WEBVTT - What is time? 0:00:06.000 --> 0:00:07.440 Hey everyone, Daniel here. 0:00:07.800 --> 0:00:11.160 My kids were into fantasy novels a few years ago, 0:00:11.560 --> 0:00:13.720 and I remember one of them asking me if I've 0:00:13.760 --> 0:00:14.600 ever seen. 0:00:14.640 --> 0:00:18.320 Magic in real life. I knew what they had in mind. 0:00:18.320 --> 0:00:22.560 Sorcerers and spells, someone turning rocks into frogs or whatever, 0:00:22.960 --> 0:00:25.759 and so of course my first answer was no. My 0:00:25.960 --> 0:00:29.520 second thought, since that felt kind of boring and deflating, 0:00:29.720 --> 0:00:33.040 was to try to help them realize how amazing and 0:00:33.280 --> 0:00:37.880 wonderful and almost magical our world is. They don't need 0:00:37.960 --> 0:00:42.040 official magic to appreciate the awesome power of the sun, 0:00:42.240 --> 0:00:46.239 or the incredible feats of technology inside their phones, or 0:00:46.280 --> 0:00:50.920 the amazing biomechanics inside their bodies. It's an extraordinary universe 0:00:50.960 --> 0:00:53.800 out there, and we love to understand it. But that 0:00:53.920 --> 0:00:57.240 doesn't feel like magic. The scientific view of the world 0:00:57.360 --> 0:01:01.760 is appreciation through explanation. The thing that makes something magic 0:01:01.920 --> 0:01:05.240 is that it's not understood. And though it feels rare 0:01:05.319 --> 0:01:08.800 today to see something truly baffling with your own eyes, 0:01:08.880 --> 0:01:12.160 it used to be a very common experience. What did 0:01:12.240 --> 0:01:16.080 prehistoric people, biologically equivalent to us, and with just as 0:01:16.160 --> 0:01:19.160 much brain power, What did they think when they saw 0:01:19.280 --> 0:01:22.840 lightning or an eclipse or got sick. To them, it 0:01:22.959 --> 0:01:25.399 might as well have been magic, because none of it 0:01:25.640 --> 0:01:28.920 was understood. I think that's kind of what my kids 0:01:28.959 --> 0:01:32.480 were asking about, and it made me realize that actually, 0:01:32.720 --> 0:01:35.840 there's still a lot of magic in our lives, because 0:01:36.040 --> 0:01:40.520 there's plenty of the universe that remains unexplained, Not little 0:01:40.560 --> 0:01:44.200 details of scientific trivia, but things as basic and as 0:01:44.240 --> 0:01:48.520 every day as lightning and disease, things so fundamental to 0:01:48.560 --> 0:01:52.480 our existence that we sometimes don't even realize how magical 0:01:52.600 --> 0:01:56.080 they are. So here's a magic trick for you. Turn 0:01:56.200 --> 0:01:59.880 the future into the present, turn the present into the past. 0:02:00.560 --> 0:02:04.800 The universe is doing that all the time, unintended, and 0:02:04.880 --> 0:02:07.720 yet we don't really understand it or how it works. 0:02:08.480 --> 0:02:11.280 And it does it without any apparent lag or delay. 0:02:12.040 --> 0:02:15.440 So on today's episode, we'll dig deep into the nature 0:02:15.440 --> 0:02:18.640 of time and explore what physics can tell us about 0:02:18.639 --> 0:02:21.840 what it is, why we have it, and why it works. 0:02:22.639 --> 0:02:26.200 Today in the pod, we're asking what is time? 0:02:40.080 --> 0:02:41.320 Hi? I'm Daniel Whitson. 0:02:41.440 --> 0:02:44.639 I'm a particle physicist and a professor at UC Irvine, 0:02:44.639 --> 0:02:45.320 which means my. 0:02:45.320 --> 0:02:46.720 Time is not my own. 0:02:47.040 --> 0:02:47.239 Hi. 0:02:47.520 --> 0:02:50.040 I'm Kelly Wiener Smith and ever since having kids I 0:02:50.120 --> 0:02:52.240 never feel like I have enough time, but the time 0:02:52.280 --> 0:02:57.600 has been higher quality. And welcome to Daniel and Kelly's 0:02:57.720 --> 0:03:01.119 extraordinary universe where you'll have the time of your life. 0:03:01.200 --> 0:03:04.639 That was really corny. I should lose my job, but 0:03:04.680 --> 0:03:07.720 I'm going with it. I'm leaning in. So Daniel, speaking 0:03:07.720 --> 0:03:10.200 of corny, here is my question for you today. So 0:03:10.880 --> 0:03:14.480 last episode we talked about space, and this episode we're 0:03:14.480 --> 0:03:18.280 talking about time. So space time and space time are 0:03:18.560 --> 0:03:21.280 topics that sci fi deals with a lot. So what 0:03:21.520 --> 0:03:26.880 is the worst, most inaccurate representation of those concepts in 0:03:26.919 --> 0:03:29.519 any movie or TV show that you have experienced? 