1 00:00:09,480 --> 00:00:12,680 Speaker 1: Hey, Daniel, what's the best question anyone has ever asked 2 00:00:12,680 --> 00:00:15,480 Speaker 1: you about dark matter? Well, it's tough to pick. There's 3 00:00:15,520 --> 00:00:17,960 Speaker 1: so many good ones. But I remember a nine year 4 00:00:18,000 --> 00:00:19,959 Speaker 1: old who read our book once and emailed me to 5 00:00:20,000 --> 00:00:24,200 Speaker 1: ask is dark matter bad matter? It must be a 6 00:00:24,200 --> 00:00:27,200 Speaker 1: Star Wars fan. You know the dark side doesn't sound 7 00:00:27,280 --> 00:00:31,080 Speaker 1: very friendly. Yeah, dark matter sounds world of unfriendly and mean. 8 00:00:31,160 --> 00:00:33,680 Speaker 1: It's doesn't never a really good pr team. Well, you know, 9 00:00:33,800 --> 00:00:36,440 Speaker 1: if there are dark matter physicists out there that we 10 00:00:36,520 --> 00:00:39,120 Speaker 1: can't see or touch, what do you think they would 11 00:00:39,120 --> 00:00:42,200 Speaker 1: call us? M I guess they'll probably call us dork matter. 12 00:00:42,960 --> 00:00:46,280 Speaker 1: We wouldn't seem dark to them and insidious. No, actually 13 00:00:46,320 --> 00:00:48,800 Speaker 1: we would. I mean if they have their own dark photons, 14 00:00:48,840 --> 00:00:52,080 Speaker 1: they wouldn't see ours, so we would be dark to them. Man, 15 00:00:52,320 --> 00:00:54,520 Speaker 1: I can just imagine the conferences. You know, you just 16 00:00:54,560 --> 00:00:56,520 Speaker 1: spent the whole day saying you're a dark matter. No, 17 00:00:56,640 --> 00:00:59,240 Speaker 1: you're a dark matter. That's probably actually true. That's exactly 18 00:00:59,320 --> 00:01:17,320 Speaker 1: what would happen. I am, forhand, a cartoonist and the 19 00:01:17,440 --> 00:01:20,560 Speaker 1: creator of PhD comments. Hi, I'm Daniel Whitson, I'm a 20 00:01:20,560 --> 00:01:24,560 Speaker 1: particle physicist, and I'm mostly made out of dork particles. Particles, 21 00:01:26,520 --> 00:01:30,399 Speaker 1: dark dork particles. That's the worst. Well, mostly in the 22 00:01:30,400 --> 00:01:32,640 Speaker 1: summer right now. I'm not going outside very much, so 23 00:01:33,400 --> 00:01:35,840 Speaker 1: pale dark. My dork particles are not very dark. But 24 00:01:35,920 --> 00:01:38,680 Speaker 1: welcome to our podcast Daniel and Jorge Explain the Universe, 25 00:01:38,720 --> 00:01:41,400 Speaker 1: a production of I Heart Radio, in which we take 26 00:01:41,440 --> 00:01:44,280 Speaker 1: you on a mental tour of the universe, zooming down 27 00:01:44,319 --> 00:01:46,120 Speaker 1: to see what the universe is made out of, what 28 00:01:46,160 --> 00:01:49,800 Speaker 1: it looks like at its largest scale, what crazy weird 29 00:01:49,840 --> 00:01:52,240 Speaker 1: stuff we encounter in it, and how we can all 30 00:01:52,360 --> 00:01:55,440 Speaker 1: understand it because humanity is on a journey, a journey 31 00:01:55,480 --> 00:01:59,040 Speaker 1: to understand this universe. We started out really kind of 32 00:01:59,040 --> 00:02:01,560 Speaker 1: clueless about the way things work, and we slowly put 33 00:02:01,600 --> 00:02:04,280 Speaker 1: together little pieces of the picture. But we're here to 34 00:02:04,320 --> 00:02:06,080 Speaker 1: give you a tour of what we have figured out 35 00:02:06,120 --> 00:02:08,880 Speaker 1: and what still remains unknown. Yeah, and it turns out 36 00:02:08,919 --> 00:02:11,720 Speaker 1: we haven't even left the garage, it seems, Daniel, in 37 00:02:11,720 --> 00:02:15,040 Speaker 1: our journey of discovery, because a huge percentage of the 38 00:02:15,160 --> 00:02:17,440 Speaker 1: universe is made out of stuff that we have no 39 00:02:17,520 --> 00:02:20,639 Speaker 1: idea about. You know, twenty five percent of the universe 40 00:02:20,760 --> 00:02:23,680 Speaker 1: is made out of something we call dark matter, which 41 00:02:24,320 --> 00:02:26,120 Speaker 1: is a huge mystery. Right, that's right, And that might 42 00:02:26,160 --> 00:02:28,560 Speaker 1: seem a bit deflating to you, like, wow, we haven't 43 00:02:28,560 --> 00:02:31,760 Speaker 1: figured anything out, But to me that's exciting, Like, wow, 44 00:02:31,840 --> 00:02:35,839 Speaker 1: we haven't figured anything out, which means more discoveries are 45 00:02:35,880 --> 00:02:39,000 Speaker 1: to come, which means mind blowing revelations about the true 46 00:02:39,040 --> 00:02:41,720 Speaker 1: nature of the universe are in our future. You know, 47 00:02:41,760 --> 00:02:43,400 Speaker 1: if you haven't left the garage, that means you can 48 00:02:43,400 --> 00:02:46,520 Speaker 1: still go back inside. If you forget something that's positive, 49 00:02:46,639 --> 00:02:48,720 Speaker 1: that's right, Like you forgot to pack your banana. How 50 00:02:48,720 --> 00:02:51,400 Speaker 1: can you even take a journey of discovery without banana? 51 00:02:52,200 --> 00:02:55,839 Speaker 1: About these days, who can go anywhere? Yeah, we're talking 52 00:02:55,840 --> 00:02:58,280 Speaker 1: about dark matter today and it's a huge mystery and 53 00:02:58,320 --> 00:03:00,840 Speaker 1: it's out there. But a big question is what is 54 00:03:00,880 --> 00:03:03,359 Speaker 1: it made out of? What is it? Is it a fluid, 55 00:03:03,600 --> 00:03:06,520 Speaker 1: is it a an energy? Or is it made out 56 00:03:06,520 --> 00:03:09,959 Speaker 1: of particles or something totally different. That's right, Everything we've 57 00:03:10,000 --> 00:03:13,280 Speaker 1: ever experienced, everything you've ever eaten or touched or tasted, 58 00:03:13,360 --> 00:03:16,760 Speaker 1: are made out of quarks and electrons and stuff like that, 59 00:03:17,040 --> 00:03:20,080 Speaker 1: and so we wonder does the same thing hold for 60 00:03:20,200 --> 00:03:22,960 Speaker 1: dark matter. But it's a pretty big extrapolation. I mean, 61 00:03:22,960 --> 00:03:24,919 Speaker 1: the kind of matter that we're made out of that's 62 00:03:25,000 --> 00:03:28,320 Speaker 1: very familiar, is unusual in the universe, and so it 63 00:03:28,320 --> 00:03:31,360 Speaker 1: seems kind of odd to extrapolate from this tiny little 64 00:03:31,400 --> 00:03:35,080 Speaker 1: corner to a huge fraction of the universe. And so 65 00:03:35,280 --> 00:03:37,760 Speaker 1: particle physicists think maybe it's made of particles, but I 66 00:03:37,880 --> 00:03:40,640 Speaker 1: like to think, hey, maybe it's made of something totally 67 00:03:40,680 --> 00:03:43,200 Speaker 1: weird and new. Yeah, we really have no idea. And 68 00:03:43,240 --> 00:03:46,920 Speaker 1: it's there's five times more dark matter in the universe 69 00:03:46,920 --> 00:03:49,640 Speaker 1: than there is of the stuff that we are made 70 00:03:49,640 --> 00:03:51,560 Speaker 1: out of. And it really could be anything like it 71 00:03:51,560 --> 00:03:54,000 Speaker 1: could be something that's not even a particle. That's right, 72 00:03:54,000 --> 00:03:57,160 Speaker 1: we've never seen matter that's not made of particles. Everything 73 00:03:57,200 --> 00:04:00,840 Speaker 1: we've ever experienced can be broken down into these units. 74 00:04:00,880 --> 00:04:03,200 Speaker 1: But that doesn't mean that everything is like that, Right. 75 00:04:03,520 --> 00:04:06,480 Speaker 1: We have to be very careful about generalizing. We've seen 76 00:04:06,560 --> 00:04:10,000 Speaker 1: so many times in physics when we've learned something we thought, oh, 77 00:04:10,000 --> 00:04:12,640 Speaker 1: this must be the way everything works, and then we 78 00:04:12,720 --> 00:04:15,760 Speaker 1: discover it's not. Actually and there are bigger stories, is 79 00:04:15,760 --> 00:04:18,640 Speaker 1: a larger context, and that's the goal of science, is 80 00:04:18,720 --> 00:04:22,880 Speaker 1: to reveal the actual truth, not just confirm our expectations. Yeah, 81 00:04:22,920 --> 00:04:25,320 Speaker 1: and so one thing we know about dark matter is 82 00:04:25,360 --> 00:04:28,400 Speaker 1: that we know that it feels gravity, because that's how 83 00:04:28,440 --> 00:04:30,560 Speaker 1: we know that it's there. I mean, we can't see it, 84 00:04:30,560 --> 00:04:32,880 Speaker 1: it's dark, but we know it's there because of gravity. 85 00:04:32,920 --> 00:04:36,440 Speaker 1: It's keeping the gaxies together, it's pulling things together, and 86 00:04:36,440 --> 00:04:40,599 Speaker 1: it's you know, affecting the trajectories of galaxies and stars. 87 00:04:41,520 --> 00:04:43,920 Speaker 1: So we know it feels gravity. We certainly do. It's 88 00:04:43,960 --> 00:04:48,080 Speaker 1: basically an invention to explain missing gravity. It's like a 89 00:04:48,120 --> 00:04:50,880 Speaker 1: gravity fudge factor. Yeah. We see things in the universe 90 00:04:50,880 --> 00:04:53,480 Speaker 1: that gravity has done, and we don't see the source 91 00:04:53,520 --> 00:04:56,920 Speaker 1: of that gravity. We're like, what's this invisible thing that's 92 00:04:57,000 --> 00:05:00,160 Speaker 1: making this gravity? And so dark matter is basically an 93 00:05:00,160 --> 00:05:03,960 Speaker 1: explanation for this gravity that we do observe, and so 94 00:05:04,000 --> 00:05:06,279 Speaker 1: it has to feel gravity otherwise it doesn't fit the 95 00:05:06,279 --> 00:05:09,200 Speaker 1: bill at all. But then the question is what else 96 00:05:09,240 --> 00:05:11,479 Speaker 1: does it do? Does it feel anything else? Does it 97 00:05:11,480 --> 00:05:14,479 Speaker 1: feel lonely? Does it feel resentful that we call it 98 00:05:14,560 --> 00:05:18,160 Speaker 1: dark matter? Yeah, we know that it feels gravity, and 99 00:05:18,200 --> 00:05:20,520 Speaker 1: so the question is does it feel any other forces? 100 00:05:20,640 --> 00:05:24,160 Speaker 1: And I think more interestingly about this question is does 101 00:05:24,200 --> 00:05:27,240 Speaker 1: it feel itself like canna bump into itself? Yeah, And 102 00:05:27,240 --> 00:05:30,279 Speaker 1: we got a really interesting question from a listener. Here's 103 00:05:30,279 --> 00:05:32,640 Speaker 1: an email I god from Joe from China, who I 104 00:05:32,680 --> 00:05:35,679 Speaker 1: think really put his finger on the question. He says, 105 00:05:35,960 --> 00:05:38,760 Speaker 1: if you were to take two particles of dark matter 106 00:05:38,839 --> 00:05:41,360 Speaker 1: and let them go in a vacuum, the gravity would 107 00:05:41,400 --> 00:05:44,640 Speaker 1: attract the two particles together. But then would they pass 108 00:05:44,800 --> 00:05:47,680 Speaker 1: right through each other and keep moving? Eventually would they 109 00:05:47,760 --> 00:05:50,000 Speaker 1: settle down and be able to share the same point 110 00:05:50,040 --> 00:05:55,760 Speaker 1: in space like overlapping? Can too dark matter particles? But 111 00:05:55,800 --> 00:05:59,119 Speaker 1: I guess bump into each other or occupy the same space? Yeah? 112 00:05:59,240 --> 00:06:01,479 Speaker 1: Do they not into each other and push back? Do 113 00:06:01,560 --> 00:06:03,520 Speaker 1: they pass right through each other? Can they sit right 114 00:06:03,560 --> 00:06:06,279 Speaker 1: on top of each other. It's a really fascinating question, 115 00:06:06,320 --> 00:06:07,640 Speaker 1: and it goes right to the heart of the sort 116 00:06:07,680 --> 00:06:10,640 Speaker 1: of the science matter of whether dark matter feels itself? 