The following is a conversation with Konstantin Batygin, 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.

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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 Lux Friedman Podcast, and here's my conversation with Konstantin Batygin.

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 is about five Earth masses.

So that's a hypothesized object.

There's some evidence 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% of the orbital separation of where the Earth is.

It's closer to the sun, Venus is about 70%, then Mars is about 160% further away from

the sun than is the Earth.

These planets that we, one of them we occupy, right, are pretty small, okay?

They're two leading order sort of heavily overgrown asteroids, if you will.

And 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 the separation

from the sun as 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 between Mars and Jupiter,

right?

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 and 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.

Wow, Pluto the planet.

Pluto the dwarf planet, the former planet, you know.

Why is Pluto not a planet anymore?

I mean, it's tiny.

We used to...

So size matters when it comes to planets.

Oh, 100%, 100%.

It's actually a fascinating story.

When Pluto was discovered in 1930, the reason it was discovered in the first place is 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 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, you know, I guess 40 years, Pluto's mass kept getting revised

downwards, downwards, downwards until it was realized that it'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 touch more on that.

That's another discussion.

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 astral 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 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 maybe a factor of one and a half, 1.3 times bigger 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 a little bit smaller.

If you then zoom out 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

in, 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 they're objects which are stable, which

Neptune does not mess with gravitationally, and unstable objects.

The unstable objects are basically all over the place because they're being 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 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 there's

kind of multiple ways to do the exercise, you can either ask the question of if I have

a telescope that has 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?

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 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 ascension 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, 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 Kuiper Belt?

This is the actual stuff we see in the Kuiper Belt.

The way you go about discovering Kuiper Belt objects is pretty easy.

I mean, it's easy in theory, right?

Hard in practice.

All you do is you take snapshots of the sky, right?

Use that direction, say, and take a 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 trees are

going by you faster than the clouds, right?

This is parallax.

That's it.

It's 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, 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 something like 40 times the distance between the earth and the sun and then get reflected

back.

Was that like an hour travel?

Yeah, that's right.

That's something like that because the earth to the sun is eight minutes, I believe.

Something in that order of magnitude.

So that's interesting.

So you have to account for all of that.

And then there's a huge amount of data, pixels that are coming from the pictures and you

have to integrate all of 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, one of them 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.

Not yet.

I don't know.

I don't know for that.

But like the way it works is if you discover one, you right away get a license plate for

it.

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 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

Nine story is called VP113, because Joe Biden was vice president at the time, you know,

got nicknamed Biden.

VP113?

Yeah.

He got nicknamed Biden.

Beautiful.

What's the fingerprint for any particular object?

Like how do you know it's the same one?

Or you 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

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 appear to move only slightly, but then on

the third night will move away.

So that third night is really there to detect acceleration.

Now the thing that I didn't really realize until, you know, I started observing together

with my partner in crime in all this, Mike Brown, is just the fact that for the first

year when you make these detections, the only thing you really know with confidence is where

it is on the night sky and how far away it is, okay?

That's it.

It's all about the orbit because over three days the object just moves so little, right?

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 move.

So then to get some confident information about what its orbit looks like, you have

to come back a year later and then measure it again.

Oh, interesting.

So three nights then come back a year later and do another three nights so you get the

velocity of the acceleration from the three nights and then you have the maybe the additional

information.

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 really pin down the orbit well.

And from that you're able to construct for that one particular object and 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 COVID these things are a little bit more uncertain, but they've actually been

making great progress with construction.

And so that telescope is just going to sort of scan the night sky every day automatically

and just, it's such an efficient survey that it might increase the census of the distant

Kuiper Belt, the things that I'm interested in by a factor of a hundred.

I mean that would be, that would be really cool.

And yeah, that's a, that's an incredible...

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.

Now you can study it.

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 a year to determine the orbit.

And over time you figure out if sort of from a cosmic perspective, this, this whole thing

works.

Yeah.

I have no dating advice to give.

I was going to use this as a metaphor to somehow map it onto the human condition.

Okay.

You mentioned the Kuiper Belt.

What's the Oort cloud?

If you look at the Neptune orbit as a one, then the Kuiper Belt is like 1.3 out there

and then we get farther and farther into the darkness.

What's the Oort cloud?

So okay, you've got the kind of main Kuiper Belt, which is about say 1.3, 1.5.

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 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.

Now if you keep moving out, okay, eventually once you're at sort of 10,000 to 100,000 roughly,

that's where the Oort cloud is.

Now the Oort cloud is a distinct population of icy bodies and is distinct from the Kuiper

Belt.

In fact, it's so expansive that it ends roughly halfway between us and the next star.

It's edge is just dictated by to what extent does the solar gravity reach.

Solar gravity reaches that far?

So it has to, wow, 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, 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 and occasionally like a comet will come in and it seemingly comes

out of nowhere.

The reason these long period comets appear on very, very long timescales, right?

These Oort cloud objects that are sitting 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 in the night sky, et cetera, but they're all coming from 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 environment.

I don't know.

I think that probably in the age of the solar system have literally been zero collisions

in the Oort cloud.

Wow.

So if you like draw a picture of the solar system, everything's really close together.

So everything I guess here is spaced far apart.

Do rogue planets like fly in 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.

We've seen a couple of them in the last three or so years, maybe four years now.

The first one was the one called Uamuamua and 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 constantly ejecting Kuiper belt objects into interstellar space.

Our solar system itself is sort of leaking icy debris and ejecting it.

So presumably every planetary systems around other stars do exactly the same thing.

Let me ask you about the millions of objects that are part of the Kuiper belt and part

of the Oort 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.

Yeah.

Like how many of them do you think have life, like bacterial life?

Probably a negligible amount.

Zero with like a plus on top.

Right.

Zero plus plus.

Yeah.

So, you know, if you and I took a little trip to the interstellar medium, I think we would

develop cancer and die 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 idea of, you know, life kind of traveling between places, it's not

entirely implausible, but 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 think you require water, but, and that's certainly the case

for the earth, but you know, 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.

I mean, like we know that there are planets around almost every star.

Of course there are other life forms.

Life is not some specific thing that happened on the earth and that's it, right?

That's a statistical impossibility.

Yeah.

Yeah, but 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, like formalizing

a kind of picture of, in terms of the mechanism we would use 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 maybe not even a rock,

something else?

I got to tell you, I want to know what life is, okay?

And I want you to show me.

I think there's a song to basically accompany every single thing we talk about today and

probably half of them are love songs 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, it's entirely plausible.

I think there's intelligent life on earth 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 a definition of intelligence, they're pretty good and then humans are pretty

good in that regard.

And then there's like pigs are very intelligent.

I got actually a chance to hang out with pigs recently and they're, aside from the fact

they were trying to eat me, they love food, they love food, but there's an intelligence

to their eyes that was kind of like haunts me because I also love to eat meat and then

to meet the thing I later ate and that was very intelligent and almost charismatic with

the way he was expressing himself, herself, itself was quite incredible.