0:03:29.680 --> 0:03:29.960 Wow? 0:03:30.000 --> 0:03:31.519 How much time do you have? We should go a 0:03:31.560 --> 0:03:34.040 whole lot last episode just on that. 0:03:34.240 --> 0:03:35.200 Oh my gosh. 0:03:35.640 --> 0:03:37.760 I think one of my least favorite trips in science 0:03:37.760 --> 0:03:42.760 fiction is subspace or hyperspace that you've like dropped into 0:03:42.880 --> 0:03:45.920 some other kind of space where you can move faster 0:03:46.040 --> 0:03:49.440 than light or something. And I'm always wondering, like, you know, 0:03:49.520 --> 0:03:52.440 if space has multiple dimensions, you're still in that other 0:03:52.520 --> 0:03:54.920 space and you're in this space. What does this even mean? 0:03:54.960 --> 0:03:57.360 Where are we? What is the physics of this space? 0:03:57.680 --> 0:04:01.320 To me, it feels like you're just escaping rules and 0:04:01.360 --> 0:04:04.560 there's always gotta be rules, even in subspace or hyperspace. 0:04:04.720 --> 0:04:06.960 So yeah, it's pretty hard to watch science fiction as 0:04:06.960 --> 0:04:07.520 a physicist. 0:04:08.920 --> 0:04:11.360 So it actually like detracts from your enjoyment of it. 0:04:11.760 --> 0:04:12.920 Oh, absolutely it does. 0:04:13.000 --> 0:04:15.920 Yeah, And you know, I don't mind if the rules 0:04:15.960 --> 0:04:18.760 on the screen are different from the rules in our universe. 0:04:18.760 --> 0:04:20.520 That's awesome, that's cool, that's. 0:04:20.320 --> 0:04:22.520 What I want. But I want them to follow them. 0:04:22.560 --> 0:04:24.279 I want them to always be rules, because you know, 0:04:24.480 --> 0:04:27.880 without rules, there's no story, anything can happen, there's no stakes. 0:04:28.000 --> 0:04:28.960 It's not worth watching. 0:04:29.360 --> 0:04:31.120 So I know this movie was loved by many, but 0:04:31.160 --> 0:04:32.880 I kind of felt that way about like from dust 0:04:32.880 --> 0:04:36.000 till Dawn, like everything seemed normal and then vampires and 0:04:36.040 --> 0:04:40.800 you're like, what, this is not okay with me. Tarantino 0:04:41.040 --> 0:04:42.920 has more fans than I ever will have, so good 0:04:42.920 --> 0:04:43.240 for him. 0:04:43.320 --> 0:04:45.240 Maybe we should add vampires to this podcast. 0:04:45.520 --> 0:04:49.120 Oh sure, why not? I loved Anne Rice books when 0:04:49.120 --> 0:04:51.279 I was a kid. I don't know what that says 0:04:51.320 --> 0:04:51.640 about me. 0:04:52.279 --> 0:04:54.839 I worked with somebody in educational television who used to 0:04:54.839 --> 0:04:56.919 work in publishing, and she told me the day she 0:04:56.960 --> 0:04:59.320 had to leave publishing was the day she pitched a 0:04:59.320 --> 0:05:02.400 really great book. And the executive told her this is wonderful, 0:05:02.440 --> 0:05:06.000 but can you add sexy vampires to it? No, she 0:05:06.160 --> 0:05:08.040 was like, h we're done, yes. 0:05:08.320 --> 0:05:11.440 Up the end. Oh my goodness. Yeah, that's a good 0:05:11.440 --> 0:05:12.440 time to throw in your head. 0:05:13.400 --> 0:05:15.240 All right, But today on the podcast, we are not 0:05:15.360 --> 0:05:19.000 talking about sexy vampires or travel through subspace. We're talking 0:05:19.040 --> 0:05:22.320 about one of the slipperiest questions in all of physics, 0:05:22.480 --> 0:05:24.520 the kind of question that's hard to answer and hard 0:05:24.520 --> 0:05:27.560 to ask and hard to think about, which means