Kind: captions
Language: en
the following is a conversation with
constantine bategan
planetary astrophysicist at caltech
interested in
among other things the search for the
distant the mysterious
planet nine in the outer regions of our
solar system quick mention of our
sponsors
squarespace literati on it and
and i check them out in the description
to support this podcast
as a side note let me say that our
little sun is orbited by
not just a few planets in the planetary
region but trillions of
objects in the kuiper belt and the oort
cloud that extends over three
light years out this to me is amazing
since proxima centauri
the closest star to our sun is only 4.2
light years away
and all of it is mostly covered in
darkness
when i get a chance to go out swimming
in the ocean far from the shore
i'm sometimes overcome by the terrifying
and the exciting feeling of not knowing
what's there
in the deep darkness that's how i feel
about the edge of our solar system
one day i hope humans will travel there
or at the very least
ai systems that carry the flame of human
consciousness
this is the lex friedman podcast and
here's my conversation
with constantine bategan
what is planet nine planet nine
is an object that we believe
lives in the solar system beyond the
orbit of neptune it orbits the sun
with a period of about 10 000 years
and uh is about five earth masses
so that's a hypothesized object there's
some evidence
uh for this kind of object there's a
bunch of different explanations
can you give like an overview of the
planets in our solar system how many are
there
what do we know and not know about them
at a high level
all right that sounds like a good plan
so look the solar system
basically is comprised of two parts the
inner and the outer solar system
the inner solar system has the planets
mercury venus
earth and mars now mercury is about
40 percent of the orbital separation
of where the earth is is closer to the
sun venus
about 70 percent uh then mars is about
160 further away from the sun than is
the earth
these planets that we uh one of them
we occupy right are pretty small okay
they're
too leading order sort of heavily
overgrown asteroids
if you will um and this is
this becomes evident when you move out
further
in the solar system and encounter
jupiter which is 316
earth masses right 10 times the size
you know and saturn is another huge one
90 earth masses at about 10 times
uh the separation from the sun this is
the earth and then you have uranus and
neptune
at 20 and 30 respectively for a long
time
that is where the kind of massive
part of the solar system ended
but what we've learned in the last 30
years
is that beyond neptune there's this
expansive field of icy debris a second
icy asteroid belt in the solar system a
lot of people have
heard of the asteroid belt which lives
be between
mars and jupiter right like that's a
pretty common thing that people like to
imagine and draw on lunch boxes and
stuff but beyond neptune
there's a much more massive much more
radially
expansive field of debris pluto by the
way
it belongs to that second
you know icy asteroid belt which we call
the kuiper belt it's just a big
object within that population of bodies
oh pluto
the planet pluto the the dwarf planet
the former planet
you know why is pluto not a planet
anymore
i mean it's tiny were you used to size
matters when it comes to planets
100 100 it's a actually a fascinating
story
when pluto was discovered in 1930
the the reason it was discovered in the
first place because astronomers at the
time were looking for a seven earth mass
planet
somewhere beyond neptune it was
hypothesized that such an object exists
when they found something they
interpreted that
as a seven earth mass planet and
immediately revised its mass downward
because they couldn't resolve the object
with the telescope so it looked like a
just a point mass you know
star rather than a physical disk they
said well maybe it's not seven maybe
it's one
right and then so over the next um you
know i guess 40 years
pluto's mass kept getting revised down
downwards downwards downwards until
uh it was realized that's like 500 times
less massive than the earth i mean like
pluto's
surface area is almost perfectly equal
to the surface area of russia actually
and you know russia is big but it's not
a planet
well i mean actually we can we can touch
more on that that's that's another
discussion
uh so in some sense earlier in the
century pluto represented
kind of our ignorance about the edges of
the solar system
and perhaps planet nine is the thing
that represents our ignorance
about now the modern set of ignorances
about the edges of our solar system
that's a good way to put it by the way
just
imagining this belt of astero of debris
at the edge of our solar system is
incredible
can you talk about it a little bit what
is the kuiper belt and
what it what is the oort cloud yeah
okay so look the simple way to think
about it is that if you imagine
you know neptune's orbit like a circle
right
kind of uh maybe a factor of one and a
half 1.3
uh times bigger uh on a radius of
1.3 times bigger you've got a whole
collection of icy objects most of these
objects
are sort of the size of austin you know
maybe maybe a little bit smaller if you
then
zoom out right and
explore the orbits of the most long
period kuiper belt object these are the
things that have the
biggest orbits and take the longest time
to go around the sun
then what you find is that beyond a
critical
orbit size beyond a critical orbit
period which is about 4 000 years
you start to see weird structure like
all the orbits
sort of point into one direction and
all the orbits are kind of tilted in the
same
way by about 20 degrees with respect to
sun this is particularly pronounced
in orbits that are not heavily affected
by neptune
so there you start to see this weird
dichotomy where there are
objects which are stable which are which
neptune
does not mess with gravitationally and
unstable objects the unstable objects
are basically all over the place
because they're being you know kicked
around by neptune the stable
orbits show this remarkable pattern of
clustering
we back i guess five years ago
interpreted this pattern of clustering
as a gravitational one-way sign the
