1 00:00:08,600 --> 00:00:10,719 Speaker 1: Hey, or hey, I think I may have lost something. 2 00:00:11,160 --> 00:00:14,159 Speaker 1: Oh did you lose your mind again? I happened a 3 00:00:14,280 --> 00:00:17,480 Speaker 1: long time ago. This is something new? Is it important? 4 00:00:17,920 --> 00:00:21,239 Speaker 1: It's actually kind of a big deal. Is it like 5 00:00:21,360 --> 00:00:23,759 Speaker 1: really small and easy to lose, like your keys or 6 00:00:23,880 --> 00:00:26,920 Speaker 1: your wedding band. No, it's much more embarrassing because it's 7 00:00:27,080 --> 00:00:31,880 Speaker 1: really enormous, like cosmically large, like most of the stuff 8 00:00:31,920 --> 00:00:34,919 Speaker 1: in the universe, and you can't find it. I've been 9 00:00:34,960 --> 00:00:37,839 Speaker 1: looking everywhere for it. Well, I guess you know what 10 00:00:37,880 --> 00:00:39,920 Speaker 1: to do. Oh yeah, what's that? You know? Give it 11 00:00:39,920 --> 00:00:42,479 Speaker 1: a cool sounding name, and then ask the federal government 12 00:00:42,479 --> 00:00:44,800 Speaker 1: to help you find it. Do you think anybody would 13 00:00:44,840 --> 00:01:03,360 Speaker 1: actually fall for that? I think they already have. Hi 14 00:01:03,440 --> 00:01:06,560 Speaker 1: am jorhammy cartoonists and the creator of PhD comics. Hi. 15 00:01:06,680 --> 00:01:09,200 Speaker 1: I'm Daniel. I'm a particle physicist and a professor you 16 00:01:09,280 --> 00:01:11,960 Speaker 1: see Irvine, and I am actually paid to hunt for 17 00:01:12,080 --> 00:01:15,559 Speaker 1: missing things. M interesting, You're like the Lost and Found 18 00:01:15,600 --> 00:01:19,160 Speaker 1: of the universe department. That sounds very unglamorous. I like 19 00:01:19,240 --> 00:01:21,600 Speaker 1: to think of myself more of the Sherlock Holmes of 20 00:01:21,640 --> 00:01:25,840 Speaker 1: the universe. I see you're not in like in the 21 00:01:25,880 --> 00:01:29,160 Speaker 1: basement office with a little window that people go there 22 00:01:29,160 --> 00:01:31,479 Speaker 1: and claim lost things. That's right. I'm not sitting here 23 00:01:31,480 --> 00:01:35,479 Speaker 1: surrounded by people's lost purses or socks. Where do all 24 00:01:35,520 --> 00:01:37,520 Speaker 1: the socks and the dryers go? That's what I want 25 00:01:37,520 --> 00:01:39,399 Speaker 1: to know. We should have a whole episode about that. 26 00:01:39,520 --> 00:01:41,720 Speaker 1: They're orbiting the Earth in the hose zone layer. Well, 27 00:01:41,760 --> 00:01:45,760 Speaker 1: that socks made. They're all connected by wormholes. You think dryers, Well, 28 00:01:45,760 --> 00:01:48,320 Speaker 1: that's spinning and that he could that create a warmhole. 29 00:01:48,520 --> 00:01:50,960 Speaker 1: Keep running your dryer let us know. But welcome to 30 00:01:50,960 --> 00:01:53,920 Speaker 1: our podcast Daniel and Jorge Explain the Universe, a production 31 00:01:53,960 --> 00:01:56,240 Speaker 1: of I Heart Radio, which we operated as a sort 32 00:01:56,280 --> 00:01:59,840 Speaker 1: of lost and found of ideas about the universe. Everything 33 00:01:59,840 --> 00:02:02,280 Speaker 1: we have found about the universe and all the ideas 34 00:02:02,320 --> 00:02:05,320 Speaker 1: we have lost. Everything we do know about what's going 35 00:02:05,400 --> 00:02:08,120 Speaker 1: on out there, the size of the universe, the number 36 00:02:08,120 --> 00:02:11,440 Speaker 1: of dimensions of space, whether or not they're alien creators 37 00:02:11,440 --> 00:02:15,040 Speaker 1: on other planets looking through their telescopes at us. Every 38 00:02:15,160 --> 00:02:18,120 Speaker 1: deep and enormous question about the universe you might consider 39 00:02:18,240 --> 00:02:20,960 Speaker 1: we talk about here on the podcast. Yeah, because it 40 00:02:21,080 --> 00:02:23,639 Speaker 1: is a huge universe full of amazing and wonderful things 41 00:02:23,680 --> 00:02:25,680 Speaker 1: that seem to be screaming at us for us to 42 00:02:25,880 --> 00:02:28,560 Speaker 1: find them. We get light from distant stars all the 43 00:02:28,560 --> 00:02:32,200 Speaker 1: time at all times, radiation, cosmic rays, and it's all 44 00:02:32,280 --> 00:02:34,720 Speaker 1: coming to us sort of one thing for us to 45 00:02:34,800 --> 00:02:38,280 Speaker 1: find out and what's out there and to discover and 46 00:02:38,440 --> 00:02:41,160 Speaker 1: learn about how it all works. You make the universe 47 00:02:41,200 --> 00:02:43,480 Speaker 1: sounds sort of cooperative, like it wants to play a 48 00:02:43,600 --> 00:02:46,959 Speaker 1: role in our science and be helpful. Universe, right, I mean, 49 00:02:47,120 --> 00:02:49,400 Speaker 1: it's constantly shouting at us, isn't it. It is? But 50 00:02:49,520 --> 00:02:53,120 Speaker 1: sometimes these clues are very, very subtle and frustratingly difficult 51 00:02:53,120 --> 00:02:55,560 Speaker 1: to grasp. I feel like the universe is sort of 52 00:02:55,560 --> 00:02:58,720 Speaker 1: playing cat and mouse with us, sometimes hiding all the 53 00:02:58,760 --> 00:03:02,240 Speaker 1: best bits. It's like coy universe, mean, like it wants 54 00:03:02,280 --> 00:03:04,800 Speaker 1: us to find it, but it's not telling us everything 55 00:03:04,840 --> 00:03:07,040 Speaker 1: that it can about itself. Yeah, it doesn't just come 56 00:03:07,120 --> 00:03:10,000 Speaker 1: right out and tell us it's deep nature. It sometimes 57 00:03:10,040 --> 00:03:11,720 Speaker 1: seems to make sense, and then you dig deeper and 58 00:03:11,760 --> 00:03:15,080 Speaker 1: discover oh my gosh, it's bonkers underneath. But there is 59 00:03:15,120 --> 00:03:18,800 Speaker 1: a lot of fascinating information in those little hints that 60 00:03:18,880 --> 00:03:21,960 Speaker 1: do arrive here on Earth. Yeah, and it's pretty amazing that, 61 00:03:22,000 --> 00:03:23,440 Speaker 1: you know, if you think about it, that we're sitting 62 00:03:23,440 --> 00:03:25,760 Speaker 1: on this little rock floating through space in a corner 63 00:03:25,800 --> 00:03:27,920 Speaker 1: of the galaxy, in a little corner of the universe. 64 00:03:27,919 --> 00:03:31,359 Speaker 1: And somehow, from this light that we're getting from distant stars, 65 00:03:31,400 --> 00:03:34,840 Speaker 1: we can somehow piece together the whole structure almost of 66 00:03:34,920 --> 00:03:37,520 Speaker 1: the universe. I like how you just say somehow, you know, 67 00:03:37,560 --> 00:03:40,000 Speaker 1: It's like the information comes and dot dot dot, we 68 00:03:40,080 --> 00:03:43,200 Speaker 1: know these things. You just like, somehow my entire career 69 00:03:43,280 --> 00:03:45,520 Speaker 1: right there. Yeah, somehow it goes to the lost and 70 00:03:45,520 --> 00:03:48,880 Speaker 1: found department in the basement and we get a little 71 00:03:48,880 --> 00:03:53,160 Speaker 1: memo about what happened. That's right. Somehow, because the government 72 00:03:53,200 --> 00:03:56,640 Speaker 1: decides to fund basic science research, we have uncovered some 73 00:03:56,760 --> 00:03:59,560 Speaker 1: truths about the universe. I guess what I mean by 74 00:03:59,600 --> 00:04:02,400 Speaker 1: somehow thought dot dot is you know, mostly engineering and 75 00:04:02,400 --> 00:04:07,400 Speaker 1: then some science, some happy collaboration between scientists and engineers. 76 00:04:07,760 --> 00:04:10,000 Speaker 1: But yeah, we are learning more and more about the universe. 77 00:04:10,120 --> 00:04:13,520 Speaker 1: And there's a big question, especially a big question about 78 00:04:13,520 --> 00:04:16,120 Speaker 1: the universe, about what it's made out of and how 79 00:04:16,160 --> 00:04:19,360 Speaker 1: it's what structured it has out there in the galaxies 80 00:04:19,400 --> 00:04:22,280 Speaker 1: and also in between galaxies. What does it all look like, 81 00:04:22,520 --> 00:04:24,400 Speaker 1: how's it all put together? It's really one of the 82 00:04:24,440 --> 00:04:26,640 Speaker 1: biggest questions in the universe, and one of the first 83 00:04:26,720 --> 00:04:30,840 Speaker 1: questions you might ask, which is what is in the universe? 84 00:04:31,040 --> 00:04:33,839 Speaker 1: What's the universe made out of? Where is all the 85 00:04:34,000 --> 00:04:37,479 Speaker 1: stuff out there? And what kind of stuff is it? Really, 86 00:04:37,520 --> 00:04:40,760 Speaker 1: it's sort of shocking and amazing that we don't know 87 00:04:40,839 --> 00:04:44,320 Speaker 1: the answer to that very basic question about the nature 88 00:04:44,320 --> 00:04:47,120 Speaker 1: of our own reality. Yeah, because the universe sort of 89 00:04:47,120 --> 00:04:48,839 Speaker 1: pulled a fast one on us, right Like it did 90 00:04:48,880 --> 00:04:52,039 Speaker 1: this big reveal twist somewhere a few decades ago where 91 00:04:52,040 --> 00:04:54,080 Speaker 1: we thought we knew what the universe was made out of. 92 00:04:54,120 --> 00:04:57,640 Speaker 1: It was stars and matter and atoms and things like that, 93 00:04:57,720 --> 00:05:00,839 Speaker 1: But suddenly we learned that that was only like five 94 00:05:00,839 --> 00:05:02,800 Speaker 1: percent of it. You know. It's kind of like when 95 00:05:02,839 --> 00:05:05,200 Speaker 1: you're watching a show and Sony you realize that you 96 00:05:05,240 --> 00:05:08,680 Speaker 1: still have like ninety five episodes ago. It's sort of 97 00:05:08,680 --> 00:05:11,240 Speaker 1: like the universe was wearing a mask and then somebody 98 00:05:11,279 --> 00:05:13,400 Speaker 1: pulled it off and we discovered, oh my gosh, there's 99 00:05:13,440 --> 00:05:16,000 Speaker 1: a lot more to it. So much for the universe 100 00:05:16,040 --> 00:05:18,880 Speaker 1: being helpful and revealing, right, well, I think it just 101 00:05:18,920 --> 00:05:21,400 Speaker 1: wants you to keep watching, I guess, trying to parse 102 00:05:21,480 --> 00:05:24,359 Speaker 1: out the information, trying to keep it interesting. Maybe the 103 00:05:24,400 --> 00:05:26,719 Speaker 1: show runners of the Universe are just trying to dole 104 00:05:26,760 --> 00:05:30,680 Speaker 1: out the reveals a little bit at a time. Show runners, Huh, 105 00:05:30,800 --> 00:05:34,680 Speaker 1: so you're a multitheist. I think it's got to be 106 00:05:34,720 --> 00:05:37,279 Speaker 1: a committee. I mean, who, there's so much to do. 107 00:05:38,560 --> 00:05:41,520 Speaker 1: That's not a flattering I guess description of it looks 108 00:05:41,520 --> 00:05:43,880 Speaker 1: like it was made by a committee. The universe looks 109 00:05:43,920 --> 00:05:46,040 Speaker 1: like it had too many writers. Well, it does sometimes 110 00:05:46,080 --> 00:05:48,839 Speaker 1: seem inconsistent, you know. Well, it is sort of a 111 00:05:48,960 --> 00:05:51,200 Speaker 1: mysterious question. What is the universe made out of? And 112 00:05:51,240 --> 00:05:54,040 Speaker 1: as we've learned in the last few decades, it's not 113 00:05:54,120 --> 00:05:57,560 Speaker 1: made out of just stars and atoms and elements. It's 114 00:05:57,600 --> 00:06:00,839 Speaker 1: mostly made out of other things, namely dark matter and 115 00:06:00,960 --> 00:06:03,359 Speaker 1: dark energy. The kind of stuff that makes up you 116 00:06:03,640 --> 00:06:06,960 Speaker 1: and me and hamsters and ice cream and bologna sandwiches 117 00:06:07,160 --> 00:06:11,359 Speaker 1: is actually quite unusual in the universe. Most of the 118 00:06:11,400 --> 00:06:14,520 Speaker 1: stuff that's out there is not stars and gas and 119 00:06:14,640 --> 00:06:18,400 Speaker 1: dust and all the visible stuff. It's something else, something dark, 120 00:06:18,520 --> 00:06:23,159 Speaker 1: something we've only recently discovered exists out there. Yeah, and 121 00:06:23,200 --> 00:06:25,760 Speaker 1: so dark energy is this sort of the phenomenon where 122 00:06:25,800 --> 00:06:29,160 Speaker 1: the universe's expanding faster and faster every second, but dark 123 00:06:29,200 --> 00:06:32,799 Speaker 1: matter is especially sort of weird and concerning because it's matter, 124 00:06:32,920 --> 00:06:35,720 Speaker 1: it's stuff. It's like exerting gravity. You can feel it, 125 00:06:35,800 --> 00:06:38,120 Speaker 1: but we can't see it, which means we don't know 126 00:06:38,160 --> 00:06:40,960 Speaker 1: where it is exactly. We know that dark matter is 127 00:06:41,040 --> 00:06:45,640 Speaker 1: some kind of stuff. There's something out there exerting gravity 128 00:06:45,680 --> 00:06:47,719 Speaker 1: on the rest of the universe, and we can sort 129 00:06:47,760 --> 00:06:50,760 Speaker 1: of tell that it exists, but we don't know what 130 00:06:50,800 --> 00:06:53,200 Speaker 1: it is. And we've done a lot of podcasts digging 131 00:06:53,200 --> 00:06:55,719 Speaker 1: into what it might be. Is it axons? Is it 132 00:06:55,800 --> 00:06:59,200 Speaker 1: black holes? Is it whimps? Is this something else? Something 133 00:06:59,240 --> 00:07:02,760 Speaker 1: weird in there? Even more crazy ideas we haven't yet covered. 