So all that to say is if we have intelligent life here on earth, if you take dolphins,

pigs, humans, from the perspective of like planetary science, how unique is earth?

Okay.

So earth is not a common outcome of the planet formation process.

It's probably a something on the order of maybe a 1% effect.

And by earth, I mean not just an earth mass planet, okay?

I mean the architecture of the solar system that allows the earth to exist in its kind

of very temperate way.

One thing to understand and this is pretty crucial, right, is 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 disk 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 two, three decades discovered thousands of extra solar planets

as an orbit or other stars.

What we see is that many of them 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, well, at least in most places, that's why the atmosphere is not completely

opaque.

With that, you know, kind of thinking in mind, I would argue that we're getting the kind

of emergent pictures that the earth is not, you know, everywhere, right?

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 even a low probability event, even if you imagine that earth is a one in a million

or one in 10 million occurrence, there are 10 to the 12 stars in the galaxy, right?

So you just, you always win by, that's right, by supply.

They save you.

Well, you've hypothesized that our solar system once possessed a population of short period

planets that were destroyed by the evil Jupiter migrating through the solar nebula.

Can you explain?

Well, if I was to say what was the kind of the key outcome of searches for extra solar

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 and have orbital periods that kind of range from days

to weeks.

Now if you go 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 think, you know, from the sun is not some, you know, special star that decided that it

was going to form the solar system.

So I think, you know, the natural thing to assume 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 planets.

So then we asked ourselves, would such a system survive to this day?

And the answer is no, at least our calculations suggested 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 Jupiter look like?

Like, why was it wandering?

It didn't have the orbit it has today?

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 just in a qualitative sense, they form in this fluid disk of gas and dust.

So it's kind of like, okay, if I plop down a raft somewhere in the ocean, will it stay

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 advected by the

currents of gas and dust, but the way it migrates is it carves out a hole in the disk and then

by interacting with the disk gravitationally, it can change its orbit.

The fact that the solar system has both Jupiter and Saturn here complicates things a lot because

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 last million years of the lifetime of the solar system's primordial disk.

So while this is happening, if our calculations are correct, which I think they are, you can

destroy 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 Jupiter clears out the space, and then there's a few terrestrial planets that come

in and those come in from the disk somewhere, like one of the larger objects?

What actually happens in these calculations, you leave behind a rather mass depleted, like

remnant disk, only a couple Earth masses.

So then from that remnant population, annulus of material, over a hundred million years,

by just collisions, you grow the Earth and the Moon and everything else.

You said annulus?

Annulus.

Annulus.

Annulus, yeah.

That's a beautiful word.

What does that mean?

Well, it's like a disk that's kind of thin.

It's like a, yeah, it's something that is, you know, a disk that's so thin it's almost

flirting with being a ring.

Like I was going to say, this reminds me of Lord of the Rings, so like this, the word

just feels like it belongs in a token though.

Yeah.

Okay.

So that's incredible.

And so that, in your senses, you said like 1%, that's a rare, the way Jupiter and Saturn

danced and cleared out 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 even 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 like stars.

They themselves, like you kind of have to score an A minus or better on the planet formation

test to become a solar system analog, even in that basic sense.

And moreover, you know, lower mass stars, which are very numerous in the galaxy, so

called M dwarfs, think like 0% 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.

I mean, 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, and then eventually you get the Jupiter and the

Saturn that clear out a disk, 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, every other star in the

galaxy, and then be able to do that for other galaxies as well.

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 just not that hard.

But you know, 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.

There's gravity, like yeah, I guess it's important to try to, 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.

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,

I don't think you, yeah, you don't need to know calculus.

It helps to know calculus, but you don't necessarily need to know calculus.

Three objects that are gravitationally interacting, the solution is chaotic.

Doesn't matter how many simulations you do, the answer loses meaning after some time.

I feel like that is a metaphor for dating as well, but go on.

Now look, yeah, so the fact that you go from analytically solvable to unpredictable, you

know, when your simulation goes from two bodies to three bodies should immediately tell you

that the exercise of trying to engineer a calculation where you form the entire solar

system from scratch and hope to have some predictive answer is a futile one, right?

We will never succeed at such a simulation.

I feel like, just to clarify, you mean like explicitly having a clear equation that generalizes

the whole process enough to be able to make a prediction, or do you mean actually like

literally simulating the objects is a hopeless pursuit once it goes beyond three?

The simulating them is not a hopeless pursuit, but the outcome becomes a statistical one.

What's actually quite interesting is I think we have all the equations figured out, right?

You know, in order to really understand this, the formation of the solar system, it suffices

to know gravity and magnetohydrodynamics, I mean, like a combination of Maxwell's equations

and Navier Stokes equations for the fluids.

You need to know quantum mechanics to understand the capacities 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 amount, some, you know, minor change in your

calculation to start with, you would 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, 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 Schrodinger's

equation.

I sure did.

Why?

Like, how does quantum mechanics become relevant when you consider the evolution of objects

in the solar system?

Yeah.

Well, let me 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 that whole field,

you know, seems to come out of nowhere, right?

The way that I was sort of explaining it, I remember asking, you know, my professor

is like, but where does it come from?

And I'm like, well, it's 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 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 disks.

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 thought, okay, what if I just imagine a disk as an infinite number of concentric

circles, right?

That interact with each other gravitationally.

That's a problem in some sense that I can solve using methods from like the late 1700s.

I can write down Hamiltonian, well, I can write down the energy function basically of

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 governing equation becomes the Schrodinger equation.

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 get me thinking a little bit.

So the fact that waves in astrophysical disks behave just like wave functions of particles

is 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 not turtles.

It's waves all the way down.

You can pick which level you pick the wave at.

So it could be at the solar system level that you can use it.

And also it actually provides a pretty neat calculational tool because it's difficult.

So we just talked about simulations, but it's difficult to simulate the behavior of astrophysical

disks on timescales that are in between a few orbits and their entire evolution.

So it's over a timescale 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 timescale

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?

To get access to that, as it turns out, it's pretty, it's pretty cute.

You can use, you can use the Schrodinger equation to get the answer rapidly, so it's a calculational

tool.

That's fascinating.

So astrophysical disks, how, what are they?

How broad is this definition?

Okay.

So astrophysical disks span a huge, 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 disk.

You've got this little potato shaped asteroid, you know, which is, you know, sort of the

size of LA or something, and around it 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 a disk.

Then you have black hole disks.

You have galaxies.

Disks are super common in the universe.

The reason is that stuff rotates, right?

I mean, that's...

Yeah.

So, and those rings could be the material that composes those rings could be, it could

be gas, it could be solid, it could be anything.

That's right.

So, the disk 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, icicle, ice, little

like ice cubes this big, about a centimeter across.

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.

So, you're like, have you ever been to the desert?

Yes.

I've been to the Death Valley and actually it was terrifying, just a total tangent, I'm

distracting you.

No.

But I was 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.

I'm like, what the hell?

It was the apocalypse.

Yes.

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.