existence of
a planet in a distant planet right
something that is shepherding and
confining
these orbits together of course
right you have to have some skepticism
when you're
when you're talking about these things
you have to ask the question of okay how
statistically significant
is this clustering and there are many
authors that
have indeed called that into question we
have done
our own analyses and basically just like
with all statistics where
you know there's kind of like you know
multiple ways
to uh do the exercise
you can either ask the question if i
have a telescope
that has you know surveyed this part of
the sky
what are the chances that i would
discover this clustering
that basically tells you that you have
zero confidence
right like that's not that does not give
you
a confident answer one way or another
another way to do the statistics which
is what we
prefer to do is to take to say we have a
whole
night sky of discoveries in the kuiper
belt
right and if we have some object over
there
which has right tension and declination
which is a way to say it's
there on the sky and it has some
brightness
that means somebody looked over there
and discovered an object
of was able to discover an object of
that brightness or
brighter through that analysis you can
construct a whole map
on the sky of kind of where all of the
surveys that have ever been done
have collectively looked so if you do
the exercise this way
the false alarm probability of
the clustering on which the planet nine
hypothesis is built is about 0.4
wow okay so there's a million questions
here one when you say bright objects
why are they bright are we talking about
actual objects within the kuiper belt or
the stuff we see through the kupper belt
this is the actual stuff we see in the
kuiper belt the way
you go about discovering kuiper belt
objects pretty easy
i mean it's easy in theory right hard in
practice
yeah all you do is you take snapshots of
the sky
right choose that direction say and take
you know
the high exposure snapshot then you wait
a night
and you do it again and then you wait
another night and you do it again
objects that are just random stars in
the galaxy don't move
on the sky whereas objects in the solar
system will slowly move
this is no different than if you're
driving down the freeway
it looks like you know trees are going
by you faster than the clouds right this
is parallax
that's it it's just they're reflecting
light off
of the sun and it's going back and
hitting this there's a little bit of a
glimmer
from the different objects that you can
see based on the reflection from the sun
so like
there's actual light yeah it's not
darkness that's right these are just
big icicles basically that are just
reflecting sunlight back at you
it's then easy to understand why it's so
hard to discover them because
light has to travel to you know
something like 40 times the distance
um between the earth and the sun and
then get reflected back was it like an
hour
travel or yeah that's right that's
something like that because the
the earth to the sun is eight minutes i
believe um
and so something you know yeah yeah in
that
in that order magnitude so that's
interesting so you have to
like account for all of that and then
there's this huge amount of
data pixels that are coming from the
pictures
and you have to uh integrate all that
together
to paint a sort of like a high estimate
of the different objects
can you track them can you be like
that's bob like can you like
yes exactly in fact uh one of them is
is named joe biden i mean i'm not like
this is not even a joke
right is there a trump one or no no no
no
i don't know i haven't checked for for
for that but
uh like the way it works is if you
discover one
you right away get a license plate for
it okay
so like the first four numbers is the
first
year that this object has appeared on
you know
in the data set if you will and then um
there's like this code that follows it
which basically tells you where in the
sky it is
right so one of the really interesting
kuiper belt objects which is very much
part of the planet 9 story is called
vp113
because joe biden was vice president at
the time
you know got nicknamed biden
vp113 said yeah you got nickname button
beautiful
what's the fingerprint for any
particular
object like how do you know it's the
same one okay just kind of like
yeah from night to night you take a
picture how do you know it's the same
object
yeah so the way you know is it appears
in almost exactly the same part of the
sky except for the move but it moves but
this is why actually you need at least
three nights
because oftentimes asteroids
which are much closer to the earth like
will um
appear to move only
slightly but then on the third night
will move away so that third knight
is really there to detect acceleration
now
the the thing that i didn't really
realize until
you know i started observing together
with my partner in crime and all this
mike brown
is just the fact that for the first year
when you make these detections
the only thing you really know is
confidence is where it is on the night
sky
and how far away it is okay that's it
you don't know anything about the orbit
because over three days the object just
moves so little right the that whole
motion on the sky is entirely coming
from
motion of the earth right so the earth
is kind of the car
the object is the tree and you see it
moving so then
to get some confident information about
what its orbit looks like you have to
come back
a year later um and then measure it
again
interesting to do three nights then come
back a year later and do another three
nights
so you get the velocity the acceleration
from the three nights and then you have
the
maybe the additional the additional
formation
because an orbit is basically described
by six parameters
so you at least need six independent
points but in reality you need
many more observations to to really
pin down the orbit well and from that
you're able to construct for that one
particular object in orbit and then
there's
of course like how many objects are
there
there's like four-ish thousand now
but like the
in the future that could be like
millions
oh sure oh sure so in fact these things
are hard to predict but there's a
