1 00:00:08,480 --> 00:00:11,800 Speaker 1: Hey, Orge, do you think stuff in science is typically 2 00:00:11,920 --> 00:00:14,560 Speaker 1: well named or sometimes misleading? 3 00:00:15,160 --> 00:00:17,599 Speaker 2: Depends on which science. Do you mean physics? Then no? 4 00:00:20,079 --> 00:00:21,919 Speaker 1: I mean sometimes we do a good job, right, like 5 00:00:21,960 --> 00:00:22,520 Speaker 1: black hole? 6 00:00:22,800 --> 00:00:25,520 Speaker 2: Yeah? Yeah, those are black and their holes in space. 7 00:00:25,600 --> 00:00:27,479 Speaker 2: So I guess you did good on that one. 8 00:00:27,880 --> 00:00:30,200 Speaker 1: But in other cases you're saying we didn't do as well. 9 00:00:30,400 --> 00:00:34,320 Speaker 2: Well, let's see, how about quark flavors which don't have flavor, 10 00:00:34,320 --> 00:00:36,960 Speaker 2: how about quantum colors which don't have colored? 11 00:00:37,600 --> 00:00:40,960 Speaker 1: All right, that's fair, So let's do a little experiment. 12 00:00:41,080 --> 00:00:42,800 Speaker 1: I'm going to give you a physics name, and you're 13 00:00:42,800 --> 00:00:44,919 Speaker 1: gonna guess what it means. All right, go for it. 14 00:00:44,920 --> 00:00:46,400 Speaker 1: It's called the dark flow. 15 00:00:46,640 --> 00:00:49,479 Speaker 2: That sounds like maybe a plumbing product to get your 16 00:00:49,560 --> 00:00:50,440 Speaker 2: toilet moving again? 17 00:00:52,280 --> 00:00:52,560 Speaker 1: Nice? 18 00:00:52,720 --> 00:00:55,240 Speaker 2: Did I get that right? Stay tuned and find out 19 00:00:55,440 --> 00:00:56,680 Speaker 2: you have to go with the flow. Is that what 20 00:00:56,720 --> 00:00:57,120 Speaker 2: you're saying? 21 00:01:12,240 --> 00:01:12,399 Speaker 1: Hi? 22 00:01:12,400 --> 00:01:15,880 Speaker 2: I'm Horia mccartoonist and the author of Oliver's Great Big Universe. 23 00:01:16,040 --> 00:01:18,760 Speaker 1: Hi, I'm Daniel. I'm a particle physicist and a professor 24 00:01:18,760 --> 00:01:21,320 Speaker 1: at U see erline, and I hate plumbing projects. 25 00:01:21,600 --> 00:01:23,800 Speaker 2: Who loves plumbing projects? I guess plumbers? 26 00:01:24,280 --> 00:01:28,400 Speaker 1: Yeah? Maybe, I mean I hope they love plumbing projects. 27 00:01:28,400 --> 00:01:29,440 Speaker 1: Otherwise it's kind of sad. 28 00:01:29,520 --> 00:01:31,959 Speaker 2: It's probably interesting to them. Sure, But how many plumbing 29 00:01:31,959 --> 00:01:33,319 Speaker 2: projects have you worked on recently? 30 00:01:33,480 --> 00:01:36,320 Speaker 1: Oh? Too many? You know, anytime you have a plumbing project, 31 00:01:36,319 --> 00:01:40,240 Speaker 1: that means bad news. Something's leaking somewhere, something's broken somewhere. 32 00:01:40,440 --> 00:01:42,200 Speaker 1: You know, the joys of home ownership. 33 00:01:42,319 --> 00:01:43,480 Speaker 2: What did you call a plumber? 34 00:01:43,600 --> 00:01:45,800 Speaker 1: Yeah, that's like paying somebody to deliver the bad news 35 00:01:45,800 --> 00:01:46,080 Speaker 1: to you. 36 00:01:46,720 --> 00:01:49,520 Speaker 2: Hey, yeah, and then then hopefully they fix it for you. 37 00:01:49,680 --> 00:01:51,000 Speaker 2: What kind of plumbers are you calling? 38 00:01:52,320 --> 00:01:53,960 Speaker 1: Yeah, they fix it. We had a leak in our 39 00:01:54,040 --> 00:01:57,160 Speaker 1: upstairs bathroom recently and had to tear out and rehab 40 00:01:57,280 --> 00:01:59,080 Speaker 1: all the walls in our garage. It was a big 41 00:01:59,120 --> 00:01:59,760 Speaker 1: pain in the butt. 42 00:01:59,800 --> 00:02:02,960 Speaker 2: Oh boy, what happened? The tub overfluid or something? 43 00:02:03,040 --> 00:02:04,080 Speaker 1: It was a dark flow. 44 00:02:04,320 --> 00:02:06,640 Speaker 2: You took too long of a bath there thinking about physics. 45 00:02:06,720 --> 00:02:08,760 Speaker 1: I was dunking stuff in the bathtub hoping for a 46 00:02:08,840 --> 00:02:10,639 Speaker 1: Eureka moment, and it just didn't happen. 47 00:02:10,840 --> 00:02:13,680 Speaker 2: It just didn't happen. You didn't figure out how bullyiancy works. 48 00:02:15,240 --> 00:02:17,280 Speaker 1: No, it's too complicated for a particle physicists. 49 00:02:18,080 --> 00:02:21,040 Speaker 2: Too many particles in a tub of water. But anyways, 50 00:02:21,080 --> 00:02:23,600 Speaker 2: welcome to our podcast Daniel and Jorge Explain the Universe, 51 00:02:23,639 --> 00:02:26,079 Speaker 2: a production of iHeartRadio. 52 00:02:25,400 --> 00:02:27,800 Speaker 1: In which we teach you to think like a physicist 53 00:02:27,840 --> 00:02:30,480 Speaker 1: instead of a plumber. Don't dunk stuff in a tub 54 00:02:30,520 --> 00:02:33,560 Speaker 1: of water, but immerse your brain in the mysteries of 55 00:02:33,680 --> 00:02:36,320 Speaker 1: the universe and try to learn how the universe works. 56 00:02:36,320 --> 00:02:38,440 Speaker 1: By Oz most is hanging out with us as we 57 00:02:38,480 --> 00:02:41,120 Speaker 1: talk and joke about everything that's out there in the 58 00:02:41,200 --> 00:02:43,679 Speaker 1: universe and try to explain all of it to you. 59 00:02:43,880 --> 00:02:45,640 Speaker 2: That's right. We try to fill the tub in your 60 00:02:45,680 --> 00:02:49,440 Speaker 2: mind of knowledge and wonder until it overflows and hopefully 61 00:02:50,200 --> 00:02:51,919 Speaker 2: maybe leaks into your garage a little bit. 62 00:02:53,720 --> 00:02:55,800 Speaker 1: You know, in that scenario, maybe a plumbing project is 63 00:02:55,840 --> 00:02:57,880 Speaker 1: good news because you got to rip everything out and 64 00:02:57,919 --> 00:03:00,400 Speaker 1: build up a new understanding of the universe. That's what 65 00:03:00,440 --> 00:03:02,079 Speaker 1: I'm always saying I want to do. Wait. 66 00:03:02,080 --> 00:03:04,160 Speaker 2: Wait, you're saying the universe is plumbing. 67 00:03:05,120 --> 00:03:07,959 Speaker 1: I'm saying, our mental understanding of how the universe works 68 00:03:08,200 --> 00:03:10,399 Speaker 1: has plumbing. When you got to tear all that out 69 00:03:10,440 --> 00:03:12,320 Speaker 1: and rebuild it, that means you're coming up with a 70 00:03:12,400 --> 00:03:16,079 Speaker 1: new idea about how the universe works, and that's a revolution. 71 00:03:15,800 --> 00:03:19,240 Speaker 2: Oh wait, what's the plumbing for ideas? Also, what do 72 00:03:19,240 --> 00:03:20,880 Speaker 2: you flush down the toilet of physics? 73 00:03:21,160 --> 00:03:23,720 Speaker 1: Imagine the inside of a physicist mind and model it 74 00:03:23,760 --> 00:03:26,600 Speaker 1: as a bunch of pipes with ideas flushing and flowing 75 00:03:26,639 --> 00:03:27,320 Speaker 1: and swirling. 76 00:03:28,560 --> 00:03:32,000 Speaker 2: I see. I always love physicists sticky pipes themselves in 77 00:03:32,080 --> 00:03:35,040 Speaker 2: their brains. But aren't physicists sort of the plumbers of 78 00:03:35,040 --> 00:03:37,200 Speaker 2: the universe? Kind of you're trying to figure out how 79 00:03:37,200 --> 00:03:38,760 Speaker 2: the plumbing of the universe works. 80 00:03:39,000 --> 00:03:42,120 Speaker 1: Yeah, everything in the universe is out there, sloshing around, 81 00:03:42,240 --> 00:03:45,440 Speaker 1: banging it into itself. It's not like a stable situation. 82 00:03:45,600 --> 00:03:47,360 Speaker 1: You look up at the night sky and you might think, Hi, 83 00:03:47,360 --> 00:03:49,400 Speaker 1: everything's just sort of hanging it out. But that's just 84 00:03:49,440 --> 00:03:53,040 Speaker 1: because we live for such brief moments. On cosmic scales, 85 00:03:53,200 --> 00:03:55,760 Speaker 1: if you look at the universe over millions or billions 86 00:03:55,760 --> 00:03:58,640 Speaker 1: of years, you would see things expanding and exploding and 87 00:03:58,680 --> 00:04:00,160 Speaker 1: smashing and flowing. 88 00:04:00,320 --> 00:04:03,840 Speaker 2: Well, usually pipes expanding is not a good sign. Like, 89 00:04:03,880 --> 00:04:06,360 Speaker 2: if your pipe expands, it's probably going to burst. 90 00:04:06,480 --> 00:04:09,480 Speaker 1: M Yes, that's true. Dark energy would be bad news 91 00:04:09,480 --> 00:04:10,120 Speaker 1: for your plumbing. 92 00:04:10,240 --> 00:04:12,280 Speaker 2: Yeah, better flush it down the toilet or call a 93 00:04:12,280 --> 00:04:13,560 Speaker 2: real professional. 94 00:04:14,400 --> 00:04:16,520 Speaker 1: Someone who has actually useful skills you mean. 95 00:04:16,520 --> 00:04:20,560 Speaker 2: Yeah, someone who can fix a leak, someone who knows 96 00:04:20,560 --> 00:04:21,360 Speaker 2: how to use a wrench. 97 00:04:22,160 --> 00:04:24,919 Speaker 1: You mean not a physicist and not a cartoonist. 98 00:04:24,440 --> 00:04:26,719 Speaker 2: No, but an engineer. Maybe I'm also an engineer. I 99 00:04:26,760 --> 00:04:27,360 Speaker 2: have that skill. 100 00:04:27,720 --> 00:04:29,640 Speaker 1: So you tackle the plumbing projects in your house to 101 00:04:29,680 --> 00:04:30,640 Speaker 1: do you call it professional? 102 00:04:30,839 --> 00:04:33,280 Speaker 2: Sometimes I do fix it. Yeah, I fix my washing 103 00:04:33,320 --> 00:04:36,280 Speaker 2: machine the other day. I was pretty proud of myself. 104 00:04:36,200 --> 00:04:37,599 Speaker 1: My kicking it and swearing at it. 105 00:04:38,200 --> 00:04:41,000 Speaker 2: No, but looking it up on YouTube and looking at 106 00:04:41,000 --> 00:04:44,120 Speaker 2: a video of how to replace the little valve there inside. 107 00:04:44,279 --> 00:04:45,520 Speaker 2: We're all YouTube engineers. 108 00:04:45,560 --> 00:04:47,520 Speaker 1: Did you type how to replace that little valve there 109 00:04:47,560 --> 00:04:49,160 Speaker 1: into Google and just follow the instructions? 110 00:04:49,520 --> 00:04:49,599 Speaker 3: No? 111 00:04:49,680 --> 00:04:51,800 Speaker 2: I think I just typed the model of my dishwasher, 112 00:04:51,839 --> 00:04:54,320 Speaker 2: and then, you know, helpfully, a lot of people out 113 00:04:54,320 --> 00:04:57,360 Speaker 2: there have posted videos about it. I had to order apart, 114 00:04:57,720 --> 00:05:02,760 Speaker 2: pulled it apart. Surprisingly, nothing exploded. 115 00:05:02,960 --> 00:05:03,400 Speaker 1: So far. 116 00:05:03,640 --> 00:05:04,080 Speaker 2: That's right. 117 00:05:04,120 --> 00:05:07,040 Speaker 1: So far the Jorge has mastered his washing machine and 118 00:05:07,080 --> 00:05:09,400 Speaker 1: the plumbing of his house. Physicists are still trying to 119 00:05:09,400 --> 00:05:11,480 Speaker 1: figure out how the universe out there works. 120 00:05:11,720 --> 00:05:14,039 Speaker 2: Yeah, because it is an amazing universe full of what 121 00:05:14,200 --> 00:05:18,240 Speaker 2: seems like internal plumbing where forces and things like particles 122 00:05:18,279 --> 00:05:21,080 Speaker 2: and quantum fields all flow around and flush together and 123 00:05:21,080 --> 00:05:23,240 Speaker 2: get mixed up and flow from one side to the other. 124 00:05:23,400 --> 00:05:25,800 Speaker 1: There's all sorts of stuff involved. There's normal matter, there's 125 00:05:25,880 --> 00:05:29,640 Speaker 1: dark matter, there's dark energy. There's the expansion of the universe. 126 00:05:29,680 --> 00:05:32,080 Speaker 1: There's the shape of the universe, in the size of 127 00:05:32,120 --> 00:05:34,760 Speaker 1: the universe, all of which play a role in what's 128 00:05:34,800 --> 00:05:35,800 Speaker 1: going on out there. 129 00:05:35,920 --> 00:05:37,760 Speaker 2: Yeah, we've learned a lot about the universe, but there's 130 00:05:37,760 --> 00:05:41,200 Speaker 2: still a lot we don't know, big giant concepts that 131 00:05:41,279 --> 00:05:43,800 Speaker 2: are still a big mystery. So today on the podcast, 132 00:05:43,880 --> 00:05:53,440 Speaker 2: we'll be tackling the question what is the dark flow? Now, 133 00:05:53,480 --> 00:05:55,400 Speaker 2: this is not related to on flow, is it. 134 00:05:55,480 --> 00:05:58,080 Speaker 1: Well, there are a lot of bodily functions that do flow, 135 00:05:58,279 --> 00:06:01,400 Speaker 1: but we are strictly a physics podcast asked not biology. 136 00:06:01,960 --> 00:06:04,040 Speaker 2: Although putting the word dark in front of it it 137 00:06:04,080 --> 00:06:06,520 Speaker 2: does make me think of toilet functions. 