134 00:07:02,920 --> 00:07:04,479 Speaker 1: It's sort of like we know there's an elephant in 135 00:07:04,480 --> 00:07:06,960 Speaker 1: the room or in the in the galaxy or the universe, 136 00:07:07,040 --> 00:07:09,320 Speaker 1: but we don't know what it's. What this elephant is doing, 137 00:07:09,760 --> 00:07:12,400 Speaker 1: or you know, what is it like striking a post? 138 00:07:12,480 --> 00:07:15,400 Speaker 1: Is it jogging? Is it sleeping. It's kind of a 139 00:07:15,400 --> 00:07:17,920 Speaker 1: big mystery, like we know it's there, but we sort 140 00:07:17,920 --> 00:07:21,440 Speaker 1: of don't know what it's doing or what structure it has. Yeah, 141 00:07:21,480 --> 00:07:24,120 Speaker 1: you can ask so many fascinating questions. So far, we've 142 00:07:24,160 --> 00:07:27,240 Speaker 1: mostly focused on what is dark matter? Is it this 143 00:07:27,320 --> 00:07:29,520 Speaker 1: kind of particle. Is it that kind of particle but 144 00:07:29,680 --> 00:07:32,560 Speaker 1: equally interesting without even knowing what it's made out of, 145 00:07:32,760 --> 00:07:36,160 Speaker 1: is just wondering, like where is the dark matter? Is 146 00:07:36,200 --> 00:07:38,440 Speaker 1: it here with us in this room? Is it out 147 00:07:38,440 --> 00:07:41,320 Speaker 1: there in deep space? Does it form planets and other 148 00:07:41,360 --> 00:07:44,720 Speaker 1: kinds of structure? Is it smoothly spread out throughout the universe? 149 00:07:44,960 --> 00:07:48,040 Speaker 1: Where in the universe is all of this stuff? So 150 00:07:48,080 --> 00:07:55,360 Speaker 1: today on the podcast, we'll be asking the question, how 151 00:07:55,400 --> 00:07:59,360 Speaker 1: do we know where dark matter is? It sounds like 152 00:07:59,400 --> 00:08:01,960 Speaker 1: he lost you lost it again? Then I feel like 153 00:08:02,000 --> 00:08:03,520 Speaker 1: we said a new word. It was, but now we 154 00:08:03,560 --> 00:08:05,760 Speaker 1: don't know where it is. It is a really important 155 00:08:05,840 --> 00:08:09,040 Speaker 1: question because knowing where the dark matter is can help 156 00:08:09,120 --> 00:08:12,480 Speaker 1: us get clues about what it might be, because certain 157 00:08:12,600 --> 00:08:15,360 Speaker 1: kinds of dark matter might clump up in different ways, 158 00:08:15,400 --> 00:08:18,280 Speaker 1: and other kinds of dark matter might not. Yeah, is 159 00:08:18,320 --> 00:08:20,440 Speaker 1: it is it chunky or smooth? I guess it's a 160 00:08:20,480 --> 00:08:24,560 Speaker 1: big question about the peanut butter dark matter of the universe. Well, 161 00:08:24,560 --> 00:08:26,840 Speaker 1: I hope the showrunners don't disagree about that, because then 162 00:08:26,880 --> 00:08:29,320 Speaker 1: you might get chunky parts of the universe and creamy 163 00:08:29,360 --> 00:08:32,839 Speaker 1: parts of the universe. You're not a creamy peanut butter fan. 164 00:08:33,000 --> 00:08:36,280 Speaker 1: It's all about the chunks, man, It's all about the chunks. Well, 165 00:08:36,360 --> 00:08:38,439 Speaker 1: to each their own may there's a different flavor of 166 00:08:38,520 --> 00:08:40,680 Speaker 1: dark matter for every tape. New Tella there you go, 167 00:08:40,760 --> 00:08:45,600 Speaker 1: New Tella is the best flavor of dark rutter and 168 00:08:45,640 --> 00:08:48,720 Speaker 1: everyone gets a heart attack from being surrounded by all 169 00:08:48,800 --> 00:08:51,440 Speaker 1: this saturated fat. But yeah, it's a big question. Where 170 00:08:51,600 --> 00:08:54,439 Speaker 1: is dark matter and sort of like what structure it 171 00:08:54,480 --> 00:08:57,240 Speaker 1: has in the universe. Is it sort of smoothed out 172 00:08:57,240 --> 00:09:00,560 Speaker 1: there like a big cloud or is it is it chunky? 173 00:09:00,640 --> 00:09:03,440 Speaker 1: Is it in like strands? Is it in clumps? What's 174 00:09:03,480 --> 00:09:05,760 Speaker 1: it doing out there? And this is something that scientists 175 00:09:05,760 --> 00:09:08,720 Speaker 1: are eager to figure out because they just want to 176 00:09:08,720 --> 00:09:10,960 Speaker 1: know where all of this stuff is. They're trying to 177 00:09:11,000 --> 00:09:15,760 Speaker 1: develop a picture of the universe both visible and invisible, 178 00:09:15,880 --> 00:09:18,559 Speaker 1: and of course the invisible stuff much harder to see, 179 00:09:18,600 --> 00:09:20,760 Speaker 1: but since there's much more of it than there is 180 00:09:20,800 --> 00:09:24,079 Speaker 1: the visible stuff, it's a very important question. So, as usual, 181 00:09:24,120 --> 00:09:26,040 Speaker 1: we were wondering how many people out there had thought 182 00:09:26,080 --> 00:09:29,640 Speaker 1: about this question of the location and structure of dark matter. 183 00:09:30,000 --> 00:09:32,800 Speaker 1: So Daniel went out there to ask people on the internet, 184 00:09:32,960 --> 00:09:35,000 Speaker 1: how do we know where dark matter is? So if 185 00:09:35,040 --> 00:09:37,000 Speaker 1: you'd like to put your brain in the test and 186 00:09:37,080 --> 00:09:41,040 Speaker 1: answer questions that leading physicists don't know the answer to, 187 00:09:41,440 --> 00:09:44,720 Speaker 1: please write to me two questions at Daniel and Jorge 188 00:09:45,000 --> 00:09:48,000 Speaker 1: dot com. Here's what people had to say. Well, doc 189 00:09:48,040 --> 00:09:53,280 Speaker 1: matter reacts with gravity, so by looking out into the universe, Um, 190 00:09:53,320 --> 00:09:55,840 Speaker 1: we can sort of detect where the doc matter is 191 00:09:55,880 --> 00:09:58,760 Speaker 1: because of its effect on gravity. I know that it's 192 00:09:58,800 --> 00:10:02,800 Speaker 1: by gravity. Is the gravitational lensing that makes it possible 193 00:10:02,840 --> 00:10:05,680 Speaker 1: to have like some kind of ideas where it could 194 00:10:05,679 --> 00:10:09,920 Speaker 1: be dark matter in the universe. The distortion of light 195 00:10:10,000 --> 00:10:13,320 Speaker 1: suggests that there are more matter out there that we 196 00:10:13,360 --> 00:10:17,319 Speaker 1: can actually say whenever it's like bands. Well, once again, 197 00:10:17,360 --> 00:10:21,560 Speaker 1: I assume this has to do with the pot with 198 00:10:21,679 --> 00:10:24,640 Speaker 1: the examples and instance, as you were talking of these 199 00:10:24,720 --> 00:10:28,679 Speaker 1: massive tubs of argone if I'm not mistaken, that are 200 00:10:28,760 --> 00:10:32,320 Speaker 1: deep underground. We cannot see what dark matter itself is. 201 00:10:32,640 --> 00:10:35,960 Speaker 1: Light travels straight through it, but we can see other 202 00:10:36,000 --> 00:10:40,080 Speaker 1: planets and we can see light being distorted by the 203 00:10:40,160 --> 00:10:43,480 Speaker 1: gravitational effects of what dark matter is itself. I'd say 204 00:10:43,520 --> 00:10:45,439 Speaker 1: we know where the dark matter is because we can 205 00:10:45,480 --> 00:10:49,199 Speaker 1: see the gravitational force it exerts on the visible matter 206 00:10:49,240 --> 00:10:54,280 Speaker 1: around it. Next to that, it also bends light from 207 00:10:54,320 --> 00:10:59,120 Speaker 1: distant galaxies when it comes towards us. So I'd say 208 00:10:59,400 --> 00:11:03,320 Speaker 1: gravity is the usual suspect for us knowing where dark 209 00:11:03,360 --> 00:11:06,680 Speaker 1: matter is. Who is d M? I think I've heard 210 00:11:06,720 --> 00:11:10,559 Speaker 1: that dark matter is everywhere, that it just kind of 211 00:11:10,600 --> 00:11:15,599 Speaker 1: permeates the universe, so all over the place. So my 212 00:11:15,640 --> 00:11:18,160 Speaker 1: guess is for what we know dark matter is, or 213 00:11:18,200 --> 00:11:21,400 Speaker 1: how we know it is, if it gives off gravitational 214 00:11:21,400 --> 00:11:26,280 Speaker 1: waves because it interacts with stuff through gravity, then we 215 00:11:26,320 --> 00:11:30,160 Speaker 1: would use something that detects gravitational waves to see either 216 00:11:30,200 --> 00:11:34,200 Speaker 1: how far away it is or where it is in 217 00:11:34,280 --> 00:11:37,000 Speaker 1: respect to something else. I think we know where dark 218 00:11:37,080 --> 00:11:41,840 Speaker 1: matter is by looking for localized gravitational effects like lensing 219 00:11:41,960 --> 00:11:46,480 Speaker 1: or relative velocities that aren't completely explained by matter we 220 00:11:46,520 --> 00:11:50,920 Speaker 1: can observe in other ways. Right, A pretty interesting answer 221 00:11:50,920 --> 00:11:54,640 Speaker 1: is a lot of people went with gravity, which is true, right, Like, 222 00:11:54,640 --> 00:11:58,600 Speaker 1: like that's how we initially discovered dark matter is through gravity. Yeah, 223 00:11:58,640 --> 00:12:01,880 Speaker 1: that's basically the only way we can sense dark matter, 224 00:12:02,280 --> 00:12:05,080 Speaker 1: and so gravity is basically the answered. Gravity is the 225 00:12:05,120 --> 00:12:07,880 Speaker 1: reason we know dark matter exists, and dark matter is 226 00:12:07,920 --> 00:12:13,360 Speaker 1: basically an explanation for otherwise unexplainable gravity. So yeah, gravity 227 00:12:13,440 --> 00:12:16,600 Speaker 1: is basically our portal into the dark universe. And I 228 00:12:16,640 --> 00:12:20,760 Speaker 1: like this person who said who is dark matter? It's 229 00:12:20,800 --> 00:12:23,920 Speaker 1: like who it this new phone? I think that's because 230 00:12:24,000 --> 00:12:26,520 Speaker 1: in the question I wrote d M instead of dark matter, 231 00:12:26,760 --> 00:12:31,040 Speaker 1: assuming that everybody would know what DM meant, right, who 232 00:12:31,120 --> 00:12:34,559 Speaker 1: doesn't know what DM is? I was sliding into some 233 00:12:34,640 --> 00:12:36,160 Speaker 1: of these d M s with that one. I guess 234 00:12:37,120 --> 00:12:40,959 Speaker 1: you're being a physicism using acronyms on people who had 235 00:12:40,960 --> 00:12:43,720 Speaker 1: no idea what those acronyms are. But yeah, a lot 236 00:12:43,760 --> 00:12:46,080 Speaker 1: of people seem to set and have a basic idea 237 00:12:46,120 --> 00:12:48,440 Speaker 1: that it's through gravity. But the picture is a little 238 00:12:48,480 --> 00:12:50,880 Speaker 1: bit more complicated than that, right, I mean, we sort 239 00:12:50,880 --> 00:12:54,120 Speaker 1: of know that it's there because of gravity, but sort 240 00:12:54,160 --> 00:12:56,719 Speaker 1: of finding out exactly where it is or whether it 241 00:12:56,840 --> 00:13:00,440 Speaker 1: clumps or strands or smooth, that's much harder because we 242 00:13:00,480 --> 00:13:02,840 Speaker 1: can't see it right exactly. We can't see it in 243 00:13:02,880 --> 00:13:05,000 Speaker 1: the way that we can see the other kinds of matter. 