1 00:00:08,480 --> 00:00:11,840 Speaker 1: Hey, Daniel, has particle physics done anything useful lately? 2 00:00:12,039 --> 00:00:15,880 Speaker 2: M you mean other than revealing the fundamental nature of reality? 3 00:00:16,040 --> 00:00:16,599 Speaker 1: Have you done that? 4 00:00:17,760 --> 00:00:18,919 Speaker 2: I mean it's a project. 5 00:00:21,400 --> 00:00:23,880 Speaker 1: I mean that's all nice and cool, but it doesn't 6 00:00:23,920 --> 00:00:26,640 Speaker 1: really help me, you know, with the dishes or you know, 7 00:00:26,880 --> 00:00:27,520 Speaker 1: with my diet. 8 00:00:27,600 --> 00:00:29,840 Speaker 2: I guess we did also invent the World Wide Web. 9 00:00:29,880 --> 00:00:30,720 Speaker 2: That's pretty helpful. 10 00:00:31,000 --> 00:00:34,879 Speaker 1: You mean web surfing. I would say that's not the 11 00:00:34,880 --> 00:00:36,479 Speaker 1: most helpful thing in my life, but that was a 12 00:00:36,479 --> 00:00:39,040 Speaker 1: long time ago. Anyways, what have you done for us recently? 13 00:00:39,159 --> 00:00:40,919 Speaker 2: Yeah, maybe we should be coming up with like a 14 00:00:41,040 --> 00:00:42,720 Speaker 2: fundamental physics diet plan. 15 00:00:43,680 --> 00:00:46,760 Speaker 1: It's just coffee and doughnuts all. 16 00:00:46,680 --> 00:00:50,519 Speaker 2: The time, existential angst about the nature of the universe. 17 00:00:50,600 --> 00:00:52,640 Speaker 1: I guess the problem with physics is that it says 18 00:00:52,640 --> 00:00:55,279 Speaker 1: that the faster you go, the more massive you get. Right, 19 00:00:55,360 --> 00:00:57,040 Speaker 1: that's kind of an anti diet. 20 00:00:57,120 --> 00:00:59,320 Speaker 2: I guess I was thinking, you know, black holes something 21 00:00:59,360 --> 00:01:01,960 Speaker 2: something something liposuction, black holes. I don't know. I didn't 22 00:01:01,960 --> 00:01:02,760 Speaker 2: really have it worked out. 23 00:01:03,520 --> 00:01:05,479 Speaker 1: Quantum cosmetic surgery. 24 00:01:05,600 --> 00:01:08,399 Speaker 2: Whoa, Orange County is definitely the place for. 25 00:01:08,360 --> 00:01:15,240 Speaker 1: That, and you can get a ten to the color bage. 26 00:01:26,400 --> 00:01:29,360 Speaker 1: Hi am jorhammy cartoonist and the creator of PhD comics. 27 00:01:29,640 --> 00:01:32,320 Speaker 2: Hi. I'm Daniel. I'm a particle physicist and a professor 28 00:01:32,400 --> 00:01:36,000 Speaker 2: at UC Irvine, and I was shocked when a pediatrician 29 00:01:36,120 --> 00:01:38,399 Speaker 2: offered my one year old plastic surgery. 30 00:01:38,600 --> 00:01:41,520 Speaker 1: Wait what they do that on one year. 31 00:01:41,400 --> 00:01:44,720 Speaker 2: Old in Orange County? You're never too young for plastic surgery. 32 00:01:45,080 --> 00:01:48,160 Speaker 1: Oh boy. I get to the offer like a subscription service, 33 00:01:49,520 --> 00:01:51,560 Speaker 1: like a membership or something. 34 00:01:51,840 --> 00:01:54,240 Speaker 2: It's a long term relationship. No. Our son had like 35 00:01:54,280 --> 00:01:56,680 Speaker 2: a vein on his eyelid and the doctor was like, 36 00:01:56,680 --> 00:01:57,880 Speaker 2: do you want me to remove that? 37 00:01:58,200 --> 00:02:02,840 Speaker 1: And we were like, no, please, wait the eyelid or 38 00:02:02,880 --> 00:02:06,400 Speaker 1: the vein. You're like, I think my son needs. It's 39 00:02:06,480 --> 00:02:07,640 Speaker 1: his eyelid exactly. 40 00:02:08,760 --> 00:02:10,720 Speaker 2: We were like, I'm pretty sure that's going to be fine, 41 00:02:11,000 --> 00:02:12,720 Speaker 2: And newsflash, he's fine. 42 00:02:12,880 --> 00:02:14,680 Speaker 1: Where You're like, I'm a real doctor, I don't think 43 00:02:14,680 --> 00:02:15,680 Speaker 1: he meets any surgery. 44 00:02:17,520 --> 00:02:19,239 Speaker 2: I'm not a real doctor, but I'm pretty sure he 45 00:02:19,320 --> 00:02:21,520 Speaker 2: didn't need any surgery. 46 00:02:22,080 --> 00:02:23,840 Speaker 1: Like, I'm not a real doctor, I just play one 47 00:02:23,880 --> 00:02:26,560 Speaker 1: in the lab. But anyways, welcome to our podcast. Daniel 48 00:02:26,560 --> 00:02:30,200 Speaker 1: and Jorge Explain the Universe, a production of iHeartRadio. 49 00:02:29,560 --> 00:02:31,600 Speaker 2: In which we try to show you the nature of 50 00:02:31,639 --> 00:02:35,040 Speaker 2: the universe in all of its unvarnished glory. We don't 51 00:02:35,040 --> 00:02:37,880 Speaker 2: want to edit out the ugly bits and smooth over 52 00:02:37,919 --> 00:02:39,880 Speaker 2: the bumps and wrinkles. We want to show you the 53 00:02:40,000 --> 00:02:43,240 Speaker 2: universe the way it actually is, even when it conflicts 54 00:02:43,320 --> 00:02:46,680 Speaker 2: with our intuition and runs aground for our preconceived ideas 55 00:02:46,720 --> 00:02:50,160 Speaker 2: for how things move and flow and dance in the universe. 56 00:02:50,480 --> 00:02:52,520 Speaker 1: That's right, that's because we love the universe just the 57 00:02:52,560 --> 00:02:55,760 Speaker 1: way it is. We love the og universe, the original 58 00:02:55,919 --> 00:03:01,240 Speaker 1: organic version of the universe, untreated, unvarnished, and pretty mysterious. 59 00:03:02,880 --> 00:03:05,960 Speaker 2: That's right. We prefer the granola crunchy Berkeley version, with 60 00:03:06,120 --> 00:03:08,360 Speaker 2: all of its hair and all the original places, even 61 00:03:08,360 --> 00:03:09,560 Speaker 2: on all of its black holes. 62 00:03:09,880 --> 00:03:12,960 Speaker 1: Well, let's not go too far there. I mean, I'm 63 00:03:12,960 --> 00:03:15,000 Speaker 1: a big fan of socks and sandals, but you know, 64 00:03:15,200 --> 00:03:16,200 Speaker 1: there's a time and a place. 65 00:03:16,280 --> 00:03:19,160 Speaker 2: I'm all for accepting people and universes just the way 66 00:03:19,200 --> 00:03:19,600 Speaker 2: they are. 67 00:03:19,720 --> 00:03:22,360 Speaker 1: But it is a wonderful and beautiful universe. It doesn't 68 00:03:22,400 --> 00:03:24,520 Speaker 1: need any cosmic surgery because when we look at it, 69 00:03:24,600 --> 00:03:28,040 Speaker 1: we're just stricken with awe an amazement at how wonderfully 70 00:03:28,280 --> 00:03:30,760 Speaker 1: complex and intriguing it all is. 71 00:03:30,919 --> 00:03:33,280 Speaker 2: And one of my favorite things about the universe is 72 00:03:33,320 --> 00:03:36,400 Speaker 2: that it's surprising. It's not like we look out into 73 00:03:36,440 --> 00:03:38,560 Speaker 2: the universe and we're like, oh, yeah, that's pretty much 74 00:03:38,560 --> 00:03:40,960 Speaker 2: how I expected, or oh yeah, there's nothing new out 75 00:03:41,000 --> 00:03:44,280 Speaker 2: there to discover. Every time we dig deep into something, 76 00:03:44,560 --> 00:03:47,320 Speaker 2: every time we scratch under the surface, we find out, Wow, 77 00:03:47,400 --> 00:03:49,840 Speaker 2: the universe is quite different from the way that we 78 00:03:49,960 --> 00:03:52,720 Speaker 2: imagined it, which is wonderful because it's an opportunity to 79 00:03:52,840 --> 00:03:56,120 Speaker 2: learn to discover the truth instead of just coasting on 80 00:03:56,280 --> 00:03:57,040 Speaker 2: our intuition. 81 00:03:57,440 --> 00:04:00,240 Speaker 1: Yeah, the universe is very different out there in space, 82 00:04:00,480 --> 00:04:04,000 Speaker 1: beyond our galaxy, beyond our cluster of galaxies, and it's 83 00:04:04,040 --> 00:04:07,960 Speaker 1: also very different at the molecular and atomic and particle scills. 84 00:04:08,000 --> 00:04:11,640 Speaker 1: Things are actually very different than our everyday experience. 85 00:04:11,840 --> 00:04:14,880 Speaker 2: And we're tempted when we discover these new weird wrinkles 86 00:04:14,880 --> 00:04:17,359 Speaker 2: in the universe to explain them in terms of things 87 00:04:17,360 --> 00:04:19,960 Speaker 2: that we know, things we understand. It's a very natural 88 00:04:20,000 --> 00:04:22,240 Speaker 2: a way to try to understand the universe, to describe 89 00:04:22,279 --> 00:04:25,800 Speaker 2: it in terms of the language that you already have. Sometimes, though, 90 00:04:25,800 --> 00:04:29,120 Speaker 2: that gets awkward. It's hard to understand how quantum particles 91 00:04:29,200 --> 00:04:31,719 Speaker 2: dance around if you're thinking about them as little dots 92 00:04:31,720 --> 00:04:34,159 Speaker 2: of stuff, And that's because they're not really little dots 93 00:04:34,160 --> 00:04:36,960 Speaker 2: of stuff. And it's hard to think about velocity and 94 00:04:37,080 --> 00:04:39,400 Speaker 2: energy and mass as things approach the speed of life 95 00:04:39,440 --> 00:04:42,400 Speaker 2: because the definitions of those things have to change, and 96 00:04:42,440 --> 00:04:44,440 Speaker 2: the way things move and bounce against each other and 97 00:04:44,480 --> 00:04:47,680 Speaker 2: transfer energy and momentum is really very different at high 98 00:04:47,720 --> 00:04:50,800 Speaker 2: speeds than it is down here in the slow motion 99 00:04:50,960 --> 00:04:51,719 Speaker 2: life on Earth. 100 00:04:51,960 --> 00:04:54,600 Speaker 1: Yeah, things are very weird and awkward in general when 101 00:04:54,600 --> 00:04:56,560 Speaker 1: you talk to physicists, I feel, not just when you 102 00:04:56,680 --> 00:04:58,599 Speaker 1: learn learn what they have to say. 103 00:04:58,680 --> 00:05:00,560 Speaker 2: All right, this is not a therapy podcast. We're talking 104 00:05:00,600 --> 00:05:01,880 Speaker 2: about the nature of the universe here. 105 00:05:02,040 --> 00:05:04,120 Speaker 1: That's right. That's right. In the universe is not awkward 106 00:05:04,200 --> 00:05:05,599 Speaker 1: or weird. It's just the way it is. And I 107 00:05:05,600 --> 00:05:08,080 Speaker 1: guess it's us that are weird and awkward, right, because 108 00:05:08,160 --> 00:05:10,440 Speaker 1: we have this picture of how the world works, but 109 00:05:10,480 --> 00:05:12,479 Speaker 1: that may not be how the universe actually works. 110 00:05:12,640 --> 00:05:14,800 Speaker 2: Yeah, And in physics, our project is to build a 111 00:05:14,800 --> 00:05:18,159 Speaker 2: mathematical description of how things work in the universe, something 112 00:05:18,200 --> 00:05:20,480 Speaker 2: that lets us make predictions and gives us a peek 113 00:05:20,480 --> 00:05:23,039 Speaker 2: at the machinery behind the curtains that's deciding like what 114 00:05:23,160 --> 00:05:25,919 Speaker 2: happens when two balls bounce against each other. But that 115 00:05:25,960 --> 00:05:29,919 Speaker 2: doesn't always translate in an easy or simple way to English, 116 00:05:29,960 --> 00:05:33,080 Speaker 2: the language that most humans speak. So when physicists are 117 00:05:33,120 --> 00:05:36,440 Speaker 2: trying to explain how things work when the universe gets weird, 118 00:05:36,800 --> 00:05:40,080 Speaker 2: they use the terms that we're familiar with, mass and energy, momentum, 119 00:05:40,080 --> 00:05:43,040 Speaker 2: et cetera, and try to translate the weirdness in those terms. 120 00:05:43,160 --> 00:05:45,280 Speaker 2: And so you hear a lot of explanations for what 121 00:05:45,360 --> 00:05:48,320 Speaker 2: happens when things get fast. Some of those explanations are 122 00:05:48,360 --> 00:05:50,880 Speaker 2: bang on, and some of them are a little bit misleading. 123 00:05:51,120 --> 00:05:53,880 Speaker 1: Yeah, because I guess one of the biggest mind bending 124 00:05:53,920 --> 00:05:56,400 Speaker 1: moments and autism and strangest moments in the history of 125 00:05:56,440 --> 00:05:58,600 Speaker 1: science was when we found out that the universe is 126 00:05:58,680 --> 00:06:02,000 Speaker 1: kind of difference once you start are moving really fast exactly. 127 00:06:02,000 --> 00:06:05,320 Speaker 2: We've had Newtonian and Gallean mechanics for centuries, things that 128 00:06:05,360 --> 00:06:07,640 Speaker 2: did a very good job of explaining what happens when 129 00:06:07,640 --> 00:06:10,839 Speaker 2: two balls bounce against each other, and how momentum is transferred, 130 00:06:10,839 --> 00:06:13,520 Speaker 2: and how things look when you're going fast. If you're 131 00:06:13,600 --> 00:06:15,479 Speaker 2: driving in a car at thirty miles an hour, and 132 00:06:15,520 --> 00:06:17,440 Speaker 2: you throw a ball at thirty miles an hour, then 133 00:06:17,480 --> 00:06:19,440 Speaker 2: you know that ball should be moving at sixty miles 134 00:06:19,480 --> 00:06:21,760 Speaker 2: an hour relative to the ground. All that stuff made 135 00:06:21,800 --> 00:06:24,200 Speaker 2: sense for a long time until we started looking at 136 00:06:24,240 --> 00:06:26,920 Speaker 2: things that weren't moving really really fast. We discovered there's 137 00:06:26,960 --> 00:06:29,360 Speaker 2: a speed limit to the universe, and that really changed 138 00:06:29,440 --> 00:06:32,880 Speaker 2: everything we thought about the nature of space and time 139 00:06:33,080 --> 00:06:35,520 Speaker 2: and velocity and gives rise to all sorts of weird 140 00:06:35,520 --> 00:06:37,400 Speaker 2: stuff that's very tricky to unpack. 