Latest / Daniel and Kelly’s Extraordinary Universe / What happened in the dark ages of the Universe?

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What happened in the dark ages of the Universe? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Hey, Daniel, what do you think about when you look
0:10
Speaker 1: at the night Scott. Well, it's just staggeringly gorgeous, of course.
0:14
Speaker 1: But what I'm most amazed at is the depth of
0:17
Speaker 1: the view. What do you mean, Well, it's just incredible,
0:20
Speaker 1: Like how far we can see from the Moon that's
0:23
Speaker 1: kind of close by, all the way to the Sun
0:26
Speaker 1: two stars that are like billions of light years away. Yeah,
0:29
Speaker 1: that is pretty deep. That's like the deepest view. Yeah,
0:33
Speaker 1: it makes you feel lucky, right, What do you mean lucky?
0:35
Speaker 1: Are you imagining that space could have been foggy? Yeah?
0:38
Speaker 1: In fact, the universe didn't always offer such crystal clear
0:43
Speaker 1: views of crystals. The yell Per views from the early
0:46
Speaker 1: universe had fewer stars. I am Orgemmaye, cartoonists and the
1:04
Speaker 1: creator of PhD comics. Hi, I'm Daniel, I'm a particle physicist,
1:08
Speaker 1: and on Yelp, I give our universe five stars. Do
1:12
Speaker 1: physicists have Yelp reviews? No? I wish we did, though.
1:15
Speaker 1: I wish we could just review parts of physics and
1:17
Speaker 1: be like, Wow, this part is awesome, or this part
1:19
Speaker 1: is kind of sticky, and go in and look at that.
1:21
Speaker 1: When I got terrible service, when I try to order
1:25
Speaker 1: a black hole. This collider works great, but this one
1:29
Speaker 1: is usually down. My collider accidentally destroyed the universe. Down
1:35
Speaker 1: zero stars and Welcome to our podcast Daniel and Jorge
1:38
Speaker 1: Explain the Universe, a production of I Heart Radio in
1:41
Speaker 1: which we explore all the amazing and wonderful star filled
1:45
Speaker 1: the universe, all the things that are incredible and visible
1:48
Speaker 1: that are out there that we can see from Earth,
1:50
Speaker 1: all the things that we can't see that we have
1:52
Speaker 1: to use our imagination, all the things that are happening
1:55
Speaker 1: right now, and things that happened in the deep dark past. Yeah,
1:58
Speaker 1: because it is a huge universe and we can see
2:01
Speaker 1: a lot of it out there. There's a billions and
2:04
Speaker 1: trimons of stars that we can see in galaxies, and
2:06
Speaker 1: there's a lot that we can't see as well. That's right.
2:10
Speaker 1: It's amazing to me. It sort of feels like you're
2:12
Speaker 1: standing on the top of a mountain and you're looking
2:14
Speaker 1: out and you can see things that are like billions
2:17
Speaker 1: of light years away. It's like looking across a vast,
2:20
Speaker 1: vast ocean of space, and those photons, you know, they
2:23
Speaker 1: had to travel so far and for so long just
2:27
Speaker 1: to get to your eyeball. It's amazing that nothing stopped
2:30
Speaker 1: them along the way. Yeah, it seems like we just
2:32
Speaker 1: happened to be looking at the universe on a clear day.
2:36
Speaker 1: You know, it could have been an overcast day, or
2:38
Speaker 1: a foggy day, or a hazy day, or you know,
2:40
Speaker 1: there could have been small from all those aliens. But
2:43
Speaker 1: somehow it's a pretty clear view of really far away stuff.
2:47
Speaker 1: And imagine what life would be like if we didn't
2:49
Speaker 1: have which a clear view, if the universe was foggy,
2:52
Speaker 1: if you looked out into space and it was just
2:54
Speaker 1: sort of like a gray blob. You couldn't see the
2:57
Speaker 1: stars and the galaxies. We couldn't learn about the shape
3:00
Speaker 1: of the universe and its structure and its history. We
3:02
Speaker 1: would be so clueless if we couldn't see as far
3:05
Speaker 1: as we do. Yeah, we would probably still think that
3:06
Speaker 1: we are like the center of the universe and that
3:10
Speaker 1: just the things we see around is all there is
3:12
Speaker 1: to it. Yeah. Absolutely, And we can see pretty far
3:15
Speaker 1: in the universe in the wavelengths were familiar with, you know,
3:18
Speaker 1: in the wavelengths of visible light, but there are lots
3:20
Speaker 1: of different wavelengths of light, and in some wavelengths the
3:23
Speaker 1: universe is more or less transparent, and so these days
3:27
Speaker 1: we've opened up lots of new kinds of eyeballs onto
3:30
Speaker 1: the universe, infrared light and UV light and X ray
3:33
Speaker 1: telescopes to be able to see different parts of the
3:36
Speaker 1: universe at different depths. Yeah, it's a clear day in
3:38
Speaker 1: the universe. But it sort of makes you wonder if
3:41
Speaker 1: it was always this clear, where you always able in
3:45
Speaker 1: the universe to look so far away and to see
3:47
Speaker 1: so many stars and galaxies. Yeah, and there's actually a
3:50
Speaker 1: really fascinating period at the beginning of the universe. You know,
3:53
Speaker 1: people think about the universe starting the big bang boom,
3:56
Speaker 1: huge explosion, lots of stuff rushing out, dot dot dot
4:00
Speaker 1: galaxies are formed and we have stars and stuff. But
4:02
Speaker 1: there's a lot of interesting stuff happening in that dot
4:05
Speaker 1: dot dot period where stars get formed, before we actually
4:09
Speaker 1: have the structure of the universe that we're familiar with today,
4:12
Speaker 1: before we can see as far as we can out
4:15
Speaker 1: into the deep reaches of the universe. That a lot
4:17
Speaker 1: of YadA YadA happened, I imagine in those dot dot
4:21
Speaker 1: dot moments. But yeah, the big bank does get a
4:23
Speaker 1: lot of attention, and you sort of assume that it's
4:25
Speaker 1: really bright the Big Bang, I guess, because it's a
4:28
Speaker 1: big expansion and a big explosion. But uh, there happens
4:32
Speaker 1: to be a period right after it in which you
4:34
Speaker 1: couldn't see a lot of stuff. Yeah, it's fascinating to
4:37
Speaker 1: imagine why the universe is bright at all. You know,
4:40
Speaker 1: we only have light in the universe because it's created
4:44
Speaker 1: by these pin pricks of stars. If we didn't have those,
4:46
Speaker 1: the universe wouldn't be super dark. And so there was
4:49
Speaker 1: this period after the Big Bang and before the first
4:52
Speaker 1: stars when we didn't have light in the universe, another
4:56
Speaker 1: really fascinating period after we had stars or the universe
5:00
Speaker 1: cleared up. And so it doesn't usually get as much
5:03
Speaker 1: attention as I think it should, but it's a really
5:06
Speaker 1: interesting period of the universe and helps us understand like
5:09
Speaker 1: how stars and galaxies actually came together. Yeah, so to
5:12
Speaker 1: the other podcast, we'll be asking the question what happened
5:20
Speaker 1: during the dark ages of the universe before the Renaissance
5:24
Speaker 1: for the cosmic Renaissance, I guess, yeah, And there actually
5:28
Speaker 1: is something of a cosmic renaissance. It's a fascinating parallel
5:31
Speaker 1: to sort of human intellectual history. Was a universe full
5:35
Speaker 1: of like feudal societies and everyone wore armor and you sword. Yeah,
5:40
Speaker 1: it makes for really great like television epic dramas. Yeah,
5:43
Speaker 1: so there was a long period and where the universe
5:46
Speaker 1: wasn't as bright as it is now. In fact that
5:48
Speaker 1: it was hundreds of millions of years of darkness and fog, right, Yeah,
5:53
Speaker 1: exactly before the universe looked the way that it did today.
