Lex Fridman Podcast - #355 - David Kipping: Alien Civilizations and Habitable Worlds

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The following is a conversation with David Kipping,

an astronomer and astrophysicist at Columbia University,

director of the Cool Worlds Lab,

and he’s an amazing educator

about the most fascinating scientific phenomena

in our universe.

I highly recommend you check out his videos

on the Cool Worlds YouTube channel.

David quickly became one of my favorite human beings.

I hope to talk to him many more times in the future.

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And now dear friends, here’s David Kipping.

Your research at Columbia is in part focused

on what you call cool worlds

or worlds outside our solar system

where temperature is sufficiently cool

to allow for moons, rings, and life to form

and for us humans to observe it.

So can you tell me more about this idea,

this place of cool worlds?

Yeah, I mean, I think the cool world

is a place where we’re constantly

in contact with the universe.

So we’re constantly in contact with the universe.

So we’re constantly in contact with the universe.

Yeah, the history of discovering planets

outside our solar system was really dominated

by these hot planets.

And that’s just because of the fact

they’re easier to find.

When the very first methods came online,

these were primarily the Doppler spectroscopy method,

looking for wobbling stars,

and also the transit method.

And these two both have a really strong bias

towards finding these hot planets.

Now, hot planets are interesting.

The chemistry in their atmosphere is fascinating.

It’s very alien.

An example of one that’s particularly close to my heart

is TrES-2b, whose atmosphere is so dark,

it’s less reflective than coal.

And so they have really bizarre photometric properties,

yet at the same time,

they resemble nothing like our own home.

And so I said there’s two types of astrophysicists.

The astrophysicists who care about how the universe works.

They wanna understand the mechanics

of the machinery of this universe.

Why did the Big Bang happen?

Why is the universe expanding?

How are galaxies formed?

And there’s another type of astrophysicist,

which perhaps speaks to me a little bit more.

It whispers into your ear.

And that is, why are we here?

Are we alone?

Are there others out there?

And ultimately, along this journey,

the hot planets aren’t gonna get us there.

When we’re looking for life in the universe,

seems to make perfect sense

that there should be planets like our own out there.

Maybe even moons like our own planet

around gas giants that could be habitable.

And so my research has been driven

by trying to find these more traqueous globes

that might resemble our own planet.

So they’re the ones that lurk more in the shadows

in terms of how difficult it is to detect.

They’re much harder.

They’re harder for several reasons.

The method we primarily use is the transit method.

So this is really eclipses.

As the planet passes in front of the star,

it blocks out some starlight.

The problem with that is that not all planets

pass in front of their star.

They have to be aligned correctly from your line of sight.

And so the further away the planet is from the star,

the cooler it is, the less likely it is

that you’re gonna get that geometric alignment.

So whereas a hot Jupiter, about 1% of hot Jupiters

will transit in front of their star,

only about 0.5%, maybe even a quarter of a percent

of Earth-like planets will have

the right geometry to transit.

And so that makes it much, much harder for us.

What’s the connection between temperature of the planet

and geometric alignment,

probability of geometric alignment?

There’s not a direct connection,

but they’re connected via an intermediate parameter,

which is their separation from the star.

So the planet will be cooler

if it’s further away from the star,

which in turn means that the probability

of getting that alignment correct is going to be less.

On top of that,

they also transit their star less frequently.

So if you go to the telescope

and you want to discover a hot Jupiter,

you could probably do it in a week or so

because the orbital period is of order of one, two, three days

so you can actually get the full orbit

two or three times over.

Whereas if you want to detect an Earth-like planet,

you have to observe that star for three, four years.

And that’s actually one of the problems with Kepler.

Kepler was this very successful mission

that NASA launched over a decade ago now, I think.

And it discovered thousands of planets.

It’s still the dominant source of exoplanets

that we know about,

but unfortunately it didn’t last as long

as we would have liked it to.

It died after about 4.35 years, I think it was.

And so for an Earth-like planet,

that’s just enough to catch four transits.

Four transits was kind of seen as the minimum.

But of course, the more transits you see,

the easier it is to detect it

because you build up signal to noise.

If you see the same thing, tick, tick, tick, tick, tick,

the more ticks you get, the easier it is to find it.

And so it was really a shame

that Kepler was just at the limit

of where we were expecting it

to start to see Earth-like planets.

And in fact, it really found zero.

Zero planets that are around stars like the Sun,

that orbit similar to the Earth around the Sun,

and could potentially be similar to our own planet

in terms of its composition.

And so it’s a great shame,

but that’s why it gives astronomers

more to do in the future.

Just to clarify, the transit method

is our primary way of detecting these things.

And what it is, is when the object passes,

occludes the source of light just a tiny bit, a few pixels.

And from that, we can infer something

about its mass, and size, and distance,

and geometry, and all of that.

That’s like trying to tell, what?

At a party, you can’t see anything about a person,

but you can just see by the way they occlude others.

So this is the method.

But is this a super far away?

How many pixels of information do we have, basically?

How high resolution is the signal

that we can get about these occlusions?

You’re right in your description.

I think just to build upon that a little bit more,

it might be almost like your vision is completely blurry.

Like you have an extreme eye prescription,

and so you can’t resolve anything.

Everything’s just blurs.

But you can tell that something was there

because it just got fainter for a short amount of time.

Someone passed in front of a light.

And so that light in your eyes

would just dim for a short moment.

Now, the reason we have that problem

with blurriness or resolution

is just because the stars are so far away.

The closest stars are four light years away,

but most of the stars Kepler looked at

were thousands of light years away.

And so there’s absolutely no chance

that the telescope can physically resolve the star,

or even the separation between the planet and the star

is too small, especially for a telescope like Kepler.

It’s only a meter across.

In principle, you can make those detections,

but you need a different kind of telescope.

We call that direct imaging.

And direct imaging is a very exciting,

distinct way of detecting planets.

But it, as you can imagine,

is going to be far easier to detect planets

which are really far away from their star to do that,

because that’s gonna make that separation really big.

And then you also want the star to be really close to us,

so the nearest stars.

Not only that, but you would prefer that planet

to be really hot,

because the hotter it is, the brighter it is.

And so that tends to bias direct imaging

towards planets which are in the process of forming.

So things which have just formed,

the planet’s still got all of its primordial heat

embedded within it, and it’s glowing.

We can see those quite easily.

But for the planets more like the Earth,

of course, they’ve cooled down,

and so we can’t see that.

The light is pitiful compared to a newly formed planet.

We would like to get there with direct imaging.

That’s the dream, is to have the pale blue dot,

an actual photograph of it,

maybe even just a one-pixel photograph of it.

But for now, the entire solar system is one pixel,

certainly with the transit method

and most other telescopes.

And so all you can do is see where that one pixel,

which contains potentially dozens of planets,

and the star, maybe even multiple stars,

dims for a short amount of time.

It dims just a little bit,

and from that, you can infer something.

Yeah, I mean, it’s like being a detective in the scene,

right, it’s very, it’s indirect clues

of the existence of the planet.

It’s amazing that humans can do that.

We’re just looking out in these immense distances,

and looking, you know,

if there’s alien civilizations out there,

like let’s say one exactly like our own,

we’re like, would we even be able to see an Earth

that passes in the way of its sun and slightly dims?

And that’s the only sign we have

of that alien human-like civilization out there,

is it’s just a little bit of a dimming.

Yeah, I mean, it depends on the type of star we’re talking.

If it is a star truly like the sun,

the dip that causes is 84 parts per million.

I mean, that’s just, it’s like the same as a,

it’s like a firefly flying in front

of like a giant floodlight at a stadium or something.

That’s the kind of the brightness contrast

that you’re trying to compare to.

So it’s extremely difficult detection.

And in the very, very best cases, we can get down to that.

But as I said, we don’t really have any true Earth analogs

that have been in the exoplanet candidate yet.

Unless you relax that definition, you say,

it’s not just, doesn’t have to be a star just like the sun.

It could be a star that’s smaller than the sun.

It could be these orange dwarfs,

or even the red dwarf stars.

And the fact those stars are smaller means that

for the same size planet passing in front of it,

more light is blocked out.

And so a very exciting system, for example, is TRAPPIST-1,

which has seven planets, which are smaller than the Earth.

And those are quite easily detectable,

not with a space-based telescope,

but even from the ground.

And that’s just because the star is so much smaller

that the relative increase in or decrease in brightness

is enhanced significantly because that smaller size.

So TRAPPIST-1e, it’s a planet

which is in the right distance for liquid water.

It has a slightly smaller size than the Earth.

It’s about 90% the size of the Earth, about 80% the mass.

And it’s one of the top targets right now

for potentially having life.

And yet it raises many questions about

what would that environment be like?

This is a star which is one eighth the mass of the sun.

Stars like that take a long time

to come off their adolescence.

When stars first form, like the sun,

it takes them maybe 10, 100 million years

to sort of settle into that main sequence lifetime.

But for stars like these late M dwarfs, as we call them,

they can take up to a billion years or more to calm down.

And during that period,

they’re producing huge amounts of X-rays,

ultraviolet radiation,

that could potentially rip off the entire atmosphere.

It may desiccate the planets in the system.

And so even if water arrived by comets or something,

it may have lost all that water

due to this prolonged period of high activity.

So we have lots of open-ended questions

about these M dwarf planets,

but they are the most accessible.

And so in the near term,

if we detect anything in terms of biosignatures,

it’s gonna be for one of these red dwarf stars,

it’s not gonna be a true Earth twin,

as we would recognize it as having a yellow star.

Well, let me ask you,

I mean, there’s a million ways to ask this question.

I’m sure I’ll ask it about habitable worlds.

Let’s just go to our own solar system.

What can we learn about the planets and moons

in our solar system that might contain life?

Whether it’s Mars or some of the moons of Jupiter

and Saturn, what kind of characteristics,

because you said it might not need to be Earth-like,

what kind of characteristics might we be looking for?

When we look for life,

it’s hard to define even what life is,

but we can maybe do a better job

in defining the sorts of things that life does.

And that provides some aspects to,

some avenue for looking for them.

In the, classically, conventionally,

I think we thought the way to look for life

was to look for oxygen.

Oxygen is a byproduct of photosynthesis on this planet.

We didn’t always have it.

Certainly if you go back to the Archean period,

there was, you have this period

called the Great Oxidation Event,

where the Earth floats with oxygen for the first time

and starts to saturate the oceans and then the atmosphere.

And so that oxygen, if we detect it on another planet,

whether it be Mars, Venus, or an exoplanet, whatever it is,

that was long thought to be evidence

for something doing photosynthesis.

Because if you took away all the plant life on the Earth,

the oxygen wouldn’t just hang around here

as a highly reactive molecule.

It would oxidize things.

And so within about a million years,

you would probably lose all the oxygen on planet Earth.

So that was conventionally

how we thought we could look for life.

And then we started to realize that it’s not so simple

because A, there might be other things that life does

apart from photosynthesis.

Certainly the vast majority of the Earth’s history

had no oxygen, and yet there was living things on it.

So that doesn’t seem like a complete test.

And secondly, could there be other things

that produce oxygen besides from life?

A growing concern has been these false positives

in biosignature work.

And so one example of that would be photolysis

that happens in the atmosphere.

When ultraviolet light hits the upper atmosphere,

it can break up water vapor.

The hydrogen splits off to the oxygen.

The hydrogen is a much lighter atomic species,

and so it can actually escape,

certainly planets like the Earth’s gravity.

That’s why we don’t have any hydrogen or very little helium.

And so that leaves you with the oxygen,

which then oxidizes the surface.

And so there could be a residual oxygen signature

just due to this photolysis process.

So we’ve been trying to generalize.

And certainly in recent years,

there’s been other suggestions,

things we could look for in the solar system beyond.

Nitrous oxide, basically laughing gas,

is a product of microbes.

That’s something that we’re starting

to get more interest in looking for.

Methane gas in combination with other gases

can be an important biosignature.

Phosphine as well, and phosphine’s particularly relevant

to the solar system because there was a lot of interest

for Venus recently.

You may have heard that there was a claim

of a biosignature in Venus’s atmosphere.

I think it was like two years ago now.

And the judge and jury are still out on that.

There was a very provocative claim and signature

of a phosphine-like spectral absorption.

But it could have also have been some other molecule

in particular, sulfur dioxide, which is not a biosignature.

So this is a detection of a gas in the atmosphere, Venus.

And it might be controversial in several dimensions.

So one, how to interpret that.

Two, is this the right gas?

And three, is this even the right detection?

Is there an error in the detection?

Yeah, I mean, how much do we believe

the detection in the first place?

If you do believe it, does that necessarily mean

there’s life there?

And what gives?

How can you have life in Venus’s atmosphere

in the first place?

That’s been seen as like a hellhole place

for imagining life.

But I guess the counter to that has been that,

okay, yes, the surface is a horrendous place

to imagine life thriving.

But as you go up in altitude,

the very dense atmosphere means that there is a cloud layer

where the temperature and the pressure

become actually fairly similar to the surface of the Earth.

And so maybe there are microbes stirring around

in the clouds, which are producing phosphine.

At the moment, this is fascinating.

It’s got a lot of us reinvigorated about the prospects

of going back to Venus and doing another mission there.

In fact, there’s now two NASA missions,

Veritas and Da Vinci, which are gonna be going back

and before 2030, the 2030s.

And then we have a European mission,

I think, that’s slated now,

and even a Chinese mission

might be coming along the way as well.

So we might have multiple missions going to Venus,

which has long been overlooked.

I mean, apart from the Soviets,

there really has been very little

in the way of exploration of Venus,

certainly as compared to Mars.

Mars has enjoyed most of the activity

from NASA’s rovers and surveys.

And Mars is certainly fascinating.

There’s this signature of methane

that has been seen there before.

Again, there, the discussion is whether that methane

is a product of biology, which is possible,

something that happens on the Earth,

or whether it’s some geological process

that we are yet to fully understand.

It could be, for example, a reservoir of methane

that’s trapped under the surface

and is leaking out seasonally.

So the nice thing about Venus is

if there’s a giant living civilization there,

it’ll be airborne, so you can just fly through

and collect samples.

With Mars and moons of Saturn and Jupiter,

you’re gonna have to dig under to find the civilizations,

dead or living.

Right, and so, yeah, maybe it’s easier then for Venus

because certainly you can imagine just a balloon

floating through the atmosphere,

or a drone or something that would have the capability

of just scooping up and sampling.

To dig under the surface of Mars is maybe feasible-ish,

especially with something like Starship

that could launch a huge digger, basically, to the surface

and you could just excavate away at the surface.

But for something like Europa,

we really are still unclear about how thick the ice layer is,

how you would melt through that huge thick layer

to get to the ocean,

and then potentially also discussions about contamination.

The problem with looking for life in the solar system,

which is different from looking for life with exoplanets,

is that you always run the risk of,

especially if you visit there,

of introducing the life yourself.

Right, it’s very difficult to completely exterminate

every single microbe and spore on the surface of your rover

or the surface of your lander,

and so there’s always a risk of introducing something.

I mean, to some extent, there is continuous exchange

of material between these planets,

naturally, on top of that as well,

and now we’re sort of accelerating that process

to some degree.

And so if you dig into Europa’s surface,

which probably is completely pristine,

it’s very unlikely there has been much exchange

with the outside world for its subsurface ocean,

you are, for the first time,

potentially introducing bacterial spores

into that environment that may compete

or may introduce spurious signatures

for the life you’re looking for.

And so it’s almost an ethical question

as to how to proceed with looking for life

on those subsurface oceans,

and I don’t think we really have a good resolution

for it at this point.

So you mean ethical in terms of concern

for preserving life elsewhere,

not to murder it, as opposed to a scientific one?

I mean, we always worry about a space virus

coming here or some kind of external source,

and we would be the source of that potential contamination.

Or the other direction.

I mean, whatever survives in such harsh conditions

might be pretty good at surviving in all conditions.

It might be a little bit more resilient and robust,

so it might actually take a ride on us back home.


I mean, I’m sure that some people

would be concerned about that.

I think we would hopefully have some containment procedures

as if we did sample return,

or I mean, you don’t even really need a sample return.

These days, you can pretty much send

like a little micro laboratory to the planet

to do all the experiments in situ,

and then just send them back to your planet, the data.

And so I don’t think this is necessary,

especially for a case like that,

where you might have contamination concerns

that you have to bring samples back.

Although, probably if you brought back European sushi,

it would probably sell for quite a bit

with the billionaires in New York City.

Sushi, yeah.

I would love from an engineering perspective

just to see all the different candidates

and designs for like the scooper,

for Venus and the scooper for Europa and Mars.

I haven’t really looked deeply into how they actually,

like the actual engineering of collecting the samples,

because the engineering of that is probably essential

for not either destroying life

or polluting it with our own microbes and so on.

So that’s like an interesting engineering challenge.

I usually, for rovers and stuff,

focus on the sort of the mobility aspect of it,

on the robotics, the perception,

and the movement and the planning and the control.

But there’s probably the scooper

is probably where the action is.

The microscopic sample collection.

So basically you have to first clean your vehicle,

make sure it doesn’t have any earth-like things on it.

And then you have to put it into some kind of thing

that’s perfectly sealed from the environment.

So if we bring it back or we analyze it,

it’s not going to bring anything else externally.

Yeah, I don’t know.

That would be an interesting engineering design there.

Yeah, I mean, Curiosity has been leaving

these little pods on the surface quite recently.

There’s some neat photos that you can find online.

And they kind of look like lightsaber hilts,

which is so, yeah, to me,

I think I tweeted something like,

this weapon is your life.

Like, don’t lose it, Curiosity,

because it’s just dumping these little vials everywhere.

And yeah, it is scooping up these things.

And the intention is that in the future

there will be a sample return mission

that will come and pick these up.