But look, when you've got the boss, you're ready to meet the boss.

Yeah.

So, look, I mean.

That's a good line.

Anyway, sorry.

That does, yes.

It's true.

Yeah.

By the way, to continue on this tangent, I absolutely love the Southwest for this reason.

During the pandemic, I drove from LA to New Mexico a bunch of times.

The madness of weather?

Yeah.

The chaos.

The madness of weather, the fact that it will be blazing hot one minute and then it's just

like, we'll decide to have a little thunderstorm, maybe we'll decide to go back momentarily

to like a thousand degrees and then go back to the thunderstorm.

It's amazing.

It's that, by the way, is chaos theory in action.

Right.

But let's get back to talking about the desert.

So, in the desert, tumbleweeds have a tendency to roll because the wind rolls them.

And if you're careful, you'll occasionally see this family of tumbleweeds where there's

like a big one and then a bunch of little ones that kind of hide in its wake and are

all rolling together and almost looks like a family of ducks crossing the street or something.

Or for example, if you watch Tour de France, you've got a whole bunch of cyclists and they're

like cycling within 10 centimeters of each other.

They're not BFFs, right?

They're not trying to be, trying to ride together.

They are riding together to minimize the collective air resistance, if you will, that they experience.

Turns out solids in the protoplanetary disk do just this.

There's an instability wherein solid particles, 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 this 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.

And people do these types of calculations.

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 beautifully rich dynamic, 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 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 design your experiments,

your numerical computer experiments so that they test some specific aspect of that evolution.

I am not a proponent of doing huge simulations because 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 have made an actual universe.

It's not the simulation, right?

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, comes from

taking complex things and reducing them down to something that, you know, some mechanism

that you can actually quantify.

That's the fun part of astrophysics, just kind of simulating things in extreme detail

is we'll make cool visualizations, but that doesn't get you to any better understanding

than you had before you did the simulation.

So if you ask very specific questions, then you'll be able to 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 then

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,

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 will

seem realistic without actually building your solar system from scratch?

I'm speculating, but one of the, yeah, I know you have a deep understanding of this, but

for me, I'm just going to speculate that for at least in the types of simulations that

we can do today, inevitably, you run into the problem of resolution, right?

Doesn't matter what you're doing, it is discrete.

Now, the way you would go about asking, you know, what we're observing, is that a simulation

or is that, you know, some real continuous thing, is you zoom in, right?

You zoom in and try and find the, you know, the grid scale, if you will.

Yeah, I mean, it's a really interesting question, and because the solar system itself and really,

you know, the double pendulum is chaotic, right?

From sitting on another pendulum, it moves unpredictably once you let them go.

You really don't need to, like, inject any randomness into a simulation for it to give

you stochastic and unpredictable answers.

Weather is a great example of this.

Weather has a lapen of time of, you know, typical weather systems have a lapen 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 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 came, I mean, it's accelerated.

I just recently saw that WoW and Fortnite were played 140 billion hours, and those are

just video games.

And that's, like, increasing very, very quickly, especially with the people coming up now,

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 in the world around us.

But our cognitive abilities, like our perception system as humans, is very limited in terms

of zooming in.

So we might be very easily fooled.

Some of the video games, like, on the PS4, like, look pretty real to me, right?

I think, you know, you would really have to interrogate, I mean, I think even with what

we have today, like, I don't know, Ace Combat 7 is a great example, right?

Like, I mean, the way that the clouds are rendered, it's, I mean, it looks just like

when you're flying, you know, on a real airplane, 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, you know, some of the differences.

There's a game called Skyrim.

It's an Elder Scrolls role playing game.

And I just, I played it for quite a bit.

And I think I played it very different than others.

Like, there'll be long stretches 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 third, like, Witcher

game was astonishingly beautiful, right?

Especially like playing 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, like you're going to a gym to box with

a guy.

Why not box with Mike Tyson when you yourself is 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.

No, no, no, no.

I enjoy teeth, you know, 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 a musician, you're an incredible scientist.

You only have so much time in the, in the day, but in the video game world, you can

expand your capabilities and 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 in the video game world.

But I still, you enjoy sucking and stuff.

Yeah, 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 with my band again, you know, after not playing

for a year and you know, it's just, it was terrible.

Like it was 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.

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 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, being in person.

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.

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 easier to maintain than cars.

It doesn't make sense to have, you know, all the ways that cars break down and there's

not enough infrastructure in terms of roads for cars.

It doesn't make any sense.

Like horses and like nature, you could do the nature, like where, you know, you should

be living more natural life.

Horses are real.

You don't want machines in your life that are going to pollute your mind and the minds

of young people, but then eventually just cars took over.

So in that same way, it just seems, going back to horses, I'm just, you know, well,

you can be, you can play, what is it?

Red dead, red dead redemption, redemption, and that you can ride horses in the video

game world.

That's true.

So let me return us back to planet nine.

Always a good place to come back to.

So now that we did a big historical overview of our solar system, what is planet nine?

Okay.

Planet nine is a hypothetical object that orbits the solar system, right?

On orbital period of about 10,000 years and an orbit, which is slightly tilted with respect

to the plane of the solar system, slightly eccentric and the object itself we think is

five times more massive than the earth.

We have never seen planet nine in a telescope, but we have gravitational evidence for it.

And so this is where all the stuff we've been talking about, this clustering ideas, maybe

you can speak to the approximate location that we suspect.

And also the question I wanted to ask is what are we supposed to be imagining here?

Because you said there are certain objects in the Kuiper Belt that are kind of have a

direction to them that they're all like flocking in some kind of way.

So that's the sense that there's some kind of gravitational object, not changing their

orbit, but kind of confining them, like grouping their orbits together.

See, what would happen if planet nine were not there is these orbits that roughly share

a common orientation, they would just disperse, right?

They would just become as a mutually symmetric point everywhere.

Planet nine's gravity makes it such that these objects stay in a state that's basically anti

aligned with respect to the orbit of planet nine and sort of hang out there and kind of

oscillate on a timescale of about a billion years.

That's one of the lines of evidence for the existence of planet nine.

There are others.

That's the one that's easiest to maybe visualize just because it's fun to think about orbits

that all point into the same direction, but I should, you know, emphasize that, for example,

the existence of objects, again, Kuiper Belt objects that are heavily out of the plane

of the solar system, things that are tilted by say 90 degrees, that's not, we don't expect

that as an outcome of planet formation.

Indeed, planet formation simulations have never produced such objects without some extrinsic

gravitational force.

Planet nine, on the other hand, generates them very readily, so that provides kind of

an alternative, you know, population of small bodies in the solar system that also get produced

by planet nine through an independent kind of gravitational effect.

So they're kind of, there's basically five different things that planet nine does individually

that are like kind of maybe a one sigma effect where you'd say, yeah, okay, if that's all

it was, maybe it's not, no reason to jump up and down, but because it's a multitude

of these puzzles that all are explained by one hypothesis, that's really the magnetism,

the attraction of the planet nine model.

