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Language: en
if we don't ask how long do they last
but instead ask what's the probability
that there have been any civilizations
at all no matter how long they lasted
I'm not asking whether they exist now or
not I'm just asking in general um about
probabilities to make a technological
civilization anywhere and at any time in
the history of the universe and that we
were able to constrain and so what we
found was basically uh that the there
have been 10 billion trillion habitable
zone planets in the universe and what
that means is that are those are 10
billion trillion experiments that have
been run um and the only way that we're
the only time that this is you know this
whole process from you know a biogenesis
to a civilization has occurred is if
every one of those experiments failed
right so therefore you could put a a
probability you could we called it the
pessimism line right we don't really
know what nature sets for the
probability of making intelligent
civilizations right but we could set a
limit using this we could say look as if
the probability per habitable zone
planet is less than 10 Theus 22 one in
10 billion trillion then yeah we're
alone if it's anywhere larger than that
then they're we're not the first it's
happened somewhere else and to me that
was an an that was mindblowing doesn't
tell me there's anybody nearby the
Galaxy could be sterile it just told me
that like you know unless Nature's
really against has some bias against
civilizations we're not the first time
this has happened this has happened
elsewhere over the course of cosmic
history the following is a conversation
with Adam Frank an astrophysicist
interested in the evolution of star
systems and the search for alien
civilizations in our
universe this is Alex Freedman podcast
to support it please check out our
sponsors in the description and now dear
friends here's Adam
Frank you wrote a book about aliens so
the big question how many alien
civilizations are out there yeah that's
the question right the amazing thing is
that after two and a half Millennia of
you know people yelling at each other or
setting each other on fire occasionally
over the answer we now actually have the
capacity to answer that question so in
the next 10 20 30 years we're going to
have data relevant to the answer to that
question we're going to have hard data
finally that will one way or the other
you know even if we don't find it
anything immediately we will have gone
through a number of planets we'll be
able to start putting limits on how
common life is uh the one answer I can
tell you uh which is was an important
part of the problem is how many planets
are there right and just like people
have been arguing about the uh existence
of life elsewhere for 2,500 years people
have been arguing about planets for the
exact same amount of time right you can
see Aristotle yelling at democratus
about this you know you can see they had
very wildly different opinions about how
common planets were going to be and how
unique Earth was and that question got
answered right which is pretty
remarkable that in a lifetime you can
have a 2,500 year old question the
answer is they're everywhere there are
planets everywhere and it was possible
that uh planets were really rare we
didn't really understand how planets
formed and so if you go back to say the
turn of the 20th century uh there was a
theory that said planets formed when two
stars passed by each other closely and
then mat was gravitationally squeezed
out in which case those kinds of uh
collisions are so rare that you would
expect one in a trillion stars to have
planets instead every star in the night
sky has planets so one of the things
you've done is uh simulated the
formation of stars how difficult do you
think it is to simulate the formation of
planets like simulator solar system the
through the entire evolution of the
solar system this is kind of a a
numerical simulation sneaking up to the
question of how many planets are there
that actually we're able to do now there
is you can run simulations of the
formation of planetary system so if you
run the simulation really where you want
to start is a cloud of gas these giant
interstellar clouds of gas that may have
you know a million times the mass of the
Sun in them and so you run a simulation
of that it's turbulent the gas is
roiling and tumbling and every now and
then you get a place where the uh the
gas is dense enough that gravity gets
hold of it and it can pull pull it
downward so you'll start to form a
protostar and a protostar is basically
the young star of you know this ball of
gas where uh nuclear reactions are
getting started but it's also a dis so
you as material falls inward because
it's everything's rotating as it falls
inward it'll spin up and then it'll form
a disc material will collect in what's
called an accretion disc or a
protoplanetary disc and you can simulate
all of that once you get into the disc
itself and you want to do planets things
get a little bit more complicated
because the physics gets more
complicated now you got to start
worrying about dust because actually
dust which is just dust is the wrong
word it's smoke really these are the
tiniest bits of solids they will
coagulate in the dis to form Pebbles
right and then the Pebbles will collide
to form rocks and then the rocks will
form Boulders etc etc that process is
super complicated but we've been able to
simulate enough of it to begin to get a
handle on how planets form how you creat
enough material to get the first Proto
planets or planetary embryos as we call
them and then then some the next step is
those things start slamming into each
other to form you know planetary siiz
bodies and then the planetary bodies
slam into each other Earth the moon came
about because there was a mars-sized
body that slammed into the Earth and
basically blew off all the material then
then eventually formed the moon and all
of them have uh different chemical
compositions different temperatures
yeah so the the the temperature of the
material in the disc depends on how far
away you are from the Star so it
decreases right and so there's a really
interesting point so like you know close
