0:00

All right, Katie. So we've learned

0:02

so far that the universe was

0:04

in a very hot, very dense

0:06

state, and then it began to

0:08

expand. We've learned a lot about

0:10

what happened in the first second.

0:13

We've learned that the rules

0:16

of the universe were different

0:19

and are different when things are

0:21

very hot and very dense. And

0:24

we've learned that over the first

0:26

couple minutes things started to cool

0:28

down and spread out, and

0:30

as they did, we

0:34

got the laws of physics that we

0:36

know today. Yeah. Yeah.

0:38

Approximately. Yeah, that's right. We

0:41

got the strong and weak nuclear forces.

0:43

We've got the Higgs

0:46

field. We've got

0:48

gravity. And we've

0:50

got electromagnetism. Mm-hmm. We've

0:53

also gotten two

0:55

episodes into this podcast, Dr.

0:57

Mack, and we're like

1:00

a minute and a half into the history

1:02

of the universe. So today we're

1:04

going to start to speed up a little bit. Yes.

1:14

Hey, I'm John Green. Welcome to

1:17

Crash Course, the universe. On

1:19

today's episode, the universe as we know it starts

1:21

to come into focus. I knew

1:23

Dr. Mack was going to start to walk

1:25

me through what happened after the earliest moments

1:27

of the universe, but I

1:29

did not expect the connection

1:31

between that hot, dense, early

1:33

universe and today to be

1:36

so intensely weird. And

1:39

at the same time, so intensely

1:42

logical? Like, the only thing

1:44

that could have possibly happened

1:46

mathematically happened. And

1:49

that's what led us to photons and

1:51

stars and us. And

1:53

we can actually see that

1:55

trajectory, which is just

1:58

wild. as

2:00

wild as knowing there might

2:02

actually be a multiverse. All

2:05

right, here's our conversation. Okay,

2:11

so up to this point, we've talked

2:14

about the hot, dense, early universe. We've

2:16

talked about the sort of cork glue

2:18

on plasma, how nucleosynthesis happened in the

2:20

universe, brought together protons and neutrons and

2:22

created the first nuclei. So

2:25

you can imagine that

2:27

the place we are in the timeline, as

2:29

far as we've covered now, is there's a kind of

2:31

hot sort of plasma of a lot

2:34

of nuclei of hydrogen and helium

2:36

mostly, and a bunch of

2:38

electrons going around. And this is where the

2:40

cosmic microwave background kind of comes in. So

2:42

we talked about the cosmic microwave background. It's

2:44

the view of the universe as it was

2:47

when it was a hot plasma. Okay, so

2:49

we're still in that hot plasma stage. We

2:51

haven't quite got to the place where everything's like

2:53

cooled down yet, as far as the timeline

2:55

we've covered so far. And so when we

2:57

look at the cosmic microwave background from here,

3:00

we can see kind of patterns in it.

3:03

And we can see that when the universe

3:05

was that hot, dense plasma, it

3:07

wasn't perfectly uniform. Everything

3:09

wasn't kind of perfectly spread out. When

3:11

you look at an image of the

3:13

cosmic microwave background, it looks kind of splotchy.

3:16

Certainly the way it's colorized is like blue

3:20

and yellow kind of patches,

3:22

or blue and sort of red patches,

3:24

depending on how you do the colors.

3:27

And it looks splotchy kind of in

3:29

the same way that clouds on a

3:31

sort of moderately cloudy day

3:33

might be splotchy. So there are regions

3:35

where it's more blue dots and regions where

3:37

it's more yellow dots. It's

3:40

splotchy, but not like a uniform fuzz.

3:42

It's like clumpy and splotchy. Okay. And

3:45

it tells us something about how that

3:48

matter, that kind of plasma of

3:51

the early universe was Clumped

3:53

in the very early times. It Tells us that

3:55

there were places where that plasma was a little

3:57

bit more dense and a little bit less dense.

4:00

That a kind of it had these these old

4:02

some saw around it. And when

4:04

I say a little bit more, dance, a little

4:06

bit less sense, I mean a very little. Those

4:08

clumps. Are in a when? We look

4:10

at the picture of the cause, my

4:12

career backgrounds if it's basically just a

4:14

uniform glow. In order to see

4:16

the pettiness, we have to stress. The

4:18

contrast to that we're seeing. Changes

4:20

in the color, the temperature, Of the

4:23

microwave lights in light of what

4:25

part in one hundred thousand. So

4:27

we're really, really stressing the contrast

4:29

in order to see that spiciness.

4:31

Oh so it's like almost uniform.

4:33

Instead of being one percent not

4:35

uniform. it's like one thousand spot.

4:38

For said not uniform. Yeah, okay,

4:40

Got. It yeah it's tend to the minus

4:42

five. It's like a tiny little bit. Of

4:45

non uniformity. But there

4:47

is that splotchy this so we can

4:49

do something really interesting with that data,

4:51

which is that we can take the

4:53

distribution of. Temperatures. In the

4:55

cause microwave background and weekend. We interpret

4:57

those as differences and density. As

5:00

that primordial plasma. And we can

5:02

make a computer simulation or the into the

5:04

computer. Okay, the places where it's a little

5:06

bit more dance, those places have a few more particles

5:08

and the places where it's a little bit last census.

5:10

oh a few. Fewer particles rights. He can

5:13

set up a computer simulation where. You

5:15

give each particle little bit of mass and then

5:17

use that that simulates running so that it has

5:19

gravity and so the little particles started come together

5:22

as they have a bit more mass and the

5:24

places that are more dense gonna. Start a clump

5:26

of the places. they're less sense that empty. Out little

5:28

bit and you set that simulation running

5:30

and after a while. You. Get

5:33

a picture that looks like a web ah

5:35

that could sell Looks like this sort of

5:37

where the. Structure Like the So Me

5:39

structure. And then that same

5:42

pattern. Is. The

5:44

pattern of how galaxies.

5:46

Are distributed in the universe for

5:49

the cosmic web, Know. Nowhere.

5:51

Yes, yes sir. known as such

5:53

As I said. That's.