But it’s, I mean,

the engineering behind those things is so impressive.

The thing that blows me away the most has been the landings,

especially I’m trained to be a pilot at the moment.

So that’s the sort of,

watching landings has become like my pet hobby

on YouTube at the moment,

and how not to do it,

how to do it with different levels of conditions and things.

But when you think about landing on Mars,

just the light travel time effect

means that there’s no possibility

of a human controlling that descent.

And so you have to put all of your faith

and your trust in the computer code

or the AI or whatever it is that you’ve put on board that thing

to make the correct descent.

And so there’s this famous period called seven minutes of hell

where you’re basically waiting for that light travel time

to come back to know whether your vehicle successfully

landed on the surface or not.

And during that period,

you know in your mind simultaneously

that it is doing these multi-stages

of deploying its parachute, deploying the crane,

activating its jets to come down

and controlling its descent to the surface.

And then the crane has to fly away

so it doesn’t accidentally hit the rover.

And so there’s a series of multi-stage points

where any of them go wrong,

the whole mission could go awry.

And so the fact that we are fairly consistently able

to build these machines that can do this autonomously

is to me one of the most impressive acts of engineering

that NASA have achieved.

Yes, the unfortunate fact about physics

is the takeoff is easier than the landing.

Yes, yes.

And you mentioned Starship,

one of the incredible engineering feats

that you get to see is the reusable rockets

that take off but they land.

And they land using control and they do so perfectly.

And sometimes when it’s synchronous,

it’s just, it’s beautiful to see.

And then with Starship,

you see the chopsticks that catch the ship.

I mean, there’s just so much incredible engineering.

But you mentioned Starship is somehow helpful here.

So what’s your hope with Starship?

What kind of science might it enable possibly?

There’s two things.

I mean, it’s the launch cost itself,

which is hopefully gonna mean per kilogram,

it’s gonna dramatically reduce the cost of it.

Even if it’s a factor of 10 higher

than what Elon originally promised,

this is gonna be a revolution for the cost to launch.

That means you could do all sorts of things.

You could launch large telescopes,

which could be basically like JWST,

but you don’t even have to fold them up.

JWST had this whole issue with its design

that it’s six and a half meters across.

And so you have to, there’s no fuselage,

which is that large at the time.

The Ares IV wasn’t large enough for that.

And so they had to fold it up

in this kind of complicated origami.

And so a large part of the cost

was figuring out how to fold it up,

testing that it unfolded correctly,

repeated testing.

And there was something like 130 fail points

or something during this unfolding mechanism.

And so all of us were holding our breath

during that process.

But if you have the ability to just launch

arbitrarily large masses,

at least comparatively compared to JWST,

and very large mirrors into space,

you can more or less repurpose ground-based mirrors.

The Hubble Space Telescope mirror and the JWST mirrors

are designed to be extremely lightweight,

and that increased their cost significantly.

They have this kind of honeycomb design on the back

to try and minimize the weight.

If you don’t really care about weight,

because it’s so cheap,

then you could just literally grab

many of the existing ground-based mirrors

across telescopes across the world,

four-meter, five-meter mirrors,

and just pretty much attach them to a chassis

and have your own space-based telescope.

I think the Breakthrough Foundation, for instance,

is an entity that has been interested

in doing this sort of thing.

And so that raises the prospects

of having not just one JWST,

that just, you know,

JWST is a fantastic resource,

but it’s split between all of us.

Cosmologists, star formation astronomers,

those of us studying exoplanets,

those of us wanting to study the ultra-deep fields

and the origin of the first galaxies,

the expansion of the universe.

Everyone has to share this resource,

but we could potentially each have one JWST each

that is maybe just studying a handful

of the brightest exoplanet stars

and measuring their atmospheres.

This is important because if you,

and we talked about this planet Trappist-1e earlier,

that planet, if JWST stared at it

and tried to look for biosignatures,

by which I mean oxygen, nitrous oxide, methane,

it would take it of order of 200 transits

to get even a very marginal,

what we’d call two and a half sigma detection of those,

which basically nobody would believe with that.

100 transits, this thing transits once every six days,

so you’re talking about four years

of staring at the same star with one telescope.

There’d be some breaks,

but it’d be hard to schedule much else

because you have to continuously catch

each one of these transits

to build up your signal-to-noise.

And so JWST’s never gonna do that.

In principle, technically, JWST could technically

have the capability of just about detecting a biosignature

on an Earth-like planet around a non-Sun-like star,

but still, impressively,

we have basically the technology to do that,

but we simply cannot dedicate all of its time practically

to that one resource.

And so Starship opens up opportunities like that

of mass-producing these kinds of telescopes,

which will allow us to survey for life in the universe,

which, of course, is one of the grand goals of astronomy.

I wonder if you can speak to the bureaucracy,

the political battles, the scientific battles

for time on the James Webb Telescope.

There must be a fascinating process of scheduling that.

All scientists, they’re trying to collaborate,

figure out what the most important problems are,

and there’s an interesting network

of interfering scientific experiments, probably,

they have to somehow optimize over.

It’s a really difficult process.

I don’t envy the tech

that are gonna have to make this decision.

We call it the tech, the time allocation committee

that make this decision.

And I’ve served on these before, and it’s very difficult.

Typically for Hubble, we were seeing at least 10,

sometimes 20 times the number of proposals

for telescope time versus available telescope time.

For GDST, there has been one call already

that has gone out, we call it cycle one,

and that was oversubscribed by,

I think something like six to one, seven to one.

And the cycle two, which has just been announced

fairly recently, and the deadline

is actually the end of this month,

so my team are totally laser-focused

on running our proposals right now.

That is expected to be much more competitive,

probably more comparable to what Hubble saw.

And so, it’s hard.

More competitive than the cycle one, you said, already?

Because that’s already super competitive.

More competitive than the first cycle.

So I said the first cycle of James Webb

was about six to one, and this will probably be more like

20 to one, I would expect.

So these are all proposals by scientists and so on,

and it’s not like you can schedule at any time,

because if you’re looking for transit times.

Yeah, you have a time-critical element.

Yes, time-critical element.

And they’re conflicting in non-obvious ways,

because the frequency is different,

the duration is different,

there’s probably computational needs that are different,

there’s the type of sensors, the direction pointing,

all that.

Yeah, it’s hard, and there are certain programs

like doing a deep field study,

where you just more or less point the telescope,

and that’s pretty open.

I mean, you’re just accumulating photons.

You can just point at that patch of the sky,

whenever the telescope’s not doing anything else,

and just get to your month,

let’s say a month of integration time is your goal

over the lifetime of JWST.

So that’s maybe a little bit easier to schedule.

It’s harder, especially for us looking at cool worlds,

because as I said earlier,

these planets transit very infrequently.

So we have to wait.

If you’re looking at the Earth transiting the Sun,

an alien watching us,

they would only get one opportunity per year

to do that observation.

The transit lasts for about 12 hours.

And so if they don’t get that time, it’s hard.

That’s it.

If it conflicted with another proposal

that wants to use another time-critical element.

It’s much easier for planets like these hot planets

or these close-in planets,

because they transit so frequently,

there’s maybe 100 opportunities.

And so then the TAT can say, okay, they want 10 transits.

There’s 100 opportunities here.

It’s easier for us to give them time.

We’re almost in the worst-case scenario.

We’re proposing to look for exoplanets

around two cool planets.

And so we really only have one bite of the cherry

for each one.

And so our sales pitch has been

that these are extremely precious events.

And more importantly, JWST is the only telescope,

the only machine humanity has ever constructed,

which is capable of finding moons

akin to the moons in our solar system.

Kepler can’t do it.

Even Hubble can’t do it.

JWST is the first one.

And so there is a new window to the universe,

because we know these moons exist.

They’re all over the place in the solar system.

You have the Moon, you have Io, Callisto,

Europa, Ganymede, Titan.

Lots of moons of fairly similar size,

sort of 30% the size of the Earth.

And this telescope is the first one that can find them.

And so we’re very excited about the profound implications

of ultimately solving this journey we’re on in astronomy,

which is to understand our uniqueness.

We want to understand how common is the solar system,

are we the architecture that frequently emerges naturally,

or is there something special about what happened here?

I think this is not the worst case, it’s the best case.

It’s obvious, it’s super rare.

I love scheduling from a computer science perspective.

That’s my background.

So algorithmically, to solve a schedule problem,

I will schedule the rarest things first.

And obviously, JWST is the first thing

that can actually detect a cool world.

So this is a big new thing.

You can show off that new thing.

Happens rarely, schedule it first, it’s perfect.

You should be in the TAC, this is perfect.

I will, I’ll file my application

after we’re done with this.

This part of me is the OCD,

part of me is the computational aspect.

I love scheduling.

Computing device, because you have that kind of scheduling

on supercomputers, that scheduling problem’s fascinating.

How do you prioritize computation?

How do you prioritize science?

Data collection, sample collection,

all that kind of stuff.

That’s actually kind of fascinating,

because data, in ways you expect and don’t expect,

will unlock a lot of solutions

to some fascinating mysteries.

And so collecting the data and doing so

in a way that maximizes the possibility of discovery

is really interesting, from a computational perspective.

I agree, there’s a real satisfaction

extracting the maximum science per unit time

out of your telescope.

That’s the TAC’s job.

But the TAC are not machines,

they’re not a piece of computer code.

They will make their selections based off human judgment.

And a lot of the telescope,

certainly within the field of exoplanets,

because there’s different fields of astronomy,

but within the field of exoplanets,

I think a good expectation is that most of the telescope time

that JWC have will go towards atmospheric retrieval,

which is sort of alluded to earlier,

like detecting molecules in the atmospheres,

not biosignatures, because as I said,

it’s really not designed to do that.

It’s pushing JWST probably too far to expect it to do that.

But it could detect, for example,

a carbon dioxide rich atmosphere on TRAPPIST-1e.

That’s not a biosignature,

but you could prove it’s like a Venus in that case,

or maybe like a Mars in that case,

like both those have carbon dioxide rich atmospheres.

Doesn’t prove or disprove the existence of life either way,

but it is our first characterization

of the nature of those atmospheres.

Maybe we can even tell the pressure level

and the temperature of those atmospheres.

So that’s very exciting.

But we are competing with that.

And I think that science

is completely mind-blowing and fantastic.

We have a completely different objective,

which is in our case to try and look for the first evidence

of these small moons around these planets,

potentially even moons which could be habitable, of course.

So I think it’s a very exciting goal,

but ATT&CK has to make a human judgment

essentially about which science are they most excited by,

which one has the highest promise of return,

the most highest chance of return.

And so that’s hard,

because if you look at a planetary atmosphere,

well, you know most of the time

the planet has an atmosphere already.

And so there’s almost a guaranteed success

that you’re gonna learn something about the atmosphere

by pointing judiciously at it.

Whereas in our case, there’s a harder sell.

We are looking for something

that we do not know for sure exists yet or not.

And so we are pushing the telescope to do something

which is inherently more risky.

Yeah, but the existence, if shown,

already gives a deep lesson

about what’s out there in the universe.

That means that other stars have similar types of variety

as we have in our solar system.

They have an Io, they have a Europa and so on,

which means there’s a lot of possibility

for icy planets, for water,

for planets that enable planets and moons.

I mean, that’s super exciting,

because that means everywhere through our galaxy and beyond

that there is just innumerable possibility

for weird creatures.

I agree.

You don’t have to convince me.

I mean, NASA has been on this quest for a long time

and it’s sometimes called Eater Earth.

It’s the frequency of Earth-like,

usually they say planets, in the universe.

How common are planets similar to our Earth?

In terms of, ultimately,

we’d like to know everything about these planets

in terms of the amount of water they have,

how much atmosphere they have.

But for now, it’s kind of focused just on the size

and the distance from the star, essentially.

How often do you get similar conditions to that?

That was Kepler’s primary mission

and it really just kind of flirted with the answer.

It didn’t quite get to a definitive answer.

But I always say, look, if that’s our primary goal,

to look for Earth-like, I would say, worlds,

then moons has to be a part of that.

Because we know that Earth-like,

from the Kepler data, the preliminary result

is that Earth-like planets around sun-like stars

is not an inevitable outcome.

It seems to be something like a one to 10% outcome.

So it’s not particularly inevitable that that happens.

But we do often see about half of all sun-like stars

have either a mini-Neptune, a Neptune, or a Jupiter

in the habitable zone of their stars.

That’s a very, very common occurrence that we see.

Yet we have no idea how often they have moons around them,

which could also be habitable.

And so there may very well be,

if even one in five of them has an Earth-like moon

or even a Mars-like moon around them,

then there would be more habitable real estate

in terms of exomoons than exoplanets in the universe.

Essentially, 2x, 3x, 5x, maybe 10x,

the number of habitable worlds out there in the universe.

Our current estimate, like the Drake equation.

Absolutely, yeah.

So this is one way to increase the confidence

and increase the value of that parameter.

And just know where to look.

I mean, we would like to know

where should we listen for technosignatures?

Where should we be looking for biosignatures?

And not only that, but what role does the moon have

in terms of its influence on the planet?

We talked about these directly imaged telescopes earlier,

these missions that want to take a photo

to quote Carl Sagan, the pale blue dot of our planet,

but the pale blue dot of an exoplanet.

And that’s the dream, to one day capture that.

But as impressive as the resolution is

that we are planning and conspiring to design

for the future generation telescopes to achieve that,

even those telescopes will not have the capability

of resolving the Earth and the moon within that.

It’ll be a pale blue dot pixel,

but the moon’s grayness will be intermixed with that pixel.

And so this is a big problem,

because one of the ways that we are claiming

to look for life in the universe

is a chemical disequilibrium.

So you see two molecules that just shouldn’t be there.

They normally react with each other.

Or even one molecule that’s just too reactive

to be hanging around the atmosphere by itself.

So if you had oxygen and methane hanging out together,

those would normally react fairly easily.

And so if you detected those two molecules

in your pale blue dot spectra,

you’d be like, okay, we have evidence for life.

Something’s metabolizing on this planet.

However, the challenge here is what if that moon was Titan?

Titan has a methane-rich atmosphere.

And what if the pale blue dot

was in fact a planet devoid of life,

but it had oxygen because of water

undergoing this photolysis reaction,

splitting into oxygen and hydrogen separately?

So then you have all of the hallmarks

of what we would claim to be life.

But all along you were tricked.

It was just a moon that was deceiving you.

And so we are never going to,

we’re never going to, I would claim,

really understand or complete this quest

of looking for life by signatures in the universe

unless we have a deep knowledge of the prevalence

and role that moons have.

They may even affect the habitability

of the planets themselves.

Of course, our own moon is freakishly large.

By mass ratio, it’s the largest moon in the solar system.

It’s a 1% mass moon.

If you look at Jupiter’s moons,

they’re like 10 to the power minus four, much smaller.

And so our own moon seems to stabilize

the obliquity of our planet.

It gives rise to tides,

especially early on when the moon was closer,

those tides would have covered entire continents.

And those rock pools that would have been scattered

across the entire plateau

may have been the origin of life on our planet.

The moon forming impact may have stripped

a significant fraction of lithosphere off the Earth,

which without it, plate tectonics may not have been possible.

We’d have had a stagnant lid

because there was just too much lithosphere

stuck on the top of the planet.

And so there are speculative reasons,

but intriguing reasons as to why a large moon

may be not just important,

but central to the question

of having the conditions necessary for life.

So moons can be habitable in their own right,

but they can also play a significant influence

on the habitability of the planets they orbit.

And further, they will surely interfere

with our attempts to detect life remotely from afar.

So taking a tangent upon a tangent,

you’ve written about binary planets.

What’s, and that they’re surprisingly common,

or they might be surprisingly common.

What’s the difference between a large moon

and binary planets?

What are binary planets?

What’s interesting to say here

about giant rocks flying through space

and orbiting each other?

The thing that’s interesting about binary objects

is that they’re very common in the universe.

Binary stars are everywhere.

In fact, the majority of stars

seem to live in binary systems.

When we look at the outer edges of the solar system,

we see binary Kuiper Belt objects all the time.

Asteroids basically bound to one another.

Pluto-Charon is kind of an example of that.

It’s a 10% mass ratio system.

It almost is, by many definitions, a binary planet,

but now it’s a dwarf planet.

So I don’t know what you’d call that now.

But we know that the universe likes to make things in pairs.


So you’re saying our sun is an incel.

It’s looking, so most things are dating,

they’re in relationships, and ours is alone.

It’s not a complete freak of the universe to be alone,

but it’s more common for sun-like stars.

If you count up all the sun-like stars in the universe,

about half of the sun-like star systems

are in binary or trinary systems,

and the other half are single.

But because those binaries are two or three stars,

then cumulatively, maybe a third of all sun-like stars

are single.

I’m trying hard to not anthropomorphize

the relationship the stars have with each other.

But yeah.

The triplets.

Yeah, I’ve met those folks also.

So is there something interesting to learn

about the habitability, how that affects the probability

of habitable worlds when they kind of couple up like that

in those different ways?

It depends which way the stars of the planet.

Certainly, if stars couple up,

that has a big influence on the habitability.

Of course, this is very famous from Star Wars.

Tatooine in Star Wars is a binary star system,

and you have Luke Skywalker looking at the sunset

and seeing two stars come down.

And for years, we thought that was purely a product

of George Lucas’s incredibly creative mind,

and we didn’t think that planets would exist

around binary star systems.

It seems like too tumultuous an environment

for a quiescent planetary disc,

circumstellar disc to form planets from.

And yet, one of the astounding discoveries from Kepler

was that these appear to be quite common.

In fact, as far as we can tell,

they’re just as common around binary stars as single stars.

The only caveat to that is that you don’t get planets

close into binary stars.

They have like a clearance region on the inside

where planets, maybe they form there, but they don’t last.

