Transcript of YouTube Video: Life In Our Universe | Crash Course Pods: The Universe #8

I've been excited for this conversation

Katie because I've mentioned it online a

few times but I don't know if I've

talked to you about it I've been having

the

depression MH and it's not been fun it's

been challenging but in this process of

kind of going through a period

of of darkness and uh and difficulty I

have taken an astonishing amount of

solace in this project that we've been

doing oh good I've been thinking about

my

protons and how complicated they are and

how of course it's difficult for a

collection of protons this large to make

it

through together sticking together you

know as as a body must and it's made me

think a lot about what you're calling

the astrophysics of

life right but I realize I don't

actually know anything about the

astrophysics of life and so it's had me

thinking speculatively but I'm excited

for this conversation because after it

hopefully I'll be able to think in a

more grounded way about the fact that

I'm big bang

stuff and understand a little bit more

about the relationship

between the universe and uh

me a reality I've faced over and over

again as I've had these conversations

with Dr Mack is how insignificant life

on Earth is in respect to our universe

not only are we living on a speck of

dust in a tremendously vast space But

even the type of matter we're made of is

an afterthought compared to dark energy

and dark matter that negligibility or

sheer smallness can evoke a sense of

wonder but also a sense of futility so

life typically does not factor into

cosmology but what about the inverse how

does cosmology factor into life well

here's our

[Music]