5:56
Speaker 1: There's a lot of work that had to happen between
5:59
Speaker 1: the Big Bang and molecules form and you get this hot,
6:01
Speaker 1: dense gas and then for stars to actually pull together
6:05
Speaker 1: and to light up. Yeah, it's kind of interesting to
6:08
Speaker 1: think because you know, you don't usually assume that there
6:10
Speaker 1: was a dark age. You just assumed that, you know,
6:13
Speaker 1: the real dark age happened before the Big Bang. But
6:16
Speaker 1: I guess we don't know what happened before the Big
6:18
Speaker 1: Bang really, Yeah, we have no idea if that was
6:20
Speaker 1: dark or it was crazy bright, or if it was
6:23
Speaker 1: part of the meta universe or space didn't even exist.
6:26
Speaker 1: Those are the kind of questions we can't even really ask.
6:29
Speaker 1: We don't even know how to probe those questions. But
6:31
Speaker 1: this is a part of the universe when things actually
6:34
Speaker 1: had formed when the rules of physics as we know
6:37
Speaker 1: them were in charge, and so we could ask these questions.
6:40
Speaker 1: But it's a period that's also very difficult to study
6:43
Speaker 1: because it was so dark, and so this happened right
6:46
Speaker 1: after the Big Bang, and maybe a lot of people
6:48
Speaker 1: don't know that we had a dark age at all
6:51
Speaker 1: in the universe. I imagine most people just assumed that
6:53
Speaker 1: there was a big bang and then thanks got brighter
6:55
Speaker 1: from there. And so as usual, Daniel went out there
6:58
Speaker 1: into the wild to the Internet to ask listeners what
7:01
Speaker 1: they thought happened during the Dark Ages of the universe.
7:04
Speaker 1: Thank you to everybody who participated in this exercise. And
7:07
Speaker 1: if you would like to stand answers to questions for
7:10
Speaker 1: which you are totally unprepared to give responses to, please
7:13
Speaker 1: write to us two questions at Daniel and Jorge dot com.
7:16
Speaker 1: Think about it for a second. Have you heard or
7:19
Speaker 1: know what are the Dark Ages of the universe. It's
7:23
Speaker 1: what people had to say, something to do with the
7:25
Speaker 1: point in time where the universe was so hot and
7:28
Speaker 1: tense that no light could escape. My guess is that
7:31
Speaker 1: the dark Ages of the universe was when you know
7:33
Speaker 1: there was no light so you couldn't see what else
7:35
Speaker 1: is in the universe. I would put this dark ages
7:39
Speaker 1: before being a big bank. That's it. I think it's
7:42
Speaker 1: a time before the universe schooled down enough to be
7:45
Speaker 1: transparent to photons. That's the photons emitted in that time
7:48
Speaker 1: are stuck in that time and not detectable by us.
7:51
Speaker 1: The universe is for ten billion years old, give or
7:54
Speaker 1: take a few, so maybe it was at a time
7:58
Speaker 1: when the universe had had had time to cool off
8:03
Speaker 1: and not be so intensely hot. So maybe five six
8:09
Speaker 1: billion years ago. I think that was after the universe
8:14
Speaker 1: was cool enough such that um the gas was not
8:17
Speaker 1: emitting light anymore, at least not in a visible spectrum,
8:22
Speaker 1: but before the first stars formed. All Right, a lot
8:25
Speaker 1: of interesting answers here. Some of them sort of band
8:28
Speaker 1: your brain a little bit, like the universe is so
8:31
Speaker 1: bright that you couldn't see light or something like that,
8:34
Speaker 1: or there was no light so you couldn't see anything, yeah,
8:37
Speaker 1: or somebody else suggesting that it was pretty big bang
8:40
Speaker 1: like you were. That's a fun idea. Yeah, And so
8:43
Speaker 1: it's pretty tricky, I guess, because you know, the big
8:45
Speaker 1: band was such a chaotic mess and it's hard to
8:48
Speaker 1: tell when light could go around and when it could
8:51
Speaker 1: not go around, or when it was created, or when
8:54
Speaker 1: even light was created itself, because light didn't always exist, right, Yeah, exactly.
9:00
Speaker 1: And there are a lot of these answers that thought
9:02
Speaker 1: that the Dark Ages were somehow before the cosmic microwave background,
9:06
Speaker 1: and so I think there's a bit of confusion out
9:08
Speaker 1: there about the order of events. So it's a good idea,
9:10
Speaker 1: I think, for us to clear it up and walk
9:12
Speaker 1: through what happened before, during, and after the Dark Ages
9:16
Speaker 1: of the universe. And I guess nobody gets that it
9:18
Speaker 1: involved armor and castles and shields and feudal societies and
9:23
Speaker 1: epic love poems, probably with loot Alright, So step us
9:26
Speaker 1: through here, Daniel, let's go all the way back. I guess,
9:30
Speaker 1: so before there was even a dark age in the universe.
9:33
Speaker 1: What happened. Step us through from the moment of birth
9:36
Speaker 1: of the universe to the first Dark Age. Yeah. So
9:39
Speaker 1: it's pretty fascinating. And it always amazes me that we
9:42
Speaker 1: know as much as we do about these first few
9:45
Speaker 1: moments of the universe, you know, the big bang happens.
9:49
Speaker 1: We don't really understand that at all. But we think
9:51
Speaker 1: that it happened. There's some moment of singularity there, and
9:54
Speaker 1: then the universe is filled with this very high density
9:58
Speaker 1: of energy and very bidly things start to stretch. In
10:01
Speaker 1: this period we call inflation, when the universe grew very
10:04
Speaker 1: very quickly in a very short amount of time. So
10:07
Speaker 1: you have a universe that's really hot and dense and
10:09
Speaker 1: filled with stuff gets stretched out to a much cooler,
10:13
Speaker 1: more dilute universe by a factor of ten to the
10:16
Speaker 1: thirty and about ten to the minus thirty seconds. So
10:19
Speaker 1: that's the very beginning of the universe. And after, you know,
10:22
Speaker 1: like tend the minus five micro seconds, you have things happening,
10:27
Speaker 1: like quarks are forming, particles are coming into existence. Before that,
10:31
Speaker 1: you have this really dense soup of energy, but you
10:34
Speaker 1: can't really think of it as particles. It's more like
10:37
Speaker 1: thinking about an ocean of droplets rather than thinking about
10:40
Speaker 1: an individual drop on its own. Yeah, and you can't
10:43
Speaker 1: even think about forces like it. It was a point
10:46
Speaker 1: right after the Big Bang or during inflation in which
10:49
Speaker 1: you couldn't even say, hey there's gravity, Hey there's electromaniatism.