5:56

A setting. It's upsetting

5:58

that such a small. Variation lead

6:00

to galaxies which I don't think

6:02

of a small yeah. Well the thing

6:05

is that each seat a little bit of a

6:07

seed and then gravity will mana magically make some

6:09

places that are more dance more and more dense

6:11

than those in the places that are less than

6:14

six on empty. Out those things are moving

6:16

away, you know, toward the more dense

6:18

regions. It's kind of rich, get rich

6:20

or poor get poorer kind of saying

6:22

that the gravity does mean, right? Okay,

6:24

that makes sense if. You get enough time

6:26

then you'll automatically get the more

6:29

higher density regions. Will compress and compressing

6:31

pull in more matter. And and

6:33

so it was a very small variations

6:35

of in the very beginning but those

6:38

races earthly on kind a large scales

6:40

because what we see in the cause

6:42

micro background were you know we're looking

6:44

This is. Like the distribution across the

6:46

whole sky. And and these variations

6:49

are. On order of like a a

6:51

square degrees owes as angle on the

6:53

skies. it's these are you know that

6:55

they're kind of big regions in the

6:57

sky is it. Adds up to been

6:59

quite a lot of matter at the time even

7:01

though we think goes in the universe was very

7:03

small then as. Or this observable universe is very

7:05

small. Then it would think of it as being a

7:07

lot of faith as if you can work out the

7:09

the scales and it works out that the that the

7:11

clumps that we see in the in the cause. Micro

7:14

background work out to be things that

7:16

become some skills of clusters of galaxies.

7:18

So what's the what's happening? It's just

7:20

it's just that plasma as it cools

7:22

and compresses. I'm living at

7:24

it cools. As the universe is expanding

7:26

and than the than the matter comes together

7:29

through gravity. And that

7:31

treats these. But with all over

7:33

densities these these clumps of matter

7:35

and those consummate are destined to

7:37

become galaxy clusters. And it. And it's kind

7:39

of amazing that that when we do these simulations,

7:41

we can take just the data from the my.

7:43

Crew Background: Just the data from this glow. From

7:46

the Us ago, the universe and evolved that

7:48

forward in time and see that those variations

7:50

really are the seeds of the structure. Of

7:53

all the galaxies in the universe of of

7:55

how galaxies are distributed through the entire cosmos,

7:58

it's. Exactly the same. Pattern.

8:00

That's why things are not

8:02

distributed evenly through the universe

8:04

because the universe was a

8:07

little bit spotty him that

8:09

very, very early time in

8:11

the The Radiation era. Was in

8:13

the time when the universe was this hot plasma? It

8:16

was. Already a little bit spotty then and

8:18

we can see that directly with him. Look

8:20

right at it, looked right at that reduce

8:22

Naira. See those little slices and we know

8:24

how. Gravity allow those to grow

8:26

into clusters of galaxies. We

8:34

talked about the cosmic microwave background

8:37

in episode one when we discussed

8:39

evidence for why we know the

8:41

Big Bang happened and estate explained.

8:43

if you look at a distant

8:46

objects you're looking into the pissed

8:48

because white takes time to travel

8:50

and looking far enough away where

8:53

able to detect microwave light from

8:55

the hot, dense early universe lights

8:57

from the Big Bang. This light

9:00

is equally far away in every

9:02

direction we look. And it's

9:04

what we refer to as

9:06

the Cosmic Microwave Background. So

9:08

to underline this incredible thing

9:11

that Katie just explained, this

9:13

light from the Big Bang

9:15

is very uniform, but not

9:17

perfectly uniform. There are small

9:19

variations, and when we analyze

9:21

the Cosmic Microwave background of

9:23

these fluctuations we detect correlates

9:25

to how galaxies are distributed

9:27

in the universe. which is

9:29

incredible, right? Anyway, you're about

9:31

to hear me marvel at

9:33

what. State he just told me. so I'll

9:35

save you from hearing it twice. Wow.

9:42

I'm I'm definitely having that experience that

9:44

I've had a few times talking with

9:46

you were my mind is completely blown

9:49

and I can't believe that I live

9:51

in this universe. And I can't believe

9:53

that. There. Was a. Primordial.

9:56

Soup and I can't It's yet and and

9:58

I can't believe we got protons! It. Neutrons.

10:00

And then those protons and neutrons in

10:02

electrons became you. That's.

10:04

Weird. That. Is intensely

10:07

intensely weird. so I.

10:10

I'm. Gonna make it more weird and minutes

10:12

since Sept as a warning their sorry, well

10:14

I've I'm already there. I'm already in the

10:16

mind blown plate which is an exciting place

10:19

to be. I love being here. it makes

10:21

me anxious but I like it's do we

10:23

know that the why. Of why

10:25

there were these small inconsistent seized

10:28

y there was this slights block

10:30

genius in the early early universe.

10:32

Okay, so we have a really does theory of

10:35

why there are things we don't know there. Are

10:37

still arguments about whether this is

10:39

the correct interpretation but we saying.

10:42

That. It comes down to. The

10:45

process of cosmic. Inflation was. as

10:47

recap. We think that the universe went through

10:49

a very very very rapid expansion in the

10:51

first. Like tiny tiny fraction of a second.

10:54

like a trillionth of a trillionth of trillions

10:56

of something of a second of tend to

10:58

the minus thirty five. There was this very

11:00

very rapid expansion and and there a couple

11:02

of reasons we think that that happens and

11:05

one of them as to do with the

11:07

fact that the cause my group akron really

11:09

is very uniform, which suggests that whatever the

11:11

primordial seat. Was it was very

11:14

very uniform and with another reason for

11:16

that to have been the case ends

11:18

with the standard kind of thinking as

11:20

the interest starting with like a singularity

11:22

and than going on snare it it

11:24

wouldn't work out that it would be

11:26

that uniform. So we think that this

11:28

this cosmic inflation kind of basically says

11:30

how the universe. So much that it's

11:33

zoomed in on a on I'm on

11:35

a very small part of the earlier universe

11:37

where that small part might have been already

11:39

kind of about the same temperature everywhere. It's

11:41

kinda like because a stressing out everything so

11:44

much our entire observable universe is contained within

11:46

what would have been a very, very small

11:48

patch of. You. Know did the

11:50

whole universe before that cosmic inflation

11:53

happens? Oh no. So.

11:55

There was a lot of other space. That.

11:57

That is probably beyond our observable. yeah,

12:00

Verse yeah, yeah, so is causing

12:02

inflation happen in implies. That we are

12:04

very small part of a very very huge

12:06

universe or or multiverse if you want to

12:08

think about it that way. So no, no,

12:11

go it. But all of that stuff all

12:13

that other sources is so far away from

12:15

us now because of the that rapid expansion

12:17

that it can't possibly affect us. That's. That.

12:20

That might be some comfort. Yeah, That's.