conversation I should say you know

before we start that my usual area of

research does not touch life in any way

but there are some very clear things

that we can say as astrophysicists

about the relationship between the

cosmos and humans and like what we are

made of and how life works I mean so I

think that one of the things that we've

talked about before but I think is is

good to reiterate is what you just

mentioned that we are big bang stuff I

mean if you think about like what we are

made of by mass if you just kind of add

up all of our our molecules and atoms

and stuff by mass we're mostly oxygen

and then car carbon and then hydrogen

nitrogen phosphorus calcium but if you

count by the number of particles that we

have in us like the number of atoms by

number we are we are vastly more

hydrogen so we're something like 63%

hydrogen wow you know the hydrogen

nuclei the protons those do come just

right from The Big Bang and may or may

not have ever been inside a star that's

just the Big Bang made a bunch of

protons and those protons became us most

of what we are made of is that stuff

that came from The Big Bang and has not

become another kind of atom so it's not

even like a processed hydrogen it's a

raw

unfiltered organic hydrogen Straight

From the

Source yes exactly yeah so some of the

hydrogen has been through stars but a

lot of it is just it was in space it was

part of the cloud of gas that the Milky

Way formed out of and the cloud of gas

that the solar system formed out of and

became us right became the stuff that we

are made of those those protons those

hydrogen nuclei now the rest of the

atoms in our body the oxygen the carbon

the Hy the nitrogen the calcium the

phosphor sulfur all of that kind of

stuff that was formed inside Stars so in

order to make us we needed to get

together not just the protons but a

bunch of these heavier elements that can

make structures can make you know solid

materials that kind of stuff so the Big

Bang made hydrogen helium a little tiny

bit of lithium maybe a little little

tiny bit of

burum but was mostly hydrogen and

everything else gets formed in stars or

through some other process involving

Stars involving cosmic rays that kind of

thing so if if you look at like the

other stuff we're made of so carbon was

mostly made in low mass stars at the end

of their lives so like stars like the

sun when they die they create this you

know sort of big nebula blow off their

outer layers and there's processes that

happen inside and that makes some carbon

and then also massive stars when they

explode that creates some heavier

elements carbon is one of the things

that's made in that nitrogen is kind of

similar oxygen is mainly made in the

explosions of massive stars and then you

know calcium phosphorus sulfur those are

all kind of similarly mostly in these

these massive star explosions sometimes

in exploding white dwarfs so stars are

creating everything else that were made

of there are some elements that are

mostly made when cosmic rays slam into

other particles and break them apart and

so you get like burum and Boron and a

little bit of lithium some of those are

made from like cosmic rays like cracking

open other atoms like doing fion but for

the most part you look at most of the

periodic table and it's massive stars or

end of life processes of stars and the

reason for that is that you need a lot

of energy to create heavy elements and I

think we've talked about this to some

degree where you know with like a a star

like our sun fuses hydrogen into helium

in its core uh that's pretty much all

the Sun is going to do at some point

it's going to run out of hydrogen in the

core it's going to Puff out it's going

to make a few heavier elements in the

sort of end of life process but mostly

it's just going to do hydrogen into

helium but more massive stars have

processes going on in their cores that

can fuse heavier elements they've got

way more temperature higher temperatures

more pressure and they can squish

together all these elements when it gets

to iron you can't fuse iron and still

get energy out and so then things get

more complicated and that things heavier

than iron you really need like super NOA

or some kind of much more complicated

process to get those heavier elements

you know you can make some amount of

heavier elements inside the core of the

star and then most of the stuff that's

made is really in the Supernova

explosions and we can look like

literally just look at the periodic

table and that will tell us how massive

an element is and like where it fits in

that realm right not really well sort of

yeah I mean you can look at the periodic

table and see the masses of the elements

yeah there's a little bit of a some

subtleties to how those Fusion events

happen and I don't doubt that man I mean

the subtleties involved in just like

what a proton weighs uh has has thrown

me for an absolute Loop so but in

general you know if something's heavier

than iron or not heavier than iron yeah

but the I mean but the thing is like so

when I first started learning about

Stellar Fusion like about you know Stars

making heavier elements I thought like

uh you know you you kind of of you kind

of first learn about like massive stars

burning carbon and nitrogen and oxygen

and and they make sort of shells of

heavier elements in the core and and and

I kind of thought okay so that's how it

happens you create these shells of these

different elements and then those of the

element that that gets kind of blown out

into the universe and that's how the

that's how the um right so like when the

star explodes that gets spread out and

that's how we get all the iron and

oxygen that we need yeah but like a lot

of it's actually formed like during the

Supernova so oh like a lot of the carbon

that's formed in the core of stars kind

of stays there in the remnant depending

on what kind of star it is but you know

the the Supernova itself is is not just

something that spreads the elements but

it's also part of what makes the

elements so you get you dump so much

energy into all this material so quickly

a lot of that creat creates a lot of

these heavier elements so it's it's a

mix between some of the stuff is just

formed in the star and you know and gets

disperse but but in a lot of cases it's

it's really that those explosions that

have to happen to create most of like

the periodic table okay and to create a

lot of that um a lot of the stuff that

that's coming out so there's there's

some interesting subtleties that I was

kind of reading about um last night and

I got I got a little bit fixated on

carbon and I I wasn't sure how much we

wanted to talk about carbon specifically

I love talking about carbon because you

know one of my obsessions is uh biomass

Global biomass like what is life on

Earth actually made out of and the way

they determine that is by number of

carbon atoms right yeah yeah so carbon

is a super useful atom for life for for

creating anything any kind of

complicated molecules there's a lot of