138 00:06:07,640 --> 00:06:09,719 Speaker 1: There are a lot of dark matters that get flushed 139 00:06:09,720 --> 00:06:10,640 Speaker 1: down the toilet, that's true. 140 00:06:10,720 --> 00:06:12,440 Speaker 2: Yeah, a lot of dark matter that requires a lot 141 00:06:12,440 --> 00:06:15,320 Speaker 2: of dark energy. Especially if you haven't been eating fiber. 142 00:06:16,880 --> 00:06:18,720 Speaker 1: When your plumber is telling you you need a new diet, 143 00:06:18,800 --> 00:06:20,320 Speaker 1: then you definitely have a problem. 144 00:06:20,920 --> 00:06:24,640 Speaker 2: Yeah, aren't doctors sort of like body plumbers? 145 00:06:24,680 --> 00:06:28,400 Speaker 1: Hmmm, yeah, exactly. Yeah, the digestive system sometimes needs a 146 00:06:28,480 --> 00:06:29,080 Speaker 1: new valves. 147 00:06:29,120 --> 00:06:31,800 Speaker 2: But this is an intriguing name for a concept, that 148 00:06:31,960 --> 00:06:35,240 Speaker 2: dark flow. And so as usual, we were wondering how 149 00:06:35,240 --> 00:06:38,360 Speaker 2: many people out there had heard of this concept or 150 00:06:38,640 --> 00:06:40,560 Speaker 2: have any idea what it could meet. 151 00:06:40,640 --> 00:06:42,920 Speaker 1: Thanks to all the volunteers who answered this question. If 152 00:06:42,920 --> 00:06:45,560 Speaker 1: it sounds like fun to you to get a dose 153 00:06:45,600 --> 00:06:48,440 Speaker 1: of random physics questions in your inbox every week, right 154 00:06:48,520 --> 00:06:51,320 Speaker 1: to me too, questions at Danielandhorghey dot com. 155 00:06:51,360 --> 00:06:52,960 Speaker 2: So think about it for a second. What do you 156 00:06:53,000 --> 00:06:56,280 Speaker 2: think is the dark flow? Here's what people have to say. 157 00:06:56,440 --> 00:06:59,600 Speaker 3: That sounds like it has to do with dark energy 158 00:07:00,200 --> 00:07:05,520 Speaker 3: and or dark matter and it's relative distribution through the 159 00:07:05,600 --> 00:07:07,080 Speaker 3: cosmos over time. 160 00:07:07,520 --> 00:07:09,080 Speaker 1: I want to say, has something to do with like 161 00:07:09,360 --> 00:07:14,360 Speaker 1: dark matter flowing between stars or galaxies, or like how 162 00:07:14,360 --> 00:07:17,040 Speaker 1: we have a solar wind, so like a dark matter wind. 163 00:07:17,320 --> 00:07:19,680 Speaker 2: All right, I'm going to go with Batman as well. 164 00:07:20,840 --> 00:07:23,800 Speaker 2: It's like when Batman's in a state where he's totally 165 00:07:23,840 --> 00:07:26,880 Speaker 2: concentrated in his crime fighting, it's just you know, having 166 00:07:27,200 --> 00:07:29,120 Speaker 2: the artistic flow of fighting crime. 167 00:07:29,200 --> 00:07:31,480 Speaker 1: At least it would be something new in the Batman story. 168 00:07:31,520 --> 00:07:33,800 Speaker 1: I feel like Batman is just the same story over 169 00:07:33,880 --> 00:07:34,600 Speaker 1: and over again. 170 00:07:34,720 --> 00:07:37,040 Speaker 2: Oh boy, are we're going to get into Batman in 171 00:07:37,080 --> 00:07:41,120 Speaker 2: this episode? How long is this episode? It sounds like 172 00:07:41,160 --> 00:07:42,400 Speaker 2: you've thought about Batman a lot. 173 00:07:42,480 --> 00:07:45,120 Speaker 1: I just saw like Batman Year one rebooted. It's like, 174 00:07:45,160 --> 00:07:46,760 Speaker 1: how many times can you go back and tell the 175 00:07:46,760 --> 00:07:49,840 Speaker 1: same story about his parents getting shot and he's a 176 00:07:49,920 --> 00:07:53,280 Speaker 1: dark soul? Dot dot dot, Like, come up with something new, people, Well, 177 00:07:53,240 --> 00:07:54,880 Speaker 1: do you mean like change his origin story? 178 00:07:54,920 --> 00:07:55,840 Speaker 2: Then he wouldn't be Batman. 179 00:07:56,360 --> 00:08:00,960 Speaker 1: Tell us a story about somebody else. Don't just keep 180 00:08:01,000 --> 00:08:02,080 Speaker 1: rehashing the same. 181 00:08:01,880 --> 00:08:05,400 Speaker 2: Ipedi tell us about possum Man. 182 00:08:05,600 --> 00:08:09,760 Speaker 1: Yeah, exactly, And squirrel Man squirrel girl is a thing, right. 183 00:08:09,840 --> 00:08:11,280 Speaker 1: Ryan North writes that it's great. 184 00:08:11,480 --> 00:08:17,119 Speaker 2: Yeah, yeah, But anyways, without getting too dark here about 185 00:08:17,160 --> 00:08:21,239 Speaker 2: comic books, this is apparently a real physics concept, dark flow. 186 00:08:21,400 --> 00:08:24,440 Speaker 1: It is a real physics concept, and it's kind of 187 00:08:24,480 --> 00:08:27,520 Speaker 1: connected to dark matter and dark energy, but it's neither 188 00:08:27,720 --> 00:08:31,600 Speaker 1: of those things. It's more related to the overall expansion 189 00:08:31,640 --> 00:08:33,760 Speaker 1: and flow of galaxies in the universe. 190 00:08:34,600 --> 00:08:37,960 Speaker 2: I wonder if maybe you've overused the word dark in 191 00:08:38,000 --> 00:08:40,560 Speaker 2: physics that's a dark thought, yeah, because people think it's 192 00:08:40,600 --> 00:08:42,680 Speaker 2: just all connected. If you use the same word for 193 00:08:42,760 --> 00:08:44,160 Speaker 2: the set for different things. 194 00:08:44,040 --> 00:08:46,720 Speaker 1: You're absolutely right. People confuse dark matter and dark energy 195 00:08:46,840 --> 00:08:49,320 Speaker 1: all the time because they're both called dark. Really, what 196 00:08:49,360 --> 00:08:51,719 Speaker 1: we mean by dark is we don't understand this. It's 197 00:08:51,840 --> 00:08:53,920 Speaker 1: mysterious and unknown. 198 00:08:53,720 --> 00:08:56,360 Speaker 2: And invisible, right that you can't see it in space. 199 00:08:56,440 --> 00:08:59,600 Speaker 2: M hmm, yeah, exactly, all right, Well, Daniel step us 200 00:08:59,600 --> 00:09:03,320 Speaker 2: through this. So what is the dark flow? What's exactly 201 00:09:03,480 --> 00:09:06,160 Speaker 2: flowing in the universe and where is it flowing too 202 00:09:06,400 --> 00:09:07,000 Speaker 2: or down too? 203 00:09:07,160 --> 00:09:09,320 Speaker 1: That's part of the question. How is the universe flowing 204 00:09:09,360 --> 00:09:12,480 Speaker 1: and where is it flowing to? So to understand the 205 00:09:12,559 --> 00:09:15,280 Speaker 1: dark flow, we have to think about the expansion of 206 00:09:15,320 --> 00:09:18,440 Speaker 1: the universe, like where all the galaxies are going, because 207 00:09:18,440 --> 00:09:20,079 Speaker 1: the dark flow is a mystery that sort of sits 208 00:09:20,160 --> 00:09:23,040 Speaker 1: on top of our current understanding of the expansion of 209 00:09:23,080 --> 00:09:25,880 Speaker 1: the universe, how all the galaxies are moving away from 210 00:09:25,920 --> 00:09:26,320 Speaker 1: each other. 211 00:09:26,440 --> 00:09:29,360 Speaker 2: And like expansion, you mean, like the expansion of space itself, 212 00:09:29,440 --> 00:09:32,560 Speaker 2: Like the space where all the galaxies sit in is expanding, 213 00:09:32,559 --> 00:09:33,720 Speaker 2: It's getting bigger and bigger. 214 00:09:33,840 --> 00:09:38,760 Speaker 1: Exactly, space is being created between galaxies, which effectively increases 215 00:09:38,880 --> 00:09:42,680 Speaker 1: the distance between those galaxies, and that's the expansion of 216 00:09:42,720 --> 00:09:46,400 Speaker 1: the universe, which is a really interesting and fascinating history. Right. 217 00:09:46,400 --> 00:09:49,600 Speaker 1: We know that the universe expanded very quickly early. 218 00:09:49,360 --> 00:09:51,640 Speaker 2: On, that's the Big Bang, right, and inflation. 219 00:09:52,000 --> 00:09:54,800 Speaker 1: Yeah, loosely speaking, though we don't understand what caused that 220 00:09:54,840 --> 00:09:58,600 Speaker 1: initial expansion. And then after that period things were still expanding, 221 00:09:58,880 --> 00:10:01,400 Speaker 1: but the signs sort of flow. The universe took its 222 00:10:01,400 --> 00:10:04,040 Speaker 1: foot off the gas and started hitting the brake. So 223 00:10:04,240 --> 00:10:07,280 Speaker 1: still expanding, but now it was decelerating. There's all this 224 00:10:07,400 --> 00:10:09,720 Speaker 1: mass in the universe that was starting to slow down 225 00:10:09,760 --> 00:10:13,200 Speaker 1: the expansion. So universe still getting bigger, space still getting 226 00:10:13,200 --> 00:10:15,920 Speaker 1: created between the galaxies, but at a lower. 227 00:10:15,720 --> 00:10:19,400 Speaker 2: Rate now, meaning like the mass of the stuff in 228 00:10:19,440 --> 00:10:22,959 Speaker 2: the universe was somehow slowing down the expansion. Why was that? 229 00:10:23,200 --> 00:10:26,320 Speaker 2: Was it like the gravity of the stuff or just 230 00:10:26,440 --> 00:10:29,880 Speaker 2: the having stuff in space makes it not expand. 231 00:10:29,679 --> 00:10:32,960 Speaker 1: That's just the gravity, right. What determines whether space is 232 00:10:33,040 --> 00:10:37,360 Speaker 1: expanding or contracting, and whether it's accelerating or decelerating is 233 00:10:37,400 --> 00:10:39,760 Speaker 1: the amount of stuff in space, like the matter density, 234 00:10:39,840 --> 00:10:42,439 Speaker 1: and that sends to pull stuff together. And then also 235 00:10:42,480 --> 00:10:45,040 Speaker 1: the shape of the universe, is it flat, is it negative? 236 00:10:45,120 --> 00:10:48,120 Speaker 1: Is it open? And the amount of dark energy which 237 00:10:48,160 --> 00:10:50,880 Speaker 1: is pushing things out and accelerating things. Early on in 238 00:10:50,920 --> 00:10:53,400 Speaker 1: the universe, there really wasn't a whole lot of dark energy, 239 00:10:53,440 --> 00:10:57,079 Speaker 1: and so matter dominated and it was slowing down that expansion. 240 00:10:57,760 --> 00:11:01,480 Speaker 1: But because it was still expanding, and as the universe expands, 241 00:11:01,520 --> 00:11:04,920 Speaker 1: it makes more dark energy because dark energy doesn't get diluted, 242 00:11:05,000 --> 00:11:08,000 Speaker 1: and then dark energy makes the universe expand more. That 243 00:11:08,040 --> 00:11:12,240 Speaker 1: continuing expansion, even though it was decelerating, made more dark energy, 244 00:11:12,480 --> 00:11:16,520 Speaker 1: which turned things around again back to acceleration. So we 245 00:11:16,559 --> 00:11:20,800 Speaker 1: had constant expansion, but we had like initial acceleration, then deceleration, 246 00:11:21,200 --> 00:11:23,640 Speaker 1: and now for the last five or six billion years 247 00:11:23,920 --> 00:11:27,000 Speaker 1: we've had acceleration. Again that's dark energy. 248 00:11:27,559 --> 00:11:29,680 Speaker 2: So it's been sort of a roller coaster ride for 249 00:11:29,720 --> 00:11:33,120 Speaker 2: the universe, right, Like it stressed out really fast and 250 00:11:33,160 --> 00:11:35,880 Speaker 2: then its slowed down and now it's picking up speed 251 00:11:35,880 --> 00:11:39,040 Speaker 2: again and potentially it's going to keep picking up speed 252 00:11:39,080 --> 00:11:42,040 Speaker 2: until it grows it and super duper fast rate. 253 00:11:42,280 --> 00:11:44,200 Speaker 1: Yeah, we don't know what the future holds because we 254 00:11:44,200 --> 00:11:47,640 Speaker 1: don't really understand dark energy like at all. If this 255 00:11:47,760 --> 00:11:50,760 Speaker 1: simple model of dark energy is just like some energy 256 00:11:50,800 --> 00:11:54,320 Speaker 1: that permeates space and causes the expansion of the universe 257 00:11:54,360 --> 00:11:57,320 Speaker 1: to accelerate. Is valid, then yeah, I'll just keep going 258 00:11:57,360 --> 00:11:59,760 Speaker 1: forever and things will get more and more distant. Space 259 00:11:59,800 --> 00:12:04,560 Speaker 1: will continue to expand between galaxies, creating vaster and vaster 260 00:12:04,679 --> 00:12:09,000 Speaker 1: distances between superclusters which will collapse into supermassive black holes. 261 00:12:09,400 --> 00:12:11,640 Speaker 1: And that's sort of the far future of the universe. 262 00:12:11,760 --> 00:12:14,440 Speaker 1: And we're talking about this today because this expansion of 263 00:12:14,480 --> 00:12:17,959 Speaker 1: the universe, this creation of space between galaxies, is sometimes 264 00:12:18,000 --> 00:12:20,320 Speaker 1: called by astronomers the Hubble flow. 265 00:12:20,720 --> 00:12:23,520 Speaker 2: Now, first of all, I guess this expansion of space 266 00:12:23,600 --> 00:12:27,120 Speaker 2: is happening everywhere, all at once, the same everywhere, or 267 00:12:27,160 --> 00:12:29,040 Speaker 2: does it happen more in certain spots. 