic is
Speaker 1: that nobody, nobody has really thought about it in terms
Speaker 1: of general public, but as soon as they do, they're
Speaker 1: very curious. Right, this is the best questions. It's amazing
Speaker 1: how little you actually kind of need to know about
Speaker 1: the universe to live a full and happy life, you
Speaker 1: know what I mean, that's the protective happy life. There's
Speaker 1: so much you don't need to know. Ignorance is bliss,
Speaker 1: you know, that does have a meeting. People have been
Speaker 1: living in this universe for hundreds of thousands of years,
Speaker 1: depending on how you count the beginning of humanity, and
Speaker 1: there's been a lot of happiness and joy without really
Speaker 1: any understanding. I mean, I would say people five years
Speaker 1: ago basically knew nothing about the way the universe actually works.
Speaker 1: But you know, people had birthday parties and eight cakes
Speaker 1: and had moments of joy. So yeah, I mean like
Speaker 1: a hundred only a hundred years ago, right in the
Speaker 1: nine hundreds, early nineteen hundreds, people didn't know the concept
Speaker 1: of Adams or quantum physics, right, Yeah, that was about
Speaker 1: a hundred years old. We didn't know how long the
Speaker 1: universe had been around, right, so pretty basic stuff about
Speaker 1: the way the universe works is pretty modern. Right, So
Speaker 1: we didn't know there were other galaxies, right, No, they didn't. Um,
Speaker 1: So what's your point here? Your point is you don't
Speaker 1: need physics to be happy? Is that what you're trying
Speaker 1: to say is irrelevant happiness? You think of how much
Speaker 1: of a richer life you can lead if you know physics. Okay,
Speaker 1: I like the way you spun that back, right, using
Speaker 1: all this technology to talk to me. That's based on physics,
Speaker 1: not not like not like money rich, but you know,
Speaker 1: like spiritually right right? Um? Isn't your career based on
Speaker 1: technology that was developed with the help of physicists? Where
Speaker 1: would you be? Isn't your science dependent on technology? Yes?
Speaker 1: I am a tiny little mite standing on the shoulders
Speaker 1: of giants, absolutely, But so are we all? So are
Speaker 1: we all? Yeah? Well maybe it's time we got back
Speaker 1: on topic here, and um, so let's break it down
Speaker 1: for people, Daniel, what how do physicists see time? Like
Speaker 1: if if you're at a conference and you guys are
Speaker 1: talking and somebody said, hey, guys, what is time? What
Speaker 1: do you think people would generally say, I think there'd
Speaker 1: be a lot of disagreements because we don't really have
Speaker 1: a great description of time, you know, one that really
Speaker 1: makes sense. And you know, the way physics approaches the
Speaker 1: problem is first you try to build like a model
Speaker 1: of the problem. You're trying to describe it in a
Speaker 1: way that we can grapple using the language that we're
Speaker 1: familiar with, which is mathematics. You try to find an
Speaker 1: equation that tells you what what's what's happening? Yeah, exactly,
Speaker 1: you know, something's happening in the real world. Maybe it's
Speaker 1: like a ball is being thrown the air, and we
Speaker 1: try to understand it. So we write down a bunch
Speaker 1: of equations to describe it um and that lets us
Speaker 1: build that model in our heads and manipulate it and
Speaker 1: then use information from the model to describe what's happening
Speaker 1: in the world. Cool. How do we do that with time? Right?
Speaker 1: How do we ask this question about like why can
Speaker 1: I remember the past and not the future? Why does
Speaker 1: ice melt but not unmelt? Right? These kinds of questions
Speaker 1: about time, it's pretty hard to to wrap your mind around.
Speaker 1: One approach is to think about the universe in terms
Speaker 1: of a bunch of snapshots. Like you think about a movie. Right,
Speaker 1: what is a movie? It's not really a continuous experience
Speaker 1: in time. If you're looking at the screen, you're not
Speaker 1: really seeing smooth motion. You're seeing a bunch of snapshots.
Speaker 1: You're seeing like a little cells in a film, or
Speaker 1: like a bunch of screenshots. Yeah, it's a bunch of screenshots,
Speaker 1: and they're just packed so tightly together that you don't
Speaker 1: notice that they're not actually smoothly varying. Right. Your brain
Speaker 1: does the interpolation for you. It tells you a story.
Speaker 1: So sometimes we think about the universe that way. We
Speaker 1: think about like all the universe at this moment, and
Speaker 1: then all the universe at the next moment, and all
Speaker 1: the universe at the next moment, like snapshots of the universe.
