WEBVTT - Why Does Time Go Forwards? 0:00:07.800 --> 0:00:10.480 Hey or hey, I think it's time we confronted a 0:00:10.600 --> 0:00:13.159 really tricky topic. Do you think we have time for that? 0:00:13.520 --> 0:00:16.160 You know, there's no time like the present. It could 0:00:16.200 --> 0:00:18.120 be a good time. It might be a fun way 0:00:18.120 --> 0:00:20.599 to pass some time. All right, I'll make time for it. 0:00:20.600 --> 0:00:28.320 It's about time. That's so corny. How many time puns 0:00:28.360 --> 0:00:31.320 can one fit into a single podcast? That's right? How 0:00:31.360 --> 0:00:35.400 much time do you have? Um, I've got time. I 0:00:35.400 --> 0:00:38.559 think it's a timely set of puns. Well, you use 0:00:38.680 --> 0:00:44.360 that pun time after time, commending else. Now is the 0:00:44.440 --> 0:00:47.360 time to start the podcast. Now is the time to 0:00:47.440 --> 0:01:07.640 tackle this tricky topic. I am and I'm Daniel. It's 0:01:07.720 --> 0:01:11.000 time for our podcast, Daniel and Jorge Explain the Universe, 0:01:11.160 --> 0:01:13.600 a production of I Heart Radio in which we take 0:01:13.640 --> 0:01:17.000 everything about the universe, the now, the future, the past, 0:01:17.200 --> 0:01:19.880 the deep, deep, deep past and try to explain it 0:01:19.880 --> 0:01:22.600 to you. That's worry. We take the time to take 0:01:22.640 --> 0:01:25.039 a little bit of your time and maybe get you 0:01:25.080 --> 0:01:28.120 to understand a little bit more about this amazing and 0:01:28.520 --> 0:01:31.680 spacious place that we live in called the universe. That's right. 0:01:31.840 --> 0:01:34.560 And sometimes we have to grapple with topics that are 0:01:34.640 --> 0:01:36.520 sort of obvious. You know sort of things that are 0:01:36.600 --> 0:01:39.399 right in front of you and understand like does physics 0:01:39.400 --> 0:01:41.360 know how to make sense of it? Does physics have 0:01:41.400 --> 0:01:44.040 a good definition of it? Do we understand why it's 0:01:44.080 --> 0:01:46.280 this way and not that way? That's right? And so 0:01:46.319 --> 0:01:49.919 today we're tackling a topic that is probably in everybody's 0:01:49.960 --> 0:01:53.000 mind all the time. That's right. This is something you 0:01:53.040 --> 0:01:55.640 think about every day from when your alarm clock goes 0:01:55.680 --> 0:01:57.720 off to when it's time to go to bed. To 0:01:57.720 --> 0:02:05.760 stay on the podcast, we will be talking about out time. 0:02:06.240 --> 0:02:09.280 What is time anyway? Yeah? And why does it only 0:02:09.520 --> 0:02:12.640 go forwards? Why do you remember the past and not 0:02:12.840 --> 0:02:15.440 the future? Can you remember the future? That would be 0:02:15.480 --> 0:02:18.680 pretty cool. Well, that's the whole question. Right on one hand, 0:02:19.080 --> 0:02:21.720 very intuitive understanding of time. We all know what time 0:02:21.840 --> 0:02:25.480 is right, yesterday was yesterday, tomorrow's tomorrow, right now is now, 0:02:26.040 --> 0:02:27.600 But when you get down to it, we don't really 0:02:27.680 --> 0:02:30.799 understand why we have it right. Why is it like that? 0:02:30.880 --> 0:02:33.800 Why does it only go forwards? Why is the future 0:02:33.919 --> 0:02:36.040 different from the past. Yeah, it's weird to think that 0:02:36.080 --> 0:02:37.880 we are in the pressing right now and there's a 0:02:37.960 --> 0:02:41.119 past going backwards in time, and there's a future going 0:02:41.120 --> 0:02:43.760 forwards in time? But what's really the difference between those 0:02:43.800 --> 0:02:48.480 two things? Yeah? Why can't I see or feel or 0:02:48.720 --> 0:02:51.480 have any kind of memory about the future? Yeah? Exactly 0:02:51.480 --> 0:02:54.079 what makes it different? Why is the past fixed? Right, 0:02:54.280 --> 0:02:58.160 unchangeable unless you believe in crazy science fiction time travel stories, 0:02:58.160 --> 0:03:01.880 which I don't, and the future undetermined? Right? What's the difference? 