268 00:12:29,440 --> 00:12:31,839 Speaker 1: We think it happens the same everywhere. 269 00:12:31,400 --> 00:12:33,520 Speaker 2: Even the spots with lots of stuff in it. 270 00:12:33,640 --> 00:12:35,600 Speaker 1: Yeah, that's the current idea, and it's sort of a 271 00:12:35,640 --> 00:12:38,439 Speaker 1: theory and an observation. It's sort of the simplest idea 272 00:12:38,440 --> 00:12:40,160 Speaker 1: you could have if you don't know what dark energy is. 273 00:12:40,559 --> 00:12:43,720 Speaker 1: Possibly it's something like a cosmological constant, some energy in 274 00:12:43,800 --> 00:12:46,480 Speaker 1: space that causes this to happen. The simplest thing to 275 00:12:46,480 --> 00:12:48,600 Speaker 1: do is to say, oh, that's just a number it's 276 00:12:48,600 --> 00:12:51,200 Speaker 1: the same everywhere. We don't see any evidence for it 277 00:12:51,240 --> 00:12:54,680 Speaker 1: being different in different parts of the universe. But you know, 278 00:12:54,760 --> 00:12:57,040 Speaker 1: that's a tricky because we can't see it in different 279 00:12:57,040 --> 00:12:59,160 Speaker 1: parts of the universe. At the same time, we can 280 00:12:59,200 --> 00:13:02,320 Speaker 1: see the expansion happening locally now ish we can see 281 00:13:02,320 --> 00:13:06,080 Speaker 1: the expansion happening far away, like a billion years ago. 282 00:13:06,400 --> 00:13:08,080 Speaker 1: It's hard to compare point to point. 283 00:13:08,480 --> 00:13:10,760 Speaker 2: But didn't you say stuff slows down the expansion of 284 00:13:10,760 --> 00:13:13,360 Speaker 2: the universe. So I wonder if in this bus, where 285 00:13:13,360 --> 00:13:16,000 Speaker 2: there's a lot of stuff in it, maybe it's expanding 286 00:13:17,320 --> 00:13:17,880 Speaker 2: less fast. 287 00:13:18,280 --> 00:13:20,840 Speaker 1: Stuff does slow down the expansion of the universe. That 288 00:13:20,880 --> 00:13:23,960 Speaker 1: sort of contributes overall, but everything is actually balanced so 289 00:13:24,000 --> 00:13:27,240 Speaker 1: that overall the universe is flat. But yeah, we don't 290 00:13:27,360 --> 00:13:30,199 Speaker 1: know how stuff and dark energy interact with each other. 291 00:13:30,320 --> 00:13:33,680 Speaker 1: Dark energy is so dilute and so actually weak that 292 00:13:33,800 --> 00:13:36,360 Speaker 1: anywhere there is stuff, you can basically just ignore the 293 00:13:36,480 --> 00:13:38,839 Speaker 1: dark energy and just treat it as if there was 294 00:13:38,920 --> 00:13:40,920 Speaker 1: gravity there, just like from its stuff. 295 00:13:41,720 --> 00:13:44,440 Speaker 2: But I guess as we look around, we see the 296 00:13:44,480 --> 00:13:46,800 Speaker 2: whole of the universe expanding evenly in all. 297 00:13:46,640 --> 00:13:49,199 Speaker 1: Directions exactly, And the idea of the Hubble flow, I 298 00:13:49,240 --> 00:13:51,559 Speaker 1: think It's kind of helpful visually for you to think 299 00:13:51,600 --> 00:13:53,800 Speaker 1: about this because we tend to think about this in 300 00:13:53,920 --> 00:13:58,320 Speaker 1: terms of velocities, Like those galaxies are moving away from 301 00:13:58,400 --> 00:14:01,319 Speaker 1: us at some speed, and we measure those velocities in 302 00:14:01,400 --> 00:14:04,359 Speaker 1: terms of red shift. How the light from those galaxies 303 00:14:04,440 --> 00:14:07,120 Speaker 1: is getting stretched out because those galaxies are moving away 304 00:14:07,120 --> 00:14:10,160 Speaker 1: from us. This is how Hubble sort of initially described it. 305 00:14:10,400 --> 00:14:13,160 Speaker 1: You know, the velocity of these galaxies. It makes more sense, 306 00:14:13,200 --> 00:14:14,880 Speaker 1: it's sort of more natural to think about it in 307 00:14:15,000 --> 00:14:19,200 Speaker 1: terms of general relativity. Has expansion of space itself, That 308 00:14:19,280 --> 00:14:22,280 Speaker 1: those galaxies aren't accelerating away from us, but space is 309 00:14:22,320 --> 00:14:25,280 Speaker 1: being created between us, and so like, there is an 310 00:14:25,280 --> 00:14:28,040 Speaker 1: increased distance between us and those galaxies, but you're not 311 00:14:28,080 --> 00:14:29,560 Speaker 1: feeling any acceleration. 312 00:14:30,520 --> 00:14:33,200 Speaker 2: And you said, this motion is called the Hubble flow. 313 00:14:33,440 --> 00:14:35,680 Speaker 2: What do you mean motion? And why is it called 314 00:14:35,920 --> 00:14:36,320 Speaker 2: a flow? 315 00:14:36,520 --> 00:14:39,280 Speaker 1: So motion there is a bit misleading. The distance between 316 00:14:39,320 --> 00:14:43,920 Speaker 1: the galaxies is increasing, and so for nearby galaxies, you 317 00:14:43,960 --> 00:14:46,840 Speaker 1: can like measure their velocity and say that galaxy has 318 00:14:46,880 --> 00:14:50,040 Speaker 1: a certain velocity in our reference frame. But across really 319 00:14:50,080 --> 00:14:52,560 Speaker 1: really big distances, it doesn't make sense to talk about 320 00:14:52,800 --> 00:14:55,680 Speaker 1: relative velocity for objects that are super far away from 321 00:14:55,680 --> 00:14:59,520 Speaker 1: each other and have different non inertial frames. So astronomers 322 00:14:59,520 --> 00:15:02,520 Speaker 1: sometimes use velocities as a sort of way to talk 323 00:15:02,560 --> 00:15:05,720 Speaker 1: about those objects. But it doesn't actually make any sense 324 00:15:05,800 --> 00:15:08,080 Speaker 1: in terms of general relativity. And why it's called the 325 00:15:08,120 --> 00:15:10,040 Speaker 1: hubble flow. Yeah, it's a good question. I think it 326 00:15:10,120 --> 00:15:12,640 Speaker 1: just helps you visualize how like space is being created 327 00:15:12,680 --> 00:15:16,000 Speaker 1: everywhere and things are being carried along by that stream. 328 00:15:16,000 --> 00:15:18,600 Speaker 2: Okay, so the hubble flow. And then I guess maybe 329 00:15:18,600 --> 00:15:21,040 Speaker 2: it's sort of like the flow of space being created 330 00:15:21,400 --> 00:15:23,280 Speaker 2: pushing everything apart in the universe. 331 00:15:23,560 --> 00:15:26,280 Speaker 1: Yeah, exactly, And so you can think about those galaxies 332 00:15:26,280 --> 00:15:28,760 Speaker 1: as sort of like sitting in that hubble flow. Space 333 00:15:28,840 --> 00:15:31,280 Speaker 1: is being created, everything is moving further and further apart. 334 00:15:31,520 --> 00:15:33,880 Speaker 1: But there's a wrinkle on top of that motion. Right, 335 00:15:33,880 --> 00:15:36,360 Speaker 1: the hubble flow is not the only thing that's happening 336 00:15:36,440 --> 00:15:38,920 Speaker 1: in the universe. Each of these galaxies is also moving 337 00:15:39,280 --> 00:15:42,560 Speaker 1: relative to the hubble flow. Like people often write in 338 00:15:42,600 --> 00:15:45,680 Speaker 1: and ask, hey, if galaxies are being pushed apart because 339 00:15:45,680 --> 00:15:47,920 Speaker 1: of dark energy, why is the Milky Way going to 340 00:15:47,960 --> 00:15:50,720 Speaker 1: slam into Andromeda? And the answer is that these things 341 00:15:50,760 --> 00:15:53,280 Speaker 1: are moving because of gravity. Right, we talked earlier about 342 00:15:53,320 --> 00:15:56,479 Speaker 1: how dark energy sort of wins over really large distances, 343 00:15:56,800 --> 00:15:59,760 Speaker 1: but for short distances it's too weak. Well, gravity is 344 00:15:59,800 --> 00:16:03,120 Speaker 1: the opposite. Gravity gets really weak at large distances, so 345 00:16:03,200 --> 00:16:06,600 Speaker 1: like between superclusters you hardly feel anything. But short distances, 346 00:16:06,640 --> 00:16:09,160 Speaker 1: like just between two galaxies or between the Sun and 347 00:16:09,200 --> 00:16:12,560 Speaker 1: the Earth, gravity totally dominates dark energy right like. 348 00:16:12,600 --> 00:16:15,920 Speaker 2: Right now, even where I'm sitting, space is expanding, right like, 349 00:16:15,920 --> 00:16:17,280 Speaker 2: if I look at my hand in front of me, 350 00:16:17,560 --> 00:16:20,240 Speaker 2: the space that my hand is in is technically expanding, 351 00:16:20,280 --> 00:16:22,280 Speaker 2: just like the rest of the universe is just expanding 352 00:16:22,400 --> 00:16:24,800 Speaker 2: so little that the force is keeping my hand together 353 00:16:25,440 --> 00:16:28,520 Speaker 2: when over the expansion of the space. 354 00:16:28,720 --> 00:16:31,240 Speaker 1: Yeah, that's exactly right. And in the case of your 355 00:16:31,240 --> 00:16:34,680 Speaker 1: body and your hand, the forces are electromagnetic, those chemical 356 00:16:34,720 --> 00:16:37,600 Speaker 1: bonds are tying everything together, So the hubble flow is 357 00:16:37,640 --> 00:16:40,280 Speaker 1: like the gentless little current that your body can overpower. 358 00:16:40,400 --> 00:16:42,600 Speaker 1: Even on the scale of the Solar System, gravity winds 359 00:16:42,880 --> 00:16:44,960 Speaker 1: and the motion of the Earth around the Sun is 360 00:16:45,040 --> 00:16:47,760 Speaker 1: totally dominated just by gravity. Like if it wasn't, we 361 00:16:47,800 --> 00:16:50,640 Speaker 1: might have discovered dark energy much much earlier, because we 362 00:16:50,640 --> 00:16:53,080 Speaker 1: wouldn't have understood the orbits of the planets without it, 363 00:16:53,120 --> 00:16:55,480 Speaker 1: and we have very precise measurements of things happening in 364 00:16:55,520 --> 00:16:58,600 Speaker 1: the Solar System. Any little deviation from gravity we would 365 00:16:58,640 --> 00:17:01,280 Speaker 1: have noticed if it was at all measurable. But dark 366 00:17:01,400 --> 00:17:03,360 Speaker 1: energy is not even measurable on the scale of our 367 00:17:03,400 --> 00:17:06,200 Speaker 1: Solar System. You have to go out to between clusters 368 00:17:06,240 --> 00:17:08,159 Speaker 1: of galaxy in order to see it. So on the 369 00:17:08,200 --> 00:17:11,360 Speaker 1: local scale, dark energy is basically irrelevant, and it's gravity 370 00:17:11,400 --> 00:17:13,840 Speaker 1: that winds over and so these galaxies are moving in 371 00:17:13,920 --> 00:17:16,440 Speaker 1: random directions and feeling tugs from gravity and having all 372 00:17:16,440 --> 00:17:19,280 Speaker 1: sorts of dynamics. We talked about how galaxies merge and 373 00:17:19,320 --> 00:17:23,240 Speaker 1: form together and make superclusters. So this motion relative to 374 00:17:23,280 --> 00:17:26,639 Speaker 1: the hubble flow, that's called the peculiar motion of a galaxy. 375 00:17:26,920 --> 00:17:29,720 Speaker 1: It just means how it's moving relative to the flow 376 00:17:30,040 --> 00:17:30,440 Speaker 1: I see. 377 00:17:30,520 --> 00:17:33,080 Speaker 2: So like, for example, in our Solar System, the space 378 00:17:33,160 --> 00:17:35,600 Speaker 2: is expanding, but our planet is tied to the Sun, 379 00:17:35,720 --> 00:17:37,560 Speaker 2: just like we're tied to the Earth. So like me 380 00:17:37,680 --> 00:17:40,960 Speaker 2: sitting here on Earth and not moving relative to the Earth, 381 00:17:41,000 --> 00:17:43,960 Speaker 2: there is sort of almost like space flowing through me 382 00:17:44,040 --> 00:17:46,440 Speaker 2: as it expands through. 383 00:17:46,200 --> 00:17:50,320 Speaker 1: Me exactly, So your peculiar motion is towards the Earth, 384 00:17:50,320 --> 00:17:53,360 Speaker 1: and the Earth's peculiar motion is towards you. And then 385 00:17:53,400 --> 00:17:56,320 Speaker 1: on the scale of galaxies, like the Milky Way's peculiar 386 00:17:56,359 --> 00:17:59,639 Speaker 1: motion is relative to Andromeda, and Andromeda's peculiar motion is 387 00:17:59,640 --> 00:18:02,560 Speaker 1: relative to the Milky Way. If we only were following 388 00:18:02,560 --> 00:18:05,040 Speaker 1: the Hubble flow and had no peculiar motion, then the 389 00:18:05,080 --> 00:18:07,760 Speaker 1: space between us would be expanding, right, the distance would 390 00:18:07,760 --> 00:18:10,320 Speaker 1: be growing. But it's not. Milky Way Andromeda are coming 391 00:18:10,359 --> 00:18:13,200 Speaker 1: towards each other. And that's the case for lots of galaxies, 392 00:18:13,400 --> 00:18:15,320 Speaker 1: even the ones that aren't going to smash into each other. 