Speaker 1: By snapshots, I mean like what is every particle doing
Speaker 1: and where is it going? Yeah, exactly and time. Then
Speaker 1: is a way to sort of order those snapshots is
Speaker 1: to say this one first, that one next, that one next,
Speaker 1: um and to sort of put them together. This one
Speaker 1: can go in front of the other one. Yes, you
Speaker 1: know what I mean. It limits um the ordering. Yeah,
Speaker 1: And in that sense, physics. The job of physics is
Speaker 1: to take all the snapshots in the past and predict
Speaker 1: the ones in the future and to say, Okay, according
Speaker 1: to the laws of physics, the next snapshot will look
Speaker 1: like this, or if you want to talk quantum mechanically,
Speaker 1: there's a probability distribution of the next snapshots. These are likely,
Speaker 1: these are unlikely, these are impossible. Right, So physics um
Speaker 1: takes sort of that view of time, and there's a
Speaker 1: bunch of caveats there. Like, you can't have a snapshot
Speaker 1: of the whole universe, right because time is not universal.
Speaker 1: It means different things for different people. You can't know
Speaker 1: everything about the universe. But you know, you take a
Speaker 1: small enough model or a single particle or something, you
Speaker 1: can also have quantum and you also have quantum states,
Speaker 1: right Like it' isn't that prevent you from getting an
Speaker 1: exact snapshot of the universe? Yeah, exactly. So you can't
Speaker 1: really get an exact snapshot, but you could do a
Speaker 1: quantum mechanical version. You could say, well, what's the quantum
Speaker 1: state of all the particles or you know, what's the
Speaker 1: wave function. What's the state of the wave function right
Speaker 1: now that you can talk about, and that determines probabilities.
Speaker 1: I see, So you describe me kind of how physicists
Speaker 1: see the universe. They don't see it as um. They
Speaker 1: see it as as this kind of sequence of snapshots
Speaker 1: of how things are arranged. Yeah. For example, think about
Speaker 1: the Shortinger equation. The Shortinger equation famous equation describes how
Speaker 1: a particles a wave function um moves through time, right,
Speaker 1: and it tells you how it moves. It says, if
Speaker 1: you have this wave function now and you experience this,
Speaker 1: then your way function will be that later. Right. So
Speaker 1: that's that's what physics tries to do, or or go
Speaker 1: back to them making the mechanical example of a ball
Speaker 1: going through the air right tells you, well, you you
Speaker 1: shot your ball in this direction. Where is your ball
Speaker 1: going to be in the future. So that's the role
Speaker 1: of time in physics, right to predict the future snapshots. Oh,
Speaker 1: I see. So to you guys, time is like a
Speaker 1: like an input that tells you what the universe is
Speaker 1: likely to do. You you know what I mean? Like
Speaker 1: you do you It's an input. It's not like an
Speaker 1: output or something that you can vary or that it
Speaker 1: is affected by all the other variables. Yeah, exactly. And
Speaker 1: so for example, you want to predict the flight of
Speaker 1: your ball, it's an input. You can dial that knob
Speaker 1: and say I want to know where the ball is
Speaker 1: going to be in one second or five seconds or
Speaker 1: eight point two nine seconds or whatever. So it's sort
Speaker 1: of that knob. The thing we don't the thing that
Speaker 1: that doesn't explain at all is like why it only
Speaker 1: go forwards and who's controlling how fast that knob is turning?
Speaker 1: Or why do we have time at all? Why don't
Speaker 1: we just have a static universe? It's just sort of
Speaker 1: like there, you know, it's the first step. Of course,
Speaker 1: they just try to describe it, and then you can
Speaker 1: build from that and try to answer some of these questions.
Speaker 1: But you mean, like, how come we don't have a
Speaker 1: static universe, Like, um, why do we have time at all?
Speaker 1: Boom right, I don't know, you don't know, nobody knows, Like, well,
Speaker 1: I know, there's this idea that time is the fourth dimensions.
Speaker 1: We have three dimensions up, down, left and right, backwards
Speaker 1: and forwards, and maybe time is just another direction of
Speaker 1: the universe. And so we and I think the days
Speaker 1: that we do sort of exist in this a state
Speaker 1: of being still in all four dimensions, but it just
Speaker 1: so happens that we somehow feel one of the mensitions.
Speaker 1: Do you know what I mean? Yeah? I love the
Speaker 1: it just so happens part of that explanation, right, Okay,
Speaker 1: here's the hardest part. I'll just YadA, YadA, YadA over
Speaker 1: that bit. That's that's my that's my Nobel Prize, Nobel
Speaker 1: Prize winning paper officer. It just so happens. I was
Speaker 1: going ninety miles an hour. Um, you know, I can't
Speaker 1: explain it now, You're right. Um, time is sometimes thought
Speaker 1: of as the fourth dimension. And so let's dig into
Speaker 1: that a little bit. What does that mean? Why do
Speaker 1: we think of it that way? We think of it
Speaker 1: that way because it's helpful mathematically. Like when Einstein was
Speaker 1: developing his theory of special relativity and we talked all
Speaker 1: about time dilation and stuff like that on a previous episode,
Speaker 1: he discovered that the equations have a certain symmetry. They
Speaker 1: look really nice like that you can write them down
Speaker 1: really simply and compactly if you include time as the
Speaker 1: fourth dimension of this larger concept he called space time.