to the star temperatures are really high
and the only thing that can condense
that can kind of freeze out is going to
be stuff like Metals so that's why you
find Mercury is this giant ball of iron
basically and then as you go further out
stuff you know the gas gets cooler and
now you can start getting things like
water to freeze right so there's
something we call the snow line which is
somewhere in our solar system out around
between Mars and Jupiter and that's the
reason why the giant planets in our
solar system Jupiter Saturn um Uranus
and Neptune all have huge amounts of ice
in them or water and ice um actually
Jupiter and Saturn don't have so much
but the moons do the moons have so much
water in them that there's there's
oceans right that we've got a number of
those moons have got more water on them
than there's water on Earth do you think
it's possible to do that of simulation
to have a stronger and stronger estimate
of uh How likely an earthlike planet is
can we get the physics simulation done
well enough to where we can start
estimating like what are the possible
earthlike things that could be generated
yeah I think we can and I think we're
learning how to do that now um so you
know one part is like trying to just
figure out how to how planets form
themselves and doing the simulations
like that that Cascade from uh dust
grains up to planetary embryos that's
hard to simulate because it's both you
got to do both the gas and you got to do
the dust and the dust colliding and all
that physics um once you get up to a
plane sized body then you know you kind
of have to switch over to almost like a
different kind of simulation there often
what you're doing is you're doing you
know sort of you're assuming the planet
is this sort of spherical ball and then
you're doing you know like a 1D a radial
calculation and you're just asking like
all right how is this thing going to
what is the structure of it going to be
like am I going have a solid iron core
or am I going to get a solid iron core
with that liquid iron core out around it
like we have on on Earth and then you
get you know a silicate kind of a rocky
mantle and then a crust all those
details those are kind of Beyond being
able to do full 3d simulations from aono
from scratch we're not there yet uh how
important are those details like the
crust and the atmosphere do you think
hugely important so I'm part of a
collaboration at the University of
Rochester where we're using uh the giant
laser it's literally this is called the
laboratory for laser energetics we got a
huge Grant from the NSF to use that
laser to like slam tiny pieces of silica
to understand what the conditions are
like at you know the center of the Earth
or even more importantly the center of
super Earths like the most this is
what's Wild the most common kind of
planet in the universe we don't have in
our solar system which is amazing right
so the uh we've been able to study
enough or observe enough planets now to
get a census you know we pretty you know
we kind of have an idea of what who's
average who's weird um and our solar
system is weird because the average
planet has a mass between somewhere
between a few times the mass of the
Earth to maybe you know 10 times the
mass of the Earth and that's exactly
where there are no planets in our solar
system so um the smaller ones of those
we call Super Earths the larger ones we
call sub Neptunes and they're anybody's
guess like we don't really know what
happens to material when squeezed to
those pressures which is like Millions
tens of millions of times the the
pressure on the surface of the Earth so
those details really will matter of
what's going on in there because that
will determine whether or not you have
say for example PL tectonics we think PL
tectonics may have been really important
for life on Earth for the evolution of
complex life on Earth so it turns out
and this is sort of the Next Generation
where we're going with the the
understanding the evolution of planets
and life it turns out that you actually
have to think hard about the planetary
context for life you can't just be like
oh there's a warm Pond you know and then
some interesting you know chemistry
happens in the warm Pond you actually
have to think about the planet as a
whole and what it's gone through in
order to really understand whether a
planet is a good place for life or not
why do you think PL tectonics might be
uh useful for the formation of complex
life there's a bunch of different things
one is that you know the Earth went
through a couple of phases of being a
snowball Planet like we you know we went
went into a period of glaciation where
the pretty much the entire planet was
under ice the the oceans were Frozen um
you know early on in Earth's history
there was no there was barely any land
we were actually a water world you know
with just a couple of um australas sized
cratons they called them protoc
continents so those uh we went through
these snowball Earth phases and if it
wasn't for the fact that we had kind of
an active plate tectonics which had a
lot of vulcanism on it um we could have
been locked in that forever like once
you get into a snowball State a planet
can be trapped there forever which is
you know maybe you already had life form
but then because it's so cold you may
never get anything more than just
microbes right so what PL tectonics does
is it because it Fosters more um
vulcanism is that you're going to get
carbon dioxide pumped into the
atmosphere which warms the planet up and
gets you out of the uh the uh snowball
Earth phase but even more there's even
more really important things I just
finished a paper where we were looking
at something called hard steps model
which is this model that's been out
there for a long time that purports to
say intelligent life of the universe
will be really rare and it made all
these assumptions about the Earth's
history particularly that the history of
life and the history of the planet or
have nothing to do with each other and
it turns out as I was doing the reading
for this that uh Earth probably early on
had a had a more mild form of plate
tectonics and then somewhere about a
billion years ago it ramped up and that
ramping up changed everything on the
