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Transcript

Supervoids · Daniel and Kelly’s Extraordinary Universe

• 0:07
  Speaker 1: When you look out into the night sky on a
• 0:09
  Speaker 1: camping trip, you're seeing the best view in the universe.
• 0:14
  Speaker 1: Much better than standing on a mountain top or on
• 0:17
  Speaker 1: the top floor of a building. Stretching over zillions of
• 0:21
  Speaker 1: light years of cosmic space, you're seeing entire stars and
• 0:25
  Speaker 1: galaxies across this black ocean. It's amazing. But there's something
• 0:30
  Speaker 1: else for you to see up there, for us to
• 0:32
  Speaker 1: learn about. The empty bits. Between the galaxies stretch huge
• 0:37
  Speaker 1: regions without all that flashy, glowy stuff. How is that
• 0:41
  Speaker 1: all arranged? What is the map of galaxies in the universe?
• 0:45
  Speaker 1: And what does that tell us about how the universe
• 0:49
  Speaker 1: forms and the forces that shape it? Today in the pod,
• 0:53
  Speaker 1: we're digging into the biggest maps we can make of
• 0:55
  Speaker 1: the biggest stuff and the biggest non-stuff in the universe.
• 1:00
  Speaker 1: Welcome to Daniel and Kelly's Extraordinary Mostly Empty Universe.
• 1:18
  Speaker 2: Hello, I'm Kelly Wienersmith.
• 1:19
  Speaker 3: I study parasites and space, and super void sounds like
• 1:23
  Speaker 3: a sort of gothy concept, so 16-year-old Kelly is totally
• 1:27
  Speaker 3: into it.
• 1:27
  Speaker 1: Hi, I'm Daniel. I'm a particle physicist who likes to
• 1:32
  Speaker 1: think about aliens, and I'm about 0% goth. So when
• 1:36
  Speaker 1: I hear super void, I don't think black lipstick. I
• 1:39
  Speaker 1: think Marvel characters.
• 1:41
  Speaker 2: Oh, all right.
• 1:42
  Speaker 3: Well, so Super Voids does make me think of gothy stuff,
• 1:44
  Speaker 3: which reminds me of some of my favorite gothy characters,
• 1:48
  Speaker 3: which are Frankenfurter from the Rocky.
• 1:50
  Speaker 2: Horror Picture Show.
• 1:51
  Speaker 1: Yes. R.I.P. Tim Curry.
• 1:54
  Speaker 2: Exactly. And the devil in Legend, which, yes.
• 1:58
  Speaker 3: So my question for you today is, what was Tim
• 2:01
  Speaker 3: Curry's best role and why is it the saddest thing
• 2:03
  Speaker 3: in the whole world that Tim Curry is gone?
• 2:05
  Speaker 1: Okay.
• 2:06
  Speaker 2: Because it's the saddest thing in the world that Tim
• 2:08
  Speaker 2: Curry is gone.
• 2:09
  Speaker 1: It is sad. He was wonderful. I loved him in Clue. Oh.
• 2:12
  Speaker 1: You know, the hilarious movie. Wonderful. And I love a mystery.
• 2:17
  Speaker 1: You know, for me, science is the biggest mystery in
• 2:20
  Speaker 1: the universe. How does this all work? Who caused the
• 2:23
  Speaker 1: ripples in the primordial plasma? You know, was it the
• 2:28
  Speaker 1: butler with the candlestick in the early universe? Who knows?
• 2:32
  Speaker 2: You are so good at keeping us on track.
• 2:35
  Speaker 1: I'm doing my best here. Oh, my gosh. This car
• 2:38
  Speaker 1: is going off into the weeds of Virginia.
• 2:39
  Speaker 3: I just needed a moment to like vent and feel
• 2:44
  Speaker 3: seen because I am just devastated about the loss of
• 2:47
  Speaker 3: Tim Curry.
• 2:48
  Speaker 1: Would you say that the loss of Tim Curry creates
• 2:50
  Speaker 1: a void in your heart?
• 2:51
  Speaker 2: A super void, Daniel. And so, and my heart is
• 2:55
  Speaker 2: now cold and empty.
• 2:57
  Speaker 3: And let's go ahead and change the subject before I
• 3:00
  Speaker 3: get too emotional here and dig into super voids.
• 3:03
  Speaker 2: Why are we talking about super voids today?
• 3:06
  Speaker 1: We're talking about supervoids because they're super awesome. They're fascinating.
• 3:10
  Speaker 1: They're one of the biggest things or non-things in the universe.
• 3:14
  Speaker 1: They tell us so much about its history, about its future,
• 3:17
  Speaker 1: about its formation, about how it works. And it's so
• 3:20
  Speaker 1: hard to get them in your mind because they give
• 3:23
  Speaker 1: you a sense of scale of the universe, you know?
• 3:26
  Speaker 1: how tiny, how small, how insignificant we are, and yet
• 3:30
  Speaker 1: how we can cast our minds to understanding the largest
• 3:34
  Speaker 1: scale structures in the universe, which stretch across billions and
• 3:38
  Speaker 1: zillions of light years. It's super awesome to think about
• 3:41
  Speaker 1: super voids. And I'm not the only one who thinks so.
• 3:44
  Speaker 1: We got a request from two listeners, Levi and Nathan,
• 3:48
  Speaker 1: who wrote and said, hey, would you tell us why
• 3:50
  Speaker 1: the universe has super voids. So that's why we're talking
• 3:54
  Speaker 1: about super voids specifically today.
• 3:57
  Speaker 3: Well, and I noted in that email that Levi also
• 4:00
  Speaker 3: says he enjoys my poop jokes. And so this is
• 4:03
  Speaker 3: a family that gets our podcast.
• 4:06
  Speaker 1: Exactly. And we'll try to make as many poo jokes
• 4:08
  Speaker 1: as we can in today's episode, just for you, Levi.
• 4:12
  Speaker 3: I am trying to connect super voids to poo jokes.
• 4:15
  Speaker 3: And the only thing I can think about is the
• 4:16
  Speaker 3: prep for a colonoscopy. You are super voided at that point.
• 4:21
  Speaker 3: But probably that joke's over Levi's head because Levi's a
• 4:24
  Speaker 3: little bit younger, isn't he?
• 4:25
  Speaker 2: Yeah.
• 4:26
  Speaker 1: Yes, exactly. But maybe Levi thinks about super voids every
• 4:29
  Speaker 1: time he's voiding himself.
• 4:31
  Speaker 2: Okay. Well, good.
• 4:32
  Speaker 1: Look it.
• 4:32
  Speaker 2: We did it. We did it. We got the poop
• 4:34
  Speaker 2: jokes in there.
• 4:35
  Speaker 3: Yes.
• 4:36
  Speaker 1: And, you know, a really important thing for understanding super
• 4:38
  Speaker 1: voids and the structure of the universe is, is dark matter,
• 4:42
  Speaker 1: which is its own poo joke right there.
• 4:44
  Speaker 3: Oh, man, I love the work we do together, Daniel.
• 4:47
  Speaker 2: It's the best.
• 4:49
  Speaker 1: We are out here doing hard-hitting science. No, really, we
• 4:52
  Speaker 1: are proving that it's possible to do deep dives into
• 4:55
  Speaker 1: science and also make poo jokes. That is our niche
• 4:58
  Speaker 1: in the SciComm community. That's right. But before we tell
• 5:01
  Speaker 1: you what we think about super voids and dig into
• 5:04
  Speaker 1: the cosmic history that created them and our confusion about them...
• 5:08
  Speaker 1: I wondered what the extraordinaries thought about why the universe
• 5:12
  Speaker 1: has super voids. So I reached out to our group
• 5:15
  Speaker 1: of volunteers, which you are very, very welcome to join.
• 5:19
  Speaker 1: Just write to us to questions at danielandkelly.org and you
• 5:23
  Speaker 1: can join this crew. In the meantime, think about it
• 5:25
  Speaker 1: for a minute. Why do you think the universe has
• 5:28
  Speaker 1: super voids?
• 5:30
  Speaker 2: The universe is expanding and the amount of stuff in
• 5:33
  Speaker 2: it is not increasing.
• 5:35
  Speaker 1: So we can fight all of those dastardly dark energy
• 5:39
  Speaker 1: and dark matter criminals. Initial randomness allowed some parts to
• 5:44
  Speaker 1: get denser and presumably some parts to get a lot sparser.
• 5:49
  Speaker 1: It's for the same reason that my gravy has lumps
• 5:51
  Speaker 1: in it. I don't know what that reason is, but
• 5:53
  Speaker 1: I think it's the same reason. Collects in some places,
• 5:56
  Speaker 1: then it has to clear out in others.
• 5:58
  Speaker 2: I think it has to do with the way matter
• 6:02
  Speaker 2: was created during the Big Bang.
• 6:05
  Speaker 1: I would guess some astronomers saw some very cold or
• 6:08
  Speaker 1: empty patch in space and could not avoid to give
• 6:13
  Speaker 1: it a super name.
• 6:15
  Speaker 2: Does not have to be uniform. I have no idea
• 6:17
  Speaker 2: what a super void is. Is it like a really,
• 6:20
  Speaker 2: really big void? Because of dark matter. A void is
• 6:25
  Speaker 2: just void.