393 00:18:15,440 --> 00:18:18,040 Speaker 1: They're all basically pointing in random directions. Very few are 394 00:18:18,080 --> 00:18:20,359 Speaker 1: like at rest relative to the Hubble flow. 395 00:18:20,640 --> 00:18:23,960 Speaker 2: So like our galaxy and Andromena galaxy are moving relative 396 00:18:24,000 --> 00:18:27,359 Speaker 2: to each other. And there's two components to that. You're saying, right, like, 397 00:18:27,400 --> 00:18:31,800 Speaker 2: there's how much we're moving because the space is expanding 398 00:18:31,840 --> 00:18:35,080 Speaker 2: between us, and there's also how much we're moving if 399 00:18:35,080 --> 00:18:37,119 Speaker 2: the space wasn't expanding between us. 400 00:18:37,240 --> 00:18:39,640 Speaker 1: Yeah, that's exactly right. You can think about it either 401 00:18:39,760 --> 00:18:42,160 Speaker 1: just from the reference frame of the Milky Way and say, look, 402 00:18:42,200 --> 00:18:44,879 Speaker 1: everything is moving away from us, and then just break 403 00:18:44,920 --> 00:18:47,520 Speaker 1: that motion into two components. Say one of that is 404 00:18:47,600 --> 00:18:50,119 Speaker 1: due to dark energy and the other is everything else 405 00:18:50,280 --> 00:18:52,359 Speaker 1: relative to that, And then a more natural way to 406 00:18:52,400 --> 00:18:54,639 Speaker 1: think about it is, instead of just having one reference 407 00:18:54,680 --> 00:18:57,600 Speaker 1: frame centered at our heads, think about dark energy is 408 00:18:57,680 --> 00:19:00,880 Speaker 1: just creating this like expanding frame, and then think about 409 00:19:00,880 --> 00:19:03,960 Speaker 1: the motion relative to those frames. The hubble flow is 410 00:19:03,960 --> 00:19:05,879 Speaker 1: sort of the most natural way to think about the 411 00:19:05,880 --> 00:19:09,480 Speaker 1: expanding universe. And in that frame they're called co moving frames. 412 00:19:09,640 --> 00:19:12,600 Speaker 1: The only motion is the peculiar motion, because you just 413 00:19:12,640 --> 00:19:14,679 Speaker 1: sort of set the expansion of the universe as like 414 00:19:14,760 --> 00:19:15,800 Speaker 1: the baseline thing. 415 00:19:16,119 --> 00:19:18,320 Speaker 2: Right, It's sort of like maybe like the river analogies 416 00:19:18,359 --> 00:19:21,119 Speaker 2: you just brought up earlier, like we're all moving in 417 00:19:21,200 --> 00:19:24,400 Speaker 2: a river, and the flow of the river is the 418 00:19:24,520 --> 00:19:27,159 Speaker 2: hubble flow, or like the expansion of the universe. But 419 00:19:27,240 --> 00:19:29,760 Speaker 2: you know, within my little raft, I can have something 420 00:19:29,800 --> 00:19:32,080 Speaker 2: moving relative to each other, or I can try like 421 00:19:32,240 --> 00:19:34,520 Speaker 2: rowing towards your raft, and then there would be some 422 00:19:34,560 --> 00:19:36,240 Speaker 2: peculiar motion between our rafts. 423 00:19:36,400 --> 00:19:38,720 Speaker 1: Yeah, exactly right. Maybe we have engines and we're trying 424 00:19:38,720 --> 00:19:41,480 Speaker 1: to push towards each other against the current, or we're 425 00:19:41,480 --> 00:19:43,800 Speaker 1: trying to get away from each other or whatever, so 426 00:19:43,840 --> 00:19:45,119 Speaker 1: that's our peculiar motion. 427 00:19:45,240 --> 00:19:48,680 Speaker 2: All right, Well, these are peculiar concepts. And so let's 428 00:19:48,680 --> 00:19:52,760 Speaker 2: dig into Now, what is the dark flow of the universe? 429 00:19:52,960 --> 00:19:55,119 Speaker 2: Why is it dark? Where is it flowing? And is 430 00:19:55,160 --> 00:19:57,760 Speaker 2: it something we want to touch or take a bath in. 431 00:19:57,960 --> 00:19:59,720 Speaker 2: So let's dig into that. But first let's take a 432 00:19:59,760 --> 00:20:14,879 Speaker 2: qu break. All right, we're talking about the dark flow 433 00:20:14,960 --> 00:20:17,959 Speaker 2: of the universe, which sounds a little bit sinister. I 434 00:20:18,000 --> 00:20:22,280 Speaker 2: feel like there's something going on under the surface. 435 00:20:22,160 --> 00:20:24,879 Speaker 1: That is not light, sort of like a Batman tinged 436 00:20:25,080 --> 00:20:27,160 Speaker 1: story the Dark Knights of Gotham. 437 00:20:27,480 --> 00:20:31,960 Speaker 2: I can underplot you like, there's something going on in 438 00:20:32,000 --> 00:20:32,800 Speaker 2: the streets. 439 00:20:32,440 --> 00:20:33,920 Speaker 1: Of Gotham exactly. 440 00:20:34,720 --> 00:20:37,240 Speaker 2: There's a flow of villainy in the sewers. 441 00:20:37,520 --> 00:20:40,160 Speaker 1: Yeah, or maybe it's financial plumbing, right, it's a flow 442 00:20:40,200 --> 00:20:41,919 Speaker 1: of dark money through politics. 443 00:20:42,320 --> 00:20:44,840 Speaker 2: Oh there you go. Well again, maybe you should have 444 00:20:44,840 --> 00:20:48,640 Speaker 2: called it something different and not dark and confuse everybody. 445 00:20:48,800 --> 00:20:51,280 Speaker 1: You there means the entire physics community, right, because I 446 00:20:51,359 --> 00:20:52,960 Speaker 1: certainly didn't call this dark flow. 447 00:20:53,040 --> 00:20:55,960 Speaker 2: But you keep using it though, so you're complicit. 448 00:20:56,440 --> 00:21:01,040 Speaker 1: Yes, I am complicit. Admit to that. Toss me in 449 00:21:01,040 --> 00:21:03,080 Speaker 1: physical naming jail and throw away the key. 450 00:21:03,960 --> 00:21:05,920 Speaker 2: Yes, we'll lock you up an archem asylum with the 451 00:21:05,960 --> 00:21:09,240 Speaker 2: rest of the Batman villains. All right, we're talking about 452 00:21:09,240 --> 00:21:12,480 Speaker 2: the dark flow of the universe, and we talked about 453 00:21:12,480 --> 00:21:17,040 Speaker 2: how the universe is expanding, and it's because space is expanding. 454 00:21:17,080 --> 00:21:20,720 Speaker 2: All of space in the universe is expanding. And that flow, 455 00:21:20,760 --> 00:21:23,680 Speaker 2: that flow of new space flowing everywhere, being created everywhere, 456 00:21:24,000 --> 00:21:26,840 Speaker 2: stretching things out they're in space. We call that the 457 00:21:26,920 --> 00:21:29,920 Speaker 2: hubble flow. Now is that the same as the dark flow? 458 00:21:30,080 --> 00:21:32,840 Speaker 1: So that's the Hubble flow. The dark flow is a 459 00:21:32,920 --> 00:21:37,520 Speaker 1: question about this peculiar motion. Are there any patterns in 460 00:21:37,560 --> 00:21:40,919 Speaker 1: the peculiar motion? Like we expect that the universe is 461 00:21:40,960 --> 00:21:44,520 Speaker 1: the same everywhere and it's all just random, there's nothing special, 462 00:21:45,080 --> 00:21:47,479 Speaker 1: and so that if you look at the directions and 463 00:21:47,520 --> 00:21:51,280 Speaker 1: the magnitudes of these peculiar motions, like where's every galaxy going, 464 00:21:51,480 --> 00:21:53,680 Speaker 1: and you add them all up, they should basically add 465 00:21:53,760 --> 00:21:56,440 Speaker 1: up to zero, right, there should be no preferred direction 466 00:21:56,680 --> 00:21:57,960 Speaker 1: in the universe. 467 00:21:57,800 --> 00:22:02,560 Speaker 2: Meaning like like let's say we ignore the expansion of 468 00:22:02,600 --> 00:22:06,199 Speaker 2: the universe, or like take that into account, or you 469 00:22:06,240 --> 00:22:09,960 Speaker 2: substract the expansion of the universe from the motion of everything. 470 00:22:10,119 --> 00:22:12,639 Speaker 2: How is everything moving? How are all those superclusters of 471 00:22:12,680 --> 00:22:16,119 Speaker 2: galaxies on those galaxies and stars? How's it all moving? 472 00:22:16,480 --> 00:22:18,600 Speaker 2: If the universe wasn't expanding, that's what you mean? 473 00:22:18,840 --> 00:22:22,320 Speaker 1: Yeah, essentially relative to the expansion. How is everything moving? 474 00:22:22,359 --> 00:22:24,800 Speaker 1: Does it point in some particular direction? Does it average 475 00:22:24,800 --> 00:22:28,200 Speaker 1: out to zero? We expect, based on like very simple, 476 00:22:28,359 --> 00:22:31,679 Speaker 1: kind of naive but powerful arguments, that it should average 477 00:22:31,680 --> 00:22:34,879 Speaker 1: out to zero. We think the universe is the same everywhere, 478 00:22:35,200 --> 00:22:37,200 Speaker 1: and the Big Bang happened at every point in the 479 00:22:37,280 --> 00:22:40,000 Speaker 1: universe the same time, and there was no global over 480 00:22:40,080 --> 00:22:43,040 Speaker 1: density anywhere, and so we expect it to basically average 481 00:22:43,080 --> 00:22:43,560 Speaker 1: out to zero. 482 00:22:43,760 --> 00:22:45,560 Speaker 2: Now, what do you mean by average out to zero? 483 00:22:45,680 --> 00:22:48,440 Speaker 2: Like why should that be the case? Like the motion 484 00:22:48,560 --> 00:22:50,440 Speaker 2: of our solar system does it add up to zero? 485 00:22:50,720 --> 00:22:53,600 Speaker 1: So our solar system reflects the spin of the initial 486 00:22:53,640 --> 00:22:56,280 Speaker 1: blob of gas that formed it. Right, that blob of 487 00:22:56,320 --> 00:22:59,000 Speaker 1: gas had a bunch of particles heading and render directions, 488 00:22:59,000 --> 00:23:01,400 Speaker 1: and it was a regularly shape. Then it was spinning, 489 00:23:01,480 --> 00:23:03,760 Speaker 1: and so the spinning, the motion of our solar system, 490 00:23:03,880 --> 00:23:05,920 Speaker 1: including the motion of the Solar system around the center 491 00:23:05,920 --> 00:23:09,600 Speaker 1: of the galaxy, does reflect the motion of that initial blob. 492 00:23:10,160 --> 00:23:13,520 Speaker 1: And we expect all those blobs were basically created equal, 493 00:23:13,600 --> 00:23:15,440 Speaker 1: and so you'll get some spinning one way and some 494 00:23:15,440 --> 00:23:17,600 Speaker 1: spinning another way, and some moving this way and some 495 00:23:17,680 --> 00:23:20,320 Speaker 1: moving that way, and you do see a big variation 496 00:23:20,440 --> 00:23:22,840 Speaker 1: of like directions of stars, et cetera. 497 00:23:23,520 --> 00:23:24,960 Speaker 2: I see, it's sort of like maybe if you had 498 00:23:25,000 --> 00:23:27,880 Speaker 2: like a gas canister full of gas molecules, you sort 499 00:23:27,880 --> 00:23:30,639 Speaker 2: of expect all the gas molecules, all the motions of 500 00:23:30,960 --> 00:23:34,240 Speaker 2: all those particles and molecules to average out to zero, right, 501 00:23:34,280 --> 00:23:37,840 Speaker 2: because it's all sort of random. The canister's not going anywhere, 502 00:23:38,080 --> 00:23:40,760 Speaker 2: and it's had some time to like diffuse and even. 503 00:23:40,600 --> 00:23:44,040 Speaker 1: Out exactly unless there was something outside that cannister pulling 504 00:23:44,080 --> 00:23:46,399 Speaker 1: on them, or something pushing on the whole canister, or 505 00:23:46,440 --> 00:23:49,120 Speaker 1: something else acting that you weren't aware of, the motion 506 00:23:49,200 --> 00:23:51,479 Speaker 1: of all the molecules should add up to zero. So 507 00:23:51,520 --> 00:23:52,200 Speaker 1: that's the question. 508 00:23:52,480 --> 00:23:54,159 Speaker 2: And so that's kind of what you were saying we 509 00:23:54,160 --> 00:23:56,639 Speaker 2: should expect from the universe. Like if you subtract the 510 00:23:56,760 --> 00:23:59,679 Speaker 2: expansion of the unverse from the motion of everything, then 511 00:24:00,080 --> 00:24:02,520 Speaker 2: basically all the stars and galaxies out there shots sort 512 00:24:02,520 --> 00:24:05,359 Speaker 2: of look like a canister of gas where everything's just 513 00:24:05,400 --> 00:24:07,760 Speaker 2: moving in random directions, but it should all add up to. 514 00:24:07,800 --> 00:24:11,520 Speaker 1: Zero, exactly. And there's one more little bit of trickiness 515 00:24:11,520 --> 00:24:13,439 Speaker 1: that we need to think about before we're ready to 516 00:24:13,560 --> 00:24:17,159 Speaker 1: actually look at those galaxies and answer the question. And 517 00:24:17,200 --> 00:24:20,360 Speaker 1: that's the frame of reference when we talked about subtracting 518 00:24:20,400 --> 00:24:23,080 Speaker 1: out the expansion of the universe, and that's helpful for 519 00:24:23,160 --> 00:24:26,480 Speaker 1: like removing something we already understand that's causing everything to 520 00:24:26,520 --> 00:24:28,520 Speaker 1: get away from each other. But we still need to 521 00:24:28,560 --> 00:24:30,960 Speaker 1: pick a frame of reference in order to calculate the 522 00:24:31,040 --> 00:24:34,480 Speaker 1: velocity of a galaxy, because galaxies don't have velocity relative 523 00:24:34,520 --> 00:24:37,480 Speaker 1: to space, they only have velocity in some reference frame. 