planet cuz here's a funny thing the
Earth used to be flat what I mean by
that right so all the flat earthers out
there can get excited for one second
clip
it but at what I mean by that is that
there really weren't many mountain
ranges right the beginning of I think
the term is orogenesis mountain building
the true Himalayan style giant mountains
didn't happen until this more robust
form of plate tectonics where the plates
are really being driven around the
planet and that is when you get the
crusts hitting each other and they start
pushing you know into these Himalayan
style mountains the weathering of that
the erosion of that puts huge amounts of
nutrients you know things that microbes
want to use uh into the oceans and then
the what we call the net primary
productivity the you know the photo the
the the bottom of the food chain how
much sugars they are producing how much
photosynthesis they're doing shot up by
a factor of almost a thousand right so
the the fact that you had play tectonics
supercharged evolution in some sense you
know like we're not exactly sure how how
it happened but it's clear that the
amount of Life the amount of living
activity that was happening really got a
boost from the fact that suddenly there
was plate this new vigorous form of
plate tectonics so it's nice to have
turmoil in terms of temperature in terms
of uh surface geometries in terms of the
chemistry of the planet turmoil yeah
that's actually really true because what
happens is if you look at the history of
life that's a really you know it's an
excellent point you're bringing up if
you look at the history of life on Earth
we get uh you know a biogenesis
somewhere around at least 3.8 billion
years ago and that's the first microbes
they kind of take over enough that they
really do you get a biosphere you get a
biosphere that is actively changing the
planet but then you go through this
period they call the boring billion
where like it's a billion years and it's
just microbes nothing's happening it's
just microbes I mean they're do the
microbes are doing amazing things
they're inventing uh um fermentation
thank you very much for we appreciate
that um but it's not until sort of you
get probably this these continents
slamming into each other you really get
the beginning of continents forming and
driving changes that Evolution has to
respond to that on a planetary scale
this turmoil this chaos is creating new
niches as well as closing other ones and
biology Evolution has to respond to that
and somewhere around there is when you
get the Cambrian explosion is when
suddenly every body plan um you know
Evolution goes on an orgy essentially uh
so yeah it does look like the that chaos
or that turmoil was actually very
helpful to Evolution I wonder if there
is some uh extremely elevated levels of
chaos almost like catastrophes behind
every Leap of evolution like you're not
going to have
Leaps um like in in in human societies
we have like an Einstein that comes up
with a good idea but it feels like on an
evolutionary time scale you
need some real big drama going on for
for The evolutionary system to have to
come up to a solution to that drama like
extra ra complex solution to that drama
well I think what's I'm not sure if
that's true I don't know if it needs to
be like an an almost Extinction event
right because it's certainly true that
we have gone through almost Extinction
events right we had you know five ma
mass extinctions but you don't
necessarily see that like there was this
giant evolutionary leap happening after
those so you know with the uh comet
impact um the KT boundary certainly you
know lots of niches opened up and that's
why we're here right because you know
our ancestors were just little basically
rodents rats living under the footsteps
of the dinosaurs and it was that comet
impact that opened the um the route for
us but it wasn't I mean that still took
another you know 65 million years it
wasn't like this thing immediately
happened but what we found with this
hard steps paper because the whole idea
of the hard steps paper was it was one
of these uh anthropic reasoning kinds of
things where Brandon Carter said Oh look
The intelligence doesn't show up on
Earth until about um you know almost
close to when the end of the sun's
lifetime uh and so he's like well there
should be no reason why the sun's
Lifetime and the time for evolution to
produced intelligence should be the same
uh and so therefore and he goes through
all this reasoning anthropic reasoning
and and and he ends up with the idea
that like oh it must be that the odds of
getting intelligence are super low and
so that's the hard steps right so there
was a series of steps in evolution that
were you know very very hard and because
that you can calculate some probability
distributions um and everybody loves a
good probability distribution and they
went a long way with this but it turns
out that the whole thing is flawed
because on one you know when you look at
it of course the time scale for the
sun's Evolution and the time scale for
evolution on life are coupled because
life and the the time scale for
evolution of the earth is coupled is
about the same time scale as the
evolution as the sun it's billions of
years the earth evolves over billions of
years and life and the Earth co-evolve
that's what Brandon Carter didn't see is
that actually the fate of the earth and
the fate of Life are inextricably
combined uh and this is really important
for astrobiology too um life doesn't
happen on on a planet it happens to a
planet so this is something that David
grinspoon and Sarah Walker both say and
you know uh I agree with this it's a
really nice way of putting it um so uh
you know PL tectonics um the evolution
of oxygen of an oxygen atmosphere which
only happened because of life um these
things you know these are are things
that are happening where life and the
planet are sort of slashing back and
forth and so rather than to your your
point about do you need giant
catastrophes maybe not giant
catastrophes but what happens is as the
Earth and life are evolving together
windows are opening up evolutionary
Windows like for example life put oxygen
into the atmosphere when when life
invented this new form of photosynthesis
