1 00:00:08,440 --> 00:00:10,960 Speaker 1: Hey, Daniel, how do your kids get to school these days? Oh? 2 00:00:11,000 --> 00:00:13,920 Speaker 1: They're super independent and awesome about it. They actually bike 3 00:00:14,000 --> 00:00:17,599 Speaker 1: themselves there and back nice And how long does it 4 00:00:17,640 --> 00:00:20,880 Speaker 1: take them? Oh? That depends on what the weather, what 5 00:00:20,920 --> 00:00:23,840 Speaker 1: they had for breakfast, those but mostly on the direction. 6 00:00:24,160 --> 00:00:26,760 Speaker 1: It's about twice as long on the way to school 7 00:00:26,880 --> 00:00:28,960 Speaker 1: as it is on the way home. Is that because 8 00:00:28,960 --> 00:00:32,199 Speaker 1: it's downhill one way and uphill the other way? Nope? 9 00:00:32,360 --> 00:00:35,159 Speaker 1: So what's going on? Is it some kind of quantum effect? 10 00:00:35,240 --> 00:00:37,440 Speaker 1: I asked my daughter about it. Actually, she said, well, 11 00:00:37,479 --> 00:00:40,160 Speaker 1: you know, I'm excited to get home. That's my time. 12 00:00:41,080 --> 00:00:42,839 Speaker 1: She didn't say because she was excited to see you. 13 00:00:44,560 --> 00:00:46,920 Speaker 1: I'm sure that's what she meant. That's the quantum effect 14 00:00:47,000 --> 00:01:04,240 Speaker 1: right there. Hi am poor handmade cartoonists and the co 15 00:01:04,319 --> 00:01:08,080 Speaker 1: author of Frequently Asked Questions about the Universe. Hi. I'm Daniel. 16 00:01:08,120 --> 00:01:11,280 Speaker 1: I'm a particle physicist and a professor at U C Irvine, 17 00:01:11,480 --> 00:01:14,160 Speaker 1: and I am a quantum mechanics. Yeah. Do you fix 18 00:01:14,240 --> 00:01:16,840 Speaker 1: quantum cars? I do when I don't, and then they 19 00:01:16,880 --> 00:01:19,280 Speaker 1: work and not work at the same time. And do 20 00:01:19,360 --> 00:01:21,520 Speaker 1: people pay you and not pay you? Also? Yeah, I 21 00:01:21,520 --> 00:01:23,440 Speaker 1: build them and I don't. That's not like a cool 22 00:01:23,720 --> 00:01:27,040 Speaker 1: Marvel movie plot device, like a quantum engine. Yeah exactly. 23 00:01:27,200 --> 00:01:29,759 Speaker 1: It generates any plot you need to fill any hole 24 00:01:29,800 --> 00:01:32,440 Speaker 1: in the Marvel universe. It's like magic, you know. I 25 00:01:32,440 --> 00:01:35,840 Speaker 1: mean you're a quantum mechanical engineer, because I'm a mechanical engineer, 26 00:01:35,880 --> 00:01:38,039 Speaker 1: but you know, I would love to add quantum in 27 00:01:38,040 --> 00:01:40,240 Speaker 1: front of it. You just need to use super tiny 28 00:01:40,319 --> 00:01:42,960 Speaker 1: little tools. That's the trick. I just need to pretend 29 00:01:43,000 --> 00:01:44,800 Speaker 1: to know what I'm talking about. Is that the secret? 30 00:01:45,040 --> 00:01:47,400 Speaker 1: Just wave your hands a bunch. That's especially effective on 31 00:01:47,400 --> 00:01:52,320 Speaker 1: a podcast. I see. Yeah, just say you know Shoredinger, Shoredinger, Heisenberg, Heisenberg, 32 00:01:52,360 --> 00:01:58,280 Speaker 1: her mission matrices, way function, way function. Suddenly I get 33 00:01:58,280 --> 00:02:02,600 Speaker 1: a promotion. Yeah exactly. Mechanics is just handway functioning. But anyways, 34 00:02:02,640 --> 00:02:05,240 Speaker 1: welcome to our podcast, Daniel and Jorge Explain the Universe, 35 00:02:05,320 --> 00:02:07,480 Speaker 1: a production of My Heart Radio, in which we talk 36 00:02:07,560 --> 00:02:11,120 Speaker 1: about the craziness of our universe, everything that can be 37 00:02:11,200 --> 00:02:14,000 Speaker 1: understood and everything that can't be understood, and everything that 38 00:02:14,040 --> 00:02:17,119 Speaker 1: you think you might understand but you simultaneously are confused 39 00:02:17,120 --> 00:02:21,280 Speaker 1: about all at the same time. Your quantum mechanical understanding 40 00:02:21,360 --> 00:02:25,120 Speaker 1: of our crazy universe. We embrace it, we explore it, 41 00:02:25,160 --> 00:02:28,280 Speaker 1: we explode it, and mostly we explain all of it 42 00:02:28,320 --> 00:02:31,280 Speaker 1: to you. That's right, because humanity is cruising through this 43 00:02:31,440 --> 00:02:34,520 Speaker 1: universe driven by an engine of curiosity, and we love 44 00:02:34,560 --> 00:02:36,640 Speaker 1: to look out the window and wonder about all the 45 00:02:36,680 --> 00:02:38,320 Speaker 1: things that are out there and how they work. And 46 00:02:38,320 --> 00:02:42,120 Speaker 1: that curiosity has led us to some very strange conclusions 47 00:02:42,120 --> 00:02:46,679 Speaker 1: about the nature of that universe out there beyond our skulls. 48 00:02:47,000 --> 00:02:49,880 Speaker 1: It seems to follow rules, but those rules are very 49 00:02:50,000 --> 00:02:53,120 Speaker 1: different from the ones that we imagined they were many 50 00:02:53,160 --> 00:02:56,240 Speaker 1: many years ago. Yeah, it is a very perplexing universe, 51 00:02:56,280 --> 00:02:58,920 Speaker 1: and our physicists and scientists asking questions about it all 52 00:02:58,960 --> 00:03:00,520 Speaker 1: the time, and we like to talk talked about what 53 00:03:00,560 --> 00:03:03,760 Speaker 1: they talk about, what questions they're asking, and break it 54 00:03:03,800 --> 00:03:06,080 Speaker 1: down for you. And most importantly, we like to think 55 00:03:06,120 --> 00:03:09,200 Speaker 1: about what science has figured out and what science still 56 00:03:09,360 --> 00:03:12,800 Speaker 1: does not yet know. The boundaries of our knowledge, the 57 00:03:12,840 --> 00:03:17,120 Speaker 1: realms where future discoveries lie, where crazy revelations for the 58 00:03:17,200 --> 00:03:21,919 Speaker 1: future will upend our entire understanding of how the universe works. Yeah, because, 59 00:03:21,960 --> 00:03:23,440 Speaker 1: as you said, I think the universe has sort of 60 00:03:23,480 --> 00:03:26,280 Speaker 1: surprises quite a few times in the history of science 61 00:03:26,320 --> 00:03:28,919 Speaker 1: for humans right, Oh, so many times in the past, 62 00:03:29,000 --> 00:03:31,840 Speaker 1: and I hope many many times in the future, moments 63 00:03:31,840 --> 00:03:35,360 Speaker 1: when the whole field collectively went, what are you additic 64 00:03:35,520 --> 00:03:38,520 Speaker 1: to plot? Twist? Is that what it is? You just 65 00:03:38,520 --> 00:03:41,280 Speaker 1: go to the movies for the shocking moment? I think 66 00:03:41,320 --> 00:03:44,160 Speaker 1: fundamentally it comes from the fact that the universe seems 67 00:03:44,160 --> 00:03:47,960 Speaker 1: to work very differently on different scales. You know, the 68 00:03:48,080 --> 00:03:51,440 Speaker 1: rules of big quantum mechanics, things that apply to like 69 00:03:51,880 --> 00:03:54,360 Speaker 1: ten to twenty five particles like me and you and 70 00:03:54,440 --> 00:03:56,960 Speaker 1: baseballs seem to be different than the rules that apply 71 00:03:57,080 --> 00:04:00,000 Speaker 1: the very very small scale. The rules are very slow 72 00:04:00,000 --> 00:04:02,360 Speaker 1: things seem to be different from the rules for very 73 00:04:02,480 --> 00:04:05,000 Speaker 1: very fast things. So because we can't have a single 74 00:04:05,000 --> 00:04:08,680 Speaker 1: effective description that works for every situation, we keep getting 75 00:04:08,680 --> 00:04:11,720 Speaker 1: surprised when we discover a new situation that requires a 76 00:04:11,800 --> 00:04:14,960 Speaker 1: new understanding. Yeah, because the universe seems to work differently 77 00:04:15,000 --> 00:04:17,719 Speaker 1: a different scale scales of size and skills of speed. 78 00:04:17,760 --> 00:04:20,800 Speaker 1: And you know, we're as humans used to one scale 79 00:04:21,000 --> 00:04:23,680 Speaker 1: of and moving in one kind of speed. But somehow 80 00:04:23,720 --> 00:04:25,719 Speaker 1: the universe kind of likes to change things up. It 81 00:04:25,800 --> 00:04:28,800 Speaker 1: certainly does, And we've spent hundreds or thousands of years 82 00:04:28,839 --> 00:04:31,280 Speaker 1: trying to figure out how the universe works. But as 83 00:04:31,320 --> 00:04:33,880 Speaker 1: you said, we live at a certain speed, and as 84 00:04:33,920 --> 00:04:36,640 Speaker 1: we explore the universe more broadly, we discover that the 85 00:04:36,720 --> 00:04:40,360 Speaker 1: rules we devised that work for throwing rocks at each 86 00:04:40,360 --> 00:04:43,720 Speaker 1: other or hunting antelope or climbing up to get that 87 00:04:43,760 --> 00:04:46,440 Speaker 1: fresh piece of fruit don't always work when it comes 88 00:04:46,480 --> 00:04:49,640 Speaker 1: to planets whizzing very close to their stars or approaching 89 00:04:49,720 --> 00:04:51,720 Speaker 1: black holes. Yeah, you know, I kind of like the 90 00:04:51,720 --> 00:04:53,680 Speaker 1: speed we're moving out right now, you know, I feel 91 00:04:53,720 --> 00:04:55,480 Speaker 1: like I don't I'm not sure I want to go faster, 92 00:04:56,600 --> 00:04:58,200 Speaker 1: or maybe I'm just getting gold. Well, then, you know, 93 00:04:58,320 --> 00:05:00,520 Speaker 1: just don't volunteer to go up in space sort visit 94 00:05:00,560 --> 00:05:03,240 Speaker 1: that black hole. Send them of our podcast listeners instead, 95 00:05:03,839 --> 00:05:07,120 Speaker 1: send the physicist, no, thank you. They're the ones who 96 00:05:07,120 --> 00:05:09,960 Speaker 1: want to go anyways, Right, why would you send anyone else? 97 00:05:10,040 --> 00:05:12,320 Speaker 1: I want to know where they're I don't want to 98 00:05:12,360 --> 00:05:15,120 Speaker 1: be there myself, Right, you don't. But what if nobody 99 00:05:15,160 --> 00:05:19,200 Speaker 1: else wants to go? Would you go? How? Situation depends 100 00:05:19,240 --> 00:05:21,320 Speaker 1: on the snacks they're offering along the way. I suppose 101 00:05:21,920 --> 00:05:24,880 Speaker 1: What if it's just bananas all the way down? Scratch it? 102 00:05:25,560 --> 00:05:29,200 Speaker 1: Forget about it. You can slide your way into the 103 00:05:29,240 --> 00:05:32,800 Speaker 1: black hole. It's a slippery slope. But science has blown 104 00:05:32,839 --> 00:05:35,280 Speaker 1: our minds many times over the last few centuries, and 105 00:05:35,320 --> 00:05:39,640 Speaker 1: maybe no instance more so than when Einsang discovered special relativity. 106 00:05:39,720 --> 00:05:43,279 Speaker 1: Einstein's new view of how space and time are linked together, 107 00:05:43,400 --> 00:05:47,279 Speaker 1: how light moves through space, how time is not universal, 108 00:05:47,600 --> 00:05:50,279 Speaker 1: really blew up a lot of basic ideas we had 109 00:05:50,400 --> 00:05:53,240 Speaker 1: about the way the universe worked, ideas that date all 110 00:05:53,240 --> 00:05:56,159 Speaker 1: the way back to Isaac Newton. Yeah, he blew everyone's mind, 111 00:05:56,200 --> 00:05:57,839 Speaker 1: and he sort of did it, like from the comfort 112 00:05:57,839 --> 00:06:00,360 Speaker 1: of his desk, right, he did, and would with a 113 00:06:00,400 --> 00:06:02,200 Speaker 1: pen on a piece of paper. It all sort of 114 00:06:02,240 --> 00:06:04,560 Speaker 1: started with a little thought experiment. There were a lot 115 00:06:04,600 --> 00:06:06,920 Speaker 1: of thought experiments, but you know, he was motivated by 116 00:06:06,960 --> 00:06:09,120 Speaker 1: the work and the experiments done by a lot of 117 00:06:09,120 --> 00:06:12,080 Speaker 1: other folks. In the hundred years before Einstein, people have 118 00:06:12,160 --> 00:06:16,120 Speaker 1: been studying light and electromagnetism, which raised some questions about 119 00:06:16,120 --> 00:06:19,000 Speaker 1: how fast things moved and whether they were moving relative 120 00:06:19,080 --> 00:06:22,200 Speaker 1: to something else, whether life propagated through an either or 121 00:06:22,200 --> 00:06:24,720 Speaker 1: whether it just moved through empty space. And so there 122 00:06:24,720 --> 00:06:27,840 Speaker 1: were a lot of really interesting and puzzling experimental results 123 00:06:27,839 --> 00:06:30,120 Speaker 1: in the last hundred years that needed somebody to sort 124 00:06:30,120 --> 00:06:33,800 Speaker 1: of sit down and think clearly and bring it all together. 125 00:06:33,960 --> 00:06:36,440 Speaker 1: I think that's really motivating in the history of physics 126 00:06:36,880 --> 00:06:39,280 Speaker 1: times when all of the ideas were out there, all 127 00:06:39,279 --> 00:06:42,680 Speaker 1: the information you needed to make that discovery, it was 128 00:06:42,760 --> 00:06:46,080 Speaker 1: already present. It was public information, and it just needed 129 00:06:46,080 --> 00:06:49,160 Speaker 1: somebody to sit down and think carefully and make those connections. 