WEBVTT - How does relativity affect our perception of time? 0:00:08.360 --> 0:00:12.320 Ay, Daniel, what's the most mind blowing thing that physics 0:00:12.360 --> 0:00:15.960 has taught us about the universe? Wow? It is hard 0:00:16.000 --> 0:00:19.480 to pick just one. Could I do a top five? Maybe? No? 0:00:19.640 --> 0:00:23.880 I want your single all time one thing that you 0:00:23.960 --> 0:00:28.360 think is the most bonkers that we've learned about Who 0:00:28.520 --> 0:00:31.840 had to challenge? All Right? I got one. There is 0:00:32.000 --> 0:00:34.320 one thing about the universe that, to me is the 0:00:34.360 --> 0:00:38.519 most brain scrambling thing I've ever learned. The hardest thing 0:00:38.520 --> 0:00:41.200 for me to get my brain around is that people 0:00:41.240 --> 0:00:44.879 can disagree about the order in which events happened. We 0:00:44.920 --> 0:00:50.160 don't all see the same things happening sometimes in the universe. Yeah, 0:00:50.440 --> 0:00:52.839 you can see things happening in one order, and then 0:00:52.960 --> 0:00:55.840 I can see things happening in a totally different order, 0:00:56.080 --> 0:01:16.399 and we can both be correct. Hi'm poor hammade cartoonists 0:01:16.440 --> 0:01:20.080 and the creator of PhD Commics. Hi. I'm Daniel. I'm 0:01:20.080 --> 0:01:23.960 a particle physicist, sometimes in a podcast host other times, 0:01:24.080 --> 0:01:27.440 and everybody disagrees about when I do what. Welcome to 0:01:27.440 --> 0:01:31.640 our podcast. Daniel and Jorge agree to disagree about the universe, 0:01:32.640 --> 0:01:35.520 in which we explained to you the craziest, the most 0:01:35.560 --> 0:01:40.080 amazing but true things about our universe. Yeah, and this 0:01:40.200 --> 0:01:42.640 is again a production of I Heart Radio, and in 0:01:42.680 --> 0:01:45.520 our podcast we try to take you to the forefront 0:01:45.520 --> 0:01:48.480 of science to talk about the craziest things that scientists 0:01:48.480 --> 0:01:51.720 are thinking about today, and also delve into the history 0:01:51.760 --> 0:01:54.400 of science to tell you why we think the universe 0:01:54.480 --> 0:01:56.880 is so nuts and how we figured that out. Is 0:01:56.920 --> 0:01:59.400 there a history of science, Daniel, or is that also 0:01:59.440 --> 0:02:02.400 open for this agreement people disagree about in what order 0:02:02.560 --> 0:02:05.960 we discover things, or what was the most important, or 0:02:05.960 --> 0:02:08.520 how we change people's minds. Yeah. I think in our 0:02:08.520 --> 0:02:12.000 podcast we also not just talk about scientific discoveries or 0:02:12.120 --> 0:02:15.880 scientific theories, but also a little bit about how that 0:02:16.000 --> 0:02:18.880 affects how we see the universe, you know, and how 0:02:19.480 --> 0:02:25.880 it challenges what we believe about how the universe works. Yeah. Absolutely. 0:02:26.040 --> 0:02:28.320 I think a lot of the deepest questions in physics 0:02:28.360 --> 0:02:31.480 come from a sort of a philosophical motivation. We want 0:02:31.520 --> 0:02:34.600 to know how the universe works because it matters to 0:02:34.720 --> 0:02:37.600 us that we can make sense of the universe. And 0:02:37.600 --> 0:02:39.800 when we ask the universe questions and it gives us 0:02:39.840 --> 0:02:42.960 answers that force us to totally change the way we 0:02:43.000 --> 0:02:46.519 think about the universe. That has pretty deep philosophical implications, 0:02:46.560 --> 0:02:49.720 and so that's sometimes the most fun topic. Yeah, And 0:02:49.760 --> 0:02:52.760 so basically, we're just trying to blow your mind in 0:02:52.800 --> 0:02:57.560 the gentlest, most podcasts friendly way possible. Or we're trying 0:02:57.600 --> 0:03:00.079 to share with you how the minds of physics this 0:03:00.200 --> 0:03:01.960 have been blown, and we want your mind to be 0:03:01.960 --> 0:03:05.600 blown just as much. But yeah, a little bit more gently. Yes, please, 0:03:05.639 --> 0:03:08.560 I'm not sure my brain can handle this much mind 0:03:08.560 --> 0:03:11.280 blowing is in in one hour. But you know, when 0:03:11.320 --> 0:03:14.480 I was learning