about two and a half billion years ago
that broke water apart to you know work
to do its its shenan chemical
Shenanigans um it broke water apart and
pushed oxygen into the atmosphere that's
why there's oxygen in the atmosphere
it's only because of life um that opened
up huge possibilities new spaces for
evolution to happen but it also changed
the chemistry of the planet forever so
the Evol the introduction of of a of
oxygen photosynthesis changed the planet
forever and it opened up a bunch of
Windows for evolution that wouldn't have
happened otherwise like for example you
and I we need that amount of o oxygen
big brained creatures need an oxygen
rich atmosphere because oxygen is so
potent um for metabolism so you couldn't
get intelligent creatures 100 million
years after the planet formed so really
on a scale of a planet when there's a
billions trillions of organisms on a
planet they can actually have planetary
scale
impact yeah so the chemical Shenanigans
of an individual organism once scaled
out to trillions can actually change a
plan
yeah and we know this for a fact now
like this is so there was this thing
Gaia theory that you know was James
Lovelock introduced in the 70s um and
then Lin margalis the biologist Lin
margalis together so this Gaia theory
was the idea that planets pretty much
take or sorry life takes over a planet
life hijacks a planet in a way that um
the sum total of Life creates these
feedbacks between the planet and the
life such that it keeps the planet
habitable it's kind of a homeostasis
right I can go out like right now
outside it's 100° right and I go outside
but my internal temperature is going to
the same and I can go back to you know
Rochester New York in the winter and
it's going to be you know zero degrees
but my internal temperature is going to
be the same that's homeostasis the idea
of Gia theory was that life the
biosphere exerts this pressure on the
planet or these feedbacks on the planet
that even as other things are changing
the planet will always stay in the right
kinds of conditions for life now when
this Theory came out it was very
controversial people like oh my God you
know what are you smoking weed you know
and like there were all these guyan
festivals with guyan uh dances and so
you know became very popular in the New
Age Community but love loock actually
they were able to show that no this has
nothing to do with like the planet being
conscious or anything it was about these
feedbacks that that bi the biology the
biosphere can exert these feedbacks and
now that's become whether or not it's
still we're still unclear whether there
are true guyan feedbacks in the sense
that the planet can really exert
complete control but it is absolutely
true that um the biosphere is a major
player in Earth's history so the
biosphere fights for homostasis on Earth
the bio so okay what I would say right
now is I don't know if I can say that
scientifically I can certainly say that
the biosphere does a huge amount of the
regulation of the planetary State and
over billions of years has strongly
modified the evolution of the planet so
whether or not a guy a true guy in
feedback would be exactly what you said
right the guy the biosphere is is
somehow and Sarah Walker and David
grinspoon and I actually did a paper on
this about the idea of planetary
intelligence or cognition across a
planetary scale and I think that
actually is possible it's not conscious
but there is a kind of cognitive
activity going on the biosphere in some
sense knows what is happening because of
these feedbacks um so but so it's still
unclear whether we have these full guyan
feedbacks but we certainly have semian
feedbacks if there's a pertubation on
the planetary scale temperature you know
insulation how much sunlight's coming in
the biosphere will start to have
feedbacks that will damp that
pertubation temperature goes up the
biosphere starts doing something
temperature comes down now I wonder if
the technosphere also has a guyan
feedback or elements of a guyan feedback
such that the technosphere will also
fight to some degree for homeostasis
open question I guess well that's I'm
glad you asked that question because
that that that paper that David and uh
Sarah and I wrote what we were arguing
was is that over the history of a planet
right when life first forms you know 3.8
billion years ago it's kind of thin on
the ground right you've got the first
species you know um these are all
microbes and they have not yet uh been
they're not going to enough of them to
exert any kind of these guyan feedback
so we call that an immature biosphere
but then as time goes on his life
becomes more robust and it begins to
exert these feedbacks keeping the planet
in the place where it needs to be for
life we call that a mature biosphere
spere right and the important thing and
we're going to I'm sure later on we're
going to talk about definitions of life
and such there's this great term called
autop poesis uh that Francisco uh verel
the neurobiologist Francisco verela came
up with and he said you know one of the
defining things about life is this
property of autop poesis which means
self-creating and
self-maintaining life does not create
the conditions which will destroy itself
right it's always trying to keep itself
in a place where it can stay alive so
the biosphere from this perspective has
been autoptic for you know billions of
years now we just invented this
technosphere in the last you know couple
of hundred years and what we were
arguing in that paper is that it's an
immature technosphere right because
right now with climate change and all
the other things we're doing you know
we're destroy the technosphere right now
is sort of destroying the conditions
under which it needs to maintain itself
so the real job for us if we're going to
last over you know geologic time scales
if we want a technosphere that's going
to last
tens of thousands hundreds of thousands
millions of years then we've got to
become mature which means to not uh
undermine the conditions to not subvert
the conditions that you need to stay
alive so as of right now I'd say we're
not autopoetic well I wonder if we look
across thousands tens of thousands
hundreds of thousands of years that