130 00:06:49,480 --> 00:06:51,640 Speaker 1: That's inspiring to me because we're in a similar moment 131 00:06:51,720 --> 00:06:53,359 Speaker 1: right now when there are a lot of results we 132 00:06:53,440 --> 00:06:56,360 Speaker 1: just don't understand. Maybe somebody just needs to think about 133 00:06:56,400 --> 00:06:59,880 Speaker 1: it the right way and have that moment of clarity. Yeah. 134 00:07:00,120 --> 00:07:02,120 Speaker 1: Pretty cool, And I guess I'm just saying that. You know, 135 00:07:02,240 --> 00:07:05,320 Speaker 1: he revolutionized physics, but he did it without a fifty 136 00:07:05,360 --> 00:07:09,040 Speaker 1: billion particle collider. You know, is that a challenge? Are 137 00:07:09,080 --> 00:07:10,760 Speaker 1: you saying I should be able to do the same thing. 138 00:07:10,840 --> 00:07:12,880 Speaker 1: You're not a real physicist if you can do it 139 00:07:12,920 --> 00:07:15,680 Speaker 1: for the price of pen and paper. I didn't say that, 140 00:07:15,720 --> 00:07:18,280 Speaker 1: You just said that. Well, the point I'm making is that, yeah, 141 00:07:18,360 --> 00:07:20,120 Speaker 1: he only spent money and pen and paper, but he 142 00:07:20,160 --> 00:07:23,600 Speaker 1: was relying on the experiments of people who spent a 143 00:07:23,600 --> 00:07:26,120 Speaker 1: lot more time and money and blood and sweat to 144 00:07:26,240 --> 00:07:30,200 Speaker 1: extract that information from the universe. Something that really distinguishes 145 00:07:30,240 --> 00:07:33,200 Speaker 1: modern science from like what the Greeks were doing is 146 00:07:33,240 --> 00:07:35,600 Speaker 1: that it's empirical. We actually demand that it describes the 147 00:07:35,680 --> 00:07:39,480 Speaker 1: universe and that it survives experimental tests, not just ideas 148 00:07:39,520 --> 00:07:42,920 Speaker 1: in our minds. Yeah, I guess he collided ideas sort of. Right. 149 00:07:43,000 --> 00:07:45,600 Speaker 1: It's a two part harmony experiment in theory, right, you 150 00:07:45,640 --> 00:07:49,000 Speaker 1: need both voices to really make the song sing. Yeah, 151 00:07:49,040 --> 00:07:51,800 Speaker 1: but he upturned our notion of the universe, and he 152 00:07:51,840 --> 00:07:53,520 Speaker 1: did it from his desk with a piece of paper, 153 00:07:53,600 --> 00:07:55,520 Speaker 1: and he did it sort of by asking a very 154 00:07:55,600 --> 00:07:58,920 Speaker 1: kind of simple question, right about the universe and the 155 00:07:58,960 --> 00:08:01,080 Speaker 1: speed of light. So it's day on the podcast we'll 156 00:08:01,080 --> 00:08:08,800 Speaker 1: be tackling the question is the speed of light the 157 00:08:08,960 --> 00:08:12,960 Speaker 1: same in all directions? I'm not even sure why we're 158 00:08:13,000 --> 00:08:15,720 Speaker 1: asking this question, Like is it possible for light to 159 00:08:15,760 --> 00:08:18,400 Speaker 1: go a different speeds in the like up or down 160 00:08:19,400 --> 00:08:22,800 Speaker 1: rather than side to side. Yeah, it's a really fascinating question, 161 00:08:22,920 --> 00:08:25,720 Speaker 1: and there's sort of two steps in getting here. One 162 00:08:25,840 --> 00:08:29,320 Speaker 1: is first, just like accepting the idea that the speed 163 00:08:29,360 --> 00:08:32,120 Speaker 1: of light should be the same for all observers. This 164 00:08:32,160 --> 00:08:35,680 Speaker 1: is sort of the big revelation of special relativity from 165 00:08:35,679 --> 00:08:38,400 Speaker 1: Einstein that the speed of light is the speed of light, 166 00:08:38,440 --> 00:08:40,920 Speaker 1: no matter who's measuring it, no matter what the sources. 167 00:08:41,120 --> 00:08:43,040 Speaker 1: If you're holding a flashlight and you flick the switch, 168 00:08:43,320 --> 00:08:45,719 Speaker 1: light leaves the flashlight at the speed of light. If 169 00:08:45,720 --> 00:08:48,760 Speaker 1: you're sitting in a car going sixty miles per hour 170 00:08:49,200 --> 00:08:51,560 Speaker 1: and turn on a flashlight, then for you, light still 171 00:08:51,640 --> 00:08:54,120 Speaker 1: leaves your flashlight at the speed of light. But somebody 172 00:08:54,160 --> 00:08:56,880 Speaker 1: on the ground seeing you move at sixty miles per 173 00:08:56,920 --> 00:08:59,560 Speaker 1: hour relative to the ground and seeing you flick on 174 00:08:59,600 --> 00:09:02,680 Speaker 1: that fly light, they don't measure that light going at 175 00:09:02,720 --> 00:09:05,400 Speaker 1: the speed of light plus sixty miles per hour. They 176 00:09:05,440 --> 00:09:07,959 Speaker 1: still see it going at the speed of light. This 177 00:09:08,000 --> 00:09:10,720 Speaker 1: is one of the core ideas of special relativity and 178 00:09:10,760 --> 00:09:12,880 Speaker 1: one of the hardest to get your minds around, that 179 00:09:12,920 --> 00:09:15,520 Speaker 1: the speed of light is invariant. Yeah, it's kind of 180 00:09:15,520 --> 00:09:18,640 Speaker 1: a fundamental feature of the universe. But I guess it 181 00:09:18,720 --> 00:09:21,080 Speaker 1: gets a little tricky, right because we also know that 182 00:09:21,360 --> 00:09:25,080 Speaker 1: kind of like gravity and heavy objects bend space, so 183 00:09:25,120 --> 00:09:27,079 Speaker 1: you can also sort of bend the speed of light 184 00:09:27,120 --> 00:09:29,600 Speaker 1: in a way. Absolutely everything we're talking about today is 185 00:09:29,600 --> 00:09:33,320 Speaker 1: assuming that space is flat. There's no curvature, there's no 186 00:09:33,400 --> 00:09:36,760 Speaker 1: heavy masses, there's no black holes. In general relativity, where 187 00:09:36,800 --> 00:09:40,040 Speaker 1: space is curved, things get even wank here, and light 188 00:09:40,080 --> 00:09:42,040 Speaker 1: can have all sorts of weird speeds. And you can 189 00:09:42,080 --> 00:09:45,480 Speaker 1: observe light going at crazy higher speeds or even crawling 190 00:09:45,520 --> 00:09:48,280 Speaker 1: to zero as it tries to escape the gravity well 191 00:09:48,400 --> 00:09:51,160 Speaker 1: of a black hole. But that's a completely separate rabbit hole, 192 00:09:51,200 --> 00:09:54,120 Speaker 1: which I think we should close off for today. Wait, 193 00:09:54,160 --> 00:09:56,920 Speaker 1: so you're saying speed of light can change kind of 194 00:09:57,280 --> 00:10:00,520 Speaker 1: depending on what's around it. It's an even weirder because 195 00:10:00,559 --> 00:10:04,360 Speaker 1: in general relativity we can't even talk about the definition 196 00:10:04,400 --> 00:10:06,920 Speaker 1: of the speed of light. If the light is far away. 197 00:10:06,960 --> 00:10:09,560 Speaker 1: You can only measure the speed of light confidently in 198 00:10:09,600 --> 00:10:12,640 Speaker 1: your local frame because we don't know how to define 199 00:10:12,720 --> 00:10:16,719 Speaker 1: the velocity of distant objects in general relativity in an 200 00:10:16,720 --> 00:10:19,000 Speaker 1: invariant way. If you're talking about the speed of light 201 00:10:19,200 --> 00:10:21,200 Speaker 1: for a photon that's very very far away from you 202 00:10:21,240 --> 00:10:24,480 Speaker 1: in general relativity and there's curvature between you and there, 203 00:10:24,800 --> 00:10:27,560 Speaker 1: then you don't even really know how to define velocity. 204 00:10:27,720 --> 00:10:29,480 Speaker 1: So wait, so then the speed of light doesn't move 205 00:10:29,520 --> 00:10:31,240 Speaker 1: the same in all directions, or is it that we 206 00:10:31,280 --> 00:10:32,839 Speaker 1: just don't know how to measure it. We don't even 207 00:10:32,840 --> 00:10:35,600 Speaker 1: know how to define what we mean by velocity of 208 00:10:35,640 --> 00:10:40,240 Speaker 1: a photon for very different objects in curved space. Right. 209 00:10:40,280 --> 00:10:42,520 Speaker 1: We talked about this once on the podcast, about how 210 00:10:42,559 --> 00:10:45,480 Speaker 1: to compare things that are moving that are very very 211 00:10:45,480 --> 00:10:48,400 Speaker 1: far apart from each other if the universe is curved 212 00:10:48,480 --> 00:10:52,640 Speaker 1: between those objects. Like if you have runners near each 213 00:10:52,679 --> 00:10:55,360 Speaker 1: other running in a race in Chicago, you can talk 214 00:10:55,400 --> 00:10:58,239 Speaker 1: about who's faster because they're all in the same location 215 00:10:58,280 --> 00:11:00,520 Speaker 1: in space is pretty much flat between. But if the 216 00:11:00,559 --> 00:11:02,400 Speaker 1: Earth is curved and one of your runners is in 217 00:11:02,480 --> 00:11:05,120 Speaker 1: Chicago and the other one is in South America, then 218 00:11:05,240 --> 00:11:07,840 Speaker 1: you have to take that curvature into account when you're 219 00:11:07,880 --> 00:11:10,920 Speaker 1: comparing their velocities, and there's different ways to do that, 220 00:11:11,040 --> 00:11:13,360 Speaker 1: and so their relative velocity is no longer like a 221 00:11:13,480 --> 00:11:16,560 Speaker 1: crisply defined thing. You can get different answers based on 222 00:11:16,640 --> 00:11:19,200 Speaker 1: exactly how you compare them. The same is true in 223 00:11:19,280 --> 00:11:21,600 Speaker 1: general relativity. If you fire a photon on the other 224 00:11:21,640 --> 00:11:23,920 Speaker 1: side of a black hole, for example, then people could 225 00:11:23,920 --> 00:11:26,800 Speaker 1: disagree about how you define the velocity of that photon 226 00:11:27,040 --> 00:11:29,960 Speaker 1: because space is curved between us and them. I guess 227 00:11:30,000 --> 00:11:34,760 Speaker 1: that feels like maybe next level podcast um topic. But 228 00:11:34,760 --> 00:11:36,520 Speaker 1: I think when you talk about Einstein and what he 229 00:11:36,600 --> 00:11:39,000 Speaker 1: was thinking about back then, he was maybe mostly thinking 230 00:11:39,000 --> 00:11:41,920 Speaker 1: about the local velocity of light, right, Like, if I'm 231 00:11:41,960 --> 00:11:44,839 Speaker 1: sitting here and I point a flash light up, down, left, right, 232 00:11:44,960 --> 00:11:46,920 Speaker 1: bowards or back, is that flash of light going to 233 00:11:47,040 --> 00:11:50,160 Speaker 1: move at the same speed? That's right? So Einstein first says, look, 234 00:11:50,200 --> 00:11:52,800 Speaker 1: the speed of light is invariant. Everybody measures it to 235 00:11:52,800 --> 00:11:55,000 Speaker 1: be the same thing. But there's a wrinkle there. It 236 00:11:55,040 --> 00:11:58,439 Speaker 1: turns out that Einstein's equations that all of our experiments 237 00:11:58,800 --> 00:12:01,439 Speaker 1: could also be consisting it with light moving at different 238 00:12:01,559 --> 00:12:05,520 Speaker 1: speeds in different directions. That maybe light moves faster in 239 00:12:05,600 --> 00:12:08,520 Speaker 1: one direction than in the other direction. All right, well, 240 00:12:08,520 --> 00:12:10,280 Speaker 1: I guess that question is more about whether the speed 241 00:12:10,320 --> 00:12:12,439 Speaker 1: of light is the same whether you're moving or not. 242 00:12:12,600 --> 00:12:15,120 Speaker 1: But I think today we're asking a different question, which 243 00:12:15,160 --> 00:12:17,440 Speaker 1: is like, does the universe have kind of a preferred 244 00:12:17,440 --> 00:12:19,480 Speaker 1: direction for the speed of light or does the speed 245 00:12:19,520 --> 00:12:22,959 Speaker 1: of light somehow move faster or slower in a particular direction. 246 00:12:23,160 --> 00:12:26,160 Speaker 1: I guess relative to the rest of the stuff in 247 00:12:26,160 --> 00:12:29,120 Speaker 1: the universe exactly. And remember there are famous experiments the 248 00:12:29,200 --> 00:12:32,160 Speaker 1: Michaelson Morley experiment that tried to ask the question about 249 00:12:32,160 --> 00:12:35,240 Speaker 1: whether light is moving relative to some ether or whether 250 00:12:35,240 --> 00:12:38,200 Speaker 1: it's just propagetting through empty space. And people were trying 251 00:12:38,240 --> 00:12:40,320 Speaker 1: to measure that, and so they did these experiments where 252 00:12:40,320 --> 00:12:42,800 Speaker 1: they shot beams of light against a mirror and back 253 00:12:42,920 --> 00:12:44,800 Speaker 1: to measure it. And they discovered that the speed of 254 00:12:44,880 --> 00:12:47,360 Speaker 1: light seems to be the same in all directions, even 255 00:12:47,400 --> 00:12:49,840 Speaker 1: as the Earth turns, etcetera. And so there probably wasn't 256 00:12:49,920 --> 00:12:52,600 Speaker 1: any ether. But you know, in special relativity, there are 257 00:12:52,640 --> 00:12:55,920 Speaker 1: always loopholes and you have to ask questions about those loopholes. 