10:52
Speaker 1: It was all just part of the same soup. Yeah,
10:55
Speaker 1: that bit's a bit more speculative, but we think that
10:58
Speaker 1: when you have really high energy, really high density of stuff,
11:02
Speaker 1: that all the forces are the same, that they have
11:04
Speaker 1: the same strength, and as you cool down, they sort
11:07
Speaker 1: of break out into different strengths, which is why we
11:09
Speaker 1: have the strong force is the strongest force, and gravity
11:12
Speaker 1: is the weakest one, and they all have sort of
11:14
Speaker 1: different characteristics. We think that only happens when things sort
11:17
Speaker 1: of get cold and separate, But when things were hot
11:20
Speaker 1: and dense in the early universe, we think they unified
11:22
Speaker 1: into one force. And so as you go forwards in
11:25
Speaker 1: time and the universe cools, we think of those things
11:28
Speaker 1: that sort of breaking out. So the forces separated into
11:31
Speaker 1: the forces we know now, and then particles formed and
11:34
Speaker 1: you get like corks and gluons, But things are still
11:37
Speaker 1: super duper hot, and so those corks and gluons they
11:40
Speaker 1: don't like break off and make little particles like we
11:42
Speaker 1: know now like protons and neutrons. They were in this
11:45
Speaker 1: state called a cork gluon plasma, which is sort of
11:48
Speaker 1: like the way we think about a plasma like hydrogen gas,
11:51
Speaker 1: where the electrons have so much energy that they just
11:54
Speaker 1: fly around. You don't get little bound states here for
11:57
Speaker 1: cork flu on plasma. There's so much that you don't get,
12:00
Speaker 1: like bound states of quarks, like protons and masons and
12:04
Speaker 1: other kinds of stuff. It's just a big sea of
12:06
Speaker 1: quarks and gluons all mixing around together. Really, they don't
12:09
Speaker 1: snap together. I thought you couldn't have quarks by themselves. Yeah,
12:12
Speaker 1: you can't have them by themselves, but you can have
12:14
Speaker 1: them in a super dense ocean of quarks and gluons.
12:18
Speaker 1: So they're not on their own. They're just sort of
12:20
Speaker 1: like enmeshed in this soup. Or you can think about
12:23
Speaker 1: like the whole universe is one big quark particle, you know,
12:27
Speaker 1: fields with quarks and gluons all mixing around, sort of
12:30
Speaker 1: like the interior of a proton, right, is a bunch
12:32
Speaker 1: of quarks and luons flying around together. Think about like
12:36
Speaker 1: the whole universe in that state. So the universe is
12:39
Speaker 1: like a giant proton exactly. It's like a giant proton.
12:42
Speaker 1: The proton universe was a proton, but then it continued
12:46
Speaker 1: to expand and to cool, and then it sort of
12:49
Speaker 1: broke up. Right, instead of being one massive quirk gluon plasma,
12:53
Speaker 1: we have these hadrons forming, so you get things like
12:55
Speaker 1: kaons and pons and protons and neutrons. Things that are
12:59
Speaker 1: combinating should have corks is sort of like snap out
13:01
Speaker 1: into their own little lego pieces. And that happened about
13:04
Speaker 1: a second after the Big Bang. We think, so we're
13:07
Speaker 1: a second into the universe and we already have particles
13:11
Speaker 1: made out of corks. Okay, so now it's starting to
13:14
Speaker 1: look more familiar to what we know, like protons and neutrons,
13:18
Speaker 1: and so that universe is like a sea of them,
13:20
Speaker 1: like still a hot soup and not as hot. Yeah,
13:22
Speaker 1: still a hot soup. And you also had particles like
13:24
Speaker 1: electrons flying around um and then the next twenty minutes
13:28
Speaker 1: or so, the universe spent some time building atoms, and
13:32
Speaker 1: so you get protons and electrons that come together and
13:35
Speaker 1: make hydrogen. For example. Wait, how did the electrons form?
13:38
Speaker 1: They just formed out of the energy and the hanging around.
13:41
Speaker 1: They just popped into existence the same way the corks did.
13:44
Speaker 1: You have this sort of raw energy that was in
13:46
Speaker 1: all of these matter fields, slashing around between them, using
13:49
Speaker 1: the forces to interact, and then it sort of crystallized
13:52
Speaker 1: out into the various matter fields. You get quarks, you
13:55
Speaker 1: can electrons, you get heavier stuff probably also, which then decayed.
14:00
Speaker 1: All right, so now we're starting to form nuclei and atoms,
14:04
Speaker 1: and that's where the most of the I guess hydrogen
14:06
Speaker 1: came from. Yeah, And so then it crystallizes out and
14:09
Speaker 1: you get hydrogen. You get some helium also, but mostly hydrogen.
14:13
Speaker 1: You get very small amounts of lithium. But things are
14:16
Speaker 1: still very very hot and dense, like you would want
14:18
Speaker 1: to be in this situation. That temperature is very very high.
14:22
Speaker 1: It's sort of like the interior of the sun. You know,
14:24
Speaker 1: it's still a hot soup. I mean, we spent twenty
14:27
Speaker 1: minutes already expanding and cooling in the universe from the
14:30
Speaker 1: much hotter initial state. But it's still very hot. It's
14:33
Speaker 1: still emitting photons, it's still sort of glowing and absorbing
14:37
Speaker 1: that light. It's still a hot mess. It's still hot.
14:39
Speaker 1: You don't you want no part of that? Yeah, exactly.
14:42
Speaker 1: And at this point we still have about fifteen percent
14:45
Speaker 1: of the matter in the universe is the kind of
14:47
Speaker 1: matter we're familiar with. It's made out of baryons. You know,
14:49
Speaker 1: it's going to be atomic matter eventually, but dark matter
14:52
Speaker 1: is also formed right, you don't just make corks and electrons.
14:55
Speaker 1: We don't know the particle nature of dark matter, but
14:57
Speaker 1: we think it was created. We're pretty sure it was
15:00
Speaker 1: created back in those same moments when you made your
15:02
Speaker 1: quarks and electrons. So whatever dark matter is made out of,
15:05
Speaker 1: it was already present back then in the early universe.
15:08
Speaker 1: It was created just out of thin air. It just
15:10
Speaker 1: like the corks and electrons too. Yeah, it was just
15:13
Speaker 1: the energy in those fields collapsed into the matter fields,
15:16
Speaker 1: and that's what making particles is. And so all that
15:20
Speaker 1: stuff was made. And then you know, that soup sort
15:22
Speaker 1: of sat around, you know, oscillating and glowing it itself
15:25
Speaker 1: for like a hundred thousand years or so until you
15:29
Speaker 1: get to the moment when it cools enough that the
15:32
Speaker 1: electrons like to hang out around the nuclei, that the
15:34
Speaker 1: nuclei could sort of grab their own electrons and become neutral.
15:39
Speaker 1: So before, I mean before you had hydrogen and maybe helium,
15:42
Speaker 1: but maybe the electrons weren't sticking around to the nuclear
15:47
Speaker 1: to form like a regular hydrogen atom. Yeah, it was
15:50
Speaker 1: more like a plasma. Right. You have electrons and they're
15:52
Speaker 1: flying around. You have protons and they're flying around but
15:55
Speaker 1: they haven't like cooled off together where they're going to
15:58
Speaker 1: pair off and become neutral. And so you have helium
16:01
Speaker 1: nuclei and hydrogen nuclei and electrons all flying around in
16:05
Speaker 1: this big, messy plasma. But sort of an analogy to
16:08
Speaker 1: the way we were talking about cork luon plasma before.