117 00:06:11,160 --> 00:06:13,120 Speaker 1: This question blow your mind a little bit? Yeah, I 118 00:06:13,160 --> 00:06:14,800 Speaker 1: did blow my mind a little bit. I just love 119 00:06:14,839 --> 00:06:17,280 Speaker 1: when somebody asks a new question, a question I haven't 120 00:06:17,320 --> 00:06:20,120 Speaker 1: heard before, or asks it in a new way. So 121 00:06:20,160 --> 00:06:23,839 Speaker 1: I haven't really thought about whether dark matter feels itself? Okay, 122 00:06:23,880 --> 00:06:25,799 Speaker 1: so it's kind of a funny question. Does dark matter 123 00:06:26,720 --> 00:06:30,680 Speaker 1: feel itself? That means that you know it feels itself. Gravitationally, right, 124 00:06:31,080 --> 00:06:33,440 Speaker 1: if you have one bit of dark matter here and 125 00:06:33,440 --> 00:06:35,120 Speaker 1: a bit of dark matter, they're they're gonna be They're 126 00:06:35,120 --> 00:06:37,080 Speaker 1: going to feel each other. They're gonna be attracted to 127 00:06:37,080 --> 00:06:39,960 Speaker 1: each other by gravity. But the question is, you know 128 00:06:40,040 --> 00:06:43,400 Speaker 1: what happens after they feel attracted by gravity. You know, 129 00:06:43,560 --> 00:06:46,520 Speaker 1: they they're moving towards each other. Are they gonna bump 130 00:06:46,560 --> 00:06:49,240 Speaker 1: against and and repel it themselves or are they going 131 00:06:49,279 --> 00:06:51,040 Speaker 1: to pass through each other? Or are they going to 132 00:06:51,120 --> 00:06:53,560 Speaker 1: stick together? Yeah, it's a great question. I mean, if 133 00:06:53,760 --> 00:06:55,960 Speaker 1: you and I have gravitational attraction, if we were out 134 00:06:56,000 --> 00:06:58,640 Speaker 1: in the middle of space, then gravity would very slowly 135 00:06:58,680 --> 00:07:00,640 Speaker 1: pulls together and we would bump into each other. I 136 00:07:00,680 --> 00:07:04,000 Speaker 1: wouldn't phase through each other. You woul get uncomfortable really fast. 137 00:07:04,120 --> 00:07:08,640 Speaker 1: What you're saying more awkward than in space. No one 138 00:07:08,680 --> 00:07:11,280 Speaker 1: can hear you say, hey, I need more space, Daniel, 139 00:07:11,320 --> 00:07:17,320 Speaker 1: get off me. But you couldn't write. You'd be stuck together. 140 00:07:17,760 --> 00:07:20,000 Speaker 1: That's right, we need some other kind of force. But 141 00:07:20,080 --> 00:07:21,960 Speaker 1: you and I do have other kind of forces, right, 142 00:07:22,000 --> 00:07:24,520 Speaker 1: the electromagnetic force who keep us from passing through each other. 143 00:07:24,760 --> 00:07:26,480 Speaker 1: So it's a good way to ask the questions. Yeah, 144 00:07:26,680 --> 00:07:29,320 Speaker 1: so the question is does dark matter feel itself? And so, 145 00:07:29,360 --> 00:07:31,960 Speaker 1: as usual, we went out into the world, and in 146 00:07:31,960 --> 00:07:35,000 Speaker 1: this case, the Internet, to see how many people felt 147 00:07:35,040 --> 00:07:37,400 Speaker 1: that they knew the answer to this question. That's right, 148 00:07:37,440 --> 00:07:40,680 Speaker 1: So thank you to everybody who volunteered to answer random 149 00:07:40,760 --> 00:07:44,400 Speaker 1: Internet physics questions. If you'd like to volunteer right to 150 00:07:44,520 --> 00:07:47,600 Speaker 1: us at questions at Daniel and Jorge dot com. Yeah, 151 00:07:47,640 --> 00:07:51,040 Speaker 1: you can ask us questions or get questions from us. 152 00:07:51,760 --> 00:07:55,080 Speaker 1: Questions in and questions out. It's an eternal flux of questions, right. 153 00:07:55,240 --> 00:07:56,720 Speaker 1: But think about it for a second. If you were 154 00:07:56,760 --> 00:07:59,760 Speaker 1: to try to answer the question does dark matter feel itself? 155 00:08:00,160 --> 00:08:03,160 Speaker 1: What would you answer? And no googling, no googling? What? 156 00:08:03,200 --> 00:08:08,920 Speaker 1: How about? Wikipedia? Also not allowed? About calling my physicist friend? 157 00:08:09,280 --> 00:08:12,920 Speaker 1: Totally allowed, totally allowed. All right, Well, here's what people 158 00:08:13,000 --> 00:08:15,280 Speaker 1: on the Internet had to say. I guess I'm really 159 00:08:15,320 --> 00:08:19,120 Speaker 1: not sure. I know that some scientists hypothesize the dark 160 00:08:19,160 --> 00:08:22,080 Speaker 1: matter is comprised of filaments, and if there were these 161 00:08:22,080 --> 00:08:24,640 Speaker 1: filaments in the dark matter, one would think that they 162 00:08:24,960 --> 00:08:28,040 Speaker 1: would interact in some way. I really don't think so. 163 00:08:28,400 --> 00:08:33,040 Speaker 1: I remember it interacting with something visible. That's a good one. 164 00:08:33,160 --> 00:08:36,840 Speaker 1: The interaction between light matter and dark matter is for 165 00:08:37,320 --> 00:08:39,600 Speaker 1: obviously still figuring that out, but I would think that 166 00:08:39,640 --> 00:08:42,880 Speaker 1: it does interact with itself. I don't think that turn 167 00:08:43,120 --> 00:08:47,359 Speaker 1: dark matter interacts with itself. Um. I think whether discussed 168 00:08:47,360 --> 00:08:50,439 Speaker 1: two galaxies colliding with each other, but there wasn't an 169 00:08:50,480 --> 00:08:56,240 Speaker 1: evidence or the details, so not itself. I would guess 170 00:08:56,400 --> 00:09:00,320 Speaker 1: that dark matter would interact with itself because I know 171 00:09:00,440 --> 00:09:04,160 Speaker 1: that one guess of what dark matter is is the 172 00:09:04,600 --> 00:09:09,840 Speaker 1: dark matter particle axion. And it's kind of hard to 173 00:09:10,040 --> 00:09:14,480 Speaker 1: visualize how a particle can pass through another particle. I 174 00:09:14,520 --> 00:09:17,160 Speaker 1: don't know. I've never thought about it. Okay, Um, dark 175 00:09:17,360 --> 00:09:20,680 Speaker 1: matter and dark energy confuse me a little bit. I 176 00:09:20,760 --> 00:09:25,440 Speaker 1: thought that dark matter was just a theory, and so 177 00:09:25,520 --> 00:09:28,800 Speaker 1: it's like we've we've seen something out there, and the 178 00:09:28,800 --> 00:09:30,920 Speaker 1: theory is that this dark matter, but we don't really know. 179 00:09:31,520 --> 00:09:34,680 Speaker 1: I don't think it can interact with normal matter. I 180 00:09:35,440 --> 00:09:39,400 Speaker 1: surely if it could pass through itself, we would be 181 00:09:39,440 --> 00:09:42,680 Speaker 1: able to see it. It might be a dark force, 182 00:09:42,800 --> 00:09:45,720 Speaker 1: which helps them incorrect. I know it doesn't interact with 183 00:09:45,880 --> 00:09:48,280 Speaker 1: regular matter. I think we don't know whether how it 184 00:09:48,320 --> 00:09:51,040 Speaker 1: interacts with itself. It is matter, so it has maths 185 00:09:51,080 --> 00:09:55,440 Speaker 1: al must interact gravitationally. I don't know. Well, I think 186 00:09:55,440 --> 00:09:58,800 Speaker 1: it does on some level. I don't know whether there 187 00:09:58,840 --> 00:10:02,480 Speaker 1: would be quantum or molecular, but I think it's got 188 00:10:02,480 --> 00:10:06,720 Speaker 1: to interact with itself enough to come together and blobs 189 00:10:06,760 --> 00:10:09,960 Speaker 1: big enough to cause gravitational lensing that we can see 190 00:10:09,960 --> 00:10:13,000 Speaker 1: here from Earth. I guess it's interact with yourself, since 191 00:10:13,040 --> 00:10:18,000 Speaker 1: it's i've gravity. All right, pretty thoughtful answers, you know, 192 00:10:18,000 --> 00:10:19,920 Speaker 1: people sort of thoughts through it. Yeah, there's some good 193 00:10:19,960 --> 00:10:21,760 Speaker 1: stuff in here. People are really thinking about what it 194 00:10:21,840 --> 00:10:25,280 Speaker 1: means to interact and whether gravity counts, and whether gravity 195 00:10:25,280 --> 00:10:31,400 Speaker 1: would make something bump or not? Does gravity count? Does 196 00:10:31,440 --> 00:10:34,480 Speaker 1: the Earth feel USh? Yeah? But also some people getting 197 00:10:34,480 --> 00:10:38,720 Speaker 1: confused about dark energy versus dark matter. That's another rabbit 198 00:10:38,760 --> 00:10:43,040 Speaker 1: hole there. Does dark energy feel? What is dark energy? Anyway? 199 00:10:43,120 --> 00:10:45,080 Speaker 1: We have no idea, all right, So the question is 200 00:10:45,120 --> 00:10:48,280 Speaker 1: that does dark matter feel? And so Daniel Um maybe 201 00:10:48,440 --> 00:10:50,760 Speaker 1: step us through what we know about dark matter and 202 00:10:50,800 --> 00:10:54,880 Speaker 1: it's it's not very sensitive. Unfortunately, you know, we wish 203 00:10:54,880 --> 00:10:57,559 Speaker 1: you would react more. Oh good, that's a good thing, 204 00:10:57,640 --> 00:11:00,240 Speaker 1: right as a thick skin. Well, perhaps know if you 205 00:11:00,240 --> 00:11:01,959 Speaker 1: want to get along with your dark matter roommate. But 206 00:11:01,960 --> 00:11:04,079 Speaker 1: if you want to do experiments to reveal the nature 207 00:11:04,080 --> 00:11:07,000 Speaker 1: of dark matter, you'd like it to respond sometimes, and 208 00:11:07,080 --> 00:11:09,720 Speaker 1: dark matter turns out to be very difficult to probe 209 00:11:09,920 --> 00:11:11,800 Speaker 1: because the only way we've been able to interact with 210 00:11:11,880 --> 00:11:15,360 Speaker 1: dark matter so far at all is with gravity. Like 211 00:11:15,400 --> 00:11:18,000 Speaker 1: we said, we've discovered dark matter because we looked at 212 00:11:18,000 --> 00:11:21,360 Speaker 1: how galaxies spin, and we notice that to spin as 213 00:11:21,400 --> 00:11:24,120 Speaker 1: fast as they do and hold all the stars in place, 214 00:11:24,280 --> 00:11:27,120 Speaker 1: you need a lot more gravity than is generated by 215 00:11:27,160 --> 00:11:30,040 Speaker 1: the stars we see, which means there must be something 216 00:11:30,120 --> 00:11:34,200 Speaker 1: else they're making that gravity. And we see blobs of 217 00:11:34,280 --> 00:11:36,520 Speaker 1: dark matter in the sky. We don't see them. We 218 00:11:36,640 --> 00:11:39,720 Speaker 1: deduce blobs of dark matter in the sky because they're 219 00:11:39,800 --> 00:11:43,160 Speaker 1: bending the light that passes through them. That's a gravitational effect. 