141 00:06:37,520 --> 00:06:40,080 Speaker 1: Yeah, it gets super tricky. Well, first of all, the 142 00:06:40,160 --> 00:06:42,120 Speaker 1: idea that we have a speed limit in the universe 143 00:06:42,200 --> 00:06:44,159 Speaker 1: is kind of wild. Like, you know, you sort of 144 00:06:44,160 --> 00:06:46,520 Speaker 1: grew up thinking that disguise the limit. The more that 145 00:06:46,560 --> 00:06:48,560 Speaker 1: you push something, the faster you go. But at some 146 00:06:48,600 --> 00:06:51,960 Speaker 1: point the universe says, I think that's fast enough. It 147 00:06:51,960 --> 00:06:53,919 Speaker 1: doesn't let you go faster than a certain speed. 148 00:06:54,160 --> 00:06:56,800 Speaker 2: Yeah, it's a really bizarre feature of our universe, one 149 00:06:56,839 --> 00:07:00,680 Speaker 2: that we've discovered experimentally at the Michaelson Morley. The experiments 150 00:07:00,720 --> 00:07:03,679 Speaker 2: prove that light travels the same speed in every direction 151 00:07:04,040 --> 00:07:06,799 Speaker 2: and effectively demonstrating that there is no absolute reference, framing 152 00:07:06,800 --> 00:07:10,120 Speaker 2: that there is a maximum speed of information and transmission 153 00:07:10,280 --> 00:07:14,320 Speaker 2: in the universe, which leads to all sorts of weird consequences, 154 00:07:14,600 --> 00:07:17,640 Speaker 2: changes what we think about time and the nature of simultaneity. 155 00:07:18,200 --> 00:07:20,560 Speaker 2: Things that happen at the same time for one person 156 00:07:20,760 --> 00:07:23,480 Speaker 2: might happen in a different order for somebody else. The 157 00:07:23,480 --> 00:07:26,080 Speaker 2: whole nature of reality becomes different when there is a 158 00:07:26,120 --> 00:07:28,120 Speaker 2: maximum speed limit to the universe. 159 00:07:28,520 --> 00:07:30,680 Speaker 1: Yeah, and I think it kind of makes people wonder 160 00:07:30,880 --> 00:07:32,840 Speaker 1: what would happen if you try to go faster than 161 00:07:32,880 --> 00:07:34,920 Speaker 1: the speed of light? Does the universe police come and 162 00:07:35,080 --> 00:07:38,040 Speaker 1: flag you down and stop you? Or do you hit 163 00:07:38,080 --> 00:07:38,480 Speaker 1: a wall? 164 00:07:38,760 --> 00:07:40,600 Speaker 2: Or what are you considering trying to break some laws 165 00:07:40,640 --> 00:07:42,720 Speaker 2: of the universe? Be asking for physics legal advice? 166 00:07:43,160 --> 00:07:44,960 Speaker 1: Well, I'm trying to toe the line, you know. I'm 167 00:07:45,000 --> 00:07:47,560 Speaker 1: kind of max out my life here. I need to 168 00:07:47,600 --> 00:07:48,480 Speaker 1: know how far I can go. 169 00:07:50,200 --> 00:07:51,760 Speaker 2: I just don't want to be held responsible if you 170 00:07:51,760 --> 00:07:52,760 Speaker 2: get thrown in physics. 171 00:07:52,560 --> 00:07:54,120 Speaker 1: Jail when I need a physics lawyer. 172 00:07:54,480 --> 00:07:56,480 Speaker 2: I wonder if people who are lawyers are always on 173 00:07:56,560 --> 00:07:58,240 Speaker 2: the look at for like, is this person asking me 174 00:07:58,320 --> 00:08:00,000 Speaker 2: legal advice? I'm not going to get them in trouble 175 00:08:00,080 --> 00:08:01,720 Speaker 2: if I say the wrong thing. I don't usually have 176 00:08:01,720 --> 00:08:03,920 Speaker 2: to worry about that because most people aren't capable of 177 00:08:04,000 --> 00:08:05,320 Speaker 2: trying to break the laws of the universe. 178 00:08:05,440 --> 00:08:08,400 Speaker 1: I think most lawyers don't really care that much. 179 00:08:10,600 --> 00:08:12,520 Speaker 2: But no, there is no physics police that are just 180 00:08:12,560 --> 00:08:15,080 Speaker 2: going to pull you over. It's just that acceleration and 181 00:08:15,160 --> 00:08:18,600 Speaker 2: momentums start working differently at high speeds. So you discover 182 00:08:18,840 --> 00:08:21,080 Speaker 2: that you can pour energy into a particle, it just 183 00:08:21,160 --> 00:08:23,840 Speaker 2: doesn't go much faster. So you can discover that as 184 00:08:23,880 --> 00:08:25,680 Speaker 2: things approach the speed of light, you can keep pouring 185 00:08:25,840 --> 00:08:28,840 Speaker 2: energy into something a rock, a particle of spaceship, whatever, 186 00:08:28,920 --> 00:08:31,840 Speaker 2: it just doesn't go much faster. The same amount of 187 00:08:31,920 --> 00:08:35,320 Speaker 2: energy doesn't get you increases in velocity the same rate. 188 00:08:35,559 --> 00:08:38,280 Speaker 2: It's no longer linear. It becomes asymptotic. 189 00:08:38,480 --> 00:08:45,760 Speaker 1: So today end podcast, we'll be tackling the question do 190 00:08:45,880 --> 00:08:49,640 Speaker 1: things get more massive the faster they move? This is 191 00:08:49,720 --> 00:08:52,320 Speaker 1: kind of like the anti diet, or at least I 192 00:08:52,320 --> 00:08:54,839 Speaker 1: feel like it justifies maybe sitting down on your couch 193 00:08:55,000 --> 00:08:57,280 Speaker 1: all the time, because if I get up up for 194 00:08:57,360 --> 00:08:58,880 Speaker 1: my couch and I move, then I'm just going to 195 00:08:58,920 --> 00:09:01,200 Speaker 1: gain more mass, Right, that's true. 196 00:09:01,280 --> 00:09:02,880 Speaker 2: Well, what we're going to learn on the podcast today 197 00:09:02,920 --> 00:09:05,040 Speaker 2: is that it's a little bit more complicated than that 198 00:09:05,160 --> 00:09:07,520 Speaker 2: this is the kind of popular science thing you hear 199 00:09:07,640 --> 00:09:10,480 Speaker 2: all the time and people write in and ask me about. 200 00:09:10,520 --> 00:09:12,319 Speaker 2: And I think it was wide they taught in textbooks 201 00:09:12,360 --> 00:09:15,160 Speaker 2: until about thirty forty years ago, the feeling that everything 202 00:09:15,160 --> 00:09:17,400 Speaker 2: gets weird as you approach the speed of light, and 203 00:09:17,440 --> 00:09:20,080 Speaker 2: then even your mass might change, things might get like 204 00:09:20,160 --> 00:09:23,280 Speaker 2: infinitely heavy as you approach the speed of light. It's 205 00:09:23,280 --> 00:09:26,040 Speaker 2: an attractive concept for people, I think, because it gives 206 00:09:26,080 --> 00:09:28,520 Speaker 2: you a sense of the strange. But as we'll talk 207 00:09:28,559 --> 00:09:30,480 Speaker 2: about today on the podcast, it's a little bit more 208 00:09:30,520 --> 00:09:33,280 Speaker 2: complicated than that, and it's actually something of an outdated notion. 209 00:09:33,400 --> 00:09:37,480 Speaker 1: Wait, wait, are you saying it's a massive lie. 210 00:09:38,520 --> 00:09:39,959 Speaker 2: You know, there's a lot of different ways you can 211 00:09:39,960 --> 00:09:44,000 Speaker 2: try to translate the crisp mathematics of relativity into English 212 00:09:44,040 --> 00:09:47,400 Speaker 2: and into popular culture. This was one attempt early on 213 00:09:47,480 --> 00:09:49,080 Speaker 2: that I don't think really works very well. 214 00:09:49,800 --> 00:09:52,720 Speaker 1: I see it was just heavily exaggerated. Well, as usual, 215 00:09:52,760 --> 00:09:54,960 Speaker 1: you were wondering how many people had wondered about this 216 00:09:55,120 --> 00:09:58,040 Speaker 1: question at ask this about themselves, about the universe, about 217 00:09:58,080 --> 00:09:59,880 Speaker 1: what happens when you try to go faster and faster, 218 00:10:00,080 --> 00:10:02,080 Speaker 1: And so Daniel went out there into the Internet to 219 00:10:02,120 --> 00:10:05,400 Speaker 1: ask people do you think things get more massive as 220 00:10:05,440 --> 00:10:06,960 Speaker 1: you approach the speed of light? 221 00:10:07,320 --> 00:10:10,360 Speaker 2: I am so grateful to everybody who answers these questions. 222 00:10:10,360 --> 00:10:12,560 Speaker 2: They give me a sense for what people already know, 223 00:10:12,640 --> 00:10:15,280 Speaker 2: and they give listeners a sense of what everybody else 224 00:10:15,400 --> 00:10:18,360 Speaker 2: is thinking. If you would like to participate, please don't 225 00:10:18,400 --> 00:10:20,880 Speaker 2: be shy. You're really very welcome to join the club. 226 00:10:21,360 --> 00:10:24,760 Speaker 2: Just write to me two questions at Danielandjorge dot com. 227 00:10:24,840 --> 00:10:26,800 Speaker 1: So think about it for a second. Do you think 228 00:10:27,120 --> 00:10:28,679 Speaker 1: you should stay in your couch if you don't want 229 00:10:28,720 --> 00:10:31,200 Speaker 1: to gain any mess? Here's what people had to say. 230 00:10:31,400 --> 00:10:35,080 Speaker 3: This question just blows my mind. I'm just stumped. Do 231 00:10:35,200 --> 00:10:39,160 Speaker 3: they get more massive? I guess maybe. I don't know how, 232 00:10:39,280 --> 00:10:41,760 Speaker 3: but maybe something related to quantum mechanics. 233 00:10:41,760 --> 00:10:42,120 Speaker 4: I don't know. 234 00:10:42,280 --> 00:10:44,880 Speaker 2: As you approached the speed of light, I thought Einstein's 235 00:10:44,880 --> 00:10:48,840 Speaker 2: equations told us that you would gain mess, But to 236 00:10:48,840 --> 00:10:51,880 Speaker 2: an outside observer, I don't think you would actually look bigger. 237 00:10:52,040 --> 00:10:53,960 Speaker 5: I mean, at the speed of lighte time was slower. 238 00:10:54,480 --> 00:10:57,720 Speaker 5: Maybe space gets contracted. 239 00:10:57,880 --> 00:11:00,760 Speaker 2: So I'm kind of stormy here. 240 00:11:01,240 --> 00:11:03,920 Speaker 5: Maybe if that is true, then you will have a 241 00:11:04,000 --> 00:11:07,319 Speaker 5: higher density and in that sense, wibly be more massive. 242 00:11:07,600 --> 00:11:08,079 Speaker 2: Not sure. 243 00:11:08,280 --> 00:11:12,360 Speaker 6: I think they do get more massive, but because it's 244 00:11:12,640 --> 00:11:16,520 Speaker 6: it gets harder to move things at that speed, and 245 00:11:16,559 --> 00:11:18,840 Speaker 6: not because they get more the feet. 246 00:11:18,960 --> 00:11:22,760 Speaker 7: My understanding is mass and energy are interchangeable, so the 247 00:11:22,800 --> 00:11:26,800 Speaker 7: more energy you have to pump into something to accelerate 248 00:11:26,840 --> 00:11:29,520 Speaker 7: it closer and closer to the speed of light is 249 00:11:29,559 --> 00:11:32,920 Speaker 7: really no different than making it more massive to begin with. 250 00:11:33,080 --> 00:11:36,880 Speaker 7: So I think, yes, it gets more massive as you 251 00:11:36,920 --> 00:11:39,600 Speaker 7: approach the speed of light, just because mass and energy 252 00:11:39,640 --> 00:11:41,439 Speaker 7: are essentially the same thing. 253 00:11:41,920 --> 00:11:44,000 Speaker 4: I think I remember hearing that they do get more 254 00:11:44,000 --> 00:11:47,280 Speaker 4: massive as they approach the speed of light. I think 255 00:11:47,280 --> 00:11:50,560 Speaker 4: it takes more energy to increase the speed, and like, yeah, 256 00:11:50,800 --> 00:11:53,280 Speaker 4: they just can't really get to the speed of light 257 00:11:54,080 --> 00:11:55,640 Speaker 4: unless it's like, you know, massless. 258 00:11:55,720 --> 00:11:58,360 Speaker 5: I guess so based on the question. I'm not sure 259 00:11:58,400 --> 00:12:01,960 Speaker 5: exactly why, but if has something to do with like 260 00:12:02,000 --> 00:12:08,120 Speaker 5: the kinetic energy of something affecting its mass, then I 261 00:12:08,160 --> 00:12:08,920 Speaker 5: would guess so. 262 00:12:09,120 --> 00:12:11,440 Speaker 8: I think the answer is yes. First I was taught 263 00:12:11,480 --> 00:12:13,800 Speaker 8: it that way. I've since heard that's an old school 264 00:12:13,800 --> 00:12:18,200 Speaker 8: way of thinking about it. But definitely, if we consider 265 00:12:19,520 --> 00:12:25,600 Speaker 8: energy as being mass, you know the way it works relativistically, 266 00:12:25,600 --> 00:12:28,920 Speaker 8: you can concentrate energy as well as matter, and that 267 00:12:29,080 --> 00:12:32,319 Speaker 8: is all mass energy. Then as you add velocity, you're 268 00:12:32,360 --> 00:12:34,480 Speaker 8: adding energy and you become more massive. 