1 00:00:01,280 --> 00:00:03,320 Speaker 1: Hey, it Jorhan Daniel here, and we want to tell 2 00:00:03,360 --> 00:00:06,880 Speaker 1: you about our new book. It's called Frequently Asked Questions 3 00:00:06,960 --> 00:00:09,719 Speaker 1: about the Universe because you have questions about the universe, 4 00:00:09,800 --> 00:00:12,399 Speaker 1: and so we decided to write a book all about them. 5 00:00:12,400 --> 00:00:14,800 Speaker 1: We talk about your questions, we give some answers, we 6 00:00:14,880 --> 00:00:17,520 Speaker 1: make a bunch of silly jokes as usual, and we 7 00:00:17,600 --> 00:00:20,159 Speaker 1: tackle all kinds of questions, including what happens if I 8 00:00:20,200 --> 00:00:22,880 Speaker 1: fall into a black hole? Or is there another version 9 00:00:22,920 --> 00:00:25,480 Speaker 1: of you out there that's right? Like usual, we tackle 10 00:00:25,600 --> 00:00:29,960 Speaker 1: the deepest, darkest, biggest, craziest questions about this incredible cosmos. 11 00:00:29,960 --> 00:00:31,800 Speaker 1: If you want to support the podcast, please get the 12 00:00:31,800 --> 00:00:33,879 Speaker 1: book and get a copy not just for yourself, but 13 00:00:34,120 --> 00:00:39,360 Speaker 1: you know, for your nieces and nephews, cousins, friends, parents, dogs, hamsters, 14 00:00:39,400 --> 00:00:42,640 Speaker 1: and for the aliens. So get your copy of Frequently 15 00:00:42,720 --> 00:00:46,440 Speaker 1: Asked Questions about the Universe is available for pre order now, 16 00:00:46,560 --> 00:00:49,239 Speaker 1: coming out November two. You can find more details at 17 00:00:49,240 --> 00:00:53,160 Speaker 1: the book's website, Universe f a Q dot com. Thanks 18 00:00:53,159 --> 00:00:55,000 Speaker 1: for your support, and if you have a hamster that 19 00:00:55,040 --> 00:00:57,240 Speaker 1: can read, please let us know. We'd love to have 20 00:00:57,320 --> 00:01:11,440 Speaker 1: them on the podcast. Hey Daniel, I have a question 21 00:01:11,600 --> 00:01:15,039 Speaker 1: about the physics of the Internet. Oh, that sounds like fun. 22 00:01:15,360 --> 00:01:18,039 Speaker 1: Like what is the speed of email? You know, how 23 00:01:18,080 --> 00:01:20,240 Speaker 1: fast does it travel? If I write you an email? 24 00:01:20,319 --> 00:01:22,040 Speaker 1: When does it get to you? You know, I think 25 00:01:22,120 --> 00:01:25,720 Speaker 1: email might actually violate the laws of physics. What do 26 00:01:25,800 --> 00:01:27,600 Speaker 1: you mean they go faster than the speed of light? 27 00:01:28,480 --> 00:01:30,200 Speaker 1: Or do you mean like if it falls into a 28 00:01:30,240 --> 00:01:33,479 Speaker 1: black hole it's actually my inbox? Yeah, exactly like that. 29 00:01:33,720 --> 00:01:36,000 Speaker 1: I can tell you a story about one time I 30 00:01:36,040 --> 00:01:40,919 Speaker 1: had email violate causality No way. What happened? Well in college, 31 00:01:40,959 --> 00:01:43,360 Speaker 1: one time I sent a draft of an essay to 32 00:01:43,440 --> 00:01:46,559 Speaker 1: my TA for comments. She wrote back, Hey, looks great, 33 00:01:46,600 --> 00:01:49,760 Speaker 1: no comments. Then I realized I'd never attached it to 34 00:01:49,800 --> 00:01:52,840 Speaker 1: the email. It sounds actually violated the laws of her 35 00:01:53,120 --> 00:01:55,880 Speaker 1: responsibilities as a t A, not the laws of physics. 36 00:01:56,520 --> 00:02:01,320 Speaker 1: That's one interpretation. Is there a non physical interpretation? The 37 00:02:01,360 --> 00:02:03,520 Speaker 1: grad student union won't allow me to talk about that. 38 00:02:03,720 --> 00:02:21,720 Speaker 1: It breaks their laws. Hi. I'm Orge, my cartoonist and 39 00:02:21,720 --> 00:02:24,560 Speaker 1: the creator of PhD comics. Hi, I'm Daniel. I'm a 40 00:02:24,600 --> 00:02:28,280 Speaker 1: particle physicist and a professor UC Irvine, and I'm recording 41 00:02:28,280 --> 00:02:31,520 Speaker 1: this podcast on the same microphone Michael Jackson used to 42 00:02:31,520 --> 00:02:36,040 Speaker 1: record thriller. What what do you mean, like the same 43 00:02:36,080 --> 00:02:38,760 Speaker 1: microphone or the same brand, the same brand. I just 44 00:02:38,800 --> 00:02:42,440 Speaker 1: discovered yesterday that apparently I'm using a very well known, 45 00:02:42,560 --> 00:02:45,840 Speaker 1: famous microphone, which in the industry is known as the thriller. 46 00:02:45,880 --> 00:02:49,360 Speaker 1: Mike no way, Wow, is it extra? Kind of like 47 00:02:49,400 --> 00:02:51,600 Speaker 1: it has ex extra pops and extras to go a 48 00:02:51,680 --> 00:02:54,400 Speaker 1: little bit higher in your falsetto voice. It does make 49 00:02:54,440 --> 00:02:56,240 Speaker 1: me do a little dance every time you make a 50 00:02:56,240 --> 00:02:59,840 Speaker 1: really funny joke. So, yeah, you do the moonwalk when 51 00:03:00,040 --> 00:03:02,360 Speaker 1: we talk about the moon. I don't want you to 52 00:03:02,400 --> 00:03:04,639 Speaker 1: think about that too much in your head, but yeah, 53 00:03:04,680 --> 00:03:07,280 Speaker 1: let's say that's what happens. Yeah, But welcome to our podcast. 54 00:03:07,360 --> 00:03:09,840 Speaker 1: Daniel and Jorge explain the Universe, a production of I 55 00:03:09,919 --> 00:03:12,680 Speaker 1: Heart Radio, which is sort of like Thriller, and that 56 00:03:12,800 --> 00:03:15,760 Speaker 1: we take you on a thrill ride around the universe. 57 00:03:16,040 --> 00:03:18,560 Speaker 1: We don't raise the dead and dance them around, but 58 00:03:18,639 --> 00:03:21,240 Speaker 1: we do talk about everything in this universe that happens, 59 00:03:21,240 --> 00:03:25,560 Speaker 1: everything that gets extinguished, everything that flies around and amazes 60 00:03:25,680 --> 00:03:28,440 Speaker 1: us with everything that can do, and all the laws 61 00:03:28,440 --> 00:03:31,400 Speaker 1: of physics that seem to work together in harmony to 62 00:03:31,600 --> 00:03:35,120 Speaker 1: make this universe so crazy, so bonkers, so amazing and 63 00:03:35,200 --> 00:03:39,480 Speaker 1: yet so discoverable. Yeah, because it is a pretty thrilling universe. 64 00:03:39,640 --> 00:03:42,280 Speaker 1: And we like to take you on the moonwalk every 65 00:03:42,320 --> 00:03:45,680 Speaker 1: episode so we can think about the universe and possibly 66 00:03:45,880 --> 00:03:48,520 Speaker 1: even beat it. What is the moonwalk analogy? There? It 67 00:03:48,600 --> 00:03:51,760 Speaker 1: looks like you're moving forward, you're actually sliding backwards. Does 68 00:03:51,800 --> 00:03:54,200 Speaker 1: that mean like we're doing physics? We think we're understanding, 69 00:03:54,240 --> 00:03:57,480 Speaker 1: but really we understand less and less every year. You know, 70 00:03:57,840 --> 00:04:01,200 Speaker 1: basically we're faking the whole thing. We're actually moving the 71 00:04:01,280 --> 00:04:05,360 Speaker 1: progress of science backwards. We're walking backwards on evolution here, 72 00:04:05,480 --> 00:04:07,720 Speaker 1: but it looks like we're moving forward. I like to 73 00:04:07,720 --> 00:04:10,240 Speaker 1: think that our podcast helps science move forward in a 74 00:04:10,280 --> 00:04:13,080 Speaker 1: real way because it excites people and engages them in 75 00:04:13,080 --> 00:04:16,839 Speaker 1: this Species Why project, they're trying to uncover the mysteries 76 00:04:16,880 --> 00:04:19,720 Speaker 1: of the universe. Yeah. And also we're wearing red leather 77 00:04:19,800 --> 00:04:22,480 Speaker 1: jackets right now with a lot of zippers in it. 78 00:04:22,640 --> 00:04:24,720 Speaker 1: That's right. I only have one sparkly glove on. Does 79 00:04:24,760 --> 00:04:26,800 Speaker 1: that make me Michael Jackson? I have the other one. 80 00:04:26,839 --> 00:04:31,760 Speaker 1: It's like we're handshaking glittering gloves across the internet. That's right. 81 00:04:31,920 --> 00:04:34,560 Speaker 1: And we're trying to merge all the Jackson siblings into 82 00:04:34,600 --> 00:04:40,479 Speaker 1: one theory of Jackson, the unified theory of entertainment. Yeah, 83 00:04:40,680 --> 00:04:43,440 Speaker 1: of soul and R and P. But it is a 84 00:04:43,440 --> 00:04:46,040 Speaker 1: pretty thrilling universe, as we said. And this is an 85 00:04:46,040 --> 00:04:49,240 Speaker 1: interesting question about how fast do emails travel? Like, if 86 00:04:49,279 --> 00:04:51,680 Speaker 1: I read you an email and I hit send, does 87 00:04:51,720 --> 00:04:53,880 Speaker 1: it go to you at the speed of light? Right? 88 00:04:53,920 --> 00:04:58,279 Speaker 1: Because sort of, right, because electricity and signals over telephone lines, 89 00:04:58,360 --> 00:05:00,720 Speaker 1: they sort of go basically as fast this light. Right, 90 00:05:00,760 --> 00:05:03,640 Speaker 1: that's right. That information does travel at the speed of light. 91 00:05:03,800 --> 00:05:06,200 Speaker 1: You take like a wire, you send a pulse down it, 92 00:05:06,200 --> 00:05:09,039 Speaker 1: It does travel very very fast, essentially at the speed 93 00:05:09,040 --> 00:05:10,760 Speaker 1: of light. But we all know, of course, that email 94 00:05:10,760 --> 00:05:13,760 Speaker 1: doesn't arrive that quickly when you send it, because it's 95 00:05:13,760 --> 00:05:15,640 Speaker 1: got to go through all sorts of like computers who 96 00:05:15,720 --> 00:05:18,479 Speaker 1: do algorithms and weight on it and analyze it. And 97 00:05:18,520 --> 00:05:20,440 Speaker 1: so for example, my email here at you see I 98 00:05:20,520 --> 00:05:22,800 Speaker 1: sometimes it takes ten minutes to get one. Yeah, and 99 00:05:22,839 --> 00:05:25,000 Speaker 1: that's not even the emails you send me, which takes 100 00:05:25,040 --> 00:05:27,839 Speaker 1: me hours to even read. But yeah, the speed of 101 00:05:27,880 --> 00:05:30,919 Speaker 1: light is pretty fast. It seems to be basically the 102 00:05:30,960 --> 00:05:33,279 Speaker 1: speed limit of the universe. Right, Nothing in the universe 103 00:05:33,320 --> 00:05:35,280 Speaker 1: can go faster than the speed of light. That's right, 104 00:05:35,320 --> 00:05:37,600 Speaker 1: it seems to be this hard and fast limit. It's 105 00:05:37,640 --> 00:05:40,280 Speaker 1: just like a feature of our universe that there's a 106 00:05:40,360 --> 00:05:44,760 Speaker 1: maximum speed of information, which is really super cool philosophically 107 00:05:44,800 --> 00:05:47,279 Speaker 1: to think about, like why is that and how could 108 00:05:47,279 --> 00:05:49,680 Speaker 1: the universe have been different? And what does it mean? 109 00:05:50,040 --> 00:05:52,440 Speaker 1: But it's also really fun to think about, like how 110 00:05:52,440 --> 00:05:55,680 Speaker 1: did we figure that out? You know, something we know now, 111 00:05:55,880 --> 00:06:00,000 Speaker 1: it's something we definitely understand, but like obviously early humans 112 00:06:00,200 --> 00:06:02,440 Speaker 1: know that, and so I think it's always fun to 113 00:06:02,520 --> 00:06:05,480 Speaker 1: return to the moments that we cracked at these problems 114 00:06:05,480 --> 00:06:08,120 Speaker 1: that we like gained a new understanding of how the 115 00:06:08,200 --> 00:06:10,920 Speaker 1: universe worked. Yeah, because it's crazy to think that at 116 00:06:10,960 --> 00:06:12,919 Speaker 1: some point we didn't know what the speed of light was, 117 00:06:13,080 --> 00:06:15,520 Speaker 1: or even that it sort of had a speed I imagine, right, 118 00:06:15,680 --> 00:06:19,520 Speaker 1: Like I imagine early man probably thought light was instantaneous, 119 00:06:19,560 --> 00:06:22,880 Speaker 1: like you light a stick on fire and immediately the 120 00:06:23,000 --> 00:06:25,479 Speaker 1: light hits your eyeballs. Yeah. The Greeks had a lot 121 00:06:25,560 --> 00:06:29,280 Speaker 1: of totally uninformed debates on the topic, you know, speculating 122 00:06:29,360 --> 00:06:32,479 Speaker 1: endlessly about what light was, did it emanate from objects, 123 00:06:32,520 --> 00:06:35,880 Speaker 1: did it reflect from things? Did it travel instantaneously? Was 124 00:06:35,960 --> 00:06:37,920 Speaker 1: it a thing or not a thing? What does it 125 00:06:37,960 --> 00:06:40,240 Speaker 1: mean to be a thing? Man? Like the Greeks went 126 00:06:40,320 --> 00:06:43,000 Speaker 1: on and on and on with no information. It's amazing 127 00:06:43,040 --> 00:06:45,400 Speaker 1: to me, for thousands of years you could have uninformed 128 00:06:45,400 --> 00:06:49,520 Speaker 1: debates because of our discussions these days are informed. Well, 129 00:06:49,520 --> 00:06:52,440 Speaker 1: we have data, we can do experiments, we can learn things, 130 00:06:52,760 --> 00:06:55,600 Speaker 1: we can make progress, you know, without just like smoking 131 00:06:55,600 --> 00:06:59,120 Speaker 1: more of Bannan appeals and thinking about how the universe works. Man, Well, 132 00:06:59,120 --> 00:07:00,840 Speaker 1: it is pretty interesting thing to think about the speed 133 00:07:00,839 --> 00:07:02,719 Speaker 1: of light. And I think what's also interesting is that 134 00:07:02,760 --> 00:07:05,640 Speaker 1: it's not infinite, like it's a number, you know, like 135 00:07:05,680 --> 00:07:07,919 Speaker 1: the craziest you can go into the universe is a 136 00:07:08,000 --> 00:07:11,640 Speaker 1: specific number and nothing can go faster than that number. 