it it's very abundant in the universe

and it it has the ability to form these

four bonds right so it has four veence

electrons which means that there's kind

of four places you can kind of attach to

a carbon atom and that means that you

can create really complex chains really

complex structures with that carbon very

stable bonds and you can also form

really strong double or even triple

bonds with carbon because of the way

that the electrons are set up and so it

makes a really great basis for something

as complicated as life and all life is

is kind of based on carbon as far as we

are aware there's in science fiction

people talk about like Silicon based

life because you can have sort of

similar things going on but in in

practice everything we've seen is is

carbon based so the carbon is forming

kind of the backbone of the stuff that

life is made of there was this this

weird bit of History around people

trying to understand how nuclear fusion

in Stars Works where they ran into this

problem with carbon which is that like

it's it's reasonably straightforward to

create you know helium out of hydrogen

there's a kind of chain of processes

that happens but the energetics kind of

works out in a in a way that makes some

sense creating carbon in a star is kind

of complicated in a way that like for a

long time scientists kind of couldn't

figure out how that could even happen so

what you need to do to do that is you

first fuse together two helium nuclei

helium four so that's helium with two

neutrons and two protons in the nucleus

you fuse the helium four together to

make burum burum 8 and then somehow you

need to get another helium to combine

with the burum to make carbon 12 okay so

so brillium has has four protons then

you know add two more you can get um you

got to do something complicated you can

get carbon 12 out of that in principle

but in practice that burum is really

unstable and just decays very

quickly and if you throw the helium into

the brillium that's also really unstable

and decays really quickly and so you end

up with this situation where it just

doesn't seem like there should be enough

time to create a lot of stable carbon

right so we're living in a universe that

has more stable carbon than we would

anticipate

based on carb getting made that way yeah

yeah and there was there was a lot of

lot of discussion of like can you even

get all of those elements to fuse do you

need um do you need like ridiculously

high temperatures so the first

calculations needed like billions of

degrees of temperature to get this

Fusion to even happen in the first place

there was some revised calculations they

they had to figure out Quantum tunneling

because before they knew about Quantum

tunneling they couldn't even figure out

how to get any of these Fusion events to

happen because these nuclei would be

positively charged they would repel each

other and they wouldn't get close enough

for the strong nuclear force to take

over for them to actually fuse so they

had to figure out Quantum tunnel and get

them to actually fuse but they knew

these Decay times were really really

fast and so there was this effort to

like figure out how carbon ever happens

and uh Fred Hoy who is a famous

astronomer and he was what he was an

interesting figure because he also was

like super opposed to the idea of the

big bang and he thought that there must

be a steady safe universe and I think

this was sometime around like the 20s or

30s or I don't know exactly the dates

but it was early on he was trying to

figure out how this how carbon could be

made and he figured out there there had

to be some kind of like resonance state

so some kind of excited state of a

carbon nucleus that would allow it to

more favorably like form from the burum

and the helium and then that state could

Decay into the ground state of carbon 12

that is kind of stable right and so he

just predicted there had to be this had

to exist and he wrote down what the

energy of it had to be and he's like

this has to be there or else you know

Carbon can't happen in any reasonable

amount and then uh subsequently he

convinced some experimentalists to do

some experiments and try and find this

excited state of carbon and they found

it and it was there it was where it had

to be because if it hadn't been there

you know we wouldn't have carbon and and

oil was like we have to have carbon

there has to be this state and so he

predicted it turns out there is this

excited state one and something like

2,000 times that excited state will

Decay to carbon instead of everything

just decaying into helium nuclei again

and that's enough to allow carbon to be

formed at reasonable levels in Stars

there's just so many things that had to

go right yeah it gets weirder too like

you talked about fine-tuning in the past

but like this feels like and I know that

like we're biased because we live in the

universe that that ended up happening

right and so like that's going to bias

us but it is so weird that we needed

that to happen one out of every 2,000

times so there could be carbon so there

could be us and it's one of these things

like when you look this stuff up because

I was reading about this to to you know

prepare to to talk about it because I've

only only kind of read about it a little

bit in the past and a lot of the sources

you find for it are like well this

proves God yeah yeah yeah I definitely

call people telling me over the years

that the universe's bias toward carbon

is the best indication of a

God yeah I mean you know and I don't I

don't think that's a particularly

compelling argument but it is it is a

fascinating process and and it gets even

more interesting because once you have

carbon 12 you need to make oxygen and

you do that by throwing another helium

nucleus at Carbon 12 and if there were a

resonance in that state also then every

all the carbon 12 would just turn into

oxygen and then you wouldn't have carbon

again and so hoil predicted okay so now

there can't be an oxygen resonance State

and there isn't wow turns out and and I

was reading up on this and some people

calculated that if you had like a0 5%

change in the strength of the nucleon

interactions then Stars would either all

make carbon or all make oxygen but not

the other one wow

and so and so either way if it if it

went this way or that way there's no us

yeah yeah yeah and so it's this kind of

wild I don't know if it's a coincidence

or just something that because we see it

it has to have existed right you know

but there's this kind of interesting set

of circumstances where it's just not as

straightforward as you might think to

form all of the elements that we need to

form in order for like us to exist but

and I know that you don't like it when I

apply scientific reasoning to real life

um

but isn't that also true for humans

right like for individual human lives

like it's very easy for me to say like

oh if Sarah hadn't taken that Boxing

class we would have never met and we

would have never had kids and our so our