269 00:12:35,280 --> 00:12:37,600 Speaker 1: All right, a lot of great answers here. I feel 270 00:12:37,640 --> 00:12:40,280 Speaker 1: like some people were blown away and some people were like, oh, 271 00:12:40,280 --> 00:12:43,080 Speaker 1: I've heard of this. The answer is yes or no. 272 00:12:43,360 --> 00:12:45,520 Speaker 2: Yeah, I thought this was really interesting. There's a lot 273 00:12:45,559 --> 00:12:48,360 Speaker 2: of different ideas here about what energy is and what 274 00:12:48,480 --> 00:12:52,160 Speaker 2: mass is. Very few people mentioned momentum even, but there's 275 00:12:52,160 --> 00:12:55,880 Speaker 2: definitely this understanding that things change as you approach the 276 00:12:55,920 --> 00:12:59,480 Speaker 2: speed of light, and that it's harder to go faster. Yeah. 277 00:12:59,559 --> 00:13:01,760 Speaker 1: Somebody one of the listeners said that it's kind of 278 00:13:01,960 --> 00:13:05,000 Speaker 1: strange that your mass would change, right, And that goes to. 279 00:13:04,920 --> 00:13:07,679 Speaker 2: The heart of what we mean by mass. I think 280 00:13:07,720 --> 00:13:09,679 Speaker 2: a lot of people think of mass is like the 281 00:13:09,720 --> 00:13:12,800 Speaker 2: amount of stuff they have, and so it's really weird 282 00:13:12,840 --> 00:13:15,400 Speaker 2: for them to imagine them getting like more stuff as 283 00:13:15,480 --> 00:13:17,640 Speaker 2: they approach the speed of light. And that's one reason 284 00:13:17,679 --> 00:13:20,160 Speaker 2: why I really don't like this concept of relativistic mass. 285 00:13:20,160 --> 00:13:23,480 Speaker 2: It gives people the impression that something physical is happening, 286 00:13:23,480 --> 00:13:24,920 Speaker 2: which isn't interesting. 287 00:13:24,960 --> 00:13:27,360 Speaker 1: All right, Well, let's dig into it, and I guess 288 00:13:27,400 --> 00:13:29,640 Speaker 1: let's start with the basics. As you said, let's start 289 00:13:29,679 --> 00:13:32,240 Speaker 1: with the concept of mass. Now. I know mass is 290 00:13:32,320 --> 00:13:34,520 Speaker 1: kind of a big mystery. We talked about it in 291 00:13:34,559 --> 00:13:36,679 Speaker 1: our book, like what is mass? Anyways, we have a 292 00:13:36,720 --> 00:13:39,439 Speaker 1: whole chapter about how we don't kind of know what 293 00:13:39,480 --> 00:13:41,360 Speaker 1: mass is. But Daniel maybe step us through it. What 294 00:13:41,440 --> 00:13:43,360 Speaker 1: do we know about what mass is? 295 00:13:43,679 --> 00:13:46,200 Speaker 2: I think in the context of relativity and motion, the 296 00:13:46,200 --> 00:13:49,400 Speaker 2: most important thing to think about is inertia, like the 297 00:13:49,480 --> 00:13:52,920 Speaker 2: fact that it's not easy to change your velocity. You're 298 00:13:52,960 --> 00:13:55,920 Speaker 2: flying through the universe at some speed. In order to 299 00:13:56,080 --> 00:13:58,960 Speaker 2: change that speed, you need a push. Right. That's really 300 00:13:58,960 --> 00:14:03,040 Speaker 2: what F equals is trying to say that to accelerate, 301 00:14:03,400 --> 00:14:05,360 Speaker 2: you need to have a force applied to you, and 302 00:14:05,360 --> 00:14:08,280 Speaker 2: that M in that equation, and F equals MA is 303 00:14:08,320 --> 00:14:11,240 Speaker 2: the mass. It relates how much acceleration you get for 304 00:14:11,559 --> 00:14:13,800 Speaker 2: how much force. We've all heard, for example, that the 305 00:14:13,840 --> 00:14:16,439 Speaker 2: Earth's gravity on you is the same as your gravity 306 00:14:16,520 --> 00:14:19,400 Speaker 2: on the Earth, Right, But we feel a much stronger 307 00:14:19,440 --> 00:14:21,440 Speaker 2: force than the Earth does because the Earth has a 308 00:14:21,600 --> 00:14:24,760 Speaker 2: huge mass. So we feel a much stronger acceleration than 309 00:14:24,760 --> 00:14:27,560 Speaker 2: the Earth does because the Earth has a huge mass, 310 00:14:27,840 --> 00:14:30,560 Speaker 2: and so its acceleration is tiny. Even though the force 311 00:14:30,720 --> 00:14:33,920 Speaker 2: is the same. So really important concept in mass is inertia. 312 00:14:33,960 --> 00:14:36,520 Speaker 2: That's really what mass is about when we're talking about motion, 313 00:14:36,720 --> 00:14:40,480 Speaker 2: and that's connected to this idea of momentum. Right. Another 314 00:14:40,480 --> 00:14:43,200 Speaker 2: way to think about F equals MA is that F 315 00:14:43,360 --> 00:14:46,080 Speaker 2: is actually a change in momentum. When you're flying through 316 00:14:46,080 --> 00:14:49,200 Speaker 2: the universe at a certain velocity, you have a certain momentum. 317 00:14:49,240 --> 00:14:51,480 Speaker 2: In order to change your momentum, you need to have 318 00:14:51,600 --> 00:14:54,360 Speaker 2: a force applied. So mass is this concept that tells 319 00:14:54,400 --> 00:14:58,360 Speaker 2: us basically how hard it is to change your momentum. 320 00:14:58,360 --> 00:15:00,480 Speaker 1: I feel like you're making us go that a rabbit 321 00:15:00,480 --> 00:15:02,880 Speaker 1: hole a little bit, because then it makes me wonder, like, 322 00:15:02,960 --> 00:15:04,240 Speaker 1: what is momentum anyways? 323 00:15:04,400 --> 00:15:07,000 Speaker 2: Yeah, a momentum is something we know is important in 324 00:15:07,040 --> 00:15:09,680 Speaker 2: the universe. It's a quantity that's conserved. Like we look 325 00:15:09,680 --> 00:15:12,480 Speaker 2: at in the universe, we watch stuff, we see things happen, 326 00:15:12,680 --> 00:15:15,080 Speaker 2: and we look for patterns, and a very important pattern 327 00:15:15,120 --> 00:15:18,760 Speaker 2: are conservation laws. Things that don't change. So two balls 328 00:15:18,760 --> 00:15:21,200 Speaker 2: bounce against each other, for example, you calculate all the 329 00:15:21,200 --> 00:15:23,800 Speaker 2: momentum beforehand and all the momentum afterwards, and you notice 330 00:15:23,880 --> 00:15:26,320 Speaker 2: it's the same. It is conserved. We actually know that 331 00:15:26,320 --> 00:15:28,880 Speaker 2: there's a deep reason for why momentum is conserved. It's 332 00:15:28,920 --> 00:15:32,000 Speaker 2: because space is the same everywhere. We did a whole 333 00:15:32,000 --> 00:15:34,680 Speaker 2: fun podcast on Nother's theorem, which tells you that because 334 00:15:34,720 --> 00:15:37,359 Speaker 2: space is the same everywhere, momentum has to be conserved. 335 00:15:37,600 --> 00:15:40,520 Speaker 2: This is deep link there. So momentum is an important 336 00:15:40,520 --> 00:15:43,400 Speaker 2: physical quantity in the universe. It's something that's really powerful 337 00:15:43,440 --> 00:15:45,480 Speaker 2: and it really gives us insight into what's happened. And 338 00:15:45,560 --> 00:15:48,520 Speaker 2: momentum is flowing through a system, right, but it's conserved 339 00:15:48,520 --> 00:15:51,720 Speaker 2: in the universe. The universe at least thinks momentum is important, 340 00:15:51,760 --> 00:15:53,000 Speaker 2: so maybe we should. 341 00:15:52,800 --> 00:15:56,040 Speaker 1: Also well, how is it different from like energy? And 342 00:15:56,400 --> 00:15:59,240 Speaker 1: is momentum the same as energy? Is the momentum of 343 00:15:59,280 --> 00:16:02,640 Speaker 1: a particle or a baseball the same as its kinetic energy? 344 00:16:02,720 --> 00:16:03,640 Speaker 1: How do the two connect? 345 00:16:03,760 --> 00:16:07,680 Speaker 2: Yeah? Great question. First of all, momentum has directionality. You 346 00:16:07,680 --> 00:16:09,600 Speaker 2: can have a momentum in one direction or momentum in 347 00:16:09,600 --> 00:16:12,400 Speaker 2: another direction. It's a vector it points and for example, 348 00:16:12,520 --> 00:16:15,760 Speaker 2: the Earth has a constant magnitude momentum, but the direction 349 00:16:15,880 --> 00:16:18,320 Speaker 2: of its momentum is changing as it goes around the Sun. 350 00:16:18,440 --> 00:16:20,760 Speaker 2: It's like an arrow that tells you which way the 351 00:16:20,800 --> 00:16:23,560 Speaker 2: Earth is headed, and that's constantly changing. So the length 352 00:16:23,560 --> 00:16:26,440 Speaker 2: of that vector isn't changing, but the direction of it is. 353 00:16:27,000 --> 00:16:29,800 Speaker 2: And that's why it takes acceleration to move around the Sun, 354 00:16:29,880 --> 00:16:32,680 Speaker 2: because you're changing the direction of that momentum vector. So 355 00:16:32,760 --> 00:16:35,880 Speaker 2: momentum is a direction, right. Energy doesn't have a direction, 356 00:16:35,920 --> 00:16:38,760 Speaker 2: it's just a number, right. And also, and energy includes 357 00:16:38,800 --> 00:16:42,000 Speaker 2: something else. The energy of an object has two components. 358 00:16:42,040 --> 00:16:44,680 Speaker 2: There's the internal energy what we call it's inertial mass, 359 00:16:45,040 --> 00:16:48,720 Speaker 2: and the energy of its motion, it's kinetic energy. So 360 00:16:48,760 --> 00:16:51,640 Speaker 2: there's two separate components there. So things could have energy 361 00:16:51,680 --> 00:16:54,320 Speaker 2: when they're not moving, like an electron just sitting there 362 00:16:54,520 --> 00:16:57,240 Speaker 2: has some mass, then that corresponds to some energy, and 363 00:16:57,280 --> 00:17:00,600 Speaker 2: there's also energy of motion. Things can have only energy 364 00:17:00,600 --> 00:17:03,440 Speaker 2: of motion, like a photon is just motion energy has 365 00:17:03,480 --> 00:17:06,120 Speaker 2: no mass, or they can have both, like an electron 366 00:17:06,160 --> 00:17:09,159 Speaker 2: flying through the universe has mass and that's energy and 367 00:17:09,320 --> 00:17:12,400 Speaker 2: also has kinetic energy. So energy has two components. There's 368 00:17:12,440 --> 00:17:15,200 Speaker 2: the mass and there's a contribution from the momentum, which 369 00:17:15,240 --> 00:17:16,639 Speaker 2: we also call kinetic energy. 370 00:17:16,720 --> 00:17:19,879 Speaker 1: And so the universe conserves both things, right, like it 371 00:17:19,960 --> 00:17:24,680 Speaker 1: somehow conserves momentum, and it also conserves energy, but not 372 00:17:24,720 --> 00:17:26,640 Speaker 1: necessarily the same way I think, right. 373 00:17:26,600 --> 00:17:29,720 Speaker 2: So there's a little asterisk there in flat space. Yes, 374 00:17:29,840 --> 00:17:33,639 Speaker 2: energy is conserved in the global universe. As space expands, 375 00:17:33,880 --> 00:17:37,560 Speaker 2: actually energy increases, so energy is not strictly conserved in 376 00:17:37,600 --> 00:17:40,160 Speaker 2: the universe. There's a whole podcast episode we did about 377 00:17:40,160 --> 00:17:41,880 Speaker 2: that if you want to dig into it. But let's 378 00:17:41,920 --> 00:17:44,119 Speaker 2: just assume we're like living in flat space and we're 379 00:17:44,160 --> 00:17:46,480 Speaker 2: bouncing balls and particles off each other. We wouldn't notice 380 00:17:46,480 --> 00:17:48,359 Speaker 2: the expansion of the universe. So let's just say for 381 00:17:48,400 --> 00:17:50,840 Speaker 2: the sake of this discussion that, yes, energy is conserved. 382 00:17:50,880 --> 00:17:54,160 Speaker 2: And so you're right, momentum is conserved and energy is conserved, 383 00:17:54,240 --> 00:17:57,480 Speaker 2: and those are actually related. Those are four separate conservation 384 00:17:57,600 --> 00:18:01,080 Speaker 2: laws because energy is one number and momentum is three numbers. 385 00:18:01,200 --> 00:18:04,080 Speaker 2: Because we have three dimensions of space, and momentums can 386 00:18:04,119 --> 00:18:07,359 Speaker 2: serve separately in each of those dimensions. So we have 387 00:18:07,440 --> 00:18:11,000 Speaker 2: four conservation laws, three from momentum and one from energy. 388 00:18:11,119 --> 00:18:13,399 Speaker 2: And in particle physics at least we group energy and 389 00:18:13,440 --> 00:18:16,000 Speaker 2: momentum together into something we call four momentum, like the 390 00:18:16,000 --> 00:18:18,760 Speaker 2: four dimensions of space time, and we say there's conservation 391 00:18:18,880 --> 00:18:22,280 Speaker 2: of form momentum, which combines momentum and energy into one 392 00:18:22,359 --> 00:18:23,200 Speaker 2: conservation law. 393 00:18:23,520 --> 00:18:27,320 Speaker 1: So then mass is related to both things, like mass 394 00:18:27,480 --> 00:18:29,879 Speaker 1: makes your momentum go higher and it makes your energy 395 00:18:29,880 --> 00:18:30,320 Speaker 1: go higher. 396 00:18:30,400 --> 00:18:32,840 Speaker 2: Yeah, that's right. So mass is like your internal stored energy. 397 00:18:33,080 --> 00:18:35,760 Speaker 2: Take a proton, for example, it has a bunch of mass. 398 00:18:35,800 --> 00:18:37,320 Speaker 2: Where does that mass come from. It comes from the 399 00:18:37,320 --> 00:18:40,119 Speaker 2: internal energy of the proton, Like there's the mass of 400 00:18:40,119 --> 00:18:42,200 Speaker 2: the quarks. They get their mass from the Higgs boson. 