it's 0:05:27.600 --> 0:05:29.800 one of the most important questions. It's a question you 0:05:29.839 --> 0:05:32.279 shouldn't shy away from. It's the kind of question you 0:05:32.279 --> 0:05:35.559 should dig into, you should confront, you should really try 0:05:35.600 --> 0:05:37.520 to tackle with everything that you have. 0:05:37.880 --> 0:05:39.960 And that's what we're gonna do today. We're gonna have 0:05:40.000 --> 0:05:45.480 another brain bending but absolutely critical discussion about something that 0:05:45.560 --> 0:05:47.880 feels like it makes sense but then doesn't when you 0:05:47.920 --> 0:05:48.679 dig a little deeper. 0:05:48.960 --> 0:05:52.000 And i'd encourage you to remember that in the history 0:05:52.040 --> 0:05:54.680 of physics and the history of science, there's been lots 0:05:54.680 --> 0:05:56.920 of times when a topic has gone from like weird 0:05:57.000 --> 0:06:00.200 and fuzzy and hard to grapple with to totally understood 0:06:00.200 --> 0:06:03.840 and like mathematically formulated and that's just the process of science. 0:06:03.880 --> 0:06:06.520 But the beginning steps, the first bites of the apple 0:06:06.839 --> 0:06:09.200 are hard, you know. When people were thinking about like 0:06:09.279 --> 0:06:11.960 what is everything made out of? Or like where did 0:06:12.000 --> 0:06:14.480 the earth come from? Or where are those shiny dots 0:06:14.520 --> 0:06:17.560 in the sky. Those were fuzzy questions, and people had 0:06:17.600 --> 0:06:20.560 pretty silly ideas and went down the wrong path lots 0:06:20.600 --> 0:06:23.159 of times. But hey, we got there, and we only 0:06:23.160 --> 0:06:25.960 got there because people took those first bites of the apple. 0:06:26.000 --> 0:06:28.920 People tried when it was still hard. So that's why 0:06:28.960 --> 0:06:32.600 we're asking these weird, fuzzy questions about something so basic 0:06:32.760 --> 0:06:33.320 as time. 0:06:33.760 --> 0:06:36.480 It's exciting. I remember when I was in undergrad and 0:06:36.600 --> 0:06:38.480 I was learning, you know, so much in my classes, 0:06:38.480 --> 0:06:40.479 but I started to think about grad school, which wasn't 0:06:40.520 --> 0:06:42.839 on my radar until I took like thiss ecology class 0:06:42.880 --> 0:06:45.240 that I loved, And I remember thinking, like a but 0:06:45.320 --> 0:06:47.720 we figured out so much already, Like what is there 0:06:47.839 --> 0:06:50.960 left to learn because it's all new when you're an undergrad, 0:06:51.000 --> 0:06:53.160 and it's like, no, there's so much left to learn 0:06:53.200 --> 0:06:55.760 and some of it is still fundamental, and I don't know, 0:06:55.839 --> 0:06:58.040 it's just exciting to know that there's still so much. 0:06:57.920 --> 0:07:00.800 To contribute, absolutely, and some of the things we have 0:07:00.960 --> 0:07:03.239 left to learn are things that we don't think about 0:07:03.240 --> 0:07:05.800 because they are just at the base level of our understanding. 0:07:05.839 --> 0:07:09.320 They're like the assumed context. And later, in one hundred 0:07:09.400 --> 0:07:11.880 years or a thousand years, when we understand these things better, 0:07:12.040 --> 0:07:13.520 people are going to look back and be like, Wow, 0:07:13.520 --> 0:07:16.000 what was it like to be human back then when 0:07:16.000 --> 0:07:17.800 they thought time worked this way? And now we know 0:07:17.840 --> 0:07:20.760 what actually is this completely other thing? And ha ha ha, 0:07:20.960 --> 0:07:21.880 how silly were they? 0:07:22.120 --> 0:07:22.320 Right? 0:07:22.880 --> 0:07:25.440 Yeah, it shapes our very existence and the way we 0:07:25.480 --> 0:07:28.160 think about our lives, and so it's definitely worth digging into. 0:07:28.560 --> 0:07:31.360 And if we don't do this work today, then they're 0:07:31.400 --> 0:07:33.320 not going to figure it out in a thousand years. 