Speaker 1: Ay, Daniel, what's the most mind blowing thing that physics
Speaker 1: has taught us about the universe? Wow? It is hard
Speaker 1: to pick just one. Could I do a top five? Maybe? No?
Speaker 1: I want your single all time one thing that you
Speaker 1: think is the most bonkers that we've learned about Who
Speaker 1: had to challenge? All Right? I got one. There is
Speaker 1: one thing about the universe that, to me is the
Speaker 1: most brain scrambling thing I've ever learned. The hardest thing
Speaker 1: for me to get my brain around is that people
Speaker 1: can disagree about the order in which events happened. We
Speaker 1: don't all see the same things happening sometimes in the universe. Yeah,
Speaker 1: you can see things happening in one order, and then
Speaker 1: I can see things happening in a totally different order,
Speaker 1: and we can both be correct. Hi'm poor hammade cartoonists
Speaker 1: and the creator of PhD Commics. Hi. I'm Daniel. I'm
Speaker 1: a particle physicist, sometimes in a podcast host other times,
Speaker 1: and everybody disagrees about when I do what. Welcome to
Speaker 1: our podcast. Daniel and Jorge agree to disagree about the universe,
Speaker 1: in which we explained to you the craziest, the most
Speaker 1: amazing but true things about our universe. Yeah, and this
Speaker 1: is again a production of I Heart Radio, and in
Speaker 1: our podcast we try to take you to the forefront
Speaker 1: of science to talk about the craziest things that scientists
Speaker 1: are thinking about today, and also delve into the history
Speaker 1: of science to tell you why we think the universe
Speaker 1: is so nuts and how we figured that out. Is
Speaker 1: there a history of science, Daniel, or is that also
Speaker 1: open for this agreement people disagree about in what order
Speaker 1: we discover things, or what was the most important, or
Speaker 1: how we change people's minds. Yeah. I think in our
Speaker 1: podcast we also not just talk about scientific discoveries or
Speaker 1: scientific theories, but also a little bit about how that
Speaker 1: affects how we see the universe, you know, and how
Speaker 1: it challenges what we believe about how the universe works. Yeah. Absolutely.
Speaker 1: I think a lot of the deepest questions in physics
Speaker 1: come from a sort of a philosophical motivation. We want
Speaker 1: to know how the universe works because it matters to
Speaker 1: us that we can make sense of the universe. And
Speaker 1: when we ask the universe questions and it gives us
Speaker 1: answers that force us to totally change the way we
Speaker 1: think about the universe. That has pretty deep philosophical implications,
Speaker 1: and so that's sometimes the most fun topic. Yeah, And
Speaker 1: so basically, we're just trying to blow your mind in
Speaker 1: the gentlest, most podcasts friendly way possible. Or we're trying
Speaker 1: to share with you how the minds of physics this
Speaker 1: have been blown, and we want your mind to be
Speaker 1: blown just as much. But yeah, a little bit more gently. Yes, please,
Speaker 1: I'm not sure my brain can handle this much mind
Speaker 1: blowing is in in one hour. But you know, when
Speaker 1: I was learning physics as an undergrad, I remember these
Speaker 1: moments when I finally really deeply understood a concept, and
Speaker 1: that concept would force me to relax or destroy or
Speaker 1: get rid of some assumption I had about the universe,
Speaker 1: and I realized that that just wasn't true, that the
Speaker 1: way I'd been thinking about the world was just fundamentally wrong. Yeah,
Speaker 1: it's amazing. And so today we'll be talking about one
Speaker 1: such topic that honestly gives me a headache every time
Speaker 1: we talked about it, Daniel. We've written about it in
Speaker 1: actually a couple of chapters in our book We Have
Speaker 1: No Idea, A Guide to the Unknown Universe, And I
Speaker 1: have to admit I never really got my head around it.
Speaker 1: I authored the book, but didn't actually understood what was
Speaker 1: in it. Yeah, and this is a topic that people
Speaker 1: email us about, they ask us about, they listen to
Speaker 1: some of our podcasts about it, and still right in
Speaker 1: with questions. I think there's a lot of popular misconceptions
Speaker 1: about how this works and some consequences that I think
Speaker 1: a lot of people have not really realized. There's some
Speaker 1: really deep philosophical implications to these ideas that I don't
Speaker 1: think have been widely enough appreciated. Yeah, So to the
Speaker 1: on the podcast, we'll be talking about how does relativity
Speaker 1: affect our understanding of time? Time? Or I guess the
Speaker 1: short title is is there a consistent order of events
Speaker 1: in the universe? Yeah, and spoiler alert, the answer might
Speaker 1: be it's relatively surprising that the answer is not what
Speaker 1: you expect. We've talked to this podcast before about time dilation,
Speaker 1: the effect of speed on the rate of which clocks
Speaker 1: move forward, and that's weird and that's hard for people
Speaker 1: to get their mind around, and there's some misconceptions there.
Speaker 1: But you know, time and relativity is even weirder than that.
Speaker 1: It's more than just making things run slowly or making
Speaker 1: things run quickly. It's about how things happen here versus
Speaker 1: how things happen there. Do you think age also affects
Speaker 1: how you perceive time? Like I feel like my kids,
Speaker 1: I have no patients at all, and that the world
Speaker 1: just moves at a snail's pace for them, whereas for me,
Speaker 1: as I get older, things he's moved fast. Well, I
Speaker 1: mean I moved slower, but the world seems to move fast. Yeah,
Speaker 1: And I think that Actually you raise an interesting point,
Speaker 1: because we are all imperfect observers if you just sort
Speaker 1: of watch something and describe it later. There's all these
Speaker 1: studies about how people give terrible accounts, you know, even
Speaker 1: eyewitnesses give different accounts of the same events, And so
Speaker 1: that's certainly one problem. It's like people are unreliable observers.
Speaker 1: But even in the case when everybody was a perfect observer,
Speaker 1: everybody had a video camera, I've already had, you know,
Speaker 1: perfect measuring devices, and everybody accounted for transmission of light
Speaker 1: and all that stuff. Even in those cases, it's hard
Speaker 1: to make sense of the universe. Like if we were
Speaker 1: all robots but the exact same you know, clock in
Speaker 1: our chips, and we were all measuring things exactly, we
Speaker 1: it would still be kind of a weird universe where
Speaker 1: not everyone would agree maybe on the order of events, Yeah, precisely.
