1 00:00:05,920 --> 00:00:09,799 Speaker 1: The world out there is a wonderful, intriguing puzzle. Sometimes 2 00:00:09,840 --> 00:00:12,840 Speaker 1: it feels like it makes little sense, constantly refusing to 3 00:00:12,880 --> 00:00:15,640 Speaker 1: obey our intuition or behave the way that we expect 4 00:00:15,680 --> 00:00:19,480 Speaker 1: it to. Quantum mechanics tells us electrons don't follow smooth paths, 5 00:00:19,600 --> 00:00:23,040 Speaker 1: relativity tells us time doesn't flow the same way for everyone, 6 00:00:23,320 --> 00:00:26,720 Speaker 1: And yet we can make some sense of it. We 7 00:00:26,800 --> 00:00:30,280 Speaker 1: have math that describes it and predicts it. It's incredible 8 00:00:30,560 --> 00:00:34,280 Speaker 1: that the universe is so finely balanced. It's complicated enough 9 00:00:34,320 --> 00:00:37,800 Speaker 1: that it's taking us thousands of years to unravel its truths, 10 00:00:38,000 --> 00:00:41,000 Speaker 1: but it's simple enough that our tiny brains can make 11 00:00:41,080 --> 00:00:45,840 Speaker 1: progress year after year. So let's keep hoping that truant continues. 12 00:00:46,280 --> 00:00:48,840 Speaker 1: But even when we have wrangled a bit of math 13 00:00:48,880 --> 00:00:51,760 Speaker 1: that seems to work, it doesn't mean our intuition goes 14 00:00:51,760 --> 00:00:54,920 Speaker 1: along for the ride. Sometimes when we translate the math 15 00:00:54,960 --> 00:00:59,480 Speaker 1: into popular science intuition and dramatic clickbait, the reality is lost. 16 00:01:00,160 --> 00:01:02,400 Speaker 1: You've heard that a potato approaching the speed of light 17 00:01:02,440 --> 00:01:05,199 Speaker 1: can turn into a black hole, or that photons don't 18 00:01:05,240 --> 00:01:09,759 Speaker 1: experience time. Unfortunately, neither of those things are accurate. Today, 19 00:01:09,760 --> 00:01:12,199 Speaker 1: we're going to try to untangle some of these widespread 20 00:01:12,280 --> 00:01:15,720 Speaker 1: misconceptions about special relativity and show you that the truth 21 00:01:15,760 --> 00:01:19,039 Speaker 1: of the universe is plenty weird and wonderful without clickbait. 22 00:01:19,600 --> 00:01:23,000 Speaker 1: Do Photon's experience time. Does a potato become a black 23 00:01:23,000 --> 00:01:26,440 Speaker 1: hole if it goes fast enough? Welcome to Daniel and 24 00:01:26,560 --> 00:01:30,240 Speaker 1: Kelly's extraordinary but amazingly comprehensible universe. 25 00:01:44,040 --> 00:01:46,880 Speaker 2: Hello, I'm Kelly Widerspin. I'm a biologist, and I am 26 00:01:46,959 --> 00:01:49,680 Speaker 2: super excited to let Daniel be the wet blanket today. 27 00:01:52,440 --> 00:01:55,880 Speaker 1: Hi, I'm Daniel. I'm a particle physicist, and I'm not 28 00:01:55,920 --> 00:01:57,760 Speaker 1: going to throw a wet blanket on the universe. I'm 29 00:01:57,760 --> 00:02:00,480 Speaker 1: going to show you how it's even weirder than what 30 00:02:00,560 --> 00:02:01,320 Speaker 1: you've been told. 31 00:02:01,560 --> 00:02:03,600 Speaker 2: Yeah, that's what I do all the time. Also, Daniel, 32 00:02:04,520 --> 00:02:06,440 Speaker 2: it's all about packaging the idea. 33 00:02:06,800 --> 00:02:10,720 Speaker 1: That's right, exactly, make it sound positive, that's right. 34 00:02:10,760 --> 00:02:12,880 Speaker 2: So my question for you today is when you were 35 00:02:12,919 --> 00:02:16,000 Speaker 2: a kid and you watched like physics y kinds of movies, 36 00:02:16,400 --> 00:02:19,200 Speaker 2: were you concerned with whether or not they were accurate 37 00:02:19,360 --> 00:02:22,280 Speaker 2: or did kid Daniel just enjoy whatever he was watching. 38 00:02:23,480 --> 00:02:27,600 Speaker 1: Hey, there's an implication there that adult Daniel can't enjoy movies. 39 00:02:27,720 --> 00:02:29,800 Speaker 1: I don't appreciate that. That's not true. 40 00:02:30,320 --> 00:02:32,960 Speaker 2: Go ahead and tell us about the trajectory of your 41 00:02:33,000 --> 00:02:35,200 Speaker 2: life and how it has evolved with movie watching. 42 00:02:35,480 --> 00:02:37,440 Speaker 1: You know, when I watched movies like that as a kid, 43 00:02:37,560 --> 00:02:39,800 Speaker 1: I was just amazed and odd. I thought it was 44 00:02:39,840 --> 00:02:42,360 Speaker 1: fantastic to think about these things and to push against 45 00:02:42,400 --> 00:02:44,560 Speaker 1: the edge of our knowledge. Could we live in four 46 00:02:44,600 --> 00:02:48,120 Speaker 1: dimensional space? Could aliens be six dimensional beings? Is it 47 00:02:48,160 --> 00:02:51,160 Speaker 1: possible to travel through time? I thought those movies were 48 00:02:51,200 --> 00:02:53,960 Speaker 1: wonderful because they pushed us past the edge of our 49 00:02:53,960 --> 00:02:57,160 Speaker 1: current knowledge and imagined how the universe could be different. 50 00:02:57,639 --> 00:02:59,840 Speaker 1: And now, of course, as a grown up scientist, I 51 00:02:59,840 --> 00:03:01,800 Speaker 1: know something about what we do and don't know, and 52 00:03:01,800 --> 00:03:03,880 Speaker 1: which of those ideas are possible and which of those 53 00:03:03,919 --> 00:03:07,560 Speaker 1: ideas are not really possible. But I appreciate the creativity 54 00:03:07,600 --> 00:03:09,440 Speaker 1: in that. I think it's important that we push past 55 00:03:09,480 --> 00:03:11,200 Speaker 1: that and then we try to break outside of the 56 00:03:11,240 --> 00:03:12,639 Speaker 1: box of our current ideas. 57 00:03:12,919 --> 00:03:15,000 Speaker 2: So you could watch a movie that clearly had an 58 00:03:15,000 --> 00:03:20,200 Speaker 2: incorrect physics concept and straight up enjoy it. Is that right? 59 00:03:21,280 --> 00:03:23,079 Speaker 1: You know, if they're going to embrace life in a 60 00:03:23,120 --> 00:03:25,600 Speaker 1: different universe with different laws, that's fine. Go for it. 61 00:03:25,600 --> 00:03:27,000 Speaker 1: But if they're going to pretend to be in this 62 00:03:27,160 --> 00:03:29,919 Speaker 1: universe and then they drop a bunch of like pop 63 00:03:29,960 --> 00:03:32,440 Speaker 1: sign nonsense to make it sound like they talk to 64 00:03:32,480 --> 00:03:35,000 Speaker 1: a physicist when they didn't, and they're all higgs bos 65 00:03:35,040 --> 00:03:38,040 Speaker 1: on this and quantum fluctuation that, then yeah, that's annoying 66 00:03:38,080 --> 00:03:40,400 Speaker 1: because like, hey, reach out to a scientist. It's not 67 00:03:40,440 --> 00:03:44,440 Speaker 1: so hard to get like actual realistic scientific babble. Instead 68 00:03:44,480 --> 00:03:48,240 Speaker 1: appear nonsense from your chat GPT, like come on email me, 69 00:03:48,360 --> 00:03:51,520 Speaker 1: I'll answer. I'll help you get actual science into your movie. 70 00:03:51,600 --> 00:03:54,080 Speaker 2: I think the one time where I was like, maybe 71 00:03:54,080 --> 00:03:56,200 Speaker 2: I'm going to ask for my money back? What was? 72 00:03:56,240 --> 00:03:59,200 Speaker 2: The movie was with John Cusack and I loved John Cusack, 73 00:03:59,320 --> 00:04:03,400 Speaker 2: but it was like the new Trinos have mutated and everything. 74 00:04:03,560 --> 00:04:05,360 Speaker 2: I was like, oh, can I get past this? I 75 00:04:05,360 --> 00:04:06,920 Speaker 2: don't think I can. It was one of those like 76 00:04:07,000 --> 00:04:08,360 Speaker 2: Ends of the World disaster movies. 77 00:04:10,600 --> 00:04:13,119 Speaker 1: The new Trenos are going to kill us, all that's right. 78 00:04:13,760 --> 00:04:17,200 Speaker 2: I was like, they're neutral, guys, It's all right anyway. 79 00:04:17,839 --> 00:04:20,320 Speaker 1: Yeah. I mean, if people want to embrace something awesome 80 00:04:20,400 --> 00:04:22,680 Speaker 1: and new, that's fantastic. And I think that being created 81 00:04:22,680 --> 00:04:24,480 Speaker 1: that way is cool but if you want to use 82 00:04:24,520 --> 00:04:27,120 Speaker 1: real physics, like reach out to a real scientist. There's 83 00:04:27,160 --> 00:04:29,520 Speaker 1: so many folks who would happily help you make the 84 00:04:29,600 --> 00:04:32,640 Speaker 1: science in your show real. And you know, then it's 85 00:04:32,640 --> 00:04:34,720 Speaker 1: even better because the people who are listening and know 86 00:04:34,839 --> 00:04:38,080 Speaker 1: something are then like not jerked out of their experience 87 00:04:38,560 --> 00:04:41,880 Speaker 1: by the bizarre nonsense you just injected into their brains. 88 00:04:42,160 --> 00:04:44,480 Speaker 2: We would all love to be involved in TV shows 89 00:04:44,520 --> 00:04:46,440 Speaker 2: and movies that makes us like the cool kid in 90 00:04:46,440 --> 00:04:48,320 Speaker 2: the room, So like, give us the chance to be 91 00:04:48,360 --> 00:04:49,240 Speaker 2: the cool kid man. 92 00:04:49,960 --> 00:04:52,039 Speaker 1: Yeah, Christopher Nolan write to me, come. 93 00:04:51,880 --> 00:04:54,440 Speaker 2: On, that's right, that's right, And there's got to be 94 00:04:54,480 --> 00:04:56,640 Speaker 2: a bunch of parasite movies that people could be, you know, 95 00:04:56,839 --> 00:04:59,240 Speaker 2: talking to me about. But all right, well, today we're 96 00:04:59,279 --> 00:05:03,240 Speaker 2: focusing on two very specific ideas that are often wrong 97 00:05:03,440 --> 00:05:04,159 Speaker 2: in popsid. 98 00:05:04,440 --> 00:05:06,719 Speaker 1: Yeah, that's right, because there's a lot of popular science 99 00:05:06,760 --> 00:05:10,279 Speaker 1: descriptions of special relativity what happens as you approach the 100 00:05:10,279 --> 00:05:12,160 Speaker 1: speed of light and what's it like to be a 101 00:05:12,200 --> 00:05:14,960 Speaker 1: photon and all this kind of stuff, and some of 102 00:05:15,000 --> 00:05:17,719 Speaker 1: it sounds really cool and it's really fun to read about, 103 00:05:17,760 --> 00:05:20,479 Speaker 1: but it's actually kind of nonsense, and the worst part 104 00:05:20,560 --> 00:05:24,840 Speaker 1: is that it's obscuring the reality, the awesomeness of our universe, 105 00:05:25,400 --> 00:05:29,080 Speaker 1: and the truth is always so much weirder than the nonsense, 106 00:05:29,480 --> 00:05:31,720 Speaker 1: which I love. And so because people write in quite 107 00:05:31,720 --> 00:05:34,440 Speaker 1: often asking these kinds of questions, I thought it'd be 108 00:05:34,440 --> 00:05:37,640 Speaker 1: fun to try to disentangle some of the common misconceptions 109 00:05:37,680 --> 00:05:41,920 Speaker 1: about special relativity. But before we dig into those particular topics, 110 00:05:41,960 --> 00:05:44,479 Speaker 1: I was curious what people thought were the most popular 111 00:05:44,520 --> 00:05:49,159 Speaker 1: misconceptions about special relativity, the things that people didn't understand 112 00:05:49,200 --> 00:05:51,680 Speaker 1: about it. So I went out and asked our listeners 113 00:05:51,720 --> 00:05:54,159 Speaker 1: if you would like to join our group of volunteers, 114 00:05:54,200 --> 00:05:56,080 Speaker 1: please don't be shy or right to us two questions 115 00:05:56,120 --> 00:05:58,080 Speaker 1: at Danielankelly dot org. 116 00:05:58,279 --> 00:06:00,559 Speaker 2: We were going through and Daniel and I really to survey, 117 00:06:00,640 --> 00:06:02,760 Speaker 2: which you can get on our website Daniel and Kelly 118 00:06:02,760 --> 00:06:05,120 Speaker 2: dot com. And I was going through some of the answers. 119 00:06:05,200 --> 00:06:07,599 Speaker 1: Daniel and Kelly dot org unless you're a guest at 120 00:06:07,680 --> 00:06:09,760 Speaker 1: Daniel and Kelly's wedding, in which case go to Daniel 121 00:06:09,880 --> 00:06:13,520 Speaker 1: Kelly dot com. Congratulations you too, love he thank you 122 00:06:13,560 --> 00:06:14,160 Speaker 1: for the correction. 