12:23

A little bit of comfort. I mean, it's good to know

12:25

that like you know, We. Won't be

12:28

attacked by that. You know there's

12:30

other universes or whatever, but it's

12:32

more just a feeling of like

12:34

is that was a tiny part.

12:36

A relatively uniform part of a

12:39

much much larger. Soup.

12:43

Dot. Implies that our universe, which

12:45

is Unser has them ugly

12:47

large, is not nearly. Unfathomable.

12:50

The Na Cl. Here and

12:52

there are serious. It may be

12:54

that larger space is constantly inflating

12:57

and just it's It's searching and

12:59

searching kind of forever. It's called

13:01

eternal inflation. And like in our

13:03

bit of universe and our observable

13:05

universe, lights are part of the

13:07

universe. Stops that. Super.

13:09

Inflated expense and like it is, it

13:11

shifted in of that the super Celery

13:13

expansion soft as analysis regular expansion and

13:15

so we got this little pocket of

13:18

the universe that's kind of able to

13:20

have you know stuff in it as

13:22

the universe is kind of in it's

13:24

normal expansion. Say is there might be

13:26

other pocket universes in this much larger

13:28

space that are creating their own little

13:30

hot big Bang seizes where the universe

13:32

has you know, salsa thousand then and

13:34

then cools down and than grows galaxies

13:36

and so on. There might be all

13:38

these. Little pocket universes.

13:41

Did. Had their own inflationary say is

13:43

and then the hot say and then the

13:45

matter phase. In an incisive

13:48

he said we can be attacked by

13:50

any suisse's true but it's but there

13:52

are some hypotheses were maybe or little

13:54

pocket universe and another little pocket universe

13:56

kind of. Dropped. Out of

13:58

this inflating. Seeds closer. other

14:00

and could like bump up against each

14:02

other. Mm-hmm. Yikes. Well, so

14:04

I mean, the observational effect would be that there

14:06

would be like a little spot, like a little

14:09

bruise in the cosmic background and people have looked

14:11

for that and haven't seen it. So,

14:13

you know, probably. But it wouldn't, it

14:15

wouldn't be the end of me. It

14:17

would not annihilate us all, no, no.

14:20

Anyway, yeah. So if inflation is indeed what happened,

14:22

then the process is that there was this very,

14:25

very rapid expansion. And then for whatever

14:27

reason that expansion stopped happening that

14:29

rapidly and the kind of field

14:31

that was responsible for that very,

14:33

very rapid extension would have

14:36

itself sort of decayed into radiation, which

14:39

is what would have like ignited that

14:41

hot phase in the very early universe.

14:43

Then that radiation then turned into, you

14:45

know, quarks, the gluons and all

14:48

the particles and that the plasma

14:50

that we see in the cosmic background. So

14:52

there's this kind of like several

14:54

step process that we think happened

14:57

to create the universe we have

14:59

to date. But the way that that connects

15:01

with those little variations, those

15:03

little density variations, is

15:06

that we think that as inflation

15:08

was happening and especially

15:11

as it was ending, the fluctuations

15:13

in the energy field driving inflation,

15:15

we called it, so we call

15:18

it the inflaton field. So it's

15:20

not a very creative name, but there was inflation,

15:23

it was driven by the inflaton field. I know,

15:25

I know. It's like unobtainium. That's how bad it

15:27

is. I don't want to criticize the person who

15:29

came up with it. They're probably still alive. They're

15:32

probably listening to this podcast, but like that's not

15:34

a good, that's not a good one. And it's

15:36

frustrating too, because whenever you're writing a paper

15:38

about these things, like the spell checker

15:40

is constantly taking issue with the word

15:42

inflaton, because it's like, you didn't you mean inflation?

15:45

Like, no, that's the other, that's the concept we're

15:47

talking about the field. It gets very, anyway, so

15:50

the inflaton field would have been a scalar

15:52

field, which is like the Higgs field, where

15:54

it's a field with some value everywhere.

15:56

Right. And it evolves according

15:58

to a potential. is a concept

16:01

where it kind of tells the field how

16:03

to change. But we think that basically that field,

16:05

it was a quantum field and it was like wiggling

16:07

around due to quantum uncertainty. Just that all

16:09

fields wiggle around due to quantum uncertainty. That's

16:11

part of quantum mechanics, the way that a

16:13

particle can be in kind of two places

16:15

at once or you don't know where it

16:17

is or how fast it's moving at the

16:19

same time. There's this quantum uncertainty.

16:22

So we think that that field was

16:24

kind of wiggling around with quantum uncertainty

16:26

as inflation was happening. And that

16:28

caused some parts of the universe to inflate a

16:30

little bit more and some parts to inflate a

16:32

little bit less because of that quantum uncertainty. And

16:36

if that's true, it would create exactly

16:39

the kinds of density fluctuations that we

16:41

see in the cosmograe background. Those

16:44

density fluctuations can be traced back

16:47

to the fluctuations, the wiggling of

16:49

this quantum field, the inflaton.

16:52

And so now we have

16:55

a direct line from quantum

16:57

uncertainty, from these

16:59

random fluctuations of a

17:02

quantum field to the

17:04

features in the background light of the

17:06

universe, the direct

17:09

view of that hot plasma of the

17:11

Big Bang, to the

17:13

distribution of galaxies in

17:16

the cosmos. It's

17:18

wild. That is wild.

17:21

So there are equations that can tell us

17:23

that this inflation

17:27

with quantum wiggling would

17:30

lead to a cosmic background radiation that looks

17:33

about like the cosmic background radiation we see.

17:35

And then there are equations that tell us that

17:38

the cosmic background radiation we see would create approximately

17:42

the clumping of galaxies

17:44

that we see today. Yeah,

17:46

yeah. The large scale structure of the universe. Wow. I

17:49

mean, that is... Wait, what do you call

17:51

it? The large scale structure of the universe.

17:53

Yeah, the cosmic... That's good. The

17:56

cosmic web is good. The

17:58

large scale structure of the universe. versus good,

18:01

that's really beautiful.

18:05

I mean it's a little terrifying, but it's also

18:08

just gorgeous that

18:10

like it's still so

18:12

weird to me. And

18:14

I know that this is partly

18:16

a function of my imagining because

18:18

like I'm applying language and like

18:20

my high school chemistry and physics

18:22

and whatever to this. And

18:25

of course like language

18:27

and reality never have

18:30

a one-to-one map, but like it's so weird

18:32

to me that what happened was

18:34

protons and gluons. And then that

18:36

led to us. Like

18:41

that's so mind-blowing. So

18:50

yeah, there were some protons and gluons.