0:03:02.080 --> 0:03:05.680 Can physics reveal that? Is there some understanding of time? 0:03:06.400 --> 0:03:08.680 From physics? It tells us why one is different from 0:03:08.720 --> 0:03:11.239 the other? Yeah? Why is there an arrow of time 0:03:11.320 --> 0:03:14.760 like a one way sign in the universe, in the 0:03:14.840 --> 0:03:17.799 highway of time of the universe? Yeah, this is one 0:03:17.800 --> 0:03:20.720 of those wonderful questions because on the surface of it 0:03:20.720 --> 0:03:23.280 it seems kind of dumb, Like somebody asks you what 0:03:23.480 --> 0:03:25.120 is time? You're gonna tell him, Oh, it's three o'clock. 0:03:25.480 --> 0:03:27.240 And if they dig deeper and ask you though, like 0:03:27.280 --> 0:03:30.000 what does time even mean? Man? Sometimes I say it's 0:03:30.040 --> 0:03:34.400 two o'clock. Depending on the circumstances, I always give the 0:03:34.400 --> 0:03:37.760 same answer no matter what. That way, people stop asking. 0:03:38.560 --> 0:03:40.560 My kids are aways what time is it? And they 0:03:40.560 --> 0:03:42.720 have like a watch on their hand. There's like two 0:03:42.760 --> 0:03:44.840 watches on the wall, Like why are you asking me? 0:03:44.880 --> 0:03:46.800 So I would just say it's three o'clock no matter what, 0:03:47.160 --> 0:03:50.800 so that they stop. It sounds like it sounds like 0:03:50.840 --> 0:03:53.400 the same parenting strategy my my wife has when we 0:03:53.440 --> 0:03:55.640 going road trips to always ask how long are we 0:03:55.760 --> 0:03:57.720 do we get there? Is it? Are we there yet? 0:03:57.760 --> 0:04:01.240 And she always answers, nope, scant twenty more hours, no 0:04:01.280 --> 0:04:03.680 matter what. You're like pulling into the place, and she's like, 0:04:03.720 --> 0:04:07.480 twenty more hours, yeah, no matter what, she always says 0:04:07.600 --> 0:04:10.280 twenty It's a great strategy. You know, me and your wife, 0:04:10.320 --> 0:04:12.520 we would really get along. It seems like we see 0:04:12.520 --> 0:04:15.520 eye to eye about how to handle these approaches. How Tom, 0:04:17.080 --> 0:04:23.040 you would have some very um sarcastic kids probably exactly. Um. Anyway, 0:04:23.080 --> 0:04:25.279 I love these questions you know that are like, on 0:04:25.320 --> 0:04:28.760 the surface so simple, when you dig deep, they reveal 0:04:28.880 --> 0:04:32.560 like enormous gaps in our knowledge about the universe. Those 0:04:32.640 --> 0:04:35.760 questions are the best because those are the opportunities to 0:04:35.839 --> 0:04:38.720 reveal that the universe is different from the way we understood. 0:04:38.920 --> 0:04:41.240 Like the way we think about the universe reflects just 0:04:41.560 --> 0:04:44.080 our experience, the way we've lived and grown up, and 0:04:44.120 --> 0:04:47.520 not something fundamental, something universal, right, And that's the whole 0:04:47.560 --> 0:04:50.520 goal of physics. Yeah, it's one of those questions, like 0:04:51.000 --> 0:04:54.080 it makes you kind of look almost inwards or look 0:04:54.120 --> 0:04:57.360 in your like you one day you just wake up 0:04:57.360 --> 0:05:00.240 and you don't even know where you're standing, or how 0:05:00.520 --> 0:05:02.560 how the house that you live in was built. Who 0:05:02.880 --> 0:05:05.400 don't lose grasp of reality there? Or or hey, we're 0:05:05.400 --> 0:05:08.520 trying to dig deeper, trying to make you go crazy. 0:05:09.080 --> 0:05:11.120 Doesn't it make it kind of question at like the 0:05:11.240 --> 0:05:13.960 very nature of the universe. It does. It's sort of 0:05:14.000 --> 0:05:16.640 like if you say a word like a hundred times, 0:05:16.680 --> 0:05:19.880 like say the word marriage a hundred times, it starts 0:05:19.920 --> 0:05:21.840 to turn into a really weird word. Right, you take 0:05:21.880 --> 0:05:23.840 it apart, you look at you like, that's really strange. 