They are dynamically unstable in that zone.

But once you get out to about the distance

that the Earth orbits the Sun,

or even a little bit closer in,

you start to find planets emerging.

And so, that’s the right distance for liquid water,

it’s the right distance for potentially life

on those planets.

And so, there may very well be plenty of habitable planets

around the binary stars.

Binary planets is a little bit different.

Binary planets, I don’t think we have any serious connection

of planet banality to habitability.

Certainly when we investigated it, that wasn’t our drive,

that this is somehow the solution

to life in the universe or anything.

It was really just a, like all good science questions,

a curiosity-driven question.

What’s the dynamic?

Are they legit orbiting each other

as they orbit the star?

So, the formation mechanism proposed here,

because it is very difficult to form two proto-planets

close to each other like this.

They would generally merge within the disk,

and so that’s why you normally get single planets.

But you could have something like Jupiter and Saturn

form at separate distances.

They could dynamically be scattered in towards one another

and basically not quite collide,

but have a very close-on encounter.

Now, because tidal forces increase dramatically

as the distance decreases between two objects,

the tides can actually dissipate the kinetic energy

and bring them bound into one another.

So, that seems, when you first hear that,

you think, well, that seems fairly contrived

that you’d have the conditions just right

to get these tides to cause a capture.

But numerical simulations have shown that about 10%

of planet-planet encounters are shown to produce

something like binary planets,

which is a startling prediction.

And so, that seems at odds with, naively,

the exoplanet catalogue, for which we know of,

so far, no binary planets.

And we propose one of the resolutions to this

might be that the binary planets

are just incredibly difficult to detect,

which is also counterintuitive,

because, remember how they form

is through this tidal mechanism,

and so they form extremely close to each other.

So, the distance that Io is away from Jupiter,

just a few planetary radii,

they’re almost touching one another,

and they’re just tidally locked,

facing each other for eternity.

And so, in that configuration,

as it transits across the star,

it kind of looks like you can’t really resolve

those two planets.

It just looks like one planet to you

that’s going across the star.

The temporal resolution of the data

is rarely good enough to distinguish that.

And so, you’d see one transit,

but in fact, it’s two planets very close together,

which are transiting at once.

And so, yeah, we wrote a paper just recently

where we developed some techniques

to try and get around this problem,

and hopefully provide a tool

where we could finally look for these planets.

The problem of detection of these planets

when they’re so close together.

That was our focus, was how do you get around

this merging problem?

So, whether they’re out there or not,

we don’t know.

We’re planning to do a search for them,

but it remains an open question.

And I think just one of those fun

astrophysics curiosities questions,

whether binary planets exist in the universe.

Because then you have binary Earths,

you could have binary Neptune,

all sorts of wild stuff that would

float the sci-fi imagination.

I wonder what the physics on a binary planet feels like.

It might be trivial.

I have to think about that.

I wonder if there’s some interesting dynamics.

Like, if you have multiple,

or would gravity feel different

at different parts of the surface of the sphere

when there’s another large sphere that’s interesting?

Yeah, I would think that the force

would be fairly similar,

because the shape of the object

would deform to a flat geopotential,

essentially, a uniform geopotential.

But it would lead to a distorted shape

for the two objects.

I think they’d become ellipsoids facing one another.

So, it would be pretty wild when you,

people like flat Earth or spherical Earth,

you fly from space and you see a football-shaped Earth.

It’s your own planet.

Finally, there’s proof.

And I wonder how difficult it would be

to travel from one to the other,

because you have to overcome the one.

No, it might be kind of easy.

Yeah, I mean, they’re so close to each other, that helps.

And I think the most critical factor

would be how massive is the planet?

That’s always, I mean,

one of the challenges with escaping planets,

there was a fun paper one of my colleagues wrote

that suggested that super-Earth planets may be inescapable.

If you’re a civilization that were born on a super-Earth,

the surface gravity is so high

that the chemical potential energy of hydrogen

or methane, whatever fuel you’re using,

simply is at odds with the gravity of the planet itself.

And so you would, you know,

our current rockets, I’m not sure of the fraction,

but maybe like 90% of the rocket is fuel or something

by mass.

These things would have to be,

like the size of the Giza pyramids of fuel

with just a tiny tip on the top

in order just to escape that planetary atmosphere.

And so it has been argued that if you live on a super-Earth,

you may be forced to live there forever.

There may be no escape

unless you invent a space elevator or something,

but then how do you even build the infrastructure in space

to do something like that

in the absence of a successful rocket program?

And so the more and more we look at our Earth

and think about the sorts of problems we’re facing,

the more you see things about the Earth

which make it ideally suited in so many regards.

It’s almost spooky, right,

that we not only live on a planet

which has the right conditions for life,

for intelligent life,

for sustained fossil fuel industry

just happens to be in the ground.

We have plenty of fossil fuels

to get our industrial revolution going,

but also the chemical energy contained

within those fossil fuels and hydrogen and other fuels

is sufficient that we have the ability

to escape our planetary atmosphere and planetary gravity

to have a space program.

And we also happen to have a celestial body

which is just within reach, the Moon,

which doesn’t also necessarily have to be true.

Were the Moon not there,

what effect would that have had

on our aspirations of a space program in the 1960s?

Would there have ever been a space race to Mars or to Venus?

It’s a much harder, certainly for a human program,

that seems almost impossible with 1960s technology

to ever come to fruition.

It’s almost as if somebody constructed

a set of challenging obstacles before us,

challenging problems to solve.

They’re challenging, but they’re doable.

And there’s a sequence to them.

Gravity is very difficult to overcome,

but we have, given the size of Earth,

it’s not so bad that we can still actually

construct propulsion systems that can escape it.

Yeah, and the same with climate change, perhaps.

I mean, climate change is the next major problem

facing our civilization,

but we know it is technically surmountable.

You know, it does seem sometimes

like there has been a series of challenges laid out

to progress us towards a mature civilization

that can one day perhaps expand to the stars.

I’m a little more concerned about nuclear weapons,

AI, and natural or artificial pandemics,

but yes, climate change.

Yeah, well, there you go.

I mean, plenty of milestones that we need to cross.

And we can argue about the severity of each of them,

but there is no doubt that we live in a world

that has serious challenges

that are pushing our intellects and our will

to the limit of whether we’re really ready

to progress to the next stage of our development.

So thank you for taking the tangent,

and there’ll be a million more,

but can we step back to Kepler-1625b?

What is it?

And you’ve talked about this kind of journey,

this effort to discover exomoons,

so moons out there, or small, cool objects out there.

Where does that effort stand,

and what is Kepler-1625b?

Yeah, I mean, I’ve been searching for exomoons

for most of my professional career,

and I think a lot of my colleagues think

I’m kind of crazy to still be doing it.

You know, after five years of not finding anything,

I think most people would probably

try doing something else.

I even had people say that to me.

They said, you know, professors,

and I remember at a cocktail party,

took me to the side, an MIT professor,

and he said, you know,

you should just look for hot Jupiters.

They’re everywhere.

It’s really, you can write papers.

They’re so easy to find.

And I was like, yeah, but hot Jupiters just,

they’re not interesting to me.

I wanna do something that I feel

intellectually pushes me to the edge,

and it’s maybe a contribution

that not no one else could do,

but maybe is not certainly the thing

that anybody could do.

I don’t wanna just be the first to something

for the sake of being first.

I wanna do something that feels like

a meaningful intellectual contribution to our society.

And so, you know, this exomoon problem

has been haunting me for years to try and solve this.

Now, as I said, we looked for years and years using Kepler,

and the closest we ever got was just a hint

for this one star, Kepler-1625,

has a Jupiter-like planet in orbit of it,

and that Jupiter-like planet is on a 287-day period,

so it’s almost the same distance

as the Earth around the Sun, but for a Jupiter.

So that was already unusual.

I don’t think people realize that Jupiter-like planets

are quite rare in the universe.

Certainly mini-Neptunes and Neptunes are extremely common,

but Jupiters, only about 10% of Sun-like stars

have Jupiters around them, as far as we can tell.

When you say Jupiter, which aspect of Jupiter?

In terms of its mass and its semi-major axis.

So anything beyond about half an AU,

so half the distance of the Earth and the Sun,

and something of order of a tenth of a Jupiter mass,

that’s the mass of Saturn, up to, say, 10 Jupiter masses,

which is basically where you start to get to brown dwarfs,

those types of objects appear to be somewhat unusual.

Most solar systems do not have Jupiters,

which is really interesting, because Jupiter, again,

like the Moon, seems to have been a pivotal character

in the story of the development of our solar system,

perhaps especially having a large influence

on the development of the late heavy bombardment

and the rate of asteroid impacts

that we receive and things like this.

Anyway, to come back to 1625,

this Jupiter-like planet had a hint

of something in the data.

But what I mean by that is when we looked at the transit,

we got the familiar decrease in light

that we always see when a planet tries to confront the star,

but we saw something extra, just on the edges,

we saw some extra dips around the outside.

It was right at the hairy edge of detectability.

We didn’t believe it, because I think one of the challenges

of looking for something for 10 years

is that you become your own greatest skeptic.

And no matter what you’re shown,

you’re always thinking,

I’ve been falling in love so many times,

and it’s not working out.

You convince yourself it’s never gonna happen.

Not for me, this just isn’t gonna happen.

And so I saw that, and I didn’t really believe it,

because I didn’t dare let myself believe it.

But being a good scientist,

we knew we had an obligation to publish it,

to talk about the result, and to follow it up,

and to try and resolve what was going on.

So we asked for Hubble Space Telescope time,

which was awarded in that case.

So we were one of those lucky 20 that got telescope time.

And we studied it for about 40 hours continuously.

And to provide some context,

the dip that we saw in the Kepa data

corresponded to a Neptune-sized moon

around a Jupiter-sized planet,

which was another reason why I was skeptical.

We don’t have that in the solar system.

That seems so strange.

And then when we got the Hubble data,

it seemed to confirm exactly that.

There was two really striking pieces of evidence

in the data that suggested this moon was there.

Another was a fairly clear second dip in light,

pretty clearly resolved by Hubble.

It was about a five-sigma detection.

And on top of that,

we could see the planet didn’t transit

when it should have done.

It actually transited earlier than we expected it to,

by about 20 minutes or so.

And so that’s a hallmark of a gravitation interaction

between the planet and the moon.

We actually expected that.

You can also expect that if the moon transits

after the planet,

then the planet should come in earlier than expected,

because the barycenter, the center of mass,

lives between the two of them,

kind of like on a balancing arm between them.

And so we saw that as well.

So the phase signature matched up.

The mass of the moon was measured to be Neptune mass,

and the size of the moon was measured to be Neptune radius.

And so everything just really lined up.

And we spent months and months trying to kill it.

This is my strategy for anything interesting.

We just try to throw the kitchen sink at it and say,

we must be tricked by something.

And so we tried looking at the centroid motion

of the telescope,

but the different wavelength channels have been observed,

the pixel level information.

And no matter what we did, we just couldn’t get rid of it.

And so we submitted it to Science.

And I think at the time,

Science, which is one of the top journals, said to us,

would you mind calling your paper discovery of an exomoon?

And I had to push back.

And we said, no, we’re not calling it that.

I don’t, even despite everything we’ve done,

we’re not calling it a discovery.

We’re calling it evidence for an exomoon.

Because for me, I’d wanna see this repeat

two times, three times, four times

before I really would bet my house

that this is the real deal.

And I do worry, as I said,

that perhaps that’s my own self-skepticism going too far.

But I think it was the right decision.

And since that paper came out,

there has been continuous interest in the subject.

Another team independently analyzed that star

and recovered actually pretty much exactly

the same results as us, the same dip,

the same wobble of the planet.

And a third team looked at it

and actually got something different.

They saw the dip was diminished compared to what we saw.

They saw a little hint of a dip,

but not as pronounced as what we saw.

And they saw the wobble as well.

So there’s been a little bit of tension

about analyzing the reduction of the Hubble data.

And so the only way in my mind to resolve this

is just to look again.

We actually did propose to Hubble straight after that.

And we said, look, if our model is right,

if the moon is there, it came in late last time.

It transited after the planet.

Because of the orbit,

we can calculate that it should transit

before the planet next time.

If it’s not there, if it doesn’t transit before,

and even if we see a dip afterwards,

we know that’s not our moon.

It’s obviously some instrumental effect with the data.

We had a causal prediction as to where the moon should be.

And so I was really excited about that,

but we didn’t get the telescope time.

And unfortunately, if you go further into the future,

we no longer have the predictive capability

because it’s like predicting the weather.

You might be able to predict the weather next week

to some level of accuracy,

but predicting the weather next year becomes incredibly hard.

The uncertainties just grow and compound

as you go forward into the future more and more.

How were you able to know

where the moon would be positioned?

So you’re able to tell the orbiting geometry and frequency?

Yeah, so basically from the wobbles of the planet itself,

that tells us the orbital motion of the moon.

It’s the reflex motion of the moon on the planet.

Isn’t it just an estimate to where,

like I’m concerned about you making a strong prediction here

because if you don’t get the moon

where the moon leads on the next time around,

if you did get Hubble time,

couldn’t that mean something else if you didn’t see that?

Because you said it would be an instrumental.

I feel the strong urge to disprove your own,

which is a really good imperative.

It’s a good way to do science,

but like this is such a noisy signal, right?

Or blurry signal, maybe.

Low resolution signal, maybe.

Yeah, I mean, it’s a five sigma signal.

That’s at the slightly uncomfortable edge.

I mean, it’s often said that for any detection

of a first new phenomena,

you really want like a 20, 25 sigma detection.

Then there’s just no doubt that what you’re seeing is real.

This was at that edge.

I mean, I guess it’s comparable to the Higgs boson,

but the Higgs boson was slightly different

because there was so much theoretical impetus

as to expect a signal at that precise location.

A Neptune-sized moon was not predicted by anyone.

No one, there was no papers you can find

that expect Neptune-sized moons around Jupiter-sized planets.

So I think we were inherently skeptical

about its reality for that reason.

But this is science in action.

When we fit the wobbles, we fit the dips,

and we have this 3G geometric model

for the motion of the orbit,

and projecting that forward,

we found that about 80% of our projections

led to the moon to be before.

So it’s not 100%.

There was maybe 20% of the cases it was over here.

But to me, that was a hard enough projection

that we felt confident that we could refute the,

which was what I really wanted.

I wanted a refutable,

that’s the basis of science,

a falsifiable hypothesis.

How can you make progress in science

if you don’t have a falsifiable testable hypothesis?

And so that was the beauty of this particular case.

So there’s a numerical simulation with a moon

that fits the data that we observed,

and then you can now make predictions

based on that simulation.


That’s so cool.


It’s fun.

These are like little solar systems

that we can simulate on the computer

and imagine their motions.

But we are pushing things

to the very limits of what’s possible,

and that’s double-edged sword.

It’s both incredibly exciting intellectually,

but you’re always risking, to some degree,

the pushing too far.

So I’d like to ask you about the recent paper

you coauthored,

an exomoon survey of 70 cool giant exoplanets

and the new candidate Kepler 1708 Bi.

I would say there’s like three or four candidates

at this point,

of which we have published two of them.

And to me, two are quite compelling

and deserve follow-up observations.

And so to get a confirmed detection,

at least in our case,

we would need to see it repeat, for sure.

One of the problems with some of the other methods

that have been proposed

is that you don’t get that repeatability.

So for instance, an example of a technique

that would lack that

would be gravitational microlensing.

So it is possible with a new telescope

coming up in the future

called the Roman Space Telescope,

which is basically a repurpose by satellite

that’s the size of the Hubble mirror

going up into space.

It will stare at millions of stars simultaneously

and it will look to see,

instead of whether any of those stars

get dimmer for a short amount of time,

which would be a transit,

it’ll look for the opposite.

It’ll look to see if anything can get brighter.

And that brightness increase

is caused by another planetary system passing in front

and then gravitationally lensing light around it

to cause a brightening.

This is a method of discovering an entire solar system,

but only for a glimpse.

You just get a short glimpse of it

passing like a ship sailing through the night,

just that one photo of it.

Now the problem with that is that

it’s very difficult.

The physics of gravitational lensing

are not surprisingly quite complicated.

And so there’s many, many possible solutions.

So you might have a solution

which is this could be a red dwarf star

with a Jupiter-like planet around it.

That’s one solution.

But another solution is that it’s a free-floating planet,

a rogue planet like Jupiter

with an Earth-like moon around it.

And those two solutions are almost indistinguishable.

Now, ideally, we would be able to repeat the observation.

We’d be able to go back and see,

well, if the moon really is there,

then we could predict its mass,

it’s predicted its motion

and expect it to be maybe over here next time or something.

With microlensing, it’s a one snapshot event.

And so, for me, it’s intriguing

as a way of revealing something

about the exomoon population.

But I always come back to transits

because it’s the only method we really have

that’s absolutely repeatable,

that we’ll be able to come back and prove everyone,

prove to everyone that, look,

on the 17th of October, the moon will be over here

and the moon will look like this

and we can actually capture that image.

And that’s what we see with, of course, many exoplanets.

So we wanna get to that same point of full confidence,

full confirmation, the slam-dunk detection

of these exomoons.

But yeah, it’s been a hell of a journey

to try and push the field into that direction.

Is there some resistance to the transit method?

Not to the transit method, I just say to exomoons.

So the transit method is by far the most popular method

for looking for exoplanets.

But yeah, as I’ve alluded to,

exomoons is kind of a niche topic

within the discipline of exoplanets.

And that’s largely because there are people,

I think, are waiting for those slam-dunks.

And it was like the,

if you go back to the first exoplanet discovery

that was made in 1995 by Michel Mayor and Didier Queloz,

I think it’s true at the time

that they were seen as mavericks,

that the idea of looking for planets around stars

was considered fringe science.