So can you just clarify, so most orbit, most planets in the solar system orbit at approximately

the same, so it's flat.

Yeah, it's like one degree.

The difference between them is about one degree.

But nevertheless, if we looked at our solar system, it would look, and I could see every

single object, it would look like a sphere.

The inner part where the planets are would look like, you know, flat, right?

The Kuiper belt and the asteroid belt have a larger, it gets fatter and fatter and fatter

and becomes a sphere.

That's right.

And if you look at the very outside, it's polluted by this quasi spheroidal thing.

Nobody's of course ever seen the Oort cloud, right?

We've only seen comments that come from the Oort cloud so that the Oort cloud, which is

this, right, population of distant debris, its existence is also inferred.

You could say alternatively, there is, you know, there's a big cosmic creature that occasionally,

you know, sitting at 20,000 AU and occasionally throws an icy rock towards the sun like that.

Spaghetti monster, I think it's called.

Okay.

I mean, so it's a mystery in many ways, but you can kind of infer a bunch of things about

it.

And by the way, both terrifying and exciting that there's this vast darkness all around

us that's full of objects that they're just throwing.

Just there.

Yeah.

It's actually kind of astonishing, right, that we have only explored a small fraction

of the solar system, right?

That really kind of baffles me because I remember as a student, you know, studying physics,

you know, you do the problem where you put the earth around the sun, you solve that and

like, it's one line of math and you say, okay, well, that surely was figured out by Newton.

So like all the interesting stuff is not in the solar system, but that it's just plainly

not true.

There are mysteries in the solar system that are remarkable that we are only now starting

to just kind of scratch the surface of.

And some of those objects probably have some information about the history of our solar

system.

Absolutely.

Like a great example is, you know, small meteorites, right?

Small meteorites are melted, right?

They have, they're differentiated, meaning some of the iron sinks, you say, well, how

can that be?

Because they're so small that they wouldn't have melted just from the heat of their accretion.

Turns out the fact that the solar nebula, the disk that made the planets was polluted

by aluminum 26 is in itself a remarkable thing.

It means the solar system did not form in isolation.

It formed in a giant cloud of thousands of other stars that were also forming, some of

which were undergoing, you know, going through supernova explosions, some of, and releasing

these unstable isotopes that, of which we now see kind of the traces of.

It's so cool.

Do you think it's possible that life from other solar systems was injected and that

was what was the origin of life on Earth?

Yeah, the Panspermia idea.

That's seen as a low probability event by people who studied the origin of life, but

that's because then they would be out of a job.

Well, I don't think they'd be out of the job because you just then say, you have to figure

out how life started there.

But then you have to go there.

We can study life on Earth much easier.

We could study it in the lab much easier because we can replicate conditions there from an

early Earth much easier from a chemistry perspective, from a biology perspective.

You can intuit a bunch of stuff.

You can look at different parts of Earth and just.

To an extent, I mean, the early Earth was completely unlike the current Earth, right?

There was no oxygen.

So one of my colleagues at Caltech, Joe Kirshnik, is certain, something like 100% certainty

that life started on Mars and came to Earth on Martian meteorites.

This is not a problem that I like to kind of think about too much, like the origin of

life.

It's a fascinating problem, but you know, it's not physics and I just like, I just don't

love it.

It's the same reason you don't love, I thought you're a musician, so music is not physics

either.

So why are you so into it?

It's 100% physics.

No, no, look, in all seriousness though, there are a few things that I really, really enjoy.

I genuinely enjoy physics.

I genuinely enjoy music.

I genuinely, you know, enjoy martial arts and I genuinely enjoy my family.

I should have said that all in a reverse order or something, but I like to focus on these

things and not worry too much about everything else.

You know what I mean?

Yes.

Just because there is a, like you said earlier, there's a time constraint.

You can't do it all.

There's many mysteries all around us.

And they're all beautiful in different ways.

To me, that thing I love is artificial intelligence that perhaps I love it because eventually

I'm trying to suck up to our future overlords.

The question of, you said there's a lot of kind of little pieces of evidence for this

thing that's Planet Nine.

If we were to try to collect more evidence or be certain, like a paper that says, like

you drop it, clear, we're done.

What does that require?

Are sending probes out or do you think we can do it from telescopes here on earth?

What are the different ideas for conclusive evidence for Planet Nine?

The moment Planet Nine gets imaged from a telescope on earth, it's done.

I mean, it's just there.

Can you clarify it?

Cause you mentioned that before from an image, would you be able to tell?

Yes.

So from an image, the moment you see something, something that is reflecting sunlight back

at you and you know that it's hundreds of times as far away from the sun as the earth,

you're done.

So you're thinking, so basically if you have a really far away thing that's big, five times

the size of earth, that means that is Planet Nine.

Could there be multiple objects like that?

I guess.

In principle, yeah.

I mean, there's no law of physics that doesn't allow you to have multiple, there's also no

evidence at present for there being multiple.

I wonder if it's possible, just like we're finding exoplanets, whether given the size

of the Oort Cloud, there's basically, it's rarer and rarer, but there are sprinkled Planet

Nine, 10, 11, 12, like these, some.

Got 13.

It goes after that.

I can just keep counting.

So just something about the dynamic system, it becomes lower and lower probability event,

but they gather up, they become larger and larger maybe, something like that.

I wonder if discovering Planet Nine will just be almost like a springboard, it's like, well,

what's beyond that?

It's entirely plausible.

The Oort Cloud itself probably holds about five earth masses or seven earth masses of

material.

Right, so it's not nothing.

And it all ultimately comes down to at what point will the observational surveys sample

enough of the solar system to kind of reveal interesting things.

There's a great analogy here with Neptune and the story of how Neptune was discovered.

Neptune was not discovered by looking at the sky, right?

It was discovered mathematically, right?

So yeah, the orbit of Uranus, when Uranus was found, this was 1781, both the tracking

of the orbit of Uranus as well as the reconstruction of the orbit of Uranus immediately revealed

that it was not following the orbit that it was supposed to, right?

The predicted orbit deviated away from where it actually was.

So in the mid 1800s, right, a French mathematician by the name of Orban Le Verrier did a beautifully

sophisticated calculation which said if this is due to gravity of a more distant planet,

then that planet is there, okay?

And then they found it.

But the point is the understanding of where to look for Neptune came entirely out of celestial

mechanics.

The case with Planet Nine is a little bit different because what we can do I think relatively

well is predict the orbit and mass of Planet Nine.

We cannot tell you where it is on its orbit.

The reason is we haven't seen the Kuiper Belt objects complete an orbit, their own orbit,

even once because it takes 4,000 years.

But I plan to live on as an AI being, and I'll be tracking those orbits as, you know,

for…

So it takes 4,000 or 5,000 years.

I mean, it doesn't have to be AI.

It could be longevity.

There's a lot of really exciting genetic engineering research.

So you'll just be a brain waiting for the, your brain waiting for the orbit to complete

for the basic Kuiper Belt objects.

That's right.