137 00:07:11,840 --> 00:07:14,600 Speaker 1: That's right, Yeah, And it's interesting, right every time you 138 00:07:14,640 --> 00:07:17,320 Speaker 1: see a number in the theory of physics, you wonder 139 00:07:17,640 --> 00:07:21,000 Speaker 1: why that number? Did it have to be that? Could 140 00:07:21,000 --> 00:07:24,080 Speaker 1: it have been something else? If it could have been anything, 141 00:07:24,120 --> 00:07:26,320 Speaker 1: then why is it this value? Or if it could 142 00:07:26,320 --> 00:07:28,520 Speaker 1: only be one thing, then what are the rules that 143 00:07:28,640 --> 00:07:30,800 Speaker 1: make it have to be that one thing? And what 144 00:07:30,840 --> 00:07:33,480 Speaker 1: does that mean? So it's like a huge screaming clue 145 00:07:33,520 --> 00:07:35,880 Speaker 1: to me. Every time we see a number in physics, 146 00:07:36,000 --> 00:07:38,640 Speaker 1: what is it? Screaming and screaming, there's a secret here, 147 00:07:38,680 --> 00:07:41,200 Speaker 1: there's something else to be understood that in a hundred 148 00:07:41,280 --> 00:07:43,920 Speaker 1: years somebody else is going to win a Nobel Prize 149 00:07:43,920 --> 00:07:46,160 Speaker 1: for an explanation. And you have all the information you 150 00:07:46,200 --> 00:07:48,880 Speaker 1: need to arrive at that idea. You just don't see 151 00:07:48,880 --> 00:07:51,320 Speaker 1: it right. Yeah, And isn't it weird to think about that? 152 00:07:51,400 --> 00:07:53,720 Speaker 1: All other speeds that are greater than the speed of 153 00:07:53,800 --> 00:07:59,040 Speaker 1: light are basically impossible, like one per second faster than 154 00:07:59,080 --> 00:08:03,160 Speaker 1: the speed of light, impact any number from that number 155 00:08:03,240 --> 00:08:07,200 Speaker 1: to infinity is basically impossible in the universe. Yeah, the 156 00:08:07,280 --> 00:08:10,120 Speaker 1: universe says no, and it doesn't negotiate. There's no whidle 157 00:08:10,200 --> 00:08:13,360 Speaker 1: room there. You can't charm the universe into letting you 158 00:08:13,400 --> 00:08:15,520 Speaker 1: do something a little bit past the speed of light. 159 00:08:15,560 --> 00:08:18,120 Speaker 1: It's a firm no, it's a hard pass from the universe. 160 00:08:18,320 --> 00:08:20,240 Speaker 1: And what exactly is the speed of light? Daniel? How 161 00:08:20,240 --> 00:08:22,120 Speaker 1: how many digits do you know it? Too? Well? It's 162 00:08:22,120 --> 00:08:25,120 Speaker 1: funny you should ask, because in particle physics we say 163 00:08:25,160 --> 00:08:27,840 Speaker 1: the speed of light is one, like we use units 164 00:08:27,920 --> 00:08:30,200 Speaker 1: where the speed of light is just one, because we 165 00:08:30,200 --> 00:08:32,040 Speaker 1: can't be bothered to write it down all the time 166 00:08:32,320 --> 00:08:35,319 Speaker 1: because it's everywhere. So we have equations with like speed 167 00:08:35,320 --> 00:08:37,160 Speaker 1: of light square speed of light to the four speed 168 00:08:37,160 --> 00:08:38,680 Speaker 1: of light to the eighth, and so it just sort 169 00:08:38,679 --> 00:08:41,040 Speaker 1: of gets annoying. So we just say, let's just set 170 00:08:41,120 --> 00:08:43,640 Speaker 1: see equal to one, and then we can ignore it. Mostly, 171 00:08:43,840 --> 00:08:48,000 Speaker 1: let's ignore reality for our convenience. Let's have another lens 172 00:08:48,120 --> 00:08:50,800 Speaker 1: in which we look at reality in which it makes 173 00:08:50,800 --> 00:08:52,679 Speaker 1: more sense than we can boil it down to its 174 00:08:52,720 --> 00:08:56,400 Speaker 1: true fundamental essence and not get tangled up in little numbers. Right, 175 00:08:56,440 --> 00:08:58,520 Speaker 1: so you can take more naps, right, you can take 176 00:08:58,559 --> 00:09:01,360 Speaker 1: more naps. So a particle physicist is the wrong person 177 00:09:01,400 --> 00:09:03,520 Speaker 1: to ask about the actual value of the speed of 178 00:09:03,600 --> 00:09:06,880 Speaker 1: light insensible units. But we do define it as two 179 00:09:07,000 --> 00:09:11,840 Speaker 1: hundred nine million, seven hundred thousand, four hundred and fifty 180 00:09:11,840 --> 00:09:15,120 Speaker 1: eight meters per second. So that's the exact value of 181 00:09:15,120 --> 00:09:16,880 Speaker 1: the speed of light. The most people when they do 182 00:09:16,920 --> 00:09:20,719 Speaker 1: calculations just say three times tended them per second, right, 183 00:09:20,840 --> 00:09:23,640 Speaker 1: or like three hundred million meters per second. But it 184 00:09:24,000 --> 00:09:28,480 Speaker 1: is a very specific number, right, it's like eight and 185 00:09:28,679 --> 00:09:30,400 Speaker 1: like four or five. Nine is too fast. You can't 186 00:09:30,400 --> 00:09:33,439 Speaker 1: go that fast. That's right. It's a no on four 187 00:09:33,480 --> 00:09:37,000 Speaker 1: or five, nine and a half, no, five point one. No, 188 00:09:37,240 --> 00:09:40,360 Speaker 1: there's no flexibility, there's no negotiation. This is in Hollywood. 189 00:09:40,360 --> 00:09:42,480 Speaker 1: We're like, hey, we can find a deal. Right. It's 190 00:09:42,520 --> 00:09:44,319 Speaker 1: kind of weird, right that the universe would just pick 191 00:09:44,400 --> 00:09:46,640 Speaker 1: the number and nothing can go faster. Yeah, it's a 192 00:09:46,720 --> 00:09:49,240 Speaker 1: huge clue. That's telling you something really deep about the 193 00:09:49,320 --> 00:09:53,000 Speaker 1: nature of space and time itself, right, Like if the 194 00:09:53,000 --> 00:09:55,520 Speaker 1: loop quantum gravity is true and space really is a 195 00:09:55,520 --> 00:09:58,520 Speaker 1: big quantized foam bubble, then maybe this tells us about 196 00:09:58,520 --> 00:10:00,440 Speaker 1: how those foam bubbles talk to e other and you 197 00:10:00,480 --> 00:10:02,920 Speaker 1: can't get information from one phone bubble to the other 198 00:10:03,160 --> 00:10:06,240 Speaker 1: faster than that because they just aren't closely enough connected 199 00:10:06,360 --> 00:10:08,360 Speaker 1: or something. So I think it really does tell you 200 00:10:08,480 --> 00:10:11,120 Speaker 1: something deep about the nature of the universe. Yeah, and 201 00:10:11,120 --> 00:10:12,960 Speaker 1: it's a very specific number, and so I guess the 202 00:10:13,000 --> 00:10:15,720 Speaker 1: big question is like, how do you know it's that number? 203 00:10:15,880 --> 00:10:18,200 Speaker 1: To what accuracy do we know that's the right number, 204 00:10:18,440 --> 00:10:20,679 Speaker 1: that it's a maximum speed limit of the universe, and 205 00:10:20,760 --> 00:10:22,840 Speaker 1: how did we figure it out? So to be on 206 00:10:22,840 --> 00:10:29,840 Speaker 1: the podcast, we'll be asking the question, how do we 207 00:10:29,920 --> 00:10:33,160 Speaker 1: actually know what the speed of light is? That we 208 00:10:33,200 --> 00:10:35,640 Speaker 1: actually measured it, or are we guessing? You're right, you 209 00:10:35,679 --> 00:10:39,200 Speaker 1: figured out we always been guessing this whole time, and 210 00:10:39,360 --> 00:10:41,760 Speaker 1: you have revealed this like a Scooby Doo episode. You've 211 00:10:41,800 --> 00:10:43,719 Speaker 1: pulled off the mask. Well, a few minutes ago you 212 00:10:43,800 --> 00:10:46,520 Speaker 1: just said one, right, So I don't know what's true 213 00:10:46,520 --> 00:10:49,280 Speaker 1: anymore than you. They're all true. It just depends on 214 00:10:49,320 --> 00:10:51,640 Speaker 1: the units. Well, I guess I'm wondering, like, has anyone 215 00:10:51,679 --> 00:10:54,520 Speaker 1: actually tested, right, because nobody has actually tried to go 216 00:10:54,600 --> 00:10:57,400 Speaker 1: faster than the speed of light technically right, Like you haven't, 217 00:10:57,440 --> 00:11:00,840 Speaker 1: I haven't. I have totally tried apps. I've tried so 218 00:11:00,880 --> 00:11:02,920 Speaker 1: many times as a kid. I mean I didn't get 219 00:11:02,960 --> 00:11:05,000 Speaker 1: anywhere near the speed of light. But that doesn't mean 220 00:11:05,000 --> 00:11:10,160 Speaker 1: I didn't try to try. I mean like a credible try, 221 00:11:10,760 --> 00:11:14,559 Speaker 1: not like a far off by by ten decimal places. 222 00:11:14,600 --> 00:11:16,320 Speaker 1: That's true. But you know I did grow up to 223 00:11:16,360 --> 00:11:19,720 Speaker 1: work at a particle accelerator, which makes a pretty credible 224 00:11:19,760 --> 00:11:22,600 Speaker 1: attempt to get particles to go faster than the speed 225 00:11:22,640 --> 00:11:24,960 Speaker 1: of light. We take protons and we accelerate them. We 226 00:11:25,000 --> 00:11:27,760 Speaker 1: give them so much energy, and they go faster and 227 00:11:27,800 --> 00:11:29,960 Speaker 1: faster and faster, And what we see is that as 228 00:11:30,000 --> 00:11:33,400 Speaker 1: you add energy, the particles just don't get going much faster. 229 00:11:33,720 --> 00:11:35,760 Speaker 1: It's sort of a mind bend there, Like you can 230 00:11:35,880 --> 00:11:38,960 Speaker 1: add energy, there's more kinetic energy in these particles, but 231 00:11:39,000 --> 00:11:41,960 Speaker 1: they're not moving much faster. Right, it approaches a speed 232 00:11:41,960 --> 00:11:43,800 Speaker 1: of light. But I guess a big question is how 233 00:11:43,800 --> 00:11:45,600 Speaker 1: do you know what the actual speed of light is? 234 00:11:45,640 --> 00:11:48,240 Speaker 1: Like the actual number, Yes, so that you can measure 235 00:11:48,240 --> 00:11:50,280 Speaker 1: by actually looking at light and measuring it, but you 236 00:11:50,280 --> 00:11:52,640 Speaker 1: can also see the protons approach it. Right. We have 237 00:11:52,720 --> 00:11:54,600 Speaker 1: these limits in physics all the time where you can 238 00:11:54,600 --> 00:11:57,880 Speaker 1: see something is approaching a limit and as em topically 239 00:11:57,880 --> 00:11:59,920 Speaker 1: gets closer and closer and closer, and so you can 240 00:12:00,000 --> 00:12:02,920 Speaker 1: alculate what that limit would be if you went to 241 00:12:03,040 --> 00:12:06,760 Speaker 1: infinite energy. You can extrapolate mathematically to figure out like 242 00:12:06,840 --> 00:12:09,480 Speaker 1: what is the limiting case, either from looking at protons 243 00:12:09,520 --> 00:12:12,000 Speaker 1: to see what they are approaching, or just by directly 244 00:12:12,040 --> 00:12:15,080 Speaker 1: measuring the speed of actual beams of light itself. Well, 245 00:12:15,160 --> 00:12:16,840 Speaker 1: that's kind of what we're going to get into today 246 00:12:16,920 --> 00:12:19,440 Speaker 1: is kind of the history of how we've gone about 247 00:12:19,520 --> 00:12:22,160 Speaker 1: measuring light and also what are some of our best 248 00:12:22,240 --> 00:12:25,959 Speaker 1: current measurements of it and some really surprising twists about 249 00:12:25,960 --> 00:12:28,559 Speaker 1: what we do and don't know about the speed of light, 250 00:12:29,160 --> 00:12:34,000 Speaker 1: some light twists or some dark twists a little both. So, 251 00:12:34,000 --> 00:12:36,080 Speaker 1: as usually, we were wondering how many people out there 252 00:12:36,520 --> 00:12:39,559 Speaker 1: knew the answer to this question, how we measure the 253 00:12:39,600 --> 00:12:41,760 Speaker 1: speed of light? So Daniel went out there and ask 254 00:12:41,800 --> 00:12:44,240 Speaker 1: people on the internet if they knew how we measured 255 00:12:44,360 --> 00:12:46,600 Speaker 1: the speed of light. That's right, So thank you to 256 00:12:46,679 --> 00:12:50,200 Speaker 1: everybody who, during these strange pandemic times, have stepped up 257 00:12:50,240 --> 00:12:52,400 Speaker 1: to fill in the gap left by you see Irvine 258 00:12:52,400 --> 00:12:56,360 Speaker 1: students and answered questions online. If you'd like to participate 259 00:12:56,400 --> 00:12:58,839 Speaker 1: for a future episode of the podcast, please don't be 260 00:12:58,880 --> 00:13:01,680 Speaker 1: shy and right to us two questions at Daniel and 261 00:13:01,760 --> 00:13:04,120 Speaker 1: Jorge dot com. So think about it for a second. 