0:00

Hello, dear Hank and John listeners. It's John here. I

0:02

just wanted to share with you our new

0:05

podcast. It's called Crash Course

0:07

the Universe, and it is Complexly's

0:09

attempt, along with myself and Dr.

0:11

Katie Mack, an astrophysicist, to

0:14

share with you the baffling,

0:16

thrilling, somewhat terrifying history of

0:18

our entire universe, from how

0:21

the protons inside of me

0:23

came to be, to

0:25

the deep future of our

0:27

universe, and how everything, everything,

0:30

will eventually cease to be.

0:32

Crash Course the Universe is

0:34

available wherever you get your

0:36

podcasts, including where you're listening

0:38

right now, and at our

0:40

YouTube channel, youtube.com/Crash Course. I

0:43

wanted to make this project with Dr.

0:45

Mack because she is a physicist, and

0:47

I am a person who just barely

0:49

passed high school physics, but

0:51

what we share is an insatiable

0:54

curiosity, a desire to understand the

0:56

world around us, and to engage

0:59

with the beauty of

1:01

the world around us, and it

1:03

turns out that that world extends

1:05

far, far beyond the confines of

1:07

the little rock where we find

1:09

ourselves. So here's Crash Course the

1:11

Universe. Thanks for listening. So,

1:14

we live in a universe. Yes.

1:20

How big is it? That's

1:23

a great question. It depends on what you

1:25

mean by universe. So, already, it's

1:28

complicated. Oh no. Oh no. A

1:36

few years ago, I came across

1:39

a book by the astrophysicist Katie

1:41

Mack called The End of Everything,

1:43

Astrophysically Speaking. The book

1:45

tells the story of our universe, how

1:47

we understand its beginning, its expansion, and

1:50

what we know about its future,

1:53

including, well, the end of

1:55

everything. We are only here for a

1:57

little while, of course, and the universe will be here

1:59

for much longer. much longer, but

2:01

everything we've seen so far in

2:03

our universe will inevitably die, and

2:06

it seems the universe itself will

2:08

as well. In short,

2:11

there will be no season two. I

2:14

was so moved by this book that I

2:16

wrote Dr. Mack an email to thank her

2:18

for writing it. She replied

2:20

and we struck up a friendship. We

2:23

make a bit of an odd couple. I'm

2:25

a novelist by trade who barely passed high

2:27

school physics, largely by being the kind of

2:30

student my teacher did not want to have

2:32

in class for a second consecutive year. Dr.

2:35

Mack, meanwhile, holds the Hawking

2:37

Chair in Cosmology and Science

2:39

Communication at the renowned

2:41

Perimeter Institute. But she

2:44

is a patient teacher, and I am

2:46

curious about the vast and strange universe

2:48

in which I find myself. So

2:51

we decided to make a podcast together about

2:53

the history of the entire universe,

2:55

including the parts of its history that haven't yet

2:58

been written, and more broadly,

3:00

about why we seek to understand

3:02

what's keeping the stars apart, as

3:05

E.E. Cummings once wrote. Here

3:07

in the first episode, Dr. Mack

3:09

helped me understand the Big Bang,

3:11

which initially caused me a lot

3:13

of anxiety, but then, by the

3:15

end of our conversation, I learned

3:17

something so phenomenally beautiful about the

3:19

universe that I've been clinging with

3:22

hope to it ever since, which

3:24

is that we are not just made of stardust.

3:27

We are also made of Big Bang

3:29

stuff, with pieces of

3:31

us directly born in the vast

3:34

first cacophony. Here's

3:37

our conversation. Okay,

3:40

I already have a lot of questions.

3:42

Okay, great. I would like to ask

3:44

you why there is a universe. Why

3:50

there is a universe. And

3:52

then I want to follow that up by saying

3:54

that in my line of work, there's a famously

3:57

boring question. That is the question

3:59

that everyone asks. which is where do you get

4:01

your ideas? And in my wife's

4:03

line of work, she's a

4:05

curator of contemporary art, there is

4:07

a famously boring question, which is

4:09

what is art? Right. Is

4:11

the question of why there is a universe the

4:14

astrophysicist version of those

4:17

questions? I think that it's just

4:19

a question that really

4:21

has no answer. And there

4:23

are very few people in astrophysics

4:25

or physics or cosmology, any of

4:28

those areas who are

4:30

thinking really about that question

4:32

in the sense that there are some people

4:34

working on like, how did the universe begin?

4:37

What started it? We kind of step

4:39

away from that kind of question,

4:41

because that suggests purpose

4:44

or intent or meaning in

4:46

some way that there's

4:50

no empirical approach

4:52

to that. To

4:54

establishing purpose. Yeah. Do

4:57

we know why there's stuff in the

5:00

universe? We

5:02

don't. Am

5:05

I again asking a why question and you don't

5:07

want me to ask a why question? No, that's

5:10

not a why question. That's an embarrassing question, because

5:15

our current understanding of the theories

5:17

kind of suggests there shouldn't be

5:19

stuff. Oh, there

5:21

shouldn't be stuff. That's discouraging. Yeah,

5:24

there's this concept of

5:26

matter-antimatter asymmetry. So, antimatter is

5:28

kind of like a mirror image

5:30

of matter in some sense. There's

5:32

an electron, an electron is a

5:34

particle that's part of the atom.

