Daniel and Kelly’s Extraordinary Universe - What Is Time Dilation?

Episode Date: March 12, 2019

Why does time slow down when you go fast? Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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That never happens to me when I'm talking to you, Jorge. Every conversation with you is riveting. It goes back super fast. That's right. Time just flies by, you know, and call you up, and then all of a sudden it's hours later. Do you know what I mean? Like, it's the idea that maybe time is relative in our heads. No, I think that's true.

When you're waiting for something, time feels like it goes really slow. When you're listening to your favorite podcast hosts, it just whizzes right by. We're pretty bad at measuring time as a species. Are we really? Like our brains are not good at estimating time? Oh, yeah. They do all these experiments where they ask people that, estimate how long something has been and they always over underestimated.

Oh, wow. So psychologically, time can be relative. That's proven. But what about physics? Can that actually happen? Yeah, it turns out that physics also doesn't provide a bedrock layer of truth. That time can slow down. Huh.

So there's no universal clock. Like, there's no impartial, godlike measure of time. That's right. So if next time you're late for a meeting, you can just say, hey, I got my own clock. And my observer says I was on time. Physics gives you an excuse to be late for your meeting. Hi, I'm Jorge. And I'm Daniel.

Welcome to our podcast, Daniel and Jorge, Explain the Universe. In which we take plenty of time to explain to you how time. works in the universe. Yeah, we're here to help you whatever it is you're doing, commuting to work on a subway, going out for a jog. We're here to help the time move a little bit faster for you. That's right. We're here to kill some time for you. And now it's time to get on with it.

So today's topic is Why do clocks run slower when they are moving fast? That's right. This is a really popular thing for people to get confused. about in relativity. It's technically called time dilation. The fact that clocks that move fast run slow, and it's a topic that confuses people from here to infinity.

Yeah, it's the idea that if you're going really fast, maybe at close to the speed of light, then time slows down for you. That's right. And the thing we want to understand today is not just does it happen, but why does it happen? What is it about the universe that makes that the way it really works? And the thing that I love about this is that it's one of the best examples of how the universe doesn't work the way you think it does.

That it doesn't make sense to our sort of intuitive understanding of the way the world should work. Right. Especially at these extreme conditions, right? That's right, because we're not used to those extreme conditions. So we've like operated in, you know, on the surface of the Earth, which is pretty slow speeds for thousands and thousands of years. We've built up these intuitive models for how we think the universe behaves. right, what the rules are. And one of those rules is that we think that there is a absolute history, right?

We think that there is a reality out there and that something actually happens. And in the end, everybody should agree if they're honest observers about what happened. It turns out that's just not true. And hopefully this is kind of a topic that a lot of people have, hopefully, I think, maybe have heard about it. It's sort of permeated out into popular culture a little bit, right? Like it's the basis of that movie, Interstellar. I knew you were going to talk about Interstellar. Your favorite movie.

Interstellar reference. But it's a big example of it in pop culture, right? I think really Interstellar was a pretty big movie regardless of what your physicist thinks of it. Am I your physicist? Is that how you refer to me? No, Interstellar actually did a pretty good job of modeling the relativity portion.

My issues with Interstellar more about the time travel and going inside a black hole. But from the point of view of relativity, that made a lot of sense. I mean, I thought it was good that they actually built into the plot what would happen to various people's clocks. And that's the key thing, is that relativity is all about comparing clocks.

How fast is my clock going to compare to your clock? So we're going to assume that you have heard of this concept that if you are in a spaceship going really fast, then time will slow down for you. But we were wondering how many people out there know why. So as usual, I tortured the undergraduates of UC Irvine by walking around and asking them random questions without any preparation. And remember, for those of you,

who think that these answers are silly. These are hard questions to answer on the top of your head, so give them some slack. Yeah, it's torture. The CIA calls it physics boarding. Enhanced physics. Exactly. Enhanced physics.