258 00:12:56,040 --> 00:12:58,080 Speaker 1: And more of the loopholes and those experiments is that 259 00:12:58,120 --> 00:13:01,960 Speaker 1: they're measuring the speed of light there and back, sort 260 00:13:02,000 --> 00:13:04,079 Speaker 1: of like you throw a baseball to somebody and they 261 00:13:04,120 --> 00:13:06,920 Speaker 1: throw it back, and you're measuring the average velocity in 262 00:13:06,960 --> 00:13:10,319 Speaker 1: both directions. And so there's a question there about whether 263 00:13:10,320 --> 00:13:13,200 Speaker 1: the speed of light really is the same there and back, 264 00:13:13,360 --> 00:13:15,200 Speaker 1: or whether it could be different on the way there 265 00:13:15,320 --> 00:13:17,200 Speaker 1: and on the way back. So it's not about up 266 00:13:17,240 --> 00:13:19,320 Speaker 1: and down, lift and right. It's more about their on back. 267 00:13:19,400 --> 00:13:21,040 Speaker 1: It's more about their and back. There have to be 268 00:13:21,080 --> 00:13:24,080 Speaker 1: some direction in which is preferred for it to be 269 00:13:24,280 --> 00:13:27,200 Speaker 1: the same or not. Okay, So then does this scenario 270 00:13:27,280 --> 00:13:30,560 Speaker 1: then assume that we're both sort of stationary and not 271 00:13:30,720 --> 00:13:32,640 Speaker 1: moving with the rest with the rest of the universe, 272 00:13:32,720 --> 00:13:35,680 Speaker 1: or can we be moving super fast? This question isn't 273 00:13:35,679 --> 00:13:37,840 Speaker 1: about how fast you're moving a relative to the rest 274 00:13:37,840 --> 00:13:40,600 Speaker 1: of the universe or whether there's an ether. The question 275 00:13:40,679 --> 00:13:45,359 Speaker 1: asks does light actually move the same speed in both directions? 276 00:13:45,559 --> 00:13:47,480 Speaker 1: Eyeshine and beam of light at you and you hold 277 00:13:47,480 --> 00:13:49,640 Speaker 1: a mirror and reflective back to me. How do we 278 00:13:49,720 --> 00:13:51,560 Speaker 1: know that it's gone at the same speed on the 279 00:13:51,559 --> 00:13:55,079 Speaker 1: way to you and on the way back. And this 280 00:13:55,160 --> 00:13:58,079 Speaker 1: is no matter where you're standing, Like if I you're 281 00:13:58,120 --> 00:13:59,800 Speaker 1: standing in front of me and I shine a light 282 00:13:59,800 --> 00:14:01,760 Speaker 1: to you and back, or to the side of me 283 00:14:01,760 --> 00:14:03,360 Speaker 1: and I shoud a light to you and back, doesn't 284 00:14:03,400 --> 00:14:05,640 Speaker 1: matter where you are relative to me? Or are we 285 00:14:05,679 --> 00:14:08,280 Speaker 1: always just thinking about there and back? It might matter. Yeah, 286 00:14:08,400 --> 00:14:10,320 Speaker 1: The question is sort of like, does the universe have 287 00:14:10,360 --> 00:14:13,320 Speaker 1: a preferred direction where the speed of light is faster 288 00:14:13,679 --> 00:14:16,760 Speaker 1: in one direction and slower in the opposite direction. And 289 00:14:16,800 --> 00:14:18,640 Speaker 1: that would be really weird, you know, because we expect 290 00:14:18,679 --> 00:14:20,920 Speaker 1: the universe to not prefer any directions, So that would 291 00:14:20,960 --> 00:14:23,600 Speaker 1: be very, very strange. That would be super strange. Should 292 00:14:23,640 --> 00:14:25,680 Speaker 1: be like if there was some kind of like wind 293 00:14:26,040 --> 00:14:29,320 Speaker 1: overall winds to the universe that that always pushes light 294 00:14:29,400 --> 00:14:31,800 Speaker 1: faster in one way and not the other exactly. So 295 00:14:31,880 --> 00:14:34,760 Speaker 1: might surprise people how little we know about the relative 296 00:14:34,800 --> 00:14:36,720 Speaker 1: speed of light on the way there and on the 297 00:14:36,720 --> 00:14:38,760 Speaker 1: way back. So, as usually, we were wondering how many 298 00:14:38,760 --> 00:14:41,040 Speaker 1: people have thought about this question, whether the speed of 299 00:14:41,080 --> 00:14:43,280 Speaker 1: light can need the same in all directions, And so 300 00:14:43,400 --> 00:14:46,080 Speaker 1: Daniel went out there into the internet to find out 301 00:14:46,080 --> 00:14:49,000 Speaker 1: what people thought. So thanks very much to everybody who 302 00:14:49,080 --> 00:14:52,800 Speaker 1: answered this question and our entire team of question answers. 303 00:14:52,840 --> 00:14:55,400 Speaker 1: If you'd like to join that team, please don't be shy. 304 00:14:55,440 --> 00:14:58,320 Speaker 1: Everybody's welcome right to us. Two questions at Daniel and 305 00:14:58,440 --> 00:15:00,600 Speaker 1: Jorge dot com. Think about it for a second. Do 306 00:15:00,640 --> 00:15:02,440 Speaker 1: you think the speed of light is the same in 307 00:15:02,520 --> 00:15:05,240 Speaker 1: all directions? There's what people have to say. I don't 308 00:15:05,640 --> 00:15:12,280 Speaker 1: think so. I think it is it should be the 309 00:15:12,360 --> 00:15:18,160 Speaker 1: same in all directions unless there's a something blocking it 310 00:15:18,800 --> 00:15:21,640 Speaker 1: or bending of space time. I believe that the speed 311 00:15:21,680 --> 00:15:25,960 Speaker 1: of lights is the same in all directions. However, I'm 312 00:15:26,000 --> 00:15:28,480 Speaker 1: not sure because when we measure the speed of lights 313 00:15:28,600 --> 00:15:32,040 Speaker 1: we send lights in one direction and then it comes 314 00:15:32,080 --> 00:15:34,480 Speaker 1: back to us, and we measure the time and then 315 00:15:35,120 --> 00:15:40,120 Speaker 1: divided that by true getting through um the speed of light. 316 00:15:40,200 --> 00:15:41,840 Speaker 1: But we don't know if the speed is the same 317 00:15:42,480 --> 00:15:46,520 Speaker 1: when it's going towards the mirror as it is when 318 00:15:46,520 --> 00:15:50,120 Speaker 1: it's coming back. We just know that the total speeds there. 319 00:15:50,240 --> 00:15:53,080 Speaker 1: Space has no preferred direction, and the speed of light 320 00:15:53,160 --> 00:15:56,680 Speaker 1: is the constant vacuum. So I'm gonna say, yes, the 321 00:15:56,680 --> 00:15:58,760 Speaker 1: speed of light is the same in all directions, should 322 00:15:58,760 --> 00:16:01,480 Speaker 1: be the same in all directions. And you see, it 323 00:16:01,880 --> 00:16:06,600 Speaker 1: depends on what direction do you do you go, for instance, 324 00:16:07,320 --> 00:16:11,800 Speaker 1: when you go on a vocation. Yes, um, the speed 325 00:16:11,800 --> 00:16:16,120 Speaker 1: of light is faster than you come back from your vacation. 326 00:16:17,120 --> 00:16:21,240 Speaker 1: Coming back from a vacation might affect even the speed 327 00:16:21,280 --> 00:16:23,680 Speaker 1: of light. I'm pretty sure the speed of light is 328 00:16:23,800 --> 00:16:26,440 Speaker 1: the same in all directions because it is a constant. 329 00:16:27,400 --> 00:16:31,960 Speaker 1: So you can't really have light going above the speed 330 00:16:31,960 --> 00:16:34,440 Speaker 1: of light, or I guess slower than the speed of light. 331 00:16:35,120 --> 00:16:39,520 Speaker 1: I'm not sure. I thought the speed of light was continuous, 332 00:16:39,680 --> 00:16:44,160 Speaker 1: so it was that six thousand miles per second, so 333 00:16:44,280 --> 00:16:47,600 Speaker 1: that would be surely the same in all directions. Is 334 00:16:47,680 --> 00:16:50,280 Speaker 1: it's not. It doesn't kind of follow the same rules 335 00:16:50,280 --> 00:16:54,160 Speaker 1: that we would apply to normal speed limits. Saying that, 336 00:16:54,440 --> 00:16:57,200 Speaker 1: oh god, yeah, no, I'm going to say now, so immediately, 337 00:16:57,240 --> 00:17:00,000 Speaker 1: I'm kind of thinking of like a star and lights 338 00:17:00,040 --> 00:17:04,679 Speaker 1: shining from every angle because it's uh spherical. Um, I 339 00:17:04,720 --> 00:17:07,520 Speaker 1: think it's shines more brightly in the direction where there's 340 00:17:07,520 --> 00:17:10,960 Speaker 1: like solar flares, because those are essentially like the matter 341 00:17:11,080 --> 00:17:14,520 Speaker 1: shooting out and then the light leaving those bits of matter. 342 00:17:14,960 --> 00:17:17,919 Speaker 1: So no, I think it kind of depends where the 343 00:17:17,920 --> 00:17:20,440 Speaker 1: star is most active in the vacuum of space. The 344 00:17:20,480 --> 00:17:23,800 Speaker 1: speed of light is the same in every direction. I 345 00:17:23,880 --> 00:17:27,200 Speaker 1: learned that by listening to your podcast. Yes, the speed 346 00:17:27,200 --> 00:17:30,480 Speaker 1: of light is the same in all directions. Relative directionality 347 00:17:30,520 --> 00:17:33,359 Speaker 1: can affect wavelength, and I believe there's experiments where they've 348 00:17:33,400 --> 00:17:37,120 Speaker 1: captured or slowed down photons, But the speed of light 349 00:17:37,240 --> 00:17:39,440 Speaker 1: is the same in all directions. I want to say, yes, 350 00:17:39,960 --> 00:17:46,800 Speaker 1: it's a constant. However, things may change with specitification occurs, 351 00:17:47,680 --> 00:17:51,480 Speaker 1: or lensing around the black hole. Perhaps, all right, most 352 00:17:51,480 --> 00:17:53,880 Speaker 1: people think that it should be the same. A few 353 00:17:53,880 --> 00:17:57,040 Speaker 1: people thought it shouldn't be the same. Yeah, Overwhelmingly people think, look, 354 00:17:57,040 --> 00:17:58,919 Speaker 1: it's a constant, and so it's the speed of light 355 00:17:59,000 --> 00:18:01,360 Speaker 1: is the speed of light, and that's been really drummed 356 00:18:01,359 --> 00:18:04,280 Speaker 1: into people in physics and in popular science for a 357 00:18:04,280 --> 00:18:06,920 Speaker 1: long time. So it makes sense that people believe that. Yeah, because, 358 00:18:07,000 --> 00:18:08,679 Speaker 1: as you said, I think everyone has heard of, you know, 359 00:18:08,680 --> 00:18:11,720 Speaker 1: that famous experiment where you should light in one way 360 00:18:11,760 --> 00:18:13,359 Speaker 1: and the other way and you measure the speed of 361 00:18:13,400 --> 00:18:15,520 Speaker 1: light to be the same. So I guess people just 362 00:18:15,560 --> 00:18:17,919 Speaker 1: assume that it's always the same exactly. But in physics 363 00:18:17,960 --> 00:18:20,520 Speaker 1: we always have to ask, what did we really learn 364 00:18:20,600 --> 00:18:25,960 Speaker 1: from this experiment? What other ideas might also explain this experiment, 365 00:18:26,119 --> 00:18:28,360 Speaker 1: and is there any way we can distinguish between these 366 00:18:28,359 --> 00:18:32,320 Speaker 1: like alternative hypotheses and the one that we favor. I see, 367 00:18:32,320 --> 00:18:34,960 Speaker 1: you can't just leave well enough alone. Never we will 368 00:18:35,000 --> 00:18:39,960 Speaker 1: always have more questions. Keep picking. That's how we got 369 00:18:39,960 --> 00:18:41,639 Speaker 1: to where we are, right. The whole way that we 370 00:18:41,720 --> 00:18:44,960 Speaker 1: discovered crazy new ideas about the universe is by picking 371 00:18:44,960 --> 00:18:47,320 Speaker 1: at things, by tugging on those little threads that didn't 372 00:18:47,359 --> 00:18:50,359 Speaker 1: quite sit well with somebody. Yes, and are we better off? Danny, 373 00:18:52,160 --> 00:18:55,280 Speaker 1: I have a job, so yeah, I guess, so one 374 00:18:55,320 --> 00:18:57,440 Speaker 1: person is better off? All right, Well, let's get down 375 00:18:57,480 --> 00:18:59,399 Speaker 1: to the nitty gritty of it, and let's start with 376 00:18:59,400 --> 00:19:02,359 Speaker 1: the basics, Daniel, what is the speed of light? How 377 00:19:02,400 --> 00:19:04,639 Speaker 1: do you define it? What does it mean in the universe? 