401 00:18:42,280 --> 00:18:44,800 Speaker 2: Then there's the mass of the binding of those quarks together, 402 00:18:45,240 --> 00:18:47,000 Speaker 2: and that's where most of the mass of the proton 403 00:18:47,080 --> 00:18:49,720 Speaker 2: comes from. So that proton has mass, and you're right, 404 00:18:49,760 --> 00:18:52,720 Speaker 2: that's part of its energy, and the proton could also 405 00:18:52,840 --> 00:18:55,800 Speaker 2: have momentum that's another part of its energy. So we 406 00:18:55,800 --> 00:18:58,119 Speaker 2: think of the mass as the thing that makes it 407 00:18:58,160 --> 00:19:00,200 Speaker 2: hard to push on something or easier to put push 408 00:19:00,240 --> 00:19:02,240 Speaker 2: on something but has low mass, and then there's also 409 00:19:02,400 --> 00:19:03,879 Speaker 2: energy stored in its motion. 410 00:19:04,160 --> 00:19:07,080 Speaker 1: Okay, So then generally speaking, mass is just what makes 411 00:19:07,160 --> 00:19:09,440 Speaker 1: things harder to move, right. 412 00:19:09,600 --> 00:19:12,840 Speaker 2: Basically, that's exactly right. That's the concept of inertial mass 413 00:19:12,840 --> 00:19:15,800 Speaker 2: basically relate to the objects inertia, which tells you how 414 00:19:15,840 --> 00:19:17,919 Speaker 2: hard is it to change its momentum. 415 00:19:18,080 --> 00:19:21,119 Speaker 1: Right, And then there's a concept of gravitational mass, which 416 00:19:21,200 --> 00:19:23,760 Speaker 1: is a different concept, but it's the same number. 417 00:19:24,000 --> 00:19:26,120 Speaker 2: Yeah, And there's a bunch of really fascinating wrinkles here. 418 00:19:26,160 --> 00:19:29,120 Speaker 2: Like in Newton's world, he had F equals maa, which 419 00:19:29,160 --> 00:19:30,879 Speaker 2: tells you about how hard it is to push something. 420 00:19:31,160 --> 00:19:33,920 Speaker 2: And he also had this number m in his gravitational 421 00:19:34,000 --> 00:19:37,080 Speaker 2: law gmm over r square, which tells you the force 422 00:19:37,160 --> 00:19:40,720 Speaker 2: between two objects. And in Newtonian physics, these two things 423 00:19:40,760 --> 00:19:43,240 Speaker 2: are different numbers. They're written in the same way, the 424 00:19:43,280 --> 00:19:46,240 Speaker 2: same letter M in F equals ma and M in 425 00:19:46,520 --> 00:19:49,760 Speaker 2: gmm over r squared. But in principle they could have 426 00:19:49,800 --> 00:19:51,879 Speaker 2: been totally different, right. It was a bit of a 427 00:19:51,920 --> 00:19:55,240 Speaker 2: mystery in Newtonian physics why these two numbers always seem 428 00:19:55,320 --> 00:19:58,199 Speaker 2: to have the same value. Einstein unified these things in 429 00:19:58,240 --> 00:20:02,200 Speaker 2: general relativity and told us that actually inertial gravitational masses 430 00:20:02,320 --> 00:20:04,840 Speaker 2: have to be the same because the corner to Einstein, 431 00:20:05,080 --> 00:20:07,520 Speaker 2: there is no acceleration due to gravity. There is no 432 00:20:07,680 --> 00:20:12,080 Speaker 2: force due to gravity. It's just inertial motion through curved 433 00:20:12,119 --> 00:20:15,440 Speaker 2: space time that when you are having inertial motion, there's 434 00:20:15,480 --> 00:20:19,080 Speaker 2: no forces on you through space time. That's what gravity 435 00:20:19,119 --> 00:20:21,919 Speaker 2: looks like. So motion due to gravity is actually just 436 00:20:22,000 --> 00:20:24,280 Speaker 2: inertial motion and you're just really in free fall. 437 00:20:24,560 --> 00:20:27,240 Speaker 1: Right, So like, for example, the Earth orbiting around the Sun. 438 00:20:27,280 --> 00:20:31,160 Speaker 1: It's not like there's a force pulling the Earth towards 439 00:20:31,200 --> 00:20:33,800 Speaker 1: the Sun, or there's no centripetal force there is, just 440 00:20:33,840 --> 00:20:37,159 Speaker 1: that the space around the Sun for the Earth is 441 00:20:37,200 --> 00:20:41,119 Speaker 1: sort of curved and it's shaped like a circle basically. 442 00:20:40,800 --> 00:20:43,080 Speaker 2: Right, Yeah, that's right. If space were flat, everything we 443 00:20:43,280 --> 00:20:45,359 Speaker 2: just move in what looks to us like straight lines. 444 00:20:45,560 --> 00:20:48,439 Speaker 2: But when space is curved, things move differently and it 445 00:20:48,520 --> 00:20:51,480 Speaker 2: looks like there's a force there bending their paths. But 446 00:20:51,600 --> 00:20:55,000 Speaker 2: really it's just motion through curved space. Because we can't 447 00:20:55,080 --> 00:20:57,720 Speaker 2: see that curvature. You can like look through space and 448 00:20:57,840 --> 00:20:59,920 Speaker 2: see the curvature of space the way you can see 449 00:21:00,119 --> 00:21:01,960 Speaker 2: curvature of a road. It seems like a bit of 450 00:21:02,000 --> 00:21:04,800 Speaker 2: a mystery why things are moving in curves, and of 451 00:21:04,800 --> 00:21:07,120 Speaker 2: course is that space is curved, so there's an apparent 452 00:21:07,200 --> 00:21:08,120 Speaker 2: force there, or. 453 00:21:08,080 --> 00:21:10,720 Speaker 1: More accurately, you mean like space time, right, Like maybe 454 00:21:10,760 --> 00:21:12,600 Speaker 1: space is not curve, but space time is. 455 00:21:12,760 --> 00:21:15,399 Speaker 2: It's definitely more coherent to think about relativity in terms 456 00:21:15,400 --> 00:21:18,240 Speaker 2: of space time because the way like energy and momentum 457 00:21:18,240 --> 00:21:20,880 Speaker 2: are linked, space and time are definitely linked. You can't 458 00:21:20,920 --> 00:21:23,520 Speaker 2: talk about the curvature of space as well and the 459 00:21:23,520 --> 00:21:26,440 Speaker 2: curvature of time separately. They make more sense when you 460 00:21:26,480 --> 00:21:28,960 Speaker 2: think about them together. But yes, space itself can also 461 00:21:29,000 --> 00:21:30,880 Speaker 2: be curved, but space time as well. 462 00:21:30,920 --> 00:21:33,800 Speaker 1: All right, So then that's mess. It's how hard it 463 00:21:33,840 --> 00:21:36,399 Speaker 1: is to push on something, and it's also sort of 464 00:21:36,440 --> 00:21:39,639 Speaker 1: like the effect something has on space time around it. 465 00:21:39,760 --> 00:21:42,480 Speaker 2: Yeah, and this is very intuitive if you're like playing billiards, 466 00:21:42,520 --> 00:21:45,480 Speaker 2: or you're shooting a basketball, or you're rolling rocks down hills, 467 00:21:45,480 --> 00:21:47,840 Speaker 2: and it's aligns with our sense that like things that 468 00:21:47,920 --> 00:21:51,360 Speaker 2: have more stuff to them are harder to push, and 469 00:21:51,400 --> 00:21:53,840 Speaker 2: that all makes sense at low speeds. Things change a 470 00:21:53,840 --> 00:21:56,520 Speaker 2: little bit as you get very high velocity, and then 471 00:21:56,560 --> 00:21:58,480 Speaker 2: you have a question for like, what do you change 472 00:21:58,560 --> 00:22:01,520 Speaker 2: you change momentum, do you change maths, change energy? What's 473 00:22:01,560 --> 00:22:03,800 Speaker 2: the most sensible way to think about these things? 474 00:22:04,040 --> 00:22:06,600 Speaker 1: Yeah, because, as we mentioned, there's the idea out there 475 00:22:06,640 --> 00:22:08,919 Speaker 1: that the faster you go, and as you approach the 476 00:22:08,920 --> 00:22:11,960 Speaker 1: speed of light, your mass starts to get bigger and bigger, 477 00:22:12,080 --> 00:22:14,359 Speaker 1: which is a problem for us who are trying to 478 00:22:14,400 --> 00:22:18,320 Speaker 1: stay slim, and so let's dig into that scenario and 479 00:22:18,480 --> 00:22:21,160 Speaker 1: the problems with that scenario and what it all means 480 00:22:21,200 --> 00:22:24,000 Speaker 1: about the loss of the universe. But first, let's take 481 00:22:24,000 --> 00:22:38,960 Speaker 1: a quick break. All right. We are talking about a 482 00:22:39,040 --> 00:22:42,119 Speaker 1: massive topic here, and it's going by really fast, and 483 00:22:42,200 --> 00:22:46,680 Speaker 1: it's about how really massive things go really fast. Things 484 00:22:46,720 --> 00:22:48,240 Speaker 1: get massive as they go really fast. 485 00:22:48,359 --> 00:22:50,720 Speaker 2: Yeah, things definitely do change as you approach the speed 486 00:22:50,760 --> 00:22:52,680 Speaker 2: of light, and a lot of your intuition goes out 487 00:22:52,720 --> 00:22:55,920 Speaker 2: the window. You can just lean into the mathematics and say, well, 488 00:22:55,960 --> 00:22:57,840 Speaker 2: there are new formulas and I can just use them 489 00:22:57,880 --> 00:22:59,480 Speaker 2: and calculate stuff. But we also want to have like 490 00:22:59,480 --> 00:23:02,200 Speaker 2: an understanding of how the universe works. We want to 491 00:23:02,240 --> 00:23:05,960 Speaker 2: develop a new intuition. So it's important that we make 492 00:23:06,080 --> 00:23:08,280 Speaker 2: sense of what the words mean as things change. 493 00:23:08,840 --> 00:23:11,680 Speaker 1: Okay, so let's talk about change. I guess now, before 494 00:23:11,720 --> 00:23:14,560 Speaker 1: when we just had Newtonian physics, things were kind of simple, 495 00:23:14,600 --> 00:23:17,200 Speaker 1: like if you wanted to change the velocity of something, 496 00:23:18,000 --> 00:23:20,879 Speaker 1: you had to apply a certain force, and a certain 497 00:23:20,880 --> 00:23:24,600 Speaker 1: force would always give you the same amount of velocity change, 498 00:23:24,760 --> 00:23:27,000 Speaker 1: kind of like no matter if you're standing still or 499 00:23:27,040 --> 00:23:29,480 Speaker 1: if you're going fast. If you applied and have you 500 00:23:29,520 --> 00:23:32,199 Speaker 1: always got that change in velocity acceleration. 501 00:23:32,359 --> 00:23:35,080 Speaker 2: Yeah, that's right, F used to equal M in a 502 00:23:35,200 --> 00:23:38,400 Speaker 2: very simple and straightforward way. Or equivalently, we could say 503 00:23:38,600 --> 00:23:40,440 Speaker 2: F is the change in momentum. 504 00:23:40,600 --> 00:23:42,840 Speaker 1: Right, So that's Newtonian physics. But then we sort of 505 00:23:42,960 --> 00:23:45,800 Speaker 1: learned a little bit more about relativity, which says that 506 00:23:45,800 --> 00:23:46,720 Speaker 1: that's not quite true. 507 00:23:46,800 --> 00:23:49,880 Speaker 2: Yeah, because there is a maximum speed to the universe. 508 00:23:50,160 --> 00:23:52,639 Speaker 2: If you pour energy into something trying to get it 509 00:23:52,680 --> 00:23:55,840 Speaker 2: going faster, you don't always get the same amount of 510 00:23:56,000 --> 00:23:59,560 Speaker 2: speed up, which means like it's harder to add velocity 511 00:23:59,680 --> 00:24:03,160 Speaker 2: in the direction something is moving. You have rocket ship 512 00:24:03,160 --> 00:24:05,040 Speaker 2: and it's already going at ninety percent of the speed 513 00:24:05,080 --> 00:24:07,600 Speaker 2: of light, and you fire the engines the same amount 514 00:24:07,680 --> 00:24:09,640 Speaker 2: you did earlier, you're not going to get the same 515 00:24:09,680 --> 00:24:12,800 Speaker 2: amount of speed up even if you're applying the same. 516 00:24:12,640 --> 00:24:15,360 Speaker 1: Force, right, Because I guess under Newtonian physics, you could 517 00:24:15,359 --> 00:24:19,080 Speaker 1: technically go infinitely fast, right, Like if you just kept 518 00:24:19,160 --> 00:24:22,440 Speaker 1: pushing on an object over a long long period of time, 519 00:24:22,520 --> 00:24:24,840 Speaker 1: we just keep going faster and faster and faster because 520 00:24:24,960 --> 00:24:27,280 Speaker 1: F equals ma A And so if I apply a 521 00:24:27,359 --> 00:24:30,440 Speaker 1: constant force to something the velocity is going to keep increasing, 522 00:24:30,520 --> 00:24:33,679 Speaker 1: increasing and increasing, and eventually you would go faster than 523 00:24:33,720 --> 00:24:35,719 Speaker 1: the speed of light in a Newtonian universe. 524 00:24:35,800 --> 00:24:36,800 Speaker 2: Yeah, that's exactly right. 525 00:24:36,920 --> 00:24:39,119 Speaker 1: But we seem to have this speed limit that says 526 00:24:39,160 --> 00:24:41,840 Speaker 1: you can go faster and faster, and so I guess 527 00:24:41,920 --> 00:24:43,760 Speaker 1: my question is what happened then? Did we have to 528 00:24:43,800 --> 00:24:46,840 Speaker 1: adjust our math or does the math tell you why 529 00:24:46,840 --> 00:24:48,359 Speaker 1: you can't go faster than the speed of light. 