Speaker 1: And you have to separate those because we're interested not
Speaker 1: in the question of our people good eyewitnesses, because we
Speaker 1: already know the answer to that is no um, but
Speaker 1: the question of how does the universe actually work, because
Speaker 1: we want to know the answer to the question, not
Speaker 1: just for humanity, but in general, you know, the deep
Speaker 1: fundamental questions, so that when the aliens come, when we
Speaker 1: talk to them about physics, we can make sense of
Speaker 1: what they've learned. And we don't want to learn human physics,
Speaker 1: we want to learn fundamental physics. And so this idea
Speaker 1: of time dilation, this idea that time move slowly depending
Speaker 1: on maybe how fast you're going or or where you are,
Speaker 1: is kind of weird and pretty mind blowing. And so
Speaker 1: we were wondering out there how many people really sort
Speaker 1: of understood what it means and what the ramification, what
Speaker 1: it means for our basic understanding of time. So I
Speaker 1: walked around campus that use the irvine, and I asked folks,
Speaker 1: not people in the physics department, not people who have
Speaker 1: taken my class on special relativity, just random people on campus,
Speaker 1: willing to answer questions from a scrafty looking physicist. So
Speaker 1: I think for a moment, what do you know about
Speaker 1: how relativity affects our understanding of time? Here's what people
Speaker 1: had to say. Do you know how relativity affects our
Speaker 1: understanding of time? No? I do not. Actually, no, I'm
Speaker 1: not share Newton's theory of relativity. I'm sorry, I don't.
Speaker 1: Is this physics like a physics question, I'm not. I
Speaker 1: don't know much about physics. Okay, I don't know how
Speaker 1: to answer that. I'm an English Ready, if there was
Speaker 1: a whole like demonstration of that, where if like you
Speaker 1: go at like in a spaceship, like near the speed
Speaker 1: of light or something, and then you can come back
Speaker 1: and then like some amount of time has changed on
Speaker 1: Earth while like no, really time has changed for you
Speaker 1: or somewhere about and thinking Planet of the Apes when
Speaker 1: they're in the spaceship and then by the time they
Speaker 1: come back, they've only aged a couple of years, but
Speaker 1: timeline Earth has passed a lot because they're traveling at
Speaker 1: a different speed. Remain Planet Apes is a well known
Speaker 1: physics documentary. Right, yes, yes, I believe relativity. That's from
Speaker 1: Einstein is the idea that like time doesn't flow at
Speaker 1: the same rate like across the universe. I think something
Speaker 1: like I think gravity or something affects like how it
Speaker 1: flows in other places. All Right, a couple of knows,
Speaker 1: but a couple of people did have a lot of
Speaker 1: pretty good ideas, or at least they said a lot
Speaker 1: of physics terms. And I mean like Newton's theory of relativity,
Speaker 1: like the Planet of the Apes. You know, I've seen
Speaker 1: that movie. Yeah, Planet of the Apes. That's a that's
Speaker 1: a documentary about physics. Yeah, there you go. Now, you're right.
Speaker 1: People had the people who knew anything about it definitely
Speaker 1: knew that relativity and time connected and that relativity changes
Speaker 1: have time moves. And I think already that's a big success, right,
Speaker 1: the idea that time is not universal, that we don't
Speaker 1: have clocks everywhere in the universe ticking forward at the
Speaker 1: same rate. That's a big step forward to to break
Speaker 1: that assumption. You don't think you didn't have a theory
Speaker 1: of relativity. I mean he could have had one about
Speaker 1: his relatives or something, but just not not the one
Speaker 1: that caught up right. His theory relativity was don't bring
Speaker 1: up politics at Christmas dinner. Yeah, also also useful things
Speaker 1: to live by. But yeah, I think it seems like
Speaker 1: maybe there is a general sense right that relativity effects
Speaker 1: our understanding of time and makes things weird, but maybe
Speaker 1: a lot of people don't know how or what. Yeah.
Speaker 1: And I think also there's a lot of misunderstandings based
Speaker 1: on the emails that we get from listeners who are
Speaker 1: asking us questions about relativity and tweets and stuff that
Speaker 1: people have posted. I have the feeling that people think
Speaker 1: that if you move fast and your clock will slow down,
Speaker 1: which is not the right way to think about time
Speaker 1: and relativity. That's how I thought time and relativity works.
Speaker 1: So we're in for a long conversation. So, um, so
Speaker 1: people have been writing with questions about time. Yeah, a
Speaker 1: lot of people ask the questions like what is it
Speaker 1: like to be a photon? Or how does a photon
Speaker 1: move at the speed of light? If moving at the
Speaker 1: speed of light means that it's time is frozen, they're
Speaker 1: asking what would be the human experience of moving at
Speaker 1: these velocities where physics gets really weird. Yeah, and so
Speaker 1: let's clear that up. First of all, the key thing
Speaker 1: to understand about relativity and time and clocks. Is that
Speaker 1: the speed at which o'clock moves depends on its relative
Speaker 1: velocity to you. Now, these things are always relative. So
Speaker 1: if you're holding a clock and it's not moving relative
Speaker 1: to you, it's just going to go forward at one
Speaker 1: second per second. Like you always experience time the same
Speaker 1: way because you're not moving relative to yourself. Right, it's
Speaker 1: all the relative motion that distorts time. If you see
Speaker 1: a clock moving fast, and you're watching the face of
Speaker 1: that clock, then it runs slowly, but only according to you.
Speaker 1: I think maybe we need to step back a little
Speaker 1: bit paint the picture of Like I'm standing here and
Speaker 1: I'm holding a clock in front of me. You're saying
Speaker 1: that because the clock is not moving relative to me,
Speaker 1: I'm not going to see or feel anything strange about that.