16:11
Speaker 1: Here we have a nuclei electron plasma. So it's very
16:15
Speaker 1: hot and it's emitting a lot of light, but it's
16:17
Speaker 1: also absorbing that light, and so it's opaque. It glows
16:21
Speaker 1: giving off light, but it also absorbs that same light,
16:24
Speaker 1: so it's kind of like the sun. It's hot and
16:26
Speaker 1: it's glowy, but it's not see through yet. And then
16:31
Speaker 1: there's this moment when it cools enough that the protons
16:34
Speaker 1: and electrons come together to make neutral hydrogen and it
16:38
Speaker 1: doesn't absorb that light anymore, and so it becomes transparent. Right,
16:42
Speaker 1: But at this stage they say that still the universe
16:45
Speaker 1: was transparent because like a light could still move around
16:51
Speaker 1: almost unimpeded, right, Like nothing really absorbed light. That's why
16:54
Speaker 1: they say it was transparent. Yeah, Well, there's this threshold
16:56
Speaker 1: here about three d and eighty thousand years after the
16:59
Speaker 1: Big Bay when the universe becomes transparent, and so before
17:03
Speaker 1: that it was like a big, hot, glowing mess, and
17:06
Speaker 1: photons were being created, but they were also being absorbed
17:09
Speaker 1: because any particle that's making photons can also absorb those photons,
17:13
Speaker 1: so the photons can always go very far. But there's
17:16
Speaker 1: this moment when the universe cooled sort of crystallized, literally
17:20
Speaker 1: around three thousand years after the Big Bang. That's the
17:23
Speaker 1: moment when things became neutral. And so now the photons
17:26
Speaker 1: that had been created at that moment there was no
17:29
Speaker 1: longer anything around that could absorb them as well, so
17:31
Speaker 1: those started just flying through the universe. Because neutral atoms
17:35
Speaker 1: don't absorb light. They do absorb light, but not at
17:37
Speaker 1: the same wavelengths right. Free electrons and free protons can
17:40
Speaker 1: absorb stuff at lots of different wavelengths, but neutral atoms
17:43
Speaker 1: they're much more constrained into what wavelengths of light they
17:46
Speaker 1: can create and they can absorb because of the quantization effects.
17:50
Speaker 1: Like electrons have layers of energies that they can be in,
17:53
Speaker 1: they can't just be at any energy that's different. For
17:55
Speaker 1: a free electron that's just wandering around the universe, they
17:58
Speaker 1: can admit a huge spec room of light and it
18:00
Speaker 1: can absorb it a huge spectrum. Alright, So then the
18:04
Speaker 1: universe went from transparent to non transparent, and that's ironically
18:11
Speaker 1: sort of like when things when dark. Yeah, Actually the
18:14
Speaker 1: universe went from opaque too transparent, and that light emitted
18:18
Speaker 1: at that moment was sort of the last light emitted
18:21
Speaker 1: before the universe went dark. Right. It was hot and
18:23
Speaker 1: glowing but opaque, and then it switched to being transparent
18:27
Speaker 1: but not really creating any more light like any light
18:30
Speaker 1: that was there, it just flew away. Yes, And that light,
18:33
Speaker 1: of course is famously still flying around. The cosmic microwave
18:36
Speaker 1: background light that was created at that moment is the
18:39
Speaker 1: stuff we see in the sky. You know. People write
18:42
Speaker 1: in and they ask questions like, how can we can
18:44
Speaker 1: still see the cosmic microway background radiation? It was just
18:48
Speaker 1: created at one moment, right, hasn't it washed over us already?
18:52
Speaker 1: Why can we still see it in the sky, Which
18:55
Speaker 1: is a cool question, And the answer is it because
18:57
Speaker 1: remember that it sort of happened everywhere, like the universe
19:00
Speaker 1: was a big, hot, glowing plasma. It was emitting this
19:04
Speaker 1: cosmic market wave background radiation everywhere at the same moment,
19:08
Speaker 1: and so we're still seeing it because it's coming to
19:10
Speaker 1: us from different parts of the universe, from further and
19:12
Speaker 1: further away, all right, And so that's when the Dark
19:16
Speaker 1: Ages of the Universe started. And so let's get into
19:20
Speaker 1: what actually happened during those Dark ages and how we
19:23
Speaker 1: know about what happened then. But first let's take a
19:26
Speaker 1: quick break. All right, we're talking about the Dark Ages
19:41
Speaker 1: of the universe, so that there was a point in
19:44
Speaker 1: the universe's childhood teenage years, Yeah, exactly when you couldn't
19:49
Speaker 1: see anything. I mean, it was really bright the universe.
19:52
Speaker 1: It was dance and bright, and then suddenly it became
19:55
Speaker 1: transparent and not bright. And that's kind of when things
19:59
Speaker 1: went yeah, because two things happen at once, right at
20:02
Speaker 1: the universe goes from being opaque to being transparent, and
20:06
Speaker 1: everything that was creating light sort of switched off. The
20:09
Speaker 1: ionized particles are no longer glowing because they became mostly
20:13
Speaker 1: neutral hydrogen. So now you have the universe is just
20:16
Speaker 1: filled with neutral hydrogen but not creating any light, and
20:21
Speaker 1: so light can pass through that universe, but there's not
20:24
Speaker 1: anything really glowing. The only thing that's left is the
20:28
Speaker 1: light from the cosmic market way background radiation, which is
20:31
Speaker 1: gradually getting redder and redder as the universe expands. It's
20:35
Speaker 1: kind of like the party ended, or you know, like
20:38
Speaker 1: the club suddenly turn off the music and so everyone's like,
20:41
Speaker 1: all right, I'll conserve my energy, I'll stop dancing. Yeah, exactly.
20:44
Speaker 1: And so the stuff is still there, right, the stuff
20:47
Speaker 1: that made the hot plasma of the CNB is still around.
20:50
Speaker 1: It's just a little cooler, which is why it sort
20:52
Speaker 1: of fell into these neutral atoms, and it's not glowing
20:56
Speaker 1: as much anymore. It's a little bit of glow because
20:59
Speaker 1: neutral hydrogen and which is still pretty hot, can glow
21:02
Speaker 1: at one wavelength, a one centimeter wavelength, but it doesn't
21:06
Speaker 1: give this broad spectrum of light that you get from
21:09
Speaker 1: the hot plasma. So the only light you have in
21:12
Speaker 1: the universe at this point is this gentle cosmic microwave
21:16
Speaker 1: background radiation left over from the hot plasma that was there,
21:20
Speaker 1: and then the very very light glow of neutral hydrogen.
21:23
Speaker 1: So it's basically just all black in the universe. Interesting,
21:26
Speaker 1: so I guess the universe it's just full of hot
21:28
Speaker 1: hydrogen and that glows a little bit, but not like
21:31
Speaker 1: a regular light. Yeah. And also it glows at a
21:34
Speaker 1: certain frequency, and it also absorbs at that frequency, so
21:38
Speaker 1: that light doesn't really go very far. So if you're
21:40
Speaker 1: in the universe at that point, you basically really don't
21:43
Speaker 1: see anything except for the CMB if you can detect it.
21:47
Speaker 1: And so, you know, if you were transported in your
21:50
Speaker 1: time machine back to the dark age of the universe
21:52
Speaker 1: and you unroll the window or whatever, you look out,
21:55
Speaker 1: it's just black. There no stars, there's no galaxies, there's
21:58
Speaker 1: no nebula. There is really nothing to see in that view.
22:02
Speaker 1: And also you get a lot of hot hydgroen hitting
22:04
Speaker 1: you in the face if you roll down the window. Yeah, exactly,
22:08
Speaker 1: make sure to put your space suit on before you
22:10
Speaker 1: roll down the way. Just crack it open a little
22:12
Speaker 1: bit first, just to check. Because the universe was pretty hot.
22:15
Speaker 1: I mean it's not it's not like warm hydrogen. It's
22:18
Speaker 1: like four thousand degrees hydrogen. Yeah, exactly. It's cool relative
22:22
Speaker 1: to the early Universe, but it's still pretty hot relative
22:26
Speaker 1: to where we are today. And so the early universe
22:30
Speaker 1: is like four thousand degrees and then it gradually cools
22:33
Speaker 1: down to you know, like sixty degrees kelvin and it's
22:36
Speaker 1: cooling just because the universe is expanding or you know,
22:39
Speaker 1: things are bumping into each other. Words, that all that
22:42
Speaker 1: energy going it's just cooling because the universe is expanding.