Physics boarding. Yeah, exactly. I'm going to cover your face with a towel and pour physics on your face. Eventually, I think the undergrads are going to recognize me, and they're going to be like, don't let that guy talk to you. He'll embarrass you.

Run away. We're not trying to embarrass these people. No, it's great. I think I would be totally. flabbergasted if you asked me these questions out of the street. All right, I'll plan to ambush you one day. So before you listen to these answers, think for yourself. Do you know what time dilation is? Can you explain

why moving clocks run more slowly? Here's what people had to say. Have you heard of time dilation? No. Do you know that clocks that move really fast go slower? No. This is a brand new information to me. Yes. Do you know why that is?

No, I don't know the real reason. No. I'm sorry. Okay. Wonderful. No. No? Okay. There is no time.

Okay. Thanks very much. All right. So maybe I was a little wrong. Not a lot of people have heard about this concept. That's right. And there are even people out there that deny the time exists, right? There is no time.

That's my favorite. That was totally blew me away. There is no concept of time or that there was not enough time to explain it to you. You know, I was so flabbergasted by the response. I couldn't even formulate a follow-up question. I was just like still processing. Like, what does that even mean? Wow.

Did he just dropped, or she dropped the bike? There is no time. Straight face. She said it with a lot of finality, yeah. So there wasn't a whole lot of opening there for interrogation or follow-up questions. It was like, this is a clearly known fact. There is no time. Well, she was just in a rush, and she's like, I have no time for this.

No. I think it was definitely more of the time is an illusion, so of an answer. Yeah, I've heard that. Time is an illusion. Yeah. Well, I think we have to do a whole other podcast episode about what is time how does it work, and why does it only go forward and all that kind of stuff? But this is kind of related, this topic is related to that idea that time is not what we think it is.

That's right. We've made a lot of progress in the last 100 years in understanding time, and we've connected it to space. You've probably heard the concept of space time, right? We have three dimensions at least of space and one dimension of time, and Einstein's relativity tied them together and showed us how time and space are connected. But that doesn't mean that time can be simply understood as a fourth dimension of space. it's much more complicated. It's different from the other dimensions of space. Yeah. They're all tied together. Time, speed, space. It's all one big molasses of a universe.

It's all one big tangle. The amazing thing is that it actually all does work. You know, we have this new version of our understanding of the universe, not that new anymore, it's 100 years old, but this revised version of our understanding of the universe. And it actually hangs together. I mean, the answers it gives you don't make any sense to your intuition. Like they fly in the face of what you. think should happen. They require you to like throw out the way you think the universe works. But they actually do hang together mathematically and they are correct. Like every time we make a ridiculous prediction from relativity and go out and check it, the universe is like, yep, that ridiculous thing actually happens. Well, let's break it down for people. So what does it mean for clocks to run slower when they move fast? So that's what we're exploring. And that's what we're trying to explain is why when you're moving really fast your clock is going to

actually slow down. Right. And so let's be very careful in how we say this because a lot of people get confused. People think that if you are moving fast, that your clock slows down. That like if you're looking at your watch and running that you can see the seconds tick slower. That's not true. If you're

holding a clock and the clock is not moving relative to you, you'll always see it moving at one second per second. No matter how fast you're going relative to anything else. Your clock always runs the same way. It's not like I get on a spaceship, hit the warp speed, and then that's not what I experienced.

That's right. You never notice your own time changing. You experience time at one second per second, no matter what. The thing that does happen is that clock's moving relative to you, right? So if I'm standing still and Jorge has a clock and he runs,

because he's a pretty zippy guy, if he runs at half the speed of light... Because I'm running late, probably. If I noticed that he's moving really fast, then I will see his clock running more slowly. Right? So now, from his point of view, he will see his clock running normally, but I will see his clock running more slowly.