220 00:11:43,640 --> 00:11:47,400 Speaker 1: So we have very concrete evidence that dark matter feels gravity. 221 00:11:47,440 --> 00:11:50,520 Speaker 1: That's why we call it matter, not just like dark 222 00:11:50,600 --> 00:11:54,160 Speaker 1: mysterious thing in the space right because it has gravity. 223 00:11:54,360 --> 00:11:56,960 Speaker 1: I see. It's sort of like the probervial elephant in 224 00:11:57,000 --> 00:11:59,520 Speaker 1: the room. You know it's there, everyone knows it's there, 225 00:12:00,080 --> 00:12:02,800 Speaker 1: but it's, uh, it's nobody's talking about. Sort of. It's 226 00:12:02,840 --> 00:12:05,160 Speaker 1: also sort of like the opposite of that, because the 227 00:12:05,240 --> 00:12:07,880 Speaker 1: elf in the room. Everybody is ignoring it, right though 228 00:12:07,880 --> 00:12:09,800 Speaker 1: you can all see it. In this case, we're all 229 00:12:09,880 --> 00:12:13,080 Speaker 1: desperately searching for it, but nobody can find it. It's 230 00:12:13,080 --> 00:12:16,200 Speaker 1: like you're right or right, except you're not. Well. You know, 231 00:12:16,360 --> 00:12:19,240 Speaker 1: sometimes being exactly the opposite direction is also a way 232 00:12:19,240 --> 00:12:23,640 Speaker 1: of being right. Yeah, yeah, you know up bean staff 233 00:12:24,000 --> 00:12:27,520 Speaker 1: yes times minus one. Alright, So we know it feels gravity, 234 00:12:27,559 --> 00:12:29,600 Speaker 1: but there are other forces that we know about in 235 00:12:29,640 --> 00:12:32,000 Speaker 1: the universe, and as far as we know, the dark 236 00:12:32,000 --> 00:12:34,360 Speaker 1: matter doesn't feel them. That's right. And so for example, 237 00:12:34,440 --> 00:12:37,200 Speaker 1: electromagnetism is a very powerful force and when that we 238 00:12:37,280 --> 00:12:40,200 Speaker 1: experience every day. The reason that your hand doesn't go 239 00:12:40,280 --> 00:12:42,320 Speaker 1: through the wall when you're trying to touch it is 240 00:12:42,400 --> 00:12:45,000 Speaker 1: that the wall has particles that are bound together with 241 00:12:45,040 --> 00:12:48,400 Speaker 1: electromagnetic forces, and so it does your hand and so 242 00:12:48,440 --> 00:12:50,400 Speaker 1: you think of them like a chain link fence trying 243 00:12:50,400 --> 00:12:53,040 Speaker 1: to pass through another chain link fence. That's what prevents 244 00:12:53,080 --> 00:12:57,080 Speaker 1: you from passing through another object. It's Electromagnetism is also 245 00:12:57,120 --> 00:13:00,280 Speaker 1: responsible for why things glow right, why we can see things, 246 00:13:01,040 --> 00:13:03,440 Speaker 1: or why they reflect light. To write like, it's light 247 00:13:03,559 --> 00:13:06,360 Speaker 1: hits it and then it interacts and it comes back out. 248 00:13:06,400 --> 00:13:08,760 Speaker 1: That's right. Even blobs of rock that don't glow on 249 00:13:08,800 --> 00:13:11,200 Speaker 1: their own, we can see them in the sky because 250 00:13:11,200 --> 00:13:14,400 Speaker 1: they reflect the sun's light, like the moon or like asteroids. 251 00:13:14,720 --> 00:13:17,160 Speaker 1: And so we know dark matter isn't like that because 252 00:13:17,200 --> 00:13:20,200 Speaker 1: it doesn't give off light, doesn't reflect light. Light passes 253 00:13:20,320 --> 00:13:24,880 Speaker 1: right through it. So right through it, yeah, exactly. And 254 00:13:25,000 --> 00:13:27,920 Speaker 1: I see this all the time in science fiction television, 255 00:13:28,320 --> 00:13:32,319 Speaker 1: that they encounter dark matter and it obscures their view. Right. Oh, 256 00:13:32,360 --> 00:13:34,520 Speaker 1: we can't get out of this cloud of dark matter 257 00:13:34,559 --> 00:13:36,959 Speaker 1: and we can't see where we are. What show are 258 00:13:36,960 --> 00:13:40,319 Speaker 1: you watching and seen that one? I don't remember the 259 00:13:40,400 --> 00:13:42,600 Speaker 1: name of it right now. I watched too much science fiction, 260 00:13:42,880 --> 00:13:44,320 Speaker 1: But you know that, to me, that sounds like a 261 00:13:44,320 --> 00:13:47,439 Speaker 1: fantastic situation, like, oh my gosh, look we found dark matter. 262 00:13:47,880 --> 00:13:50,120 Speaker 1: That's right home. We win the Nobel Prize. It's not like, 263 00:13:50,160 --> 00:13:52,640 Speaker 1: get out of my picture, my photo. It's like I 264 00:13:52,679 --> 00:13:56,000 Speaker 1: got a photo of dark matter. Exactly. We've been trying 265 00:13:56,040 --> 00:13:58,560 Speaker 1: to spot dark matter forever and you just figured it 266 00:13:58,559 --> 00:14:00,600 Speaker 1: out and now it seems like a hassled you. But 267 00:14:00,679 --> 00:14:02,320 Speaker 1: if you were in a cloud of dark matter, you 268 00:14:02,320 --> 00:14:05,240 Speaker 1: couldn't tell because it's invisible right. In fact, we think 269 00:14:05,280 --> 00:14:07,120 Speaker 1: we are in a cloud of dark matter. We think 270 00:14:07,120 --> 00:14:10,000 Speaker 1: the Earth is surrounded by dark matter, but we can't 271 00:14:10,040 --> 00:14:12,720 Speaker 1: see it because it doesn't reflect light. It doesn't feel 272 00:14:12,720 --> 00:14:15,920 Speaker 1: any electromagnetic forces at all. Yeah, we're swimming in dark 273 00:14:15,960 --> 00:14:19,160 Speaker 1: matter right, Like everyone who's listening to this podcast right 274 00:14:19,200 --> 00:14:22,240 Speaker 1: now is probably swimming in dark matter. Like right in 275 00:14:22,240 --> 00:14:25,160 Speaker 1: front of their eyes, is dark matter passing through or 276 00:14:25,560 --> 00:14:28,080 Speaker 1: sitting there? That's right. Dark matter, we think is spread 277 00:14:28,120 --> 00:14:31,440 Speaker 1: out through the galaxy. It's fairly dilute, so it's there's 278 00:14:31,440 --> 00:14:33,320 Speaker 1: a lot of it. There's a lot more dark matter 279 00:14:33,360 --> 00:14:35,480 Speaker 1: than normal matter, but it's much more spread out we 280 00:14:35,520 --> 00:14:38,280 Speaker 1: think the normal matter, which tends to cluster into planets 281 00:14:38,320 --> 00:14:40,920 Speaker 1: and stars and stuff. So we think there's like one 282 00:14:41,040 --> 00:14:44,560 Speaker 1: squirrel's worth of dark matter in the volume of the Earth. 283 00:14:44,640 --> 00:14:49,240 Speaker 1: But it's there, it's out there. Wait, what one squirrels worth? 284 00:14:51,800 --> 00:14:55,160 Speaker 1: One squirrel? Yeah, well it's a standard international unit of mass. 285 00:14:55,200 --> 00:14:59,520 Speaker 1: One squirrel. Are you not familiar with squirrels? I don't. 286 00:14:59,560 --> 00:15:03,760 Speaker 1: I didn't usually baked with squirrels. All my favorite recipes 287 00:15:03,800 --> 00:15:06,440 Speaker 1: are in units of squirrels. You know, a third of 288 00:15:06,480 --> 00:15:08,840 Speaker 1: a squirrel of oats and you know, half a squirrel 289 00:15:08,840 --> 00:15:12,680 Speaker 1: of sugar man. That's that's the pandemic for you. It's 290 00:15:12,720 --> 00:15:15,760 Speaker 1: forcing us into a more primitive Yeah, come over to 291 00:15:15,800 --> 00:15:18,080 Speaker 1: my house sometime. We'll have a squirrel roast. So wait, 292 00:15:18,200 --> 00:15:20,480 Speaker 1: the Earth you're saying is in a pool of dark 293 00:15:20,480 --> 00:15:23,080 Speaker 1: matter that has the same amount of mass as a squirrel. 294 00:15:23,200 --> 00:15:25,560 Speaker 1: That's what it means. That's right, And there's more dark 295 00:15:25,600 --> 00:15:27,800 Speaker 1: matter than this normal matter, but the dark matter is 296 00:15:27,800 --> 00:15:30,360 Speaker 1: more diffuse, it's more spread out, and so out there 297 00:15:30,400 --> 00:15:33,240 Speaker 1: in empty space is about as much dark matter as 298 00:15:33,240 --> 00:15:35,520 Speaker 1: there is here in our solar system. You just made 299 00:15:35,560 --> 00:15:37,920 Speaker 1: me think of a giant squirrel the size of the 300 00:15:37,960 --> 00:15:41,720 Speaker 1: Earth that a dark matter. You're a very visual person, 301 00:15:41,760 --> 00:15:43,160 Speaker 1: so I'd love to see a drawing of that of 302 00:15:43,160 --> 00:15:47,680 Speaker 1: a squirrel attacking the Earth and earth size squirrel attacking us. Finally, 303 00:15:47,680 --> 00:15:50,520 Speaker 1: the aliens have come and they're just giants space squirrels. 304 00:15:51,280 --> 00:15:53,480 Speaker 1: You did it again. Just because it's a dark matter squirrel, 305 00:15:53,480 --> 00:15:55,800 Speaker 1: you assume it was bad, Daniel. Yeah, maybe it's a 306 00:15:55,840 --> 00:15:59,560 Speaker 1: friendly planet sized space squirrel. Yeah, you're right. Now, so 307 00:15:59,640 --> 00:16:02,320 Speaker 1: we we know that it doesn't feel electromagnetism, and that's 308 00:16:02,360 --> 00:16:05,000 Speaker 1: principally because it's dark, we can't see it. But there 309 00:16:05,000 --> 00:16:07,280 Speaker 1: are other forces out there, right, we talk about the 310 00:16:07,320 --> 00:16:11,800 Speaker 1: weak nuclear force. That's a very very non powerful force. 311 00:16:11,840 --> 00:16:15,800 Speaker 1: It's a weak force between particles. Neutrinos feel this force, 312 00:16:15,920 --> 00:16:18,400 Speaker 1: Leptons feel this force. All the particles we know feel 313 00:16:18,440 --> 00:16:21,720 Speaker 1: this force, but it's not very powerful. Like neutrinos pass 314 00:16:21,840 --> 00:16:25,040 Speaker 1: through a light year of lead and have a fifty 315 00:16:25,040 --> 00:16:28,480 Speaker 1: percent chance of feeling anything using the weak force. Our 316 00:16:28,560 --> 00:16:31,160 Speaker 1: particles also feeling, like the particles in my body that 317 00:16:31,240 --> 00:16:33,280 Speaker 1: they feel the weak force. Yeah, all the particles in 318 00:16:33,320 --> 00:16:35,800 Speaker 1: your body, on the electrons and the corks, they all 319 00:16:35,880 --> 00:16:39,600 Speaker 1: feel this force. It's responsible, for example, for a beta decay. 