WEBVTT - Supervoids 0:00:07.810 --> 0:00:09.569 When you look out into the night sky on a 0:00:09.590 --> 0:00:13.680 camping trip, you're seeing the best view in the universe. 0:00:14.240 --> 0:00:17.299 Much better than standing on a mountain top or on 0:00:17.320 --> 0:00:21.000 the top floor of a building. Stretching over zillions of 0:00:21.079 --> 0:00:24.950 light years of cosmic space, you're seeing entire stars and 0:00:25.070 --> 0:00:30.090 galaxies across this black ocean. It's amazing. But there's something 0:00:30.170 --> 0:00:32.230 else for you to see up there, for us to 0:00:32.310 --> 0:00:37.740 learn about. The empty bits. Between the galaxies stretch huge 0:00:37.800 --> 0:00:41.820 regions without all that flashy, glowy stuff. How is that 0:00:41.960 --> 0:00:45.780 all arranged? What is the map of galaxies in the universe? 0:00:45.860 --> 0:00:49.150 And what does that tell us about how the universe 0:00:49.229 --> 0:00:53.010 forms and the forces that shape it? Today in the pod, 0:00:53.030 --> 0:00:55.650 we're digging into the biggest maps we can make of 0:00:55.690 --> 0:00:59.750 the biggest stuff and the biggest non-stuff in the universe. 0:01:00.590 --> 0:01:04.970 Welcome to Daniel and Kelly's Extraordinary Mostly Empty Universe. 0:01:18.280 --> 0:01:19.759 Hello, I'm Kelly Wienersmith. 0:01:19.819 --> 0:01:23.290 I study parasites and space, and super void sounds like 0:01:23.330 --> 0:01:27.290 a sort of gothy concept, so 16-year-old Kelly is totally 0:01:27.330 --> 0:01:27.699 into it. 0:01:27.709 --> 0:01:32.750 Hi, I'm Daniel. I'm a particle physicist who likes to 0:01:32.790 --> 0:01:36.600 think about aliens, and I'm about 0% goth. So when 0:01:36.640 --> 0:01:39.260 I hear super void, I don't think black lipstick. I 0:01:39.280 --> 0:01:40.560 think Marvel characters. 0:01:41.170 --> 0:01:41.990 Oh, all right. 0:01:42.010 --> 0:01:44.710 Well, so Super Voids does make me think of gothy stuff, 0:01:44.730 --> 0:01:48.110 which reminds me of some of my favorite gothy characters, 0:01:48.210 --> 0:01:50.890 which are Frankenfurter from the Rocky. 0:01:50.710 --> 0:01:51.570 Horror Picture Show. 0:01:51.950 --> 0:01:54.090 Yes. R.I.P. Tim Curry. 0:01:54.510 --> 0:01:58.060 Exactly. And the devil in Legend, which, yes. 0:01:58.360 --> 0:02:01.240 So my question for you today is, what was Tim 0:02:01.280 --> 0:02:03.840 Curry's best role and why is it the saddest thing 0:02:03.900 --> 0:02:05.860 in the whole world that Tim Curry is gone? 0:02:05.880 --> 0:02:05.960 Okay. 0:02:06.610 --> 0:02:08.570 Because it's the saddest thing in the world that Tim 0:02:08.590 --> 0:02:09.370 Curry is gone. 0:02:09.510 --> 0:02:12.480 It is sad. He was wonderful. I loved him in Clue. Oh. 0:02:12.720 --> 0:02:17.010 You know, the hilarious movie. Wonderful. And I love a mystery. 0:02:17.169 --> 0:02:20.210 You know, for me, science is the biggest mystery in 0:02:20.230 --> 0:02:22.990 the universe. How does this all work? Who caused the 0:02:23.050 --> 0:02:28.220 ripples in the primordial plasma? You know, was it the 0:02:28.280 --> 0:02:31.480 butler with the candlestick in the early universe? Who knows? 0:02:32.120 --> 0:02:34.579 You are so good at keeping us on track. 0:02:35.020 --> 0:02:38.100 I'm doing my best here. Oh, my gosh. This car 0:02:38.139 --> 0:02:39.960 is going off into the weeds of Virginia. 0:02:39.980 --> 0:02:44.250 I just needed a moment to like vent and feel 0:02:44.340 --> 0:02:47.330 seen because I am just devastated about the loss of 0:02:47.370 --> 0:02:47.769 Tim Curry. 0:02:48.190 --> 0:02:50.160 Would you say that the loss of Tim Curry creates 0:02:50.190 --> 0:02:51.179 a void in your heart? 0:02:51.580 --> 0:02:55.040 A super void, Daniel. And so, and my heart is 0:02:55.100 --> 0:02:57.459 now cold and empty. 0:02:57.480 --> 0:03:00.310 And let's go ahead and change the subject before I 0:03:00.330 --> 0:03:03.169 get too emotional here and dig into super voids. 0:03:03.610 --> 0:03:05.770 Why are we talking about super voids today? 0:03:06.570 --> 0:03:10.750 We're talking about supervoids because they're super awesome. They're fascinating. 0:03:10.850 --> 0:03:14.250 They're one of the biggest things or non-things in the universe. 0:03:14.280 --> 0:03:17.400 They tell us so much about its history, about its future, 0:03:17.500 --> 0:03:20.419 about its formation, about how it works. And it's so 0:03:20.500 --> 0:03:23.390 hard to get them in your mind because they give 0:03:23.410 --> 0:03:25.790 you a sense of scale of the universe, you know? 0:03:26.120 --> 0:03:30.120 how tiny, how small, how insignificant we are, and yet 0:03:30.360 --> 0:03:33.780 how we can cast our minds to understanding the largest 0:03:34.000 --> 0:03:38.470 scale structures in the universe, which stretch across billions and 0:03:38.590 --> 0:03:41.850 zillions of light years. It's super awesome to think about 0:03:41.910 --> 0:03:44.630 super voids. And I'm not the only one who thinks so. 0:03:44.970 --> 0:03:48.110 We got a request from two listeners, Levi and Nathan, 0:03:48.270 --> 0:03:50.690 who wrote and said, hey, would you tell us why 0:03:50.730 --> 0:03:54.350 the universe has super voids. So that's why we're talking 0:03:54.370 --> 0:03:56.610 about super voids specifically today. 0:03:57.030 --> 0:04:00.370 Well, and I noted in that email that Levi also 0:04:00.430 --> 0:04:03.120 says he enjoys my poop jokes. And so this is 0:04:03.190 --> 0:04:05.000 a family that gets our podcast. 0:04:06.320 --> 0:04:08.920 Exactly. And we'll try to make as many poo jokes 0:04:08.980 --> 0:04:12.000 as we can in today's episode, just for you, Levi. 0:04:12.780 --> 0:04:15.260 I am trying to connect super voids to poo jokes. 0:04:15.300 --> 0:04:16.919 And the only thing I can think about is the 0:04:16.960 --> 0:04:21.870 prep for a colonoscopy. You are super voided at that point. 0:04:21.950 --> 0:04:24.610 But probably that joke's over Levi's head because Levi's a 0:04:24.690 --> 0:04:25.810 little bit younger, isn't he? 0:04:25.970 --> 0:04:26.410 Yeah. 0:04:26.430 --> 0:04:29.830 Yes, exactly. But maybe Levi thinks about super voids every 0:04:29.880 --> 0:04:31.040 time he's voiding himself. 0:04:31.620 --> 0:04:32.480 Okay. Well, good. 0:04:32.580 --> 0:04:32.859 Look it. 0:04:32.900 --> 0:04:34.680 We did it. We did it. We got the poop 0:04:34.700 --> 0:04:35.360 jokes in there. 0:04:35.440 --> 0:04:35.700 Yes. 0:04:36.040 --> 0:04:38.560 And, you know, a really important thing for understanding super 0:04:38.580 --> 0:04:41.450 voids and the structure of the universe is, is dark matter, 0:04:42.130 --> 0:04:44.190 which is its own poo joke right there. 0:04:44.630 --> 0:04:47.070 Oh, man, I love the work we do together, Daniel. 0:04:47.450 --> 0:04:49.169 It's the best. 0:04:49.589 --> 0:04:52.810 We are out here doing hard-hitting science. No, really, we 0:04:52.850 --> 0:04:55.370 are proving that it's possible to do deep dives into 0:04:55.390 --> 0:04:58.740 science and also make poo jokes. That is our niche 0:04:58.779 --> 0:05:01.659 in the SciComm community. That's right. But before we tell 0:05:01.680 --> 0:05:04.400 you what we think about super voids and dig into 0:05:04.440 --> 0:05:08.480 the cosmic history that created them and our confusion about them... 0:05:08.900 --> 0:05:12.539 I wondered what the extraordinaries thought about why the universe 0:05:12.720 --> 0:05:15.560 has super voids. So I reached out to our group 0:05:15.580 --> 0:05:18.940 of volunteers, which you are very, very welcome to join. 0:05:19.000 --> 0:05:23.240 Just write to us to questions at danielandkelly.org and you 0:05:23.260 --> 0:05:25.920 can join this crew. In the meantime, think about it 0:05:25.940 --> 0:05:28.400 for a minute. Why do you think the universe has 0:05:28.660 --> 0:05:29.700 super voids? 0:05:30.400 --> 0:05:33.870 The universe is expanding and the amount of stuff in 0:05:33.910 --> 0:05:34.890 it is not increasing. 0:05:35.350 --> 0:05:39.290 So we can fight all of those dastardly dark energy 0:05:39.770 --> 0:05:44.919 and dark matter criminals. Initial randomness allowed some parts to 0:05:44.960 --> 0:05:48.820 get denser and presumably some parts to get a lot sparser. 0:05:49.220 --> 0:05:51.860 It's for the same reason that my gravy has lumps 0:05:51.940 --> 0:05:53.640 in it. I don't know what that reason is, but 0:05:53.680 --> 0:05:56.480 I think it's the same reason. Collects in some places, 0:05:56.540 --> 0:05:58.289 then it has to clear out in others. 0:05:58.910 --> 0:06:01.969 I think it has to do with the way matter 0:06:02.010 --> 0:06:04.630 was created during the Big Bang. 0:06:05.360 --> 0:06:08.690 I would guess some astronomers saw some very cold or 0:06:08.830 --> 0:06:13.170 empty patch in space and could not avoid to give 0:06:13.230 --> 0:06:14.589 it a super name. 0:06:15.130 --> 0:06:17.910 Does not have to be uniform. I have no idea 0:06:17.950 --> 0:06:20.729 what a super void is. Is it like a really, 0:06:20.990 --> 0:06:25.460 really big void? Because of dark matter. A void is 0:06:25.520 --> 0:06:26.060 just void. 0:06:26.360 --> 0:06:28.500 Because of dark matter. 0:06:28.620 --> 0:06:29.440 It's because of dark matter. 0:06:29.480 --> 0:06:29.720 Yeah. 0:06:29.839 --> 0:06:30.840 We're confused. 0:06:30.900 --> 0:06:31.279 Help us. 0:06:32.080 --> 0:06:33.880 Oh, my gosh. I love the answers. 