kids wouldn't exist well well that's

true right but like if Sarah hadn't

taken that Boxing class something else

might have happened right right so in in

science we call the anthropic principle

like this idea that like It's tricky to

assign probabilities to things and so on

when not having that observation would

mean you cannot do that observation you

know what I mean like so often the

anthropic principle is applied to like

you know we live on the surface of a

planet we don't live in the middle of

the Sun and that's not because there's

more space on the surface of the planet

than in the middle of the sun it's just

because if we lived in the middle of the

sun we wouldn't be living and we

wouldn't be able to say that we live in

the middle of the sun we just wouldn't

exist right so the fact that we live on

the surface of Planet means we can talk

about living on the surface of a planet

and so that's a kind of anthropic

argument for the fact that we live here

or we live in the habitable zone of our

solar system right we live in a part of

our solar system where liquid water is

possible if we lived on you know the

surface of Neptune or something liquid

water is impossible we wouldn't be

living we wouldn't be there to talk

about it stuff like that and yet it is

also true that if it's astonishing that

Sarah took that Boxing class like what

you know like and it's astonishing that

we ended up existing like the fact that

anything exists at all my main

conclusion from seven and a half

episodes of learning from you is the

fact that anything exists at all is a

real mind blower yes yeah yeah no I'd

agree I'd agree with that and I guess

the thing that I'm constantly finding

out is just all of the kind of the nice

little stories we have about you know

this happened then this happened then

this happened it's all just so much more

complicated than that if you really dig

into it and and the the things that feel

like inevitabilities are kind of not you

know like life is kind of not an

inevitability of chemistry in some sense

right or Nuclear Physics I mean in the

sense that like Nuclear Physics might

have happened differently in a way that

was not going to ever set up the

conditions for chemistry in life right

and and you know it's it's nice that it

came out this way because existence is

cool but it's also not something that is

like you know it was it was written into

the laws of physics that we were going

to be here and talking about you know

the

universe so you don't think that there's

necessarily anything inherent to the

laws of physics that

made life or us inevitable given the

constant of nature that we observe you

can draw a straight line in some sense

from The Big Bang to us right because

you do get to this point where it's like

okay big bang makes hydrogen hydrogen

and helium and then helium hydrogen

makes stars and stars make more helium

and make all these other elements and

because the nuclear interactions are

what they are it's it's possible to

create these heavier elements and those

are going to collect into rocky planets

and then those rocky planets are

sometimes going to have life because of

a sort of process of chemistry to

biology that happens so in that sense

yeah I mean I don't know if it's

inevitable but it's there's a clear

through line there's a clear story that

goes there but at some point I guess one

wonders if the constant of nature as

they are were inevitable right and and

that goes that that comes into questions

about like kind of about Multiverse

ideas about this idea that maybe there

are regions of the universe where the

laws of physics are different which

could be the case you know when when

people talk about multiverses usually in

fiction what they mean is like the many

worlds interpretation of quantum

mechanics this idea that every time a

Quantum event happens the universe

splits into two where it went different

ways that's what people use for like

fictional parallel universe stories

stuff like that great for fiction great

for fiction but in physics a lot of what

we mean when we talk about Multiverse is

is just the idea that there could be

different regions of a larger space that

includes our observable universe but

beyond that as well in which laws of

physics might be different you know the

circumstances the environment might be

different and different things could

happen so there could be regions of this

larger Multiverse where the nuclear

interactions are slightly different and

chemistry can't happen or maybe it

happens very very differently I don't

know so that could be another anthropic

bias that we happen to be in this

situation yeah and that's how ropic

principle comes up most often in physics

is this idea of you know I mean

essentially we don't know why the Conant

of nature are what they are in a lot of

cases like the biggest one that people

complain about is the value of the

cosmological constant so the strength of

dark energy essentially we don't know

why dark energy is here but not zero

right or not large like the cosmological

constant is kind of small in some sense

that makes sense if you're talking about

the the value of this number and so you

know we get this acceleration but not

until the universe has existed for many

billions of years and you know it

doesn't prevent the existence of

galaxies and and things it just after

they've existed for a long time then at

some point they're going to not form

anymore you know so there's this weird

middle place where the cosmological

constant is small but not zero and

people use anthropics to argue that that

makes sense because a lot of predictions

from first principles depend depending

on what your sort of starting

assumptions are might lead you to a

cosmological constant that's either zero

or very large and a universe with a very

large cosmological constant is not going

to have planets it's not going to have

galaxies like it's it's going to be

accelerating too fast too quickly for

structure to form a cosmological

constant of zero is not a problem really

for the formation of structures so

arguing that it should be small but not

zero is a little bit tricky but people

use anthropic arguments to argue that it

should be small or zero and the fact

that it's small is maybe just because of

you know Chance in This bigger space But

It's tricky to make those arguments

because you can't really Place

probabilities on where we end up in this

larger space with different values in a

way that is consistent you have to put

in a whole lot of assumptions and the

anthropic principle can kind of help

with that but it can't push you to exact

numbers in certain ways and so then you

have to do something more complicated so

that that's how it usually comes up is

something to do with dark energy or or

maybe even dark matter but yeah it could

apply to this you know Carbon thing as

well right like right we wouldn't be

here if if the carbon resonance weren't

there right so yeah but it is and we are

yeah so it's an interesting question

[Music]