18:53

And then there was like us.

18:56

Like I'm at least partly made

18:58

out of a slightly cooled plasma

19:00

soup from 16 billion

19:03

years ago, which I find to

19:05

be an encouragement. My protons

19:07

will be around a lot longer than I

19:09

will. And it's nice

19:11

to know they'll still be doing

19:14

that vastly complicated mind-bendingly weird proton

19:16

stuff long after I'm gone.

19:19

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19:22

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20:09

Protons are complex. Life

20:12

insurance doesn't have to be. That's

20:14

not their tagline, but I think it's a good one. I

20:25

guess like of all the things that might

20:27

have happened, the only thing that could have

20:29

happened happened, which is

20:31

like maybe that's the way I

20:33

need to think about it, but it

20:35

is very weird to me that all of this

20:37

was set up so early. Yeah, I

20:40

mean, it's evolution, right? Like one thing happened

20:43

and led to another and led to another and led to

20:45

another. The amazing thing is that we can

20:47

see that whole evolution, that

20:50

we can see so much of that

20:52

story very directly because we can look

20:54

into the past with astronomy. I mean,

20:57

we're making inferences about cosmic inflation.

21:00

There have been other theories about what

21:03

caused those fluctuations and stuff. Inflation

21:05

is the most accepted, but there's

21:07

some uncertainty there because we can't

21:10

see inflation specifically, but we

21:12

can see the cosmicrow

21:14

background. So we can directly see,

21:16

very, very directly look at the

21:19

universe as it was about 380,000 years after

21:23

whatever the very first moment was. I use

21:26

that term. I don't like to say after

21:28

the Big Bang because the term Big Bang is a

21:30

little bit nebulous. Sometimes it refers to

21:32

the hot Big Bang, which is the whole

21:35

period when the universe was hot, that radiation era,

21:37

and some people refer to it as the first

21:39

moment. So I try to not

21:41

be those terms confused, but we can directly see back

21:43

to about 380,000 years after the beginning. We can make

21:45

inferences through

21:49

really good inferences through

21:51

both theory and experiment down

21:53

to like picoseconds or something like that.

21:56

Then We can infer through theory down

21:58

to this. The the my thirty

22:01

five seconds or whatever when they when

22:03

cause inflation happened than an with in

22:05

a direct observations we see the the

22:07

whole time on after that with astronomy

22:09

as we can see the cause micro

22:11

background of them we conceive very early

22:13

galaxies and and how those have changed

22:15

over time by seeing more recent stuff

22:17

compared to the older stuff. So

22:20

we can. really? What's that? evolution?

22:22

Very directly So we can compare

22:24

early galaxies like especially now with

22:26

the Jade of U S T,

22:29

We can compare early galaxies to

22:31

more recent galaxies. Yeah. And there's

22:33

some as them Wilde Six and why we can

22:35

do that. I think that us on this. And

22:37

the first episode. but. That the

22:39

reason that we can see details in very,

22:42

very early galaxies has to do with the

22:44

fact that a galaxy of the same size.

22:46

Farther and farther away from us at some

22:48

point starts to look bigger. Than. One

22:50

that's closer said it's because like the most

22:53

distant galaxies that we can see, the ones

22:55

we're seeing was it a bit seats they

22:57

were actually closer to us. When

22:59

they're light, lest them. Because.

23:02

The universe was so much smaller. Than.

23:05

Some of the nearer galaxies.

23:08

Were when they're light less them. It's

23:10

not a as oh as

23:12

straightforward thing, like galaxies a

23:14

different distances now. The. Farther

23:16

away it is now the longer it's light

23:18

left us. But. The light might have left it

23:20

at a time when it was actually. Closer to us

23:23

than it is now. In It.

23:25

And you know I mean it definitely was close to

23:27

assert ourselves. Might be closer to us

23:29

than a than a galaxy currently closer

23:31

to us than it is it was

23:33

when it happened he the tenses get

23:36

complicated here. yeah I was gonna see

23:38

this becomes a real tense challenge but

23:40

but I think I get it. Basically

23:42

the universe with smaller and so those

23:45

galaxies appeared larger to us because they

23:47

were closer to us, then because the

23:49

universe was smaller and now the universe

23:51

is much bigger. But the white take

23:53

so long to get to was that

23:56

it's as if the universe. Where smaller?

23:58

Yeah. Yet the picture that galaxy took

24:00

up more of the sky than the picture

24:02

of a galaxy that scene of currently a

24:05

little bit closer to us would have taken

24:07

out because the universe was a small time.

24:25

So. We got this cosmic web that we

24:27

can see. And. We understand

24:29

that because of gravity thing started

24:31

to clump together more and more

24:34

over time. Bootleg. What

24:36

are they? What? What Is that? What? What

24:38

Are the cops In the times I that

24:40

we go through so far we got to

24:43

the point where we had we had the

24:45

first nuclei right? So we had that hot,

24:47

dense sort of the whole universe as a

24:49

nuclear furnace. It created a hydrogen. And

24:51

helium nuclei and a couple a

24:54

smattering. Of other elements. Okay, so we're still

24:56

in that that plasma say And there are

24:58

places where the plaza little bit more than

25:00

splitsville puzzles, little bit less and so things

25:02

are destined to turn into galaxy clusters and

25:04

so on. But but at the moment is

25:06

this plaza. So what happens is the universe

25:08

gets bigger and bigger and so that plasma

25:10

kind of spreads out and cools and so

25:12

that's just. kind of as you may go.

25:14

A gas bigger, it gets cooler. The

25:17

the know that the atoms are farther

25:19

apart. That's kind of us astray, Ford

25:21

saying. And so Seat of asserts the

25:23

cool. And so there's a transistor some

25:25

point where. When. You're

25:27

still in the hot

25:29

plasma sate light bouncing

25:32

around between the particles.