320 00:16:39,640 --> 00:16:42,640 Speaker 1: So one of the corks in a neutron can turn 321 00:16:42,680 --> 00:16:45,240 Speaker 1: into another kind of quirk which turns your neutron into 322 00:16:45,280 --> 00:16:48,440 Speaker 1: a proton. That happens through the weak force, and that's 323 00:16:48,440 --> 00:16:52,240 Speaker 1: why a little neutrinos emitted along with the electron that's created. 324 00:16:52,480 --> 00:16:55,000 Speaker 1: So all the particles in your body are sensitive to 325 00:16:55,000 --> 00:16:58,400 Speaker 1: the weak force. Neutrinos that pass through you can interact 326 00:16:58,400 --> 00:17:00,920 Speaker 1: with you. It's just very very un likely, like there's 327 00:17:00,920 --> 00:17:05,440 Speaker 1: a hundred billion newtrinos passing through your fingernail every second, 328 00:17:05,920 --> 00:17:07,920 Speaker 1: and you don't feel them well, and we know that 329 00:17:07,960 --> 00:17:10,080 Speaker 1: the dark matter doesn't feel it. We suspect that dark 330 00:17:10,080 --> 00:17:12,840 Speaker 1: matter doesn't feel it because we've looked very very carefully. 331 00:17:13,080 --> 00:17:16,840 Speaker 1: We've set up these big underground experiments filled with very quiet, 332 00:17:16,920 --> 00:17:20,080 Speaker 1: heavy liquids, and we have a lot of those atoms 333 00:17:20,080 --> 00:17:21,919 Speaker 1: in there, and we hope that a dark matter particle 334 00:17:21,960 --> 00:17:25,159 Speaker 1: would come by and bump into one of those xenon atoms, 335 00:17:25,200 --> 00:17:27,240 Speaker 1: for example, and we could spot it. And this is 336 00:17:27,440 --> 00:17:31,159 Speaker 1: similar to how newtrinos were first discovered with vast tanks 337 00:17:31,160 --> 00:17:34,680 Speaker 1: of underground liquid waiting for a little recoil from one 338 00:17:34,680 --> 00:17:37,280 Speaker 1: of those atoms. So we have a similar in spirit 339 00:17:37,359 --> 00:17:41,440 Speaker 1: kind of experiment done underground to look for passing dark 340 00:17:41,480 --> 00:17:44,200 Speaker 1: matter particles. All right, So, and there's also the strong force, 341 00:17:44,320 --> 00:17:46,600 Speaker 1: right which that one is pretty important, but dark matter 342 00:17:46,600 --> 00:17:48,560 Speaker 1: doesn't feel that one either. That's right. The strong force 343 00:17:48,720 --> 00:17:51,600 Speaker 1: is very powerful and so unlike the weak force, which 344 00:17:51,800 --> 00:17:53,520 Speaker 1: you know, if dark matter felt it, it would be 345 00:17:53,600 --> 00:17:57,439 Speaker 1: difficult but possible to detect in large underground experiments. If 346 00:17:57,520 --> 00:17:59,560 Speaker 1: dark matter felt the strong force, we would notice that 347 00:17:59,680 --> 00:18:02,040 Speaker 1: right way. I mean, it's very powerful. It wouldn't take 348 00:18:02,040 --> 00:18:04,760 Speaker 1: a very big experiment. If dark matter felt the strong force, 349 00:18:04,920 --> 00:18:07,400 Speaker 1: then it would react to almost every particle in your 350 00:18:07,440 --> 00:18:09,840 Speaker 1: body and every particle in the Earth. It wouldn't be 351 00:18:09,840 --> 00:18:12,080 Speaker 1: hard to notice. It would break up particles all the time. 352 00:18:12,119 --> 00:18:14,280 Speaker 1: It would be a very powerful force. All right. So 353 00:18:14,320 --> 00:18:17,359 Speaker 1: then those are the four main forces that we know about, 354 00:18:17,680 --> 00:18:20,560 Speaker 1: and as far as we know, dark matter only feels gravity. 355 00:18:21,160 --> 00:18:24,719 Speaker 1: And so the question is what what happens to dark matter? Then? 356 00:18:24,720 --> 00:18:27,680 Speaker 1: Does it bump into itself or does it ignore it 357 00:18:27,760 --> 00:18:30,760 Speaker 1: even itself? And so let's get into the question of 358 00:18:30,840 --> 00:18:33,600 Speaker 1: does dark matter feel itself? But first let's take a 359 00:18:33,680 --> 00:18:49,480 Speaker 1: quick break right there. We're talking about dark matter and 360 00:18:49,520 --> 00:18:52,760 Speaker 1: whether it can feel itself, and so we know it 361 00:18:52,800 --> 00:18:56,280 Speaker 1: feels gravity, and we know it doesn't feel the other forces. 362 00:18:56,320 --> 00:18:58,680 Speaker 1: So I guess the question is, you know what happens 363 00:18:58,680 --> 00:19:00,959 Speaker 1: when too dark matter? Part of goals if they are 364 00:19:01,040 --> 00:19:03,920 Speaker 1: particles get attracted to each other, what's going to happen 365 00:19:03,960 --> 00:19:05,760 Speaker 1: and are they gonna bump into each other or just 366 00:19:05,840 --> 00:19:07,960 Speaker 1: totally ignore each other. It's a really fun sort of 367 00:19:07,960 --> 00:19:10,919 Speaker 1: thought experiment. This is exactly what Joe is asking. And 368 00:19:11,000 --> 00:19:14,119 Speaker 1: so you know, let's assume for the dark matter only 369 00:19:14,160 --> 00:19:17,479 Speaker 1: feels gravity, that no other forces we don't know about 370 00:19:17,600 --> 00:19:20,280 Speaker 1: that are involved, that it's just a gravitational thing. And 371 00:19:20,440 --> 00:19:23,359 Speaker 1: you know, that is totally possible. It's possible for a 372 00:19:23,400 --> 00:19:26,399 Speaker 1: particle to have mass and no other interactions. It's sort 373 00:19:26,440 --> 00:19:28,560 Speaker 1: of incredible, but it would be something that we've never 374 00:19:28,600 --> 00:19:32,199 Speaker 1: seen before. But hey, this physics is full of surprises. Well, 375 00:19:32,240 --> 00:19:35,320 Speaker 1: because we know about neutrinos, right, Neutrinos are also sort 376 00:19:35,320 --> 00:19:37,880 Speaker 1: of selective about which forces it feels. Yeah, we don't 377 00:19:37,960 --> 00:19:40,879 Speaker 1: understand that at all, Like why do neutrinos only feel 378 00:19:40,960 --> 00:19:43,159 Speaker 1: the weak force? You know, why don't they feel the 379 00:19:43,200 --> 00:19:46,160 Speaker 1: strong force? Why don't electrons feel the strong force. It's 380 00:19:46,200 --> 00:19:48,680 Speaker 1: just sort of like a thing we observe. We notice 381 00:19:48,720 --> 00:19:51,600 Speaker 1: these things. All the corks feel the strong force. None 382 00:19:51,600 --> 00:19:54,160 Speaker 1: of the electrons or neutrinos or muans or towels, those 383 00:19:54,160 --> 00:19:57,440 Speaker 1: particles feel it. Why not? I mean, we don't know. 384 00:19:57,800 --> 00:20:01,399 Speaker 1: We know that neutrinos don't feel elect a magnetism because 385 00:20:01,400 --> 00:20:03,840 Speaker 1: they don't have a charge. Only things with electric charge 386 00:20:03,880 --> 00:20:06,679 Speaker 1: can feel that. But we don't understand this. It's just 387 00:20:06,760 --> 00:20:09,120 Speaker 1: it's something we observe, something that we hope one day 388 00:20:09,119 --> 00:20:12,199 Speaker 1: to explain From the bottoms of principle. But at this 389 00:20:12,240 --> 00:20:15,760 Speaker 1: point we're pretty clueless. All right, So then what happens, 390 00:20:15,920 --> 00:20:18,600 Speaker 1: Like Joe put it, What if I take two particles 391 00:20:18,600 --> 00:20:21,399 Speaker 1: of dark matter in an empty universe, said I'm a 392 00:20:21,440 --> 00:20:24,040 Speaker 1: meter apart, and then I let go. Well, they attract 393 00:20:24,080 --> 00:20:26,840 Speaker 1: each other, right, gravity pulls them together. But then now 394 00:20:26,880 --> 00:20:29,680 Speaker 1: imagine what happens when sort of their edges meet, right, 395 00:20:29,680 --> 00:20:32,399 Speaker 1: what happens that one blob versus the other blob. Now, 396 00:20:32,440 --> 00:20:35,719 Speaker 1: if this was normal matter, when their edges meet, then 397 00:20:35,760 --> 00:20:38,440 Speaker 1: they would repel each other. They would bump, literally, because 398 00:20:38,440 --> 00:20:41,520 Speaker 1: they have forces to push against each other with. But 399 00:20:42,280 --> 00:20:46,320 Speaker 1: if all you have is gravity, gravity can't push. Gravity 400 00:20:46,400 --> 00:20:50,480 Speaker 1: only pulls. Right, you have two objects with positive mass, 401 00:20:50,520 --> 00:20:53,280 Speaker 1: they only pull on each other unless you have negative 402 00:20:53,320 --> 00:20:56,040 Speaker 1: mass particles. And we have a whole other podcast episode 403 00:20:56,080 --> 00:20:59,120 Speaker 1: about that. Gravity can only attract. So there's no way 404 00:20:59,119 --> 00:21:02,040 Speaker 1: for gravity to put ish, which means these particles just 405 00:21:02,080 --> 00:21:06,119 Speaker 1: get closer and closer. There's no repelling force, and eventually 406 00:21:06,200 --> 00:21:08,919 Speaker 1: they pass through each other. Right, Because there I guess 407 00:21:09,320 --> 00:21:11,840 Speaker 1: point particles right, Well, we don't know if they're made 408 00:21:11,840 --> 00:21:14,480 Speaker 1: of particles, right, but imagine they are mative particles. So 409 00:21:14,520 --> 00:21:16,399 Speaker 1: I think these arguments hold even if they're made of 410 00:21:16,440 --> 00:21:19,120 Speaker 1: some weird other kind of thing that you know isn't 411 00:21:19,119 --> 00:21:23,120 Speaker 1: divided up into little particles. But they can basically cohabitate 412 00:21:23,200 --> 00:21:25,840 Speaker 1: the same space. Right. The only thing that prevents things 413 00:21:25,840 --> 00:21:29,760 Speaker 1: from overlapping are the forces. Right. The reason that one 414 00:21:29,800 --> 00:21:32,200 Speaker 1: proton doesn't want to be next to another proton isn't 415 00:21:32,200 --> 00:21:35,679 Speaker 1: because the stuff in them is like you're crowding me 416 00:21:35,800 --> 00:21:38,240 Speaker 1: or something. It's all about the forces. As you said, 417 00:21:38,240 --> 00:21:40,920 Speaker 1: if you imagined that their point particles, they have zero volume. 418 00:21:41,480 --> 00:21:44,000 Speaker 1: So the only thing that gives distance to things are 419 00:21:44,040 --> 00:21:46,920 Speaker 1: forces that repel, and gravity can't do that. Well. I 420 00:21:46,920 --> 00:21:49,480 Speaker 1: think what's interesting to think about is that you know 421 00:21:49,480 --> 00:21:52,159 Speaker 1: they wouldn't share the same space for very long, right, 422 00:21:52,359 --> 00:21:54,640 Speaker 1: because if you set them a meter apart, they're gonna 423 00:21:54,640 --> 00:21:56,359 Speaker 1: ask some velocity by the time that you get to 424 00:21:56,400 --> 00:21:58,240 Speaker 1: the center, and so they'll just keep going. Yeah, they 425 00:21:58,280 --> 00:22:00,640 Speaker 1: pass through each other, but then gravity will slow them down, 426 00:22:01,280 --> 00:22:03,239 Speaker 1: stop them, turn them around, and they'll come through each 427 00:22:03,280 --> 00:22:06,320 Speaker 1: other again. So like slash back and forth forever and 428 00:22:06,440 --> 00:22:10,320 Speaker 1: right forever, right, because there's nothing, nothing would be making 429 00:22:10,320 --> 00:22:13,600 Speaker 1: you lose energy. Yeah, in your hypothetical universe where there 430 00:22:13,760 --> 00:22:16,520 Speaker 1: is nothing else, then they would slash back and forth forever. 