0:05:24.279 --> 0:05:27.040 It's the same thing with the concept of time, Like 0:05:27.360 --> 0:05:30.040 you know, pick up your hand and rub your fingers together, right, 0:05:30.480 --> 0:05:34.080 you're feeling that right now? Right? But what does now mean? 0:05:34.480 --> 0:05:38.599 Right now? Sort of like it's always it's infinitely short, 0:05:38.640 --> 0:05:41.000 and it's slipping constantly into the past. You can never 0:05:41.080 --> 0:05:43.280 grasp onto it, you can never hold it, right, it's 0:05:43.520 --> 0:05:46.679 always you're always losing it. It's a really strange concept 0:05:46.720 --> 0:05:50.760 of concept of now. Yeah. Yeah, although I don't know 0:05:50.800 --> 0:05:55.720 if that's what makes marriage weird. But there's lots of 0:05:55.760 --> 0:05:58.320 things that make marriage weird. Um, saying it a hundred 0:05:58.360 --> 0:06:01.239 times is not it. But I remember reading a book 0:06:01.360 --> 0:06:03.800 about consciousness back when I was really interested in the 0:06:03.800 --> 0:06:06.240 science of consciousness, which we can talk about another podcast. 0:06:06.480 --> 0:06:09.080 But the basic idea in that book, as by Daniel 0:06:09.120 --> 0:06:12.039 Dennit it's called Consciousness Explained, is that there is no 0:06:12.040 --> 0:06:15.719 now that you're the consciousness is basically an illusion that 0:06:15.839 --> 0:06:19.920 all you're ever doing is remembering the immediate past. And 0:06:20.040 --> 0:06:21.440 I don't know if I believe that, but it really 0:06:21.440 --> 0:06:23.839 made me think about what now is and how you 0:06:23.880 --> 0:06:26.240 can never really grasp it. It's always just like sliding 0:06:26.279 --> 0:06:28.800 away from you and you know, whether it really exists, 0:06:28.839 --> 0:06:31.600 whether there is a now, right, whether there's a special 0:06:31.720 --> 0:06:35.000 instant that that differentiates between the past and the future 0:06:35.560 --> 0:06:39.120 right right, because sort of technically in physics of time 0:06:39.400 --> 0:06:42.600 could go both ways right like you could in time 0:06:42.680 --> 0:06:44.279 is kind of just like an arrow you can flip 0:06:44.279 --> 0:06:47.080 back and forth in the equations that you guys use, right. Yeah, 0:06:47.200 --> 0:06:49.800 time is not really very central to physics. Yeah, I mean, 0:06:49.920 --> 0:06:51.520 on one hand, it is. On one hand, it isn't. 0:06:51.560 --> 0:06:53.760 Tom you could write a lot of physics down without 0:06:53.800 --> 0:06:56.600 ever thinking about time. On the other hand, time is 0:06:57.160 --> 0:06:59.400 essential property physics because we're trying to use physics to 0:06:59.520 --> 0:07:03.000 predict the future. So um, this time is both like 0:07:03.279 --> 0:07:05.920 not part of physics and deeply entwined in it at 0:07:05.920 --> 0:07:09.720 the same time. So it's, uh, it's an important topic. Yeah, no, 0:07:09.800 --> 0:07:12.920 And it's a topic that everybody experiences right at every 0:07:12.960 --> 0:07:15.960 second of the day, every day of the year, every 0:07:16.040 --> 0:07:19.360 year their lives. They're experiencing time, and they're moving forwards 0:07:19.440 --> 0:07:22.440 in it, and they feel it, right. Yeah, they think 0:07:22.480 --> 0:07:24.840 about it, they think about the future, they remember the past, 0:07:24.880 --> 0:07:27.920 and so it kind of makes you wonder how many 0:07:27.960 --> 0:07:35.120 people actually think about or know what time actually is. Yeah, exactly. 0:07:35.720 --> 0:07:39.800 So I was wondering do people know why time goes forward? Like, 0:07:39.960 --> 0:07:42.160 I mean, physicists don't really, but it's always fun to 0:07:42.200 --> 0:07:46.200 ask general public questions that scientists don't know the answer to, 0:07:46.320 --> 0:07:48.640 just to see what they come up with. So I 0:07:48.680 --> 0:07:50.600 walked around the US of Irvine campus and I asked 0:07:50.640 --> 0:07:53.760 people why does time only go forwards? Here's what people 0:07:53.760 --> 0:07:58.480 had to say. Do you know why time only goes forwards? Um? 0:07:58.520 --> 0:08:02.120 Not really, honestly, I have like some sort of like 0:08:02.640 --> 0:08:05.960 intuition why it only goes forward? But I don't think 0:08:05.960 --> 0:08:10.920 we can't explain that. Yeah, okay, cool, I have no idea. No, 0:08:10.960 --> 0:08:12.880 I don't any guess. If I had to go, I 