5:36

There's an antimatter version of electron

5:38

called a positron, has the opposite

5:41

charge, and there's some technical

5:43

mathematical sense in which they're kind of reversed in

5:46

some way. And if you take an electron and

5:48

a positron and you put them together,

5:50

they will annihilate with each other and

5:52

create gamma rays. This is why, you

5:54

know, spaceships in science fiction often use

5:57

antimatter as propulsion, because if you collide

5:59

matter and... you get a big

6:01

boom, right? Like if you started the universe

6:03

with just a bunch of radiation and that

6:05

radiation then turned into matter,

6:07

it should turn into like an equal amount

6:09

of matter and antimatter. So if you

6:12

just had sort of radiation turned into matter

6:14

and all that and in the way that

6:16

our equations kind of suggest it should work,

6:19

you should get the same amount of both and then

6:21

they would just annihilate against each other. And

6:24

then you would just have radiation again. You

6:27

wouldn't have a whole bunch of

6:29

matter and almost no antimatter which is what we see. So

6:32

if you got into the universe, everything

6:34

we observe is matter unless there's

6:37

been some kind of big high

6:39

energy event like a pulsar or

6:41

a supernova or some

6:44

kind of high energy beam

6:46

of gamma rays that splits into

6:48

electrons and positrons. Then

6:51

you can get antimatter in those high energy events and

6:53

you get a little tiny bit of it and then

6:55

it annihilates against the matter but all the stuff in

6:57

the universe is matter. Like all

6:59

the stars and planets and all that, that's made of matter.

7:02

So there's way more matter than there is

7:04

antimatter which means at some point there had

7:06

to have been something that like changed the

7:08

balance that created an asymmetry between matter and

7:10

antimatter so that all of the antimatter would

7:12

be annihilated away and there'd be

7:14

matter left over. Okay,

7:20

so I know we're only a few minutes in

7:22

here but this point is really, really important so

7:24

I want to emphasize what Dr. Mack is saying

7:26

here. Matter is everything

7:29

you see in the universe. It's

7:31

you, it's me, it's planets, it's

7:33

stars and galaxies and

7:35

antimatter is essentially the opposite

7:37

of matter and when

7:40

matter and antimatter meet, they

7:42

basically cancel each other out

7:44

so nothing but energy remains.

7:47

Based on everything we know about the

7:49

universe, there should be equal parts

7:51

matter and antimatter but

7:54

that's clearly not the case because you're

7:56

listening to this and I'm here trying

7:58

to explain antimatter to you. So

8:01

there is more matter than antimatter in

8:03

our universe and that is the reason

8:05

our universe exists and

8:08

We don't know why And

8:13

we don't know why that happened We

8:16

don't we don't know the mechanism for that there are

8:18

theories But we don't have an answer to that question

8:21

But it had to have happened at the at the

8:23

beginning right because we know there's

8:25

been stuff for a long time Yeah Yeah,

8:27

I mean our best guess is that it

8:29

happened like sometime within

8:32

the first like fraction

8:34

of a nanosecond basically What

8:37

really? Yeah, yeah, it

8:39

happened very early on like before Whoa,

8:42

whoa, whoa We know

8:44

what happened in the first second. Oh,

8:46

yeah. Yeah, we can go

8:48

down way earlier than that We

8:51

have we have a lot of information about the beginning

8:54

We know what happened in the first second of

8:56

the universe Yes, the first nanosecond of the

8:58

universe the first fraction of a nanosecond of

9:00

the we can we can go down with

9:02

reasonable confidence to a Microsecond

9:05

well actually let's see Maybe

9:08

like a fraction of a nanosecond something

9:10

like that. We're pretty sure okay We

9:13

have good like theoretical and experimental evidence

9:15

for what happened in that time before

9:18

that things get fuzzy We have a really really

9:20

good theory, but we're not certain.

9:22

Okay? So that's great. That's great.

9:24

We know what happened in the first fraction

9:26

of a nanosecond. Yeah What

9:29

was that? Take

9:31

me back. Okay. Okay to the

9:34

very beginning of the universe and

9:36

then After

9:38

you tell me the story of what

9:41

the first second the first nanosecond I'll get

9:43

I'll get into the first minute or so.

9:45

Yeah How the heck do

9:47

we know what happened in the first minute of the universe 13.8

9:49

billion years ago? I

10:08

Okay, okay, so I'll

10:10

start with the Big Bang Theory. When

10:12

people talk about the Big Bang Theory,

10:14

usually what they mean is like

10:17

they're like, oh yeah,

10:20

I heard, you know, the universe was a singularity,

10:22

is a tiny infinitesimal point that

10:24

exploded in all directions. And that's not

10:26

really what we as astronomers mean when

10:28

we say the Big Bang Theory. When

10:31

astronomers say the Big Bang Theory, we actually mean

10:33

something a lot closer to the

10:36

theme song of the TV show, the Big Bang

10:38

Theory. Because I

10:40

use this example because it's actually pretty good. In

10:43

that theme song that says, the whole

10:45

universe was in a hot, dense state, then

10:48

nearly 14 billion years ago, expansion

10:50

started, then the song goes on to

10:52

other things, right? But that's it. So the

10:54

Big Bang Theory is just the idea that the universe

10:56

was hot and dense in the beginning,

10:59

13.8 billion years ago, it was hot and dense. And

11:02

it's been expanding and cooling since then.

11:05

The origin of that theory is the

11:07

idea that currently the universe is expanding,

11:09

right? So we observe that because

11:11

we see all the distant galaxies are moving

11:14

away from us. Essentially, what's happening is that we

11:16

see the light from all these very, very distant

11:18

galaxies, that light is being kind of stretched out

11:20

by the expansion of the universe. So what that

11:22

does is it moves it from sort

11:25

of visible light to infrared light as the wavelength

11:27

is kind of stretched out. And it's a similar

11:29

effect to like if a siren goes past

11:31

your house and it goes into lower

11:33

pitch, like that, the same kind

11:35

of thing happens with light. When things are moving

11:37

away from you, they get redder or to

11:41

longer wavelengths. When they're moving toward you, they get

11:43

bluer to shorter wavelengths. And this

11:45

happens at all the different wavelengths of light,

11:47

from radio to gamma rays and so on.