431 00:22:17,080 --> 00:22:19,760 Speaker 1: If they had some other way to lose energy. There's 432 00:22:19,800 --> 00:22:22,520 Speaker 1: like larger blobs of dark matter that are sort of 433 00:22:22,720 --> 00:22:25,320 Speaker 1: you know, equilibrating them or something. Then eventually they would 434 00:22:25,359 --> 00:22:27,679 Speaker 1: slow down and then stop and sit right in the 435 00:22:27,720 --> 00:22:31,560 Speaker 1: same place. But maybe not dark matter what you're saying. 436 00:22:31,560 --> 00:22:34,120 Speaker 1: In in the real universe, that would it is possible 437 00:22:34,160 --> 00:22:36,880 Speaker 1: out there that dark matter has settled. Yeah, it is possible. 438 00:22:36,960 --> 00:22:39,000 Speaker 1: In fact, we think that dark matter is not moving 439 00:22:39,080 --> 00:22:41,680 Speaker 1: very much. There's two theories of dark matter. There's warm 440 00:22:41,760 --> 00:22:44,880 Speaker 1: dark matter and cold dark matter. And warm dark matter 441 00:22:44,960 --> 00:22:47,480 Speaker 1: just means that the dark matter sort of zipping around everywhere. 442 00:22:47,520 --> 00:22:50,720 Speaker 1: It's like has high velocity, and cold dark matter means 443 00:22:50,920 --> 00:22:54,040 Speaker 1: it's mostly sitting around. It's like sluggist chilling and not 444 00:22:54,119 --> 00:22:58,240 Speaker 1: moving very fast. It's chilling matter exactly, chill dark matter. 445 00:23:00,160 --> 00:23:03,159 Speaker 1: That's for a statement of its feelings. Man. Yeah, so 446 00:23:03,200 --> 00:23:06,200 Speaker 1: we think the dark matter is cold. It's cold dark matter, 447 00:23:06,200 --> 00:23:08,119 Speaker 1: and so it's not moving very much. But yeah, if 448 00:23:08,119 --> 00:23:11,359 Speaker 1: you imagine so, like a gravitational well constructed by something else, 449 00:23:11,400 --> 00:23:14,520 Speaker 1: some larger object than two pieces of dark matter in 450 00:23:14,560 --> 00:23:17,000 Speaker 1: that well would fall together to the bottom of it, 451 00:23:17,040 --> 00:23:18,879 Speaker 1: and then they could just sit on top of each other. 452 00:23:19,280 --> 00:23:21,320 Speaker 1: And I guess the same would happen with dark matter 453 00:23:21,400 --> 00:23:25,280 Speaker 1: and regular matter, right, they would technically, like we only 454 00:23:25,320 --> 00:23:28,240 Speaker 1: interact with gravity with dark matter, and so therefore we 455 00:23:28,480 --> 00:23:30,720 Speaker 1: would just pass through us back and forth. Oh that's 456 00:23:30,720 --> 00:23:32,240 Speaker 1: a good point. Yeah, And I think you're right, And 457 00:23:32,240 --> 00:23:34,800 Speaker 1: I think dark matter is passing through us right now, 458 00:23:35,000 --> 00:23:37,720 Speaker 1: or we're passing through dark matter in the same way 459 00:23:37,720 --> 00:23:40,440 Speaker 1: that like neutrinos passed through us. But if there literally 460 00:23:40,640 --> 00:23:44,080 Speaker 1: is no interaction other than gravity, then you're right. Dark 461 00:23:44,080 --> 00:23:46,080 Speaker 1: matter can be in you and you can be in 462 00:23:46,200 --> 00:23:48,800 Speaker 1: dark matter. Oh man, I feel like now we're getting 463 00:23:49,040 --> 00:23:52,919 Speaker 1: ethereal here about dark matter and spiritual It's in you, 464 00:23:53,480 --> 00:23:56,480 Speaker 1: in all of us, and it's not just a hypothetical question. 465 00:23:56,560 --> 00:23:59,880 Speaker 1: We sort of did this experiment on a massive cause, 466 00:24:00,000 --> 00:24:02,159 Speaker 1: a logical scale. Oh yeah, we did it. Oh we 467 00:24:02,280 --> 00:24:03,800 Speaker 1: didn't sort of do what I mean, as much as 468 00:24:03,800 --> 00:24:06,800 Speaker 1: astronomers do anything. They just sort of watched the universe 469 00:24:06,840 --> 00:24:10,600 Speaker 1: do stuff. You say, astronomers don't do anything, Well, they 470 00:24:10,600 --> 00:24:13,679 Speaker 1: don't construct experiments, right, They don't go like, let's build 471 00:24:13,680 --> 00:24:17,080 Speaker 1: a sun that has these properties and distribute these planets 472 00:24:17,119 --> 00:24:18,760 Speaker 1: around it and let it go. Right. They don't do 473 00:24:18,800 --> 00:24:22,160 Speaker 1: that except in simulations, but they just look around and 474 00:24:22,320 --> 00:24:25,359 Speaker 1: find that situation because the universe is so vast and 475 00:24:25,400 --> 00:24:28,359 Speaker 1: so varied that they can usually find whatever they're looking for. 476 00:24:28,440 --> 00:24:33,160 Speaker 1: The shoppers, not doers. I love astronomers. Nothing I say 477 00:24:33,200 --> 00:24:38,040 Speaker 1: should be construed as negative towards astronomy or astronomers. But yeah, 478 00:24:38,200 --> 00:24:42,560 Speaker 1: they're mostly observers, right, And what they found was these 479 00:24:42,640 --> 00:24:46,680 Speaker 1: two clusters of galaxies that had slammed into each other. Yeah, 480 00:24:46,800 --> 00:24:49,879 Speaker 1: it's called the Bullet cluster. Right, it's called the Bullet cluster. 481 00:24:50,160 --> 00:24:51,960 Speaker 1: And this is a collision that happened a long long 482 00:24:52,000 --> 00:24:55,600 Speaker 1: time ago. And by galaxy cluster, we just mean literally 483 00:24:55,640 --> 00:24:59,040 Speaker 1: a group of galaxies, because galaxies orbit each other and 484 00:24:59,080 --> 00:25:00,879 Speaker 1: are sort of grouped to either the same way that 485 00:25:01,000 --> 00:25:04,920 Speaker 1: like stars are grouped together into a galaxy, galaxies themselves 486 00:25:04,920 --> 00:25:08,480 Speaker 1: are grouped together into clusters of galaxies, and sometimes these 487 00:25:08,480 --> 00:25:12,359 Speaker 1: things collide. Right. Dark energy is pushing the whole universe apart, 488 00:25:12,440 --> 00:25:15,800 Speaker 1: creating spaces between things, but there are still forces and 489 00:25:15,840 --> 00:25:19,240 Speaker 1: still directions that can pull things together. And so gravity 490 00:25:19,280 --> 00:25:22,920 Speaker 1: pulled these two clusters together and they slammed into each other, 491 00:25:23,520 --> 00:25:26,320 Speaker 1: and so we basically got to see this experiment happened. Yeah, 492 00:25:26,320 --> 00:25:28,840 Speaker 1: you can look it up online if you google bullet cluster, 493 00:25:29,000 --> 00:25:32,320 Speaker 1: and they're pretty spectacular images. Like, imagine a cluster of 494 00:25:32,320 --> 00:25:35,520 Speaker 1: galaxies slamming into another cluster of galaxies. It's like a 495 00:25:35,560 --> 00:25:39,000 Speaker 1: special effects bonanza. It's like a large hadron collider on 496 00:25:39,080 --> 00:25:45,440 Speaker 1: the biggest scale possible, the largest, the large gaxy collider collider. Yeah, 497 00:25:45,520 --> 00:25:48,360 Speaker 1: and of course you can't see it happen in real time. 498 00:25:48,400 --> 00:25:51,080 Speaker 1: The whole collision took, you know, hundreds of millions of years. 499 00:25:51,320 --> 00:25:53,040 Speaker 1: What we're looking at when we see it in the sky, 500 00:25:53,520 --> 00:25:56,040 Speaker 1: it's just the after effects, and we can reconstruct what 501 00:25:56,080 --> 00:25:58,920 Speaker 1: we think happened from what we're seeing now. And so, 502 00:25:59,240 --> 00:26:01,080 Speaker 1: you know, the clusters are made of sort of three 503 00:26:01,119 --> 00:26:03,679 Speaker 1: basic constituents. You have the stars, of course, so the 504 00:26:03,720 --> 00:26:06,359 Speaker 1: things that are visible in the galaxy, and then between 505 00:26:06,400 --> 00:26:09,160 Speaker 1: the stars you have gas, the things that make the stars. 506 00:26:09,400 --> 00:26:12,000 Speaker 1: And then of course each one has dark matter, these 507 00:26:12,119 --> 00:26:15,040 Speaker 1: huge blobs of dark matter. Remember that most of the 508 00:26:15,080 --> 00:26:17,480 Speaker 1: things that are out there in the sky, the visible galaxies, 509 00:26:17,760 --> 00:26:21,320 Speaker 1: have these halos of dark matter around them. So wherever 510 00:26:21,400 --> 00:26:23,760 Speaker 1: you see stuff in the sky is probably where the 511 00:26:23,840 --> 00:26:26,360 Speaker 1: dark matter is. They tend to follow each other. We've 512 00:26:26,359 --> 00:26:28,919 Speaker 1: never seen or have we seen dark matter by itself. 513 00:26:29,119 --> 00:26:32,040 Speaker 1: We have noticed some clumps, like that's what gravitational lensing is, 514 00:26:32,359 --> 00:26:35,080 Speaker 1: so it is distributed. It goes out further past the 515 00:26:35,160 --> 00:26:37,639 Speaker 1: edge of the galaxy, Like each galaxy has a halo 516 00:26:37,800 --> 00:26:40,960 Speaker 1: that's longer and wider and larger than the galaxy itself. 517 00:26:41,200 --> 00:26:43,480 Speaker 1: And we have seen blobs of dark matter in the 518 00:26:43,560 --> 00:26:46,919 Speaker 1: universe by themselves. They do this gravitational lensing, but for 519 00:26:46,960 --> 00:26:49,680 Speaker 1: the most part, the structure they follow each other. And 520 00:26:49,720 --> 00:26:52,560 Speaker 1: that's not an accident. That's because of gravity. The structure 521 00:26:52,600 --> 00:26:55,679 Speaker 1: of dark matter created the structure of normal matter, like 522 00:26:55,840 --> 00:26:59,200 Speaker 1: created these gravitational wells for normal matter to fall into. 523 00:26:59,400 --> 00:27:03,040 Speaker 1: That's why we have galaxies and stars and planets and squirrels. 524 00:27:03,160 --> 00:27:05,520 Speaker 1: It's like, which came first, the dark matter or the galaxies, 525 00:27:05,560 --> 00:27:07,639 Speaker 1: And the answer is the dark matter. Yeah, well, all 526 00:27:07,680 --> 00:27:09,520 Speaker 1: the matter was created, i think at the same time, 527 00:27:09,560 --> 00:27:11,840 Speaker 1: but dark matter there's more of it, and so it 528 00:27:11,880 --> 00:27:15,280 Speaker 1: has a huge influence on the shape of the universe. 