And I’m sure many colleagues told them,

why don’t you do something more safe,

like study eclipsing stars?

There are two binary star systems, we know those exist.

So why are you wasting your time looking for planets?

You’re gonna get this alien moniker or something,

and you’ll be seen as a fringe maverick scientist.

And so I think it was quite difficult

for those early planet hunters to get legitimacy

and be taken seriously.

And so very few people risked their careers to do it,

except for those that were either emboldened to try

or had maybe the career, maybe like tenure or something,

so they didn’t have to necessarily worry

about the implications of failure.

And so once that happened,

once they made the first discoveries,

overnight, everyone and their dog

was getting into exoplanets,

and all of a sudden the whole astronomy community shifted

and huge numbers of people

that were once upon a time studying eclipsing binaries

changed to becoming exoplanet scientists.

And so that was the first wave of exoplanet scientists.

We’re now in a kind of a second wave,

or maybe a third wave,

where people like me to some degree

grew up with the idea of exoplanets as being normal.

I was 11 years old, I guess,

when the first exoplanet was discovered.

And so to me, it was a fairly normal idea to grow up with.

And so we’ve been trained in exoplanets

from the very beginning.

And so that brings a different perspective

to those who have maybe transitioned

from a different career path.

And so I suspect with exomoons

and probably technosignatures, astrobiology,

many of the topics which are seen

at the fringes of what’s possible,

they will all open up into becoming mainstream one day.

But there’s a lot of people who are just waiting,

waiting for that assuredness

that there is a secure career net ahead of them

before they commit.

Yeah, it does seem to me that exomoons open wider

or open for the first time the door to aliens.

So more seriously, academically studying,

all right, let’s look at alien worlds.

So I think it’s still pretty fringe

to talk about alien life,

even on Mars and the moons and so on.

You’re kind of like, it would be nice,

but imagine the first time you discover a living organism.

That’s gonna change.

Then everybody will look like an idiot

for not focusing everything on this.

Because the possibility of the things will,

it’s possible it might be super boring.

It might be very boring bacteria.

But even the existence of life elsewhere,

I mean, that changes everything.

That means life is everywhere.

If you knew now that in five years, 10 years,

the first life would be discovered elsewhere,

you knew that in advance,

it would surely affect the way

you approach your entire career.

Especially someone junior in astronomy,

you would surely be like,

well, this is clearly gonna be the direction

I have to dedicate my classes and my training

and my education towards that direction.

All the new textbooks, all the-

You have to be written.

And I think there’s a lot of value to hedging,

like allocating some of the time to that possibility.

Because the kind of discoveries we might get

in the next few decades,

it feels like we’re on the verge of a lot of,

getting a lot of really good data

and having better and better tools

that can process that data.

So there’s just going to be a continuous increase

of the kind of discoveries that will open.

But a slam dunk, that’s hard to come by.

Yeah, I think a lot of us are anticipating,

I mean, we’re already seeing it to some degree

with Venus and the phosphine incident.

But we’ve seen it before with Bill Clinton.

It’s on the White House lawn announcing life from Mars.

And there are inevitably gonna be spurious claims,

or at least claims which are ambiguous to some degree.

There will be, for sure, a high profile journal,

like Nature or Science, that will one day publish a paper

saying, by a signature discovered or something like that

on Trappist-1 or some other planet.

And then there will be years of back and forth

in the literature.

And that might seem frustrating,

but that’s how science works.

That’s the mechanism of science at play,

of people scrutinizing the results

to intense skepticism.

And it’s like a crucible.

You burn away all irrelevances

until whatever is left is the truth.

And so you’re left with this product,

which is that, okay, we either believe or don’t believe

that bite signatures are there.

So there’s inevitably gonna be a lot of controversy

and debate and argument about it.

We just have to anticipate that.

And so I think you have to basically have a thick skin,

to some degree, academically, to dive into that world.

And you’re seeing that with phosphine.

It’s been uncomfortable to watch from the outside

the kind of dialogue that some of the scientists

have been having with each other about that, because-

They get a little aggressive.

Yeah, and you can understand why, because-


I don’t know.

That’s me saying, not you.

That’s me talking.

I’m sure there’s some envy and jealousy involved

on the behalf of those who are not part

of the original discovery.

But there’s also, in any case,

just leave the particular people involved in Venus alone,

in any case of making a claim of that magnitude,

especially life, because life is pretty much

one of the biggest discoveries of all time,

you can imagine, scientifically, you can see,

and I’m so conscious of this in myself,

when I get close to, as I said,

even the much smaller goal of setting an exomoon,

the ego creep in.

And so, as a scientist, we have to be so guarded

against our own egos.

You see the lights in your eyes of a Nobel Prize,

or the fame and fortune and being remembered

in the history books, and we all grew up in our training,

learning about Newton and Einstein,

these giants of the field, Feynman, Maxwell,

and you get the idea of these individual contributions

which get immortalized for all time, and that’s seductive.

It’s why many of us with the skillset

to go into maybe banking instead decided,

actually, there’s something about the idea

of being immortalized and contributing towards society

in a permanent way that is more attractive

than the financial reward of applying my skills elsewhere.

So, to some degree, that ego can be a benefit,

because it brings in skillful people into our field

who might otherwise be tempted by money elsewhere.

But, on the other hand, the closer you get

towards when you start flirting

with that Nobel Prize in your eyes,

or you think you’re on the verge of seeing something,

you can lose objectivity.

A very famous example of this is Barnard’s Star.

There was a planet claimed there by Peter van de Kamp,

I think it was in 1968, 69, and at the time,

it would have been the first ever exoplanet ever claimed.

And he felt assured that this planet was there.

He was actually using the wobbling star method,

but using the positions of the stars

to see them to claim this exoplanet.

It turned out that this planet was not there.

Subsequent analyses by both dynamicists and theorists

and those looking at the instrumental data

established fairly unanimously

that there was no way this planet was really there.

But Peter van de Kamp insisted it was there,

despite overwhelming evidence

that was accruing against him.

And even to the day he died,

which was I think in the early 90s,

he was still insisting this planet was there,

even when we were starting to make

the first genuine exoplanet discoveries.

And even at that point, I think Hubble

had even looked at that star

and had totally ruled out any possibility

of what he was talking about.

And so that’s a problem.

How do you get to a point as a scientist

where you just can’t accept

anything that comes otherwise?

Because it starts out with the dream of fame,

and then it ends in a stubborn refusal to ever back down.

Of course, the flip side of that

is sometimes you need that to have the strength

to carry a belief against the entire scientific community

that resists your beliefs.

And so it’s a double-edged sword.

That can happen, but I guess the distinction here

is evidence.

So in this case, the evidence was so overwhelming,

it wasn’t really a matter of interpretation.

It was, you had to collect,

you’d observe this star with the same star,

but with maybe 10, even 100 times greater precision

for prolonged, much longer periods of time.

And there was just no doubt at this point

this planet was a mirage.

And so that’s why you have to be very careful.

I always say, don’t ever name my wife and my daughter,

name this planet after me that you discover.

I’m like, I can’t ever name a planet after you

because I won’t be objective anymore.

How could I ever turn around to you

and say that planet wasn’t real that I named after you?

So you’re somebody that talks about,

and it’s clear in your eyes and in your way of being,

that you love the process of discovery,

that joy, the magic of just, you know,

seeing something, a new observation, a new idea, right?

But I guess the point is, when you have that great feeling,

is to then switch on the skepticism,

like to start testing, what does this actually mean?

Is this real?

What are the possible different interpretations

that could make this a lot less grand

than I first imagined?

So both have the wonder and the skepticism all in one brain.

Yeah, I think generally the more I want something to be true,

the more I inherently doubt it.

I grew up with a religious family

and was just sort of indoctrinated to some degree,

like many children are, that, okay, this is normal,

that there’s a God and this is the way the world is.

God created the Earth.

And then as I became more well-read and illiterate

of what was happening in the world scientifically,

I started to doubt.

And it really just struck me

that the hardest thing to let go of

when you do decide not to be religious anymore,

and it’s not really like a light bulb moment,

but it just kind of happens over sort of 11 to 13,

I think for me it was happening.

But it’s that sadness of letting go of this beautiful dream,

which you had in your mind of eternal life,

for behaving yourself on Earth,

you would have this beautiful heaven

that you could go to and live forever.

And that’s very attractive.

And for me personally,

that was one of the things that pulled me against it,

was this, it’s like, it’s too good to be true.

And it’s very convenient that this could be so.

And I have no evidence directly

in terms of a scientific sense to support this hypothesis.

And it just became really difficult

to reconcile my growth as a scientist.

And I know some people find that reconciliation.

I have not.

Maybe I will one day.

But as a general guiding principle,

which I think I obtained from that experience,

was that I have to be extremely guarded

about what I want to be true,

because it’s going to sway me to say things

which are not true if I’m not careful.

And that’s not what we’re trying to do as scientists.

So you felt from a religious perspective

that there was a little bit of a gravitational field

in terms of your opinions,

like it was affecting how you could be as a scientist.

Like as a scientific thinker, obviously, you were young.

Yeah, I think that’s true,

that whenever there’s something you want to be true,

it’s the ultimate seduction intellectually.

And I worry about this a lot with UFOs and with,

it’s true already with things like Venus,

phosphine and searching for astrobiological signals.

We have to guard against this all the way through

from however we’re looking for life,

however we’re looking for whatever this big question is.

There is a part of us,

I think I would love there to be life in the universe.

I hope there is life in the universe,

but I’m somewhat been on record several times

as being fairly firm about trying to remain consciously

agnostic about that question.

I don’t want to make up my mind about what the answer is

before I’ve collected evidence to inform that decision.

That’s how science should work.

If I already know what the answer is,

then what am I doing?

That’s not a scientific experiment anymore.

You’ve already decided, so what are you trying to learn?

What’s the point of doing the experiment

if you already know what the answer is?

There’s no point.

It’s so complicated because,

so if I’m being honest with myself,

when I imagine the universe,

so first thing I imagine about our world

is that we humans and me certainly

as one particular human know very,

my first assumption is I know almost nothing

about how anything works.

So first of all, that actually applies

for things that humans do know,

like quantum mechanics,

all the things that there’s different expertises

that I just have not dedicated to.

So even that’s starting point.

But if we take all of knowledge as human civilization,

we know almost nothing.

That’s kind of an assumption I have

because it seems like we keep discovering mysteries

and it seems like history,

human history is defined by moments when we said,

okay, we pretty much figured it all out

and then you realize a century later,

when you said that, you didn’t figure out anything.

Okay, so that’s like a starting point.

The second thing I have is I feel like

the entirety of the universe is just filled

with alien civilizations.

Statistically, there’s the important thing

that enables that belief for me

is that they don’t have to be human-like.

They can be anything.

And it’s just the fact that life exists

and just seeing the way life is on Earth,

that it just finds a way.

It finds a way in so many different complicated environments.

It finds a way.

Whatever that force is,

that same force has to find a way elsewhere also.

But then if I’m also being honest,

I don’t know how many hours in a day I spend

seriously considering the possibility that we’re alone.

I don’t know when my heart is in mind

or filled with wonder,

I think about all the different life that’s out there.

But to really imagine that we’re alone,

really imagine all the vastness that’s out there,

we’re alone, not even bacteria.

I would say you don’t have to believe that we are alone,

but you have to admit it’s a possibility

of our ignorance of the universe so far.

You can have a belief about something

in the absence of evidence.

And Carl Sagan famously described that

as the definition of faith.

If you believe something when there’s no evidence,

you have faith that there’s life in the universe.

But you can’t demonstrate,

you can’t prove it mathematically,

you can’t show me evidence of that.

Is there some, so mathematically, math is a funny thing,

is there, I mean, the way physicists think, like intuition,

so basic reasoning, is there some value to that?

Well, I’d say we’re always,

there’s certainly, you can certainly make

a very good argument,

I think you’ve kind of already made one,

just the vastness of the universe

is the default argument people often turn to,

that surely there should be others out there.

It’s hard to imagine.

There are of order of 10 to the 22 stars

in our observable universe.

And so, really the question comes down to

what is the probability of one of those

10 to the 22 planets, let’s say,

Earth-like planets, if they all have Earth-like planets,

going on to form life, spontaneously?

That’s the process of abiogenesis,

the spontaneous emergence of life.

Also, the word spontaneous is a funny one.

Well, okay, maybe we won’t use spontaneous,

but not being, let’s say,

seeded by, say, some other civilization

or something like that, it naturally emerges.

Because even the word spontaneous

makes it seem less likely.


Like there’s just this chemistry

and an extremely random process.

Right, it could be a very gradual process

over millions of years of growing complexity

in chemical networks.

Maybe there’s a force in the universe

that pushes it towards interesting complexity,

pockets of complexity,

that ultimately creates something like life

which we can’t possibly define yet.

And sometimes it manifests itself

into something that looks like humans.

But it could be a totally different

kind of computational information processing system

that we’re too dumb to even visualize.

Yeah, I mean, certainly,

I mean, it’s kind of weird

that complexity develops at all, right?

Because it seems like the opposite

to our physical intuition,

if you’re training in physics,

of entropy, that things should,

complexity’s hard to spontaneously,

or I shouldn’t say spontaneously,

but hard to emerge in general.


And so that’s an interesting problem.

I think there’s been,

certainly from an evolutionary perspective,

you do see growing complexity.

And there’s a nice argument,

I think it’s by Gould,

who shows that if you have

a certain amount of complexity,

it can either become less complex

or more complex through random mutation.

And the less complex things

are stripping away something,

something that was necessary,

potentially, to their survival.

And so in general,

that’s gonna be not particularly useful

in its survival.

And so it’s gonna be detrimental

to strip away a significant amount

of its useful traits.

Whereas if you add something,

the most typical thing that you add

is probably not useful at all.

It’s probably just,

doesn’t really affect its survival negatively,

but neither does it provide any significant benefit.

But sometimes, on rare occasions, of course,

it will be of benefit.

And so if you have a certain level of complexity,

it’s hard to go back in complexity,

but it’s fairly easy to go forward

with enough bites at the cherry.

You will eventually build up in complexity.

And that tends to be why we see complexity

grow in, certainly in an evolutionary sense,

but also perhaps it’s operating

in chemical networks

that led to the emergence of life.

I guess the real problem I have

with the numbers game,

just to come back to that,

is that we are talking about

a certain probability of that occurring.

It may be to go from the primordial soup,

however you want to call it,

the ingredients that the earth started with,

the organic molecules,

the probability of going from that initial condition

to something that was capable

of Darwinian natural selection

that maybe we could define as life,

the probability of that is maybe 1%,

1% of the time that happens,

in which case you’re right.

The universe will be absolutely teeming with life,

but it could also be 10 to the power of minus 10,

in which case it’s one per galaxy,

or 10 to the power of minus 100,

in which case the vast majority of universes even

do not have life within it.

Or 90%.

Or 90%.

You said 1%,

but it could be 90% if the conditions,

the chemical conditions of a planet are correct

or a moon are correct.

I admit that.

It could be any of those numbers.

And the challenge is we just have no rigorous reason

to expect why 90% is any,

because we’re talking about a probability for probability.

Is 90% more a priori likely

than 10 to the power of minus 20?

Well, the thing is,

we do have an observation, N of one, of Earth.

And it’s difficult to know what to do with that,

what kind of intuition you build on top of that,

because on Earth, it seems like life finds a way

in all kinds of conditions,

in all kinds of crazy conditions.

And it’s able to build up from the basic chemistry.

You could say, okay, maybe it takes a little bit of time

to develop some complicated technology,

like mitochondria, I don’t know, like photosynthesis.

Fine, but it seems to figure it out

and do it extremely well.

Yeah, but I would say you’re describing

a different process.

I mean, maybe I’m at fault

for separating these two processes,

but to me, you’re describing basically natural selection

evolution at that point.

Whereas I’m really describing abiogenesis,

which is, to me, a separate distinct process.

To you, limited to human scientists, yes,

but why would it be a separate process?

Why is the birth of life a separate process

from the process of life?

I mean, we’re uncomfortable with the Big Bang.

We’re uncomfortable with the first thing, I think.

Like, where does this come from?

Right, so I think I would say,

I just twist that question around and say,

you’re saying, why is it a different process?

And I would say, why shouldn’t it be a different process?

Which isn’t really a good defense,

except to say that we have knowledge

of how natural selection evolution works.

We think we understand that process.

We have almost no information about the earlier stages

of how life emerged on our planet.

It may be that you’re right,

and it is a part of a continuum.

It may be that it is also a distinct,

improbable set of circumstances

that led to the emergence of life.

As a scientist, I’m just trying to be open-minded

to both possibilities.

If I assert that life must be everywhere,

to me, you run the risk of experimenter’s bias.

If you think you know what the answer is,

if you look at an Earth-like planet,

and you are preconditioned to think

there’s a 90% chance of life on this planet,

it’s going to, at some level,

affect your interpretation of that data.

Whereas if I, however critical you might be

of the agnosticism that I impose upon myself,

remain open to both possibilities,

then I trust in myself to make a fair assessment

as to the reality of that evidence for life.

Yeah, but I wonder, sort of scientifically,

and that’s really beautiful to hear,

and inspiring to hear.

I wonder scientifically how many firsts we truly know of,

and then we don’t eventually explain

as actually a step number one million in a long process.

So I think that’s a really interesting thing

if there’s truly firsts in this universe.

For us, whatever happened at the Big Bang

is a kind of first, the origin of stuff.

Again, it seems like history shows

that we’ll figure out

that it’s actually a continuation of something.

But then physicists say that time is emergent,

and that our causality in time

is a very human kind of construct,

that it’s very possible that all of this,

so there could be really firsts

of a thing to which we attach a name.