0:07:33.680 --> 0:07:35.720 All right, Well, I am hoping that by the end 0:07:35.720 --> 0:07:39.200 of today's episode I have a science based excuse for 0:07:39.240 --> 0:07:41.280 why I'm late all the time that has something to 0:07:41.280 --> 0:07:45.160 do with the confusing nature of time. So first, let's 0:07:45.160 --> 0:07:47.760 hear what our listeners had to say about what time 0:07:47.800 --> 0:07:48.280 really is. 0:07:48.840 --> 0:07:50.760 That's right, I went out there into the internet and 0:07:50.840 --> 0:07:54.440 asked a bunch of folks this hard question, what is time? 0:07:54.960 --> 0:07:56.920 If you would like to answer questions like this for 0:07:57.000 --> 0:07:59.000 the podcast. Please don't be shy. Right to us two 0:07:59.120 --> 0:08:02.320 questions at the day, and Kelly dot Org will hook 0:08:02.360 --> 0:08:04.920 you up and you can hear your voice on the podcast. 0:08:05.160 --> 0:08:07.600 In the meantime, here are fuzzy thoughts about a fuzzy 0:08:07.680 --> 0:08:08.880 question about time. 0:08:09.680 --> 0:08:14.800 Time is represented as its own dimension, like a column 0:08:15.240 --> 0:08:18.280 in an array. But I just think of it as 0:08:18.560 --> 0:08:20.200 one thing happening after the other. 0:08:20.720 --> 0:08:25.800 Time is a human experience. Time, I think is a 0:08:25.840 --> 0:08:26.920 measure of change. 0:08:27.600 --> 0:08:35.440 Time is change made measurable by quantification of entropy and 0:08:36.400 --> 0:08:39.120 by using some caesium oscillations. 0:08:40.320 --> 0:08:43.800 Time is an artificial. 0:08:45.200 --> 0:08:49.160 Construct humans have created to try and help explain. 0:08:50.280 --> 0:08:50.960 The universe. 0:08:51.640 --> 0:08:53.880 Is the second law of thermodynamics. 0:08:54.280 --> 0:08:57.200 Our perception of change. 0:08:57.200 --> 0:09:00.319 Time is a one way trip into the future. 0:09:00.679 --> 0:09:04.680 The human constructor rived from the sound cycles. I think 0:09:04.720 --> 0:09:08.480 that time is an abstraction. It's our capability to perceive 0:09:08.679 --> 0:09:13.600 changes occurring, to make connections between events and their consequences. 0:09:14.000 --> 0:09:16.200 But I don't believe that time is some sort of 0:09:16.320 --> 0:09:21.000 substance with an arrow of direction that can be flipped entropy. 0:09:22.040 --> 0:09:25.760 I guess the fourth dimension in Albert Einstein's theory. 0:09:26.480 --> 0:09:30.240 Oh wow, I would say it's how we experience events. 0:09:30.280 --> 0:09:33.359 Happening one after the other in a sequence. 0:09:33.960 --> 0:09:39.880 I'd have to say that it's the result of quantum processes, decisions, 0:09:40.000 --> 0:09:44.599 random interactions that occur between inside fields. It's kind of 0:09:44.640 --> 0:09:49.600 a direction of events in succession. 0:09:50.920 --> 0:09:53.040 So before we got to the listener questions, you said, 0:09:53.080 --> 0:09:55.640 these are fuzzy thoughts about a fuzzy question about time. 0:09:55.960 --> 0:09:59.320 And I gotta say, I was really impressed by how 0:09:59.360 --> 0:10:02.440 deep some of the these answers were and how seemingly 0:10:02.480 --> 0:10:04.400 thought out they were. And I guess how many like 0:10:04.800 --> 0:10:08.560 polysyllabic words they used in these explanations. That made me 0:10:08.640 --> 0:10:10.959 think you are kind of aware of the underpinnings of 0:10:11.000 --> 0:10:14.440 this question. And so yeah, I was impressed with the answers. 