new observatory called the vera rubin
observatory which is coming online
maybe next year i mean with covet these
things are
a little bit more uncertain but they've
actually been making great progress
uh with construction and so that
uh telescope is gonna sort of scan the
night sky
uh every day automatically and it's just
it's such an efficient survey that it
might uh increase the census
of the distant kuiper belt the things
that i'm interested in
by a factor of 100 i mean that would be
that would be really cool
and yeah that's a that's an incredible
uh
maybe i mean they might just find planet
nine
i mean that's like almost like literally
pictures like visually
i mean sure yeah like the first
detection you make all you know is where
it is in the sky and how far away it is
if something is you know 500 times away
from the sun
as far away from the sun as is the earth
you know that's planet nine that's when
the story concludes
and then you can study it right now you
can study yeah by the way
i'm going to use that as like i don't
know a pickup line or a dating strategy
like see the person for three days and
then don't see them at all and then see
them again in
in a year to determine the orbit and
over time
you figure out if sort of uh
from a cosmic perspective this this
whole thing
i have no dating advice to give i was
good i was going to use this as a
metaphor to uh to somehow
uh map it on to the human condition okay
you mentioned the kuiper belt what's the
oor cloud
if you look at the neptune orbit as uh
one then the kuiper bell is like 1.3 out
there
and then we get farther and farther into
the darkness what
so okay you've got the kind of main
kuiper belt was about
say 1.3 1.5
um then you have something called the
scattered disc
which is kind of an extension of the
kuiper belt it's a bunch of these
long very elliptical orbits that hug
the orbit of neptune but come out very
far so
that the scattered disc
with the current senses like the some of
the
longest orbits we know of
um have a
semi-major axis so half the orbit length
roughly speaking of about a thousand
thousand times the distance between the
earth and the sun
wow now if you keep moving out okay
eventually once you're sort of you know
ten thousand to a hundred thousand
roughly that's where the oort cloud is
now the oort cloud is a distinct
population of
icy bodies and it's distinct from the
kuiper belt it's in fact it's so
expansive
that it ends roughly halfway between
us and the next star um it's it's edge
is just
dictated by to what extent does the
solar gravity reach
solar gravity reaches that far yeah so
it has to
wow yeah so in fact
imagining this is a little bit
overwhelming so there's like a giant
like vast
icy rock thingy it's like a sphere
it's like you know it's like it's an
almost spherical structure
that engulfs that encircles the sun
and all the long period comets come
from the oort cloud they come the way
that they appear
i mean for already i don't know hundreds
of years
we've been detecting occasionally like a
comet will come in
and it comes seemingly comes out of
nowhere
the reason these long period comets
appear
that very on very very long time scales
right
these oort cloud objects that are
sitting you know 30
000 times as far away from the sun as is
the earth
actually interact with the gravity of
the galaxy the tide
effectively the tide that the galaxy
exerts upon them and their orbits slowly
change and they elongate
to the point where once they their
closest approach to the sun starts to
reach
a critical distance where ice starts to
sublimate
then we discover them as comets because
then the ice comes off of them
they look beautiful on the night sky etc
but they're all coming from
you know really really far away so is
there
are any of them coming our way from
collisions like how many collisions are
there
or is there a bunch of space for them to
move around yeah there's zero it's
completely collisionless
out there the physical radii of objects
are so small compared to the distance
between them
right it's just it is truly a
collisionless
uh environment i don't know there i
think that probably in the age
of the solar system there have literally
been zero collisions in the word cloud
wow when you like draw a picture of the
solar
system everything's really close
together so that everything i guess here
is
spaced far apart do rogue planets
like flying every once in a while and
join not rogue planets but rogue objects
from
out there oh sure oh sure yeah join the
party
yeah absolutely uh we've seen a couple
of them um
in the last three or f or so years uh
maybe four years now
uh one the first one uh was
the one called it's been
all over the news the second one was
comet borisov
discovered by a guy named borisov
yeah so the way you know they're coming
from elsewhere is
unlike solar system objects which travel
on elliptical paths
around the sun these guys travel on
hyperbolic paths
so they come in say hello and then
they're gone
and the fact that they exist
is totally like not surprising
right the neptune is con constantly
ejecting
kuiper belt objects into interstellar
space our solar system itself
is sort of leaking icy debris and
injecting it so
presumably every you know planetary
systems around other stars do exactly
the same thing
let me ask you about the the millions of
objects that are
part of the kuiper belt and the part of
the ore cloud do you think some of them
have
primitive life it kind of makes you sad
if there's like primitive life there and
they're just kind of like lonely out
there in space
like how many of them do you think have
life like bacterial life probably a
negligible amount
zero you know like zero was like a plus
on top
uh right yeah
um if so you know if you and i
took a little trip to the interstellar
medium i think we would develop cancer
and die uh real fast right that's rough
yeah it's a pretty hostile radiation
environment
you don't actually have to go to the
interstellar medium you just have to
leave the earth's magnetic field too
and then you're not doing so well
suddenly
so you know this this idea of
you know life kind of traveling between
places it's not
it's not entirely implausible but you
you really have to