• 6:26
  Speaker 1: Because of dark matter.
• 6:28
  Speaker 2: It's because of dark matter.
• 6:29
  Speaker 1: Yeah.
• 6:29
  Speaker 2: We're confused.
• 6:30
  Speaker 1: Help us.
• 6:32
  Speaker 2: Oh, my gosh. I love the answers.
• 6:34
  Speaker 3: Astronomers saw an empty patch and couldn't avoid giving it
• 6:38
  Speaker 3: a super name.
• 6:39
  Speaker 2: You are my new best friend.
• 6:42
  Speaker 1: That's got everything you love, right? It's got a pun.
• 6:44
  Speaker 1: It's got a dig against astronomers.
• 6:48
  Speaker 3: I feel like it implies that astronomers give things good names.
• 6:51
  Speaker 2: Oh, maybe they do. No, no, they don't, actually. What
• 6:53
  Speaker 2: is it?
• 6:54
  Speaker 3: The rings around Saturn or Jupiter or like A, B, C,
• 6:57
  Speaker 3: and D or.
• 6:59
  Speaker 1: Yeah, exactly. The solar system is a disaster. Even beyond
• 7:02
  Speaker 1: planets and dwarf planets, you've got like centaurs and meteors
• 7:06
  Speaker 1: and all sorts of stuff. It's a mess.
• 7:09
  Speaker 2: It's a mess.
• 7:09
  Speaker 3: But we are here to clear up confusion. And so
• 7:12
  Speaker 3: let's jump right in. Daniel, what the heck is the
• 7:15
  Speaker 3: super void?
• 7:18
  Speaker 1: So to understand super voids, we first have to understand
• 7:21
  Speaker 1: our cosmic context, like the structure of the universe around us.
• 7:25
  Speaker 1: So let's start here in California or Virginia. California, by
• 7:29
  Speaker 1: the way, feeling more like Virginia these days, you know,
• 7:32
  Speaker 1: because it's like stinky and humid and gross and like,
• 7:37
  Speaker 1: where do I even live anymore, man?
• 7:39
  Speaker 3: I see that your handle on Riverside today is humidity hater.
• 7:43
  Speaker 3: This is really living rent free in your brain. I'm
• 7:47
  Speaker 3: not a humidity fan either.
• 7:48
  Speaker 1: I mean, since we're putting ourselves in the cosmic context,
• 7:50
  Speaker 1: it's important to note that Los Angeles yesterday was the
• 7:52
  Speaker 1: most humid place in the country, which is breaking all
• 7:56
  Speaker 1: the rules, if you ask me.
• 7:58
  Speaker 2: That does not seem fair.
• 7:59
  Speaker 1: Anyway, zoom out from the sticky issues here on planet Earth.
• 8:03
  Speaker 1: And of course, we have our solar system. And the
• 8:05
  Speaker 1: sun is just one of hundreds of billions of stars
• 8:10
  Speaker 1: in the Milky Way swirling around in roughly a disk.
• 8:14
  Speaker 1: And then our galaxy is not just one of zillions
• 8:16
  Speaker 1: scattered through the universe. Galaxies themselves cluster. So we have
• 8:21
  Speaker 1: the local cluster of galaxies, a bunch of galaxies that
• 8:24
  Speaker 1: are gravitationally bound together, which doesn't mean that there's like
• 8:28
  Speaker 1: some big object in the center around which everything is
• 8:31
  Speaker 1: orbiting the way it is in the solar system. But
• 8:33
  Speaker 1: it does mean that there is a center of mass
• 8:35
  Speaker 1: of the local cluster and everything is swirling around that.
• 8:39
  Speaker 2: Okay, I'm with you.
• 8:40
  Speaker 1: All right, so we have clusters. And now clusters organize
• 8:43
  Speaker 1: into superclusters, right? Astronomers, great names. And superclusters are not
• 8:49
  Speaker 1: always gravitationally bound. They're like near each other in that
• 8:53
  Speaker 1: you can look at them and say, oh, these clusters
• 8:55
  Speaker 1: are near each other. But it's not clear whether gravity
• 8:58
  Speaker 1: is strong enough to hold them together. Because remember, the
• 9:00
  Speaker 1: universe is expanding. It's creating new space between everything. And
• 9:04
  Speaker 1: that includes new space between California and Virginia, new space
• 9:08
  Speaker 1: between Earth and the Sun, new space between the Sun
• 9:11
  Speaker 1: and the center of the Milky Way. But because there's
• 9:13
  Speaker 1: enough gravity to hold the Earth together and hold the
• 9:16
  Speaker 1: Sun to the Earth and hold the Sun to the
• 9:18
  Speaker 1: rest of the galaxy, those distances are not increasing. So
• 9:22
  Speaker 1: the expansion of the universe is losing to gravity. But
• 9:26
  Speaker 1: gravity gets weaker as distances get greater. So when you
• 9:29
  Speaker 1: get to super voids, dark energy is starting to get
• 9:31
  Speaker 1: powerful enough that it's going to overcome gravity. And that's
• 9:35
  Speaker 1: right about the cutoff. So we don't think that all
• 9:38
  Speaker 1: superclusters are technically objects in the sense that they're not
• 9:41
  Speaker 1: gravitationally bound. We think that as time goes on, they
• 9:44
  Speaker 1: probably will get pulled apart. But they're still sort of
• 9:47
  Speaker 1: objects in the sense that they're near each other. And
• 9:49
  Speaker 1: if you looked at them on a map, you'd probably
• 9:51
  Speaker 1: draw a circle around them.
• 9:52
  Speaker 2: Okay. That doesn't sound void-y.
• 9:55
  Speaker 1: No, we're not at the voids yet. Okay. But now
• 9:58
  Speaker 1: we've already zoomed out incredibly, right? Like from the Earth
• 10:01
  Speaker 1: to the Sun to the galaxy to like clusters of
• 10:05
  Speaker 1: galaxies to now super clusters of galaxies. It might feel
• 10:09
  Speaker 1: like this is the biggest thing you could ever have
• 10:11
  Speaker 1: in your head. Okay, now collapse all those super clusters
• 10:14
  Speaker 1: down to a point because now we're going to zoom
• 10:16
  Speaker 1: out so far that structure inside a super cluster is irrelevant.
• 10:20
  Speaker 1: We're just going to treat each super cluster like a
• 10:22
  Speaker 1: dot and we're going to ask, How are the superclusters
• 10:26
  Speaker 1: organized across the universe? And they're not organized evenly. It's
• 10:30
  Speaker 1: not like somebody sprinkled sand across the universe, each one
• 10:34
  Speaker 1: being a supercluster. Instead, they form filaments. They form walls.
• 10:39
  Speaker 1: They form bubbles. So there are sheets and filaments of superclusters.
• 10:44
  Speaker 1: And inside those bubbles are the voids. That's where there
• 10:47
  Speaker 1: are fewer galaxies and fewer superclusters. And so imagine like
• 10:52
  Speaker 1: a foam, right? Where super clusters lie on the edges
• 10:56
  Speaker 1: of the bubbles and inside the bubbles, there's comparatively less.
• 10:59
  Speaker 3: All right, so my brain is now wondering why you
• 11:01
  Speaker 3: can't get super voids on the outsides of the bubbles too.
• 11:04
  Speaker 3: Am I just letting this analogy get stuck in my
• 11:07
  Speaker 3: head too much?
• 11:07
  Speaker 1: There is no outside to the bubbles. The universe is
• 11:10
  Speaker 1: filled with these bubbles.
• 11:12
  Speaker 3: Oh.
• 11:13
  Speaker 1: Yes, the bubbles are everywhere. The universe is just bubbles.
• 11:15
  Speaker 1: And it's the foam fills the whole universe. And everywhere
• 11:19
  Speaker 1: you have a bubble edge where the bubbles meet, that's
• 11:22
  Speaker 1: where you have superclusters, walls, sheets of superclusters. And inside,
• 11:26
  Speaker 1: those are the voids.
• 11:27
  Speaker 2: Whoa, okay.
• 11:29
  Speaker 1: Yeah.
• 11:29
  Speaker 3: Are they totally empty or just less empty than the
• 11:32
  Speaker 3: outside of the bubble?
• 11:33
  Speaker 1: Yeah, great question. They're not completely empty, right? It's a
• 11:36
  Speaker 1: relative density. So we measure the density of stuff in
• 11:39
  Speaker 1: the universe and we say anything less than like 10%
• 11:42
  Speaker 1: of the mean density, we call that a void. And
• 11:46
  Speaker 1: these things are pretty big. They have diameters like 10
• 11:49
  Speaker 1: to 100 megaparsecs, which is like 300 million light years across.
• 11:56
  Speaker 1: Oh my gosh. These are vast structures. And these are
• 11:58
  Speaker 1: not super voids. These are just voids. These are just normal, everyday,
• 12:02
  Speaker 1: run-of-the-mill voids. Already, these things are much, much bigger than
• 12:07
  Speaker 1: one individual supercluster relative to To a void, a supercluster
• 12:10
  Speaker 1: is so tiny you just think of it as a dot.