That's like kind of the worst reason to want to live a long time, right, just like can

the brain like smoke a cigarette?

I know, right?

Can you just like light one up while you're waiting or?

But you're making me actually realize that the one way to explore the galaxy is by just

sitting here on Earth and waiting.

So if we can just get really good at waiting, it's like a mua mua or these interstellar

objects that fly in, you can just wait for them to come to you.

Same with the aliens.

You can wait for them to come to you.

If you get really good at waiting, then that's one way to do the exploration because eventually

the thing will come to you.

Maybe that's the, maybe the intelligent alien civilizations get much better at waiting,

and so they all decide, so game theoretically, to start waiting, and it's just a bunch of

like ancient intelligent civilizations of aliens all throughout the universe, they're

just sitting there waiting for each other.

Look, you can't just be good at waiting.

You gotta know how to chill, okay?

Like you can't just like sit around and do nothing.

You gotta be, you gotta know how to chill.

I honestly think that as we progress, if the aliens are anything like us, we enjoy loving

things we do, and it's very possible that we just figure out mechanisms here on Earth

to enjoy our life, and we just stay here on Earth forever, that exploration becomes less

and less of an interesting thing to do, and so you basically, yes, wait and chill.

You get really optimally good at chilling, and thereby exploring is not that interesting,

so in terms of 4,000 years, it would be nothing for scientists.

We'll be chilling and just all kinds of scientific explorations will become possible because

we'll just be here on Earth.

So chill.

So chill.

You have a paper out recently, because you already mentioned some of these ideas, but

I'd love it if you could dig into it a little bit.

Yeah, of course.

The injection of inner Oort Cloud objects into the distant Kuiper Belt by Planet Nine.

What is this idea of Planet Nine injecting objects into the Kuiper Belt?

Okay, let me take a brief step back, and when we do calculations of Planet Nine, when we

do the simulations, as far as our simulations are concerned, sort of the Neptune, like kind

of the transneptunian solar system is entirely sourced from the inside, namely the Kuiper

Belt gets scattered by Neptune, and then Planet Nine does things to it and aligns the orbits

and so on, and then we calculate what happens on the lifetime of the solar system, yada,

yada, yada.

During the pandemic, one of the kind of questions we asked ourselves, and this is indeed something

we, Mike and I, Mike Brown, who's a partner in crime on this, and I do regularly, is we

say how can we A, disprove ourselves, and B, how can we improve our simulations?

Like what's missing?

One idea that maybe should have been obvious in retrospect is that all of our simulations

treated the solar system as some isolated creature, right?

But the solar system did not form in isolation, right?

It formed in this cluster of stars, and during that phase of forming together with thousands

of other stars, we believe the solar system formed this almost spherical population of

icy debris that sits maybe at a few thousand times the separation between the Earth and

the Sun, maybe even a little bit closer.

If Planet Nine's not there, that population is completely dormant, and these objects just

slowly orbit the Sun.

Nothing interesting happens to them ever, but when we realize that if Planet Nine is

there, Planet Nine can actually grab some of those objects and gravitationally reinject

them into the distant solar system.

So we thought, okay, let's look into this with numerical experiments.

Do our simulations, does this process work, and if it works, what are its consequences?

So it turns out, indeed, not only does Planet Nine inject these distant inner Oort cloud

objects into the Kuiper Belt, they follow roughly the same pathway as the objects that

are being scattered out.

So there's this kind of river, two way river of material.

Some of it is coming out by Neptune scattering, some of it is moving in.

And if you work through the numbers, you kind of, at the end of the day, it has an effect

on the best fit orbit for Planet Nine itself.

So if you realize that the data set that we're observing is not entirely composed of things

that came out of the solar system, but also things that got reinjected back in, then turns

out the best fit Planet Nine is slightly more eccentric.

That's kind of getting into the weeds.

The point here is that the existence of Planet Nine itself provides this natural bridge that

connects an otherwise dormant population of icy debris of the solar system with things

that we're starting to directly observe.

So it can flow back, so it's not just a river flowing one way, it's maybe a smaller stream

going back.

Backwash.

You want a backwash, you want to incorporate that into the simulations, into your understanding

of those distant objects when you're trying to make sense of the various observations

and so on.

Exactly.

That's fascinating.

I gotta ask you, some people think that many of the observations that you're describing

could be described by a primordial black hole.

First, what is a primordial black hole and what do you think about this idea?

So primordial black hole is a black hole which is made not through the usual pathway of making

a black hole, which is that you have a star, which is more massive than 1.4 or so solar

masses and basically when it runs out of fuel, runs out of its nuclear fusion fuel, it can't

hold itself up anymore and just the whole thing collapses on itself, right?

You create a, I mean one, I guess, simple way to think about it is you create an object

with zero radius, that has mass but zero radius, that singularity.

Now such black holes exist all over the place.

In the galaxy, there's in fact a really big one at the center of the galaxy that's like,

that one's always looking at you when you're not looking, okay, and it's always talking

about you.

And when you turn off the lights, it wakes up.

That's right.

So such black holes are all over the place.

When they merge, we get to see incredible gravitational waves that they emit, etc, etc.

One kind of plausible scenario, however, is that when the universe was forming, basically

during the Big Bang, you created a whole spectrum of black holes, some with masses of five Earth

masses, some with masses of 10 Earth masses, like the entire, you know, mass spectrum size,

some the massive asteroids.

Now on the smaller end, over the lifetime of the universe, the smaller ones kind of

evaporate and they're not there anymore.

At least this is what we, what the calculations tell us.

But five Earth masses is big enough to not have evaporated.

So one idea is that Planet Nine is not a planet and instead it is a five Earth mass black

hole.

And that's why it's hard to find.

Now can we right away from our calculations say that's definitely true or that's not true?

Absolutely not.

We can't, in fact, our calculations tell you nothing other than the orbit and the mass.

And that means the black hole, I mean, it could be a five Earth mass, you know, cup.

It could be a five Earth mass hedgehog or a black hole or really anything that's five

Earth masses will do because the gravity of a black hole is no different than the gravity

of a planet, right?

If the sun became a black hole tomorrow, it would be dark, but the Earth would keep orbiting

it.

And like this notion that, oh, black holes suck everything in, it's not, that's like

a sci fi notion.

All right.

It's just mass.

What would be the difference between a black hole and a planet in terms of observationally?

Probably the difference would be that you will never find the black hole, right?

The truth is they're kind of, I'm actually not, you know, I never looked into this very

carefully, but there are some constraints that you can get just statistically and say,

okay, if the sun has a binary companion, which is a five Earth mass black hole, then that

means such black holes would be extremely common and, you know, you can sort of look

for lensing events and then you say, okay, maybe that's not so likely.

But you know, that said, I want to emphasize that there's a limit to what our calculations

can tell you.

That's the orbit and the mass.

So I think there's a bunch, like Ed Witten, I think wishes it's a black hole because I

think one exciting things about black holes in our solar system is that we could go there

and we can maybe study the singularity somehow because that allows us to understand some

fundamental things about physics.