0:10:15.080 --> 0:10:17.280 And there's also an extraordinary breadth here. I mean, there 0:10:17.280 --> 0:10:21.400 are folks who are philosophizing about it it's an artificial construct, 0:10:21.440 --> 0:10:24.480 and then folks are just trying to describe it. You know, 0:10:24.520 --> 0:10:26.480 it's a one way trip into the future. People talk 0:10:26.520 --> 0:10:29.960 about how we measure it. It's really interesting how many 0:10:30.000 --> 0:10:32.839 different responses there are to this question. They tell you, 0:10:32.920 --> 0:10:35.400 like how many facets there are to it, and how 0:10:35.440 --> 0:10:37.240 hard it is to answer a basic question because we 0:10:37.240 --> 0:10:40.079 don't all necessarily even agree on, like what form the 0:10:40.120 --> 0:10:42.840 answer is. Like if you ask me what's one plus two? 0:10:42.880 --> 0:10:44.760 We all know the answer should be a number, right, 0:10:44.800 --> 0:10:46.240 and maybe we get it right or we can get 0:10:46.280 --> 0:10:48.680 it wrong. But the answer to the question like what 0:10:48.880 --> 0:10:50.760 is time? What does that answer look like? 0:10:51.000 --> 0:10:51.200 You know? 0:10:51.880 --> 0:10:54.680 Is it just a description of our experience? Is it 0:10:54.720 --> 0:10:58.559 a mathematical structure that tells us how time works? Is 0:10:58.600 --> 0:11:02.160 it a philosophical delve into like why it exists and 0:11:02.360 --> 0:11:05.199 why the universe needs it, or maybe why it doesn't 0:11:05.240 --> 0:11:07.920 need it, where it actually comes from, why we have it, 0:11:07.960 --> 0:11:10.720 and how it began. There's such a breadth of things 0:11:10.720 --> 0:11:11.560 to explore there. 0:11:11.920 --> 0:11:13.960 Yeah, And I feel like we had pretty much the 0:11:14.000 --> 0:11:16.560 same conversation when we were talking about space in the 0:11:16.559 --> 0:11:19.040 prior episode that, like, you can just come at it 0:11:19.040 --> 0:11:22.040 from so many different angles. There's so many absolutely fundamental 0:11:22.080 --> 0:11:24.520 things where it's even hard to figure out what kind 0:11:24.559 --> 0:11:25.800 of question we should be asking. 0:11:26.320 --> 0:11:29.160 That's right, And since this isn't a philosophy podcast or 0:11:29.160 --> 0:11:31.320 an engineering podcast, we're going to sort of take the 0:11:31.320 --> 0:11:34.440 middle road. We're not going to describe the details of 0:11:34.480 --> 0:11:38.520 how caesium atoms measure time or delve into like the 0:11:38.520 --> 0:11:43.120 philosophical underpinnings of a theory versus b theory. In philosophical 0:11:43.200 --> 0:11:45.640 questions of time, we're going to talk about the physics 0:11:45.720 --> 0:11:48.720 of time and what physics tells us about time, because 0:11:49.120 --> 0:11:51.720 obviously time is really important to physics, and it is 0:11:51.800 --> 0:11:54.480 deeply woven into how we have made sense of the 0:11:54.520 --> 0:11:56.720 world so far. And so what we can do is 0:11:56.720 --> 0:11:59.000 turn that around and say, all right, time is part 0:11:59.000 --> 0:12:01.559 of our understanding of how the world works. What does 0:12:01.559 --> 0:12:04.440 that tell us about what time is? And as usual, 0:12:04.520 --> 0:12:06.640 the answer is going to be a bunch of incoherent, 0:12:06.679 --> 0:12:10.560 inconsistent ideas that don't really come together because we don't 0:12:10.600 --> 0:12:13.120 understand it. And so we'll do our best to try 0:12:13.160 --> 0:12:15.560 to weave that all together into an excuse for Kelly 0:12:15.640 --> 0:12:16.760 for why she's always late. 0:12:16.960 --> 0:12:20.040 Yes, anyone who's thinking about working with me in the future, 0:12:20.080 --> 0:12:23.440 I'm actually usually five minutes early that I'm worried about 0:12:23.440 --> 0:12:28.680 my reputation here. But so for our space episode, the 0:12:28.800 --> 0:12:32.800 answer depended on whether you are in a quantum mechanics 0:12:33.000 --> 0:12:35.440 or a general relativity framework. Is that where we're going 0:12:35.520 --> 0:12:37.880 to get again, there's not just one answer. It depends 0:12:37.880 --> 0:12:38.559 who you talk to. 0:12:38.880 --> 0:12:39.720 Yes, exactly. 0:12:39.880 --> 0:12:42.840 There's a fascinating evolution of our understanding of time with 0:12:42.880 --> 0:12:47.400 respect to space and gravity, and that's super interesting and counterintuitive. 