0:06:34.320 --> 0:06:38.159 Astronomers saw an empty patch and couldn't avoid giving it 0:06:38.279 --> 0:06:39.780 a super name. 0:06:39.960 --> 0:06:41.540 You are my new best friend. 0:06:42.100 --> 0:06:44.400 That's got everything you love, right? It's got a pun. 0:06:44.839 --> 0:06:48.219 It's got a dig against astronomers. 0:06:48.260 --> 0:06:51.110 I feel like it implies that astronomers give things good names. 0:06:51.200 --> 0:06:53.520 Oh, maybe they do. No, no, they don't, actually. What 0:06:53.560 --> 0:06:54.130 is it? 0:06:54.170 --> 0:06:56.970 The rings around Saturn or Jupiter or like A, B, C, 0:06:57.010 --> 0:06:57.589 and D or. 0:06:59.330 --> 0:07:02.830 Yeah, exactly. The solar system is a disaster. Even beyond 0:07:02.850 --> 0:07:06.589 planets and dwarf planets, you've got like centaurs and meteors 0:07:06.690 --> 0:07:08.650 and all sorts of stuff. It's a mess. 0:07:09.089 --> 0:07:09.650 It's a mess. 0:07:09.750 --> 0:07:12.680 But we are here to clear up confusion. And so 0:07:12.800 --> 0:07:15.300 let's jump right in. Daniel, what the heck is the 0:07:15.360 --> 0:07:16.040 super void? 0:07:18.600 --> 0:07:21.040 So to understand super voids, we first have to understand 0:07:21.180 --> 0:07:24.890 our cosmic context, like the structure of the universe around us. 0:07:25.460 --> 0:07:29.460 So let's start here in California or Virginia. California, by 0:07:29.480 --> 0:07:32.200 the way, feeling more like Virginia these days, you know, 0:07:32.240 --> 0:07:35.980 because it's like stinky and humid and gross and like, 0:07:37.060 --> 0:07:38.660 where do I even live anymore, man? 0:07:39.460 --> 0:07:43.000 I see that your handle on Riverside today is humidity hater. 0:07:43.160 --> 0:07:45.960 This is really living rent free in your brain. I'm 0:07:47.160 --> 0:07:48.140 not a humidity fan either. 0:07:48.160 --> 0:07:50.380 I mean, since we're putting ourselves in the cosmic context, 0:07:50.440 --> 0:07:52.940 it's important to note that Los Angeles yesterday was the 0:07:52.980 --> 0:07:56.380 most humid place in the country, which is breaking all 0:07:56.400 --> 0:07:58.160 the rules, if you ask me. 0:07:58.200 --> 0:07:59.280 That does not seem fair. 0:07:59.360 --> 0:08:03.480 Anyway, zoom out from the sticky issues here on planet Earth. 0:08:03.520 --> 0:08:05.820 And of course, we have our solar system. And the 0:08:05.900 --> 0:08:09.929 sun is just one of hundreds of billions of stars 0:08:10.110 --> 0:08:13.950 in the Milky Way swirling around in roughly a disk. 0:08:14.370 --> 0:08:16.570 And then our galaxy is not just one of zillions 0:08:16.750 --> 0:08:21.270 scattered through the universe. Galaxies themselves cluster. So we have 0:08:21.320 --> 0:08:24.840 the local cluster of galaxies, a bunch of galaxies that 0:08:24.860 --> 0:08:27.960 are gravitationally bound together, which doesn't mean that there's like 0:08:28.020 --> 0:08:31.060 some big object in the center around which everything is 0:08:31.200 --> 0:08:33.690 orbiting the way it is in the solar system. But 0:08:33.710 --> 0:08:35.569 it does mean that there is a center of mass 0:08:35.790 --> 0:08:38.810 of the local cluster and everything is swirling around that. 0:08:39.250 --> 0:08:39.970 Okay, I'm with you. 0:08:40.309 --> 0:08:43.349 All right, so we have clusters. And now clusters organize 0:08:43.410 --> 0:08:49.390 into superclusters, right? Astronomers, great names. And superclusters are not 0:08:49.530 --> 0:08:53.309 always gravitationally bound. They're like near each other in that 0:08:53.350 --> 0:08:55.010 you can look at them and say, oh, these clusters 0:08:55.120 --> 0:08:58.200 are near each other. But it's not clear whether gravity 0:08:58.260 --> 0:09:00.500 is strong enough to hold them together. Because remember, the 0:09:00.559 --> 0:09:04.839 universe is expanding. It's creating new space between everything. And 0:09:04.860 --> 0:09:08.120 that includes new space between California and Virginia, new space 0:09:08.160 --> 0:09:11.079 between Earth and the Sun, new space between the Sun 0:09:11.120 --> 0:09:13.780 and the center of the Milky Way. But because there's 0:09:13.840 --> 0:09:16.440 enough gravity to hold the Earth together and hold the 0:09:16.480 --> 0:09:18.619 Sun to the Earth and hold the Sun to the 0:09:18.660 --> 0:09:22.520 rest of the galaxy, those distances are not increasing. So 0:09:22.550 --> 0:09:26.130 the expansion of the universe is losing to gravity. But 0:09:26.190 --> 0:09:29.170 gravity gets weaker as distances get greater. So when you 0:09:29.210 --> 0:09:31.830 get to super voids, dark energy is starting to get 0:09:31.870 --> 0:09:35.340 powerful enough that it's going to overcome gravity. And that's 0:09:35.500 --> 0:09:38.220 right about the cutoff. So we don't think that all 0:09:38.260 --> 0:09:41.460 superclusters are technically objects in the sense that they're not 0:09:41.559 --> 0:09:44.280 gravitationally bound. We think that as time goes on, they 0:09:44.370 --> 0:09:47.349 probably will get pulled apart. But they're still sort of 0:09:47.490 --> 0:09:49.270 objects in the sense that they're near each other. And 0:09:49.290 --> 0:09:51.069 if you looked at them on a map, you'd probably 0:09:51.150 --> 0:09:52.290 draw a circle around them. 0:09:52.770 --> 0:09:54.709 Okay. That doesn't sound void-y. 0:09:55.250 --> 0:09:58.110 No, we're not at the voids yet. Okay. But now 0:09:58.150 --> 0:10:01.110 we've already zoomed out incredibly, right? Like from the Earth 0:10:01.330 --> 0:10:05.550 to the Sun to the galaxy to like clusters of 0:10:05.650 --> 0:10:09.890 galaxies to now super clusters of galaxies. It might feel 0:10:09.929 --> 0:10:11.570 like this is the biggest thing you could ever have 0:10:11.610 --> 0:10:14.430 in your head. Okay, now collapse all those super clusters 0:10:14.450 --> 0:10:16.390 down to a point because now we're going to zoom 0:10:16.460 --> 0:10:20.220 out so far that structure inside a super cluster is irrelevant. 0:10:20.660 --> 0:10:22.640 We're just going to treat each super cluster like a 0:10:22.760 --> 0:10:25.990 dot and we're going to ask, How are the superclusters 0:10:26.170 --> 0:10:30.500 organized across the universe? And they're not organized evenly. It's 0:10:30.520 --> 0:10:33.900 not like somebody sprinkled sand across the universe, each one 0:10:34.000 --> 0:10:38.560 being a supercluster. Instead, they form filaments. They form walls. 0:10:39.000 --> 0:10:43.320 They form bubbles. So there are sheets and filaments of superclusters. 0:10:44.040 --> 0:10:47.829 And inside those bubbles are the voids. That's where there 0:10:47.850 --> 0:10:52.000 are fewer galaxies and fewer superclusters. And so imagine like 0:10:52.059 --> 0:10:56.230 a foam, right? Where super clusters lie on the edges 0:10:56.270 --> 0:10:59.370 of the bubbles and inside the bubbles, there's comparatively less. 0:10:59.910 --> 0:11:01.910 All right, so my brain is now wondering why you 0:11:01.950 --> 0:11:04.690 can't get super voids on the outsides of the bubbles too. 0:11:04.750 --> 0:11:06.980 Am I just letting this analogy get stuck in my 0:11:07.020 --> 0:11:07.520 head too much? 0:11:07.920 --> 0:11:10.160 There is no outside to the bubbles. The universe is 0:11:10.240 --> 0:11:11.280 filled with these bubbles. 0:11:12.260 --> 0:11:12.340 Oh. 0:11:13.020 --> 0:11:15.740 Yes, the bubbles are everywhere. The universe is just bubbles. 0:11:15.760 --> 0:11:19.560 And it's the foam fills the whole universe. And everywhere 0:11:19.580 --> 0:11:22.000 you have a bubble edge where the bubbles meet, that's 0:11:22.040 --> 0:11:25.860 where you have superclusters, walls, sheets of superclusters. And inside, 0:11:26.179 --> 0:11:27.000 those are the voids. 0:11:27.559 --> 0:11:28.420 Whoa, okay. 0:11:29.059 --> 0:11:29.280 Yeah. 0:11:29.340 --> 0:11:32.559 Are they totally empty or just less empty than the 0:11:32.920 --> 0:11:33.540 outside of the bubble? 0:11:33.559 --> 0:11:36.319 Yeah, great question. They're not completely empty, right? It's a 0:11:36.440 --> 0:11:39.319 relative density. So we measure the density of stuff in 0:11:39.340 --> 0:11:42.820 the universe and we say anything less than like 10% 0:11:42.820 --> 0:11:46.200 of the mean density, we call that a void. And 0:11:46.240 --> 0:11:49.959 these things are pretty big. They have diameters like 10 0:11:49.960 --> 0:11:55.700 to 100 megaparsecs, which is like 300 million light years across. 0:11:56.040 --> 0:11:58.370 Oh my gosh. These are vast structures. And these are 0:11:58.410 --> 0:12:02.349 not super voids. These are just voids. These are just normal, everyday, 0:12:02.390 --> 0:12:06.810 run-of-the-mill voids. Already, these things are much, much bigger than 0:12:07.030 --> 0:12:10.620 one individual supercluster relative to To a void, a supercluster 0:12:10.750 --> 0:12:12.589 is so tiny you just think of it as a dot. 0:12:12.870 --> 0:12:16.030 And remember, inside that supercluster is a bunch of clusters 0:12:16.070 --> 0:12:19.209 of galaxies, and inside each cluster of galaxies is a 0:12:19.230 --> 0:12:22.410 bunch of galaxies, each of which is unfathomably huge to 0:12:22.429 --> 0:12:25.370 the human mind. So this is like a real brain 0:12:25.410 --> 0:12:28.150 stretcher to even get this in your head, what a 0:12:28.210 --> 0:12:29.800 supervoid is and how big it is. 0:12:30.250 --> 0:12:31.070 Yeah, I was. 0:12:31.210 --> 0:12:34.610 So you said 30 to 300 million light years. And 0:12:34.630 --> 0:12:36.429 I was still having a little trouble wrapping my head 0:12:36.450 --> 0:12:37.790 around that number. 