twist i think a lot of parameters one of
the problems we have is we don't
actually know how life originates
right so it's kind of a second order
question of survival in the interstellar
medium and how resilient it is because
we we think you require
water but and that's certainly the case
for the earth but you know we uh
we really don't know for sure that said
i will argue that the question of like
are there aliens out there
is a very boring question because
the answer is of course there are right
i mean like
we know that there are planets around
almost every star um
of course there of course there are
other life forms life is not some
specific thing that happened on the
earth and that's it
right just that's a statistical
impossibility yeah um
yeah but the the difficult question is
before even
the fact that we don't know how life
originates i don't think we even know
what life
is like definitionally yeah like
formalizing a kind of picture
of in terms of the mechanism we would
use
to to search for life out there or even
when we're on a planet
to say is this life is this rock that
just moved
from where it was yesterday life or or
maybe not even
rock something else i got to tell you i
want to know what life
is okay and i want you to show me
uh i think there's a song to basically
accompany every single
thing we talk about today and probably
uh half of them are love songs
um and somehow we'll integrate george
michael into the whole thing okay
so your intuition is there's life
everywhere in our universe
do you think there's intelligent life
out there i think it's entirely
plausible
i mean i it's entirely plausible um
i think i think there's intelligent life
on earth
um and so yeah taking that like say
whatever this thing we got on earth
whether it's dolphins or humans
say that's intelligent definitely
dolphins
i mean have you seen the dolphins
well they do some cruel stuff to each
other so if cruelty
is uh is the definition of intelligence
that they're pretty good yeah and then
humans are pretty good on that
regard then there's like uh uh pigs
are very intelligent i got actually a
chance to hang out with pigs recently
and they're um aside from the fact
they're trying to
eat me they're very uh
they're very they love food they love
food but there's an intelligence to
their eyes that was kind of
uh like haunts me because i also
love to eat meat and then to to me the
thing
i later ate and i was very intelligent
and uh almost charismatic with the way
it was expressing its uh
himself herself itself was uh was quite
incredible
so and all that to say is if we have
intelligent life here on earth if we
take dolphins pigs
humans from the perspective of like
planetary science
how unique is earth okay so earth is not
a com
common outcome of the planet formation
process
um it's probably a
something on the order of maybe a one
percent effect
and by earth i mean it's not just an
earth mass planet
okay i mean the architecture of the
solar system
that allows the earth to exist in in its
kind of
very temperate um
way one thing to understand
uh and this is this is pretty crucial uh
right it's that the
earth itself formed well after
the gas disk that formed
the giant planets
had already dissipated you see stars
start out
with you know the star and then a disc
of gas and dust that encircles it
okay from this disk of gas and dust
big planets can emerge and we have
over the last uh you know two three
decades discovered
thousands of extra solar planets as an
orbit of other studs
what we see is that uh many of them
are you know have these expansive
hydrogen helium
atmospheres the fact that the earth
doesn't is deeply connected to the fact
that
earth took about 100 million years to
form so we missed that
you know train so to speak to get that
hydrogen helium atmosphere
that's why actually we can see the sky
right that's why the
sky is uh well at least in most places
that's why the
the atmosphere is not completely opaque
um
with that you know kind of thinking in
mind i
i would argue that we're getting the
kind of emergent pictures that the earth
is
is not you know everywhere
right we there's sort of the sci-fi view
of things where we go to some other star
and we just land on random planets and
they're all earth-like that's totally
not true
but the even a low probability
event even if you imagine that earth is
a one in a million
or one in a you know one in 10 million
occurrence there are 10 to the 12 stars
in the galaxy
right so you just you always win by
by large numbers that's right by supply
they save you well
you've hypothesized that our our solar
system once possessed a
population of short-period planets that
were destroyed by the evil jupiter
uh migrating through the the solar
nebula can you explain
if i was to say what was the kind of the
key outcome of searches for extrasolar
planets
it is that most stars are encircled by
short period planets
that are you know a few earth masses
right so a few times bigger than the
earth um
and have orbital periods that kind of
range from days to
to weeks now if you go in
and ask the solar system what's in our
region
right in that region it's completely
empty right
it's just it's astonishingly hollow
and thank you from
the sun is not some you know special
star that decided that it was going to
form
the the solar system so i think you know
the natural thing to assume
is is that the same processes of planet
formation that occurred
everywhere else also occurred in the
solar system
following this logic it's not
implausible to imagine that the solar
system once possessed
a system of intra mercurian
like you know compact system of
of planets so then we asked ourselves
would
such a system survive to this day and
the answer is no
uh at least our calculations um suggest
it's highly unlikely because of the
formation of jupiter
and jupiter's primordial kind of
wandering through the solar system
would have sent this collisional field
of debris that would have pushed
that system of planets onto the sun so
was jupiter
this primordial wandering what did what
did jupiter look like
like why was it wandering it didn't have
the orbit it has today
uh we're pretty certain that giant
planets like jupiter when they form they
migrate
the reason they migrate is you know on a