physics as an undergrad, I remember these 0:03:14.560 --> 0:03:18.640 moments when I finally really deeply understood a concept, and 0:03:18.720 --> 0:03:22.080 that concept would force me to relax or destroy or 0:03:22.120 --> 0:03:24.720 get rid of some assumption I had about the universe, 0:03:24.760 --> 0:03:27.280 and I realized that that just wasn't true, that the 0:03:27.320 --> 0:03:31.399 way I'd been thinking about the world was just fundamentally wrong. Yeah, 0:03:31.480 --> 0:03:33.919 it's amazing. And so today we'll be talking about one 0:03:33.960 --> 0:03:37.520 such topic that honestly gives me a headache every time 0:03:37.520 --> 0:03:40.200 we talked about it, Daniel. We've written about it in 0:03:40.280 --> 0:03:42.720 actually a couple of chapters in our book We Have 0:03:42.760 --> 0:03:44.840 No Idea, A Guide to the Unknown Universe, And I 0:03:44.840 --> 0:03:47.600 have to admit I never really got my head around it. 0:03:48.080 --> 0:03:53.000 I authored the book, but didn't actually understood what was 0:03:53.040 --> 0:03:55.440 in it. Yeah, and this is a topic that people 0:03:55.520 --> 0:03:58.400 email us about, they ask us about, they listen to 0:03:58.440 --> 0:04:00.960 some of our podcasts about it, and still right in 0:04:01.000 --> 0:04:04.000 with questions. I think there's a lot of popular misconceptions 0:04:04.040 --> 0:04:07.040 about how this works and some consequences that I think 0:04:07.040 --> 0:04:09.440 a lot of people have not really realized. There's some 0:04:09.800 --> 0:04:13.880 really deep philosophical implications to these ideas that I don't 0:04:13.920 --> 0:04:16.640 think have been widely enough appreciated. Yeah, So to the 0:04:16.680 --> 0:04:25.040 on the podcast, we'll be talking about how does relativity 0:04:25.080 --> 0:04:32.040 affect our understanding of time? Time? Or I guess the 0:04:32.080 --> 0:04:36.280 short title is is there a consistent order of events 0:04:36.600 --> 0:04:40.599 in the universe? Yeah, and spoiler alert, the answer might 0:04:40.640 --> 0:04:45.760 be it's relatively surprising that the answer is not what 0:04:45.880 --> 0:04:49.360 you expect. We've talked to this podcast before about time dilation, 0:04:49.720 --> 0:04:52.360 the effect of speed on the rate of which clocks 0:04:52.400 --> 0:04:55.400 move forward, and that's weird and that's hard for people 0:04:55.400 --> 0:04:57.680 to get their mind around, and there's some misconceptions there. 0:04:57.920 --> 0:05:01.040 But you know, time and relativity is even weirder than that. 0:05:01.560 --> 0:05:04.600 It's more than just making things run slowly or making 0:05:04.600 --> 0:05:07.919 things run quickly. It's about how things happen here versus 0:05:07.920 --> 0:05:10.440 how things happen there. Do you think age also affects 0:05:10.440 --> 0:05:12.560 how you perceive time? Like I feel like my kids, 0:05:13.279 --> 0:05:15.440 I have no patients at all, and that the world 0:05:15.520 --> 0:05:20.000 just moves at a snail's pace for them, whereas for me, 0:05:20.080 --> 0:05:22.720 as I get older, things he's moved fast. Well, I 0:05:22.760 --> 0:05:26.560 mean I moved slower, but the world seems to move fast. Yeah, 0:05:26.640 --> 0:05:28.880 And I think that Actually you raise an interesting point, 0:05:29.000 --> 0:05:32.400 because we are all imperfect observers if you just sort 0:05:32.440 --> 0:05:35.200 of watch something and describe it later. There's all these 0:05:35.240 --> 0:05:38.680 studies about how people give terrible accounts, you know, even 0:05:38.720 --> 0:05:42.200 eyewitnesses give different accounts of the same events, And so 0:05:42.240 --> 0:05:45.880 that's certainly one problem. It's like people are unreliable observers. 0:05:45.920 --> 0:05:48.960 But even in the case when everybody was a perfect observer, 0:05:49.040 --> 0:05:51.360 everybody had a video camera, I've already had, you know, 0:05:51.640 --> 0:05:55.279 perfect measuring devices, and everybody accounted for transmission of light 0:05:55.320 --> 0:05:58.320 and all that stuff. Even in those cases, it's hard 0:05:58.520 --> 0:06:00.520 to make sense of the universe. Like if we were 0:06:00.560 --> 0:06:04.000 all robots but the exact same you know, clock in 0:06:04.040 --> 0:06:08.400 our chips, and we were all measuring things exactly, we 0:06:08.560 --> 0:06:11.480 it would still be kind of a weird universe where 0:06:11.560 --> 0:06:15.279 not everyone would agree maybe on the order of events, Yeah, precisely. 