perturbations the technosphere should
create
perturbations a as a way for developing
greater and greater defenses against
perturbations which sounds like a
ridiculous statement but basically uh go
out and play in the yard and hurt
yourself to to strengthen the or like
drink water from the from the pond from
the pond yeah right get sick a few times
to strengthen the immune system yeah
well you know it's interesting with the
technosphere we could talk about this
more but like you know the te we're just
emerging as a technosphere in terms of
as a interplanetary technosphere right
that's really the next step for us is to
um David grinspoon talks about I love
this idea of anti- accretion like this
amazing thing that for the first time
you know over the entire history of the
planet stuff is coming off the planet
right used to be everything just fell
down all the meteorites fell down but
now we're starting to push stuff out um
and you know like the idea of planetary
defense or such you know we are actually
going to start exerting pertubations on
the solar system as a whole we're going
to start engineering if we make it right
I always like to say that if we can get
through climate change the prize that
the end is the solar system right uh so
we will um we'll be change literally
engineering the solar system but what
you can think of right now with what's
happening with the anthropos scine the
great acceleration that that uh the is
the technosphere you know is the
creation of that is a giant pertubation
on the biosphere right and what you
can't do is you know the technosphere
sits on top of the biosphere and the
tech if the technosphere undermines the
biosphere for its own conditions of
habitability then you're in trouble
right I mean the biosphere is not going
away there's nothing we could do like
the idea that we have to save the Earth
is a little ridiculous like the Earth is
not a furry little bunny that we need to
protect but it's the conditions for us
right we Humanity emerged out of this
out of the holos scene the last 10,000
years interglacial period we can't
tolerate very different kinds of earths
um so that's what I mean about a
puration before we forget I got to ask
you about this paper pretty interesting
uh it's an interesting table here about
hard steps abiogenesis glucose
fermentation to perovic acid all kinds
of steps all the way to homo sapians
animal intelligence land ecosystems
endoskeletons eye precursor so formation
of the eye yeah complex
multicellularity that's definitely one
of the big ones yeah so interesting I
mean what can you say about this chart
there are all kinds of papers talking
about what the difficulty of these steps
right and so this was the idea so what
said was you know using anthropic
reasoning he said there must be a few
very hard steps for evolution to get
through to make it to intelligence right
so there's some steps are going to be
easy so every generation you know you
roll the dice and yeah it won't take
long for you to get that step but there
must be a few of them and he said you
could even calculate what how many there
were five six in order to get to
intelligence and so this paper here this
plot is all these different people
who've written all these papers and this
is the point actually you can see all
these papers that were written on the
hard steps each one proposing a
different set of what those steps should
be and there's this other idea from
biology of the major transitions in
evolution mte that those were the hard
steps but what we actually found was
that none of those are actually hard the
whole idea of hard steps that there are
hard steps is actually suspect so you
know this what's amazing about this
model is it shows how important it is to
actually work with people who are in the
field right so you know Brandon Carter
was a you know brilliant physicist the
guy who came up with this um and then
lots of physicists and astrophysicists
like me have used this but the people
who actually study Evolution and the
planet were never involved right and if
you went and talk to an evolutionary
biologist or a biog geophysicist they'd
look at you when you explain this to
them and they'd be like what like what
are you guys doing turns out none of the
uh details or none of the conceptual
structure of this matches with what the
people actually study the planet and its
evolution is it mostly about the the
fact that there's not really discret big
steps is it's a gradual continual kind
of process well there's two things the
first most important one was that the
planet and the biosphere have evolved
together that's something that every you
know most biog geophysicists completely
accept and it was the first thing that
Carter kind of rejected he said like no
that's probably not possible and yet you
know like if he'd only sort of had more
discussions with this other community
would have seemed like no there you
there are actually windows that open up
and then the next thing is this idea of
whether a step is hard or not because
for hard what what you mean by a hard
step is that like I said every time
there's a generation every time there's
the Next Generation born you're rolling
the dice on whether this mutation will
happen and the idea of something being a
hard steps there's two ways in which
something might even appear as a hard
step and not be or actually not be a
hard Step at all one is that you see
something that is a heard an evolution
has only happened once right so let's
take the opposite uh you see something
that's happened multiple times like
wings lots of examples of Wings Over
lots of different evolutionary lineages
so that's clearly not a making wings is
not a hard step there are certain other
things that people say no that's a hard
step uh oxygen you know the oxygen
photosynth synthesis but they are so
they tend to be so long ago that we've
lost all the information there could be
other things in the fossil record that
uh you know went made this Innovation
but they're just gone now so you can't
tell so there's information loss the
other thing is the idea of pulling up
the ladder that somebody you know some
species makes the Innovation but then it
fills the niche and nobody else can do
it again so yeah it only happened once