262 00:13:04,160 --> 00:13:07,200 Speaker 1: What would you answer? Here's what people had to say. Well, 263 00:13:07,280 --> 00:13:09,959 Speaker 1: if we already had space travel by the time we 264 00:13:09,960 --> 00:13:15,080 Speaker 1: were trying to measure that, we could have sent a 265 00:13:15,200 --> 00:13:19,880 Speaker 1: radio transmission from the moon with time stamp and see 266 00:13:19,920 --> 00:13:22,880 Speaker 1: how long it took to get there. So I don't 267 00:13:22,880 --> 00:13:26,080 Speaker 1: know exactly how we measured the speed of light, but 268 00:13:26,280 --> 00:13:29,320 Speaker 1: I would guess by measuring the time required for light 269 00:13:29,400 --> 00:13:33,920 Speaker 1: to travel a certain distance, maybe by using the mirror experiment, 270 00:13:34,559 --> 00:13:38,160 Speaker 1: where the time required for light to travel to the 271 00:13:38,200 --> 00:13:42,959 Speaker 1: mirror and back from the mirror is recorded, and since 272 00:13:43,000 --> 00:13:45,440 Speaker 1: we know the distance and time, we can find the 273 00:13:45,480 --> 00:13:53,160 Speaker 1: speed of light. Oh, no idea. I mean it was 274 00:13:53,200 --> 00:13:56,959 Speaker 1: theoretical at first, and then they tested it. So then 275 00:13:57,200 --> 00:14:01,840 Speaker 1: a particle accelerator I think Galla Lao tried to measure 276 00:14:01,880 --> 00:14:06,040 Speaker 1: the speed of light using lanterns at set distances across fields. 277 00:14:06,679 --> 00:14:09,960 Speaker 1: I assumed that wasn't successful, though, and I assumed that 278 00:14:10,000 --> 00:14:12,520 Speaker 1: we've also tried to measure it by bouncing signals off 279 00:14:12,520 --> 00:14:16,320 Speaker 1: the moon in more recent times. I don't know, though, 280 00:14:16,360 --> 00:14:19,480 Speaker 1: what the first successful measurement of the speed of light was. 281 00:14:20,320 --> 00:14:22,880 Speaker 1: I guess maybe they worked out like the distance between 282 00:14:22,920 --> 00:14:27,640 Speaker 1: two objects in space, and then worked out how quickly 283 00:14:27,680 --> 00:14:30,360 Speaker 1: light traveled between them and did the maths. I don't know. 284 00:14:30,920 --> 00:14:34,440 Speaker 1: That's a really good question. So I've been racking my 285 00:14:34,520 --> 00:14:36,800 Speaker 1: brain trying to think of this, because I swear I've 286 00:14:36,880 --> 00:14:39,920 Speaker 1: learned this in high school or college physics. But I 287 00:14:39,960 --> 00:14:42,440 Speaker 1: couldn't tell you know how we measured the speed of light. 288 00:14:43,320 --> 00:14:47,000 Speaker 1: A guy climbed a mountain and shone a light at 289 00:14:47,000 --> 00:14:52,360 Speaker 1: a rotating mirror on another mountain and counted how long 290 00:14:52,480 --> 00:14:56,360 Speaker 1: in between for the late come back. So what do 291 00:14:56,400 --> 00:14:58,320 Speaker 1: you think of these engineering ideas for how to measure 292 00:14:58,360 --> 00:15:02,360 Speaker 1: this incredible speed. I think they're a little light on substance, 293 00:15:03,600 --> 00:15:05,600 Speaker 1: but they're pretty good attempts. A lot of people didn't 294 00:15:05,600 --> 00:15:07,760 Speaker 1: seem to have sort of an idea of how we've 295 00:15:07,800 --> 00:15:10,080 Speaker 1: done it. Maybe, you know, they could think about ways 296 00:15:10,120 --> 00:15:12,400 Speaker 1: that they could do it, but I guess not a 297 00:15:12,480 --> 00:15:14,840 Speaker 1: lot of people. You know what the latest and greatest 298 00:15:14,840 --> 00:15:17,320 Speaker 1: measurement is. Yeah, and the challenge, of course is that 299 00:15:17,360 --> 00:15:20,880 Speaker 1: it's super duper duper fast. Like we talked about the 300 00:15:20,920 --> 00:15:24,800 Speaker 1: speed of light being three million meters per second, that's 301 00:15:24,840 --> 00:15:26,720 Speaker 1: sort of hard to understand, you know, what does that 302 00:15:26,760 --> 00:15:28,880 Speaker 1: really mean? I think it's easier sometimes to think about 303 00:15:28,880 --> 00:15:31,560 Speaker 1: it in terms of how far light goes in a 304 00:15:31,680 --> 00:15:35,200 Speaker 1: very short amount of time, rather than in a full second. Actually, 305 00:15:35,200 --> 00:15:38,680 Speaker 1: think about light is traveling about one foot every nanosecond, 306 00:15:39,160 --> 00:15:41,560 Speaker 1: so like a light nanosecond. You know the concept of 307 00:15:41,600 --> 00:15:43,680 Speaker 1: a light year, how far light travels in a year. 308 00:15:43,960 --> 00:15:47,280 Speaker 1: A light nanosecond is about one ft or thirty centimeters. 309 00:15:47,520 --> 00:15:49,840 Speaker 1: For those of you on the metric system, I totally 310 00:15:49,840 --> 00:15:53,480 Speaker 1: reject that that way of looking at the first of all, 311 00:15:53,560 --> 00:15:58,560 Speaker 1: it's English units using feet instead of meters, and also 312 00:15:58,800 --> 00:16:00,920 Speaker 1: a nanosecond that doesn't have a lot of meaning to me. 313 00:16:00,960 --> 00:16:02,320 Speaker 1: I guess, well, I guess you don't get a lot 314 00:16:02,320 --> 00:16:04,480 Speaker 1: of things done in a nanosecond. But I'm pretty efficient, 315 00:16:04,520 --> 00:16:06,480 Speaker 1: you know, I can answer ten emails in a nanoseconds. 316 00:16:06,520 --> 00:16:10,920 Speaker 1: So you live in another reality, it seems no, no, 317 00:16:11,000 --> 00:16:14,040 Speaker 1: obviously not. But you know, when you're talking about like signals, 318 00:16:14,040 --> 00:16:16,360 Speaker 1: like how long is it going to take my information 319 00:16:16,400 --> 00:16:18,520 Speaker 1: to go down this cable? I have one piece of 320 00:16:18,560 --> 00:16:20,840 Speaker 1: equipment over here, another piece of equipment over there ten 321 00:16:20,880 --> 00:16:23,400 Speaker 1: feet away, so you know it's gonna take ten nanoseconds 322 00:16:23,400 --> 00:16:25,120 Speaker 1: to get from here or there. And sometimes if you're 323 00:16:25,160 --> 00:16:27,880 Speaker 1: building electronics, right, you need to know are these signals 324 00:16:27,880 --> 00:16:30,200 Speaker 1: gonna be coordinated with the gap going to be between them? 325 00:16:30,240 --> 00:16:32,680 Speaker 1: And so it's helpful sometimes to think about light in 326 00:16:32,760 --> 00:16:34,520 Speaker 1: terms of how long it takes to move across a 327 00:16:34,600 --> 00:16:37,760 Speaker 1: reasonable distance, because I don't really know what three hundred 328 00:16:37,760 --> 00:16:40,160 Speaker 1: million meters is, but how can we measure it in 329 00:16:40,240 --> 00:16:42,280 Speaker 1: terms of like in the blink of an eye, Like 330 00:16:42,360 --> 00:16:45,200 Speaker 1: let's say a blink of an eye, is I don't know, 331 00:16:45,240 --> 00:16:48,840 Speaker 1: a hundred milliseconds, how long can that light travel in 332 00:16:48,880 --> 00:16:52,680 Speaker 1: those hundred milliseconds. Well, you know, a hundred milliseconds is 333 00:16:52,720 --> 00:16:55,400 Speaker 1: only a tenth of a second, right, and so a 334 00:16:55,440 --> 00:16:58,880 Speaker 1: tenth of a second would be thirty million meters, So 335 00:16:59,120 --> 00:17:01,040 Speaker 1: it's still pretty are that light can go in the 336 00:17:01,160 --> 00:17:03,920 Speaker 1: tense of a second, right, thirty million meters, it's about 337 00:17:03,920 --> 00:17:08,320 Speaker 1: thirty tho kilometers, right, which is about yeah, that's right, 338 00:17:08,400 --> 00:17:12,080 Speaker 1: thirty millions is just under twenty thousand miles. So like, 339 00:17:12,200 --> 00:17:15,600 Speaker 1: if I blink, then light can travel basically once around 340 00:17:15,640 --> 00:17:17,960 Speaker 1: the world kind of almost maybe if you're at the 341 00:17:18,400 --> 00:17:21,440 Speaker 1: latitude of like North America, like could go around the 342 00:17:21,480 --> 00:17:23,400 Speaker 1: Earth in the blink of an eye. And that's really 343 00:17:23,440 --> 00:17:25,720 Speaker 1: the challenge of measuring the speed of light that it's 344 00:17:25,800 --> 00:17:29,280 Speaker 1: so darn fast that for all extents and purposes, for 345 00:17:29,320 --> 00:17:32,360 Speaker 1: the things we do, it's essentially infinite. And that makes 346 00:17:32,359 --> 00:17:35,919 Speaker 1: it really really challenging because you either need incredibly vast 347 00:17:36,040 --> 00:17:39,040 Speaker 1: distances so you can accumulate some like reasonable amount of 348 00:17:39,040 --> 00:17:41,800 Speaker 1: time between when you send a message and when it arrives, 349 00:17:42,240 --> 00:17:44,760 Speaker 1: or you need to be able to measure really really 350 00:17:44,840 --> 00:17:48,439 Speaker 1: short times. And so imagine you're like Aristotle five thousand 351 00:17:48,560 --> 00:17:51,480 Speaker 1: years ago, How could you possibly set up an experiment 352 00:17:51,720 --> 00:17:56,240 Speaker 1: to measure something over vast distances or very short times? Yeah, 353 00:17:56,280 --> 00:17:58,520 Speaker 1: because I guess you know, it's hard to measure something 354 00:17:58,520 --> 00:18:00,639 Speaker 1: that happens in the blink of an eye, right, especially 355 00:18:00,720 --> 00:18:03,879 Speaker 1: if you're in the thousand years BC or something that's right, 356 00:18:03,880 --> 00:18:05,960 Speaker 1: if all you have is like you know, a clay tablet, 357 00:18:06,160 --> 00:18:08,200 Speaker 1: a stick and a robe, then like what are you 358 00:18:08,240 --> 00:18:10,679 Speaker 1: gonna do? And these days, even for us, it's not 359 00:18:10,720 --> 00:18:12,960 Speaker 1: easy to see the impact of the speed of light. 360 00:18:13,400 --> 00:18:16,960 Speaker 1: You know, it impacts things like spaceflight communication. If you're 361 00:18:17,000 --> 00:18:19,840 Speaker 1: on Mars driving a rover, then sure, and there's an 362 00:18:19,840 --> 00:18:22,240 Speaker 1: impact of the speed of light not being infinite. But 363 00:18:22,320 --> 00:18:24,000 Speaker 1: here on Earth, you know, it doesn't really make a 364 00:18:24,040 --> 00:18:26,760 Speaker 1: difference in your life very much. If you're like the 365 00:18:26,800 --> 00:18:29,480 Speaker 1: designer of a computer, then you think about this, like 366 00:18:29,520 --> 00:18:31,760 Speaker 1: how long did it take the information and go across 367 00:18:31,880 --> 00:18:34,960 Speaker 1: my CPU? And can I optimize the design of it 368 00:18:35,000 --> 00:18:37,359 Speaker 1: to bring things closer to speed up my computer? But 369 00:18:37,520 --> 00:18:41,040 Speaker 1: unless you're driving rovers on Mars or designing CPUs, you 370 00:18:41,119 --> 00:18:43,680 Speaker 1: probably don't think about the speed of light very much. Yeah, 371 00:18:43,720 --> 00:18:46,800 Speaker 1: it's probably pretty instantaneous to you in an intuitive sense. 372 00:18:46,880 --> 00:18:48,320 Speaker 1: But I think if a big question is like, how 373 00:18:48,320 --> 00:18:51,880 Speaker 1: do we know it's this particular number, right or not? Yeah, 374 00:18:51,920 --> 00:18:53,800 Speaker 1: well that comes from the things we measure, and we 375 00:18:53,880 --> 00:18:56,719 Speaker 1: have no like theoretical preference for that number. It's not 376 00:18:56,760 --> 00:18:58,640 Speaker 1: like the kind of thing we could have derived where 377 00:18:58,680 --> 00:19:00,720 Speaker 1: we're like, well, it has to be this number, it 378 00:19:00,800 --> 00:19:03,560 Speaker 1: can only be this number. It's just a measurement, right. 379 00:19:03,920 --> 00:19:06,280 Speaker 1: Often in physics there are things where you know, there's 380 00:19:06,320 --> 00:19:08,760 Speaker 1: something we know happens in the universe, but we don't 381 00:19:08,800 --> 00:19:10,640 Speaker 1: know why it's this way and not the other way, 382 00:19:10,680 --> 00:19:12,879 Speaker 1: and so we just have to measure it. Things like 383 00:19:13,080 --> 00:19:15,080 Speaker 1: the mass of the Higgs boson, or the mass of 384 00:19:15,119 --> 00:19:17,520 Speaker 1: all the particles, or you know, the strength of gravity. 