244 00:13:05,280 --> 00:13:08,080 Speaker 1: It doesn't give off light, it doesn't reflect light. Remember 245 00:13:08,080 --> 00:13:10,240 Speaker 1: that dark matter is a bit of a confusing name 246 00:13:10,600 --> 00:13:14,920 Speaker 1: because dark matter is not actually dark. It's transparent, it's invisible. 247 00:13:15,040 --> 00:13:17,360 Speaker 1: It's not like a cloud of dark matter between you 248 00:13:17,440 --> 00:13:20,680 Speaker 1: and another star would block your view of that star. 249 00:13:21,160 --> 00:13:23,080 Speaker 1: If that were tue would be much easier to see 250 00:13:23,160 --> 00:13:26,440 Speaker 1: dark batter than it is today. Instead, light passes right 251 00:13:26,480 --> 00:13:29,040 Speaker 1: through dark matter. So give us, maybe start us off 252 00:13:29,040 --> 00:13:32,040 Speaker 1: with a refresher of dark matter or d M as 253 00:13:32,080 --> 00:13:34,080 Speaker 1: the physicist call it. You know, what do we know 254 00:13:34,120 --> 00:13:36,520 Speaker 1: about it? Well, we know that dark matter is about 255 00:13:36,600 --> 00:13:40,280 Speaker 1: twenty five of the energy budget of the universe. That 256 00:13:40,360 --> 00:13:42,839 Speaker 1: means if you take like a cubic light year of space, 257 00:13:42,920 --> 00:13:46,560 Speaker 1: or any volume of space, then of the energy in 258 00:13:46,640 --> 00:13:50,000 Speaker 1: that space is devoted to the mass of dark matter, 259 00:13:50,240 --> 00:13:53,840 Speaker 1: whereas five percent of the energy budget of any chunk 260 00:13:53,880 --> 00:13:57,280 Speaker 1: of space on average, you know, averaging over big distances, 261 00:13:57,600 --> 00:14:00,400 Speaker 1: is devoted to making things like stars and gala seas 262 00:14:00,440 --> 00:14:02,600 Speaker 1: and dust and giraffes and all of that kind of 263 00:14:02,800 --> 00:14:05,400 Speaker 1: normal matter made out of atoms. And that means that 264 00:14:05,440 --> 00:14:08,480 Speaker 1: there's a huge amount of dark matter. That a galaxy, 265 00:14:08,520 --> 00:14:11,959 Speaker 1: for example, is mostly dark matter. That the universe, the 266 00:14:12,080 --> 00:14:15,040 Speaker 1: stuff in the universe, the matter, you know, the physical 267 00:14:15,080 --> 00:14:18,360 Speaker 1: form of the universe is mostly dark matter. So we've 268 00:14:18,400 --> 00:14:20,960 Speaker 1: been studying the universe for thousands of years looking up 269 00:14:20,960 --> 00:14:24,080 Speaker 1: at the sky wondering how things work, and only recently 270 00:14:24,120 --> 00:14:26,880 Speaker 1: have we discovered that we've been missing most of it. 271 00:14:27,080 --> 00:14:29,800 Speaker 1: So that's pretty exciting. And we know that dark matter 272 00:14:29,960 --> 00:14:32,640 Speaker 1: is not made out of atoms, not made out of 273 00:14:32,640 --> 00:14:34,600 Speaker 1: the kind of stuff that you and I are made 274 00:14:34,600 --> 00:14:36,960 Speaker 1: out of. If it were, then it would probably interact 275 00:14:37,040 --> 00:14:39,600 Speaker 1: with light. And we can also do some careful accounting 276 00:14:39,600 --> 00:14:41,920 Speaker 1: from the very beginning of the universe, where we know 277 00:14:42,040 --> 00:14:44,840 Speaker 1: something about how much material there was to make atoms, 278 00:14:45,040 --> 00:14:47,080 Speaker 1: we can kind of account for where all of that went. 279 00:14:47,280 --> 00:14:49,920 Speaker 1: So we're pretty sure. We're almost certain that dark matter 280 00:14:49,960 --> 00:14:52,600 Speaker 1: is some kind of matter that doesn't give off light 281 00:14:52,680 --> 00:14:55,480 Speaker 1: or reflect light. It must be made out of something else. 282 00:14:55,720 --> 00:14:57,800 Speaker 1: And we know that it doesn't move very fast. We 283 00:14:57,880 --> 00:15:00,480 Speaker 1: call it cold dark matter, the as if it did, 284 00:15:00,520 --> 00:15:03,600 Speaker 1: it would spread out much more throughout the universe. Yeah, 285 00:15:03,600 --> 00:15:05,720 Speaker 1: and it's kind of interesting because I think I almost 286 00:15:05,720 --> 00:15:08,320 Speaker 1: feel like like, in a way, physicists called this thing 287 00:15:08,560 --> 00:15:10,760 Speaker 1: or named it a little bit too early, you know 288 00:15:10,840 --> 00:15:12,360 Speaker 1: what I mean, Like we gave it a name like 289 00:15:12,400 --> 00:15:14,400 Speaker 1: a dark matter, maybe a little too early, Like maybe 290 00:15:14,400 --> 00:15:16,280 Speaker 1: you should have kept going and say that you know 291 00:15:17,120 --> 00:15:20,040 Speaker 1: of the universe is just something that we don't understand 292 00:15:20,200 --> 00:15:22,560 Speaker 1: or something that is not like the rest of the 293 00:15:22,640 --> 00:15:25,000 Speaker 1: stuff in the universe. Well, that doesn't work as well 294 00:15:25,000 --> 00:15:28,800 Speaker 1: in grand proposals as a nice zingy phrase like dark matter. 295 00:15:31,280 --> 00:15:33,880 Speaker 1: But yeah, but I know what, I guess the point 296 00:15:33,920 --> 00:15:35,640 Speaker 1: is it really we don't know that much about it. 297 00:15:35,680 --> 00:15:37,680 Speaker 1: I mean, we sort of know it's presence, or at 298 00:15:37,760 --> 00:15:39,480 Speaker 1: least we know it's the effect on the rest of 299 00:15:39,480 --> 00:15:41,720 Speaker 1: the universe, but we don't even know if it's matter. Right, Well, 300 00:15:41,760 --> 00:15:44,720 Speaker 1: we know that it generates gravity, which suggests that it's 301 00:15:44,800 --> 00:15:49,320 Speaker 1: curves space according to general relativity. And so either our 302 00:15:49,440 --> 00:15:53,320 Speaker 1: understanding of how space curves is wrong, or it's some 303 00:15:53,440 --> 00:15:56,520 Speaker 1: new kind of energy and matter that does curve space. 304 00:15:57,000 --> 00:16:00,600 Speaker 1: And it's possible that we don't understand gravity. It's certain 305 00:16:00,800 --> 00:16:03,840 Speaker 1: that we don't have complete understanding of gravity. There are 306 00:16:03,960 --> 00:16:08,480 Speaker 1: alternative ideas to explain dark matter using variations on gravitational theory, 307 00:16:08,600 --> 00:16:11,520 Speaker 1: but none of them can really explain everything that we see. 308 00:16:12,000 --> 00:16:15,160 Speaker 1: And so you're right that we're not certain that it's matter. 309 00:16:15,360 --> 00:16:18,200 Speaker 1: But it's the simplest explanation that fits all of the data. 310 00:16:18,360 --> 00:16:21,800 Speaker 1: A new kind of particle that only interacts gravitationally, explains 311 00:16:21,880 --> 00:16:24,840 Speaker 1: basically everything that we see out there in the universe, 312 00:16:25,120 --> 00:16:28,280 Speaker 1: from the ripples in the earliest light to the structure 313 00:16:28,280 --> 00:16:31,480 Speaker 1: of the universe today to the rotations of galaxies. So 314 00:16:31,520 --> 00:16:34,800 Speaker 1: we're not certain, but it's the best candidate. Maybe should 315 00:16:34,840 --> 00:16:38,760 Speaker 1: have called it dark probably matter or dark most likely 316 00:16:38,760 --> 00:16:42,760 Speaker 1: matter d M M L D d M l M. 317 00:16:43,160 --> 00:16:45,160 Speaker 1: But we, as you said, so far, we only know 318 00:16:45,200 --> 00:16:48,080 Speaker 1: about it because of its gravitational effects, right, But we 319 00:16:48,120 --> 00:16:50,640 Speaker 1: sort of know quite a few things about sort of 320 00:16:50,840 --> 00:16:53,160 Speaker 1: generally where it is. We do have a good idea 321 00:16:53,320 --> 00:16:57,280 Speaker 1: of where it might be because of its gravitational effects. Right, 322 00:16:57,360 --> 00:17:00,440 Speaker 1: it is invisible. It doesn't give off light or interact 323 00:17:00,480 --> 00:17:03,280 Speaker 1: with any other kind of force. But gravity is local. Right, 324 00:17:03,320 --> 00:17:05,920 Speaker 1: if you are close to something, it tugs on you 325 00:17:06,119 --> 00:17:08,720 Speaker 1: more strongly than if you're far from something. So if 326 00:17:08,760 --> 00:17:10,840 Speaker 1: you're measuring the gravity of an object, if you can 327 00:17:10,920 --> 00:17:13,640 Speaker 1: only tell if something is there because of its gravity, 328 00:17:13,920 --> 00:17:16,240 Speaker 1: you can get an idea for where it is based 329 00:17:16,240 --> 00:17:18,880 Speaker 1: on what it tugs on. For example, we can see 330 00:17:18,880 --> 00:17:21,080 Speaker 1: the black holes are there because of the way the 331 00:17:21,119 --> 00:17:25,600 Speaker 1: stars move around them without actually directly seeing black holes, 332 00:17:25,800 --> 00:17:28,320 Speaker 1: and so gravity definitely can give you a picture as 333 00:17:28,320 --> 00:17:30,840 Speaker 1: to where things are in the universe, and we have 334 00:17:30,880 --> 00:17:33,480 Speaker 1: a rough idea for where dark matter is. We think 335 00:17:33,520 --> 00:17:37,280 Speaker 1: that dark matter is mostly lined up with the normal matter. 336 00:17:37,440 --> 00:17:40,000 Speaker 1: That where you see a galaxy is where there's a 337 00:17:40,080 --> 00:17:43,520 Speaker 1: huge clump of dark matter. So every galaxy, we think, 338 00:17:43,560 --> 00:17:46,600 Speaker 1: for example, is embedded in a huge cloud. We call 339 00:17:46,640 --> 00:17:50,400 Speaker 1: it a dark matter halo for every galaxy. Yeah, it's 340 00:17:50,400 --> 00:17:53,880 Speaker 1: like where you see regular stars and planets, you see 341 00:17:54,000 --> 00:17:56,840 Speaker 1: dark matter. Or it's almost like the opposite, right, it's 342 00:17:56,880 --> 00:17:59,119 Speaker 1: like where you see dark matter is where all the 343 00:17:59,160 --> 00:18:01,880 Speaker 1: stars and planets formed. In a way, yes, stars are 344 00:18:01,880 --> 00:18:04,479 Speaker 1: more like the tracers for the rest of stuff, right, 345 00:18:04,560 --> 00:18:07,200 Speaker 1: dark matter leads the way. There's more dark matter than 346 00:18:07,240 --> 00:18:10,160 Speaker 1: everything else. And so it's actually like where the dark 347 00:18:10,200 --> 00:18:13,920 Speaker 1: matter started clumping is where the normal matter fell into 348 00:18:14,000 --> 00:18:17,320 Speaker 1: it because of its gravity and then formed galaxies and 349 00:18:17,440 --> 00:18:19,840 Speaker 1: stars and all kinds of stuff that we can see. 350 00:18:20,040 --> 00:18:22,320 Speaker 1: So you know how when the military is fighting at night, 351 00:18:22,359 --> 00:18:24,280 Speaker 1: they shoot bullets and then occasionally, like one out of 352 00:18:24,320 --> 00:18:27,320 Speaker 1: every thousand bullets is a tracer. It's like glows, so 353 00:18:27,359 --> 00:18:29,840 Speaker 1: they can see where they're shooting. Stars are sort of 354 00:18:29,880 --> 00:18:32,000 Speaker 1: like that. They follow the dark matter, and they give 355 00:18:32,040 --> 00:18:34,960 Speaker 1: us a clue as to where that dark matter is. 356 00:18:35,520 --> 00:18:38,640 Speaker 1: And that's why we think that most galaxies are embedded 357 00:18:38,640 --> 00:18:42,639 Speaker 1: in this cloud, this halo of sort of spherical, sort 358 00:18:42,680 --> 00:18:46,040 Speaker 1: of a little bit elliptical dark matter that goes well 359 00:18:46,119 --> 00:18:49,080 Speaker 1: beyond actually where the stars are. Yeah, I've heard this 360 00:18:49,240 --> 00:18:52,359 Speaker 1: sort of analogy that regular matter like planets and stars. 