• 12:12
  Speaker 1: And remember, inside that supercluster is a bunch of clusters
• 12:16
  Speaker 1: of galaxies, and inside each cluster of galaxies is a
• 12:19
  Speaker 1: bunch of galaxies, each of which is unfathomably huge to
• 12:22
  Speaker 1: the human mind. So this is like a real brain
• 12:25
  Speaker 1: stretcher to even get this in your head, what a
• 12:28
  Speaker 1: supervoid is and how big it is.
• 12:30
  Speaker 2: Yeah, I was.
• 12:31
  Speaker 3: So you said 30 to 300 million light years. And
• 12:34
  Speaker 3: I was still having a little trouble wrapping my head
• 12:36
  Speaker 3: around that number.
• 12:38
  Speaker 2: So I just looked it up.
• 12:38
  Speaker 3: The distance between our galaxy and Andromeda is 2.5 million
• 12:43
  Speaker 3: light years away. So we are talking about voids that
• 12:46
  Speaker 3: are like, I don't know, 15 times bigger than that minimum.
• 12:51
  Speaker 2: That is huge.
• 12:53
  Speaker 1: Yeah. And, you know, the size of our galaxy is
• 12:55
  Speaker 1: like 100,000 light years across. And so if you can
• 12:59
  Speaker 1: somehow get the Milky Way into your brain, then we're
• 13:02
  Speaker 1: talking about distances that are thousands of times bigger than
• 13:06
  Speaker 1: the Milky Way.
• 13:07
  Speaker 2: Oh, my gosh.
• 13:07
  Speaker 1: And so, yeah, these are big, empty regions of space. Wow.
• 13:12
  Speaker 2: We should put something in there.
• 13:17
  Speaker 1: I mean, I know your house is filled to the
• 13:19
  Speaker 1: brim with all kinds of Interesting stuff. And so you're
• 13:23
  Speaker 1: always looking for more storage space.
• 13:25
  Speaker 3: I was thinking we could put all the stuff in
• 13:26
  Speaker 3: my house into the super void so that I don't have,
• 13:29
  Speaker 3: but I think Zach might fill the super void pretty quick.
• 13:34
  Speaker 2: With Dorito bags.
• 13:37
  Speaker 1: Not just Dorito bags, but you know, you've got all
• 13:39
  Speaker 1: these projects. They're always half done. You're like, I'm storing
• 13:42
  Speaker 1: all these cabinets in this room because I can't put
• 13:44
  Speaker 1: them on the wall yet. They're on the wall now.
• 13:46
  Speaker 2: Do you imagine?
• 13:48
  Speaker 1: Do you imagine someday in the future you will be
• 13:50
  Speaker 1: done with projects and the house will just be like
• 13:52
  Speaker 1: actually totally functional?
• 13:54
  Speaker 2: No.
• 13:55
  Speaker 1: No? No. She says with resignation.
• 13:58
  Speaker 2: I don't know when I'll have time to finish everything.
• 14:01
  Speaker 2: Maybe when I die.
• 14:03
  Speaker 1: All right. Well, maybe your house never will have voids.
• 14:05
  Speaker 1: It's always going to be filled with stuff. But the
• 14:08
  Speaker 1: universe has voids and they're fascinating. And they were kind
• 14:11
  Speaker 1: of a surprise when we learned that the universe had
• 14:14
  Speaker 1: this structure.
• 14:15
  Speaker 2: So why?
• 14:16
  Speaker 3: OK, so if I'm like imagining a giant space, I
• 14:20
  Speaker 3: would imagine that if you like distributed stuff around that space,
• 14:24
  Speaker 3: you would expect there to be some empty areas for
• 14:26
  Speaker 3: random reasons. But you've I think you've already explained to
• 14:30
  Speaker 3: us that these voids aren't random because they tend to
• 14:32
  Speaker 3: be on the inside of like bubbles. Does that tell
• 14:35
  Speaker 3: us something about how they're formed?
• 14:37
  Speaker 1: It does tell us something about how they're formed. And
• 14:39
  Speaker 1: you put your finger on exactly what the discovery was.
• 14:42
  Speaker 1: Until around the 70s, we thought that galaxies were distributed
• 14:45
  Speaker 1: roughly equally. That, you know, any galaxy had an equal
• 14:49
  Speaker 1: chance to be here or there. And if you took
• 14:51
  Speaker 1: any chunk of space, you would find roughly the same
• 14:53
  Speaker 1: number of galaxies. You know, that the density was pretty smooth.
• 14:58
  Speaker 1: And it wasn't until the 70s that they went out
• 15:00
  Speaker 1: and they started measuring these things and trying to map
• 15:02
  Speaker 1: out the structure of the universe. You know, I love
• 15:05
  Speaker 1: when we have an idea about how the universe works.
• 15:07
  Speaker 1: And then we develop the technology, the capacity to actually
• 15:09
  Speaker 1: measure it. And the universe is like, no, what you
• 15:12
  Speaker 1: thought was natural, what you thought was intuitive, what you
• 15:15
  Speaker 1: thought made sense. That's not how things work. Because those
• 15:18
  Speaker 1: are the best moments. Those are the moments when the
• 15:20
  Speaker 1: universe is confronting your intuition and teaching you something about
• 15:24
  Speaker 1: how things work. I mean, not like the universe is
• 15:26
  Speaker 1: a teacher, you know, that cares what we understand. But
• 15:29
  Speaker 1: those are the best moments of discovery. And it was
• 15:32
  Speaker 1: in the 70s that people first started measuring red shifts
• 15:35
  Speaker 1: of these galaxies and trying to assemble them into sort
• 15:38
  Speaker 1: of a 3D map. What you need to understand the
• 15:40
  Speaker 1: structure of the universe is to know where is a galaxy?
• 15:43
  Speaker 1: How far away is it? If you know those two things,
• 15:46
  Speaker 1: you can start to build a 3D map of where
• 15:48
  Speaker 1: all the galaxies are and you can start to see structure.
• 15:51
  Speaker 1: And so people started doing this seriously in the 70s.
• 15:54
  Speaker 1: The Center for Astrophysics at Harvard and the Smithsonian started
• 15:57
  Speaker 1: to do this with the Tillinghast Telescope. And they were surprised.
• 16:01
  Speaker 1: They surveyed like 2,200 galaxies. And they saw that things
• 16:05
  Speaker 1: were not smooth, right? It didn't look like galaxies were
• 16:08
  Speaker 1: distributed randomly across the universe. They were clustered together into
• 16:12
  Speaker 1: these bubbles. Imagine a sheet of paper and you throw
• 16:15
  Speaker 1: sand over it and you expect there, as you said,
• 16:17
  Speaker 1: to be some places where there are galaxies and some
• 16:19
  Speaker 1: places where there are not. It's not going to be
• 16:21
  Speaker 1: perfectly smooth. You don't expect the galaxies to be like
• 16:24
  Speaker 1: in a grid, you know, perfectly arranged. There'd be some
• 16:27
  Speaker 1: clustering accidentally. But what they saw was definite structure, not
• 16:31
  Speaker 1: just random distributions. they saw like a bubble bath of
• 16:35
  Speaker 1: cosmic voids and filaments. And they discovered what they call
• 16:38
  Speaker 1: the Great Wall, a superstructure over 500 million light years wide.
• 16:43
  Speaker 1: And what a moment, you know, to be the first
• 16:45
  Speaker 1: person to map the universe, right? Like I always imagined...
• 16:50
  Speaker 1: The joy of being like a first person to land
• 16:52
  Speaker 1: on a new shore or to cross a land bridge or,
• 16:55
  Speaker 1: you know, get in a boat 10,000 years ago and
• 16:57
  Speaker 1: cross the Pacific to the South Pacific islands or whatever, right?
• 17:01
  Speaker 1: What a moment of discovery. But this is just on
• 17:03
  Speaker 1: another scale, you know? This is like, oh my gosh,
• 17:06
  Speaker 1: the universe has patterns and we're part of this and
• 17:09
  Speaker 1: there's a huge wall over there. And like, oh my God,
• 17:12
  Speaker 1: what a moment. And, you know, I think that's sort
• 17:15
  Speaker 1: of natural for us to think about now because we've
• 17:17
  Speaker 1: known about it for 50 years. But at the time,
• 17:19
  Speaker 1: this was a real revolution in the way people thought
• 17:22
  Speaker 1: about our entire cosmic context. So that was very cool,
• 17:26
  Speaker 1: and that was in the 70s. And again, the primary
• 17:29
  Speaker 1: way we figured this out is that we look at
• 17:30
  Speaker 1: galaxies and we measure their redshift, meaning that the light
• 17:34
  Speaker 1: that comes from them has been shifted to lower frequencies.
• 17:38
  Speaker 1: And we measure their redshift, which tells us how the
• 17:40
  Speaker 1: light has been shifted, which tells us how fast they're
• 17:43
  Speaker 1: moving away from us. Because remember, the things that are
• 17:45
  Speaker 1: moving away from us have their light shifted into the red.