detailed level perhaps
difficult to explain but you know if
just in a qualitative sense
they form in this fluid disk
of gas and dust so it's kind of like if
i
plop down a raft somewhere in the ocean
will it stay in where you plop it down
or will it
kind of get carried around it's not
really a good analogy because it's not
like jupiter is being
affected by the currents of you know gas
and dust but the way
it migrates is it carves out a hole
in the in the disk and then uh through
by interacting with the disk
gravitationally right it can change its
orbit the fact that the solar system has
both jupiter and saturn
here complicates things a lot right
because it's you have to
solve the problem of the evolution of
the gas disk the evolution of jupiter's
orbit in the gas disk plus
evolution of saturn's and their mutual
interaction
the common outcome of solving
that problem though is pretty easy to
explain
jupiter forms its orbit shrinks and then
once saturn forms
its orbit catches up basically to the
orbit of jupiter and then both come out
so there's this inward outward pattern
of jupiter's
early motion that happens sort of within
the firm within the last million years
of the lifetime of the solar system's
primordial disk
so do while this is happening
if our calculations are correct which i
think they are
you can destroy these in this inner
system of
you know few earth mass planets
and then in the aftermath of all this
violence
you form the terrestrial planets where
would they come from in that case so
so jupiter clears out the space and then
there's a a few terrestrial planets that
come in and those coming from
the from the disk somewhere like one of
the larger
yeah what actually happens in these
calculations is you leave behind
a rather mass depleted like
remnant remnant disk only a couple earth
masses
so then from that
remnant population annulus of material
over 100 or about 100 million years by
just collisions
you grow the earth and the moon and
everything else you said amulous
annulus and yours annulus yeah that's a
beautiful word what does that mean
well it's like it's like a disc that's
kind of thin it's like a
yeah it's something that is you know a
disc that's so thin it's almost
flirting with being a ring like
i was gonna say this reminds me lord of
the rings so like this the word just
feels like it belongs in a toll canal
okay uh
so that that's incredible and so that in
your senses you said like one percent
that's a rare
the way jupiter and saturn danced and
cleared out and you know cleared out the
the the short period debris and then
changed the gravitational landscape
that's a pretty rare thing too
it's rare and moreover like you don't
have to go to our calculations you can
just
ask the night sky how many stars
have jupiter and saturn analogs the
answer is
jupiter and saturn analogs are found
around only 10
of sun-mic stars so they are they
themselves like you kind of have to
score an a minus or better
on the test to you know on the planet
formation test to become
a solar system analog even in that basic
sense
and moreover um you know low lower mass
stars
which are uh very numerous in the galaxy
so-called m dwarfs think like zero
percent
of them well maybe like a negligible
fraction of them have giant planets
giant planets are a rare
you know outcome of planet formation one
of the
really big problems that remain
unanswered is why we don't actually
understand
why they're so rare how hard is it to
simulate
all of the things that we've been
talking about each of the things we've
been talking about
and maybe one day all of the things
we've been talking about and beyond
meaning like from the initial
primordial solar system you know a bunch
of disks with
i don't know billions trillions of
objects in them
like simulate that such that you
eventually get a jupiter
and a saturn then eventually you get the
jupiter and the saturn they clear out a
disc change the gravitational landscape
then earth pops up
like that whole thing and then be able
to do that
for every other system
in the uh every other star in the galaxy
and then
be able to do that for other galaxies as
well
um yeah so look maybe start from the
smallest simulation
like what is actually being done today i
mean even the smallest simulation is
probably super super difficult
even just like one object in the kuiper
belt is probably super difficult to
simulate
i mean i think it's super easy i mean
like it's
it's just not that hard um but um
you know let's let's ask the most kind
of
basic problem okay so the problem of
having a star
and something in orbit of it that you
don't need a simulation for like
you can just write that down on a piece
of paper this gravity
would like yeah i guess i guess it's
important to try to
uh you know one way to simulate objects
in our solar system is to build the
universe from scratch okay
we'll get to building the universe from
scratch in a sec um but let me just kind
of go through the hierarchy of
what you know what we do two objects two
objects
analytically solvable like we can figure
it out
very easily if you just you don't i
don't think you yeah you don't need to
know calculus
uh it helps to know calculus but you
don't necessarily need to know calculus
um three objects that are
gravitationally
interacting the solution is chaotic
doesn't matter
how many simulations you do you the
answer loses meaning after
um after some time i feel like that is a
metaphor for dating as well but go on
now look yes yeah so so
the fact that you go from analytically
solvable
to unpredictable you know when you are
when your simulation goes from two up
bodies to three bodies
should immediately tell you that the
exercise
of trying to engineer a calculation
where you form this whole
entire solar system from scratch and
hope to have some predictive answer
is is a futile one right we will never
uh succeed at such a simulation just to
clarify you mean like explicitly having
a clear equation that generalizes
the the whole process enough to be able
to make a prediction what do you mean
actually like literally simulating the
objects as a hopeless pursuit
once it increases beyond three the
simulating them is not a hopeless
pursuit but the
outcome becomes a statistical one