378 00:19:04,720 --> 00:19:06,240 Speaker 1: Usually when we talk about the speed of light, we 379 00:19:06,280 --> 00:19:08,600 Speaker 1: mean the speed of light of a photon moving in 380 00:19:08,680 --> 00:19:11,480 Speaker 1: a vacuum. And it's really not just the speed of light, 381 00:19:11,600 --> 00:19:16,840 Speaker 1: it's the speed of information. Any massless particle, a gluon graviton, 382 00:19:16,960 --> 00:19:19,600 Speaker 1: if it exists, would move at the speed of light 383 00:19:19,640 --> 00:19:21,520 Speaker 1: and has to move at the speed of light because 384 00:19:21,520 --> 00:19:24,280 Speaker 1: things that are massless have nothing to them. They are 385 00:19:24,440 --> 00:19:28,320 Speaker 1: just motion. So these objects move at this ridiculously high 386 00:19:28,359 --> 00:19:32,399 Speaker 1: speed three million meters per second, and so it seems 387 00:19:32,400 --> 00:19:35,360 Speaker 1: to be sort of like a fundamental speed to the universe, 388 00:19:35,440 --> 00:19:37,840 Speaker 1: not just to light. Right, It's kind of like the 389 00:19:38,240 --> 00:19:41,399 Speaker 1: basic speed of information. But I guess maybe a basic 390 00:19:41,480 --> 00:19:43,600 Speaker 1: question is how do you define it? How do you 391 00:19:43,640 --> 00:19:45,520 Speaker 1: how do you measure it? Like I shoot a photon 392 00:19:45,880 --> 00:19:47,800 Speaker 1: here and then I measure how long it takes for 393 00:19:47,840 --> 00:19:50,000 Speaker 1: it to get to a meter in front of me. 394 00:19:50,280 --> 00:19:52,520 Speaker 1: Is that how you would define the speed of light? 395 00:19:52,520 --> 00:19:54,320 Speaker 1: But then how does a person a meter in front 396 00:19:54,359 --> 00:19:57,160 Speaker 1: of me know when I shot the photon? Yeah, exactly. 397 00:19:57,160 --> 00:19:59,159 Speaker 1: And this is precisely the kind of question you need 398 00:19:59,200 --> 00:20:03,000 Speaker 1: to think very carefully about in special relativity, because measuring 399 00:20:03,320 --> 00:20:06,399 Speaker 1: velocity and special relativity is a bit subtle. What you 400 00:20:06,440 --> 00:20:09,320 Speaker 1: need to do is define a distance. Actually, have a 401 00:20:09,440 --> 00:20:11,959 Speaker 1: point A and the point B. You measure the distance 402 00:20:12,000 --> 00:20:15,119 Speaker 1: between them. You shoot something from A to B, and 403 00:20:15,160 --> 00:20:16,919 Speaker 1: then you need to measure the time it took to 404 00:20:16,960 --> 00:20:18,920 Speaker 1: go from A to B, right, And that's where the 405 00:20:18,960 --> 00:20:21,320 Speaker 1: subtlety comes in, knowing how long it took to go 406 00:20:21,400 --> 00:20:23,240 Speaker 1: from A to B because you have a clock at 407 00:20:23,280 --> 00:20:25,199 Speaker 1: A and you have a clock could be But to 408 00:20:25,240 --> 00:20:27,199 Speaker 1: measure the time from A to B, you can't just 409 00:20:27,359 --> 00:20:30,359 Speaker 1: necessarily subtract the time on the clock at B and 410 00:20:30,440 --> 00:20:32,080 Speaker 1: the time on the clock at A, because how do 411 00:20:32,119 --> 00:20:34,320 Speaker 1: you know they were synchronized, right, So you have to 412 00:20:34,359 --> 00:20:37,000 Speaker 1: come up with some way to synchronize those clocks. And 413 00:20:37,080 --> 00:20:39,200 Speaker 1: so this is where a lot of the complication comes 414 00:20:39,240 --> 00:20:43,560 Speaker 1: in is in how to synchronize clocks at different locations. 415 00:20:43,640 --> 00:20:48,480 Speaker 1: And all special relativity is about simultaneity across distances and 416 00:20:48,520 --> 00:20:50,960 Speaker 1: how you define these kinds of things. Right, It's really 417 00:20:50,960 --> 00:20:53,880 Speaker 1: hard to synchronize clocks because I guess like you could 418 00:20:53,920 --> 00:20:56,400 Speaker 1: come here to South Pasadena and we could make sure 419 00:20:56,400 --> 00:20:58,359 Speaker 1: our clocks start at the same time. But by the 420 00:20:58,400 --> 00:21:00,840 Speaker 1: time you get down there to Orange Tinny, where you live, 421 00:21:01,000 --> 00:21:02,720 Speaker 1: your clock might be out of sink. In fact, it 422 00:21:02,840 --> 00:21:06,119 Speaker 1: certainly will be, because what we've learned is that moving 423 00:21:06,200 --> 00:21:09,880 Speaker 1: clocks runs slow. So if I get in my car 424 00:21:09,960 --> 00:21:12,560 Speaker 1: and I drive at sixty or you know, in l 425 00:21:12,600 --> 00:21:15,680 Speaker 1: a more like five relative to your house, than by 426 00:21:15,680 --> 00:21:18,679 Speaker 1: the time my clock arrives in Irvine, it will no 427 00:21:18,760 --> 00:21:22,600 Speaker 1: longer be synchronized with yours, right, And so it's very 428 00:21:22,640 --> 00:21:26,760 Speaker 1: complicated to synchronize separated clocks. What if I drive the 429 00:21:26,760 --> 00:21:29,840 Speaker 1: opposite way the same amount, wouldn't they still be in sync? 430 00:21:29,920 --> 00:21:32,000 Speaker 1: Then you're just gonna give me a big calculational headache. 431 00:21:34,520 --> 00:21:36,959 Speaker 1: I mean, I'll end up in the mountains here, sanka 432 00:21:37,080 --> 00:21:39,160 Speaker 1: Ro mountains. But wouldn't that work. Wouldn't the clocks still 433 00:21:39,200 --> 00:21:42,040 Speaker 1: be synchronized. No, fundamentally, that doesn't change anything, because it's 434 00:21:42,040 --> 00:21:45,960 Speaker 1: still just relative. Velocity just increases my relative velocity to 435 00:21:46,000 --> 00:21:48,920 Speaker 1: you or your relative velocity to me. But because velocity 436 00:21:48,960 --> 00:21:51,879 Speaker 1: is all relative, it doesn't matter what your velocity is 437 00:21:51,920 --> 00:21:54,359 Speaker 1: relative to the ground. Doesn't change the fact that our 438 00:21:54,440 --> 00:21:58,600 Speaker 1: relative velocities is what determines the time dilation. I see. 439 00:21:58,840 --> 00:22:01,119 Speaker 1: I think what you're saying is it's complicated. I'm saying 440 00:22:01,119 --> 00:22:04,040 Speaker 1: stay home or hey, yeah good, I hate I hate 441 00:22:04,119 --> 00:22:06,000 Speaker 1: driving anywhere? Can I take an uber? What if I 442 00:22:06,000 --> 00:22:09,440 Speaker 1: take an uber or lift? Does it still dilate time? Oh? 443 00:22:09,520 --> 00:22:11,280 Speaker 1: You have to pay extra to not dilate time in 444 00:22:11,320 --> 00:22:13,800 Speaker 1: your uber. It's the uber quantum. All right. Well, so 445 00:22:13,840 --> 00:22:15,720 Speaker 1: that's the speed of light, and let's get into whether 446 00:22:15,840 --> 00:22:17,879 Speaker 1: or not it moves the same in all directions and 447 00:22:17,920 --> 00:22:20,600 Speaker 1: whether or not we've actually measured that. But first, let's 448 00:22:20,640 --> 00:22:34,960 Speaker 1: take a quick break. All right, we're talking about the 449 00:22:34,960 --> 00:22:38,440 Speaker 1: speed of light, which is the I guess, the opposite 450 00:22:38,440 --> 00:22:41,560 Speaker 1: of how fast my kids move whenever they don't want 451 00:22:41,600 --> 00:22:45,439 Speaker 1: to go somewhere, the speed of parenting exactly. Yeah. The 452 00:22:45,440 --> 00:22:47,399 Speaker 1: speed of light is something that really comes up a 453 00:22:47,400 --> 00:22:50,159 Speaker 1: lot in questions about the universe because it seems to 454 00:22:50,200 --> 00:22:53,600 Speaker 1: be something deep and true, something like that reflects how 455 00:22:53,640 --> 00:22:56,239 Speaker 1: the universe itself works. You know that if you have 456 00:22:56,680 --> 00:22:59,600 Speaker 1: empty space with nothing in it, that photons ripple through 457 00:22:59,640 --> 00:23:02,760 Speaker 1: it at certain speed, and people are often asking, you know, why, 458 00:23:02,840 --> 00:23:04,800 Speaker 1: why is the speed of light? This number and not 459 00:23:05,000 --> 00:23:07,960 Speaker 1: some other number, right, like is it a fundamental part 460 00:23:08,000 --> 00:23:10,600 Speaker 1: of the universe. But you just raise an interesting point, 461 00:23:10,600 --> 00:23:12,320 Speaker 1: which is that the speed of light is really just 462 00:23:12,400 --> 00:23:15,879 Speaker 1: kind of like how fast of photon or ripple in 463 00:23:15,920 --> 00:23:19,600 Speaker 1: the electromagnetic field moves. So maybe the real question we're 464 00:23:19,600 --> 00:23:23,679 Speaker 1: asking here is whether those fields themselves can move or 465 00:23:24,000 --> 00:23:26,720 Speaker 1: maybe they have a preferred direction for ripples to move it. Yeah, 466 00:23:26,720 --> 00:23:29,080 Speaker 1: we're talking about the rippling of these quantum fields and 467 00:23:29,320 --> 00:23:31,440 Speaker 1: how well we understand it, you know. And I think 468 00:23:31,480 --> 00:23:34,399 Speaker 1: the thing to remember is that our description of special 469 00:23:34,440 --> 00:23:39,479 Speaker 1: relativity doesn't come from some deep underlying understanding of space 470 00:23:39,480 --> 00:23:42,320 Speaker 1: and time. We haven't like derived the speed of light 471 00:23:42,640 --> 00:23:46,280 Speaker 1: from saying, oh, space is a bunch of quantum foam 472 00:23:46,600 --> 00:23:48,840 Speaker 1: and they're linked together in this way, and the speed 473 00:23:48,840 --> 00:23:50,879 Speaker 1: of light comes from how those things are linked or 474 00:23:50,880 --> 00:23:54,280 Speaker 1: anything like that. It's just our most successful and most 475 00:23:54,359 --> 00:23:58,159 Speaker 1: compact description of all the experiments that we've seen. So 476 00:23:58,200 --> 00:24:00,000 Speaker 1: you can look at it and you can ask, like, well, 477 00:24:00,040 --> 00:24:01,680 Speaker 1: under why it's this way and not some other way, 478 00:24:01,680 --> 00:24:03,879 Speaker 1: And we don't have an answer to that. We just 479 00:24:03,960 --> 00:24:07,840 Speaker 1: have like a very effective description that works really really well, 480 00:24:08,000 --> 00:24:09,600 Speaker 1: and we can ask questions about it and we can 481 00:24:09,720 --> 00:24:12,840 Speaker 1: use it. We don't always understand why this is the 482 00:24:12,840 --> 00:24:15,600 Speaker 1: theory of the universe or why the number is this number. 483 00:24:15,680 --> 00:24:19,040 Speaker 1: It might be that is determined by deeper underlying truths 484 00:24:19,080 --> 00:24:20,800 Speaker 1: about the universe, or it might be that it's not 485 00:24:21,000 --> 00:24:23,199 Speaker 1: you know, that we live in a multiverse, and in 486 00:24:23,280 --> 00:24:25,520 Speaker 1: different universes there are different speeds of light, and this 487 00:24:25,600 --> 00:24:27,520 Speaker 1: is just the one we got right, or even just 488 00:24:27,560 --> 00:24:30,080 Speaker 1: the idea that there is a speed limit to the universe, 489 00:24:30,119 --> 00:24:32,840 Speaker 1: you know, like, you know, we assume that nothing can 490 00:24:32,840 --> 00:24:34,960 Speaker 1: move faster than the speed of light, and physicists always 491 00:24:34,960 --> 00:24:37,440 Speaker 1: saying and I think people have internalized that, but really 492 00:24:37,480 --> 00:24:39,840 Speaker 1: we don't know why, Like we only know that because 493 00:24:39,880 --> 00:24:42,320 Speaker 1: we've measured that. Right, that's right, that is our best 494 00:24:42,320 --> 00:24:45,720 Speaker 1: description of the universe. It really isn't a great why. 495 00:24:45,880 --> 00:24:48,040 Speaker 1: The answer to why is like, well, if you assume 496 00:24:48,119 --> 00:24:51,240 Speaker 1: that that's true, then you develop a theory which is 497 00:24:51,359 --> 00:24:54,760 Speaker 1: very effective and seems very accurate and describes our universe. 498 00:24:55,080 --> 00:24:58,000 Speaker 1: It's not really an answer to the why. It's a 499 00:24:58,119 --> 00:25:01,280 Speaker 1: whether you should think this is probably accurate, not why 500 00:25:01,359 --> 00:25:03,560 Speaker 1: is it this way and not some other way? Right? 501 00:25:03,640 --> 00:25:07,399 Speaker 1: And it's all based on what we've observed exactly. And 502 00:25:07,440 --> 00:25:10,439 Speaker 1: that's why it's so important to remember what the experiments 503 00:25:10,480 --> 00:25:13,560 Speaker 1: actually tell us and what they don't tell us, because 504 00:25:13,600 --> 00:25:16,440 Speaker 1: it can be tempting to draw like overly broad conclusions 505 00:25:16,480 --> 00:25:18,919 Speaker 1: about what's going on in the universe and what we understand. 