22:45
Speaker 1: As you expand the volume of a gas, it's temperature
22:48
Speaker 1: goes down, right, And so here we're expanding space. Space
22:52
Speaker 1: is getting bigger and bigger, but we're not creating any
22:55
Speaker 1: more matter, and so it's getting more dilute, and so
22:57
Speaker 1: the temperature is just dropping. And you know that's still
23:00
Speaker 1: happening today. I guess this is a little technical, but
23:02
Speaker 1: I thought temperature was related to like the kinetic energy,
23:05
Speaker 1: not really the density. Temperatures are really tricky quantity, as
23:08
Speaker 1: we've dug into on the podcast before. But you know,
23:11
Speaker 1: it's connected not just to the energy of the particles,
23:14
Speaker 1: but it's the statistical quantity that you can only really
23:17
Speaker 1: talk about for a large number of particles. And so
23:20
Speaker 1: the temperature of a gas, for example, depends also on
23:23
Speaker 1: the pressure. You know, there's the ideal gas formula that
23:26
Speaker 1: tells you that as you lower the pressure, the temperature
23:28
Speaker 1: will drop. All right, So the gas got more diluted,
23:31
Speaker 1: so that cooled it down, and that's pretty much the
23:35
Speaker 1: dark ages of the universe. Right, it's all you know,
23:37
Speaker 1: no light out there when you look out, it's just
23:40
Speaker 1: pitch black. And it lasts for hundreds of millions of years, right,
23:45
Speaker 1: Like it wasn't just a short period, Like there were
23:47
Speaker 1: hundreds of millions of years where you there was nothing
23:50
Speaker 1: going on. You can't see anything. Yeah, and if you've
23:52
Speaker 1: been around in the universe at this point, you might think, well,
23:55
Speaker 1: I guess this is it. You know, we had a
23:57
Speaker 1: moment of creation. Things were hot and dense for a
23:59
Speaker 1: while and exciting and glowy, and I guess we're just
24:02
Speaker 1: going to sort of settle in comfortably to this boring,
24:05
Speaker 1: dark universe. And yeah, it lasted for a long long time.
24:09
Speaker 1: But you know, things eventually happen, and there's this transition
24:12
Speaker 1: between when the really powerful forces are in charge, you know,
24:16
Speaker 1: like electromagnetism, which is what gives you the neutralization of
24:20
Speaker 1: the hydrogena, pulls those protons and those electrons together, and
24:24
Speaker 1: it's happy. Now, it's like, all right, I've done my job.
24:26
Speaker 1: I've made a bunch of neutral stuff. And then finally
24:29
Speaker 1: the weakest force in the universe, gravity, it wakes up
24:32
Speaker 1: and it's time for gravity to be in charge, right,
24:35
Speaker 1: But it's not like it just suddenly wakes up and
24:37
Speaker 1: turns on. It's just that as things cool down, gravity
24:41
Speaker 1: sort of becomes more significant, right, Like it's always been there,
24:46
Speaker 1: it's always been acting. But you know, the party was
24:48
Speaker 1: too crazy at the beginning for it to really be
24:51
Speaker 1: able to control anything. Yeah, exactly, it was basically irrelevant.
24:54
Speaker 1: I mean the very early universe, gravity play a little
24:57
Speaker 1: bit of a role in how these things come together
25:00
Speaker 1: and the over densities in the very very early universe,
25:03
Speaker 1: but then it's electricity and magnetism and the strong force
25:06
Speaker 1: that really dominate the formation of these particles and then
25:09
Speaker 1: their neutralization into hydrogen gas and helium gas. And you're right,
25:14
Speaker 1: gravity was around. It was doing its thing. It was
25:16
Speaker 1: tugging on stuff. But remember that gravity is like ten
25:19
Speaker 1: to the forty times weaker than the other forces, and
25:22
Speaker 1: so until the other forces get neutralized, gravity really can't
25:25
Speaker 1: do its thing, right, And so then that's what it
25:28
Speaker 1: was doing. During all those hundreds of millions of years
25:31
Speaker 1: of the Dark Ages, gravity was getting to work making stuff. Yeah,
25:35
Speaker 1: and so you have these huge clouds of hydrogen and
25:38
Speaker 1: just like we still have happening in our universe. Something
25:41
Speaker 1: can see them, like a small spot of over density
25:45
Speaker 1: where dark matter has clumped stuff together, or for some
25:48
Speaker 1: random quantum fluctuation. In the early universe, you have more
25:51
Speaker 1: stuff there than you know, one meter over, and that
25:54
Speaker 1: can sde sort of gravitational runaway effect where it has
25:58
Speaker 1: more stuff to it, so it has more grab so
26:00
Speaker 1: it pulls other stuff nearby, which then gives it more mass,
26:04
Speaker 1: which means it has more gravity. So gravity pulls stuff together,
26:08
Speaker 1: and then eventually it can do things like make a star. Right,
26:11
Speaker 1: And a lot of it had to do with dark matter, right,
26:14
Speaker 1: Like I guess dark matter was important in the dark ages. Yeah,
26:19
Speaker 1: the reason this happened at the speed that it did
26:22
Speaker 1: was because of dark matter. Remember that most of the
26:25
Speaker 1: matter in the universe is dark matter. Of the matter, right,
26:29
Speaker 1: of all the stuff that's out there that has gravity
26:32
Speaker 1: is dark matter, and so it dominates this early universe.
26:35
Speaker 1: It dominates the structure. Like where are you going to
26:38
Speaker 1: get a star? You're going to get a star in
26:40
Speaker 1: a little gravity well determined by the dark matter. So
26:43
Speaker 1: it doesn't really matter in the early universe how the
26:45
Speaker 1: hydrogen is distributed. It's much more important how the dark
26:48
Speaker 1: matter is distributed, and that's kind of cool because it
26:51
Speaker 1: means that the normal matter, which turned into stars and galaxies,
26:55
Speaker 1: is sort of like a tracer for the dark matter.
26:57
Speaker 1: It tells you where the dark matter was because as
27:00
Speaker 1: this sort of follows it because it has to because
27:02
Speaker 1: it's gravity pulls it in. It's not a pioneer in
27:05
Speaker 1: making stuff like it was just following what dark matter
27:08
Speaker 1: was doing, which was clumped for some reason in the
27:11
Speaker 1: early universe. Quantum fluctuations in dark matter led to small
27:16
Speaker 1: amounts of clumping in dark matter, and then gravity did
27:18
Speaker 1: his job, and then the normal matter sort of follows
27:21
Speaker 1: along in that process. But you know, it doesn't dictate
27:24
Speaker 1: what happens because it's only a small bit of it.