Speaker 1: That's right. Like it's it's gonna I'm gonna hear it ticking,
Speaker 1: and I'm gonna it's gonna sound like it's taking at
Speaker 1: one second. That's right. And you always experience time the
Speaker 1: same way, Like you don't experience time going slowly or
Speaker 1: going quickly. But if I'm zipping past you at half
Speaker 1: the speed of light and I look at your clock,
Speaker 1: that it looks to me like your clock is running slowly. Now,
Speaker 1: according to you, the clock is not moving. You're holding it,
Speaker 1: so the clock runs at the normal pace one second
Speaker 1: per second like usual. You don't experience time slowing down
Speaker 1: just because I'm moving past you and I see your
Speaker 1: time slowing down. But again, if i'm is it being
Speaker 1: passed you at half the speed of light, then it
Speaker 1: looks to me like your clock is running slowly. Well,
Speaker 1: first of all, how would you look at my clock
Speaker 1: if you were moving back? Remember would you have time? Daniel? Really,
Speaker 1: I'm super robot observer. Remember I can observe anything accurately. Oh,
Speaker 1: I see you're running at a basilian giga hurt. I
Speaker 1: am super physics scratched. No, you have to imagine I
Speaker 1: have like some awesome telescope and I'm watching the face
Speaker 1: of your clock or something. All right, So I'm in
Speaker 1: my little space here and I have my clock, and
Speaker 1: it's taking away and you're zooming bye. And as you're
Speaker 1: zooming by, we're going to go into super matrix slow
Speaker 1: motion and you'r and so you're looking at my clock,
Speaker 1: and my clock is moving relative to you like you're
Speaker 1: seeing it go by. And if you were to measure
Speaker 1: its ticks you, it would to you it would seem
Speaker 1: like it's ticking slower like tick take right, is that
Speaker 1: kind of what you mean by that? My clock seems
Speaker 1: slower to you precisely, and your clock seems slow to me,
Speaker 1: But it doesn't seem slow to you. Right, It looks
Speaker 1: to me like you are aging slowly because your time
Speaker 1: is running slowly. In a year, for me, less time
Speaker 1: will have passed for you, and I will see you
Speaker 1: aging slowly. But for you time just moves forward because again,
Speaker 1: you're not moving relative to you. The thing to remember
Speaker 1: is moving clocks run slowly, so you're not moving relative
Speaker 1: to yourself, So your clock doesn't run anymore slowly, but
Speaker 1: they only move slowly relative to the person who's not moving. Yeah,
Speaker 1: everybody has a frame of reference that's centered at them,
Speaker 1: and things are moving or not moving in their frame.
Speaker 1: And if they're moving fast, then their clocks run slowly.
Speaker 1: If they're not moving, then their clocks run normally, all right,
Speaker 1: And that's that's basic general relativity is that time seems
Speaker 1: to slow down in a pocket of space that's moving
Speaker 1: fast relative to you. So that's special relativity or relativity
Speaker 1: has to do with how space is bent by mass.
Speaker 1: Special relativity is all these effects of light speed and
Speaker 1: clocks and stuff. And it's not just that it appears
Speaker 1: to go slowly, like your time really does move slowly
Speaker 1: according to me. And that's the crux is that I
Speaker 1: have a story about the universe that I'm telling based
Speaker 1: on my perfect observations, and that's a true story. And
Speaker 1: you're telling a different story about the order in which
Speaker 1: things happened, in the rate at which time flowed, and
Speaker 1: that's your story. And your story is different because you're
Speaker 1: in a different place and moving in a different speed
Speaker 1: relative to me. But both our stories can be correct, meaning, um,
Speaker 1: I can experience my clock taking it one second per second,
Speaker 1: but you would say that my clock is not taking
Speaker 1: it one second per second precisely. And it's not just
Speaker 1: that it appears that way, it actually is. I guess
Speaker 1: it depends on what the deffer nition of is. Thank you, Bill.
Speaker 1: And so you know a lot of people write in
Speaker 1: they say things like, you know, a photon is moving
Speaker 1: at the speed of light, which is true. And if
Speaker 1: a photon had a clock on it, somehow, I don't
Speaker 1: know how you could have a photon with a clock
Speaker 1: on it. But imagine you could then wouldn't that clock
Speaker 1: be frozen? Yes? True, because something moving at the speed
Speaker 1: of light, it's time slows down to an effective rate
Speaker 1: of zero. But that doesn't mean that photon is not
Speaker 1: experiencing time. It's experiencing time maybe normally, but by the
Speaker 1: time it blinks, it's made it across the whole length
Speaker 1: of the universe. Yeah, because from the point of view
Speaker 1: the photon, I guess the whole universe is moving past
Speaker 1: it at the speed of light, and so the whole
Speaker 1: universe is like length contracted down to zero. We'll have
Speaker 1: to do a whole other episode about the effect of
Speaker 1: relativity on length and distances and crazy stuff like that.
Speaker 1: But the idea is that moving clocks runs slowly. That's
Speaker 1: the thing to keep in mind, because all these statements
Speaker 1: have to be made in a relative sense. You can't
Speaker 1: say I'm moving really fast, and therefore my clock has
Speaker 1: run slowly. You have to say I'm moving with fast
Speaker 1: relative to what. And it's for that observer that your
Speaker 1: clock is running slowly, not for you, right, Because I'm
Speaker 1: sitting here in my pocket of space and I'm watching
Speaker 1: you sit by and if I look at your clock,
Speaker 1: I would say that your clock is moving slowly, and
Speaker 1: you would be correct. And I would look at your
Speaker 1: clock and say your clock is moving slowly and I
Speaker 1: would be correct. Well, it would be a really short conversation.