0:08:12.960 --> 0:08:16.960 just said gravity or something. Okay, No, I don't any idea, 0:08:17.040 --> 0:08:22.360 best guess. Sorry. I think time is lack of force 0:08:22.520 --> 0:08:28.920 dimensional right, So actually I don't know, creaky right, Okay, 0:08:29.600 --> 0:08:35.000 I'm not sure. Okay, Well, when I think of time, 0:08:35.040 --> 0:08:37.400 I think of it kind of almost as a linear progression, 0:08:38.240 --> 0:08:42.000 meaning that it's a constant in the universe, and it's 0:08:42.040 --> 0:08:44.040 always kind of moving forward, and that's something that we 0:08:44.120 --> 0:08:47.120 accept as being a fact of the universe, at least 0:08:47.120 --> 0:08:49.679 as we understand it now. So in that regards, I 0:08:49.760 --> 0:08:52.200 think that's why we can only see it as moving forwards, 0:08:52.200 --> 0:08:54.319 because it doesn't kind of make sense to us or 0:08:54.360 --> 0:08:57.120 it's not even physically possible currently for us to move 0:08:57.160 --> 0:09:00.240 backwards in time, so we don't consider it in that way. 0:09:00.280 --> 0:09:02.880 I think it might be a matter of observation. So 0:09:03.000 --> 0:09:05.880 relative to us, time moves forward, and the way that 0:09:05.920 --> 0:09:09.240 you experienced the world biologically is designed to be in 0:09:09.240 --> 0:09:12.400 a manner that is sort of one dimentional and a 0:09:12.440 --> 0:09:16.079 forward mind all the time. But in reality it might 0:09:16.160 --> 0:09:20.760 be that the fourth dimension of time in space time 0:09:20.840 --> 0:09:23.040 might just be a way of describing the universe that 0:09:23.080 --> 0:09:27.520 the math predicts a from physics and my option perhaps 0:09:27.520 --> 0:09:30.880 other related science fills. Okay, cool, Yeah, so I got 0:09:30.960 --> 0:09:33.360 a pretty good mix of answers there, right from the 0:09:33.559 --> 0:09:36.720 standard physics, like gravity, which is you know, that's a 0:09:36.720 --> 0:09:39.640 good answer. You never know, it might be, right, gravity. 0:09:40.160 --> 0:09:44.079 Somebody actually said gravity. I don't know gravity, It could 0:09:44.080 --> 0:09:46.120 be it could be. Yeah, well, gravity is like the 0:09:46.120 --> 0:09:48.120 answer to half the questions in physics, the way like 0:09:48.520 --> 0:09:50.679 pie is the answer to half the questions in math. Right, 0:09:50.679 --> 0:09:52.240 so if you have no idea, you could just say 0:09:52.240 --> 0:09:55.240 gravity and have the time. You'll be right. Not the 0:09:55.240 --> 0:09:59.880 movie the fourth right, yeah, the fabric of space time itself. 0:10:00.080 --> 0:10:02.440 That's right, it's gravity. Yeah. And then you know, some 0:10:02.480 --> 0:10:07.400 other folks had some more elaborate discussions, But people had opinions. 0:10:07.600 --> 0:10:10.120 People did have opinions. Yeah, some of them were sort 0:10:10.160 --> 0:10:12.559 of longer word salad. Right, you know, some of them 0:10:12.640 --> 0:10:14.960 hit on some of the scientific concepts time being a 0:10:15.000 --> 0:10:19.160 fourth dimension, etcetera. Um, but um, yeah, a lot of 0:10:19.160 --> 0:10:20.719 people want to ask them this question. You could just 0:10:20.760 --> 0:10:23.560 see in their faces that they had not ever considered this. 0:10:23.640 --> 0:10:26.480 They're not even question they had imagined, but as soon 0:10:26.520 --> 0:10:28.720 as they thought about it, they realized they didn't know. 0:10:28.840 --> 0:10:31.960 And that's my favorite part of this this topic is 0:10:31.960 --> 0:10:34.680 that nobody, nobody has really thought about it in terms 0:10:34.720 --> 0:10:37.320 of general public, but as soon as they do, they're 0:10:37.480 --> 0:10:40.760 very curious. Right, this is the best questions. It's amazing 0:10:40.760 --> 0:10:43.520 how little you actually kind of need to know about 0:10:43.520 --> 0:10:47.680 the universe to live a full and happy life, you 0:10:47.720 --> 0:10:51.360 know what I mean, that's the protective happy life. There's 0:10:51.400 --> 0:10:53.720 so much you don't need to know. Ignorance is bliss, 0:10:53.800 --> 0:10:55.520 you know, that does have a meeting. People have been 0:10:55.559 --> 0:10:58.600 living in this universe for hundreds of thousands of years, 0:10:58.600 --> 0:11:01.480 depending on how you count the beginning of humanity, and 0:11:01.559 --> 0:11:03.720 there's been a lot of happiness and joy without really 0:11:03.760 --> 0:11:07.520 any understanding. I mean, I would say people five years 0:11:07.520 --> 0:11:11.480 ago basically knew nothing about the way the universe actually works. 