11:50

So we see that distant galaxies are moving away from us,

11:52

they're moving away from each other. There's

11:55

more and more empty space happening all the

11:57

time. The universe is expanding. It doesn't

11:59

mean that like objects are expanding it just

12:01

means that there's like empty space in between objects

12:03

that's expanding and we've known that the expansion is

12:06

happening we've known that for a long time since

12:08

like the I guess 20s 1920s it's

12:10

not that long well

12:13

I mean since we started to be able to

12:15

know that like there are other galaxies essentially we

12:17

started to see that the ones

12:19

that are far enough away are moving away from us

12:21

right the conclusion you get from that

12:23

is that if the universe is expanding now it

12:25

must have been smaller in the past like if

12:27

all those galaxies are getting farther away now they

12:30

must have been closer together and

12:32

you know if you push things

12:34

closer together it it makes them

12:37

hotter you know it makes them denser like you

12:39

can squeeze things and they get hot and dense

12:42

and so you you can just kind of

12:44

extrapolate and say well the beginning of the

12:46

universe things must have been hot and dense and

12:48

really close together right and then you you kind

12:50

of keep going with that extrapolation you you arrive

12:53

at the idea that the universe was this kind of

12:55

hot dense soup of energy in the

12:57

very beginning and that idea

12:59

has been around for a long time it's been kind

13:02

of floated in different ways and the kind

13:04

of confirmation of that came in

13:07

the 1960s when we

13:09

started to actually see the light

13:11

of that hot dense soup so we

13:13

know that the universe is expanding both

13:15

because we can tell that galaxies are

13:17

getting further away from us but also

13:19

because we can glimpse this hot dense

13:21

soup that the universe was at the

13:24

very beginning so we have two independent

13:26

ways of knowing that the universe

13:28

used to be a hot dense place yeah

13:30

essentially I mean one is kind of indirect evidence in

13:32

the sense that you know you just

13:35

kind of extrapolate the expansion backward and you

13:37

get that everything was close together but

13:39

the seeing seeing the light of

13:41

the hot dense early universe is very

13:44

direct yeah what's happening there is that

13:46

you know if you look at distant objects you're

13:48

looking at farther into the past

13:50

because light takes time to travel and

13:52

so you look at the Sun it's

13:54

eight minutes ago you look at the

13:56

nearby stars it's years ago different galaxies

13:58

millions of years ago You keep

14:01

going with that and one

14:03

would expect that eventually you stop being

14:05

able to see galaxies because you're looking at so

14:08

far away That you're looking so far back in time

14:10

the galaxies haven't formed yet And if

14:12

you look far enough away, you should be able to

14:14

see that hot dense bright shining

14:18

universe and It's counterintuitive

14:20

because people think like oh if the universe was

14:22

small like there should be some direction that the

14:24

Big Bang was and you Look toward that direction,

14:27

but it's not what it is

14:29

is that the whole universe was hot and dense So

14:31

imagine like a large universe a large space

14:34

and the whole thing is filled with this

14:36

like hot dense plasma And then

14:38

the whole thing is expanding and

14:40

cooling down and if you're in one

14:42

spot And you look far enough away

14:45

You can look far out into a

14:47

part of the universe where from your

14:49

perspective. It's still in that early hot

14:51

dense state It's very hard

14:53

to picture. I'm going to imagine Incorrectly

14:57

that we can either look to the left or

14:59

the right okay if we look to the left

15:01

far enough We will see that Evidence

15:05

of what the universe was like when it

15:07

was hot and dense because we can if we

15:09

see all the way out And then we can also see

15:11

that in any direction is that right

15:13

yeah I mean what we're seeing is we're

15:15

actually seeing the universe as it was When

15:18

it was hot and dense because we're you know we're

15:20

looking at it as it was 13.8

15:23

billion years ago And if we look at a part

15:25

of the universe that's so far away that the light took 13.8

15:28

billion years to get to us Then that means

15:30

the light that's getting to us is the light from the

15:32

Big Bang light from that hot

15:34

dense Promordial soup and so

15:36

yeah, we see this like wall of fire around

15:39

us this like shell of fire

15:41

yes Yes, so is

15:43

this wall of fire which is a very helpful way

15:45

of imagining it for me Is

15:47

it equally far away in every direction we

15:50

look yeah? Yeah, just cuz like you know

15:52

the time that the light took to travel

15:54

is the same in any direction We

15:57

are in the center of our observable

15:59

universe Exactly. And so this

16:02

wall of fire is the same distance from us in

16:04

every direction. But if we were in

16:06

a different galaxy, the wall

16:09

of fire would also be the

16:11

same distance in every direction

16:13

because that would be the center of

16:15

the observable universe. Yeah, yeah. It's very

16:17

much like if you're standing on the Earth

16:19

and you look out in all directions, the

16:21

horizon is the same distance from you, assuming you're

16:23

on a flat. Like let's say you're in the

16:26

middle of the ocean, so we're not getting complicated with mountains and stuff.

16:29

The horizon is the same distance in every direction.

16:32

And it depends on where you are. If you're

16:34

in a different part of the ocean, the horizon

16:36

is the same distance in every direction, but it's

16:38

not the same part of the ocean that you

16:40

see. So there's your observable ocean, which

16:43

is the part within the horizon. And

16:45

we have an observable universe, which is the

16:47

part within our horizon, which goes out to

16:49

this distance that light could have traveled in

16:51

13.8 billion years. Okay.

16:55

Okay. And so it's kind of

16:57

this weird thing where when we

16:59

look out into the universe, we're like flipping

17:02

back in time. We're like looking at this sort of

17:04

scrapbook of the universe because the farther away we look

17:06

at the farther back we're looking. So we're kind of

17:09

seeing the cosmic timeline very directly when

17:11

we look out into space. And

17:13

so we can't see the Andromeda galaxy as

17:16

it is today. We can see it as

17:18

it was millions of years

17:20

ago. We can't see

17:23

the sun as it is right now. We can see the sun

17:25

as it was eight minutes ago. However

17:27

far away you're looking, you see it at a different

17:29

time because of the way that

17:32

the light has been traveling. So when we look

17:34

at something, you know,

17:36

billions of light years away,

17:38

we're seeing it as it was billions of

17:40

years ago. And that hot primordial soup, that

17:43

wall of fire is actually 46 billion

17:45

light years away because the light

17:47

has been traveling for 13.8 billion years, but

17:49

the universe has been expanding. So it's been

17:51

carried away from us in that time. Wow.