506 00:25:19,119 --> 00:25:21,840 Speaker 1: But in the end it's always grounded in those experiments, 507 00:25:21,880 --> 00:25:24,400 Speaker 1: not just the pen and paper folks. Right, So let's 508 00:25:24,440 --> 00:25:27,040 Speaker 1: get into that maybe in more detail. And when you 509 00:25:27,080 --> 00:25:29,000 Speaker 1: talk about the speed of light and measuring the speed 510 00:25:29,000 --> 00:25:31,040 Speaker 1: of light, like what does that actually mean? Like I 511 00:25:31,080 --> 00:25:33,119 Speaker 1: asked earlier, like does it mean that somebody shot a 512 00:25:33,160 --> 00:25:35,160 Speaker 1: flash light here and somebody measured how long it took 513 00:25:35,200 --> 00:25:36,760 Speaker 1: to get to the other person? But then how did 514 00:25:36,800 --> 00:25:38,639 Speaker 1: they do it? Where the clock sinks? And all that 515 00:25:38,720 --> 00:25:40,760 Speaker 1: gets kind of tricky. It gets pretty tricky. If you 516 00:25:40,800 --> 00:25:42,720 Speaker 1: want to measure the speed of light like from me 517 00:25:42,840 --> 00:25:46,320 Speaker 1: to you, then either you have to know exactly how 518 00:25:46,400 --> 00:25:49,600 Speaker 1: our clocks go out of sync when we move them apart, 519 00:25:50,040 --> 00:25:53,200 Speaker 1: but that require special relativity which depends on the speed 520 00:25:53,240 --> 00:25:55,480 Speaker 1: of light. Or you can try to use like light 521 00:25:55,560 --> 00:25:59,080 Speaker 1: pulses to synchronize our clocks which are separated, but again 522 00:25:59,160 --> 00:26:01,879 Speaker 1: that requires under standing how long it takes light to 523 00:26:01,920 --> 00:26:04,240 Speaker 1: go from me to you, So there's no way to 524 00:26:04,440 --> 00:26:08,960 Speaker 1: independently think two distant clocks in order to measure the 525 00:26:09,040 --> 00:26:11,320 Speaker 1: speed of light just in one direction. And so what 526 00:26:11,440 --> 00:26:14,480 Speaker 1: people have done, the actual experiments we have done, is 527 00:26:14,520 --> 00:26:16,800 Speaker 1: to measure the round trip speed of light. So you 528 00:26:16,800 --> 00:26:19,320 Speaker 1: don't have a clock in Pasadena, you just have a mirror. 529 00:26:19,640 --> 00:26:22,000 Speaker 1: I have a clock, one single clock. I shoot my 530 00:26:22,080 --> 00:26:24,639 Speaker 1: laser beam up to Pasadena, bounces off of your mirror, 531 00:26:24,640 --> 00:26:27,040 Speaker 1: it comes back to me, and I can measure that 532 00:26:27,160 --> 00:26:29,679 Speaker 1: they're in back time on my clock, and we know 533 00:26:29,720 --> 00:26:32,359 Speaker 1: what the distance is, so then we can derive the 534 00:26:32,400 --> 00:26:34,679 Speaker 1: speed of light. But what I'm measuring there is the 535 00:26:34,800 --> 00:26:37,600 Speaker 1: round trip speed of light, not the one way speed 536 00:26:37,640 --> 00:26:42,159 Speaker 1: of light. Interesting, then you don't need to clocks right exactly, Okay, 537 00:26:42,200 --> 00:26:44,399 Speaker 1: So then that is that kind of the basis of 538 00:26:44,440 --> 00:26:46,760 Speaker 1: most experiments that have measured the speed of light is 539 00:26:46,760 --> 00:26:49,280 Speaker 1: that there and back kind of timing. That's the basis 540 00:26:49,320 --> 00:26:52,119 Speaker 1: of every measurement of the speed of light. We had 541 00:26:52,119 --> 00:26:54,520 Speaker 1: a whole podcast episode about how this was measured, and 542 00:26:54,560 --> 00:26:56,280 Speaker 1: you know, the first ones were pretty cool. There were 543 00:26:56,280 --> 00:27:00,200 Speaker 1: tricks about like Io disappearing behind Jupiter and how along 544 00:27:00,280 --> 00:27:02,760 Speaker 1: that takes when I was moving towards US versus away 545 00:27:02,800 --> 00:27:05,040 Speaker 1: from us. But more recent measurements are all about like 546 00:27:05,160 --> 00:27:08,040 Speaker 1: shooting beams of light against distant mirrors and having them 547 00:27:08,080 --> 00:27:12,040 Speaker 1: come back. Phizoue did this cool experiment with rotating gears 548 00:27:12,080 --> 00:27:14,520 Speaker 1: that moved really fast and blocking the light, etcetera. But 549 00:27:14,640 --> 00:27:17,840 Speaker 1: all of them are there and back measurements for that reason, 550 00:27:17,880 --> 00:27:20,639 Speaker 1: because there's no way to synchronize two distant clocks without 551 00:27:20,720 --> 00:27:23,840 Speaker 1: knowing what the speed of light is already, right, right, 552 00:27:23,880 --> 00:27:26,159 Speaker 1: So that seems like a pretty straightforward way to measure 553 00:27:26,200 --> 00:27:27,800 Speaker 1: the speed of light. Is you shoot it to get 554 00:27:27,920 --> 00:27:29,679 Speaker 1: up to a mirror, You know the distance from you 555 00:27:29,800 --> 00:27:31,800 Speaker 1: to the mirror, so you measure how long light takes 556 00:27:31,840 --> 00:27:33,880 Speaker 1: to go to the mirror and back. And why isn't 557 00:27:33,920 --> 00:27:37,280 Speaker 1: that just isn't that straightforward? Like that should tell you 558 00:27:37,280 --> 00:27:39,320 Speaker 1: how fast light moves? Right, that should tell you how 559 00:27:39,359 --> 00:27:41,320 Speaker 1: fast light moves. But if you go back and read 560 00:27:41,320 --> 00:27:45,399 Speaker 1: Einstein's original paper from five, he makes a point that 561 00:27:45,480 --> 00:27:48,000 Speaker 1: we don't actually know what the speed of light is 562 00:27:48,080 --> 00:27:50,879 Speaker 1: in all directions like his special relativity, and all of 563 00:27:50,920 --> 00:27:55,160 Speaker 1: these experiments are also consistent with a very different, very 564 00:27:55,160 --> 00:27:58,520 Speaker 1: strange idea of the universe that light could move faster 565 00:27:58,760 --> 00:28:01,720 Speaker 1: between Irvine and Passive NA than it does between Pasadena 566 00:28:01,800 --> 00:28:03,879 Speaker 1: and Irvine. Let's say, for the sake of argument, that 567 00:28:03,880 --> 00:28:06,080 Speaker 1: it should take two seconds for light to get from 568 00:28:06,080 --> 00:28:09,119 Speaker 1: Irvine to Pasadena and back. One possibility is that it 569 00:28:09,119 --> 00:28:11,639 Speaker 1: takes one second to get from Irvine to Pasadena and 570 00:28:11,720 --> 00:28:14,199 Speaker 1: one second to get back. Another possibility is that it 571 00:28:14,200 --> 00:28:16,879 Speaker 1: takes half a second to get from Irvine to Pasadena 572 00:28:16,960 --> 00:28:19,080 Speaker 1: and a second and a half to get back, And 573 00:28:19,119 --> 00:28:21,639 Speaker 1: both of those would be consistent with what we measure, 574 00:28:21,680 --> 00:28:24,800 Speaker 1: because we only measure the round trip time. And Einstend 575 00:28:24,840 --> 00:28:27,400 Speaker 1: and his paper pointed out, like, there's an ambiguity here. 576 00:28:27,440 --> 00:28:29,119 Speaker 1: We don't actually know what the one way time is. 577 00:28:29,119 --> 00:28:32,520 Speaker 1: So let's just assume that it's the same in every 578 00:28:32,560 --> 00:28:36,440 Speaker 1: direction because that's simplest. So that's called the Einstein convention, 579 00:28:37,040 --> 00:28:39,200 Speaker 1: and that's the one on which special relativity is built. 580 00:28:39,440 --> 00:28:42,520 Speaker 1: But we've never actually checked that that's true. WHOA, That 581 00:28:42,640 --> 00:28:44,560 Speaker 1: is pretty land blowing. I guess that the idea is 582 00:28:44,560 --> 00:28:47,040 Speaker 1: that you wouldn't be able to tell the difference between 583 00:28:47,040 --> 00:28:49,080 Speaker 1: the two scenarios, right, like you wouldn't be able to 584 00:28:49,080 --> 00:28:51,880 Speaker 1: tell if light took one second each way, or whether 585 00:28:51,920 --> 00:28:53,680 Speaker 1: it took one and a half seconds one way and 586 00:28:53,720 --> 00:28:56,000 Speaker 1: half a second the other way. Like, there's no real 587 00:28:56,040 --> 00:28:58,640 Speaker 1: way for you to know, right, there's no experiment you 588 00:28:58,680 --> 00:29:00,880 Speaker 1: can do to tell the friends. But what if I, 589 00:29:00,960 --> 00:29:04,160 Speaker 1: like do Irvine to Pasadena and Pasadian back, Right, that's 590 00:29:04,200 --> 00:29:07,160 Speaker 1: one sort of direction. What if I go, let's say 591 00:29:07,200 --> 00:29:09,840 Speaker 1: that's like north south. What if I go east west 592 00:29:10,200 --> 00:29:11,800 Speaker 1: and I measure it to be the same. Wouldn't that 593 00:29:11,840 --> 00:29:13,600 Speaker 1: sort of tell me that there is some sort of 594 00:29:13,600 --> 00:29:16,240 Speaker 1: invariants in the universe. That's a Michael said Morley experiment. Right, 595 00:29:16,240 --> 00:29:19,600 Speaker 1: it doesn't matter what direction your apparatus has pointed relative 596 00:29:19,640 --> 00:29:22,280 Speaker 1: to the Earth or the cosmos or anything. You always 597 00:29:22,320 --> 00:29:24,160 Speaker 1: get the same answer. But it could be that the 598 00:29:24,200 --> 00:29:26,440 Speaker 1: east west version is different from the north south version. 599 00:29:26,480 --> 00:29:28,720 Speaker 1: But again you can't tell because you don't measure the 600 00:29:28,760 --> 00:29:32,320 Speaker 1: intermediate time. You only measure the round trip time. And 601 00:29:32,360 --> 00:29:35,680 Speaker 1: it's even possible for it to be instantaneous in one 602 00:29:35,720 --> 00:29:38,720 Speaker 1: direction and then take the full round trip time on 603 00:29:38,760 --> 00:29:42,520 Speaker 1: the way back. Zero seconds from Ermine to Pasadena, two 604 00:29:42,520 --> 00:29:45,719 Speaker 1: seconds on the way back. I see, So even if 605 00:29:45,720 --> 00:29:48,640 Speaker 1: you measure in north south, east west, up and down 606 00:29:49,000 --> 00:29:51,720 Speaker 1: because you're measuring a round trip thing. If there was 607 00:29:51,760 --> 00:29:53,560 Speaker 1: sort of a bias, let's say the universe out of 608 00:29:53,560 --> 00:29:57,080 Speaker 1: bias towards northwest to southeast, you still wouldn't be able 609 00:29:57,120 --> 00:29:58,840 Speaker 1: to tell the difference. I think that's what you're saying. 610 00:29:58,920 --> 00:30:01,120 Speaker 1: That's right. All round trip measurements of the speed of 611 00:30:01,200 --> 00:30:04,320 Speaker 1: light are not sensitive to the one way speed of light. 612 00:30:04,400 --> 00:30:07,960 Speaker 1: The speed of light just from a to be what 613 00:30:08,040 --> 00:30:10,720 Speaker 1: if I don't know, should shoot a triangle like a 614 00:30:10,880 --> 00:30:14,040 Speaker 1: form of triangle with like tumors, Do you know what 615 00:30:14,120 --> 00:30:15,960 Speaker 1: I mean? Like, wouldn't that give me a little bit 616 00:30:16,040 --> 00:30:18,840 Speaker 1: more of a sensitivity to the direction of the universe. Yeah, 617 00:30:18,840 --> 00:30:21,480 Speaker 1: But if you're not measuring the time and the intermediate steps, 618 00:30:21,520 --> 00:30:24,080 Speaker 1: that doesn't matter how many intermediate steps you have. You're 619 00:30:24,120 --> 00:30:26,440 Speaker 1: still just measuring the round trip time. As long as 620 00:30:26,480 --> 00:30:29,280 Speaker 1: you have a single clock in one location, you can't 621 00:30:29,320 --> 00:30:31,640 Speaker 1: tell how long it's taken to get part of the 622 00:30:31,720 --> 00:30:34,480 Speaker 1: way through the trip, right, all right? So that sounds 623 00:30:34,480 --> 00:30:37,440 Speaker 1: like a quite a pickle there that we can't tell 624 00:30:37,480 --> 00:30:39,880 Speaker 1: the universe has a preferred direction for the speed of light. 625 00:30:40,000 --> 00:30:42,440 Speaker 1: So what does that mean? It means two things, right, 626 00:30:42,560 --> 00:30:45,080 Speaker 1: It means on one hand that we should think deeply 627 00:30:45,160 --> 00:30:48,480 Speaker 1: about what we actually know about the universe, what's really 628 00:30:48,560 --> 00:30:50,920 Speaker 1: happening out there, And on the other hand, it also 629 00:30:50,960 --> 00:30:53,280 Speaker 1: means we should think carefully about the questions we're asking, 630 00:30:53,320 --> 00:30:56,400 Speaker 1: like does this question have any meaning? It sounds really 631 00:30:56,440 --> 00:30:58,760 Speaker 1: deep and meaningful, but is it just really the same 632 00:30:58,760 --> 00:31:01,560 Speaker 1: as like saying that zones or time zones and it 633 00:31:01,600 --> 00:31:04,480 Speaker 1: just depends on how you define time. So it raises 634 00:31:04,480 --> 00:31:07,000 Speaker 1: some interesting questions about like what we mean by these 635 00:31:07,000 --> 00:31:10,000 Speaker 1: theories and how we understand the universe. Wait, wait, are 636 00:31:10,000 --> 00:31:12,120 Speaker 1: you saying that you're giving up like we we can't 637 00:31:12,160 --> 00:31:15,240 Speaker 1: tell from an experiment where you bounce light off of 638 00:31:15,280 --> 00:31:17,440 Speaker 1: a mirror, So does that mean we can never tell 639 00:31:17,760 --> 00:31:20,160 Speaker 1: if light has a preferred direction in the universe. If 640 00:31:20,200 --> 00:31:23,720 Speaker 1: special relativity is correct, then it's consistent with all of 641 00:31:23,760 --> 00:31:26,960 Speaker 1: these different ideas, and there should be no way to 642 00:31:26,960 --> 00:31:30,480 Speaker 1: tell the difference between these various ideas that light is 643 00:31:30,520 --> 00:31:33,200 Speaker 1: instantaneous in one direction and half the speed of light 644 00:31:33,200 --> 00:31:36,320 Speaker 1: in the other, or the speed of light in every direction. 