and what's actually quite interesting is
i think we have
all the equations uh figured out
right like you know in order to really
understand this
the formation of the the solar system it
suffices to know
gravity and magneto hydrodynamics i mean
like
the combination of uh maxwell's
equations and
you know navier-stokes equations for the
fluids you need to know quantum
mechanics to understand
opacities and and so on but we have
those equations in hand it's not that we
don't
have that understanding it's that
putting it all together
is a very very difficult and b if you
were to run
the same evolution twice
changing you know the initial conditions
by
some infinitesimal amounts i'm you know
minor change in your calculation to
start with you would get the or you'd
get a different answer
this is one this is part of the reason
why planetary systems are so diverse you
don't
have like a you know very predictive
path
for you start with a disk of this mass
and
it's around this star therefore you're
going to form the solar system
right you start with this and therefore
you will conform this huge
outcome a huge set of outcomes and some
percentage of it
will resemble the solar system you
mentioned quantum mechanics and
we're talking about cosmic scale
objects you've talked about that the
evolution of astrophysical disks can be
modeled with
uh schroedinger's equation i sure did
why it's like how does quantum mechanics
uh become relevant at when you
consider the evolution of objects in the
solar system yeah
well let me take a take a step back and
just say like i remember
being you know utterly confused
by quantum mechanics when i first
learned it and
the schrodinger equation which is kind
of the parent equation
of of that whole field you know seems to
come out of nowhere
right the way that the way that i was
sort of explaining it i remember asking
you know my professor is like but where
does it come from is that like well just
just like don't worry about it and just
like calculate the
hydrogen you know energy levels right so
it's like i could do all the problems i
just did not have any intuition for
for where this parent you know super
important equation came from
now down the line i was remember i was
preparing for my own
lecture and i was trying to understand
how waves
travel in self-gravitating discs so
you know again there's a very broad
theory that's already developed but i
was looking for some simpler
way to explain it really for the
purposes of teaching class
and so i i thought okay what if i just
imagine a disc as an infinite uh
number of concentric circles right that
interact with
the with each other gravitationally
that's a problem in some sense that um
i can solve using methods from like the
late 1700s right so i can write down
hamiltonian well i can write down the
energy function basically of their
their interactions and what i
found is that when you take the
continuum limit when you
go from discrete circles that are
talking to each other gravitationally to
a
continuum disk suddenly
this gravitational interaction among
them
right the the governing equation becomes
the schrodinger equation
and i had to think about that for a
little bit did you just unify
quantum mechanics and gravity no this is
not the same thing as like
you know fusing relativity and quantum
mechanics
but it did uh it did get me thinking a
little bit
so the fact that waves in astrophysical
disks
behave just like wave functions of
of particles kind of like an interesting
analogy because for me it's easier to
imagine waves traveling through you know
astrophysical disks or really just
sheets of paper and
the reason this is that analogy exists
is because there's actually nothing
quantum about the schrodinger equation
the schrodinger equation
is just a wave equation
and all of the interpretation that comes
from it
is quantum but the equation itself
is not a quantum being so you can use it
to model
waves it's way it's not turtles it's
waves all the way down
you can pick which level you pick the
wave at and so it could be at the solar
system level that you can use right
and also it actually provides a pretty
neat calculational tool
because um it's it's difficult so we
just talked about simulations but it's
difficult to simulate
the behavior of astrophysical disks on
time scales
that are in between a few orbits
and their entire evolution so it's
over a time scale of a few orbits you
have you do a hydrodynamic you know
simulation
right you do that basically that's
something that you can do
on a modern computer on a time scale of
say a week
when it comes to their evolution over
their entire lifetime you don't hope to
resolve the orbits you just kind of
hope to understand how the system
behaves in between
right you to get access to that as it
turns out it's pretty
um it's pretty cute you can use uh you
can use the schrodinger equation to get
the answer
rapidly so it's a calculational tool
that's fascinating by the way the
astrophysical disks how what are they
how broad is this definition okay so
astrophysical disks span
a huge uh huge amount of ranges
they start maybe at the smallest scale
they start with actually kuiper belt
objects some kuiper belt objects have
rings
so that's maybe the smallest example of
an astrophysical disc
we've got this little potato shaped
asteroid
you know which is you know sort of the
size of la or something and around it
is are some rings of icy matter that
object is a small astrophysical disk
then you have
saturn the rings of saturn you have the
next set of scale you have the solar
system itself when it was forming you
have
this then you have black hole discs
you have galaxies discs are super common
in the universe
and the reason is that stuff rotates
right i mean gravity works yeah so uh
and those rings could be the material
that uh composes those rings could be
it could be gas it could be solid it
could be anything that's right so
the disc that made from which the
planets emerged was predominantly
hydrogen helium gas on the other hand
the rings of saturn
are made up of you know icicles ice
little like
ice cubes this big about a centimeter
across
that sounds refreshing so that's
incredible hydrogen helium gas
so in the beginning it was just hydrogen