but it happened once because basically
the the the the creature was so
successful it took over and there was no
space for anybody else to evolve it so
yeah so the interesting thing about this
was seeing how how much once you look at
the details of life's history on Earth
how it really shifts you away from this
hard steps model and it shows you that
those details as we were talking about
like with do you have to know about the
planet do you have to know about PL
tectonics yeah you're going to have
to I mean to be fair to Carter on the
first point it makes it much more
complicated uh if life and the planet
are coold evolving because it's not it
would be nice to consider the planet as
a static thing that sets the initial
conditions yeah and then we can sort of
from a outside perspective analyze
planets based on the initial conditions
they create and then then there's a
binary yes or no will it create life but
if they cool it's just like a it's a
really complex dynamical system where
everything is uh becomes much more
difficult from the perspective of SEI of
looking out there and trying to figure
out which ones yeah are actually
producing life but I think we're at the
point now so now there may be other
kinds of principles that actually
because you know coevolution actually
has its own not determin IC you're done
with determinism right but but you but
complex systems have patterns complex
systems have constraints and that's
actually what we're going to be looking
for our constraints on them and so you
know and again nothing against Carter
was a brilliant idea but it just goes to
show you know there's this great XT you
I'm a theoretical physicist right uh and
so I love simplified give me a
simplified model with you know it's a
dynamical equation some initial
conditions I'm very happy but there's
this great xdc comic where like you know
somebody's working something out on the
board and this physicist is looking over
and saying oh oh I just I just wrote
down an equation for that I I solved
your problem do you guys even have a
journal for this and you know subtitle
is why everybody hates physicists yeah
so sometimes that approach totally works
sometimes physicists you know we can be
very good at like zooming in on what is
important and casting the details aside
so you can get to the heart of an issue
and that's very useful sometimes other
times it obfuscates right other times it
clouds over actually what you needed to
focus on especially when it comes to
complexity uh speaking of simplifying
everything down to an equation uh let's
return back to the question of how many
alien civilizations are out there and uh
talk about the Drake equation yeah can
you uh explain the Drake equation you
know people have various uh feelings
about the Drake equation uh you know it
can be abused but basically it was the
the story actually is really interesting
so Frank Drake in uh 1960 does the first
ever astrobiological IC experiment he
gets a radio telescope points it at a
couple of stars and listens for signals
that was the first time anybody done any
experiment about any kind of life in the
history of humanity um and he does it
and he's kind of waiting for everybody
to make fun of him in still he gets a
phone call from the government says hey
we want you to have do a um a meeting on
Interstellar Communications right he's
like okay so they organize a meeting
with like just eight people a young Carl
Sean is going to be there as well uh and
like the night before Drake has to come
up with a uh an agenda how do you come
up for an with an agenda for a meeting
on a topic that no one's ever talked
about before right and so he actually
write he breaks what he does what's so
brilliant about the Drake equation is he
breaks the problem of how many
civilizations are there out there into a
bunch of sub problems right and he
breaks it into seven sub problems each
one of them is a factor in an equation
that when you multiply them all together
you get the number of civilizations out
there that we could communicate with so
the first term is the rate at which
stars form the second term is the
fraction of those stars that have
planets F ofp the next term is the
number of planets in the habitable zone
the place where we think life could form
uh the next term after that is the
fraction of those planets where actually
an abiogenesis event life forms occurs
the next one is the fraction of planets
on which you start to get intelligence
after that it's the fraction of planets
where that intelligence goes on to
create a civilization and then finally
the last term which is the one that we
really care about is the lifetime how
long you have a civilization now how
long does it last what you say we we
humans we humans right because we're
standing we're staring at the you know
multiple guns pointing out you know
nuclear war climate change AI um so you
know how long on in general does
civilizations last now each one of these
terms was brilliant about what he did
was what he was doing was he was
quantifying our ignorance right by
breaking the problem up into these seven
sub problems he gave astronomers
something to do right and so you know
this is always with a new research field
you need a research program or else you
just have a bunch of vague questions you
don't even know really what you're
trying to do um so you know the star
people could figure out how many stars
were forming per year the the people who
were interested in planets could go out
and find techniques to discover planets
uh etc etc I mean these are their own
Fields essentially by creating this
equation he's launching new Fields yeah
that's exactly gave astrobiology which
wasn't even a term then a road map like
okay you guys go do this you go do that
you go do that and it had such
far-reaching effect on astrobiology
because it did break the problem up in a
way that gave useful uh uh you know sort
of marching orders for all these
different groups like for example it's
because of the Drake equation in some
sense that um people who were involved
in seti pushed NASA to develop the
Technologies for Planet hunting there
this amazing meeting in 1978 192
meetings 1978 and 1979 that were driven
in some part by the people who were