0:12:47.600 --> 0:12:50.960 It's also completely at odds with our understanding of time 0:12:51.120 --> 0:12:53.839 in a quantum mechanical universe. So, yeah, we're going to 0:12:53.920 --> 0:12:55.520 have a couple of threads here, we're going to show 0:12:55.520 --> 0:12:57.920 how they don't tie together. And then on top of that, 0:12:57.960 --> 0:13:01.440 there's statistical mechanics and particles iss which also have different 0:13:01.520 --> 0:13:04.319 views on time, and so we hope that one day 0:13:04.320 --> 0:13:07.440 somebody's being able to pull us all together into one answer. 0:13:07.679 --> 0:13:09.760 What we have right now are a bunch of threads, 0:13:09.760 --> 0:13:12.320 none of which are completely satisfactory. And you know, the 0:13:12.360 --> 0:13:14.120 thing that we're trying to describe in the end is 0:13:14.120 --> 0:13:17.480 something pretty intuitive, right, it's our daily experience. It's this 0:13:17.920 --> 0:13:21.000 kind of magic where like we have the present, like 0:13:21.120 --> 0:13:24.960 right now I'm experiencing something and five seconds ago you 0:13:25.000 --> 0:13:27.040 were saying something and I was laughing about it, and 0:13:27.080 --> 0:13:29.120 there's a difference between that. There's like what I'm doing 0:13:29.280 --> 0:13:31.360 right now and what I was doing and what I 0:13:31.440 --> 0:13:34.199 will be doing. And we know that there's a difference there. 0:13:34.280 --> 0:13:37.679 Right when we experience, when we remember when we anticipate, 0:13:38.200 --> 0:13:41.040 and that's just like our intuitive understanding of what time is. 0:13:41.080 --> 0:13:42.839 I think that's what we're trying to grapple with. 0:13:43.320 --> 0:13:45.680 I feel like, even in our day to day life, though, 0:13:45.920 --> 0:13:48.720 time can sometimes feel weird. And this is the biologist 0:13:48.720 --> 0:13:52.080 in me. You know, my daughter is not very coordinated. 0:13:52.559 --> 0:13:54.360 And once we were playing a game on a wooden 0:13:54.400 --> 0:13:56.200 floor where we were kicking a ball around, and she 0:13:56.280 --> 0:13:58.520 kicked it and one foot went up and landed on 0:13:58.559 --> 0:14:00.760 the ball, and she stood on top and she started 0:14:00.800 --> 0:14:03.480 falling forward and she didn't put her arms out to 0:14:03.520 --> 0:14:06.520 catch her. No, because she's my daughter. And I swear 0:14:06.720 --> 0:14:09.720 the world slowed down as her teeth hit the wood floor. 0:14:09.960 --> 0:14:12.120 Oh my gosh, something as easy as time. I feel 0:14:12.120 --> 0:14:14.360 like I've had jobs where I had like two weeks 0:14:14.440 --> 0:14:17.560 left and it felt like time had fundamentally changed. But anyway, 0:14:17.600 --> 0:14:20.320 this is the biologist's perspective and how brains work, I suppose. 0:14:20.600 --> 0:14:22.040 I guess we're not getting into that today. 0:14:22.120 --> 0:14:24.880 That is a really important angle. And if you've read 0:14:24.880 --> 0:14:27.880 folks like Daniel Dennett, he suggests that there is no 0:14:28.080 --> 0:14:31.720 present moment of consciousness, that the only experience we have 0:14:31.840 --> 0:14:35.920 is actually remembering the immediate past, that your brain assembles 0:14:36.000 --> 0:14:39.280 the present as an illusion. You never experience it, you 0:14:39.360 --> 0:14:42.040 just remember it. It's a weird concept. It makes a 0:14:42.040 --> 0:14:43.320 lot of sense when you're reading the book, and then 0:14:43.360 --> 0:14:46.360 later you're like, what, how does that possible? Like with 0:14:46.400 --> 0:14:48.800 a lot of philosophy. So, yeah, that's not something we're 0:14:48.800 --> 0:14:52.120 going to dive into today, but we will ask questions like, 0:14:52.480 --> 0:14:53.360 how does time work? 0:14:53.440 --> 0:14:54.000 What is it? 0:14:54.080 --> 0:14:56.960 Can we travel through time? Did time have a beginning? 