Speaker 1: Then if you're moving past, have dispeeded, like, hey, that
Speaker 1: well he's gone already, forget it. If this podcast was
Speaker 1: in stereo, we could do some cool effects. They're resooming
Speaker 1: back and forth. Make it happen, engineers, you started to
Speaker 1: treat engineers the same way I have now. Just engineers
Speaker 1: are just people out there to make things happen. I
Speaker 1: think people who make things happen are awesome. By the way,
Speaker 1: my caveat to day engineers. All right, So that's that's
Speaker 1: special relativity. That's the general idea that, uh, time seems
Speaker 1: to move totally depending on how fast you're going relative
Speaker 1: to other people who might be watching your clock. Yeah,
Speaker 1: I would say time moves slowly for people that are
Speaker 1: moving fast relative to you. I think that's pretty close
Speaker 1: to what it's just said. I'm sure it's not. We
Speaker 1: can disagree on that, all right. So that's special relativity,
Speaker 1: and it's it creates a weird situation for arguments about
Speaker 1: what happened and in what order things happen, and just
Speaker 1: in general um about time and in the universe. So
Speaker 1: let's get into that, but first let's take a quick break,
Speaker 1: all right, Daniel, Let's maybe get into the details here
Speaker 1: of how time or how special relativity messes with our
Speaker 1: understanding of time. So what what's them? Are we going
Speaker 1: to paint a picture for people? Are are were gonn
Speaker 1: to be on trains on rockets? Or Alice and Bob
Speaker 1: going to be involved? Or yeah, let's let's mix it
Speaker 1: up a little bit, because usually special relativity is like
Speaker 1: people on trains, because when they invented special relativity, trains
Speaker 1: are like the fastest thing around. But that's old and
Speaker 1: usually quantum mechanics thought experiments involved two experimenters named Alice
Speaker 1: and Bob. But let's pick it up. Let's use Alice
Speaker 1: and Bob for a special relativity thought experiment. Let's use
Speaker 1: Alicia Andrew berta perfect though, just to mix it up,
Speaker 1: all right, So if um, Alicia and Roberto are having
Speaker 1: a race, say, it's like some family events right there
Speaker 1: there with their relatives, so it's all about relativity and
Speaker 1: they've all had their you know, Christmas Ham or whatever,
Speaker 1: and now they're going to go out and make an
Speaker 1: ill advised hundred yard dash in the backyard. And they're
Speaker 1: both really fast, and people are watching the race, and
Speaker 1: then afterwards, of course they're going to argue about who one.
Speaker 1: But let's say that everybody who's watching the race is
Speaker 1: a perfect observer. Everybody has um a clock that they
Speaker 1: can start and stop, and everybody's really paying attention and
Speaker 1: knows what they're doing. Then the question is who wins
Speaker 1: the race? So they're both at the starting line, you know,
Speaker 1: we said go, they start running towards the finish line,
Speaker 1: and I'm sitting there at the finish line waiting to
Speaker 1: see who gets there first, precisely and all right. The
Speaker 1: amazing thing is that there is no one, single correct
Speaker 1: answer for who wins this race. Now, if you're sitting
Speaker 1: at the finish line, and my money is on Alicia,
Speaker 1: to be honest, you've always liked her more than Roberto,
Speaker 1: and frankly, Roberto is pissed about it. Well, she's my cousin,
Speaker 1: So it's Roberto, man, what's wrong with you? Anyway? Um,
Speaker 1: if you are sitting at the finish line, so you
Speaker 1: have um no velocity relative to the ground. Then you
Speaker 1: might see Alice. You might see Alicia beat Roberto in
Speaker 1: the race. Cool, and might think, well, that's it, that's
Speaker 1: the answer, right, she won time to celebrate. So so
Speaker 1: I'm sitting in a chair by the finish line, and
Speaker 1: to me, Alicia was running faster than Bob, so she
Speaker 1: got to the finish line first, precisely, And you might think, well,
Speaker 1: that's it, right. Other people might see from another angle,
Speaker 1: or other people might be sitting somewhere differently, or you know,
Speaker 1: maybe even if somebody is driving by in a car,
Speaker 1: they might see the velocity of Alicia and Roberto be different.
Speaker 1: But everybody should agree about the basic facts because there's
Speaker 1: a single thing that happened. That's the way you grew
Speaker 1: up thinking about the universe. That's what sort of makes
Speaker 1: intuitive sense to you. It's true, right, Like if there's
Speaker 1: somebody sitting on the opposite side of the finish line,
Speaker 1: sitting in a chair as well, you're saying that they
Speaker 1: could also see a different result, even if they're not
Speaker 1: moving like me. Actually, the other observer would have to
Speaker 1: have a different velocity and you not just be separated
Speaker 1: in distance. But you're right, The order of events that
Speaker 1: you see depends on two things. Your location relative to
Speaker 1: Alicia and Roberto and your speed relative to them. So
Speaker 1: if you are in a to make it simple, if
Speaker 1: you are in a car, and your car is super
Speaker 1: fast and you're going at like half the speed of
Speaker 1: light or something, then you could see the race differently
Speaker 1: and you could see you have a different outcome. You
Speaker 1: could see Roberto cross the finish line before Alicia. This
Speaker 1: is not some trick where like the life from you
Speaker 1: takes longer to get there or anything like that. But
Speaker 1: if you have a different relative distance to Alicia and Roberto,
Speaker 1: and you're moving at a certain velocity, then you can
Speaker 1: actually see the events happen in a different order. I
Speaker 1: am sitting in my chair, I'm going to measure who wins.
Speaker 1: But if you're moving, driving by at really fast velocities,
Speaker 1: you might see something totally different than what I see. Yeah,
Speaker 1: I could see Roberto across the finish line before Alicia,
Speaker 1: and I would also be right. But do you have
Speaker 1: to drive towards them perpendicular to them? You know what
Speaker 1: I mean? Like what's actually happening there to make you
Speaker 1: see something different? Now, let's imagine It's pretty simple. Let's
Speaker 1: say I'm moving in the same direction as Alicia and Roberto. Right,
Speaker 1: you started way before them and or way back, and
Speaker 1: by the time they cross the finish line, you're crossing
Speaker 1: the finish line too, but you're going really fast. Right,
Speaker 1: I started on the moon or something like that, so
Speaker 1: that I'm passing the race at exactly the same moment
Speaker 1: that Alicia and Roberto are actually running, so that I'm
Speaker 1: parallel with them but moving at some very high velocity.