17:55

It was actually a lot closer when the light left it. How

18:13

big was it? Okay, so we can

18:15

talk about how big the observable universe

18:17

was at various times in the early

18:19

universe. But it's complicated because

18:21

we think the universe

18:23

is much larger than our observable universe. And

18:26

it might be infinitely large. You

18:31

had me, but now I'm lost again. How

18:34

could it be infinitely large? We

18:38

have no evidence that there's any kind of edge to the universe. There's

18:40

an edge to our observable universe in the sense that there's a

18:42

distance we can't see, just like there's a horizon on the Earth.

18:45

But there's no edge to the Earth

18:47

in that sense. You

18:49

can keep walking around the Earth and you just keep going

18:51

forever. And if the

18:53

universe is like that, that maybe it wraps around itself,

18:55

maybe it doesn't, maybe it's just infinitely large in all

18:58

directions and you can just keep

19:00

going in one direction forever. We don't know.

19:02

We don't have any reason to hypothesize either

19:04

it's infinite or finite because we don't have

19:06

any evidence for it to

19:09

have a boundary. And it would be

19:11

hard to find that evidence since we

19:13

know that we can't see past the

19:15

beginning. Yeah, exactly. So we

19:17

can't see past our observable

19:20

universe, which is defined by how far

19:22

light's traveled since the beginning. And since

19:24

in our observable universe we see no

19:26

evidence for an edge, if

19:29

there is an edge beyond that, we wouldn't know. And

19:31

we never could know. Yeah. So the whole universe

19:34

could be infinite and it could be just growing

19:37

anyway, which is like a thing because

19:39

you can have different sizes of infinities

19:41

in mathematics. So it's

19:43

possible that the early

19:45

universe was an infinitely

19:47

large, hot, dense place

19:50

and the current universe is

19:52

an infinitely large, less hot,

19:54

less dense place. It's

19:57

just that those are infinities of different

19:59

sizes. Yeah, yeah, essentially.

20:03

Yeah. Okay. That

20:06

makes me nervous. I feel

20:08

anxious. I'm sorry.

20:12

Personally, I would prefer I liked

20:15

the image I had when we started out

20:17

that it was just a singularity, that all

20:19

the matter was just inside of an infinitely

20:21

small point. That made me less

20:23

anxious, that an infinitely

20:25

large hot dense space that led

20:28

to an infinitely large, less hot,

20:30

less dense space. I mean, it

20:32

probably isn't going to help, but you can

20:35

also have a singularity that is spatially extended

20:38

and still infinitely dense. Yikes.

20:43

No, that made it worse. You're right.

20:45

That made it worse. Okay.

20:52

So, we've been talking about the mysterious existence

20:54

of matter and the expansion of our observable

20:56

universe, but before getting too much further, I

20:58

just want to zoom in on the idea

21:00

of the singularity. The singularity

21:03

is the idea that the universe was

21:05

once an infinitely small point, and then

21:07

it started to expand and has been

21:09

expanding ever since. That's

21:11

a story about the beginning of the universe

21:14

you may have heard before, but it turns

21:16

out it may be too neat of a

21:18

story to actually be true. I'll

21:21

let Katie explain. Okay,

21:27

but we don't know if there was a

21:29

singularity at all, because when we do this

21:31

timeline of the very early universe, it

21:34

turns out that just saying

21:36

there was a singularity and everything was super,

21:38

super hot and infinitely hot, and then it's

21:41

expanded and cooled, just following

21:43

that timeline doesn't work. Let

21:45

me just kind of tell the story as we think

21:47

it went, and then we can talk about why we

21:49

think that. Okay. So,

21:52

maybe there was a singularity. We don't

21:54

know if there was or not. The reason

21:56

that people talk about a singularity, the reason

21:58

that that idea comes in. to play is that

22:01

if you write down the equations of how

22:04

a universe can evolve, how space-time can evolve,

22:06

then there's a solution to those

22:08

equations. There's a mathematical picture

22:11

that works where the

22:13

universe evolves from a singularity, expands,

22:16

and then either keeps expanding forever or evolves

22:18

back into a singularity in

22:20

a big crunch. So there are kind of

22:22

different ways that that can go. But those

22:24

are consistent with equations of general relativity, the

22:26

gravitational theory of the universe. But

22:30

if you actually work out

22:32

what the consequences of coming from

22:34

a singularity and just expanding in

22:37

that normal way, if you

22:40

work out those consequences, you get a universe that

22:42

doesn't look like what our early universe looks like.

22:45

So when we look at the background

22:47

light of the early universe, the light that's

22:49

the sort of wall of fire in every

22:52

direction, the properties of that light,

22:55

essentially it's like it's

22:58

too uniform. It looks to

23:00

be basically the same in every direction in

23:03

a way that wouldn't make sense if

23:05

the universe really started from a single point

23:07

and then expanded. And it's

23:10

a complex story why that's a

23:12

problem. It has to do with

23:14

the idea that there should have

23:17

been kind of quantum fluctuations

23:19

that changed the

23:21

properties of the universe when it was

23:23

very, very small. And then you'd see

23:25

big changes in the pattern of the

23:27

background light. So in

23:30

the 1980s, there was a suggestion that

23:32

maybe we didn't go

23:34

just straight from singularity to expansion.