524 00:24:37,600 --> 00:24:40,040 Speaker 1: Like put a reference frame on one galaxy, measure the 525 00:24:40,080 --> 00:24:43,440 Speaker 1: velocity of another one relative to that or your spaceship 526 00:24:43,560 --> 00:24:46,960 Speaker 1: or something. Right, velocities are not a property of objects. 527 00:24:47,000 --> 00:24:50,159 Speaker 1: There are properties of pairs of objects. So basically have 528 00:24:50,280 --> 00:24:52,359 Speaker 1: to pick a reference frame in which you're going to 529 00:24:52,400 --> 00:24:54,440 Speaker 1: measure the velocity of all these objects. 530 00:24:54,680 --> 00:24:56,600 Speaker 2: And is it going to change if you changed the 531 00:24:56,960 --> 00:24:58,960 Speaker 2: point of reference, like it shouldn't it add up to 532 00:24:59,080 --> 00:24:59,840 Speaker 2: zero no matter what? 533 00:25:00,240 --> 00:25:02,359 Speaker 1: Yeah, this is a really interesting and subtle point, like 534 00:25:02,440 --> 00:25:05,840 Speaker 1: space itself has no frame of reference, doesn't prefer any 535 00:25:05,880 --> 00:25:07,960 Speaker 1: frame of reference, and so it's often said like the 536 00:25:08,080 --> 00:25:11,199 Speaker 1: universe has no preferred frame, and that's mostly true, But 537 00:25:11,320 --> 00:25:14,359 Speaker 1: the stuff in the universe definitely does have a frame 538 00:25:14,400 --> 00:25:17,240 Speaker 1: of reference. Like if you add up the velocities of 539 00:25:17,280 --> 00:25:19,960 Speaker 1: all the stuff in the universe, that has a frame 540 00:25:20,000 --> 00:25:22,359 Speaker 1: of reference, right, that has a location that has an 541 00:25:22,400 --> 00:25:25,800 Speaker 1: average velocity, and so the stuff in the universe has 542 00:25:25,800 --> 00:25:27,600 Speaker 1: a frame and you can sort of pick that frame 543 00:25:27,640 --> 00:25:31,320 Speaker 1: of reference just by looking at the cosmic microwave background radiation. 544 00:25:31,520 --> 00:25:33,800 Speaker 2: But wait, I thought every other motion of the other 545 00:25:33,840 --> 00:25:35,960 Speaker 2: stuff out there should add up to zero. Are you 546 00:25:36,000 --> 00:25:38,439 Speaker 2: saying it doesn't or it may not. Like if you 547 00:25:38,560 --> 00:25:40,639 Speaker 2: calculate the average velocity of all the galaxies in the 548 00:25:40,720 --> 00:25:43,920 Speaker 2: universe observable universe, shouldn't that be zero? 549 00:25:44,160 --> 00:25:46,600 Speaker 1: It should be if you pick the right reference frame, right, 550 00:25:46,640 --> 00:25:49,560 Speaker 1: and you understand everything that's happening. So that's why the 551 00:25:49,560 --> 00:25:52,400 Speaker 1: answer depends a little bit on the reference frame. So 552 00:25:52,440 --> 00:25:54,640 Speaker 1: we go back to the very early universe and say, well, 553 00:25:54,680 --> 00:25:56,840 Speaker 1: what was the reference frame of all the stuff in 554 00:25:56,880 --> 00:25:59,399 Speaker 1: the early universe, like when things were still hot and 555 00:25:59,480 --> 00:26:02,720 Speaker 1: dense and a big plasma. We can actually measure that 556 00:26:02,760 --> 00:26:05,439 Speaker 1: because we can look at the cosmic microwave background radiation 557 00:26:05,720 --> 00:26:07,920 Speaker 1: the life from that plasma, and we can look at 558 00:26:07,920 --> 00:26:10,639 Speaker 1: like whether it's bluer or redder in one direction. So 559 00:26:10,680 --> 00:26:14,280 Speaker 1: we can measure our motion through this cosmic microwave background 560 00:26:14,359 --> 00:26:16,439 Speaker 1: radiation and that tells us what the frame of the 561 00:26:16,520 --> 00:26:19,080 Speaker 1: universe was like fourteen billion years ago, and so it 562 00:26:19,119 --> 00:26:20,840 Speaker 1: gives us a frame. Then we can ask, like, are 563 00:26:20,880 --> 00:26:25,880 Speaker 1: the galaxies now moving relative to the cosmic microwave background radiation? 564 00:26:26,440 --> 00:26:28,280 Speaker 1: We expect that to be no, because we think the 565 00:26:28,280 --> 00:26:31,440 Speaker 1: galaxies came from the same stuff that formed the CMB, 566 00:26:32,040 --> 00:26:35,119 Speaker 1: so it'd be weird if that stuff was moving relative 567 00:26:35,200 --> 00:26:36,080 Speaker 1: to the CMB. 568 00:26:36,359 --> 00:26:38,880 Speaker 2: Wait wait, wait, wait, are you saying the cosmic microwave 569 00:26:38,920 --> 00:26:42,159 Speaker 2: background radiation is not the same in all directions? You're saying, like, 570 00:26:42,160 --> 00:26:44,240 Speaker 2: it's redder to the right than to our left. 571 00:26:44,400 --> 00:26:46,800 Speaker 1: Kind of yeah, because we're moving through the CMB, we 572 00:26:46,880 --> 00:26:50,600 Speaker 1: have a non zero velocity relative to the CMB. If 573 00:26:50,600 --> 00:26:53,440 Speaker 1: you just measure the CMB overall is very obviously redder 574 00:26:53,520 --> 00:26:56,000 Speaker 1: in one direction and bluer in the other. And then 575 00:26:56,040 --> 00:26:58,240 Speaker 1: typically you see these maps of the CNB, but they've 576 00:26:58,280 --> 00:27:01,440 Speaker 1: already subtracted that out. They've already measured our overall motion 577 00:27:01,600 --> 00:27:04,239 Speaker 1: relative to the CMB and subtracted that out, and then 578 00:27:04,240 --> 00:27:07,320 Speaker 1: they're looking for like tiny little wiggles in the CMB 579 00:27:07,760 --> 00:27:08,480 Speaker 1: on top of that. 580 00:27:09,240 --> 00:27:11,159 Speaker 2: Oh, I see what it's saying. So like, if you 581 00:27:11,160 --> 00:27:14,640 Speaker 2: look at the cosmic microwrate background, it has a certain 582 00:27:14,720 --> 00:27:18,600 Speaker 2: velocity or motion to it, and so you have to 583 00:27:18,680 --> 00:27:21,399 Speaker 2: sort of assume that's like the motion of the universe 584 00:27:21,480 --> 00:27:24,560 Speaker 2: kind of, that's like the home base of the universe. 585 00:27:24,680 --> 00:27:27,640 Speaker 1: Yes, the zero of the universe. That's really the only 586 00:27:27,680 --> 00:27:30,160 Speaker 1: thing we can compare two. Right, You can't just measure 587 00:27:30,240 --> 00:27:33,280 Speaker 1: velocities relative to space. That doesn't have any meaning. You 588 00:27:33,320 --> 00:27:35,760 Speaker 1: have to measure relative to something. So you need like 589 00:27:35,760 --> 00:27:38,600 Speaker 1: a baseline. So we go back to the early universe 590 00:27:38,720 --> 00:27:41,399 Speaker 1: and take the frame of the CMB and say, our 591 00:27:41,520 --> 00:27:45,920 Speaker 1: galaxies overall moving in some direction relative to the motion 592 00:27:46,040 --> 00:27:48,400 Speaker 1: of the CNB. That would be weird. It's not weird 593 00:27:48,440 --> 00:27:50,960 Speaker 1: for one galaxy to be moving relative to the CNB 594 00:27:51,320 --> 00:27:53,640 Speaker 1: or like stuff happens, it gets pulled in some direction. 595 00:27:53,920 --> 00:27:56,400 Speaker 1: The Earth is moving relative to the CNB. No big deal. 596 00:27:56,680 --> 00:27:59,080 Speaker 1: But if you add up everything relative to the CMB 597 00:27:59,320 --> 00:28:03,320 Speaker 1: after subtract the expansion also, then the question is where 598 00:28:03,359 --> 00:28:04,200 Speaker 1: is everything going? 599 00:28:04,680 --> 00:28:06,840 Speaker 2: Okay, I see, so we've measured the velocities of all 600 00:28:06,880 --> 00:28:09,600 Speaker 2: the galaxies and superclusters and stars out there in space, 601 00:28:09,720 --> 00:28:11,760 Speaker 2: and we've measured how they move relative to the cosmic 602 00:28:11,800 --> 00:28:14,720 Speaker 2: microrerate background radiation. And you're saying it should be zero 603 00:28:14,880 --> 00:28:17,280 Speaker 2: if you think about it, because it should average out, 604 00:28:17,400 --> 00:28:18,280 Speaker 2: but is it. 605 00:28:18,280 --> 00:28:21,159 Speaker 1: It does not average out to zero. And that's the 606 00:28:21,280 --> 00:28:26,120 Speaker 1: dark flow. The dark flow is this extra unexplained velocity 607 00:28:26,160 --> 00:28:29,679 Speaker 1: of all of these galaxies relative to the CMB. After 608 00:28:29,800 --> 00:28:33,680 Speaker 1: subtracting out the expansion, turns out the galaxies are pointing 609 00:28:33,760 --> 00:28:34,719 Speaker 1: in a certain direction. 610 00:28:35,000 --> 00:28:36,520 Speaker 2: Wait, what where are they going? 611 00:28:38,360 --> 00:28:40,680 Speaker 1: So they did this really cool study where they measured 612 00:28:40,720 --> 00:28:43,160 Speaker 1: the velocities of a bunch of different galaxies. 613 00:28:43,480 --> 00:28:45,880 Speaker 2: And this is you've measured like everything like the whole 614 00:28:45,920 --> 00:28:47,480 Speaker 2: observable universe that we can see. 615 00:28:47,920 --> 00:28:50,600 Speaker 1: No, definitely not. That would take way too long. What 616 00:28:50,640 --> 00:28:53,640 Speaker 1: they did is they found like seven hundred clusters out 617 00:28:53,680 --> 00:28:56,560 Speaker 1: there in the universe and they measure the velocities of those. 618 00:28:56,920 --> 00:29:00,720 Speaker 1: So again, not even individual galaxies like galaxy cluster. They 619 00:29:00,720 --> 00:29:03,120 Speaker 1: wanted to like scan as far as they could across 620 00:29:03,160 --> 00:29:06,440 Speaker 1: the observable universe. But you know there's zillions and zillions 621 00:29:06,480 --> 00:29:08,600 Speaker 1: of galaxies. If you did the whole project, it would 622 00:29:08,600 --> 00:29:09,120 Speaker 1: take forever. 623 00:29:09,400 --> 00:29:12,320 Speaker 2: So then isn't that a really tiny sample of the 624 00:29:12,360 --> 00:29:13,120 Speaker 2: whole universe. 625 00:29:13,600 --> 00:29:16,840 Speaker 1: Absolutely, it's a tiny sample, but they measured it across 626 00:29:16,880 --> 00:29:20,320 Speaker 1: the universe, so they hope there's no bias. And they 627 00:29:20,480 --> 00:29:22,760 Speaker 1: know how much data they have, so they can measure 628 00:29:22,760 --> 00:29:25,960 Speaker 1: the statistical uncertainty there. So if they measure a velocity 629 00:29:25,960 --> 00:29:28,280 Speaker 1: that's smaller than their uncertainty, then they say, okay, it's 630 00:29:28,320 --> 00:29:31,560 Speaker 1: consistent with zero. If they measure something much bigger than 631 00:29:31,560 --> 00:29:34,760 Speaker 1: their uncertainty, they can still tell that it's happening. Like 632 00:29:34,800 --> 00:29:37,040 Speaker 1: if you only measure the speed of two cars zooming 633 00:29:37,040 --> 00:29:39,480 Speaker 1: biber they're going one hundred miles an hour, then that's 634 00:29:39,560 --> 00:29:42,520 Speaker 1: very likely the average speed of your road is not zero, 635 00:29:42,640 --> 00:29:44,040 Speaker 1: it's closer to one hundred. 636 00:29:44,880 --> 00:29:48,280 Speaker 2: Okay, so that's a big mystery. Like you've measured the 637 00:29:48,320 --> 00:29:50,800 Speaker 2: velocity of while the superclusters out there, or at least 638 00:29:50,800 --> 00:29:53,440 Speaker 2: a sample of them, and they don't seem to be 639 00:29:53,520 --> 00:29:57,000 Speaker 2: standing still relative to the background of the universe. 640 00:29:57,760 --> 00:30:00,160 Speaker 1: And they use this very cool technique to measure the 641 00:30:00,200 --> 00:30:03,200 Speaker 1: velocities of these galaxies because these clusters can be hard 642 00:30:03,240 --> 00:30:05,440 Speaker 1: to see. And so what they did is they looked 643 00:30:05,480 --> 00:30:09,240 Speaker 1: at CMB photons passing through these clouds of hot gas. 644 00:30:09,360 --> 00:30:11,880 Speaker 1: As the CMB photons passed through them, they get a 645 00:30:11,920 --> 00:30:15,000 Speaker 1: little bit of boost of energy from interacting with these clouds. 