645 00:31:36,440 --> 00:31:40,120 Speaker 1: So according to special relativity, Einstein's ideas are consistent with 646 00:31:40,200 --> 00:31:42,920 Speaker 1: all of those right, And every experiment we've ever done 647 00:31:43,080 --> 00:31:46,640 Speaker 1: is also consistent with all of those ideas. There is 648 00:31:46,680 --> 00:31:49,880 Speaker 1: no way that we are aware of to tell the difference. Wow, 649 00:31:49,960 --> 00:31:52,840 Speaker 1: does that mean we'll never know or does it mean 650 00:31:52,880 --> 00:31:55,440 Speaker 1: we just, um, you know, need a bit of better theory. 651 00:31:55,560 --> 00:31:58,160 Speaker 1: If this theory is correct, then we'll never know. But 652 00:31:58,320 --> 00:32:01,600 Speaker 1: it might be possible that special relativity is not correct. 653 00:32:01,720 --> 00:32:04,560 Speaker 1: We know that it's part of general relativity and general relativity. 654 00:32:04,760 --> 00:32:07,520 Speaker 1: It's probably not the fundamental theory of the universe that 655 00:32:07,600 --> 00:32:10,080 Speaker 1: needs to be modified to include quantum mechanics, which has 656 00:32:10,080 --> 00:32:13,040 Speaker 1: its own weird ideas about time. So you know, in 657 00:32:13,120 --> 00:32:16,480 Speaker 1: some future theory of quantum gravity, perhaps we'll figure this out. 658 00:32:16,640 --> 00:32:19,240 Speaker 1: Or if we develop a deep understanding of space and 659 00:32:19,280 --> 00:32:21,400 Speaker 1: time and we understand, like where the speed of light 660 00:32:21,440 --> 00:32:24,640 Speaker 1: actually comes from, then maybe that'll put some constraint on it. 661 00:32:24,680 --> 00:32:27,040 Speaker 1: But if our current theories are true, then there's no 662 00:32:27,080 --> 00:32:29,560 Speaker 1: way to tell the difference. I mean, there isn't anything 663 00:32:29,640 --> 00:32:32,440 Speaker 1: that would like, I don't know, give you a theoretical 664 00:32:32,640 --> 00:32:36,560 Speaker 1: like inconsistency if the universe wasn't if it had a 665 00:32:36,600 --> 00:32:38,160 Speaker 1: preferred direction, you know what I mean, like if it 666 00:32:38,200 --> 00:32:40,600 Speaker 1: had a preferred like Let's assume it hasn't preferred direction. 667 00:32:40,800 --> 00:32:43,720 Speaker 1: Wouldn't that make the equations break or wouldn't that make things, 668 00:32:44,000 --> 00:32:46,720 Speaker 1: you know, all these symmetries break somehow. No, it makes 669 00:32:46,720 --> 00:32:50,160 Speaker 1: the equations much more complicated because, now, like time dilation 670 00:32:50,320 --> 00:32:54,360 Speaker 1: is asymmetric, clocks run slower differently depending on the direction 671 00:32:54,400 --> 00:32:57,080 Speaker 1: there are going. But it always makes the same predictions. 672 00:32:57,080 --> 00:32:59,600 Speaker 1: It always cancels itself out. It always comes out to 673 00:32:59,640 --> 00:33:03,680 Speaker 1: predict the same conclusions for every experiment. The twin paradox 674 00:33:03,760 --> 00:33:07,040 Speaker 1: and spaceships and general relativity and all that stuff, time 675 00:33:07,080 --> 00:33:10,280 Speaker 1: dilation all comes out to them the same answers. So 676 00:33:10,440 --> 00:33:13,880 Speaker 1: the math is more complicated, and it's also not as appealing, right, 677 00:33:13,960 --> 00:33:16,760 Speaker 1: it's weird, it's strange, it doesn't sit well with us. 678 00:33:16,800 --> 00:33:19,960 Speaker 1: It's not the simplest possible explanation, which is why Einstein 679 00:33:20,000 --> 00:33:22,840 Speaker 1: made his choice. He's like, this seems more reasonable, This 680 00:33:22,920 --> 00:33:25,800 Speaker 1: seems like the right way to go. But theoretically it 681 00:33:25,840 --> 00:33:28,920 Speaker 1: all does hang together. Well, well, I guess let's think 682 00:33:28,960 --> 00:33:32,160 Speaker 1: about the scenario where the the universe does have a 683 00:33:32,200 --> 00:33:35,880 Speaker 1: preferred direction, like let's say the universe northeast to southwest 684 00:33:35,960 --> 00:33:38,320 Speaker 1: or something like that. What could be the cause of that? 685 00:33:39,160 --> 00:33:41,440 Speaker 1: Does that mean that all of the quantum fields are 686 00:33:41,480 --> 00:33:45,200 Speaker 1: somehow moving in that direction, and why that direction. Well, 687 00:33:45,240 --> 00:33:47,640 Speaker 1: I think there's two schools have thought about this. One 688 00:33:47,800 --> 00:33:50,560 Speaker 1: is like, this could be real. It could be true 689 00:33:50,560 --> 00:33:54,239 Speaker 1: that things actually move instantaneously in one direction and you know, 690 00:33:54,240 --> 00:33:56,440 Speaker 1: our half the speed of light in the other. And 691 00:33:56,480 --> 00:33:59,080 Speaker 1: you ask, like what could cause that? And yeah, it 692 00:33:59,120 --> 00:34:01,840 Speaker 1: could be you know, of resulting from the way space 693 00:34:01,920 --> 00:34:04,400 Speaker 1: and time is linked together. You know, remember that we 694 00:34:04,480 --> 00:34:07,840 Speaker 1: just don't really understand what space is. Space is not 695 00:34:07,960 --> 00:34:11,000 Speaker 1: just this backdrop in which the universe happens. It might 696 00:34:11,080 --> 00:34:14,880 Speaker 1: emerge somehow from like woven together quantum pieces, and the 697 00:34:14,920 --> 00:34:17,760 Speaker 1: way that information travels through that space could be determined 698 00:34:17,800 --> 00:34:20,000 Speaker 1: by the rules for how that space works at the 699 00:34:20,040 --> 00:34:22,879 Speaker 1: lowest level. So because we don't know why the speed 700 00:34:22,880 --> 00:34:25,120 Speaker 1: of light is what it is, we have no reason 701 00:34:25,160 --> 00:34:27,480 Speaker 1: to expect that it is some value in this direction 702 00:34:27,480 --> 00:34:30,759 Speaker 1: and some value in another direction. There's interesting consequences there also, 703 00:34:30,880 --> 00:34:34,760 Speaker 1: for like momentum conservation and angular momentum conservation, because remember 704 00:34:34,760 --> 00:34:37,800 Speaker 1: that momentum conservation comes from assuming that the universe is 705 00:34:37,840 --> 00:34:41,320 Speaker 1: the same everywhere. An angular momentum conservation comes from assuming 706 00:34:41,440 --> 00:34:44,040 Speaker 1: that it's same in every direction. That if you spin 707 00:34:44,120 --> 00:34:47,200 Speaker 1: your experiment, you don't get any different answers. That's one 708 00:34:47,200 --> 00:34:49,920 Speaker 1: school of thought. Another school of thought is that this 709 00:34:50,040 --> 00:34:53,000 Speaker 1: is all overblown and none of this really means anything. 710 00:34:53,080 --> 00:34:55,440 Speaker 1: It just has to do with like how you define 711 00:34:55,560 --> 00:34:59,480 Speaker 1: time and simultaneity. But really, nothing mysterious is going on. Well, 712 00:34:59,719 --> 00:35:01,200 Speaker 1: did us to go back to what you said a 713 00:35:01,440 --> 00:35:03,560 Speaker 1: moment earlier? I did have a question about that light, 714 00:35:03,640 --> 00:35:05,960 Speaker 1: Like if the light is moving faster in one direction 715 00:35:05,960 --> 00:35:08,520 Speaker 1: than another direction, and I shoot a photon to a 716 00:35:08,520 --> 00:35:11,239 Speaker 1: mirror in that direction, I mean it's going faster one 717 00:35:11,280 --> 00:35:14,960 Speaker 1: way and slow the other way. I guess what's causing 718 00:35:15,000 --> 00:35:18,040 Speaker 1: that photon to slow down? Does it need something to 719 00:35:18,160 --> 00:35:20,960 Speaker 1: like push it, or like, wouldn't it take some energy 720 00:35:21,000 --> 00:35:23,440 Speaker 1: to change its speed? And that's an interesting question. Remember 721 00:35:23,480 --> 00:35:26,160 Speaker 1: that photons don't just bounce off of mirrors, right, So 722 00:35:26,200 --> 00:35:28,960 Speaker 1: it's not really the same photon that goes there and 723 00:35:29,040 --> 00:35:32,080 Speaker 1: comes back. A photon is like absorbed and re emitted 724 00:35:32,320 --> 00:35:35,480 Speaker 1: in a really complicated process. The microphysics of like how 725 00:35:35,520 --> 00:35:38,600 Speaker 1: photons bounce off of objects and are reflected at the 726 00:35:38,600 --> 00:35:41,480 Speaker 1: correct angle. It is actually really complicated. We should dig 727 00:35:41,480 --> 00:35:43,400 Speaker 1: into it in some future episode of the podcast. But 728 00:35:43,440 --> 00:35:44,920 Speaker 1: you can sort of think of it like as a 729 00:35:44,960 --> 00:35:47,759 Speaker 1: new photon and what could cause it? You know, like 730 00:35:47,800 --> 00:35:49,520 Speaker 1: we don't know why the speed of light is what 731 00:35:49,680 --> 00:35:51,799 Speaker 1: it is, and so this is just saying that there's 732 00:35:51,840 --> 00:35:54,640 Speaker 1: more freedom to our theories of the universe than we expected. 733 00:35:54,680 --> 00:35:56,880 Speaker 1: That there's a knob that can be set to different 734 00:35:56,920 --> 00:35:59,920 Speaker 1: values in different directions and everything is still sort of 735 00:36:00,000 --> 00:36:02,239 Speaker 1: works out. Because we don't know why that knobby is 736 00:36:02,280 --> 00:36:05,080 Speaker 1: what it is at all, then it's a little bit 737 00:36:05,120 --> 00:36:08,920 Speaker 1: suspect to assume that it's the same knob in every direction. 738 00:36:10,360 --> 00:36:12,560 Speaker 1: I see. What about things moving in a circle, like 739 00:36:12,680 --> 00:36:15,920 Speaker 1: you have particles and sometimes light, you know, light instead 740 00:36:15,960 --> 00:36:18,040 Speaker 1: of go around a black hole in a circle, would 741 00:36:18,040 --> 00:36:21,799 Speaker 1: in a preferred direction cossum walking? Isn't that or some 742 00:36:21,920 --> 00:36:26,319 Speaker 1: weird kind of angular momentum differences? You can think of 743 00:36:26,360 --> 00:36:29,280 Speaker 1: motion in a circle is decomposed into just two different 744 00:36:29,280 --> 00:36:32,600 Speaker 1: one directional motions, right, It's just like put an access 745 00:36:32,600 --> 00:36:35,200 Speaker 1: on an X and Y. Motion is circle is motion 746 00:36:35,239 --> 00:36:37,920 Speaker 1: in X and motion in WHY and so you can 747 00:36:37,960 --> 00:36:40,720 Speaker 1: just break it down into two pieces of linear motion. 748 00:36:40,920 --> 00:36:43,040 Speaker 1: And if the speed of light is different in one direction, 749 00:36:43,400 --> 00:36:45,200 Speaker 1: then you know it would be faster around the back 750 00:36:45,200 --> 00:36:47,279 Speaker 1: of the black hole, for example, and then slow down 751 00:36:47,320 --> 00:36:49,080 Speaker 1: on the way back. But if you're not measuring it 752 00:36:49,280 --> 00:36:51,920 Speaker 1: halfway around the black hole, then you have no idea 753 00:36:52,239 --> 00:36:54,280 Speaker 1: how long it's taken to do the orbit, and whether 754 00:36:54,320 --> 00:36:57,800 Speaker 1: it's gone smoothly around the black hole, like zipped faster 755 00:36:58,040 --> 00:37:01,319 Speaker 1: around one bit and taking its time around another bit. Right, 756 00:37:01,320 --> 00:37:03,520 Speaker 1: But it's weird to think that the photon would slow 757 00:37:03,560 --> 00:37:06,120 Speaker 1: down in the middle, Right, wouldn't that cost some different 758 00:37:06,120 --> 00:37:09,040 Speaker 1: forces on on it or the black hole? Yeah, and 759 00:37:09,080 --> 00:37:11,000 Speaker 1: it's complicated because you have to account for all the 760 00:37:11,040 --> 00:37:15,240 Speaker 1: forces here. But we're talking about photons moving through curved space, 761 00:37:15,560 --> 00:37:18,319 Speaker 1: then there's already effective forces on them. You need to 762 00:37:18,320 --> 00:37:21,600 Speaker 1: think about space as curved and photons moving along geodesics, 763 00:37:21,680 --> 00:37:23,560 Speaker 1: or you could think about space as flat, sort of 764 00:37:23,600 --> 00:37:25,759 Speaker 1: in a Newtonian way, thinking about the force on the 765 00:37:25,760 --> 00:37:28,520 Speaker 1: photon to make it move in a circle. So in 766 00:37:28,560 --> 00:37:31,560 Speaker 1: any case, there's already like strange things happening to this 767 00:37:31,600 --> 00:37:35,760 Speaker 1: photon to change its direction and therefore its energy. Remember 768 00:37:35,880 --> 00:37:39,520 Speaker 1: that energy itself is not an invariant in the universe. 