385 00:19:17,760 --> 00:19:19,719 Speaker 1: These are things we don't know why they are that 386 00:19:19,840 --> 00:19:22,280 Speaker 1: number and not some other number. And the speed of 387 00:19:22,359 --> 00:19:24,000 Speaker 1: light is like that. It's just something we have to 388 00:19:24,040 --> 00:19:26,679 Speaker 1: go out and measure, like it could have been another number, right, 389 00:19:26,720 --> 00:19:30,960 Speaker 1: it could have been three, or we don't know, right, 390 00:19:31,000 --> 00:19:33,520 Speaker 1: it could be that it has to be this number 391 00:19:33,560 --> 00:19:36,760 Speaker 1: because there's some deeper theory of physics that constrains it 392 00:19:36,840 --> 00:19:39,159 Speaker 1: and makes it only work for this value. But we 393 00:19:39,200 --> 00:19:41,359 Speaker 1: don't have that theory of physics. According to our theory, 394 00:19:41,400 --> 00:19:43,720 Speaker 1: it could have been any other number. But of course 395 00:19:43,760 --> 00:19:45,800 Speaker 1: we don't expect that our theory of physics is the 396 00:19:45,840 --> 00:19:48,240 Speaker 1: final answer. And it's exactly the kind of place where 397 00:19:48,240 --> 00:19:50,680 Speaker 1: I see there are opportunities right where we say, well, 398 00:19:50,680 --> 00:19:53,200 Speaker 1: we don't have an explanation for this, so let's keep 399 00:19:53,280 --> 00:19:56,600 Speaker 1: looking for an explanation. To me, it's unsatisfying. People say, well, 400 00:19:56,720 --> 00:19:58,920 Speaker 1: it could have been anything. It was just random or 401 00:19:59,000 --> 00:20:01,199 Speaker 1: one element in the multi verse. So this is just 402 00:20:01,320 --> 00:20:03,919 Speaker 1: what it is. There is no explanation to me. It's 403 00:20:03,960 --> 00:20:07,760 Speaker 1: a clue that says that probably is an explanation. Keep digging, right, like, 404 00:20:07,840 --> 00:20:11,360 Speaker 1: maybe it tells you something specifically about why the universe 405 00:20:11,520 --> 00:20:13,680 Speaker 1: was the way it had to be. We just don't 406 00:20:13,720 --> 00:20:16,040 Speaker 1: see it yet. And it's also interesting to think that 407 00:20:16,080 --> 00:20:18,480 Speaker 1: it's not just the speed of light. It's like the 408 00:20:18,600 --> 00:20:23,080 Speaker 1: maximum speed that information can travel in the universe, like anything. 409 00:20:23,160 --> 00:20:25,160 Speaker 1: It's not just light that travels at the speed of light. 410 00:20:25,640 --> 00:20:28,119 Speaker 1: It's any particle without mass. Yeah, and it's sort of 411 00:20:28,160 --> 00:20:31,399 Speaker 1: a misnomer, right. We discovered light moves at this speed first, 412 00:20:31,400 --> 00:20:33,840 Speaker 1: and it is the speed of light in a vacuum. 413 00:20:34,119 --> 00:20:36,280 Speaker 1: But really it should be like the speed of space 414 00:20:36,320 --> 00:20:39,480 Speaker 1: time or the speed of information, because, as you say, 415 00:20:39,520 --> 00:20:42,080 Speaker 1: anything that doesn't have mass, and that means like a 416 00:20:42,119 --> 00:20:46,360 Speaker 1: graviton if they exist, or a gluon for example, anything 417 00:20:46,359 --> 00:20:48,600 Speaker 1: that doesn't have mass has to travel at the speed 418 00:20:48,640 --> 00:20:51,399 Speaker 1: of light, and only the speed of light, and nothing 419 00:20:51,440 --> 00:20:54,840 Speaker 1: else that does have mass can travel at that speed. 420 00:20:55,160 --> 00:20:57,160 Speaker 1: So it really is a special speed in the universe, 421 00:20:57,400 --> 00:21:00,040 Speaker 1: more than just the speed of photons. Right, maybe you 422 00:21:00,080 --> 00:21:02,800 Speaker 1: should have been called the speed of nothing. You like 423 00:21:02,920 --> 00:21:06,399 Speaker 1: that because light is technically nothing. It has no mass, 424 00:21:06,560 --> 00:21:08,919 Speaker 1: and nothing can go faster than it. No, because it 425 00:21:08,920 --> 00:21:10,800 Speaker 1: takes no time to do nothing, Right, like you didn't 426 00:21:10,840 --> 00:21:12,920 Speaker 1: do anything? How long? Did that take? No time at all? 427 00:21:13,040 --> 00:21:16,919 Speaker 1: So nothing is instantaneous. It's zero divided by zero. So, 428 00:21:19,160 --> 00:21:21,120 Speaker 1: if anything, I think that would have been more confusing. 429 00:21:21,320 --> 00:21:24,800 Speaker 1: All right, well, let's get into what we've done throughout 430 00:21:24,840 --> 00:21:27,280 Speaker 1: the thousands of years of human history to measure the 431 00:21:27,280 --> 00:21:29,679 Speaker 1: speed of light, and then let's get into our latest 432 00:21:29,680 --> 00:21:33,000 Speaker 1: measurements of that number. But first let's take a quick break. 433 00:21:45,640 --> 00:21:47,680 Speaker 1: All right, Daniel, we are measuring the speed of light 434 00:21:47,760 --> 00:21:50,359 Speaker 1: today on the episode Are you ready? I'm gonna clap 435 00:21:50,400 --> 00:21:53,040 Speaker 1: and then you tell me how long it took. All right, 436 00:21:55,240 --> 00:21:59,600 Speaker 1: that was exactly one clap per clap. There you go. 437 00:22:00,359 --> 00:22:02,960 Speaker 1: That's the joy of particle physics. Units. The answer is 438 00:22:03,000 --> 00:22:06,200 Speaker 1: always one or E or pie in particle physics. That's 439 00:22:06,240 --> 00:22:09,000 Speaker 1: why it's always one of the three. But yeah, like 440 00:22:09,040 --> 00:22:11,280 Speaker 1: you were saying earlier, it's pretty hard to measure the 441 00:22:11,320 --> 00:22:13,480 Speaker 1: speed of light because it's so fast, right, Like, you 442 00:22:13,520 --> 00:22:15,720 Speaker 1: can't just like turn on a flashlight, run over there 443 00:22:15,760 --> 00:22:18,720 Speaker 1: and see when the light arise. Like it moves faster 444 00:22:18,760 --> 00:22:21,080 Speaker 1: than anything can move. So it's hard to like you know, 445 00:22:21,280 --> 00:22:24,639 Speaker 1: beat it or coordinate the measurement of it. So, like, 446 00:22:24,680 --> 00:22:28,000 Speaker 1: how did the people in ancient times even approach this question? 447 00:22:28,119 --> 00:22:30,760 Speaker 1: I think in ancient times they had a different attitude, right, 448 00:22:30,800 --> 00:22:33,440 Speaker 1: They were not empirical. They were not of the mind 449 00:22:33,520 --> 00:22:36,160 Speaker 1: to go out and discover things in the universe by 450 00:22:36,200 --> 00:22:39,240 Speaker 1: doing experiments. They were much more internal. They thought that 451 00:22:39,320 --> 00:22:42,320 Speaker 1: they could understand the universe just by thinking about it. 452 00:22:42,680 --> 00:22:44,600 Speaker 1: You know. They had lots of crazy theories about the 453 00:22:44,600 --> 00:22:47,240 Speaker 1: way things work, theories that could be easily disproved in 454 00:22:47,359 --> 00:22:51,760 Speaker 1: like an afternoon of experimentation, you know. Aristatilian physics really 455 00:22:51,760 --> 00:22:54,320 Speaker 1: doesn't make any sense if you do any experiments. So 456 00:22:54,359 --> 00:22:56,800 Speaker 1: they really didn't even try to measure the speed of life. 457 00:22:56,800 --> 00:22:59,280 Speaker 1: They mostly just like talked about it and thought about it. 458 00:22:59,400 --> 00:23:02,000 Speaker 1: It wasn't all about five hundred years ago when this 459 00:23:02,080 --> 00:23:04,600 Speaker 1: concept of like, oh, let's go out and measure things 460 00:23:04,600 --> 00:23:07,120 Speaker 1: in the universe, let's try to see if our theories 461 00:23:07,200 --> 00:23:10,720 Speaker 1: actually work. This concept of empirical science came about that 462 00:23:10,760 --> 00:23:13,760 Speaker 1: people really started to actually try to measure things. And 463 00:23:13,760 --> 00:23:16,960 Speaker 1: the earliest recorded measurement I could find was from Galileo 464 00:23:17,160 --> 00:23:19,800 Speaker 1: about five years ago. Well do you think maybe people 465 00:23:19,800 --> 00:23:22,560 Speaker 1: didn't try before because they just had no means to 466 00:23:22,560 --> 00:23:25,240 Speaker 1: do it. You know, they didn't have accurate clocks or 467 00:23:25,840 --> 00:23:28,880 Speaker 1: ways to measure things. They certainly didn't have the means 468 00:23:28,920 --> 00:23:30,600 Speaker 1: to do it. If they had tried, they definitely would 469 00:23:30,640 --> 00:23:32,680 Speaker 1: have failed. But you know, I don't think they even 470 00:23:32,720 --> 00:23:35,160 Speaker 1: thought to try. Like I think, it's hard to take 471 00:23:35,200 --> 00:23:38,360 Speaker 1: your mind out of the current modern concept of science, 472 00:23:38,640 --> 00:23:41,600 Speaker 1: where we learned from the universe by doing experiments. That's 473 00:23:41,640 --> 00:23:45,040 Speaker 1: a fairly new idea. Aristotle, for example, had this idea 474 00:23:45,359 --> 00:23:47,800 Speaker 1: of how things fall, and he thought, for example, if 475 00:23:47,800 --> 00:23:50,080 Speaker 1: you're on a boat, that was moving and you dropped 476 00:23:50,119 --> 00:23:52,000 Speaker 1: a ball while you were on the boat, that the 477 00:23:52,040 --> 00:23:54,359 Speaker 1: ball would somehow get left behind, that it wouldn't just 478 00:23:54,400 --> 00:23:56,639 Speaker 1: like move with the boat. And like if you just 479 00:23:56,720 --> 00:23:58,720 Speaker 1: went out with a boat and a ball, you could 480 00:23:58,720 --> 00:24:04,400 Speaker 1: disprove this idea in an afternoon, right unless it's windy. Yeah, 481 00:24:04,480 --> 00:24:07,560 Speaker 1: and Galileo, like thousands of years later, proved that this 482 00:24:07,640 --> 00:24:10,800 Speaker 1: was false and literally overturned all of physics with a 483 00:24:10,840 --> 00:24:14,000 Speaker 1: boat and a ball in about ten minutes. So these 484 00:24:14,000 --> 00:24:17,080 Speaker 1: guys weren't limited by their physical capabilities, they just were 485 00:24:17,119 --> 00:24:19,280 Speaker 1: limited by the idea that you should go out and 486 00:24:19,320 --> 00:24:21,440 Speaker 1: actually measure stuff. What can you do with the boat 487 00:24:21,440 --> 00:24:24,359 Speaker 1: and a ball? Galileo used it all up right, like 488 00:24:24,520 --> 00:24:27,880 Speaker 1: early Nobel prizes. That's all the equipment you needed. I see, 489 00:24:28,240 --> 00:24:31,880 Speaker 1: the fruit was hanging lower before. Yes, exactly. Nobody even 490 00:24:31,880 --> 00:24:34,320 Speaker 1: tried to measure stuff back then, so he said, Galileo 491 00:24:34,400 --> 00:24:36,280 Speaker 1: tried to measure the speed of light. And then how 492 00:24:36,280 --> 00:24:38,520 Speaker 1: did he do it with lanterns? Yeah, he had lanterns 493 00:24:38,520 --> 00:24:40,560 Speaker 1: and he put them about a mile apart, and he 494 00:24:40,600 --> 00:24:42,920 Speaker 1: tried to time it the most accurate clocks you could 495 00:24:42,920 --> 00:24:45,240 Speaker 1: back then, and he tried to like you know, shine 496 00:24:45,240 --> 00:24:47,879 Speaker 1: a lantern and then measure how long it took to 497 00:24:47,880 --> 00:24:51,040 Speaker 1: get from one spot to the other with two coordinated clocks. 498 00:24:51,480 --> 00:24:54,080 Speaker 1: And you know, he failed to notice any difference. He 499 00:24:54,119 --> 00:24:58,360 Speaker 1: couldn't measure any time between when the lantern was revealed 500 00:24:58,400 --> 00:25:01,280 Speaker 1: and when the information arrived at the other side. Interesting 501 00:25:01,280 --> 00:25:04,280 Speaker 1: like he synchronized two clocks or two watches, and then 502 00:25:04,320 --> 00:25:07,440 Speaker 1: he had one watch, like go a mile away, and 503 00:25:07,520 --> 00:25:09,359 Speaker 1: then he said, Okay, I'm gonna turn on this lantern, 504 00:25:09,400 --> 00:25:11,840 Speaker 1: and when you see it turn on, you record the time. 505 00:25:12,000 --> 00:25:13,440 Speaker 1: And they came back and said it was the same 506 00:25:13,440 --> 00:25:16,399 Speaker 1: time exactly. They couldn't measure any difference, right, They couldn't 507 00:25:16,400 --> 00:25:19,199 Speaker 1: tell the difference between light being super duper fast but 508 00:25:19,359 --> 00:25:23,080 Speaker 1: finite speed and light actually being infinite speed. And the 509 00:25:23,119 --> 00:25:25,240 Speaker 1: reason is that the delay, like how long it takes 510 00:25:25,320 --> 00:25:28,879 Speaker 1: light to go a mile, is just eleven microseconds, and 511 00:25:28,920 --> 00:25:31,680 Speaker 1: so to measure that unique clocks that are more accurate 512 00:25:31,680 --> 00:25:34,680 Speaker 1: than eleven microseconds, and five years ago he definitely did 513 00:25:34,720 --> 00:25:37,399 Speaker 1: not have that. So did he conclude that speed was 514 00:25:37,480 --> 00:25:40,600 Speaker 1: infinitely fast or that he just didn't He couldn't measure it. 515 00:25:40,600 --> 00:25:42,480 Speaker 1: It was too fast to measure. It was too fast 516 00:25:42,520 --> 00:25:44,800 Speaker 1: to measure and these days, what you would conclude from 517 00:25:44,800 --> 00:25:47,399 Speaker 1: an experiment like that is you would measure a minimum speed. 