0:12:38.090 --> 0:12:38.850 So I just looked it up. 0:12:38.870 --> 0:12:43.830 The distance between our galaxy and Andromeda is 2.5 million 0:12:43.870 --> 0:12:46.910 light years away. So we are talking about voids that 0:12:46.970 --> 0:12:50.620 are like, I don't know, 15 times bigger than that minimum. 0:12:51.540 --> 0:12:52.920 That is huge. 0:12:53.020 --> 0:12:55.020 Yeah. And, you know, the size of our galaxy is 0:12:55.040 --> 0:12:58.939 like 100,000 light years across. And so if you can 0:12:59.059 --> 0:13:02.949 somehow get the Milky Way into your brain, then we're 0:13:02.990 --> 0:13:06.309 talking about distances that are thousands of times bigger than 0:13:06.350 --> 0:13:07.030 the Milky Way. 0:13:07.130 --> 0:13:07.709 Oh, my gosh. 0:13:07.770 --> 0:13:11.850 And so, yeah, these are big, empty regions of space. Wow. 0:13:12.010 --> 0:13:13.319 We should put something in there. 0:13:17.500 --> 0:13:19.420 I mean, I know your house is filled to the 0:13:19.480 --> 0:13:23.059 brim with all kinds of Interesting stuff. And so you're 0:13:23.100 --> 0:13:24.819 always looking for more storage space. 0:13:25.040 --> 0:13:26.599 I was thinking we could put all the stuff in 0:13:26.640 --> 0:13:29.100 my house into the super void so that I don't have, 0:13:29.160 --> 0:13:31.719 but I think Zach might fill the super void pretty quick. 0:13:34.059 --> 0:13:35.100 With Dorito bags. 0:13:37.200 --> 0:13:39.000 Not just Dorito bags, but you know, you've got all 0:13:39.040 --> 0:13:42.170 these projects. They're always half done. You're like, I'm storing 0:13:42.190 --> 0:13:44.150 all these cabinets in this room because I can't put 0:13:44.190 --> 0:13:46.349 them on the wall yet. They're on the wall now. 0:13:46.370 --> 0:13:46.970 Do you imagine? 0:13:48.400 --> 0:13:50.540 Do you imagine someday in the future you will be 0:13:50.559 --> 0:13:52.439 done with projects and the house will just be like 0:13:52.880 --> 0:13:54.040 actually totally functional? 0:13:54.520 --> 0:13:54.870 No. 0:13:55.370 --> 0:13:58.170 No? No. She says with resignation. 0:13:58.490 --> 0:14:00.670 I don't know when I'll have time to finish everything. 0:14:01.770 --> 0:14:02.770 Maybe when I die. 0:14:03.610 --> 0:14:05.650 All right. Well, maybe your house never will have voids. 0:14:05.730 --> 0:14:08.170 It's always going to be filled with stuff. But the 0:14:08.250 --> 0:14:11.460 universe has voids and they're fascinating. And they were kind 0:14:11.480 --> 0:14:14.460 of a surprise when we learned that the universe had 0:14:14.500 --> 0:14:15.059 this structure. 0:14:15.480 --> 0:14:16.100 So why? 0:14:16.120 --> 0:14:20.760 OK, so if I'm like imagining a giant space, I 0:14:20.800 --> 0:14:24.350 would imagine that if you like distributed stuff around that space, 0:14:24.370 --> 0:14:26.670 you would expect there to be some empty areas for 0:14:26.750 --> 0:14:30.230 random reasons. But you've I think you've already explained to 0:14:30.310 --> 0:14:32.810 us that these voids aren't random because they tend to 0:14:32.830 --> 0:14:35.050 be on the inside of like bubbles. Does that tell 0:14:35.110 --> 0:14:36.330 us something about how they're formed? 0:14:37.050 --> 0:14:39.080 It does tell us something about how they're formed. And 0:14:39.100 --> 0:14:41.620 you put your finger on exactly what the discovery was. 0:14:42.250 --> 0:14:45.770 Until around the 70s, we thought that galaxies were distributed 0:14:45.850 --> 0:14:49.050 roughly equally. That, you know, any galaxy had an equal 0:14:49.090 --> 0:14:51.190 chance to be here or there. And if you took 0:14:51.330 --> 0:14:53.910 any chunk of space, you would find roughly the same 0:14:53.980 --> 0:14:57.600 number of galaxies. You know, that the density was pretty smooth. 0:14:58.140 --> 0:15:00.320 And it wasn't until the 70s that they went out 0:15:00.340 --> 0:15:02.440 and they started measuring these things and trying to map 0:15:02.660 --> 0:15:05.300 out the structure of the universe. You know, I love 0:15:05.320 --> 0:15:07.200 when we have an idea about how the universe works. 0:15:07.540 --> 0:15:09.880 And then we develop the technology, the capacity to actually 0:15:09.940 --> 0:15:12.930 measure it. And the universe is like, no, what you 0:15:12.950 --> 0:15:15.570 thought was natural, what you thought was intuitive, what you 0:15:15.590 --> 0:15:18.770 thought made sense. That's not how things work. Because those 0:15:18.790 --> 0:15:20.340 are the best moments. Those are the moments when the 0:15:20.390 --> 0:15:24.280 universe is confronting your intuition and teaching you something about 0:15:24.320 --> 0:15:26.840 how things work. I mean, not like the universe is 0:15:26.880 --> 0:15:29.160 a teacher, you know, that cares what we understand. But 0:15:29.440 --> 0:15:32.240 those are the best moments of discovery. And it was 0:15:32.280 --> 0:15:35.620 in the 70s that people first started measuring red shifts 0:15:35.750 --> 0:15:38.390 of these galaxies and trying to assemble them into sort 0:15:38.410 --> 0:15:40.890 of a 3D map. What you need to understand the 0:15:40.930 --> 0:15:43.620 structure of the universe is to know where is a galaxy? 0:15:43.960 --> 0:15:46.380 How far away is it? If you know those two things, 0:15:46.440 --> 0:15:48.740 you can start to build a 3D map of where 0:15:48.760 --> 0:15:51.000 all the galaxies are and you can start to see structure. 0:15:51.620 --> 0:15:54.380 And so people started doing this seriously in the 70s. 0:15:54.990 --> 0:15:57.730 The Center for Astrophysics at Harvard and the Smithsonian started 0:15:57.770 --> 0:16:01.450 to do this with the Tillinghast Telescope. And they were surprised. 0:16:01.930 --> 0:16:05.460 They surveyed like 2,200 galaxies. And they saw that things 0:16:05.500 --> 0:16:07.980 were not smooth, right? It didn't look like galaxies were 0:16:08.020 --> 0:16:12.220 distributed randomly across the universe. They were clustered together into 0:16:12.280 --> 0:16:15.020 these bubbles. Imagine a sheet of paper and you throw 0:16:15.060 --> 0:16:17.380 sand over it and you expect there, as you said, 0:16:17.420 --> 0:16:19.500 to be some places where there are galaxies and some 0:16:19.520 --> 0:16:20.930 places where there are not. It's not going to be 0:16:21.330 --> 0:16:23.730 perfectly smooth. You don't expect the galaxies to be like 0:16:24.110 --> 0:16:27.730 in a grid, you know, perfectly arranged. There'd be some 0:16:27.790 --> 0:16:31.610 clustering accidentally. But what they saw was definite structure, not 0:16:31.670 --> 0:16:34.980 just random distributions. they saw like a bubble bath of 0:16:35.060 --> 0:16:37.860 cosmic voids and filaments. And they discovered what they call 0:16:38.100 --> 0:16:42.740 the Great Wall, a superstructure over 500 million light years wide. 0:16:43.320 --> 0:16:45.200 And what a moment, you know, to be the first 0:16:45.260 --> 0:16:50.340 person to map the universe, right? Like I always imagined... 0:16:50.340 --> 0:16:52.680 The joy of being like a first person to land 0:16:52.820 --> 0:16:55.530 on a new shore or to cross a land bridge or, 0:16:55.550 --> 0:16:57.830 you know, get in a boat 10,000 years ago and 0:16:57.870 --> 0:17:01.010 cross the Pacific to the South Pacific islands or whatever, right? 0:17:01.350 --> 0:17:03.550 What a moment of discovery. But this is just on 0:17:03.610 --> 0:17:06.850 another scale, you know? This is like, oh my gosh, 0:17:06.890 --> 0:17:09.929 the universe has patterns and we're part of this and 0:17:09.950 --> 0:17:12.380 there's a huge wall over there. And like, oh my God, 0:17:12.760 --> 0:17:15.000 what a moment. And, you know, I think that's sort 0:17:15.020 --> 0:17:17.320 of natural for us to think about now because we've 0:17:17.359 --> 0:17:19.859 known about it for 50 years. But at the time, 0:17:19.940 --> 0:17:22.200 this was a real revolution in the way people thought 0:17:22.300 --> 0:17:26.660 about our entire cosmic context. So that was very cool, 0:17:26.680 --> 0:17:29.260 and that was in the 70s. And again, the primary 0:17:29.320 --> 0:17:30.879 way we figured this out is that we look at 0:17:30.920 --> 0:17:34.700 galaxies and we measure their redshift, meaning that the light 0:17:34.740 --> 0:17:37.719 that comes from them has been shifted to lower frequencies. 0:17:38.500 --> 0:17:40.879 And we measure their redshift, which tells us how the 0:17:40.920 --> 0:17:43.140 light has been shifted, which tells us how fast they're 0:17:43.160 --> 0:17:45.939 moving away from us. Because remember, the things that are 0:17:45.980 --> 0:17:48.970 moving away from us have their light shifted into the red. 0:17:49.880 --> 0:17:51.919 And if we know how fast they're moving away from us, 0:17:51.960 --> 0:17:54.300 then we can tell how far away they are because 0:17:54.320 --> 0:17:56.500 that's the Hubble relationship. It tells us that things that 0:17:56.540 --> 0:17:59.540 are further away are moving away faster. So if you 0:17:59.580 --> 0:18:01.879 just measure the light from one of these galaxies, you 0:18:01.900 --> 0:18:05.060 measure the redshift, you say, I know where hydrogen should be. 0:18:05.180 --> 0:18:07.659 I know where helium should be on my spectrum. And 0:18:07.700 --> 0:18:10.260 I see it shifted. You measure that shift. You can 0:18:10.320 --> 0:18:13.500 translate that to the distance to the galaxies. And now 0:18:13.560 --> 0:18:15.399 you know the angle in the sky, right? You know, 0:18:15.420 --> 0:18:17.320 I saw this galaxy at this angle. I saw that 0:18:17.359 --> 0:18:19.879 galaxy at the other angle. You put those together and 0:18:19.920 --> 0:18:22.290 you start to make your 3D map of the universe. 