530 00:24:48,440 --> 00:24:51,560 Speaker 2: We definitely had to adjust our math, right, because those 531 00:24:51,560 --> 00:24:53,640 Speaker 2: formulas are wrong. As you say, they predict you could 532 00:24:53,680 --> 00:24:57,719 Speaker 2: go infinitely fast. So what was wrong about those formulas? Well, 533 00:24:57,760 --> 00:25:01,000 Speaker 2: it turns out our formula form momentum was wrong. We 534 00:25:01,040 --> 00:25:03,760 Speaker 2: thought momentum was just like mass times velocity, and then 535 00:25:03,800 --> 00:25:07,480 Speaker 2: we thought that quantity was conserved in the universe. Turns 536 00:25:07,520 --> 00:25:10,399 Speaker 2: out we were missing a term. There's another term in 537 00:25:10,440 --> 00:25:13,320 Speaker 2: that equation, this thing we call the boost factor. We 538 00:25:13,400 --> 00:25:15,560 Speaker 2: write it as gamma in relativity. It's just a number, 539 00:25:15,560 --> 00:25:17,480 Speaker 2: but if you're going at slow speeds, that number is 540 00:25:17,520 --> 00:25:20,000 Speaker 2: basically one, so it doesn't change your equation. But as 541 00:25:20,040 --> 00:25:22,280 Speaker 2: you approach to the speed of light, that number grows 542 00:25:22,320 --> 00:25:24,959 Speaker 2: to infinity. So what it means is momentum is different 543 00:25:25,000 --> 00:25:27,320 Speaker 2: from what we thought it was. We talked about how 544 00:25:27,359 --> 00:25:30,480 Speaker 2: momentum is this important quantity in the universe that's conserved. 545 00:25:30,600 --> 00:25:33,520 Speaker 2: That's true, but it's not M times V. There's a 546 00:25:33,520 --> 00:25:36,800 Speaker 2: different expression for momentum, and that's the thing that's actually 547 00:25:36,800 --> 00:25:39,840 Speaker 2: conserved in the universe. It turns out M times V 548 00:25:40,080 --> 00:25:44,199 Speaker 2: times this gamma factor. So momentum changes as you approach 549 00:25:44,240 --> 00:25:47,159 Speaker 2: the speed of light, and that's why it's harder to 550 00:25:47,280 --> 00:25:50,360 Speaker 2: increase your velocity as you approach the speed of light, 551 00:25:50,440 --> 00:25:54,119 Speaker 2: because your momentum is changing. It requires a larger force 552 00:25:54,200 --> 00:25:55,640 Speaker 2: to change your momentum. 553 00:25:55,720 --> 00:25:58,840 Speaker 1: I guess this is where it gets kind of confusing, because, 554 00:25:59,480 --> 00:26:01,399 Speaker 1: first of all, all like you're saying that as I 555 00:26:01,480 --> 00:26:05,439 Speaker 1: go faster, my momentum decreases, But doesn't that depend on 556 00:26:06,080 --> 00:26:08,520 Speaker 1: how fast I'm going relative to who or what? Like? 557 00:26:08,560 --> 00:26:10,360 Speaker 1: To me, I'm not going fast at all. If I'm 558 00:26:10,359 --> 00:26:12,399 Speaker 1: going really fast. To me, it just looks like the 559 00:26:12,520 --> 00:26:14,240 Speaker 1: universe is moving around me. 560 00:26:14,720 --> 00:26:17,119 Speaker 2: So, first of all, as you go faster, your momentum 561 00:26:17,200 --> 00:26:20,600 Speaker 2: still increases. That's always true, it's just not a linear increase. 562 00:26:20,720 --> 00:26:23,320 Speaker 2: And you're absolutely right that all of these things depend 563 00:26:23,400 --> 00:26:26,320 Speaker 2: on your frame right, depends on who's watching. Somebody who's 564 00:26:26,359 --> 00:26:27,920 Speaker 2: in a spaceship with you is going to see you 565 00:26:27,960 --> 00:26:30,840 Speaker 2: at zero velocity, and somebody who's on Earth as you 566 00:26:30,960 --> 00:26:32,760 Speaker 2: zip by, it's going to see you moving at very 567 00:26:32,800 --> 00:26:34,919 Speaker 2: high speed. So you're absolutely right. There's no sense of 568 00:26:35,040 --> 00:26:38,360 Speaker 2: talking about, like, what is my velocity in an absolute way. 569 00:26:38,400 --> 00:26:41,359 Speaker 2: It's always measured relative to some observer. So there's an 570 00:26:41,359 --> 00:26:44,959 Speaker 2: important difference between things that are invariant, where everybody agrees 571 00:26:44,960 --> 00:26:47,680 Speaker 2: on them no matter their velocity, and things that are conserved, 572 00:26:48,200 --> 00:26:51,240 Speaker 2: things that don't change in a frame of reference. So momentum, 573 00:26:51,240 --> 00:26:54,920 Speaker 2: for example, is conserved for some observer. You always see 574 00:26:54,960 --> 00:26:59,159 Speaker 2: momentum conserved, like before collision. After collision is the same momentum, 575 00:26:59,200 --> 00:27:02,399 Speaker 2: but momentum is not invariant. Another observer moving at a 576 00:27:02,440 --> 00:27:05,320 Speaker 2: different speed will see a different set of momentum, but 577 00:27:05,400 --> 00:27:09,120 Speaker 2: they will also see momentum conserved. So momentum is conserved, 578 00:27:09,400 --> 00:27:12,720 Speaker 2: meaning for a given observer it doesn't ever disappear or appear, 579 00:27:13,200 --> 00:27:16,480 Speaker 2: but it's not invariant, meaning different people will measure different 580 00:27:16,520 --> 00:27:18,040 Speaker 2: amounts at different velocities. 581 00:27:19,200 --> 00:27:21,240 Speaker 1: Okay, so then I think what you're saying is that 582 00:27:21,320 --> 00:27:24,960 Speaker 1: momentum is not linear. It gets kind of wonky the 583 00:27:25,040 --> 00:27:27,240 Speaker 1: faster you go. And the way it gets wonky is 584 00:27:27,240 --> 00:27:30,400 Speaker 1: that it gets kind of ridiculously big as you get 585 00:27:30,440 --> 00:27:33,200 Speaker 1: closer to the speed of light. Right, you said, momentum 586 00:27:33,200 --> 00:27:37,800 Speaker 1: equals mass time velocity times gamma, and gamma is basically 587 00:27:37,880 --> 00:27:40,959 Speaker 1: one when we're standing still, but it gets to infinity 588 00:27:41,240 --> 00:27:42,760 Speaker 1: as we get closer to the speed of light. 589 00:27:42,920 --> 00:27:45,200 Speaker 2: Exactly. And if you think about force not just as 590 00:27:45,280 --> 00:27:48,639 Speaker 2: mass times acceleration, but as the change in momentum, then 591 00:27:48,680 --> 00:27:51,879 Speaker 2: if your momentum is really really big, then it becomes 592 00:27:51,960 --> 00:27:54,600 Speaker 2: hard to change your momentum. You need to apply a 593 00:27:54,640 --> 00:27:57,560 Speaker 2: really really big force to change your momentum. And your 594 00:27:57,600 --> 00:28:00,440 Speaker 2: momentum grows very very quickly near the speed of light. 595 00:28:00,600 --> 00:28:04,000 Speaker 2: As you say, it approaches infinity as velocity approaches the 596 00:28:04,040 --> 00:28:04,600 Speaker 2: speed of light. 597 00:28:04,720 --> 00:28:06,960 Speaker 1: So I guess I get more concretely, it would mean 598 00:28:07,000 --> 00:28:10,520 Speaker 1: like my couch, me sitting in my couch, my momentum 599 00:28:10,520 --> 00:28:12,760 Speaker 1: would be my mass times my velocity, which in this 600 00:28:12,840 --> 00:28:14,720 Speaker 1: case I guess it's zero, but it would just in 601 00:28:14,840 --> 00:28:17,639 Speaker 1: my mass timeline my velocity. But if I was moving 602 00:28:17,760 --> 00:28:21,800 Speaker 1: at two hundred thousand kilometers per second, then my momentum 603 00:28:21,800 --> 00:28:24,640 Speaker 1: would be not just my mask my velocity, but it'ld 604 00:28:24,640 --> 00:28:28,480 Speaker 1: be mass time my velocity times a really big number, 605 00:28:28,520 --> 00:28:31,240 Speaker 1: which is this adjustment factor that gets bigger the closer 606 00:28:31,280 --> 00:28:32,200 Speaker 1: you move to the speed of light. 607 00:28:32,280 --> 00:28:34,840 Speaker 2: Exactly. This gamma factor is the thing that Newton missed 608 00:28:35,040 --> 00:28:37,679 Speaker 2: in momentum basically, and he missed it because for everything 609 00:28:37,720 --> 00:28:40,120 Speaker 2: he measured and he saw, it was just one, so 610 00:28:40,160 --> 00:28:43,280 Speaker 2: it didn't change any of his calculations. Any number multiplied 611 00:28:43,280 --> 00:28:44,920 Speaker 2: by one is just itself. So you have like a 612 00:28:45,000 --> 00:28:48,080 Speaker 2: hidden factor in your equations that's always one. You can't 613 00:28:48,120 --> 00:28:50,480 Speaker 2: discover it. You can only discover it when it changes 614 00:28:50,520 --> 00:28:52,800 Speaker 2: from one, and it only changes from one as you 615 00:28:52,880 --> 00:28:54,040 Speaker 2: approach the speed of light. 616 00:28:54,160 --> 00:28:55,960 Speaker 1: So I think kind of the message is that the 617 00:28:56,040 --> 00:28:57,840 Speaker 1: universe is kind of like, Okay, if you want to 618 00:28:57,840 --> 00:29:00,240 Speaker 1: move something from your couch to your kitchen, that's fine, 619 00:29:00,280 --> 00:29:01,920 Speaker 1: you can do that. It's going to cost you this much. 620 00:29:02,080 --> 00:29:03,640 Speaker 1: But if you want to move it from you know, 621 00:29:03,720 --> 00:29:06,120 Speaker 1: your couch to almost as to the speed of light 622 00:29:06,200 --> 00:29:08,239 Speaker 1: or super duper fast, it's going to cost you that 623 00:29:08,680 --> 00:29:12,600 Speaker 1: plus an extra like universe tax or something exactly that 624 00:29:12,640 --> 00:29:14,520 Speaker 1: says that, oh, that's going to cost you a lot 625 00:29:14,600 --> 00:29:17,160 Speaker 1: a lot, and somehow the idea is that it that 626 00:29:17,320 --> 00:29:19,920 Speaker 1: kind of lets the universe prevent you from going faster 627 00:29:20,000 --> 00:29:20,720 Speaker 1: than the speed of light. 628 00:29:20,840 --> 00:29:23,960 Speaker 2: Yeah, and the universe tax it's basically zero if you're 629 00:29:24,200 --> 00:29:26,840 Speaker 2: not moving very fast. Even if you're moving at like 630 00:29:26,960 --> 00:29:29,800 Speaker 2: half the speed of light, this gamma factor, this boost, 631 00:29:29,800 --> 00:29:33,040 Speaker 2: this universe tax is like fifteen percent. So even at 632 00:29:33,080 --> 00:29:36,040 Speaker 2: half the speed of light, it's barely noticeable. As you 633 00:29:36,040 --> 00:29:37,880 Speaker 2: get to like ninety percent of the speed of light, 634 00:29:37,960 --> 00:29:40,400 Speaker 2: it's like two point three. And if you get to 635 00:29:40,440 --> 00:29:42,560 Speaker 2: like ninety nine percent of the speed of light, it's 636 00:29:42,560 --> 00:29:45,120 Speaker 2: like seven ninety nine point nine percent of the speed 637 00:29:45,120 --> 00:29:47,320 Speaker 2: of light, it's like twenty two. So it increases very 638 00:29:47,400 --> 00:29:49,520 Speaker 2: very quickly as things get fast. 639 00:29:49,640 --> 00:29:51,840 Speaker 1: Well, I didn't know the universe was so progressive. 640 00:29:53,480 --> 00:29:58,680 Speaker 2: Exactly. Momentum, billionaires, the universe is coming for you. Yeah, 641 00:29:58,720 --> 00:30:01,240 Speaker 2: And so really that's fundamentally what's happening. We like to 642 00:30:01,240 --> 00:30:04,000 Speaker 2: think about momentum because that's something the universe conserves. That's 643 00:30:04,000 --> 00:30:07,959 Speaker 2: something that's important to the universe, energy and momentum, and 644 00:30:08,000 --> 00:30:11,200 Speaker 2: that's really what's driving this experience that it's harder to 645 00:30:11,280 --> 00:30:13,520 Speaker 2: accelerate as you get towards the speed of light. And 646 00:30:13,560 --> 00:30:17,640 Speaker 2: remember that momentum is directional, right, and so adding velocity 647 00:30:17,680 --> 00:30:20,960 Speaker 2: in the direction you're already going takes actually different amounts 648 00:30:21,000 --> 00:30:24,160 Speaker 2: of momentum than adding velocity like perpendicular to your motion. 649 00:30:24,440 --> 00:30:25,800 Speaker 2: It gets very complicated. 650 00:30:26,600 --> 00:30:28,800 Speaker 1: So I think you're saying that momentum is conserved in 651 00:30:28,800 --> 00:30:32,080 Speaker 1: the universe, but there's there's sort of a premium on 652 00:30:32,320 --> 00:30:37,880 Speaker 1: higher momenti momentumus like the bigger momentum has somehow cost 653 00:30:37,920 --> 00:30:38,440 Speaker 1: you more. 654 00:30:38,400 --> 00:30:40,560 Speaker 2: Exactly, And that raises the question like, well, what do 655 00:30:40,640 --> 00:30:43,280 Speaker 2: we do about mass. We used to have this notion 656 00:30:43,320 --> 00:30:45,480 Speaker 2: and that mass told us how hard it is to 657 00:30:45,520 --> 00:30:47,760 Speaker 2: push something, and in the old sense of momentum, it's 658 00:30:47,800 --> 00:30:50,880 Speaker 2: just mass times velocity. Then it all made sense, and 659 00:30:50,920 --> 00:30:53,240 Speaker 2: then you get the equation F equals MA, AND's a 660 00:30:53,360 --> 00:30:58,040 Speaker 2: very natural linear relationship between acceleration and force. That all 661 00:30:58,160 --> 00:31:01,520 Speaker 2: changes when we change the definition of momentum. You no 662 00:31:01,560 --> 00:31:03,840 Speaker 2: longer have F equals M, and so you have to 663 00:31:03,840 --> 00:31:05,840 Speaker 2: think about, like what do you do with mass. 664 00:31:06,840 --> 00:31:09,360 Speaker 1: I think you're saying, like, we have this tax that 665 00:31:09,400 --> 00:31:11,959 Speaker 1: the universe puts on momentum. Now do you take that 666 00:31:12,080 --> 00:31:15,440 Speaker 1: tax and fold it into the definition of mass, or 667 00:31:15,560 --> 00:31:18,240 Speaker 1: is mass still mass, but then you have this extra tax, 668 00:31:18,240 --> 00:31:19,720 Speaker 1: which is not mass exactly. 