0:11:11.520 --> 0:11:14.960 But you know, people had birthday parties and eight cakes 0:11:15.040 --> 0:11:17.840 and had moments of joy. So yeah, I mean like 0:11:17.880 --> 0:11:20.280 a hundred only a hundred years ago, right in the 0:11:20.440 --> 0:11:25.080 nine hundreds, early nineteen hundreds, people didn't know the concept 0:11:25.160 --> 0:11:28.320 of Adams or quantum physics, right, Yeah, that was about 0:11:28.360 --> 0:11:30.160 a hundred years old. We didn't know how long the 0:11:30.240 --> 0:11:33.920 universe had been around, right, so pretty basic stuff about 0:11:33.920 --> 0:11:36.280 the way the universe works is pretty modern. Right, So 0:11:36.440 --> 0:11:39.560 we didn't know there were other galaxies, right, No, they didn't. Um, 0:11:39.600 --> 0:11:41.240 So what's your point here? Your point is you don't 0:11:41.280 --> 0:11:42.880 need physics to be happy? Is that what you're trying 0:11:42.880 --> 0:11:46.760 to say is irrelevant happiness? You think of how much 0:11:46.760 --> 0:11:50.800 of a richer life you can lead if you know physics. Okay, 0:11:50.880 --> 0:11:53.520 I like the way you spun that back, right, using 0:11:53.559 --> 0:11:56.280 all this technology to talk to me. That's based on physics, 0:11:56.640 --> 0:11:58.960 not not like not like money rich, but you know, 0:11:59.120 --> 0:12:03.400 like spiritually right right? Um? Isn't your career based on 0:12:03.520 --> 0:12:07.960 technology that was developed with the help of physicists? Where 0:12:07.960 --> 0:12:14.480 would you be? Isn't your science dependent on technology? Yes? 0:12:14.559 --> 0:12:16.960 I am a tiny little mite standing on the shoulders 0:12:16.960 --> 0:12:19.720 of giants, absolutely, But so are we all? So are 0:12:19.760 --> 0:12:26.199 we all? Yeah? Well maybe it's time we got back 0:12:26.240 --> 0:12:28.400 on topic here, and um, so let's break it down 0:12:28.400 --> 0:12:31.600 for people, Daniel, what how do physicists see time? Like 0:12:31.960 --> 0:12:34.160 if if you're at a conference and you guys are 0:12:34.160 --> 0:12:36.400 talking and somebody said, hey, guys, what is time? What 0:12:36.480 --> 0:12:39.280 do you think people would generally say, I think there'd 0:12:39.280 --> 0:12:42.080 be a lot of disagreements because we don't really have 0:12:42.320 --> 0:12:45.160 a great description of time, you know, one that really 0:12:45.200 --> 0:12:47.760 makes sense. And you know, the way physics approaches the 0:12:47.880 --> 0:12:50.440 problem is first you try to build like a model 0:12:50.480 --> 0:12:52.200 of the problem. You're trying to describe it in a 0:12:52.240 --> 0:12:55.280 way that we can grapple using the language that we're 0:12:55.280 --> 0:12:58.240 familiar with, which is mathematics. You try to find an 0:12:58.240 --> 0:13:03.359 equation that tells you what what's what's happening? Yeah, exactly, 0:13:03.520 --> 0:13:05.839 you know, something's happening in the real world. Maybe it's 0:13:05.880 --> 0:13:08.240 like a ball is being thrown the air, and we 0:13:08.360 --> 0:13:10.360 try to understand it. So we write down a bunch 0:13:10.360 --> 0:13:13.199 of equations to describe it um and that lets us 0:13:13.440 --> 0:13:15.720 build that model in our heads and manipulate it and 0:13:15.720 --> 0:13:18.920 then use information from the model to describe what's happening 0:13:18.920 --> 0:13:21.920 in the world. Cool. How do we do that with time? Right? 