yeah so every element we are made of

either comes from The Big Bang itself or

was made by stars from their core or as

a result of them exploding that adds a

bit more of a wow factor to the periodic

table for me and it turns out it's very

difficult for stars to create a stable

version of carbon that element essential

to Life as We Know It physicists had to

discover Quantum tunneling the ability

of some particles to Tunnel through

barriers and an excited state of carbon

to prove it was even possible and for us

to exist they also had to determine that

oxygen didn't have an excited state add

that to the fact that we live in a part

of the universe that allows liquid water

to exist and that we have just enough

dark energy to allow planets to form and

life can seem inevitable but the

existence of the building blocks of life

was not inevitable and knowing what we

know it might even have been

improbable so I want to ask if I can

take you forward to the rocky planets

these rocky planets are

forming I don't really understand how

but I trust you that they formed we can

just kind of walk through how we got

here great from the beginning of the

solar system so the solar

system has been around for something

like 4 and a half billion years maybe

just a little bit longer than that so

the sun formed somewhere around maybe

4.6 billion years ago so the universe is

13.8 billion years old it took a while

for the sun to form and you know it's

not surprising really that we weren't

formed way way earlier

because you need a certain number of

generations of stars to create enough

heavy elements to create rocky planets

and life and depending on where what

kind of environment you're in in the

universe that can take a while I mean if

you were in an environment where there

are lots of stars forming very very

quickly like in a really Rich center of

a galaxy cluster or something like that

then those time scales can be very short

cuz massive stars don't live very long

you can in in some handful of millions

of years you can have a a situation

where stars are forming and and you're

creating a lot of heavy elements in the

part of the universe that we're in it

took about three generations of stars

before like our star is about a third

generation Star as far as we know so a

couple of generations of stars did their

Supernova created their elements

polluted the interstellar medium we call

it pollution that's that's a great line

polluting the interstellar medium yeah

yeah or

enrichment sometimes we say enrichment

we're being nice about it enriching

feels better than polluting yeah I'm

quite fond of the idea that we're sort

of living in some kind of Galactic

suburb and so things just happen a

little later here you know like the way

that a little further out from the city

people might find out about the hot new

band a few months after the folk

yeah yeah and you know there's there's

arguments about a galactic habitable

zone this idea that if you live too far

out or too far in in a galaxy things are

not as suitable for life so too far out

you just don't have enough heavy

elements like there aren't enough

generations of stars you don't have

enough enrichment too far in you have to

deal with like there's a super massive

black hole there's a lot of radiation

there's you know maybe Stars forming

very very quickly going Supernova a lot

and it's just dangerous

it's just a dangerous place to be

because you're you're you're going to

get zapped by something before life can

really develop and and that's that's a

very poorly defined kind of region of

the of the Galaxy but like we're inside

a region where it seems like that's a

reasonable place to live it's a you know

it's a decent kind of neighborhood for

you know it's it's not too boring it's

not too scary right so we live in a

decent not too boring not too scary

region of our gy Galaxy and as a result

this third generation star was able to

form about 4.6 billion years ago yeah

yeah and so what happened was the you

know you had a big cloud of gas and dust

and and it coalesced and created a a

disc of material and the sun formed in

the center where it was really dense

there was a lot of material there and

then this the disc first it was like a

protocell cloud and then it was the star

and then there's this protoplanetary

disc and it's just a disc of like gas

and dust and you know little bits of

metals or whatever material from that

protostellar cloud and that slowly

coalesces into planets so planets sort

of form in these edes in this uh these

little knots in this disc and for a long

time there's you know collisions between

these protoplanets and you know

everything's really chaotic but

eventually the gas and dust in this disc

gets kind of you know hoovered up by the

forming planets and you you end up with

a stable set of of planets going around

okay and we still don't have a very good

understanding of that whole process it's

a complicated process you know you get

lots of different kinds of solar systems

that form some with really massive

planets really close in called hot

Jupiters those seem to be pretty common

in the universe we're not entirely sure

how that goes we don't entirely know why

the planets are distributed the way they

are in our solar system and there are

some tricky bits you know going from

certain scales where it seems

complicated to get the material to stick

together at those scales and not like

bounce off and so Planet formation is a

complicated science but eventually you

end up with you know we have this this

sort of hot protoplanet like sort of

molten because everything's kind of been

crashing together that's the the young

Earth and then it gets crashed into by

something about the size of Mars and

that creates a you know blob of material

that sort of shoots out and and becomes

probably some kind of ring and then

turns into the moon that's the story

that we think is happening there and so

then we have the Earth and the moon and

over time the Earth cools and at some

point in this process you know it it

sort of develops water maybe the water

was kind of already there maybe comets

came in and brought in water it's a

little bit unclear it seems like

probably the water was already there and

then it kind of was able to collect on

the surface and the Moon is kind of

possibly helpful for life and we're not

really sure of the details of that but

it it sort of stabilizes the seasons a

bit so having a large Moon might be

helpful for life but at this stage it

doesn't really matter cuz at this stage

it's just you know there's water there's

Rock Earth is still kind of warm and we

think that probably life began like near

a hydrothermal vent under the ocean most

likely that seems like a good place

right like that seems like a good place

for chemistry to happen it's warm it's

wet yeah what you really need for life

as far as we understand it is some kind

of source of nutrients so you need

chemicals that can react with each other

you need energy and specifically you

need need a gradient of energy there

needs to be a way to move energy from

one place to another right so you can't

just be in a in a uniformly hot space or

something it has to be possible to you

know move the energy so you know maybe

sunlight is a source of energy coming

from outside and you can do something

with that or something like a

hydrothermal vent where you have the hot