669 00:31:19,800 --> 00:31:22,560 Speaker 2: And so the modern idea, the one that most physicists use, 670 00:31:22,640 --> 00:31:25,080 Speaker 2: is exactly that to say, let's just leave mass alone. 671 00:31:25,240 --> 00:31:28,120 Speaker 2: Mass is related to your internal stored energy. Let's define 672 00:31:28,120 --> 00:31:30,800 Speaker 2: mass to be something everybody agrees on, no matter what 673 00:31:30,840 --> 00:31:34,320 Speaker 2: their velocity is. And let's just change the definition momentum, 674 00:31:34,480 --> 00:31:37,280 Speaker 2: so mass stays as M whatever it was before, and 675 00:31:37,320 --> 00:31:39,680 Speaker 2: now momentum is M comes v and we conclude the 676 00:31:39,720 --> 00:31:42,800 Speaker 2: gamma factor there in momentum. The other idea, the one 677 00:31:42,840 --> 00:31:46,280 Speaker 2: that leads to this confusion, is this concept of relativistic mass, 678 00:31:46,280 --> 00:31:50,600 Speaker 2: and say, oh, let's redefine mass to be mass times gamma. 679 00:31:50,680 --> 00:31:53,240 Speaker 2: Let's fold that gamma factor into the mass, and that 680 00:31:53,320 --> 00:31:56,440 Speaker 2: lets us keep momentum as mass times velocity because we 681 00:31:56,600 --> 00:31:58,880 Speaker 2: like that equation. And so there's sort of a choice 682 00:31:58,880 --> 00:32:01,640 Speaker 2: to be made there, like do you redefine momentum or 683 00:32:01,680 --> 00:32:02,920 Speaker 2: do you redefine mass? 684 00:32:03,200 --> 00:32:04,640 Speaker 1: Well, I see, it kind of depends on whether you 685 00:32:04,720 --> 00:32:07,520 Speaker 1: define mass as how hard you are to push when 686 00:32:07,560 --> 00:32:11,160 Speaker 1: you're just sitting on your couch, or how hard you 687 00:32:11,200 --> 00:32:13,560 Speaker 1: are to push at any point, or no matter how 688 00:32:13,560 --> 00:32:14,560 Speaker 1: fast you're moving. 689 00:32:14,400 --> 00:32:16,880 Speaker 2: It's definitely a choice, right, It's a definition, and you 690 00:32:16,920 --> 00:32:19,160 Speaker 2: can make one choice or the other, and the equations 691 00:32:19,200 --> 00:32:21,280 Speaker 2: all work. I think it's more coherent. It makes more 692 00:32:21,320 --> 00:32:24,240 Speaker 2: sense if you call mass as you say how hard 693 00:32:24,240 --> 00:32:26,200 Speaker 2: it is to push you when you're sitting on your couch. 694 00:32:26,280 --> 00:32:28,480 Speaker 2: It's tempting to say, well, it makes more sense to 695 00:32:28,560 --> 00:32:30,480 Speaker 2: use masses how hard it is to push when you're 696 00:32:30,480 --> 00:32:32,960 Speaker 2: moving fast as well. But as we can dig into 697 00:32:33,040 --> 00:32:35,800 Speaker 2: in a moment that doesn't actually hang together. You can't 698 00:32:35,800 --> 00:32:38,160 Speaker 2: have just a single number that tells you how hard 699 00:32:38,200 --> 00:32:40,880 Speaker 2: it is to speed up, because that actually depends a 700 00:32:40,920 --> 00:32:43,840 Speaker 2: little bit on the direction of your speed up. So 701 00:32:44,000 --> 00:32:46,960 Speaker 2: relativistic mass is a little bit complicated and problematic. It 702 00:32:46,960 --> 00:32:49,040 Speaker 2: doesn't really do that job. Doesn't let you use F 703 00:32:49,080 --> 00:32:52,600 Speaker 2: equals ma again by redefining m I see. 704 00:32:52,640 --> 00:32:55,160 Speaker 1: So I think maybe for the people who had heard 705 00:32:55,200 --> 00:32:57,160 Speaker 1: that the faster you go, or the closer you get 706 00:32:57,160 --> 00:32:58,960 Speaker 1: to the speed of light, the more mass if you get, 707 00:32:59,120 --> 00:33:01,880 Speaker 1: what they probably heard at that time was that you 708 00:33:01,880 --> 00:33:04,120 Speaker 1: do get harder to push as you get closer to 709 00:33:04,120 --> 00:33:05,840 Speaker 1: the speed of light. But that doesn't mean that your 710 00:33:05,880 --> 00:33:09,920 Speaker 1: mass went up, but that there's an adjustment to your momentum, 711 00:33:10,120 --> 00:33:13,920 Speaker 1: or there's a premium to how much momentum cause, which 712 00:33:14,160 --> 00:33:16,040 Speaker 1: makes it harder for you to push you, but it 713 00:33:16,080 --> 00:33:18,520 Speaker 1: doesn't change how hard you are to get off the couch. 714 00:33:18,640 --> 00:33:21,200 Speaker 2: Yeah, and physics has sort of changed its mind about this. 715 00:33:21,600 --> 00:33:25,200 Speaker 2: Even Einstein for a while used this concept of relativistic mass, 716 00:33:25,200 --> 00:33:28,000 Speaker 2: and it was taught in textbooks. So people who were told, like, 717 00:33:28,400 --> 00:33:30,480 Speaker 2: your mass increases as you approached the speed of light, 718 00:33:30,720 --> 00:33:33,080 Speaker 2: that's not wrong. It just depends on what you mean 719 00:33:33,160 --> 00:33:36,000 Speaker 2: by mass. So it really is our choice what do 720 00:33:36,000 --> 00:33:37,840 Speaker 2: we mean by this word mass. You used to have 721 00:33:37,880 --> 00:33:40,400 Speaker 2: a very crisp and clear definition that everybody agreed about 722 00:33:40,640 --> 00:33:43,360 Speaker 2: at low speeds. At high speeds, it becomes a little 723 00:33:43,400 --> 00:33:46,440 Speaker 2: bit trickier, and you can use the word relativistic mass. 724 00:33:46,480 --> 00:33:48,200 Speaker 2: It's not like it's wrong. It's just a choice for 725 00:33:48,240 --> 00:33:51,080 Speaker 2: how to organize the ideas. And now we think it 726 00:33:51,120 --> 00:33:54,120 Speaker 2: makes more sense to just describe mass as how hard 727 00:33:54,120 --> 00:33:56,000 Speaker 2: it is to push you when you're sitting on your couch, 728 00:33:56,280 --> 00:33:58,920 Speaker 2: and to leave momentum to absorb all the messiness. 729 00:33:59,040 --> 00:34:01,720 Speaker 1: I guess you're saying, like mask can just be how 730 00:34:01,800 --> 00:34:03,400 Speaker 1: hard it is to push you off your couch, but 731 00:34:03,640 --> 00:34:06,880 Speaker 1: we can introduce maybe a constantly called relativistic mass, where 732 00:34:06,880 --> 00:34:09,960 Speaker 1: people did introduce a concept called relativistic mass, which is 733 00:34:10,000 --> 00:34:13,120 Speaker 1: how hard you are to push at all speeds, and 734 00:34:13,160 --> 00:34:14,520 Speaker 1: that changes the faster you go. 735 00:34:14,760 --> 00:34:16,560 Speaker 2: That does change the faster you go, though I would 736 00:34:16,560 --> 00:34:18,719 Speaker 2: say the two choices are not equal. I would say 737 00:34:18,760 --> 00:34:21,439 Speaker 2: there's some problems with relativistic mass. I mean, problem number 738 00:34:21,480 --> 00:34:24,160 Speaker 2: one is that it's just a number, whereas momentum is 739 00:34:24,200 --> 00:34:27,120 Speaker 2: three numbers. It's a direction. And so if you're going 740 00:34:27,200 --> 00:34:29,719 Speaker 2: to talk about how hard it is to change your momentum, 741 00:34:29,800 --> 00:34:31,960 Speaker 2: then if you have a high speed in one direction, 742 00:34:32,200 --> 00:34:35,680 Speaker 2: you basically have a different relativistic mass in each direction, 743 00:34:36,239 --> 00:34:38,799 Speaker 2: because it's harder to push you in the direction you're 744 00:34:38,840 --> 00:34:41,800 Speaker 2: already going fast than it is to push you perpendicular 745 00:34:41,840 --> 00:34:44,920 Speaker 2: to that direction. So then you need like a transverse 746 00:34:45,040 --> 00:34:49,320 Speaker 2: relativistic mass and the longitudinal relativistic mass. It gets messy 747 00:34:49,440 --> 00:34:50,240 Speaker 2: very very quickly. 748 00:34:50,400 --> 00:34:52,680 Speaker 1: Well, I think what you're saying is that it's not 749 00:34:52,719 --> 00:34:55,560 Speaker 1: that it gets message is that the word relativistic mass 750 00:34:56,080 --> 00:34:58,839 Speaker 1: is a vector, like you have to define which way 751 00:34:59,000 --> 00:35:01,680 Speaker 1: you're pointing your li relativistic mass, just like you have 752 00:35:01,760 --> 00:35:03,719 Speaker 1: to define which way you're pointing your momentum. 753 00:35:03,719 --> 00:35:06,000 Speaker 2: Well, we already have that concept of momentum, right, so 754 00:35:06,000 --> 00:35:09,000 Speaker 2: we don't really need a vector of relativistic mass. And 755 00:35:09,280 --> 00:35:12,120 Speaker 2: the formula for relativistic mass, it turns out, is actually 756 00:35:12,200 --> 00:35:15,759 Speaker 2: just energy divided by the speed of light. So relativistic 757 00:35:15,800 --> 00:35:18,319 Speaker 2: mass doesn't actually give you anything new that you don't 758 00:35:18,320 --> 00:35:23,000 Speaker 2: already have for momentum and energy, so sort of unnecessary. 759 00:35:23,000 --> 00:35:26,400 Speaker 2: Whereas invariant mass, your rest mass is actually something independent 760 00:35:26,480 --> 00:35:29,239 Speaker 2: and interesting. It tells you, like what is the thing. 761 00:35:29,840 --> 00:35:33,600 Speaker 2: You know, photons and electrons and protons all have different 762 00:35:34,000 --> 00:35:36,040 Speaker 2: rest masses. That tells you a little bit about like 763 00:35:36,040 --> 00:35:39,120 Speaker 2: what the thing is, what it has to it, which 764 00:35:39,160 --> 00:35:41,680 Speaker 2: I think is more closely connected to like our intuitive 765 00:35:41,760 --> 00:35:44,319 Speaker 2: idea for what mass is that it tells you something 766 00:35:44,360 --> 00:35:45,719 Speaker 2: about like what you're made of. 767 00:35:46,480 --> 00:35:48,600 Speaker 1: And I guess for people who maybe missed it or 768 00:35:48,640 --> 00:35:53,160 Speaker 1: are not super familiar with this idea of directionality, I 769 00:35:53,160 --> 00:35:54,840 Speaker 1: think what you're saying is that, like, if I'm going 770 00:35:54,880 --> 00:35:58,279 Speaker 1: really fast from here to Andromeda, for example, in one 771 00:35:58,320 --> 00:36:00,759 Speaker 1: particular direction, and I'm going at the speed of light, 772 00:36:00,960 --> 00:36:04,040 Speaker 1: then my momentum in the direction from here to Andromeda 773 00:36:04,160 --> 00:36:06,239 Speaker 1: is really high because I'm going really fast, and so 774 00:36:06,280 --> 00:36:09,680 Speaker 1: it's really hard to accelerate be more in the direction 775 00:36:09,760 --> 00:36:12,000 Speaker 1: of Andromeda. But maybe if you're going along with me 776 00:36:12,080 --> 00:36:13,919 Speaker 1: and you try to push me in a direction that's 777 00:36:14,120 --> 00:36:17,160 Speaker 1: perpendicular to the side of the direction from here to Andromeda, 778 00:36:17,320 --> 00:36:20,960 Speaker 1: then you're not going to notice me being super massive 779 00:36:21,040 --> 00:36:23,799 Speaker 1: or having this huge relativistic mass. Is just going to 780 00:36:23,920 --> 00:36:26,080 Speaker 1: feel to you like I'm sitting on the couch, Like 781 00:36:26,120 --> 00:36:27,680 Speaker 1: I'm sitting on the couch in one direction, but I'm 782 00:36:27,719 --> 00:36:29,080 Speaker 1: going really fast in another direction. 783 00:36:29,280 --> 00:36:32,600 Speaker 2: Yeah, that's approximately true, because your motion towards and Drameda 784 00:36:32,760 --> 00:36:35,839 Speaker 2: does change your overall velocity, and the limit is on 785 00:36:35,880 --> 00:36:39,320 Speaker 2: the total velocity in any direction, not just in one direction. 786 00:36:39,440 --> 00:36:41,719 Speaker 2: But for the most part that's true. You know, what 787 00:36:41,760 --> 00:36:43,880 Speaker 2: happens at those very high speeds is like, if you 788 00:36:43,960 --> 00:36:46,840 Speaker 2: push in one direction, you don't get accelerated in the 789 00:36:46,880 --> 00:36:49,840 Speaker 2: direction you were pushing, because the pushing has a different 790 00:36:49,880 --> 00:36:52,600 Speaker 2: impact based on your momentum, right, and so in some 791 00:36:52,680 --> 00:36:54,960 Speaker 2: directions you already have a lot of momentum, and other 792 00:36:55,000 --> 00:36:57,080 Speaker 2: directions you don't have as much momentum, and so the 793 00:36:57,080 --> 00:37:00,680 Speaker 2: pushing changes your momentum differently in those different directions. So 794 00:37:00,840 --> 00:37:04,880 Speaker 2: force and acceleration no longer line up. So F doesn't 795 00:37:04,920 --> 00:37:08,279 Speaker 2: equal ME at very high velocities. Instead, you have to 796 00:37:08,360 --> 00:37:11,920 Speaker 2: use F equals change in momentum. That's the real formula. 