518 00:25:47,440 --> 00:25:50,440 Speaker 1: If you knew how accurate your clocks were, you could say, well, 519 00:25:50,680 --> 00:25:53,560 Speaker 1: light is at least as fast as some number. He 520 00:25:53,640 --> 00:25:56,359 Speaker 1: just said, well, I don't know. It's either infinite or 521 00:25:56,400 --> 00:25:59,200 Speaker 1: it's very very fast. Right. He didn't have the right clocks. 522 00:25:59,280 --> 00:26:01,760 Speaker 1: But then later the people had better clocks. People had 523 00:26:01,840 --> 00:26:05,159 Speaker 1: better clocks. But actually the first measurement of the speed 524 00:26:05,160 --> 00:26:08,119 Speaker 1: of light being not infinite didn't come from using a 525 00:26:08,240 --> 00:26:12,480 Speaker 1: very fast clock. It came from using really really long distances, right, 526 00:26:12,480 --> 00:26:15,240 Speaker 1: Because that's that's two ways to kind of slow speed down, right, 527 00:26:15,280 --> 00:26:18,520 Speaker 1: Either give it a long distance to go over, or 528 00:26:18,920 --> 00:26:22,440 Speaker 1: use a really accurate clock. Yeah. So a Danish astronomer 529 00:26:22,480 --> 00:26:26,639 Speaker 1: about a hundred years later he realized that light bouncing 530 00:26:26,720 --> 00:26:30,440 Speaker 1: off of Jupiter's moon Io could be used to measure 531 00:26:30,560 --> 00:26:34,919 Speaker 1: the speed of light. What. Yeah, because Io orbits Jupiter. Right, 532 00:26:35,040 --> 00:26:37,240 Speaker 1: it's a moon of Jupiter and it goes around It 533 00:26:37,280 --> 00:26:39,719 Speaker 1: takes like forty two and a half hours to go 534 00:26:39,760 --> 00:26:42,680 Speaker 1: around Jupiter. And when it comes around the back of Jupiter, 535 00:26:43,040 --> 00:26:45,280 Speaker 1: it emerges from the back of Jupiter, and you can 536 00:26:45,320 --> 00:26:48,720 Speaker 1: see it. So if you're watching Io from Earth, then 537 00:26:48,760 --> 00:26:51,760 Speaker 1: you see it emerged from behind Jupiter every forty two 538 00:26:51,800 --> 00:26:53,840 Speaker 1: and a half hours. And so that's sort of like 539 00:26:53,880 --> 00:26:56,280 Speaker 1: a clock for the universe, right, it should happen every 540 00:26:56,280 --> 00:26:58,440 Speaker 1: forty two and a half hours, because Io's orbit is 541 00:26:58,560 --> 00:27:01,400 Speaker 1: very regular. It's a little bit more complicated because either 542 00:27:01,440 --> 00:27:03,600 Speaker 1: it can be in Jupiter's shadow or can be physically 543 00:27:03,640 --> 00:27:06,200 Speaker 1: behind Jupiter. But let's put that aside for now. Oh, 544 00:27:06,240 --> 00:27:08,359 Speaker 1: I see, because you can actually see the moves of 545 00:27:08,440 --> 00:27:11,840 Speaker 1: Jupiter if you have a telescope from the sixteen hundreds, right, Like, 546 00:27:11,920 --> 00:27:13,600 Speaker 1: you can see the little dots and you can see 547 00:27:13,600 --> 00:27:16,000 Speaker 1: the little little dots kind of floating around it. Yeah, 548 00:27:16,000 --> 00:27:18,320 Speaker 1: and Galileo is the first person to see these, and 549 00:27:18,400 --> 00:27:21,080 Speaker 1: so with a pretty basic telescope five years ago, you 550 00:27:21,080 --> 00:27:23,280 Speaker 1: can see these dots and you can plot the trajectory 551 00:27:23,280 --> 00:27:25,119 Speaker 1: of them, and you can see, like, okay, Io is 552 00:27:25,160 --> 00:27:28,200 Speaker 1: coming out from behind Jupiter. And people watch these things 553 00:27:28,200 --> 00:27:31,120 Speaker 1: and look for patterns, and they noticed something really interesting. 554 00:27:31,240 --> 00:27:33,840 Speaker 1: They noticed that it is true that Io comes out 555 00:27:33,840 --> 00:27:36,320 Speaker 1: from behind Jupiter every forty two and a half hours, 556 00:27:36,359 --> 00:27:38,720 Speaker 1: but that during some parts of the year that time 557 00:27:38,800 --> 00:27:41,080 Speaker 1: is a little bit shorter, and other times of the 558 00:27:41,160 --> 00:27:43,760 Speaker 1: year that time is a little bit longer. So like 559 00:27:43,800 --> 00:27:47,920 Speaker 1: the time between Io emerging from behind Jupiter gets longer 560 00:27:48,160 --> 00:27:51,719 Speaker 1: during one season and shorter during other seasons. And somehow 561 00:27:51,760 --> 00:27:53,640 Speaker 1: that tells you the speed of light, and that tells 562 00:27:53,640 --> 00:27:55,760 Speaker 1: you the speed of light because the reason those times 563 00:27:55,760 --> 00:27:58,879 Speaker 1: gets shorter is because the Earth has now gotten closer 564 00:27:58,920 --> 00:28:01,560 Speaker 1: to Jupiter and Io than it was last time, and 565 00:28:01,600 --> 00:28:03,760 Speaker 1: so the light doesn't have is far to go to 566 00:28:03,880 --> 00:28:06,320 Speaker 1: get to Earth. And the reason the times between the 567 00:28:06,320 --> 00:28:09,520 Speaker 1: reappearances get longer is when the Earth is moving away 568 00:28:09,560 --> 00:28:12,000 Speaker 1: from Jupiter. So now the light has further to go 569 00:28:12,480 --> 00:28:14,159 Speaker 1: when it has to reach Earth to tell you that 570 00:28:14,200 --> 00:28:17,000 Speaker 1: Io has emerged. If speed of light was infinite, then 571 00:28:17,040 --> 00:28:19,520 Speaker 1: I would always appear every forty two and a half hours. 572 00:28:19,560 --> 00:28:22,399 Speaker 1: This wouldn't matter at all. But because the distance between 573 00:28:22,440 --> 00:28:26,360 Speaker 1: Earth and Io is growing or shrinking, then this period 574 00:28:26,440 --> 00:28:29,920 Speaker 1: grows or shrinks. And so this Danish astronomer realized, oh 575 00:28:29,920 --> 00:28:32,800 Speaker 1: my gosh, I can use this information to calculate the 576 00:28:32,840 --> 00:28:37,000 Speaker 1: speed of light. Whoa interesting right, because sometimes we're in 577 00:28:37,040 --> 00:28:40,280 Speaker 1: between measurements of when you see the moon the Earth 578 00:28:40,320 --> 00:28:42,560 Speaker 1: will have moved. Is that what you mean, like sometimes 579 00:28:42,600 --> 00:28:44,680 Speaker 1: it moves a lot in that time, and sometimes it 580 00:28:44,720 --> 00:28:46,960 Speaker 1: doesn't move a lot exactly. And so when we are 581 00:28:47,000 --> 00:28:49,640 Speaker 1: moving further away from Io during that part of the 582 00:28:49,720 --> 00:28:52,400 Speaker 1: year that we're like zooming away from it, than those 583 00:28:52,440 --> 00:28:55,640 Speaker 1: times between Io's appearances will get longer. And when we've 584 00:28:55,640 --> 00:28:57,120 Speaker 1: come around the other side of the Sun and we're 585 00:28:57,200 --> 00:29:00,640 Speaker 1: zooming towards Io, then we're shortening that instance that light 586 00:29:00,640 --> 00:29:02,960 Speaker 1: has to go. Like, if you were making these measurements 587 00:29:03,040 --> 00:29:05,560 Speaker 1: from the Sun where the distance between you and I 588 00:29:05,800 --> 00:29:09,040 Speaker 1: wasn't changing, then they would be perfectly regular. Or if 589 00:29:09,040 --> 00:29:11,480 Speaker 1: the speed of light was infinite, so that every time 590 00:29:11,520 --> 00:29:14,160 Speaker 1: Io came around the back of Jupiter you instantly saw it, 591 00:29:14,400 --> 00:29:17,280 Speaker 1: then the measurements would be regular. But since the distance 592 00:29:17,400 --> 00:29:20,560 Speaker 1: is changing and it takes a finite time for light 593 00:29:20,600 --> 00:29:23,240 Speaker 1: to cross that distance, then you can measure how fast 594 00:29:23,360 --> 00:29:27,440 Speaker 1: light moves across these incredible distances. I guess the distance 595 00:29:27,480 --> 00:29:30,280 Speaker 1: is changing, and it's changing in a kind of predictable way, 596 00:29:30,320 --> 00:29:32,640 Speaker 1: so you can measure the speed of light. And so 597 00:29:32,760 --> 00:29:34,520 Speaker 1: what did they find. They get pretty close to what 598 00:29:34,600 --> 00:29:36,640 Speaker 1: the actual speed of light is. He got to within 599 00:29:36,640 --> 00:29:39,520 Speaker 1: about twenty of the real speed of light. Which is 600 00:29:39,600 --> 00:29:45,560 Speaker 1: pretty incredible. That's like a B B minus. Yeah, well 601 00:29:45,680 --> 00:29:47,960 Speaker 1: it's much better than Galileo. Did you know Galileo got 602 00:29:47,960 --> 00:29:51,760 Speaker 1: an F So at least this guy is passing well technically, 603 00:29:51,840 --> 00:29:54,320 Speaker 1: I don't know, because Galileo thought it was pretty fast. Yeah. 604 00:29:54,360 --> 00:29:56,720 Speaker 1: But I love these stories where you like tricked the 605 00:29:56,800 --> 00:30:00,360 Speaker 1: universe or corner the universe into revealing some piece of formation. 606 00:30:00,640 --> 00:30:04,360 Speaker 1: This guy didn't build this experiment. He discovered this experiment. 607 00:30:04,400 --> 00:30:07,840 Speaker 1: He's like, wait a second, this random configuration of stuff 608 00:30:08,000 --> 00:30:11,880 Speaker 1: reveals this piece of information everybody wants to know, And 609 00:30:11,920 --> 00:30:13,640 Speaker 1: all I have to do is use my telescope and 610 00:30:13,640 --> 00:30:18,040 Speaker 1: calculate a few numbers and boom, now I have this number. Interesting, 611 00:30:18,040 --> 00:30:20,960 Speaker 1: but did he know like the relative positions of the 612 00:30:20,960 --> 00:30:23,240 Speaker 1: planet in order for him to know exactly like how 613 00:30:23,320 --> 00:30:25,719 Speaker 1: much more the Earth at moved? Like do we know 614 00:30:26,240 --> 00:30:28,240 Speaker 1: the orbits that will back then? We didn't know the 615 00:30:28,320 --> 00:30:30,880 Speaker 1: orbits that well back then. But actually, all you have 616 00:30:30,960 --> 00:30:33,520 Speaker 1: to know is the orbital distance of the Earth. You 617 00:30:33,600 --> 00:30:35,520 Speaker 1: just have to know the radius of the Earth's orbit, 618 00:30:35,720 --> 00:30:38,160 Speaker 1: because that's the difference between the path of light when 619 00:30:38,160 --> 00:30:40,720 Speaker 1: the Earth is furthest away and when it is closest away, 620 00:30:40,840 --> 00:30:42,800 Speaker 1: So you can look at the calculations online, but you 621 00:30:42,800 --> 00:30:46,320 Speaker 1: can do with some pretty basic information about the orbits. Wow, 622 00:30:46,400 --> 00:30:48,200 Speaker 1: I imagine you could do it today, right Like if 623 00:30:48,200 --> 00:30:50,560 Speaker 1: you just had a nice back yard telescope, you could 624 00:30:50,560 --> 00:30:53,360 Speaker 1: measure the speed of light to you could get a 625 00:30:53,360 --> 00:30:57,160 Speaker 1: b in your back yard. Absolutely you can. And I 626 00:30:57,200 --> 00:30:59,920 Speaker 1: was chatting with one of our listeners, Brian Fields, if 627 00:30:59,920 --> 00:31:02,200 Speaker 1: the theoretical particle physicists, and he said he did this 628 00:31:02,320 --> 00:31:05,360 Speaker 1: lab in college and he actually sent me his rite up, 629 00:31:05,600 --> 00:31:07,000 Speaker 1: And so it's the kind of thing you can now 630 00:31:07,120 --> 00:31:11,040 Speaker 1: assign to undergraduates in physics and they can totally extract 631 00:31:11,160 --> 00:31:14,120 Speaker 1: this basic constant of the universe using simple tools and 632 00:31:14,200 --> 00:31:16,640 Speaker 1: everyone gets a D in the class. Then what was it? 633 00:31:16,720 --> 00:31:18,719 Speaker 1: The next step in measuring the speed of light? So 634 00:31:18,760 --> 00:31:22,080 Speaker 1: the next step was improving on Galileo strategy rather than 635 00:31:22,120 --> 00:31:25,000 Speaker 1: doing astronomical measurements. There was a guy in the eighteen 636 00:31:25,080 --> 00:31:28,960 Speaker 1: hundreds named Fizzo who sent a beam of light further away, 637 00:31:29,040 --> 00:31:31,800 Speaker 1: so instead of one mile, he sent it five miles. 638 00:31:31,840 --> 00:31:33,960 Speaker 1: So he was trying to measure a longer time distance. 639 00:31:34,120 --> 00:31:37,160 Speaker 1: He had this really clever trick for measuring really short 640 00:31:37,160 --> 00:31:40,480 Speaker 1: time periods. He put a beam of light that passed 641 00:31:40,560 --> 00:31:43,440 Speaker 1: very close to a gear that was rotating. So imagine 642 00:31:43,560 --> 00:31:45,360 Speaker 1: like gear like the one you have on your bicycle. 