361 00:18:52,400 --> 00:18:54,760 Speaker 1: It's sort of like the sprinkling on the icing of 362 00:18:54,800 --> 00:18:57,720 Speaker 1: a cupcake. Like, not just like in terms of our 363 00:18:57,800 --> 00:19:00,840 Speaker 1: relative importance to that and this the eye of the universe, 364 00:19:00,880 --> 00:19:02,760 Speaker 1: but also kind of like you know, sprinkles stick to 365 00:19:02,800 --> 00:19:05,120 Speaker 1: the icing in a cupcake. You know, you can't sort 366 00:19:05,160 --> 00:19:08,159 Speaker 1: of have sprinkles anywhere else. They're like, you know, the 367 00:19:08,200 --> 00:19:12,640 Speaker 1: sprinkles sort of tell you where the icing is. Yeah, 368 00:19:12,640 --> 00:19:15,240 Speaker 1: the sprinkles are sort of the stars, and the icing 369 00:19:15,280 --> 00:19:17,600 Speaker 1: is sort of dark matter, and the cupcake itself is 370 00:19:17,680 --> 00:19:20,359 Speaker 1: dark energy. That gives you sort of a sense of 371 00:19:20,400 --> 00:19:24,080 Speaker 1: the relative fractions of the energy budget of the universe. Yeah, 372 00:19:24,240 --> 00:19:26,439 Speaker 1: so I guess we are just the hangar ons of 373 00:19:26,480 --> 00:19:29,879 Speaker 1: the universe. We're just hanging onto dark matter. And so 374 00:19:30,000 --> 00:19:32,239 Speaker 1: let's get into a little bit more detail about what 375 00:19:32,320 --> 00:19:35,600 Speaker 1: we know about this halo around galaxies and also how 376 00:19:35,680 --> 00:19:38,399 Speaker 1: we know where it is, but first let's take a 377 00:19:38,480 --> 00:19:53,760 Speaker 1: quick break. All right, we're talking about dark matter and 378 00:19:54,119 --> 00:19:57,359 Speaker 1: where exactly it is, because I guess we know it's there, 379 00:19:57,359 --> 00:20:00,520 Speaker 1: but physicists can't find it. It's pretty tricky to nail 380 00:20:00,560 --> 00:20:04,159 Speaker 1: down an individual piece of dark matter, for example, because 381 00:20:04,160 --> 00:20:07,719 Speaker 1: it only interacts gravitationally, imagine trying to find like an 382 00:20:07,760 --> 00:20:10,840 Speaker 1: invisible piece of sand in your room. How would you 383 00:20:10,880 --> 00:20:14,440 Speaker 1: detect it? It's gravity is essentially nothing because gravity is 384 00:20:14,440 --> 00:20:17,359 Speaker 1: a really really weak force. All of the other forces 385 00:20:17,400 --> 00:20:21,760 Speaker 1: of electromagnetism, even the weak force, is much stronger than gravity. 386 00:20:22,119 --> 00:20:24,800 Speaker 1: So in order to detect something through gravity, you need 387 00:20:24,840 --> 00:20:26,760 Speaker 1: to have a huge force. You need to have like 388 00:20:26,920 --> 00:20:30,160 Speaker 1: a planet sized force or a solar system sized force 389 00:20:30,520 --> 00:20:33,680 Speaker 1: because gravity is so weak. So when we use gravity 390 00:20:33,720 --> 00:20:36,040 Speaker 1: to look for dark matter, we can only sort of 391 00:20:36,080 --> 00:20:39,360 Speaker 1: tell the large scale structure. It's very difficult to get 392 00:20:39,359 --> 00:20:42,480 Speaker 1: a fine grained picture of where things are. But even 393 00:20:42,520 --> 00:20:45,119 Speaker 1: though it's very weak gravitation, and we do have a 394 00:20:45,200 --> 00:20:47,600 Speaker 1: kind of a pretty good idea of what shape it 395 00:20:47,680 --> 00:20:50,280 Speaker 1: has in the galaxy, right like this halo, it's not 396 00:20:50,440 --> 00:20:53,240 Speaker 1: just like a blob. It has some sort of shaped 397 00:20:53,280 --> 00:20:55,720 Speaker 1: to it. That's right. It tends to be denser at 398 00:20:55,720 --> 00:20:59,040 Speaker 1: the core and thinner further out, much like the visible 399 00:20:59,080 --> 00:21:01,320 Speaker 1: matter in the galaxy. See, and we can tell where 400 00:21:01,320 --> 00:21:03,760 Speaker 1: it is because it has an effect on how the 401 00:21:03,800 --> 00:21:07,040 Speaker 1: stars spin. Right, Like, the old familiar story is that 402 00:21:07,080 --> 00:21:09,840 Speaker 1: we know that dark matter is there because we see 403 00:21:09,840 --> 00:21:12,960 Speaker 1: the speed of stars is way too high. If dark 404 00:21:13,000 --> 00:21:16,119 Speaker 1: matter wasn't there, then if the galaxy was spinning this quickly, 405 00:21:16,119 --> 00:21:19,280 Speaker 1: you should be throwing its stars out into interstellar space. 406 00:21:19,640 --> 00:21:23,240 Speaker 1: It needs more gravity, something out there to hold those 407 00:21:23,280 --> 00:21:26,439 Speaker 1: stars in place for the galaxy to spin this fast. 408 00:21:26,800 --> 00:21:28,680 Speaker 1: That's the old story that just tells us that dark 409 00:21:28,760 --> 00:21:31,280 Speaker 1: matter is there. But we can get much more fine 410 00:21:31,400 --> 00:21:35,000 Speaker 1: grained information. We can tell where in the galaxy that 411 00:21:35,119 --> 00:21:38,080 Speaker 1: dark matter is by measuring the velocity of stars at 412 00:21:38,119 --> 00:21:41,320 Speaker 1: different points as you move closer in or further out 413 00:21:41,440 --> 00:21:44,119 Speaker 1: from the center of the galaxy. Right, Because I guess 414 00:21:44,160 --> 00:21:46,240 Speaker 1: what you're saying is that if the dark matter was 415 00:21:46,320 --> 00:21:49,879 Speaker 1: all clumped together in the very very center of the galaxy, 416 00:21:50,119 --> 00:21:52,200 Speaker 1: the stars will move differently than if it was more 417 00:21:52,200 --> 00:21:54,920 Speaker 1: spread out throughout the whole galaxy. Right. Yeah, If you 418 00:21:55,000 --> 00:21:57,840 Speaker 1: are a star moving through the galaxy, then the thing 419 00:21:57,880 --> 00:22:01,000 Speaker 1: that determines your speed is how much stuff there is 420 00:22:01,560 --> 00:22:04,080 Speaker 1: closer to the center of the galaxy than you are. 421 00:22:04,320 --> 00:22:06,719 Speaker 1: You're not sensitive to anything that's further out than you. 422 00:22:06,920 --> 00:22:09,080 Speaker 1: It's sort of like if you dig into the Earth, 423 00:22:09,280 --> 00:22:12,080 Speaker 1: then everything that's further out from you, that's above you 424 00:22:12,640 --> 00:22:15,560 Speaker 1: doesn't affect your gravity at all because it all cancels out. 425 00:22:15,600 --> 00:22:17,639 Speaker 1: It's only stuff that's closer to the center of the 426 00:22:17,640 --> 00:22:20,240 Speaker 1: Earth than you are. So it's the same for a star. 427 00:22:20,520 --> 00:22:23,600 Speaker 1: The star is speed basically tells you how much stuff 428 00:22:23,640 --> 00:22:26,560 Speaker 1: there is between it and the center of the galaxy. 429 00:22:26,680 --> 00:22:28,520 Speaker 1: So as you look at the velocity of the star 430 00:22:28,760 --> 00:22:30,960 Speaker 1: as you move further out from the center, it gives 431 00:22:31,000 --> 00:22:33,159 Speaker 1: you a picture for where that dark matter has to 432 00:22:33,160 --> 00:22:36,720 Speaker 1: be to explain that velocity. The dark matter was all 433 00:22:36,720 --> 00:22:39,560 Speaker 1: clumped together at the very center of the galaxy, then stars, 434 00:22:39,560 --> 00:22:41,840 Speaker 1: you know, halfway out from the disk would be moving 435 00:22:41,920 --> 00:22:44,600 Speaker 1: faster because it would be a stronger force from all 436 00:22:44,640 --> 00:22:48,000 Speaker 1: of that gravity. Instead, if it's spread out really, really far, 437 00:22:48,320 --> 00:22:50,600 Speaker 1: then some of that stuff is outside those stars and 438 00:22:50,640 --> 00:22:53,280 Speaker 1: it doesn't affect them. It doesn't pull them towards the center, 439 00:22:53,280 --> 00:22:55,960 Speaker 1: it doesn't speed them up as much. Yeah, I guess 440 00:22:56,000 --> 00:22:58,080 Speaker 1: it's sort of like, if you're in the middle of 441 00:22:58,440 --> 00:23:00,800 Speaker 1: a cloud of dark matter, you're not to feel its 442 00:23:00,840 --> 00:23:03,919 Speaker 1: gravitation effects a much because it's pulling you in all directions, 443 00:23:04,119 --> 00:23:06,919 Speaker 1: Whereas if you're really really far away from it, the 444 00:23:06,920 --> 00:23:08,840 Speaker 1: whole blob, then you are going to feel sort of 445 00:23:08,880 --> 00:23:11,439 Speaker 1: its entire gravity. Yeah, and so that's how we know 446 00:23:11,520 --> 00:23:13,640 Speaker 1: that it's more dense in the middle. And that's kind 447 00:23:13,640 --> 00:23:16,160 Speaker 1: of important, right, It is important, and it's not something 448 00:23:16,160 --> 00:23:19,760 Speaker 1: that we really fully understand. Like if you do simulations 449 00:23:19,760 --> 00:23:22,240 Speaker 1: and you say we think we understand how galaxies might 450 00:23:22,240 --> 00:23:24,600 Speaker 1: have formed, and how this halo formed and all the 451 00:23:24,640 --> 00:23:27,680 Speaker 1: dark matter swirls together to make this well that forms 452 00:23:27,680 --> 00:23:30,399 Speaker 1: the galaxy, then we predict a certain shape for that 453 00:23:30,480 --> 00:23:32,840 Speaker 1: dark matter density. We predicted to be sort of like 454 00:23:32,960 --> 00:23:35,880 Speaker 1: peaky near the center, that like most of the dark 455 00:23:35,880 --> 00:23:38,280 Speaker 1: matter should be right at the center and then should 456 00:23:38,320 --> 00:23:40,520 Speaker 1: fall off kind of quickly. But what we observe when 457 00:23:40,520 --> 00:23:42,160 Speaker 1: we go out there and we look at the dark 458 00:23:42,200 --> 00:23:45,560 Speaker 1: matter see where it actually is based on these rotation curves, 459 00:23:46,080 --> 00:23:48,720 Speaker 1: is that it's not as peaky near the center. It's 460 00:23:48,720 --> 00:23:51,879 Speaker 1: more like a broad, flat core, like a big blob 461 00:23:52,000 --> 00:23:54,919 Speaker 1: of dark matter, it's not as like pointed at the center. 462 00:23:55,240 --> 00:23:58,640 Speaker 1: So that's a current mystery we don't really understand. Dark 463 00:23:58,680 --> 00:24:01,600 Speaker 1: matter doesn't seem to be as clumped towards the center 464 00:24:01,720 --> 00:24:03,639 Speaker 1: as we thought. And I guess part of it is that, 465 00:24:03,720 --> 00:24:05,119 Speaker 1: you know, a lot of people sort of wonder like, 466 00:24:05,160 --> 00:24:07,280 Speaker 1: if there is that much dark matter out there, why 467 00:24:07,320 --> 00:24:10,040 Speaker 1: doesn't it just collapse into a dark matter black hole? 468 00:24:10,160 --> 00:24:13,160 Speaker 1: But we we've talked about before how dark matter basically 469 00:24:13,359 --> 00:24:17,360 Speaker 1: is not sticky with itself, like it doesn't feel besides gravity, 470 00:24:17,440 --> 00:24:19,600 Speaker 1: It doesn't feel any other force that would make it 471 00:24:19,680 --> 00:24:23,359 Speaker 1: stick together, Like our adoms have the electromagnetic force to 472 00:24:23,480 --> 00:24:25,879 Speaker 1: make them stick, but dark matter doesn't appear to have 473 00:24:26,040 --> 00:24:28,479 Speaker 1: something like that. And that force is important if you're 474 00:24:28,480 --> 00:24:30,359 Speaker 1: going to fall into the black hole, because you have 475 00:24:30,400 --> 00:24:33,400 Speaker 1: to have some way to lose your angular momentum. Dark matter, 476 00:24:33,480 --> 00:24:36,520 Speaker 1: like everything else, is spinning and swirling, and the reason 477 00:24:36,560 --> 00:24:38,920 Speaker 1: that things don't fall into a black hole is because 478 00:24:38,960 --> 00:24:41,480 Speaker 1: they are swirling around it, the way the Earth is 479 00:24:41,560 --> 00:24:44,280 Speaker 1: orbiting the Sun and not falling into it. For the 480 00:24:44,280 --> 00:24:46,320 Speaker 1: Earth to fall into the Sun, it would have to 481 00:24:46,400 --> 00:24:49,679 Speaker 1: somehow lose its velocity. It would have to bump into 482 00:24:49,760 --> 00:24:52,919 Speaker 1: something we have to get slowed down. That only happens 483 00:24:52,960 --> 00:24:55,240 Speaker 1: if there's some sort of like sticky force that can 484 00:24:55,320 --> 00:24:58,000 Speaker 1: do that. So for a dark matter, that's really hard 485 00:24:58,080 --> 00:25:00,960 Speaker 1: because it passes right through itself, it passes right through 486 00:25:01,080 --> 00:25:03,720 Speaker 1: normal matter. It's very hard for it to lose its 487 00:25:03,720 --> 00:25:06,439 Speaker 1: speed or its angular momentum. So that's why this halo 488 00:25:06,520 --> 00:25:10,000 Speaker 1: of dark matter is bigger than the visible galaxy because 489 00:25:10,040 --> 00:25:13,040 Speaker 1: dark matter actually finds it harder to collapse, harder to 490 00:25:13,160 --> 00:25:16,080 Speaker 1: fall into black holes, right, you know, And so it's 491 00:25:16,160 --> 00:25:18,840 Speaker 1: been this big diffusion. It has this interesting shape. So 492 00:25:18,880 --> 00:25:20,640 Speaker 1: then how else can we sort of know about its 493 00:25:20,640 --> 00:25:23,800 Speaker 1: structure besides it's sort of general blobby shape. Well, one 494 00:25:23,840 --> 00:25:26,520 Speaker 1: of the listeners got it right thinking about how dark 495 00:25:26,560 --> 00:25:29,600 Speaker 1: matter distorts the path of light. We can tell when 496 00:25:29,600 --> 00:25:32,439 Speaker 1: there's a big blob of dark matter between us and 497 00:25:32,560 --> 00:25:35,920 Speaker 1: something else because it acts like a lens in the sky. 498 00:25:36,119 --> 00:25:39,320 Speaker 1: Remember that dark matter, even though it's invisible and light 499 00:25:39,359 --> 00:25:42,760 Speaker 1: can pass through it, it does change the shape of space. 