0:06:15.480 --> 0:06:18.440 And you have to separate those because we're interested not 0:06:18.560 --> 0:06:21.320 in the question of our people good eyewitnesses, because we 0:06:21.320 --> 0:06:23.760 already know the answer to that is no um, but 0:06:23.880 --> 0:06:26.640 the question of how does the universe actually work, because 0:06:26.800 --> 0:06:28.360 we want to know the answer to the question, not 0:06:28.440 --> 0:06:31.360 just for humanity, but in general, you know, the deep 0:06:31.400 --> 0:06:33.800 fundamental questions, so that when the aliens come, when we 0:06:33.800 --> 0:06:36.159 talk to them about physics, we can make sense of 0:06:36.200 --> 0:06:38.599 what they've learned. And we don't want to learn human physics, 0:06:38.680 --> 0:06:41.599 we want to learn fundamental physics. And so this idea 0:06:41.640 --> 0:06:46.480 of time dilation, this idea that time move slowly depending 0:06:46.520 --> 0:06:49.640 on maybe how fast you're going or or where you are, 0:06:50.760 --> 0:06:53.840 is kind of weird and pretty mind blowing. And so 0:06:53.880 --> 0:06:56.279 we were wondering out there how many people really sort 0:06:56.279 --> 0:07:00.200 of understood what it means and what the ramification, what 0:07:00.279 --> 0:07:05.359 it means for our basic understanding of time. So I 0:07:05.400 --> 0:07:08.520 walked around campus that use the irvine, and I asked folks, 0:07:08.839 --> 0:07:11.240 not people in the physics department, not people who have 0:07:11.320 --> 0:07:15.440 taken my class on special relativity, just random people on campus, 0:07:15.680 --> 0:07:18.480 willing to answer questions from a scrafty looking physicist. So 0:07:18.480 --> 0:07:20.480 I think for a moment, what do you know about 0:07:20.480 --> 0:07:24.360 how relativity affects our understanding of time? Here's what people 0:07:24.360 --> 0:07:27.560 had to say. Do you know how relativity affects our 0:07:27.680 --> 0:07:32.680 understanding of time? No? I do not. Actually, no, I'm 0:07:32.680 --> 0:07:38.040 not share Newton's theory of relativity. I'm sorry, I don't. 0:07:38.200 --> 0:07:40.880 Is this physics like a physics question, I'm not. I 0:07:40.920 --> 0:07:43.680 don't know much about physics. Okay, I don't know how 0:07:43.720 --> 0:07:47.840 to answer that. I'm an English Ready, if there was 0:07:47.840 --> 0:07:50.200 a whole like demonstration of that, where if like you 0:07:50.360 --> 0:07:53.760 go at like in a spaceship, like near the speed 0:07:53.800 --> 0:07:55.960 of light or something, and then you can come back 0:07:56.000 --> 0:07:58.640 and then like some amount of time has changed on 0:07:58.720 --> 0:08:01.080 Earth while like no, really time has changed for you 0:08:01.160 --> 0:08:03.440 or somewhere about and thinking Planet of the Apes when 0:08:03.440 --> 0:08:05.080 they're in the spaceship and then by the time they 0:08:05.120 --> 0:08:08.200 come back, they've only aged a couple of years, but 0:08:08.320 --> 0:08:10.760 timeline Earth has passed a lot because they're traveling at 0:08:10.760 --> 0:08:13.360 a different speed. Remain Planet Apes is a well known 0:08:13.360 --> 0:08:19.000 physics documentary. Right, yes, yes, I believe relativity. That's from 0:08:19.000 --> 0:08:24.280 Einstein is the idea that like time doesn't flow at 0:08:24.280 --> 0:08:27.840 the same rate like across the universe. I think something 0:08:27.920 --> 0:08:30.520 like I think gravity or something affects like how it 0:08:30.560 --> 0:08:33.839 flows in other places. All Right, a couple of knows, 0:08:33.880 --> 0:08:35.880 but a couple of people did have a lot of 0:08:35.880 --> 0:08:39.199 pretty good ideas, or at least they said a lot 0:08:39.200 --> 0:08:42.520 of physics terms. And I mean like Newton's theory of relativity, 0:08:43.559 --> 0:08:46.440 like the Planet of the Apes. You know, I've seen 0:08:46.440 --> 0:08:49.760 that movie. Yeah, Planet of the Apes. That's a that's 0:08:49.760 --> 0:08:55.240 a documentary about physics. Yeah, there you go. Now, you're right. 