643 00:31:45,520 --> 00:31:47,960 Speaker 1: It's got a little teeth on it, and as it spins, 644 00:31:48,440 --> 00:31:51,840 Speaker 1: light can go through sometimes when it's not blocked, and 645 00:31:51,880 --> 00:31:53,800 Speaker 1: then when it hits the gear, when it hits the 646 00:31:53,840 --> 00:31:55,880 Speaker 1: tooth of the gear, then it's blocked. And if you 647 00:31:56,000 --> 00:32:01,000 Speaker 1: arrange things just right, then light flies through between the teeth, 648 00:32:01,320 --> 00:32:04,400 Speaker 1: HiT's a mirror, comes back, and then flies through the 649 00:32:04,440 --> 00:32:07,440 Speaker 1: next tooth. And so if you arrange things just right, 650 00:32:07,640 --> 00:32:09,720 Speaker 1: then the light can make it there and come back 651 00:32:09,840 --> 00:32:11,920 Speaker 1: and not be blocked. And if you're going at the 652 00:32:11,920 --> 00:32:13,840 Speaker 1: wrong speed, then it's going to hit one of the teeth, 653 00:32:13,880 --> 00:32:16,160 Speaker 1: either on the way out or the way there. And 654 00:32:16,200 --> 00:32:18,360 Speaker 1: so you can arrange things just right to get the 655 00:32:18,440 --> 00:32:20,560 Speaker 1: right speed in the right distance, so you can get 656 00:32:20,600 --> 00:32:23,040 Speaker 1: light to go there and back and not miss a tooth. 657 00:32:23,520 --> 00:32:25,520 Speaker 1: And this is the way to measure how long it 658 00:32:25,520 --> 00:32:27,520 Speaker 1: takes light to go there and back if you know 659 00:32:27,680 --> 00:32:31,120 Speaker 1: like the rotation speed of your gear. Well, this sounds 660 00:32:31,160 --> 00:32:34,120 Speaker 1: pretty tricky in advance, I guess the big question is 661 00:32:34,320 --> 00:32:36,600 Speaker 1: how did they get the light to go five miles 662 00:32:36,600 --> 00:32:38,760 Speaker 1: bounce off a mirror and come back and still be 663 00:32:38,800 --> 00:32:41,480 Speaker 1: sort of like you know, legible. Like they didn't have 664 00:32:41,560 --> 00:32:45,120 Speaker 1: lasers back then today. They only did not have lasers 665 00:32:45,120 --> 00:32:48,760 Speaker 1: back then. Five a lot, right, Like any beam of light, 666 00:32:48,840 --> 00:32:50,840 Speaker 1: if it's a little foggy or something, it will make 667 00:32:50,880 --> 00:32:52,800 Speaker 1: it five miles and back. That's true. But you know, 668 00:32:52,840 --> 00:32:55,600 Speaker 1: they did have optics, and they had powerful lenses. Even 669 00:32:55,680 --> 00:32:58,160 Speaker 1: Newton was studying lenses, and so they had ways to 670 00:32:58,200 --> 00:33:00,440 Speaker 1: concentrate beams of light. But yeah, that was definitely a 671 00:33:00,520 --> 00:33:03,280 Speaker 1: challenge back then making a powerful enough beam of light. 672 00:33:03,640 --> 00:33:05,600 Speaker 1: But you know, light can go pretty far, so you 673 00:33:05,640 --> 00:33:07,440 Speaker 1: need like a clear night, right, This would be an 674 00:33:07,480 --> 00:33:10,560 Speaker 1: experiment would be better to do in space because you say, 675 00:33:10,640 --> 00:33:13,040 Speaker 1: light will scatter off of the atmosphere, but you only 676 00:33:13,040 --> 00:33:15,280 Speaker 1: need a few photons. Also, I see, so they had 677 00:33:15,280 --> 00:33:17,680 Speaker 1: some sort of like focused beam of light, I guess, 678 00:33:17,760 --> 00:33:19,680 Speaker 1: but they didn't have electricity, so they must have used 679 00:33:19,720 --> 00:33:22,000 Speaker 1: like candles or fire. Yeah, that's a really good question. 680 00:33:22,040 --> 00:33:24,440 Speaker 1: You know. I read a few descriptions of this experiment 681 00:33:24,440 --> 00:33:26,840 Speaker 1: and they all just say the light source, So I 682 00:33:26,880 --> 00:33:29,160 Speaker 1: wasn't able to figure out what the actual source of 683 00:33:29,240 --> 00:33:32,240 Speaker 1: light is. So either some time traveling physicists lend them 684 00:33:32,240 --> 00:33:34,840 Speaker 1: a laser, or they like really focused beams of light 685 00:33:34,880 --> 00:33:38,040 Speaker 1: from the sun, or maybe like early electricity allowed them 686 00:33:38,040 --> 00:33:43,600 Speaker 1: to generate really bright bulbs or aliens. Possibility, the simplest 687 00:33:43,600 --> 00:33:46,440 Speaker 1: explanation first, that's also on an experiment that like people 688 00:33:46,480 --> 00:33:48,560 Speaker 1: can do in their backyards, right kind of Yeah, if 689 00:33:48,560 --> 00:33:50,920 Speaker 1: you have a rotating gear that's very precise and a 690 00:33:50,960 --> 00:33:54,280 Speaker 1: five mile long backyard, then yeah, go for it. That's right. 691 00:33:54,280 --> 00:33:57,880 Speaker 1: If you're a billionaire and live in a state, anything 692 00:33:57,960 --> 00:33:59,920 Speaker 1: is possible for that's right right to us. We'll send 693 00:34:00,080 --> 00:34:02,520 Speaker 1: a kid for one billion dollars from measuring the speed 694 00:34:02,520 --> 00:34:05,400 Speaker 1: of light. And then I imagine that we've gotten much 695 00:34:05,440 --> 00:34:07,880 Speaker 1: better at these kinds of measurements, and so let's get 696 00:34:07,880 --> 00:34:10,799 Speaker 1: into those and our current understanding of what the speed 697 00:34:10,840 --> 00:34:13,800 Speaker 1: of light is. But first let's take another quick break. 698 00:34:26,520 --> 00:34:29,040 Speaker 1: All right, we are measuring the speed of light, and 699 00:34:29,200 --> 00:34:30,680 Speaker 1: you can do it in your back yard if you're 700 00:34:30,680 --> 00:34:33,080 Speaker 1: a billionaire. Yeah, you can actually also do it in 701 00:34:33,120 --> 00:34:36,319 Speaker 1: your kitchen these days. Oh no kidding, Wow, I have 702 00:34:36,400 --> 00:34:39,359 Speaker 1: a five mile long kitchen. You don't need a five 703 00:34:39,360 --> 00:34:41,960 Speaker 1: mile long kitchen. Actually, all you need is say microwave 704 00:34:42,040 --> 00:34:44,320 Speaker 1: and a chocolate bar, and you can measure the speed 705 00:34:44,360 --> 00:34:47,240 Speaker 1: of light at home in about twenty seconds, no kidding, 706 00:34:47,320 --> 00:34:49,880 Speaker 1: How does that work? Well, Light, of course is a wave, 707 00:34:50,239 --> 00:34:52,440 Speaker 1: and so if you know the frequency of the wave 708 00:34:52,800 --> 00:34:55,799 Speaker 1: and you know the wavelength, you can combine those two 709 00:34:55,800 --> 00:34:59,040 Speaker 1: pieces of information to get the speed of the waves. 710 00:34:59,280 --> 00:35:01,440 Speaker 1: And so people do of these now in very high 711 00:35:01,560 --> 00:35:06,080 Speaker 1: end experiments using cavity residences. The most precise measurements of 712 00:35:06,120 --> 00:35:08,520 Speaker 1: the speed of light we have sort of inexperiments, come 713 00:35:08,600 --> 00:35:12,080 Speaker 1: from these cavity residence experiments where you measure the wavelength 714 00:35:12,280 --> 00:35:14,880 Speaker 1: of the light and you measure it's resident frequency. But 715 00:35:15,040 --> 00:35:17,680 Speaker 1: you can also do a simpler version of that at home. 716 00:35:18,120 --> 00:35:20,320 Speaker 1: You just take a chocolate bar and you put it 717 00:35:20,320 --> 00:35:24,239 Speaker 1: in the microwave. You microwave for about twenty seconds, not 718 00:35:24,360 --> 00:35:26,759 Speaker 1: enough so it's totally melted, but enough that it's just 719 00:35:26,920 --> 00:35:29,439 Speaker 1: started to melt. And take it out and you'll notice something. 720 00:35:29,480 --> 00:35:32,200 Speaker 1: You'll notice that it's more melted in some places than 721 00:35:32,239 --> 00:35:35,719 Speaker 1: in others. There's like hot spots m interesting, and that 722 00:35:35,960 --> 00:35:38,080 Speaker 1: is basically the shape of the wave of light of 723 00:35:38,160 --> 00:35:40,960 Speaker 1: the microwave light that's right. The distance between those hot 724 00:35:40,960 --> 00:35:44,640 Speaker 1: spots is one half of the wavelength of the microwaves, 725 00:35:45,000 --> 00:35:47,680 Speaker 1: because that's where they have like added up concretely to 726 00:35:47,760 --> 00:35:50,239 Speaker 1: give you like the most energy. And so what you're 727 00:35:50,239 --> 00:35:53,040 Speaker 1: seeing there is like the actual physical wavelength of the 728 00:35:53,080 --> 00:35:56,360 Speaker 1: photons passing through your chocolate bar, and it's like a 729 00:35:56,400 --> 00:35:59,560 Speaker 1: few centimeters. So it's something you can reasonably measure using 730 00:35:59,600 --> 00:36:02,200 Speaker 1: a chalk the bar in your microwave. And then all 731 00:36:02,239 --> 00:36:04,759 Speaker 1: you have to do is look up the frequency that 732 00:36:04,800 --> 00:36:07,560 Speaker 1: your microwave uses. Usually it's like two and a half 733 00:36:07,640 --> 00:36:10,880 Speaker 1: giga hurts or something. Combine those two numbers together and boom, 734 00:36:11,120 --> 00:36:13,840 Speaker 1: that's the speed of light. Interesting, but I guess you 735 00:36:13,880 --> 00:36:17,040 Speaker 1: know inside the microwave, isn't it bombarded by microwaves from 736 00:36:17,080 --> 00:36:19,560 Speaker 1: all directions? Is that the wave inside of my microwave 737 00:36:19,680 --> 00:36:24,360 Speaker 1: that like coherent, that untouched, that sort of neat? Yeah, unfortunately, 738 00:36:24,400 --> 00:36:26,200 Speaker 1: it is right, and that's why you have hot spots 739 00:36:26,200 --> 00:36:28,239 Speaker 1: and cold spots. We have a whole episode about how 740 00:36:28,280 --> 00:36:31,560 Speaker 1: microwave ovens work, and usually they have like one source 741 00:36:31,600 --> 00:36:33,759 Speaker 1: of the radiation and so it puts the stuff out 742 00:36:33,880 --> 00:36:35,920 Speaker 1: in this kind of pattern where you get this constructive 743 00:36:36,080 --> 00:36:38,680 Speaker 1: and destructive modes. It would be much better if it 744 00:36:38,760 --> 00:36:42,160 Speaker 1: was like incoherent and evenly distributing the energy, which is 745 00:36:42,200 --> 00:36:44,160 Speaker 1: why you usually have like a spinner to move your 746 00:36:44,200 --> 00:36:47,239 Speaker 1: food through this field of microwaves. So they use a 747 00:36:47,280 --> 00:36:49,760 Speaker 1: sort of a simpler radiator and it has these features 748 00:36:49,760 --> 00:36:52,000 Speaker 1: to it. I guess the tricky part though, is measuring 749 00:36:52,000 --> 00:36:54,839 Speaker 1: the frequency of the LightWave, right, because I mean that's 750 00:36:54,880 --> 00:36:58,200 Speaker 1: like gigaherts. You don't really have a clock that can 751 00:36:58,360 --> 00:37:01,279 Speaker 1: measure that. You'd have to trust the greave manufacturer. Yeah, 752 00:37:01,280 --> 00:37:03,560 Speaker 1: it's sort of cheating because they've done the hard part 753 00:37:03,600 --> 00:37:06,200 Speaker 1: for you of measuring the frequency. But it's also a 754 00:37:06,200 --> 00:37:09,359 Speaker 1: cool thing to like physically see the impact of light 755 00:37:09,400 --> 00:37:12,200 Speaker 1: being a wave, to like to see the distance between 756 00:37:12,239 --> 00:37:14,920 Speaker 1: the crests of the light wave in a physical thing 757 00:37:14,920 --> 00:37:17,120 Speaker 1: that you can do in your kitchen. That's sort of cool. 758 00:37:17,280 --> 00:37:19,920 Speaker 1: But you're right, when we make the actual measurements, like 759 00:37:19,920 --> 00:37:23,000 Speaker 1: when we actually want to figure this out ourselves, then 760 00:37:23,040 --> 00:37:25,760 Speaker 1: we use very precise cavities and we measure the residents 761 00:37:25,800 --> 00:37:29,200 Speaker 1: frequency and the wavelength of the most simultaneously, because you 762 00:37:29,239 --> 00:37:31,280 Speaker 1: can't just look that stuff up. And is it required 763 00:37:31,280 --> 00:37:34,080 Speaker 1: that you have to eat the chocolate afterwards, because then 764 00:37:34,160 --> 00:37:36,719 Speaker 1: you're cheating not just the universe, but you're diet a 765 00:37:36,719 --> 00:37:39,120 Speaker 1: little bit. No, that's the bonus of doing physics. Man, 766 00:37:39,280 --> 00:37:43,760 Speaker 1: Sometimes you make a delicious experiment that gets a little messy, 767 00:37:45,120 --> 00:37:48,640 Speaker 1: all right, So nowadays we use much more like constraint environments. 