0:13:21.960 --> 0:13:24.200 How do we ask this question about like why can 0:13:24.280 --> 0:13:27.280 I remember the past and not the future? Why does 0:13:27.440 --> 0:13:31.120 ice melt but not unmelt? Right? These kinds of questions 0:13:31.160 --> 0:13:35.560 about time, it's pretty hard to to wrap your mind around. 0:13:36.320 --> 0:13:39.880 One approach is to think about the universe in terms 0:13:39.880 --> 0:13:43.520 of a bunch of snapshots. Like you think about a movie. Right, 0:13:43.559 --> 0:13:46.839 what is a movie? It's not really a continuous experience 0:13:46.840 --> 0:13:48.840 in time. If you're looking at the screen, you're not 0:13:48.920 --> 0:13:52.480 really seeing smooth motion. You're seeing a bunch of snapshots. 0:13:52.679 --> 0:13:54.840 You're seeing like a little cells in a film, or 0:13:54.920 --> 0:13:58.319 like a bunch of screenshots. Yeah, it's a bunch of screenshots, 0:13:58.520 --> 0:14:00.760 and they're just packed so tightly together that you don't 0:14:00.840 --> 0:14:04.120 notice that they're not actually smoothly varying. Right. Your brain 0:14:04.160 --> 0:14:06.880 does the interpolation for you. It tells you a story. 0:14:06.960 --> 0:14:10.000 So sometimes we think about the universe that way. We 0:14:10.040 --> 0:14:13.440 think about like all the universe at this moment, and 0:14:13.480 --> 0:14:15.800 then all the universe at the next moment, and all 0:14:15.800 --> 0:14:18.920 the universe at the next moment, like snapshots of the universe. 0:14:19.240 --> 0:14:22.360 By snapshots, I mean like what is every particle doing 0:14:23.120 --> 0:14:27.040 and where is it going? Yeah, exactly and time. Then 0:14:27.360 --> 0:14:29.640 is a way to sort of order those snapshots is 0:14:29.680 --> 0:14:32.760 to say this one first, that one next, that one next, 0:14:33.360 --> 0:14:35.360 um and to sort of put them together. This one 0:14:35.440 --> 0:14:37.520 can go in front of the other one. Yes, you 0:14:37.560 --> 0:14:41.680 know what I mean. It limits um the ordering. Yeah, 0:14:41.760 --> 0:14:46.040 And in that sense, physics. The job of physics is 0:14:46.080 --> 0:14:48.800 to take all the snapshots in the past and predict 0:14:48.840 --> 0:14:51.400 the ones in the future and to say, Okay, according 0:14:51.440 --> 0:14:53.800 to the laws of physics, the next snapshot will look 0:14:53.840 --> 0:14:56.520 like this, or if you want to talk quantum mechanically, 0:14:56.880 --> 0:15:00.920 there's a probability distribution of the next snapshots. These are likely, 0:15:00.960 --> 0:15:04.680 these are unlikely, these are impossible. Right, So physics um 0:15:04.960 --> 0:15:06.920 takes sort of that view of time, and there's a 0:15:06.920 --> 0:15:09.080 bunch of caveats there. Like, you can't have a snapshot 0:15:09.120 --> 0:15:12.080 of the whole universe, right because time is not universal. 0:15:12.400 --> 0:15:14.600 It means different things for different people. You can't know 0:15:14.640 --> 0:15:17.280 everything about the universe. But you know, you take a 0:15:17.280 --> 0:15:20.000 small enough model or a single particle or something, you 0:15:20.000 --> 0:15:23.040 can also have quantum and you also have quantum states, 0:15:23.160 --> 0:15:25.840 right Like it' isn't that prevent you from getting an 0:15:25.880 --> 0:15:29.080 exact snapshot of the universe? Yeah, exactly. So you can't 0:15:29.080 --> 0:15:30.880 really get an exact snapshot, but you could do a 0:15:30.960 --> 0:15:33.680 quantum mechanical version. You could say, well, what's the quantum 0:15:33.720 --> 0:15:35.840 state of all the particles or you know, what's the 0:15:36.360 --> 0:15:38.640 wave function. What's the state of the wave function right 0:15:38.640 --> 0:15:41.680 now that you can talk about, and that determines probabilities. 