0:18:22.869 --> 0:18:23.350 Amazing. 0:18:23.400 --> 0:18:27.030 Okay, so now we know what the pattern is. Let's 0:18:27.070 --> 0:18:27.629 take a break. 0:18:27.670 --> 0:18:29.310 And when we come back, we'll talk about now that 0:18:29.350 --> 0:18:31.510 we know what the pattern is, what does that imply 0:18:31.609 --> 0:18:34.429 about how everything ended up where it finally ended up? 0:18:54.369 --> 0:18:57.310 And we're back. We've been talking about how. 0:18:57.050 --> 0:19:01.580 Like the universe is like this foamy wash full of 0:19:01.700 --> 0:19:04.280 clusters that are like on the edges of the bubbles. 0:19:04.660 --> 0:19:07.080 And then inside of the bubbles, we have super voids. 0:19:07.800 --> 0:19:11.350 What does that tell us about how the universe formed? 0:19:11.790 --> 0:19:13.270 And like, have we figured that out yet? Because that's 0:19:13.290 --> 0:19:14.050 not what we expected. 0:19:14.470 --> 0:19:18.250 Right, yeah. So first, slight clarification. Inside the bubbles are voids. 0:19:18.450 --> 0:19:18.790 Oh, okay. 0:19:18.830 --> 0:19:21.680 Super voids we haven't really talked about exactly yet. Super 0:19:21.700 --> 0:19:25.379 voids are essentially like really, really big voids. In many cases, 0:19:25.500 --> 0:19:27.980 bigger than we expect. And so that's why we have 0:19:28.000 --> 0:19:29.720 to dive into the history of the universe to think 0:19:29.740 --> 0:19:31.879 about like, do we expect to see voids? Do we 0:19:31.940 --> 0:19:34.620 expect to see super voids? Does what we see line 0:19:34.660 --> 0:19:36.659 up with what we expect? And to do that, we 0:19:36.680 --> 0:19:38.699 have to go all the way back to the earliest 0:19:38.740 --> 0:19:39.880 known thing in the universe. 0:19:40.270 --> 0:19:40.850 Which is? 0:19:41.310 --> 0:19:44.100 The cosmic microwave background, of course, which, you know, physics 0:19:44.150 --> 0:19:46.239 is always going back to. You might be like, oh, 0:19:46.260 --> 0:19:48.610 my gosh, these guys lean on the CMB so much. 0:19:48.710 --> 0:19:52.670 It's just such a. rich and incredible source of information. 0:19:52.730 --> 0:19:55.190 You know, if you were trying to understand somebody's life 0:19:55.609 --> 0:19:57.930 and you had like a picture of them in kindergarten, 0:19:58.390 --> 0:20:00.430 it would tell you so much about where they grew 0:20:00.570 --> 0:20:02.730 up and what they were like. And that's basically what 0:20:02.770 --> 0:20:07.440 we have. We And so when we want to understand 0:20:07.500 --> 0:20:09.179 how the universe got to be the way it is, 0:20:09.220 --> 0:20:11.100 we look back at that baby picture. We're like, huh, 0:20:11.320 --> 0:20:13.399 did it have seven toes when it was born? Or 0:20:13.440 --> 0:20:16.680 was that surgery that came later? You know, what features 0:20:16.720 --> 0:20:18.980 of the universe can you trace back to the origin? 0:20:19.040 --> 0:20:21.080 And if they're not there, what does that tell you? 0:20:21.180 --> 0:20:24.050 So it's incredibly valuable. And that's why we look back. 0:20:24.590 --> 0:20:26.290 And for those of you who don't remember, the cosmic 0:20:26.330 --> 0:20:29.690 microwave background light is light that came from the universe 0:20:29.730 --> 0:20:32.659 the first moment that it was transparent. So we don't 0:20:32.680 --> 0:20:34.699 know how the universe began or when it began, but 0:20:34.720 --> 0:20:36.960 we do know that it was filled with a hot, 0:20:37.160 --> 0:20:40.100 dense plasma and that plasma was glowing and it was opaque. 0:20:40.440 --> 0:20:42.060 Just like plasma at the center of the sun, it 0:20:42.359 --> 0:20:45.520 gives off light and then is immediately reabsorbed. Which, you know, 0:20:45.580 --> 0:20:49.300 you hear maybe on pop-sci channels like a photon takes 0:20:49.300 --> 0:20:50.720 50,000 years to get from the center of the sun 0:20:50.780 --> 0:20:52.700 to the surface of the sun. And that's like mostly 0:20:52.720 --> 0:20:56.300 pop-sci nonsense. because a photon is emitted at the center 0:20:56.320 --> 0:20:58.220 of the sun and then immediately absorbed. It never gets 0:20:58.260 --> 0:21:01.440 to the surface. Like, you know, maybe you could say 0:21:01.480 --> 0:21:03.880 that heat waves travel through the sun at some velocity 0:21:03.900 --> 0:21:07.640 or whatever, but you're not tracing a photon. Anyway, photons 0:21:07.660 --> 0:21:10.179 that were created in the very early universe, no longer around, 0:21:10.400 --> 0:21:14.119 immediately absorbed because the universe they were born into was opaque. 0:21:14.609 --> 0:21:17.130 But the universe is expanding and the universe is cooling. 0:21:17.470 --> 0:21:19.970 And at some point, the universe expanded and cooled enough 0:21:20.310 --> 0:21:23.909 that protons and electrons found each other and became neutral. 0:21:24.330 --> 0:21:28.669 And then the universe became suddenly transparent. So photons that 0:21:28.690 --> 0:21:31.930 were born after that moment are still around. And they 0:21:31.970 --> 0:21:34.210 are still here for us to measure and for us 0:21:34.230 --> 0:21:36.970 to learn about the early universe. And what we see 0:21:37.030 --> 0:21:41.690 in those photons is not a smooth plasma. Not like 0:21:41.880 --> 0:21:44.660 everything was filled with stuff equally. We see some places 0:21:44.700 --> 0:21:47.200 with more density and some places with less density. 0:21:47.730 --> 0:21:51.480 And that is not what we expected initially. And why 0:21:51.580 --> 0:21:53.720 is that not what we expected initially? 0:21:54.060 --> 0:21:56.820 Yeah, good question. Here we have like two threads we 0:21:56.859 --> 0:22:01.139 have to follow. One is the density of galaxies as 0:22:01.180 --> 0:22:04.190 we're seeing them like today. And that started in the 70s. 0:22:05.170 --> 0:22:08.090 And by the 70s, we had seen the cosmic microwave 0:22:08.130 --> 0:22:09.990 background light. That happened in the 60s. It was a 0:22:10.320 --> 0:22:13.500 huge confirmation that the universe had an early hot, dense state. 0:22:13.780 --> 0:22:16.420 But we had not yet seen its wiggles. It wasn't 0:22:16.480 --> 0:22:18.879 until like the 80s and the 90s that we measured 0:22:18.920 --> 0:22:22.219 the CMB light with enough precision to see, oh, there 0:22:22.260 --> 0:22:24.100 are some little hot spots and there are some little 0:22:24.160 --> 0:22:27.690 cold spots. It just seemed sort of smooth. And so 0:22:27.750 --> 0:22:29.710 it wasn't until later that we saw wiggles in the 0:22:29.750 --> 0:22:33.420 CMB and we saw structure in the universe. And you're 0:22:33.460 --> 0:22:35.280 right to ask about that because those two things are 0:22:35.300 --> 0:22:37.970 definitely connected. And the listener who made that connection is 0:22:38.010 --> 0:22:41.609 totally right. We think that all the structure in the 0:22:41.670 --> 0:22:44.890 current universe comes from that structure in the early universe. 0:22:45.390 --> 0:22:47.830 That you had places with more density and that had 0:22:47.869 --> 0:22:50.690 more gravity and that pulled in more stuff. And that 0:22:50.880 --> 0:22:53.480 in those regions, you now have more galaxies and more 0:22:53.540 --> 0:22:56.500 dark matter than in places where you didn't. And so 0:22:56.520 --> 0:22:58.700 you should be able to line up a place in 0:22:58.720 --> 0:23:01.520 the early universe where there was less dense stuff with 0:23:01.640 --> 0:23:02.500 voids today. 0:23:02.869 --> 0:23:03.720 Okay, got it. 0:23:03.950 --> 0:23:06.090 And you might be tempted to say, oh, well, can 0:23:06.130 --> 0:23:09.850 we trace an individual like hotspot or cold spot in 0:23:09.869 --> 0:23:14.359 the CMB to something in the universe today? And you 0:23:14.380 --> 0:23:17.000 might be preparing yourself for disappointment because usually the answer 0:23:17.020 --> 0:23:19.460 to that is no. We can just do it statistically. 0:23:19.500 --> 0:23:22.480 We can say, oh, we expect this kind of distribution 0:23:22.520 --> 0:23:25.959 of galaxies in the late universe based on this kind 0:23:26.000 --> 0:23:28.310 of density in the early universe. But we can't say 0:23:28.350 --> 0:23:32.040 like this photon caused that galaxy or whatever, right? But 0:23:32.200 --> 0:23:34.720 there is one feature that seems to correlate. 