0:08:55.320 --> 0:08:57.960 People had the people who knew anything about it definitely 0:08:58.080 --> 0:09:02.240 knew that relativity and time connected and that relativity changes 0:09:02.280 --> 0:09:05.720 have time moves. And I think already that's a big success, right, 0:09:05.760 --> 0:09:08.240 the idea that time is not universal, that we don't 0:09:08.280 --> 0:09:11.199 have clocks everywhere in the universe ticking forward at the 0:09:11.280 --> 0:09:14.240 same rate. That's a big step forward to to break 0:09:14.280 --> 0:09:16.680 that assumption. You don't think you didn't have a theory 0:09:16.720 --> 0:09:19.720 of relativity. I mean he could have had one about 0:09:19.720 --> 0:09:22.280 his relatives or something, but just not not the one 0:09:22.320 --> 0:09:25.800 that caught up right. His theory relativity was don't bring 0:09:25.880 --> 0:09:32.439 up politics at Christmas dinner. Yeah, also also useful things 0:09:32.480 --> 0:09:34.640 to live by. But yeah, I think it seems like 0:09:34.760 --> 0:09:40.120 maybe there is a general sense right that relativity effects 0:09:40.120 --> 0:09:44.080 our understanding of time and makes things weird, but maybe 0:09:44.120 --> 0:09:47.080 a lot of people don't know how or what. Yeah. 0:09:47.080 --> 0:09:49.480 And I think also there's a lot of misunderstandings based 0:09:49.520 --> 0:09:51.640 on the emails that we get from listeners who are 0:09:51.640 --> 0:09:55.320 asking us questions about relativity and tweets and stuff that 0:09:55.360 --> 0:09:58.080 people have posted. I have the feeling that people think 0:09:58.120 --> 0:10:01.800 that if you move fast and your clock will slow down, 0:10:02.280 --> 0:10:04.280 which is not the right way to think about time 0:10:04.280 --> 0:10:07.400 and relativity. That's how I thought time and relativity works. 0:10:07.440 --> 0:10:13.000 So we're in for a long conversation. So, um, so 0:10:13.040 --> 0:10:15.280 people have been writing with questions about time. Yeah, a 0:10:15.280 --> 0:10:17.800 lot of people ask the questions like what is it 0:10:17.840 --> 0:10:20.559 like to be a photon? Or how does a photon 0:10:20.720 --> 0:10:22.880 move at the speed of light? If moving at the 0:10:22.920 --> 0:10:25.360 speed of light means that it's time is frozen, they're 0:10:25.400 --> 0:10:28.199 asking what would be the human experience of moving at 0:10:28.240 --> 0:10:33.120 these velocities where physics gets really weird. Yeah, and so 0:10:33.200 --> 0:10:36.040 let's clear that up. First of all, the key thing 0:10:36.120 --> 0:10:40.000 to understand about relativity and time and clocks. Is that 0:10:40.360 --> 0:10:43.000 the speed at which o'clock moves depends on its relative 0:10:43.080 --> 0:10:47.080 velocity to you. Now, these things are always relative. So 0:10:47.120 --> 0:10:49.680 if you're holding a clock and it's not moving relative 0:10:49.720 --> 0:10:51.800 to you, it's just going to go forward at one 0:10:51.840 --> 0:10:55.400 second per second. Like you always experience time the same 0:10:55.480 --> 0:10:59.760 way because you're not moving relative to yourself. Right, it's 0:10:59.760 --> 0:11:03.640 all the relative motion that distorts time. If you see 0:11:03.679 --> 0:11:06.360 a clock moving fast, and you're watching the face of 0:11:06.400 --> 0:11:10.280 that clock, then it runs slowly, but only according to you. 0:11:10.600 --> 0:11:12.360 I think maybe we need to step back a little 0:11:12.400 --> 0:11:15.280 bit paint the picture of Like I'm standing here and 0:11:15.320 --> 0:11:17.679 I'm holding a clock in front of me. You're saying 0:11:17.720 --> 0:11:21.880 that because the clock is not moving relative to me, 0:11:22.320 --> 0:11:26.280 I'm not going to see or feel anything strange about that. 0:11:26.280 --> 0:11:28.880 That's right. Like it's it's gonna I'm gonna hear