529 00:27:15,880 --> 00:27:18,359 Speaker 1: So we saw this collision happen and we looked at it, 530 00:27:18,400 --> 00:27:21,560 Speaker 1: and what we noticed is that when these two galaxy 531 00:27:21,720 --> 00:27:24,879 Speaker 1: clusters passed through each other, the gas reacted like you 532 00:27:24,920 --> 00:27:28,000 Speaker 1: would expect what to happen when two huge piles of 533 00:27:28,000 --> 00:27:30,800 Speaker 1: stuff hit each other, right, big special effects, explosions, lots 534 00:27:30,800 --> 00:27:33,280 Speaker 1: of friction and radiation at the edges and all that 535 00:27:33,320 --> 00:27:35,719 Speaker 1: kind of stuff. And so you could see the gas 536 00:27:35,720 --> 00:27:37,959 Speaker 1: not just kind of mixing with itself but actually like 537 00:27:38,119 --> 00:27:42,280 Speaker 1: violently reacting. Oh yeah, these things are moving really fast. Absolutely, 538 00:27:42,320 --> 00:27:44,920 Speaker 1: like if you shoot gas really fast and another cloud 539 00:27:44,960 --> 00:27:47,399 Speaker 1: of gas, then things would happen. Things will happen, and 540 00:27:47,440 --> 00:27:49,359 Speaker 1: they slow down, right, And so that energy had to 541 00:27:49,400 --> 00:27:51,879 Speaker 1: go somewhere, and that energy went to heating up the 542 00:27:51,880 --> 00:27:53,560 Speaker 1: gas and then it radiates, and you have all this 543 00:27:53,680 --> 00:27:57,280 Speaker 1: friction between these two colliding clouds of gas. But the 544 00:27:57,359 --> 00:28:00,679 Speaker 1: dark matter in these clusters got stripped way. It passed 545 00:28:00,800 --> 00:28:04,080 Speaker 1: right through. It went right through the clouds of gas 546 00:28:04,280 --> 00:28:06,879 Speaker 1: and right through the clouds of dark matter from the 547 00:28:06,920 --> 00:28:10,040 Speaker 1: other galaxy and passed through to the other side like 548 00:28:10,080 --> 00:28:12,440 Speaker 1: it went through the windshield or you know, thinking maybe 549 00:28:12,440 --> 00:28:14,760 Speaker 1: like in the matrix, remember when they're fighting those ghosts 550 00:28:15,040 --> 00:28:17,080 Speaker 1: and they're in the car and they slammed the brakes 551 00:28:17,119 --> 00:28:19,640 Speaker 1: and the ghosts just keep going. Yeah, kind of like that, 552 00:28:19,920 --> 00:28:21,920 Speaker 1: or like you're walking down the sidewalk with your kid 553 00:28:22,359 --> 00:28:24,480 Speaker 1: and they notice something interesting and they stop and you 554 00:28:24,640 --> 00:28:26,520 Speaker 1: just on your phone, and so you don't even pay 555 00:28:26,520 --> 00:28:28,359 Speaker 1: attention to a block later, you're like, wait a second, 556 00:28:28,359 --> 00:28:32,600 Speaker 1: where's my kid? I mean, that's never happened to me. 557 00:28:32,800 --> 00:28:35,359 Speaker 1: They're reacting with some gas or is it running to 558 00:28:35,400 --> 00:28:38,719 Speaker 1: another kid that you didn't spot? Right, there's the analogy, 559 00:28:38,800 --> 00:28:40,960 Speaker 1: and the two parents just keep going looking at their phone. 560 00:28:41,880 --> 00:28:44,720 Speaker 1: We're really modeling responsible parenting. I know, we're really talking 561 00:28:44,720 --> 00:28:47,400 Speaker 1: about our feelings. And so we can see the dark 562 00:28:47,440 --> 00:28:50,360 Speaker 1: matter came at the other side because we use gravitational lensing, 563 00:28:50,400 --> 00:28:53,600 Speaker 1: we can see it distorting the light from background galaxies. 564 00:28:54,360 --> 00:28:58,200 Speaker 1: So dark matter passed right through normal matter, gas, etcetera. 565 00:28:58,520 --> 00:29:01,880 Speaker 1: Collided and so they got separated. So we really can't 566 00:29:01,880 --> 00:29:03,840 Speaker 1: see in that case, this is a you know, collidab 567 00:29:03,920 --> 00:29:06,040 Speaker 1: lab of dark matter with another lav of dark matter. 568 00:29:06,120 --> 00:29:10,320 Speaker 1: What happens, Well, they massed right through nothing exactly, nothing happens. 569 00:29:10,320 --> 00:29:14,880 Speaker 1: It just it just passes right through at least exciting collision. Ever, Well, 570 00:29:14,920 --> 00:29:16,800 Speaker 1: I'm sure if it's exciting for them to lose their 571 00:29:16,880 --> 00:29:20,160 Speaker 1: kids A few blocks back. All right. So we know 572 00:29:20,360 --> 00:29:24,360 Speaker 1: then for sure through observational experiments that dark matter doesn't 573 00:29:24,400 --> 00:29:26,240 Speaker 1: seem to feel itself, at least not in the way 574 00:29:26,280 --> 00:29:28,840 Speaker 1: that we know about or with any forces that we 575 00:29:28,920 --> 00:29:31,440 Speaker 1: know about. And so the question is, is there maybe 576 00:29:32,040 --> 00:29:34,440 Speaker 1: another way that dark matter can feel itself that we 577 00:29:34,520 --> 00:29:36,760 Speaker 1: don't know about? And so let's get into that. But 578 00:29:36,840 --> 00:29:51,960 Speaker 1: first let's take a quick break. All right, Daniel, have 579 00:29:52,000 --> 00:29:54,719 Speaker 1: you have you find your child yet? I've got your 580 00:29:54,800 --> 00:29:56,920 Speaker 1: child and still looking for mine. Oh well no, wait, 581 00:29:56,960 --> 00:30:01,160 Speaker 1: this one looks like, oh man, what take mishap here? Yeah, 582 00:30:01,240 --> 00:30:03,560 Speaker 1: it's like parent trapped galaxy style. All right. So we're 583 00:30:03,600 --> 00:30:05,360 Speaker 1: talking about dark matter and whether or not it can 584 00:30:05,480 --> 00:30:08,320 Speaker 1: feel itself. And we know you can feel itself with gravity, 585 00:30:08,360 --> 00:30:12,120 Speaker 1: but gravity doesn't help you really, you know, permanently feel 586 00:30:12,240 --> 00:30:14,760 Speaker 1: or clump or things like that. And so the question 587 00:30:14,840 --> 00:30:16,760 Speaker 1: is it could there be maybe another way that dark 588 00:30:16,800 --> 00:30:19,760 Speaker 1: matter interacts with itself that we don't know? There absolutely 589 00:30:19,840 --> 00:30:22,240 Speaker 1: could be, I mean, the existence of dark matter and 590 00:30:22,280 --> 00:30:26,000 Speaker 1: the existence of dark energy, and our sheer ignorance about 591 00:30:26,000 --> 00:30:28,640 Speaker 1: how the universe works, how it begins, and what controls 592 00:30:28,680 --> 00:30:31,200 Speaker 1: its largest dynamics tells us that there's a lot to 593 00:30:31,280 --> 00:30:34,080 Speaker 1: learn about the universe, and so there's certainly could be 594 00:30:34,120 --> 00:30:37,960 Speaker 1: a whole other force out there, some force we've never discovered, 595 00:30:38,280 --> 00:30:41,040 Speaker 1: some force that only dark matter feels and feels with 596 00:30:41,240 --> 00:30:43,880 Speaker 1: other dark matter, and that might be the reason we've 597 00:30:43,920 --> 00:30:46,960 Speaker 1: never seen it, the dark side of the force. Yeah, 598 00:30:47,000 --> 00:30:50,720 Speaker 1: there's nothing preventing another kind of force from existing. It's 599 00:30:50,720 --> 00:30:53,440 Speaker 1: not like we have any idea as to the number 600 00:30:53,480 --> 00:30:56,360 Speaker 1: of forces that there could be, or is any limit 601 00:30:56,480 --> 00:30:58,120 Speaker 1: to how many forces there are. It's just sort of 602 00:30:58,160 --> 00:31:01,160 Speaker 1: like a list of stuff we've seen so far in 603 00:31:01,200 --> 00:31:04,959 Speaker 1: our attempt to understand it. And so that's it. That 604 00:31:05,000 --> 00:31:08,160 Speaker 1: list is almost certainly incomplete, the way our list of 605 00:31:08,280 --> 00:31:12,959 Speaker 1: particles is incomplete, or the list of Beatles is incomplete. Right, 606 00:31:13,040 --> 00:31:15,320 Speaker 1: Like every year he's scovered like a a thousand new kinds 607 00:31:15,320 --> 00:31:23,640 Speaker 1: of Beatle. It's amazing. Yeah, Ringo, Paul Bob Robert And 608 00:31:23,720 --> 00:31:26,360 Speaker 1: that was such a bad joke. I'm sorry. I did 609 00:31:26,440 --> 00:31:28,880 Speaker 1: learn about a new Beatle last week. Actually, I discovered 610 00:31:28,920 --> 00:31:31,959 Speaker 1: that they brought Ringo in, that they fired the original drummer, 611 00:31:31,960 --> 00:31:34,040 Speaker 1: and he's still kind of better about the fifth One 612 00:31:34,040 --> 00:31:36,920 Speaker 1: of the fifth Beatles is usually refers to their producer. 613 00:31:37,120 --> 00:31:39,560 Speaker 1: But yeah, that the Ringo was not the original drummer. Yeah, 614 00:31:39,560 --> 00:31:42,160 Speaker 1: not a music podcast, So let's stick to our strengths 615 00:31:42,160 --> 00:31:49,080 Speaker 1: here matters. Yeah, well, this is a really interesting idea. 616 00:31:49,160 --> 00:31:51,240 Speaker 1: I think that the you know, because it's it's like 617 00:31:51,320 --> 00:31:53,760 Speaker 1: totally possible for there to be a whole another universe 618 00:31:53,800 --> 00:31:56,040 Speaker 1: on top of us, right, Like there could be a 619 00:31:56,080 --> 00:31:59,120 Speaker 1: whole set of other particles to feel, a whole other 620 00:31:59,200 --> 00:32:01,520 Speaker 1: set of forces, but we just can't see them or 621 00:32:01,600 --> 00:32:04,000 Speaker 1: feeling or touch them. Yeah, there's a whole party going on, 622 00:32:04,120 --> 00:32:06,680 Speaker 1: and we weren't invited, and even if we had been invited, 623 00:32:06,720 --> 00:32:10,560 Speaker 1: we couldn't even really attend because it just ignores us completely, right, 624 00:32:11,040 --> 00:32:13,080 Speaker 1: And we know that there's a lot going out there 625 00:32:13,080 --> 00:32:15,360 Speaker 1: that we can't see. Right, what we see in the 626 00:32:15,480 --> 00:32:19,040 Speaker 1: universe is a tiny fraction what's actually happening, even just 627 00:32:19,160 --> 00:32:22,240 Speaker 1: here on Earth with your eyeballs. Your eyeballs see a 628 00:32:22,440 --> 00:32:26,200 Speaker 1: little sliver of all the electromagnetic radiation that's out there. 