0:14:57.040 --> 0:14:59.080 What does that even mean? Why does time seem to 0:14:59.120 --> 0:14:59.960 only go forward? 0:15:00.040 --> 0:15:01.880 Words, all this kind of stuff. 0:15:02.400 --> 0:15:04.680 All right, So we could have a whole podcast called 0:15:04.920 --> 0:15:08.600 Daniel and Kelly's Extraordinary Conversations about Time. We could take 0:15:08.640 --> 0:15:12.560 biology philosophy anyway. But today we're just doing physics, all right. 0:15:12.640 --> 0:15:14.560 So when we were talking about space, we went through 0:15:14.600 --> 0:15:17.560 sort of like the history of ideas about space? Where 0:15:17.680 --> 0:15:21.040 should our history of ideas about time start? 0:15:21.080 --> 0:15:21.600 This time? 0:15:21.960 --> 0:15:24.280 So, like so many things in physics, we got to 0:15:24.320 --> 0:15:27.520 start with Newton. I mean, people talk about time before Newton, 0:15:27.560 --> 0:15:30.240 but really Newton was the first person to systematize it 0:15:30.600 --> 0:15:33.080 and to incorporate it into his physics. And you know, 0:15:33.280 --> 0:15:35.440 he figured out gravity and the loss of motion and 0:15:35.480 --> 0:15:39.400 all this stuff so much depends on time. And for Newton, 0:15:39.680 --> 0:15:43.920 time was absolute. He imagined like a single clock for 0:15:44.000 --> 0:15:47.680 the whole universe. And the way Newton thinks about time 0:15:48.160 --> 0:15:50.720 is sort of like the way a movie works. You know, 0:15:50.800 --> 0:15:54.240 you imagine a movie is like some continuous motion, but 0:15:54.360 --> 0:15:56.320 really it's a bunch of snapshots. 0:15:56.520 --> 0:15:56.640 Right. 0:15:56.640 --> 0:15:58.360 If you slowed down a movie, you'd see it's a 0:15:58.400 --> 0:16:01.360 bunch of still frames and those are tied together in 0:16:01.400 --> 0:16:03.720 a sequence. Right, So you're watching like a whole movie 0:16:03.720 --> 0:16:05.920 of your daughter falling into the floor. You see her 0:16:05.960 --> 0:16:08.240 standing on the ball. The next frame she's falling a 0:16:08.280 --> 0:16:10.680 little closer to the floor, and the next frame, the 0:16:10.680 --> 0:16:12.440 next frame. Finally there is a frame where like the 0:16:12.440 --> 0:16:14.240 teeth make contact with the wooden floor. 0:16:14.320 --> 0:16:16.600 Right, yeah, yeah, why did I bring this up? I'm 0:16:16.640 --> 0:16:18.480 gonna have to relive it so many times? 0:16:19.800 --> 0:16:23.040 And it's a series of moments, right, still moments, and 0:16:23.200 --> 0:16:27.080 time is what ties those still moments together. In Newton's universe, 0:16:27.640 --> 0:16:30.760 time is what connects those as well, Like the laws 0:16:30.760 --> 0:16:33.400 of physics tell us if the universe was at this 0:16:33.560 --> 0:16:36.680 state in this organization, if your daughter's face was this 0:16:36.800 --> 0:16:39.960 far above the floor, then when is her face going 0:16:40.000 --> 0:16:43.400 to impact the floor. The physics predicts the future from 0:16:43.440 --> 0:16:46.520 the past. It connects all of these into a causal chain, 0:16:47.080 --> 0:16:50.560 and the whole universe ticks forward together like tic tick. 0:16:50.640 --> 0:16:53.600 You imagine the whole universe as a still frame, and 0:16:53.640 --> 0:16:55.840 then you tick it forward, and everything in the universe 0:16:55.880 --> 0:16:57.440 has taken one time step. 0:16:57.760 --> 0:17:02.040 So intuitively this makes sense to me who was the 0:17:02.040 --> 0:17:05.359 first person to make it? Confusing but more accurate, Confusing 0:17:05.400 --> 0:17:06.440 but probably more accurate. 