0:23:34.740 --> 0:23:35.300 What? 0:23:35.320 --> 0:23:38.100 So there's a feature in the early universe, the cosmic 0:23:38.140 --> 0:23:41.240 microwave background, that seems to line up with a super 0:23:41.280 --> 0:23:44.760 void in the universe. Yeah. So the feature in the 0:23:44.780 --> 0:23:48.720 cosmic microwave background is called the CMB cold spot. This 0:23:48.790 --> 0:23:52.429 is a region where it's redder than everywhere else. So 0:23:52.470 --> 0:23:55.190 we expect there to be some variations in the cosmic 0:23:55.230 --> 0:23:59.510 microwave background. They vary by like microkelvin. And we talk 0:23:59.550 --> 0:24:01.950 about the CMB in terms of temperature, which is equivalent 0:24:01.970 --> 0:24:05.750 to thinking about wavelength, because blackbody radiation rules tell us 0:24:05.869 --> 0:24:07.990 that something at a certain temperature will radiate at a 0:24:08.010 --> 0:24:11.020 certain wavelength. So when we measure light at a certain wavelength, 0:24:11.040 --> 0:24:13.100 we say, oh, that came from an object at a 0:24:13.119 --> 0:24:16.540 certain temperature. So for example, the CMB light came from 0:24:16.580 --> 0:24:19.420 a really hot plasma, thousands and thousands of degrees, I 0:24:19.500 --> 0:24:22.720 think 3,000 K. But that light has been redshifted by 0:24:22.770 --> 0:24:25.050 the expansion of the universe down to about 2.7 K. 0:24:25.090 --> 0:24:27.950 So if you read that like oh, the CMB light 0:24:28.210 --> 0:24:30.129 is 2.7K, that's what it means. It means that it's 0:24:30.170 --> 0:24:33.450 the wavelength that an object at 2.7 Kelvin would emit. 0:24:33.730 --> 0:24:37.540 So very, very cold light. And we see variations like 0:24:37.540 --> 0:24:41.760 20 microkelvin in the CMB. That's like typical expected hot 0:24:41.800 --> 0:24:44.260 spots and cold spots. But there is one spot in 0:24:44.300 --> 0:24:46.360 the CMB, one spot in the sky when we look 0:24:46.420 --> 0:24:50.860 at it, that it's like 70 microkelvin colder. So some 0:24:50.900 --> 0:24:55.340 places like 150 microK colder. It's in the southern hemisphere 0:24:55.700 --> 0:24:59.400 in the direction of the constellation Eridanus, which is maybe 0:24:59.480 --> 0:25:01.320 the source of a poop joke for those of you 0:25:01.780 --> 0:25:04.180 who are interested in the southern hemisphere. 0:25:04.480 --> 0:25:07.450 If you could see how it's spelled, you would get 0:25:07.490 --> 0:25:08.730 why this could be a poop joke. 0:25:09.850 --> 0:25:13.290 Maybe all constellations in the southern hemisphere should have anus 0:25:13.330 --> 0:25:14.970 in them, you know? Absolutely. 0:25:14.990 --> 0:25:15.410 Yes. 0:25:16.150 --> 0:25:17.430 Astronomers, get on that. 0:25:17.590 --> 0:25:20.659 Or synonyms of anus. Yes. Because you need some options. 0:25:21.000 --> 0:25:23.940 Yeah. So this is really interesting. You know, it could 0:25:24.000 --> 0:25:27.060 just be random. It could just be like a fluctuation. 0:25:27.240 --> 0:25:29.650 And they've done a calculation to suggest it's like, there's 0:25:29.690 --> 0:25:33.409 like a 1.5% chance of this happening randomly. So it's 0:25:33.470 --> 0:25:37.450 like weird. It sticks out, but it's not insane. But 0:25:37.510 --> 0:25:41.609 it does also correspond with a place in the late 0:25:41.750 --> 0:25:45.010 universe that there seems to be a super void. 0:25:45.490 --> 0:25:48.150 And you said at one point, well, we haven't really 0:25:48.190 --> 0:25:49.370 talked about super voids yet. 0:25:49.470 --> 0:25:52.540 And super voids are just like Really big voids, right? 0:25:52.900 --> 0:25:55.880 Yes, exactly. Okay. And so if you look in the 0:25:55.960 --> 0:25:59.730 structure of the universe today, in the same direction, you 0:25:59.830 --> 0:26:03.630 do see a really, really big void there. It's like 0:26:03.650 --> 0:26:07.250 a thousand times the size of a typical void. Wow. 0:26:07.290 --> 0:26:09.649 So it's like you have bubbles in your sink and 0:26:09.670 --> 0:26:11.730 they're all roughly the same size. And then there's one 0:26:11.770 --> 0:26:14.270 that's just like a thousand times bigger than all the 0:26:14.390 --> 0:26:18.070 other bubbles. This one's a billion light years across. It's 0:26:18.090 --> 0:26:20.130 like five to 10 billion light years away. 0:26:20.770 --> 0:26:23.650 So is this like most mornings you eat Special K, 0:26:24.070 --> 0:26:26.250 but one morning you eat Poops Like a Champion? 0:26:26.270 --> 0:26:29.429 And that's the difference between void and super void? 0:26:29.450 --> 0:26:36.780 Yes, exactly. You feel it about 24 hours later, exactly, 0:26:36.820 --> 0:26:39.700 when you have a super void. And here the universe 0:26:39.920 --> 0:26:41.500 has formed a void like a champion. 0:26:41.520 --> 0:26:44.649 And just to be clear, Poops Like a Champion... Is 0:26:44.670 --> 0:26:46.700 an actual cereal you told me about the other day. 0:26:48.080 --> 0:26:50.000 It is an actual cereal and we have boxes of 0:26:50.040 --> 0:26:53.550 it at home. Because some company out there that makes 0:26:53.630 --> 0:26:56.899 it heard about Katrina and her fiber journey and her, 0:26:57.750 --> 0:27:00.229 you know, her effort to make everybody poop better by 0:27:00.320 --> 0:27:03.360 eating fiber and improve their gut microbiome. So they sent 0:27:03.380 --> 0:27:05.619 her a bunch of free boxes of poop like a champion. 0:27:06.260 --> 0:27:08.500 And I am not on their payroll, so I can 0:27:08.540 --> 0:27:10.220 tell you that it tastes like cardboard. 0:27:11.480 --> 0:27:13.440 But still, you know, I think Katrina is one of 0:27:13.500 --> 0:27:14.740 the better people on this planet. 0:27:16.050 --> 0:27:17.350 That's what that story tells me. 0:27:18.170 --> 0:27:21.350 She's out there. She really does want to improve your pooping. Yeah. 0:27:21.390 --> 0:27:23.260 Even though she has nothing to do with super voids. 0:27:23.710 --> 0:27:26.420 I tried really hard to derail this conversation. 0:27:26.480 --> 0:27:29.600 Let's go back to super voids of the universe. 0:27:30.020 --> 0:27:33.280 Yeah. So this is really interesting because when you run 0:27:33.300 --> 0:27:36.220 the simulations in the universe, you don't get these kinds 0:27:36.260 --> 0:27:39.679 of super voids. Like it's really unusual. And so it 0:27:39.720 --> 0:27:42.380 helps us try to understand, like, you know, we talked 0:27:42.400 --> 0:27:46.000 about in our simulating the universe episode recently that, How 0:27:46.020 --> 0:27:48.379 when you see something different in your simulation and in 0:27:48.420 --> 0:27:50.720 your data, it tells you that there's a gap. There's 0:27:50.740 --> 0:27:54.000 something in your simulation that isn't describing the universe correctly, 0:27:54.060 --> 0:27:56.389 or there's an element of the universe that you're not 0:27:56.430 --> 0:28:00.190 describing correctly. And these are super fascinating, especially because they're 0:28:00.230 --> 0:28:04.130 very sensitive to the expansion of the universe. How we 0:28:04.170 --> 0:28:06.490 see these cold spots and these hot spots in the 0:28:06.590 --> 0:28:09.530 CMB tells us a lot about the expansion of the 0:28:09.609 --> 0:28:13.480 universe because photons fly through the universe as they get 0:28:13.540 --> 0:28:16.730 to us. And there's two different effects here to disentangle. 0:28:16.750 --> 0:28:18.790 When we're looking at the CMB and we see some 0:28:18.830 --> 0:28:22.410 places are hotter, some places are colder, there's two different 0:28:22.430 --> 0:28:25.300 reasons why. One is, well, we could just be looking 0:28:25.359 --> 0:28:28.140 at a place that was denser or it was less dense. 0:28:28.520 --> 0:28:31.899 And so there's like initial over-density or initial under-density. That's 0:28:31.920 --> 0:28:34.780 what we typically think about. But remember that the photons 0:28:34.859 --> 0:28:37.679 also have to fly through the universe to get to us. 0:28:38.340 --> 0:28:43.390 And those photons are red-shifted by the expansion of the universe. And... 0:28:43.580 --> 0:28:46.060 they fly through the universe, which means that they're sensitive 0:28:46.440 --> 0:28:49.940 to gravitational density. Because if you fly through a region 0:28:49.960 --> 0:28:53.070 with a lot of mass, you get redshifted, right? Like 0:28:53.150 --> 0:28:57.350 black holes produce gravitational redshifts. And so a photon that's 0:28:57.430 --> 0:29:01.230 flown through the universe, in some senses, measures the density 0:29:01.250 --> 0:29:04.690 of the universe along its path. which is super duper cool. 0:29:04.910 --> 0:29:07.890 That is super duper cool. That photo from our childhood 0:29:08.010 --> 0:29:10.290 is telling us a lot. Although is it more like, 0:29:10.310 --> 0:29:12.330 I mean, you should never really dig into an analogy, 0:29:12.350 --> 0:29:15.270 but it's more like a video from your childhood, isn't it, 0:29:15.350 --> 0:29:15.990 than a photo? 0:29:16.880 --> 0:29:19.060 It is like a video because if you keep watching it, 0:29:19.140 --> 0:29:21.520 you see different things, right? We are looking at the 0:29:21.560 --> 0:29:24.220 cosmic microwave background radiation and we can't see it for 0:29:24.240 --> 0:29:27.080 the whole universe. We see the light that's arriving right now, 0:29:27.700 --> 0:29:30.370 which left, of course, many, many, many billions of years ago. 0:29:31.000 --> 0:29:33.700 And it's arriving to us from a shell of that 0:29:33.790 --> 0:29:37.150 original plasma that's very far away and around the Earth. 