629 00:32:26,360 --> 00:32:28,200 Speaker 1: There's a lot of stuff going on you can't see. 630 00:32:28,600 --> 00:32:31,280 Speaker 1: And imagine if you could see, you know, cell phone 631 00:32:31,320 --> 00:32:35,200 Speaker 1: signals and television signals and radio waves, the world would 632 00:32:35,200 --> 00:32:38,160 Speaker 1: be a much different looking place. And so we see 633 00:32:38,200 --> 00:32:41,840 Speaker 1: a little fraction of what's actually happening. Wow, and good 634 00:32:41,880 --> 00:32:45,400 Speaker 1: thing to write like it be overwhelmed me. I mean, 635 00:32:45,440 --> 00:32:48,080 Speaker 1: you can get Netflix in the Hulu for free, but 636 00:32:49,800 --> 00:32:52,200 Speaker 1: you know, cloud based delivery would be a different kind 637 00:32:52,200 --> 00:32:54,120 Speaker 1: of thing. All right, So there could be another force 638 00:32:54,160 --> 00:32:57,040 Speaker 1: out there, and it's im possible the dark matter feels 639 00:32:57,080 --> 00:32:59,720 Speaker 1: it then when we see it in these collisions, that 640 00:33:00,080 --> 00:33:02,440 Speaker 1: was interacting with itself in another way. Yeah. So there's 641 00:33:02,440 --> 00:33:06,000 Speaker 1: sort of two different categories of ideas. One is, could 642 00:33:06,040 --> 00:33:09,560 Speaker 1: there be another force that dark matter feels and uses 643 00:33:09,640 --> 00:33:12,800 Speaker 1: to interact with our kind of matter, some new kind 644 00:33:12,800 --> 00:33:15,840 Speaker 1: of force we've never seen before that mediates the interaction 645 00:33:15,920 --> 00:33:18,800 Speaker 1: between those two kinds of particles and that we're looking 646 00:33:18,840 --> 00:33:21,320 Speaker 1: for and we haven't ever seen, and we're looking for 647 00:33:21,400 --> 00:33:23,640 Speaker 1: that in the same way we're looking for like its 648 00:33:23,640 --> 00:33:26,280 Speaker 1: interaction via the weak force. We have these big tanks 649 00:33:26,280 --> 00:33:29,200 Speaker 1: of underground normal matter particles and we wait for dark 650 00:33:29,240 --> 00:33:31,880 Speaker 1: matter to bump into It doesn't matter if it's the 651 00:33:31,920 --> 00:33:34,360 Speaker 1: weak force or some other new kind of force. Like 652 00:33:34,440 --> 00:33:36,640 Speaker 1: would it be really hard to, for example, to take 653 00:33:36,840 --> 00:33:40,760 Speaker 1: one squirrel that's flying through the earth. Yes, And now 654 00:33:40,800 --> 00:33:44,400 Speaker 1: you're talking about one squirrel particle and it's flying through 655 00:33:44,480 --> 00:33:48,680 Speaker 1: like a ton of liquid zenon. These are very difficult experiments, 656 00:33:49,040 --> 00:33:52,440 Speaker 1: and they're done underground, like a kilometer underground to keep 657 00:33:52,480 --> 00:33:55,880 Speaker 1: them cold and isolated from all of the sources of background. 658 00:33:56,200 --> 00:33:59,360 Speaker 1: They're very hard experiments, and they haven't seen anything so far. Right, 659 00:33:59,680 --> 00:34:02,240 Speaker 1: But can you say it conclusively, like there's a pink 660 00:34:02,400 --> 00:34:05,280 Speaker 1: squirrel out there with the purple polka dots, but we 661 00:34:05,320 --> 00:34:07,920 Speaker 1: haven't found it on Earth, so therefore it must not exist. 662 00:34:07,960 --> 00:34:09,799 Speaker 1: You're right. We can't say it does not exist. We 663 00:34:09,840 --> 00:34:14,320 Speaker 1: can say it's less common than one squirrel per cubic 664 00:34:14,400 --> 00:34:17,720 Speaker 1: volume per year. Right, We can just say how likely 665 00:34:17,719 --> 00:34:20,320 Speaker 1: it is to exist at a certain level, and so 666 00:34:20,680 --> 00:34:22,520 Speaker 1: it could still be there. And people are still running 667 00:34:22,560 --> 00:34:25,279 Speaker 1: these experiments, and the longer we run them, the more 668 00:34:25,320 --> 00:34:27,719 Speaker 1: we can push those limits. We can say, if this 669 00:34:27,760 --> 00:34:31,920 Speaker 1: force does exist between standard model A matter and dark matter, 670 00:34:32,120 --> 00:34:35,239 Speaker 1: that it must be even weaker than this limit, than 671 00:34:35,280 --> 00:34:37,320 Speaker 1: this limit, than this lem We keep pushing that down. 672 00:34:37,840 --> 00:34:40,200 Speaker 1: But there's a whole other category, which is like maybe 673 00:34:40,280 --> 00:34:43,759 Speaker 1: dark matter just feel stuff with itself, not with our experiments, 674 00:34:43,760 --> 00:34:46,960 Speaker 1: not with our bodies, but just between itself, like is 675 00:34:47,000 --> 00:34:49,720 Speaker 1: it possible that dark matter bumps into itself and feels 676 00:34:49,719 --> 00:34:54,879 Speaker 1: something right or repels each other with because you're telling 677 00:34:54,880 --> 00:34:57,880 Speaker 1: me that this idea that it only feels gravity is 678 00:34:58,280 --> 00:35:02,520 Speaker 1: sort of on thin nice like maybe there's evidence that 679 00:35:02,560 --> 00:35:04,440 Speaker 1: maybe it does feel something else. Yeah, And this is 680 00:35:04,480 --> 00:35:07,800 Speaker 1: really hard to probe because you can't do experiments using 681 00:35:08,280 --> 00:35:13,040 Speaker 1: normal matter material to probe dark matters interactions with itself. 682 00:35:13,080 --> 00:35:15,799 Speaker 1: You need to like build your experiment out of dark matter, right, 683 00:35:16,239 --> 00:35:18,400 Speaker 1: So all we can do is look at how the 684 00:35:18,480 --> 00:35:20,799 Speaker 1: dark matter is laid out in the universe, like where 685 00:35:20,840 --> 00:35:23,040 Speaker 1: did it end up, and then try to see is 686 00:35:23,080 --> 00:35:26,120 Speaker 1: that consistent with how it should end up if it 687 00:35:26,160 --> 00:35:29,200 Speaker 1: only feels gravity, because if it is bumping into itself, 688 00:35:29,320 --> 00:35:31,719 Speaker 1: that will change the way it's laid out, just like 689 00:35:32,040 --> 00:35:34,440 Speaker 1: if it's hot or cold, if it's fast or slow, 690 00:35:34,640 --> 00:35:37,680 Speaker 1: will also change the distribution of dark matter. So we 691 00:35:37,719 --> 00:35:39,840 Speaker 1: look at the distribution and try to ask is it 692 00:35:39,880 --> 00:35:43,000 Speaker 1: consistent with gravity only or do we need another piece 693 00:35:43,040 --> 00:35:44,840 Speaker 1: of the puzzle aid And what do we see do 694 00:35:44,920 --> 00:35:47,800 Speaker 1: we see out there in the universe that maybe it 695 00:35:47,800 --> 00:35:50,919 Speaker 1: does feel another force? We see that mostly gets things 696 00:35:51,040 --> 00:35:54,040 Speaker 1: right sort of on the scale of galaxies, and larger 697 00:35:54,560 --> 00:35:57,560 Speaker 1: like the distribution of galaxies and how they cluster together 698 00:35:57,680 --> 00:36:00,400 Speaker 1: and superclusters. That all seems right, and you run a 699 00:36:00,400 --> 00:36:03,319 Speaker 1: simulation of the universe with dark matter and normal matter 700 00:36:03,560 --> 00:36:06,239 Speaker 1: and dark matter is only gravity, it mostly gets that right. 701 00:36:06,560 --> 00:36:08,320 Speaker 1: But then if you zoom in, like on the smaller 702 00:36:08,360 --> 00:36:12,000 Speaker 1: scale here, smaller scales like less than a galaxy siza, 703 00:36:12,400 --> 00:36:16,400 Speaker 1: then sub galaxy, then it's not quite right. It doesn't 704 00:36:16,400 --> 00:36:20,680 Speaker 1: predict things the way we see them. For example, we 705 00:36:20,719 --> 00:36:22,760 Speaker 1: know that we have a big blob of dark matter 706 00:36:22,800 --> 00:36:24,960 Speaker 1: in our galaxy, and we know it's the densest at 707 00:36:24,960 --> 00:36:28,280 Speaker 1: the center just because of gravity, But the exact shape 708 00:36:28,320 --> 00:36:31,200 Speaker 1: of that blob is not something that we understand, like 709 00:36:31,680 --> 00:36:34,279 Speaker 1: dark matter with only gravity predicts it sort of like 710 00:36:34,400 --> 00:36:36,520 Speaker 1: peaked right at the center, that the center is like 711 00:36:36,640 --> 00:36:39,120 Speaker 1: a hot spot for dark matter. But we go out 712 00:36:39,120 --> 00:36:40,960 Speaker 1: and measure it, we see it's much more spread out 713 00:36:41,000 --> 00:36:43,520 Speaker 1: than that. It's like much more of a rod core, 714 00:36:43,680 --> 00:36:46,600 Speaker 1: not so much like peaked like a cusp, and so 715 00:36:47,080 --> 00:36:51,000 Speaker 1: that's not something we understand. Fuzzier than what you would expect. 716 00:36:51,040 --> 00:36:54,040 Speaker 1: You would expect it to sort of cluster more, but 717 00:36:54,440 --> 00:36:57,240 Speaker 1: it's actually kind of fuzzy it's like a big fuzzy squirrel, 718 00:36:57,320 --> 00:37:01,440 Speaker 1: not a little tiny intense squirrel. Yeah, it's a hedgehog 719 00:37:01,600 --> 00:37:04,400 Speaker 1: or or something like that rather than a tiny little squirrel. 720 00:37:04,960 --> 00:37:07,919 Speaker 1: And if you change your simulations and you add a 721 00:37:07,960 --> 00:37:09,960 Speaker 1: little bit of bumping this like a little bit like 722 00:37:10,080 --> 00:37:13,600 Speaker 1: maybe sometimes dark matter does bump into itself, that describes 723 00:37:13,600 --> 00:37:15,520 Speaker 1: what we see better, meaning like a little bit of 724 00:37:15,560 --> 00:37:19,120 Speaker 1: a repulsive force with itself. You just add in a 725 00:37:19,160 --> 00:37:21,440 Speaker 1: made up force. You're like, we don't know, but let's 726 00:37:21,480 --> 00:37:24,279 Speaker 1: see if it describes a situation, just like we made 727 00:37:24,360 --> 00:37:27,600 Speaker 1: up dark matter to describe this gravity we were seeing. 728 00:37:27,880 --> 00:37:30,280 Speaker 1: We're like, all right, well, now let's give another force 729 00:37:30,360 --> 00:37:32,880 Speaker 1: to these particles that are creating the gravity, so that 730 00:37:32,960 --> 00:37:35,560 Speaker 1: the distribution of gravity is the way we are seeing it. 731 00:37:35,640 --> 00:37:37,680 Speaker 1: Let's make something up about something that we've made up. 732 00:37:39,600 --> 00:37:42,600 Speaker 1: You're talking about all the physics, now, man, we'll come 733 00:37:42,600 --> 00:37:46,440 Speaker 1: to science. What if that thing we made up for 734 00:37:46,520 --> 00:37:50,200 Speaker 1: the thing we made up, that's something else we make up. Yeah, 735 00:37:50,239 --> 00:37:51,960 Speaker 1: and so this is sort of the state of the art. 736 00:37:52,000 --> 00:37:55,280 Speaker 1: Now we're like looking really carefully trying to understand where 737 00:37:55,440 --> 00:37:57,800 Speaker 1: is the dark matter? Does it agree with what we 738 00:37:57,920 --> 00:38:00,839 Speaker 1: predict and it turns out it doesn't quite agree, and 739 00:38:00,880 --> 00:38:04,720 Speaker 1: there are other little details that the gravity only theory 740 00:38:05,280 --> 00:38:08,440 Speaker 1: is getting wrong, so that they're sort of strong maybe 741 00:38:08,640 --> 00:38:11,600 Speaker 1: or at least a hint of an indication that maybe 742 00:38:11,640 --> 00:38:14,759 Speaker 1: dark matter does feel a whole new force or could 743 00:38:14,760 --> 00:38:16,279 Speaker 1: it be one of the old force. It couldn't be 744 00:38:16,320 --> 00:38:17,799 Speaker 1: one of the old forces. It would have to be 745 00:38:17,880 --> 00:38:20,840 Speaker 1: some sort of self interaction. So this theory is called 746 00:38:21,120 --> 00:38:24,160 Speaker 1: self interacting dark matter, and it solves some of these 747 00:38:24,440 --> 00:38:27,720 Speaker 1: nagging problems that we've had in the gravity only theory 748 00:38:27,760 --> 00:38:30,120 Speaker 1: of dark matter. So that makes it compelling. It's not 749 00:38:30,200 --> 00:38:33,560 Speaker 1: proof at all that this is happening, but it's like, huh, 750 00:38:33,600 --> 00:38:36,120 Speaker 1: we've had this problem. We add this new idea. It 751 00:38:36,160 --> 00:38:39,200 Speaker 1: gives a better explanation. That's cool. And you always have 752 00:38:39,280 --> 00:38:42,359 Speaker 1: to be careful when you're adding more stuff to your theory. Right, 753 00:38:42,400 --> 00:38:46,239 Speaker 1: you'd like the simplest possible explanation, but if that doesn't work, 754 00:38:46,280 --> 00:38:48,360 Speaker 1: then you have to add a little widget to your theory, 755 00:38:48,880 --> 00:38:52,120 Speaker 1: like maybe what if there are two kinds of squirrels matter? Yeah, 756 00:38:52,160 --> 00:38:54,600 Speaker 1: and and that's a whole other idea, right, Like if 757 00:38:54,680 --> 00:38:57,080 Speaker 1: dark matter made of particles, is it one kind of particles? 