769 00:37:39,840 --> 00:37:43,520 Speaker 1: Different people will see the same photons having different energies anyway, Right, 770 00:37:43,560 --> 00:37:46,799 Speaker 1: based on their velocity relative to the object that emitted it. 771 00:37:47,200 --> 00:37:49,200 Speaker 1: I could see a photon is being redder than you 772 00:37:49,280 --> 00:37:52,880 Speaker 1: see that same photon based on our velocities relative to 773 00:37:52,920 --> 00:37:56,880 Speaker 1: what sent that photon out because of relativistic Doppler effects. 774 00:37:56,880 --> 00:38:00,120 Speaker 1: So energy already is pretty wonky, even if you think 775 00:38:00,160 --> 00:38:02,040 Speaker 1: that the speed of light is the same in all directions. 776 00:38:02,239 --> 00:38:04,560 Speaker 1: I see, all right, I guess you can. I'll just 777 00:38:04,560 --> 00:38:08,759 Speaker 1: blame it on the universe being wonky. Al Right, Well, 778 00:38:08,760 --> 00:38:11,040 Speaker 1: it seems like we may never know if light can 779 00:38:11,120 --> 00:38:13,759 Speaker 1: go faster in any particular speed. It could it could 780 00:38:13,800 --> 00:38:15,520 Speaker 1: be pretty wild and crazy out there, or it could 781 00:38:15,520 --> 00:38:17,920 Speaker 1: be pretty boring and the same everywhere. But we we 782 00:38:18,040 --> 00:38:20,239 Speaker 1: might never know. And so let's get into what it 783 00:38:20,239 --> 00:38:23,440 Speaker 1: could all mean about our understanding of the universe and 784 00:38:23,560 --> 00:38:26,719 Speaker 1: our future experiments. But first, let's take another quick break. 785 00:38:39,480 --> 00:38:41,319 Speaker 1: We're talking about the speed of light and whether it's 786 00:38:41,360 --> 00:38:43,879 Speaker 1: the same in all directions. Daniel, seems like you're telling 787 00:38:43,920 --> 00:38:48,359 Speaker 1: us that it's not possible to know ever, maybe whether 788 00:38:48,400 --> 00:38:51,320 Speaker 1: it's going faster in any particular direction. It's not possible 789 00:38:51,360 --> 00:38:55,040 Speaker 1: to know whether the universe prefers our current description where 790 00:38:55,040 --> 00:38:56,840 Speaker 1: the speed of light is the same in every direction 791 00:38:57,080 --> 00:38:59,960 Speaker 1: or a different description. We change the speed of light 792 00:39:00,200 --> 00:39:03,040 Speaker 1: to be different in different directions. You know, they all 793 00:39:03,120 --> 00:39:06,280 Speaker 1: describe the universe in the same way. And so until 794 00:39:06,320 --> 00:39:08,160 Speaker 1: you like get into the heart of black holes and 795 00:39:08,239 --> 00:39:11,680 Speaker 1: understand quantum gravity and have a reason to predict why 796 00:39:11,680 --> 00:39:13,880 Speaker 1: the speed of light should be a certain number, than 797 00:39:14,000 --> 00:39:16,680 Speaker 1: all these theories work the same way. And remember, the 798 00:39:16,760 --> 00:39:19,360 Speaker 1: reason we like special relativity, that we accept it, not 799 00:39:19,440 --> 00:39:23,280 Speaker 1: that we believe that it's fundamentally true, is because it works. 800 00:39:23,360 --> 00:39:26,160 Speaker 1: And so if you apply that same premise right like, 801 00:39:26,200 --> 00:39:28,600 Speaker 1: you should apply that to all theories that work. The 802 00:39:28,640 --> 00:39:30,239 Speaker 1: reason that we prefer the one where the speed of 803 00:39:30,320 --> 00:39:31,960 Speaker 1: light is the same in all directions is just that 804 00:39:32,000 --> 00:39:35,120 Speaker 1: it's simpler. It makes the math easier, and we like 805 00:39:35,280 --> 00:39:38,719 Speaker 1: simpler explanations of the universe. Some people think, like, all right, 806 00:39:38,719 --> 00:39:41,560 Speaker 1: this is kind of like overblown clickbait. Really doesn't mean 807 00:39:41,640 --> 00:39:44,520 Speaker 1: anything different about the physical universe. It's just about like 808 00:39:44,719 --> 00:39:47,440 Speaker 1: how we write things down on paper. I see, like 809 00:39:47,520 --> 00:39:50,200 Speaker 1: it's maybe gets to a more philosophical area of like 810 00:39:50,239 --> 00:39:52,920 Speaker 1: what is even time or what is even distance or 811 00:39:52,920 --> 00:39:55,040 Speaker 1: what is even speed? Exactly? It has a lot to 812 00:39:55,080 --> 00:39:57,759 Speaker 1: do with how you define time all these measurements of 813 00:39:57,800 --> 00:40:01,560 Speaker 1: the speed of light are really ratios of distances and times. 814 00:40:01,640 --> 00:40:04,320 Speaker 1: As you're talking about time intervals, and it's very easy 815 00:40:04,640 --> 00:40:08,360 Speaker 1: to get confused about what time intervals mean. In special relativity, 816 00:40:08,400 --> 00:40:10,880 Speaker 1: it's simplest if you just have one clock never moves 817 00:40:10,880 --> 00:40:13,040 Speaker 1: relative to you. But now we're trying to do something else. 818 00:40:13,080 --> 00:40:15,040 Speaker 1: We're trying to think about, like what is the reading 819 00:40:15,040 --> 00:40:17,440 Speaker 1: of a clock that's far away? And you know this 820 00:40:17,560 --> 00:40:19,600 Speaker 1: is hard to do even with time zones on Earth. 821 00:40:19,680 --> 00:40:22,440 Speaker 1: You know, for example, like France is an hour ahead 822 00:40:22,480 --> 00:40:25,440 Speaker 1: of England in time zones, right, or like Arizona is 823 00:40:25,480 --> 00:40:28,960 Speaker 1: an hour ahead of California in time zones. So you 824 00:40:29,000 --> 00:40:33,400 Speaker 1: could like set off on a journey from Arizona to California, 825 00:40:33,760 --> 00:40:37,239 Speaker 1: leaving at noon in Arizona and arriving after an hour 826 00:40:37,560 --> 00:40:42,120 Speaker 1: at noon in California. Does that mean that you've traveled instantaneously? Right? 827 00:40:42,200 --> 00:40:45,320 Speaker 1: Like you left at noon, you arrived at noon. According 828 00:40:45,360 --> 00:40:48,440 Speaker 1: to some definition velocity, you've gone a distance and no 829 00:40:48,600 --> 00:40:51,760 Speaker 1: time is elapsed on the clocks, and so you've moved 830 00:40:51,800 --> 00:40:54,680 Speaker 1: instantaneously in some senses. This is sort of making that 831 00:40:54,760 --> 00:40:58,480 Speaker 1: same argument that you can r raturely define the meaning 832 00:40:58,520 --> 00:41:01,239 Speaker 1: of clocks at distant location, so that the speed of 833 00:41:01,320 --> 00:41:04,520 Speaker 1: light becomes really weird and wonky. Right, And I was thinking, like, 834 00:41:04,600 --> 00:41:07,120 Speaker 1: not even our notions of time or how we measure 835 00:41:07,120 --> 00:41:10,880 Speaker 1: it is that pure in themselves, right, Like we measure 836 00:41:10,960 --> 00:41:14,560 Speaker 1: time by how some crystal oscillates, right usually, or some 837 00:41:14,680 --> 00:41:17,120 Speaker 1: atom like spins or something like that. But even those 838 00:41:17,120 --> 00:41:20,760 Speaker 1: things have to do with motion of these particles through space, 839 00:41:20,840 --> 00:41:23,000 Speaker 1: and then so those are also dependent on the speed 840 00:41:23,040 --> 00:41:25,960 Speaker 1: of light, right, Yeah, absolutely everything is linked in that way. 841 00:41:26,080 --> 00:41:28,560 Speaker 1: As you say, time is linked to motion, right, Time 842 00:41:28,640 --> 00:41:31,840 Speaker 1: is a measurement of change. You can't have a clock 843 00:41:32,120 --> 00:41:34,759 Speaker 1: that doesn't change. And everything there is linked to the 844 00:41:34,760 --> 00:41:37,560 Speaker 1: fundamental processes which are connected to the speed of light. 845 00:41:37,640 --> 00:41:41,440 Speaker 1: So more than thinking like wow, light might move instantaneously 846 00:41:41,520 --> 00:41:43,920 Speaker 1: between here and Mars and take twice as long on 847 00:41:43,960 --> 00:41:45,960 Speaker 1: the way back, instead of thinking that that might be 848 00:41:46,000 --> 00:41:48,120 Speaker 1: the way our universe is. The point is to realize 849 00:41:48,160 --> 00:41:50,239 Speaker 1: that there's a deep connection between the speed of light 850 00:41:50,440 --> 00:41:52,960 Speaker 1: and the whole idea of time, and to understand how 851 00:41:53,000 --> 00:41:55,520 Speaker 1: those ideas flow from one to the other, and how 852 00:41:55,520 --> 00:41:58,440 Speaker 1: little we really know about what's happening far away. And 853 00:41:58,440 --> 00:42:01,239 Speaker 1: I think there's a temptation to say we have special relativity. 854 00:42:01,440 --> 00:42:03,400 Speaker 1: Therefore we can think about how long it takes, like 855 00:42:03,520 --> 00:42:05,520 Speaker 1: to get from here to there, But really we get 856 00:42:05,520 --> 00:42:08,840 Speaker 1: confused when we think about what's happening somewhere far away. 857 00:42:08,880 --> 00:42:11,680 Speaker 1: We don't really know what's happening to clocks that are 858 00:42:11,719 --> 00:42:13,799 Speaker 1: far away from us. Right. It kind of goes back 859 00:42:13,800 --> 00:42:16,040 Speaker 1: to what we talked about earlier, how we're used to 860 00:42:16,160 --> 00:42:18,640 Speaker 1: the world working one way because that's what it seems 861 00:42:18,680 --> 00:42:21,000 Speaker 1: to work on as we grow up, and maybe there 862 00:42:21,040 --> 00:42:23,560 Speaker 1: the real universe works in a totally different way, you know, 863 00:42:23,600 --> 00:42:25,840 Speaker 1: Like we're used to this idea of you know, my 864 00:42:26,080 --> 00:42:28,239 Speaker 1: time being the same as your time, or if I 865 00:42:28,280 --> 00:42:30,400 Speaker 1: synchronize clocks and then we walk away from each other, 866 00:42:30,480 --> 00:42:32,880 Speaker 1: the clocks will still be synchronized. But really that's not 867 00:42:33,040 --> 00:42:36,200 Speaker 1: maybe how the universe really work in these extreme or 868 00:42:36,320 --> 00:42:39,400 Speaker 1: nitty gritty situations. Yeah, and we have to be careful 869 00:42:39,480 --> 00:42:43,160 Speaker 1: about relying too much on conventions that sound reasonable and 870 00:42:43,239 --> 00:42:46,600 Speaker 1: seem like good assumptions, but in the end are just conventions, 871 00:42:47,000 --> 00:42:49,640 Speaker 1: you know, Like, for example, we set the electrons charge 872 00:42:49,719 --> 00:42:52,160 Speaker 1: to be minus one, we could have chosen to be 873 00:42:52,239 --> 00:42:54,759 Speaker 1: something else. We could have chosen to be plus sixty two, 874 00:42:54,800 --> 00:42:56,279 Speaker 1: and then a lot of things would be different, but 875 00:42:56,320 --> 00:42:59,040 Speaker 1: fundamentally the universe wouldn't be different. It's just like how 876 00:42:59,080 --> 00:43:01,680 Speaker 1: we're writing things down on paper, how we are thinking 877 00:43:01,760 --> 00:43:04,759 Speaker 1: about things that we shouldn't describe too much universality to 878 00:43:04,920 --> 00:43:07,880 Speaker 1: these arbitrary choices that we make. And in this case, 879 00:43:07,920 --> 00:43:10,279 Speaker 1: the lesson is relating back to what you were talking 880 00:43:10,320 --> 00:43:13,959 Speaker 1: about earlier about local measurements. Right, Really, what this tells 881 00:43:14,040 --> 00:43:16,080 Speaker 1: us is that we can only measure things that are 882 00:43:16,200 --> 00:43:18,200 Speaker 1: very very close to us and know what that means 883 00:43:18,200 --> 00:43:21,040 Speaker 1: in any intuitive sense. Once we start talking about things 884 00:43:21,040 --> 00:43:23,360 Speaker 1: that are really any distance away from us with respect 885 00:43:23,400 --> 00:43:25,840 Speaker 1: to the speed of light, then things start to get fuzzy, 886 00:43:26,000 --> 00:43:28,360 Speaker 1: and the ideas you have about what's happening far away 887 00:43:28,520 --> 00:43:32,279 Speaker 1: relying more on convention than actual experiment. Right, It's all 888 00:43:32,360 --> 00:43:34,840 Speaker 1: sort of depending on how you measure things or what 889 00:43:34,960 --> 00:43:36,959 Speaker 1: things in. But there has to be something true about 890 00:43:37,000 --> 00:43:40,200 Speaker 1: the universe that is invariant, right, like it Maybe our 891 00:43:40,320 --> 00:43:43,480 Speaker 1: note of what time is is not sort of immovable, 892 00:43:43,520 --> 00:43:45,480 Speaker 1: but there has to be some nugget of truth in 893 00:43:45,520 --> 00:43:48,319 Speaker 1: the universe, right, some consistency in the law. Maybe we 894 00:43:48,360 --> 00:43:51,239 Speaker 1: just need to sort of like realign our conceptions and 895 00:43:51,320 --> 00:43:53,759 Speaker 1: to get at that to sort of understand the truth. Yeah, 896 00:43:53,800 --> 00:43:56,600 Speaker 1: it's possible, but it's also possible that we have an 897 00:43:56,680 --> 00:44:00,799 Speaker 1: overblown sense of