0:29:37.450 --> 0:29:39.470 And as time goes on, we get light from a 0:29:39.530 --> 0:29:42.230 different shell. So it's not like we're watching the same 0:29:42.310 --> 0:29:46.150 place over time. Over time, we're scanning more and more 0:29:46.260 --> 0:29:49.920 distant shells of that original CMB. Got it. Cool. So 0:29:49.940 --> 0:29:52.320 let's trace the trajectory of a photon as it's moving 0:29:52.340 --> 0:29:56.200 through the universe. And let's think first about overdensities, places 0:29:56.240 --> 0:29:59.020 where there's a lot of mass. So say a photon 0:29:59.060 --> 0:30:01.300 is on its way to us, but it's passing by 0:30:01.500 --> 0:30:05.420 a black hole, right? And so as it falls in 0:30:05.480 --> 0:30:08.160 towards the black hole, it gains energy, right? So it's 0:30:08.180 --> 0:30:11.090 getting blue shifted. And then if it doesn't get eaten 0:30:11.130 --> 0:30:12.790 by the black hole, it makes it out and it 0:30:12.830 --> 0:30:15.330 comes towards us. And as it's leaving the black hole, 0:30:15.390 --> 0:30:17.550 it's losing energy. It's having to climb out of that 0:30:17.590 --> 0:30:20.490 gravitational well. So it gets red shifted. And so you 0:30:20.510 --> 0:30:24.120 might think, okay, blue shifted more energy, red shifted less energy. 0:30:24.400 --> 0:30:27.150 It all balances out. So how could a photon that's 0:30:27.210 --> 0:30:30.790 coming to us tell us anything about that dense region 0:30:31.150 --> 0:30:34.130 if it's all got canceled out, if it's basically unchanged, right? 0:30:34.750 --> 0:30:37.190 So you can't watch it as it changes? You just 0:30:37.210 --> 0:30:39.530 see like the average of what happened to it over 0:30:39.570 --> 0:30:40.010 a distance? 0:30:40.470 --> 0:30:42.320 Yeah, you can't watch a photon go through the universe. 0:30:42.340 --> 0:30:44.700 You just see one here on Earth. And you're like, oh, 0:30:44.760 --> 0:30:46.459 is it hotter than I expected or colder? 0:30:46.480 --> 0:30:47.760 Okay, got it. 0:30:48.080 --> 0:30:51.000 And so the opposite is true for voids, right? If 0:30:51.020 --> 0:30:53.590 you go near a black hole, then you get blue 0:30:53.650 --> 0:30:55.790 shifted as you fall in and red shifted as you 0:30:55.830 --> 0:30:57.770 fall out. And the opposite is true for a void. 0:30:58.110 --> 0:31:01.130 You get red shifted as you fall in and blue 0:31:01.200 --> 0:31:02.810 shifted as you fall out. Okay. 0:31:02.830 --> 0:31:05.510 And so if we only see the average of what 0:31:05.530 --> 0:31:08.270 happened to a photon when it gets here, how do 0:31:08.310 --> 0:31:08.850 we know that? 0:31:09.210 --> 0:31:12.710 So that's our theoretical calculation, but it's missing something really important, 0:31:13.250 --> 0:31:16.080 which is as time goes on, when the photon is 0:31:16.230 --> 0:31:18.980 in that void or near that black hole, the universe 0:31:19.040 --> 0:31:23.200 is not static. The universe is expanding. And so the 0:31:23.240 --> 0:31:25.800 amount of energy the photon loses or gains when it 0:31:25.840 --> 0:31:28.370 goes in or out of that void changes because the 0:31:28.450 --> 0:31:31.380 void is changing or the black hole is changing as 0:31:31.450 --> 0:31:35.160 time goes on. So it doesn't perfectly cancel out. And 0:31:35.200 --> 0:31:38.680 so it does leave an overall effect on these photons. 0:31:38.740 --> 0:31:42.350 And so you can get cold spots in the CMB 0:31:42.870 --> 0:31:46.770 if photons have moved through a super void on their 0:31:46.810 --> 0:31:50.270 way here, if the universe is expanding. And so not 0:31:50.410 --> 0:31:52.910 only do super voids tell us about like, hey, what 0:31:52.970 --> 0:31:54.870 is the evolution of the universe? How do you get 0:31:54.910 --> 0:31:58.990 these bubbles? Do they come from initial overdensities? Also, the 0:31:59.030 --> 0:32:02.180 CMB tells us about photons moving through the universe and 0:32:02.360 --> 0:32:06.260 measuring existing voids, not from the early universe, but today. 0:32:06.880 --> 0:32:10.880 So there's like so many dimensions of information in the CMB. 0:32:10.930 --> 0:32:13.570 It's not just a baby picture. It's a baby picture 0:32:13.590 --> 0:32:17.000 that was then like dragged through your life and distorted 0:32:17.060 --> 0:32:19.540 by the way your life turned out. And then here 0:32:19.560 --> 0:32:22.320 we are, like we can disentangle those two things in 0:32:22.340 --> 0:32:24.520 the single picture from the CMB and be like, oh, 0:32:24.880 --> 0:32:27.650 this is a primordial hotspot. Or this is one that 0:32:27.690 --> 0:32:31.250 appeared because of how the photons moved through the universe. Wow. 0:32:31.370 --> 0:32:34.600 So all these incredibly clever little effects. We can use 0:32:34.640 --> 0:32:37.760 to try to disentangle the history of the universe. And 0:32:37.780 --> 0:32:40.239 this is why, like, people seem like they're in love 0:32:40.270 --> 0:32:43.810 with the CMB. It's just such a gift. It's such 0:32:43.870 --> 0:32:45.050 a gift. Oh, my gosh. 0:32:45.630 --> 0:32:48.650 So what if a photon went through a black or 0:32:48.710 --> 0:32:51.170 past a black hole and then through a super void? Like, 0:32:51.490 --> 0:32:54.370 how do you how can you know what a photon 0:32:54.470 --> 0:32:56.730 saw when it could have seen a bunch of things 0:32:56.770 --> 0:32:57.500 before it gets to us? 0:32:57.510 --> 0:33:01.320 Wow. You get it in that interview room. Okay. You 0:33:01.400 --> 0:33:04.380 shine the lights in its face. Oh, boy. No, you're right. 0:33:04.420 --> 0:33:07.080 You can't. And all you can do is look for patterns. 0:33:07.620 --> 0:33:10.500 And we see in the universe, we see a big 0:33:10.680 --> 0:33:13.620 cold spot, right, in the sky. Okay. And that's in 0:33:13.660 --> 0:33:16.300 the same direction as a super void. And so that 0:33:16.340 --> 0:33:19.790 means either there was like an initial underdensity there, which 0:33:19.870 --> 0:33:23.830 created a colder region, or the photons getting here from 0:33:23.930 --> 0:33:28.070 there have passed through a super void on the way. Okay. 0:33:28.270 --> 0:33:30.540 And so it's just like, It's fascinating to see that 0:33:30.660 --> 0:33:33.380 in the CMB and also then to look at our 0:33:33.420 --> 0:33:37.170 late-time measurements of galactic structure and see, oh, there's also 0:33:37.210 --> 0:33:39.930 a super void over there. So, like, things are lining up. 0:33:39.970 --> 0:33:42.490 They're clicking together. You know, that's exciting when you're doing 0:33:42.510 --> 0:33:45.810 science and you see two completely separate measurements that are 0:33:45.850 --> 0:33:48.590 sensitive to the same thing lining up and telling you 0:33:48.630 --> 0:33:50.650 the same story. That's when you feel like, ooh, we're 0:33:50.670 --> 0:33:51.620 going to crack this case. 0:33:52.130 --> 0:33:52.360 All right. 0:33:52.380 --> 0:33:54.580 We're getting super excited over here, but we have to 0:33:54.620 --> 0:33:57.450 take a break. Super Void if you must, but come 0:33:57.490 --> 0:34:01.890 back in just a moment. But when we get back, 0:34:02.280 --> 0:34:04.760 we're going to talk about how Super Voids get made. 0:34:06.060 --> 0:34:08.319 The space ones, not the one you just made. 0:34:08.340 --> 0:34:16.799 Super Voids. 0:34:28.410 --> 0:34:28.630 All right. 0:34:28.790 --> 0:34:31.950 And we're back. So, all right, Daniel, how do super 0:34:31.969 --> 0:34:32.629 voids get made? 0:34:33.070 --> 0:34:34.710 So this is really fun to think about how you 0:34:34.730 --> 0:34:37.930 get super voids. One is that you can just have 0:34:38.010 --> 0:34:41.350 an underdense region initially and, you know, you could just 0:34:41.370 --> 0:34:44.890 have a fluctuation. Like these things we think are seeded 0:34:44.969 --> 0:34:49.560 originally by quantum fluctuations. Why anyway are there regions that 0:34:49.600 --> 0:34:52.160 are higher or lower density? You know, one theory is 0:34:52.200 --> 0:34:55.259 you have quantum fluctuations in the very early universe and 0:34:55.300 --> 0:34:59.470 then inflation is this pre-Big Bang theory we talked about recently, 0:34:59.800 --> 0:35:05.050 stretch those out into macroscopic actual fluctuations that matter to gravity. 0:35:05.969 --> 0:35:08.010 That's just a speculative theory. We don't know for sure. 0:35:08.570 --> 0:35:11.350 But that would suggest that the fluctuations themselves, the reason 0:35:11.390 --> 0:35:14.250 we have more stuff here and less stuff there, comes 0:35:14.450 --> 0:35:17.450 initially randomly, which means that lots of stuff could happen. 0:35:18.090 --> 0:35:20.550 For example, you're flipping coins. You don't expect to get 0:35:20.930 --> 0:35:22.420 heads in the tails and then heads in the tails. 0:35:22.440 --> 0:35:25.379 You'll have runs of heads and runs of tails. And so, 0:35:26.020 --> 0:35:28.580 If somebody's flipping coins for the early universe, it's like, 0:35:28.620 --> 0:35:30.500 are we getting stuff here or not? They could have 0:35:30.540 --> 0:35:32.739 just come up with no stuff in this part of 0:35:32.780 --> 0:35:35.750 the universe a lot of times, occasionally, right? So that 0:35:35.790 --> 0:35:38.670 kind of thing can happen, but it's unlikely, right? The 0:35:38.730 --> 0:35:40.910 bigger the void, the less likely it is that can happen. 