Speaker 1: So he took three dimensions of space. He tacked on
Speaker 1: a fourth dimension, which is time, and he constructed this
Speaker 1: thing called space time. And because your perception of time
Speaker 1: depends on where you are in space and how fast
Speaker 1: you are moving through space, the equations get much simpler
Speaker 1: if you think about all four dimensions in that way, right,
Speaker 1: if you think about time parallel to space in that way.
Speaker 1: And that's a clue when you write down equations, and
Speaker 1: they become simpler if you think about them a certain way.
Speaker 1: That's a clue from the universe that it's maybe the
Speaker 1: right way to think about things. Okay, so that's um,
Speaker 1: that's time is a different dimension. Let's get more into it.
Speaker 1: Let's go down that rabbit hole. But first let's take
Speaker 1: a quick break. So I think it's fun to think
Speaker 1: about time as the fourth dimension. But it's also kind
Speaker 1: of a trick, right, It's not. It doesn't really fit.
Speaker 1: So wait, So the idea that it's a fourth dimension
Speaker 1: you're saying, came from mathematical convenience by Einstein, do you
Speaker 1: know what I mean? Like, it's not. It was just
Speaker 1: easier to treat it like a dimension. Yeah, And I
Speaker 1: wouldn't you blow that off? Mathematical convenience is not a
Speaker 1: small thing, you know. The whole goal of physics, remember,
Speaker 1: is to like write down an equation of the universe
Speaker 1: in one line. And so if you can write things
Speaker 1: more simply, that's a clue that it's probably more correct,
Speaker 1: it's more and it's like a deeper understanding. So yeah,
Speaker 1: he discovered that if you write things down with time
Speaker 1: is sort of the fourth column of your vector, then
Speaker 1: a lot of the equations are simpler to write down.
Speaker 1: There's it's there's a connection. There's a symmetry there. Right.
Speaker 1: We talked about symmetry in another episode. You can treat
Speaker 1: time the same way you treat space in many ways.
Speaker 1: And that's that's tempting because you think, oh, well, that
Speaker 1: answers the question time is just another dimension, right, But
Speaker 1: it doesn't answer the question because it's not just another dimension. Right.
Speaker 1: You know time is not space? Right? Time? What does
Speaker 1: that mean? Time is not space? Well, for money, you
Speaker 1: can move forwards and backwards in space, right, you can
Speaker 1: go left, you can go right, you have some control
Speaker 1: over it. You can't do that with time. But isn't
Speaker 1: it just sort of a matter of perspective, Like I think,
Speaker 1: like in the grand scheme of the history of the universe, Um,
Speaker 1: you know, I existed for this amount of time, but
Speaker 1: while I'm living it, I can only go forward. I
Speaker 1: kind of get the experience of moving forward in time. Yeah,
Speaker 1: that's true. Technically, I sort of existed all throughout my
Speaker 1: life in space time, you existed all throughout your life, Yeah,
Speaker 1: but you don't exist all throughout time. Right, There's no
Speaker 1: limit to where you can visit. In space, you can
Speaker 1: go from here to there to the other places. But
Speaker 1: in time, you can only visit between your birth and
Speaker 1: your death, and you can only go to each time once. Right,
Speaker 1: that's not true for space. I imagine there are lots
Speaker 1: of places you go to many many times, like your
Speaker 1: refrigerator or your bed. Right, Um, you visit those places
Speaker 1: many times. So space is quite different from time. Right,
Speaker 1: there's a special loops in space, but I can't do
Speaker 1: loops in time exactly. And time time has this special difference.
Speaker 1: Right then now, right, there's no now in space. I mean,
Speaker 1: I'm here, I'm there, you're over here, but there's no
Speaker 1: there's no special location in a what time has this
Speaker 1: special location? This thing we call now, which exists weirdly
Speaker 1: and slides forward weirdly. So I was saying earlier, wh
Speaker 1: why isn't the universe static? Why is time move forwards?
Speaker 1: Why isn't it just stuck at to equal zero? Nothing happens?
Speaker 1: What's pushing it forward? What's turning the engine of the universe? Right?
