WEBVTT - What Is Time Dilation? 0:00:07.280 --> 0:00:10.280 Hey, Daniel, do you somebody's feel when you're bored time 0:00:10.800 --> 0:00:13.880 slows down? That never happens to me when I'm talking 0:00:13.880 --> 0:00:16.599 to you, or Hey, every conversation with you is riveting, 0:00:16.600 --> 0:00:20.680 It goes back super fast. That's right. Time just flies by, 0:00:21.400 --> 0:00:22.680 you know, and call you up, and then all of 0:00:22.720 --> 0:00:24.680 a sudden it's hours later. Do you know what I mean? Like, 0:00:24.720 --> 0:00:29.200 it's the idea that maybe time is relative in our heads. No, 0:00:29.360 --> 0:00:31.680 I think that's true. When you're waiting for something, time 0:00:31.760 --> 0:00:34.600 feels like it goes really slow. When you're listening to 0:00:34.640 --> 0:00:37.920 your favorite podcast hosts, it just whizzes right by. We're 0:00:38.000 --> 0:00:41.440 pretty bad at measuring time as a species, are we really? 0:00:41.440 --> 0:00:44.640 Like our brains are not good at estimating time? Oh yeah, 0:00:44.680 --> 0:00:46.479 they do all these experiments where they ask people to 0:00:46.560 --> 0:00:49.839 estimate how long something has been, and they always over underestimated. 0:00:50.960 --> 0:00:54.680 So psychologically time can be relative. That's proven. But what 0:00:54.800 --> 0:00:58.600 about physics can that actually happen? Yeah? It turns out 0:00:58.640 --> 0:01:02.440 that physics also doesn't provide a bedrock layer of truth 0:01:02.920 --> 0:01:07.560 that time can slow down. Huh, So there's no universal clock, like, 0:01:07.640 --> 0:01:12.720 there's no impartial, godlike measure of time. That's right. So 0:01:12.880 --> 0:01:14.600 if next time you're late for a meeting, you can 0:01:14.600 --> 0:01:16.880 just say, hey, I got my own clock and my 0:01:16.920 --> 0:01:20.840 observer says I was on time. Physics gives you an 0:01:20.880 --> 0:01:39.880 excuse to be late for your meeting. And I'm Daniel. 0:01:40.120 --> 0:01:43.400 Welcome to our podcast Daniel and Jorgey explain the universe, 0:01:43.520 --> 0:01:45.720 in which we take plenty of time to explain to 0:01:45.760 --> 0:01:48.920 you how time works in the universe. Hey, yeah, we're 0:01:48.960 --> 0:01:51.480 here to help you. Whatever it is you're doing, communing 0:01:51.480 --> 0:01:54.200 to work on a subway, going out for a jog. 0:01:54.480 --> 0:01:56.440 We're here to help the time move a little bit 0:01:56.440 --> 0:01:58.720 faster for you. That's right. We're here to kill some 0:01:58.840 --> 0:02:01.080 time for you, and out's time to get on with it. 0:02:01.200 --> 0:02:11.000 So today's topic is why do clocks run slower when 0:02:11.040 --> 0:02:14.359 they are moving fast? That's right. This is a really 0:02:14.440 --> 0:02:17.720 popular thing for people to get confused about in relativity. 0:02:18.560 --> 0:02:22.760 It's technically called time dilation, the fact that clocks that 0:02:22.840 --> 0:02:26.440 move fast run slow, and it's a topic that confuses 0:02:26.480 --> 0:02:30.040 people from here to infinity. Yeah, it's the idea that 0:02:30.080 --> 0:02:32.639 if you're going really fast, maybe it close up the 0:02:32.680 --> 0:02:36.440 speed of light, then time slows down for you. That's right. 0:02:36.760 --> 0:02:38.800 And the thing we want to understand today is not 0:02:38.880 --> 0:02:41.640 just does it happen, but why does it happen? What 0:02:41.760 --> 0:02:43.959 is it about the universe that makes that the way 0:02:43.960 --> 0:02:47.040 it really works? And the thing that I love about 0:02:47.080 --> 0:02:49.440 this is that it's one of the best examples of 0:02:49.440 --> 0:02:52.720 how the universe doesn't work the way you think it does, 0:02:52.919 --> 0:02:55.919 that it doesn't make sense to our sort of intuitive 0:02:56.000 --> 0:02:59.120 understanding of the way the world should work, right, especially 0:02:59.200 --> 0:03:02.040 at these extreme conditions. Right, that's right, because we're not 0:03:02.120 --> 0:03:05.280 used to those extreme conditions. So we've like operated in 0:03:05.480 --> 0:03:07.280 you know, on the surface of the Earth, which is 0:03:07.280 --> 0:03:10.640 pretty slow speeds for thousands and thousands of years. We 0:03:10.720 --> 0:03:13.240 build up these intuitive models for how we think the 0:03:13.360 --> 0:03:17.320 universe behaves right, what the rules are, And one of 0:03:17.360 --> 0:03:20.160 those rules is that we think that there is a 0:03:20.160 --> 0:03:22.600 absolute history, right, We think that there is a reality 0:03:22.639 --> 0:03:25.919 out there and that something actually happens and in the end, 0:03:26.000 --> 0:03:29.680 everybody should agree if they're honest observers about what happened. 