27:26
Speaker 1: And you would still get even without dark matter. You
27:28
Speaker 1: would still get formation of structure and stars and stuff
27:32
Speaker 1: even if you just had normal matter, but it would
27:34
Speaker 1: take a lot longer, Like the dark ages were only
27:38
Speaker 1: as short as they were a brief few hundred million
27:41
Speaker 1: years because of dark matter. Without dark matter, they could
27:44
Speaker 1: have lasted billions of years, right, And so then that's
27:47
Speaker 1: how the first stars were born. And these were huge, right,
27:51
Speaker 1: These weren't like the stars we know today. Like the
27:54
Speaker 1: first stars were much bigger than the ones we have,
27:58
Speaker 1: for example, in our solar system. Yeah, weirdly, these are
28:00
Speaker 1: called population three stars even though they're the first population
28:04
Speaker 1: of stars. Why would you name something confusing because they're
28:09
Speaker 1: not as smart as particle physicists astronomers. They have no
28:12
Speaker 1: idea what they're doing when it comes to me, we
28:15
Speaker 1: just lost a couple of astronomy listeners there. Obviously I'm
28:19
Speaker 1: making fun of particle physics there, but I think they
28:22
Speaker 1: count backwards. The stars we have the most recently creator
28:25
Speaker 1: called population one, and the stars in the previous generation
28:28
Speaker 1: are called population two, and then the previous generation, which
28:32
Speaker 1: happens to be the first one ever made, are called
28:34
Speaker 1: population three stars. That is kind of smart, actually, because
28:39
Speaker 1: you don't know, maybe there are more populations than initially
28:43
Speaker 1: thoughts it makes sense to go, you know, in the
28:46
Speaker 1: negative direction. Yeah, maybe they should have called them population
28:49
Speaker 1: minus three or something. Anyway, we don't actually know about
28:52
Speaker 1: population three stars. They're still theoretical. We've never observed one
28:56
Speaker 1: on its own because they existed for such a brief
29:00
Speaker 1: period in the very early universe. They were brief because
29:03
Speaker 1: they were so big. Remember that a star burns faster
29:06
Speaker 1: and hotter if it's much bigger. And you're right, these
29:09
Speaker 1: stars were much bigger than the stars we have in
29:11
Speaker 1: our universe. They're like thirty to three hundred times the
29:15
Speaker 1: mass of our sun and they're just hydrogen. And they
29:18
Speaker 1: burned really quickly after a few million years and spewed
29:21
Speaker 1: out their light. And so these are starting to form
29:24
Speaker 1: in the Dark Ages. So that is this kind of
29:26
Speaker 1: when the Dark ages and when you first have these stars, Like,
29:30
Speaker 1: how long did it take for them to start forming? Well,
29:32
Speaker 1: it didn't take that long for them to start forming,
29:35
Speaker 1: but the Dark Ages didn't end as soon as you
29:38
Speaker 1: got stars because these stars were burning, but they were
29:41
Speaker 1: still surrounded by these shrouds of hydrogen. Like you didn't
29:45
Speaker 1: get all the hydrogen and clumped together into stars. You
29:48
Speaker 1: got these like little pockets that collapsed into a star,
29:51
Speaker 1: but then they're still surrounded by huge cloud of hydrogen gas.
29:55
Speaker 1: And the light that's created by these stars is mostly
29:58
Speaker 1: the light that hydrogen makes when it glows, and that
30:01
Speaker 1: light is also absorbed by hydrogen. So you have this
30:05
Speaker 1: universe filled with hydrogen clouds and then pinpricks of it
30:08
Speaker 1: start to glow, but that light can't really penetrate the
30:11
Speaker 1: hydrogen cloud. Oh, I see, there's there is light. Light
30:15
Speaker 1: is being created in these dark ages, but it's also
30:17
Speaker 1: really foggy. So this is more like the foggy Ages.
30:20
Speaker 1: I mean, you couldn't really call it the dark Ages.
30:22
Speaker 1: It's more like the dark Ages became the foggy Ages. Yeah,
30:25
Speaker 1: but if you were anywhere far away from any of
30:27
Speaker 1: these stars, you couldn't see any of them. It wouldn't
30:29
Speaker 1: look any different to you. You couldn't tell that these
30:31
Speaker 1: stars had started to burn. It's like it's nighttime and
30:35
Speaker 1: you're in deep, deep fog. And yes, somebody turns on
30:37
Speaker 1: a light a mile away, but the light is totally
30:40
Speaker 1: absorbed by the fog, so you can't see it. But
30:42
Speaker 1: wouldn't there be likely a somebody turning on light near you,
30:47
Speaker 1: because you know the stars are forming everywhere. Yeah, well,
30:50
Speaker 1: in a random spot in the universe, you're probably not
30:52
Speaker 1: that close to a star. Remember, space is much much
30:55
Speaker 1: bigger than we can even possibly grasp in our minds,
30:58
Speaker 1: even in our current space. Like, if you pick a
31:00
Speaker 1: random cubic meter of space, you would be far away
31:03
Speaker 1: from any supercluster, not to mention any galaxy you not
31:06
Speaker 1: to mention any star. Space is really vast and these
31:09
Speaker 1: stars are few and far between in comparison. I see,
31:12
Speaker 1: So things were that foggy like I guess we're thinking
31:15
Speaker 1: as separate as they are now, Like we're there big
31:18
Speaker 1: patches of empty universe like there are now? Or was
31:20
Speaker 1: it pretty, you know, foggy throughout? Oh that's a great question.
31:24
Speaker 1: But we think structure forms sort of bottom up. So
31:26
Speaker 1: what happens first is that these stars form, and then
31:29
Speaker 1: later they gathered together into galaxies. So things are more
31:32
Speaker 1: spread out in the early universe than they are today.
31:35
Speaker 1: Like today we have these dense clusters of stars that
31:38
Speaker 1: we call galaxies and superclusters and stuff, and then the
31:41
Speaker 1: huge voids where there's basically nothing. Back in the early universe,
31:45
Speaker 1: things were more evenly spread out, sort of sprinkled through
31:47
Speaker 1: the universe because the stars hadn't pulled together to form galaxies.
31:52
Speaker 1: All right, Well, let's get into what else happens in
31:54
Speaker 1: this foggy, dark ages, and let's talk about how we
31:59
Speaker 1: know any of the is because it happens so long
32:01
Speaker 1: ago and it was dark, so how do we know
32:03
Speaker 1: anything about it? But first, let's take another quick break.
32:18
Speaker 1: All right, Daniel, I have my fog lights on now
32:22
Speaker 1: because we're in the foggy part of the Dark Ages
32:25
Speaker 1: and everything is a giant cloud of hydrogen. There are stars,
32:28
Speaker 1: they're burning bright, but yeah, everything is so foggy you
32:31
Speaker 1: can't really see anything. And so that is part of
32:34
Speaker 1: the Dark Ages. There there is light, but it's foggy.
32:37
Speaker 1: There is light, but it's foggy. And what happens next
32:41
Speaker 1: is that that fog clears. And remember what happened to
32:44
Speaker 1: make the universe go dark was that we went from
32:46
Speaker 1: ions nuclei that didn't have electrons around them, to neutral
32:51
Speaker 1: atoms like hydrogen mostly and then a little bit of helium.
32:54
Speaker 1: So what happens next is called reionization, is when we
32:57
Speaker 1: break that neutral hydrogen back up into the proton and
33:01
Speaker 1: the electron so that it's transparent to light. So the
33:05
Speaker 1: next thing that happens is that these stars or maybe
33:08
Speaker 1: black holes or maybe we don't know what broke up
33:11
Speaker 1: this fog. Yeah, it broke apart all of those hydrogen
33:14
Speaker 1: atoms and that made it transparent again eventually. So you
33:18
Speaker 1: have this picture of like, you know, a foggy universe
33:21
Speaker 1: with these little dots of light in it. And then
33:23
Speaker 1: we don't exactly understand how this happened. One theory is
33:26
Speaker 1: that the light from these stars eventually started to ionize
33:30
Speaker 1: that hydrogen because the stars emit light that's absorbed by
33:32
Speaker 1: that hydrogen, but they also admit higher energy light, these
33:36
Speaker 1: ultra violet waves that the hydrogen can't absorb. Instead of
33:39
Speaker 1: breaks up those nuclei and knocks off those electrons sometimes,
33:43
Speaker 1: and so you break them up and you reionize, and
33:46
Speaker 1: then you've broken that up. It's become transparent and so
33:49
Speaker 1: eventually sort of pushes through that cloud the way sort
33:51
Speaker 1: of like the sun can burn the fog off on
33:54
Speaker 1: a really sunny day. So you get these kind of
33:58
Speaker 1: like bubbles of visibility forming in a giant, foggy universe. Yeah,
34:03
Speaker 1: it's sort of like the universe is a huge Swiss
34:05
Speaker 1: cheese with these bubbles in it, and the bubbles are
34:07
Speaker 1: growing and growing and growing, and eventually they meet and
34:10
Speaker 1: then the universe essentially is more clear than it is foggy.