If it's a planet, so planet nine, we may not, you know, and we go there, we may not discover

anything profoundly new.

The interesting thing, perhaps you can correct me about planet nine is like the big picture

of it.

The whole big story of the Kuiper belt and all those kinds of things.

It's not that planet nine would be somehow fundamentally different from, I don't know,

Neptune in terms of, in terms of the kind of things we could learn from it.

So I think that there's kind of a hope that it's a black hole because it's an entirely

new kind of object.

Maybe you can correct me on that.

Yeah.

I mean, of course here, my own biases creep in because I'm interested, you know, in planets

around other stars.

And I would say, I would disagree that, you know, we wouldn't find things that would be

truly, you know, fundamentally new because as it turns out, the galaxy is really good

at making five or three earth mass objects, right?

The most common type of planet that we see, that we, you know, discover orbiting around

other stars is a few earth masses.

In the solar system, there's no analog for that, right?

We go from one earth mass object, which is this one and to skipping to Neptune and Uranus,

which themselves are actually relatively poorly understood, especially Uranus from the interior

structure point of view.

If planet nine is a planet, going there will give us the closest window into understanding

what other planets look like.

And I will, you know, I'll say this, that, you know, planets kind of in terms of their

complexity on some logarithmic scale fall somewhere between a star and an insect, right?

An insect is way more complicated than a star, right?

Just all kinds of physical processes and really biochemical processes that occur inside of

an insect that just make a star look like, you know, somebody is like playing with a

spring or something, right?

So the, I think, you know, it would be, you know, arguably, you know, more interesting

to go to, you know, to go to planet nine if it's a planet, because black holes are simple.

They're just kind of, they're basically macroscopic like particles, right?

Yeah.

And so just like a star that you mentioned in terms of complexity.

So it's possible that planet nine is supposed to being like homogeneous is like super like

heterogeneous is a bunch of cool stuff going on that could give us an intuition.

I never thought about that, that it's basically Earth number two in terms of size and gives

us, starts giving us intuition that could be generalizable to Earth like planets elsewhere

in the galaxy.

I mean, yeah, Pluto is also in the sense like, you know, Pluto is a tiny, tiny thing, right?

Just like you would imagine that it's just a tiny ball of ice, like who cares, but the

New Horizons images of Pluto reveal so much remarkable structure, right?

They reveal glaciers flowing and these are glaciers not made out of water ice, but you

know, CO ice, it turns out at those temperatures, right, of like 40 or so Kelvin, water ice

looks like metal, right?

It just doesn't flow at all, but then ice made up of carbon monoxide starts to flow.

I mean, there's just like all kinds of really cool phenomena that you otherwise just wouldn't

really even imagine that occur.

So yeah, I mean, there's a reason why I like planets.

Well, let me ask you, I find as I read the idea that Ed Witten was thinking about this

kind of stuff fascinating.

So he's a mathematical physicist who's very interested in string theory, won the Fields

Medal for his work in mathematics.

So I read that he proposed a fleet of probes accelerated by radiation pressure that could

discover a Planet Nine primordial black holes location.

What do you think about this idea of sending a bunch of probes out there?

Yeah, look, the way the idea is a cool one, right?

You go and you say, you know, launch them basically, isotropically, you track where

they go.

And if I understand the idea correctly, basically measure the deflection and you say, okay,

that must be something there since the probe trajectories are being altered.

Oh, so the measurement, the basic sensory mechanism is the, it's not like you have senses

on the probes.

It's more like you're, because you're very precisely able to capture, to measure the

trajectory of the probes, you can then infer the gravitational fields.

I think that's the basic idea.

You know, back a few years ago, we had conversations like these with, you know, engineers from

JPL.

They more or less convinced me that this is more, much more difficult than it seems because

you don't, at that level of precision, right?

Things like solar flares matter, right?

Solar flares, right, are completely chaotic.

You can't predict which, where a solar flare will happen.

That will drive radiation pressure gradients.

You don't know where every single asteroid is.

So like actually doing that problem, I think it's possible, but it's not a trivial matter,

right?

Well, I wonder, not just about Planet 9, I wonder if that's kind of the future of doing

science in our solar system is to just launch a huge number of probes.

So like a whole order of magnitude, many orders of magnitude, larger numbers of probes, and

then starting for a bunch of different stuff, not just gravity, but everything else.

So in this regard, I actually think there is a huge revolution that's to some extent

already started, right?

The standard kind of like timescale for a NASA mission is that you like propose it and

it launches, I don't know, like 150 years after your proposal.

I'm over exaggerating, but you know, it's just like some huge development cycle and

it gets delayed 55 times, like that is not going away, right?

The really cutting edge things, you have to do it this way because you don't know what

you're building, so to speak.

But the CubeSat kind of world is starting to provide an avenue for like launching something

that costs a few million dollars and has a turnaround timescale of like a couple of years.

You can imagine doing PhD theses where you design the mission, the mission goes to where

you're going, and you do the science all within a time span of five, six years.

That has not been fully executed on yet, but I absolutely think that's on the horizon and

we're not talking a decade, I think we're talking like this decade.

Yeah, and the company is accelerating all this with Blue Origin and SpaceX, and there's

a bunch of more CubeSat oriented companies that are pushing this forward.

Well let me ask you on that topic, what do you think about either one?

Elon Musk with SpaceX going to Mars, I think he wants SpaceX to be the first to put a first

human on Mars, and then Jeff Bezos, gotta give him props, wants to be the first to fly

his own rocket out into space.

Wasn't there a guy who like built his rocket out of garbage?

This was like a couple years ago, and somewhere in the desert he launched himself.

I'm not tracking this closely, but I think I am familiar with folks who built their own

rocket to try to prove the earth is flat.

Yes, that's the guy I'm talking about, he also jumped some limousine.

Truly revolutionary mind, you have to have greater men than either you or I.

It's been astonishing to watch how really over the last decade the commercial sector

took over this industry that traditionally has really been a government thing to do.

Motivated primarily by the competition between nations, like the Cold War, and now it's motivated

more and more by the natural forces of capitalism.

That's right, so here I have many ideas about it.

I think on the one hand, like what SpaceX has been able to do, for example, phenomenal.

If that brings down the price of space exploration, that turnaround time scale for space exploration,

which I think it inevitably will, that's a huge boost to the human condition.

The same time, if we're talking astronomy, it comes at a huge cost, and the Starlink

satellites is a great example of that cost.

In fact, I was just camping in the Mojave with a friend of mine, and they saw this string

of satellites just kind of appear and then disappear into nowhere.

That is beginning to interfere with Earth based observations, so I think there's tremendous

potential there, it's also important to be responsible about how it's executed.

Now with Mars and the whole idea of exploring Mars, I don't have strong opinions on whether

a manned mission is required or not required, but I do think the thing to keep in mind is

that I'm not signed on, if you will, to the idea that Mars is some kind of a safe haven

that we can escape to.

Mars sucks.