hydrothermal vent and the cooler ocean

and you can extract energy from that and

then you need a liquid and probably

water it seems like I mean all all life

on Earth involves water in some way

that's the liquid that life on Earth

uses there's speculation that maybe you

can use other liquids as the thing that

allows the chemicals to move around you

know people talk about the possibility

of life in like the methane ocean on

Titan possibly I mean it's unclear it's

unclear if you can use other liquids but

water seems to be the one that I mean

it's the one everything on Earth uses

and it's it's how we Define a habitable

zone when we talk about a habitable zone

of a solar system is there's kind of a

distance from the center of the solar

system where you're close enough to the

star that it's possible for water to

exist as liquid but not so far that it's

all ice right so you don't want it to be

either steam or ice you want it to be

able to be liquid on the surface of the

planet and that's all IL defined because

you could also have you know a really

thick atmosphere that would make it so

that everything is too hot for liquid

water like on Venus so Venus is

nominally in the habitable zone of our

solar system but it's too hot for Life

Life as We Know It Anyways too hot for

liquid water and then Mars is nominally

also in the habital zone but it's got

basically no atmosphere and so so it

doesn't have enough atmosphere to have

liquid water yeah it's it's a little bit

too cold I mean there are times of the

year in places in on Mars when it can be

above freezing on the surface above Z

Celsius but the um because the

atmosphere is so thin you can't have

liquid water MH the ice will sulate but

that's it so you don't just need to be

in the habitable zone you also need to

have the right amount of atmosphere so

that you can have liquid water yeah yeah

and that probably took time to develop

on Earth I would imagine yeah so so at

some point we had liquid water so we had

this hydrothermal vent and probably what

happened at that place is that you had a

bunch of chemicals and you got this

chemistry kind of happening and then

that chemistry sort of by chance created

some stuff that's like the ingredients

of RNA so we think it's probably started

with RNA and then there was this sort of

what they call molecular natural

selection which is just kind of like

lots of sort of interactions between

molecules that are kind of random but

then some are like a little bit more

likely to happen and then that turns

into biology and actual natural

selection you get these first RNA cells

and then those evolve into DNA and and

that whole process is very complicated

but there's a kind of logical

progression that that scientists have

worked out where you can go from very

simple sets of organic molecules like

amino acids and things and through a lot

of time um I mean we're talking probably

a billion years or something maybe half

a billion years I don't know somewhere

around there to go from these simple

chemicals to life but if you have a

whole lot of these chemicals a lot of

water and a lot of time just from the

bouncing around from the energy

injection from the thermal events is

going to kind of happen and and we've

done lab experiments where you can make

the components of RNA from molecules

that we get just from like Interstellar

dust or like things that we see out

there in space so we we see amino acids

on comets Interstellar dusts meteors

this stuff just kind of exists out there

the the sort of building blocks of the

kinds of chemicals that we think formed

the first life and then through these

interactions near this energy source and

just lots of time and r events we think

that that can eventually turn into

something that becomes single cell life

and so over

this half billion years or whatever that

occurs and then we have single cell life

and then natural selection kicks in in a

more formal way where the life wants to

hang around and the only only the life

that wants to hang around ends up

hanging around um a different version of

the anthropic principle perhaps um well

I mean you end up with you know the

natural selection in the form of like

the things that are most adapted to the

environment progress and the other

things don't yeah yeah right I don't

mean to imply that these um single-

celled organisms were making conscious

choices about whether to be here um or

indeed that any of us are right I'm not

I'm not convinced of that so then we

have this very very long period yes

where life is is single cell that's

about a billion I think yeah before the

first not single celled right so we had

single only single- celled organisms for

longer than we didn't have life on Earth

that's wild yeah and depending on how

long you think this all happened I mean

the earliest fossils are from like half

a billion years after the formation of

the earth as far as we know but like it

could have been much much faster than

that it could have been like some number

of millions of years uh we don't know

exactly but um it could have been

reasonably quick that the first life

formed out of this chemistry and then it

just took a long time for these single

cells to turn into anything that

persists enough that we have a a solid

record of it so when you talk about it

that way when you talk about it as

chemistry it doesn't actually seem that

different from astrophysics like it

doesn't seem totally separate for me

that there's a chemistry process that

leads

to hydrogen becoming helium or that that

leads to these massive Supernova

creating stable carbon and then there's

a chemistry process that allows amino

acids to become RNA and then there's a

chemistry process that allows is just

everything chemistry well I mean I I

would call the the earlier bits of that

sort of nuclear physics rather than

chemistry but it's all just kind of the

rearrangement of of matter yeah right

like through physical processes yeah

which makes me think about how

everything is just the rearrangement of

matter like yeah writing a novel is just

the rearrangement of matter or making

making a painting is just the

rearrangement of matter right you're

just rearranging paint and canvas into a

representation of something yeah and

you're messing around with like

information content and entropy in in

complicated ways yeah that's so true

you're messing around with entropy when

you're writing a novel maybe that's the

problem I'm

having need to accept that I'm

just just I'm trying to do something

that's

fundamentally against what the universe

wants to do I'm trying to I'm trying to

make a story that makes sense and the

universe is like I'm trying to have a

little more

disorder that tension is is causing me a

lot of problems right now Dr Mack I mean

you'll be comforted to know that it at

all moments you are actually increasing

the entropy of the universe because

you're putting so much Blood Sweat and

Tears into trying that to to make that

process of order that it it it is the

total amount of entropy is still going

up sure yeah have no of course there's

no way that I can yeah and even in even

in that work that I'm doing I'm

increasing entropy yeah yeah always cool

yeah that isn't that comforting Just for

future

reference I'm

[Laughter]

[Music]

sorry this podcast has experienced a

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[Music]