123 00:06:14,839 --> 00:06:17,120 Speaker 2: Yeah, I was looking through the answers and somebody wrote 124 00:06:17,160 --> 00:06:18,640 Speaker 2: to say that they would like to hear a lot 125 00:06:18,640 --> 00:06:22,240 Speaker 2: more female voices for this question and answer session, and 126 00:06:22,400 --> 00:06:25,599 Speaker 2: so if you are a woman who is on that list, 127 00:06:26,040 --> 00:06:27,840 Speaker 2: we would really love to hear from you. Or if 128 00:06:27,839 --> 00:06:29,839 Speaker 2: you're a woman who would like to answer these questions, 129 00:06:29,839 --> 00:06:31,680 Speaker 2: we would really love to hear from you. I had 130 00:06:31,720 --> 00:06:33,640 Speaker 2: a journalist reach out to me the other day and 131 00:06:33,720 --> 00:06:35,479 Speaker 2: I told them, oh, sorry, I'm not an expert in 132 00:06:35,480 --> 00:06:38,320 Speaker 2: that area, so I'm gonna pass. And they wrote back 133 00:06:38,360 --> 00:06:43,080 Speaker 2: and they said, men never pass. Women are the ones 134 00:06:43,080 --> 00:06:44,520 Speaker 2: who are like, oh, I'm not quite sure I'm an 135 00:06:44,560 --> 00:06:47,080 Speaker 2: expert in this. And so what I'm saying is, ladies, 136 00:06:47,160 --> 00:06:49,839 Speaker 2: let's go all in on the confidence and just answer it. 137 00:06:49,880 --> 00:06:51,680 Speaker 2: And if the answer is I don't know, that's fine too. 138 00:06:51,800 --> 00:06:52,960 Speaker 2: Let's get your voice out there. 139 00:06:53,160 --> 00:06:57,919 Speaker 1: Absolutely, ladies, please chime in. All right, without further ado, 140 00:06:58,000 --> 00:06:59,960 Speaker 1: here's what our listeners had to say. 141 00:07:00,839 --> 00:07:04,920 Speaker 3: Whether I'm thinking of special general relativity a time dilation. 142 00:07:05,320 --> 00:07:07,719 Speaker 2: If you put a gun to my head, I couldn't 143 00:07:07,760 --> 00:07:08,400 Speaker 2: tell you. 144 00:07:08,320 --> 00:07:12,040 Speaker 1: The difference between special and general relativity time dilation. 145 00:07:12,160 --> 00:07:15,840 Speaker 3: That if you somehow get into a ship and approach 146 00:07:15,880 --> 00:07:18,080 Speaker 3: the speed of light or close to the speed of light, 147 00:07:18,120 --> 00:07:19,560 Speaker 3: that your clock or un slower. 148 00:07:19,680 --> 00:07:24,080 Speaker 1: The speed of light is constant for all observers, regardless 149 00:07:24,120 --> 00:07:27,320 Speaker 1: of their motion or location or whatever. Why does the 150 00:07:27,320 --> 00:07:30,400 Speaker 1: speed of light always appear to be at the speed 151 00:07:30,440 --> 00:07:34,280 Speaker 1: of light regardless of my speed? Well, I'm ashamed to 152 00:07:34,280 --> 00:07:38,840 Speaker 1: say I can't remember the difference between special and general relativity. 153 00:07:39,400 --> 00:07:44,120 Speaker 1: How to become special enough to be recognized by the 154 00:07:44,160 --> 00:07:48,280 Speaker 1: Special relativity crew. The visualizations of invisible fabrics, as well 155 00:07:48,320 --> 00:07:51,560 Speaker 1: as two dimensional sheets used to explain four dimensional curvature, 156 00:07:51,960 --> 00:07:54,920 Speaker 1: makes wascetime more confusing. Why is it special? 157 00:07:56,440 --> 00:07:59,960 Speaker 3: There's more photons than anything else, so when that kind 158 00:08:00,080 --> 00:08:01,080 Speaker 3: to be a general thing? 159 00:08:01,520 --> 00:08:04,920 Speaker 1: How observers can see events in different orders. 160 00:08:05,000 --> 00:08:08,600 Speaker 2: That if you exceed light speed the time will run backwards. 161 00:08:08,800 --> 00:08:11,360 Speaker 3: I've never understood why we say the universe is about 162 00:08:11,400 --> 00:08:15,680 Speaker 3: fourteen billion years old, but a photon traveling at the 163 00:08:15,680 --> 00:08:19,080 Speaker 3: speed of light since the Big Bang has experienced no 164 00:08:19,360 --> 00:08:20,080 Speaker 3: change in. 165 00:08:20,040 --> 00:08:23,960 Speaker 1: Time god fact of the speed of light. Why is 166 00:08:24,000 --> 00:08:27,240 Speaker 1: the speed of light three times twenty eighth meters per 167 00:08:27,280 --> 00:08:28,880 Speaker 1: second and not some other number. 168 00:08:29,720 --> 00:08:35,000 Speaker 4: I don't understand how, despite the variables, light can never 169 00:08:35,280 --> 00:08:40,120 Speaker 4: exceed three hundred thousand kilometers per second, that. 170 00:08:40,000 --> 00:08:43,000 Speaker 3: The speed of light is constant, no matter where you're 171 00:08:43,040 --> 00:08:45,640 Speaker 3: observing it from or how fast you're going. 172 00:08:46,040 --> 00:08:48,640 Speaker 1: It's the fact that the speed of light is a constant. 173 00:08:49,120 --> 00:08:52,920 Speaker 1: Misunderstood is E equals mc squared because most people think 174 00:08:52,960 --> 00:08:55,319 Speaker 1: it's got something to do with relativity. 175 00:08:55,080 --> 00:08:57,600 Speaker 3: That there is no god beside the universe with an 176 00:08:57,640 --> 00:09:00,840 Speaker 3: absolute clock who judges who was right. 177 00:09:01,160 --> 00:09:05,120 Speaker 1: Fixed speed in a vacuum, no matter what your speed is, All. 178 00:09:05,080 --> 00:09:07,320 Speaker 2: Right, some great answers. And I got to say, every 179 00:09:07,320 --> 00:09:11,000 Speaker 2: time we have a conversation, I get closer to understanding relativity, 180 00:09:11,440 --> 00:09:14,440 Speaker 2: but not all of it sticks. And so I'm looking 181 00:09:14,520 --> 00:09:17,679 Speaker 2: forward to being reminded of the difference between special and 182 00:09:17,760 --> 00:09:19,120 Speaker 2: general relativity today. 183 00:09:19,480 --> 00:09:22,800 Speaker 1: Right, So today we're only digging into special relativity. General 184 00:09:22,800 --> 00:09:25,560 Speaker 1: relativity is a whole other hairy beast we're not even 185 00:09:25,559 --> 00:09:28,480 Speaker 1: going to try to tackle today because special relativity, even 186 00:09:28,480 --> 00:09:31,920 Speaker 1: though it's simpler than general relativity, is plenty confusing. You know, 187 00:09:32,000 --> 00:09:35,160 Speaker 1: it already requires you to distort how your brain works 188 00:09:35,200 --> 00:09:38,079 Speaker 1: and accept the time flows differently for people in different 189 00:09:38,080 --> 00:09:41,360 Speaker 1: parts of the universe. Briefly, special relativity is physics in 190 00:09:41,440 --> 00:09:44,960 Speaker 1: flat space, where there's no curvature, there's no mass, there's 191 00:09:44,960 --> 00:09:47,959 Speaker 1: no gravity, it's just like beams of light and clocks 192 00:09:48,000 --> 00:09:51,079 Speaker 1: and things moving fast, and it tells us how time 193 00:09:51,160 --> 00:09:54,360 Speaker 1: flows and how things are relative, even outside of like 194 00:09:54,440 --> 00:09:56,600 Speaker 1: black holes and all that weirdness. 195 00:09:56,960 --> 00:09:59,520 Speaker 2: So this is not dealing with any bending of space 196 00:09:59,640 --> 00:09:59,960 Speaker 2: or time. 197 00:10:00,360 --> 00:10:03,960 Speaker 1: That's right, Yeah, exactly. Imagine space is purely flat and 198 00:10:04,000 --> 00:10:06,520 Speaker 1: we got a bunch of physics nerds doing experiments with 199 00:10:06,679 --> 00:10:09,320 Speaker 1: lasers and clocks and cats and all sorts of stuff. 200 00:10:09,360 --> 00:10:12,520 Speaker 1: But we've got no black holes, no gravity, nothing like that. 201 00:10:12,840 --> 00:10:14,400 Speaker 2: All right, great, I think I can wrap my head 202 00:10:14,400 --> 00:10:15,760 Speaker 2: around that. Where do we start. 203 00:10:15,559 --> 00:10:20,200 Speaker 1: Then, Well, my favorite thing about special relativity is that 204 00:10:20,240 --> 00:10:22,560 Speaker 1: it lets you dig deep into your understanding of like 205 00:10:22,600 --> 00:10:25,880 Speaker 1: the very fabric of reality. And I know that sounds 206 00:10:25,920 --> 00:10:28,800 Speaker 1: like pomps and grandiose, but it's true because that's what 207 00:10:28,840 --> 00:10:32,040 Speaker 1: it's dealing with. It's describing space and time and helping 208 00:10:32,120 --> 00:10:35,480 Speaker 1: us grapple with like what that really means. And you know, philosophically, 209 00:10:35,480 --> 00:10:38,400 Speaker 1: it's awesome that you can say, hey, here's a mathematical 210 00:10:38,480 --> 00:10:41,320 Speaker 1: model that describes what's happening out there in the universe. 211 00:10:41,840 --> 00:10:44,680 Speaker 1: And if it works, if it describes the universe faithfully, 212 00:10:44,880 --> 00:10:46,680 Speaker 1: then I can look at that model and say, hmm, 213 00:10:47,160 --> 00:10:49,720 Speaker 1: maybe I can learn something about the universe by studying 214 00:10:49,720 --> 00:10:52,680 Speaker 1: this model. If I have a mathematical description of the universe, 215 00:10:52,960 --> 00:10:56,160 Speaker 1: does that description reveal something about reality to me? That's 216 00:10:56,200 --> 00:10:58,280 Speaker 1: the juice in all of this physics. And you know, 217 00:10:58,320 --> 00:11:00,200 Speaker 1: one of the most important things to understand and in 218 00:11:00,240 --> 00:11:05,600 Speaker 1: special relativity are very basic things like location, like velocity, 219 00:11:05,960 --> 00:11:09,559 Speaker 1: like acceleration. Like what do these things mean in special relativity? 220 00:11:09,720 --> 00:11:12,640 Speaker 1: And how are they different from how Newton or Archimedes 221 00:11:12,760 --> 00:11:15,840 Speaker 1: or Aristotle thought about these very basic concepts. 222 00:11:16,080 --> 00:11:17,920 Speaker 2: A while back, we had two topics that I think 223 00:11:17,960 --> 00:11:20,520 Speaker 2: would be helpful intros to this, if anybody wants to 224 00:11:20,520 --> 00:11:22,360 Speaker 2: go back and get some more background. We had an 225 00:11:22,360 --> 00:11:24,680 Speaker 2: episode on what is time and what is space? And 226 00:11:24,720 --> 00:11:26,360 Speaker 2: as I was looking at your outline, I thought, oh, 227 00:11:26,400 --> 00:11:28,520 Speaker 2: that's helpful background information for this discussion. 228 00:11:28,720 --> 00:11:31,800 Speaker 1: Yeah, And so the headlines for special relativity are that 229 00:11:31,920 --> 00:11:36,840 Speaker 1: location and velocity are purely relative. There's no absolute measure 230 00:11:36,840 --> 00:11:40,920 Speaker 1: of location velocity, but acceleration is not. Acceleration is an 231 00:11:40,960 --> 00:11:44,600 Speaker 1: absolute quantity. So let's start with location. What do we 232 00:11:44,679 --> 00:11:47,960 Speaker 1: mean when we say location is relative? It just means 233 00:11:48,000 --> 00:11:51,920 Speaker 1: that your location can only be described relative to other stuff. 234 00:11:52,320 --> 00:11:55,320 Speaker 1: There's no like set of markers in the universe, no 235 00:11:55,520 --> 00:11:58,280 Speaker 1: like axis glowing in space where you can say my 236 00:11:58,440 --> 00:12:01,480 Speaker 1: location is in this quadrant. It's always like I am 237 00:12:01,640 --> 00:12:05,960 Speaker 1: five kilometers from that, or I am two meters from this. 238 00:12:06,600 --> 00:12:10,000 Speaker 1: That's the only way to define your location in space. 239 00:12:10,040 --> 00:12:12,560 Speaker 1: There's no reference points. Another way to think about this 240 00:12:12,720 --> 00:12:16,200 Speaker 1: is that location is a property of a pair of points, 241 00:12:16,559 --> 00:12:18,720 Speaker 1: not a single object. Like a single object doesn't have 242 00:12:18,760 --> 00:12:23,320 Speaker 1: a location. Two objects have a distance between them, But 243 00:12:23,400 --> 00:12:26,800 Speaker 1: there's no meaning to say my coffee is at this location. 244 00:12:27,000 --> 00:12:29,840 Speaker 1: You can say my coffee is a meter from the ground, 245 00:12:29,920 --> 00:12:32,480 Speaker 1: or my coffee is six thousand kilometers from the center 246 00:12:32,559 --> 00:12:35,679 Speaker 1: of the Earth. But my coffee has no location on 247 00:12:35,760 --> 00:12:36,719 Speaker 1: its own, and. 248 00:12:36,679 --> 00:12:42,120 Speaker 2: There's no greater question than where is my coffee? So 249 00:12:42,200 --> 00:12:43,839 Speaker 2: thank you physicists. 