• 17:49
  Speaker 1: And if we know how fast they're moving away from us,
• 17:51
  Speaker 1: then we can tell how far away they are because
• 17:54
  Speaker 1: that's the Hubble relationship. It tells us that things that
• 17:56
  Speaker 1: are further away are moving away faster. So if you
• 17:59
  Speaker 1: just measure the light from one of these galaxies, you
• 18:01
  Speaker 1: measure the redshift, you say, I know where hydrogen should be.
• 18:05
  Speaker 1: I know where helium should be on my spectrum. And
• 18:07
  Speaker 1: I see it shifted. You measure that shift. You can
• 18:10
  Speaker 1: translate that to the distance to the galaxies. And now
• 18:13
  Speaker 1: you know the angle in the sky, right? You know,
• 18:15
  Speaker 1: I saw this galaxy at this angle. I saw that
• 18:17
  Speaker 1: galaxy at the other angle. You put those together and
• 18:19
  Speaker 1: you start to make your 3D map of the universe.
• 18:22
  Speaker 3: Amazing.
• 18:23
  Speaker 2: Okay, so now we know what the pattern is. Let's
• 18:27
  Speaker 2: take a break.
• 18:27
  Speaker 3: And when we come back, we'll talk about now that
• 18:29
  Speaker 3: we know what the pattern is, what does that imply
• 18:31
  Speaker 3: about how everything ended up where it finally ended up?
• 18:54
  Speaker 2: And we're back. We've been talking about how.
• 18:57
  Speaker 3: Like the universe is like this foamy wash full of
• 19:01
  Speaker 3: clusters that are like on the edges of the bubbles.
• 19:04
  Speaker 3: And then inside of the bubbles, we have super voids.
• 19:07
  Speaker 3: What does that tell us about how the universe formed?
• 19:11
  Speaker 3: And like, have we figured that out yet? Because that's
• 19:13
  Speaker 3: not what we expected.
• 19:14
  Speaker 1: Right, yeah. So first, slight clarification. Inside the bubbles are voids.
• 19:18
  Speaker 2: Oh, okay.
• 19:18
  Speaker 1: Super voids we haven't really talked about exactly yet. Super
• 19:21
  Speaker 1: voids are essentially like really, really big voids. In many cases,
• 19:25
  Speaker 1: bigger than we expect. And so that's why we have
• 19:28
  Speaker 1: to dive into the history of the universe to think
• 19:29
  Speaker 1: about like, do we expect to see voids? Do we
• 19:31
  Speaker 1: expect to see super voids? Does what we see line
• 19:34
  Speaker 1: up with what we expect? And to do that, we
• 19:36
  Speaker 1: have to go all the way back to the earliest
• 19:38
  Speaker 1: known thing in the universe.
• 19:40
  Speaker 2: Which is?
• 19:41
  Speaker 1: The cosmic microwave background, of course, which, you know, physics
• 19:44
  Speaker 1: is always going back to. You might be like, oh,
• 19:46
  Speaker 1: my gosh, these guys lean on the CMB so much.
• 19:48
  Speaker 1: It's just such a. rich and incredible source of information.
• 19:52
  Speaker 1: You know, if you were trying to understand somebody's life
• 19:55
  Speaker 1: and you had like a picture of them in kindergarten,
• 19:58
  Speaker 1: it would tell you so much about where they grew
• 20:00
  Speaker 1: up and what they were like. And that's basically what
• 20:02
  Speaker 1: we have. We And so when we want to understand
• 20:07
  Speaker 1: how the universe got to be the way it is,
• 20:09
  Speaker 1: we look back at that baby picture. We're like, huh,
• 20:11
  Speaker 1: did it have seven toes when it was born? Or
• 20:13
  Speaker 1: was that surgery that came later? You know, what features
• 20:16
  Speaker 1: of the universe can you trace back to the origin?
• 20:19
  Speaker 1: And if they're not there, what does that tell you?
• 20:21
  Speaker 1: So it's incredibly valuable. And that's why we look back.
• 20:24
  Speaker 1: And for those of you who don't remember, the cosmic
• 20:26
  Speaker 1: microwave background light is light that came from the universe
• 20:29
  Speaker 1: the first moment that it was transparent. So we don't
• 20:32
  Speaker 1: know how the universe began or when it began, but
• 20:34
  Speaker 1: we do know that it was filled with a hot,
• 20:37
  Speaker 1: dense plasma and that plasma was glowing and it was opaque.
• 20:40
  Speaker 1: Just like plasma at the center of the sun, it
• 20:42
  Speaker 1: gives off light and then is immediately reabsorbed. Which, you know,
• 20:45
  Speaker 1: you hear maybe on pop-sci channels like a photon takes
• 20:49
  Speaker 1: 50,000 years to get from the center of the sun
• 20:50
  Speaker 1: to the surface of the sun. And that's like mostly
• 20:52
  Speaker 1: pop-sci nonsense. because a photon is emitted at the center
• 20:56
  Speaker 1: of the sun and then immediately absorbed. It never gets
• 20:58
  Speaker 1: to the surface. Like, you know, maybe you could say
• 21:01
  Speaker 1: that heat waves travel through the sun at some velocity
• 21:03
  Speaker 1: or whatever, but you're not tracing a photon. Anyway, photons
• 21:07
  Speaker 1: that were created in the very early universe, no longer around,
• 21:10
  Speaker 1: immediately absorbed because the universe they were born into was opaque.
• 21:14
  Speaker 1: But the universe is expanding and the universe is cooling.
• 21:17
  Speaker 1: And at some point, the universe expanded and cooled enough
• 21:20
  Speaker 1: that protons and electrons found each other and became neutral.
• 21:24
  Speaker 1: And then the universe became suddenly transparent. So photons that
• 21:28
  Speaker 1: were born after that moment are still around. And they
• 21:31
  Speaker 1: are still here for us to measure and for us
• 21:34
  Speaker 1: to learn about the early universe. And what we see
• 21:37
  Speaker 1: in those photons is not a smooth plasma. Not like
• 21:41
  Speaker 1: everything was filled with stuff equally. We see some places
• 21:44
  Speaker 1: with more density and some places with less density.
• 21:47
  Speaker 3: And that is not what we expected initially. And why
• 21:51
  Speaker 3: is that not what we expected initially?
• 21:54
  Speaker 1: Yeah, good question. Here we have like two threads we
• 21:56
  Speaker 1: have to follow. One is the density of galaxies as
• 22:01
  Speaker 1: we're seeing them like today. And that started in the 70s.
• 22:05
  Speaker 1: And by the 70s, we had seen the cosmic microwave
• 22:08
  Speaker 1: background light. That happened in the 60s. It was a
• 22:10
  Speaker 1: huge confirmation that the universe had an early hot, dense state.
• 22:13
  Speaker 1: But we had not yet seen its wiggles. It wasn't
• 22:16
  Speaker 1: until like the 80s and the 90s that we measured
• 22:18
  Speaker 1: the CMB light with enough precision to see, oh, there
• 22:22
  Speaker 1: are some little hot spots and there are some little
• 22:24
  Speaker 1: cold spots. It just seemed sort of smooth. And so
• 22:27
  Speaker 1: it wasn't until later that we saw wiggles in the
• 22:29
  Speaker 1: CMB and we saw structure in the universe. And you're
• 22:33
  Speaker 1: right to ask about that because those two things are
• 22:35
  Speaker 1: definitely connected. And the listener who made that connection is
• 22:38
  Speaker 1: totally right. We think that all the structure in the
• 22:41
  Speaker 1: current universe comes from that structure in the early universe.
• 22:45
  Speaker 1: That you had places with more density and that had
• 22:47
  Speaker 1: more gravity and that pulled in more stuff. And that
• 22:50
  Speaker 1: in those regions, you now have more galaxies and more
• 22:53
  Speaker 1: dark matter than in places where you didn't. And so
• 22:56
  Speaker 1: you should be able to line up a place in
• 22:58
  Speaker 1: the early universe where there was less dense stuff with
• 23:01
  Speaker 1: voids today.
• 23:02
  Speaker 2: Okay, got it.
• 23:03
  Speaker 1: And you might be tempted to say, oh, well, can
• 23:06
  Speaker 1: we trace an individual like hotspot or cold spot in
• 23:09
  Speaker 1: the CMB to something in the universe today? And you
• 23:14
  Speaker 1: might be preparing yourself for disappointment because usually the answer
• 23:17
  Speaker 1: to that is no. We can just do it statistically.
• 23:19
  Speaker 1: We can say, oh, we expect this kind of distribution
• 23:22
  Speaker 1: of galaxies in the late universe based on this kind
• 23:26
  Speaker 1: of density in the early universe. But we can't say
• 23:28
  Speaker 1: like this photon caused that galaxy or whatever, right? But
• 23:32
  Speaker 1: there is one feature that seems to correlate.
• 23:34
  Speaker 2: What?