crashcourse so a few generations of

stars formed super noi that spread their

elements across the interstellar medium

polluting or enriching it depending on

how you look at it and those elements

coales to form our solar system from

there the process was actually quite

linear Nuclear Physics led to the

formation of RNA which led to the

formation of DNA which led to the

formation of unicellular life likely

near a hydrothermal vent beneath the

surface of the ocean that whole process

can seem very orderly given that all

creation cre

disorder in the grand scheme of

things I don't know if if this is more

or less comforting to you

but it seems like if this process

happened on Earth and it happened

probably pretty

quickly then it's very likely to have

happened in other places right it has to

have right because like

otherwise the idea that Earth is alone

in this just seems kind of absurd

yeah I hear arguments you know where

it's like well we just don't know either

way but like like we we have a pretty

good idea of how this chemistry stuff

happens in an environment like the early

Earth and we know of something like

5,000 planets around other stars that

exist those planets exist and and maybe

only you know a few dozen are what we

would call habitable in the sense of

being like at the right distance from

their star and we don't know anything

about their atmospheres so maybe they're

all like Venus we don't know or maybe

they're all like Mars but like some of

them must have some kind of environment

that's not horribly dissimilar to that

of the early Earth and and even like in

our own solar system there are several

places where we think this kind of life

might have happened I mean we don't have

another planet in the habitable zone

right now that seems to have liquid

water on the surface but Mars probably

had liquid water billions of years ago

a few billion years ago it seems to have

had liquid water we have really good

evidence of that in fact that a few

billion years ago Mars did have liquid

water we see evidence of you know River

beds stuff like that and and there's an

active search for you know signs of past

life on Mars it may or may not exist we

don't know but it certainly had

conditions that were pretty similar to

Earth in a lot of ways in its early

history and un fortunately something

happened where it kind of lost its

atmosphere possibly because the magnetic

field failed because the planet might

have cooled down too quickly or

something like that and the atmosphere

was blown off by the Sun so it did have

a thick atmosphere that was suitable for

liquid water it doesn't anymore but at

some time it did right and then the

other interesting thing about our solar

system is we have several other

candidates for where life could

currently exist and they're not anywhere

near the habitable zone because the

habitable zone is this narrowly defined

like could you have liquid water on the

surface of a rocky planet but what you

really need for life is chemistry an

energy source and water right and if you

go out to the outer solar system some of

the moons of Jupiter and Saturn have

chemistry we've seen evidence of the

right kind of mix of chemicals in those

moons they seem to have liquid water

under the surface one way or another and

they have the energy source of the tidal

heating of being in orbit around a gas

giant so they're constantly being like

pulled and stretched by the gravity of

the planet they're orbiting so we've got

around Jupiter we've got Europa gamine

and Kalisto all seem to have the

possibility of subsurface oceans Europa

is a particularly exciting one because

we have evidence that there's like salty

water under the icy surface it's like

100 km of ice and then we think there's

like salty water underneath that

and there's some likelihood we think of

hydrothermal vents under the surface of

Europa I mean anything could be under

the surface of Europe I mean there could

be fish like like we have no idea but it

seems like it has the right conditions

right and then Saturn we got Enceladus

which also has very clear evidence of

undersurface water well there's there's

like a spray coming out of of Enceladus

we can see like venting liquid you know

coming out of Enceladus so we think that

there's hydrothermal vents probably

under enceladus's surface as well and

this giant ocean that's spraying

material out into the universe right and

then Titan is an interesting one too

because Titan also seems to have

probably a subsurface liquid water ocean

we're not certain about that but it

looks like it probably has that but also

it has like a whole like hydrosphere

like it's got It's got liquid on the

surface it's just not liquid water it's

liquid methane so Titan has this really

thick atmosphere like methane

clouds and there's liquid methane oceans

and and and rivers and and ponds and

like lakes on the

surface and then the rocks and things

are solid water ice so you have all

these like Boulders of solid water ice

and mountains of solid water ice and

then you have these lakes and it really

is liquid methane and I mean we don't

know if anything can live in liquid

methane but it's it's liquid it's got

complex organic chemicals probably maybe

there's something living in those oceans

we don't know so it's not just

that life we presume would be common

because it wasn't that hard to make it

here it was hard to make complex life

but it wasn't that that hard obviously

we've done it we've done a bunch of it

right like we've got a lot of different

life on Earth it does seem like if

correct me if I'm wrong that we only

made eukaryotic cells once so that seems

to have been a big jump that seems to

have been kind of challenging but we did

it of course you don't have to have a

eukariotic cell to have life and there

may be other ways of developing life and

everything and what this makes me

think and I'm interested to see if I'm

on the wrong track here because I

probably am is that it may be in fact

that life is sort of inevitable if you

have these elements of of water or some

kind of liquid that works and you have

the potential for chemistry and you have

this ability to do energy transfer like

it could be that it just happens almost

every time it it could be yeah we we

really don't know I mean it seems

logical that when all the ingredients

are together probably it'll happen but

yeah we really don't know and there's

been lots of efforts over the years to

try to quantify our uncertainty in that

and the one that's most famous is What's

called the Drake equation so Frank Drake

who who passed away only just very

recently I think within the last year

was this famous astronomer who who just

wrote down an equation to like quantify

how many specifically how many

technological civilizations are there

out there in the galaxy we can talk to

okay so this is a very specific question

this isn't how much life is there this

is can we talk to them on the radio

right how many how many people can we

talk to on the radio this equation I

should say is not meant to be like you

write down the solution to this equation

and it gives you a number and you trust

that number this equation is really

about like how to talk about what we

don't understand understanding the

variables even if we don't understand

the numbers yeah yeah so the the

equation is really about like let's

write down what we need to know to

answer this question what's write down

what are the big uncertainties right and

so the there are lots of different ways

to write down this equation one way you

can do it is you can say okay the the

number of technological civilizations we

can talk to okay that's going to be

equal to First you need to know the

number of stars right then you need to

know what fraction of those stars have

planets which we think I mean we know

there's a large number of stars there's

like 400 billion in our galaxy right

okay uh we think that

probably quite a lot of them most stars

probably have planets that number is

somewhere close to one okay um wow in

terms of stars that have planets then

then you want to know the number of

habitable zone planets per Star right

and that number is pretty uncertain but

it's also probably not that far from one

really maybe like a tenth somewhere in

that range like on average it's such an

astrophysicist thing to say it's not

that far from one it's probably like

0.1 yeah or maybe like 01 if you're

really pessimistic right but

like which is pretty close to one it's

pretty close to one to you guys it's

it's within a it's within a couple

orders of magnitude right like as a

cosmologist that's basically one

Whatever Right Round Up round down you

get it's it's somewhere around one

between

1% and

90% yeah these are all very very

uncertain numbers okay sure of course

okay but you need that yeah so somewhere

around there and then but then then it

gets to the point where we just have no

idea right okay so then the fraction

that have life okay that's the next

number in this in this equation so the

textbook that I that I taught my inro to

astronomy class from a couple years ago

says that for that number the

pessimistic estimate is 01 the

optimistic estimate is one we don't

actually have any idea right like we

have no idea right of course because

we've never seen a second example of it

yeah and we have no idea how inevitable

any of those steps were that we looked

at okay so then let's say that's

fraction of that have life maybe it's

close to one we don't know and then the

next one is the fraction of those

planets with life in which some species

evolves to intelligence okay so there's

the fraction that has life and then the

fraction that have intelligence out of

the ones that have life okay and again

no idea the textbook also puts it

between 01 and one but like we don't