250 00:12:45,120 --> 00:12:47,120 Speaker 1: Exactly. I mean, I'm trying to be practical here. You know, 251 00:12:47,600 --> 00:12:50,040 Speaker 1: it's not all space ships and cats flying through space. 252 00:12:50,240 --> 00:12:51,760 Speaker 1: And this is sort of hard for a lot of 253 00:12:51,760 --> 00:12:54,679 Speaker 1: people to wrap their minds around because they think of 254 00:12:54,800 --> 00:12:57,440 Speaker 1: locations as absolute the way Newton did. Right. Newton thought 255 00:12:57,440 --> 00:13:00,120 Speaker 1: of space as absolutely thought. Even if there's nothing in 256 00:13:00,160 --> 00:13:02,880 Speaker 1: the universe, there is still space. But you know, we 257 00:13:02,920 --> 00:13:05,520 Speaker 1: think of space as just the distance between things, and 258 00:13:05,960 --> 00:13:09,720 Speaker 1: that's really important framework for understanding general relativity if you 259 00:13:09,760 --> 00:13:12,679 Speaker 1: get there, because the bending of space can be understood 260 00:13:12,840 --> 00:13:16,080 Speaker 1: not as like the curature of space relative to some 261 00:13:16,280 --> 00:13:19,320 Speaker 1: other external metric. There is no other external metric, but 262 00:13:19,440 --> 00:13:23,680 Speaker 1: just the changing distances between things, because that's all we have. 263 00:13:24,400 --> 00:13:27,440 Speaker 1: So it's important to remember that distances are just relative. Right, 264 00:13:27,440 --> 00:13:32,960 Speaker 1: your location is just relative, And that's also true about velocity. 265 00:13:33,080 --> 00:13:37,160 Speaker 1: Velocity also purely a relative quantity. This one, I think 266 00:13:37,240 --> 00:13:39,080 Speaker 1: is even harder for people to grapple with. 267 00:13:39,440 --> 00:13:41,960 Speaker 2: So you said, there's no like grid, and this is 268 00:13:41,960 --> 00:13:46,080 Speaker 2: a stupid question, but like, would our understanding of location 269 00:13:46,320 --> 00:13:48,839 Speaker 2: change if we had infinite money and we put a 270 00:13:48,880 --> 00:13:52,640 Speaker 2: grid in space and like you know, every one light 271 00:13:52,720 --> 00:13:55,400 Speaker 2: year we put like a blinking buoy like in the ocean. 272 00:13:55,559 --> 00:13:57,360 Speaker 2: How would we still be in the same position even 273 00:13:57,360 --> 00:13:58,240 Speaker 2: if we had that grid. 274 00:13:58,440 --> 00:14:00,959 Speaker 1: Yeah, if we had infinite money, wouldn't coommend spending it 275 00:14:01,000 --> 00:14:03,760 Speaker 1: on that grid because it wouldn't change our relationship with space, 276 00:14:03,920 --> 00:14:06,920 Speaker 1: Like you could still define your location relative to a 277 00:14:07,000 --> 00:14:10,160 Speaker 1: point on that grid. That's fine, But now you've created 278 00:14:10,200 --> 00:14:12,520 Speaker 1: an object. You've put it there, and you said I'm 279 00:14:12,520 --> 00:14:15,599 Speaker 1: going to create axis at this location, and therefore I 280 00:14:15,640 --> 00:14:17,760 Speaker 1: can define my distance from this buoy or from that 281 00:14:17,800 --> 00:14:20,000 Speaker 1: booey or from the other thing. That's no different from 282 00:14:20,040 --> 00:14:22,080 Speaker 1: saying here I am relative to my coffee or a 283 00:14:22,120 --> 00:14:24,520 Speaker 1: relative to the center of the earth. But you haven't 284 00:14:24,520 --> 00:14:27,720 Speaker 1: anchored those booies to like space itself. Right. You could 285 00:14:27,760 --> 00:14:30,400 Speaker 1: shift all of space over and nothing would change in 286 00:14:30,440 --> 00:14:33,560 Speaker 1: your measurements because space itself doesn't have a location. There's 287 00:14:33,600 --> 00:14:37,320 Speaker 1: no frame to space itself. Right. You can't say my 288 00:14:37,440 --> 00:14:41,320 Speaker 1: booys are here relative to space. That means nothing, right, 289 00:14:41,600 --> 00:14:42,800 Speaker 1: space has no frame. 290 00:14:43,160 --> 00:14:46,640 Speaker 2: You just saved us all a lot of money. 291 00:14:47,040 --> 00:14:49,400 Speaker 1: I'd like to take five percent of that infinite dollars 292 00:14:49,560 --> 00:14:50,920 Speaker 1: divert it to my own research. 293 00:14:51,840 --> 00:14:53,800 Speaker 2: You might need it, all right, So let's move on 294 00:14:53,880 --> 00:14:56,440 Speaker 2: to velocity and acceleration. And I'm going to be honest, 295 00:14:56,920 --> 00:14:59,960 Speaker 2: I often forget the definition of velocity and the definition 296 00:15:00,080 --> 00:15:02,720 Speaker 2: of acceleration. So let's just start there. 297 00:15:03,160 --> 00:15:06,880 Speaker 1: Okay, cool, Well, velocity and principle is very simple. It's 298 00:15:06,960 --> 00:15:10,280 Speaker 1: how is your location changing? Okap. Location is in units 299 00:15:10,400 --> 00:15:15,880 Speaker 1: of like distance, meters, kilometers, whatever. Velocity is distance per time, right, 300 00:15:15,960 --> 00:15:19,640 Speaker 1: So meters per second? How is your location changing? So 301 00:15:19,840 --> 00:15:22,360 Speaker 1: if you're in a car on the ground, your location 302 00:15:22,640 --> 00:15:25,200 Speaker 1: is where are you relative to your house, for example, 303 00:15:25,800 --> 00:15:30,240 Speaker 1: and your velocity is how quickly is that location changing? Right, 304 00:15:30,280 --> 00:15:32,120 Speaker 1: So that's why you measure it in like meters per 305 00:15:32,160 --> 00:15:34,360 Speaker 1: second or kilometers per hour something. 306 00:15:34,600 --> 00:15:36,800 Speaker 2: Okay, So the way you just said it, it's also 307 00:15:36,880 --> 00:15:38,280 Speaker 2: relative to something. 308 00:15:38,360 --> 00:15:42,120 Speaker 1: You don't have an absolute velocity exactly. You always measure 309 00:15:42,280 --> 00:15:45,480 Speaker 1: relative to something because there are no absolute references, right, 310 00:15:45,560 --> 00:15:47,840 Speaker 1: How could you measure it in an absolute sense? If 311 00:15:47,840 --> 00:15:50,680 Speaker 1: space itself is not absolute, if there's nothing to grab 312 00:15:50,720 --> 00:15:53,840 Speaker 1: onto on space, nothing everybody can agree on. So you 313 00:15:53,880 --> 00:15:56,120 Speaker 1: and I can measure the speed of a passing baseball 314 00:15:56,160 --> 00:15:58,800 Speaker 1: and we can disagree because maybe you're in a car 315 00:15:58,880 --> 00:16:00,520 Speaker 1: and I'm on the ground, and so you measure the 316 00:16:00,560 --> 00:16:02,840 Speaker 1: baseball traveling at one speed and I'm measured traveling at 317 00:16:02,880 --> 00:16:06,760 Speaker 1: another speed. The baseball has no speed inherently. It has 318 00:16:06,760 --> 00:16:09,560 Speaker 1: a speed relative to you and a speed relative to me. 319 00:16:10,320 --> 00:16:12,680 Speaker 1: I think that makes sense to people, but it tells 320 00:16:12,720 --> 00:16:15,600 Speaker 1: us that speeding in is not a property of the object. 321 00:16:15,680 --> 00:16:18,600 Speaker 1: It's a property of a pair of objects. And I 322 00:16:18,600 --> 00:16:20,560 Speaker 1: think most people are totally cool with that, and I 323 00:16:20,600 --> 00:16:22,840 Speaker 1: see you nodding. But then you get a lot of 324 00:16:22,880 --> 00:16:26,000 Speaker 1: people talking about what happens when you're moving near the 325 00:16:26,040 --> 00:16:29,120 Speaker 1: speed of light. My question is always near the speed 326 00:16:29,120 --> 00:16:32,520 Speaker 1: of light relative to what There is no I'm moving 327 00:16:32,560 --> 00:16:34,280 Speaker 1: near the speed of light or I'm not moving near 328 00:16:34,320 --> 00:16:37,040 Speaker 1: the speed of light. You're already moving near the speed 329 00:16:37,080 --> 00:16:40,600 Speaker 1: of light relative to particles that are shooting at the Earth. 330 00:16:40,880 --> 00:16:43,120 Speaker 1: If those particles are moving towards the Earth at near 331 00:16:43,160 --> 00:16:45,400 Speaker 1: the speed of light, the Earth is moving towards them 332 00:16:45,480 --> 00:16:48,000 Speaker 1: at near the speed of light. So you're already moving 333 00:16:48,040 --> 00:16:50,600 Speaker 1: near the speed of light. You're also moving at zero 334 00:16:50,680 --> 00:16:53,960 Speaker 1: velocity relative to your shoes right, which are probably I 335 00:16:53,960 --> 00:16:56,440 Speaker 1: hope attached to you, or to your head, let's say 336 00:16:56,480 --> 00:16:59,640 Speaker 1: your head, for example. So you have multiple speeds. You 337 00:16:59,640 --> 00:17:02,960 Speaker 1: have speed relative to any potential observer. So it makes 338 00:17:02,960 --> 00:17:05,359 Speaker 1: no sense to say I'm moving near the speed of 339 00:17:05,400 --> 00:17:07,600 Speaker 1: light or I'm not moving near the speed of light. 340 00:17:07,960 --> 00:17:10,760 Speaker 1: You're moving at any speed relative to any observer that 341 00:17:10,840 --> 00:17:11,840 Speaker 1: could be observing you. 342 00:17:12,240 --> 00:17:13,920 Speaker 2: I didn't realize I could claim that I was going 343 00:17:13,920 --> 00:17:16,560 Speaker 2: so fast. I'm gonna go ahead and across the exercise 344 00:17:16,640 --> 00:17:19,360 Speaker 2: box off of my new year's resolution list. I am 345 00:17:19,440 --> 00:17:20,840 Speaker 2: speeding around this universe. 346 00:17:22,080 --> 00:17:23,560 Speaker 1: I always tell people you're very quick. 347 00:17:23,840 --> 00:17:26,639 Speaker 2: Yes, you're very quick too, We're all very quick. It 348 00:17:26,680 --> 00:17:28,119 Speaker 2: depends on what you're comparing to. 349 00:17:28,440 --> 00:17:31,040 Speaker 1: Yeah, exactly. And this is an amazing and confusing thing 350 00:17:31,080 --> 00:17:36,280 Speaker 1: about special relativity because time depends on this speed. Right. 351 00:17:36,480 --> 00:17:38,880 Speaker 1: What we say in special relativity is that moving clocks 352 00:17:38,960 --> 00:17:42,720 Speaker 1: run slow. So if there's a spaceship zooming past the 353 00:17:42,800 --> 00:17:46,840 Speaker 1: Earth and it has high speed relative to the Earth, right, 354 00:17:46,840 --> 00:17:49,600 Speaker 1: people writing with relativity questions and they say a spaceship 355 00:17:49,640 --> 00:17:51,160 Speaker 1: is moving near the speed of light, and I say 356 00:17:51,359 --> 00:17:54,280 Speaker 1: near the speed of light relative to who? Right, relative 357 00:17:54,280 --> 00:17:56,439 Speaker 1: to what? In this case, the spaceship is moving near 358 00:17:56,520 --> 00:17:59,000 Speaker 1: the speed of light relative to the Earth. The Earth 359 00:17:59,280 --> 00:18:02,360 Speaker 1: sees a space ship's clocks as running slowly. That might 360 00:18:02,400 --> 00:18:05,960 Speaker 1: make sense. People are cool with that. But then because 361 00:18:06,000 --> 00:18:09,960 Speaker 1: it's symmetric, because the spaceship also sees the Earth as 362 00:18:10,040 --> 00:18:11,960 Speaker 1: moving near the speed of light. Because hey, we just 363 00:18:11,960 --> 00:18:15,000 Speaker 1: told you velocity is relative, right, That means that the 364 00:18:15,040 --> 00:18:19,160 Speaker 1: spaceship sees the Earth's clocks as running slow. And that's 365 00:18:19,160 --> 00:18:22,040 Speaker 1: the amazing thing about special relativity. If you really grasp 366 00:18:22,240 --> 00:18:25,880 Speaker 1: the relativity of velocity. It means that you can't have 367 00:18:26,240 --> 00:18:29,160 Speaker 1: the same clock everywhere, that everybody doesn't have to agree 368 00:18:29,240 --> 00:18:32,960 Speaker 1: about how time flows. I'm right that the spaceship's clocks 369 00:18:32,960 --> 00:18:35,480 Speaker 1: are running slow. The spaceship is right that my clocks 370 00:18:35,480 --> 00:18:38,520 Speaker 1: are running slow. That's both true because we don't have 371 00:18:38,600 --> 00:18:41,240 Speaker 1: to have the same story about what's happening in the universe. 