If I'm zooming past you and you just look at my clock as I'm zooming by, it's not going to be running at the same speed as your clock. That's right. If I'm watching you as you go by and I'm watching your clock's hands tick forward, right? Then they don't agree with mine. Yours mark the seconds more slowly than my clock does. Whoa. And that's the key thing is that.

the observation of time depends on your relative velocity to the clock. So it's not that it actually slowed down, for me at least. It just, you saw it run slower. Right. I love how you try to use the word actually, right? Because you're imagining there's some true version of the effect, right? I'm just, this is an illusion or it looks this way, but it's not actually happening. The problem is there is no what actually happened.

Okay, I observe one thing. you observe something else we can both be right even if those accounts disagree whoa okay so then i'm running past you really fast with a clock and you see it run slower than i do or it's running slower than your clock then what happens if i stop like if i stop a few paces after you does that mean our clocks are going to be out of sync yes our clocks will definitely be out of sync exactly and there's a lot of interesting effects there right so i'm at i'm standing still from my point of view right And you're running past me. I see your clock moving more slowly.

I see my clock running normally, right? Yeah. What do you see? Well, you see your clock running normally, right? Because everybody sees their own clock running normally. Right. But you also see my clock running slowly. What?

Because even though you're doing the running, I'm moving relative to you and your clock. So then what happens if I stop? Because I'm going to think time move normally. But when I compare my clock to your clock, your clock will have skipped ahead because, right? or no, it'll have skip back.

This is really tricky, okay? And we should probably avoid this topic. Well, maybe we won't. Let's dig into it. This is called the twin paradox, right? This is people say, well, how do you reconcile this, right? So the classic framing of this is, say, we're twins, right? And I stay on, we draw, straws for who goes to go to Alpha Centauri, and you lose.

So you have to go to Alpha Centauri, or you win, you have to go. go to Alpha Centauri. I stay on Earth and you take a rocket ship to Alphacentari and I see your clock running more slowly. Well, we sink, first of all, we sink clocks. Like before I take off, we're just going to sink clocks. Time zero, start, go. Now. That's right. And I see your clock running more slowly.

Meanwhile, you have a telescope, you're looking at my clock, you see mine running more slowly, right? So we both see the other person as aging more slowly, right? So now after 100 years, you see me as only being 10 years older and I see you is only being 10 years older right right so then I come back and then what happened who's older all right let's break this down really carefully because it is tricky so when the earth twin is watching the ship twins clock he of course sees time moving more slowly on the

ship right that's relativity the same way when the ship twin watches the earth twins clock he also sees time moving more slowly on earth so far everything is symmetric right and that's where we like it because you could be in ship, you can be in the Earth, it shouldn't really matter, right? Now, if they just kept going this way, nothing would change. Of course, they would have conflicting views of whose clock is moving slower, right? But that's okay in relativity. You can have two people with conflicting, but both correct views of the same situation, right? Because there is no ultimate truth, right?

Your answers depend on your speed and your location. So what happens to break the symmetry? The symmetry is broken when the space twin turns around. That's an acceleration, right? That changes everything. Only the space twin does in the acceleration, so that makes his case different, right? And during that acceleration, the time on Earth seems to zoom forward really fast from the point of view of the Space Twin. So on the way back, yeah, he sees Earth moving fast and Earth's clock going slowly,

but during that acceleration, Earth's time has leapt forward really far. So that when the Space Twin gets back to Earth, he's younger than his twin on Earth, right? And the reason they're no longer symmetric is that only the space twin has done any acceleration. So you shouldn't expect them to be the same from each point of view. It's the coming back that then lets me stay younger. Yeah, exactly. Okay, let's dig into it even more. But let's take a quick break.

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you know. I got blown up on a React mission. I ended up having amputation below the knee of my right leg and a traumatic brain injury because I landed on my head. Welcome to season two of the Good Stuff. Listen to the Good Stuff podcast on the Iheart Radio app, Apple Podcast, or wherever you get your podcast. All right, so this idea that time moves lower when you're going fast, it's, what's cool is that it's always happening, right? It doesn't just happen when you're going at the speed of light or close to the speed of light.