768 00:37:48,640 --> 00:37:50,719 Speaker 1: I guess a cavity and you have a wave of 769 00:37:50,840 --> 00:37:53,239 Speaker 1: light and you know exactly what the frequency is, and 770 00:37:53,360 --> 00:37:55,240 Speaker 1: you can sort of see the wavelength and that gives 771 00:37:55,239 --> 00:37:57,920 Speaker 1: you one measurement of the speed. Like nowadays, we don't 772 00:37:57,960 --> 00:38:01,360 Speaker 1: really like do these experiments meants where we send it 773 00:38:01,400 --> 00:38:03,239 Speaker 1: off to one place and then measure how light it 774 00:38:03,320 --> 00:38:05,279 Speaker 1: takes to come back. We use something like this. Yeah, 775 00:38:05,280 --> 00:38:08,680 Speaker 1: it's much more precise to use interference effects or residence 776 00:38:08,719 --> 00:38:12,040 Speaker 1: effects because they're very very sensitive to very small shifts 777 00:38:12,239 --> 00:38:14,480 Speaker 1: in one wave to the other. And so the way 778 00:38:14,520 --> 00:38:18,279 Speaker 1: the cavity residence experiment works is you measure both the 779 00:38:18,320 --> 00:38:21,920 Speaker 1: wavelength and the resident frequency. Are you build some precise 780 00:38:21,960 --> 00:38:25,920 Speaker 1: cavity and that determines the wavelengths of like standing modes 781 00:38:26,000 --> 00:38:29,480 Speaker 1: inside the cavity, or do you have like two mirrors essentially, 782 00:38:29,760 --> 00:38:31,760 Speaker 1: and you want light to go back and forth between 783 00:38:31,760 --> 00:38:34,879 Speaker 1: those mirrors in a way that it doesn't cancel itself out. 784 00:38:35,040 --> 00:38:37,239 Speaker 1: You need light to have a wavelength so that an 785 00:38:37,239 --> 00:38:40,480 Speaker 1: integer number of those wavelengths adds up to exactly the 786 00:38:40,480 --> 00:38:43,240 Speaker 1: width of the cavity. So there's only like certain modes 787 00:38:43,320 --> 00:38:45,600 Speaker 1: of the cavity where you can get this sort of effect. 788 00:38:45,920 --> 00:38:48,400 Speaker 1: And then you just measure the resident frequency, like at 789 00:38:48,440 --> 00:38:51,239 Speaker 1: what frequency of light? What color of light do you 790 00:38:51,280 --> 00:38:53,480 Speaker 1: get these residences? So you can measure the width of 791 00:38:53,560 --> 00:38:56,759 Speaker 1: your cavity and measure the frequency the color of light 792 00:38:56,800 --> 00:38:59,239 Speaker 1: that goes in there that achieves residents, and together you 793 00:38:59,280 --> 00:39:01,399 Speaker 1: can get a very accurate measurement of the speed of light. 794 00:39:01,480 --> 00:39:04,280 Speaker 1: And that was like nine seventy five. The people really 795 00:39:04,320 --> 00:39:07,880 Speaker 1: perfected this and got like a super duper precise measurements 796 00:39:07,880 --> 00:39:09,680 Speaker 1: of the speed of light. But I guess, doesn't that 797 00:39:09,719 --> 00:39:12,600 Speaker 1: depend on how accurate your clock is to measure the 798 00:39:12,719 --> 00:39:16,239 Speaker 1: frequency of light and also how good you're you know, 799 00:39:16,400 --> 00:39:19,120 Speaker 1: ruler is to measure the size of your cavity, right, Like, 800 00:39:19,160 --> 00:39:22,600 Speaker 1: there are still I guess imagine limitations to how well 801 00:39:22,640 --> 00:39:25,600 Speaker 1: we know the speed of light. There were still limitations 802 00:39:25,600 --> 00:39:29,160 Speaker 1: for just those reasons, like people used crazy techniques to 803 00:39:29,239 --> 00:39:31,960 Speaker 1: measure the size of these cavities. Very very accurately, and 804 00:39:32,000 --> 00:39:34,960 Speaker 1: it's like a real tourtive force of experimental physics, the 805 00:39:35,040 --> 00:39:37,960 Speaker 1: clever strategies people came up with to measure these precisely. 806 00:39:38,280 --> 00:39:42,279 Speaker 1: These days, however, we have actually zero uncertainty on the 807 00:39:42,280 --> 00:39:44,960 Speaker 1: speed of light, zero uncertainty, like we know it to 808 00:39:45,120 --> 00:39:47,480 Speaker 1: an infinite number of digits. Yeah, so it's a bit 809 00:39:47,520 --> 00:39:49,719 Speaker 1: of a cob out answer, right, we don't know the 810 00:39:49,760 --> 00:39:52,560 Speaker 1: speed of light to an infinite precision if you set 811 00:39:52,600 --> 00:39:55,200 Speaker 1: an arbitrary length for the meter and an arbitrary length 812 00:39:55,239 --> 00:39:58,319 Speaker 1: for the second. Instead, we've decided we're going to use 813 00:39:58,360 --> 00:40:01,040 Speaker 1: the speed of light to define the length. We're going 814 00:40:01,080 --> 00:40:03,640 Speaker 1: to say we know this better than anything else, so 815 00:40:03,719 --> 00:40:06,839 Speaker 1: let's define everything else in terms of the speed of light. 816 00:40:07,280 --> 00:40:09,640 Speaker 1: So now the official definition of a meter is no 817 00:40:09,719 --> 00:40:13,200 Speaker 1: longer like here's a platinum rod in Paris. Instead, it's 818 00:40:13,360 --> 00:40:17,000 Speaker 1: how far light travels in a certain amount of time. Right, 819 00:40:17,000 --> 00:40:20,080 Speaker 1: Because I guess you're saying that if we picked a 820 00:40:20,200 --> 00:40:22,120 Speaker 1: valley for the meter in a valley for the second, 821 00:40:22,360 --> 00:40:24,160 Speaker 1: then that makes the speed of light that we measure 822 00:40:24,239 --> 00:40:26,920 Speaker 1: kind of dependent on what we pick for the meter 823 00:40:27,040 --> 00:40:30,000 Speaker 1: in the second. So instead it makes more sense maybe 824 00:40:30,440 --> 00:40:33,359 Speaker 1: from a global point of view. To define the meter 825 00:40:33,480 --> 00:40:36,279 Speaker 1: and the second by the speed of light. Yes, so 826 00:40:36,280 --> 00:40:39,400 Speaker 1: we define the meter by how far light travels in 827 00:40:39,440 --> 00:40:42,760 Speaker 1: a second, and we define the second by the oscillations 828 00:40:42,800 --> 00:40:46,040 Speaker 1: of some caesium atom. So now the meter is something 829 00:40:46,080 --> 00:40:48,879 Speaker 1: which depends on the speed of light and the oscillations 830 00:40:48,920 --> 00:40:51,400 Speaker 1: of the caesium atom. So now instead of asking like, 831 00:40:51,800 --> 00:40:54,120 Speaker 1: how well do we know the speed of light, it's like, well, 832 00:40:54,160 --> 00:40:56,040 Speaker 1: how well do you know the length of this platinum 833 00:40:56,120 --> 00:40:58,400 Speaker 1: rod in Paris? Oh? I see, So you're kind of 834 00:40:58,440 --> 00:41:01,560 Speaker 1: saying almost like we're coming up with the speed of light, 835 00:41:01,680 --> 00:41:03,719 Speaker 1: like we're inventing the speed of light, right, because we 836 00:41:03,840 --> 00:41:06,839 Speaker 1: just picked some numbers and then we call that the meter. 837 00:41:07,040 --> 00:41:08,719 Speaker 1: So therefore the speed of light is so and so 838 00:41:08,880 --> 00:41:11,360 Speaker 1: meters per second. Yeah, And it's just like in particle physics, 839 00:41:11,400 --> 00:41:13,040 Speaker 1: we could define the speed of light to be one 840 00:41:13,360 --> 00:41:16,719 Speaker 1: and everything is set relative to that. And so here 841 00:41:16,760 --> 00:41:19,719 Speaker 1: we're defining the meter so that the speed of light 842 00:41:19,880 --> 00:41:25,920 Speaker 1: is exactly two eight with no decimal places, like it's 843 00:41:25,960 --> 00:41:29,040 Speaker 1: exactly that number. And you know, I said, we know 844 00:41:29,200 --> 00:41:31,440 Speaker 1: it accurately. Really, we just define it to be that, 845 00:41:31,520 --> 00:41:34,160 Speaker 1: and everything is now relative to that. Number just kind 846 00:41:34,160 --> 00:41:35,640 Speaker 1: of blew my mind. It means we don't know what 847 00:41:35,719 --> 00:41:40,080 Speaker 1: the speed of light is, right, Like, technically, philosophically, you're 848 00:41:40,160 --> 00:41:41,839 Speaker 1: trying to say that we don't know what the speed 849 00:41:41,880 --> 00:41:43,839 Speaker 1: of light is. We just picked the number and said 850 00:41:43,920 --> 00:41:45,800 Speaker 1: that's it. We picked the number. We said, this is 851 00:41:45,840 --> 00:41:47,239 Speaker 1: what we call the speed of light. The speed of 852 00:41:47,320 --> 00:41:49,360 Speaker 1: light is a number, right, and we just assigned to 853 00:41:49,360 --> 00:41:52,480 Speaker 1: say it's this number, this length. And now the question 854 00:41:52,520 --> 00:41:54,799 Speaker 1: is what is length to mean? Length is relative to 855 00:41:54,840 --> 00:41:57,120 Speaker 1: the speed of light. It's just as good as saying 856 00:41:57,239 --> 00:41:59,640 Speaker 1: length is relative to this rot in Paris. But this 857 00:41:59,840 --> 00:42:03,239 Speaker 1: row in Paris has no real meeting or physical significance, 858 00:42:03,280 --> 00:42:05,080 Speaker 1: so it's sort of silly, whereas the speed of light 859 00:42:05,120 --> 00:42:07,160 Speaker 1: obviously does. And so it makes a lot more sense 860 00:42:07,200 --> 00:42:09,480 Speaker 1: to define things relative to the speed of light rather 861 00:42:09,480 --> 00:42:12,600 Speaker 1: than relative to an arbitrary chunk of metal. But yeah, 862 00:42:12,680 --> 00:42:14,640 Speaker 1: I think by using a number that doesn't have any 863 00:42:14,640 --> 00:42:17,239 Speaker 1: decimal places, right, you get that to be the meter, 864 00:42:17,360 --> 00:42:19,080 Speaker 1: and then you use that meter to measure the speed 865 00:42:19,080 --> 00:42:22,200 Speaker 1: of light. But then the number gives you was it's 866 00:42:22,200 --> 00:42:24,759 Speaker 1: a consequence of you picking that random number. Yeah, you 867 00:42:24,800 --> 00:42:27,440 Speaker 1: can't measure the speed of light anymore. You're exactly right. 868 00:42:27,480 --> 00:42:30,200 Speaker 1: It doesn't make any sense to define the meter in 869 00:42:30,280 --> 00:42:31,759 Speaker 1: terms of the speed of light and then trying to 870 00:42:31,760 --> 00:42:33,719 Speaker 1: measure the speed of light. Like, you can't measure the 871 00:42:33,719 --> 00:42:35,480 Speaker 1: speed of light in terms of the meter because the 872 00:42:35,520 --> 00:42:37,239 Speaker 1: meter is defined in terms of the speed of light. 873 00:42:37,280 --> 00:42:39,160 Speaker 1: It's circular. Instead, when you can do is define the 874 00:42:39,160 --> 00:42:41,040 Speaker 1: speed of light and then measure the length of a 875 00:42:41,160 --> 00:42:44,040 Speaker 1: rod in Paris in terms of that. Why anybody would 876 00:42:44,040 --> 00:42:46,000 Speaker 1: care the length of rod in Paris, I don't know, 877 00:42:46,320 --> 00:42:48,759 Speaker 1: But philosophically that's what you can do now. But I 878 00:42:48,760 --> 00:42:51,000 Speaker 1: feel like that's kind of like you're avoiding the question. 879 00:42:51,080 --> 00:42:52,960 Speaker 1: Like there is a speed of light, like there is 880 00:42:53,000 --> 00:42:55,719 Speaker 1: a certain amount of distance that light covers in in 881 00:42:55,800 --> 00:42:58,719 Speaker 1: one second in the universe, but it doesn't seem like 882 00:42:58,800 --> 00:43:01,719 Speaker 1: we know what that is to any sort of decimal place. Well, 883 00:43:01,719 --> 00:43:04,680 Speaker 1: we don't know what that is relative to that stick 884 00:43:04,719 --> 00:43:07,480 Speaker 1: in Paris. You're right, and we could spend a lot 885 00:43:07,480 --> 00:43:10,720 Speaker 1: of time and money measuring how fast light goes relative 886 00:43:10,760 --> 00:43:13,759 Speaker 1: to this arbitrary unit of distance we defined according to 887 00:43:13,760 --> 00:43:15,880 Speaker 1: this stick in Paris. But I think people decided that 888 00:43:15,920 --> 00:43:19,000 Speaker 1: doesn't mean anything anyway, Like what does it matter? How 889 00:43:19,000 --> 00:43:22,360 Speaker 1: many decimal places you get when your unit is arbitrary. 890 00:43:22,640 --> 00:43:25,560 Speaker 1: We prefer to make a reasonable unit when that makes sense. 891 00:43:25,880 --> 00:43:28,280 Speaker 1: And the speed of light is the most important physical 892 00:43:28,360 --> 00:43:30,800 Speaker 1: constant in the universe, and so let's just define everything 893 00:43:31,080 --> 00:43:33,720 Speaker 1: relative to that, right, But then you're picking an arbitrary 894 00:43:33,800 --> 00:43:38,640 Speaker 1: number for that speed, Yes, absolutely, I don't know. I 895 00:43:38,640 --> 00:43:40,440 Speaker 1: guess it makes it more sense to me as a 896 00:43:40,520 --> 00:43:43,920 Speaker 1: lay person to pick an arbitrary length and then measure 897 00:43:44,000 --> 00:43:46,000 Speaker 1: the speed of light than to pick an arbitrary speed 898 00:43:46,000 --> 00:43:48,200 Speaker 1: of light and then define lights from that. Well, it's 899 00:43:48,200 --> 00:43:50,840 Speaker 1: philosophically their equivalent, you know. Check out our episode on 900 00:43:50,960 --> 00:43:53,359 Speaker 1: the basic constants of the universe, and you'll realize that 901 00:43:53,640 --> 00:43:56,800 Speaker 1: no number that has units on it ever has any meaning, 902 00:43:56,960 --> 00:43:59,480 Speaker 1: because it just depends on your definition of the units. 