372 00:18:41,480 --> 00:18:44,639 Speaker 1: Special relativity tells us there's no absolute space, there's no 373 00:18:44,680 --> 00:18:48,480 Speaker 1: absolute time, there is no absolute history of the universe. 374 00:18:48,760 --> 00:18:50,280 Speaker 1: Boom boom. 375 00:18:50,480 --> 00:18:52,240 Speaker 2: Now that does seem like a good place to start 376 00:18:52,280 --> 00:18:54,119 Speaker 2: a movie or a sci fi novel. So I can 377 00:18:54,160 --> 00:18:55,760 Speaker 2: see why this comes up so often. 378 00:18:55,640 --> 00:18:57,919 Speaker 1: Right, So keep that in mind when we're later talking 379 00:18:57,960 --> 00:19:01,600 Speaker 1: about whether potatoes can into black holes or what it's 380 00:19:01,680 --> 00:19:03,800 Speaker 1: like to be a photon. But there is one thing 381 00:19:03,840 --> 00:19:08,400 Speaker 1: in the universe which really amazingly, fascinatingly is absolute about 382 00:19:08,400 --> 00:19:12,000 Speaker 1: the universe, and that's acceleration. So we started with location. 383 00:19:12,080 --> 00:19:15,440 Speaker 1: That's just like, where are you relative to some arbitrary 384 00:19:15,520 --> 00:19:19,119 Speaker 1: grid where you anchorated some object. You know, distance from 385 00:19:19,160 --> 00:19:21,320 Speaker 1: my coffee cup, or distance from my toes, or distance 386 00:19:21,320 --> 00:19:24,879 Speaker 1: from the center of the sun. That's location. Velocity is 387 00:19:24,920 --> 00:19:28,240 Speaker 1: how is your location changing acceleration is how is your 388 00:19:28,400 --> 00:19:31,400 Speaker 1: velocity changing. So for the math nerds out there, we're 389 00:19:31,400 --> 00:19:35,240 Speaker 1: now two derivatives. In right, velocity is the slope or 390 00:19:35,280 --> 00:19:38,960 Speaker 1: derivative of your location. If you're plotting where is your 391 00:19:39,000 --> 00:19:43,000 Speaker 1: location versus time, then velocity is the slope of that plot. 392 00:19:43,160 --> 00:19:46,320 Speaker 1: If you then plot your velocity, acceleration is the slope 393 00:19:46,320 --> 00:19:48,600 Speaker 1: of the velocity plot. So it's just like, how much 394 00:19:48,640 --> 00:19:51,439 Speaker 1: is velocity changing? Velocity is how much is location changing? 395 00:19:51,680 --> 00:19:54,240 Speaker 2: Got it? I kind of liked calculus. 396 00:19:56,200 --> 00:19:59,000 Speaker 1: I love the connection between calculus and physics, right, Like 397 00:19:59,359 --> 00:20:03,440 Speaker 1: knowing this makes physics so simple and straightforward. You're like, oh, 398 00:20:03,520 --> 00:20:06,280 Speaker 1: acceleration is just the derivative of velocity, which is just 399 00:20:06,320 --> 00:20:09,400 Speaker 1: the derivative of location. So I can just like derive 400 00:20:09,640 --> 00:20:14,200 Speaker 1: my equations of emotions from one fact like a constant acceleration. Boom, 401 00:20:14,200 --> 00:20:16,720 Speaker 1: I know the accelerations emotion, Just integrate twice to get 402 00:20:16,760 --> 00:20:18,399 Speaker 1: the position. Boom, You're done. 403 00:20:18,560 --> 00:20:23,359 Speaker 2: Elementary maybe not quite that easy. 404 00:20:23,400 --> 00:20:25,800 Speaker 1: But I had this great moment because my son is 405 00:20:25,800 --> 00:20:28,680 Speaker 1: taking physics right now, and he's also taking calculus, and 406 00:20:28,720 --> 00:20:31,680 Speaker 1: so he knows these tools and he was learning about 407 00:20:31,720 --> 00:20:33,680 Speaker 1: equations of motion and I was like dude, you can 408 00:20:33,760 --> 00:20:36,159 Speaker 1: just integrate this twice and get that answer. And he 409 00:20:36,200 --> 00:20:38,640 Speaker 1: was like, oh, and that's why it's one half at squared. 410 00:20:38,680 --> 00:20:40,639 Speaker 1: I get it. Cool. And he had this like moment, 411 00:20:40,640 --> 00:20:42,800 Speaker 1: We're all clicked in his mind, and I was like, dude, 412 00:20:43,240 --> 00:20:45,960 Speaker 1: math and physics dancing together to explain the universe. 413 00:20:46,280 --> 00:20:48,359 Speaker 2: Aw. That must have been a proud moment as a 414 00:20:48,359 --> 00:20:49,720 Speaker 2: father to be able to observe that. 415 00:20:50,920 --> 00:20:53,040 Speaker 1: It was twenty years in the making, but it was cool. 416 00:20:53,640 --> 00:20:55,560 Speaker 2: Sometimes you got to wait a long time for the payoffs, 417 00:20:55,560 --> 00:20:56,240 Speaker 2: but you got there. 418 00:20:56,640 --> 00:21:00,000 Speaker 1: But the amazing thing about acceleration is that it is absolute. 419 00:21:00,320 --> 00:21:03,360 Speaker 1: It's the one thing which does belong to you. Right. 420 00:21:03,400 --> 00:21:05,800 Speaker 1: Your location is relative, it's a property of a pair 421 00:21:05,840 --> 00:21:09,480 Speaker 1: of objects. Your velocity is relative. It only has meaning 422 00:21:09,520 --> 00:21:12,199 Speaker 1: in relation to something else you're measuring with respect to 423 00:21:12,680 --> 00:21:16,480 Speaker 1: acceleration is something you own. Your acceleration is just your own. 424 00:21:16,520 --> 00:21:18,920 Speaker 1: You don't need to measure it relative to anything else. 425 00:21:19,680 --> 00:21:22,879 Speaker 1: And this is Einstein's famous thought experiment. Right in a box, 426 00:21:23,000 --> 00:21:24,960 Speaker 1: you can't tell where you are or how fast you're 427 00:21:25,000 --> 00:21:28,000 Speaker 1: going because those things only have meaning relative to stuff 428 00:21:28,040 --> 00:21:30,840 Speaker 1: outside the box. But inside the box, you can measure 429 00:21:30,920 --> 00:21:31,639 Speaker 1: your acceleration. 430 00:21:31,880 --> 00:21:34,360 Speaker 2: My first question is, so is it because the reference 431 00:21:34,400 --> 00:21:36,600 Speaker 2: point is now what you were doing like a second ago, 432 00:21:36,680 --> 00:21:40,440 Speaker 2: and because that's like an internal comparison, that's why it's 433 00:21:40,480 --> 00:21:45,000 Speaker 2: not relative silences. I always think, was this a great 434 00:21:45,119 --> 00:21:47,200 Speaker 2: question or a really dumb question? Dane was trying to 435 00:21:47,200 --> 00:21:49,639 Speaker 2: figure out, how do I not insult Kelly's intelligence? 436 00:21:49,760 --> 00:21:52,240 Speaker 1: No, not at all. The fun moments for me and 437 00:21:52,320 --> 00:21:55,040 Speaker 1: teaching are hearing somebody's question and then trying to work 438 00:21:55,119 --> 00:21:57,720 Speaker 1: backwards to what is going on in your mind that 439 00:21:57,840 --> 00:22:00,240 Speaker 1: made you ask that question, so that my an or 440 00:22:00,840 --> 00:22:02,720 Speaker 1: is the most helpful, and for me, like that's the 441 00:22:02,760 --> 00:22:05,040 Speaker 1: fun part about teaching. That's always the puzzle. 442 00:22:05,280 --> 00:22:07,200 Speaker 2: I enjoy giving you lots of those opportunities. 443 00:22:07,280 --> 00:22:14,400 Speaker 1: Daniel, You know, it's a really amazing property of the universe, 444 00:22:14,920 --> 00:22:18,680 Speaker 1: and it's not something I think we understand philosophically. It's 445 00:22:18,720 --> 00:22:22,000 Speaker 1: just something we observe, like this is our description of 446 00:22:22,040 --> 00:22:24,720 Speaker 1: the universe as we experience it. We know that you 447 00:22:24,720 --> 00:22:27,680 Speaker 1: cannot measure your velocity or your location, but you can 448 00:22:27,800 --> 00:22:31,879 Speaker 1: measure your acceleration, So fundamentally, this is a description of 449 00:22:31,920 --> 00:22:33,959 Speaker 1: something we see in the universe, and this is one 450 00:22:33,960 --> 00:22:35,800 Speaker 1: of those moments when you can say, Okay, this is 451 00:22:35,800 --> 00:22:38,040 Speaker 1: the description of the universe. What does it mean about 452 00:22:38,040 --> 00:22:41,359 Speaker 1: the universe that velocity is relative and acceleration is not. 453 00:22:41,720 --> 00:22:44,159 Speaker 1: And it's actually one of the connections to general relativity 454 00:22:44,240 --> 00:22:48,959 Speaker 1: because acceleration can be seen as equivalent to curvature. Acceleration 455 00:22:49,040 --> 00:22:51,240 Speaker 1: has all the same effects on the motion of an 456 00:22:51,280 --> 00:22:55,880 Speaker 1: object as curvature. In fact, we describe curvature sometimes as 457 00:22:55,920 --> 00:22:59,840 Speaker 1: a pseudo force, right, that's what gravity is. Curvature is gravity, 458 00:22:59,880 --> 00:23:04,440 Speaker 1: and gravity is a pseudoforce that generates apparent acceleration. So 459 00:23:04,600 --> 00:23:07,639 Speaker 1: that's actually a much more complex topic and connect special 460 00:23:07,680 --> 00:23:09,840 Speaker 1: in general relativity. So I think for the purposes of 461 00:23:09,880 --> 00:23:12,520 Speaker 1: today's conversation, let's just say this is something we observe 462 00:23:12,600 --> 00:23:15,160 Speaker 1: in the universe, and we do our best to describe it. 463 00:23:15,760 --> 00:23:17,399 Speaker 1: And I think the best way to get your handle 464 00:23:17,440 --> 00:23:20,120 Speaker 1: on the intuition for acceleration is to imagine, like, well, 465 00:23:20,160 --> 00:23:22,560 Speaker 1: how would you measure it? I told you you can't 466 00:23:22,600 --> 00:23:25,560 Speaker 1: measure your velocity accept relative to other stuff, And you 467 00:23:25,560 --> 00:23:28,040 Speaker 1: can imagine, like being in a box flying through space 468 00:23:28,040 --> 00:23:30,520 Speaker 1: where you don't have access to anything outside, how would 469 00:23:30,600 --> 00:23:33,280 Speaker 1: you measure your velocity? There's no experiment you can come 470 00:23:33,359 --> 00:23:35,640 Speaker 1: up with that can measure your velocity because you need 471 00:23:35,720 --> 00:23:37,840 Speaker 1: access to stuff outside because that's the only way to 472 00:23:37,840 --> 00:23:41,600 Speaker 1: define your velocity. But you can measure your acceleration inside 473 00:23:41,640 --> 00:23:42,159 Speaker 1: that box. 474 00:23:42,280 --> 00:23:44,080 Speaker 2: And how would I do that? Like say I was 475 00:23:44,119 --> 00:23:46,280 Speaker 2: standing in there with the ball, would that help me? 476 00:23:46,440 --> 00:23:50,480 Speaker 1: Yes? Absolutely? Just drop the ball. See what happens right now. 477 00:23:50,560 --> 00:23:53,120 Speaker 1: If you're not accelerating, the ball will just hang there 478 00:23:53,160 --> 00:23:56,200 Speaker 1: with you. If you are accelerating, then the ball will 479 00:23:56,240 --> 00:24:00,120 Speaker 1: move because there'll be a pseudo force generated by your acceleration. 480 00:24:00,600 --> 00:24:02,119 Speaker 1: And we do this all the time. You feel this 481 00:24:02,160 --> 00:24:05,040 Speaker 1: every time you drive somewhere. Right, If you're driving the 482 00:24:05,040 --> 00:24:08,160 Speaker 1: car and somebody hits the accelerator right, then what happens. 483 00:24:08,320 --> 00:24:11,280 Speaker 1: You feel pressed back into your seat. If you dropped 484 00:24:11,320 --> 00:24:14,360 Speaker 1: a ball right, then the ball would fly backwards. If 485 00:24:14,400 --> 00:24:17,480 Speaker 1: somebody hits the brakes, which is also an acceleration, then 486 00:24:17,520 --> 00:24:18,639 Speaker 1: you feel pushed forwards. 487 00:24:18,720 --> 00:24:18,840 Speaker 3: Right. 488 00:24:18,880 --> 00:24:20,919 Speaker 1: There's a phudo force there as you're pushed forward. If 489 00:24:20,960 --> 00:24:23,840 Speaker 1: you dropped the ball, it would fly forwards. Right. The 490 00:24:23,880 --> 00:24:26,399 Speaker 1: reason you have a seat belt is because of this effect. 