500 00:25:43,280 --> 00:25:45,200 Speaker 1: And that means the space can act like a lens, 501 00:25:45,320 --> 00:25:47,360 Speaker 1: and so light will pass through it, but it will 502 00:25:47,400 --> 00:25:49,639 Speaker 1: get bent on the way. And so if there's a 503 00:25:49,680 --> 00:25:52,720 Speaker 1: big blob of dark matter between us and a distant galaxy, 504 00:25:52,760 --> 00:25:56,080 Speaker 1: for example, it will change the shape of that galaxy distorted, 505 00:25:56,359 --> 00:25:58,000 Speaker 1: just as if there was a lens there. So we 506 00:25:58,040 --> 00:26:00,399 Speaker 1: can use that to try to get idea is for 507 00:26:00,480 --> 00:26:03,959 Speaker 1: where dark matter might be interesting. So dark matter does 508 00:26:04,000 --> 00:26:07,399 Speaker 1: seem to clump within our galaxy? Is that what you're saying? Like, 509 00:26:07,440 --> 00:26:10,680 Speaker 1: maybe within our galaxy there are spots where dark matter 510 00:26:10,760 --> 00:26:13,960 Speaker 1: seems to be denser than others. That's hard to tell 511 00:26:14,040 --> 00:26:17,040 Speaker 1: because this kind of gravitational effect is kind of rare, 512 00:26:17,280 --> 00:26:20,359 Speaker 1: Like you need a clear background galaxy and then you 513 00:26:20,400 --> 00:26:22,639 Speaker 1: need a blob of dark matter right in front of 514 00:26:22,640 --> 00:26:25,280 Speaker 1: it has to be like perfectly lined up, so it's 515 00:26:25,320 --> 00:26:28,760 Speaker 1: tough to use this. They call this strong gravitational lensing 516 00:26:29,119 --> 00:26:31,439 Speaker 1: to get a clear picture for where the dark matter is, 517 00:26:31,480 --> 00:26:34,359 Speaker 1: because we don't have really enough examples, so it's not 518 00:26:34,400 --> 00:26:36,800 Speaker 1: a great way to tell where the dark matter is. 519 00:26:36,960 --> 00:26:39,520 Speaker 1: A better way to tell if dark matter clumps up 520 00:26:39,880 --> 00:26:43,000 Speaker 1: is to look for its effect on stars. So not 521 00:26:43,080 --> 00:26:45,920 Speaker 1: just like the velocity of stars as they weave around 522 00:26:45,960 --> 00:26:48,919 Speaker 1: the center of the galaxy, but their motion in other directions, 523 00:26:48,960 --> 00:26:51,680 Speaker 1: like if there is a big clump of dark matter 524 00:26:51,720 --> 00:26:54,840 Speaker 1: and especially dense blob of dark matter. It will affect 525 00:26:54,840 --> 00:26:57,840 Speaker 1: how stars are moving around it. It will change the 526 00:26:57,880 --> 00:27:01,520 Speaker 1: motion of those stars. It will attract them, it'll reflect them. 527 00:27:01,520 --> 00:27:03,439 Speaker 1: I see. So if you look sort of look at 528 00:27:03,480 --> 00:27:05,680 Speaker 1: the overall motion of all the stars in the galaxy, 529 00:27:05,760 --> 00:27:07,359 Speaker 1: if you see that there are you know, sort of 530 00:27:07,359 --> 00:27:10,320 Speaker 1: wiggles here and there or little you know, eddies or 531 00:27:10,400 --> 00:27:13,240 Speaker 1: little clumps of stars forming, then you know that there's 532 00:27:13,240 --> 00:27:15,840 Speaker 1: something else there and that it's not the dark matter 533 00:27:15,960 --> 00:27:18,959 Speaker 1: is not perfectly smooth. Yes, And we recently launched a 534 00:27:19,000 --> 00:27:23,000 Speaker 1: satellite called Gaya which is mapping the galaxy in four dimensions. 535 00:27:23,400 --> 00:27:26,480 Speaker 1: It measures the position, the location of all these stars 536 00:27:26,560 --> 00:27:30,000 Speaker 1: and their velocity. So we're getting this incredible map. It 537 00:27:30,080 --> 00:27:33,320 Speaker 1: has like a billion stars with their position and their 538 00:27:33,359 --> 00:27:36,560 Speaker 1: velocity map. Then we can use this to look for deviations. 539 00:27:36,560 --> 00:27:39,360 Speaker 1: Were like, well, if dark matter was perfectly smooth, what 540 00:27:39,359 --> 00:27:42,040 Speaker 1: would we expect all these stars to be doing. And 541 00:27:42,280 --> 00:27:45,080 Speaker 1: are any stars doing anything weird? And if they are, 542 00:27:45,160 --> 00:27:47,240 Speaker 1: we can sort of back that out and figure out 543 00:27:47,400 --> 00:27:50,440 Speaker 1: where dark matter has to be to explain any weird 544 00:27:50,480 --> 00:27:52,960 Speaker 1: patterns of the star motion. Right, Because I guess if 545 00:27:53,040 --> 00:27:56,320 Speaker 1: dark matter was perfectly smooth, Peanut butter like this kind 546 00:27:56,320 --> 00:28:00,000 Speaker 1: of smooth cloud. Then you would expect all the stars 547 00:28:00,040 --> 00:28:03,040 Speaker 1: us to be basically moving along as if it was 548 00:28:03,080 --> 00:28:05,400 Speaker 1: in a lazy river, right, like everyone sort of moving 549 00:28:05,440 --> 00:28:08,200 Speaker 1: at the same You know, nobody would be going much 550 00:28:08,240 --> 00:28:10,840 Speaker 1: faster than or slower than any of the other stars. Yeah, 551 00:28:10,840 --> 00:28:13,440 Speaker 1: at the same radius, right, we expect as you go out, 552 00:28:13,520 --> 00:28:15,679 Speaker 1: as you change your radius relative to the center of 553 00:28:15,680 --> 00:28:18,239 Speaker 1: the galaxy, these things will change, just like they do 554 00:28:18,240 --> 00:28:21,040 Speaker 1: in our solar system. Pluto's not moving around the Sun 555 00:28:21,080 --> 00:28:23,680 Speaker 1: as fast as Jupiter, which is not moving as fast 556 00:28:23,720 --> 00:28:26,640 Speaker 1: as Mercury, because as you go further out the gravitational 557 00:28:26,680 --> 00:28:29,120 Speaker 1: force is weaker. But you'd expect things at the same 558 00:28:29,240 --> 00:28:32,240 Speaker 1: radius to basically be having the same motion. And so 559 00:28:32,280 --> 00:28:35,280 Speaker 1: if you see deviations, then you know dark matter is there, 560 00:28:35,440 --> 00:28:37,920 Speaker 1: and we do sort of expect there to be clumps. 561 00:28:38,000 --> 00:28:40,719 Speaker 1: We expect that the galaxy, for example, has lots of 562 00:28:40,760 --> 00:28:44,080 Speaker 1: other galaxies inside of it that it has absorbed. We 563 00:28:44,120 --> 00:28:46,800 Speaker 1: think that the history of our galaxy includes lots of 564 00:28:46,840 --> 00:28:50,160 Speaker 1: collisions to form the Milky Way, and you would suspect 565 00:28:50,160 --> 00:28:53,120 Speaker 1: that those galaxies might still have like their dark matter 566 00:28:53,200 --> 00:28:57,360 Speaker 1: halos embedded within hours because I guess you would expect 567 00:28:57,400 --> 00:29:00,960 Speaker 1: our matter to be clumpy because regg or matter is clumpy, 568 00:29:01,040 --> 00:29:04,120 Speaker 1: so in a way, like wouldn't our regular matter also 569 00:29:04,200 --> 00:29:07,960 Speaker 1: sort of catalyze or trigger dark matter to clump. Our 570 00:29:08,000 --> 00:29:10,600 Speaker 1: matter is clumpy, But that's because it's sticky, right, It 571 00:29:10,720 --> 00:29:14,160 Speaker 1: can form these blobs, so when gravity pulls it together, 572 00:29:14,520 --> 00:29:18,160 Speaker 1: it sticks together and then that accumulates forms this runaway effect, 573 00:29:18,360 --> 00:29:21,160 Speaker 1: whereas dark matter is not sticky, and so dark matter 574 00:29:21,200 --> 00:29:24,800 Speaker 1: halos can pass right through each other without very much distortion. 575 00:29:24,920 --> 00:29:27,480 Speaker 1: The other question is a cool one, like do stars 576 00:29:27,640 --> 00:29:30,560 Speaker 1: form clumps of dark matter? And this is something people 577 00:29:30,560 --> 00:29:32,440 Speaker 1: have studied. They've tried to look to see if there's 578 00:29:32,480 --> 00:29:35,520 Speaker 1: like an intense blob of dark matter inside the sun, 579 00:29:35,640 --> 00:29:38,440 Speaker 1: for example. But remember that there's much more dark matter 580 00:29:38,560 --> 00:29:40,640 Speaker 1: than there is normal matter, and so dark matter sort 581 00:29:40,640 --> 00:29:43,720 Speaker 1: of wins the gravitational battles. You would expect it to 582 00:29:43,800 --> 00:29:46,520 Speaker 1: mostly go the other direction, that dark matter would influence 583 00:29:46,760 --> 00:29:49,920 Speaker 1: the pattern of normal matter rather than vice versa. But yeah, 584 00:29:50,000 --> 00:29:52,400 Speaker 1: it is a tug of war. Interesting you're saying dark 585 00:29:52,440 --> 00:29:56,400 Speaker 1: matter is ignoring us. Basically it's ghosting us. It mostly can. 586 00:29:56,640 --> 00:29:59,240 Speaker 1: But back to this question of like following the stars. 587 00:29:59,440 --> 00:30:02,080 Speaker 1: There are some really cool things that we do see 588 00:30:02,160 --> 00:30:05,480 Speaker 1: inside our galaxy. We can see the remnants of other 589 00:30:05,520 --> 00:30:09,320 Speaker 1: galaxies that the Milky Way has eaten, little mini galaxies 590 00:30:09,320 --> 00:30:12,680 Speaker 1: we call these dwarf galaxies, and some of these are 591 00:30:12,800 --> 00:30:16,120 Speaker 1: really really interesting because they're super high in dark matter. 592 00:30:16,640 --> 00:30:19,120 Speaker 1: Like our galaxy has a lot of dark matter, but 593 00:30:19,200 --> 00:30:22,680 Speaker 1: some of these dwarf galaxies are almost entirely dark matter, 594 00:30:23,040 --> 00:30:25,120 Speaker 1: and we can tell that they're there because we see 595 00:30:25,240 --> 00:30:29,560 Speaker 1: stars orbiting these invisible dark matter halos. So there's sort 596 00:30:29,600 --> 00:30:33,160 Speaker 1: of like many clumps of dark matter within our dark 597 00:30:33,160 --> 00:30:36,800 Speaker 1: matter halo. Interesting, so it is clumpy, but maybe because 598 00:30:36,920 --> 00:30:39,840 Speaker 1: we've we've added the clumps kind of yeah, because we've 599 00:30:39,960 --> 00:30:43,479 Speaker 1: formed our big halo from a bunch of clumps. So 600 00:30:43,520 --> 00:30:46,040 Speaker 1: we think these clumps formed initially each one of these 601 00:30:46,120 --> 00:30:49,280 Speaker 1: its own galaxy, and then galaxies eventually do merge and 602 00:30:49,320 --> 00:30:53,320 Speaker 1: collide and form bigger galaxies. And sometimes those dark matter 603 00:30:53,360 --> 00:30:57,080 Speaker 1: halos don't necessarily spread out and just join like the 604 00:30:57,120 --> 00:30:59,600 Speaker 1: original creamy blob of the Milky Way. They sort of 605 00:30:59,640 --> 00:31:02,080 Speaker 1: stay there as chunks, and you can tell of they're 606 00:31:02,200 --> 00:31:06,760 Speaker 1: because the stars swirling around those little dwarf galaxies. Well, 607 00:31:06,800 --> 00:31:08,760 Speaker 1: here's the question. Do you think the dark matter in 608 00:31:08,760 --> 00:31:11,280 Speaker 1: our galaxy is spinning also with the rest of the 609 00:31:11,400 --> 00:31:14,160 Speaker 1: stars and galaxies, or is it just standing still. It's 610 00:31:14,160 --> 00:31:17,640 Speaker 1: almost certainly spinning. That's the reason that it doesn't collapse 611 00:31:17,720 --> 00:31:19,840 Speaker 1: into the black hole in the center. If it was 612 00:31:19,880 --> 00:31:22,320 Speaker 1: standing still, then that gravity from that black hole would 613 00:31:22,320 --> 00:31:25,240 Speaker 1: just suck it up. So it's almost certain that it's rotating. 