0:03:29.960 --> 0:03:33.320 It turns out that's just not true. And hopefully this 0:03:33.440 --> 0:03:35.360 is kind of a topic that a lot of people 0:03:35.520 --> 0:03:37.760 have hopefully I think maybe have heard about. It's sort 0:03:37.760 --> 0:03:40.520 of permeated out into popular culture a little bit, right, like, 0:03:40.560 --> 0:03:43.720 it's the basis of the movie Interstellar. I knew you 0:03:43.760 --> 0:03:48.800 were going to talk about Interstellar Interstellar reference, but it's 0:03:48.800 --> 0:03:51.480 it's a big example of it in pop culture, right, 0:03:51.520 --> 0:03:54.880 Like I think, really Interstellar was a pretty big movie 0:03:55.040 --> 0:03:58.080 regardless of what your physicists thinks of it, and my 0:03:58.200 --> 0:03:59.920 year and my year physicist is that how used to 0:04:00.320 --> 0:04:03.480 refer to me? No, Interstellar actually did a pretty good 0:04:03.560 --> 0:04:06.520 job of modeling the relativity portion. My issues with the 0:04:06.520 --> 0:04:08.960 Interstellar are more about the time travel and going inside 0:04:08.960 --> 0:04:11.360 a black hole. But from the point of view of relativity, 0:04:11.400 --> 0:04:12.560 that made a lot of sense. I mean, I thought 0:04:12.560 --> 0:04:14.920 it was good that they actually built into the plot 0:04:15.040 --> 0:04:17.680 what would happen to various people's clocks. And that's the 0:04:17.760 --> 0:04:21.280 key thing, is that relativity is all about comparing clocks. 0:04:21.279 --> 0:04:23.479 How fast is my clock going to your compared to 0:04:23.520 --> 0:04:26.120 your clock? So we're going to assume that you have 0:04:26.279 --> 0:04:28.599 heard of this concept that if you are in a 0:04:28.600 --> 0:04:32.200 spaceship going really fast and time will slow down for you. 0:04:32.560 --> 0:04:36.200 But we were wondering how many people out there know why? 0:04:36.560 --> 0:04:39.560 So as usual, I tortured the undergraduates of you see 0:04:39.560 --> 0:04:42.880 Irvine by walking around and asking them random questions without 0:04:42.920 --> 0:04:45.920 any preparation. And remember, for those of you who think 0:04:45.960 --> 0:04:48.760 that these answers are silly, these are hard questions to 0:04:48.800 --> 0:04:50.680 answer on the top of your head, so give them 0:04:50.720 --> 0:04:55.200 some slack. It's tortured. This called the physics boarding, enhanced 0:04:55.240 --> 0:05:00.839 physics exactly, physics boarding, you know, exactly. I'm gonna cover 0:05:00.920 --> 0:05:05.760 your face with a towel and poor physics on your face. Um. Eventually, 0:05:05.839 --> 0:05:07.680 I think the undergrads are gonna recognize me, and they're 0:05:07.680 --> 0:05:09.320 gonna be like, don't let that guy talk to you. 0:05:09.440 --> 0:05:11.960 He'll embarrass you. Run away. We're not trying to embarrass 0:05:12.000 --> 0:05:14.560 these people. No, it's great. I think I would be 0:05:14.600 --> 0:05:17.280 totally flabbergasted if you asked me these questions out of 0:05:17.320 --> 0:05:19.360 the street. All right, I'll plan the ambush you one day. 0:05:19.640 --> 0:05:22.080 So before you listen to these answers, think for yourself. 0:05:22.440 --> 0:05:24.880 Do you know what time dilation is? Can you explain 0:05:25.320 --> 0:05:29.440 why moving clocks run more slowly? Here's what people had 0:05:29.440 --> 0:05:33.200 to say. Have you heard of time dilation? Do you 0:05:33.200 --> 0:05:37.320 know that clocks that move really fast go slower? This 0:05:37.440 --> 0:05:40.920 is trying your information to me. Yes, do you know 0:05:40.960 --> 0:05:44.240 why that is? No? I don't know the real reason. 