491 00:24:26,720 --> 00:24:29,800 Speaker 1: So it's very easy to tell whether you're accelerating. Just 492 00:24:29,880 --> 00:24:32,360 Speaker 1: bring a ball or bring a scale. Right, a scale, 493 00:24:32,359 --> 00:24:35,720 Speaker 1: it literally is measuring acceleration. That's why, for example, when 494 00:24:35,760 --> 00:24:38,560 Speaker 1: you stand on a scale in space, you measure nothing 495 00:24:38,680 --> 00:24:41,479 Speaker 1: because you're in free fall, there is no acceleration, whereas 496 00:24:41,480 --> 00:24:43,399 Speaker 1: if you stand on the surface of the Earth, you 497 00:24:43,480 --> 00:24:47,199 Speaker 1: do measure acceleration. You're measuring the Earth accelerating up and 498 00:24:47,320 --> 00:24:50,439 Speaker 1: out to keep you from falling towards the center of 499 00:24:50,520 --> 00:24:50,960 Speaker 1: the Earth. 500 00:24:51,280 --> 00:24:53,359 Speaker 2: We are recording this pretty close to the end of 501 00:24:53,359 --> 00:24:55,200 Speaker 2: the holiday, so I'm going to stick with the ball 502 00:24:55,280 --> 00:24:58,679 Speaker 2: instead of the scale. Let's take a break, and when 503 00:24:58,720 --> 00:25:00,760 Speaker 2: we get back from the break, going to talk about 504 00:25:00,800 --> 00:25:03,600 Speaker 2: whether or not potatoes turn into black holes if they're 505 00:25:03,640 --> 00:25:23,199 Speaker 2: going fast enough. Okay, Daniel, So here's my question for you. 506 00:25:23,880 --> 00:25:27,760 Speaker 2: Do things change their mass as you approach the speed 507 00:25:27,760 --> 00:25:28,040 Speaker 2: of lie? 508 00:25:29,400 --> 00:25:32,040 Speaker 1: Yeah? Right? And this question was inspired by a listener 509 00:25:32,040 --> 00:25:35,880 Speaker 1: who wrote in and heard on another podcast that potatoes, 510 00:25:35,960 --> 00:25:38,280 Speaker 1: if they approach the speed of light, were turned into 511 00:25:38,320 --> 00:25:41,199 Speaker 1: black holes. And like, I won't comment on whether you 512 00:25:41,280 --> 00:25:42,679 Speaker 1: might turn into a black hole if you eat too 513 00:25:42,720 --> 00:25:45,480 Speaker 1: many potatoes after the holidays, but I do want to 514 00:25:45,480 --> 00:25:47,800 Speaker 1: dig into this question of what happens to a potato 515 00:25:48,560 --> 00:25:50,919 Speaker 1: immediately your eyebras scrunch up when you hear this question, 516 00:25:51,400 --> 00:25:53,919 Speaker 1: because even the question like what happens to a potato 517 00:25:54,000 --> 00:25:56,240 Speaker 1: when approaches the speed of light, you might think like, well, 518 00:25:56,320 --> 00:25:59,720 Speaker 1: the speed of light relative to what? Right? Because velocity 519 00:25:59,760 --> 00:26:02,520 Speaker 1: is not the property of a potato. So it doesn't 520 00:26:02,560 --> 00:26:05,040 Speaker 1: make sense to even talk about a potato having a speed. 521 00:26:05,600 --> 00:26:07,680 Speaker 1: Is it moving at that speed relative to the Earth, 522 00:26:07,720 --> 00:26:11,160 Speaker 1: relative to a spaceship, relative to some particle? The question 523 00:26:11,280 --> 00:26:14,720 Speaker 1: itself already doesn't make sense, and that tells you that 524 00:26:14,800 --> 00:26:15,919 Speaker 1: the answer can't. 525 00:26:15,640 --> 00:26:18,320 Speaker 2: Be yes and we're done. 526 00:26:18,760 --> 00:26:21,040 Speaker 1: I mean, for example, like take a potato. Maybe have 527 00:26:21,119 --> 00:26:23,159 Speaker 1: a potato in your kitchen. What is the velocity of 528 00:26:23,200 --> 00:26:26,960 Speaker 1: that potato? Well, it's moving at zero relative to your kitchen. 529 00:26:27,000 --> 00:26:31,040 Speaker 1: Probably it's already moving near the speed of light relative 530 00:26:31,080 --> 00:26:33,840 Speaker 1: to anything that's moving towards the Earth at near the 531 00:26:33,840 --> 00:26:36,280 Speaker 1: speed of light. And there's lots of stuff moving towards 532 00:26:36,320 --> 00:26:38,680 Speaker 1: the Earth at near the speed of light. There's particles 533 00:26:38,800 --> 00:26:41,080 Speaker 1: shooting from space at super high energy. Is at ninety 534 00:26:41,160 --> 00:26:45,120 Speaker 1: nine point nine percent of the speed of light. Your 535 00:26:45,160 --> 00:26:48,040 Speaker 1: potato is moving near the speed of light relative to 536 00:26:48,080 --> 00:26:50,399 Speaker 1: that particle. Is your potato a black hole? 537 00:26:50,960 --> 00:26:51,120 Speaker 3: No? 538 00:26:51,520 --> 00:26:54,639 Speaker 1: So the answer. Everybody who has a potato is doing 539 00:26:54,680 --> 00:26:57,760 Speaker 1: this experiment right now, so we know your potato is 540 00:26:57,800 --> 00:27:00,399 Speaker 1: not turning into a black hole. And the amazing thing 541 00:27:00,440 --> 00:27:04,760 Speaker 1: about black holes is that they are observer independent. Some 542 00:27:04,800 --> 00:27:07,160 Speaker 1: of the things we talked about earlier are observer dependent, 543 00:27:07,280 --> 00:27:09,919 Speaker 1: like I see your clock as slowing down if I 544 00:27:09,960 --> 00:27:13,320 Speaker 1: see you moving quickly, and that's observer dependent because it 545 00:27:13,359 --> 00:27:17,600 Speaker 1: depends on my velocity relative to you. But black holes 546 00:27:17,760 --> 00:27:21,600 Speaker 1: are not observer dependent. They exist in every frame, if 547 00:27:21,640 --> 00:27:24,280 Speaker 1: they exist at all. So it's not like I can 548 00:27:24,320 --> 00:27:26,600 Speaker 1: see the potato as a black hole because it's moving 549 00:27:26,640 --> 00:27:29,440 Speaker 1: fast relative to me, but you don't see the potato 550 00:27:29,440 --> 00:27:31,199 Speaker 1: as a black hole because it's sitting next to you. 551 00:27:31,520 --> 00:27:33,919 Speaker 1: Everybody has to agree whether it's a black hole or not. 552 00:27:34,600 --> 00:27:36,840 Speaker 2: So if we assumed that when they were talking about 553 00:27:36,880 --> 00:27:39,119 Speaker 2: the speed of the potato it was relative to Earth, 554 00:27:39,359 --> 00:27:41,160 Speaker 2: does that solve because we all have the same frame 555 00:27:41,200 --> 00:27:41,760 Speaker 2: of reference. 556 00:27:42,000 --> 00:27:44,240 Speaker 1: No, because you can always possibly some observer are moving 557 00:27:44,240 --> 00:27:47,719 Speaker 1: with the potato somewhere else. Yeah, exactly, and there's always 558 00:27:47,720 --> 00:27:50,800 Speaker 1: some particle there to do that observing. And the root 559 00:27:50,800 --> 00:27:53,479 Speaker 1: of this comes from a historically sort of fascinating idea 560 00:27:53,520 --> 00:27:57,320 Speaker 1: about mass. You often hear that mass increases as your 561 00:27:57,320 --> 00:27:59,440 Speaker 1: approach to the speed of light. And again, I hope 562 00:27:59,480 --> 00:28:01,720 Speaker 1: your ears to turn up at that and go like, hmm, 563 00:28:02,200 --> 00:28:04,119 Speaker 1: who's measuring the speed in that case? And though this 564 00:28:04,240 --> 00:28:07,879 Speaker 1: is often quoted, it makes little sense, right, because it 565 00:28:07,920 --> 00:28:11,960 Speaker 1: doesn't make sense for mass to be observer dependent. If 566 00:28:12,000 --> 00:28:15,120 Speaker 1: you're moving past me near the speed of light, does 567 00:28:15,160 --> 00:28:18,040 Speaker 1: it make sense for me to measure mass as larger 568 00:28:18,080 --> 00:28:21,240 Speaker 1: than somebody else to measure your mass? Right? Mass can't 569 00:28:21,240 --> 00:28:24,520 Speaker 1: be observed dependent if it has consequences like if you 570 00:28:24,520 --> 00:28:26,800 Speaker 1: have enough of it you turn into a black hole, right, 571 00:28:26,920 --> 00:28:29,880 Speaker 1: And we know that's not observer dependent. So what's going 572 00:28:29,880 --> 00:28:33,959 Speaker 1: on here is an old concept in relativity which are 573 00:28:34,000 --> 00:28:36,600 Speaker 1: sort of picked up on and propagated and been repeated 574 00:28:36,640 --> 00:28:38,480 Speaker 1: over and over and over again, even though it doesn't 575 00:28:38,480 --> 00:28:39,600 Speaker 1: really make much sense. 576 00:28:39,920 --> 00:28:41,920 Speaker 2: What is the old idea that's being repeated. 577 00:28:42,080 --> 00:28:45,680 Speaker 1: So this is basically all Einstein's fault, because when Einstein 578 00:28:45,800 --> 00:28:49,120 Speaker 1: was developing relativity, he had to think about how some 579 00:28:49,160 --> 00:28:52,440 Speaker 1: of these basic concepts change in this new notion, in 580 00:28:52,480 --> 00:28:55,560 Speaker 1: this new perspective of the universe, right, And so he 581 00:28:55,720 --> 00:28:59,560 Speaker 1: was thinking about speed and momentum and energy and mass, 582 00:29:00,120 --> 00:29:02,360 Speaker 1: And you know, some of these things are the same 583 00:29:02,400 --> 00:29:04,480 Speaker 1: for Newton, and some of these things are different. Right, 584 00:29:04,920 --> 00:29:07,920 Speaker 1: velocity is similar, but it has a maximum value now, 585 00:29:08,400 --> 00:29:10,800 Speaker 1: and so that changes. And what does that mean about 586 00:29:10,880 --> 00:29:13,600 Speaker 1: changing energy and changing momentum, Because like energy doesn't have 587 00:29:13,600 --> 00:29:15,560 Speaker 1: a maximum value. You can have an infinite amount of 588 00:29:15,640 --> 00:29:18,719 Speaker 1: energy even if your speed only approaches a certain value. 589 00:29:18,760 --> 00:29:22,000 Speaker 1: So like the relationship between these quantities have to change. 590 00:29:22,320 --> 00:29:25,320 Speaker 1: And so Einstein had to reimagine what these quantities were, 591 00:29:25,360 --> 00:29:28,000 Speaker 1: and for a moment, he came up with this idea 592 00:29:28,120 --> 00:29:32,040 Speaker 1: of relativistic mass, saying like, well, let's treat an object 593 00:29:32,120 --> 00:29:35,600 Speaker 1: as if it had more mass if its velocity is greater. 594 00:29:35,880 --> 00:29:38,200 Speaker 1: And so in his early writing he came up with 595 00:29:38,240 --> 00:29:41,520 Speaker 1: this concept, and he wrote the equations for mass increasing 596 00:29:41,600 --> 00:29:42,400 Speaker 1: with velocity. 597 00:29:42,600 --> 00:29:45,000 Speaker 2: So anyone who was confused a moment ago about whether 598 00:29:45,080 --> 00:29:47,520 Speaker 2: or not mass changes with velocity can feel good knowing 599 00:29:47,520 --> 00:29:49,280 Speaker 2: that Einstein was making the same mistake. 600 00:29:49,440 --> 00:29:52,920 Speaker 1: Yes, exactly, And you know it's fair like you're exploring 601 00:29:52,920 --> 00:29:56,000 Speaker 1: these new concepts, you're wondering, like, how do we generalize 602 00:29:56,000 --> 00:29:59,200 Speaker 1: We went from one idea to another. What gets change, 603 00:29:59,240 --> 00:30:01,600 Speaker 1: what doesn't get change? What's the most sensible way for 604 00:30:01,640 --> 00:30:04,160 Speaker 1: things to change, and it's fine for your first idea 605 00:30:04,280 --> 00:30:07,280 Speaker 1: to not be the best idea. The problem with relativistic 606 00:30:07,360 --> 00:30:09,720 Speaker 1: mass is that it doesn't really make sense and it's 607 00:30:09,760 --> 00:30:13,160 Speaker 1: not really necessary. Doesn't really make sense because it means 608 00:30:13,200 --> 00:30:16,520 Speaker 1: that your mass now depends on your velocity. So like 609 00:30:16,560 --> 00:30:19,840 Speaker 1: that potato would have more mass or less mass based 610 00:30:19,920 --> 00:30:22,719 Speaker 1: on who's measuring it, and also it would have different 611 00:30:22,760 --> 00:30:27,120 Speaker 1: masses in different directions, right, Like, what does happen to 612 00:30:27,160 --> 00:30:29,400 Speaker 1: the potato as we see it approach to the speed 613 00:30:29,400 --> 00:30:32,280 Speaker 1: of light relative to us is that it gets harder 614 00:30:32,280 --> 00:30:35,080 Speaker 1: to accelerate in one direction and not in others. Like, 615 00:30:35,200 --> 00:30:37,720 Speaker 1: if the potato is already going at ninety nine percent 616 00:30:37,760 --> 00:30:39,760 Speaker 1: of the speed of light as it whizzes by us, 617 00:30:40,320 --> 00:30:42,920 Speaker 1: then it's harder for us to increase its velocity in 618 00:30:42,960 --> 00:30:46,400 Speaker 1: the direction it's already moving, right, because it's already going 619 00:30:46,440 --> 00:30:49,360 Speaker 1: near the speed of light in that direction. It's easier 620 00:30:49,360 --> 00:30:51,680 Speaker 1: for me to push it perpendicular to its motion because 621 00:30:51,720 --> 00:30:54,400 Speaker 1: it's not already moving at a very high velocity. 