25:34

Get scanners, Trapped. As

25:36

like it's so dense and so hot that

25:38

photons can't travel very. Far without bouncing

25:40

off as of particles. And

25:43

so the whole universe is kind

25:45

of glowing. And the light

25:47

is kind of bouncing around. Six hundred trapped

25:49

as kind of justice. Really bright sort

25:51

of space, but as. the universe expands

25:53

a little bit then the particle get far

25:56

enough apart the electrons in the nuclei get

25:58

far enough apart that so times can

26:00

move sort of more freely through the universe

26:02

and that light can kind of disperse. This

26:05

part of the timeline is very similar to going

26:07

from the center of the sun outward

26:09

into space. So

26:12

in terms of the timeline, it's very, very

26:14

much like going from the center of sun

26:16

out to space in the sense that you

26:18

go from a space where everything's

26:21

hot and dense and there's nuclear

26:23

reactions happening, you're fusing hydrogen and

26:26

helium, and then you get farther

26:28

out, the sun gets

26:30

a little less dense. I mean, the sun doesn't have a surface,

26:32

it just kind of gets more diffuse, it's a

26:34

ball of plasma, it just gets more diffuse

26:37

as you go toward the outside and at

26:39

some point toward the edge, you

26:41

get to the point where light can

26:43

move out of the sun. I

26:46

mean, you might have heard this statistic that

26:48

like a photon produced at the center of

26:50

the sun can take like 10,000 years to

26:53

reach the edge. This is this very

26:55

effect where the photons are kind of

26:57

bouncing around between the particles, it takes

27:00

a long time for those photons to

27:02

like diffuse outward toward the edge.

27:04

So the light that we see from the sun right now,

27:08

it took eight minutes to get from the surface of the sun

27:10

to us, but it might've taken 10,000 years to

27:12

get from the center of the sun to the surface. Because

27:15

the sun is so dense and it's this

27:17

hot plasma and that's what was happening in

27:19

the very early universe in this time,

27:21

around first few hundred thousand years of

27:24

the universe, it was this hot plasma life being

27:26

in the center of the sun. But then as

27:28

the universe expanded, it's like we're moving toward the outer

27:30

edges of the sun. And at some point

27:32

you get toward what in

27:35

the sun is called the photosphere. And

27:38

in the solar photosphere is where a photon

27:41

can now escape into the universe. It's no

27:43

longer kind of trapped bouncing around anymore. And

27:46

so when we look at a picture of

27:48

the sun, we're seeing the photosphere

27:50

because it's kind of like we're seeing the edge

27:52

of where the light can start to move to

27:54

us. And so the cosmic

27:56

microwave background is basically the photosphere of

27:58

the early universe. You know,

28:01

It's a trend this in the happen

28:03

in time but because because time and

28:05

distance or so coral are connected in

28:07

cosmology, it really is very much like

28:10

a distance to so we call out

28:12

sometimes the surface of less scattering. Oh

28:15

that's beautiful. Yeah yeah. The.

28:17

Surface of West scattering. Off.

28:21

Gorgeous. And it's amazing because it

28:23

is a surface. Us I mean as the

28:25

time but it's author says because we're. Looking.

28:27

Back at it and as we look backward, looking

28:29

further back in time. And so we're really seeing

28:31

that transition. That surface and so the cause

28:33

my gray background is a picture of the

28:36

surface of less scattering. It's the picture, the

28:38

photos. fear of the early universe. So.

28:40

It's both the surface of well scattering

28:42

and the time of us scattering. Yeah.

28:45

Yeah. Wow. As

28:47

a great title for a novel. By

28:49

the way, yeah, this year would be.

29:03

It's a beautiful in is that we're looking

29:05

back. Into the early Universe

29:08

as though we are ton of

29:10

looking back. Through layers over of

29:12

a star back to the the

29:14

time when he and other universes

29:16

like the centers are so the

29:18

surface of us guttering marset transition

29:20

from the universe being. Really?

29:23

Says Justice glowing plasma where if you

29:25

are sitting in the middle of it

29:27

all the space which is be bright

29:29

to a time when that there would

29:31

be brightness of the edges but like

29:33

could travel in between like you wouldn't

29:36

be engulfed in sire insists you for

29:38

if you were after the third his

29:40

last Gatorade it I am I not

29:42

be a pleasant universe for you not

29:44

be immediately in flames so. Same

29:47

way, like if you're outside the edge of the sun.

29:50

Or might it might take a minute. Rate is

29:52

still be a pretty hot. Pretty. Dense?

29:54

Yeah. Pretty miserable from our human

29:56

perspective, but better than being right

29:58

in the middle of. The gun?

30:00

Exactly Exactly. Yeah. So couple of

30:03

things are happening there. One is that the

30:05

photons. Are able to move around because

30:07

the universes is reducing and density, but

30:09

also because the universe is getting. Lessons

30:11

and cooler, it becomes possible

30:14

for electrons and. Protons the

30:16

find each other and and

30:18

spawns am. So before that you

30:20

know is this the hot roiling plasma

30:22

plasma means that the. Particles are ionized right

30:24

so the the proton don't have any electrons

30:27

around them. Electrons are from flowing freely. And

30:29

with the that helium nuclei. There you

30:31

know I nice helium miners. Hydrogen electrons

30:33

but once the universe cause enough than

30:36

the electrons and protons are able to

30:38

come together. The electrons in the and

30:40

the helium atoms are at some point

30:42

able to come together and so you

30:44

sort of neutral Adams witches. And this

30:46

is the first time the neutral Adams

30:49

occur in the universe. It's a

30:51

kind of unfortunately named moment because we

30:53

call it recall been a son. Is

30:56

not the right term because this is the

30:58

first son. The zebra happens. The road. Gray

31:00

road they're they're combining for the first yet.

31:02

They're. Combining for the first time it's

31:04

called me Combination because of some historical

31:06

thing around when we talk about plasmas

31:09

and sings evolving later in the universe.

31:11

Others. A process called me combination

31:13

were simply becomes neutral again after

31:15

having the been really nice. but

31:17

anyway it's it's. It's. Called recommend

31:19

a simple as this is the first. Moment when

31:21

when neutral atoms are are able to form.

31:24

And so that re combination. Era

31:26

that moment when the first neutral

31:28

Adams form. That. Begins.

31:31

What? We call the Dark Ages. Of.

31:33

The Cosmos. No. Current.

31:36

And. The reason is called the

31:38

Dark Ages is because now. The.

31:40

Primordial plasmas cool downs, But

31:42

there's no stars yet. The universe is

31:44

just hydrazine gas, mostly of the little

31:46

but a helium in it. and it's

31:48

just cooling. This. Is gas cooling

31:51

down and the universe is expanding

31:53

and at the same time you

31:55

know gravity is so pulling together.

31:57

Clouds France he has these clouds.

32:00

Cole. Das. And

32:02

those clouds are starting to condense. So

32:04

the dark ages goes on for for

32:06

a while. Wait, Like

32:09

like two seconds. Or know

32:11

that said, years. Know Lake Lake

32:13

like millions and millions of. Years.