0:05:44.880 --> 0:05:51.920 I'm sorry, No, no, there is no time, thanks very much. 0:05:52.040 --> 0:05:53.719 All right, So maybe I was a little wrong. Not 0:05:53.760 --> 0:05:56.280 a lot of people have heard about this concept. That's right, 0:05:56.279 --> 0:05:57.839 and there are even people out there that deny the 0:05:57.880 --> 0:06:03.120 time exists. Right, there is no time, there is no 0:06:03.240 --> 0:06:05.760 concept of time, or that there was not enough time 0:06:05.800 --> 0:06:07.520 to explain it to you. You know, I was so 0:06:07.560 --> 0:06:10.560 flabbergasted by the response. I couldn't even formulate a follow 0:06:10.640 --> 0:06:13.520 up question. I was like still processing, like, what does 0:06:13.560 --> 0:06:16.440 that even mean? Wow? Did he did he just dropped 0:06:16.520 --> 0:06:19.960 or she dropped the bike? There is no time? Great phase. 0:06:20.920 --> 0:06:22.960 She said it with a lot of finality. Yeah, So 0:06:23.080 --> 0:06:26.080 there wasn't a whole lot of opening there for interrogation 0:06:26.240 --> 0:06:28.520 or follow up questions. It was like, this is a 0:06:28.560 --> 0:06:31.120 clearly known fact, there is no time. Well, I mean 0:06:31.200 --> 0:06:32.719 she was just going to rush and she's like, I 0:06:32.760 --> 0:06:35.040 have no time for this. No. I think it was 0:06:35.080 --> 0:06:37.800 definitely more of the time and time is an illusion. 0:06:38.120 --> 0:06:40.400 So an answer, Yeah, I've heard of that time is 0:06:40.400 --> 0:06:42.520 an illusion. Yeah, Well, I think we have to do 0:06:42.560 --> 0:06:44.919 a whole other podcast episode about what is time and 0:06:44.960 --> 0:06:46.440 how does it work? And why does it only go 0:06:46.520 --> 0:06:48.560 forward and all that kind of stuff. But this is 0:06:48.600 --> 0:06:51.040 kind of related. This topic is related to that idea 0:06:51.120 --> 0:06:54.840 that time is not what we think it is. That's right. 0:06:55.040 --> 0:06:57.000 We've met a lot of progress in the last hundred 0:06:57.040 --> 0:06:59.920 years in understanding time, and we've connected it to space. 0:07:00.440 --> 0:07:02.919 You've probably heard the concept of space time, right. We 0:07:02.920 --> 0:07:06.159 have three dimensions at least of space and one dimension 0:07:06.200 --> 0:07:08.800 of time, and Einstein's relativity tied them together and showed 0:07:08.880 --> 0:07:11.520 us how time and space are connected. But that doesn't 0:07:11.560 --> 0:07:14.040 mean that time can be simply understood as a fourth 0:07:14.040 --> 0:07:16.920 dimension of space. It's much more complicated. It's different from 0:07:16.920 --> 0:07:22.480 the other dimensions of space. Yeah, they're all tied together, time, speed, space, 0:07:22.880 --> 0:07:26.240 It's all one big molasses of a universe. It's all 0:07:26.280 --> 0:07:28.760 one big tangle. The amazing thing is that it actually 0:07:28.840 --> 0:07:31.440 all does work. You know. We have this new version 0:07:31.560 --> 0:07:33.840 of our understanding of the universe, not that new anymore 0:07:33.880 --> 0:07:37.080 as a hundred years old, but this revised version of 0:07:37.120 --> 0:07:40.160 our understanding the universe, and it actually hangs together. I mean, 0:07:40.160 --> 0:07:42.800 the answers that gives you don't make any sense to 0:07:42.840 --> 0:07:44.880 your intuition, Like they fly in the face of what 0:07:44.960 --> 0:07:47.920 you think should happen. They require you to like throw 0:07:47.960 --> 0:07:50.760 out the way you think the universe works, but they 0:07:50.760 --> 0:07:54.640 actually do hang together mathematically and they are correct. Like 0:07:54.720 --> 0:07:57.520 every time we make a ridiculous prediction from relativity and 0:07:57.520 --> 0:07:59.840 God and check it, the universe is like, yep, that 0:08:00.120 --> 0:08:03.920 ridiculous thing actually happens. Well, let's bring it down for people. 