0:35:41.210 --> 0:35:43.070 The same way like having a run of 10 heads 0:35:43.170 --> 0:35:45.190 is less likely than a run of five heads and 0:35:45.210 --> 0:35:47.730 a run of like 50 heads in rows, essentially unheard of, 0:35:48.830 --> 0:35:51.450 though there is a probability. And so, you know, we 0:35:51.590 --> 0:35:54.820 only have this one universe. And so we can't tell like, hey, 0:35:54.960 --> 0:35:58.070 did we just get lucky or slash unlucky? We don't know. 0:35:58.510 --> 0:36:00.569 But there are also other ways people have come up 0:36:00.630 --> 0:36:04.230 with in watching these simulations to see supervoids form, which 0:36:04.270 --> 0:36:07.270 is that you can get voids merging. So these bubbles 0:36:07.330 --> 0:36:11.960 can pop because you get gravitational disturbances between these things 0:36:12.219 --> 0:36:15.420 and the walls can fall apart, essentially. And so you 0:36:15.440 --> 0:36:19.239 can get these cells merging. Basically, if you have an 0:36:19.340 --> 0:36:21.930 over density in some walls, they can attract those filaments 0:36:22.010 --> 0:36:24.890 and It's not like these super voids are totally empty. 0:36:25.330 --> 0:36:28.330 And so you still have some galaxies remaining inside of them. 0:36:29.030 --> 0:36:32.730 And so you can get mergers of these voids to 0:36:32.770 --> 0:36:35.130 form super voids. And this is the kind of example 0:36:35.150 --> 0:36:37.529 of something you can learn about in simulation. You can 0:36:37.590 --> 0:36:39.250 run a simulation in the universe. You can watch it. 0:36:39.250 --> 0:36:41.730 You'd be like, look at that. I didn't expect that 0:36:41.770 --> 0:36:44.969 to happen. But you see it in simulation. You learn that. 0:36:45.500 --> 0:36:49.620 about emergent phenomena in simulation that you didn't predict. Super 0:36:49.640 --> 0:36:50.260 duper cool. 0:36:50.520 --> 0:36:51.820 Yay, theoretical physicists. 0:36:53.810 --> 0:36:56.129 But this allows us to ask the question like, well, 0:36:56.210 --> 0:36:58.810 why are there super voids? Do they make sense in 0:36:58.850 --> 0:37:01.990 the universe? And, you know, we have this cold spot, 0:37:02.090 --> 0:37:05.900 which we can partially explain using this like photons come in, 0:37:05.940 --> 0:37:08.340 photons go out, but it's not a full explanation. It 0:37:08.400 --> 0:37:10.799 explains like part of the cold spot, but not all 0:37:10.820 --> 0:37:14.390 of it. It's really very unusual. Though it's hard to say, like, 0:37:14.630 --> 0:37:17.149 how unusual is a 1% effect? You know, you see 0:37:17.170 --> 0:37:19.529 it in one out of 100 universes. And so are 0:37:19.550 --> 0:37:21.890 we just unlucky or is this a hint that there's 0:37:21.910 --> 0:37:25.009 something else going on? Because remember that these things are 0:37:25.050 --> 0:37:27.850 very sensitive to the parameters of the universe. How much 0:37:27.910 --> 0:37:31.290 dark matter was there, dark matter forming that structure, how 0:37:31.310 --> 0:37:34.330 much dark energy was there to create this acceleration and 0:37:34.370 --> 0:37:37.910 this expansion, which is what's causing this effect, this cold 0:37:37.930 --> 0:37:40.430 spot effect. Because remember, it's only if the voids are 0:37:40.510 --> 0:37:43.410 changing as the photons are going through them that you 0:37:43.430 --> 0:37:46.560 even see an effect from the voids. And so there's 0:37:46.580 --> 0:37:49.420 a lot of questions about whether the super voids are 0:37:49.460 --> 0:37:51.759 something we expect or whether they indicate that we need 0:37:51.820 --> 0:37:55.299 something new in our theory of the universe, which of 0:37:55.360 --> 0:37:57.560 course is where the fun begins because then we get 0:37:57.580 --> 0:38:00.150 to speculate about all the crazy ideas. 0:38:00.350 --> 0:38:02.130 Daniel has a sparkle in his eye. 0:38:04.230 --> 0:38:06.630 So at the beginning of the episode, you said super 0:38:06.650 --> 0:38:09.989 voids remind you of like the Marvel Universe. So if 0:38:10.030 --> 0:38:12.670 you had like parallel universes like you do in the 0:38:12.710 --> 0:38:15.989 Marvel Universe, would you expect super voids to be distributed 0:38:16.070 --> 0:38:18.850 about the same way or like have about the same number? 0:38:18.969 --> 0:38:22.009 Like what? I'm trying to get to parallel universes for you. 0:38:24.270 --> 0:38:27.530 Well, there's an even cooler way that parallel universes connect 0:38:27.550 --> 0:38:30.390 to super voids, which is that maybe you had a 0:38:30.410 --> 0:38:33.160 bunch of initial universes early on. And remember, we talked 0:38:33.180 --> 0:38:37.380 about inflation. how our universe maybe is like a tiny 0:38:37.500 --> 0:38:42.299 dot in a vast landscape of inflationary matter. And in 0:38:42.340 --> 0:38:44.779 that dot, it just like went from inflationary matter to 0:38:44.840 --> 0:38:47.180 normal matter. And then our universe is there and expanded. 0:38:47.580 --> 0:38:50.260 And there could be other dots out there. And usually 0:38:50.340 --> 0:38:52.200 those other dots are really far away. And there's a 0:38:52.200 --> 0:38:54.360 bunch of inflationary matter between us and them, which is 0:38:54.420 --> 0:38:57.000 expanding at some insane rates. So we'll never see those 0:38:57.040 --> 0:39:01.020 other universes. But what if that's not true? What if 0:39:01.060 --> 0:39:04.190 there are other universes out there And our universe has collided. 0:39:04.710 --> 0:39:08.700 If early on our bubble bounced into another bubble, it 0:39:08.800 --> 0:39:12.640 might leave an imprint on the early universe. And according 0:39:12.680 --> 0:39:16.020 to some theories and according to some simulations, that can 0:39:16.080 --> 0:39:19.160 cause like a bruise in the density, which would be 0:39:19.200 --> 0:39:22.009 like a cold spot, which would lead to a super void. 0:39:22.590 --> 0:39:24.989 And so there are some really fun speculative theories of 0:39:25.010 --> 0:39:27.830 the early universe out there that suggest that if there 0:39:28.070 --> 0:39:33.000 are these parallel bubble universes, created in this inflationary landscape, 0:39:33.340 --> 0:39:35.760 that sometimes they'll bump into each other and they'll leave 0:39:35.800 --> 0:39:38.509 a mark, and that mark is super voids. 0:39:39.210 --> 0:39:45.759 Well, I think I'm still having one. Awesome, too. I'm 0:39:45.780 --> 0:39:48.020 having a little trouble imagining. So you get two bubbles. 0:39:48.500 --> 0:39:49.660 They like merge. 0:39:50.080 --> 0:39:52.600 And then is it like whatever was making the outside 0:39:52.640 --> 0:39:54.540 wall of the bubble where they touch just sort of 0:39:54.580 --> 0:39:57.430 like gets blown to somewhere else. And now you get 0:39:57.469 --> 0:40:00.770 a big center as those two bubbles merge. Is that 0:40:01.250 --> 0:40:02.489 how does that result in. 0:40:02.469 --> 0:40:03.109 A super void? 0:40:03.450 --> 0:40:06.029 Yeah, great question. And I realize that now we're using 0:40:06.070 --> 0:40:09.029 the word bubble to mean two different things. Shame on us. 0:40:09.050 --> 0:40:09.629 Shame on me. 0:40:09.650 --> 0:40:16.089 Yeah, I'm not taking any blame for that. Fair. 0:40:16.560 --> 0:40:18.700 No, when we talked earlier about bubbles, we were talking 0:40:18.719 --> 0:40:22.060 about the structure of our universe. And there's densities of 0:40:22.200 --> 0:40:26.020 superclusters of galaxies and under densities. And we talked about 0:40:26.080 --> 0:40:29.779 those organizing into bubbles. And those are bubbles. Now we're 0:40:29.800 --> 0:40:32.760 talking about bubbles as the whole universe is one bubble. 0:40:33.610 --> 0:40:37.969 in a vaster inflationary landscape. So let's not call them 0:40:38.010 --> 0:40:40.880 a bubble. Let's just say if our universe bumps into 0:40:40.930 --> 0:40:44.740 another universe, because remember in this theory, universes are finite. 0:40:44.760 --> 0:40:48.820 They're little regions of this inflationary landscape that have decayed 0:40:48.860 --> 0:40:52.070 into normal matter. So if our universe bumps into another 0:40:52.150 --> 0:40:55.190 universe and then bounces off, they don't merge. They bounce 0:40:55.270 --> 0:40:57.140 off each other, but they leave a mark. You know, 0:40:57.160 --> 0:40:58.850 the way like if you take two apples and you 0:40:58.870 --> 0:41:00.870 smash them together, they don't become one apple, but you 0:41:00.890 --> 0:41:03.029 get a bruise on each one. Yeah. What would that 0:41:03.070 --> 0:41:06.089 bruise look like on our universe if another universe had 0:41:06.150 --> 0:41:09.109 bumped into us and like not even left a note, just, 0:41:09.150 --> 0:41:11.880 you know, just like hit and run universe style? 0:41:11.900 --> 0:41:12.520 Not cool. 0:41:12.540 --> 0:41:14.680 Well, we would get a bruise and it would change 0:41:14.739 --> 0:41:18.700 the initial density of matter in the early universe. And 0:41:18.800 --> 0:41:22.380 simulations and calculations suggest that that would leave a cold 0:41:22.440 --> 0:41:25.130 spot and under density in that part of the universe, 0:41:25.170 --> 0:41:27.890 which would If you ran the simulations forward, leave to 0:41:27.930 --> 0:41:29.050 a super void today. 