and helium
around the sun how does that lead to the
first formations of solid
objects in terms of simulation okay
here's the story um so you're like have
you ever been to the desert
yes i've been to the death valley and
actually it was uh terrifying just as
total tangent i'm distracting you but i
was uh
driving through it and i was really
surprised because it was at first
hot and then as it was getting into the
evening there's this huge thunderstorm
like
it was raining and it got freezing cold
like what the hell is
it was the apocalypse yeah i had to like
just sit there
listening to bruce springsteen i
remember and just thinking i'm probably
going to die
and i was okay with it because bruce
springsteen was on the radio look
when you've got the boss you know you're
ready you're ready to meet the ball
yeah so look i mean it's a good line
so i'm sorry that's true um
yeah by the way like to continue on this
tangent i
i absolutely love the southwest for this
reason just um you know i know during
the pandemic i
drove from la to new mexico a bunch of
times
the madness the weather yeah the the the
chaos of
weather the fact that you know it'll be
blazing hot one minute and then it's
just like
we'll decide to have a little
thunderstorm maybe you'll decide
to go back momentarily to like a
thousand degrees and then go back to the
thunderstorm
it's amazing it's it's that by the way
is chaos theory in action yeah
right um but let's get back to talking
about the desert yeah
so in the desert um tumbleweeds
have a tendency to roll because the wind
rolls them
and if you're careful you'll
occasionally see this family of temple
weeds where like there's like a big one
and then there's a bunch of little ones
that that kind of hide in its
wake right and are all rolling together
and still almost looks like
you know a family of ducks crossing a
street or something
um or for example you know
if you watch tour de france right you've
got a whole bunch of cyclists and
they're like cycling
you know within 10 centimeters of each
other they're not
bffs right yeah but they're not yeah
trying to be
trying to write together they are
writing together to minimize the
collective
uh you know air resistance if you will
that uh
that they experience turns out solids in
the protoplanetary disk do
just this there's an instability
wherein solid particles right things
that are
a centimeter across will start to hide
behind one another and form these clouds
why because cumulatively that minimizes
the solid
component of the disk aerodynamic
interaction with the gas
now these clouds because they're kind of
a favorable
energetic condition for the dust to live
in
they grow grow grow grow grow until they
become so massive that they collapse
under their own weight
that's how the first building blocks of
planets form that's how the
big asteroids got there that's
incredible yeah so that
is that simulatable or is it not useful
to simulate no no that's simulatable
um and people do these types of
calculations
it's it's really cool that's actually
that's
one of the many fields of planet
formation theory that is really really
active
right now people are trying to
understand all kinds of aspects of that
process because of course
i've explained it you know like as if
there's one
thing that happens turns out it's a
it's a beautifully rich dynamic but the
but qualitatively formation of the first
building blocks
actually follows the same sequence as
formation of stars
right stars are just clouds of gas
hydrogen helium gas that sit in space
and slowly cool and at some point they
you know contract to a point where their
gravity overtakes the thermal
you know pressure support if you will
and they collapse under their own weight
and you get a little baby solar system
that's amazing so do you think one day
it will be possible to
simulate the full history
that took our solar system to what it is
today
yes and it will be useless okay
so you don't think your story many of
the ideas that you have about jupiter
clear in the space
like retelling that story in high
resolution is not that important
i actually think it's important but at
every stage
you have to you have to simul you have
to
design your experiments your your
numerical computer experiments so that
they test some specific aspect of that
evolution
um i am not a proponent of doing
huge simulations because um
even if we forget the information theory
aspect of not being able to simulate in
full detail
the universe because if you do then
you you have made an actual universe
it's not
the simulation right by simulation is in
some sense a compression
of information so therefore you must
lose detail
but that point aside if we are
able to simulate
the entire history of the solar system
in excruciating detail
i mean it'll be cool but it's not going
to be
any different from observing it
right because theoretical understanding
which is what
ultimately i'm interested in um
comes from taking complex things and
reducing them down to something
that you know some mechanism that you
can actually quantify
um that's the that's the fun part of
astrophysics
just kind of simulating things in
extreme detail
is we'll cool we'll make cool
visualizations but that doesn't get to
doesn't doesn't get you to any better
understanding than you had
before you did the simulation if you ask
very specific questions then you'll be
able to uh
create like very highly compressed
nice beautiful theories about how things
evolved and then you can use those to
then generalize to other solar systems
to other stars and other galaxies and
say something generalizable about the
entire universe
how difficult would it be to simulate
our solar system such that we would not
know the difference
meaning if we are living in a simulation
is there a nice think of it as a video
game
sure is there a nice compressible way of
doing that or
just kind of like you intuited with a
three body situation
is just a giant mess that you cannot
create a video game
that uh will seem realistic without
actually
building it so i'm you know i'm
speculating but
one of the yeah i know i know like
you have a deep understanding of this
but like for me
i'm just gonna like speculate that for
um at least in the types of simulations