0:08:04.120 --> 0:08:07.920 So what does it mean for clocks to run slower 0:08:07.960 --> 0:08:11.440 when they move fast? So that's that's what we're exploring, 0:08:11.640 --> 0:08:14.280 and that's what we're trying to explain, is why when 0:08:14.280 --> 0:08:17.360 you're moving really fast, your clock is going to actually 0:08:17.520 --> 0:08:20.520 slow down. Right, And so let's be very careful and 0:08:20.520 --> 0:08:22.480 how we say this, because a lot of people get confused. 0:08:22.520 --> 0:08:25.200 People think that if you are moving fast, that your 0:08:25.240 --> 0:08:27.920 clock slows down. That like, if you're looking at your 0:08:27.920 --> 0:08:31.320 watch and running that you can see the seconds tick slower. 0:08:31.440 --> 0:08:34.440 That's not true. If you're holding a clock and the 0:08:34.480 --> 0:08:37.040 clock is not moving relative to you, you'll always see 0:08:37.040 --> 0:08:39.480 it moving at one second per second. Okay, no matter 0:08:39.520 --> 0:08:42.520 how fast you're going relative to anything else, your clock 0:08:42.800 --> 0:08:44.959 always runs the same way. It's not like I get 0:08:44.960 --> 0:08:49.839 on a spaceship hit the warp speed and then that's 0:08:49.880 --> 0:08:52.840 not what I experienced. That's right. You never notice your 0:08:52.880 --> 0:08:55.960 own time changing, right, you experienced time at one second 0:08:55.960 --> 0:08:59.800 per second, no matter what. Okay, the thing that does 0:09:00.040 --> 0:09:03.920 happen is that clock's moving relative to you. Right. So, 0:09:03.960 --> 0:09:06.240 if I'm standing still and Horge has a clock and 0:09:06.320 --> 0:09:08.640 he runs because he's a pretty zippy guy, if he 0:09:08.760 --> 0:09:10.920 runs a half speed of light because I'm running late, 0:09:11.040 --> 0:09:16.199 probably if I notice that he's moving really fast, then 0:09:16.280 --> 0:09:19.360 I will see his clock running more slowly. Right. So, 0:09:19.400 --> 0:09:21.760 now from his point of view, he will see his 0:09:21.800 --> 0:09:24.360 clock running normally, but I will see his clock running 0:09:24.400 --> 0:09:26.760 more slowly. If I'm zooming past you and you just 0:09:26.920 --> 0:09:30.160 look at my clock as I'm zooing by, it's not 0:09:30.200 --> 0:09:32.600 going to be running at the same speed as your clock, 0:09:32.800 --> 0:09:34.600 that's right. If I'm watching you as you go by, 0:09:34.640 --> 0:09:37.920 and I'm watching your clock's hands tick forward, right, then 0:09:37.960 --> 0:09:40.960 they don't agree with mine. Yours mark the seconds more 0:09:41.040 --> 0:09:44.360 slowly than my clock does. And that's the key thing 0:09:44.679 --> 0:09:48.560 is that the observation of time depends on your relative 0:09:48.640 --> 0:09:52.000 velocity to the clock. So it's not that it actually 0:09:52.040 --> 0:09:55.760 slowed down for me at least, it just you saw 0:09:55.760 --> 0:09:58.040 it run slower. Right. I love how you try to 0:09:58.080 --> 0:10:00.840 use the word actually right because you're in your imagining, 0:10:01.080 --> 0:10:04.240 there's some true version of the effect of the effect, right, 0:10:04.440 --> 0:10:07.520 I'm just this is an illusion or it looks this way, 0:10:07.559 --> 0:10:10.240 but it's not actually happening. The problem is there is 0:10:10.320 --> 0:10:14.480 no what actually happened. Okay, I observe one thing, you 0:10:14.559 --> 0:10:18.040 observe something else. We can both be right even if 0:10:18.080 --> 0:10:22.600 those accounts disagree. WHOA Okay, So then I'm running past 0:10:22.679 --> 0:10:25.520 you really fast with a clock and you see it 0:10:25.600 --> 0:10:28.200 run slower than I do, or it's running slower than 0:10:28.240 --> 0:10:30.679 your clock. Then what happens if I stopped, like if 0:10:30.679 --> 0:10:33.000 I stopped a few paces after you, Does that mean 0:10:33.000 --> 0:10:35.200 our clocks are going to be out of sync? Yes, 0:10:35.240 --> 0:10:38.160 our clocks will definitely be out of sync, exactly, And 0:10:38.360 --> 0:10:40.960 there's a lot of interesting effects there. Right. So I'm 0:10:41.000 --> 0:10:43.120 a I'm standing still from my point of view, right, 0:10:43.360 --> 0:10:45.959 and you're running past me. I see your clock