0:41:29.489 --> 0:41:31.210 Wow. Okay. All right. I'm with you. 0:41:31.370 --> 0:41:34.860 Yeah. So that's one fun theory. And, you know, there's 0:41:34.900 --> 0:41:37.359 a lot of debate about that. People say, you know, 0:41:37.400 --> 0:41:40.680 you're cherry picking, you're crafting an explanation to match something 0:41:40.719 --> 0:41:43.600 you see. It would be much more compelling if you 0:41:43.620 --> 0:41:45.580 had a prediction for this before you saw the super 0:41:45.600 --> 0:41:47.480 voids and you say, I predict a super void. And 0:41:47.500 --> 0:41:49.339 then you went out and saw it. That'd be much 0:41:49.360 --> 0:41:52.560 more compelling. This is more like a post addiction. It's like, oh, 0:41:52.580 --> 0:41:54.779 we see this thing in the universe. What could explain it? 0:41:55.310 --> 0:41:57.250 Not as a criticism, but just saying it would be 0:41:57.290 --> 0:41:59.969 more powerful, more compelling if it was a prediction and 0:42:00.010 --> 0:42:01.410 not a postdiction. Okay. 0:42:01.450 --> 0:42:04.359 I mean, I totally see that. But on the other hand, like, okay, 0:42:04.380 --> 0:42:06.010 but you've seen the thing and you can't unsee it. 0:42:06.040 --> 0:42:07.839 And now you have to try to explain it. And so, 0:42:07.900 --> 0:42:10.500 but I agree. It would have been more powerful if 0:42:10.560 --> 0:42:12.160 it had met expectations. 0:42:12.200 --> 0:42:14.540 But the universe doesn't care about our expectations. 0:42:15.040 --> 0:42:19.470 Yeah. So another potential explanation for this is a favorite 0:42:19.530 --> 0:42:23.190 alternative for dark matter. You remember that we talked about 0:42:23.250 --> 0:42:25.970 dark matter being out there. We have lots of independent 0:42:25.989 --> 0:42:28.630 lines of evidence for it. But there are alternatives, and 0:42:28.670 --> 0:42:31.899 it's healthy that people are thinking about other things and 0:42:32.040 --> 0:42:35.100 trying to understand if those other explanations are coherent, if 0:42:35.140 --> 0:42:38.540 they can explain multiple things and not just galactic rotation curves. 0:42:39.180 --> 0:42:42.440 One of those is modified gravity. To say maybe gravity 0:42:42.480 --> 0:42:45.700 doesn't work the way we expect. Maybe it's not that 0:42:45.760 --> 0:42:49.000 there is more invisible stuff out there causing gravity, but 0:42:49.020 --> 0:42:52.020 that gravity behaves differently and there isn't any dark matter. 0:42:52.680 --> 0:42:56.590 This is called MOND, Modified Newtonian Dynamics. I remember how 0:42:56.610 --> 0:42:58.799 we talked about some of these cold spots are due 0:42:58.860 --> 0:43:02.029 to the expansion of the universe as photons fall in 0:43:02.150 --> 0:43:04.670 and out of these voids or in and out of 0:43:04.710 --> 0:43:07.490 the neighborhood of a black hole. Well, that could also 0:43:07.570 --> 0:43:11.980 be explained in some models of modified gravity. Okay. Because 0:43:12.020 --> 0:43:14.780 you're changing how gravity works, so it's going to change 0:43:14.820 --> 0:43:18.319 how these photons experience the universe. And even some theories 0:43:18.360 --> 0:43:21.379 of the universe isn't expanding, and these things are just 0:43:21.480 --> 0:43:24.190 due to evidence that gravity doesn't work the way that 0:43:24.210 --> 0:43:27.730 we expect. And it's true that we can't fully explain 0:43:27.770 --> 0:43:30.430 these supervoids. We don't know where they come from. Our 0:43:30.489 --> 0:43:33.710 current theories do definitely need something. Do you need to 0:43:33.750 --> 0:43:37.150 go all the way to modified gravity to explain supervoids? 0:43:37.600 --> 0:43:39.460 I don't think so. But, you know, maybe I'm just 0:43:39.500 --> 0:43:41.569 not a fan of the modified gravity theory, and so 0:43:41.610 --> 0:43:44.630 I'm blind to it. I do respect that they're trying 0:43:44.650 --> 0:43:47.810 to find other ways to support this theory, other places 0:43:48.450 --> 0:43:50.870 to look for evidence that might indicate that it's the 0:43:50.950 --> 0:43:54.160 real explanation for the universe and not just a single 0:43:54.200 --> 0:43:57.020 fudge factor they're using to fix galactic rotation curves. 0:43:57.400 --> 0:44:00.460 Now, when we finish getting through all of the explanations, 0:44:00.500 --> 0:44:02.920 are you going to tell us which explanation is your favorite? 0:44:05.680 --> 0:44:07.400 Or are you just going to super void on this one? 0:44:10.060 --> 0:44:12.100 No, instead, I'm going to tell you about how we 0:44:12.140 --> 0:44:14.880 might learn more about the universe rather than betting on 0:44:14.960 --> 0:44:18.760 any individual one. Because we talked about how in the 70s, 0:44:18.800 --> 0:44:21.520 they started putting this together when they were measuring the 0:44:21.560 --> 0:44:24.580 cosmic structure. And they've continued to do that. There was 0:44:24.620 --> 0:44:27.660 a big survey in the 2000s called the Sloan Digital 0:44:27.680 --> 0:44:30.830 Sky Survey, mapped out a huge number of these big 0:44:30.910 --> 0:44:35.100 walls and bubbles and and really giving us a broader 0:44:35.200 --> 0:44:38.540 sense of where we are in the universe. And that's continuing. 0:44:38.600 --> 0:44:42.359 We now have this telescope called DESI, D-E-S-I, the Dark 0:44:42.440 --> 0:44:46.219 Energy Survey Instrument, which is the most powerful telescope we've 0:44:46.280 --> 0:44:49.780 ever had for understanding where things are in the universe 0:44:50.219 --> 0:44:52.840 in terms of measuring the redshift of a huge number 0:44:52.860 --> 0:44:56.950 of distant galaxies. And so like, what's more important? What's 0:44:56.989 --> 0:44:59.930 more exciting than like mapping out the universe? And that's 0:44:59.950 --> 0:45:02.190 what we're doing. And just yesterday we saw the launch 0:45:02.710 --> 0:45:05.270 of the Nancy Grace Roman telescope, which is also going 0:45:05.290 --> 0:45:07.270 to tell us about the expansion of the universe and 0:45:07.350 --> 0:45:11.569 red shifts and the structure of the universe. So we 0:45:11.630 --> 0:45:14.969 are learning so much more. It reminds me of like, 0:45:15.210 --> 0:45:17.310 have you seen early maps? I love looking at like 0:45:17.610 --> 0:45:21.339 maps people drew of the world in like 1200, you know, 0:45:21.360 --> 0:45:23.469 when like they didn't know about this whole continent and 0:45:23.489 --> 0:45:26.060 they misunderstood this whole piece, but you see truth in there. 0:45:26.520 --> 0:45:28.540 You see like the shape of Portugal or you see 0:45:28.580 --> 0:45:31.910 like the coast of Madagascar or whatever. And that's what 0:45:31.969 --> 0:45:33.930 our maps are like today. And I think in a 0:45:33.969 --> 0:45:37.350 thousand years, people will look back at our primitive, basic 0:45:37.450 --> 0:45:40.790 maps of our neighborhood and be like, wow, they knew nothing. 0:45:41.710 --> 0:45:44.280 But the information is coming. We are building those maps. 0:45:44.320 --> 0:45:47.800 We are exploring the universe. We're figuring out. And along 0:45:47.820 --> 0:45:50.580 the way, we're discovering mysteries and puzzles, which are going 0:45:50.600 --> 0:45:52.900 to clue us into how the universe works. There are 0:45:53.610 --> 0:45:57.109 answers out there to questions we haven't thought to ask 0:45:57.210 --> 0:46:00.250 because we haven't even mapped out what the universe looks like, 0:46:00.570 --> 0:46:03.549 you know? And so we can't, we don't even know 0:46:03.590 --> 0:46:04.420 what to ask yet. 0:46:04.719 --> 0:46:04.859 Yep. 0:46:05.040 --> 0:46:08.120 We are constantly pushing the boundaries of our ignorance back 0:46:08.180 --> 0:46:08.980 farther and farther. 0:46:09.040 --> 0:46:09.420 I love it. 0:46:09.520 --> 0:46:12.580 Yeah. And super voids are really fascinating hole in our 0:46:12.600 --> 0:46:16.450 understanding because, you know, we don't fully understand how they form. 0:46:16.550 --> 0:46:19.509 Are we just lucky slash unlucky? Is there something else 0:46:19.550 --> 0:46:22.310 going on in the universe that makes these incredibly under 0:46:22.370 --> 0:46:24.890 dense regions? Is this a clue or is it a 0:46:24.930 --> 0:46:27.549 red herring? We don't know. And really, the only way 0:46:27.590 --> 0:46:30.840 to know is to get more data, more mapping, more structure, 0:46:31.020 --> 0:46:33.940 more images, more understanding of where we are in the universe. 0:46:34.000 --> 0:46:38.410 I'm definitely for that. And also, it's cheap. Compared to 0:46:38.430 --> 0:46:40.830 the kind of stuff we spend money on, it costs pennies. 0:46:42.050 --> 0:46:46.010 Usually physics doesn't feel super cheap, but this one's cheap, 0:46:46.050 --> 0:46:46.530 you're saying? 0:46:47.870 --> 0:46:50.190 I mean, it's a lot more expensive than, say, a 0:46:50.250 --> 0:46:53.030 week in the archives in New York City reading somebody's 0:46:53.110 --> 0:46:55.009 blood-covered notes, hypothetically. 0:46:55.090 --> 0:46:55.669 That was fun. 0:46:55.710 --> 0:46:57.430 It's a lot more expensive than a lot of stuff. 0:46:57.950 --> 0:47:01.489 But compared to aircraft carriers, you know, or wars in 0:47:01.510 --> 0:47:02.890 the Middle East, it's definitely cheap. 0:47:03.430 --> 0:47:05.770 And then you get to enjoy that knowledge forever. 0:47:06.050 --> 0:47:08.890 Yes, you do. And you create the opportunities for a 0:47:08.969 --> 0:47:11.969 new generation of scientists to study new puzzles and come 0:47:12.030 --> 0:47:15.390 up with new answers. So thanks very much to Nathan 0:47:15.489 --> 0:47:18.110 and Levi for asking about superboards and giving us an 0:47:18.150 --> 0:47:21.489 opportunity to talk about this incredible cosmic history, all the 0:47:21.530 --> 0:47:24.729 detective stories we've cracked along the way, and so many 0:47:24.850 --> 0:47:26.710 open questions we have yet to even ask. 0:47:27.210 --> 0:47:28.210 Fun science, please. 0:47:37.070 --> 0:47:39.440 Thanks everybody for listening. 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