622 00:30:54,560 --> 00:30:56,960 Speaker 2: It's easier for you to push it perpendicular because it's 623 00:30:57,040 --> 00:30:58,640 Speaker 2: not already moving at a high velocity. 624 00:30:58,800 --> 00:31:03,440 Speaker 1: Yeah, relativity velocity has this weird maximum. Right, nothing can 625 00:31:03,480 --> 00:31:06,360 Speaker 1: go faster than the speed of light relative to anything else. 626 00:31:07,000 --> 00:31:10,400 Speaker 1: And as you approach the speed of light relative to something, 627 00:31:10,640 --> 00:31:13,600 Speaker 1: you can pour additional energy into that object. You can 628 00:31:13,920 --> 00:31:16,880 Speaker 1: give it a push without increasing its velocity as much. 629 00:31:17,400 --> 00:31:19,880 Speaker 1: Like if I apply the same force to a potato 630 00:31:20,000 --> 00:31:23,280 Speaker 1: that said zero meters per second relative to me, it's 631 00:31:23,280 --> 00:31:25,280 Speaker 1: going to speed up. And if I apply that same 632 00:31:25,320 --> 00:31:27,480 Speaker 1: force to a potato that's already ninety nine point nine 633 00:31:27,480 --> 00:31:29,280 Speaker 1: to nine percent of the speed of light relative to me, 634 00:31:29,360 --> 00:31:31,160 Speaker 1: it's not going to speed up as much. It's just 635 00:31:31,240 --> 00:31:33,560 Speaker 1: like not room for it to speed up as much. 636 00:31:33,920 --> 00:31:36,000 Speaker 1: So I can pour energy into it without getting the 637 00:31:36,040 --> 00:31:37,320 Speaker 1: same velocity return. 638 00:31:37,600 --> 00:31:39,640 Speaker 2: Sure, but what was the perpendicular part? 639 00:31:39,960 --> 00:31:42,000 Speaker 1: So if you try to think of that as, oh, 640 00:31:42,040 --> 00:31:46,600 Speaker 1: the potato has additional mass, it's harder to accelerate because 641 00:31:46,600 --> 00:31:50,360 Speaker 1: it's more massive, then you might think initially, okay, that 642 00:31:50,400 --> 00:31:53,320 Speaker 1: makes sense. I can describe this as additional mass. It's 643 00:31:53,320 --> 00:31:56,560 Speaker 1: harder to accelerate the potato if it's always already going 644 00:31:56,600 --> 00:31:58,960 Speaker 1: really fast, so the same force doesn't give the same 645 00:31:59,000 --> 00:32:02,440 Speaker 1: increase in velocity. That kind of makes sense, right, except 646 00:32:02,440 --> 00:32:05,160 Speaker 1: that only makes sense in the direction the potato is going, 647 00:32:05,760 --> 00:32:08,800 Speaker 1: because the potato can have no velocity in other directions. Right, 648 00:32:09,000 --> 00:32:10,960 Speaker 1: so I'm free to apply a force to the potato 649 00:32:11,040 --> 00:32:13,080 Speaker 1: in another direction and I get the same boost as 650 00:32:13,120 --> 00:32:16,440 Speaker 1: I always did. And so now the potato has to 651 00:32:16,440 --> 00:32:19,320 Speaker 1: have like a mass in this direction because it's hard 652 00:32:19,320 --> 00:32:21,200 Speaker 1: to speed it up in that direction, and a mass 653 00:32:21,200 --> 00:32:23,800 Speaker 1: in other directions where it's easier to speed it up. 654 00:32:24,280 --> 00:32:28,600 Speaker 1: And so now mass has to have like directionality to it, right, 655 00:32:28,600 --> 00:32:32,000 Speaker 1: instead of just being like a property of the object. 656 00:32:31,760 --> 00:32:33,720 Speaker 2: I feel like I just felt the pieces click like 657 00:32:33,800 --> 00:32:35,600 Speaker 2: in my hand. There. Okay, let's keep going. 658 00:32:35,920 --> 00:32:38,040 Speaker 1: And so there is a way that could make sense 659 00:32:38,080 --> 00:32:41,400 Speaker 1: if you're willing to have mass be this weird directional thing. 660 00:32:41,840 --> 00:32:44,440 Speaker 1: But Einstein was like, Okay, actually, this doesn't make any sense, 661 00:32:44,560 --> 00:32:46,960 Speaker 1: and you don't need it because you already have a 662 00:32:47,040 --> 00:32:50,640 Speaker 1: concept of energy, the total energy. The object already captures 663 00:32:50,680 --> 00:32:53,920 Speaker 1: this behavior, So you don't need this new weird directional 664 00:32:54,000 --> 00:32:56,840 Speaker 1: relativistic mass. It doesn't give you anything, it doesn't help 665 00:32:56,880 --> 00:32:59,680 Speaker 1: you at all. Let that be part of energy. And 666 00:32:59,760 --> 00:33:02,960 Speaker 1: then Einstein and others decided, well, let's just keep mass 667 00:33:03,040 --> 00:33:06,000 Speaker 1: to be a number and it'll be the amount of 668 00:33:06,160 --> 00:33:09,240 Speaker 1: energy something has when it's at rest. So it's like 669 00:33:09,280 --> 00:33:11,760 Speaker 1: the rest energy of the object, and that makes it 670 00:33:11,840 --> 00:33:14,960 Speaker 1: invariant because you defined it to be the amount at rest. 671 00:33:15,720 --> 00:33:17,880 Speaker 1: And so this is what we call invariant mass, and 672 00:33:17,920 --> 00:33:20,840 Speaker 1: it means that energy is now nicely broken in two parts. 673 00:33:21,080 --> 00:33:22,840 Speaker 1: The energy you have a rest which you call the 674 00:33:22,880 --> 00:33:25,680 Speaker 1: invariant mass. So take for example, an electron. It has 675 00:33:25,680 --> 00:33:27,720 Speaker 1: a mass even if you're holding it in your hand, right, 676 00:33:27,960 --> 00:33:30,320 Speaker 1: that's what we call the invariant mass. That's the rest 677 00:33:30,560 --> 00:33:33,360 Speaker 1: mass of the object. And you can also have energy 678 00:33:33,400 --> 00:33:36,200 Speaker 1: if it's in motion, so that's its momentum. So energy 679 00:33:36,240 --> 00:33:39,479 Speaker 1: now has two components, the rest mass, the invariant mass, 680 00:33:39,880 --> 00:33:43,000 Speaker 1: and the motion part right, the energy of its motion. 681 00:33:43,560 --> 00:33:45,920 Speaker 1: So those are two separate things. And the invariant mass 682 00:33:45,960 --> 00:33:49,600 Speaker 1: by definition, doesn't grow with velocity because you measure it 683 00:33:49,640 --> 00:33:52,920 Speaker 1: when it's at rest. So you might think that's just 684 00:33:53,000 --> 00:33:57,320 Speaker 1: defining stuff, you're just defining it to be invariant trick. Yeah, yes, 685 00:33:57,400 --> 00:33:59,960 Speaker 1: that's true. We're defining it to be at rest. That's 686 00:34:00,120 --> 00:34:02,040 Speaker 1: really what mass is. And we're free to invent these 687 00:34:02,080 --> 00:34:04,040 Speaker 1: quantities to be useful and to make sense to us, 688 00:34:04,080 --> 00:34:05,760 Speaker 1: because hey, we're the audience of. 689 00:34:05,760 --> 00:34:08,760 Speaker 2: It, right, right, we're creating tools that help us with stuff, 690 00:34:08,760 --> 00:34:09,200 Speaker 2: so why not? 691 00:34:09,960 --> 00:34:12,800 Speaker 1: Yeah, And if you're following along, remember our original question 692 00:34:13,040 --> 00:34:16,399 Speaker 1: is does a potato turn into a black hole near 693 00:34:16,440 --> 00:34:19,040 Speaker 1: the speed of light? And our answer so far is, 694 00:34:19,480 --> 00:34:22,760 Speaker 1: let's be careful when we talk about energy of mass 695 00:34:22,800 --> 00:34:26,440 Speaker 1: and energy of momentum. Energy momentum is relative, energy of 696 00:34:26,520 --> 00:34:29,880 Speaker 1: mass is not. So listeners following along might be like, Okay, 697 00:34:29,960 --> 00:34:33,040 Speaker 1: Daniels told us about the definition of energy and how 698 00:34:33,040 --> 00:34:35,480 Speaker 1: it might be mass and how it might be menum. 699 00:34:35,680 --> 00:34:39,040 Speaker 1: But in general relativity, we know that curvature space depends 700 00:34:39,120 --> 00:34:42,040 Speaker 1: just on energy, right, It doesn't depend only on mass. 701 00:34:42,040 --> 00:34:44,640 Speaker 1: It depends on more complex notions of energy. Because like 702 00:34:44,880 --> 00:34:47,480 Speaker 1: photons can help bend space and they have no mass. 703 00:34:48,120 --> 00:34:52,759 Speaker 1: So why don't potatoes create enough curvature if they have 704 00:34:52,920 --> 00:34:56,160 Speaker 1: enough velocity, they have enough momentum, why can't that energy 705 00:34:56,200 --> 00:34:59,160 Speaker 1: density then create black holes? And I have two answers 706 00:34:59,160 --> 00:35:02,200 Speaker 1: to that. One is this is a really really complicated 707 00:35:02,280 --> 00:35:06,319 Speaker 1: calculation to do because in general relativity, it's not just 708 00:35:06,360 --> 00:35:08,800 Speaker 1: like a number. It's not like Newton's gravity where you 709 00:35:08,840 --> 00:35:12,520 Speaker 1: have mass and more mass means more gravity. Einstein's equations 710 00:35:12,560 --> 00:35:15,399 Speaker 1: are tensor equations, which means they're matrices. Is all sorts 711 00:35:15,440 --> 00:35:18,000 Speaker 1: of complicated stuff, and different kinds of energy enter in 712 00:35:18,040 --> 00:35:21,720 Speaker 1: different ways, So energy of mass enters differently from energy 713 00:35:21,719 --> 00:35:25,920 Speaker 1: of velocity, and so it's a really complicated calculation. And 714 00:35:26,000 --> 00:35:28,200 Speaker 1: we know that the answer has to be the same 715 00:35:28,760 --> 00:35:30,879 Speaker 1: for a potato at rest and a potato in motion 716 00:35:31,120 --> 00:35:34,480 Speaker 1: because black holes are not observer dependent. That's just like 717 00:35:34,520 --> 00:35:37,719 Speaker 1: a bedrock fact in general relativity. So instead of doing 718 00:35:37,719 --> 00:35:40,359 Speaker 1: a really complicated calculation where the potato is in motion, 719 00:35:40,920 --> 00:35:42,800 Speaker 1: we know we'll get the same answer when the potato 720 00:35:42,840 --> 00:35:45,360 Speaker 1: is at rest. And if the potato at rest doesn't 721 00:35:45,400 --> 00:35:47,520 Speaker 1: give you a black hole, then the potato at motion 722 00:35:47,760 --> 00:35:49,840 Speaker 1: can't give you a black hole, and it can't go 723 00:35:49,920 --> 00:35:52,560 Speaker 1: through all the complicated math here on the podcast. But 724 00:35:52,920 --> 00:35:55,239 Speaker 1: that's the sort of the end run around having to 725 00:35:55,280 --> 00:35:58,600 Speaker 1: do all that math. We know a potato turning into 726 00:35:58,640 --> 00:36:01,040 Speaker 1: a black hole if it's not already a black hole in. 727 00:36:01,000 --> 00:36:02,759 Speaker 2: Your kitchen, So I don't have to live in fear 728 00:36:02,840 --> 00:36:05,800 Speaker 2: of my potatoes. That is a relief. 729 00:36:07,000 --> 00:36:08,880 Speaker 1: Well, potatoes going to hurt you in lots of ways, 730 00:36:09,040 --> 00:36:10,640 Speaker 1: but they're not going to turn into black. 731 00:36:10,400 --> 00:36:13,680 Speaker 2: Holes, that's right, all right. So we have struck down 732 00:36:13,960 --> 00:36:18,000 Speaker 2: one misconception about potatoes and black holes, which I'm sure 733 00:36:18,040 --> 00:36:20,160 Speaker 2: everybody woke up this morning thinking that they'd hear about 734 00:36:20,160 --> 00:36:22,319 Speaker 2: potatoes and black holes. And when we get back, we're 735 00:36:22,320 --> 00:36:42,800 Speaker 2: going to ask do photons experience time? All right? Daniel? 736 00:36:43,760 --> 00:36:46,680 Speaker 2: You know I've often heard it said that light doesn't 737 00:36:46,680 --> 00:36:50,520 Speaker 2: experience time? Is that right? 738 00:36:53,120 --> 00:36:55,960 Speaker 1: Have you heard it said that photons experience our podcast 739 00:36:55,960 --> 00:36:58,080 Speaker 1: and enjoy it? Are they faithful listeners? 