moving 0:10:45.960 --> 0:10:48.960 more slowly. I see my clock running normally. Right, what 0:10:49.040 --> 0:10:52.920 do you see? Well, you see your clock running normally, right, 0:10:52.960 --> 0:10:55.640 because everybody sees their own clock running normally. But you 0:10:55.720 --> 0:10:59.720 also see my clock running slowly because even though you're 0:10:59.720 --> 0:11:03.040 doing doing the running, I'm moving relative to you and 0:11:03.080 --> 0:11:05.320 your clock. So then what happens if I stopped, Because 0:11:05.320 --> 0:11:08.320 I'm gonna think time moved normally, But when when I 0:11:08.320 --> 0:11:10.840 compare my clock to your clock, your clock will have 0:11:10.880 --> 0:11:14.800 skipped ahead because right or no, we'll have skip back. 0:11:15.280 --> 0:11:19.079 This is really tricky, okay, and we should probably avoid 0:11:19.120 --> 0:11:21.400 this topic. Well maybe we won't. Let's dig into it. 0:11:26.440 --> 0:11:30.160 This is called the twin paradox, right, This is people say, well, 0:11:30.200 --> 0:11:33.199 how do you reconcile this? Right? So the classic framing 0:11:33.240 --> 0:11:36.480 of this is, say we're twins, right, and I stay 0:11:36.640 --> 0:11:39.319 on We draw straws for Hugas to go to Alpha Centauri, 0:11:39.360 --> 0:11:41.280 and you lose. So you have to go to Alpha 0:11:41.320 --> 0:11:43.520 Centauri or you win. You have to go to Alpha Centauri. 0:11:44.000 --> 0:11:46.240 I stand on Earth and you take a rocket shipped 0:11:46.240 --> 0:11:48.880 Alpha Centauri, and I see your clock running more slowly. Okay, 0:11:48.920 --> 0:11:51.200 well we sink First of all, we sink clocks like 0:11:51.240 --> 0:11:53.680 before I take off. Yes, we're just going to sink clocks. 0:11:53.880 --> 0:11:57.400 Time zero start go now, that's right, and I see 0:11:57.400 --> 0:12:00.720 your clock running more slowly. Meanwhile, you have telescope. You're 0:12:00.720 --> 0:12:03.160 looking at my clock. You see mine running more slowly. Right, 0:12:03.559 --> 0:12:07.760 so we both see the other person as aging more slowly. Right. 0:12:07.800 --> 0:12:10.439 So now after a hundred years, you see me as 0:12:10.480 --> 0:12:12.280 only being ten years older, and I see you as 0:12:12.320 --> 0:12:14.840 only being ten years older, right, right, So then I 0:12:14.960 --> 0:12:18.320 come back and then what happened? Who's older? All right, 0:12:18.360 --> 0:12:21.400 let's break this down really carefully because it is tricky. 0:12:21.440 --> 0:12:24.760 So when the Earth twin is watching the ship twins clock, 0:12:25.200 --> 0:12:27.960 he of course sees time moving more slowly on the ship, right, 0:12:28.000 --> 0:12:31.720 that's relativity. The same way when the ship twin watches 0:12:31.760 --> 0:12:34.920 the Earth twins clock, he also sees time moving more 0:12:34.960 --> 0:12:37.640 slowly on Earth. So far everything is symmetric, right, and 0:12:37.679 --> 0:12:40.040 that's why we like it. Because you could be in ship, 0:12:40.120 --> 0:12:41.880 you could be in the Earth. That shouldn't really matter, 0:12:42.080 --> 0:12:44.960 right now. If they just kept going this way, nothing 0:12:44.960 --> 0:12:48.000 would change. Of course, they would have conflicting views of 0:12:48.080 --> 0:12:51.440 whose clock is moving slower, right, But that's okay. In relativity, 0:12:51.679 --> 0:12:54.600 you can have two people with conflicting but both correct 0:12:54.760 --> 0:12:57.679 views of the same situation, right, Because there is no 0:12:57.960 --> 0:13:00.880 ultimate truth, right, your answer is depend on your speed 0:13:00.960 --> 0:13:03.920 and your location. So what happens to break the symmetry? 0:13:04.160 --> 0:13:07.240 The symmetry is broken when the space twin turns around. 