34:14
Speaker 1: That is a pretty good analogy. A little cheesy, but
34:17
Speaker 1: pretty clear. Yeah, And it's sort of incredible to imagine,
34:21
Speaker 1: like what it could have been like to be alive. Then,
34:23
Speaker 1: you know, imagine that you are around one of these
34:26
Speaker 1: stars and you're living there and you see this fog
34:29
Speaker 1: sort of like blocking your view of the universe, and
34:31
Speaker 1: then one day it just sort of like it breaks
34:33
Speaker 1: and you can see another star or two other stars,
34:36
Speaker 1: or you know, sometimes when the fog lifts, you can
34:39
Speaker 1: see like enormous views and you can see lots and
34:42
Speaker 1: lots of other stars, and you finally understand the context
34:45
Speaker 1: you're living in. What an exciting moment that must have been. Yeah,
34:47
Speaker 1: but was it a moment It probably took you know,
34:49
Speaker 1: again millions of years in it, Yeah, absolutely, but you know,
34:52
Speaker 1: from the cosmic time scales, it's basically a moment. And
34:56
Speaker 1: of course there was nobody around then. There were no galaxies,
34:59
Speaker 1: and it probably weren't even really planets, maybe not even
35:01
Speaker 1: life and any of these early objects. And so it's
35:04
Speaker 1: just sort of like a mental exercise to imagine what
35:06
Speaker 1: that might look like if you had been around, or
35:09
Speaker 1: if we could send a time machine back in time
35:11
Speaker 1: to visualize it. To me, that's pretty cool to think
35:13
Speaker 1: about and and press the fast forward one because you
35:15
Speaker 1: don't want to wait around a few hundred million years.
35:19
Speaker 1: It's like that video on YouTube of watching paint dry
35:22
Speaker 1: that has like ten million views. People do like watching
35:24
Speaker 1: stuff happen gradually, all right, And so is that the
35:28
Speaker 1: end of the Dark Ages when now you have the
35:30
Speaker 1: flog kind of burning away. Yeah, that's it. And we
35:34
Speaker 1: have this one theory that maybe it was starlight, that
35:36
Speaker 1: the ultra violet light from these stars eventually burned these
35:39
Speaker 1: holes in the fog and clear things up, but we're
35:42
Speaker 1: not a hundred percent sure because population three stars are
35:45
Speaker 1: still sort of theoretical. We don't really understand it. Another
35:48
Speaker 1: idea is that you've got supermassive black holes created early on,
35:52
Speaker 1: maybe from primordial black holes from the Big Bang, that
35:55
Speaker 1: then grow as they eat a lot of gas and
35:57
Speaker 1: they can emit a lot of radiation which might helped
36:00
Speaker 1: clear this fog. And so it's not something we totally understand.
36:04
Speaker 1: There's like a few ideas for how the fog lifted,
36:06
Speaker 1: but again not something we totally understand because it's very
36:09
Speaker 1: difficult to study, right, all right, So then we get
36:12
Speaker 1: the universe as we know it. Then you get galaxies
36:15
Speaker 1: and galaxies clusters and superstructures, and everything's clear the way
36:19
Speaker 1: it is now. Yeah, and it's about after like a
36:21
Speaker 1: billion years that the universe starts to look familiar, things
36:25
Speaker 1: that you would recognize, as you say, stars and galaxies
36:28
Speaker 1: and structures of galaxies and black holes at the center
36:31
Speaker 1: of those galaxies and all that familiar stuff. But it
36:34
Speaker 1: took about a billion years, you know, between three d
36:37
Speaker 1: eighty thousand years after the Big Bang when the universe
36:40
Speaker 1: went transparent, to a billion years later when structure formed
36:45
Speaker 1: and the stars were created and the fog lifted. So
36:48
Speaker 1: that's a long period between the Big Bang and when
36:50
Speaker 1: the universe started to look familiar. It's kind of like
36:53
Speaker 1: the adolescence of the universe. You know, you're in a
36:56
Speaker 1: bad mood, you're feeling dark, you can't feel foggy the
37:00
Speaker 1: whole time, but then suddenly things clear up and you
37:03
Speaker 1: sort of come into your own Maybe you're not happy
37:05
Speaker 1: with your complexion, so you prefer to spend some time
37:07
Speaker 1: in the dark rather than go out into the sunlight.
37:09
Speaker 1: So yeah, exactly the awkward teenage moments of the universe,
37:12
Speaker 1: and then finally it grows up into the beautiful, gorgeous
37:15
Speaker 1: views that we know and love today. All Right, Well,
37:18
Speaker 1: maybe a big question that a lot of people might
37:20
Speaker 1: have is how do we know any of the information
37:22
Speaker 1: about the dark ages or that even that there was
37:25
Speaker 1: a dark age in the universe. I mean, it happened
37:28
Speaker 1: so long ago, fourteen billion years ago. How can we
37:32
Speaker 1: look back and know with so much detail what happened. Well,
37:35
Speaker 1: a lot of this is speculation because we don't have
37:38
Speaker 1: data about this stuff. You know, we can see the
37:41
Speaker 1: cosmic microwave background radiation that's the last light created before
37:45
Speaker 1: the universe became transparent and neutral, and we can still
37:49
Speaker 1: see that, and then we can see things start to
37:51
Speaker 1: form later, you know, hundreds of millions of years or
37:54
Speaker 1: billions of years later, and we see this gap, right,
37:57
Speaker 1: we know when the constic microway background aready happened. We
38:00
Speaker 1: can look back further and further in time and try
38:03
Speaker 1: to see these early galaxies and these early stars, but
38:06
Speaker 1: we just sort of don't see anything further. There's just
38:09
Speaker 1: nothing there to see. I see. So you're saying you're
38:12
Speaker 1: just guessing, and uh, well, also there's so you're saying
38:17
Speaker 1: there's a gap and what we can see like there's
38:19
Speaker 1: a missing spot in the our picture of the universe.
38:22
Speaker 1: You know, we don't see stars and galaxies from before
38:24
Speaker 1: that time because we think that there weren't there, and
38:27
Speaker 1: so it's sort of like, how do you see the
38:29
Speaker 1: dark ages? You're seeing the lack of something, right. The
38:33
Speaker 1: dark ages are the lack of stars and light and
38:36
Speaker 1: all sorts of fancy emissions that we could study, and
38:38
Speaker 1: so we don't see them because we don't think that
38:40
Speaker 1: information was being created there because there weren't stars and
38:43
Speaker 1: galaxies and stuff to create pictures for us to see.
38:46
Speaker 1: But I guess you're not just guessing. I mean you're
38:49
Speaker 1: piecing together what makes sense from what we know now,
38:51
Speaker 1: Like if you run a simulation of the universe backwards,
38:55
Speaker 1: this is kind of what makes sense for things to
38:57
Speaker 1: be the way they are now exactly. We're trying to
38:59
Speaker 1: put together a holistic, coherent explanation for how the universe
39:03
Speaker 1: came to be, and it makes sense for it to
39:05
Speaker 1: have a dark age, like the physics suggests that it should.
39:08
Speaker 1: You shouldn't get stars immediately after the universe gets filled
39:12
Speaker 1: with nutral hydrogen. Should take a while for gravity to
39:14
Speaker 1: pull it together, And our simulations, which now include dark matter,
39:17
Speaker 1: explained pretty well how long that should happen and what
39:20
Speaker 1: it should look like and even the nature of the structure.
39:24
Speaker 1: You know, if you didn't have dark matter, or dark
39:26
Speaker 1: matter had a different temperature even or a different distribution,
39:29
Speaker 1: you would get a whole different shape of the universe.