903 00:43:59,640 --> 00:44:02,120 Speaker 1: The old numbers that really have meeting are the ones 904 00:44:02,160 --> 00:44:05,239 Speaker 1: without any units, the ones that are pure numbers of 905 00:44:05,239 --> 00:44:07,240 Speaker 1: the universe. So the speed of light in that sense 906 00:44:07,520 --> 00:44:10,320 Speaker 1: is not actually that fundamental. It folds into the fine 907 00:44:10,360 --> 00:44:13,920 Speaker 1: structure constant, which is a unitless number and which does 908 00:44:13,960 --> 00:44:16,160 Speaker 1: determine sort of the structure and the nature of the 909 00:44:16,239 --> 00:44:19,319 Speaker 1: universe and electromagnetism. But I guess you know, like a 910 00:44:19,440 --> 00:44:22,319 Speaker 1: rod in Paris is something we can all go and 911 00:44:22,360 --> 00:44:25,040 Speaker 1: touch and see and like, hold right, and then we 912 00:44:25,040 --> 00:44:27,120 Speaker 1: can all agree that the speed of light goes so 913 00:44:27,200 --> 00:44:29,080 Speaker 1: and so fast. But I feel like this way of 914 00:44:29,120 --> 00:44:31,360 Speaker 1: doing things, like nobody can agree what the speed of 915 00:44:31,440 --> 00:44:33,880 Speaker 1: light is. Everybody can agree, we just choose a number. 916 00:44:34,080 --> 00:44:36,560 Speaker 1: Whereas a rod in Paris, it like grows and shrinks 917 00:44:36,719 --> 00:44:38,880 Speaker 1: when it gets hot in Paris. Does that change the 918 00:44:38,920 --> 00:44:41,640 Speaker 1: speed of light? Like, it's ridiculous to have the speed 919 00:44:41,640 --> 00:44:45,520 Speaker 1: of light depend on something so arbitrary as how big 920 00:44:45,560 --> 00:44:47,759 Speaker 1: this rod in the museum in Paris is like the 921 00:44:47,800 --> 00:44:50,760 Speaker 1: air conditioning breaks in Paris, and now we're all moving faster, 922 00:44:50,960 --> 00:44:53,880 Speaker 1: Like it doesn't make any sense. Yeah, why not? I 923 00:44:53,920 --> 00:44:55,960 Speaker 1: mean that's better than like making up a number for 924 00:44:56,000 --> 00:45:00,000 Speaker 1: the speed of light. Daniel, I can't handle this all right, Well, 925 00:45:00,000 --> 00:45:04,359 Speaker 1: come to Dawn and Rhee discussed philosophy. I'll give you that. 926 00:45:04,360 --> 00:45:06,200 Speaker 1: That's the way you're doing it, even though I don't 927 00:45:06,239 --> 00:45:10,200 Speaker 1: agree with them, all right, objection noted, Yeah, thank you. 928 00:45:10,480 --> 00:45:13,319 Speaker 1: I'm sure will cause waves in the physics community. So 929 00:45:13,360 --> 00:45:15,160 Speaker 1: that's kind of the way we're doing it. That means 930 00:45:15,200 --> 00:45:17,279 Speaker 1: that we kind of can measure the speed of light. Right, 931 00:45:17,480 --> 00:45:19,719 Speaker 1: once we've defined it, we can no longer measure things 932 00:45:19,719 --> 00:45:22,640 Speaker 1: in terms of it. Yes, So to answer the questions, 933 00:45:22,640 --> 00:45:24,720 Speaker 1: how do we measure the speed of light, we don't anymore. 934 00:45:24,840 --> 00:45:27,200 Speaker 1: We just picked the number. We just picked the number. Yeah, 935 00:45:27,480 --> 00:45:31,040 Speaker 1: and that number was based on almost nothing, right. Well, 936 00:45:31,080 --> 00:45:34,000 Speaker 1: that number, you know, defines a meter to be something 937 00:45:34,120 --> 00:45:35,960 Speaker 1: close to what it used to be, and so that's 938 00:45:35,960 --> 00:45:38,279 Speaker 1: pretty nice, but it could have been something else. We're 939 00:45:38,320 --> 00:45:40,520 Speaker 1: just to pick the number out of historical reasons, kind 940 00:45:40,560 --> 00:45:43,759 Speaker 1: of to approximate historical history. Yeah, we wanted the new 941 00:45:43,840 --> 00:45:46,520 Speaker 1: meter to be pretty close to the old meter so 942 00:45:46,600 --> 00:45:48,840 Speaker 1: that we didn't have to like change everything all that, 943 00:45:49,000 --> 00:45:51,359 Speaker 1: you know, make all new highway signs like oh, this 944 00:45:51,400 --> 00:45:53,719 Speaker 1: tunnel is now one meter high whereas it used to 945 00:45:53,760 --> 00:45:56,080 Speaker 1: be twenty meters high. That would be ridiculous. So once 946 00:45:56,080 --> 00:46:03,279 Speaker 1: again laziness. Yeah, consistency, manists knap consistency. It is very 947 00:46:03,320 --> 00:46:05,920 Speaker 1: important to physicists. And I'm getting the sense. But yes, 948 00:46:06,200 --> 00:46:08,200 Speaker 1: it seems like the answer is you can't measure the 949 00:46:08,239 --> 00:46:10,640 Speaker 1: speed of light anymore, right, because now we've defined the 950 00:46:10,719 --> 00:46:12,919 Speaker 1: meter as based on this number of the speed of lights, 951 00:46:12,960 --> 00:46:14,719 Speaker 1: it makes no sense to leasure the speed of light. 952 00:46:14,760 --> 00:46:16,880 Speaker 1: It's just what it is. Yeah, that's true. We can 953 00:46:16,920 --> 00:46:19,520 Speaker 1: no longer measure the speed of light relative to other 954 00:46:19,680 --> 00:46:23,279 Speaker 1: arbitrary units because it is now the arbitrary unit. Can 955 00:46:23,280 --> 00:46:25,640 Speaker 1: we measure it relative to some of these you know, 956 00:46:25,920 --> 00:46:28,759 Speaker 1: fundamental unitless constants that you measured, Like, you know, the 957 00:46:28,840 --> 00:46:32,960 Speaker 1: universe has these numbers that are immovable and fundamental to 958 00:46:33,000 --> 00:46:34,840 Speaker 1: the fabric of the universe. Can we use those to 959 00:46:34,920 --> 00:46:37,239 Speaker 1: get a real measurement of the speed of light? Now? 960 00:46:37,320 --> 00:46:39,919 Speaker 1: Because those numbers don't have units, and so they can't 961 00:46:39,960 --> 00:46:43,040 Speaker 1: determine numbers that do have units because those depend on 962 00:46:43,120 --> 00:46:45,800 Speaker 1: your choice of units, right, that's the problem with numbers 963 00:46:45,840 --> 00:46:49,080 Speaker 1: that have units. Anything that's like meters per second or 964 00:46:49,160 --> 00:46:51,960 Speaker 1: pounds per square inch or whatever is going to depend 965 00:46:52,000 --> 00:46:54,160 Speaker 1: on the units, which is why physics refers to talk 966 00:46:54,160 --> 00:46:56,960 Speaker 1: about numbers without units. But you know, I guess we 967 00:46:57,080 --> 00:47:00,879 Speaker 1: base time on some sort of fundamental physical thing, right, 968 00:47:00,880 --> 00:47:04,040 Speaker 1: like the oscillations of a crystal or whatever. Why can't 969 00:47:04,080 --> 00:47:07,319 Speaker 1: we do that with distance as well? We do, we do, 970 00:47:07,480 --> 00:47:09,959 Speaker 1: That's exactly what we do. And that's how a rod 971 00:47:10,000 --> 00:47:12,239 Speaker 1: in France. But like I don't know the width of 972 00:47:12,280 --> 00:47:14,560 Speaker 1: a proton or something like that. We'll think about it 973 00:47:14,600 --> 00:47:17,840 Speaker 1: as a certain number of light wavelengths at a certain frequency. 974 00:47:18,000 --> 00:47:20,280 Speaker 1: Because we defined the meter in terms of the speed 975 00:47:20,320 --> 00:47:23,120 Speaker 1: of light. Now light is our ruler. But then that 976 00:47:23,160 --> 00:47:27,040 Speaker 1: means we can't measure the speed of light. That's true. Yeah, 977 00:47:27,080 --> 00:47:29,080 Speaker 1: we've given that up because now it's our ruler, because 978 00:47:29,080 --> 00:47:32,480 Speaker 1: we've decided that that's exactly the most basic unit. Just 979 00:47:32,560 --> 00:47:35,760 Speaker 1: like you can no longer define how long it takes 980 00:47:36,280 --> 00:47:38,960 Speaker 1: caesium to do one oscillation because it's to find to 981 00:47:39,000 --> 00:47:41,480 Speaker 1: be one second, or is to find to be one 982 00:47:41,680 --> 00:47:44,120 Speaker 1: you know, six billions of a second or whatever. Because 983 00:47:44,120 --> 00:47:47,920 Speaker 1: we now define time in terms of that basic physical operation, 984 00:47:47,960 --> 00:47:51,040 Speaker 1: you can no longer measure how long that operation takes. 985 00:47:51,239 --> 00:47:53,040 Speaker 1: What can you say, like, let's measure the speed of 986 00:47:53,120 --> 00:47:56,080 Speaker 1: light by the frequency of caesium and also the width 987 00:47:56,080 --> 00:47:59,319 Speaker 1: of caeson Yeah, you could define distance using something else, 988 00:47:59,400 --> 00:48:01,239 Speaker 1: but you know it's not as fundamental is the speed 989 00:48:01,239 --> 00:48:03,200 Speaker 1: of light. The speed of light is really basic and 990 00:48:03,280 --> 00:48:05,080 Speaker 1: interesting to the universe. So I think that's why they 991 00:48:05,120 --> 00:48:07,239 Speaker 1: chose it. But you're right, these things are arbitrary, and 992 00:48:07,239 --> 00:48:09,239 Speaker 1: you could have said, you know, the meter is now 993 00:48:09,239 --> 00:48:12,400 Speaker 1: defined to be one third of the height of Jorge's room. Like, 994 00:48:12,600 --> 00:48:15,400 Speaker 1: you could have chosen anything. Some choices are better than others, 995 00:48:15,840 --> 00:48:17,799 Speaker 1: you know, and I think this is a pretty good one. 996 00:48:17,920 --> 00:48:19,480 Speaker 1: Let's just pick a number of It seems like a 997 00:48:19,600 --> 00:48:25,600 Speaker 1: crazy way to run thenation of the universe, Daniel, We're 998 00:48:25,640 --> 00:48:28,759 Speaker 1: doing our best. Do our best. I know it's not 999 00:48:28,800 --> 00:48:31,120 Speaker 1: your fault. You have limited power in the physics community. 1000 00:48:32,160 --> 00:48:35,040 Speaker 1: All right, Well, I've mounted the chocolate bar in my mind. 1001 00:48:35,520 --> 00:48:37,320 Speaker 1: I feel like I don't know what to trust anymore 1002 00:48:37,360 --> 00:48:40,319 Speaker 1: in physics, Daniel, things are arbitrarily fast. Now. There is 1003 00:48:40,320 --> 00:48:42,359 Speaker 1: no speed limit. There's just the speed limit that you're 1004 00:48:42,360 --> 00:48:44,359 Speaker 1: telling me is the speed limit. That's right, Go out 1005 00:48:44,360 --> 00:48:47,279 Speaker 1: there and break whatever speedimits you want. Jorhey, you're right, absolutely, 1006 00:48:48,000 --> 00:48:49,799 Speaker 1: there are no rules when it comes to you. Well, 1007 00:48:49,840 --> 00:48:52,440 Speaker 1: I think it's another kind of reminder. You know that 1008 00:48:52,480 --> 00:48:54,600 Speaker 1: this is a tricky universe. You know, it's kind of 1009 00:48:54,640 --> 00:48:58,640 Speaker 1: hard to measure things because everything is relative. Everything can change, 1010 00:48:58,680 --> 00:49:01,720 Speaker 1: everything depends on kind of you know, how fast you're moving, 1011 00:49:01,920 --> 00:49:05,040 Speaker 1: or how hot it is, or what you're measuring relative to. 1012 00:49:05,680 --> 00:49:08,160 Speaker 1: So it's kind of hard to find footing in this universe. 1013 00:49:08,320 --> 00:49:10,439 Speaker 1: It is but it also gives us a sense for 1014 00:49:10,520 --> 00:49:13,440 Speaker 1: how the universe works. And I think it's awesome how 1015 00:49:13,520 --> 00:49:16,560 Speaker 1: we as humans have figured out how to extract this 1016 00:49:16,640 --> 00:49:18,799 Speaker 1: kind of information from the universe. I mean, until we 1017 00:49:18,960 --> 00:49:22,000 Speaker 1: define it away is not interesting anymore. I think it's 1018 00:49:22,040 --> 00:49:24,640 Speaker 1: fascinating to see, sort of like the historical sweep, how 1019 00:49:24,680 --> 00:49:27,680 Speaker 1: long it takes, how the thousands and hundreds of years 1020 00:49:27,719 --> 00:49:30,279 Speaker 1: it takes to figure out this one very basic thing 1021 00:49:30,600 --> 00:49:33,840 Speaker 1: about something we literally see every day. And as the reminder, 1022 00:49:33,880 --> 00:49:39,319 Speaker 1: please obey speed limits in your driving practice, because going 1023 00:49:39,360 --> 00:49:41,200 Speaker 1: at the speed of light might get you a few 1024 00:49:41,400 --> 00:49:44,160 Speaker 1: light tickets. But if you do manage to go at 1025 00:49:44,160 --> 00:49:45,960 Speaker 1: the speed of light, please let us know. We'd like 1026 00:49:46,040 --> 00:49:48,320 Speaker 1: to hear about it. But what if they interrupt your nap, Daniel, 1027 00:49:50,000 --> 00:49:52,120 Speaker 1: It'll be worth it. They'll sit in your inbox for 1028 00:49:52,200 --> 00:49:54,520 Speaker 1: ten seconds before you check all right. Well, we hope 1029 00:49:54,520 --> 00:49:57,640 Speaker 1: you enjoyed that. Thanks for joining us, see you next time. 1030 00:50:05,520 --> 00:50:08,320 Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain 1031 00:50:08,400 --> 00:50:11,360 Speaker 1: the Universe is a production of I Heart Radio or 1032 00:50:11,400 --> 00:50:14,319 Speaker 1: more podcast from my Heart Radio. Visit the I Heart 1033 00:50:14,440 --> 00:50:18,000 Speaker 1: Radio Apple Apple Podcasts, or wherever you listen to your 1034 00:50:18,080 --> 00:50:24,400 Speaker 1: favorite shows. Ye