• 23:35
  Speaker 1: So there's a feature in the early universe, the cosmic
• 23:38
  Speaker 1: microwave background, that seems to line up with a super
• 23:41
  Speaker 1: void in the universe. Yeah. So the feature in the
• 23:44
  Speaker 1: cosmic microwave background is called the CMB cold spot. This
• 23:48
  Speaker 1: is a region where it's redder than everywhere else. So
• 23:52
  Speaker 1: we expect there to be some variations in the cosmic
• 23:55
  Speaker 1: microwave background. They vary by like microkelvin. And we talk
• 23:59
  Speaker 1: about the CMB in terms of temperature, which is equivalent
• 24:01
  Speaker 1: to thinking about wavelength, because blackbody radiation rules tell us
• 24:05
  Speaker 1: that something at a certain temperature will radiate at a
• 24:08
  Speaker 1: certain wavelength. So when we measure light at a certain wavelength,
• 24:11
  Speaker 1: we say, oh, that came from an object at a
• 24:13
  Speaker 1: certain temperature. So for example, the CMB light came from
• 24:16
  Speaker 1: a really hot plasma, thousands and thousands of degrees, I
• 24:19
  Speaker 1: think 3,000 K. But that light has been redshifted by
• 24:22
  Speaker 1: the expansion of the universe down to about 2.7 K.
• 24:25
  Speaker 1: So if you read that like oh, the CMB light
• 24:28
  Speaker 1: is 2.7K, that's what it means. It means that it's
• 24:30
  Speaker 1: the wavelength that an object at 2.7 Kelvin would emit.
• 24:33
  Speaker 1: So very, very cold light. And we see variations like
• 24:37
  Speaker 1: 20 microkelvin in the CMB. That's like typical expected hot
• 24:41
  Speaker 1: spots and cold spots. But there is one spot in
• 24:44
  Speaker 1: the CMB, one spot in the sky when we look
• 24:46
  Speaker 1: at it, that it's like 70 microkelvin colder. So some
• 24:50
  Speaker 1: places like 150 microK colder. It's in the southern hemisphere
• 24:55
  Speaker 1: in the direction of the constellation Eridanus, which is maybe
• 24:59
  Speaker 1: the source of a poop joke for those of you
• 25:01
  Speaker 1: who are interested in the southern hemisphere.
• 25:04
  Speaker 3: If you could see how it's spelled, you would get
• 25:07
  Speaker 3: why this could be a poop joke.
• 25:09
  Speaker 1: Maybe all constellations in the southern hemisphere should have anus
• 25:13
  Speaker 1: in them, you know? Absolutely.
• 25:14
  Speaker 2: Yes.
• 25:16
  Speaker 1: Astronomers, get on that.
• 25:17
  Speaker 2: Or synonyms of anus. Yes. Because you need some options.
• 25:21
  Speaker 1: Yeah. So this is really interesting. You know, it could
• 25:24
  Speaker 1: just be random. It could just be like a fluctuation.
• 25:27
  Speaker 1: And they've done a calculation to suggest it's like, there's
• 25:29
  Speaker 1: like a 1.5% chance of this happening randomly. So it's
• 25:33
  Speaker 1: like weird. It sticks out, but it's not insane. But
• 25:37
  Speaker 1: it does also correspond with a place in the late
• 25:41
  Speaker 1: universe that there seems to be a super void.
• 25:45
  Speaker 3: And you said at one point, well, we haven't really
• 25:48
  Speaker 3: talked about super voids yet.
• 25:49
  Speaker 2: And super voids are just like Really big voids, right?
• 25:52
  Speaker 1: Yes, exactly. Okay. And so if you look in the
• 25:55
  Speaker 1: structure of the universe today, in the same direction, you
• 25:59
  Speaker 1: do see a really, really big void there. It's like
• 26:03
  Speaker 1: a thousand times the size of a typical void. Wow.
• 26:07
  Speaker 1: So it's like you have bubbles in your sink and
• 26:09
  Speaker 1: they're all roughly the same size. And then there's one
• 26:11
  Speaker 1: that's just like a thousand times bigger than all the
• 26:14
  Speaker 1: other bubbles. This one's a billion light years across. It's
• 26:18
  Speaker 1: like five to 10 billion light years away.
• 26:20
  Speaker 3: So is this like most mornings you eat Special K,
• 26:24
  Speaker 3: but one morning you eat Poops Like a Champion?
• 26:26
  Speaker 2: And that's the difference between void and super void?
• 26:29
  Speaker 1: Yes, exactly. You feel it about 24 hours later, exactly,
• 26:36
  Speaker 1: when you have a super void. And here the universe
• 26:39
  Speaker 1: has formed a void like a champion.
• 26:41
  Speaker 3: And just to be clear, Poops Like a Champion... Is
• 26:44
  Speaker 3: an actual cereal you told me about the other day.
• 26:48
  Speaker 1: It is an actual cereal and we have boxes of
• 26:50
  Speaker 1: it at home. Because some company out there that makes
• 26:53
  Speaker 1: it heard about Katrina and her fiber journey and her,
• 26:57
  Speaker 1: you know, her effort to make everybody poop better by
• 27:00
  Speaker 1: eating fiber and improve their gut microbiome. So they sent
• 27:03
  Speaker 1: her a bunch of free boxes of poop like a champion.
• 27:06
  Speaker 1: And I am not on their payroll, so I can
• 27:08
  Speaker 1: tell you that it tastes like cardboard.
• 27:11
  Speaker 3: But still, you know, I think Katrina is one of
• 27:13
  Speaker 3: the better people on this planet.
• 27:16
  Speaker 2: That's what that story tells me.
• 27:18
  Speaker 1: She's out there. She really does want to improve your pooping. Yeah.
• 27:21
  Speaker 1: Even though she has nothing to do with super voids.
• 27:23
  Speaker 3: I tried really hard to derail this conversation.
• 27:26
  Speaker 2: Let's go back to super voids of the universe.
• 27:30
  Speaker 1: Yeah. So this is really interesting because when you run
• 27:33
  Speaker 1: the simulations in the universe, you don't get these kinds
• 27:36
  Speaker 1: of super voids. Like it's really unusual. And so it
• 27:39
  Speaker 1: helps us try to understand, like, you know, we talked
• 27:42
  Speaker 1: about in our simulating the universe episode recently that, How
• 27:46
  Speaker 1: when you see something different in your simulation and in
• 27:48
  Speaker 1: your data, it tells you that there's a gap. There's
• 27:50
  Speaker 1: something in your simulation that isn't describing the universe correctly,
• 27:54
  Speaker 1: or there's an element of the universe that you're not
• 27:56
  Speaker 1: describing correctly. And these are super fascinating, especially because they're
• 28:00
  Speaker 1: very sensitive to the expansion of the universe. How we
• 28:04
  Speaker 1: see these cold spots and these hot spots in the
• 28:06
  Speaker 1: CMB tells us a lot about the expansion of the
• 28:09
  Speaker 1: universe because photons fly through the universe as they get
• 28:13
  Speaker 1: to us. And there's two different effects here to disentangle.
• 28:16
  Speaker 1: When we're looking at the CMB and we see some
• 28:18
  Speaker 1: places are hotter, some places are colder, there's two different
• 28:22
  Speaker 1: reasons why. One is, well, we could just be looking
• 28:25
  Speaker 1: at a place that was denser or it was less dense.
• 28:28
  Speaker 1: And so there's like initial over-density or initial under-density. That's
• 28:31
  Speaker 1: what we typically think about. But remember that the photons
• 28:34
  Speaker 1: also have to fly through the universe to get to us.
• 28:38
  Speaker 1: And those photons are red-shifted by the expansion of the universe. And...
• 28:43
  Speaker 1: they fly through the universe, which means that they're sensitive
• 28:46
  Speaker 1: to gravitational density. Because if you fly through a region
• 28:49
  Speaker 1: with a lot of mass, you get redshifted, right? Like
• 28:53
  Speaker 1: black holes produce gravitational redshifts. And so a photon that's
• 28:57
  Speaker 1: flown through the universe, in some senses, measures the density
• 29:01
  Speaker 1: of the universe along its path. which is super duper cool.
• 29:04
  Speaker 3: That is super duper cool. That photo from our childhood
• 29:08
  Speaker 3: is telling us a lot. Although is it more like,
• 29:10
  Speaker 3: I mean, you should never really dig into an analogy,
• 29:12
  Speaker 3: but it's more like a video from your childhood, isn't it,
• 29:15
  Speaker 3: than a photo?
• 29:16
  Speaker 1: It is like a video because if you keep watching it,
• 29:19
  Speaker 1: you see different things, right? We are looking at the
• 29:21
  Speaker 1: cosmic microwave background radiation and we can't see it for
• 29:24
  Speaker 1: the whole universe. We see the light that's arriving right now,
• 29:27
  Speaker 1: which left, of course, many, many, many billions of years ago.
• 29:31
  Speaker 1: And it's arriving to us from a shell of that
• 29:33
  Speaker 1: original plasma that's very far away and around the Earth.
• 29:37
  Speaker 1: And as time goes on, we get light from a
• 29:39
  Speaker 1: different shell. So it's not like we're watching the same
• 29:42
  Speaker 1: place over time. Over time, we're scanning more and more
• 29:46
  Speaker 1: distant shells of that original CMB. Got it. Cool. So
• 29:49
  Speaker 1: let's trace the trajectory of a photon as it's moving
• 29:52
  Speaker 1: through the universe. And let's think first about overdensities, places
• 29:56
  Speaker 1: where there's a lot of mass. So say a photon
• 29:59
  Speaker 1: is on its way to us, but it's passing by
• 30:01
  Speaker 1: a black hole, right? And so as it falls in
• 30:05
  Speaker 1: towards the black hole, it gains energy, right? So it's
• 30:08
  Speaker 1: getting blue shifted. And then if it doesn't get eaten
• 30:11
  Speaker 1: by the black hole, it makes it out and it
• 30:12
  Speaker 1: comes towards us. And as it's leaving the black hole,
• 30:15
  Speaker 1: it's losing energy. It's having to climb out of that
• 30:17
  Speaker 1: gravitational well. So it gets red shifted. And so you
• 30:20
  Speaker 1: might think, okay, blue shifted more energy, red shifted less energy.