Living on Mars, if you want to live on Mars, you can have that experience by going to the

Mojave Desert and camping, and it's just not a great experience.

Well it's interesting, but there's something captivating about that kind of mission of

us striving out into space, and by making Mars in some ways habitable for at least like

months at a time, I think would lead to engineering breakthroughs that would make life in many

ways much better on Earth.

It will come up with ideas we totally don't expect yet, both on the robotics side, on

the food engineering side, on the, maybe we'll switch from, there'll be huge breakthroughs

in insect farming, as exciting as I find that idea to be, in the ways we consume protein.

Maybe it'll revolutionize, we do factory farming, which is full of cruelty and torture of animals,

we'll revolutionize that completely because of our, we shouldn't need to go to Mars to

revolutionize life here on Earth, but at the same time, I shouldn't need a deadline to

get shit done, but I do need it.

And then in the same way, I think we need Mars.

There's something about the human spirit that loves that longing for exploration.

I agree with that thesis, the going to the moon, right, and that whole endeavor has captivated

the imagination of so many, and it has led to incredible ideas, really, and probably

in nonlinear ways, not like, okay, we went to the moon, therefore some person here has

thought of this.

In that similar sense, I think space exploration is, there's some real magnetism about it,

and it's on a genetic level.

We have this need to keep exploring when we're done with a certain frontier, we move on to

the next frontier.

All that I'm saying is that I'm not moving to Mars to live there permanently ever, and

I think that, I'm glad you noted the kind of degradation of the Earth.

I think that is a true kind of the leading order challenge of our time.

That's a great engineering, that's a bunch of engineering problems.

I'm most interested in space, because as I've read extensively, it's apparently very difficult

to have sex in space, and so I just want that problem to be solved, because I think once

we solve the sex in space problem, we'll revolutionize sex here on Earth, thereby increasing the

fun on Earth, and the consequences of that can only be good.

I mean, you can, you've got a clear plan, right, and it sounds like, you know.

I'm submitting proposals to NASA as we speak.

That's right.

I keep getting rejected, I don't know why.

Okay.

You need better diagrams.

Better pictures.

I should have thought of that.

You a while ago mentioned that, you know, there's certain aspects in the history of

the solar system and Earth that resulted, it could have resulted in an opaque atmosphere,

but it didn't, we couldn't see the stars.

And somebody mentioned to me a little bit ago, and it's almost like a philosophical

question for you.

Do you think humans, like human society would develop as it did, or at all, if we couldn't

see the stars?

It would be drastically different.

Just if it ever did develop.

So I think some of the early developments, right, of like, you know, fire, you know.

First of all, that atmosphere would be so hot, because, you know, if you have an opaque

atmosphere, the temperature at the bottom is huge.

So we would be very different beings to start with.

We'd have very different.

It could be cloudy in certain kinds of ways that you could still get.

Okay.

Think about like a greenhouse, right?

A greenhouse is cloudy, effectively, but it's super hot.

Yeah.

It's hard to avoid having an atmosphere.

If you have an opaque atmosphere, it's hard to, right.

Venus is a great example, right?

Venus is, I don't remember exactly how many degrees, but it's hundreds in Celsius, right?

It's not a hundred, it's hundreds.

Even though it's only a little bit closer to the sun, that temperature is entirely coming

from the fact that the atmosphere is thick.

So it's just a sauna of sorts.

Yeah.

Yeah.

You go there, you know, you feel refreshed after you come back, you know.

But if you stay there, I mean, so, okay, take that as an assumption.

This is a philosophical question, not a biological one.

So you have a life that develops under these extremely hot conditions.

Yeah.

So let's see.

So much of the early evolution of mankind was driven by exploration, right?

And the kind of interest in stars originated in part as a tool to guide that exploration,

right?

I mean, that in itself, I think would be a huge, you know, a huge differential in the

way that we, you know, our evolution on this planet.

Yeah.

I mean, stars, that's brilliant.

So even in that aspect, but even in further aspects, astronomy just shows up in basically

every single development in the history of science up until the 20th century, it shows

up.

So I wonder without that, if we would have, if we would even get like calculus.

Yeah, look, that's a great, I mean, that's a great point.

Newton in part developed calculus because he was interested in understanding, explaining

Kepler's laws, right?

In general, that whole mechanistic understanding of the night sky, right, replacing a religious

understanding where you interpret, you know, this is, you know, this whatever fire god

riding his, you know, a little chariot across the sky, as opposed to, you know, this is

some mechanistic set of laws that transformed humanity and arguably put us on the course

that we're on today, right?

The entirety of the last 400 years and the development of kind of our technological world

that we live in today was sparked by that, right?

Understanding an effectively, you know, a non secular view of the natural world and

kind of saying, okay, this can be understood and if it can be understood, it can be utilized,

we can create our own variants of this.

Absolutely, we would be a very, very different species without astronomy.

This I think extends beyond just astronomy, right?

There are questions like why do we need to spend money on X, right?

Where X can be anything like paleontology, like, right?

The mating patterns of penguins.

Yeah, that's like, that's right.

I think, you know, there's a tremendous under appreciation for the usefulness of useless

knowledge, right?

I mean, that's brilliant.

I didn't come up with this, this is a little book by the guy who started the Institute

for Advanced Studies, but, you know, it's so true, so much of the electronics that are

on this table, right, work on Maxwell's equations.

Maxwell wasn't sitting around in the 1800s saying, you know, I hope one day, you know,

we'll make, you know, a couple mics so, you know, a couple, you know, a couple guys can

have this conversation, right?

That wasn't at no point was that the motivation, and yet, you know, it gave us the world that

we have today.

The answer is if you are a purely pragmatic person, if you don't care at all about kind

of the human condition, none of this, the answer is, you can tax it, right, like, useless

things have created way more capital than useful things.

And the sad thing, first of all, it's really important to think about, and it's brilliant

in the following context, like Neil deGrasse Tyson has this book about the role of military

based funding in the development of science, and then so much of technological breakthroughs

in the 20th century had to do with humans working on different military things.

And then the outcome of that had nothing to do with military, it had some military application,

but their impact was much, much bigger than military.

The splitting of the atom is a kind of a canonical example of this.

We all know the tragedy that, you know, arises from splitting of the atom, and yet, you know,

so much, I mean, the atom itself does not care for what purpose it is being split.

So I wonder if we took the same amount of funding as we used for war and poured it into

like totally seemingly useless things, like the mating patterns of penguins, we would

get the internet anyway.

I think so, I think so, and, you know, perhaps more of the internet would have penguins,

you know.

So we're both joking, but in some sense, like, I wonder, it's not the penguins, because penguins

is more about sort of biology, but all useless kind of tinkering and all kinds of avenues,

and also because military applications are often burdened by the secrecy required.

So it's often like so much, the openness is lacking, and if we've learned anything for

the last few decades is that when there's openness in science, that accelerates the

development of science.

That's right.

That's true.

That openness of science truly, you know, it benefits everybody, the notion that if,

you know, I share my science with you, then you're going to catch up and like know the

same thing.