32:15

Oh great. Yeah okay yeah oh

32:18

hey. we cannot have tend to

32:20

the negative thirty five seconds and

32:22

then like tend to the negative

32:24

fifteen seconds being a while and

32:26

then have like several million years

32:28

be a while. With this is

32:31

a thing night like the the time scales

32:33

get weird break as encounter based on how

32:35

much is happening and and you get out

32:37

millions of years of cold the hydrogen gas

32:39

and not. A. Lot is happening in that

32:41

called. I guess this is great for

32:44

a Td because okay, suddenly it's looking

32:46

like we can get through this season.

32:48

I am starting to believe in us

32:50

we just skipped way. I have yes,

32:53

exactly yes or it. So we've got

32:55

these millions of years where there are

32:57

some neutral Adams but. It's.

32:59

Is clouds of gas. Slowly.

33:02

Clumping together, slowly getting

33:04

colder. Yeah exactly. So guess is

33:06

as as the Cosmic Dark ages and

33:08

this is acts as it is. Very

33:11

simple. it's there. You could write down

33:13

equations for gas schooling and it just

33:15

sits is doing that but over time

33:17

because we had these little variations and

33:19

density some of the clouds of gas

33:22

start to get a little. Bit more

33:24

dance, some other classic else and so

33:26

whoa whoa whoa whoa. If we'd never

33:28

had these little variations in density,

33:30

if our observable universe had been entirely

33:33

uniform, Their. Never would have been

33:35

stars and galaxies. I

33:38

don't know that they're never, well, Are.

33:41

You still have fluctuations, just space

33:43

on the ran the movement. Of

33:45

particles Power so. Eventually something will

33:47

happen but it would it would happened differently A

33:49

would take a lot. Longer? Okay, that's

33:52

helpful and a little mind

33:54

blower. Yeah, Ok, Er.

33:56

It so we're We're only here in this

33:58

current state because it though. early

34:01

quantum fluctuations that came along with

34:03

inflation. Yes. Yeah.

34:06

Otherwise I wouldn't be here. Yeah.

34:09

Yeah. This is why there is structure

34:12

in the universe in the way that we know.

34:15

Rick. Great. Yeah. Okay.

34:18

I'm going to not panic. I'm just going to listen. Okay.

34:21

Okay. So

34:34

these, these clumps of matter are starting

34:36

to come together. And so what I've told you

34:39

so far is that these

34:41

clumps of matter are made of gas, of the, the

34:44

cold hydrogen gas mostly. I've left

34:46

out a really important piece, which

34:49

is dark matter. Oh boy. And

34:52

dark matter is really important to this story

34:54

actually. So I think that we're

34:56

going to get more into dark matter and dark energy

34:58

in a few episodes because there's, there's a

35:00

lot more to say about those things, but

35:02

I'll just tell you two things about dark

35:05

matter right now. One

35:07

thing is that we think there's way more dark matter

35:09

in the universe than regular matter. So

35:11

dark matter is something that seems to

35:13

be sort of invisible stuff that

35:16

has mass. It has matter. It

35:18

comes together with gravity, but we can't

35:20

see it. We're pretty sure that most of

35:22

the matter in the universe is dark matter, like 85%. And

35:26

so then the reason that we call it dark is

35:29

because it seems to be invisible. And

35:31

when I say invisible, there's a, there's an important

35:33

caveat. There's important thing about invisibility that we have

35:35

to, we have to cover, which is if

35:38

I say invisible, what I mean is that it doesn't

35:40

interact with light. It doesn't

35:42

reflect light. It doesn't absorb light. It doesn't emit

35:44

light and light is

35:46

just electromagnetism, right? So light is,

35:48

is photons. Monetisms

35:50

are what mediate electromagnetism. And

35:53

the important thing about something that doesn't interact with light is

35:55

that if you can't see it in that

35:57

specific way, it also means you can't touch it.

35:59

it. Because whenever you

36:02

touch something, what you're really

36:04

doing is you're pushing your

36:06

electrons against the electrons in the other

36:08

thing. And it's really electromagnetism

36:11

that's making things feel

36:13

solid. Electromagnetism

36:15

is what makes atoms hold together

36:17

with other atoms to make molecules and things.

36:20

And it's the repulsion that means that

36:23

you can't pass solid things through other

36:25

things. That's really electromagnetism. It's

36:27

electrostatic repulsion. And so

36:30

if dark matter doesn't interact with

36:32

light, it's not only invisible, it's untouchable,

36:35

which means that it can pass through itself

36:37

another matter. It doesn't collide with

36:39

things. It doesn't smash together and heat up

36:41

the way that gas does. It

36:44

doesn't feel solid. And so

36:47

that's important to this part of the

36:49

story because when inflation created those

36:51

density fluctuations, the

36:54

places that are a little bit more dense,

36:56

not only do they have more hydrogen gas

36:58

or plasma, they also have more dark matter.

37:01

And so when this gas is

37:03

starting to be able to fall together, because

37:06

now the gas is cooling and it's starting

37:08

to cool,

37:11

it's starting to be able to interact

37:13

via gravity rather than just be bouncing

37:15

around in

37:17

the plasma, the gas is starting

37:19

to fall into the clumps

37:22

of dark matter that were set down

37:25

in the initial fluctuations

37:28

from cosmic inflation. And

37:30

so because clumps of dark matter

37:32

don't collide with each other, there's no

37:34

pressure, those clumps of dark matter can

37:36

just fall together in a way

37:39

that gas has more pressure, gas

37:41

is kind of like it

37:43

bounces a little bit more and the

37:45

dark matter doesn't. And so

37:48

it's able to create these

37:51

gravitational wells that the

37:53

regular matter can fall into and it

37:55

helps the matter come together to form

37:58

the first structures. So

38:00

dark matter doesn't interact with

38:02

light. It's not

38:04

touchable. It's not

38:07

visible. But it

38:10

has mass, and so it does interact

38:12

with gravity. Yeah. And so

38:14

it feels its own gravity, and regular

38:16

matter feels the dark matter's gravity, and

38:18

dark matter feels the gravity of regular

38:21

matter. And so because there are clumps

38:23

of dark matter now that were set

38:25

down by those early scenes of structure,

38:28

those clumps of dark matter are starting to pull in

38:30

gas. And so that cold

38:32

gas is starting to fall together, aided

38:35

by those clumps of dark matter. The

38:37

clumps of dark matter are kind of providing extra

38:39

pull to get that gas together. And

38:42

as it comes together, presumably it

38:44

becomes more dense, which means it

38:46

becomes more hot. Yes.