Speaker 1: I guess what I mean is, you know, if time
Speaker 1: is you can treat it as a fourth dimension, then
Speaker 1: you know, our experience of the universe is at time
Speaker 1: is constant and the moves at a steady pace, and that, um,
Speaker 1: you're only going forwards in it, right, whereas in space
Speaker 1: you're saying we can go backwards. But what if I
Speaker 1: just kind of take another dimension and use that as
Speaker 1: my kind of ticker? Which dimension would you use as
Speaker 1: your clock? I don't know? Up, okay, yeah, so you'd
Speaker 1: be like, hey, let's have lunch at x equel's five
Speaker 1: meters or something. Yeah, I don't know, or you know,
Speaker 1: kind of mathematically, what does that mean? Different? Time and
Speaker 1: space are not the same. You can't just swap out
Speaker 1: time for space because you don't have the same freedom
Speaker 1: and time as you do in space. Right, if if
Speaker 1: space were moved always forward, the way time did, Like
Speaker 1: you could never go back to anywhere, right, Like, oh yeah, hey,
Speaker 1: I had lunch and now is sort of sliding slowly
Speaker 1: away from me. You know, Um, it would be pretty weird,
Speaker 1: but it's very natural experience. So I see you're more
Speaker 1: limited in the time dimension exactly. There's some extra rules
Speaker 1: that seemed to apply to the time dimension that don't
Speaker 1: apply to the other dimensions. And that's weird. And anytime
Speaker 1: we see symmetries where like cool. But then when those
Speaker 1: symmetries are broken, we're like, Okay, time is like the
Speaker 1: other dimensions, but it's different. Then we ask why is
Speaker 1: it different? How the different? What makes it different? Because
Speaker 1: that's the clue to solve that, not the other puzzle. Right, Okay,
Speaker 1: so time is it is sort of a fourth dimension,
Speaker 1: but there are special rules that apply to it that
Speaker 1: makes us think that maybe it's not really a fourth dimension.
Speaker 1: Maybe it's just like a mathematical um good cluage, right, yeah,
Speaker 1: Or maybe there's two kinds of dimensions. There are space
Speaker 1: dimensions and time dimensions, right, and yeah, and maybe there
Speaker 1: are other people haven't imagined yet, you know. Yeah, that's
Speaker 1: that's the kind of mind blowing, like look at the
Speaker 1: universe in a different way, discovery that I always hope
Speaker 1: to make in science, you know, to like crack something
Speaker 1: open that's so deep that it like nobody gets it
Speaker 1: but the stoner's man. Okay, so, so what are these rules?
Speaker 1: The rules are that you can only you can't visit
Speaker 1: two times in your you know, you can't go back
Speaker 1: in time, you can make gloops, and it can only
Speaker 1: go forward. Are those mainly the main restrictions here with time? Yeah, exactly,
Speaker 1: those are the main restrictions. And I think the goal
Speaker 1: of physics and the goal of our podcast is is
Speaker 1: to try to understand where that comes from. Like can
Speaker 1: we look at the laws of physics and say, oh,
Speaker 1: that comes from this, you know, like the way we
Speaker 1: can look at the laws of quantum mechanics and from
Speaker 1: that understand in the way hydrogen works or whatever. We
Speaker 1: want to look at the laws of physics and say
Speaker 1: do they require this behavior? Is it necessary? What does
Speaker 1: it come from? And it's the deepest level, right. The
Speaker 1: problem is when we look at the laws of physics,
Speaker 1: we don't get those kinds of clues. When when we
Speaker 1: look at the laws of physics, we don't so the
Speaker 1: equations in your model of the universe don't tell you
Speaker 1: that there should be restriction some time. Yeah, let's go
Speaker 1: back to those equations about like the ball moving. Right.
Speaker 1: Imagine you throw a ball, right, you're talking about basic stuff, Right,
Speaker 1: you throw a ball in the air, it goes up
Speaker 1: and it comes down. Let's start with the simplest case
Speaker 1: with there's no air resistance, Right, it's passed up and
Speaker 1: it's passed down. Are gonna be very similar. In fact,
Speaker 1: if somebody took a video of that and then plated backwards,
Speaker 1: they couldn't tell whether the video is going forwards or backwards. Right,
Speaker 1: Physicists analyzing the motion of the ball couldn't tell you
Speaker 1: whether the video was going forwards or backwards. So if
Speaker 1: you fed it a time, like if you gave it time,
Speaker 1: it would give you the same oppu whether you put
Speaker 1: negative time or positive time exactly how it breaks down
Speaker 1: exactly because the equations work in both directions. Right. The
Speaker 1: equations have time in them. They tell you how things
Speaker 1: change with time, but they work the same forwards and backwards.
Speaker 1: So they don't tell you which way the universe should run, right,
Speaker 1: They tell you how the universe changes with time, but
Speaker 1: they don't say why it has to go forwards and
Speaker 1: not backwards, why it has to go anywhere at all?
Speaker 1: Or I can't go forwards and then backwards. Right, So
Speaker 1: if the equations of the universe really represent the universe,
Speaker 1: then the universe would is okay with traveling backwards and time.