It happens like on a daily basis. That's right. It applies all the time. It always applies to things that have velocity relative to you. But it's a really. tiny effect if you're not going really, really fast. So when you're driving 60 miles an hour on the freeway, yeah, your clock is running a little bit slower,

but you'll never notice it. Wow, but it's there. Like, we're all feeling relativity and time dilation all the time everywhere. There is no way to escape relativity. It is everywhere. It's relatively everywhere. It's absolutely everywhere. The only absolute thing about relativity is that it's everywhere.

Okay, so it only happens when you get, It's only noticeable, you're saying, when you're going to close the speed up. But I heard it happens to astronauts here on Earth. Like the space shuttle, the clocks get out of sync with the clocks in Earth. That's right. Though it takes a lot of precision to measure it. It's something like every six months or so, they lose less than a hundredth of a second. So it's something we can measure, and they have really precise clocks precisely to measure this, to verify these predictions.

But it's not something that people have really, like, qualitatively experienced. We haven't had an astronaut come back, you know, deep into the future and still feel young. And it goes really nonlinear, right? As you get faster and faster, the effect gets stronger and stronger. But they did do that twin experiment with astronauts, right? Like they sent one twin into space for a whole year, and then he came back. And technically, he was 0.01 seconds younger. That's right.

I wonder if he was the one who was originally born first or the one who was originally born second. Because it'd be interesting and be like, well, you used to be the older twin, but now I'm the older twin. I should have stayed up there for 10 more years I know Do you think grown-up twins still argue by that kind of stuff? Well, I'm the older brother So you have to listen to me Why do you think they're both Austernots?

They're probably trying to one-up each other Oh yeah, I'm an engineer Oh yeah, I'm a pilot Oh yeah, I'm an astronaut, me too Yeah, probably It never ends, right? But technically that's true He went out into space

Went around the earth for a whole year When he came back, technically Time for him moved 100 of a second slower. Yeah, I wonder what he's going to do with all that extra time, you know? Scratch his nose or something, right? Oh, it's gone. He lost it. You used it up.

Yeah, but as you go faster and faster, the effect gets stronger and stronger. And as you approach the speed of light, time gets so slow that we can say that if you go the speed of light, time would actually stop. So if I'm zooming, running past you at the speed of light, you would see my clock totally frozen. Exactly. The caveats are important here. Nothing that has mass can actually go the speed of light, right? And only massless things can go the speed of light. So you can never go the speed of light.

Are you saying I have too much mass, Daniel? You're a pretty massive dude, yeah. By which I mean, you're massively funny, and you're massively awesome. Thank you. And you have a massively excellent podcast. And you are brilliant, but you're not entirely made of light. How about that? All right, yeah.

I was just fishing for relative compliments. absolutely wonderful so if you have somebody in a spaceship and they're going super duper fast and they're approaching the speed of light then time slows down further and further to the point where it almost stops

but remember for them time doesn't slow down it's not like they're living in molasses it's just our observation of their time so if somehow a photon had a clock yeah our view of the photon's clock would be that it was frozen right for us photons don't move forward in time they are frozen in time

but if you were a photon What would your experience be? Well, it's hard to answer that because you're not a photon and you have to have that concept of like a sentient photon, which seems impossible. So it's basically an impossible question to answer. But remember, your time always moves forward at one second per second. Okay, so that's the effect of time dilation.

Time moves, seems to move slower when you're going faster. So let's get into why it happens. Do we know why this happens? We do know why, and it's the consequence of another really strange, counterintuitive thing that we've observed about the universe that makes very little sense. So it's a conundrum built on a conundrum? It's a bizarre, counterintuitive consequence of something really weird about the universe, and really weird about light, actually.