0:13:07.640 --> 0:13:10.960 That's an acceleration, right, That changes everything. Well, only the 0:13:11.000 --> 0:13:14.840 space twin does any acceleration, so that makes his case different, right, 0:13:15.280 --> 0:13:18.920 And during that acceleration, the time on Earth seems to 0:13:19.040 --> 0:13:21.800 zoom forward really fast from the point of view of 0:13:21.800 --> 0:13:24.320 the space twin. So on the way back, yeah, he 0:13:24.400 --> 0:13:27.640 sees Earth moving fast and Earth clock going slowly. But 0:13:27.760 --> 0:13:31.720 during that acceleration Earth time has leapt forward really far, 0:13:32.080 --> 0:13:34.320 so that when the space twin gets back to Earth, 0:13:34.640 --> 0:13:37.560 he's younger than his twin on Earth. Right, And the 0:13:37.679 --> 0:13:40.200 reason they're no longer symmetric is that only the space 0:13:40.240 --> 0:13:43.360 twin has done any acceleration, so you shouldn't expect them 0:13:43.520 --> 0:13:46.080 to be the same from each point of view. It's 0:13:46.120 --> 0:13:51.600 the coming back that then lets me stay younger. Yeah, exactly. Okay, 0:13:51.679 --> 0:13:55.000 let's let's dig into it even more. But let's take 0:13:55.040 --> 0:14:09.960 a quick break, all right. So this idea that time 0:14:10.040 --> 0:14:13.760 moves slower when you're going fast, it's what's cool is 0:14:13.800 --> 0:14:16.880 that it's always happening, right. It doesn't just happen when 0:14:16.880 --> 0:14:18.720 you're going at the speed of light or close to 0:14:18.720 --> 0:14:21.520 the speed of light. It's it happens like on your 0:14:21.560 --> 0:14:24.800 on a daily basis, That's right. It applies all the time. 0:14:24.840 --> 0:14:27.480 It always applies to things that have velocity relative to you. 0:14:28.040 --> 0:14:31.320 But it's a really tiny effect if you're not going 0:14:31.360 --> 0:14:35.600 really really fast. So when you're driving sixty in the freeway, yeah, 0:14:35.760 --> 0:14:38.000 your clock is running a little bit slower, but you'll 0:14:38.000 --> 0:14:41.000 never notice it. Wow, but it's there. Like if we're 0:14:41.080 --> 0:14:45.320 all feeling relativity and time dilation all the time everywhere, 0:14:45.520 --> 0:14:49.360 there's no way to escape relativity. It is everywhere. It's 0:14:49.400 --> 0:14:54.440 relatively everywhere. It's absolutely every Absolutely thing about relativity is 0:14:54.480 --> 0:14:58.120 that it's everywhere. Okay, so it only happens when you 0:14:58.120 --> 0:15:01.400 get it's only noticeable. You're saying, when you're going to 0:15:01.520 --> 0:15:03.720 close the speed up. But I heard it happens to 0:15:04.080 --> 0:15:07.320 astronauts here on Earth, like the Space Shuttle. The clocks 0:15:08.160 --> 0:15:10.320 get out of sync with the clocks on Earth. That's right, 0:15:10.360 --> 0:15:12.200 though it takes a lot of precision to measure it. 0:15:12.200 --> 0:15:15.720 It's something like every six months or so they lose 0:15:15.880 --> 0:15:18.720 like less than a hundredth of a second. So it's 0:15:18.720 --> 0:15:20.920 something we can measure, and they have really precise clocks 0:15:20.960 --> 0:15:24.080 precisely to measure this to verify these predictions, but it's 0:15:24.080 --> 0:15:28.160 not something that people have really like qualitatively experienced. We 0:15:28.200 --> 0:15:30.800 haven't had an astronaut come back, you know, deep into 0:15:30.800 --> 0:15:34.200 the future and still feel young. And it goes really nonlinear, right, 0:15:34.240 --> 0:15:36.520 as you get faster and faster, the effect gets stronger 0:15:36.520 --> 0:15:40.560 and stronger. But they did do the twin experiment with astronauts, right, Like, 0:15:40.600 --> 0:15:43.360 they sent to one twin into space for a whole year, 0:15:43.480 --> 0:15:46.560 and then he came back and technically he was point 0:15:46.600 --> 0:15:49.240 oh one seconds younger. That's right. I wonder if he 0:15:49.280 --> 0:15:51.360 was the one who was originally born first or the 0:15:51.360 --> 0:15:53.560 one who's ovisually born second, because it be interesting and 0:15:53.640 --> 0:15:55.360 be like, well you used to be the older twin, 0:15:55.440 --> 0:15:58.880 but now I'm the older twin. A should have stayed 0:15:58.920 --> 0:16:02.160 up there for ten more years. Do you think growing 0:16:02.200 --> 0:16:04.320 up twins still argue by that kind of stuff. Well, 0:16:04.360 --> 0:16:06.640 I'm the older brother, so you have to listen to me. 0:16:06.920 --> 0:16:09.720 What do you think they're both austers. They're probably trying 0:16:09.720 --> 0:16:12.160 to one up each other. Well, yeah, I'm an engineer. 