646 00:30:15,240 --> 00:30:18,000 Speaker 1: You can use this to see distant galaxies just by 647 00:30:18,040 --> 00:30:21,200 Speaker 1: like their effect on the CMB, Like if those photons 648 00:30:21,240 --> 00:30:24,000 Speaker 1: have passed through the blob of gas, then you can 649 00:30:24,040 --> 00:30:26,480 Speaker 1: tell and you can tell the velocity of that blob 650 00:30:26,520 --> 00:30:29,200 Speaker 1: of gas. It's like an extra little Doppler shift there. 651 00:30:29,440 --> 00:30:32,440 Speaker 2: M Okay, So everything seems to be moving relative to 652 00:30:32,440 --> 00:30:34,680 Speaker 2: the background of the universe by a lot or is 653 00:30:34,720 --> 00:30:36,200 Speaker 2: it like a little tiny drift. 654 00:30:36,320 --> 00:30:38,280 Speaker 1: Well, it depends on your scale of reference. But like 655 00:30:38,360 --> 00:30:42,200 Speaker 1: it's moving an eight hundred to one thousand kilometers per second. 656 00:30:42,600 --> 00:30:45,400 Speaker 1: You add it all up, it's really a non zero number. 657 00:30:45,520 --> 00:30:48,360 Speaker 1: It's pointing sort of in the direction of the Centaurus 658 00:30:48,360 --> 00:30:52,520 Speaker 1: and Hydra constellations, which listeners might remember is sort of 659 00:30:52,560 --> 00:30:55,520 Speaker 1: in the same direction as what we call the great attractor, 660 00:30:56,040 --> 00:30:59,040 Speaker 1: which is behind the zone of avoidance in our galaxy. 661 00:30:59,120 --> 00:31:01,280 Speaker 1: Like our galaxy is a big disc, right, and so 662 00:31:01,320 --> 00:31:03,520 Speaker 1: you can look up above the disc, or down below 663 00:31:03,560 --> 00:31:05,960 Speaker 1: the disc, or sort of out away from the center 664 00:31:06,000 --> 00:31:08,400 Speaker 1: of the galaxy. Those directions are pretty easy to see 665 00:31:08,400 --> 00:31:10,720 Speaker 1: because you're not looking through a lot of dense galaxy. 666 00:31:10,760 --> 00:31:12,600 Speaker 1: But if you try to look through the center of 667 00:31:12,640 --> 00:31:15,200 Speaker 1: the disc itself, or even through the center of the galaxy, 668 00:31:15,320 --> 00:31:17,240 Speaker 1: there's a lot of stuff there, a lot of gas 669 00:31:17,280 --> 00:31:19,680 Speaker 1: and dust and other stars and black holes that block 670 00:31:19,720 --> 00:31:22,840 Speaker 1: our view. And in that direction there also tends to 671 00:31:22,880 --> 00:31:26,200 Speaker 1: be like a lot of gravitational motion within the observable universe. 672 00:31:26,600 --> 00:31:28,640 Speaker 1: So it's called the Great Attractor. We don't know what's 673 00:31:28,680 --> 00:31:31,480 Speaker 1: there exactly, because we can't see in that direction very well, 674 00:31:31,720 --> 00:31:34,320 Speaker 1: but they're already We thought there was a lot of 675 00:31:34,400 --> 00:31:37,560 Speaker 1: local gravitational motion in that direction towards sort of the 676 00:31:37,560 --> 00:31:40,960 Speaker 1: center of the Linikia supercluster, and now it looks like 677 00:31:41,040 --> 00:31:44,560 Speaker 1: the whole universe is also moving in that direction. Like 678 00:31:44,600 --> 00:31:47,520 Speaker 1: you add up all the galaxies in the universe, their 679 00:31:47,640 --> 00:31:51,320 Speaker 1: velocity on average points in the same direction as our 680 00:31:51,400 --> 00:31:53,000 Speaker 1: motion towards the Great Attractor. 681 00:31:53,120 --> 00:31:55,120 Speaker 2: And by all the galaxies in the universe, you mean 682 00:31:55,160 --> 00:31:56,760 Speaker 2: all the galaxies we can see. 683 00:31:56,680 --> 00:31:59,240 Speaker 1: I mean only these seven hundred clusters that were measured 684 00:31:59,240 --> 00:32:00,320 Speaker 1: by this one study. 685 00:32:01,040 --> 00:32:03,520 Speaker 2: Right right, Well, a zero sample of all of them. 686 00:32:03,840 --> 00:32:08,200 Speaker 1: Yeah, exactly, a tiny, tiny sample, but yes, statistically significant 687 00:32:08,240 --> 00:32:10,560 Speaker 1: sample of all of them, and they measured a big velocity. 688 00:32:10,560 --> 00:32:12,280 Speaker 1: This is a really surprising result. 689 00:32:12,560 --> 00:32:15,280 Speaker 2: So they've measured how things are moving, and you're saying 690 00:32:15,280 --> 00:32:18,120 Speaker 2: they're moving in a particular direction, which seems to be 691 00:32:18,160 --> 00:32:22,080 Speaker 2: in the direction of something really really extra big compared 692 00:32:22,160 --> 00:32:24,120 Speaker 2: to the size of the observable universe. 693 00:32:24,280 --> 00:32:25,960 Speaker 1: Yeah, And I don't want to confuse people, because there's 694 00:32:25,960 --> 00:32:28,600 Speaker 1: two different motions we're talking about here. Like one is 695 00:32:28,680 --> 00:32:32,080 Speaker 1: our particular peculiar motion, the motion of Andromeda and the 696 00:32:32,080 --> 00:32:35,160 Speaker 1: milky way in our little cluster is being pulled towards 697 00:32:35,160 --> 00:32:38,120 Speaker 1: the center of the Lina Kia Clue supercluster by some 698 00:32:38,280 --> 00:32:42,200 Speaker 1: big mass that's within our universe. Right, that's our sort 699 00:32:42,200 --> 00:32:44,720 Speaker 1: of local peculiar motion. But then you add up all 700 00:32:44,720 --> 00:32:47,360 Speaker 1: the peculiar motion of the whole universe, and that also 701 00:32:47,480 --> 00:32:50,560 Speaker 1: seems to be headed coincidentally, maybe I don't know, in 702 00:32:50,640 --> 00:32:54,240 Speaker 1: the same direction. So like, the whole universe is also 703 00:32:54,320 --> 00:32:56,880 Speaker 1: moving and its arrow is in the same direction as 704 00:32:56,960 --> 00:33:00,480 Speaker 1: our local motion towards the great attractor. So sort of 705 00:33:00,560 --> 00:33:02,520 Speaker 1: like back to the analogy of boats in the river, 706 00:33:02,720 --> 00:33:05,240 Speaker 1: we discover that, oh, our boat is moving in some 707 00:33:05,360 --> 00:33:07,680 Speaker 1: direction relative to the river, and then we add of 708 00:33:07,760 --> 00:33:10,040 Speaker 1: all the boats and like, oh my gosh, everybody's moving 709 00:33:10,040 --> 00:33:12,760 Speaker 1: in that direction. What's going on? It's this as something 710 00:33:12,840 --> 00:33:14,920 Speaker 1: much bigger than just the Great Attractor. 711 00:33:15,040 --> 00:33:18,040 Speaker 2: The Great Attractor is within our supercluster of galaxies, or 712 00:33:18,080 --> 00:33:19,040 Speaker 2: it's outside of it. 713 00:33:19,080 --> 00:33:20,920 Speaker 1: We don't know what the Great Attractor is. We think 714 00:33:20,920 --> 00:33:23,120 Speaker 1: it might be something super massive at the core of 715 00:33:23,160 --> 00:33:27,720 Speaker 1: our supercluster. So yeah, probably it's within our supercluster. But 716 00:33:27,840 --> 00:33:30,800 Speaker 1: the dark flow is the motion of everything in the universe, 717 00:33:31,080 --> 00:33:33,880 Speaker 1: coincidentally or not, I don't know, in the same direction 718 00:33:34,280 --> 00:33:36,560 Speaker 1: as our motion towards our supercluster. 719 00:33:37,120 --> 00:33:39,760 Speaker 2: Well, like, we're next to this great attractor and we're 720 00:33:39,760 --> 00:33:42,320 Speaker 2: moving towards it. Are you saying then that when you 721 00:33:42,360 --> 00:33:44,880 Speaker 2: measure out the whole universe, even the stuff behind the 722 00:33:44,880 --> 00:33:49,040 Speaker 2: Great Attractor is moving towards the Great Attractor, meaning towards us. 723 00:33:49,240 --> 00:33:51,240 Speaker 1: No, the stuff behind the Great Attractor is moving in 724 00:33:51,280 --> 00:33:54,880 Speaker 1: the same direction as us, meaning away from the Great Attractor. 725 00:33:55,400 --> 00:33:58,280 Speaker 1: So the overall motion is in the same direction, not 726 00:33:58,320 --> 00:34:00,400 Speaker 1: towards the Great Attractor, but in the same direct is 727 00:34:00,440 --> 00:34:02,240 Speaker 1: our motion towards as a great attractor. 728 00:34:02,440 --> 00:34:05,600 Speaker 2: Oh so the Great Attractor is just maybe a red herring, 729 00:34:05,880 --> 00:34:07,800 Speaker 2: it's not really doing anything. 730 00:34:08,040 --> 00:34:09,920 Speaker 1: Maybe, I don't know. It's sort of weird that it 731 00:34:09,920 --> 00:34:12,160 Speaker 1: would be a coincidence, but it might just be Yes. 732 00:34:12,680 --> 00:34:15,279 Speaker 2: All right, well, let's dig into what that could mean, 733 00:34:15,320 --> 00:34:18,000 Speaker 2: what could be causing the dark flow of the universe, 734 00:34:18,040 --> 00:34:19,680 Speaker 2: and whether or not we do have to call the 735 00:34:19,680 --> 00:34:22,799 Speaker 2: plumbers to fix it or not. So let's dig into that. 736 00:34:22,960 --> 00:34:38,080 Speaker 2: But first let's take another quick break. All right, we're 737 00:34:38,080 --> 00:34:40,279 Speaker 2: talking about the dark flow of the universe, which is 738 00:34:40,440 --> 00:34:42,960 Speaker 2: this idea that it seems like everything in the universe 739 00:34:43,080 --> 00:34:46,400 Speaker 2: is moving in a particular direction and we don't know why. 740 00:34:46,520 --> 00:34:49,320 Speaker 1: We definitely don't know why, which is why we slapped 741 00:34:49,360 --> 00:34:51,799 Speaker 1: our familiar dark label on this thing. 742 00:34:52,200 --> 00:34:55,360 Speaker 2: Or I guess it's moving relative to the cosmic microwave background. 743 00:34:55,440 --> 00:34:57,359 Speaker 2: Could it be a the microwave background is the one 744 00:34:57,360 --> 00:34:58,880 Speaker 2: that's moving or has a bias. 745 00:34:59,280 --> 00:35:01,799 Speaker 1: Well, the motion is relative, so I'm not sure what 746 00:35:01,880 --> 00:35:03,799 Speaker 1: it means to say the CNB is the one that's 747 00:35:03,840 --> 00:35:07,360 Speaker 1: moving like relative to what relative to all the galaxies? Yes, 748 00:35:07,480 --> 00:35:09,279 Speaker 1: but the motion is relative, so you can't just like 749 00:35:09,320 --> 00:35:12,000 Speaker 1: ascribe it to one and not the other. But it's 750 00:35:12,040 --> 00:35:15,399 Speaker 1: the relative motion that's curious, right, because we think that 751 00:35:15,440 --> 00:35:18,080 Speaker 1: the stuff that made the galaxies, it's the same stuff 752 00:35:18,200 --> 00:35:21,040 Speaker 1: that made that CMB light. So that plasma that made 753 00:35:21,040 --> 00:35:24,040 Speaker 1: the CMB light, its overall motion should be the same 754 00:35:24,320 --> 00:35:27,200 Speaker 1: as the galaxies, because the plasma is what turned into 755 00:35:27,239 --> 00:35:31,200 Speaker 1: the galaxies, unless there was something else involved, unless there's 756 00:35:31,239 --> 00:35:35,040 Speaker 1: something else pulling on these galaxies that didn't pull on 757 00:35:35,080 --> 00:35:35,600 Speaker 1: the CMB. 758 00:35:36,080 --> 00:35:38,520 Speaker 2: I mean, like, if you zoom out of where we 759 00:35:38,600 --> 00:35:42,520 Speaker 2: are our supercluster, our galaxies are superclusters, maybe we're orbiting 760 00:35:42,560 --> 00:35:46,719 Speaker 2: around something bigger then, maybe even the bigger than the 761 00:35:46,719 --> 00:35:48,320 Speaker 2: observable universe exactly. 762 00:35:48,360 --> 00:35:50,799 Speaker 1: And we often talk about the observable universe as our 763 00:35:50,880 --> 00:35:53,799 Speaker 1: limit of the things that we can see, But there's 764 00:35:53,800 --> 00:35:56,960 Speaker 1: an important subtlety there. The observable universe is what we 765 00:35:56,960 --> 00:35:59,840 Speaker 1: can see now, what we can interact with now. The 766 00:36:00,080 --> 00:36:03,080 Speaker 1: universe is expanding, right, and things used to be closer 767 00:36:03,120 --> 00:36:05,480 Speaker 1: to us. So there are things that used to be 768 00:36:05,560 --> 00:36:07,880 Speaker 1: in our observable universe that we used to be able 769 00:36:07,880 --> 00:36:09,680 Speaker 1: to interact with us, that used to be able to 770 00:36:09,760 --> 00:36:12,960 Speaker 1: affect us, which no longer can. So it might be 771 00:36:13,040 --> 00:36:16,279 Speaker 1: that by looking deep into our past and understanding how 772 00:36:16,320 --> 00:36:19,279 Speaker 1: the universe has been affected, we can see hints of 773 00:36:19,360 --> 00:36:22,840 Speaker 1: things that affected us which have now left our observable universe. 774 00:36:22,960 --> 00:36:25,600 Speaker 1: It's sort of like a way to sneak into seeing 775 00:36:25,680 --> 00:36:28,800 Speaker 1: things that are now outside the observable universe. 