23:36

Maybe there was a period of very,

23:39

very rapid expansion in the beginning called

23:41

the cosmic inflation that kind

23:43

of smoothed out the universe. Kind

23:46

of like if you smooth out like a fabric

23:48

or something, or yeah,

23:52

I guess that's one way to think about it. You kind of stretch

23:55

something out and make it really, really smooth. And

23:58

then there was regular expansion from there so that Our

24:00

expansion came from a universe

24:02

that was already made very, very uniform by

24:04

some really, really rapid expansion in the beginning.

24:07

Okay. So we're kind of zooming

24:09

in on one part. So when we look at

24:11

the wall of fire, the wall

24:14

of fire looks far more uniform

24:17

than we would expect if

24:19

the universe began with a

24:21

singularity because of certain rules

24:24

around quantum

24:26

fluctuation that should have- Yeah,

24:28

essentially. Well, believe me,

24:30

Katie, I am going to be oversimplifying.

24:32

That's fine. We

24:34

would expect it to be less uniform, this

24:37

wall of fire, than it appears when we

24:39

look at it. And that

24:41

tells us that maybe what actually happened

24:43

was that in the very, very beginning

24:45

of the universe, there

24:47

was an extraordinarily rapid expansion,

24:50

much, much faster. Was

24:52

it faster than the speed of light? That's- Oh,

24:55

no. I'm sorry. Sorry.

24:59

I'm sorry. I keep doing this. So

25:03

expansion- You're

25:05

like, that's not an interesting question. No,

25:07

it's an interesting question. It's a hard

25:10

question. Okay. Because

25:12

expansion, you can define the speed

25:14

that two points are moving away from each other, but

25:18

you can't define a speed of expansion because

25:20

let's say you spread the fingers in your

25:22

hands very quickly, right?

25:26

When you do that over the course of one

25:28

second or something, the two fingers

25:30

that were closest together at the beginning, they're still

25:32

close together. They've moved maybe two centimeters in those

25:34

two seconds, but the ones on either side of

25:36

your hand have moved maybe 10 centimeters

25:40

in those two seconds. And so the

25:42

speed of expansion of the, the

25:45

speed that the two farthest ones have

25:47

traveled is faster in terms of moving

25:49

away from each other than the speed

25:51

of the two closest ones. So my

25:53

thumb and my pinky have moved faster

25:57

because they've moved further. Yeah. like

26:00

five centimeters a second, whereas

26:03

your first finger and your middle finger

26:05

moved like two centimeters a second. Right.

26:08

Right, so the farther away things start, the

26:11

faster they've moved apart if

26:13

the expansion is uniform. So if

26:15

your hands were like infinitely large

26:17

and you did the same kind of

26:19

like, you just make them twice as

26:21

big in one second, then there's

26:23

gonna be some distance where the- There

26:28

can be variations in the

26:30

experienced speed of it or the

26:32

actual speed of it. The recession,

26:35

the like separation speed. Right. So

26:37

the separation speed of,

26:39

you know, the close by fingers is gonna be small,

26:41

the separation speed of the really far away ones is

26:43

gonna be really fast. You can always

26:45

find a distance in a uniformly expanding space where

26:47

the expansion is faster than the speed of light,

26:51

because there's always gonna be two

26:53

points that are being separated from

26:55

each other that faster than the speed of light if

26:58

the whole space is expanding. Is this related

27:00

in some way to what you mentioned earlier

27:02

that the universe is 13.8 billion years old,

27:06

but the cosmic

27:09

background radiation light that we

27:11

see is like over 40 billion light years

27:13

away from us. Well,

27:15

that's related to the fact that the

27:18

universe has been expanding the whole time that

27:20

that light has been traveling. Okay. And

27:23

those distant places have been moving, has been

27:25

moving away from us faster than any other

27:27

part of the universe because they're the farthest

27:29

part. So yeah, essentially.

27:32

So the part of the universe that's moving

27:34

away from us faster than light right now

27:37

is like most of what we see in the universe.

27:40

It's weird. Like we see lots of galaxies that

27:42

are so far away from us that they are

27:44

currently moving away from us faster than light. But

27:47

it's because the light left them a long time

27:49

ago and has been traveling toward us while they've

27:52

been sort of rushing away that

27:54

we still see that light, that light was able to catch up

27:56

to us. But if they put

27:58

out light now, you know, it's

28:00

moving away from us faster than light. If they

28:02

put out light now, we would never see it.

28:07

So it depends on, that also

28:09

gets complicated because the light can

28:11

be moving, like

28:13

the space can be pulling the

28:15

light away from us, but then different

28:17

parts of the space are moving, are

28:20

sort of moving at different speeds. There are some

28:22

things that are so far away now

28:24

that even though they're moving faster than the

28:26

speed of light from us now, as

28:28

their light spreads out to the universe, it'll

28:30

reach a part of the universe that is not leaving at faster

28:32

than the speed of light, and then it'll start to

28:35

move toward us again, and then

28:37

eventually it'll reach us in the future. That

28:39

gets really complicated. We

28:42

need graphs for that. Yeah, at that point,

28:45

it's like a train leaves Boston going 80

28:47

miles an hour, another train leaves San Francisco.

28:51

I'm out, I'm out. This gets into the stuff

28:53

where like, I tried to explain this to my

28:55

general relativity students and everybody looked at me with

28:57

blank faces. This gets

29:00

really complicated. Essentially,

29:04

the point is that the speed at

29:07

which things are moving away from us can

29:09

very easily be faster than light, just

29:12

because space is expanding in between. Nothing's

29:14

moving through space faster than light, but

29:17

the space in between us and

29:19

other things is spreading out

29:21

so fast that our relative

29:23

distance is getting larger or very fast.