So whatever we call life, maybe there is an origin of it.

Yeah, and I would also say,

I’m open to the idea of it being part of a continuation,

but the continuation maybe is more broader,

and it’s a continuation of chemical systems

and chemical networks.

And what we call this one particular type of chemistry

in this behavior of chemistry life,

but it is just one manifestation

of all the trillions of possible permutations

in which chemical reactions can occur.

And we assert specialness to it,

because that’s what we are.

And so it’s also true of intelligence.

You could extend the same thing

and say we’re looking for intelligent life in the universe,

and then you sort of, where do you define intelligence?

Where’s that continuum of something

that’s really like us, are we alone?

There may be a continuum of chemical systems,

a continuum of intelligences out there,

and we have to be careful of our own arrogance

of assuming specialness about what we are,

that we are some distinct category of phenomena,

whereas the universe doesn’t really care

about what category we are.

It’s just doing what it’s doing

and doing everything in infinite diversity

and infinite combinations is essentially what it’s doing.

And so we are taking this one slice and saying,

no, this has to be treated separately.

And I’m open to the idea

that it could be a truly separate phenomenon,

but it may just be like a snowflake.

Every snowflake’s different.

It may just be that this one particular,

iteration is another variant of the vast continuum.

And maybe the algorithm of natural selection itself

is an invention of earth.

I kind of also tend to suspect that this,

whatever the algorithm is,

it kind of operates at all levels throughout the universe.

But maybe this is a very kind of peculiar thing

that where there’s a bunch of chemical systems

that compete against each other,

somehow for survival under limited resources.

And that’s a very earth-like thing.

We have a nice balance of,

there’s a large number of resources,

enough to have a bunch of different kinds

of systems competing,

but not so many that they get lazy.

And maybe that’s why bacteria

were very lazy for a long time.

Maybe they didn’t have much competition.

Quite possibly.

I mean, I tried to,

as fun as it is to get into the speculation

about the definitions of life

and what life does

and this gross network of possibilities.

Honestly, for me,

the strongest argument for remaining agnostic

is to avoid that bias in assessing data.

I mean, we’ve seen it.

I mean, Percival Lowell,

I talked about on my channel maybe last year

or two years ago,

he’s a very famous astronomer who in the 19th century

was claiming the evidence of canals on Mars.

And from him, from his perspective,

and even at the time, culturally,

it was widely accepted that Mars would,

of course, have life.

I mean, I think it seems silly to us,

but it was kind of similar arguments

to what we’re using now about exoplanets,

that, well, of course there must be life in the universe.

How could it just be here?

And so it seemed obvious to people

that when you looked at Mars with its polar caps,

even its atmosphere, had seasons,

it seemed obvious to them

that that too would be a place

where life not only was present,

but had emerged to a civilization,

which actually was fairly comparable

in technology to our own,

because it was building canal systems.

Of course, a canal system

seems a bizarre technosignature to us,

but it was a product of their time.

To them, that was the cutting edge in technology.

It should be a warning shot, actually,

a little bit for us,

that if we think solar panels or building star links

or whatever, space mining

is like an inevitable technosignature,

that may be laughably antiquated

compared to what other civilizations

far more advanced than us may be doing.

And so anyway, Percival Lowell,

he, I think, was a product of his time

that he thought life was there.

Inevitably, he even wrote about it extensively.

And so when he saw these lines,

these lineae on the surface of Mars,

to him, it was just obvious they were canals.

And that was experimenters’ bias playing out.

He was told, for one,

that he had basically the greatest eyesight

out of any of his peers.

An ophthalmologist had told him that in Boston,

that his eyesight was absolutely spectacular.

So he just was convinced everything he saw was real.

And secondly, he was convinced there was life there.

And so to him, it just added up.

And then that kind of wasted decades of research,

of treating the idea of Mars being inhabited

by this canal civilization.

But on the other hand, it’s maybe not a waste

because it is a lesson in history

of how we should be always on guard

against our own preconceptions and biases

about whether life is out there.

And furthermore, what types of things life might do

if it is there.

If I were running this simulation,

which we’ll also talk about

because you make the case against it,

but if I were running a simulation,

I would definitely put you in a room with an alien

and just to see you mentally freak out for hours at a time.

Oh, that’d be great.

You for sure would have thought

you will be convinced that you’ve lost your mind.

I mean, no, not that.

But I mean, if we discover life,

we discover interesting new physical phenomena,

I think the right approach is definitely

to be extremely skeptical and be very, very careful

about things you want to be true.

That’s really admirable.

I’m not some extreme denialist of evidence.

If there was compelling evidence

for life on another planet,

I would be the first one to be celebrating that

and be shaking hands with the alien

on the White House lawn or whatever.

I grew up with Star Trek and that was my fantasy

was to be Captain Kirk

and fly across the stars meeting other civilizations.

So there’s nothing more I’d want to be true as I’ve said,

but we just have to guard against it

when we’re assessing data.

But I have to say I’m very skeptical

that we will ever have that Star Trek moment.

Even if there are other civilizations out there,

they’re never gonna be at a point

which is in technological lockstep with us,

similar level of development,

even intellectually the idea

that they could have a conversation with us

even through a translator.

I mean, we can’t communicate with humpback whales.

We can’t communicate with dolphins in a meaningful way.

We can sort of bark orders at them,

but we can’t have abstract conversations

with them about things.

And so the idea that we will ever have

that fulfilling conversation, I’m deeply skeptical of.

And I think a lot of us are drawn to that.

I think it is maybe a replacement for God to some degree,

that Father figure civilization that might step in,

teach us the air of our ways

and bestow wisdom upon our civilization.

But they could equally be a giant fungus

that doesn’t even understand the idea of socialization

because it’s the only entity on its planet.

It just swells over the entire surface.

And it’s incredibly intelligent

because maybe each node communicates with each other

to create essentially a giant neural net.

But it has no sense of what communication even is.

And so alien life is out there,

surely can be extremely diverse.

I’m pretty skeptical that we’ll ever get

that fantasy moment I always had as a kid

of having a dialogue within the civilization.

So dialogue, yes.

What about noticing them?

What about noticing signals?

Do you hope…

So one thing we’ve been talking about

is getting signatures, biosignatures,

technosignatures about other planets.

Maybe if we’re extremely lucky in our lifetime

to be able to meet life forms,

get evidence of living or dead life forms on Mars

or the moons of Jupiter and Saturn.

What about getting signals from outer space,

interstellar signals?

What would those signals potentially look like?

That’s a hard question to answer

because we are essentially engaging in xenopsychology

to some degree.

What are the activities of another civilization?

A lot of that is inevitable.

What does the word xenopsychology,

I apologize to interrupt, mean?

Maybe I’m just fabricating that word, really,

but trying to guess at the machinations

and motivations of another intelligent being

that was completely evolutionary divorced from us.

So it’s like you said, exo-moons,

it’s exopsychology, extrasolar psychology.

Yeah, alien psychology is another way

of maybe making it more grounded.

But we can’t really guess at their motivations too well,

but we can look at the sorts of behaviors we engage in

and at least look for them.

We’re always guilty that when we look for biosignatures,

we’re really looking for,

and even when we look for planets,

we’re looking for templates of Earth.

When we look for biosignatures,

we’re looking for templates of Earth-based life.

When we look for tetanus signatures,

we tend to be looking for templates of our own behaviors

or extrapolations of our behaviors.

So there’s a very long list of tetanus signatures

that people have suggested we could look for.

The earliest ones were, of course, radio beacons.

That was sort of Project Osma

that Frank Drake was involved in,

trying to look for radio signatures,

which could either be just like blurting out

high-power radio signals saying, hey, we’re here,

or could even have encoded within them

galactic encyclopedias for us to unlock,

which has always been the allure of the radio technique.

But there could also be unintentional signatures.

For example, you could have something

like the satellite system that we’ve produced

around the Earth, the artificial satellite system,

Starlink-type systems we mentioned.

You could detect the glint of light across those satellites

as they orbit around the planet.

You could detect a geostationary satellite belt,

which would block out some light

as the planet transited across the star.

You could detect solar panels,

potentially spectrally, on the surface of the planet.

Heat island effects.

New York is hotter than New York State

by a couple of degrees

because of the heat island effect of the city.

And so you could thermally map different planets

and detect these.

So there’s a large array of things that we do

that we can go out and hypothesize we could look for.

And then on the furthest end of the scale,

you have things which go far beyond our capabilities,

such as warp drive signatures, which have been proposed.

You get these bright flashes of light

or even gravitational wave detections

from LIGO could be detected.

You could have Dyson spheres.

The idea of covering, basically,

a star’s completely covered by some kind of structure

which collects all the light from the star

to power the civilization.

And that would be pretty easily detectable to some degree

because you’re transferring all of the visible light.

Thermodynamically, it has to be re-emitted

so it would come out as infrared light.

So you’d have an incredibly bright infrared star,

yet one that was visibly not present at all.

And so that would be a pretty intriguing

signature to look for.

Well, is there efforts to look for something like that

for Dyson spheres out there

for the strong infrared signal?

There has been.

Yeah, there has been.

And there’s been, I think in the literature,

there was one with the IRAS satellite,

which is an infrared satellite.

They targeted, I think, of order of 100,000 stars,

nearby stars,

and found no convincing examples

of what looked like a Dyson sphere star.

And then Jason Wright and his team extended this,

I think, using WISE,

which is another infrared satellite,

to look around galaxies.

So could an entire galaxy have been converted

into Dyson spheres,

or a significant fraction of the galaxy?

Which is basically the Kardashev Type III, right?

This is when you’ve basically mastered

the entire galactic pool of resources.

And again, out of 100,000 nearby galaxies,

there appears to be no compelling examples

of what looks like a Dyson galaxy,

if you want to call it that.

So that by no means proves that they don’t exist

or don’t happen,

but it seems like it’s an unusual behavior

for a civilization to get to that stage of development

and start harvesting the entire stellar output.

Unusually, yes.

And I mean, LIGO is super interesting

with gravitational waves.

If that kind of experiment could start seeing some weirdness,

some weird signals that compare

to the power of cosmic phenomena.

Yeah, yeah.

I mean, it’s a whole new window to the universe,

not just in terms of astrophysics,

but potentially for technosignatures as well.

I have to say, with the warp drives,

I am skeptical that warp drives are possible

because you have kind of a fundamental problem in relativity.

You can either really have relativity,

faster than light travel, or causality.

You can only choose two of those three things.

You really can’t have all three in a coherent universe.

If you have all three,

you basically end up with the possibility

of these kind of temporal paradoxes

and time loops and grandfather paradoxes.

Well, can’t there be pockets of causality?

Something like that?

Like where there’s like pockets of consistent causality.

You could design it in that way.

You could be, you know,

if you had a warp drive or a time machine,

essentially you could be, you know,

you could be very conscious

and careful of the way you use it

so as to not to cause paradoxes

or just do it in a local area or something.

But the real fundamental problem is

you always have the ability to do it.

And so in a vast cosmic universe,

if time machines were all over the place,

there’s too much risk of someone doing it, right?

Of somebody having the option

of essentially breaking the universe with this.

So this is a fundamental problem.

Hawking has this chronology protection conjecture

where he said that essentially this just can’t be allowed

because it breaks all our laws of physics

if time travel is possible.

Current laws of physics, yes.

Correct, yeah.

And so we need to rip up relativity.

I mean, that’s the point is the current laws of physics.

So you’d have to rip up our current law of relativity

to make sense of how FTL could live in that universe

because you can’t have relativity, FTL and causality

sit nicely and play nicely together.

But we currently don’t have quantum mechanics

and relativity playing nice together anyway.

So it’s not like everything is all a nice little fabric.

It’s certainly not the full picture.

There must be more to go.

So it’s already ripped up,

so might as well rip it up a little more.

And in the process, actually try to connect the two things.

Because maybe in the unification of the standard model

and general relativity, maybe there lies

some kind of new wisdom about warp drives.

So by the way, warp drives is somehow messing

with the fabric of the universe

to be able to travel faster than the speed of light?

Yeah, you’re basically bending space-time.

You could also do it with a wormhole or a tachy.

Some of the hypothetical FTLs,

this doesn’t have to necessarily be the Alcubierre drive,

the warp drive.

It could be any faster than light system.

As long as it travels superluminally,

it will violate causality.

And presumably that will be observable with LIGO.

Potentially, yeah, potentially.

Depends on, I think, the properties

of whatever the spacecraft is.

I mean, one problem with warp drives is,

there’s all sorts of problems with warp drives.

But when it-

Like the start of that sentence,

one problem, the warp drive.

There’s just this one minor problem

that we have to get around.

But when it arrives at its destination,

it basically collects this vast,

basically has like an event horizon

almost at the front of it.

And so it collects all this radiation

at the front as it goes.

And when it arrives,

all that radiation gets dumped on its destination,

would basically completely exterminate

the planet it arrives at.

That radiation is also incident within the shell itself.

There’s Hawking radiation occurring within the shell,

which is pretty dangerous.

And then it also has,

it raises all sorts of exacerbations

of the Fermi paradox, of course, as well.

So you might be able to explain

why we don’t see a galactic empire.

I mean, even here it’s hard.

You might be able to explain

why we don’t see a galactic empire

if everybody’s limited to Voyager 2 rocket speeds

of like 20 kilometers per second or something.

But it’s a lot harder to explain

why we don’t see the stars populated by galactic empires

when warp drive is eminently possible

because it makes expansion so much more trivial

that it makes our life harder.

There’s some wonderful simulation work

being done out of Rochester

where they actually simulate all the stars in the galaxy

or a fraction of them.

And they spawn a civilization in one of them

and they let it spread out at sub-light speeds.

And actually the very mixing of the stars themselves,

because the stars are not static,

they’re in orbit of the galactic center

and they have crossing paths with each other.

If you just have a range of even like five light years

and your speed is of order of a few percent,

the speed of light is the maximum you can muster,

you can populate the entire galaxy

within something like 100,000,

about a million years or so.

So a fraction of the lifetime of the galaxy itself.

And so this raises some fairly serious problems

because if any civilization in the entire history

of the galaxy decided to do that,

then either we shouldn’t be here

or we happen to live in this kind of rare pocket

where they chose not to populate to.

And so this is sometimes called fact A, Hart’s fact A.

As the fact A is that a civilization is not here now,

an alien civilization is not in present occupation

of the Earth.

And that’s difficult to resolve with the apparent ease

at which even a small extrapolation of our own technology

could potentially populate a galaxy

in far faster than galactic history.

So to me, by the way,

the Fermi paradox is truly a paradox for me.

But I suspect that if aliens visit Earth,

I suspect if they are everywhere,

I think they’re already here and we’re too dumb to see it.

But leaving that aside,

I think we should be able to, in that case,

have very strong, obvious signals

when we look up at the stars,

at the emanation of energy required.

We would see some weirdness

that like where these are these kinds of stars

and these are these kinds of stars

that are being messed with,

like leveraging the nuclear fusion of stars

to do something useful.

The fact that we don’t really see that,

like maybe you can correct me,

wouldn’t we be able to,

if there is like alien civilizations running galaxies,

wouldn’t we see weirdnesses from an astronomy perspective

with the way the stars are behaving?

Yeah, I mean, it depends exactly what they’re doing.

But I mean, the Dyson Sphere example is one

that we already discussed

where a survey of 100,000 nearby galaxies

find that they have all been transformed

into Dyson Sphere collectors.

You could also imagine them doing things like,

we wrote a paper about this recently, of star lifting,

where you can extend the life of your star

by scooping mass off the star.

So you’d be doing stellar engineering, essentially.

Space, if you’re doing a huge amount of asteroid mining,

you would have a spectral signature

because you’re basically filling the solar system with dust

by doing that.

There’d be debris from that activity.

And so there are some limits on this.

Certainly we don’t see bright flashes,

which would be,

one of these consequences of warp drives, as I said,

is as they decelerate,

they produce these bright flashes of light.

We don’t seem to see evidence of those kinds of things.

We don’t see anything obvious around the nearby stars

or the stars that we’ve surveyed in detail beyond that

that indicate any kind of artificial civilization.

The closest maybe we had was Boyajian star

that there was a lot of interest in.

There was a star that was just very peculiarly

dipping in and out its brightness.

And it was hypothesized for a time

that that may indeed be some kind of Dyson-like structure.

So maybe a Dyson sphere that’s half built.

And so as it comes in and out,

it’s blocking out huge swaths of the star.

It was very difficult to explain it

really with any kind of planet model at the time.

But an easier hypothesis that was proposed

was it could just be a large number of comets

or dust or something,

or maybe a planet that had broken apart.

And as its fragments orbit around,

it blocks out starlight.

And it turned out with subsequent observations of that star,

which especially the amateur astronomy community

made a big contribution to as well,

that the dips were chromatic,

which was a real important clue

that that probably wasn’t a solid structure then

that was going around it.

It was more likely to be dust.

Dust is chromatic.

By chromatic, I mean it looks different in different colors.

So it blocks out more red light than blue light.

If it was a solid structure, it shouldn’t do that.

It should be opaque, right?

A solid metal structure or something.

So that was one of the clear indications.

And the behavior of, and the way the light changed

or the dips changed across wavelength

was fully consistent with the expectations

of what small particulates would do.

And so that’s very hard.

I mean, the real problem with alien hunting,

the real problem-

The technical term.

This is the real-

The one problem.

The one problem with the warp drive

and the one problem with the alien hunting, yes.

But well, actually I’d say there’s three big problems for me

with any search for life,

which includes UFOs or the way to fossils on Mars,

is that aliens have three unique properties as a hypothesis.

One is they have essentially

unbounded explanatory capability.

So there’s almost no phenomena I can show you

that you couldn’t explain with aliens to some degree.