involved in seti getting NASA together
to say look okay look how you know
what's what's the road map for us to
develop Technologies to find find
planets so um yeah so you know the Drake
equation is absolutely uh uh
foundational for astrobiology but we
should remember that it's not a law of
nature right it's not something that's
it's not equals MC squ and so you can
see it being abused in some sense people
you know it's generated a trillion
papers some of those papers are good
I've written some of those and some of
those papers are bad um you know I'm not
sure where my paper fits in on those I'm
saying you know one should be careful
about what you're using it for but in
terms of understanding the problem that
that astrobiology faces this really
broke it up in a useful way we could
talk about each one of these but let
let's just look at EXO planets yeah so
that's a really interesting one I think
when you look back you know hundreds of
years from now what it in the 90s when
they first detected the' 92 and '95 '95
to me was really that was the discovery
of the first planet orbiting a sunlike
star to me that was the water the damn
being broken I I think that's like one
of the greatest discoveries in the in
the history of science I agree I agree
right now I guess nobody's celebrating
it too much because you don't know what
it really means but I think once we
almost certainly will find life out
there
obviously allow us to generalize across
the entire galaxy the entire universe so
if you can find life on a planet even in
the solar system you can now start
generalizing across the entire universe
you can all you need is one like right
now it's an any you know our
understanding of life we have one
example we have n equals one example of
life so that means we could be an
accident right it could be that we're
the only place in the entire universe
where this weird thing called life has
occurred get one more example and now
you're done because if you have one more
example now you're you know even you
know you don't have to find all the
other examples you just know that it's
happened more than once and now you are
you know in from a basian perspective
you can start thinking like yeah yeah
this life is not something that's hard
to make well let me get your sense of uh
estimates for the Drake equation you
also written a paper expanding on the
Drake equation but what what do you what
do you think is the answer so the paper
there was this paper we wrote uh Woody
Sullivan and I in 2016 where we said
look we have all this exoplanet data now
right the so the thing that exoplanet
science and the exoplanet census I was
talking about before have nailed is f
subp the fraction of stars that have
planets it's one every freaking star
that you see in the sky hosts a family
of Worlds I mean it's mindboggling
because every one of those those are all
places right they're either you know gas
giants probably with moons so there the
moons are places you can stand and look
out or they're like terrestrial world
where even if there's not life there's
still snow falling and there's oceans
washing up on you know on shorelines
it's incredible to think how many places
and stories there are out there so right
the first term was FS subp which is how
many stars have planets the next term is
how many planets are in the habitable
zone right on average and it turns out
to be one over five right so you know
you know around point two so that means
you just count five of them go out at
night and go 1 two 3 four five one of
them has an an earthlike planet
you know in the habitable zone like whoa
so what what defines a habitable zone
habitable zone is an idea um that was
developed in the um uh 1958 by the
Chinese American astronomer xuang and it
was it was a brilliant idea it said look
this is there you know I can do the
simple calculation if I take a planet
and just stick it at some distance from
a star of what's the temperature of the
planet what's the temperature of the
surface so now you're all you're going
to ask you give it a standard kind of
you know earthlike atmosphere and ask
could there be liquid water on the
surface right we believe that liquid
water is really important for Life there
could be other things that's happening
fine but you know if you were to start
off trying to make life you'd probably
choose water as your solvent for it so
basically the habitable zone is the band
of orbits around a star where you can
have liquid water on the surface you
could take a you know glass of water
pour it on the surface and it would just
pull up it wouldn't freeze immediately
which would happen if your planet is too
far out and it wouldn't just boil away
if your planet too close in so that's
the formal definition of the habitable
zone so it's a nice strict definition
there's probably way more going on than
that but this is a place to start right
well we should say it's a place to start
I I do think it's too strict of a
constraint I would agree we're talking
about temperature where water can be on
the surface there there's so many other
ways to get uh the aforementioned
turmoil yeah where the temperature
varies whether it's volcanic so interact
fraction of volcanoes and ice and all of
this on the moons of plants that are
much farther away all this kind of stuff
yeah well for example we know in our own
solar system we have say Europa the moon
of Jupiter which has got a 100 mile deep
ocean under 10 miles of ice right that's
not in the habitable zone that is
outside the habitable zone and that may
be the best place it's got more water
than Earth does all of its oceans or you
know it's twice as much water on Europa
than there is on Earth so you know that
may be a really great place for life to
form and it's outside the habitable zone
so you know the habitable zone is a good
place to start and it helps us and
there's reason there's reasons why you
do want to focus on the habitable zone
because like Europa I couldn't I won't
be able to see from across telescopic
distances across Lighty years I I
wouldn't be able to see life on Europa
because it's under 10 miles of ice right
so with the important thing about um
planets in the habitable zone is that
we're thinking they have atmospheres um