29:29

During cosmic inflation, yeah, everything was moving faster

29:31

than the speed of light away from everything

29:34

else, but in a much

29:36

more extreme way than is happening now, I

29:38

guess. So yeah, there's

29:40

technical sense in

29:43

which you can explain it through that, but

29:46

it gets too complicated. You, again,

29:48

need graphs. But the effect of

29:50

it is, if you think of

29:52

the universe starting as a singularity, now this is something

29:54

that always bothered me when I first learned

29:57

about this whole question The

29:59

problem was the... has a microwave background being

30:01

really uniform, the background light being really

30:03

uniform, is that

30:05

it suggests that the

30:08

universe was very uniform in

30:10

the early times when the light was produced in

30:12

a way that we wouldn't expect unless you have

30:14

a special setup. Now

30:17

people would say, well, but if it was a

30:19

singularity, then of course it was all the same. It

30:21

came from all the same thing. But the problem

30:24

with that is that if you had that

30:26

sort of infinitely dense, infinitely small thing that

30:28

kind of is expanding, because

30:30

of quantum mechanics, it can't all stay

30:33

perfectly uniform. There

30:35

would be fluctuations. And

30:38

so you shouldn't be able to go from a singularity

30:41

to a perfectly smooth, perfectly

30:44

balanced, everything is exactly the

30:46

same temperature, ball of fire. That

30:49

just isn't how that would work. You

30:51

should have some kind of fluctuations. And so what

30:53

inflation does is it's like it zooms in

30:55

on one tiny part of that ball of

30:57

fire where the

30:59

temperature is all the same. And it

31:02

zooms into that and then uses that

31:04

as the starting point of the whole

31:06

universe now, the whole

31:08

observable universe now. So that's

31:10

the sense in which inflation smooths things

31:12

out, is it kind of zooms

31:14

in on a particular part of

31:17

this complicated picture. So

31:25

rather than thinking of the beginning of the

31:27

universe as an infinitely small point, we might

31:29

think of it more like this. In the

31:32

beginning, there were these different parts that were

31:34

super close together and were sort of in

31:36

communication and in balance with each other. And

31:39

then during a period of intense inflation,

31:41

like the inflating of a balloon, all

31:44

of these parts moved rapidly farther

31:46

away from each other as the

31:48

universe first started to expand. And

31:50

this inflation works kind of like a

31:52

cosmic microscope to help us see the

31:54

quantum fluctuations that existed in the

31:57

very early universe, but

31:59

it also helps us to understand why,

32:01

at least in terms of background light,

32:03

super spread out parts of the universe

32:06

are actually shockingly uniform.

32:09

Like whichever direction we look, it

32:12

looks about the same. And

32:19

just to state the obvious, we don't

32:21

know what came before

32:23

this because we can't know what

32:25

came before this because it invented

32:28

the idea of before. Well,

32:30

yeah. I mean,

32:32

so there are two senses in which it's hard to

32:35

know things before. One is that if there was a

32:37

singularity, then that singularity

32:39

would have, you

32:41

know, you can't see through that. That would have

32:43

been the starting point for space and time in

32:45

some sense. The other sense

32:48

in which we can't see better than

32:50

that is that if there was this cosmic inflation,

32:52

then by its very virtue, it takes

32:55

most of the information of that early time and

32:57

just pushes it way outside of our cosmic horizon.

33:00

And so we only would ever get

33:02

to see a tiny piece of that

33:04

early picture because of cosmic inflation if

33:06

that's what's happened. And so

33:08

it makes it really hard to know if

33:10

anything happened before that, like what it was.

33:13

So cosmic inflation like pushes, like takes the

33:15

whole singularity problem and says, that's not even

33:18

an issue. We don't know if that happened

33:20

or not. We can't have any information from

33:22

before inflation in this picture. Like there

33:25

might be ways to gather some

33:27

information about like the setup of

33:29

the universe before that, but it's

33:32

observationally, it's basically impossible because

33:35

of that zooming in on this tiny piece.

33:37

Right. So the first thing

33:39

we can know is that

33:42

the universe was very hot

33:44

and very dense, and

33:46

then it began to expand

33:48

through this process that we think

33:50

was cosmic inflation. Well, yeah,

33:54

we don't even know for sure if cosmic inflation

33:56

happened. But the hot, dense

33:58

stuff that we see. when we

34:00

look out into the universe is after inflation ended.

34:04

So it's after inflation stretched

34:06

out the whole universe, made it uniform. Then

34:09

there was like a hot dense

34:11

soup and then regular expansion. Okay.

34:14

So the, the, the synchronic singularity,

34:16

maybe we don't know, then

34:19

cosmic inflation and then

34:21

hot dense universe. And

34:23

so when you say we know what happened in

34:25

the first second of the universe, the

34:28

universe as we're defining it begins

34:31

after this period of

34:34

inflation. Yes. Yeah. Yeah.

34:37

And do we know how long this period of inflation lasted? Well, so

34:39

we think maybe about 10 to the

34:41

minus 34 seconds. Shut

34:44

up. So that's, uh, real, real

34:46

early. Yeah.

34:50

Yeah. I

34:52

was thinking like a few billion years. I

34:54

was thinking like two to three billion years.

34:58

It's. So real fast.

35:00

10 to the negative 34 seconds is, um,

35:02

I mean, there's nothing, there's nothing that's that fast,

35:05

right? Like I can't even, there's, I

35:07

can't think of anything that would be that fast.

35:09

No, it's, it was just a tiny, tiny

35:11

fraction of a tiny, tiny fraction of a tiny, tiny fraction

35:14

of a second. We think it was

35:16

very, very quick, but the universe expanded by a

35:18

factor of a hundred trillion trillion over

35:20

that time, at least. Oh my. Yeah.

35:23

So it was a very, very rapid extension.

35:25

So after that, we have a pretty good

35:28

picture and we can, we can talk through

35:30

the sequence of events after inflation ended. Yeah.