Speaker 1: Then I can see the order of events differently. I
Speaker 1: can see the race start, and then I can see
Speaker 1: Roberto finish the race before Alicia. Even if you sitting
Speaker 1: on your plastic chair eating leftovers while you're watching sees
Speaker 1: Alicia passed the finish line first. Yeah, no, I understand
Speaker 1: that what is maybe happening, But I guess I'm trying
Speaker 1: to just understand maybe for the people listening to this
Speaker 1: is why, like, is there any way that we can
Speaker 1: understand with this example, like how special relativity makes it
Speaker 1: so that we see different things? Well, special relativity tells
Speaker 1: you that the flow of time is dependent on velocity, right,
Speaker 1: and also on distance, So the way the clocks work
Speaker 1: depends on how far away they are and how fast
Speaker 1: they are moving. So we talked earlier about how the
Speaker 1: speed that a clock will move depends on how far
Speaker 1: how fast it's moving relative to you. That's true, but
Speaker 1: there's another factor we didn't get into, which is that
Speaker 1: it also depends on where the clocks are. And so
Speaker 1: if you see two clocks moving at the same speed
Speaker 1: relative to you, but there's a distance between them, then
Speaker 1: you see a different effect on the two clocks. It's
Speaker 1: not just dependent on the velocity, it's also dependent on
Speaker 1: the distance to the clocks. Because fundamentally, what's happening is
Speaker 1: that the universe has sort of like a clock at
Speaker 1: every location and those and the way those clocks flow
Speaker 1: depends on your velocity rel tipped to them. Okay, so
Speaker 1: now you're talking about like a third person. The key
Speaker 1: thing is this separation between Roberto and Alicia. If Roberto
Speaker 1: and Alicia are like literally on top of each other,
Speaker 1: then you don't get this effect. But if there's a
Speaker 1: gap between that's a different that's a different picture there
Speaker 1: that that doesn't happen in family gatherings. But if there's
Speaker 1: a gap between them, right, if there's a their meter apart,
Speaker 1: five ms apart or something. Then their clocks are going
Speaker 1: to run differently. But how does that affect who I
Speaker 1: see getting to the finish line first? Like, like, it
Speaker 1: shouldn't mattered to me that their clocks are running slower.
Speaker 1: How does that affect how I see them and how
Speaker 1: you would see? Well, if you see if you see
Speaker 1: Alicia's clock running more slowly than Roberto's, then she's got
Speaker 1: not going to be running as fast. I only know
Speaker 1: that they're clocks are running slower because they're moving relative
Speaker 1: to me. So how why imagine that there's a clock
Speaker 1: floating in space next to Alicia and Roberto? Right, So
Speaker 1: some drone robot clock that hangs out right next to them,
Speaker 1: and it can perfectly synchronize it's motion and location relative
Speaker 1: to them to which one one for each of them.
Speaker 1: Then you would see Alicia's clock running at a different
Speaker 1: rate than you see Roberto's clock, because not only do
Speaker 1: they have a velocity relative to you, but there's a
Speaker 1: distance between them. You have a different location, and so
Speaker 1: the way at which time flows depends not just on
Speaker 1: your relative velocity but also where you are relative to
Speaker 1: that observer. All right, So you're saying that I'm going
Speaker 1: to measure. I might measure Alicia or Roberto winning sitting
Speaker 1: by the finish line, but as somebody else you on
Speaker 1: your car, running towards the race at an at an
Speaker 1: angle maybe, or going at a certain speed closest speed
Speaker 1: of light, you might see something different than what I see. Precisely,
Speaker 1: if you are sitting there and you have no velocity
Speaker 1: relative to the ground, maybe you see them tie because
Speaker 1: they've been training forever and they've been working on this,
Speaker 1: and they're both really really fast. But then if I
Speaker 1: am zipping past in a car or moving really fast,
Speaker 1: then I could see Alicia reached the finish line before Bob.
Speaker 1: Reach is the finish line. And you know, it's tricky
Speaker 1: when you're thinking about special relativity. It's really easy to
Speaker 1: get yourself confused. But the most the cleanest way to
Speaker 1: think about it is in terms of events and when
Speaker 1: those events happen. And so you see Alicia reached the
Speaker 1: finish line before Roberto. Now you might think, how is
Speaker 1: that possible, Like they're running at the same speed. Well,
Speaker 1: you know, it's there's also a question of did you
Speaker 1: see them leave the starting point at the same moment? Right,
Speaker 1: because if you're moving at a high speed relative to
Speaker 1: the race, then time is distorted for you, your your
Speaker 1: view of their time is distorted. So you're saying that
Speaker 1: it has to do a little bit with the idea
Speaker 1: that time for Alicia and Roberta are going to be
Speaker 1: moving differently relative to me and to you, and so
Speaker 1: that's going to affect kind of how what we see
Speaker 1: who we see crossing the line. First, precisely, if you
Speaker 1: are sitting there in a plastic chair, finishing your dinner
Speaker 1: and watching Alicia and Roberto across the finish line at
Speaker 1: the same moment, and you see their clocks moving at
Speaker 1: the same speed, and you see them also starting their
Speaker 1: race at the same moment, right, I think maybe that's
Speaker 1: the key insight, whereas you maybe saw them start at
Speaker 1: different times. Yeah, I see Roberto win, but might also
Speaker 1: look to me like Roberto cheated, like he left the
Speaker 1: starting point at a different moment. Right. This concept of
Speaker 1: simultaneity of things happening at the same moment depends on
Speaker 1: your relative speed to those events and your distance from them.
Speaker 1: So like in the Jorge Olympics Backyard Olympics um, Alicia
Speaker 1: would win, but in the Daniel moving at the really
Speaker 1: in a really fast car Olympics, somebody else, not only
Speaker 1: would they, somebody else would win, but somebody else would
Speaker 1: have cheated. Yeah, but you know, according to me, they've
Speaker 1: cheated it. According to you they haven't. And then we
Speaker 1: have a third cousin, you know, um, and she is
Speaker 1: driving her even faster car the other direction, right than that,
Speaker 1: different religio velocity can cause a different distortion of how
Speaker 1: time works from her perspective, and she could see Alicia
Speaker 1: totally blow Roberto away instead of just winning by little bit. Well,
Speaker 1: I think at the end of the day, you know,
Speaker 1: you're going to be by the time they finished, you're
Speaker 1: going to be, you know, hundreds of thousands of miles away,
Speaker 1: And so who cares? What do you think? And if
Speaker 1: you think they cheated, it's how I would put it.