39:31
Speaker 1: We talked about that on a podcast once, about the
39:33
Speaker 1: temperature of dark matter and how the speed of those
39:36
Speaker 1: dark matter particles changes how things clump together. So we
39:40
Speaker 1: actually have a really detailed picture of that period, but
39:43
Speaker 1: we're lacking a sort of direct evidence. But we can
39:46
Speaker 1: do something pretty cool, which is we make this whole
39:48
Speaker 1: coherent view of how the universe should have worked the
39:51
Speaker 1: history of the universe, and then we try to identify
39:54
Speaker 1: things we can do to test that. We're like, well,
39:56
Speaker 1: if this picture is true, what could we see, And
39:59
Speaker 1: there's a few opportunities there to maybe get some hints
40:02
Speaker 1: about what was going on in those dark ages? Right,
40:05
Speaker 1: And I guess if we're looking out into the universe
40:07
Speaker 1: and we're looking backwards some time, you can maybe literally
40:10
Speaker 1: see this dark age, right, you could see the fog
40:13
Speaker 1: almost or at least the first few stars that formed
40:18
Speaker 1: that broke through the fog, right, because I mean at
40:21
Speaker 1: some point and when you look out into space, you
40:22
Speaker 1: would see those, right, Yeah, exactly, the ones that were
40:25
Speaker 1: happening really far away. Yeah, And so those are the
40:27
Speaker 1: two primary areas of investigation, where it's like, let's see
40:30
Speaker 1: the oldest things we can and see when they formed
40:33
Speaker 1: and what was going on. And you know, the oldest
40:35
Speaker 1: things we see are like three hundred seventy to four
40:38
Speaker 1: hundred million years after the Big Bang, and we see,
40:40
Speaker 1: for example, clumps of stars that were all created at
40:44
Speaker 1: the same time. We think, we don't really understand why,
40:47
Speaker 1: and you know, we can't study these stars individually. These
40:50
Speaker 1: things are so far away that they're just like blobs
40:53
Speaker 1: of many, many, many stars that we can study all together.
40:57
Speaker 1: We don't have the resolving power to identify one individual
41:01
Speaker 1: population three star, but people are looking for that. And
41:04
Speaker 1: then the second area of investigation is, as you say,
41:06
Speaker 1: to look for that fog, like we should be able
41:08
Speaker 1: to see it. It did admit some light. It was
41:11
Speaker 1: neutral hydrogen, and neutral hydrogen when it's hot, does emit
41:15
Speaker 1: light at one particular wavelength, this twenty one centimeter wavelength,
41:19
Speaker 1: and so we can look for that. But that's a
41:21
Speaker 1: radio signal, which means it's really hard to listen to
41:23
Speaker 1: because frankly, our society makes a lot of radio noise,
41:27
Speaker 1: and so it's very difficult to listen for this very
41:30
Speaker 1: faint signal of the early universe hydrogen. Well, maybe in
41:34
Speaker 1: the future will be making less great a waste, right,
41:36
Speaker 1: I mean nobody watches broadcast TV now, it's all Netflix. Yeah,
41:43
Speaker 1: that's true. We still use a lot of wireless communication, however,
41:47
Speaker 1: which makes a lot of noise. All of your WiFi
41:49
Speaker 1: out there, in your cell phone signals and all that
41:51
Speaker 1: contributes to noise roughly in this spectrum. But we do
41:54
Speaker 1: have some fun ideas for how to find quiet spots
41:58
Speaker 1: that we can use to listen for the radio signal
42:01
Speaker 1: from the early universe, and one of them involves building
42:03
Speaker 1: something on the far side of the moon. Cool because
42:07
Speaker 1: it's quiet there. Yeah, because it's quiet there. It's like
42:09
Speaker 1: the quietest spot in the Solar system if you don't
42:12
Speaker 1: want to listen to all of humanity's noise. And so
42:15
Speaker 1: the idea is to build something which actually orbits the
42:18
Speaker 1: Moon and it goes around the Moon. Is called the
42:20
Speaker 1: Dark Ages Radio Explorer DARE, and it goes around the
42:25
Speaker 1: Moon and when it's on the quiet side, the far side,
42:27
Speaker 1: it listens for this hydrogen signal. And then when it's
42:30
Speaker 1: on the four side, the side that we can see
42:32
Speaker 1: it sends back us information and so that's a pretty
42:35
Speaker 1: cool idea. I like that. Right, It goes to the
42:37
Speaker 1: dark side of the moon to study the dark ages
42:39
Speaker 1: that had dark matter in them exactly, and hopefully it
42:44
Speaker 1: will brighten our day with some illuminations about the nature
42:47
Speaker 1: of the universe. There you go, lift the fog, you know,
42:50
Speaker 1: our understanding of the universe. Al right, well, that's the
42:53
Speaker 1: dark ages of the universe. It sort of makes you
42:56
Speaker 1: think when a roller coaster, Right, this whole universe is,
42:58
Speaker 1: you know, first it was really bright and and explosive,
43:01
Speaker 1: and then it was dark and quiet and foggy, and
43:04
Speaker 1: now it's pretty bright and pretty. But maybe someday it
43:08
Speaker 1: will go back to being dark and and quiet again. Right, Yeah,
43:11
Speaker 1: I think that's the lesson. You know that one period
43:13
Speaker 1: of the universe can seem sort of final, like it's
43:15
Speaker 1: sort of settled into its final form, and it could
43:18
Speaker 1: last for hundreds of millions of years, and then it
43:21
Speaker 1: can change to something totally different. Right, And so even
43:25
Speaker 1: though the universe is now fourteen billion years old and
43:28
Speaker 1: it seems like to have mostly settled into this whole
43:30
Speaker 1: structure of stars and galaxies and whatever. Who knows in
43:33
Speaker 1: another hundred billion years, if something else will happen, if
43:36
Speaker 1: we'd be in a totally new form, and people will
43:39
Speaker 1: look back at this as like the bright period of
43:41
Speaker 1: the universe, or the light ages of the universe, like
43:44
Speaker 1: the prime of the universe, the middle age of the universe,
43:48
Speaker 1: that's right, or going into the not so active part
43:52
Speaker 1: of the universe. Yeah, or maybe the universe will continue
43:55
Speaker 1: like this forever, or you know, it's one possibility is
43:58
Speaker 1: that things will keep getting pulled upon art and the
44:00
Speaker 1: universe will get dark. Not because things will turn off,
44:03
Speaker 1: but because things will just be so distant that we
44:05
Speaker 1: can't see each other, that all the other galaxies will
44:08
Speaker 1: be yanked away from us due to dark energy, and
44:11
Speaker 1: so the night sky will get darker and darker again,
44:14
Speaker 1: not because stuff is disappearing, but because it becomes invisible.
44:17
Speaker 1: It goes beyond our event horizon because it's just so
44:20
Speaker 1: far away. Yeah, So I guess people should go out
44:23
Speaker 1: there at night and hopefully somewhere where you can see
44:27
Speaker 1: stars and appreciate the view because it's not gonna last forever.
44:32
Speaker 1: You've got a few billion years, but still make some plans.
44:34
Speaker 1: I guess appreciate it on a cosmic scalpe. Al Right, well,
44:38
Speaker 1: we hope you enjoyed that little trip down memory lane
44:41
Speaker 1: for the universe and enjoyed spending some time in the
44:45
Speaker 1: dark and quiet period of the universe awkward teenage years
44:48
Speaker 1: but also nice and quiet. Thanks for joining us, See
44:52
Speaker 1: you next time. Hmm. Thanks for listening, and remember that
45:02
Speaker 1: Daniel and Jorge explain the Universe is a production of
45:05
Speaker 1: I Heart Radio or more podcast from my heart Radio.
45:08
Speaker 1: Visit the I Heart Radio Apple Apple Podcasts, or wherever
45:12
Speaker 1: you listen to your favorite shows.