You could say, well, the aliens just have

some super high-tech way of creating that illusion.

The second one would be unbounded avoidance capacity.

So I might see a UFO tomorrow,

and then the next day, and then the next day,

and then predict I should see it on Thursday

at the end of the week, but then I don’t see it.

But I could always get out of that and say,

well, that’s just because they chose not to come here.

You know, they have this-

They can always avoid future observations fairly easily.

If you survey an exoplanet for biosignatures

and you don’t see oxygen, you don’t see methane,

that doesn’t mean there’s no one living there.

They could always be either tricking their atmosphere,

engineering it, we actually wrote a paper about that,

how you can use lasers to hide your biosignatures

as advanced civilization.

Or you could just be living underground

or underwater or something where there’s no biosignatures.

So you can never really disprove there’s life

on another planet or on another star.

It has infinite avoidance.

And then finally, the third one is that we have

incomplete physical understanding of the universe.

So if I see a new phenomena,

which Boyajian’s star was a good example of that,

we saw this new phenomena of these strange dips

we’d never seen before.

It was hypothesized immediately this could be aliens.

It’s like a god of the gaps,

but it turned out to be incomplete physical understanding.

And so that happens all the time.

In the first pulsar that was discovered, same story.

Jocelyn Bell kind of somewhat tongue-in-cheek

called it Little Green Man 1

because it looked a lot like the radio signature

that was expected from an alien civilization.

But of course, it turned out to be

a completely new type of star that we had never seen before,

which was a neutron star with these two jets

coming out the top of it.

And so that’s a challenge.

Those three things are really, really difficult

in terms of experimental design

for a scientist to work around.

Something that can explain anything, can avoid anything,

so it’s almost unfalsifiable,

and could always just be, to some degree, as you said,

we have this very limited knowledge

of the infinite possibilities of physical law,

and we’re probably only scratching the surface.

Each time, and we’ve seen it so often in history,

we may just be detecting some new phenomena.

Well, that last one, I think I’m a little more okay

with making mistakes on.

Yeah, because it’s exciting still.

Because no matter, so you might exaggerate

the importance of the discovery,

but the whole point is to try to find stuff

in this world that’s weird,

and try to characterize that weirdness.

Sure, you can throw a little green man as a label on it,

but eventually, it’s as mysterious and as beautiful,

as interesting as a little green man.

Like, we tend to think that there’s some kind of threshold,

but there’s all kinds of weird organisms on this Earth

that operate very differently than humans

that are super interesting.

The human mind is super interesting.

I mean, weirdness and complexity is as interesting

in any of its forms as what we might think from Hollywood

what aliens are.

So that’s okay.

Looking for weirdnesses on Mars.

That’s one of the best sales pitches

to do technosignature work,

is that we always have that as our fallback,

that we’re gonna look for alien signatures.

If we fail, we’re gonna discover

some awesome new physics along the way.

And so, any kind of signature that we detect

is always going to be interesting.

And so, that compels us to have not only the question

of looking for life in the universe,

but it gives us a strong scientific grounding

as to why this sort of research should be funded

and should be executed,

because it always pushes the frontiers of knowledge.

I wonder if we’ll be able to discover

and be open enough to a broad definition of aliens,

where we see some kind of technosignature,

basically like a Turing test,

like this thing is intelligent.

Like it’s processing information in a very interesting way.

But you could say that about chemistry.

You could say that about physics.

Maybe not physics, chemistry.

Like interesting, complex chemistry,

you could say that this is processing.

This is storing information.

This is propagating information over time.

So, I mean, it’s a gray area

between a living organism that we would call an alien,

and a thing that’s super interesting

and is able to carry some kind of intelligence.

Yeah, information is a really useful way

to frame what we’re looking for, though,

because then you’re divorced from making assumptions

about even a civilization, necessarily,

or anything like that.

So, any kind of information-rich signature,

indeed, you can take things like the light curve

from Boyajian’s star and ask,

what is the minimum number of free parameters

the minimum information content

that must be encoded within this light curve?

And the hope is that maybe from,

a good example would be from a radio signature.

You detect something that has 1,000 megabytes

of parameters, essentially, contained within it.

That’s pretty clearly, at that point,

not the product of a natural process,

or it’s any natural process that we could possibly imagine

with our current understanding of the universe.

And so, thinking that even if we can’t decode,

which, actually, I’m skeptical we’d be able

to ever decode it in our lifetimes.

It would probably take decades to fully ever figure out

what they’re trying to tell us.

But if there was a message there,

we could at least know

that there is high information content,

and there is complexity,

and that this is a attempt at communication

and information transfer,

and leave it to our subsequent generations

to figure out what exactly it is they’re trying to say.

What, again, a wild question,

and thank you for…

Entertaining them.

Entertaining them.

I really, really appreciate that.

But what kind of signal in our lifetime,

what kind of thing do you think might happen,

could possibly happen,

where the scientific community would be convinced

that there’s alien civilizations out there?

Like what, so you already said,

maybe a strong infrared signature

for something like a Dyson sphere.

Yeah, that’s possible,

but that’s also to some degree a little bit ambiguous,


That’s the challenge, sorry to interrupt,

is where your brain would be,

like you as a scientist,

would be like, I know it’s ambiguous,

but this is really weird.


I think if you had some,

I can imagine something like a prime number sequence,

or a mathematical sequence,

like the Fibonacci series,

something being broadcasted.

Mathematically provable that this is not

a physical phenomenon.

Right, I mean, yeah,

prime numbers is a pretty good case,

because there’s no natural phenomena

that produces prime number sequences.

It seems to be a purely an abstract mathematical concept,

as far as I’m aware.

And so if we detected a series of radio blips

that were following that sequence,

it would be pretty clear to me,

or it could even be Carl Sagan suggested

that pi could be encoded in that,

or you might use the hydrogen line,

but multiply it by pi,

like some very specific frequency of the universe,

like a hydrogen line,

but multiply it by a abstract mathematical constant

that would imply strongly

that there was someone behind the scenes operating that.

Sorry, stored in which phenomena, though?

In that case, I think of a radio wave.

But the information, I mean,

we kind of toyed with this idea

in a video I did about hypothetical civilization

on my channel.

But one kind of fun way,

I do want to bring this conversation

towards time a little bit,

and thinking about not just looking

for life and intelligence around us right now,

but looking into the past and even into the future

to some degree, or communicating with the future.

And so we had this fun experiment

of imagining a civilization that was born

at the beginning of the history of the galaxy

and being the first and what it would be like for them.

And they were desperately searching for evidence of life,

but couldn’t find it.

And so they decided to try and leave something behind

for future civilizations to discover,

to tell them about themselves.

But of course, a radio scene’s just not gonna work there

because it has to have a power source,

and that’s a piece of machinery.

It’s gonna eventually break down.

It’s gonna be hard to maintain that

for billions of years timescale.

And so you wanted something that was kind of passive,

that doesn’t require an energy source,

but can somehow transmit information,

which is hard to think about something

that satisfies those criteria.

But there was a proposal

by one of my colleagues, Luke Arnold,

which inspired a lot of us in Technosignatures.

And he suggested that you could build artificial transitors.

So you could build sheets of material

that transit in front of the star.

Maybe one thin sheet passes across first,

then two, then three, then five, then seven,

so you could follow the prime number sequence of these.

And so there’d be a clear indication

that someone had manufactured those,

but they don’t require any energy source

because they’re just sheets of material in orbit of the star.

They would eventually degrade from micrometeorites,

and maybe they always would become destabilized,

but they should have lifetimes far exceeding

the lifetime of any battery or mechanical electronic system

that we could, at least with our technology,

conceive of building.

And so you could imagine then extending that,

and how could you encode not just a prime number sequence,

but maybe in the spatial pattern

of this very complex light curve we see,

you could encode more and more information

through 2D shapes and the way those occultations happen.

And maybe you could even encode messages

and in-depth information from that.

You could even imagine it being

like a lower layer of information,

which is just the prime number sequence,

but then you look closely and you see

the smaller divots embedded within those

that have a deeper layer of information to extract.

And so to me, something like that

would be pretty compelling,

that there was somebody who had,

unless it’s just a very impressive hoax,

that would be a pretty compelling evidence

for this civilization.

And actually, the methods of astronomy right now

are kind of marching towards being able

to better and better detect a signal like that.

Yeah, I mean, to some degree,

it’s just building bigger aperture in space.

The bigger the telescope,

the finer ability to detect those minute signals.

Do you think the current sort of the scientific community,

another weird question,

but just the observations that are happening now,

do you think they’re ready for a prime number sequence?

In the sort of, if we’re using the current method,

the transit timing variation method,

like do you think you’re ready?

Do you have the tools to detect the prime number sequence?

Yeah, for sure.

I mean, there’s 200,000 stars that Kepler monitored

and it monitored them all the time.

It took a photo of each one of them every 30 minutes,

measured their brightness,

and it did that for four and a half years.

And so you have already,

and Tess is doing it right now, another mission.

And so you have already an existing catalog

and people are genuinely scouring

through each of those light curves

with automated machine learning techniques.

We even developed some in our own team

that can look for weird behavior.

We wrote a code called the weird detector, for instance.

Of course.

You know, it was just the most generic thing possible.

Don’t assume anything about the signal shape.

Just look for anything that repeats.

The signal shape can be anything

and we kind of learn the template of the signal

from the data itself.

And then it’s like a template matching filter

to see if that repeats many, many times in the data.

And so we actually applied that

and found a bunch of interesting stuff,

but we didn’t see anything

that was the prime number sequence,

at least on the Kepler data.

That’s 200,000 stars, which sounds like a lot,

but compared to 200 billion stars in the Milky Way,

it’s really just scratching the surface.

So one, because there could be something

much more generalizable than the prime number sequence,

it’s ultimately the question of a signal

that’s very difficult to compress

in the general sense of what compress means.

So maybe as we get better and better

in machine learning methods

that automatically figure out, analyze the data

to understand how to compress it,

you’ll be able to discover data

that for some reason is not compressible.

But then, you know, compression really is a bottomless pit

because that’s really what intelligence is,

is being able to compress information.

Yeah, and to some degree, the more you,

I would imagine, I don’t work in compression algorithms,

but I would imagine the more you compress your signal,

the more assumptions that kind of go

on behalf of the decoder,

the more skilled they really have to be.

You know, a prime number sequence

is completely unencoded information, essentially.

But if you look at the Arecibo message,

they were fairly careful with their pixelation

of this simple image they sent

to try and make it as interpretable as possible

to be that even a dumb alien would be able to figure out

what we’re trying to show them here

because there’s all sorts of conventions

and rules that are built in

that we tend to presume when we design our messages.

And so if your message is assuming

they know how to do an MP3 decoder,

a particular compression algorithm,

I’m sure they could eventually reverse engineer it

and figure it out,

but you’re making it harder for them to get to that point.

So maybe, I always think, you know,

you probably would have a two-tier system, right?

You’d probably have some lower-tier key system,

and then maybe beneath that,

you’d have a deeper compressed layer

of more in-depth information.

What about maybe observing actual physical objects?

So first, let me go to your tweet

as a source of inspiration.

You tweeted that it’s interesting to ponder

that if Oort clouds are ever mined

by the systems of alien civilizations,

mining equipment from billions of years ago

could be in our Oort cloud

since the Oort clouds extend really, really, really,

really far outside the actual star.

So, you know, mining equipment,

just basic, boring mining equipment out there.

I don’t know if there’s something interesting to say

about Oort clouds themselves that are interesting to you

and about possible non-shiny light-emitting mining equipment

from alien civilizations.

Yeah, I mean, that’s kind of the beauty

of the field of technosignatures and looking for life

is you can find inspiration and intellectual joy

in just the smallest little thing

that starts a whole thread of building upon it

and wondering about the implications.

And so in this case, I was just really struck by,

we kind of mentioned this a little bit earlier,

the idea that stars are not static.

We tend to think of the galaxy as having stars

in a certain location from the center of the galaxy

and they kind of live there.

But in truth, the stars are not only orbiting

around the center of the galaxy,

but those orbits are themselves changing

over time, they’re processing.

And so in fact, the orbits look more like a spirograph

if you’ve ever done those as a kid,

they kind of whirl around and trace out

all sorts of strange patterns.

And so the stars intersect with one another.

And so the current closest star to us is Proxima Centauri,

which is about 4.2 light years away.

But it will not always be the closest star

and over millions of years,

it will be supplanted by other stars.

In fact, stars that will come even closer than Proxima

within just a couple of light years.

And that’s been happening, not just we can project

that will happen over the next few million years,

but that’s been happening presumably

throughout the entire history of the galaxy

for billions of years.

And so if you went back in time,

there would have been all sorts of different nearest stars

at different stages of the Earth’s history.

And those stars are so close that their Oort clouds

do intermix with one another.

So the Oort cloud can extend out to even a light year

or two around the Earth.

There’s some debate about exactly where it ends.

It probably doesn’t really have a definitive end,

but kind of more just kind of peters out

more and more and more as you go further away.

By the way, for people who don’t know an Oort cloud,

I don’t know what the technical definition is,

but a bunch of rocks that kind of, no,

objects that orbit the star.

And they can extend really, really, really far

because of gravity.

These are objects that probably are mostly icy rich.

They were probably formed fairly similar distances

to Jupiter and Saturn, but were scattered out

through the interactions of those giant planets.

We see a circular disk of objects around us,

which kind of looks like the asteroid belt,

but just further away called the Kuiper belt.

And then further beyond that,

you get the Oort cloud.

And the Oort cloud is not on a disk.

It’s just a sphere.

It kind of surrounds us in all directions.

So these are objects that were scattered out

through three-dimensionally in all different directions.

And so those objects are potentially resources for us,

especially if you were planning

to do an interstellar mission one day,

you might want to mine the water

that’s embedded within those and use that

as either oxygen or fuel for your rocket.

And so it’s quite possible.

There’s also some rare earth metals

and things like that as well,

but it’s quite possible that a civilization

might use Oort cloud objects as a jumping off point.

Or in the Kuiper belt,

you have things like planet nine even.

There might even be objects beyond in the Oort cloud,

which are actually planet-like that we just cannot detect.

These objects are very, very faint.

So that’s why they’re so hard to see.

I mean, even planet nine, it’s hypothesized to exist,

but we’ve not been able to confirm its existence

because it’s at something like a thousand AU away from us,

a thousand times the distance of the earth from the sun.

And so even though it’s probably larger than the earth,

the amount of light it reflects from the sun,

the sun just looks like a star at that point,

so far away from it that it barely reflects anything back.

It’s extremely difficult to detect.

So there’s all sorts of wonders

that may be lurking out in the outer solar system.

And so this leads you to wonder,

you know, in the Oort cloud,

that Oort cloud must have intermixed

with other Oort clouds in the past.

And so what fraction of the Oort cloud truly belongs to us,

belongs to what was scattered from Jupiter and Saturn,

what fraction of it could in fact be interstellar visitors?

And of course, we’ve got excited about this recently

because of Oumuamua, this interstellar asteroid,

which seemed to be at the time

the first evidence of an interstellar object.

But when you think about the Oort cloud intermixing,

it may be that a large fraction of comets,

comets are seeded from the Oort cloud

that eventually come in.

Some of those comets may indeed

have been interstellar in the first place

that we just didn’t know about through this process.

There even is an example, I can’t remember the name,

there’s an example of a comet

that has a very peculiar spectral signature

that has been hypothesized

to have actually been an interstellar visitor,

but one that was essentially sourced

through this Oort cloud mixing.

And so this is kind of intriguing.

And also, the outer solar system is just such a,

it’s like the bottom of the ocean.

We know so little about what’s on the bottom

of our own planet’s ocean,

and we know next to nothing

about what’s on the outskirts of our own solar system.

It’s all darkness.


So like, that’s one of the things

is to understand the phenomenon, we need light.

And we need to see how light interacts with it

or what light emanates from it.

But most of our universe is darkness.

So it’s, there could be a lot of interesting stuff.

I mean, this is where your interest is

with the cool worlds and the interesting stuff

lurks in the darkness, right?

Basically all of us, you know, 400 years of astronomy,

our only window into the universe has been light.

And that has only changed quite recently

with the discovery of gravitational waves.

That’s now a new window.

And hopefully, well, to some degree, I guess,

solar neutrinos we’ve been detecting for a while,

but they come from the sun, not interstellar space.

But we may be able to soon detect neutrino messages

has even been hypothesized as a way of communicating

between civilizations as well,

or just do neutrino telescopes to study the universe.

And so there’s a growing interest

in what we’d call multi-messenger astronomy now.

So not just messages from light,

but messages from these other physical packets

of information that are coming our way.

But when it comes to the outer solar system,

light really is our only window.

There’s two ways of doing that.

One is you detect the light from the Oort cloud object

itself, which as I just said, is very, very difficult.

There’s another trick,

which we do in the Kuiper belt especially,

and that’s called an occultation.

And so sometimes those objects will just pass in front

of a distant star, just coincidentally.

These are very, very brief moments.

They last for less than a second.

And so you have to have a very fast camera to detect them,

which conventionally astronomers

don’t usually build fast cameras.

Most of the phenomena we observe occurs on hours,

minutes, days even.

But now we’re developing cameras which can take,

you know, thousands of images per second,

and yet do it at the kind of astronomical fidelity

that we need for this kind of precise measurement.

And so you can see these very fast dips.

You even get these kind of diffraction patterns

that come around, which are really cool to look at.

And that’s, I kind of love it

because it’s almost like passive radar.

You have these pinpricks of light.

Imagine that you live in a giant black sphere,

but there’s these little pinholes that have been poked.

And through those pinholes,

almost laser light is shining through.

And inside this black sphere,

there are unknown things wandering around,

drifting around that we are trying to discover.

And sometimes they will pass in front of those

little pencil-thin laser beams, block something out.