know and and that's that's a funny thing

too because like I mean depending on how

you define

intelligence that kind of seems to have

happened once on earth right

like and and I I think about this a lot

because you know you look at a place

like like New Zealand right New Zealand

kind of broke off from other places

pretty early on when when there were a

whole bunch of birds right like

everything was kind of dinosaurs and

birds and New Zealand's like native

ecology the native species were just

Birds right like they have like birds

filled all the niches and two Atara yeah

yeah and the and the and the couple of

reptiles right so Birds filled all the

nichas but they never turned into like

talking birds like I mean talking in the

sense of like I mean they can say some

of them can say some words right but

like but they never figured out like

what's keeping the Stars apart yeah or

or got anywhere close to that yeah they

didn't turn into what we would normally

call a sort of technologically

intelligent species right right and they

had there was time there was lots of

time uh but it was the mammals that went

that direction the birds didn't yeah

right and so it really only has happened

once and then when you consider the fact

that our species which is overwhelmingly

the most technologically sophisticated

species in in the history of life on

Earth is about 250,000 years old maybe

300,000 years old brand new you know

younger than elephant younger than Bears

younger than giraffes like just brand

new and and and we don't you know we

don't know we know how old we are but

you know to get to the unknown unknowns

we have no idea how long we'll be here

we have no idea like what the end of the

temporal range is yeah and that's

another thing that comes into this

equation it's written in different ways

in this uh case it's like the fraction

of existence during which intelligent

life survives right yeah okay so it's

you can write it in terms of like the

number of years that that intelligent

life sticks around before destroying

itself or being destroyed by something

that number can vary a lot

no no joke it can yeah

so that's right so so then it's like

maybe it takes a really long time for

intelligence of the sort of like

technological intelligence to develop

and and maybe we don't have that much

time where we can exist without

something terrible happening either by

our own hand or something else we don't

seem to have any stars nearby that could

go

supernova anytime soon in an

astronomical sense but like it could

have been the case that we could have

evolved on a planet that was you know

next to a big uh massive star that was

going to go supernova and totally

sterilize the surface of the world right

like that could happen quite a lot we

don't we don't know so that's one of

those things that that is also a big

unknown in this equation is like how

long do we persist and and I should say

like I feel bad talking about

intelligent life and not including like

the Dolphins and the octopi but like

there octopuses I guess is the correct

plural anyway but we're talking

specifically about like people we can

talk to yeah and we might get better at

talking to dolphins or talking to whales

or talking to octopuses over time but in

terms of the current

technology there is a different level

now it's possible that octopuses tried

it all out for us you know like 50

million years ago and they were like

this is not good no y'all don't want to

do this and they like just went back to

living happily in the ocean and and

doing their thing we don't know but like

yeah I think we have to acknowledge that

humans are a little different from other

yes animals currently yeah and we don't

know how often stuff like this happens

and we also don't yeah to your point we

don't know how long it lasts because

it's very weird and it does feel a

little fragile because it's never

happened before so far as we can tell

and because we're becoming much more

powerful very quickly you know like

we've only been in the atomic age for

one human lifetime

so are we going to be in the atomic age

for five human lifetimes or 5,000 human

lifetimes I have no idea yeah and I and

I think it's it's probably not that easy

to do something that would wipe out all

human life on earth like I could even

easily imagine humans doing something to

ourselves that basically wipes out

technological civilization our ability

to talk to their planets right we could

slow ourselves down a lot you know we

could definitely slow ourselves down and

it's kind of hard for me to imagine

us I don't know maybe we do maybe maybe

I need to be a little more optimistic I

was about to say it's hard to imagine us

not screwing that up but maybe that's

just the darkness talking the truth is

that we've shown an astonishing capacity

so far for adapting to new um new worlds

like that's always been our gift right

is the two gifts I think we have are

that we can adapt to new spaces and that

we collaborate better than almost any

other species I guess ants but like we

we have a mix of an ability to

collaborate and an ability to reason

that's pretty cool yeah and and you know

depending on who you ask human

biological evolution may or may not be

significant anymore but we've we've

found ways to get around that by using

our big brains to change our

environments to suit us better instead

of changing us to suit our environments

better and and we have a lot of tools in

that direction well and it's just

astonishing to me that we've left our

atmosphere that took so much work that

you know that that's so hard I think if

you pitch that idea to humans 500 years

ago they would have been like that

sounds very very difficult yeah it is it

is amazing what we've done like the

thing that I find so amazing is just how

much we know right that we've been able

to understand the evolution of the

Universe from basically the beginning to

now and not just that we know it but

that we're able to share it and pass it

on that we have these technologies that

allow us to communicate that knowledge I

think about that a lot in terms of you

know why the Scientific Revolution

happened when and where it did was

partly because of like medical journals

and scientific journals and the ability

to share information really widely

across time and

space and then the miracle of being able

to learn from the dead being able to

hear from them directly you know Drake

isn't with us but but the equation is I

love that yeah yeah and there's

something lovely as well about the fact

that I mean I guess there's like

evolutionary pressure that we like to

solve puzzles right that that that's

there's evolutionary pressure for for

that making us happy to better

understand things but I think it's also

lovely that that we like to talk about

them too right that we like to teach

that we like to share information that

we like to that that it can be enough of

a reward just to have the joy of sharing

something cool and not necessarily be

personally benefiting from that like you

see that in in the scientific Community

all the time yeah the light in

somebody's eye when you help them

understand something is I mean maybe

there's an evolutionary pressure to do

that but I don't I don't think that's

ultimately why we do it and and even

where where there is no um you know

there's no profit incentive the narrow

incentives don't make sense with

something like Wikipedia or with uh

teaching college where a lot of times

the uh the the the profit incentives

don't make a ton of sense but there's

still there's still joy in it there's

still meaning in it and it doesn't have

to be grounded in those incentives it

can be grounded in something else like

something like love H yeah love for

other people love for the subject love

for the um for the joy of learning and

the joy of sharing it like that that

that there can be something there yeah

and it and it's on all sides you know

it's it's a it's a joy to learn it's a

joy to teach it's a joy to just share

enthusiasm and excitement and and be

part of all of us gaining a better

understanding of the universe that we

live in and and you know sort of

expanding our perspectives and our

Horizons that is is a wonderful

thing you've made me feel better good

I'm very glad I'm glad we got there I'm

glad we settled on that that's so

true we're not so bad after all we're

all right we're all right we might make

[Music]

it so in a strange sense our existence

wasn't inevitable until it was given

everything we learned in today's episode

it's not hard to see how life got

started and yet the fact that we exist

is still pretty astonishing to me after

all other planets and moons may be

habitable but there is no other us at

least as far as we know in one sense the

only thing that could have happened

happened but I also feel an unavoidable

sense of gratitude that matter

rearranged the way it did in a way that

formed beings who in Dr Max's words can

experience the joy of sharing something

cool in the next episode our journey

will finally lead us to now Katie will

give us a snapshot of the Universe from

our present day vantage point and I'll

ask some questions I've been patiently

holding back for eight long

[Music]

episodes the show is hosted by me John

Green and Dr Katie Mack this episode was

produced by Hannah West edited by lonus

Oben housee with music and mixed by

Joseph tuna n medish special thanks to

the perimeter Institute for theoretical

physics our associate script editor is

Annie fillenworth our editorial

directors are dror Darcy Shapiro and

Megan moery and our executive producers

are Heather di Diego and Seth Radley

this show is a production of complexly

if you want to help keep crash course

free for everyone forever you can join

our community on patreon at

patreon.com/crashcourse

h

[Music]