• 30:24
  Speaker 1: It all balances out. So how could a photon that's
• 30:27
  Speaker 1: coming to us tell us anything about that dense region
• 30:31
  Speaker 1: if it's all got canceled out, if it's basically unchanged, right?
• 30:34
  Speaker 3: So you can't watch it as it changes? You just
• 30:37
  Speaker 3: see like the average of what happened to it over
• 30:39
  Speaker 3: a distance?
• 30:40
  Speaker 1: Yeah, you can't watch a photon go through the universe.
• 30:42
  Speaker 1: You just see one here on Earth. And you're like, oh,
• 30:44
  Speaker 1: is it hotter than I expected or colder?
• 30:46
  Speaker 2: Okay, got it.
• 30:48
  Speaker 1: And so the opposite is true for voids, right? If
• 30:51
  Speaker 1: you go near a black hole, then you get blue
• 30:53
  Speaker 1: shifted as you fall in and red shifted as you
• 30:55
  Speaker 1: fall out. And the opposite is true for a void.
• 30:58
  Speaker 1: You get red shifted as you fall in and blue
• 31:01
  Speaker 1: shifted as you fall out. Okay.
• 31:02
  Speaker 3: And so if we only see the average of what
• 31:05
  Speaker 3: happened to a photon when it gets here, how do
• 31:08
  Speaker 3: we know that?
• 31:09
  Speaker 1: So that's our theoretical calculation, but it's missing something really important,
• 31:13
  Speaker 1: which is as time goes on, when the photon is
• 31:16
  Speaker 1: in that void or near that black hole, the universe
• 31:19
  Speaker 1: is not static. The universe is expanding. And so the
• 31:23
  Speaker 1: amount of energy the photon loses or gains when it
• 31:25
  Speaker 1: goes in or out of that void changes because the
• 31:28
  Speaker 1: void is changing or the black hole is changing as
• 31:31
  Speaker 1: time goes on. So it doesn't perfectly cancel out. And
• 31:35
  Speaker 1: so it does leave an overall effect on these photons.
• 31:38
  Speaker 1: And so you can get cold spots in the CMB
• 31:42
  Speaker 1: if photons have moved through a super void on their
• 31:46
  Speaker 1: way here, if the universe is expanding. And so not
• 31:50
  Speaker 1: only do super voids tell us about like, hey, what
• 31:52
  Speaker 1: is the evolution of the universe? How do you get
• 31:54
  Speaker 1: these bubbles? Do they come from initial overdensities? Also, the
• 31:59
  Speaker 1: CMB tells us about photons moving through the universe and
• 32:02
  Speaker 1: measuring existing voids, not from the early universe, but today.
• 32:06
  Speaker 1: So there's like so many dimensions of information in the CMB.
• 32:10
  Speaker 1: It's not just a baby picture. It's a baby picture
• 32:13
  Speaker 1: that was then like dragged through your life and distorted
• 32:17
  Speaker 1: by the way your life turned out. And then here
• 32:19
  Speaker 1: we are, like we can disentangle those two things in
• 32:22
  Speaker 1: the single picture from the CMB and be like, oh,
• 32:24
  Speaker 1: this is a primordial hotspot. Or this is one that
• 32:27
  Speaker 1: appeared because of how the photons moved through the universe. Wow.
• 32:31
  Speaker 1: So all these incredibly clever little effects. We can use
• 32:34
  Speaker 1: to try to disentangle the history of the universe. And
• 32:37
  Speaker 1: this is why, like, people seem like they're in love
• 32:40
  Speaker 1: with the CMB. It's just such a gift. It's such
• 32:43
  Speaker 1: a gift. Oh, my gosh.
• 32:45
  Speaker 3: So what if a photon went through a black or
• 32:48
  Speaker 3: past a black hole and then through a super void? Like,
• 32:51
  Speaker 3: how do you how can you know what a photon
• 32:54
  Speaker 3: saw when it could have seen a bunch of things
• 32:56
  Speaker 3: before it gets to us?
• 32:57
  Speaker 1: Wow. You get it in that interview room. Okay. You
• 33:01
  Speaker 1: shine the lights in its face. Oh, boy. No, you're right.
• 33:04
  Speaker 1: You can't. And all you can do is look for patterns.
• 33:07
  Speaker 1: And we see in the universe, we see a big
• 33:10
  Speaker 1: cold spot, right, in the sky. Okay. And that's in
• 33:13
  Speaker 1: the same direction as a super void. And so that
• 33:16
  Speaker 1: means either there was like an initial underdensity there, which
• 33:19
  Speaker 1: created a colder region, or the photons getting here from
• 33:23
  Speaker 1: there have passed through a super void on the way. Okay.
• 33:28
  Speaker 1: And so it's just like, It's fascinating to see that
• 33:30
  Speaker 1: in the CMB and also then to look at our
• 33:33
  Speaker 1: late-time measurements of galactic structure and see, oh, there's also
• 33:37
  Speaker 1: a super void over there. So, like, things are lining up.
• 33:39
  Speaker 1: They're clicking together. You know, that's exciting when you're doing
• 33:42
  Speaker 1: science and you see two completely separate measurements that are
• 33:45
  Speaker 1: sensitive to the same thing lining up and telling you
• 33:48
  Speaker 1: the same story. That's when you feel like, ooh, we're
• 33:50
  Speaker 1: going to crack this case.
• 33:52
  Speaker 2: All right.
• 33:52
  Speaker 3: We're getting super excited over here, but we have to
• 33:54
  Speaker 3: take a break. Super Void if you must, but come
• 33:57
  Speaker 3: back in just a moment. But when we get back,
• 34:02
  Speaker 3: we're going to talk about how Super Voids get made.
• 34:06
  Speaker 3: The space ones, not the one you just made.
• 34:08
  Speaker 2: Super Voids.
• 34:28
  Speaker 3: All right.
• 34:28
  Speaker 2: And we're back. So, all right, Daniel, how do super
• 34:31
  Speaker 2: voids get made?
• 34:33
  Speaker 1: So this is really fun to think about how you
• 34:34
  Speaker 1: get super voids. One is that you can just have
• 34:38
  Speaker 1: an underdense region initially and, you know, you could just
• 34:41
  Speaker 1: have a fluctuation. Like these things we think are seeded
• 34:44
  Speaker 1: originally by quantum fluctuations. Why anyway are there regions that
• 34:49
  Speaker 1: are higher or lower density? You know, one theory is
• 34:52
  Speaker 1: you have quantum fluctuations in the very early universe and
• 34:55
  Speaker 1: then inflation is this pre-Big Bang theory we talked about recently,
• 34:59
  Speaker 1: stretch those out into macroscopic actual fluctuations that matter to gravity.
• 35:05
  Speaker 1: That's just a speculative theory. We don't know for sure.
• 35:08
  Speaker 1: But that would suggest that the fluctuations themselves, the reason
• 35:11
  Speaker 1: we have more stuff here and less stuff there, comes
• 35:14
  Speaker 1: initially randomly, which means that lots of stuff could happen.
• 35:18
  Speaker 1: For example, you're flipping coins. You don't expect to get
• 35:20
  Speaker 1: heads in the tails and then heads in the tails.
• 35:22
  Speaker 1: You'll have runs of heads and runs of tails. And so,
• 35:26
  Speaker 1: If somebody's flipping coins for the early universe, it's like,
• 35:28
  Speaker 1: are we getting stuff here or not? They could have
• 35:30
  Speaker 1: just come up with no stuff in this part of
• 35:32
  Speaker 1: the universe a lot of times, occasionally, right? So that
• 35:35
  Speaker 1: kind of thing can happen, but it's unlikely, right? The
• 35:38
  Speaker 1: bigger the void, the less likely it is that can happen.
• 35:41
  Speaker 1: The same way like having a run of 10 heads
• 35:43
  Speaker 1: is less likely than a run of five heads and
• 35:45
  Speaker 1: a run of like 50 heads in rows, essentially unheard of,
• 35:48
  Speaker 1: though there is a probability. And so, you know, we
• 35:51
  Speaker 1: only have this one universe. And so we can't tell like, hey,
• 35:54
  Speaker 1: did we just get lucky or slash unlucky? We don't know.
• 35:58
  Speaker 1: But there are also other ways people have come up
• 36:00
  Speaker 1: with in watching these simulations to see supervoids form, which
• 36:04
  Speaker 1: is that you can get voids merging. So these bubbles
• 36:07
  Speaker 1: can pop because you get gravitational disturbances between these things
• 36:12
  Speaker 1: and the walls can fall apart, essentially. And so you
• 36:15
  Speaker 1: can get these cells merging. Basically, if you have an
• 36:19
  Speaker 1: over density in some walls, they can attract those filaments
• 36:22
  Speaker 1: and It's not like these super voids are totally empty.