And so we can tell that it’s there.

And it’s not an active radar

because we didn’t actually beam anything out

and get a reflection off,

which is what the sun does.

The sun’s light comes off and it comes back.

That’s more like an active radar system.

There’s more like a passive radar system

where we are just listening very intently.

And so I’m kind of so fascinated by that,

the idea that we could map out the rich architecture

of the outer solar system just by doing something

that we could have done potentially for a long time ago,

which is just listening in the right way,

just tuning our instrumentation

to the correct way of not listening,

but viewing the universe to catch those objects.

Yeah, I mean, it’s really fascinating.

It seems almost obvious that your efforts,

when projected out in over like 100, 200 years,

will have a really good map,

through even methods like basically transit timing,

high-resolution transit timing,

but basically the planetary

and the planet satellite movements

of all the different star systems out there.

Yeah, and it could revolutionize

the way we think about the solar system.

I mean, that revolution has happened several times

in the past when we discovered Vesta in the 19th century.

That was, I think, the seventh planet for a while

or the eighth planet when it was first discovered.

And then we discovered Ceres

and there was a bunch of asteroid objects, Janus.

And so for a while, the textbooks had,

there was something like 13 planets in the solar system.

And then that was just a new capability

that was emerging to detect those small objects.

And then we ripped that up and said,

no, no, we’re gonna change the definition of a planet.

And then the same thing happened

when we started looking at the outer skirts

of the solar system.

Again, we found Eris, we found Sedna,

these objects which resembled Pluto.

And the more and more of them we found, make, make.

And eventually we, again, had to rethink

the way we even contextualize what a planet is

and what the nature of the outer solar system is.

So regardless as to what you think about the debate

about whether Pluto should be devoted or not,

which I know often evokes a lot of strong feelings,

it is an incredible achievement

that we were able to transform our view

of the solar system in a matter of years

just by basically charge-coupled devices,

the things that’s in cameras.

Though the invention of that device

allowed us to detect objects

which were much further away, much fainter,

and revealed all of this stuff that was there all along.

And so that’s the beauty of astronomy.

There’s just so much to discover,

and even in our own backyard.

Do you ever think about this?

Do you imagine what are the things

that will completely change astronomy

over the next 100 years?

Like if you transport yourself forward 100 years,

what are the things that will blow your mind

when you look at, wait, what?

Would it be just a very high-resolution mapping of things?

Like, holy crap.

Like one surprising thing might be,

holy crap, there’s like Earth-like moons everywhere.

And another one could be

just totally different devices for sensing.

Yeah, I think usually astronomy moves forward dramatically,

and science in general,

when you have a new technological capability

come online for the first time.

And we kind of just gave examples of that there

with the solar system.

So what kind of new capabilities

might emerge in the next 100 years?

The capability I would love to see is not just,

I mean, in the next 10, 20 years,

we’re hoping to take these pale blue dot images

we spoke about.

So that requires building something like JWST,

but on an even larger scale,

and optimize for direct imaging.

You’d have to have either coronagraph

or a starshade or something to block out the starlight

and reveal those pale blue dots.

So in the next sort of decades,

I think that’s the achievement

that we can look forward to in our lifetimes

is to see photos of other Earths

going beyond that, maybe in our lifetimes,

towards the end of our lifetimes, perhaps.

I’d love it if we,

and I think it’s technically possible

as Breakthrough Starshot

are giving us a lot of encouragement with,

to maybe send a small probe to the nearest stars

and start actually taking high resolution images

of these objects.

There’s only so much you can do from far away

if you want to have,

and we can see it in the solar system.

I mean, there’s only so much you can learn about Europa

by pointing Hubble Space Telescope at it.

But if you really want to understand that moon,

you’re gonna have to send something to orbit it

to hopefully land on it and drill down to the surface.

And so the idea of even taking a flyby

and doing a snapshot photo that gets beamed back

that could be,

doesn’t even have to be more than 100 pixels by 100 pixels.

Even that would be a completely game-changing capability

to be able to truly image these objects.

And maybe at home in our own solar system,

we can certainly get to a point

where we produce crude maps of exoplanets.

One of the, kind of the ultimate limit

of what a telescope could do is governed by its size.

And so the largest telescope you could probably ever build

would be one that was the size of the sun.

There’s a clever trick for doing this

without physically building a telescope

that’s the size of the sun,

and that’s to use the sun as a gravitational lens.

This was proposed, I think, by Von Eschlemann in like 1979,

but it builds upon Einstein’s theory of general relativity,

of course, that there is a warping of light,

a bending of light from the sun’s gravitational field.

And so a distant starlight, it’s like a magnifying glass.

Anything that bends light is basically,

can be used as a telescope.

It’s gonna bend light to a point.

Now it turns out the sun’s gravity is not strong enough

to create a particularly great telescope here

because the focus point is really out in the Kuiper belt.

It’s at 550 astronomical units away from the earth.

So 550 times further away from the sun than we are.

And that’s beyond any of our spacecraft have ever gone.

So you have to send a spacecraft to that distance,

which would take 30, 40 years,

even optimistically improving

our chemical propulsion system significantly.

You’d have to bound it into that orbit,

but then you could use the entire sun as your telescope.

And with that kind of capability,

you could image planets to kilometer scale

or resolution from afar.

And that really makes you wonder.

I mean, if we can conceive, maybe we can’t engineer it,

but if we can conceive of such a device,

what might other civilizations be currently observing

about our own planet?

And perhaps that is why nobody is visiting us,

because there is so much you can do from afar

that to them, that’s enough.

Maybe they can get to the point

where they can detect our radio leakage,

they can direct our terrestrial television signals,

they can map out our surfaces,

they can tell we have cities,

they can even do infrared mapping of the heat island effects

and all this kind of stuff.

They can tell the chemical composition of our planet.

And so that might be enough.

Maybe they don’t need to come down to the surface

and study, do anthropology

and see what our civilization is like.

But there’s certainly a huge amount you can do,

which is significantly cheaper to some degree

than flying there,

just by exploiting cleverly

the physics of the universe itself.

So your intuition is, and this very well might be true,

that observation might be way easier than travel.

From our perspective, from an alien perspective,

like we could get very high resolution imaging

before we could ever get there.

It depends on what information you want.

If you want to know the chemical composition

and you want to know kilometer scale maps of the planet,

then you could do that from afar

with some version of these kind of gravitational lenses.

If you want to do better than that,

if you want to image a newspaper

sat on the porch of somebody’s house,

you’re going to have to fly there.

There’s no way, unless you had a telescope

the size of such a star or something,

you just simply cannot collect enough light

to do that from many light years away.

So there is certainly reasons

why visiting will always have its place,

depending on what kind of information you want.

We’ve proposed in my team, actually,

that the sun is the ultimate pinnacle of telescope design,

but flying to 1,000 AU is a real pain in the butt

because it’s just going to take so long.

And so a more practical way of achieving this

might be to use the Earth.

Now, the Earth doesn’t have anywhere near enough gravity

to create a substantial gravitational lens,

but it has an atmosphere,

and that atmosphere refracts light, it bends light.

So whenever you see a sunset,

just as the sun’s setting below the horizon,

it’s actually already beneath the horizon.

It’s just the light is bending through the atmosphere.

It’s actually already about half a degree down beneath,

and what you’re seeing is that curvature of the light path.

And your brain interprets it, of course,

to be following a straight line

because your brain always thinks that.

And so you can use that bending.

Whenever you have bending, you have a telescope.

And so we’ve proposed to my team

that you could use this refraction

to similarly create an Earth-sized telescope.

Called the Terrascope.

The Terrascope, yeah.

We have a great video on this.

And this-

Do you have a paper on the Terrascope?

I do, yeah.


Sometimes I get confused with this

because I’ve heard of an Earth-sized telescope

because of the,

maybe you’ve heard of the Event Horizon Telescope,

which took an image of,

well, it’s taking an image right now

of the center of our black hole.

And it’s very impressive,

and it previously did Messier 87,

a nearby supermassive black hole.

And so those images were interferometric.

So they were small telescopes scattered across the Earth,

and they combined the light paths together,


to create effectively an Earth-sized angular resolution.

Telescopes always have two properties.

There’s the angular resolution,

which is how small of a thing you can see on the surface,

and then there’s the magnification,

how much brighter does that object get

versus just your eye or some small object.

Now, what the Event Horizon Telescope did,

it traded off amplification or magnification

for the angular resolution.

That’s what it wanted.

It wanted that high angular resolution,

but it doesn’t really have much photon-collecting power

because each telescope individually is very small.

The Telescope is different

because it is literally collecting light

with a light bucket,

which is essentially the size of the Earth.

And so that gives you both benefits, potentially,

not only the high angular resolution

that a large aperture promises you,

but also actually physically collects all those photons.

So you can detect light from very, very far away,

the very outer edges of the universe.

And so we propose this as a possible future

technological way of achieving these extreme goals,

ambitious goals we have in astronomy.

It’s a very difficult system to test

because you essentially have to fly out

to these focus points,

and these focus points lie beyond the moon.

So you have to have someone who is willing

to fly beyond the moon

and hitchhike an experimental telescope onto it

and do that cheaply.

If it was something doing low Earth orbit, it’d be easy.

You could just attach a CubeSat

to the next Falcon 9 rocket or something and test it out.

It’d probably only cost you a few tens of thousands of

dollars, maybe a hundred thousand dollars.

There’s basically no one who flies out that far

except for bespoke missions,

such as like a mission that’s going to Mars or something

that would pass through that kind of space.

And they typically don’t have a lot of leeway

and excess payload that they’re willing to strap on

for radical experiments.

So that’s been the problem with it.

In theory, it should work beautifully,

but it’s a very difficult idea to experimentally test.

Can you elaborate why the focal point is that far away?

So you get about half a degree bend

from the Earth’s atmosphere

when you’re looking at the sun at the horizon

and you get that two times over

if you’re outside of the planet’s atmosphere

because it comes, you know,

the star is half a bend to you still on the horizon

and half a degree back out either way.

So you get about a one degree bend.

You take the radius of the Earth,

which is about 7,000 kilometers

and do your arctan function,

you’ll end up with a distance that’s about two,

it’s actually the inner focal point is about two thirds

of the distance of the Earth-moon system.

The problem with that inner focal point is not useful

because that light ray path

had to basically scrape the surface of the Earth.

So it passes through the clouds,

it passes through all the thick atmosphere,

it gets a lot of extinction along the way.

If you go higher up in altitude, you get less extinction.

In fact, you can even go above the clouds

and so that’s even better

because the clouds obviously are gonna be a pain in the neck

for doing anything optical.

But the problem with that is that the atmosphere,

because it gets thinner at higher altitude,

it bends light less.

And so that pushes the focal point out.

So the most useful focal point

is actually about three or four times the distance

of the Earth-moon separation.

And so that’s what we call one of the Lagrange points,

essentially, out there.

And so there is a stable orbit,

it’s kind of the outermost stable orbit

you could have around the Earth.

So the atmosphere does bad things to the signal.

Yeah, it’s absorbing light.

Is it possible to reconstruct, to remove the noise,

whatever, so it’s just strength, it’s nothing else?

It’s possible to reconstruct.

I mean, to some degree we do this,

there’s a technology called adaptive optics

that can correct for what’s called wavefront errors

that happen through the Earth’s atmosphere.

The Earth’s atmosphere is turbulent,

it is not a single plane of air of the same density,

there’s all kind of wiggles and currents in the air.

And so that each little layer is bending light

in slightly different ways.

And so the light actually kind of follows a wiggly path

on its way down.

What that means is that two light rays,

which are traveling at slightly different

spatial separations from each other,

will arrive at the detector at different times,

because one maybe goes on more or less a straight path

and the one wiggles down a bit more before it arrives.

And so you have an incoherent light source.

And when you’re trying to do imagery construction,

you always want a coherent light source.

So the way they correct for this is that this,

if this path had to travel a little bit faster,

the straight one goes faster

and the wiggly one takes longer,

the mirror is deformable.

And so you actually bend the mirror on this,

on the straight one down a little bit

to make it an equivalent light path distance.

So the mirror itself has all these little actuators,

it’s actually made up of like thousands of little elements,

almost looks like a liquid mirror,

because they can manipulate it in kind of real time.

And so they scan the atmosphere with a laser beam

to tell what the deformations are in the atmosphere

and then make the corrections to the mirror

to account for it.

That’s amazing.

So you could, you could do something like this

for the terrascope, but it would be-

It’s cheaper and easier to go above the atmosphere

and just fly out.

I think so.

It would be very, it’s a very,

that’s a very challenging thing to do.

And normally when you do adaptive optics, as it’s called,

you’re looking straight up.

So you’re, or very close to straight up.

If you look at the horizon,

we basically never do astronomical observations

on the horizon,

because you’re looking through more atmosphere.

If you go straight up,

you’re looking at the thinnest portion of atmosphere


But as you go closer and closer towards the horizon,

you’re increasing what we call the air mass,

the amount of air you have to travel through.

So here it’s kind of the worst case

because you’re going through the entire atmosphere

in and out again with a terrascope.

So you’d need a very impressive adaptive optics system

to correct for that.

So yeah, I would say it’s probably simpler,

at least for proof of principle,

just to test it with having some satellite

that was at a much wider orbit.

Now, speaking of traveling out into deep space,

you already mentioned this a little bit.

You made a beautiful video

called The Journey to the End of the Universe.

And sort of at the start of that,

you’re talking about Alpha Centauri.

So what would it take for humans

or for human-like creatures to travel out to Alpha Centauri?

There’s a few different ways of doing it, I suppose.

One is, it depends on how fast your ship is.

That’s always gonna be the determining factor.

If we devised some interstellar propulsion system

that could travel a fraction of the speed of light,

then we could do it in our lifetimes,

which is, I think, what people normally dream of

when they think about interstellar propulsion and travel,

that you could literally step onto the spacecraft.

Maybe a few years later,

you step off an Alpha Centauri B,

you walk around the surface

and come back and visit your family.

There would be, of course,

a lot of relativistic time dilation

as a result of that trip.

You would have aged a lot less than people back on Earth

by traveling close to the speed of light

for some fraction of time.

The challenge of this, of course,

is that we have no such propulsion system

that can achieve this.


But do you think it’s possible?

Like, so you have a paper called The Halo Drive,

fuel-free relativistic propulsion of large masses

via recycled boomerang photons.

So do you think, first of all, what is that?

And second of all,

how difficult are alternate propulsion systems?

Yeah, so before I took on The Halo Drive,

there was an idea,

because I think The Halo Drive

is not gonna solve this problem.

I’ll talk about The Halo Drive in a moment,

but The Halo Drive is useful for a civilization

which is a bit more advanced than us,

that has spread across the stars,

and is looking for a cheap highway system

to get across the galaxy.

For that first step,

because just to context that,

The Halo Drive requires a black hole.

So that’s why you’re not gonna be able to do this

on the Earth right now.

But there are lots of black holes in the Milky Way,

so that’s the good news.

So we’ll come to that in a moment.

But if you’re trying to travel to Alpha Centauri

without a black hole,

then there are some ideas out there.

There was a Project Daedalus and Project Icarus

that were two projects

that the British Interplanetary Society conjured up

on sort of a 20, 30 year timescale.

And they asked themselves,

if we took existing and speculatively,

but realistic attempts at future technology

that are emerging over the next few decades,

how far could we push into that travel system?

And they settled on fusion drives in that.

So if we had the ability to essentially either detonate,

you can always imagine that kind of nuclear fission

or nuclear fusion bombs going off behind the spacecraft

and propelling it that way,

or having some kind of successful nuclear fusion reaction,

which obviously we haven’t really demonstrated yet

as a propulsion system,

then you could achieve something like 10%

the speed of light in those systems.

But these are huge spacecrafts.

And I think you need a huge spacecraft

if you’re gonna take people along.

The conversation recently has actually switched

and that idea is kind of seems a little bit antiquated now.

And most of us have kind of given up on the idea

of people physically, biologically

stepping on board the spacecraft.

And maybe we’ll be sending something

that’s more like a microprobe

that maybe just weighs a gram or two.

And that’s much easier to accelerate.

You could push that with a laser system to very high speed,

get it to maybe 20% the speed of light.

It has to survive the journey.

Probably a large fraction of them won’t survive the journey,

but they’re cheap enough

that you could maybe manufacture millions of them.

And some of them do arrive and able to send back an image

or maybe even if you wanted to have a person there,

we might have some way of doing like a telepresence

or some kind of delayed telepresence

or some kind of reconstruction of the planet

which is sent back

so you can digitally interact with that environment

in a way which is not real time,

but representative of what that planet

would be like to be on the surface.

So we might be more like digital visitors to these planets,

certainly far easier practically to do that

than physically forcing this wet chunk of meat

to fly across space to do that.

And so that’s maybe something

we can imagine down the road.

The Halo Drive, as I said, is thinking even further ahead.

And if you did want to launch large masses,

large masses could even be planet-sized things

in the case of the Halo Drive,

you can use black holes.

So this is kind of a trick of physics.

You know, I often think of the universe

as like a big computer game

and you’re trying to find cheat codes, hacks,

exploits that the universe didn’t intend for you to use.

But once you find them,

you can address all sorts of interesting capabilities

that you didn’t previously have.

And the Halo Drive does that with black holes.

So if you have two black holes,

which is a very common situation,

a binary black hole,

and they’re in spiraling towards each other,

LIGO has detected, I think, dozens of these things,

maybe even over a hundred at this point.

And these things, as they merge together,

the pre-merger phase,

they’re orbiting each other very, very fast,

even close to the speed of light.

And so Freeman Dyson, before he passed away,

I think in the 70s,

he had this provocative paper called Gravitational Machines,

and he suggested that you could use neutron stars

as a interstellar propulsion system.