614 00:31:25,440 --> 00:31:28,480 Speaker 1: That we can't measure that directly, right, we haven't seen that, 615 00:31:28,880 --> 00:31:31,120 Speaker 1: but we're fairly certain that it has to be otherwise 616 00:31:31,120 --> 00:31:34,920 Speaker 1: it would have collapsed. So through strong gravitational lensing we 617 00:31:34,960 --> 00:31:38,120 Speaker 1: can tell that there are some clumps out there, and 618 00:31:38,200 --> 00:31:40,680 Speaker 1: through some of these absorbed galaxies we know there are 619 00:31:40,680 --> 00:31:42,520 Speaker 1: clumps out there, but what else do we know about 620 00:31:42,520 --> 00:31:45,200 Speaker 1: this clumpiness. We can also try to measure the clumpiness 621 00:31:45,280 --> 00:31:48,360 Speaker 1: by looking at the effect of our gravity on things 622 00:31:48,680 --> 00:31:52,200 Speaker 1: near the galaxy. So sometimes these mini galaxies or these 623 00:31:52,200 --> 00:31:55,680 Speaker 1: globular clusters get sucked inside the galaxy. Sometimes they're in 624 00:31:55,840 --> 00:31:59,240 Speaker 1: orbit around the galaxy. So for example, the large Magellanic 625 00:31:59,280 --> 00:32:01,479 Speaker 1: Cloud is a ab of stuff that's sort of like 626 00:32:01,520 --> 00:32:04,600 Speaker 1: a satellite galaxy of the Milky Way, and often these 627 00:32:04,600 --> 00:32:08,240 Speaker 1: galaxies get torn apart, they don't hold themselves together. They 628 00:32:08,240 --> 00:32:11,640 Speaker 1: turn into these streams. So around the galaxy there are 629 00:32:11,640 --> 00:32:15,000 Speaker 1: these things called stellar streams, which are these like lines 630 00:32:15,240 --> 00:32:18,880 Speaker 1: of stars moving in a loop sort of around the galaxies. 631 00:32:19,040 --> 00:32:21,640 Speaker 1: It's sort of like the galaxy has rings of stars 632 00:32:22,840 --> 00:32:28,640 Speaker 1: interesting like accidents almost, yeah, and they're sort of swooping 633 00:32:28,760 --> 00:32:31,560 Speaker 1: around the galaxy. And those are very sensitive to the 634 00:32:31,600 --> 00:32:35,160 Speaker 1: distribution of dark matter. So if, for example, the dark 635 00:32:35,200 --> 00:32:38,200 Speaker 1: matter halo is clumpy, it will affect how those stars 636 00:32:38,240 --> 00:32:41,760 Speaker 1: get pulled apart and whether they're like gaps in those streams. 637 00:32:42,040 --> 00:32:44,640 Speaker 1: So there are people right now studying these stellar streams. 638 00:32:44,640 --> 00:32:47,800 Speaker 1: They're like probes of that dark matter halo to look 639 00:32:47,840 --> 00:32:49,720 Speaker 1: to see if there are clumps in the dark matter 640 00:32:49,720 --> 00:32:52,880 Speaker 1: halo or to see if it's like perfectly spherical or 641 00:32:52,960 --> 00:32:55,440 Speaker 1: kind of elliptical. So these are very nice ways to 642 00:32:55,480 --> 00:32:58,200 Speaker 1: tell how much dark matter they're passing through and how 643 00:32:58,240 --> 00:33:01,920 Speaker 1: clumpy it is. Interesting, and so that's one way to 644 00:33:01,960 --> 00:33:04,680 Speaker 1: sort of know the clumpiness of dark matter. And what 645 00:33:04,800 --> 00:33:06,920 Speaker 1: have we learned from all of these different ways. We 646 00:33:06,920 --> 00:33:09,160 Speaker 1: don't have a great picture of where dark matter is 647 00:33:09,160 --> 00:33:11,720 Speaker 1: in the galaxy. People often write in and ask like 648 00:33:12,000 --> 00:33:14,760 Speaker 1: where is the dark matter? Can we see like planets 649 00:33:14,760 --> 00:33:17,240 Speaker 1: of dark matter or that's kind of stuff. Really, we're 650 00:33:17,280 --> 00:33:19,920 Speaker 1: not very sensitive to the details. We know that the 651 00:33:19,960 --> 00:33:22,920 Speaker 1: Milky Way has a big blob of dark matter that 652 00:33:23,000 --> 00:33:26,800 Speaker 1: it's probably elliptical, you know, it's not totally spherical. We 653 00:33:26,800 --> 00:33:30,920 Speaker 1: can see some clumps where these faint dwarf galaxies were absorbed, 654 00:33:31,040 --> 00:33:33,400 Speaker 1: but we don't have a great sense for the structure 655 00:33:33,480 --> 00:33:36,800 Speaker 1: of the dark matter. It's mostly smooth, but we can't 656 00:33:36,800 --> 00:33:39,200 Speaker 1: see things smaller than like, you know, tend to the 657 00:33:39,280 --> 00:33:42,640 Speaker 1: six stars. I see, like the smallest clump we can 658 00:33:42,720 --> 00:33:45,360 Speaker 1: sort of tell right now is is tend to the 659 00:33:45,440 --> 00:33:48,880 Speaker 1: six billions of kilometers maybe tend to the six solar 660 00:33:48,920 --> 00:33:52,520 Speaker 1: masses equivalents of dark matter? Is like the smallest chunk 661 00:33:52,520 --> 00:33:55,760 Speaker 1: of things we can tell. Well, that's like our our 662 00:33:55,800 --> 00:33:58,720 Speaker 1: best resolution of our picture of dark matter in the galaxy. 663 00:33:58,760 --> 00:34:02,480 Speaker 1: It's like a pixel this side a million sons. So 664 00:34:02,520 --> 00:34:05,560 Speaker 1: we're not very sensitive and that's just because it's mostly smooth. 665 00:34:05,800 --> 00:34:08,160 Speaker 1: There aren't a lot of features to see, who we think, 666 00:34:08,440 --> 00:34:11,240 Speaker 1: and because we're not very sensitive to it. Again, gravity 667 00:34:11,320 --> 00:34:13,759 Speaker 1: is very weak and it's our only way of interacting 668 00:34:13,760 --> 00:34:16,239 Speaker 1: with it. Which makes it kind of frustrating. All right, well, 669 00:34:16,360 --> 00:34:19,080 Speaker 1: it sounds like it's still yet to be discovered. Who knows, 670 00:34:19,120 --> 00:34:23,160 Speaker 1: Maybe it's forming giant dark matter squirrels or bananas or 671 00:34:23,200 --> 00:34:25,360 Speaker 1: grass out there, but we just can't see it with 672 00:34:25,480 --> 00:34:28,040 Speaker 1: our current resolution. And so let's get a little bit 673 00:34:28,040 --> 00:34:30,799 Speaker 1: into what the overall picture of dark matter then is 674 00:34:30,880 --> 00:34:34,279 Speaker 1: in the universe, and also what's happening between galaxies. But 675 00:34:34,360 --> 00:34:49,520 Speaker 1: first let's take another quick break. All right, Daniel has 676 00:34:49,600 --> 00:34:53,080 Speaker 1: lost his dark matter and his mind apparently. Did you 677 00:34:53,120 --> 00:34:55,080 Speaker 1: lose your mind looking for the dark matter? I did. 678 00:34:55,080 --> 00:34:59,719 Speaker 1: It's driving me crazy. Where are you? It's avoiding you, 679 00:34:59,760 --> 00:35:02,000 Speaker 1: It's else see you. It is a little bit ghosting 680 00:35:02,160 --> 00:35:05,040 Speaker 1: us as humanity because we know it's there, but it 681 00:35:05,080 --> 00:35:08,040 Speaker 1: doesn't seem to want to make expressence known to us. 682 00:35:08,080 --> 00:35:10,680 Speaker 1: In detail, we sort of have a big picture of 683 00:35:10,719 --> 00:35:12,960 Speaker 1: it that it's in a big clump around the galaxy, 684 00:35:13,120 --> 00:35:15,839 Speaker 1: mostly concentrated in the middle. We see some clumps out there, 685 00:35:15,920 --> 00:35:18,279 Speaker 1: but we don't know the exact structure of dark matter. 686 00:35:18,440 --> 00:35:20,799 Speaker 1: But we do sort of know it's density out there, right, 687 00:35:20,800 --> 00:35:23,279 Speaker 1: We have some figures for its general density. Yeah, And 688 00:35:23,280 --> 00:35:26,600 Speaker 1: it's quite interesting because we think that on average over 689 00:35:26,680 --> 00:35:30,280 Speaker 1: the universe, dark matters like eight percent of the matter 690 00:35:30,480 --> 00:35:33,000 Speaker 1: of the universe, but in our neighborhood it is actually 691 00:35:33,000 --> 00:35:35,440 Speaker 1: a little bit different. The Milky Way, for example, we 692 00:35:35,480 --> 00:35:39,720 Speaker 1: think is nine five dark matter. So our whole galaxy 693 00:35:39,840 --> 00:35:41,879 Speaker 1: is kind of badly named. It should be called like 694 00:35:42,120 --> 00:35:45,400 Speaker 1: the Dark Way or something, the Chocolate Milk Galaxy, the 695 00:35:45,520 --> 00:35:49,120 Speaker 1: darklan Milky Way, the Dark Chocolate Way or something. So 696 00:35:49,160 --> 00:35:52,120 Speaker 1: we're like nine percent dark matter, which means if we 697 00:35:52,160 --> 00:35:56,240 Speaker 1: have like you know, the equivalent of ninety billion times 698 00:35:56,320 --> 00:35:58,920 Speaker 1: the mass of the Sun in terms of stars and 699 00:35:59,040 --> 00:36:01,000 Speaker 1: gas and all that kind of stuff, that means that 700 00:36:01,000 --> 00:36:03,919 Speaker 1: there's like two trillion times the mass of the Sun 701 00:36:04,120 --> 00:36:06,960 Speaker 1: in dark matter. It's just so much more. And it's 702 00:36:07,000 --> 00:36:10,880 Speaker 1: like twenty times as much dark matter in our galaxy 703 00:36:11,080 --> 00:36:13,920 Speaker 1: as normal matter, which is a bigger ratio than the 704 00:36:13,960 --> 00:36:16,479 Speaker 1: rest of the universe. Well, that's true for regular matter. 705 00:36:16,560 --> 00:36:19,640 Speaker 1: To write like our Milky Way has a higher density 706 00:36:19,640 --> 00:36:22,000 Speaker 1: of regular matter than the rest of the universe or 707 00:36:22,080 --> 00:36:24,280 Speaker 1: some other parts of the universe. Right, Yeah, that's true. 708 00:36:24,600 --> 00:36:28,439 Speaker 1: But on average galaxies have about eighty percent dark matter, 709 00:36:28,520 --> 00:36:32,840 Speaker 1: and our galaxy is so there's a big variation. Galaxy 710 00:36:32,880 --> 00:36:35,560 Speaker 1: the galaxy and how much dark matter there is. Oh, 711 00:36:35,600 --> 00:36:39,319 Speaker 1: I mean our galaxy has more than other galaxies. Absolutely, Yeah, 712 00:36:39,360 --> 00:36:42,920 Speaker 1: we are a darker galaxy than most interesting we're more mysterious, 713 00:36:42,920 --> 00:36:45,000 Speaker 1: I guess. Yeah. And there's some galaxies out there that 714 00:36:45,040 --> 00:36:48,480 Speaker 1: are overwhelmingly dark matter, like nine points something per cent. 715 00:36:48,640 --> 00:36:50,680 Speaker 1: And then there are some galaxies that have very little 716 00:36:50,760 --> 00:36:52,920 Speaker 1: dark matter. We think that might be evidence of collisions 717 00:36:52,960 --> 00:36:55,799 Speaker 1: where dark matter gets separated from the normal matter. All 718 00:36:55,840 --> 00:36:58,560 Speaker 1: sorts of crazy stuff. These things tell you the crazy 719 00:36:58,640 --> 00:37:01,800 Speaker 1: cosmic history of all of these objects. Interesting. And again 720 00:37:01,840 --> 00:37:03,880 Speaker 1: you can tell by when you look at these galaxies 721 00:37:03,880 --> 00:37:06,760 Speaker 1: out there. You can tell that they're holding on together 722 00:37:07,080 --> 00:37:09,200 Speaker 1: more than they should by the number of stars or 723 00:37:09,239 --> 00:37:11,239 Speaker 1: the brightness of them. Right. Yeah, you can tell when 724 00:37:11,239 --> 00:37:14,239 Speaker 1: a galaxy is overwhelmingly dark matter because it's stars are 725 00:37:14,320 --> 00:37:17,279 Speaker 1: moving super duper fast compared to how bright they are, 726 00:37:17,520 --> 00:37:20,480 Speaker 1: And so we can see these faint dwarf galaxies, for example, 727 00:37:20,680 --> 00:37:23,400 Speaker 1: just have a handful of stars, but they're whizzing around 728 00:37:23,400 --> 00:37:26,040 Speaker 1: in a circle and there's not nearly enough gravity to 729 00:37:26,080 --> 00:37:28,319 Speaker 1: hold them in place. Just from the stuff that we 730 00:37:28,400 --> 00:37:30,799 Speaker 1: can see, so it's pretty cool, but it's so far away. 731 00:37:30,800 --> 00:37:32,279 Speaker 1: How do you know it's not just like filled with 732 00:37:32,600 --> 00:37:36,080 Speaker 1: the black holes or something or rocks dark rocks, because 733 00:37:36,080 --> 00:37:38,239 Speaker 1: we can see light passing through it, right, we can 734 00:37:38,239 --> 00:37:41,040 Speaker 1: see through it to something else behind it. If there 735 00:37:41,080 --> 00:37:42,880 Speaker 1: was a black hole there, it would absorb the light. 