797 00:37:12,560 --> 00:37:14,399 Speaker 1: I feel like you're kind of saying, like, just forget 798 00:37:14,440 --> 00:37:16,600 Speaker 1: about mass, like you've seen it on the couch and 799 00:37:16,600 --> 00:37:19,120 Speaker 1: nobody cares about that. Really, what we care about is 800 00:37:19,160 --> 00:37:21,720 Speaker 1: all hard you arc to push in any particular direction. 801 00:37:21,800 --> 00:37:24,240 Speaker 1: Is that kind of what you're saying, right, Like you're saying, 802 00:37:24,400 --> 00:37:27,520 Speaker 1: like res mass, that's just the thing. It doesn't really change, 803 00:37:27,560 --> 00:37:29,960 Speaker 1: nobody cares. What's really happening at these high speeds is 804 00:37:30,000 --> 00:37:32,000 Speaker 1: that weird things are happening with your momentum. 805 00:37:32,120 --> 00:37:34,360 Speaker 2: Yeah, I'm saying, let's talk about what's really important, and 806 00:37:34,400 --> 00:37:37,960 Speaker 2: it's high speeds. It's momentum that's important. Mass is still important. 807 00:37:38,000 --> 00:37:40,440 Speaker 2: It's very interesting and very important, and it tells you, 808 00:37:40,480 --> 00:37:43,040 Speaker 2: like what the thing is. In particle physics, we talk 809 00:37:43,080 --> 00:37:45,560 Speaker 2: about res mass all the time, Like we measure a 810 00:37:45,560 --> 00:37:47,520 Speaker 2: particle where like, oh, what was its mass? Okay, it 811 00:37:47,560 --> 00:37:49,560 Speaker 2: must be an electron or look we found a new 812 00:37:49,600 --> 00:37:52,319 Speaker 2: particle at one hundred and twenty five GeV mass, that's 813 00:37:52,320 --> 00:37:54,440 Speaker 2: got to be something new. We've never seen a particle 814 00:37:54,520 --> 00:37:58,320 Speaker 2: with that mass before. So mass is still very very important, 815 00:37:58,320 --> 00:38:00,520 Speaker 2: but it tells you something different. It's tells you something 816 00:38:00,560 --> 00:38:03,440 Speaker 2: about the character and the nature, the existence, the identity 817 00:38:03,560 --> 00:38:05,480 Speaker 2: of the particle. And what we're talking about here is 818 00:38:05,480 --> 00:38:07,920 Speaker 2: like motion near the speed of light, that's all about momentum. 819 00:38:08,320 --> 00:38:10,880 Speaker 2: And so really, let's talk about momentum when we're talking 820 00:38:10,880 --> 00:38:13,560 Speaker 2: about very high speed motion, and let's talk about mass 821 00:38:13,640 --> 00:38:15,600 Speaker 2: when we're talking about you know, what the thing is 822 00:38:15,719 --> 00:38:18,480 Speaker 2: made out of. I think those are two separate concepts, 823 00:38:18,480 --> 00:38:21,440 Speaker 2: and it's best to disentangle them. Is the point. Not 824 00:38:21,520 --> 00:38:23,600 Speaker 2: that nobody cares about rest mass, it's just it doesn't 825 00:38:23,600 --> 00:38:26,080 Speaker 2: help us understand motion near the speed of light as much. 826 00:38:26,320 --> 00:38:28,520 Speaker 1: No, yeah, I know what you mean. My spouse definitely 827 00:38:28,560 --> 00:38:32,480 Speaker 1: cares if I say to my count all day. But 828 00:38:32,520 --> 00:38:35,359 Speaker 1: I think what you're saying, maybe for listeners, I think 829 00:38:35,400 --> 00:38:37,560 Speaker 1: what you're saying is that if you've heard the phrase 830 00:38:37,600 --> 00:38:39,680 Speaker 1: like your mask gets bigger as you go closer to 831 00:38:39,680 --> 00:38:42,040 Speaker 1: the speed of light, then really what you should hear 832 00:38:42,080 --> 00:38:43,879 Speaker 1: in your head or how you should correct a person 833 00:38:44,000 --> 00:38:47,200 Speaker 1: saying it is that your relativistic mass gets bigger as 834 00:38:47,200 --> 00:38:49,600 Speaker 1: you get closer to the speed of light. And also 835 00:38:49,760 --> 00:38:54,359 Speaker 1: common asterisk. Nobody or modern physicists don't really talk about 836 00:38:54,400 --> 00:38:57,759 Speaker 1: relativistic mass or use that as a concept exactly. 837 00:38:57,960 --> 00:39:00,960 Speaker 2: A relativistic mass is really just another way to say energy. 838 00:39:01,239 --> 00:39:04,560 Speaker 2: Like the relationship in the formula is between relativistic mass 839 00:39:04,560 --> 00:39:06,840 Speaker 2: and energy that have exactly the same value. One is 840 00:39:06,880 --> 00:39:09,399 Speaker 2: just multiplied by the speed of light squared, so they 841 00:39:09,480 --> 00:39:12,880 Speaker 2: change in exactly the same way. So relativistic mass is 842 00:39:12,920 --> 00:39:14,919 Speaker 2: just another way to say, like how much energy does 843 00:39:14,920 --> 00:39:17,279 Speaker 2: something have. It's a way to try to combine the 844 00:39:17,320 --> 00:39:20,480 Speaker 2: rest mass and the kinetic energy together into one like 845 00:39:20,600 --> 00:39:24,359 Speaker 2: overall coherent energy, and then to say, oh, well that's 846 00:39:24,360 --> 00:39:26,200 Speaker 2: all A new kind of mass would just say that 847 00:39:26,400 --> 00:39:28,480 Speaker 2: energy of the particle is kind of like its mass 848 00:39:28,520 --> 00:39:30,759 Speaker 2: of motion. I'm just here to say, like, okay, let's 849 00:39:30,760 --> 00:39:32,960 Speaker 2: just leave mass to be mass of a rest particle 850 00:39:33,320 --> 00:39:35,919 Speaker 2: and to talk about motion. Will leave that as kinetic energy. 851 00:39:35,960 --> 00:39:38,080 Speaker 2: But we have to invent a concept called mass of motion. 852 00:39:38,200 --> 00:39:40,640 Speaker 2: We already have energy of motion. We already have this 853 00:39:40,760 --> 00:39:44,040 Speaker 2: concept described In other words, relativistic mass doesn't really add 854 00:39:44,040 --> 00:39:46,520 Speaker 2: anything if you already have momentum and you have energy. 855 00:39:46,600 --> 00:39:48,600 Speaker 2: So let's leave mass to do its job and tell 856 00:39:48,640 --> 00:39:50,640 Speaker 2: us about like the nature of the object when it's 857 00:39:50,640 --> 00:39:51,480 Speaker 2: sitting on its couch. 858 00:39:51,640 --> 00:39:53,680 Speaker 1: All right, Well, I think we've made that kind of clear, 859 00:39:53,800 --> 00:39:56,720 Speaker 1: and so let's get a little bit deeper into why 860 00:39:56,760 --> 00:39:59,920 Speaker 1: this term is not quite applicable or useful or help 861 00:40:00,360 --> 00:40:03,480 Speaker 1: or even accurate, and what it means about this speed 862 00:40:03,520 --> 00:40:06,080 Speaker 1: limit of the universe and why it exists. But first 863 00:40:06,160 --> 00:40:21,600 Speaker 1: let's take another quick break. All right, we're talking about 864 00:40:21,960 --> 00:40:25,480 Speaker 1: sitting on our couches. Who doesn't enjoy that? And when 865 00:40:25,520 --> 00:40:28,200 Speaker 1: we're sitting in our couch going at zero velocity relative 866 00:40:28,239 --> 00:40:30,279 Speaker 1: to other people, we have a certain amount of mass 867 00:40:30,280 --> 00:40:33,920 Speaker 1: and a certain resistance to movement, which Daniel, I think 868 00:40:33,960 --> 00:40:36,160 Speaker 1: you're saying, that's what we should call mass, not how 869 00:40:36,200 --> 00:40:37,920 Speaker 1: hard you are to push when you're going really. 870 00:40:37,719 --> 00:40:40,320 Speaker 2: Fast, exactly. I think the question you should ask yourself 871 00:40:40,360 --> 00:40:42,000 Speaker 2: is like what are you trying to talk about when 872 00:40:42,000 --> 00:40:44,239 Speaker 2: you talk about mass? And for me, I want to 873 00:40:44,280 --> 00:40:46,239 Speaker 2: talk about, like what is the thing made out of? 874 00:40:46,480 --> 00:40:48,520 Speaker 2: What does it have stored inside of it? And that 875 00:40:48,600 --> 00:40:51,080 Speaker 2: really doesn't change when you go to high velocity. A 876 00:40:51,160 --> 00:40:53,799 Speaker 2: proton moving and high speed doesn't have more stuff to 877 00:40:53,840 --> 00:40:56,600 Speaker 2: it doesn't have more gluons inside of it contributing to 878 00:40:56,640 --> 00:40:59,440 Speaker 2: its mass. It's the same proton. It's just moving faster. 879 00:40:59,520 --> 00:41:02,799 Speaker 2: It has energy of motion, which definitely will affect how 880 00:41:02,840 --> 00:41:04,799 Speaker 2: you accelerate it and how you push it and how 881 00:41:04,800 --> 00:41:07,920 Speaker 2: it responds to those pushes, but doesn't change what it 882 00:41:08,080 --> 00:41:10,520 Speaker 2: is fundamentally. And to me, mass is answering that question 883 00:41:10,600 --> 00:41:13,200 Speaker 2: of like, what is in this thing now? 884 00:41:13,280 --> 00:41:16,280 Speaker 1: I guess the question would be does your gravitational mass 885 00:41:16,320 --> 00:41:18,440 Speaker 1: also change as you go faster or close to the 886 00:41:18,480 --> 00:41:19,960 Speaker 1: speed of light or do you still have the same 887 00:41:20,000 --> 00:41:22,920 Speaker 1: gravity or is that not even relevant in relativity. 888 00:41:23,000 --> 00:41:26,000 Speaker 2: I think that's another reason not to use relativistic mass. 889 00:41:26,080 --> 00:41:28,919 Speaker 2: If you think about relativistic mass of things getting more 890 00:41:29,000 --> 00:41:31,040 Speaker 2: massive as their approach to speed of light and this 891 00:41:31,239 --> 00:41:34,480 Speaker 2: like mass of motion, then you're tempted to think that 892 00:41:34,560 --> 00:41:37,719 Speaker 2: things should have more gravity as they're moving faster. And 893 00:41:37,760 --> 00:41:39,520 Speaker 2: then you might go down the rabbit hole and be like, well, 894 00:41:39,560 --> 00:41:41,640 Speaker 2: if I take a proton and give it a lot 895 00:41:41,680 --> 00:41:44,120 Speaker 2: of speed, why doesn't it turn into a black hole. 896 00:41:44,160 --> 00:41:46,560 Speaker 2: Or if I throw a baseball fast enough, why doesn't 897 00:41:46,560 --> 00:41:49,319 Speaker 2: it collapse into a black hole? If it's gaining more 898 00:41:49,440 --> 00:41:53,400 Speaker 2: relativistic mass, shouldn't that give it also more gravitational mass 899 00:41:53,400 --> 00:41:56,320 Speaker 2: and collapse? Right. We talked about this once on a podcast. 900 00:41:56,320 --> 00:41:59,200 Speaker 2: It's a really interesting and fascinating question because, on one hand, 901 00:41:59,200 --> 00:42:01,600 Speaker 2: the curvature of base time, the thing that could actually 902 00:42:01,640 --> 00:42:04,720 Speaker 2: create a black hole for you, doesn't just depend on mass. 903 00:42:04,719 --> 00:42:06,680 Speaker 2: It also does depend on energy. 904 00:42:06,800 --> 00:42:07,000 Speaker 7: Right. 905 00:42:07,120 --> 00:42:10,400 Speaker 2: General relativity tells us that space bends in response to 906 00:42:10,480 --> 00:42:13,640 Speaker 2: mass and energy, and so you might think, like, oh, 907 00:42:13,680 --> 00:42:16,600 Speaker 2: it doesn't matter if you choose relativistic mass or inertial mass. 908 00:42:16,960 --> 00:42:19,680 Speaker 2: It just depends on the mass and the energy altogether. 909 00:42:19,920 --> 00:42:22,160 Speaker 2: And that's true. But general relativity is a bit more 910 00:42:22,160 --> 00:42:24,239 Speaker 2: complicated than that. You don't just like add up all 911 00:42:24,239 --> 00:42:26,840 Speaker 2: the mass and energy in space and say that tells 912 00:42:26,840 --> 00:42:29,799 Speaker 2: you the curvature. It's a stress energy tensor. There's all 913 00:42:29,880 --> 00:42:33,239 Speaker 2: these components and some ad and some subtract. It's very complicated, 914 00:42:33,280 --> 00:42:36,040 Speaker 2: and the bottom line is that kinetic energy does not 915 00:42:36,200 --> 00:42:39,480 Speaker 2: contribute to the curvature of space. We know this because 916 00:42:39,520 --> 00:42:42,759 Speaker 2: we know that black holes exist for every observer It's 917 00:42:42,800 --> 00:42:45,279 Speaker 2: not like if I'm holding a baseball, I don't see 918 00:42:45,280 --> 00:42:47,200 Speaker 2: a black hole and somebody is zipping by at high 919 00:42:47,239 --> 00:42:49,960 Speaker 2: speed sees it as a black hole. That's not possible. 920 00:42:50,200 --> 00:42:52,560 Speaker 2: Something's a black hole. It's a black hole for everybody, 921 00:42:53,000 --> 00:42:56,160 Speaker 2: And so only the rest mass can contribute to making 922 00:42:56,239 --> 00:42:58,799 Speaker 2: something a black hole, which is a long way of 923 00:42:58,840 --> 00:43:01,960 Speaker 2: saying relativistic mass confuses you because it makes you think 924 00:43:02,120 --> 00:43:04,200 Speaker 2: that you should be adding mass to this object, which 925 00:43:04,280 --> 00:43:06,000 Speaker 2: might lead it to a collapse to a black hole. 926 00:43:06,120 --> 00:43:09,200 Speaker 2: But that definitely doesn't happen, I see. 927 00:43:09,440 --> 00:43:12,279 Speaker 1: So then we just stick to mass as hell hard 928 00:43:12,280 --> 00:43:13,799 Speaker 1: it is to move me on my couch. And when 929 00:43:13,800 --> 00:43:15,719 Speaker 1: we talk about going close to the speed of light, 930 00:43:15,760 --> 00:43:19,120 Speaker 1: then we just just say that momentum gets harder to 931 00:43:19,280 --> 00:43:21,760 Speaker 1: change as you go faster and faster exactly. 