Speaker 1: Whereas I'm right there with the metals ready to hand
Speaker 1: them out, you know, precisely, yea. So in the end,
Speaker 1: your point of view is most important because you're handing
Speaker 1: out the trophies. But the point is that the folks
Speaker 1: in the car driving past on high speeds, they see
Speaker 1: different order of events, and they're not wrong. It's not
Speaker 1: like they messed it. Up because they're moving fast, or
Speaker 1: it took light more time to get to them, or
Speaker 1: any sort of trick like that. If we're assuming perfect
Speaker 1: robotic observers, they just see the order of events differently
Speaker 1: because time is moving differently according to them, and their
Speaker 1: account doesn't have to be wrong. It's just different, just
Speaker 1: like the astronaut or the or just like the photon.
Speaker 1: It's not like the photon is wrong. It's just that
Speaker 1: they experience things differently because they're moving at a different speed. Right,
Speaker 1: And you know, we as humans grew up in a
Speaker 1: world where things move pretty slowly, and so we can
Speaker 1: in the end reconcile usually a single series of events
Speaker 1: like this happened, then that happened, then this other thing happened.
Speaker 1: And sometimes it's hard to disentangle people's emotions and they're
Speaker 1: bad eyewitnesses. But you know, if we had video cameras
Speaker 1: that everybody's location, usually we can disentangle this stuff. But
Speaker 1: as you get next to the speed of light, as
Speaker 1: you get things moving really quickly, then that breaks down
Speaker 1: and time flows differently in such a way that it
Speaker 1: could actually change this order, which means that people have
Speaker 1: a different account of what happened first, and what happened second?
Speaker 1: And I remember the moment in my you know, junior
Speaker 1: special relativity class when I learned this. It just blew
Speaker 1: my mind that there's not like a universally agreed upon
Speaker 1: order of events for stuff happening. But mostly we would
Speaker 1: be all right, we would be or I don't, I
Speaker 1: don't want to say disagreeing, but we would be seeing
Speaker 1: different things. But that usually sort of happens more prominently
Speaker 1: when you get closer to the speed of light. Yeah,
Speaker 1: you can't notice these effects at slow speeds, even for
Speaker 1: the Examp Bowl of Alicia Roberto. If they're running at
Speaker 1: fairly low speeds, you know, ten per second, which actually
Speaker 1: pretty fast, and they're running only a hundred you'd have
Speaker 1: to be going really fast to change the order of
Speaker 1: events by even nano seconds. So these effects are very
Speaker 1: small unless you're approaching the speed of light. Yeah, okay, Yeah,
Speaker 1: it's not like Roberto can argue that he should have
Speaker 1: gone in the metal, because the likelihood that there's an
Speaker 1: observer going to near the speed of light near my
Speaker 1: backyard is um maybe not zero, but unlikely. Well, it
Speaker 1: depends on who's listening to his argument. I might be
Speaker 1: more sympathetic to it. I might be like, you know,
Speaker 1: you're right, Roberto, there is some universe in which you
Speaker 1: did win this and you were jilted from getting the metal. Yeah,
Speaker 1: but really you would be like, yes, Robert, but I
Speaker 1: think you're and then you'd be gone. Daniel thinks you
Speaker 1: won and he's your medal, but he's now by Alpha centauri,
Speaker 1: so you're out of yea, So so go catch up
Speaker 1: if you want your your metal. All right, that's pretty mine,
Speaker 1: bend sing um that so many things can be happening
Speaker 1: in my in my backyard, or that I have new
Speaker 1: cousins called Alicia and Roberto. But let's talk about now
Speaker 1: whether you know how that makes any sense or how
Speaker 1: physicists are able to wrap their heads around these kinds
Speaker 1: of things. But first let's take a quick break, all right, Daniel,
Speaker 1: So according to physics, my backyard Olympics are totally arbitrary,
Speaker 1: meaning that to me they the outcome might be one thing,
Speaker 1: but to you, moving at close to the speed of light,
Speaker 1: the outcome might be different. And you're saying that this
Speaker 1: really throws into question this idea of simultaneity in the universe,
Speaker 1: Like things happening at the same time, because things happening
Speaker 1: at the same time might depend on who's measuring whether
Speaker 1: they happen at the same time. And it's a kind
Speaker 1: of thing that we have to do in physics all
Speaker 1: the time, is we think the universe works a certain way,
Speaker 1: and then the universe shows us the Nope, it doesn't,
Speaker 1: and that momentarily throws us for a loop thing. What
Speaker 1: you know, um, you could do the same experiment twice
Speaker 1: and get different outcomes because quantum mechanics is really probabilistic,
Speaker 1: or you know, time doesn't work the same way for everybody.
Speaker 1: But we don't give it up. We don't say the
Speaker 1: universe therefore makes no sense. What we do is we
Speaker 1: sort of retreat to a looser sense of what sense means.
Speaker 1: We said, all right, we can't make those assumptions. What
Speaker 1: assumptions can we make? What can we say about the universe,
Speaker 1: and we find another way for it to make sense.
Speaker 1: They sort of don't make sense in the sort of
Speaker 1: like Newtonian you know, high school physics or you know
Speaker 1: what we learned as babies how the world works. It
Speaker 1: doesn't make sense in that way, just like maybe quantum
Speaker 1: mechanics doesn't make sense to us, but it does make
Speaker 1: sense if you sort of expand and you understand the
Speaker 1: sort of the equations that are happening. Yeah, Like in
Speaker 1: quantum mechanics, you can't say that the universe is deterministic.