truth and the universe sality of our 898 00:44:00,920 --> 00:44:03,799 Speaker 1: picture of the universe based on what we've learned here. 899 00:44:03,880 --> 00:44:07,120 Speaker 1: You know, Newton's biggest leap was to unify the heavens 900 00:44:07,160 --> 00:44:09,000 Speaker 1: and the Earth and say, oh, look, the law of 901 00:44:09,000 --> 00:44:11,680 Speaker 1: gravity that works down here on Earth also works on 902 00:44:11,719 --> 00:44:14,080 Speaker 1: the planets in the sky. And that must have been 903 00:44:14,120 --> 00:44:16,880 Speaker 1: a great moment. Unfortunately he was kind of wrong, right, Like, 904 00:44:16,920 --> 00:44:21,080 Speaker 1: the same rules don't apply everywhere, and so the universality 905 00:44:21,120 --> 00:44:23,839 Speaker 1: of rules that you deduced by looking at things in 906 00:44:23,920 --> 00:44:27,640 Speaker 1: your experience don't necessarily tell you anything about the rest 907 00:44:27,640 --> 00:44:29,640 Speaker 1: of the universe. And so it might be that there's 908 00:44:29,640 --> 00:44:32,040 Speaker 1: truth to the universe, but that truth might also just 909 00:44:32,160 --> 00:44:35,360 Speaker 1: be local. It might just be like, the universe is crazy, 910 00:44:35,440 --> 00:44:38,000 Speaker 1: chaotic mess, and we can summarize parts of it in 911 00:44:38,040 --> 00:44:42,239 Speaker 1: some circumstances approximately and describe them, but there might not 912 00:44:42,320 --> 00:44:45,719 Speaker 1: be any like deep, simple truth about the universe. Well, 913 00:44:45,760 --> 00:44:48,480 Speaker 1: but but it's not random, right, It's not like anything 914 00:44:48,520 --> 00:44:51,000 Speaker 1: goes like if something works at a certain scale, it 915 00:44:51,040 --> 00:44:52,960 Speaker 1: seems to work all the time at that scale, or 916 00:44:53,040 --> 00:44:54,839 Speaker 1: something works at a different scale, seems to work all 917 00:44:54,840 --> 00:44:56,759 Speaker 1: the time and that scale. Yeah, it does seem to 918 00:44:56,800 --> 00:45:00,040 Speaker 1: follow some laws. Exactly what those laws are universal, and 919 00:45:00,120 --> 00:45:03,520 Speaker 1: whether you can extend your understanding out from the cases 920 00:45:03,560 --> 00:45:06,560 Speaker 1: that you've studied is another question, right, Like, the experiments 921 00:45:06,560 --> 00:45:08,279 Speaker 1: we've done are the experiments we've done, and if you 922 00:45:08,320 --> 00:45:10,520 Speaker 1: repeat them, you get the same answers, But you should 923 00:45:10,560 --> 00:45:14,359 Speaker 1: be careful about, like drawing overly broad conclusions from those 924 00:45:14,400 --> 00:45:17,480 Speaker 1: experiments about the meaning of what's happening elsewhere and on 925 00:45:17,520 --> 00:45:20,240 Speaker 1: different scales, right, right, Well, I thought of an interesting 926 00:45:20,239 --> 00:45:22,960 Speaker 1: scenario and maybe you can run this through with us here, 927 00:45:23,120 --> 00:45:26,080 Speaker 1: like a situation where light would be different in different directions. 928 00:45:26,320 --> 00:45:29,120 Speaker 1: We've talked about how the universe is expanding, right, and 929 00:45:29,200 --> 00:45:32,719 Speaker 1: space is always expanding everywhere all the time. That would 930 00:45:32,840 --> 00:45:35,759 Speaker 1: make light sort of take a different amount of time 931 00:45:35,800 --> 00:45:39,040 Speaker 1: to go outwards than it would to come back. Right, 932 00:45:39,360 --> 00:45:41,319 Speaker 1: Like you and I, the space between you and me 933 00:45:41,480 --> 00:45:44,360 Speaker 1: is constantly expanding, It's getting bigger. If you shoot a 934 00:45:44,360 --> 00:45:46,840 Speaker 1: photon at me, it's going to travel a certain speed 935 00:45:46,920 --> 00:45:48,560 Speaker 1: or take a certain amount of time. But once it 936 00:45:48,600 --> 00:45:50,399 Speaker 1: bounces off my mirror and goes back to you. It's 937 00:45:50,400 --> 00:45:53,799 Speaker 1: sort of like going upstream off of the expansion of 938 00:45:53,840 --> 00:45:55,960 Speaker 1: the universe. That's a cool idea. But then on the 939 00:45:56,000 --> 00:45:58,920 Speaker 1: way back, it's also going upstream against the expansion of 940 00:45:58,960 --> 00:46:01,600 Speaker 1: the universe, right, because the niverse is always expanding, And 941 00:46:01,600 --> 00:46:04,200 Speaker 1: if it's expanding the same way in every direction as 942 00:46:04,200 --> 00:46:06,240 Speaker 1: we think it is, then it's sort of always expanding 943 00:46:06,280 --> 00:46:08,879 Speaker 1: in front of that photon no matter what direction it's going. 944 00:46:09,719 --> 00:46:14,680 Speaker 1: But what if the expansion is also not Oh yeah, 945 00:46:14,760 --> 00:46:17,040 Speaker 1: let's add epicycles to epicycles. Now, this is a really 946 00:46:17,080 --> 00:46:19,000 Speaker 1: cool idea. And actually, yesterday I was reading a really 947 00:46:19,000 --> 00:46:22,479 Speaker 1: fascinating paper exploring something similar about whether we could see 948 00:46:22,520 --> 00:46:25,359 Speaker 1: the impact of a non universal speed of light on 949 00:46:25,440 --> 00:46:28,040 Speaker 1: the distant universe, Like, should we be able to see 950 00:46:28,200 --> 00:46:31,480 Speaker 1: galaxies in one direction less red shifted than in another 951 00:46:31,560 --> 00:46:34,920 Speaker 1: direction because the speed of light is different in that direction, right? 952 00:46:35,040 --> 00:46:37,560 Speaker 1: Or if the universe is expanding differently in one direction 953 00:46:37,800 --> 00:46:39,759 Speaker 1: then in another direction, and the speed of light is 954 00:46:39,800 --> 00:46:42,880 Speaker 1: different in that direction, could that also explain things? And 955 00:46:42,920 --> 00:46:45,040 Speaker 1: it turns out that you can't tell the difference, right, 956 00:46:45,280 --> 00:46:47,719 Speaker 1: that it's possible for the universe to be expanding at 957 00:46:47,760 --> 00:46:50,279 Speaker 1: different speeds in different directions, and the speed of light 958 00:46:50,560 --> 00:46:53,240 Speaker 1: to be different in different directions, and it all cancels 959 00:46:53,239 --> 00:46:56,040 Speaker 1: out in a very nice way so that it looks uniform, 960 00:46:56,200 --> 00:46:58,279 Speaker 1: which is what we see today. We see the red 961 00:46:58,280 --> 00:47:00,920 Speaker 1: shift being the same in every direct action, for example. 962 00:47:00,960 --> 00:47:02,760 Speaker 1: And then it has to do with the connection between 963 00:47:02,800 --> 00:47:05,279 Speaker 1: time dilation and the speed of light. The speed of 964 00:47:05,320 --> 00:47:08,240 Speaker 1: light is different in different directions than time dilation is different, 965 00:47:08,280 --> 00:47:11,239 Speaker 1: and so like a red shifting is different in different directions. 966 00:47:11,600 --> 00:47:13,759 Speaker 1: So even if weird things are happening out there, it 967 00:47:13,800 --> 00:47:16,480 Speaker 1: all looks uniform to us, right, right, But if I, 968 00:47:16,640 --> 00:47:19,680 Speaker 1: like shoot a photon to the edge of the observable universe, 969 00:47:19,800 --> 00:47:21,560 Speaker 1: it's going to take a certain amount of time to 970 00:47:21,600 --> 00:47:24,439 Speaker 1: get there, right, because there's a certain amount of space 971 00:47:24,480 --> 00:47:27,000 Speaker 1: between here and there. But on the way back it 972 00:47:27,040 --> 00:47:30,799 Speaker 1: should take longer because there's more space on the way back. Right. Yeah, 973 00:47:31,000 --> 00:47:33,200 Speaker 1: it will take longer on the way back, exactly. But 974 00:47:33,239 --> 00:47:35,640 Speaker 1: because you don't measure it halfway there, you don't measure 975 00:47:35,640 --> 00:47:38,080 Speaker 1: when it gets to the end of the observable universe. 976 00:47:38,160 --> 00:47:39,719 Speaker 1: You don't know how long it's taken to get there 977 00:47:39,840 --> 00:47:41,879 Speaker 1: versus how long it's taken to get back if you're 978 00:47:41,880 --> 00:47:44,960 Speaker 1: only measuring the round trip time. But it should have 979 00:47:45,000 --> 00:47:47,440 Speaker 1: taken more time, right, because there was more space on 980 00:47:47,480 --> 00:47:49,640 Speaker 1: the way back. Yes, it should take more time on 981 00:47:49,680 --> 00:47:51,160 Speaker 1: the way back. But even in the case where the 982 00:47:51,160 --> 00:47:54,120 Speaker 1: speed of light is the same in every direction, that's true, right, 983 00:47:54,120 --> 00:47:56,600 Speaker 1: it's just this more space on the way back, all right. Well, 984 00:47:56,640 --> 00:47:59,040 Speaker 1: it's pretty mind blowing to think that we may not 985 00:47:59,120 --> 00:48:02,319 Speaker 1: know how the universe and it works. Even today, it 986 00:48:02,320 --> 00:48:04,200 Speaker 1: seems like maybe the speed of light could be moving 987 00:48:04,239 --> 00:48:07,320 Speaker 1: differently in different directions. Yeah, that's one way to describe 988 00:48:07,320 --> 00:48:10,480 Speaker 1: the universe. It sort of requires a weirder definition of 989 00:48:10,560 --> 00:48:12,880 Speaker 1: time than the one we have. And so I like 990 00:48:13,000 --> 00:48:15,120 Speaker 1: the idea that the speed of light on one way 991 00:48:15,160 --> 00:48:17,440 Speaker 1: trips is the same as the way it is on 992 00:48:17,520 --> 00:48:20,280 Speaker 1: the way back because it's just simpler and it describes 993 00:48:20,320 --> 00:48:23,560 Speaker 1: all of the experiments, and it also doesn't break my brain. 994 00:48:23,880 --> 00:48:25,480 Speaker 1: But the truth is that we don't know, and we 995 00:48:25,520 --> 00:48:28,919 Speaker 1: have to keep our minds open too crazier ideas about 996 00:48:28,920 --> 00:48:31,640 Speaker 1: the universe than we even imagine. Right, it's because it's 997 00:48:31,640 --> 00:48:33,480 Speaker 1: weird to think that it could be a totally different 998 00:48:33,480 --> 00:48:35,880 Speaker 1: way and still the laws of the universe that we 999 00:48:35,920 --> 00:48:38,040 Speaker 1: have now is still work. Yeah, and we have lots 1000 00:48:38,040 --> 00:48:41,239 Speaker 1: of examples of that in our history of generalizing from 1001 00:48:41,239 --> 00:48:43,920 Speaker 1: the ideas that are time tested and believed to be 1002 00:48:43,960 --> 00:48:47,279 Speaker 1: true to a larger set of ideas which reveals some 1003 00:48:47,400 --> 00:48:49,839 Speaker 1: deeper truth about the universe. Well, there is something that 1004 00:48:49,880 --> 00:48:52,960 Speaker 1: does have a preferred direction, and that is this podcast 1005 00:48:53,000 --> 00:48:56,960 Speaker 1: because we've reached the end of our time here today. 1006 00:48:57,200 --> 00:48:59,160 Speaker 1: But hopefully it made you think a little bit about 1007 00:48:59,200 --> 00:49:01,480 Speaker 1: what time really means in the universe, and it's maybe 1008 00:49:01,600 --> 00:49:03,920 Speaker 1: something that we may never really know or know the 1009 00:49:03,960 --> 00:49:06,239 Speaker 1: real truth of it out there. So are we doing 1010 00:49:06,280 --> 00:49:07,920 Speaker 1: this podcast one way? We're not going to go all 1011 00:49:07,960 --> 00:49:09,279 Speaker 1: the way to the end and then go back. That's 1012 00:49:09,280 --> 00:49:11,080 Speaker 1: why we're not going to turn around and say all 1013 00:49:11,080 --> 00:49:13,839 Speaker 1: the same things we just said. But backwards. Yeah, that's 1014 00:49:13,880 --> 00:49:16,440 Speaker 1: your job, folks. He's replayed button backwards and listen to 1015 00:49:16,480 --> 00:49:19,239 Speaker 1: it at two X speed, that's right, or listen to 1016 00:49:19,239 --> 00:49:22,840 Speaker 1: it um backwards. There might be a hidden message in 1017 00:49:22,920 --> 00:49:27,000 Speaker 1: the audio, you know, like in those old records. Send bananas, 1018 00:49:27,880 --> 00:49:34,359 Speaker 1: Send two billion dollars in bananas now, please please send 1019 00:49:34,360 --> 00:49:38,120 Speaker 1: mine in real dollars please. But anyways, thanks for joining us. 1020 00:49:38,120 --> 00:49:48,000 Speaker 1: We hope you enjoyed that. See you next time. Thanks 1021 00:49:48,000 --> 00:49:50,640 Speaker 1: for listening, and remember that Daniel and Jorge Explain the 1022 00:49:50,719 --> 00:49:53,880 Speaker 1: Universe is a production of I heart Radio. For more 1023 00:49:53,880 --> 00:49:57,240 Speaker 1: podcast for my heart Radio, visit the i heart Radio app, 1024 00:49:57,520 --> 00:50:00,960 Speaker 1: Apple Podcasts, or wherever you listen to your favorite Chills