It's the fact that everybody always observes light going at the same speed, no matter how fast they're going relative to the source of the light. Okay, let's break it down what that means. So light travels through space, but nobody can see it move faster than that speed that light moves it. That's right. There's a certain speed of light that goes through space three times 10 to the 8 meters per second,

and we'll call it the speed of light, of course. And if I'm standing on a planet and I turn on a flashlight, then the light leaves me and travels at three times 10 to the 8 meters per second away from me right and if i'm and if you're shooting it at me then i see moving towards me at three times 10 to the 8 meters per second okay that's right even if you're moving if you're on a rocket chip and you're moving towards me right say you're moving towards me at half the speed of light i shoot my laser beam at you or my flashlight at you my flashlight at you still see that flashlight the light from it coming at you at the speed of light right and that's different from you know sound waves

or rocks or something or baseball like uh that's weird right like if you throw a baseball at me me and I'm running full speed towards you, that baseball is going to be, it's going to look like it's moving really fast towards me. That's right. If I throw a baseball at you at 100 miles an hour, which I promise I can totally do, this is very realistic, and you're running towards me at 50 miles an hour, which I'm sure you're totally capable of, then obviously I see the baseball as moving away from me at 100 miles per hour, but you see the baseball is coming towards you at 150 miles per hour, right?

Yeah. That's the way it works for normal things. But you're saying that if that baseball, instead of a baseball, it was a beam of light, that wouldn't happen. That's right. Light doesn't follow those rules. Everybody who measures it as traveling at that fixed speed of light, no matter what. I mean, there are caveats here like it slows down when it travels through air or water or whatever, but let's just talk about it in a vacuum. The crazy thing is it doesn't matter how fast you're going.

Everybody sees light as traveling at this maximum speed of the universe, no matter what. And that's crazy, right? And right there is where you're constantly. that everybody sees the same thing the same way or that there is one absolute truth that we're all observing in different ways breaks down because your description of events and my description events are going to be very different if we see light moving at different speeds it's the weird it's like a weird rule of the universe not that light something can't travel at this faster than the speed of light it's a weird rule that says nothing can be seen to travel

faster than the speed of light not even light that's right light always travels at the speed of light and nothing can travel faster than the speed of light and these two things are connected right because if light operated the same way as baseballs then you could see light moving at faster than the speed of light just by moving towards me when I'm shooting a laser at you right then that light would be moving relative to you at faster than the speed of light but it doesn't right you move towards me and you still measure light as moving at the same speed it doesn't matter if you're running away from me or towards me okay so if you shoot a light beam at me and I'm running towards you really really really fast, you're going to measure

the light moving at the speed of light and I should measure the light moving faster towards me, but I'm also going to measure it moving at the speed of light. Even if I'm moving towards you or away from you or to the side of you exactly. No matter how fast I'm moving, I'm always going to measure

it moving at the speed of light. Exactly. And that's crazy, right? It's bonkers. It doesn't make any sense. And it's a famous experiment, Michael said Morley experiment that did this. They shot beams of light in two directions. And because the earth is moving. They figured, well, one of them is going to go slower than the other one because the Earth is moving,

right? So they did the experiment at different times of year. And the light came back, took the same amount of time to go in these two perpendicular directions every single time. And that told them that the speed at which light travels is not dependent on how fast you

are moving. The observer is moving. It's always the same speed. It's crazy. Is it like some kind of just like fundamental limit in the stuff of the universe itself, you know, like nothing can propagate through this thing we call space faster than the speed of light? Is that kind of what it's related to? Yeah, definitely. But it's a deep question and we don't have a solid answer to why does light always travel at this speed, regardless of the speed of the observer? We don't know

the answer to that. That's just like Einstein postulated that. He said, okay, let's start from this crazy assumption and build the math up from there. And if everything then works, will say, well, that assumption must be true. And if you start from that assumption, you get all sorts of crazy predictions, which all turn out to be true, right? So that is a deep truth of the universe, but the answer is we don't know why. We don't know why light always travels at the same speed, or a light is always observed at the same speed, no matter who is doing the measuring and how fast they're going. Wow.