0:15:42.040 --> 0:15:43.960 I see, So you describe me kind of how physicists 0:15:44.040 --> 0:15:46.720 see the universe. They don't see it as um. They 0:15:46.760 --> 0:15:50.000 see it as as this kind of sequence of snapshots 0:15:50.120 --> 0:15:53.200 of how things are arranged. Yeah. For example, think about 0:15:53.360 --> 0:15:57.120 the Shortinger equation. The Shortinger equation famous equation describes how 0:15:57.160 --> 0:16:01.280 a particles a wave function um moves through time, right, 0:16:02.120 --> 0:16:04.160 and it tells you how it moves. It says, if 0:16:04.200 --> 0:16:07.160 you have this wave function now and you experience this, 0:16:07.240 --> 0:16:09.480 then your way function will be that later. Right. So 0:16:09.560 --> 0:16:12.120 that's that's what physics tries to do, or or go 0:16:12.200 --> 0:16:14.120 back to them making the mechanical example of a ball 0:16:14.160 --> 0:16:16.040 going through the air right tells you, well, you you 0:16:16.080 --> 0:16:18.560 shot your ball in this direction. Where is your ball 0:16:18.600 --> 0:16:21.120 going to be in the future. So that's the role 0:16:21.160 --> 0:16:24.360 of time in physics, right to predict the future snapshots. Oh, 0:16:24.440 --> 0:16:27.200 I see. So to you guys, time is like a 0:16:27.800 --> 0:16:31.400 like an input that tells you what the universe is 0:16:31.440 --> 0:16:33.240 likely to do. You you know what I mean? Like 0:16:33.280 --> 0:16:35.520 you do you It's an input. It's not like an 0:16:35.520 --> 0:16:40.600 output or something that you can vary or that it 0:16:40.680 --> 0:16:43.880 is affected by all the other variables. Yeah, exactly. And 0:16:43.920 --> 0:16:46.200 so for example, you want to predict the flight of 0:16:46.240 --> 0:16:48.160 your ball, it's an input. You can dial that knob 0:16:48.160 --> 0:16:49.320 and say I want to know where the ball is 0:16:49.320 --> 0:16:51.280 going to be in one second or five seconds or 0:16:51.360 --> 0:16:54.520 eight point two nine seconds or whatever. So it's sort 0:16:54.520 --> 0:16:57.040 of that knob. The thing we don't the thing that 0:16:57.040 --> 0:17:00.360 that doesn't explain at all is like why it only 0:17:00.360 --> 0:17:03.440 go forwards and who's controlling how fast that knob is turning? 0:17:03.560 --> 0:17:05.880 Or why do we have time at all? Why don't 0:17:05.880 --> 0:17:08.000 we just have a static universe? It's just sort of 0:17:08.040 --> 0:17:12.160 like there, you know, it's the first step. Of course, 0:17:12.160 --> 0:17:14.120 they just try to describe it, and then you can 0:17:14.160 --> 0:17:16.600 build from that and try to answer some of these questions. 0:17:16.800 --> 0:17:18.399 But you mean, like, how come we don't have a 0:17:18.440 --> 0:17:21.360 static universe, Like, um, why do we have time at all? 0:17:21.640 --> 0:17:26.439 Boom right, I don't know, you don't know, nobody knows, Like, well, 0:17:26.480 --> 0:17:29.600 I know, there's this idea that time is the fourth dimensions. 0:17:29.640 --> 0:17:32.640 We have three dimensions up, down, left and right, backwards 0:17:32.640 --> 0:17:36.520 and forwards, and maybe time is just another direction of 0:17:36.560 --> 0:17:39.040 the universe. And so we and I think the days 0:17:39.040 --> 0:17:42.439 that we do sort of exist in this a state 0:17:42.600 --> 0:17:47.040 of being still in all four dimensions, but it just 0:17:47.080 --> 0:17:51.240 so happens that we somehow feel one of the mensitions. 0:17:51.320 --> 0:17:52.760 Do you know what I mean? Yeah? I love the 0:17:53.040 --> 0:17:56.399 it just so happens part of that explanation, right, Okay, 0:17:56.440 --> 0:17:58.880 here's the hardest part. I'll just YadA, YadA, YadA over 0:17:58.920 --> 0:18:03.119 that bit. That's that's my that's my Nobel Prize, Nobel 0:18:03.200 --> 0:18:06.000 Prize winning paper officer. It just so happens. I was 0:18:06.040 --> 0:18:08.600 going ninety miles an hour. Um, you know, I can't 0:18:08.640 --> 0:18:11.520 explain it now, You're right. Um, time is sometimes thought 0:18:11.520 --> 0:18:13.800 of as the fourth dimension. And so let's dig into 0:18:13.840 --> 0:18:15.320 that a little bit. What does that mean? Why do 0:18:15.400 --> 0:18:17.199 we think of it that way? We think of it 0:18:17.240 --> 0:18:21.080 that way because it's helpful mathematically. Like when Einstein was 0:18:21.080 --> 0:18:24.040 developing his theory of special relativity and we talked all 0:18:24.080 --> 0:18:27.160 about time dilation and stuff like that