0:16:12.200 --> 0:16:14.840 Oh yeah, I'm a pilot. Oh yeah, I'm a I'm 0:16:14.880 --> 0:16:19.320 an auster. Not me too, yeah, probably it never ends, right, 0:16:19.400 --> 0:16:22.280 but technically that's true. He went out into space, went 0:16:22.280 --> 0:16:25.160 around the Earth for a whole year. When he came back. Technically, 0:16:25.520 --> 0:16:29.240 time for him moved one hundred of a second slower. Yeah, 0:16:29.240 --> 0:16:31.160 I wonder what he's gonna do with all that extra time, 0:16:31.240 --> 0:16:34.840 you know, scratches nose or something. Right, it's gone, he 0:16:35.000 --> 0:16:37.840 lost it. He used it up. Yeah, But as you 0:16:37.880 --> 0:16:40.320 go faster and faster, the effect gets stronger and stronger, 0:16:40.920 --> 0:16:43.800 and as you approached the speed of light, time gets 0:16:43.840 --> 0:16:46.400 so slow that we can say that if you go 0:16:46.520 --> 0:16:50.440 the speed of light, time would actually stop. So if 0:16:50.520 --> 0:16:52.920 I'm zooming running past you at the speed of light, 0:16:53.280 --> 0:16:57.040 you would see my clock totally frozen, exactly. Now, caveats 0:16:57.040 --> 0:17:00.480 are important here. Nothing that has mass actually go the 0:17:00.480 --> 0:17:03.840 speed of light, right, and only massless things can go 0:17:03.920 --> 0:17:05.639 the speed of light, So you can never go the 0:17:05.640 --> 0:17:08.080 speed of lights. Are saying I have much mass, Daniel. 0:17:09.119 --> 0:17:12.920 You're pretty massive, dude, Yeah, by which I mean you're funny, 0:17:12.960 --> 0:17:17.080 and you're massively awesome thanking, and you have a massively 0:17:17.400 --> 0:17:20.959 excellent podcast, and you are brilliant. But you're not entirely 0:17:20.960 --> 0:17:23.639 made of light. But that all right, Yeah, I was 0:17:23.680 --> 0:17:28.399 just fishing for relative compliments. You're absolutely wonderful. So if 0:17:28.400 --> 0:17:30.920 you have somebody in a spaceship and they're going super 0:17:30.960 --> 0:17:32.960 duper fast and they're approaching the speed of light, and 0:17:33.080 --> 0:17:35.400 time slows down further and further, to the point where 0:17:35.400 --> 0:17:39.080 it almost stops. But remember, for them, time doesn't slow down. 0:17:39.160 --> 0:17:41.800 It's not like they're living in molasses. It's just our 0:17:41.920 --> 0:17:45.439 observation of their time. So if somehow a photon had 0:17:45.480 --> 0:17:48.840 a clock, yeah, our view of the photons clock would 0:17:48.840 --> 0:17:51.280 be that it was frozen. Right for us, Photons don't 0:17:51.320 --> 0:17:53.679 move forward in time. They are frozen in time. But 0:17:53.720 --> 0:17:57.120 if you were a photon, what would your experience be. Well, 0:17:57.119 --> 0:17:59.080 it's hard to answer that because you're not a photon, 0:17:59.080 --> 0:18:01.639 and you have to have that concept of like ascension photon, 0:18:01.720 --> 0:18:06.200 which seems impossible, but it's always basically an impossible question 0:18:06.200 --> 0:18:09.720 to answer. But they remember, your time always moves forward 0:18:10.119 --> 0:18:16.320 um at one second per second. Okay, so that's the 0:18:16.320 --> 0:18:20.800 effect of time dilation. Time moves seems to move slower 0:18:20.800 --> 0:18:24.680 when you're going faster. So let's get into why it happens. 0:18:24.720 --> 0:18:28.280 Do we know why this happens. We do know why, 0:18:28.440 --> 0:18:32.680 and it's a consequence of another really strange, counterintuitive thing 0:18:32.760 --> 0:18:35.960 that we've observed about the universe that makes very little sense. 