it ticking, 0:11:28.880 --> 0:11:32.320 and I'm gonna it's gonna sound like it's taking at 0:11:32.320 --> 0:11:35.280 one second. That's right. And you always experience time the 0:11:35.320 --> 0:11:38.920 same way, Like you don't experience time going slowly or 0:11:39.000 --> 0:11:42.520 going quickly. But if I'm zipping past you at half 0:11:42.520 --> 0:11:44.400 the speed of light and I look at your clock, 0:11:44.760 --> 0:11:47.920 that it looks to me like your clock is running slowly. Now, 0:11:47.960 --> 0:11:50.920 according to you, the clock is not moving. You're holding it, 0:11:51.120 --> 0:11:53.760 so the clock runs at the normal pace one second 0:11:53.760 --> 0:11:57.680 per second like usual. You don't experience time slowing down 0:11:57.760 --> 0:12:00.679 just because I'm moving past you and I see your 0:12:00.720 --> 0:12:03.760 time slowing down. But again, if i'm is it being 0:12:03.760 --> 0:12:05.640 passed you at half the speed of light, then it 0:12:05.679 --> 0:12:09.439 looks to me like your clock is running slowly. Well, 0:12:09.480 --> 0:12:10.959 first of all, how would you look at my clock 0:12:11.840 --> 0:12:14.680 if you were moving back? Remember would you have time? Daniel? Really, 0:12:14.720 --> 0:12:19.080 I'm super robot observer. Remember I can observe anything accurately. Oh, 0:12:19.160 --> 0:12:22.480 I see you're running at a basilian giga hurt. I 0:12:22.520 --> 0:12:25.960 am super physics scratched. No, you have to imagine I 0:12:26.000 --> 0:12:28.880 have like some awesome telescope and I'm watching the face 0:12:28.920 --> 0:12:30.760 of your clock or something. All right, So I'm in 0:12:30.800 --> 0:12:32.920 my little space here and I have my clock, and 0:12:32.960 --> 0:12:36.520 it's taking away and you're zooming bye. And as you're 0:12:36.600 --> 0:12:39.120 zooming by, we're going to go into super matrix slow 0:12:39.120 --> 0:12:43.080 motion and you'r and so you're looking at my clock, 0:12:44.120 --> 0:12:47.000 and my clock is moving relative to you like you're 0:12:47.000 --> 0:12:50.840 seeing it go by. And if you were to measure 0:12:50.920 --> 0:12:53.560 its ticks you, it would to you it would seem 0:12:53.559 --> 0:12:58.000 like it's ticking slower like tick take right, is that 0:12:58.120 --> 0:13:01.480 kind of what you mean by that? My clock seems 0:13:01.480 --> 0:13:05.040 slower to you precisely, and your clock seems slow to me, 0:13:05.200 --> 0:13:08.760 But it doesn't seem slow to you. Right, It looks 0:13:08.800 --> 0:13:11.600 to me like you are aging slowly because your time 0:13:11.679 --> 0:13:14.960 is running slowly. In a year, for me, less time 0:13:15.000 --> 0:13:16.720 will have passed for you, and I will see you 0:13:16.760 --> 0:13:21.360 aging slowly. But for you time just moves forward because again, 0:13:21.400 --> 0:13:23.880 you're not moving relative to you. The thing to remember 0:13:24.200 --> 0:13:28.280 is moving clocks run slowly, so you're not moving relative 0:13:28.320 --> 0:13:30.760 to yourself, So your clock doesn't run anymore slowly, but 0:13:30.840 --> 0:13:35.840 they only move slowly relative to the person who's not moving. Yeah, 0:13:35.840 --> 0:13:38.600 everybody has a frame of reference that's centered at them, 0:13:38.960 --> 0:13:41.319 and things are moving or not moving in their frame. 0:13:41.360 --> 0:13:44.160 And if they're moving fast, then their clocks run slowly. 0:13:44.160 --> 0:13:47.160 If they're not moving, then their clocks run normally, all right, 0:13:47.280 --> 0:13:52.800 And that's that's basic general relativity is that time seems 0:13:52.840 --> 0:13:55.840 to slow down in a pocket of space that's moving 0:13:56.400 --> 0:14:00.760 fast relative to you. So that's special relativity or relativity 0:14:00.960 --> 0:14:03.320 has to do with how space is bent by mass. 0:14:03.480 --> 0:14:06.120 Special relativity is all these effects of light speed and 0:14:06.200 --> 0:14:09.359 clocks and stuff. And it's not just that it appears 0:14:09.400 --> 0:14:13.640 to go slowly, like your time really does move slowly 0:14:13.679 --> 0:14:16.760 according to me. And