Speaker 1: You can't say that if you do, if you shoot
Speaker 1: an electron at the same atom in exactly the same way,
Speaker 1: you'll get the same outcome every time. You won't because
Speaker 1: there's a randomness there. But what you can do is
Speaker 1: you can say that there are still laws of physics,
Speaker 1: and those laws of physics determine which random outcomes are
Speaker 1: more likely or less likely. So you've sort of taken
Speaker 1: a step backwards. You said, well, I can determine a
Speaker 1: specific outcome, but I can say something about the distribution
Speaker 1: of outcomes, and you can do something sort of similar
Speaker 1: for relativity. You can take a step back and you
Speaker 1: can say, well, I can't say that everybody has to
Speaker 1: agree about the order in which things happen in the universe. Okay,
Speaker 1: what can I say instead? Well, you can say that
Speaker 1: everybody sees things happening according to the same laws. So
Speaker 1: you know, you sitting in your plastic chair at the
Speaker 1: edge of the finish line, you see things happening according
Speaker 1: to a certain laws, set of laws of physics. Me
Speaker 1: and my high speed Lamborghini, I see things happening according
Speaker 1: to the same laws of physics. Now I see different
Speaker 1: things happening, but they're following the same laws. Right, You're
Speaker 1: basically saying that the laws of the universe account for
Speaker 1: this difference of point of view in order of events,
Speaker 1: and so then it makes sense. It's like you're saying
Speaker 1: the laws of physics don't make sense, and that makes sense.
Speaker 1: They make a different sense. They don't make common sense,
Speaker 1: but they make mathematically, they certainly don't make common sense.
Speaker 1: Now it means that you can use the same laws
Speaker 1: to predict what's going to happen. Is I can use
Speaker 1: in my frames. So no matter how fast you're going
Speaker 1: and where you are in the universe, you should be
Speaker 1: able to use the same laws to describe what you
Speaker 1: see and to predict what's going to happen, and those
Speaker 1: laws should work. So we can still make that requirement.
Speaker 1: The events can be different from place to place. In
Speaker 1: the description of what happened can be different from place
Speaker 1: to place, but each one follows the same set of rules. Right,
Speaker 1: there's nothing inconsistent about the universe. It's just that the
Speaker 1: rules of the universe allow for this kind of of
Speaker 1: different points of view depending on your speed precisely, and
Speaker 1: that your point of your direction precisely. And I think
Speaker 1: it's a tiny bit deeper than that. It's not just
Speaker 1: that we understand how to translate what you see to
Speaker 1: what someone else going at high speeds will see. We
Speaker 1: do understand that, and that's cool. But the deeper bit
Speaker 1: is that the same rules apply no matter how fast
Speaker 1: you are going, So you can use the same laws
Speaker 1: of physics. Now, you and I can disagree about the
Speaker 1: order that we saw the race be run and who
Speaker 1: won and who cheated, but we agree on the rules
Speaker 1: of physics that describe what we saw, not just how
Speaker 1: it translates from what I saw to what you saw.
Speaker 1: We see them follow the same rules. And I think
Speaker 1: that's pretty deep. And then there's one more thing that
Speaker 1: we can still cling to. We can say that even
Speaker 1: though things can happen in a different order, sometimes there
Speaker 1: are some rules about that, you can't arbitrarily re order
Speaker 1: the universe. Oh, I see, Yeah, this is what you're
Speaker 1: saying earlier. There's a difference between simultaneity and cold. That's right,
Speaker 1: they're both impossible to pronounce words yeah and clug cool. Obviously,
Speaker 1: if I can reverse the order there of events, I
Speaker 1: would say causality, correct. Yeah. The key thing is that
Speaker 1: you can use velocity and distance and all these crazy
Speaker 1: relativistic effects to reverse the order of some events, events
Speaker 1: that are not causally connected, events where one didn't cause
Speaker 1: the other one. But some things you can't. Mean, we
Speaker 1: can see different outcomes of a race between Alicia and Roberta,
Speaker 1: but we probably wouldn't disagree on a relay raise with Alicia.
Speaker 1: Er yeah, yeah, Or for example, there's no speed at
Speaker 1: which you can go in order to see Alicia finish
Speaker 1: the race before she starts, and that order events definitely happens.
Speaker 1: She starts the race, and then later she finishes. Now
Speaker 1: when she finishes relative to Roberto, that's a different question.
Speaker 1: We can zoom around our spaceships to get whatever answer
Speaker 1: we want, But there's no But you'd have to go
Speaker 1: faster than the speed of light in order to reverse
Speaker 1: two events that are causally connected where one caused the
Speaker 1: other one. So that's why you can't, for example, make
Speaker 1: the Big Bang happened at the end of the universe,
Speaker 1: or you know, all sorts of other crazy stuff. There's
Speaker 1: some freedom here to move around the order of events,
Speaker 1: but it's not pure total freedom. Don't go crazy people.
Speaker 1: Meaning is not that the whole universe is open to interpretation,
Speaker 1: because you know, like, um, the Big Bang happened and
Speaker 1: Earth formed, and it's not like moving at any speed
Speaker 1: will change anything about that. But maybe small things, like
Speaker 1: small things that might some people might say happen or
Speaker 1: not happen simultaneously. Then people moving at different speed might
Speaker 1: have a different point of view. Yeah, And the size
Speaker 1: of these things depends on sort of how far away
Speaker 1: they are, like things that are in another galaxy, they
Speaker 1: are really really far away. Nothing over there is causally
Speaker 1: dependent on anything we do, because nothing we do here
Speaker 1: can acted for a long long time, because you know,
Speaker 1: there's because of the speed of light. So things happening
Speaker 1: on the other side of the universe, you know, the
Speaker 1: order in which those events happen is almost irrelevant for us.
Speaker 1: So we could change those are events by a billion years,
Speaker 1: probably because it makes no difference to the causal connections,
Speaker 1: because nothing that happens here affects that for a very
Speaker 1: long time. Things that are close together, right, it's much
Speaker 1: more sensitive. You can causally affect the things close to you.