35:46

So when inflation ended, I mean,

35:49

there's still some controversy about whether inflation

35:51

happened where most astronomers think it did. When

35:54

inflation ended, it created this big

35:56

dump of energy into the universe that caused that

35:59

hot, dense state. to exist. So

36:01

from there we have a really good idea

36:03

of what happened and the reason for that

36:05

is that we can calculate the temperature and

36:07

density of the universe at that time and

36:10

we can study that in a

36:12

few ways and one of them is by smashing particles

36:15

together in particle colliders to

36:17

try to mimic those temperatures and densities

36:20

and to see what it looks like. And

36:22

so that's how we have this amazing story of

36:24

the first like second because

36:26

we can actually like simulate

36:29

that in laboratories by just

36:31

creating those conditions. So for example we

36:34

know that there was something called

36:36

the quark era where the

36:38

universe was this quark gluon plasma.

36:40

So quarks are these tiny particles

36:43

that make up protons and neutrons and

36:45

gluons are the force carrying

36:48

particles that kind of stick everything together

36:50

inside an atomic nucleus. So there was

36:52

this plasma of quarks and gluons that

36:54

lasted until about a

36:56

microsecond in the

36:58

early universe and during that

37:01

time there was a sort of reshuffling

37:03

of the laws of physics that separated

37:05

the electromagnetic force from the weak nuclear force

37:07

and all this kind of stuff was

37:09

happening. But we have a really good

37:11

picture of technically exactly what was happening

37:14

during that time where we know that there were

37:16

quarks and gluons. We know that this electromagnetism

37:18

of weak nuclear force separated. And

37:20

we're going to get into the

37:22

fundamental forces in our next episode.

37:24

But for now we

37:27

know that there was this quark soup

37:30

and that these fundamental forces

37:32

were beginning to happen. Yeah,

37:34

so the sort of laws of physics

37:37

are being kind of set up by

37:39

this changing fluid of high energy matter.

37:42

And we know that because we can create a quark

37:44

gluon plasma in a laboratory by

37:46

smashing gold or lead

37:48

particles together in the

37:51

Large Hadron Collider, we can smash these particles together

37:53

and create material that dense and

37:55

that hot that we see that

37:57

quark gluon plasma. We can actually sample it.

38:00

And we can see how the laws of physics are

38:02

starting to change as you get to those

38:04

really high energies. And then we know that

38:06

at about two minutes, it all sort

38:09

of cooled down enough for protons and

38:11

neutrons and electrons to form. So

38:13

before that, you couldn't have those particles because it

38:15

was just too hot. Everything was

38:17

kind of sweeping around. And then at some point,

38:20

it cooled down just enough so that we have

38:22

these nuclear particles forming. And

38:25

then you start to get atoms. And

38:28

that starts at around two minutes. And

38:30

we can get into that a little bit more later. So

38:33

in the first second, there's this

38:36

quark soup. And then

38:38

those quarks cool off enough that

38:40

we have protons and neutrons. And

38:43

then that cools

38:45

off enough that those protons and

38:47

neutrons start to form atoms. Yeah.

38:50

And so two minutes into the universe,

38:53

we have some

38:55

version of stuff that

38:58

is analogous to the stuff

39:00

that we see today. Okay.

39:04

So this part is really fun for me. So at

39:06

this point, this sort of two-minute mark, this is when

39:08

you get Big Bang nucleosynthesis. So what

39:10

Big Bang nucleosynthesis is, is it's

39:12

the time when the whole universe

39:15

was essentially like

39:18

the center of a star. It was the same

39:20

kind of temperatures and pressures as the center of

39:22

the star. And in

39:24

the centers of stars, what's happening is

39:26

that hydrogen

39:28

nuclei are coming together to

39:31

form helium nuclei. You

39:33

have this process called nucleosynthesis, where

39:35

you're creating these heavier atoms. You

39:39

can make, in certain kinds of stars, you make carbon

39:41

and oxygen and all that kind of stuff. So

39:44

there was this time when the whole universe was as

39:46

hot as the center of a star. And

39:49

when that happened, you got these nuclear

39:51

reactions happening. So hydrogen turned into a

39:53

little bit of helium, and there was

39:55

just a little bit of lithium and

39:57

brilliant. Like, there were a couple of... trace

40:00

elements of other things, but it's mostly hydrogen

40:02

turning into helium. The whole universe was a

40:04

nuclear furnace, just like the center of our

40:07

sun doing basically the same thing as what the

40:09

center of our sun is doing, turning hydrogen into helium.

40:11

And so at that point, you

40:13

get about a quarter of the

40:15

nuclear, whatever, become helium. And so

40:17

the cool thing about this is, so

40:19

people talk about, we're all star

40:22

stuff because stars turn

40:24

atoms into carbon and oxygen and all

40:26

these things that were made of, right?

40:28

Were made of carbon, oxygen,

40:30

nitrogen, and so on. But most

40:32

of the atoms in our body are hydrogen, just

40:35

by number. You can count

40:37

up the number of the atoms in our

40:39

body. Most of them are hydrogen. And

40:41

that means they were formed in that first two minutes of

40:43

the universe. So

40:45

most of the stuff that we're made of is

40:47

actually big bang stuff. It's

40:50

actually this primordial

40:53

nucleosynthesis soup from the beginning of the

40:55

universe. So I

40:57

was, part of me

40:59

was there? Yeah. Yeah.

41:02

Like literally part of me was there? Yeah. The

41:04

hydrogen in your body, those atoms first

41:07

formed in that first two minutes of

41:09

the universe. So part of me, not

41:12

in a figurative sense, was

41:15

present two minutes in. Yeah.

41:17

Yeah. Whoa. Yeah.

41:20

And as far as I know, most of your atoms haven't even been through

41:22

a star. They coalesced

41:25

from the stuff of

41:27

the early universe, gas clouds and so

41:29

on, and then sort of fell

41:31

onto the earth. And then you

41:33

grew out of stuff that was on the earth. But yeah.