that's the crux is that I 0:14:16.840 --> 0:14:19.560 have a story about the universe that I'm telling based 0:14:19.600 --> 0:14:23.120 on my perfect observations, and that's a true story. And 0:14:23.200 --> 0:14:26.080 you're telling a different story about the order in which 0:14:26.120 --> 0:14:28.600 things happened, in the rate at which time flowed, and 0:14:28.640 --> 0:14:31.880 that's your story. And your story is different because you're 0:14:31.880 --> 0:14:34.720 in a different place and moving in a different speed 0:14:34.760 --> 0:14:39.240 relative to me. But both our stories can be correct, meaning, um, 0:14:39.360 --> 0:14:42.520 I can experience my clock taking it one second per second, 0:14:42.720 --> 0:14:44.960 but you would say that my clock is not taking 0:14:44.960 --> 0:14:47.840 it one second per second precisely. And it's not just 0:14:48.200 --> 0:14:51.320 that it appears that way, it actually is. I guess 0:14:51.320 --> 0:14:54.520 it depends on what the deffer nition of is. Thank you, Bill. 0:14:55.320 --> 0:14:57.480 And so you know a lot of people write in 0:14:57.560 --> 0:15:00.640 they say things like, you know, a photon is moving 0:15:00.720 --> 0:15:03.880 at the speed of light, which is true. And if 0:15:03.920 --> 0:15:06.400 a photon had a clock on it, somehow, I don't 0:15:06.400 --> 0:15:07.840 know how you could have a photon with a clock 0:15:07.880 --> 0:15:10.640 on it. But imagine you could then wouldn't that clock 0:15:10.760 --> 0:15:13.840 be frozen? Yes? True, because something moving at the speed 0:15:13.880 --> 0:15:16.720 of light, it's time slows down to an effective rate 0:15:16.760 --> 0:15:20.000 of zero. But that doesn't mean that photon is not 0:15:20.120 --> 0:15:25.520 experiencing time. It's experiencing time maybe normally, but by the 0:15:25.560 --> 0:15:28.720 time it blinks, it's made it across the whole length 0:15:28.760 --> 0:15:30.920 of the universe. Yeah, because from the point of view 0:15:31.000 --> 0:15:34.680 the photon, I guess the whole universe is moving past 0:15:34.800 --> 0:15:37.480 it at the speed of light, and so the whole 0:15:37.600 --> 0:15:40.440 universe is like length contracted down to zero. We'll have 0:15:40.520 --> 0:15:42.400 to do a whole other episode about the effect of 0:15:42.400 --> 0:15:45.640 relativity on length and distances and crazy stuff like that. 0:15:46.240 --> 0:15:49.400 But the idea is that moving clocks runs slowly. That's 0:15:49.400 --> 0:15:51.880 the thing to keep in mind, because all these statements 0:15:51.880 --> 0:15:54.680 have to be made in a relative sense. You can't 0:15:55.000 --> 0:15:58.240 say I'm moving really fast, and therefore my clock has 0:15:58.280 --> 0:16:00.400 run slowly. You have to say I'm moving with fast 0:16:00.520 --> 0:16:04.080 relative to what. And it's for that observer that your 0:16:04.080 --> 0:16:06.960 clock is running slowly, not for you, right, Because I'm 0:16:07.000 --> 0:16:09.280 sitting here in my pocket of space and I'm watching 0:16:09.320 --> 0:16:11.520 you sit by and if I look at your clock, 0:16:12.120 --> 0:16:15.520 I would say that your clock is moving slowly, and 0:16:15.600 --> 0:16:17.280 you would be correct. And I would look at your 0:16:17.280 --> 0:16:20.320 clock and say your clock is moving slowly and I 0:16:20.360 --> 0:16:23.760 would be correct. Well, it would be a really short conversation. 0:16:23.800 --> 0:16:28.040 Then if you're moving past, have dispeeded, like, hey, that 0:16:28.120 --> 0:16:31.720 well he's gone already, forget it. If this podcast was 0:16:31.760 --> 0:16:33.880 in stereo, we could do some cool effects. They're resooming 0:16:33.880 --> 0:16:39.080 back and forth. Make it happen, engineers, you started to 0:16:39.120 --> 0:16:41.560 treat engineers the same way I have now. Just engineers 0:16:41.560 --> 0:16:45.120 are just people out there to make things happen. I 0:16:45.160 --> 0:16:47.800 think people who make things happen are awesome. By the way, 0:16:48.480 --> 0:16:52.840 my caveat to day engineers. All right, So that's that's 0:16:53.560 --> 0:16:59.040 special relativity. That's the