Speaker 1: You're saying exactly, the equations sort of saying like, hey,
Speaker 1: you want to go backward this time, Sure, here is
Speaker 1: what would happen. Yeah, exactly, And it's sort of like
Speaker 1: you were saying earlier. It's like an input. You know.
Speaker 1: Imagine you're doing some calculation and the calculation is a
Speaker 1: function of position and time. Right, you want to know
Speaker 1: how many balls are at this location at this time. Right,
Speaker 1: you you drop a thousand balls into a box and
Speaker 1: you're wondering, like, how many balls are this location the time?
Speaker 1: You can ask that question of any point in space,
Speaker 1: at any point in time. Right. You can take the
Speaker 1: concercurrent configuration and you can evolve it forwards or evolve
Speaker 1: it backwards. The laws allow for all of that, but
Speaker 1: for some reason that there there's a difference in the
Speaker 1: way it actually works in the real world. Right, things
Speaker 1: slide forwards in time, and we don't know why. But
Speaker 1: there's no restriction on the space parts right there. The
Speaker 1: equations are functions of space and time, but there's is
Speaker 1: like extra restriction on the time part of it. When
Speaker 1: it comes to like actually implementing the universe, right, it's
Speaker 1: kind of like, um, we have them now, and if
Speaker 1: all we had was now, the equations would let us
Speaker 1: tell what happened before in negative time, and we would
Speaker 1: let it tell us what happens forwards in time, right,
Speaker 1: exactly the equations. Yeah, but but someh our experience. We
Speaker 1: only have experience of the stuff that happened in negative time.
Speaker 1: That's right. We only remember the past, right, that's the
Speaker 1: weird part, right, The past we can remember, we have
Speaker 1: access to it. Um in a affects us. The future
Speaker 1: we can't. And and and most of the laws of
Speaker 1: physics is an asterisk there. Most of the laws of
Speaker 1: physics are totally symmetric. Right. They don't care whether the
Speaker 1: universe is going forward or backwards. They're happy to do
Speaker 1: either one. Wow. So that's the mystery is the time
Speaker 1: would be sort of a fourth dimension, but there's some rules,
Speaker 1: but they those worlds are sort of not in the
Speaker 1: equations of the universe. That's the game with an asterisk,
Speaker 1: you're saying, right, Yeah, So the game is figure out
Speaker 1: if the laws of physics that we know of, that
Speaker 1: we've discovered, that we've written down, if those require things
Speaker 1: to move forwards? Um? And if so, you know, does
Speaker 1: that give us a clues to why it's happening? Or
Speaker 1: maybe there are other laws of physics out there that
Speaker 1: are much more sensage to time, that are the ones
Speaker 1: making time go forward. What do you mean, Like, so
Speaker 1: you're looking for something in the equations that would require
Speaker 1: time to only move forwards? What does that mean? Like
Speaker 1: if you put negative time, you should break or or
Speaker 1: yeah exactly, Like let's think about that. Are there is
Speaker 1: there anything in physics that does require time to move forward?
Speaker 1: So let's go back to that ball example. Right, I said,
Speaker 1: if you throw a ball in the air, Um, you
Speaker 1: can't tell whether the video of that ball in the
Speaker 1: air goes forwards or backwards. And when we did that,
Speaker 1: I said, ignore air resistance. And that's for an important reason, right,
Speaker 1: because air resistance changes the flight of the ball, right,
Speaker 1: slows it down, so that in reality, if you throw
Speaker 1: a ball in the air, right, Um, it's going to
Speaker 1: slow down. And so you can tell the difference between
Speaker 1: going forwards and going backwards right, right, because there's a
Speaker 1: there's like you lose some heat or you lose some
Speaker 1: energy in reality, right. Yeah, it's probably similar to think
Speaker 1: about like dropping a ball. You know, if you drop
Speaker 1: a ball and there's no friction, it's going to come
Speaker 1: all the way up to where where you dropped it from.
Speaker 1: If you drop a ball, it is air resistance. It's
Speaker 1: gonna lose some energy to bumping against all the air molecules. Right,
Speaker 1: It's not gonna come up quite as high as you
Speaker 1: dropped it. You just keep letting it bounce. Eventually it's
Speaker 1: it's gonna dribble down and stop right right. And that one,
Speaker 1: that one to you played it backwards, you would be
Speaker 1: able to tell the difference exactly that one if you
Speaker 1: played backwards. And that's the case for most things, right.
Speaker 1: So where does that come from? Well, that comes from entropy, right,
Speaker 1: that comes from heat. The heat really there is the key.
Speaker 1: It turns out that the universe likes to go from
Speaker 1: organized to disorganized, right, And that's this concept we call entropy. Yeah,
Speaker 1: I've heard of this before, but before we dive in.