It's a weird rule about the universe. It's a weird, weird rule. And when I meet the people who wrote the simulation, I'm going to ask them, why did you do that, man? That made everything so complicated. They're like, I don't know. I'm giving the universe one star on Yelp for that bit alone. No, I think there's a fascinating angle there, you know, because we grew up sort of as a species in an environment where nothing goes near the speed of light.

And so we never noticed this. And so we assume things like everybody's clock runs at the same time because we've always thought it did. And so that allowed us to assume things like there must be some sort of absolute sense of time and an absolute history, and there's a real universe out there. And this is, I mean, this shakes the very foundations of how we even think about the universe that's out there and whether it makes sense at all. So it's pretty crazy stuff. I feel like we're capped with weirdness at both ends of the spectrum.

What I mean is, like, if you move it close to the speed of light, things get weird. But also if you don't move at all things get weird, right, because of quantum physics and the uncertainty principle, right? Like, if you try to discern things at zero velocity, things get weird, too. Things always get weird. I think that's the takeaway, right? The universe is weird. Like I think I said last week, it is weirder and stranger and hotter and nastier and wetter than you could ever even imagine. And I think the craziest surprises about the way the universe work are still yet to come.

You know, we've made these discoveries that showed us that the universe is so different from the way our ancestors imagined. There must be more of those discoveries coming. It's certainly not the case that we figured them all out. There are crazy revelations in our future. Well, that's good for our podcast topics. That's right. Okay, so let's get into how this affects time. But first, let's take a quick break.

Hey, sis, what if I could promise you you never had to listen to a condescending finance bro? Tell you how to manage your money again. Welcome to Brown Ambition. This is the hard part when you pay down those credit cards. If you haven't gotten to the bottom of why you were racking up credit or turning to credit cards, you may just recreate the same problem a year from now. When you do feel like you are bleeding from these high interest rates, I would start shopping for a debt consolidation loan,

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So we know that this. speed of light. You can't observe it going anything faster than the speed of light. So how does this affect how we view time or how we experience time? Right. So it comes directly. The fact that light can't travel at any other speed is what directly affects how time passes and how we measure time. And it can be a complicated topic, but I think the best way to do is to think about maybe how a simple clock operates. So let's build a simple clock that uses light. You mean like an Apple Watch? No, I mean, let's imagine that you have to build a clock on all you. have is a laser, right? And so you know, for example, that light takes about 10 nanoseconds to go 10 feet, right? Light goes about one foot every nanosecond. Okay. So what you do is you measure very precisely, you know, 10 feet, you put a mirror at the end, and then you shoot your laser, you shoot a laser pulse, and you say, however long it takes to go there and back, that's two seconds, right? Ten feet there and 10 feet back. And you set up the mirrors

in the floor and in the ceiling, right? So the beam is bouncing up and down. Right. Right. So you shoot the laser up towards the ceiling and back and you know how far it is to your ceiling and how far it is back to your floor. And so you say that's 20 feet, so that's

two seconds round trip. Oh, I see. So then the way you turn that into a clock is you count how many times the light bounces up and down the ceiling. And that sort of gives you a sense of how time is moving. That's right. You want to say, well, how long does it take my cat to finish his lunch? And so you count how many times it takes

the laser pulse to go up to the ceiling and back. And that's the number of two second intervals that takes your cat to eat his lunch. Okay. So that's it seems like a pretty impractical clock, but hey, this is how we do things in physics, man. We're like, can we build this thing using lasers? What's the most inconvenient wristwatch we can build? That's With lasers. At home, the way we toast bread for breakfast is we use lasers, of course.