general idea that, uh, time seems 0:16:59.120 --> 0:17:03.600 to move totally depending on how fast you're going relative 0:17:03.720 --> 0:17:06.680 to other people who might be watching your clock. Yeah, 0:17:06.680 --> 0:17:09.280 I would say time moves slowly for people that are 0:17:09.280 --> 0:17:12.400 moving fast relative to you. I think that's pretty close 0:17:12.440 --> 0:17:15.639 to what it's just said. I'm sure it's not. We 0:17:15.680 --> 0:17:18.560 can disagree on that, all right. So that's special relativity, 0:17:18.600 --> 0:17:24.119 and it's it creates a weird situation for arguments about 0:17:24.160 --> 0:17:27.520 what happened and in what order things happen, and just 0:17:27.560 --> 0:17:31.640 in general um about time and in the universe. So 0:17:31.840 --> 0:17:34.399 let's get into that, but first let's take a quick break, 0:17:47.400 --> 0:17:49.640 all right, Daniel, Let's maybe get into the details here 0:17:49.640 --> 0:17:53.800 of how time or how special relativity messes with our 0:17:53.920 --> 0:17:57.760 understanding of time. So what what's them? Are we going 0:17:57.800 --> 0:18:00.000 to paint a picture for people? Are are were gonn 0:18:00.000 --> 0:18:03.600 to be on trains on rockets? Or Alice and Bob 0:18:03.680 --> 0:18:06.520 going to be involved? Or yeah, let's let's mix it 0:18:06.600 --> 0:18:08.959 up a little bit, because usually special relativity is like 0:18:09.000 --> 0:18:12.439 people on trains, because when they invented special relativity, trains 0:18:12.440 --> 0:18:16.000 are like the fastest thing around. But that's old and 0:18:16.280 --> 0:18:20.520 usually quantum mechanics thought experiments involved two experimenters named Alice 0:18:20.560 --> 0:18:22.959 and Bob. But let's pick it up. Let's use Alice 0:18:22.960 --> 0:18:26.359 and Bob for a special relativity thought experiment. Let's use 0:18:26.400 --> 0:18:30.840 Alicia Andrew berta perfect though, just to mix it up, 0:18:31.080 --> 0:18:34.720 all right, So if um, Alicia and Roberto are having 0:18:34.760 --> 0:18:37.760 a race, say, it's like some family events right there 0:18:37.760 --> 0:18:41.080 there with their relatives, so it's all about relativity and 0:18:41.160 --> 0:18:43.760 they've all had their you know, Christmas Ham or whatever, 0:18:43.800 --> 0:18:45.439 and now they're going to go out and make an 0:18:45.480 --> 0:18:49.520 ill advised hundred yard dash in the backyard. And they're 0:18:49.520 --> 0:18:52.880 both really fast, and people are watching the race, and 0:18:52.920 --> 0:18:55.440 then afterwards, of course they're going to argue about who one. 0:18:55.960 --> 0:18:58.520 But let's say that everybody who's watching the race is 0:18:58.560 --> 0:19:01.919 a perfect observer. Everybody has um a clock that they 0:19:01.920 --> 0:19:05.760 can start and stop, and everybody's really paying attention and 0:19:05.960 --> 0:19:09.199 knows what they're doing. Then the question is who wins 0:19:09.200 --> 0:19:12.480 the race? So they're both at the starting line, you know, 0:19:12.560 --> 0:19:15.200 we said go, they start running towards the finish line, 0:19:15.680 --> 0:19:18.480 and I'm sitting there at the finish line waiting to 0:19:18.480 --> 0:19:22.159 see who gets there first, precisely and all right. The 0:19:22.400 --> 0:19:26.640 amazing thing is that there is no one, single correct 0:19:26.720 --> 0:19:30.800 answer for who wins this race. Now, if you're sitting 0:19:30.840 --> 0:19:33.360 at the finish line, and my money is on Alicia, 0:19:33.440 --> 0:19:37.360 to be honest, you've always liked her more than Roberto, 0:19:37.480 --> 0:19:41.600 and frankly, Roberto is pissed about it. Well, she's my cousin, 0:19:41.680 --> 0:19:46.080 So it's Roberto, man, what's wrong with you? Anyway? Um, 0:19:46.119 --> 0:19:49.800 if you are sitting at the finish line, so you 0:19:49.880 --> 0:19:54.560 have um no velocity relative to the ground. Then you 0:19:54.680 --> 0:19:58.439 might see Alice. You might see Alicia beat Roberto in 0:19:58.480 --> 0:20:01.160 the race. Cool, and might think, well, that's it, that's 0:20:01.160 --> 0:20:03.879 