736 00:37:43,000 --> 00:37:45,480 Speaker 1: If it was just like a huge death star or 737 00:37:45,520 --> 00:37:48,719 Speaker 1: something cloaked, then it would absorb that light. So we 738 00:37:48,800 --> 00:37:52,120 Speaker 1: see it as invisible, not as dark all right, So then, um, 739 00:37:52,160 --> 00:37:54,719 Speaker 1: it's sort of danser in our galaxy. What about in 740 00:37:55,000 --> 00:37:57,640 Speaker 1: in our more immediate neighborhood or like a star solar 741 00:37:57,680 --> 00:38:01,080 Speaker 1: system also extra dark mattery, it's and in our neighborhood. 742 00:38:01,080 --> 00:38:04,920 Speaker 1: Remember that while the Milky Way is dark matter that 743 00:38:05,080 --> 00:38:08,200 Speaker 1: is spread out throughout the stars, we think, so normal 744 00:38:08,239 --> 00:38:11,399 Speaker 1: matter clumps up a lot more than dark matter, which 745 00:38:11,400 --> 00:38:14,239 Speaker 1: means that there isn't that much dark matter in any 746 00:38:14,320 --> 00:38:17,720 Speaker 1: like cubic light year of space. So in a cubic 747 00:38:17,800 --> 00:38:20,520 Speaker 1: light year of space, there's less than a one quarter 748 00:38:20,760 --> 00:38:23,479 Speaker 1: of one one thousands of the mass of the Sun. 749 00:38:23,880 --> 00:38:25,920 Speaker 1: In a cubic light year of space, that's like a 750 00:38:26,000 --> 00:38:28,960 Speaker 1: quarter of the mass of Jupiter in a cubic light 751 00:38:29,040 --> 00:38:31,080 Speaker 1: year of space. That's how much dark matter there is. 752 00:38:31,480 --> 00:38:34,160 Speaker 1: M t gives you took Jupiter and spread it over 753 00:38:34,280 --> 00:38:37,160 Speaker 1: billions of miles, right, it wouldn't be very much. And 754 00:38:37,160 --> 00:38:39,480 Speaker 1: you know, if you zoom in, for example, into like 755 00:38:39,520 --> 00:38:43,760 Speaker 1: a cubic meter, that's like ten the minus twenty two 756 00:38:44,200 --> 00:38:47,520 Speaker 1: grams of dark matter in a cubic meter. So you know, 757 00:38:47,560 --> 00:38:50,200 Speaker 1: if you look at the space around you in your office, 758 00:38:50,239 --> 00:38:53,360 Speaker 1: for example, then there's just like a super tiny amount 759 00:38:53,400 --> 00:38:56,200 Speaker 1: of dark matter, almost hard to measure, but some of 760 00:38:56,239 --> 00:38:58,320 Speaker 1: it's there are a few particles. And if you zoom 761 00:38:58,320 --> 00:39:00,879 Speaker 1: out to like the whole volume of the Earth, there's 762 00:39:00,960 --> 00:39:04,040 Speaker 1: less than a kilogram of dark matter in the volume 763 00:39:04,120 --> 00:39:06,839 Speaker 1: of the Earth. Again, these are sort of approximations, right, 764 00:39:06,840 --> 00:39:09,400 Speaker 1: because he told me earlier that our ability to resolve 765 00:39:09,480 --> 00:39:11,960 Speaker 1: or a resolution of dark matter is pretty bad. So 766 00:39:12,000 --> 00:39:14,239 Speaker 1: how do we know like that there isn't the sort 767 00:39:14,239 --> 00:39:16,640 Speaker 1: of clump of dark matter just around us right now? 768 00:39:16,880 --> 00:39:19,640 Speaker 1: We don't know absolutely, We do not know. We are 769 00:39:19,680 --> 00:39:21,480 Speaker 1: not sensitive to these things, so it could be a 770 00:39:21,520 --> 00:39:24,520 Speaker 1: lot clumpier than we think these numbers are, assuming that 771 00:39:24,600 --> 00:39:28,240 Speaker 1: dark matter is mostly smoothly spread out throughout the galaxy 772 00:39:28,520 --> 00:39:31,360 Speaker 1: according to the distribution that we've seen from the radius. 773 00:39:31,400 --> 00:39:33,880 Speaker 1: But we absolutely cannot tell if there's like a huge 774 00:39:33,960 --> 00:39:36,000 Speaker 1: blob of dark matter that we're sitting in, or if 775 00:39:36,040 --> 00:39:39,120 Speaker 1: there's almost no dark matter in our neighborhood. And remember 776 00:39:39,120 --> 00:39:42,560 Speaker 1: that we have experiments underground looking for dark matter particles. 777 00:39:42,600 --> 00:39:45,520 Speaker 1: They're basically trying to measure how the Earth is moving 778 00:39:45,560 --> 00:39:48,760 Speaker 1: through this dark matter wind, and they haven't seen anything. 779 00:39:49,120 --> 00:39:51,640 Speaker 1: And one of my favorite explanations is like, well, maybe 780 00:39:51,680 --> 00:39:53,840 Speaker 1: we're just happy to be sitting in a bubble that 781 00:39:53,920 --> 00:39:56,560 Speaker 1: has almost no dark matter in it, which would make 782 00:39:56,560 --> 00:39:59,200 Speaker 1: it impossible for us to detect that dark matter wind. 783 00:39:59,480 --> 00:40:02,279 Speaker 1: We just don't know it's ghosting us and avoiding is 784 00:40:02,480 --> 00:40:05,040 Speaker 1: physically at the same time. But it's kind of interesting 785 00:40:05,080 --> 00:40:07,839 Speaker 1: because I think what you talked about earlier, how like 786 00:40:07,880 --> 00:40:11,000 Speaker 1: in the volume of the Earth, there's about one squirrels 787 00:40:11,000 --> 00:40:13,640 Speaker 1: worth full of dark matter. Like that's not a lot, right, 788 00:40:13,640 --> 00:40:15,359 Speaker 1: and the whole Earth is pretty big, but you only 789 00:40:15,360 --> 00:40:18,080 Speaker 1: have one squirrel full of dark matter, And that's why 790 00:40:18,120 --> 00:40:21,880 Speaker 1: we can't ever detected gravitationally. You know, we're literally looking 791 00:40:21,920 --> 00:40:25,520 Speaker 1: for a squirrel that's hiding inside the Earth, and that's 792 00:40:25,520 --> 00:40:27,840 Speaker 1: pretty hard to tell the difference. We can't measure the 793 00:40:27,880 --> 00:40:31,440 Speaker 1: number of squirrels on Earth. Using grabic, you'd go nuts. 794 00:40:33,040 --> 00:40:35,160 Speaker 1: But yeah, so let's talk about then, now, sort of 795 00:40:35,239 --> 00:40:38,120 Speaker 1: dark matter between galaxies, because you know, there's a lot 796 00:40:38,120 --> 00:40:40,520 Speaker 1: of space between galaxies and we sort of have a 797 00:40:40,520 --> 00:40:43,560 Speaker 1: pretty good idea of the structure of the universe, you know, 798 00:40:43,680 --> 00:40:47,240 Speaker 1: the galaxy clusters and superclusters. Is does dark matter also 799 00:40:47,280 --> 00:40:50,080 Speaker 1: follow these clusters? We think that mostly does, and again 800 00:40:50,200 --> 00:40:53,080 Speaker 1: we think it's sort of the opposite that normal matter 801 00:40:53,280 --> 00:40:56,920 Speaker 1: follows the path of dark matter. But it's much harder 802 00:40:56,960 --> 00:41:01,000 Speaker 1: to see the things between galaxies because there's much less 803 00:41:01,040 --> 00:41:04,280 Speaker 1: light there and there's much less visible objects. Like mostly 804 00:41:04,320 --> 00:41:06,800 Speaker 1: we have seen where dark matter is within our galaxy 805 00:41:07,040 --> 00:41:10,440 Speaker 1: by following the path of stars, their rotation, their wiggles, 806 00:41:10,800 --> 00:41:13,480 Speaker 1: their distortions, all that kind of stuff where there are 807 00:41:13,520 --> 00:41:16,480 Speaker 1: in stars like tracers to tell us where things are 808 00:41:16,600 --> 00:41:20,399 Speaker 1: between galaxies. So it's much trickier. Yeah, I guess you 809 00:41:20,400 --> 00:41:22,720 Speaker 1: you can sort of extrapolate, right what we can see 810 00:41:22,760 --> 00:41:24,960 Speaker 1: a little bit around this, then you sort of assume 811 00:41:25,000 --> 00:41:26,960 Speaker 1: that that's what's happening maybe in the rest of the 812 00:41:27,040 --> 00:41:29,680 Speaker 1: universe sort of, But we know that the galaxies are 813 00:41:29,760 --> 00:41:31,840 Speaker 1: very different from the rest of the universe. Like, we 814 00:41:31,880 --> 00:41:35,000 Speaker 1: know that there's a huge gravitational well that we are sitting, 815 00:41:35,000 --> 00:41:37,480 Speaker 1: and that's why there's a galaxy right here, there's a 816 00:41:37,520 --> 00:41:39,960 Speaker 1: big blob of dark matter. What does it look like 817 00:41:40,080 --> 00:41:43,719 Speaker 1: between our galaxy and Andromeda? You know, are there strands 818 00:41:43,800 --> 00:41:46,680 Speaker 1: of dark matter? How quickly does it pete route? Are 819 00:41:46,719 --> 00:41:49,280 Speaker 1: there blobs of dark matter out there without any stars 820 00:41:49,280 --> 00:41:51,480 Speaker 1: in them at all? And so one way we can 821 00:41:51,520 --> 00:41:53,600 Speaker 1: try to figure that out is to look at how 822 00:41:53,719 --> 00:41:57,399 Speaker 1: light from distant galaxies is distorted as it passes through 823 00:41:57,400 --> 00:42:01,520 Speaker 1: that space. I see, based can do the gravitational lensing 824 00:42:01,520 --> 00:42:04,760 Speaker 1: but with galaxies and look for blobs in between galaxy. 825 00:42:04,800 --> 00:42:06,839 Speaker 1: But then these blobs we got to be humongous, right, 826 00:42:06,880 --> 00:42:09,400 Speaker 1: those blobs would have to be humongous. And in this 827 00:42:09,440 --> 00:42:12,239 Speaker 1: case we use a slightly different technique than we do 828 00:42:12,320 --> 00:42:15,279 Speaker 1: for looking at like one specific blob before. What we 829 00:42:15,280 --> 00:42:18,000 Speaker 1: were doing is called strong lensing, And that's like, I 830 00:42:18,040 --> 00:42:20,400 Speaker 1: want to have a blob of dark matter right between 831 00:42:20,400 --> 00:42:22,400 Speaker 1: me and another galaxy, so I can see like a 832 00:42:22,520 --> 00:42:25,920 Speaker 1: massive distortion. You can see one galaxy how it's distorted, 833 00:42:25,920 --> 00:42:28,200 Speaker 1: and you can use that to measure the massive stuff 834 00:42:28,200 --> 00:42:30,680 Speaker 1: between you and other galaxies. If instead you think the 835 00:42:30,719 --> 00:42:33,080 Speaker 1: dark matter is sort of spread out, so it doesn't 836 00:42:33,160 --> 00:42:37,200 Speaker 1: really distort any individual photon that much. You can do 837 00:42:37,239 --> 00:42:41,000 Speaker 1: something called weak gravitational lensing where you look at lots 838 00:42:41,040 --> 00:42:43,920 Speaker 1: of galaxies and you look for lots of very small 839 00:42:44,000 --> 00:42:47,080 Speaker 1: distortions and you sort of add them up statistically to 840 00:42:47,120 --> 00:42:49,440 Speaker 1: get a map for where the dark matter might be 841 00:42:49,520 --> 00:42:52,000 Speaker 1: and where it might not be. So you see sort 842 00:42:52,000 --> 00:42:55,920 Speaker 1: of like fewer generalized distortions over here and more generalized 843 00:42:55,960 --> 00:42:58,720 Speaker 1: distortions over there. It can tell you sort of where 844 00:42:58,760 --> 00:43:02,080 Speaker 1: the dark matter is dens or and where it's less dense. Interesting, 845 00:43:02,120 --> 00:43:05,360 Speaker 1: you started looking for sort of wiggles in the overall picture. 846 00:43:05,560 --> 00:43:07,720 Speaker 1: But how would you know that is dark matter? Would 847 00:43:07,719 --> 00:43:10,040 Speaker 1: that be changing? Are you assuming that it changes as 848 00:43:10,080 --> 00:43:12,360 Speaker 1: our view of the universe changes. Well, we think we 849 00:43:12,440 --> 00:43:15,040 Speaker 1: know what galaxies should look like when they're not distorted, 850 00:43:15,280 --> 00:43:18,960 Speaker 1: and so we compare how galaxies look too ideas of 851 00:43:19,000 --> 00:43:21,120 Speaker 1: how a galaxy should look when it's not distorted, and 852 00:43:21,160 --> 00:43:24,200 Speaker 1: how it should look when it's slightly distorted by dark matter. 