And cats. Cats, I feel like it's a key. No, that's just how we toast our cats, man. Oh, man. That's how you cook the food for the cat. No, I want to officially distance myself from that joke because nobody should ever fire a laser at a cat. Well, you can fire a laser near a cat to entertain it, of course, but don't actually hit your cat with a laser, please. Oh, man.

All right, so now we have our clock, right? That's the way a clock that uses light. Okay, so this is a thought experiment. We're going to build a clock where we measure time by counting how many times it bounces off the ceiling up and down. That's right. And it doesn't have to be a thought experiment. You got mirrors, you got lasers.

Go ahead, build yourself a clock. But the interesting thing is then what happens if you put that clock on a spaceship, right? On a train. Let's make it even more inconvenient. Let's put this clock on a spaceship. And so that's when things start to get interesting, right? That's when we start to see how time slows down.

Yeah, or let's put the clock on the back of your cat, right? And then see what happens when you're, well, I guess you need the ceiling on the back of the cat. Maybe that doesn't actually work. I feel like trying to get a cat to do what you want is even more difficult than getting on a spaceship. Einstein had no idea how to get your cat to do what you want. He can master the cosmos, but not of cats. All right, so we have a clock where you measure time by, Counting how many times it bounces off the ceiling on the floor,

and we stick that in a spaceship, and then we start going. What happens then? Right. So if you're in the spaceship, nothing changes. It doesn't matter that you're going at half the speed of light or nine-tenths of speed of light. You're in the spaceship. You have no velocity relative to the clock, so things work the same way in the spaceship for you as they did when you tested your clock in your living room.

You just see the beam go up and down, bounce up and down, and you count, and that's your time. That's right. And since you brought your cat along, it takes your cat the same amount of time to eat his lunch in your spaceship as it does at home. Assuming he's not wearing a silly cat spacesuit. The interesting thing is that since you left me on Earth, you didn't invite me

on your awesome spaceship, thanks, by the way. That would have been just too inconvenient. And I'm so heartbroken that I'm spying on you. I have a massive telescope and I'm watching your cat eat lunch on a spaceship. Now I'm looking at your clock, okay? And I'm wondering how long does it take his cat to eat lunch, etc. And I'm watching your clock.

You're trying to count how many times it bounces off the ceiling too. Exactly. So I see the laser pulse go up and I see the laser pulse come down, right? The problem is that I don't see the laser pulse going 10 feet up and 10 feet down. I see the laser pulse as going further because you're moving, which means the laser pulse is not just going up and down, is also going sideways in the direction of your motion. So you have the up and down and the sideways. So the light, for me, the laser is going in a diagonal, right? Diagonal up, hit the ceiling, and diagonal back down to hit the floor.

Because you see it hit the ceiling, and then on its way down, the spaceship is also moving. So it's kind of moving diagonally to hit the floor where it's going to be. Exactly. And so the mirrors and the clock move with the laser. Obviously, they're all going at the same speed sideways. And so the laser beam hits the mirror on the top, and it hits the receiver, or whatever on the bottom. But I see it traveling further than you do, right?

And this is where the absolute speed of light kicks in because you say, okay, it traveled 10 feet, right? It traveled those 10 feet at the speed of light, so I know it takes 10 seconds. But I see it traveled further, right? Depending on how fast you're going, it could have traveled like 14, 15 feet, right? Oh.

But because light always travels at the same speed, right? I see it taking longer because it's gone further. And it can go faster than the speed of light. It can go fast in the speed of light. So I see your clock running slower. It literally takes longer to count off seconds for you. Because the clock is built on the premise that it takes light a certain time to go a certain distance. But now that distance is further and the speed can't change.

Because it's going up and down. The light is going up and down and it's trying to go forward too. Exactly. So it has to take longer. Exactly. Now if you built this same kind of clock using something else like sound waves, right? You had a speaker, then this wouldn't happen. because the sound waves don't have that same property

that they always travel at a certain speed relative to observers, right? Sound waves, as we know from Doppler shifts, change their speed based on how fast you're going. So if this was a sound wave, if we use sound waves instead, then I would just see the sound waves as traveling faster.