Speaker 1: Let's take a short break. What do you mean when
Speaker 1: you say that the universe likes entropy or that it
Speaker 1: likes to go from order to disorder? What is it?
Speaker 1: What is it liking? Me? It means that if the
Speaker 1: universe had a bedroom, it would be a mess, right,
Speaker 1: and it would never want to clean it up. No,
Speaker 1: it's obviously that is our experience of it. Like, maybe
Speaker 1: what if there are aliens out there who experienced time
Speaker 1: backwards and they're like, why does the universe like order?
Speaker 1: Everything we see? It seems to get ordered exactly. So
Speaker 1: there's a big flaw in this argument. But let's put
Speaker 1: a pin in that and come back to it once
Speaker 1: we've done constructing the argument, then we can take it
Speaker 1: apart um. Yeah, so you're right that the universe likes it. Well,
Speaker 1: it just means that we've noticed, we've observed that disorder increases, right.
Speaker 1: For example, the classic example is you have a box
Speaker 1: and you put put a bunch of gas particles in
Speaker 1: the corner. Right, that's very organized. It's like only one
Speaker 1: way to arrange or a few ways to arrange gas
Speaker 1: particles in the corner. What happens if you run the
Speaker 1: clock forward? If you let that go, Well, if they're
Speaker 1: not totally frozen, they're gonna spread out through the box. Right,
Speaker 1: It's like we pour water onto a surface that spreads
Speaker 1: out things like things tend to go from organized configurations
Speaker 1: to disorganized. And that's just an observation. That's not a
Speaker 1: deep insight into the universe. It says, here's what we've seen. Right.
Speaker 1: You notice that there's a correlation between positive time and
Speaker 1: messiness exactly, And that's called the second law of thermodynamics. Right,
Speaker 1: it says that entropy always increases. Entropy is a measure
Speaker 1: of disorder. Right, So things are basically always spreading out
Speaker 1: and um and getting more diffuse, right, And that's the
Speaker 1: whole universe is doing that, Right, The universe, like on
Speaker 1: a grand scale, is spreading out and getting smoother and
Speaker 1: stuff like that. Is it a law law, like an
Speaker 1: equation or is it more like an observation, Right, It's
Speaker 1: more like we've never seen something good un messy with
Speaker 1: positive time. Yeah, that's that's a great question. It's a
Speaker 1: really deep question. I love that question. I think the
Speaker 1: answer is this, Um, The answer is that it's an observation.
Speaker 1: It's something we've noticed and we've never really seen it broken,
Speaker 1: and so we thought, well, this must be important, so
Speaker 1: let's write that down. Let's call that a law because
Speaker 1: it's something we've noticed happens all the time. Now, you
Speaker 1: can never get broken. Why is that? Does that reveal
Speaker 1: something deeper about the universe? Can we explain that from
Speaker 1: something else? And if you dig into like statistical mechanics,
Speaker 1: you can and derived the second law of thermodynamics from
Speaker 1: simpler assumptions, like if you say every possible configuration of
Speaker 1: the universe has equal probability, then it turns out there
Speaker 1: are more messy probably messy configurations than unmessy ones, right,
Speaker 1: Like there's a thousand ways to have gas particles spread
Speaker 1: out through a box, but there's only a couple ways
Speaker 1: to have them stuck in the corner. So it's just
Speaker 1: more likely to end up with the messy ones because
Speaker 1: there are more messy configurations. But that's sort of a
Speaker 1: cop out. I mean, it's just sort of another way
Speaker 1: to state that, is to say, well, we you can
Speaker 1: call this a deeper understanding, but it's also just like
Speaker 1: a posture that we came up with so that we
Speaker 1: could derive the second law, which we've observed. Right, You're
Speaker 1: you're basically down to the same argument you were saying.
Speaker 1: You're basically saying that the reason we have entropy is
Speaker 1: that when you move forward in times, you go through
Speaker 1: the most likely scenario. But then you can ask, why
Speaker 1: does when you go forward in time do you go
Speaker 1: to the most like exactly, it's just a restatement. Really,
Speaker 1: it's a sort of more fundamental statement of the same
Speaker 1: basic observation that things go from organized to messy, right,
Speaker 1: and um, yeah, exactly. So we were looking for, um, like,
Speaker 1: something in the laws of phasics that told us why
Speaker 1: going forwards in time is is preferred, And you're saying,
Speaker 1: we have this observation that it always does and it's
Speaker 1: somehow related to chaos and order and messiness. That's right,
Speaker 1: And so this is like the only thing we can
Speaker 1: really get our fingers on. You know, everything else in
Speaker 1: physics is time symmetric. And there's another asterisk there. There
Speaker 1: are some things in particle physics which are time asymmetric.