758 00:38:57,160 --> 00:38:59,480 Speaker 1: Is it two or is it ten? Didn't they decay 759 00:38:59,520 --> 00:39:01,920 Speaker 1: from one kind particle to the other? Do only some 760 00:39:02,000 --> 00:39:04,200 Speaker 1: of them have self interactions? I mean, look at the 761 00:39:04,200 --> 00:39:06,560 Speaker 1: particles that make up our kind of matter. There's all 762 00:39:06,600 --> 00:39:10,200 Speaker 1: sorts of complicated interactions with weird rules we don't understand. 763 00:39:10,560 --> 00:39:13,240 Speaker 1: Why would we imagine dark matter would be like simpler. 764 00:39:13,280 --> 00:39:16,480 Speaker 1: It could be different shades of dark matter, the darkest 765 00:39:16,520 --> 00:39:21,520 Speaker 1: matters squirrels and cats. And and then then you wonder, like, 766 00:39:21,600 --> 00:39:24,520 Speaker 1: all right, well, maybe dark matter could feel itself and 767 00:39:24,520 --> 00:39:27,239 Speaker 1: that would explain like the weird distribution of gravity that 768 00:39:27,239 --> 00:39:30,240 Speaker 1: we're seeing. But what about the bullet cluster? Right? Didn't 769 00:39:30,280 --> 00:39:34,080 Speaker 1: we do this experiment because the two clouds of dark 770 00:39:34,120 --> 00:39:36,960 Speaker 1: matter didn't repel each other. They didn't repel each other. 771 00:39:37,440 --> 00:39:39,880 Speaker 1: But people went back and looked at that again, and 772 00:39:39,920 --> 00:39:42,879 Speaker 1: they said, all right, well, can we explain this and 773 00:39:43,040 --> 00:39:46,520 Speaker 1: have some amount of interaction in there, because it's not 774 00:39:46,600 --> 00:39:49,359 Speaker 1: easy to tell exactly where all the dark matter is 775 00:39:49,680 --> 00:39:52,719 Speaker 1: very precisely, like maybe some of it did interact and 776 00:39:52,760 --> 00:39:55,280 Speaker 1: got sort of stuck in the middle. Most of it didn't, 777 00:39:55,520 --> 00:39:58,640 Speaker 1: but maybe some of it did. You know. It's like 778 00:39:58,680 --> 00:40:00,320 Speaker 1: we made it up in the first place when we 779 00:40:00,400 --> 00:40:03,160 Speaker 1: just you know, it's like there's a first pass and 780 00:40:03,200 --> 00:40:05,960 Speaker 1: there's a more precise test, right, you know, first you 781 00:40:06,000 --> 00:40:08,359 Speaker 1: try to understand the broad strokes. Then you really dig 782 00:40:08,400 --> 00:40:10,640 Speaker 1: in and see if it gets the details right. And 783 00:40:10,640 --> 00:40:12,239 Speaker 1: the other thing is it turns out that this is 784 00:40:12,360 --> 00:40:17,000 Speaker 1: not a great dark matter collider. It's too big dark matter. Well, 785 00:40:17,080 --> 00:40:19,800 Speaker 1: dark matter is very dilute, and so if you throw 786 00:40:20,239 --> 00:40:23,680 Speaker 1: a huge, very dilute cloud of dark matter at another one, 787 00:40:23,800 --> 00:40:26,200 Speaker 1: most of it's just going to pass through anyway. Like, 788 00:40:26,280 --> 00:40:28,960 Speaker 1: dark matter is not as dense as these gas clouds. 789 00:40:29,360 --> 00:40:31,759 Speaker 1: It's sort of like like the stars. Like if you 790 00:40:31,840 --> 00:40:35,600 Speaker 1: have two galaxies that pass through each other, mostly the 791 00:40:35,640 --> 00:40:39,320 Speaker 1: stars don't collide because the stars are embedded in huge, 792 00:40:39,520 --> 00:40:43,360 Speaker 1: vast empty spaces, and so they don't really collide with 793 00:40:43,360 --> 00:40:45,080 Speaker 1: each other head to head. So you were saying, like, 794 00:40:45,120 --> 00:40:47,279 Speaker 1: if I take two dark matter squirrels and I throw 795 00:40:47,320 --> 00:40:50,000 Speaker 1: them at each other, they might repel one against the other. 796 00:40:50,040 --> 00:40:53,040 Speaker 1: But if I take a whole cloud of squirrels that 797 00:40:53,120 --> 00:40:55,719 Speaker 1: are really far apart, they might just pass through each 798 00:40:55,719 --> 00:40:58,160 Speaker 1: other like we've seen in the cluster. Yeah, and they 799 00:40:58,200 --> 00:41:01,279 Speaker 1: would mostly miss, just like the large Hadron collider what 800 00:41:01,320 --> 00:41:04,840 Speaker 1: we do is we collide to clouds of protons against 801 00:41:04,880 --> 00:41:07,760 Speaker 1: each other, because one proton will never hit another proton, 802 00:41:07,800 --> 00:41:10,000 Speaker 1: they're too small. So we have like ten to the 803 00:41:10,040 --> 00:41:12,279 Speaker 1: ten protons and one cloud and ten to the ten 804 00:41:12,360 --> 00:41:14,719 Speaker 1: to the other, and we get you know, ten or 805 00:41:14,800 --> 00:41:18,560 Speaker 1: twenty or fifty collisions. And so it's not that easy 806 00:41:18,680 --> 00:41:22,120 Speaker 1: to make things collide. And so it turns out the 807 00:41:22,120 --> 00:41:25,760 Speaker 1: bullet cluster is actually also consistent with dark matter feeling 808 00:41:25,800 --> 00:41:28,680 Speaker 1: itself at sort of a low level of tweak how 809 00:41:28,719 --> 00:41:30,399 Speaker 1: you look at it. Yeah, and so you know, the 810 00:41:30,440 --> 00:41:33,120 Speaker 1: game here is come up with a theory um model 811 00:41:33,400 --> 00:41:36,920 Speaker 1: that explains everything that we do see all the same time. 812 00:41:37,320 --> 00:41:40,000 Speaker 1: And so you have to add some of this stuff 813 00:41:40,000 --> 00:41:43,120 Speaker 1: to explain the distribution of dark matter and the core 814 00:41:43,400 --> 00:41:45,680 Speaker 1: versus cup effect to the center of the galaxy, but 815 00:41:45,760 --> 00:41:47,840 Speaker 1: not too much that you mess up the description of 816 00:41:47,840 --> 00:41:49,719 Speaker 1: the bullet cluster. So you sort of hemmed in on 817 00:41:49,800 --> 00:41:53,480 Speaker 1: both sides there. Interesting, But I guess maybe the takeaways 818 00:41:53,520 --> 00:41:57,520 Speaker 1: that the answer is, yes, maybe dark matter does feel itself. 819 00:41:57,600 --> 00:42:00,560 Speaker 1: It's totally possible, and there might be some indication out 820 00:42:00,560 --> 00:42:03,319 Speaker 1: there that it does. Yeah, it's a new idea and 821 00:42:03,320 --> 00:42:06,840 Speaker 1: it's gaining traction in the community self interacting dark matter. 822 00:42:07,280 --> 00:42:10,120 Speaker 1: So it's possible that yes, dark matter could feel itself 823 00:42:10,160 --> 00:42:13,040 Speaker 1: and there could be multiple forces that it feels all right, 824 00:42:13,160 --> 00:42:16,239 Speaker 1: So maybe dark matter does have feelings, Daniel, It might 825 00:42:16,280 --> 00:42:18,719 Speaker 1: have a lot more feelings than we could ever understand. 826 00:42:19,120 --> 00:42:22,280 Speaker 1: Shades and shades of nuance. Well, I think it's all again, 827 00:42:22,320 --> 00:42:24,520 Speaker 1: just all of this is just an interesting example of 828 00:42:24,560 --> 00:42:27,719 Speaker 1: how there are things in the universe happening that we 829 00:42:27,960 --> 00:42:31,560 Speaker 1: don't really know about or see or feel or effective. 830 00:42:31,680 --> 00:42:34,600 Speaker 1: We're only seeing a tiny fraction of this grand play 831 00:42:34,600 --> 00:42:38,120 Speaker 1: of the universe, and we're making huge, broad conclusions about 832 00:42:38,160 --> 00:42:40,880 Speaker 1: how the universe works from this tiny little corner of 833 00:42:40,880 --> 00:42:43,200 Speaker 1: the stage. And there's a lot going on that we 834 00:42:43,280 --> 00:42:46,480 Speaker 1: haven't ever observed. And at least we know now. We 835 00:42:46,520 --> 00:42:49,280 Speaker 1: know that we're ignorant, so we know to be humble 836 00:42:49,320 --> 00:42:52,799 Speaker 1: and we know not to over generalize our ideas. But 837 00:42:52,880 --> 00:42:55,399 Speaker 1: it also is tantalizing because you hope that one day 838 00:42:55,440 --> 00:42:57,160 Speaker 1: we will see the rest of the action, We will 839 00:42:57,160 --> 00:42:59,719 Speaker 1: get a glimpse for what's really happening. We might all 840 00:42:59,760 --> 00:43:04,920 Speaker 1: be swimming in a giant squirrel up mr. I like 841 00:43:04,960 --> 00:43:08,160 Speaker 1: to think of myself as a physics raccoon, because it's 842 00:43:08,160 --> 00:43:10,440 Speaker 1: sneaking late at night to steal other people's garbage with 843 00:43:10,520 --> 00:43:14,000 Speaker 1: dark circles on your eyes. That makes sense eating garbage. 844 00:43:16,080 --> 00:43:19,600 Speaker 1: All right, Well that's pretty interesting and cool and or 845 00:43:19,680 --> 00:43:22,960 Speaker 1: chill um, and so we hope you enjoyed that discussion. 846 00:43:23,040 --> 00:43:25,200 Speaker 1: Thanks Joe for writing with your question. And if you 847 00:43:25,280 --> 00:43:27,719 Speaker 1: have a question you'd like us to explore on the podcast, 848 00:43:27,960 --> 00:43:31,440 Speaker 1: please write to us. We love your questions. Two questions 849 00:43:31,520 --> 00:43:35,239 Speaker 1: at Daniel and Jorge dot com. A bit mysterious. See 850 00:43:35,280 --> 00:43:46,040 Speaker 1: you next time. Thanks for listening, and remember that Daniel 851 00:43:46,040 --> 00:43:48,600 Speaker 1: and Jorge Explain the Universe is a production of I 852 00:43:48,800 --> 00:43:52,239 Speaker 1: Heart Radio. For more podcast from my Heart Radio, visit 853 00:43:52,280 --> 00:43:56,120 Speaker 1: the I Heart Radio Apple Podcasts, or wherever you listen 854 00:43:56,239 --> 00:44:03,800 Speaker 1: to your favorite shows.