740 00:36:58,239 --> 00:37:02,840 Speaker 2: I mean, Daniel, how could they not everything from super 741 00:37:03,000 --> 00:37:06,680 Speaker 2: organisms down to the smallest particles enjoy dk EU. How 742 00:37:06,760 --> 00:37:07,200 Speaker 2: could they not? 743 00:37:07,440 --> 00:37:09,640 Speaker 1: Exactly? And we're so good looking, right, and what do 744 00:37:09,680 --> 00:37:11,680 Speaker 1: photons do if not appreciate our looks? 745 00:37:11,760 --> 00:37:11,960 Speaker 2: Right? 746 00:37:12,719 --> 00:37:13,000 Speaker 1: Yeah? 747 00:37:13,040 --> 00:37:16,719 Speaker 2: Sure, I think we're getting on something ic here. But 748 00:37:17,320 --> 00:37:18,479 Speaker 2: let's move forward, all. 749 00:37:18,400 --> 00:37:22,080 Speaker 1: Right before we undermine our credibility too far. Yes, this 750 00:37:22,120 --> 00:37:24,600 Speaker 1: is something you see in popular science all the time. 751 00:37:24,760 --> 00:37:28,839 Speaker 1: Photons fly through the universe not experiencing time. So let's 752 00:37:28,880 --> 00:37:31,839 Speaker 1: try and understand where this comes from, and then let's 753 00:37:31,840 --> 00:37:33,560 Speaker 1: talk about what we actually know about it. 754 00:37:33,640 --> 00:37:33,920 Speaker 3: All right? 755 00:37:33,920 --> 00:37:34,920 Speaker 2: Where does this come from? 756 00:37:35,080 --> 00:37:38,480 Speaker 1: So it's a not unreasonable extrapolation of what we know 757 00:37:38,520 --> 00:37:42,480 Speaker 1: about special relativity, we say that moving clocks run slow. 758 00:37:43,040 --> 00:37:45,640 Speaker 1: So I put Kelly and her potato on a spaceship 759 00:37:45,640 --> 00:37:49,200 Speaker 1: with a clock, and I tell them to accelerate. They're 760 00:37:49,200 --> 00:37:51,759 Speaker 1: going now near the speed of light relative to me. 761 00:37:52,360 --> 00:37:54,799 Speaker 1: I look at their clock through a telescope. I see 762 00:37:54,800 --> 00:37:57,399 Speaker 1: that it ticks more slowly than a clock sitting next 763 00:37:57,400 --> 00:37:59,879 Speaker 1: to me. So two clocks, one that has no volo 764 00:38:00,040 --> 00:38:03,080 Speaker 1: city relative to me, taking one second per second, and 765 00:38:03,200 --> 00:38:05,640 Speaker 1: Kelly's clock near the speed of light relative to me, 766 00:38:06,000 --> 00:38:09,480 Speaker 1: ticking at one second per year or something. And that's cool, 767 00:38:09,480 --> 00:38:12,000 Speaker 1: that's fascinating, that's amazing, right, whoop. 768 00:38:12,239 --> 00:38:14,200 Speaker 2: So I'll note if you have Kelly and a potato 769 00:38:14,239 --> 00:38:16,759 Speaker 2: pretty soon, and you're only going to have Kelly, but 770 00:38:16,960 --> 00:38:18,320 Speaker 2: are fascinating and amazing. 771 00:38:18,640 --> 00:38:20,920 Speaker 1: Yeah, And special relativity tells me how to calculate that. 772 00:38:21,000 --> 00:38:24,319 Speaker 1: It says, okay, Kelly's moving fast. I can calculate how 773 00:38:24,400 --> 00:38:27,480 Speaker 1: quickly her clock is ticking. And I can also go 774 00:38:27,520 --> 00:38:29,960 Speaker 1: to Kelly's reference frame. Because Kelly has a reference frame, 775 00:38:30,040 --> 00:38:32,160 Speaker 1: she has a potatoes, she's a clock. She is sitting 776 00:38:32,200 --> 00:38:35,000 Speaker 1: in her spaceship sipping her coffee. I can go from 777 00:38:35,000 --> 00:38:37,399 Speaker 1: her reference frame to my reference frame. And that's really 778 00:38:37,400 --> 00:38:40,200 Speaker 1: the core of special relativities. It tells you how to 779 00:38:40,200 --> 00:38:43,919 Speaker 1: translate from one reference frame to another. Right, I create mine. 780 00:38:43,960 --> 00:38:45,960 Speaker 1: We said there is no absolute space. But I can 781 00:38:46,000 --> 00:38:49,080 Speaker 1: create a reference frame and say, here's my origin. Here's 782 00:38:49,160 --> 00:38:52,480 Speaker 1: location equals zero, here's location equals one. I can measure 783 00:38:52,520 --> 00:38:55,640 Speaker 1: location and velocity relative to my reference frame. Like if 784 00:38:55,640 --> 00:38:58,279 Speaker 1: we spent a zillion dollars building your grid, that would 785 00:38:58,280 --> 00:39:01,880 Speaker 1: be Kelly's reference frame. Wouldn't be special or absolute in anyway, 786 00:39:01,880 --> 00:39:04,240 Speaker 1: but it'd be yours, and it'd be wonderful. I'm sure 787 00:39:07,000 --> 00:39:09,000 Speaker 1: it'd be special to me and special to you, but 788 00:39:09,080 --> 00:39:11,800 Speaker 1: not special to the universe, all right. They wouldn't change 789 00:39:11,800 --> 00:39:14,520 Speaker 1: the laws of physics in any way. And so I 790 00:39:14,560 --> 00:39:16,360 Speaker 1: have a reference frame, You have a reference frame, and 791 00:39:16,360 --> 00:39:19,680 Speaker 1: special relativity tells us how to transform between these different 792 00:39:19,719 --> 00:39:23,520 Speaker 1: reference frames. And special relativity tells us that as the 793 00:39:23,600 --> 00:39:26,879 Speaker 1: velocity of two reference frames grows to near the speed 794 00:39:26,920 --> 00:39:29,799 Speaker 1: of light, which is the maximum, the time that they 795 00:39:29,880 --> 00:39:32,719 Speaker 1: see each other's clocks ticking goes to zero. If you're 796 00:39:32,719 --> 00:39:34,680 Speaker 1: at ninety nine percent of the speed of light, I 797 00:39:34,680 --> 00:39:37,680 Speaker 1: see your clock ticking like one second per day. If 798 00:39:37,719 --> 00:39:39,759 Speaker 1: you go to ninety nine point ninety nine percent of it, 799 00:39:39,760 --> 00:39:41,839 Speaker 1: I see your clock ticking. It's one second per year. 800 00:39:42,320 --> 00:39:45,000 Speaker 1: If you go at ninety nine point nine and whatever 801 00:39:45,080 --> 00:39:47,000 Speaker 1: percent of the speed of light, maybe I see your 802 00:39:47,000 --> 00:39:51,120 Speaker 1: clock ticking one second every thousand years. So it's tempting 803 00:39:51,360 --> 00:39:53,680 Speaker 1: to extrapolate this and say, well, what happens if you 804 00:39:53,719 --> 00:39:55,919 Speaker 1: go at the speed of light? Do I see your 805 00:39:55,960 --> 00:39:59,800 Speaker 1: time as stopping. That's where this comes from because photons 806 00:39:59,800 --> 00:40:03,080 Speaker 1: we move at the speed of light, and so people imagine, oh, okay, 807 00:40:03,320 --> 00:40:06,120 Speaker 1: put a photon in a spaceship, take that spaceship to 808 00:40:06,160 --> 00:40:08,279 Speaker 1: the speed of light. If the photon has a little 809 00:40:08,280 --> 00:40:10,919 Speaker 1: clock next to it, what does that clock read? Well, 810 00:40:11,560 --> 00:40:13,919 Speaker 1: it's very tempting to say, at the speed of light, 811 00:40:14,120 --> 00:40:14,920 Speaker 1: time stops. 812 00:40:15,120 --> 00:40:16,960 Speaker 2: All right, so is this going to be a speed 813 00:40:17,000 --> 00:40:20,560 Speaker 2: of light relative to something? I'm not going to try 814 00:40:20,560 --> 00:40:22,400 Speaker 2: to jump the gun? What do we talk about next, Daniel. 815 00:40:23,800 --> 00:40:25,880 Speaker 1: So it's very fun to say that time stops with 816 00:40:25,960 --> 00:40:28,840 Speaker 1: that photon, but it's not really true because that photon 817 00:40:28,960 --> 00:40:30,319 Speaker 1: doesn't have a reference frame. 818 00:40:30,640 --> 00:40:31,840 Speaker 2: Well, that's what I was trying to get at. Y 819 00:40:31,920 --> 00:40:35,280 Speaker 2: I'm brilliant, all right, Sorry, go ahead, PhD In physics. 820 00:40:35,400 --> 00:40:38,160 Speaker 1: Yeah, because photons don't have a reference frame. Photons move 821 00:40:38,200 --> 00:40:40,200 Speaker 1: at the speed of light relative to every observer. So 822 00:40:40,280 --> 00:40:41,719 Speaker 1: I see the move at the speed of light. You 823 00:40:41,719 --> 00:40:43,319 Speaker 1: see the move at the speed of light. You have 824 00:40:43,360 --> 00:40:47,000 Speaker 1: this confusing scenario where you're in your spaceship moving really fast, 825 00:40:47,040 --> 00:40:49,759 Speaker 1: you turn on a flashlight. You see the photons moving 826 00:40:49,840 --> 00:40:52,279 Speaker 1: relative to you at the speed of light. I see 827 00:40:52,320 --> 00:40:55,040 Speaker 1: the photons moving relative to you at the speed of light, 828 00:40:55,080 --> 00:40:58,040 Speaker 1: even though I also see you moving at nine of 829 00:40:58,080 --> 00:41:00,759 Speaker 1: the speed of light. It's very confused. But the thing 830 00:41:00,760 --> 00:41:02,800 Speaker 1: about photons, the reason they move at the speed of 831 00:41:02,840 --> 00:41:05,080 Speaker 1: light relative to everybody, is that you can never catch them. 832 00:41:05,239 --> 00:41:07,239 Speaker 1: You can't like zoom up next to a photon and 833 00:41:07,239 --> 00:41:09,239 Speaker 1: say like, hey, look there's a photon the way you 834 00:41:09,280 --> 00:41:12,319 Speaker 1: can relative to a potato, for example, or relative to 835 00:41:12,480 --> 00:41:16,359 Speaker 1: Kelly's ship. This weird fact that two observers always see 836 00:41:16,440 --> 00:41:18,480 Speaker 1: light moving at the speed of light, even if they 837 00:41:18,520 --> 00:41:21,200 Speaker 1: have a high velocity relative to each other. This is 838 00:41:21,239 --> 00:41:24,799 Speaker 1: not like a little detail. It's the whole foundation of 839 00:41:24,840 --> 00:41:28,200 Speaker 1: special relativity. From this one fact and the assumption that 840 00:41:28,200 --> 00:41:30,439 Speaker 1: the laws of physics are the same everywhere, you can 841 00:41:30,520 --> 00:41:35,200 Speaker 1: derive all of special relativity, time dilation, length contraction, Lorentz 842 00:41:35,280 --> 00:41:39,160 Speaker 1: transformations all over. That depends on this Why is that 843 00:41:39,239 --> 00:41:41,759 Speaker 1: the case? Why is there a universe this way? Well, 844 00:41:41,880 --> 00:41:45,560 Speaker 1: we aren't actually sure, but it is an observed fact 845 00:41:45,800 --> 00:41:49,920 Speaker 1: we have verified with experiments, and everything flows from it, 846 00:41:50,160 --> 00:41:53,360 Speaker 1: and it has all of these weird consequences, including that 847 00:41:53,440 --> 00:41:55,799 Speaker 1: you can't catch up to a photon. You can't ever 848 00:41:55,960 --> 00:41:59,439 Speaker 1: join a photon in its reference frame and say, hey, 849 00:41:59,480 --> 00:42:01,719 Speaker 1: what's it like to be a photon? And that's kind 850 00:42:01,760 --> 00:42:04,879 Speaker 1: of the short answer is that photons have no reference frame, 851 00:42:04,960 --> 00:42:06,799 Speaker 1: and so it makes no sense to say, what does 852 00:42:06,800 --> 00:42:10,799 Speaker 1: a photon experience? Does a photon experience time? Photons don't 853 00:42:10,840 --> 00:42:13,719 Speaker 1: experience anything the way like lumps of coal don't have 854 00:42:13,760 --> 00:42:16,360 Speaker 1: political views. Right, It's sort of like a category error 855 00:42:16,560 --> 00:42:18,040 Speaker 1: to even ask the question. 856 00:42:18,239 --> 00:42:22,040 Speaker 2: Unfortunately, Okay, I'm taking a second to wrap my head 857 00:42:22,040 --> 00:42:26,160 Speaker 2: around the fact that photons have no reference frame because essentially, 858 00:42:26,239 --> 00:42:29,239 Speaker 2: for any reference frame you pick, they're always moving at 859 00:42:29,239 --> 00:42:29,799 Speaker 2: the speed a light. 860 00:42:30,360 --> 00:42:34,040 Speaker 1: Yes, exactly, And special relativity, this calculation on which this 861 00:42:34,080 --> 00:42:37,320 Speaker 1: whole idea is based, can only translate between reference frames. 