41:36

Wow. So earlier you

41:38

made me feel very anxious. Okay. I'm

41:41

sorry. By telling me

41:43

that the universe was maybe

41:46

used to be small and infinite and is

41:48

now bigger and infinite. But

41:51

now you made me feel very

41:53

calm and connected to this universe

41:55

by thinking that I'm not just

41:58

made of star stuff. I

42:00

might actually primarily be made of

42:03

big bang stuff. So I may have

42:05

been around, albeit not in

42:07

a sentient form, for that

42:09

whole time. Yeah,

42:12

yeah, exactly. Which makes me think

42:15

that those parts

42:17

of me will also be around for a while,

42:19

right? Yeah, I mean, the hydrogen nucleus is just

42:21

a proton and we don't have

42:23

any evidence that protons decay. So

42:25

your protons will be around

42:27

for billions and billions and billions and billions

42:30

and trillions of years. And

42:32

there may be a decay time for a proton.

42:35

The best limit we've got is like, it's

42:37

got to be more than 10 to the 40 seconds

42:39

or something like that, but it's

42:41

a long, long time. So

42:44

your hydrogen atoms are going to carry on.

42:48

I don't know that I need to be around that long,

42:50

you know? Like... Well,

42:53

you know, the scenery will change. The

42:55

scenery will change. The vibe will

42:58

be very different, I think, later. Those

43:00

hydrogen atoms will probably combine to make

43:02

something that's a little less anxious. Yeah,

43:04

maybe. And a little less

43:07

self-aware. It'll be like both better and worse. Is

43:10

there a chance that some of the hydrogen atoms

43:12

inside of me, and this may not be an

43:14

astrophysicist's question, but is there a chance that some

43:16

of the hydrogen atoms inside of me will later

43:18

be inside of another

43:20

living thing? Oh, yeah. Yeah,

43:23

almost certainly. I mean,

43:26

I don't know

43:28

what your plans are in the long

43:30

term, but at some point something will

43:33

probably eat part of you. Yeah, Crown

43:35

Hill Cemetery, right

43:37

here in Indianapolis, home to

43:39

more dead American vice presidents than

43:41

any other location on Earth. Great,

43:43

yeah. All good company. People say

43:46

Indianapolis isn't a cool town, but

43:48

we got some stuff going for us. There you

43:50

go. I mean, you're also like... Your

43:53

atoms are kind of cycling around quite a

43:55

bit anyway, right? You're losing

43:58

skin... particles

44:00

and things are eating those dust mites

44:02

and so on. So

44:05

it's kind of a constant process.

44:07

Yeah. Yeah. This

44:10

is a reminder for me that the main

44:12

character on Earth is not

44:14

any individual or even our

44:16

species but sort of the

44:19

overall utter

44:21

strangeness of life that we're

44:24

part of a much larger Earth web

44:26

that's part of a much larger universe

44:29

web. Yeah. Yeah. What's

44:32

amazing to me is that we have so much

44:35

of this story, that we can

44:37

tell so much of the story, that

44:39

we can look into the sky and

44:41

see the time when the universe was

44:43

just beginning. I mean, I guess

44:45

we'll talk about the cosmic microwave background more.

44:48

But when we look at that background light,

44:50

what we see is just

44:52

a universe that's glowing because it's hot. We

44:54

see that the properties of that light just

44:56

show us that this is thermal radiation. This

44:59

is just the glow that happens

45:01

when things are hot. We can see that the

45:03

early universe was just this hot place

45:06

and we can look at it. We can directly

45:08

look at it. There's no sense in which it's

45:10

not just directly looking at it when we pick up

45:13

that radiation. So we're just looking

45:15

at the beginning of the universe. Right.

45:18

And is there a sense in which

45:20

everything ... I

45:23

don't want to make it too much

45:25

of a sphere, but is there a

45:27

sense in which everything that we see

45:29

and observe and are part of is

45:31

kind of inside of that cosmic microwave

45:35

background radiation? Yeah. Yeah.

45:38

Can I think of it

45:40

as a second extremely large Earth?

45:43

Yeah. I mean, it's a sphere. It's

45:47

a bright shell of radiation that

45:49

we are encased in. Right. And

45:52

not just that we're encased in, but everything that

45:54

we can see in the universe is encased in.

45:57

Yeah. That,

46:01

again, makes me very happy.

46:03

I like that. I feel it's warmth.

46:05

Okay, good. Yeah. Thanks

46:16

for listening to this first episode of

46:18

The Universe. Listen, even though I'm not

46:20

a scientist and Dr. Mack kicked us

46:22

off by saying that astrophysics can't answer

46:24

questions of meaning, there is

46:26

this huge sense to me

46:28

that unpacking the wild strangeness

46:30

of life and the universe

46:32

in which life happens is

46:34

a profound way to make

46:36

meaning. Like, the more I

46:38

understand myself as part of the Big Bang,

46:41

the more both anxious

46:43

and relieved I become

46:45

about everything else in human

46:48

experience. I don't know,

46:50

I just can't really get enough of this stuff,

46:52

and I hope you'll join me through this season

46:54

as we stare into the void, which

46:56

it turns out is not a void, because for

46:59

some reason we can't explain there's

47:01

more matter than antimatter. And

47:04

my goodness, that is

47:06

meaningful, even if I'm

47:08

the one making the meaning. This

47:13

show is hosted by me, John

47:15

Green, and Dr. Katie Mack. This

47:18

episode was produced by Hannah West,

47:20

edited by Linus Obenhaus, and mixed

47:22

by Joseph Tuna-Medish. Our editorial directors

47:24

are Dr. Darcy Shapiro and Megan

47:26

Motifary, and our executive producers are

47:28

Heather DiDiego and Seth Radley. This

47:31

show is a production of Complexly. If

47:33

you want to help keep Crash Course

47:35

free for everyone, forever, you can join

47:37

our community on Patreon at patreon.com slash

47:40

Crash Course. Thank

48:00

you.