But light can't do that. Light always travels to the same speed no matter who the observer is. Right. And so it slows your clock down. So let's go back a step. Okay, so I'm going to be in my spaceship counting how many times it bounces off the ceiling.

And for me, it's going to be like bounce, bounce, bounce, bounce, bounce. But for you, you're saying, because it has to travel up and down and forward, you're going to count it slower, right? Like for you, it's going to be bounds, bound, bounds. And so that's kind of the definition of time. Yeah, exactly. Exactly. And any clock, and you're thinking, okay, well, that's just one example, right?

But the same argument holds for if you're going in another direction, right? You don't have to just be going sideways. If you're shooting in the direction of the mirror, right, then the light has longer to go in one direction, right? But it can't make up the time. And if you go at an angle, the same thing happens. And also for any clock, this is just one example. It's the clearest example because we built it out of something that only uses light.

But the same happens for every physical process and for any kind of clock. Okay. So that's kind of the explanation is that time, the definition of time, is sort of tied to the speed of light and the universe has this weird rule about the speed of light which is that nobody can ever see it move faster than the speed of light. That's right. And the other important thing to understand is that your definition of time

and your definition of what happens depends on how fast you are going. There is no absolute sense of time. It's not like the universe has a big clock out there and it's keeping track of what's going on. And we're trying to make measurements of it and they're kind of sloppy sometimes when we get them wrong. Like there is no. absolute sense of time.

And you can do crazy experiments where, you know, depending on how fast people are going relative to the experiment, they can see the order of events changing. Like, I can see A happen before B, and you can see B happen before A because you're zooming in the other direction. And you might think, well, that's impossible. Either A happened before B or B happened before A. There is a real truth, right? Right.

The answer is, there is no truth. The truth is not out there. X-Files was a lie. So I feel like we should get into that in another episode. But I think the conclusion we're reaching here is that basically there is no time, after all. There's no time to talk about this anymore. That's true. No, there is time, but time is a different thing than you thought it was, right?

It's something weirder and more malleable. Now, in our safe little slow worlds, you can pretend that time is the way you thought it was, right? And you'll get by just fine. But in reality, if you want to understand the way that physics works and it's deep, deepest level, the way the universe is actually put together, what the real rules are, then it turns out time is really different than you thought it was. So that person who answered her, there is no time, sort of, I feel like she skipped ahead to the end of this conversation.

She's probably a physicist visiting from the future. From Alpha Centauri. Is it her or her twin? Maybe she's your cat evolved for thousands of years into a future physicist and then traveled back in time to deliver that message. I think she's your twin, Danny. Maybe she is, maybe she is. Well, speaking of time, I think we're out of time for this episode.

So it's time to wrap it up. Thank you, everyone, for your patience and for listening. And if you have questions about how things work in the universe or anything else crazy, please send them to us on Twitter or email us at Feedback at danielanhorpe.com. We love listener questions. Yeah, hopefully we made time move a little bit faster for you, whatever it is you're doing.

Unless you were bored, in which case it probably canceled. out. If you still have a question after listening to all these explanations, please drop us a line. We'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge, that's one word, or email us at Feedback at Danielandhorpe.com. Hi, it's Honey German, and I'm back with season two of my podcast. Grasias, come again.

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We'll talk about all that's viral and trending, with a little bit of cheesement and a whole lot of laughs. And of course, the great bevadas you've come to expect. Listen to the new season of Dresses Come Again on the IHeartRadio app, Apple Podcasts, or wherever you get your podcast. Every case that is a cold case that has DNA. Right now in a backlog will be identified in our lifetime. On the new podcast, America's Crime Lab, every case has a story to tell. And the DNA holds the truth.

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