38:49

And this is where we start to

38:51

get the beginnings of stars and

38:54

galaxies. That

38:57

gas, as it's coming together, it can compress

38:59

and it can start to heat up, and

39:01

you can get these balls of gas that

39:04

can start to get so dense in the center

39:06

that they can start to have nuclear reactions in

39:09

the center. And that begins

39:11

the epic of the first

39:13

star formation. This is how the

39:16

universe goes from the Dark Ages

39:18

to what we call cosmic dawn.

39:22

That's a good one too. Yeah. Yeah.

39:26

It's not. It's very good. It's

39:28

not as good as the what of

39:30

last scattering? The surface of last scattering.

39:33

The surface of last scattering is... I

39:36

know. I know. In

39:54

this cosmic dawn, the whole universe

39:56

was originally a gigantic nuclear reactor.

40:00

Things got. Cold.

40:03

And dark And. Not

40:05

that interesting. And. Then. As.

40:09

The gas started to come together.

40:12

With the help of dark matter,

40:14

we got these individual nuclear reactors.

40:17

Com stars? Yes, Yeah! Yeah,

40:19

and they swarmed. They formed in,

40:21

you know, closers in clumps in

40:23

these early galaxies, or that matter

40:25

having been brought together. By

40:27

the Dark Matter. But it

40:30

allowed for the first Sars to

40:32

ignite. There's still a lot of

40:34

uncertainty about what those first stars

40:36

looks like. I'm. Sorry

40:38

for me. Today has a much different

40:40

environment to form in. There are all

40:43

these these heavier elements that are around

40:45

and because of that when the guess

40:47

the former star today's is coming together

40:49

that gets us to cool in order

40:51

to keep compressing like if it's too

40:53

hot it is kind of balances. Out

40:55

right it's It's sees disuse but in

40:58

order to really really compress enough to

41:00

make a sar it has a cool

41:02

little bit to to fall together more

41:04

friendlier. The ideas As if something Suharto

41:07

supersedes. If you want to compress of the after

41:09

cool it than it. as it's compressing it gets hotter and

41:11

hotter. There's. A kind of balancing act

41:13

that has to happen but with

41:15

modern Sars a lot of that

41:17

cooling it happens through like does

41:19

it sort of causes like vibrations

41:21

and in dust and then that

41:23

radiates some some energy and things

41:25

cool down through molecular interactions through

41:27

da sa these all these different

41:30

processes to allow some of the

41:32

energy said to be loss and

41:34

and allows the some of the

41:36

the sort of heat of this

41:38

of this club have mattered. To

41:40

radiate away and allows it to cool and

41:42

cool in comparison for progress in the very

41:44

early universe. Where the Primordial Death

41:47

which was just hydrogen and helium

41:49

and this is a tiny amount

41:51

a helium. And and it's harder

41:53

there, there are fewer avenues for

41:55

cooling that girls. And so there

41:57

is still these debates about. There

42:00

may be the first stars were like. Hundreds.

42:03

Or thousands of times the mass of the

42:05

thought. Maybe there is super super massive because.

42:07

You know, in order to get enough matter

42:10

together to create those first nuclear. Actions maybe

42:12

receded Way more matter because you

42:14

couldn't cool it down. His

42:16

his visit was soo now too small a

42:18

clump and and so you had these really

42:21

big supermassive sars. And we're still debate about

42:23

that. but we we think they probably. Were more

42:25

massive than the present A stars. And

42:28

so those early as stars probably

42:30

looks. Quite different. To the

42:32

the Sars today and it was harder

42:34

to form them because you aegis. it

42:36

was harder to get that gas together

42:39

because it didn't have all these cool

42:41

a mechanisms. But somehow, who would ever

42:43

happen some of these stars. Came

42:46

together the gas was able. To compress

42:48

and and clump M and the first nuclear

42:50

actions were set off in the centers of

42:52

these stars. And that is what sparked what

42:55

we call the Cosmic dawn. Wow.

42:58

And so. Were. There immediately

43:00

planets are. did planets happened after that?

43:02

So planets require heavier elements. Okay, and

43:05

so these nuclear reactions. Part of what

43:07

they did was make elements other than

43:09

hydrogen and helium. Yes, So part of

43:12

what they did was make those heavier

43:14

elements. And kind of

43:16

spit them off yeah the whole this

43:18

whole story about what we have we

43:20

call it polluting the intergalactic mediums so

43:23

of serves a society of i feel

43:25

like yeah things are getting much better

43:27

in terms of name's. Yeah yeah

43:29

yeah yeah. so as as the

43:31

Sar is burning hydrogen and center

43:34

into helium depending on the mass

43:36

of the sorry can burn heavier

43:38

elements. And it could create the know

43:40

carbon and oxygen and nitrogen so on. And

43:43

then. The. Those elements.

43:45

Will be scattered when the sorry go

43:47

supernova. And so

43:49

you have this process of the

43:51

forming and then exploding and scattering

43:54

their are around and those those

43:56

elements can then become part. Of

43:58

than produce seller. Swamp Gas

44:00

for the next star that forms the

44:02

next generation of stars. And you go

44:05

through several generations of secret a universe. It's this

44:07

full of the kinds of elements that you need

44:09

to make things. Like planets. So

44:11

this takes. Many

44:13

millions of years or even

44:15

billions of years to have

44:17

these successive generation of stars.

44:20

That. As they explode or implode,

44:22

I don't really know what a supernova

44:24

is for, like as they do whatever

44:26

they do when they die. Then they

44:28

sped off carbon and oxygen and nitrogen

44:31

and the stuff that is in our

44:33

atmosphere now. Yeah yeah yeah so the

44:35

timeline there it's it's kind of

44:37

concerned so as we know that

44:39

the service will a scattering thousand

44:41

micro. Back for another three hundred eighty thousand

44:43

years. After the beginning and

44:45

we know that there were

44:48

so on galaxies. Within.

44:50

About four hundred million years.

44:53

Because we can see them now with

44:55

with database seats. So it was the

44:58

first. Couple hundred million years. When.

45:00

The first stars were starting to to

45:02

form. And. You know, creating

45:05

the first galaxies and then those first

45:07

Sars. Because they were supermassive, they were

45:09

probably very short lived or is it

45:11

depends? Are there certain models where they

45:13

can live longer? But generally speaking at

45:15

a very massive stars the shortest lived.