on a previous episode, 0:18:27.600 --> 0:18:30.920 he discovered that the equations have a certain symmetry. They 0:18:30.960 --> 0:18:33.560 look really nice like that you can write them down 0:18:33.640 --> 0:18:37.119 really simply and compactly if you include time as the 0:18:37.160 --> 0:18:40.600 fourth dimension of this larger concept he called space time. 0:18:40.880 --> 0:18:43.320 So he took three dimensions of space. He tacked on 0:18:43.359 --> 0:18:46.240 a fourth dimension, which is time, and he constructed this 0:18:46.280 --> 0:18:50.320 thing called space time. And because your perception of time 0:18:50.359 --> 0:18:53.359 depends on where you are in space and how fast 0:18:53.440 --> 0:18:56.800 you are moving through space, the equations get much simpler 0:18:57.080 --> 0:19:00.199 if you think about all four dimensions in that way, right, 0:19:00.200 --> 0:19:02.720 if you think about time parallel to space in that way. 0:19:03.000 --> 0:19:06.119 And that's a clue when you write down equations, and 0:19:06.160 --> 0:19:08.199 they become simpler if you think about them a certain way. 0:19:08.240 --> 0:19:10.119 That's a clue from the universe that it's maybe the 0:19:10.240 --> 0:19:13.359 right way to think about things. Okay, so that's um, 0:19:13.400 --> 0:19:16.199 that's time is a different dimension. Let's get more into it. 0:19:16.280 --> 0:19:18.840 Let's go down that rabbit hole. But first let's take 0:19:18.880 --> 0:19:33.920 a quick break. So I think it's fun to think 0:19:33.920 --> 0:19:36.920 about time as the fourth dimension. But it's also kind 0:19:36.960 --> 0:19:39.760 of a trick, right, It's not. It doesn't really fit. 0:19:40.359 --> 0:19:42.560 So wait, So the idea that it's a fourth dimension 0:19:42.760 --> 0:19:48.399 you're saying, came from mathematical convenience by Einstein, do you 0:19:48.400 --> 0:19:50.919 know what I mean? Like, it's not. It was just 0:19:51.040 --> 0:19:54.560 easier to treat it like a dimension. Yeah, And I 0:19:54.600 --> 0:19:57.560 wouldn't you blow that off? Mathematical convenience is not a 0:19:57.600 --> 0:20:00.399 small thing, you know. The whole goal of physics, remember, 0:20:00.480 --> 0:20:02.560 is to like write down an equation of the universe 0:20:02.560 --> 0:20:05.720 in one line. And so if you can write things 0:20:05.760 --> 0:20:08.600 more simply, that's a clue that it's probably more correct, 0:20:08.640 --> 0:20:12.360 it's more and it's like a deeper understanding. So yeah, 0:20:12.400 --> 0:20:14.640 he discovered that if you write things down with time 0:20:14.720 --> 0:20:17.920 is sort of the fourth column of your vector, then 0:20:18.040 --> 0:20:20.160 a lot of the equations are simpler to write down. 0:20:20.160 --> 0:20:22.480 There's it's there's a connection. There's a symmetry there. Right. 0:20:22.560 --> 0:20:25.359 We talked about symmetry in another episode. You can treat 0:20:25.400 --> 0:20:28.359 time the same way you treat space in many ways. 0:20:29.280 --> 0:20:31.520 And that's that's tempting because you think, oh, well, that 0:20:31.560 --> 0:20:34.040 answers the question time is just another dimension, right, But 0:20:34.080 --> 0:20:37.280 it doesn't answer the question because it's not just another dimension. Right. 0:20:37.560 --> 0:20:40.800 You know time is not space? Right? Time? What does 0:20:40.800 --> 0:20:44.479 that mean? Time is not space? Well, for money, you 0:20:44.520 --> 0:20:46.760 can move forwards and backwards in space, right, you can 0:20:46.800 --> 0:20:49.119 go left, you can go right, you have some control 0:20:49.160 --> 0:20:52.120 over it. You can't do that with time. But isn't 0:20:52.119 --> 0:20:55.840 it just sort of a matter of perspective, Like I think, 0:20:56.160 --> 0:21:01.000 like in the grand scheme of the history of the universe, Um, 0:21:01.040 --> 0:21:03.679 you know, I existed for this amount of time, but 0:21:03.840 --> 0:21:06.280 while I'm living it, I can only go forward. I 0:21:06.320 --> 0:21:09.640 kind of get the experience of moving forward in time. Yeah, 0:21:09.640 --> 0:21:12.480