that we can do
today inevitably you run into the
problem of resolution
right you're doesn't matter what you're
doing it is discrete
now um the way you would go
about asking you know if what we're
observing is that a simulation or
uh or is that you know some real
continuous
thing uh is you you zoom in right you
zoom in and try and find
the you know the grid scale if you will
um yeah i mean
it's a it's a really interesting it's a
really interesting question
and because the
solar system itself and really you know
the double pendulum is chaotic
right pendulum sitting on another
pendulum
moves unpredictably once you let them go
um
you really don't need to like inject any
randomness into a simulation for it to
to give you stochastic and unpredictable
answers
weather is a great example of this
weather has a happen of time
of you know typical weather systems have
a happen of time of a few days
and there's a fundamental reason why the
force
forecast always sucks you know two weeks
in advance
it's not that we don't know the
equations that govern
the atmosphere we know them well their
solutions are meaningless though after a
few days
the zooming in thing is very interesting
i
i think about this a lot whether
there'll be a time
soon where we would want to stay in
video game worlds
whether it's virtual reality or just
playing video games i mean i think that
time
like came in like the 90s and it's been
that time well it's not just it's not
just games i mean
it's accelerated i just recently saw
that
wow and fortnite were played 140 billion
hours
and those are just video games yeah and
that's like increasing very very quickly
especially with the people
coming up now and being born now and
become you know becoming teenagers
and so on let's have a thought
experiment where it's just you and a
video game character inside a room
where you remove the simulation they
need to simulate sort of
a lot of objects if it's just you and
that character
how far do you need to simulate in terms
of zooming in
for it to be very real to you as real as
reality
so like first of all you kind of
mentioned zooming in which is
fascinating because
we have these tools of science that
allow us to zoom in
quote unquote in all kinds of ways
uh in the world around us but our
cognitive abilities like our perception
system as humans
is very limited in terms of situations
so we might be very easily fooled
some of the video games like on the ps4
yeah like look pretty real to me yeah
right uh i think
you would really have to interrogate i
mean i think even with what we have
today
like uh i don't know ace combat seven
that's a great example
right like i mean the way that the
clouds are rendered
uh it's i mean it
looks just like when you're flying you
know on a real airplane the
the kind of transparency i think that
the
you know our perception is limited
enough already
to not be able to tell some of the uh
you know some of the differences there's
a game called uh
skyrim it's an elder scrolls role
playing game
and i just uh i played it for quite a
bit
and i think i played very different than
others like
there'll be long searches of time where
i would just walk around and look at
nature
in the game it's incredible oh sure it's
just like the graphics is like
wow i want to stay there it was better i
went hiking recently
it was like as good as hiking so look i
know what you mean
not to go on a huge video game you know
tangent but like
the the third like witcher game was
astonishingly beautiful right especially
like playing on
on a good hardware machine it's like
this is pretty
this is pretty legit that said um
you know i i don't resonate with the i
want to stay
here you know like one of the things
that i love to do
is to go to my like boxing gym
and and box with a guy right like that's
there's
there's nothing quite like that physical
you know
experience like that's fascinating that
might be
simply an artifact of the year you were
born maybe because if you're born today
it almost seems like stupid to go to a
gym yeah
like you're going to a gym to box with a
guy why not box with mike tyson when you
yourself was like in his prime when you
yourself are also an incredible boxer
in the video game world for me there
there's a multitude of reasons why i
don't want to box with mike tyson
right like no no no no you enjoy teeth
and i want to have an ear no but your
your skills
in this meat space in this physical
realm is very limited
and takes a lot of work and you're
you're uh you're a musician
uh your incredible scientist you only
have so much time in the in the day
but in the video game world you can
expand your capabilities in all kinds of
dimensions
that you can never have possibly have
time in the physical world
and so that it doesn't make sense like
to
to be existing to be working your ass
off in the physical world
when you can just be super successful uh
uh in the video game world but i still
you enjoy sucking and stuff
yeah i i really struggling to get better
i sure do
i mean i think like these days with
music music
is a great example right we just started
you know
practicing live uh with my band again
you know after
not playing for a year and uh you know
it's just it was terrible
right which is just kind of a lot of the
nuance
you know a lot of the detail is just
that detail that takes you know
years of collective practice to develop
uh
it's just lost but it was just an
incredible amount of fun
way more fun than all the like studio
you know sitting around and playing uh
that i did you know throughout the
entire year
so i think there's something there's
something intangible
or maybe maybe tangible about being uh
being in person
i i sure hope you're wrong and that
you know we that's not something that
will get lost because i think there's
like such a large part of the human
condition
is to hang out if we were doing this
interview on zoom right
i mean i'd already be i'd already be
bored out of my mind
[Laughter]
exactly i mean there's something to that
i mean i'm almost playing devil's
advocate but at the same time
you know i'm sure people talk about the
same way at the beginning of the 20th
century about horses
where they're they are much more
efficient
they're much uh easier to maintain than
cars
it