• 36:25
  Speaker 1: And so you still have some galaxies remaining inside of them.
• 36:29
  Speaker 1: And so you can get mergers of these voids to
• 36:32
  Speaker 1: form super voids. And this is the kind of example
• 36:35
  Speaker 1: of something you can learn about in simulation. You can
• 36:37
  Speaker 1: run a simulation in the universe. You can watch it.
• 36:39
  Speaker 1: You'd be like, look at that. I didn't expect that
• 36:41
  Speaker 1: to happen. But you see it in simulation. You learn that.
• 36:45
  Speaker 1: about emergent phenomena in simulation that you didn't predict. Super
• 36:49
  Speaker 1: duper cool.
• 36:50
  Speaker 2: Yay, theoretical physicists.
• 36:53
  Speaker 1: But this allows us to ask the question like, well,
• 36:56
  Speaker 1: why are there super voids? Do they make sense in
• 36:58
  Speaker 1: the universe? And, you know, we have this cold spot,
• 37:02
  Speaker 1: which we can partially explain using this like photons come in,
• 37:05
  Speaker 1: photons go out, but it's not a full explanation. It
• 37:08
  Speaker 1: explains like part of the cold spot, but not all
• 37:10
  Speaker 1: of it. It's really very unusual. Though it's hard to say, like,
• 37:14
  Speaker 1: how unusual is a 1% effect? You know, you see
• 37:17
  Speaker 1: it in one out of 100 universes. And so are
• 37:19
  Speaker 1: we just unlucky or is this a hint that there's
• 37:21
  Speaker 1: something else going on? Because remember that these things are
• 37:25
  Speaker 1: very sensitive to the parameters of the universe. How much
• 37:27
  Speaker 1: dark matter was there, dark matter forming that structure, how
• 37:31
  Speaker 1: much dark energy was there to create this acceleration and
• 37:34
  Speaker 1: this expansion, which is what's causing this effect, this cold
• 37:37
  Speaker 1: spot effect. Because remember, it's only if the voids are
• 37:40
  Speaker 1: changing as the photons are going through them that you
• 37:43
  Speaker 1: even see an effect from the voids. And so there's
• 37:46
  Speaker 1: a lot of questions about whether the super voids are
• 37:49
  Speaker 1: something we expect or whether they indicate that we need
• 37:51
  Speaker 1: something new in our theory of the universe, which of
• 37:55
  Speaker 1: course is where the fun begins because then we get
• 37:57
  Speaker 1: to speculate about all the crazy ideas.
• 38:00
  Speaker 2: Daniel has a sparkle in his eye.
• 38:04
  Speaker 3: So at the beginning of the episode, you said super
• 38:06
  Speaker 3: voids remind you of like the Marvel Universe. So if
• 38:10
  Speaker 3: you had like parallel universes like you do in the
• 38:12
  Speaker 3: Marvel Universe, would you expect super voids to be distributed
• 38:16
  Speaker 3: about the same way or like have about the same number?
• 38:18
  Speaker 2: Like what? I'm trying to get to parallel universes for you.
• 38:24
  Speaker 1: Well, there's an even cooler way that parallel universes connect
• 38:27
  Speaker 1: to super voids, which is that maybe you had a
• 38:30
  Speaker 1: bunch of initial universes early on. And remember, we talked
• 38:33
  Speaker 1: about inflation. how our universe maybe is like a tiny
• 38:37
  Speaker 1: dot in a vast landscape of inflationary matter. And in
• 38:42
  Speaker 1: that dot, it just like went from inflationary matter to
• 38:44
  Speaker 1: normal matter. And then our universe is there and expanded.
• 38:47
  Speaker 1: And there could be other dots out there. And usually
• 38:50
  Speaker 1: those other dots are really far away. And there's a
• 38:52
  Speaker 1: bunch of inflationary matter between us and them, which is
• 38:54
  Speaker 1: expanding at some insane rates. So we'll never see those
• 38:57
  Speaker 1: other universes. But what if that's not true? What if
• 39:01
  Speaker 1: there are other universes out there And our universe has collided.
• 39:04
  Speaker 1: If early on our bubble bounced into another bubble, it
• 39:08
  Speaker 1: might leave an imprint on the early universe. And according
• 39:12
  Speaker 1: to some theories and according to some simulations, that can
• 39:16
  Speaker 1: cause like a bruise in the density, which would be
• 39:19
  Speaker 1: like a cold spot, which would lead to a super void.
• 39:22
  Speaker 1: And so there are some really fun speculative theories of
• 39:25
  Speaker 1: the early universe out there that suggest that if there
• 39:28
  Speaker 1: are these parallel bubble universes, created in this inflationary landscape,
• 39:33
  Speaker 1: that sometimes they'll bump into each other and they'll leave
• 39:35
  Speaker 1: a mark, and that mark is super voids.
• 39:39
  Speaker 2: Well, I think I'm still having one. Awesome, too. I'm
• 39:45
  Speaker 2: having a little trouble imagining. So you get two bubbles.
• 39:48
  Speaker 2: They like merge.
• 39:50
  Speaker 3: And then is it like whatever was making the outside
• 39:52
  Speaker 3: wall of the bubble where they touch just sort of
• 39:54
  Speaker 3: like gets blown to somewhere else. And now you get
• 39:57
  Speaker 3: a big center as those two bubbles merge. Is that
• 40:01
  Speaker 3: how does that result in.
• 40:02
  Speaker 2: A super void?
• 40:03
  Speaker 1: Yeah, great question. And I realize that now we're using
• 40:06
  Speaker 1: the word bubble to mean two different things. Shame on us.
• 40:09
  Speaker 1: Shame on me.
• 40:09
  Speaker 2: Yeah, I'm not taking any blame for that. Fair.
• 40:16
  Speaker 1: No, when we talked earlier about bubbles, we were talking
• 40:18
  Speaker 1: about the structure of our universe. And there's densities of
• 40:22
  Speaker 1: superclusters of galaxies and under densities. And we talked about
• 40:26
  Speaker 1: those organizing into bubbles. And those are bubbles. Now we're
• 40:29
  Speaker 1: talking about bubbles as the whole universe is one bubble.
• 40:33
  Speaker 1: in a vaster inflationary landscape. So let's not call them
• 40:38
  Speaker 1: a bubble. Let's just say if our universe bumps into
• 40:40
  Speaker 1: another universe, because remember in this theory, universes are finite.
• 40:44
  Speaker 1: They're little regions of this inflationary landscape that have decayed
• 40:48
  Speaker 1: into normal matter. So if our universe bumps into another
• 40:52
  Speaker 1: universe and then bounces off, they don't merge. They bounce
• 40:55
  Speaker 1: off each other, but they leave a mark. You know,
• 40:57
  Speaker 1: the way like if you take two apples and you
• 40:58
  Speaker 1: smash them together, they don't become one apple, but you
• 41:00
  Speaker 1: get a bruise on each one. Yeah. What would that
• 41:03
  Speaker 1: bruise look like on our universe if another universe had
• 41:06
  Speaker 1: bumped into us and like not even left a note, just,
• 41:09
  Speaker 1: you know, just like hit and run universe style?
• 41:11
  Speaker 2: Not cool.
• 41:12
  Speaker 1: Well, we would get a bruise and it would change
• 41:14
  Speaker 1: the initial density of matter in the early universe. And
• 41:18
  Speaker 1: simulations and calculations suggest that that would leave a cold
• 41:22
  Speaker 1: spot and under density in that part of the universe,
• 41:25
  Speaker 1: which would If you ran the simulations forward, leave to
• 41:27
  Speaker 1: a super void today.
• 41:29
  Speaker 2: Wow. Okay. All right. I'm with you.
• 41:31
  Speaker 1: Yeah. So that's one fun theory. And, you know, there's
• 41:34
  Speaker 1: a lot of debate about that. People say, you know,
• 41:37
  Speaker 1: you're cherry picking, you're crafting an explanation to match something
• 41:40
  Speaker 1: you see. It would be much more compelling if you
• 41:43
  Speaker 1: had a prediction for this before you saw the super
• 41:45
  Speaker 1: voids and you say, I predict a super void. And
• 41:47
  Speaker 1: then you went out and saw it. That'd be much
• 41:49
  Speaker 1: more compelling. This is more like a post addiction. It's like, oh,
• 41:52
  Speaker 1: we see this thing in the universe. What could explain it?
• 41:55
  Speaker 1: Not as a criticism, but just saying it would be
• 41:57
  Speaker 1: more powerful, more compelling if it was a prediction and
• 42:00
  Speaker 1: not a postdiction. Okay.
• 42:01
  Speaker 3: I mean, I totally see that. But on the other hand, like, okay,
• 42:04
  Speaker 3: but you've seen the thing and you can't unsee it.
• 42:06
  Speaker 3: And now you have to try to explain it. And so,
• 42:07
  Speaker 3: but I agree. It would have been more powerful if
• 42:10
  Speaker 3: it had met expectations.
• 42:12
  Speaker 2: But the universe doesn't care about our expectations.