932 00:43:22,000 --> 00:43:24,600 Speaker 2: And those calculations in general relativity of like folding in 933 00:43:24,680 --> 00:43:27,560 Speaker 2: kinetic energy, those are a beast And I don't even 934 00:43:27,560 --> 00:43:30,360 Speaker 2: think people have actually been able to do those calculations. 935 00:43:30,719 --> 00:43:32,600 Speaker 2: When they have to do them, they use the trick 936 00:43:32,640 --> 00:43:34,359 Speaker 2: and say, oh, well, if there's a black hole in 937 00:43:34,400 --> 00:43:36,840 Speaker 2: any frame, there's a black hole in every frame, so 938 00:43:36,920 --> 00:43:39,160 Speaker 2: let's do this calculation and the simplest for him, where 939 00:43:39,160 --> 00:43:41,319 Speaker 2: the thing is at rest, where it just depends on 940 00:43:41,360 --> 00:43:44,080 Speaker 2: its mass. I think nobody knows how to do that calculation. 941 00:43:44,440 --> 00:43:46,680 Speaker 2: It's so complicated, but it's just another way of saying 942 00:43:46,719 --> 00:43:48,960 Speaker 2: when we think about gravity also not just like the 943 00:43:48,960 --> 00:43:52,080 Speaker 2: inertial nature of the thing, but also the gravitational nature 944 00:43:52,080 --> 00:43:54,239 Speaker 2: of the thing, how much it bends space time, it 945 00:43:54,280 --> 00:43:56,520 Speaker 2: makes the most sense to think about the rest mass. 946 00:43:56,600 --> 00:43:59,400 Speaker 1: Well, I guess I'll give you that. Maybe it's easier 947 00:43:59,440 --> 00:44:01,960 Speaker 1: to think about it if you don't call something relativistic mass. 948 00:44:01,960 --> 00:44:04,080 Speaker 1: But then I guess my question would be why does 949 00:44:04,160 --> 00:44:07,640 Speaker 1: momentum get harder to change as the faster you go? Yeah, 950 00:44:07,719 --> 00:44:10,040 Speaker 1: that doesn't help you with that quobate question, right, that's 951 00:44:10,080 --> 00:44:12,919 Speaker 1: a very fundamental question about the universe. You're just calling 952 00:44:12,960 --> 00:44:14,640 Speaker 1: things differently. It's still the same question. 953 00:44:14,840 --> 00:44:17,360 Speaker 2: Yeah, it's still the same question. Why does the universe 954 00:44:17,400 --> 00:44:21,520 Speaker 2: conserve this quantity mass times velocity times gamma. The fascinating 955 00:44:21,520 --> 00:44:23,680 Speaker 2: thing is that that's what it conserves. It doesn't conserve 956 00:44:23,719 --> 00:44:28,320 Speaker 2: mass times velocity. Newtonian momentum is not conserved in the universe. 957 00:44:28,560 --> 00:44:32,279 Speaker 2: It's only this Einsteinian momentum. Mass times velocity times this 958 00:44:32,400 --> 00:44:36,000 Speaker 2: gamma factor. That's the thing that's actually conserved in the universe. 959 00:44:36,400 --> 00:44:37,840 Speaker 2: And you can see this if you take a class 960 00:44:37,840 --> 00:44:40,879 Speaker 2: in special relativity and you like think about collisions at 961 00:44:40,960 --> 00:44:43,000 Speaker 2: very very high energies and you try to use like 962 00:44:43,200 --> 00:44:46,520 Speaker 2: normal Galilean velocity edition formulas, and you see the momentum 963 00:44:46,560 --> 00:44:50,120 Speaker 2: is no longer conserved. So the universe conserves this quantity 964 00:44:50,200 --> 00:44:53,920 Speaker 2: mass times velocity times gamma. Why, well, that actually comes 965 00:44:53,960 --> 00:44:57,160 Speaker 2: out of the invariance of space. Right, space is the 966 00:44:57,200 --> 00:44:59,880 Speaker 2: same everywhere in the universe. That tells you that this 967 00:45:00,080 --> 00:45:04,120 Speaker 2: quantity mass times velocity times gamma is the thing that's conserved. 968 00:45:04,239 --> 00:45:06,800 Speaker 2: Why is that. It's because of the invariance of space. 969 00:45:06,840 --> 00:45:09,719 Speaker 2: Space seems to be the same everywhere, and that's why 970 00:45:09,760 --> 00:45:12,440 Speaker 2: momentum is conserved. That's a deep principle in physics. 971 00:45:12,600 --> 00:45:16,239 Speaker 1: Noether's theorem, Well, I think you're creating a causality there 972 00:45:16,600 --> 00:45:18,839 Speaker 1: a little bit, right, Like you don't know that one 973 00:45:18,880 --> 00:45:20,959 Speaker 1: causes the other. It's just that they just both happen 974 00:45:21,000 --> 00:45:21,439 Speaker 1: to be true. 975 00:45:21,480 --> 00:45:23,719 Speaker 2: Well, Notther's theorem tells us that there is a causality. 976 00:45:23,760 --> 00:45:26,120 Speaker 2: It says that for every symmetry in the universe, there 977 00:45:26,200 --> 00:45:28,960 Speaker 2: is a conserved quantity, and so for example, the fact 978 00:45:29,000 --> 00:45:32,719 Speaker 2: that there's no preferred direction in space leads to conservation 979 00:45:32,800 --> 00:45:34,440 Speaker 2: of angular momentum. 980 00:45:34,040 --> 00:45:38,480 Speaker 1: Or maybe the conservation of angular momentum is what space 981 00:45:39,120 --> 00:45:43,359 Speaker 1: it's invariant. Philosophically, I feel like you're making a conclusion there. 982 00:45:43,400 --> 00:45:45,480 Speaker 2: Yeah, I think that conclusion does come from Northern's theorem. 983 00:45:45,520 --> 00:45:47,040 Speaker 2: I understand the point you're making. But this is not 984 00:45:47,080 --> 00:45:49,640 Speaker 2: like an equal sign, right, It's not like a equals B, 985 00:45:49,800 --> 00:45:52,520 Speaker 2: and therefore you can't infer causality. If you follow the 986 00:45:52,520 --> 00:45:55,400 Speaker 2: derivation of Notther's theorem, then it definitely goes in one direction. 987 00:45:55,560 --> 00:45:59,120 Speaker 2: The conservation wills definitely flow from symmetries in the equations. 988 00:45:59,280 --> 00:46:01,440 Speaker 2: If you have a symmet in the laws of physics, 989 00:46:01,719 --> 00:46:05,320 Speaker 2: then it gives you these conservation laws. And it's everywhere, 990 00:46:05,360 --> 00:46:08,600 Speaker 2: like even in quantum mechanics, like local gauge. Symmetry of 991 00:46:08,680 --> 00:46:12,120 Speaker 2: quantum electrodynamics is the reason we have charge conservation in 992 00:46:12,160 --> 00:46:15,080 Speaker 2: the universe. So these things are pretty deep. And what 993 00:46:15,080 --> 00:46:16,839 Speaker 2: it tells us in this case is that it's mass 994 00:46:16,880 --> 00:46:20,120 Speaker 2: times velocity times this gamma factor. That's the thing the 995 00:46:20,280 --> 00:46:22,640 Speaker 2: universe cares about. And even if you don't like others 996 00:46:22,680 --> 00:46:25,240 Speaker 2: theorem and you don't believe in it or whatever, Observationally, 997 00:46:25,480 --> 00:46:27,880 Speaker 2: that's what we've measured Empirically. We're like, look, this is 998 00:46:27,920 --> 00:46:30,520 Speaker 2: the thing the universe seems to care about. This quantity, 999 00:46:30,760 --> 00:46:33,640 Speaker 2: not mass times velocity. So in some sense that's the 1000 00:46:33,640 --> 00:46:36,239 Speaker 2: fundamental thing. That's the thing that like the universe is 1001 00:46:36,280 --> 00:46:37,560 Speaker 2: telling us it cares about. 1002 00:46:37,719 --> 00:46:39,600 Speaker 1: Right, That's what I mean. It's like, that's the thing 1003 00:46:39,600 --> 00:46:42,520 Speaker 1: that we know is true. And whether it's caused by 1004 00:46:42,680 --> 00:46:46,000 Speaker 1: symmetry or it approves the theory, or whether it enables 1005 00:46:46,040 --> 00:46:49,200 Speaker 1: a symmetry that's sort of a philosophical question a little. 1006 00:46:49,040 --> 00:46:51,680 Speaker 2: Bit, yeah, a little bit, I mean, or theoretical. Experimentally, 1007 00:46:51,680 --> 00:46:53,239 Speaker 2: you're right, this is the thing we measure, and we 1008 00:46:53,320 --> 00:46:55,759 Speaker 2: notice the universe cares about absolutely. 1009 00:46:56,080 --> 00:46:58,680 Speaker 1: I guess then the question is what does that say 1010 00:46:58,680 --> 00:47:02,480 Speaker 1: about the universe that it cares about something doesn't just 1011 00:47:02,520 --> 00:47:03,440 Speaker 1: sit in the couch all day. 1012 00:47:03,480 --> 00:47:04,880 Speaker 2: I think it tells us a little bit about the 1013 00:47:04,960 --> 00:47:07,719 Speaker 2: history of human thoughts. You know, we've been like grappling 1014 00:47:08,080 --> 00:47:10,960 Speaker 2: with how to deal with these new discoveries that we've 1015 00:47:10,960 --> 00:47:13,160 Speaker 2: made and how to talk about them. One of my 1016 00:47:13,160 --> 00:47:15,800 Speaker 2: favorite Cootes from Einstein relates to this. He says, quote, 1017 00:47:15,840 --> 00:47:19,360 Speaker 2: the only justification for our concepts and systems of concepts 1018 00:47:19,640 --> 00:47:23,280 Speaker 2: is that they serve to represent the complex of our experiences. 1019 00:47:23,640 --> 00:47:26,440 Speaker 2: Beyond that, they have no legitimacy, by which he means like, 1020 00:47:26,520 --> 00:47:29,160 Speaker 2: you know, what is mass, what is momentum, what is force? 1021 00:47:29,440 --> 00:47:32,200 Speaker 2: They only make sense if they're talking about things we experience. 1022 00:47:32,239 --> 00:47:34,640 Speaker 2: We put these labels on things we see and experience 1023 00:47:34,680 --> 00:47:36,920 Speaker 2: in the universe, and we try to give them meaning. 1024 00:47:37,400 --> 00:47:40,480 Speaker 2: And there's actually Einstein originally who created this concept of 1025 00:47:40,600 --> 00:47:43,440 Speaker 2: relativistic mass when he was playing around with these equations 1026 00:47:43,520 --> 00:47:45,560 Speaker 2: and he was like, hmm, maybe it's useful to have 1027 00:47:45,640 --> 00:47:48,959 Speaker 2: this concept of mass that depends on your velocity. Later 1028 00:47:49,000 --> 00:47:51,840 Speaker 2: on he abandoned it. He realized, n that's kind of messy. 1029 00:47:52,280 --> 00:47:54,319 Speaker 2: And then later he said, it is not good to 1030 00:47:54,440 --> 00:47:57,640 Speaker 2: introduce the concept of relativistic mass of a moving body 1031 00:47:57,680 --> 00:48:01,279 Speaker 2: for which no clear definition can be He realized it 1032 00:48:01,320 --> 00:48:03,480 Speaker 2: was a bit messy. But you know, even geniuses like 1033 00:48:03,480 --> 00:48:07,200 Speaker 2: Einstein can't immediately disentangle these discoveries when he makes them. 1034 00:48:07,280 --> 00:48:09,600 Speaker 2: It takes a few years, a few decades of thinking 1035 00:48:09,600 --> 00:48:12,000 Speaker 2: about how this really lines up with our experience in 1036 00:48:12,040 --> 00:48:14,480 Speaker 2: the universe, what's the most sensible way to organize it? 1037 00:48:14,760 --> 00:48:17,120 Speaker 2: And the end is just us talking about how humans 1038 00:48:17,160 --> 00:48:19,520 Speaker 2: think about these things. The math is very, very clear, 1039 00:48:19,800 --> 00:48:22,239 Speaker 2: there's no ambiguity about it. It's really just like, what 1040 00:48:22,280 --> 00:48:23,560 Speaker 2: do you mean by this word? 1041 00:48:23,840 --> 00:48:25,879 Speaker 1: I think the basic idea is that it is true 1042 00:48:25,880 --> 00:48:28,080 Speaker 1: that the faster you move, the harder it is to 1043 00:48:28,120 --> 00:48:30,719 Speaker 1: move faster, and so we should think about that as 1044 00:48:30,800 --> 00:48:33,320 Speaker 1: just momentum getting more and more expensive the closer you 1045 00:48:33,360 --> 00:48:35,880 Speaker 1: get to the speed of light, and not use the 1046 00:48:35,880 --> 00:48:39,279 Speaker 1: word mass to think about how hard things are to 1047 00:48:39,280 --> 00:48:40,200 Speaker 1: move at those speeds. 1048 00:48:40,440 --> 00:48:43,400 Speaker 2: Yep, the universe has a higher tax for momentum millionaires. 1049 00:48:43,480 --> 00:48:46,880 Speaker 1: It's a progressive universe. Bernie Sanders and AOC would. 1050 00:48:46,680 --> 00:48:48,760 Speaker 2: Be proud until they start their own space company. 1051 00:48:49,000 --> 00:48:51,120 Speaker 1: All right, well, we hope you enjoyed that. Thanks for 1052 00:48:51,239 --> 00:48:52,680 Speaker 1: joining us, See you next time. 1053 00:49:00,480 --> 00:49:03,280 Speaker 2: Thanks for listening, and remember that Daniel and Jorge explain 1054 00:49:03,360 --> 00:49:07,279 Speaker 2: the Universe is a production of iHeartRadio. For more podcasts 1055 00:49:07,360 --> 00:49:12,000 Speaker 2: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever 1056 00:49:12,080 --> 00:49:13,800 Speaker 2: you listen to your favorite shows.