0:17:08.560 --> 0:17:10.800 Let's not confuse people just yet. Let's marinate in how 0:17:10.880 --> 0:17:14.159 much sense it makes, just for what longer, because it 0:17:14.200 --> 0:17:17.720 is kind of wonderful, right imagining that far away in Andromeda, 0:17:18.240 --> 0:17:21.080 you know, the aliens are also rescuing their daughters from 0:17:21.119 --> 0:17:24.120 wooden floors or whatever. That the whole universe is following 0:17:24.119 --> 0:17:26.280 some laws of physics, and if you knew the state 0:17:26.280 --> 0:17:29.040 of the universe, you could predict its future, right. It's 0:17:29.080 --> 0:17:31.200 an incredible thing about physics. I remember learning it in 0:17:31.280 --> 0:17:33.760 high school and being like, oh my gosh, physics is 0:17:33.800 --> 0:17:36.119 the power to predict the future. You know, if I 0:17:36.240 --> 0:17:38.960 tell you the angle of my cannonball, I know whether 0:17:39.000 --> 0:17:40.679 it's going to go over that castle wall or not. 0:17:41.240 --> 0:17:43.440 Because it's described by the laws of physics. The past 0:17:43.520 --> 0:17:47.240 predicts the future. That's wonderful. It also tells you what 0:17:47.480 --> 0:17:50.760 can't happen right. It tells you that like your ball 0:17:50.800 --> 0:17:52.760 can't be here and then suddenly appear. 0:17:52.560 --> 0:17:53.600 On the other side of the wall. 0:17:54.280 --> 0:17:57.600 Or for example, you can't shoot a laser at those 0:17:57.760 --> 0:18:01.480 Aliens and Andromeda and fry them today because light takes 0:18:01.560 --> 0:18:05.080 time to get to Andromeda. It's like this sphere of 0:18:05.160 --> 0:18:08.440 influence you have over the universe. You can't affect things 0:18:08.520 --> 0:18:11.520 outside that sphere because light only travels at a certain 0:18:11.560 --> 0:18:14.119 speed and nothing can go faster than that. And so 0:18:14.440 --> 0:18:17.480 time is intimately connected with how the universe moves forward. 0:18:18.119 --> 0:18:19.960 And this is a beautiful vision to imagine we're all 0:18:20.040 --> 0:18:23.160 linked together in time. But Einstein was the first one 0:18:23.200 --> 0:18:26.560 to make this confusing because he realized that we don't 0:18:26.600 --> 0:18:30.320 actually have a single clock for everybody in the universe. 0:18:30.760 --> 0:18:33.480 His theory of special relativity messes that up. 0:18:34.160 --> 0:18:36.320 So for a second there you had me feeling like 0:18:36.400 --> 0:18:40.000 maybe I shouldn't have studied animal behavior, where everything is 0:18:40.040 --> 0:18:42.359 confusing and hard to predict, and you don't know if 0:18:42.359 --> 0:18:44.000 the person's going to catch the ball you were talking 0:18:44.040 --> 0:18:46.159 about But now you've made me feel like no, I 0:18:46.200 --> 0:18:48.760 made the right choice because physics is confusing too. Is 0:18:48.800 --> 0:18:53.240 it confusing in a predictable way or is it just yeah, 0:18:53.280 --> 0:18:54.400 what did Einstein say? 0:18:56.680 --> 0:18:59.119 So we're not doing quantu mechanics. Yeah, the universe isn't random. 0:18:59.320 --> 0:19:03.359 We're still dealing with the deterministic, predictable universe where the 0:19:03.400 --> 0:19:06.600 past perfectly predicts the future. It's just that it predict 0:19:06.680 --> 0:19:10.120 it differently than what Newton thought. The reason that time 0:19:10.200 --> 0:19:13.760 is all messed up is because of this amazing experimental 0:19:13.840 --> 0:19:16.880 fact that Einstein relied on about the speed of light. 0:19:17.440 --> 0:19:19.560 We are taking a break, and when we get back, 0:19:19.680 --> 0:19:23.520 we'll hear about how Einstein ruined Newton's beautiful idea of time. 0:19:40.440 --> 0:19:43.000 So we're back. One of the most exciting things to 0:19:43.040 --> 0:19:47.320 me about physics is how you have these predictions that 0:19:47.359 --> 0:19:50.520 are sort of counterintuitive but then actually help you really 0:19:50.600 --> 0:19:54.840 understand complex things and create new technologies and stuff like that. So, 0:19:54.840 --> 0:19:57.160 all right, you're about to tell us how Einstein came 0:19:57.240 --> 0:20:01.679 up with this complicated, counterintuitive idea, but it's correct and 0:20:01.680 --> 0:20:02.639