776 00:36:29,120 --> 00:36:33,879 Speaker 2: Wait, what because of this motion, like, maybe it tells 777 00:36:33,960 --> 00:36:35,160 Speaker 2: us where it's been. 778 00:36:35,480 --> 00:36:39,200 Speaker 1: Yeah, exactly. What if there was something really massive, something 779 00:36:39,400 --> 00:36:43,800 Speaker 1: crazy massive, in our universe early on, and it created 780 00:36:43,840 --> 00:36:47,160 Speaker 1: this gravitational tug towards it, and now it's left our 781 00:36:47,200 --> 00:36:50,399 Speaker 1: observable universe, so it's not in our universe anymore. If 782 00:36:50,440 --> 00:36:52,800 Speaker 1: you then looked at the motion of just the stuff 783 00:36:52,800 --> 00:36:56,000 Speaker 1: in our observable universe, you would see it all moving 784 00:36:56,040 --> 00:37:00,440 Speaker 1: towards this mysterious source of gravity and attraction, even though 785 00:37:00,480 --> 00:37:03,080 Speaker 1: you wouldn't see that thing itself because it's now left 786 00:37:03,160 --> 00:37:06,960 Speaker 1: our observable universe. So something that's now outside of our 787 00:37:07,040 --> 00:37:10,799 Speaker 1: observable universe was once inside of it, right then it 788 00:37:10,920 --> 00:37:14,319 Speaker 1: might have still left an imprint on the motion of galaxies. 789 00:37:14,640 --> 00:37:17,160 Speaker 2: Meaning like maybe we could deduce where the Sun is 790 00:37:17,200 --> 00:37:19,040 Speaker 2: and what the sun is just by looking at the 791 00:37:19,160 --> 00:37:21,520 Speaker 2: orbit of the Earth without having to actually look at 792 00:37:21,560 --> 00:37:21,759 Speaker 2: the Sun. 793 00:37:21,840 --> 00:37:23,520 Speaker 1: Yeah, exactly. You don't need to see the Sun in 794 00:37:23,600 --> 00:37:26,759 Speaker 1: order to know that the Sun is there, and so 795 00:37:26,960 --> 00:37:29,919 Speaker 1: even though this thing is outside our observable universe, it's 796 00:37:29,960 --> 00:37:33,279 Speaker 1: within our past light cone. Our past light cone is 797 00:37:33,320 --> 00:37:35,560 Speaker 1: all the stuff that we have interacted with in the 798 00:37:35,600 --> 00:37:38,719 Speaker 1: past that could have affected us in the past. And 799 00:37:38,760 --> 00:37:41,239 Speaker 1: the expansion of the universe is pulling things outside of 800 00:37:41,239 --> 00:37:43,799 Speaker 1: our light cone, making it impossible to interact with that 801 00:37:43,840 --> 00:37:46,600 Speaker 1: stuff because space is expanding faster than the speed of light. 802 00:37:46,719 --> 00:37:50,280 Speaker 1: But it is possible that there was once something very dense, 803 00:37:50,400 --> 00:37:54,800 Speaker 1: some intense mass, some source of incredible gravity that affected 804 00:37:54,800 --> 00:37:58,360 Speaker 1: the formation of the whole universe that we now can't see. 805 00:37:59,320 --> 00:38:01,759 Speaker 2: I see it like you know, how we found out 806 00:38:01,800 --> 00:38:04,719 Speaker 2: that the Earth is just orbiting around the Sun, and 807 00:38:04,760 --> 00:38:07,640 Speaker 2: then eventually we just find out that the Solar system, 808 00:38:07,680 --> 00:38:10,080 Speaker 2: the Sun is just kind of in a corner of 809 00:38:10,080 --> 00:38:12,360 Speaker 2: the Milky Way galaxy, orbiting around the center of the 810 00:38:12,360 --> 00:38:15,440 Speaker 2: Milky Way galaxy, not even close to the center of it. 811 00:38:15,480 --> 00:38:18,960 Speaker 2: And now maybe we're finding out that our whole observable universe, 812 00:38:19,080 --> 00:38:22,120 Speaker 2: everything that we can see, all those bazillions of stars, 813 00:38:22,120 --> 00:38:24,279 Speaker 2: maybe we're just like at the corner or at the 814 00:38:24,400 --> 00:38:29,560 Speaker 2: edge of some sort of a bigger massive of stuff 815 00:38:29,600 --> 00:38:30,200 Speaker 2: in the universe. 816 00:38:30,360 --> 00:38:32,880 Speaker 1: Exactly. And we like to imagine that the whole universe, 817 00:38:32,960 --> 00:38:35,360 Speaker 1: if it's infinite, is filled with the same kind of stuff, 818 00:38:35,719 --> 00:38:38,200 Speaker 1: and that our chunk and the observable universe we happen 819 00:38:38,200 --> 00:38:40,439 Speaker 1: to live in is probably an average chunk, and any 820 00:38:40,520 --> 00:38:42,640 Speaker 1: chunk you would all average out to zero. But it 821 00:38:42,719 --> 00:38:44,440 Speaker 1: might not be the case, right. It might be that 822 00:38:44,480 --> 00:38:47,279 Speaker 1: there is some larger structure. There are like things that 823 00:38:47,320 --> 00:38:49,520 Speaker 1: are denser and heavier and chance so that if you 824 00:38:49,600 --> 00:38:52,880 Speaker 1: take a random slice of the universe, you don't on 825 00:38:52,960 --> 00:38:55,600 Speaker 1: average get zero. It gives you a picture as to like, 826 00:38:55,640 --> 00:38:58,880 Speaker 1: what is that nearby larger structure. I think it's super 827 00:38:58,920 --> 00:39:02,040 Speaker 1: cool that we could like make measturements in our observable universe. 828 00:39:02,360 --> 00:39:06,080 Speaker 1: It get glimpses for what's beyond, right, which sometimes felt 829 00:39:06,080 --> 00:39:09,200 Speaker 1: like an impenetrable wall, like a dark wall beyond which 830 00:39:09,239 --> 00:39:11,879 Speaker 1: we couldn't see. But we can dig out clues from 831 00:39:11,920 --> 00:39:14,359 Speaker 1: the history of the universe to figure out what has 832 00:39:14,400 --> 00:39:16,400 Speaker 1: happened that we can no longer see. 833 00:39:16,520 --> 00:39:18,640 Speaker 2: Well, it's a little bit sort of like the picture 834 00:39:18,640 --> 00:39:20,560 Speaker 2: we have of the Milky Way galaxy where we live, 835 00:39:20,680 --> 00:39:22,480 Speaker 2: like we really can't see it. We're in the middle 836 00:39:22,520 --> 00:39:24,319 Speaker 2: of it. But we can sort of reconstruct what it 837 00:39:24,400 --> 00:39:26,759 Speaker 2: might be or what it is, just by looking at 838 00:39:26,760 --> 00:39:28,160 Speaker 2: the immediate things around us. 839 00:39:28,280 --> 00:39:30,680 Speaker 1: Yeah, that's true. The things that are obscuring our vision 840 00:39:30,719 --> 00:39:32,880 Speaker 1: are different. In the case of the Milky Way galaxy, 841 00:39:32,880 --> 00:39:34,799 Speaker 1: it's like the gas and the dust and other sort 842 00:39:34,840 --> 00:39:37,720 Speaker 1: of practical stuff, and in the case of the observable universe, 843 00:39:37,800 --> 00:39:40,600 Speaker 1: it's the speed of light. But yeah, it's a good analogy. However, 844 00:39:40,640 --> 00:39:42,359 Speaker 1: of course there's controversy about this. 845 00:39:42,520 --> 00:39:46,240 Speaker 2: Is it about the name beyond it? A dark flow 846 00:39:46,520 --> 00:39:49,200 Speaker 2: was maybe a terrible idea because it's not really dark. 847 00:39:51,360 --> 00:39:54,800 Speaker 1: It does kind of flow, though, the controversy is about 848 00:39:54,800 --> 00:39:57,759 Speaker 1: whether it exists. So this measurement was made originally with 849 00:39:57,800 --> 00:40:00,960 Speaker 1: like CMB data from the w MAP satellite, sort of 850 00:40:00,960 --> 00:40:04,200 Speaker 1: an intermediate satellite, not the most precise data we have 851 00:40:04,280 --> 00:40:06,240 Speaker 1: about the cosmic microwave background radiation. 852 00:40:06,480 --> 00:40:08,320 Speaker 2: Wait, wait, what is the WMAP. 853 00:40:08,400 --> 00:40:10,960 Speaker 1: I think it's named after Wilkinson. It's a satellite out 854 00:40:10,960 --> 00:40:14,839 Speaker 1: in space that picks up these CMB photons. They're very 855 00:40:14,920 --> 00:40:18,040 Speaker 1: very low energy photons, super long wavelengths. You need a 856 00:40:18,120 --> 00:40:20,520 Speaker 1: very sort of specialized equipment to pick them up. The 857 00:40:20,680 --> 00:40:22,920 Speaker 1: w MAP satellite is part of a long history of 858 00:40:22,960 --> 00:40:25,480 Speaker 1: these satellites. It was Kobe was the first one, then 859 00:40:25,680 --> 00:40:28,800 Speaker 1: w MAP and then PLANK these more and more precise 860 00:40:29,120 --> 00:40:31,880 Speaker 1: based telescope. Yeah, it's a space telescope. It's an instrument 861 00:40:31,960 --> 00:40:33,719 Speaker 1: out in space that picks up these photons. 862 00:40:34,320 --> 00:40:37,480 Speaker 2: And this one who specialize on the CMB and then 863 00:40:37,480 --> 00:40:40,520 Speaker 2: what we also used to measure the expansion and the 864 00:40:40,560 --> 00:40:42,560 Speaker 2: motion of these galaxies. 865 00:40:42,680 --> 00:40:45,560 Speaker 1: Yeah, you can learn so much from the CMB. Absolutely, 866 00:40:45,920 --> 00:40:49,000 Speaker 1: very very general, very powerful. That's why WMAP is such 867 00:40:49,040 --> 00:40:51,880 Speaker 1: an important thing, and why Kobe won, why the Kobe 868 00:40:51,920 --> 00:40:55,160 Speaker 1: satellite folks won a Nobel prize, and why PLANK was 869 00:40:55,160 --> 00:40:58,280 Speaker 1: such an important thing. Plank is the follow up to WMAP. Anyway, 870 00:40:58,280 --> 00:41:01,240 Speaker 1: these results came from an analysis of seven hundred clusters 871 00:41:01,320 --> 00:41:03,719 Speaker 1: with the w MAP data, and then they reanalyze this 872 00:41:03,920 --> 00:41:06,480 Speaker 1: using the PLANK data, so more precise, more recent data, 873 00:41:06,600 --> 00:41:09,719 Speaker 1: larger data set. And there's a disagreement about the results there. 874 00:41:09,760 --> 00:41:12,000 Speaker 1: Like one group says, yes, we see the dark flow 875 00:41:12,040 --> 00:41:14,720 Speaker 1: in the PLANK data. Another group says, no, we analyze 876 00:41:14,760 --> 00:41:16,440 Speaker 1: that same data, we don't see anything. 877 00:41:16,760 --> 00:41:20,000 Speaker 2: What cann't They just crosscheck and figure out why they're different. 878 00:41:20,280 --> 00:41:22,719 Speaker 1: They're working on that but it's complicated because when you 879 00:41:22,800 --> 00:41:26,040 Speaker 1: do these analysis, there's so many assumptions, and two different 880 00:41:26,080 --> 00:41:28,920 Speaker 1: groups are going to make different assumptions, and those assumptions 881 00:41:28,960 --> 00:41:30,200 Speaker 1: are sometimes hard. 882 00:41:29,920 --> 00:41:31,960 Speaker 2: To spot, like what kind of assumptions. 883 00:41:32,200 --> 00:41:34,240 Speaker 1: Well, there's all sorts of details you need to understand 884 00:41:34,280 --> 00:41:37,560 Speaker 1: about how the CMB photons are boosted as they pass 885 00:41:37,640 --> 00:41:40,120 Speaker 1: through this hot gas, so people have a model of that. 886 00:41:40,160 --> 00:41:43,520 Speaker 1: Nobody's modeling all of the details of every individual photon 887 00:41:43,800 --> 00:41:47,040 Speaker 1: down to all the microphysics. It's always a simplification, and 888 00:41:47,120 --> 00:41:50,160 Speaker 1: how those simplifications are made, and whether they're valid, and 889 00:41:50,200 --> 00:41:53,719 Speaker 1: whether the simplifications introduce errors, and whether those errors are important. 