Speaker 1: Those are really really small effects, and we don't really
Speaker 1: think that that can explain the direction of time. Um,
Speaker 1: But we can cover that in a whole other podcast
Speaker 1: topics sometimes, but Basically, entropy is the big one. Entropy
Speaker 1: is the only law that like clearly as you say,
Speaker 1: has a correlation. But that's key. You made this point,
Speaker 1: which I think is very insightful, was that there's a correlation.
Speaker 1: It's not causation, right right, we know they're related, but
Speaker 1: what's the connection between them. That's what you're looking for,
Speaker 1: right exactly. That would be something that explains why time
Speaker 1: can only go forward, right exactly. So if you just
Speaker 1: take the second law and you add it to the
Speaker 1: rest of physics, you can say, okay, there's a correlation
Speaker 1: between time and messiness. So either the universe has to
Speaker 1: go forward in time and get messier, or the universe
Speaker 1: has to go backwards in time and get less messy. Right,
Speaker 1: Either the second law of physics allows for both. Right.
Speaker 1: So it doesn't actually tell you why time goes forwards.
Speaker 1: It just says, well, if you pick forwards, then this
Speaker 1: is going to happen. If you pick backwards, that's going
Speaker 1: to happen. And there's a difference. So it breaks the
Speaker 1: symmetry of forward and backwards, but it doesn't pick one.
Speaker 1: Or or if you assume that messiness is kind of
Speaker 1: where the universe prefers to be. Then that tells you
Speaker 1: that forward time is the preferred thing in the universe. Yeah,
Speaker 1: And it doesn't even tell you that entropy determines time, right,
Speaker 1: It just tells you that they're connecting. There could be
Speaker 1: something else, something deeper, which causes both time and entropy. Right,
Speaker 1: that's the whole problem with like correlations. You know, you
Speaker 1: can find correlations between between lots of things. It doesn't
Speaker 1: explain it, right, what's some of those famous things? Like, Um,
Speaker 1: you know global warming is correlated with the decrease in
Speaker 1: the number of piracy events worldwide? Right? Does that mean
Speaker 1: that pirates kept global warming at bay for hundreds of years? Certainly?
Speaker 1: Not right? Um? So we know time and interropy are correlated.
Speaker 1: We don't know if entropy causes time or the other way,
Speaker 1: or something else deeper that we haven't even thought about yet. Um.
Speaker 1: Or maybe it's just random, Like maybe it's a random
Speaker 1: connection like pirates and global warming. I think we've observed
Speaker 1: in grid enough detail that we know it better than
Speaker 1: empirate than global warming. Um. But I love looking at
Speaker 1: these correlations. You know, there's like a correlation between the
Speaker 1: number of movies Nicolas Cage has done and the number
Speaker 1: of people per year that die because they're twisted in
Speaker 1: their own bedsheets. So they're correlated. When one goes up,
Speaker 1: the other one goes up. Yeah, exactly, or they have right,
Speaker 1: that doesn't mean they're going to continue in the few sure, right.
Speaker 1: That's the problem with the observational correlations they don't tell
Speaker 1: you is if you don't understand the mechanism of it,
Speaker 1: you can't really argue that they're connected. They could just
Speaker 1: be chance. Right, Um, I mean sometimes there are connections,
Speaker 1: Like you know that the consumption of ice cream is
Speaker 1: very well correlated with the number of murders. What. Yeah,
Speaker 1: Well people kill people more in the summer, I guess
Speaker 1: because they're grumpier and they're sweaty and hot. People also
Speaker 1: ice cream in the summer. Right, So say some rude
Speaker 1: cause cause is in charge of both ice cream consumption
Speaker 1: and murder rates. Right. It doesn't mean that ice cream
Speaker 1: causes murder, right that we know of that we know
Speaker 1: don't understand everything. That's right, the fourth law of thermodynamics,
Speaker 1: ice cream causes murder? Um? Okay, So entropies are only
Speaker 1: kind of clue you're saying, And there's three possibilities. Either
Speaker 1: time an entropy are not at all connected. They just
Speaker 1: haven't to go in the same direction, or they are
Speaker 1: both the result of something else deeper about the universe,
Speaker 1: or maybe one causes the other or right, yeah, exactly
Speaker 1: direct connect and we don't know and we don't even
Speaker 1: know if there is much of a connection. And if
Speaker 1: you know, there's a lot of deep questions. They're like
Speaker 1: if time is because of entropy, then like what happens
Speaker 1: when the universe reaches maximum entropy, because you know, if
Speaker 1: entropy is always increasing and time is going forwards, then
Speaker 1: there's no rewind right, the universe marches forward towards messier
Speaker 1: and messier, and eventually you reach the heat death of
Speaker 1: the universe when everything is perfectly spread out, right, perfectly disorganized,
Speaker 1: there's no structures at all. Does time stop? Does time
Speaker 1: turn around and go the other way? Like, you know,
Speaker 1: just saying time is connected entropy doesn't answer most of
Speaker 1: the deepest questions Time quit exactly. Some people have theories
Speaker 1: that time stops and turns around, right, and the universe
Speaker 1: then goes towards more organized configurations like maybe, um, I
Speaker 1: love reading about theories of time because people really go bonkers.