• 42:15
  Speaker 1: Yeah. So another potential explanation for this is a favorite
• 42:19
  Speaker 1: alternative for dark matter. You remember that we talked about
• 42:23
  Speaker 1: dark matter being out there. We have lots of independent
• 42:25
  Speaker 1: lines of evidence for it. But there are alternatives, and
• 42:28
  Speaker 1: it's healthy that people are thinking about other things and
• 42:32
  Speaker 1: trying to understand if those other explanations are coherent, if
• 42:35
  Speaker 1: they can explain multiple things and not just galactic rotation curves.
• 42:39
  Speaker 1: One of those is modified gravity. To say maybe gravity
• 42:42
  Speaker 1: doesn't work the way we expect. Maybe it's not that
• 42:45
  Speaker 1: there is more invisible stuff out there causing gravity, but
• 42:49
  Speaker 1: that gravity behaves differently and there isn't any dark matter.
• 42:52
  Speaker 1: This is called MOND, Modified Newtonian Dynamics. I remember how
• 42:56
  Speaker 1: we talked about some of these cold spots are due
• 42:58
  Speaker 1: to the expansion of the universe as photons fall in
• 43:02
  Speaker 1: and out of these voids or in and out of
• 43:04
  Speaker 1: the neighborhood of a black hole. Well, that could also
• 43:07
  Speaker 1: be explained in some models of modified gravity. Okay. Because
• 43:12
  Speaker 1: you're changing how gravity works, so it's going to change
• 43:14
  Speaker 1: how these photons experience the universe. And even some theories
• 43:18
  Speaker 1: of the universe isn't expanding, and these things are just
• 43:21
  Speaker 1: due to evidence that gravity doesn't work the way that
• 43:24
  Speaker 1: we expect. And it's true that we can't fully explain
• 43:27
  Speaker 1: these supervoids. We don't know where they come from. Our
• 43:30
  Speaker 1: current theories do definitely need something. Do you need to
• 43:33
  Speaker 1: go all the way to modified gravity to explain supervoids?
• 43:37
  Speaker 1: I don't think so. But, you know, maybe I'm just
• 43:39
  Speaker 1: not a fan of the modified gravity theory, and so
• 43:41
  Speaker 1: I'm blind to it. I do respect that they're trying
• 43:44
  Speaker 1: to find other ways to support this theory, other places
• 43:48
  Speaker 1: to look for evidence that might indicate that it's the
• 43:50
  Speaker 1: real explanation for the universe and not just a single
• 43:54
  Speaker 1: fudge factor they're using to fix galactic rotation curves.
• 43:57
  Speaker 3: Now, when we finish getting through all of the explanations,
• 44:00
  Speaker 3: are you going to tell us which explanation is your favorite?
• 44:05
  Speaker 2: Or are you just going to super void on this one?
• 44:10
  Speaker 1: No, instead, I'm going to tell you about how we
• 44:12
  Speaker 1: might learn more about the universe rather than betting on
• 44:14
  Speaker 1: any individual one. Because we talked about how in the 70s,
• 44:18
  Speaker 1: they started putting this together when they were measuring the
• 44:21
  Speaker 1: cosmic structure. And they've continued to do that. There was
• 44:24
  Speaker 1: a big survey in the 2000s called the Sloan Digital
• 44:27
  Speaker 1: Sky Survey, mapped out a huge number of these big
• 44:30
  Speaker 1: walls and bubbles and and really giving us a broader
• 44:35
  Speaker 1: sense of where we are in the universe. And that's continuing.
• 44:38
  Speaker 1: We now have this telescope called DESI, D-E-S-I, the Dark
• 44:42
  Speaker 1: Energy Survey Instrument, which is the most powerful telescope we've
• 44:46
  Speaker 1: ever had for understanding where things are in the universe
• 44:50
  Speaker 1: in terms of measuring the redshift of a huge number
• 44:52
  Speaker 1: of distant galaxies. And so like, what's more important? What's
• 44:56
  Speaker 1: more exciting than like mapping out the universe? And that's
• 44:59
  Speaker 1: what we're doing. And just yesterday we saw the launch
• 45:02
  Speaker 1: of the Nancy Grace Roman telescope, which is also going
• 45:05
  Speaker 1: to tell us about the expansion of the universe and
• 45:07
  Speaker 1: red shifts and the structure of the universe. So we
• 45:11
  Speaker 1: are learning so much more. It reminds me of like,
• 45:15
  Speaker 1: have you seen early maps? I love looking at like
• 45:17
  Speaker 1: maps people drew of the world in like 1200, you know,
• 45:21
  Speaker 1: when like they didn't know about this whole continent and
• 45:23
  Speaker 1: they misunderstood this whole piece, but you see truth in there.
• 45:26
  Speaker 1: You see like the shape of Portugal or you see
• 45:28
  Speaker 1: like the coast of Madagascar or whatever. And that's what
• 45:31
  Speaker 1: our maps are like today. And I think in a
• 45:33
  Speaker 1: thousand years, people will look back at our primitive, basic
• 45:37
  Speaker 1: maps of our neighborhood and be like, wow, they knew nothing.
• 45:41
  Speaker 1: But the information is coming. We are building those maps.
• 45:44
  Speaker 1: We are exploring the universe. We're figuring out. And along
• 45:47
  Speaker 1: the way, we're discovering mysteries and puzzles, which are going
• 45:50
  Speaker 1: to clue us into how the universe works. There are
• 45:53
  Speaker 1: answers out there to questions we haven't thought to ask
• 45:57
  Speaker 1: because we haven't even mapped out what the universe looks like,
• 46:00
  Speaker 1: you know? And so we can't, we don't even know
• 46:03
  Speaker 1: what to ask yet.
• 46:04
  Speaker 2: Yep.
• 46:05
  Speaker 3: We are constantly pushing the boundaries of our ignorance back
• 46:08
  Speaker 3: farther and farther.
• 46:09
  Speaker 2: I love it.
• 46:09
  Speaker 1: Yeah. And super voids are really fascinating hole in our
• 46:12
  Speaker 1: understanding because, you know, we don't fully understand how they form.
• 46:16
  Speaker 1: Are we just lucky slash unlucky? Is there something else
• 46:19
  Speaker 1: going on in the universe that makes these incredibly under
• 46:22
  Speaker 1: dense regions? Is this a clue or is it a
• 46:24
  Speaker 1: red herring? We don't know. And really, the only way
• 46:27
  Speaker 1: to know is to get more data, more mapping, more structure,
• 46:31
  Speaker 1: more images, more understanding of where we are in the universe.
• 46:34
  Speaker 1: I'm definitely for that. And also, it's cheap. Compared to
• 46:38
  Speaker 1: the kind of stuff we spend money on, it costs pennies.
• 46:42
  Speaker 3: Usually physics doesn't feel super cheap, but this one's cheap,
• 46:46
  Speaker 3: you're saying?
• 46:47
  Speaker 1: I mean, it's a lot more expensive than, say, a
• 46:50
  Speaker 1: week in the archives in New York City reading somebody's
• 46:53
  Speaker 1: blood-covered notes, hypothetically.
• 46:55
  Speaker 2: That was fun.
• 46:55
  Speaker 1: It's a lot more expensive than a lot of stuff.
• 46:57
  Speaker 1: But compared to aircraft carriers, you know, or wars in
• 47:01
  Speaker 1: the Middle East, it's definitely cheap.
• 47:03
  Speaker 3: And then you get to enjoy that knowledge forever.
• 47:06
  Speaker 1: Yes, you do. And you create the opportunities for a
• 47:08
  Speaker 1: new generation of scientists to study new puzzles and come
• 47:12
  Speaker 1: up with new answers. So thanks very much to Nathan
• 47:15
  Speaker 1: and Levi for asking about superboards and giving us an
• 47:18
  Speaker 1: opportunity to talk about this incredible cosmic history, all the
• 47:21
  Speaker 1: detective stories we've cracked along the way, and so many
• 47:24
  Speaker 1: open questions we have yet to even ask.
• 47:27
  Speaker 2: Fun science, please.
• 47:37
  Speaker 1: Thanks everybody for listening. Please go and do us a
• 47:39
  Speaker 1: favor and rate the show on whatever podcast app you're using.
• 47:42
  Speaker 1: It really helps people find us.
• 47:44
  Speaker 3: Daniel and Kelly's Extraordinary Universe is edited by the amazing
• 47:48
  Speaker 3: Matt Kesselman.
• 47:49
  Speaker 1: He really is a wizard. You can also find us
• 47:53
  Speaker 1: online on Blue Sky, Instagram, and X, D & K Universe.
• 47:58
  Speaker 1: Come engage with us.
• 47:59
  Speaker 3: You can email us at questions at danielandkelly.org. We really
• 48:03
  Speaker 3: do want to hear from you.
• 48:05
  Speaker 1: And you can find our website, www.danielandkelly.org, where you'll also
• 48:10
  Speaker 1: find an invitation to join our Discord, where everybody comes
• 48:14
  Speaker 1: and talks about the amazing universe.
• 48:16
  Speaker 3: And we also have the most amazing moderators. This is
• 48:20
  Speaker 3: an iHeart podcast. Thanks for joining us.