atmospheres are the things we can
characterize for across 10 50 light
years and we can see bio signatures as
we're going to talk about so there is a
reason why the habitable zone becomes
important for the detection of extra
solar life but for me when I look up at
the stars it's very likely that there's
a habitable planet or Moon and each of
the Stars habitable defined broadly yeah
I think that's that's not unreasonable
to say I mean especially since the the
formal definition you get one and five
right one and five is a lot there's a
lot of stars in the sky so yes saying
that in general when I look at a star
there's a pretty good chance that
there's something habitable orbiting it
is not a unreasonable scientific claim
to me it seems like there should be
alien civilizations
everywhere why the fmy Paradox why
haven't we seen them okay the fmy
Paradox let's talk about the I love
talking about the fmy Paradox because
there is no fmy
Paradox yeah so the fmy par let's talk a
little about the fmy Paradox and the
history of it um so uh enrio fery it's
1950 he's walking with his friends at
Los Alamos nuclear weapons lab to The
Cantina and there had been this um
cartoon in the New Yorker they all read
the New Yorker uh and the cartoon was
trying to explain why there there had
been this rash of uh uh garbage cans
being disappearing in New York and this
cartoon said oh it's UFOs because this
is already you know it's 1950 the first
big UFO craze happened in 47 so they'd
all they were laughing about this as
they're walking and they started being
physicist started talking about
Interstellar travel Interstellar
propulsion blah blah blah you know
conversation goes on for a while
conversation turns to something else you
know they gone on other things about 40
minutes later over lunch fmy blurts out
well where is everybody right typical
fmy sort of thing he done the
calculation in his head and he suddenly
realized that look if one if there you
know if intelligence is common that even
traveling at sublight speeds a uh a
civilization could cross you know kind
of hop from one star system to the other
and spread out across the entire galaxy
in a few hundred thousand years and he
realized this and so he was like why
aren't they here now um and that was the
beginning of the fmy Paradox it actually
got picked up as a formal thing in 1975
in a paper by Hart where he actually
kind of went through this calculation
and showed and said well there's nobody
here now therefore there's nobody
anywhere that you know okay so that is
what we will call the direct firmy
Paradox why aren't they here now but
something happened where people after
seti began where people started to there
there's this idea of the great silence
people got this idea in their head that
like oh we've been looking for decades
now for signals of extraterrestrial
intelligence and we haven't found any
therefore there's nothing out there but
that so we'll call that the indirect fmy
Paradox and there absolutely is no
indirect fmy Paradox for the most
mundane of reasons which is money
there's never been any money to look
there really SEI was always done by
researchers who were kind of like scabin
time you know some extra time from their
other projects to you know look a little
bit uh you know at the sky with a
telescope telescopes are expensive so um
Jason Wright my one of my collaborators
he and his students did a study where
they looked at the entire search space
for se you know and imagine that's an
ocean all the different Stars you have
to look at the radio frequencies you
have to look at how when you look how
often you look and they they looked then
they summed up all the sety searches
that had ever been done they went
through the literature and what they
found was if the if the if that search
space if the SC is an ocean and you're
looking for fish how much of the ocean
have we looked at and it turns out to be
a hot tub that's how much of the ocean
that we've looked up we've dragged an a
hot tub's worth of ocean water up and
there was no fish in it and so now are
we going to say up well there's no fish
in the ocean right so there is
absolutely positively no indirect firmy
pars we just haven't looked um but we're
starting to look so that's what's you
know finally we're starting to look
that's what's exciting the direct fmy
Paradox there are so many ways out of
that right there's a book called 77
solutions to the fmy Paradox that it
just you know you can pick your favorite
one it just doesn't carry a lot of
weight because there's so many ways
around it we did an actual simulation my
group uh Jonathan Carol um one of my
collaborators we actually simulated the
Galaxy and we simulated probes moving at
sublight speed from one uh uh star to
the other Gathering resources heading to
the next one um and so we could actually
track the expansion wave across the
Galaxy have one IA biogenesis event and
then watch the whole galaxy get
colonized or settled and it is
absolutely true that that wave crosses
you know Hart was right fmy was right
that wave crosses very quickly but
civilizations don't last forever right
so one question is when did they visit
when did they come to earth right so if
you give civilizations a finite lifetime
you know let them last 10,000 100
thousand years what you find is you now
have a steady state civilizations are
dying they're you know they're they're
coming back they're traveling between
the Stars what you find then is you can
have big holes opened up you can have
regions of space where there is nobody
for you know millions of years and so if
that if we're living in one of those
bubbles right now then maybe we were
visited but we were visited a 100
million years ago and there was a paper
that Gavin Schmidt and I did that showed
that if there was a civilization whether
it was like dinosaurs or aliens that was
here a 100 million years ago there's no
way to tell there's just there's no
record left over the fossil record is
too sparse the only way maybe you could
tell is by looking at the isotopic uh uh
Str
uh to see if there was anything
reminiscent of an industrial
civilization but the idea that you know
you'd be able to find you know iPhones
or or toppled buildings after a 100
million years is ther