Speaker 1: One of my favorites is that is a guy who
Speaker 1: asked the question, Okay, we have three or more dimensions
Speaker 1: of space, why should we have only one dimension of time? Right? Like,
Speaker 1: what if you had two dimensions of time? That's pretty
Speaker 1: hard to think about, which is weird because it's not
Speaker 1: so hard to think about two dimensions of space to
Speaker 1: think about like you know, a plane instead of a line,
Speaker 1: but it's pretty hard to think about two dimensions of time,
Speaker 1: like I'll meet you at three o'clock in north and
Speaker 1: you know four fifteen east west? Like what does that
Speaker 1: even mean? What is before and after? Right? Oh? You
Speaker 1: could have time coordinates? Yeah, yeah, you could have multiple
Speaker 1: dimensions of time. Um, isn't that sort of like a
Speaker 1: multiverse argument? Then, like there's maybe parallel universes besides this one.
Speaker 1: Well that's a bit of a cop out, right saying
Speaker 1: maybe there's every configuration and our universe just happens to
Speaker 1: have one core a native time And that's the explanation.
Speaker 1: I think there must be a deep reason. There must
Speaker 1: be a um, something revealing about the structure the universe
Speaker 1: as we've discovered it. There's it's got to be a
Speaker 1: clue as the way the things actually work, you know,
Speaker 1: and I suspect that it's a it's going to be
Speaker 1: a really deep answer that when we figure it out,
Speaker 1: it's gonna show us that the universe works really differently
Speaker 1: from the way we imagined. That a huge parts of
Speaker 1: our life, um, and the way we live and the
Speaker 1: things we think are fundamental about the universe are accidents.
Speaker 1: Are just constructs, right, they are timely accidents. Sorry, it
Speaker 1: took a lot of time, but eventually we we created
Speaker 1: this illusion of the universe. Yeah, alright, so then we
Speaker 1: we haven't really answered the question. I mean, it sounds
Speaker 1: like there is no answer, right, like why does time
Speaker 1: only go forwards? We know it's related to entropy, but
Speaker 1: we don't really know the connection, and that's that's kind
Speaker 1: of as far as we know. I mean, there are
Speaker 1: a lot of people out there thought about this much
Speaker 1: more deeply than I have. Sean Carroll, Carlo Rovelli, these
Speaker 1: folks have written whole books on time. But in my view,
Speaker 1: the argument mostly boils down to, you know, either it's
Speaker 1: connected to entropy, which I don't find that convincing an
Speaker 1: explanation for why it goes forwards, right, or that space
Speaker 1: and time itself are illusions and they come out of
Speaker 1: something deeper and uh, you know, and we need to
Speaker 1: dig deeper to understand like the string theory of the
Speaker 1: universe or the quantum loops that make up the fabric
Speaker 1: of space and time itself. Um, so we were pretty
Speaker 1: pretty clueless as a field. It's a it's a definitely
Speaker 1: an open time. Well until we figure it out. I
Speaker 1: hope that people out there don't lose it and they
Speaker 1: that they make the best use of it. Right. Yeah,
Speaker 1: but it's not a waste of time to think about time.
Speaker 1: It just takes a little bit of time, that's right.
Speaker 1: But it's about time, and now it's time to the
Speaker 1: end the podcast. That's right. So thanks for listening, And
Speaker 1: if you have questions about big, basic fundamental questions of
Speaker 1: the universe, send them to us. We love to dig
Speaker 1: into them and explore our ignorance and the ignorance of
Speaker 1: modern physics. So send us your questions at feedback at
Speaker 1: Daniel and Y dot com. Yeah, thanks for listening. See
Speaker 1: you next time or see you last time. We should say, oh,
Speaker 1: see you last, see you, see you anything, see anytime.
Speaker 1: That's right. Thanks for listening. If you still have a
Speaker 1: question after listening to all these explanations. Please drop us
Speaker 1: a line. We'd love to hear from you. You can
Speaker 1: find us at Facebook, Twitter, and Instagram at Daniel and
Speaker 1: Jorge That's one Word, or email us at Feedback at
Speaker 1: Daniel and Jorge dot com. Thanks for listening, and remember
Speaker 1: that Daniel and Jorge Explain the Universe is a production
Speaker 1: of I Heart Radio from More podcast from my heart Radio,
Speaker 1: visit the i heart Radio app, Apple Podcasts, or wherever
Speaker 1: you listen to your favorite shows.