862 00:42:37,400 --> 00:42:40,200 Speaker 1: It says, my potatoes reference frame, Kelly's reference frame, my 863 00:42:40,200 --> 00:42:42,799 Speaker 1: coffee is reference rame, my cats reference frame. I can 864 00:42:42,840 --> 00:42:44,719 Speaker 1: tell you how clocks in any of those reference frame 865 00:42:44,800 --> 00:42:47,920 Speaker 1: appear in my reference frame, or I can tell you 866 00:42:48,000 --> 00:42:51,520 Speaker 1: how my clocks appear in those reference frames. But photons 867 00:42:51,520 --> 00:42:55,520 Speaker 1: don't have a reference frame. There is no axis moving 868 00:42:55,600 --> 00:42:58,399 Speaker 1: with the photon where the photon is at rest. There's 869 00:42:58,480 --> 00:43:01,520 Speaker 1: no special set of buize for that photon that move 870 00:43:01,600 --> 00:43:04,759 Speaker 1: along with it where it has no velocity. Right, no 871 00:43:04,800 --> 00:43:07,200 Speaker 1: matter what set of booies you build, photons will always 872 00:43:07,200 --> 00:43:09,960 Speaker 1: be moving at the speed of light relative to those booies. 873 00:43:10,400 --> 00:43:12,400 Speaker 1: So there is no reference frame, so you can't use 874 00:43:12,440 --> 00:43:15,360 Speaker 1: special relativity to calculate what's it like to be a photon. 875 00:43:15,760 --> 00:43:19,200 Speaker 2: I think my brain feels like physics should be intuitive 876 00:43:19,320 --> 00:43:22,080 Speaker 2: because I exist in this universe and feel like I 877 00:43:22,160 --> 00:43:24,440 Speaker 2: understand it. But the more I talk to you, the 878 00:43:24,480 --> 00:43:27,000 Speaker 2: more I feel like it's not necessarily intuitive, which makes 879 00:43:27,000 --> 00:43:29,480 Speaker 2: it all the more amazing that we have figured it out. 880 00:43:29,920 --> 00:43:32,800 Speaker 2: And so I totally get why people jumped to photons 881 00:43:32,800 --> 00:43:36,080 Speaker 2: don't experience time, because intuitively, that does feel right to me. 882 00:43:36,239 --> 00:43:39,200 Speaker 2: I'll be sleeping tonight thinking about photons not having a 883 00:43:39,239 --> 00:43:42,239 Speaker 2: reference frame. Yeah, is this intuitive to you? Or is 884 00:43:42,280 --> 00:43:44,560 Speaker 2: this it makes sense now because you've been thinking about 885 00:43:44,600 --> 00:43:45,480 Speaker 2: it for so long. 886 00:43:45,360 --> 00:43:48,960 Speaker 1: It makes sense mathematically. Intuitively, it's always a struggle it 887 00:43:49,080 --> 00:43:51,560 Speaker 1: makes sense of the universe. The way I think about 888 00:43:51,560 --> 00:43:53,919 Speaker 1: it is that there's a very tempting intuitive path which 889 00:43:53,960 --> 00:43:57,279 Speaker 1: is wrong, which is to think about photons as the 890 00:43:57,360 --> 00:44:00,360 Speaker 1: extrapolation of what happens when you go really really fast, 891 00:44:00,800 --> 00:44:02,640 Speaker 1: because they're moving at the speed of light, and we 892 00:44:02,640 --> 00:44:04,759 Speaker 1: can go almost to the speed of light, and so 893 00:44:04,760 --> 00:44:07,279 Speaker 1: it seems like they're right there, like at the end 894 00:44:07,320 --> 00:44:10,080 Speaker 1: of that curve, right, But they're not. They're really in 895 00:44:10,120 --> 00:44:13,640 Speaker 1: a different category. So even though you might want to 896 00:44:13,719 --> 00:44:16,000 Speaker 1: organize them like at the end of that curve they're 897 00:44:16,239 --> 00:44:18,759 Speaker 1: similar to a spaceship moving really really fast, they're not. 898 00:44:18,800 --> 00:44:21,960 Speaker 1: They're really in a completely different regime because they have 899 00:44:22,080 --> 00:44:24,880 Speaker 1: no mass. Right, So you can't like build a clock 900 00:44:24,920 --> 00:44:27,280 Speaker 1: in this photons reference frame. You can't build a clock 901 00:44:27,360 --> 00:44:30,799 Speaker 1: out of pure photons. There's nothing it's like to be 902 00:44:31,000 --> 00:44:33,640 Speaker 1: a photon. It's really a completely different kind of object 903 00:44:33,680 --> 00:44:36,120 Speaker 1: than anything that does have mass. So think about two 904 00:44:36,160 --> 00:44:40,600 Speaker 1: different categories. Has mass, doesn't have mass. Special relativity can 905 00:44:40,640 --> 00:44:42,759 Speaker 1: tell you about the experience and how time clicks for 906 00:44:42,840 --> 00:44:46,319 Speaker 1: anything that has mass, anything that doesn't have mass. There's 907 00:44:46,320 --> 00:44:49,160 Speaker 1: no reference frame there. So special relativity has no handle 908 00:44:49,200 --> 00:44:51,319 Speaker 1: on it. It can't tell you at all what it's 909 00:44:51,360 --> 00:44:53,959 Speaker 1: like to be a photon. Does that mean photons don't 910 00:44:53,960 --> 00:44:57,160 Speaker 1: have an experience? You know, maybe alien philosophers when they 911 00:44:57,160 --> 00:44:58,960 Speaker 1: come and it tell us about how the universe works, 912 00:44:59,160 --> 00:45:01,400 Speaker 1: will have some way thinking about what it's like to 913 00:45:01,440 --> 00:45:04,040 Speaker 1: be a photon, you know, the way Thomas Nagel struggled 914 00:45:04,080 --> 00:45:06,480 Speaker 1: with what it's like to be a bat. So I 915 00:45:06,520 --> 00:45:08,719 Speaker 1: don't want to totally rule it out. And you know, 916 00:45:08,760 --> 00:45:11,399 Speaker 1: maybe there are crazy aliens out there whose minds are 917 00:45:11,440 --> 00:45:15,640 Speaker 1: just made out of photons somehow, or ripples and electromagnetism, 918 00:45:15,719 --> 00:45:17,719 Speaker 1: and so I don't want to piss them off either. 919 00:45:18,239 --> 00:45:19,880 Speaker 2: You're really hedging your bets here, Dan. 920 00:45:21,280 --> 00:45:21,480 Speaker 4: Hey. 921 00:45:21,520 --> 00:45:23,200 Speaker 1: You know, like at the beginning of the podcast, we've 922 00:45:23,200 --> 00:45:25,520 Speaker 1: got to be open minded, and we don't want to 923 00:45:25,640 --> 00:45:27,520 Speaker 1: be full of hubris and declare that we know everything 924 00:45:27,520 --> 00:45:30,319 Speaker 1: about the universe. So I think the crispest thing we 925 00:45:30,360 --> 00:45:33,960 Speaker 1: can say is that special relativity can't say anything about 926 00:45:33,960 --> 00:45:36,360 Speaker 1: what it's like to be a photon. It certainly doesn't 927 00:45:36,360 --> 00:45:40,480 Speaker 1: tell us that photons experience zero time. And you know 928 00:45:40,520 --> 00:45:43,319 Speaker 1: that already, because if you take that idea to its 929 00:45:43,360 --> 00:45:47,040 Speaker 1: logical conclusion, then there's all sorts of confusing contradictions. Like a 930 00:45:47,080 --> 00:45:50,800 Speaker 1: photon that's omitted instantly is across the universe, right like, 931 00:45:50,840 --> 00:45:52,719 Speaker 1: it doesn't that feel like it violates all sorts of 932 00:45:52,760 --> 00:45:56,640 Speaker 1: principles and transformation of information, and you get quickly into 933 00:45:56,680 --> 00:46:00,719 Speaker 1: paradoxes and confusions about causality. It really doesn't make sense 934 00:46:00,760 --> 00:46:02,920 Speaker 1: at all. And for those of you who are students 935 00:46:02,920 --> 00:46:06,759 Speaker 1: of special relativity, photons do take time to fly through 936 00:46:06,760 --> 00:46:08,759 Speaker 1: the universe. They have this thing called a space time 937 00:46:08,840 --> 00:46:12,000 Speaker 1: interval which is zero, which just means that they follow 938 00:46:12,040 --> 00:46:15,480 Speaker 1: the shortest path through space time, but they still take 939 00:46:15,600 --> 00:46:19,480 Speaker 1: time to move through space. And so, you know, special 940 00:46:19,480 --> 00:46:22,160 Speaker 1: relativity is our best description of how space works, and 941 00:46:22,160 --> 00:46:23,840 Speaker 1: it tells us a lot about the nature of space 942 00:46:23,960 --> 00:46:26,239 Speaker 1: and the nature of velocity and the nature of acceleration 943 00:46:26,440 --> 00:46:28,799 Speaker 1: even but it doesn't tell us what it's like to 944 00:46:28,800 --> 00:46:29,880 Speaker 1: be a photon. 945 00:46:29,640 --> 00:46:31,560 Speaker 2: Got it all right? Just like we'll never know what 946 00:46:31,640 --> 00:46:33,759 Speaker 2: the bees see with the colors that they can see 947 00:46:33,800 --> 00:46:36,000 Speaker 2: and we stand, we'll never know what it's like to 948 00:46:36,040 --> 00:46:37,640 Speaker 2: be a photon. I gotta be honest, I'm a little 949 00:46:37,680 --> 00:46:39,239 Speaker 2: sad that I'll never know what it's like to be 950 00:46:39,280 --> 00:46:41,080 Speaker 2: a bee, but I can live without knowing what it's 951 00:46:41,120 --> 00:46:43,120 Speaker 2: like to be a photon. But maybe this is a 952 00:46:43,120 --> 00:46:45,520 Speaker 2: fundamental difference between biologists and physicists. 953 00:46:45,760 --> 00:46:47,959 Speaker 1: But hey, if you're a photon and you've been listening 954 00:46:48,000 --> 00:46:50,680 Speaker 1: to this podcast and we offended you right in, tell 955 00:46:50,760 --> 00:46:53,080 Speaker 1: us what is it like to be a photon and 956 00:46:53,080 --> 00:46:56,080 Speaker 1: be pissed off at the podcast? I want to know. Also, 957 00:46:56,360 --> 00:46:58,600 Speaker 1: if you're a bee right in, because Kelly wants to hear. 958 00:46:58,480 --> 00:47:00,560 Speaker 2: From you, that's right, it will have you on the show. 959 00:47:01,800 --> 00:47:03,840 Speaker 1: And if you're not a photon and you're not a bee, 960 00:47:03,880 --> 00:47:06,040 Speaker 1: and you're somehow a human listening to this podcast, we 961 00:47:06,080 --> 00:47:08,439 Speaker 1: still want to hear from you. Did this make sense 962 00:47:08,480 --> 00:47:10,960 Speaker 1: to you? Did this help you understand why potatoes are 963 00:47:10,960 --> 00:47:12,880 Speaker 1: not black holes? And what it's like to be a photon? 964 00:47:13,160 --> 00:47:15,879 Speaker 1: Did we just confuse you? Send us some feedback, Send 965 00:47:15,960 --> 00:47:18,400 Speaker 1: us some love, send us some grumpy emails. Whatever. We 966 00:47:18,520 --> 00:47:21,480 Speaker 1: love to hear from you. Write to us to Danielankelly 967 00:47:21,640 --> 00:47:24,800 Speaker 1: dot org. Don't send hard physics questions to Daniel and 968 00:47:24,840 --> 00:47:27,040 Speaker 1: Kelly dot com. I don't think they know the answers. 969 00:47:27,160 --> 00:47:28,759 Speaker 2: They might just might not appreciate it. You know, a 970 00:47:28,760 --> 00:47:30,480 Speaker 2: lot of work was at the planning a wedding. They're 971 00:47:30,560 --> 00:47:31,280 Speaker 2: very busy people. 972 00:47:31,600 --> 00:47:34,440 Speaker 1: That's right, Yeah, exactly. They got a full spreadsheet. They 973 00:47:34,440 --> 00:47:36,919 Speaker 1: don't need your question on top of the to do list. 974 00:47:37,200 --> 00:47:39,359 Speaker 2: Good luck, Daniel and Kelly. 975 00:47:39,400 --> 00:47:40,400 Speaker 1: Congratulations. 976 00:47:47,280 --> 00:47:51,080 Speaker 2: Daniel and Kelly's Extraordinary Universe is produced by Iheartreading. We 977 00:47:51,120 --> 00:47:53,560 Speaker 2: would love to hear from you, We really would. 978 00:47:53,719 --> 00:47:56,480 Speaker 1: We want to know what questions you have about this 979 00:47:56,680 --> 00:47:58,360 Speaker 1: Extraordinary Universe. 980 00:47:58,440 --> 00:48:01,440 Speaker 2: I want to know your thoughts on research shows, suggestions 981 00:48:01,440 --> 00:48:04,439 Speaker 2: for future shows. If you contact us, we will get 982 00:48:04,480 --> 00:48:04,880 Speaker 2: back to you. 983 00:48:05,120 --> 00:48:08,600 Speaker 1: We really mean it. We answer every message. Email us 984 00:48:08,640 --> 00:48:11,520 Speaker 1: at questions at Danielankelly dot org. 985 00:48:11,719 --> 00:48:13,840 Speaker 2: You can find us on social media. We have accounts 986 00:48:13,920 --> 00:48:17,840 Speaker 2: on x, Instagram, Blue Sky and on all of those platforms. 987 00:48:17,920 --> 00:48:20,840 Speaker 2: You can find us at D and K Universe. 988 00:48:21,000 --> 00:48:22,520 Speaker 1: Op chaye right to us