That is a short sighted viewpoint, because if you catch up and you open, you know, you

discover something that puts me in a position to do the next step, right?

So I absolutely agree with all of this.

I mean, the kind of question of like military funding versus non military funding is obviously

a complicated one, but at the end of the day, I think we have to get over the notion as

a society that we are going to, you know, pay for this, and then we will get that, right?

That's true if you're buying like, I don't know, toilet paper or something, right?

It's just not true in the intellectual pursuit.

That's not how it works, and sometimes it'll fail, right?

Like sometimes, like a huge fraction of what I do, right?

I come up with an idea, I think, oh, it's great, and then I work it out, it's totally

not great, right?

It fails immediately.

Failure is not a sign that the initial pursuit was worthless, so failure is just part of

this kind of this whole exploration thing, and we should fund more and more of this exploration,

the variety of the exploration.

That's right.

I think it was Linus Pauling or somebody from, you know, that generation of scientists, you

know, a good way to have good ideas is to have a lot of ideas.

Yeah.

So I think that's true.

If you are conservative in your thinking, if you worry about proposing something that's

going to fail and, oh, what if, you know, like, there's no science police that's going

to come and arrest you for proposing the wrong thing, and, you know, it's also just like,

why would you do science if you're afraid of, you know, taking that step?

It'd be so much better to propose things that are plausible, that are interesting, and then

for a fraction of them to be wrong than to just kind of, you know, make incremental progress

all your life, right?

Speaking of wild ideas, let me ask you about the thing we mentioned previously, which is

this interstellar object Amuamua.

Could it be space junk from a distant alien civilization?

You can't immediately discount that by saying absolutely it cannot.

Anything can be space junk.

I mean, from that point of view, can any of the Kuiper Belt objects we see be space junk?

Everything on the night sky can, in principle, be space junk.

And Kuiper Belt would catch interstellar objects potentially and, like, force them into an

orbit if they're, like, small enough?

Not the Kuiper Belt itself, but you can imagine, like, Jupiter family comets being captured,

you know.

So you can actually capture things.

It's even easier to do this very early in the solar system, like, early in the solar

system's life while it's still in a cluster of stars.

It's unavoidable that you capture debris, whether it be natural debris or unnatural

debris, or just debris of some kind from other stars.

It's like a daycare center, right?

Like, everybody passes their infections on to other kids.

Yeah.

You know, Amuamua, there's been a lot of discussion about it, and there's been a lot of interest

in this over, like, is it aliens or is it not?

It's, like, if you just kind of look at the facts, like, what we know about it is it's

kind of, like, a weird shape, and it also accelerated, you know?

Right?

Like, that's the two, those are the two interesting things about it.

There are puzzles about it, and perhaps the most daring resolution to this puzzle is that

it's not, you know, aliens or it's not, like, a rock, it's actually a piece of hydrogen

ice.

Right?

So, this is a friend of mine, you know, Daryl Seligman, Greg Laughlin, came up with this

idea that in giant molecular clouds that are just clouds of hydrogen, helium, gas that

live throughout the galaxy, at their cores, you can condense ice to become these hydrogen,

you know, icebergs, if you will.

And then that explains many of the aspects of, in fact, I think that explains all of

the Oumuamua mystery, how it becomes elongated, because basically the hydrogen ice sublimates

and kind of like a bar of soap that, you know, slowly kind of elongates as you strip away

the surface layers, how it was able to accelerate because of a jet that is produced from, you

know, the hydrogen coming off of it, but you can't see it because it's hydrogen gas, like,

all of this stuff kind of falls together nicely.

I'm intrigued by that idea, truly, because it's like, if that's true, that's a new type

of astrophysical object.

And it would be produced by, what's the monster that produced it initially, that kind of object?

So these giant molecular clouds, they're everywhere.

I mean, the fact that they exist is not...

Are they rogue clouds or are they part of like an Oort cloud?

No, no, they're rogue clouds.

They're just floating about?

Yeah, so if you go, like, a lot of people imagine the galaxy as being a, you know, a

bunch of stars, right, and they're just orbiting, right?

But the truth is, if you fly between stars, you run into clouds.

They don't have any large object that creates orbits, so they're just floating about?

Just floating.

But why are they floating together?

Or they just float together for a time and not...

Well, so these eventually become the nurseries of stars.

So as they cool, they contract and, you know, then collapse into stars or into groups of

stars.

And some of them, the starless molecular clouds, according to the calculations that Daryl

and Greg did, can create these, like, icicles of hydrogen ice.

I wonder why they would be flying so fast, because they seem to be moving pretty fast

at a quick pace.

You mean Oumuamua?

Oumuamua, yeah.

Oh, that's just because of the acceleration due to the sun.

If you stop, it's like, take something really far away, let it go, and the sun is here.

By the time it comes close to the sun, right, it's moving pretty fast.

So that's an attractive explanation, I think, not so much because it's cool, but it makes

a clear prediction, right, of when Vera Rubin Observatory comes online next year or so.

We will discover many, many more of these objects, right?

And they have, so I like theories that are falsifiable.

Not just testable, but falsifiable.

It's good to have a falsifiable theory where you can say, that's not true.

Aliens is one that's fundamentally difficult to say, no, that's not aliens.

Well, the interesting thing to me, if you look at one alien civilization, and then we

look at the things it produces, in terms of if we were to try to detect the alien civilization,

there is like, say there's 10 billion aliens, there would probably be trillions of dumb

drone type things produced by the aliens, and then be many, many, many more orders of

magnitude of junk.

So if you were to look for an alien civilization, in my mind, you would be looking for the junk.

That's the more efficient thing to look for.

So I'm not saying Oumuamua has any characteristics of space junk, but it kind of opened my eyes

to the idea that we shouldn't necessarily be looking to the queen of the ant colony.

We should be looking at, I don't know, I don't know, traces of alien life that doesn't look

intelligent in any way, may not even look like life.

It could be just garbage.

We should be looking for garbage.

Just generically.

Well, garbage that's producible by unnatural forces.

For me at least, that was kind of interesting, because if you have a successful alien civilization,

that we will be producing many more orders of magnitude of junk, and that would be easier

potentially to detect.

Well, so you have to produce the junk, but you have to also launch it.

So this is the, this is where, I mean, let's, let's imagine.

Garbage disposal.

Yeah.

But let's imagine we are a successful civilization that, you know, has made it to space.

We clearly have, right?

And yes, we're in the infancy of that pursuit, but, you know, we've launched, I don't know

how many satellites.

If you count GPS satellites, it must be at least thousands.

It's certainly thousands.

I don't know if it's over 10,000, but it's on that order.

But it's on that, like a large order of magnitude.

How many of the things that we've launched will ever leave the solar system?

I think two.

Two so far.

Well, maybe the Voyager, the Voyager 1, Voyager 2, I don't know if the Pioneer.

So maybe three.

Oh, there's also a Tesla Roadster out there.

That one, it will never leave the solar system.