the answer, right, she won time to celebrate. So so 0:20:03.920 --> 0:20:06.560 I'm sitting in a chair by the finish line, and 0:20:06.920 --> 0:20:10.240 to me, Alicia was running faster than Bob, so she 0:20:10.320 --> 0:20:13.560 got to the finish line first, precisely, And you might think, well, 0:20:13.600 --> 0:20:16.440 that's it, right. Other people might see from another angle, 0:20:16.640 --> 0:20:19.479 or other people might be sitting somewhere differently, or you know, 0:20:19.480 --> 0:20:21.760 maybe even if somebody is driving by in a car, 0:20:22.080 --> 0:20:25.520 they might see the velocity of Alicia and Roberto be different. 0:20:25.560 --> 0:20:29.040 But everybody should agree about the basic facts because there's 0:20:29.080 --> 0:20:31.800 a single thing that happened. That's the way you grew 0:20:31.920 --> 0:20:34.280 up thinking about the universe. That's what sort of makes 0:20:34.280 --> 0:20:36.600 intuitive sense to you. It's true, right, Like if there's 0:20:36.600 --> 0:20:39.000 somebody sitting on the opposite side of the finish line, 0:20:39.359 --> 0:20:41.280 sitting in a chair as well, you're saying that they 0:20:41.280 --> 0:20:43.679 could also see a different result, even if they're not 0:20:43.760 --> 0:20:46.720 moving like me. Actually, the other observer would have to 0:20:46.720 --> 0:20:49.359 have a different velocity and you not just be separated 0:20:49.359 --> 0:20:53.119 in distance. But you're right, The order of events that 0:20:53.240 --> 0:20:58.159 you see depends on two things. Your location relative to 0:20:58.440 --> 0:21:03.640 Alicia and Roberto and your speed relative to them. So 0:21:03.680 --> 0:21:06.880 if you are in a to make it simple, if 0:21:06.880 --> 0:21:09.280 you are in a car, and your car is super 0:21:09.320 --> 0:21:11.359 fast and you're going at like half the speed of 0:21:11.440 --> 0:21:14.760 light or something, then you could see the race differently 0:21:14.800 --> 0:21:16.760 and you could see you have a different outcome. You 0:21:16.800 --> 0:21:20.479 could see Roberto cross the finish line before Alicia. This 0:21:20.560 --> 0:21:22.679 is not some trick where like the life from you 0:21:22.760 --> 0:21:25.760 takes longer to get there or anything like that. But 0:21:26.200 --> 0:21:29.840 if you have a different relative distance to Alicia and Roberto, 0:21:30.080 --> 0:21:33.080 and you're moving at a certain velocity, then you can 0:21:33.160 --> 0:21:36.000 actually see the events happen in a different order. I 0:21:36.080 --> 0:21:39.000 am sitting in my chair, I'm going to measure who wins. 0:21:39.320 --> 0:21:45.240 But if you're moving, driving by at really fast velocities, 0:21:45.440 --> 0:21:48.600 you might see something totally different than what I see. Yeah, 0:21:48.720 --> 0:21:52.280 I could see Roberto across the finish line before Alicia, 0:21:52.480 --> 0:21:54.959 and I would also be right. But do you have 0:21:55.000 --> 0:21:59.720 to drive towards them perpendicular to them? You know what 0:21:59.800 --> 0:22:03.639 I mean? Like what's actually happening there to make you 0:22:03.680 --> 0:22:06.600 see something different? Now, let's imagine It's pretty simple. Let's 0:22:06.600 --> 0:22:10.639 say I'm moving in the same direction as Alicia and Roberto. Right, 0:22:10.680 --> 0:22:15.760 you started way before them and or way back, and 0:22:15.800 --> 0:22:18.199 by the time they cross the finish line, you're crossing 0:22:18.200 --> 0:22:20.879 the finish line too, but you're going really fast. Right, 0:22:20.880 --> 0:22:23.040 I started on the moon or something like that, so 0:22:23.080 --> 0:22:26.080 that I'm passing the race at exactly the same moment 0:22:26.119 --> 0:22:28.480 that Alicia and Roberto are actually running, so that I'm 0:22:28.760 --> 0:22:32.000 parallel with them but moving at some very high velocity. 0:22:32.440 --> 0:22:34.919 Then I can see the order of events differently. I 0:22:34.960 --> 0:22:38.040 can see the race start, and then I can see 0:22:38.119 --> 0:22:42.000 Roberto finish the race before Alicia. Even if you sitting 0:22:42.040 --> 0:22:45.520