890 00:41:53,840 --> 00:41:56,239 Speaker 1: There's a long series of decisions people make when they 891 00:41:56,239 --> 00:41:58,640 Speaker 1: analyze these data. That's why it's important to have cross 892 00:41:58,719 --> 00:42:02,239 Speaker 1: checks because helps you reveal where those decisions could be 893 00:42:02,280 --> 00:42:04,600 Speaker 1: biasing your results. So what that tells us is like, 894 00:42:04,640 --> 00:42:06,719 Speaker 1: there's something funky in one of these analyzes, and you're right, 895 00:42:06,719 --> 00:42:08,640 Speaker 1: they need to cross check and drill down. But it's 896 00:42:08,680 --> 00:42:10,799 Speaker 1: not trivial. It's not like they're doing the same calculation 897 00:42:11,080 --> 00:42:14,200 Speaker 1: and expect to get exactly the same number. They're probing 898 00:42:14,239 --> 00:42:16,520 Speaker 1: the same physical thing, but they're doing the calculation in 899 00:42:16,600 --> 00:42:17,360 Speaker 1: very different ways. 900 00:42:17,960 --> 00:42:21,239 Speaker 2: M I mean, couldn't they just like go to a 901 00:42:21,280 --> 00:42:25,520 Speaker 2: meeting together and figure it out, like I'm doing this, 902 00:42:25,719 --> 00:42:27,040 Speaker 2: what are you doing? Or are you doing that? 903 00:42:27,080 --> 00:42:27,239 Speaker 1: Oh? 904 00:42:27,239 --> 00:42:29,640 Speaker 2: Wait, that doesn't make any sense. What if you tried that? 905 00:42:30,480 --> 00:42:32,200 Speaker 1: Yeah? I think they are working on that. But I 906 00:42:32,280 --> 00:42:35,439 Speaker 1: think there's also a little bit of acrimony between these 907 00:42:35,480 --> 00:42:38,760 Speaker 1: two groups. I'm not sure it's always a friendly disagreement. Yes, 908 00:42:38,800 --> 00:42:43,840 Speaker 1: exactly is it dark drama? I mean, nobody's like murdering 909 00:42:43,880 --> 00:42:45,880 Speaker 1: other people's parents in the alleyway and leading them to 910 00:42:45,880 --> 00:42:48,400 Speaker 1: become the dark Knight of Justice or anything. It's not that. 911 00:42:48,320 --> 00:42:53,080 Speaker 2: Dark, but not yet apparently, stay tuned. Maybe there's a 912 00:42:53,080 --> 00:42:55,640 Speaker 2: Nobel prize at stake. Things will get ugly. 913 00:42:56,840 --> 00:42:59,600 Speaker 1: But what lies in the future is a deeper analysis 914 00:42:59,640 --> 00:43:02,160 Speaker 1: of this same data, and we hope maybe even more 915 00:43:02,200 --> 00:43:05,000 Speaker 1: refined data. Future measurements of the CNB can give us 916 00:43:05,000 --> 00:43:07,719 Speaker 1: an even clearer picture of what's out there, the motion 917 00:43:07,840 --> 00:43:10,640 Speaker 1: of the CMB and the motion of all these blobs 918 00:43:10,680 --> 00:43:13,480 Speaker 1: of gas and galaxies relative to the CMB. 919 00:43:13,760 --> 00:43:16,240 Speaker 2: So these folks are talking, and what are they saying 920 00:43:16,320 --> 00:43:19,680 Speaker 2: is maybe the probable cause if if there is a 921 00:43:19,719 --> 00:43:23,000 Speaker 2: relative motion to all these stars and galaxies around us. 922 00:43:23,040 --> 00:43:24,120 Speaker 2: What could be the cause of it? 923 00:43:24,360 --> 00:43:26,600 Speaker 1: So the only idea that's out there, if this thing 924 00:43:26,680 --> 00:43:29,640 Speaker 1: is real, is what we talked about earlier, some big 925 00:43:29,800 --> 00:43:33,320 Speaker 1: blob of stuff that's out there beyond our observable universe, 926 00:43:33,440 --> 00:43:37,239 Speaker 1: past our horizon, something very dense that once pulled on 927 00:43:37,360 --> 00:43:39,680 Speaker 1: all of us. So we all have this overall bias 928 00:43:39,719 --> 00:43:43,320 Speaker 1: in our peculiar motion. What that could be, nobody knows. 929 00:43:43,520 --> 00:43:46,560 Speaker 2: Wait, are you saying that maybe there was something bigger 930 00:43:46,560 --> 00:43:49,480 Speaker 2: than the observable universe that was pulling on all of 931 00:43:49,480 --> 00:43:52,359 Speaker 2: our galaxies that we can see, but now that it's 932 00:43:52,719 --> 00:43:55,240 Speaker 2: so far away from us, it doesn't affect us anymore, 933 00:43:55,400 --> 00:43:56,400 Speaker 2: or can't affect us. 934 00:43:56,680 --> 00:43:59,600 Speaker 1: Yeah, that's exactly right. Because the expansion of the universe 935 00:44:00,200 --> 00:44:03,560 Speaker 1: is faster than light. This expansion increases as distance grows, 936 00:44:03,880 --> 00:44:06,880 Speaker 1: and so things fall off the edge of our horizon. 937 00:44:07,280 --> 00:44:09,480 Speaker 1: There are some things which could interact with us, could 938 00:44:09,520 --> 00:44:12,839 Speaker 1: send us photons or pull on us, which now can 939 00:44:12,920 --> 00:44:16,360 Speaker 1: no longer. Like things near the edge of the observable universe. 940 00:44:16,360 --> 00:44:18,920 Speaker 1: We see photons from them, but some of them are 941 00:44:18,960 --> 00:44:21,839 Speaker 1: now past the edge of the observable universe, and if 942 00:44:21,840 --> 00:44:25,000 Speaker 1: they send us photons, those photons will never arrive because 943 00:44:25,000 --> 00:44:28,640 Speaker 1: space is expanding between us and those galaxies faster than 944 00:44:28,640 --> 00:44:31,719 Speaker 1: the speed of light. Sort of mind boggling to think about, right. 945 00:44:31,640 --> 00:44:34,440 Speaker 2: This thin gravity can only go as fast as the 946 00:44:34,440 --> 00:44:37,319 Speaker 2: speed of light. Right, so if something's moving or being 947 00:44:37,360 --> 00:44:39,759 Speaker 2: expanded away from most faster than the speed of light, 948 00:44:39,800 --> 00:44:41,680 Speaker 2: then even where we'll never feel it's gravity. 949 00:44:41,800 --> 00:44:44,359 Speaker 1: Exactly. Like if they shine a flashlight at you, you'll 950 00:44:44,400 --> 00:44:46,839 Speaker 1: never see it no matter how long you wait, which 951 00:44:46,880 --> 00:44:50,000 Speaker 1: also means you'll never feel its gravity. You might have 952 00:44:50,040 --> 00:44:52,560 Speaker 1: seen that flashlight earlier on, you might have felt their 953 00:44:52,600 --> 00:44:56,040 Speaker 1: gravity early on, but no longer. So again, this is 954 00:44:56,080 --> 00:44:57,920 Speaker 1: like a way to probe things that we might have 955 00:44:58,000 --> 00:45:01,000 Speaker 1: interacted with earlier in the history the universe that we 956 00:45:01,040 --> 00:45:02,120 Speaker 1: can no longer see. 957 00:45:02,320 --> 00:45:04,719 Speaker 2: You're saying, we'll see it like the spin it gave 958 00:45:04,840 --> 00:45:07,359 Speaker 2: us or the orbit it gave us. 959 00:45:07,480 --> 00:45:09,799 Speaker 1: Yeah, exactly. It's sort of like what happens if you 960 00:45:09,840 --> 00:45:13,520 Speaker 1: walk into a party five seconds after some celebrity does right, 961 00:45:13,560 --> 00:45:15,759 Speaker 1: and everybody's looking in the same direction, and you're like, 962 00:45:15,760 --> 00:45:17,239 Speaker 1: what's going on? Who was just here? 963 00:45:17,440 --> 00:45:18,560 Speaker 2: Who was that? Was that badman? 964 00:45:20,560 --> 00:45:23,520 Speaker 1: Or was that Kim Kardashian or is Kim Kardashian actually batman? 965 00:45:24,400 --> 00:45:26,760 Speaker 1: And you see the effect on the conversations. In everybody's 966 00:45:26,800 --> 00:45:28,880 Speaker 1: head is pointing in some direction. You don't see the person, 967 00:45:28,920 --> 00:45:30,839 Speaker 1: but you see the effect they left on. 968 00:45:30,800 --> 00:45:33,279 Speaker 2: The room, or so we think, right, we still have 969 00:45:33,360 --> 00:45:34,520 Speaker 2: to confirm these measurements. 970 00:45:34,719 --> 00:45:37,480 Speaker 1: Yeah, exactly. These are very difficult measurements to make. And 971 00:45:37,520 --> 00:45:39,920 Speaker 1: as you hear, there's not a consensus about whether the 972 00:45:40,000 --> 00:45:41,319 Speaker 1: dark flow is even a thing. 973 00:45:41,560 --> 00:45:45,000 Speaker 2: Well, boy, maybe should give it a different name. Would 974 00:45:45,000 --> 00:45:45,480 Speaker 2: you call it? 975 00:45:45,520 --> 00:45:47,520 Speaker 1: What would you call it? The dark Kardashian? 976 00:45:48,120 --> 00:45:50,600 Speaker 2: Well, I feel like the word dark didn't that originate 977 00:45:50,640 --> 00:45:53,160 Speaker 2: from the being invisible? Like dark matter. You can't see 978 00:45:53,160 --> 00:45:55,959 Speaker 2: it because it doesn't interact with the electromagnetic light. Because 979 00:45:56,040 --> 00:45:58,600 Speaker 2: if you're going to call anything that's mysterious dark, then 980 00:45:58,640 --> 00:45:59,719 Speaker 2: that's everything, isn't it. 981 00:46:00,080 --> 00:46:02,920 Speaker 1: The whole universe is kind of mysterious. I think that 982 00:46:03,040 --> 00:46:05,920 Speaker 1: dark means mysterious. It doesn't mean invisible because dark it 983 00:46:05,920 --> 00:46:08,800 Speaker 1: doesn't actually mean invisible, right, You can have invisible things 984 00:46:08,800 --> 00:46:12,239 Speaker 1: in bright light. Also, dark corners mean dark corners are 985 00:46:12,280 --> 00:46:14,200 Speaker 1: things that are like obscured, right, right. 986 00:46:14,239 --> 00:46:15,920 Speaker 2: But I guess what I mean is if you start 987 00:46:15,920 --> 00:46:19,160 Speaker 2: calling everything that's mysterious dark, then that's just going to 988 00:46:19,200 --> 00:46:20,080 Speaker 2: confuse everybody. 989 00:46:20,200 --> 00:46:21,359 Speaker 1: Yeah, that's probably true. Dark. 990 00:46:21,400 --> 00:46:24,760 Speaker 2: There's dark particles, there's you know, dark things in my fridge. 991 00:46:25,719 --> 00:46:29,080 Speaker 2: They're going to think people are thinking they're related to 992 00:46:29,160 --> 00:46:31,000 Speaker 2: dark matter and dark energy in the dark night. 993 00:46:31,280 --> 00:46:33,919 Speaker 1: Well, they're all mysterious, so they are all related in 994 00:46:33,920 --> 00:46:36,719 Speaker 1: that sense, the dark in the dark minds of physicists. 995 00:46:37,320 --> 00:46:39,759 Speaker 2: Maybe not in the physical in the physics sense, right. 996 00:46:39,719 --> 00:46:43,319 Speaker 1: Yeah, no, absolutely, they could have completely different physical explanations. 997 00:46:43,520 --> 00:46:45,400 Speaker 1: They're just currently not understood. 998 00:46:45,480 --> 00:46:47,080 Speaker 2: All right, Well, maybe you should just call it the 999 00:46:47,160 --> 00:46:49,239 Speaker 2: hubble flow and then just follow it up with we 1000 00:46:49,280 --> 00:46:51,920 Speaker 2: don't know what the hubble flow is or what's causing. 1001 00:46:51,760 --> 00:46:54,759 Speaker 1: It, but this is an addition to the hubble flow, Like, 1002 00:46:55,200 --> 00:46:57,400 Speaker 1: what on top of the hubble flow is happening in 1003 00:46:57,400 --> 00:46:58,880 Speaker 1: the universe? Is really the question? 1004 00:46:59,320 --> 00:47:01,919 Speaker 2: All right? Well, it sounds like the answer once again 1005 00:47:02,040 --> 00:47:05,880 Speaker 2: is stay tuned. There are mysterious workings in the universe, 1006 00:47:05,920 --> 00:47:08,960 Speaker 2: mysterious flows plumbing that we can't yet see out there 1007 00:47:09,000 --> 00:47:12,319 Speaker 2: in the universe that is hopefully leaking a little bit 1008 00:47:12,360 --> 00:47:14,640 Speaker 2: so that we know and we can to study. 1009 00:47:14,360 --> 00:47:16,400 Speaker 1: It, and we'd love to understand the universe, and so 1010 00:47:16,440 --> 00:47:18,560 Speaker 1: we're looking out there into the nice sky and trying 1011 00:47:18,560 --> 00:47:22,000 Speaker 1: to squeeze every tiny little drop of information out of 1012 00:47:22,000 --> 00:47:24,920 Speaker 1: the photons that do arrive to us. And it's incredible 1013 00:47:24,960 --> 00:47:26,719 Speaker 1: that we can even figure out that the universe is 1014 00:47:26,760 --> 00:47:29,319 Speaker 1: out there and what it's doing, and maybe even get 1015 00:47:29,320 --> 00:47:32,600 Speaker 1: a glimpse of what's past the edge of the observable universe. 1016 00:47:32,800 --> 00:47:34,920 Speaker 2: I wonder if physicists are like Batman. You know, you're 1017 00:47:34,920 --> 00:47:37,640 Speaker 2: looking up at the sky, you see a bad signal 1018 00:47:37,760 --> 00:47:40,880 Speaker 2: in the motion of the stars, and you're like duty calls. 1019 00:47:41,120 --> 00:47:45,879 Speaker 1: We're all totally ripped, just like Batman. Ripped. That wasn't 1020 00:47:45,920 --> 00:47:47,080 Speaker 1: a joke, man, Why are you laughing? 1021 00:47:48,200 --> 00:47:50,440 Speaker 2: Ripped in your minds and the abs of your minds 1022 00:47:50,880 --> 00:47:56,640 Speaker 2: and in the biceps of your typing fingers. Well, in 1023 00:47:56,680 --> 00:47:59,879 Speaker 2: any case, we hope you enjoyed that. Thanks for joining 1024 00:47:59,920 --> 00:48:01,960 Speaker 2: us us see you next time. 1025 00:48:06,360 --> 00:48:09,240 Speaker 1: For more science and curiosity, come find us on social 1026 00:48:09,280 --> 00:48:14,160 Speaker 1: media where we answer questions and post videos. We're on Twitter, Disborg, Insta, 1027 00:48:14,280 --> 00:48:17,720 Speaker 1: and now TikTok. Thanks for listening, and remember that Daniel 1028 00:48:17,760 --> 00:48:21,200 Speaker 1: and Jorge Explain the Universe is a production of iHeartRadio. 1029 00:48:21,480 --> 00:48:26,640 Speaker 1: For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple podcasts, 1030 00:48:26,760 --> 00:48:29,120 Speaker 1: or wherever you listen to your favorite shows.