0:18:36.760 --> 0:18:40.879 So it's a conundrum built on a conundrum. It's a bizarre, 0:18:41.080 --> 0:18:45.439 counterintuitive consequence of something really weird about the universe and 0:18:45.600 --> 0:18:49.520 really weird about light. Actually, it's the fact that everybody 0:18:49.600 --> 0:18:53.320 always observes light going at the same speed, no matter 0:18:53.400 --> 0:18:57.160 how fast they're going relative to the source of the light. Okay, 0:18:57.240 --> 0:19:00.520 let's break it down what that means. So light travels 0:19:00.560 --> 0:19:04.480 through space, but nobody can see it move faster than 0:19:04.800 --> 0:19:07.359 that speed that light losing. That's right. There's a certain 0:19:07.400 --> 0:19:09.520 speed of light that goes through space three times ten 0:19:09.600 --> 0:19:11.720 to the eights per second. And we'll call it the 0:19:11.720 --> 0:19:14.639 speed of light. Of course. And if I'm standing on 0:19:14.680 --> 0:19:17.480 a planet and I turn on a flashlight, then the 0:19:17.560 --> 0:19:21.280 light leaves me and travels at three times tended them 0:19:21.440 --> 0:19:24.960 per second away from me. Right, And if I'm and 0:19:25.000 --> 0:19:27.120 if you're shooting it at me, then I see moving 0:19:27.160 --> 0:19:29.639 towards me at three times ten to the eight meters 0:19:29.680 --> 0:19:32.320 per second. Okay, that's right, even if you're even if 0:19:32.359 --> 0:19:34.520 you're on a rocket ship and you're moving towards me, right, 0:19:34.720 --> 0:19:36.840 say you're moving towards me at half the speed of light. 0:19:37.480 --> 0:19:40.320 I shoot my laser beam at you're my flashlight at you, 0:19:40.320 --> 0:19:42.480 you still see that flashlight, the light from it coming 0:19:42.480 --> 0:19:44.920 at you at the speed of light, right, And that's 0:19:44.960 --> 0:19:48.040 different from you know, sound waves or rocks or something, 0:19:48.200 --> 0:19:50.919 or a baseball. Like that's weird. Right, Like, if you 0:19:51.000 --> 0:19:54.080 throw a baseball at me and I'm running full speed 0:19:54.080 --> 0:19:57.120 towards you, that baseball is going to be it's gonna 0:19:57.160 --> 0:19:59.600 look like it's moving really fast towards me. That's right. 0:19:59.640 --> 0:20:01.119 If I threw a baseball at you at a hundred 0:20:01.119 --> 0:20:03.199 miles an hour, which I promise I can totally do, 0:20:03.280 --> 0:20:06.399 this is very realistic, and you're running towards me at 0:20:06.440 --> 0:20:10.480 fifty miles an hour, which I'm sure you're totally capable of. Um, 0:20:10.840 --> 0:20:13.760 then obviously I see the baseball is moving away from 0:20:13.800 --> 0:20:15.720 me at a hundred miles per hour, but you see 0:20:15.720 --> 0:20:17.879 the baseball is coming towards you at a hundred fifty 0:20:17.920 --> 0:20:20.119 miles per hour. Right. That's the way it works for 0:20:20.160 --> 0:20:22.639 normal things. But you're saying that if that baseball instead 0:20:22.640 --> 0:20:24.760 of a baseball, it was a beam of light, that 0:20:24.800 --> 0:20:28.240 wouldn't happen. That's right. Light doesn't follow those rules. Everybody 0:20:28.240 --> 0:20:31.359 who measures it measures it as traveling at that fixed 0:20:31.400 --> 0:20:33.480 speed of light. No matter what. I mean, there are 0:20:33.520 --> 0:20:36.280 caveats here, like it slows down and it travels through 0:20:36.320 --> 0:20:38.520 air or water, whatever, But let's just talk about it 0:20:38.520 --> 0:20:41.280 in a vacuum. The crazy thing is that doesn't matter 0:20:41.280 --> 0:20:43.920 how fast you're going, everybody sees light is traveling at 0:20:43.920 --> 0:20:47.359 this maximum speed of the universe, no matter what. And 0:20:47.400 --> 0:20:50.960 that's crazy, right and right there is where your concept 0:20:51.040 --> 0:20:54.000 that everybody sees the same thing the same way, or 0:20:54.000 --> 0:20:57.080 that there is one absolute truth that we're all observing 0:20:57.080 --> 0:21:00.320 in different ways breaks down because your description of events 0:21:00.320 --> 0:21:02.440 and my description events are going to be very different. 0:21:02.560 --> 0:21:05.200 If we see light moving at different speeds. It's the 0:21:05.320 --> 0:21:08.199 weird It's like a weird rule of the universe. Not 0:21:08.359 --> 0:21:11.159 that light something can't travel at this faster than the 0:21:11.200 --> 0:21:13.680 speed of light. It's a weird rule that says nothing 0:21:13.720 --> 0:21:16.400 can be seen to travel faster than the speed of light, 0:21:16.640 --> 0:21:19.080