853 00:43:24,520 --> 00:43:27,160 Speaker 1: And so we can use that to estimate like how 854 00:43:27,239 --> 00:43:30,719 Speaker 1: much distortion galaxies have. But it's very very weak. You know, 855 00:43:30,760 --> 00:43:32,920 Speaker 1: it's hard to tell the difference between a galaxy that's 856 00:43:32,960 --> 00:43:35,920 Speaker 1: undistorted and slightly distorted. And that's why we need like 857 00:43:36,040 --> 00:43:39,000 Speaker 1: thousands of galaxies to add this up statistically to get 858 00:43:39,000 --> 00:43:41,440 Speaker 1: a sense for where the dark matter is interesting. And 859 00:43:41,480 --> 00:43:43,640 Speaker 1: this is like an ongoing thing, right, Like there's people 860 00:43:44,040 --> 00:43:47,040 Speaker 1: looking for these ripples in our view of the universe. Yeah, 861 00:43:47,120 --> 00:43:49,760 Speaker 1: this is recent. Actually there's a program using a huge 862 00:43:49,800 --> 00:43:53,719 Speaker 1: telescope with a massive camera five hundred and seventy megapixels. 863 00:43:53,719 --> 00:43:56,640 Speaker 1: It's called the Dark Energy Survey, and this camera is 864 00:43:56,680 --> 00:43:59,560 Speaker 1: basically build just to do this, just to look at 865 00:43:59,600 --> 00:44:02,440 Speaker 1: all the galaxies and build a huge map. And they've 866 00:44:02,440 --> 00:44:06,200 Speaker 1: studied a hundred million galaxies out there, like think about 867 00:44:06,200 --> 00:44:09,520 Speaker 1: all the crazy stars and planets and everything that's out there, 868 00:44:09,520 --> 00:44:12,359 Speaker 1: a hundred million of those. And they have built a 869 00:44:12,400 --> 00:44:15,520 Speaker 1: map of where they think the dark matter is between 870 00:44:15,719 --> 00:44:19,000 Speaker 1: galaxies using this weak lensing idea. Because I guess we 871 00:44:19,040 --> 00:44:21,359 Speaker 1: can tell how old they are the galaxies, right, and 872 00:44:21,400 --> 00:44:23,279 Speaker 1: how far away they are from from us, not just 873 00:44:23,360 --> 00:44:25,080 Speaker 1: in the night sky, and so we can build the 874 00:44:25,239 --> 00:44:28,080 Speaker 1: three D map right exactly. We know where galaxies are 875 00:44:28,120 --> 00:44:30,520 Speaker 1: because we can look at like Type one A supernova 876 00:44:30,560 --> 00:44:33,040 Speaker 1: within them. We can measure their brightness, and we can 877 00:44:33,040 --> 00:44:35,319 Speaker 1: tell how far away they are based on how bright 878 00:44:35,360 --> 00:44:38,239 Speaker 1: they appear to be here on Earth. So we have 879 00:44:38,360 --> 00:44:41,080 Speaker 1: this incredible three D map of all the galaxies and 880 00:44:41,080 --> 00:44:43,600 Speaker 1: then this thing is taking careful pictures of them to 881 00:44:43,680 --> 00:44:46,640 Speaker 1: try to estimate how much each one is distorted, and 882 00:44:46,640 --> 00:44:49,160 Speaker 1: then it's comparing that to our idea for where we 883 00:44:49,200 --> 00:44:51,800 Speaker 1: think the dark matter should be. We have an idea 884 00:44:51,840 --> 00:44:53,840 Speaker 1: for where we think dark matter should be based on 885 00:44:53,880 --> 00:44:56,759 Speaker 1: where all the galaxies are. Sort of back that up 886 00:44:56,800 --> 00:44:59,759 Speaker 1: to the early universe and say where were the dark 887 00:44:59,800 --> 00:45:02,319 Speaker 1: matter are have to have been in order to make 888 00:45:02,360 --> 00:45:05,080 Speaker 1: these galaxies end up here and that galaxy end up 889 00:45:05,120 --> 00:45:07,880 Speaker 1: there to sort of create the large scale structure that 890 00:45:07,920 --> 00:45:11,440 Speaker 1: we see, because we think that mostly where galaxies ended 891 00:45:11,520 --> 00:45:14,160 Speaker 1: up depends on where dark matter was. So we have 892 00:45:14,280 --> 00:45:16,359 Speaker 1: like a simulation for where we think the dark matter 893 00:45:16,440 --> 00:45:19,240 Speaker 1: should be based on our idea of how it all works. 894 00:45:19,440 --> 00:45:20,960 Speaker 1: And then we go out of measure and build a 895 00:45:21,000 --> 00:45:23,759 Speaker 1: real map of where the dark matter is, and then 896 00:45:23,920 --> 00:45:26,799 Speaker 1: we can compare the two and that's when the fund starts. WHOA, 897 00:45:26,960 --> 00:45:29,120 Speaker 1: So what have we found? Do they match or are 898 00:45:29,160 --> 00:45:32,600 Speaker 1: they very different? They mostly match, like it mostly makes sense. 899 00:45:32,640 --> 00:45:35,000 Speaker 1: The dark matter is mostly where we expect, but there 900 00:45:35,000 --> 00:45:37,640 Speaker 1: are some deviations. It looks like dark matter sort of 901 00:45:37,680 --> 00:45:40,920 Speaker 1: more spread out than we expected. Instead of being in 902 00:45:40,960 --> 00:45:44,560 Speaker 1: these like thin strands between galaxies, it tends to be 903 00:45:44,760 --> 00:45:47,640 Speaker 1: sometimes in places where you don't expect. It's like spread 904 00:45:47,680 --> 00:45:50,880 Speaker 1: out and globbed out more than we expected, more than 905 00:45:50,880 --> 00:45:54,279 Speaker 1: our simulations predict. It's just a few percent compared to 906 00:45:54,320 --> 00:45:57,480 Speaker 1: our predictions, but it's an important deviation. It means that 907 00:45:57,560 --> 00:45:59,920 Speaker 1: like maybe something's going on with that dark matter, or 908 00:46:00,000 --> 00:46:01,920 Speaker 1: maybe dark matter is made out of something weird we 909 00:46:01,920 --> 00:46:04,680 Speaker 1: didn't understand, or maybe we've made a mistake in building 910 00:46:04,680 --> 00:46:06,719 Speaker 1: our map of dark matter. But it's sort of like 911 00:46:06,800 --> 00:46:09,160 Speaker 1: at the edge of science. These are very very recent 912 00:46:09,200 --> 00:46:14,080 Speaker 1: results that dark matter just wants to be alone between 913 00:46:14,080 --> 00:46:16,040 Speaker 1: the galaxy or maybe it got timed out. But I 914 00:46:16,040 --> 00:46:18,760 Speaker 1: guess what's surprising is that there is dark matter between 915 00:46:18,800 --> 00:46:22,399 Speaker 1: galaxies because there's not much matter out there, so why 916 00:46:22,400 --> 00:46:26,360 Speaker 1: wouldn't this dark matter also accumulate regular matter. There is 917 00:46:26,400 --> 00:46:28,640 Speaker 1: actually a good bit of regular matter out there is 918 00:46:28,680 --> 00:46:31,400 Speaker 1: it's just not glowing like a huge amount of the 919 00:46:31,640 --> 00:46:34,880 Speaker 1: atoms in the universe are actually between galaxies and this 920 00:46:35,080 --> 00:46:39,520 Speaker 1: intergalactic matter, these streams of stuff, and so there's a 921 00:46:39,560 --> 00:46:41,640 Speaker 1: good bit of stuff out there. There's just not enough 922 00:46:41,719 --> 00:46:45,759 Speaker 1: density to form stars and planets and galaxies and all 923 00:46:45,840 --> 00:46:47,960 Speaker 1: kinds of stuff. And so that's why it's not as 924 00:46:48,040 --> 00:46:51,600 Speaker 1: visible because it doesn't glow interesting. But then what what 925 00:46:51,760 --> 00:46:54,200 Speaker 1: make some dark matter have a lot of bright matter 926 00:46:54,280 --> 00:46:56,960 Speaker 1: in it and some nut the denser blobs of dark 927 00:46:57,000 --> 00:47:00,600 Speaker 1: batter did form enough stuff to create galaxies and stars. 928 00:47:00,760 --> 00:47:04,120 Speaker 1: The kind of strands we're talking about between galaxies is 929 00:47:04,120 --> 00:47:06,440 Speaker 1: a smaller fraction of the amount of dark matter. The 930 00:47:06,480 --> 00:47:09,560 Speaker 1: density is not there in order to create the gravitational Well, 931 00:47:09,600 --> 00:47:13,080 Speaker 1: you need to attract enough hydrogen to get stars to form. 932 00:47:13,600 --> 00:47:16,360 Speaker 1: Pretty cool, so the galaxy still show you where like 933 00:47:16,400 --> 00:47:19,200 Speaker 1: the densest blobs of dark matter are in the universe, 934 00:47:19,480 --> 00:47:23,600 Speaker 1: Like the dark matter also various in density out there. Absolutely, yeah, alright, 935 00:47:23,600 --> 00:47:25,160 Speaker 1: well it sort of sounds like do you sort of 936 00:47:25,200 --> 00:47:27,759 Speaker 1: know where dark matter is but maybe not too super 937 00:47:27,840 --> 00:47:30,920 Speaker 1: high resolution where you can tell if it's super clumpy 938 00:47:31,040 --> 00:47:34,279 Speaker 1: or super smooth. And also we have a pretty good 939 00:47:34,280 --> 00:47:36,879 Speaker 1: picture of where it is in the whole universe. Yeah, 940 00:47:36,920 --> 00:47:39,560 Speaker 1: and scientists are working very hard to build more and 941 00:47:39,600 --> 00:47:43,240 Speaker 1: more sensitive tools to try to use these little gravitational 942 00:47:43,280 --> 00:47:46,560 Speaker 1: clues to build as accurate and as localized a map 943 00:47:46,600 --> 00:47:49,400 Speaker 1: of dark matter as possible, because the better map of 944 00:47:49,480 --> 00:47:51,759 Speaker 1: dark matter we get in our galaxy, the more we 945 00:47:51,800 --> 00:47:54,279 Speaker 1: can study what it might be and how it came 946 00:47:54,320 --> 00:47:56,960 Speaker 1: to be where it is. Yeah. I guess the big 947 00:47:57,040 --> 00:47:58,560 Speaker 1: question now is what are you gonna do when you 948 00:47:58,560 --> 00:48:03,600 Speaker 1: find it? Daniel retire. Yeah, like the dog that finally 949 00:48:03,600 --> 00:48:05,400 Speaker 1: catches up the car and doesn't know what to do 950 00:48:05,440 --> 00:48:07,879 Speaker 1: with it. Oh, we'll find some other mystery to focus on. 951 00:48:08,080 --> 00:48:11,080 Speaker 1: You'll come up with another cool name darkest. We always 952 00:48:11,120 --> 00:48:13,960 Speaker 1: have the seventy of the universe called dark energy that 953 00:48:14,000 --> 00:48:17,640 Speaker 1: we haven't even gotten started on. Yeah, that's another huge mystery, 954 00:48:17,760 --> 00:48:20,279 Speaker 1: huge hole in our view of the universe and them. 955 00:48:20,320 --> 00:48:22,319 Speaker 1: Hopefully you won't lose your mind trying to find them. 956 00:48:22,520 --> 00:48:27,000 Speaker 1: I lost eight years ago. All right, Well, another awesome 957 00:48:27,000 --> 00:48:29,000 Speaker 1: reminder that there's still a lot of universe out there 958 00:48:29,000 --> 00:48:31,759 Speaker 1: to be discoverned. You know, anyone listening to this could 959 00:48:31,800 --> 00:48:33,880 Speaker 1: be the person that comes up with the next great 960 00:48:33,920 --> 00:48:37,440 Speaker 1: idea or the next grade concept that makes sense of 961 00:48:37,480 --> 00:48:39,719 Speaker 1: all this and helps us find these big mysteries in 962 00:48:39,760 --> 00:48:42,279 Speaker 1: the universe. If you're in trance by the concept of 963 00:48:42,360 --> 00:48:45,319 Speaker 1: building maps and discovering the way the world is and 964 00:48:45,360 --> 00:48:48,760 Speaker 1: how everything looks. Remember, the biggest map of the most 965 00:48:48,800 --> 00:48:51,799 Speaker 1: important stuff in the universe is still being drawn. You 966 00:48:51,800 --> 00:48:54,600 Speaker 1: can really lose yourself in that search for lost things. 967 00:48:54,800 --> 00:48:57,839 Speaker 1: Come join me in the asylum or the basement Lost 968 00:48:57,840 --> 00:49:00,759 Speaker 1: and Found department. Well, if they for joining us, we 969 00:49:00,800 --> 00:49:11,880 Speaker 1: hope you enjoyed that. See you next time. Thanks for listening, 970 00:49:11,880 --> 00:49:14,600 Speaker 1: and remember that Daniel and Jorge explained. The Universe is 971 00:49:14,640 --> 00:49:18,160 Speaker 1: a production of I Heart Radio. Or more podcast from 972 00:49:18,160 --> 00:49:21,920 Speaker 1: my Heart Radio visit the I Heart Radio app, Apple Podcasts, 973 00:49:22,040 --> 00:49:24,400 Speaker 1: or wherever you listen to your favorite shows.