45:18

it burns through it's feel more quickly

45:20

and go supernova early. And see you

45:22

could have sars that were very very masses

45:24

that would have lifetimes of of see you

45:26

are tens of millions of years and then

45:28

season go through. Generations pretty quickly. That

45:30

ways to compete. not that quickly from

45:32

my perspective, but it out there on

45:35

a cosmic scale. that breath, for I

45:37

wrote, shifted from thinking about you know,

45:39

pico seconds to thinking about millions of

45:41

years and. This is that This is a weird

45:43

thing to do a bit. As a Cosmologist, you gotta

45:45

gotta be flexible and. Your time cells. In

45:49

as you go to different of epics of the

45:51

universe. Yes! A We know that

45:53

there were in a fully evolved galaxies

45:55

within the first. Foreigner Million Years While

45:57

or. maybe even two hundred million years depending

45:59

on what we think of the current

46:01

observational sort of limits. And so somewhere

46:03

in that first couple hundred million years, the

46:07

first stars formed exploded, next stars

46:09

formed exploded, and

46:12

clumps of stars formed in galaxies. Those

46:15

first galaxies happened, as far

46:17

as we know, very, very quickly. Wow. And

46:20

it seems like every generation

46:22

of stars is a little bit easier

46:24

to make, is that right? Because there's

46:27

a little bit more heavier elements around

46:29

to kind of force

46:31

that cooling that leads to the heating.

46:33

Yeah, yeah. I mean, specifically the very first

46:36

stars are, I would say, the hardest

46:38

to make. And then as you

46:40

have some heavier elements, it helps

46:42

the cooling processes. And so it

46:44

becomes easier as you go. Wow.

46:48

Just like life, you know, it's so

46:50

hard at the beginning. You don't even

46:52

know how to do anything. And then it gets a little easier.

46:54

It never gets easy. Right.

46:57

Yeah. It does get a little easier. Wow.

47:02

Oh, I'm going to treasure so many of these terms

47:05

and concepts. I have to ask you,

47:07

do you still feel

47:09

awe? Yes.

47:13

When you think about this stuff? All

47:15

the time, all the time. Yeah, absolutely.

47:18

I mean, I don't know if you can hear it in my

47:20

voice, but like, it's, yeah,

47:22

it's amazing. I mean, it's

47:24

amazing to think about these

47:26

huge forces and these incredibly

47:31

violent and important processes that

47:33

happened throughout the course of the cosmos.

47:36

But it's also, I mean,

47:39

it's awe inspiring that we can even tell

47:41

this story, that we have so much information.

47:43

Right. We're within the first sort of 10%

47:46

of the universe that we've talked about so far.

47:48

Right. But we have such a coherent story about

47:50

all of that. We know how it all fit together so

47:53

well. And it all,

47:55

it all kind of follows mathematically

47:57

from every previous point. in

48:00

a way that is beautiful

48:02

and confirmed by experiments and observations, and

48:04

we can look at this stuff and

48:06

see the cosmic timeline. I mean, yeah,

48:09

it's incredibly awe-inspiring. It's amazing. And

48:11

it's amazing when we see these

48:13

images of early galaxies from JWLC

48:15

and things like that. We're

48:18

looking at some of the first

48:20

things that ever existed in the universe. I

48:22

mean, we're just looking at them. Yeah.

48:25

But there's also, with awe, there's an

48:28

element of being overwhelmed by

48:30

the beauty and really feeling

48:34

small in the face of something

48:36

large. Yeah. I mean,

48:38

I think about this in a religious

48:41

experience context of the definition of awe.

48:44

There was this famous theologian who

48:46

said, who talked about this concept

48:48

of the numinous, which was encountering

48:50

the radical other and feeling very

48:53

small before it, and that feeling

48:55

of awe has a lot of

48:58

wonder and thrill in it, but also

49:00

has an element of terror and fear

49:03

and really feeling your

49:06

size in the face of the universe's

49:08

forces. However, you construct that.

49:12

And I have to say, when you talk,

49:14

I do feel both. I feel

49:16

the wonder. I feel the thrill of it. But

49:19

I also do feel a tinge

49:21

of what I keep referring

49:24

to as, oh boy, almost

49:29

like an overwhelmedness. Yeah. Yeah.

49:33

No, I get that for sure. And sometimes

49:36

when I'm thinking about this stuff, I get this feeling of

49:38

standing at the edge

49:40

of this giant chasm

49:42

and just this huge

49:45

space that I can't quite

49:48

conceptualize. I can't fully understand,

49:52

but I'm right at the edge of it.

49:54

I'm looking down and I'm trying to see

49:56

to the other side. And it's

49:58

a little bit frightening to think about. about the

50:00

just that fastness, you know,

50:03

and the power of it. Yeah.

50:16

We started this episode in the

50:19

first few minutes of our universe

50:21

and we're ending it millions of

50:23

years later. As Katie mentioned, cosmologists

50:25

need to be flexible with time

50:28

scales. I'm eager to continue our

50:30

conversation because I'm starting to be

50:32

able to understand, like, how we

50:34

got from the first picoseconds to

50:37

now, but I'm still

50:39

pretty overwhelmed to be honest.

50:41

It's just unbelievable to me

50:43

that we can conceptualize the

50:45

hot, dense, early universe and

50:48

be able to connect the dots all

50:50

the way to stars forming millions of

50:53

years later. As I said

50:55

earlier, of all the things that

50:57

might have happened, the only thing

50:59

that could have happened happened. And

51:01

it's a thrill to start seeing

51:03

why, even as it also has

51:05

me asking some pretty serious questions

51:07

about free will and determinism. This

51:17

show is hosted by me, John

51:19

Green and Dr. Katie Mack. This

51:22

episode was produced by Hannah West,

51:24

edited by Linus Obenhaus, and mixed

51:26

by Joseph Tuna-Medish. Special thanks to

51:28

the Perimeter Institute for Theoretical Physics.

51:31

Our editorial directors are Dr. Darcy

51:33

Shapiro and Megan Motifery, and our

51:35

executive producers are Heather DiDiego and

51:37

Seth Waldwee. This show is a

51:39

production of Complexly. If you want

51:41

to help keep Crash Course free

51:43

for everyone forever, you can join

51:45

our community on Patreon at

51:48

patreon.com/ Crash Course. Thanks

51:55

for

51:57

watching.