Speaker 1: You can touch things, you can push things over, You
Speaker 1: can shine a flashlight and affect things nearby. So you're
Speaker 1: saying that that a raise in the backyard in another
Speaker 1: galaxy could have happened before or after my race, maybe
Speaker 1: because there's a long separation between them. But because they
Speaker 1: don't affect each other, then it's it's okay to sort
Speaker 1: of move them around in terms of our perception of
Speaker 1: when they happen. Yeah, And we talked about this thing
Speaker 1: called the light cone, which is this cone of in
Speaker 1: space that that opens up at the speed of light
Speaker 1: around you. You can only affect things that are in
Speaker 1: your light cone. Things that are sort of downstream from you,
Speaker 1: you can affect them. Those things are causally dependent on
Speaker 1: what you do. Things that are not in your light
Speaker 1: cone that they're too far away from you for you
Speaker 1: to affect them now or in the near future, there's
Speaker 1: no way for you to have any influence over them.
Speaker 1: So their relativity can go crazy and it can change
Speaker 1: the order events without breaking anything. Right, But we're still
Speaker 1: all in the same universe, right, we are all in
Speaker 1: the same universe. Yeah. Yeah, it's not like I'm disconnected
Speaker 1: from that galaxy or things that are not in my
Speaker 1: light cone. Something in my light cone might be in
Speaker 1: that other things like cone, and so I'm sort of
Speaker 1: still connected to the rest of the universe. Yeah, And
Speaker 1: your light cone goes on forever and so eventually will
Speaker 1: encompass the entire universe. Right, things you do now could
Speaker 1: affect things fifteen billion light years away, but it's going
Speaker 1: to take fifteen billion years. So your light cone is growing,
Speaker 1: and eventually everything is like cone overlaps, right, So things
Speaker 1: do come into contact. And I think my ego needs
Speaker 1: any more feeding, Daniel, just to think that I can
Speaker 1: affect the entire universe eventually. That's pretty big step up
Speaker 1: from handing out medals from the backyard backyard Olympics to
Speaker 1: expecting the entire universe. Small steps, my friend, backyard Olympics today,
Speaker 1: galaxy collisions tomorrow. No, I think the thing to understand
Speaker 1: is that we are all living the same universe, and
Speaker 1: that universe has a certain set of rules. But those
Speaker 1: rules are not necessarily the rules you thought they were,
Speaker 1: and it allows for some fudging and some flexibility and
Speaker 1: for some weird stuff to happen. But it's not throwing
Speaker 1: everything out the window. It has to be consistent with
Speaker 1: the you know, the the universe we've lived and the
Speaker 1: things we've observed. You don't get to go really fast
Speaker 1: and go back in time. You don't get to go
Speaker 1: really fast and you know, change your order from a
Speaker 1: chicken sandwich to a burger or whatever. Right. There are
Speaker 1: still rules to the universe. They're just not as hard
Speaker 1: and fast as you thought. And fundamentally it means that
Speaker 1: the universe is different from the one we thought it was.
Speaker 1: You know, the way quantum mechanics has deep implications for
Speaker 1: the way the universe works, but doesn't really change your
Speaker 1: day to day. Right. You if you don't go to work,
Speaker 1: you still lose your job. Right. There are some things
Speaker 1: that are deterministic. We don't fix climate change. The planet
Speaker 1: might get too hot. Right, It's not like we can
Speaker 1: disagree about that. No, And this is not an excuse
Speaker 1: to say that you can have just whatever facts you want, right,
Speaker 1: It's just that the facts are sort of local. Right,
Speaker 1: depending on where you are and how fast you're going.
Speaker 1: Your account of what happened in the universe is different,
Speaker 1: but it's always just blown my mind that people can
Speaker 1: have correct but different accounts of the order in which
Speaker 1: things happened. Although I think one thing that never changes
Speaker 1: is I think Roberto is a cheater. I think he
Speaker 1: cheats in any universe, in any galaxy, and no matter
Speaker 1: who you're looking, I think the question in my mind
Speaker 1: and in listeners minds is do you actually have a
Speaker 1: cousin named Roberto? And if so, does he listen to
Speaker 1: the podcast? Oh my god, I justly do have a
Speaker 1: cousin named Roberto. That's what happened. I don't need to
Speaker 1: say you're a cheater talking about our other cousins. Cousin
Speaker 1: Roberto Prime, and do you have a cousin named Alicia,
Speaker 1: because now she's going to be your favorite. Let me
Speaker 1: think I don't have a cousin name. Let me think
Speaker 1: who has to say? Let me think, like dozens of cousins,
Speaker 1: so one of the thirty six cousins needs a little
Speaker 1: bit of a second there to think about, where were
Speaker 1: you last night? Honey? Let me think? You know? Never
Speaker 1: a very inspiring answer, especially in Latin American culture, where
Speaker 1: everyone has a nickname that is totally unrelated to their
Speaker 1: actual name. You have to think a little bit. Oh,
Speaker 1: so when you're talking about Roberto, that's actually a nickname
Speaker 1: for your other cousin, Nicholas or something. Yes, that's right,
Speaker 1: something like that. That is how it goes. It sounds
Speaker 1: like a Russian novel. All right. Well, I hope that
Speaker 1: sufficiently altered or bent your mind there for at least
Speaker 1: at the time of this podcast. And remember that the
Speaker 1: university is crazy. The university's bonkers, but it's our universe
Speaker 1: and we love it, and eventually we hope it will
Speaker 1: make sense to us. That's right, just like we love
Speaker 1: that crazy cousin we all have who we now have
Speaker 1: to apologize to after this podcast. Well, nobody listens to
Speaker 1: this podcast, I think so. All right, Thanks everyone for
Speaker 1: listening and for asking us crazy questions. And if you
Speaker 1: still don't understand special relativity in the flow of time,
Speaker 1: don't worry. Nobody else really does either. Thanks for listening.
Speaker 1: See you next time. Before you still have a question
Speaker 1: after listening to all these explanations, please drop us a line.
Speaker 1: We'd love to hear from you. You can find us
Speaker 1: on Facebook, Twitter, and Instagram at Daniel and Jorge. That's
Speaker 1: one word or email us at feedback at Daniel and
Speaker 1: Jorge dot com. Thanks for listening, and remember that Daniel
Speaker 1: and Jorge explained. The Universe is a production of I
Speaker 1: Heart Radio. From more podcast from my heart Radio, visit
Speaker 1: the i heart Radio app, Apple Podcasts, or wherever you
Speaker 1: listen to your favorite shows.