And neutron stars are sort of the lower mass version

of a binary black hole system, essentially.

In this case,

he suggested just doing gravitational slingshot,

just fly your spacecraft into this very compact

and relativistic binary system.

And you do need neutron stars

because if there were two stars,

they’d be physically touching each other.

So the neutron stars are so small,

like 10 kilometers across,

they can get really close to each other

and have these very, very fast orbits

with respect to each other.

You shoot your spacecraft through,

right through the middle,

like it’s flying through the eye of a needle,

and you do a slingshot around one of them,

and you do it around the one

that’s coming sort of towards you.

So one will be coming away,

one will be coming towards you at any one point.

And then you could basically steal

some of the kinetic energy in the slingshot.

In principle, you can set up to twice the speed.

You can take your speed,

and it becomes your speed

plus twice the speed of the neutron star in this case.

And that would be your new speed after the slingshot.

This seems great because it’s just free energy, basically.

You’re not doing any,

you’re not generating to have a nuclear power reactor

or anything to generate this,

you’re just stealing it.

And indeed, you can get to relativistic speeds this way.

So I loved that paper,

but I had a criticism.

And the criticism was that this is like

trying to fly your ship into a blender, right?

This is two neutron stars,

which have huge tidal forces.

And they’re whipping around each other

once every second or even less than a second.

And you’re trying to fly your spaceship

and do this maneuver that is pretty precarious.

And so it just didn’t seem practical to me

to have to do this, but I loved it.

And so I took that idea,

and this is how science is.

It’s iterative.

You take a previous great man’s idea

and you just sort of maybe slightly tweak it and improve it.

That’s how I see the Hiller drive.

And I just suggested,

why not replace those out for black holes?

Which is certainly very common.

And rather than flying your ship

into that hell hole of a blender system,

you just stand back and you fire a laser beam.

Now, because black holes

have such intense gravitational fields,

they can bend light into complete 180s.

They can actually become mirrors.

So the sun bends light by maybe a fraction of a degree

through gravitational lensing,

but a compact object like a black hole can do a full 180.

In fact, obviously, if you went too close,

if you put the laser beam too close,

the black hole would just fall into it

and never come back out.

So you just kind of push it out, push it out, push it out

until you get to a point

where it’s just skirting the event horizon.

And then that laser beam skirts around and it comes back.

Now, the laser beam wants to do a,

I mean, it is doing a gravitational slingshot,

but laser, I mean, light photons can’t speed up

unlike the spaceship case.

So instead of speeding up,

the way they steal energy is they increase their frequency.

So they become higher energy photon packets, essentially.

They get blue shifted so that you send

maybe a red laser beam that comes back blue.

It’s got more energy in it.

And because photons carry momentum,

which is somewhat unintuitive in everyday experience,

but they do, that’s how solar sails work.

They carry momentum, they push things.

You can even use them as laser tweezers

and things to pick things up.

Because they push,

it comes back with more momentum than it left.

So you get an acceleration force from this.

And again, you’re just seeing energy

from the black hole to do that.

So you can get up to the same speed.

It’s basically the same idea as Freeman Dyson,

but doing it from a safer distance.

And there should be of order of a million or so

or 10 million black holes in the Milky Way galaxy.

Some of them would be even as close

as sort of 10 to 20 light years

when you do the occurrence rate statistics

of how close you might expect, feasibly want to be.

They’re of course difficult to detect because they’re black.

And so they’re inherently hard to see.

But statistically, there should be plenty out there

in the Milky Way.

And so these objects would be natural waypoint stations.

You could use them to both accelerate away

and to break and slow down.

And on top of all this,

you know, we’ve been talking about astronomy and cosmology.

There’s been a lot of exciting breakthroughs

in detection and exploration of black holes.

So the boomerang photons that you’re talking about,

there’s been a lot of work on photon rings

and just all the fun stuff going on outside the black holes.

So all the garbage outside is actually might be the thing

that holds a key to understanding what’s going on inside.

And there’s the Hawking radiation.

There’s all kinds of fascinating stuff like,

I mean, there’s trippy stuff about black holes

that I can’t even, well, most people don’t understand.

I mean, the holographic principle with the plate

and the information being stored potentially outside

of the black hole.

I don’t even, I can’t even comprehend

how you can project a three-dimensional object

onto a 2D and somehow store information

where it doesn’t destroy it.

And if it does destroy it, challenging all the physics.

All of this is very interesting,

especially for kind of more practical applications

of how the black hole can be used for propulsion.

Yeah, I mean, it may be that black holes are used

in all sorts of ways by advanced civilizations.

I think, again, it’s been a popular idea

in science fiction or science fiction trope

that Sagittarius A star, the supermassive black hole

in a centrified galaxy could be the best place

to look for intelligent life in the universe

because it is a giant engine in a way.

You know, a unique capability of a black hole

is you can basically throw matter into it

and you can get these jets that come out,

the accretion disks and the jets that fly out.

And so you can more or less use them to convert matter

into energy V equals MC squared.

And there’s pretty much nothing else

except for annihilation with its own antiparticle

as a way of doing that.

So they have some unique properties.

You could perhaps power a civilization

by just throwing garbage into a black hole, right?

Just throwing asteroids in and power your civilization

with as much energy as you really would ever plausibly need.

And you could also use them to accelerate

away across the universe.

And you can even imagine using small artificial black holes

as thermal generators, right?

So the Hawking radiation from them

kind of exponentially increases

as they get smaller and smaller in size.

And so a very small black hole,

one that you can almost imagine like holding in your hand

would be a fairly significant heat source.

And so that raises all sorts of prospects

about how you might use that in an engineering context

to power your civilization as well.

Oh, you have a video

on becoming a Kardashev Type I civilization.

What’s our hope for doing that?

We’re a few orders of magnitude away from that.

Yeah, it is surprising.

I think people tend to think

that we’re close to this scale.

The Kardashev Type I is defined as a civilization

which is using as much energy

as is essentially incident upon the planet from the star.

So as of order, I think for the Earth

of something like 10 to the five terawatts

or 10 to the seven terawatts

is a gigantic amount of energy.

And we’re using a tiny, tiny, tiny fraction

of that right now.

So if you became a Kardashev Type I civilization,

which is seen not necessarily as a goal into itself,

I think people think, well, why are we aspiring

to become this energy hungry civilization?

Surely our energy needs might improve our efficiency

or something as time goes on.

But ultimately the more energy you have access to,

the greater your capabilities will be.

I mean, if you wanna lift Mount Everest into space,

there is just a calculable amount of potential energy change

that that’s going to take in order to accomplish that.

And the more energy you have access to as a civilization,

then clearly the easier that energy achievement

is going to be.

So it depends on what your aspirations are

as a civilization.

It might not be something you wanna ever do, but.

Well, but we should make clear

that lifting heavy things isn’t the only thing.

It’s just doing work.

So it could be computation.

It could be more and more and more and more sophisticated

and larger and larger and larger computation,

which is, it does seem where we’re headed

with the very fast increase in the scale

and the quality of our computation

outside the human brain, artificial computation.

Yeah, I mean, computation is a great example of,

I mean, already I think something like 10%

of US power electricity use

is going towards the supercomputing centers.

There’s a vast amount of current energy needs

which are already going towards computing

and will surely only increase over time.

If we start ever doing anything like mind uploading

or creating simulated realities,

that cost will surely become almost a dominant source

of our energy requirements at that point

if civilization completely moves over

to this kind of post-humanism stage.

And so it’s not unreasonable that our energy needs

would continue to grow.

Certainly historically, they always have

at about 2% per year.

And so if that continues,

there is gonna be a certain point

where you’re running up against the amount of energy

which you can harvest

because you’re using,

even if you cover the entire planet in solar panels,

there’s no more energy to be had.

And so there’s a few ways of achieving this.

I sort of talked about in the video

how there were several renewable energy sources

that we’re excited about,

like geothermal, wind power, waves,

but pretty much all of those

don’t really scratch the surface

or don’t really scratch the itch

of getting to a Kardashev type one civilization.

They’re meaningful now.

I would never tell anybody don’t do wind power now

because it’s clearly useful

at our current stage of civilization,

but it’s gonna be a pretty negligible fraction

of our energy requirements

if we got to that stage of development.

And so there has to be a breakthrough

in either our ability to harvest solar energy,

which would require maybe something like a space array

of solar panels of beaming the energy back down,

or some developments and innovations in nuclear fusion

that would allow us to essentially

reproduce the same process

of what’s producing the solar photons, but here on Earth.

But even that comes with some consequences.

If you’re generating the energy here on Earth

and you’re doing work on it on Earth,

then that work is gonna produce waste heat,

and that waste heat is gonna increase

the ambient temperature of the planet.

And so even if this isn’t really a greenhouse effect

that you’re increasing the temperature of the planet,

this is just the amount of computers that are churning.

You put your hand to a computer,

you can feel the warmth coming off them.

If you do that much work of literally

the entire instant energy of the planet is doing that work,

the planet’s gonna warm up significantly

as a result of that.

And so that clearly indicates

that this is not a sustainable path,

that civilizations, as they approach Kailashev Type I,

are gonna have to leave planet Earth,

which is really the point of that video,

to show that it’s, a Kailashev Type I civilization,

even though it’s defined as instant energy upon a planet,

that is not a species that is gonna still be living

on their planet, at least in isolation.

They will have to be harvesting energy from afar,

they will have to be doing work on that energy

outside of their planet,

because otherwise you’re gonna dramatically change

the environment in which you live.

Well, yeah, so the more energy you create,

the more energy you use,

the more, the higher the imperative

to expand out into the universe,

but also not just the imperative, but the capabilities.

And you’ve kind of, as a side on your lab page,

mentioned that you’re sometimes interested

in astroengineering, so what kind of space architectures

do you think we can build to house humans

that are interesting things outside of Earth?

Yeah, I mean, there’s a lot of fun ideas here.

One of the classic ideas is an O’Neill cylinder,

or a Stanford torus.

These are like two rotating structures

that were devised in space.

They’re basically using the centrifugal force

as artificial gravity, and so these are structures

which tend to be many kilometers across

that you’re building in space,

but could potentially habitat millions of people

in orbit of the Earth.

Of course, you could imagine putting them,

if the expanse does a pretty good job, I think,

of exploring the idea of human exploration

of the solar system and having many objects,

many of the small near-Earth objects and asteroids

inhabited by mining colonies.

One of the ideas we’ve played around with our group

is this technology called a quasite.

A quasite is an extension, again,

we always tend to extend previous ideas.

Ideas build upon ideas.

An extension idea called a statite.

A statite was an idea proposed, I think,

by Ron Forwood in the 1970s.

1970s seemed to have all sorts of wacky ideas.

I don’t know what was going on then.

I think the Stanford torus, the O’Neill cylinder, statites,

the gravitational lens, people were really having fun

with dreaming about space in the 70s.

The statite is basically a solar sail,

but it’s such an efficient solar sail

that the outward force of radiation pressure

equals the inward force of gravity from the sun.

And so it doesn’t need to orbit.

Normally you avoid, the sun is pulling on us right now

through force of gravity, but we are not getting closer

towards the sun, even though we are falling towards the sun

because we’re in orbit, which means our translational speed

is just enough to keep us at the same altitude,

essentially, from the sun.

And so you’re in orbit,

and that’s how you maintain distance.

A statite doesn’t need to do that.

It could be basically completely static in inertial space,

but it’s just balancing the two forces

of radiation pressure and inward gravitational pressure.

A quasite is the in-between of those two states.

So it has some significant outward pressure,

but not enough to resist fully falling into the star.

And so it compensates for that

by having some translational motion.

So it’s in between an orbit and a statite.

And so what that allows you to do

is maintain artificial orbits.

So normally, if you want to calculate your orbital speed

of something at, say, half an AU,

you would use Kepler’s third law and go through that,

and you’d say, okay, if it’s at half an AU,

I can calculate the period by p squared

as proportional to a cubed and go through that.

But for a quasite, you can basically have any speed you want.

It’s just a matter of how much of the gravitational force

are you balancing out.

You effectively enter an orbit

where you’re making the mass of the star

be less massive than it really is.

So it’s as if you were orbiting a 0.1 solar mass star

or a 0.2 solar mass star, whatever you want.

And so that means that Mercury orbits

with a pretty fast orbital speed around the sun

because it’s closer to the sun than we are.

But we could put something in Mercury’s orbit

that would have a slower speed,

and so it would co-track with the Earth.

And so we would always be aligned with them at all times.

And so this could be useful

if you wanted to have either a chain of colonies

or something that were able to easily communicate

and move between one another, between these different bases.

You’d probably use something like this

to maintain that easy transferability.

Or you could even use it

as a space weather monitoring system,

which was actually proposed in the paper.

We know that major events like the Carrington event

that happened, it can knock out

all of our electromagnetic systems quite easily.

A major solar flare could do that, a geomagnetic storm.

But if we had the ability to detect

those higher elevated activity cycles in advance,

the problem is they travel, obviously, pretty fast,

and so it’s hard to get ahead of them.

But you could have a station

which is basically sampling solar flares

very close to the surface of the Earth,

and as soon as it detects anything suspicious magnetically,

it could then send that information

straight back at the speed of light to your Earth

and give you maybe a half an hour warning or something,

that something bad was coming,

and you should shut off all your systems

or get in your Faraday cage now and protect yourself.

And so these quasites are kind of a cool trick

of, again, kind of hacking the laws of physics.

It’s like another one of these exploits

that the universe seems to allow us to do

to potentially manifest these artificial systems

that would otherwise be difficult to produce.

So leveraging natural phenomena.


That’s always the key, is to work,

in my mind, is to work with nature.

That’s how I see astroengineering, rather than against it.

You’re not trying to force it to do something.

That’s why I always think solar energy is so powerful,

because in the battle against nuclear fusion,

you’re really fighting a battle

where you’re trying to confine plasma

into this extremely tight space.

The sun does this for free.

It has gravitation.

And so that’s, in essence, what a solar panel does.

It is a nuclear fusion reactor-fueled energy system,

but it’s just using gravitation for the confinement

and having a huge standoff distance

for its energy collection.

And so there are tricks like that.

It’s a very naive, simple trick in that case,

where we can, rather than having to reinvent the wheel,

we can use the space infrastructure, if you like,

the astrophysical infrastructure

that’s already there to our benefit.

Yeah, I think in the long arc of human history,

probably natural phenomena is the right solution.

That’s the simple, that’s the elegant solution,

because all the power’s already there.

That’s why a Dyson sphere in the long, sort of,

well, you don’t know what a Dyson sphere would look like,

but some kind of thing that leverages the power,

the energy that’s already in the sun,

is better than creating artificial nuclear fusion reaction.

But then again, that brings us to the topic of AI.

How much of this, if we’re traveling out there,

interstellar travel, or doing some of the interesting things

we’ve been talking about,

how much of those ships would be occupied

by AI systems, do you think?

What would the,

what would be the living organisms occupying those ships?

Yeah, it’s depressing to think about AI

in the search for life, because it has,

I mean, I’ve been thinking about this a lot

over the last few weeks with playing around

with Chat GPT-3, like many of us,

and being astonished with its capabilities.

And you see that our society is undergoing a change

that seems significant in terms of the development

of artificial intelligence.

We’ve been promised this revolution,

this singularity for a long time,

but it really seems to be stepping up

its pace of development at this point.

And so that’s interesting, because as someone

who looks for alien life out there in the universe,

it sort of implies that our current stage of development

is highly transitional, and that, you know,

you go back for the last four and a half billion years,

the planet was dumb, essentially.

If you go back the last few thousand years,

there was a civilization,

but it wasn’t really producing any technosignatures.

And then over the last maybe hundred years,

there’s been something that might be detectable from afar.

But we’re potentially approaching this cusp

where we might imagine it, I mean,

we’re thinking of like maybe years and decades

with AI development, typically when we talk about this,

but as an astronomer, I have to think about

much longer timescales of centuries,

millennia, millions of years.

And so if this wave continues over that timescale,

which is still the blink of an eye on a cosmic timescale,

that implies that everything will be AI,

essentially, out there,

if this is a common behavior.

And so that’s intriguing,

because it sort of implies that we are special

in terms of our moment in time as a civilization,

which normally is something

we’re averse to as astronomers.

We normally like this mediocrity principle,

we’re not special, we’re a typical part of the universe,

similar to the cosmological principle.

But in a temporal sense, we may be in a unique location.

And perhaps that is part of the solution

to the Fermi paradox, in fact,

that if it is true that planets tend to go through

basically three phases,

dumb life for the vast majority,

a brief period of biological intelligence,

and then an extended period of artificial intelligence

that they transition to,

then we would be at a unique and special moment

in galactic history that would be of particular interest

for any anthropologists out there in the galaxy, right?

This would be the time

that you would want to study a civilization very carefully.

You wouldn’t want to interfere with it,

you would just want to see how it plays out.

Kind of similar to the ancestor simulations,

though sometimes talked over the simulation argument,

that you are able to observe perhaps your own origins

and study how the transformation happens.

And so yeah, that has for me recently been throwing

the Fermi paradox a bit on its head.

And this idea of the zoo hypothesis that we may be monitored

which has for a long time been sort of seen as a fringe idea

even amongst the SETI community.

But if we live in this truly transitional period,

it adds a lot of impetus to that idea, I think.

Well, even AI itself would,

by its very nature, would be observing us.

By, you know, it’s like a human,

there used to be this concept of human computation,

which is actually exactly what’s feeding

the current language models,

which is leveraging all the busy stuff we’re doing

to do the hard work of learning.

So like the language models are trained

on human interaction and human language on the internet.

And so AI feeds on the output of brain power from humans.

And so like it would be observing and observing

and it gets stronger as it observes.

So it actually gets extremely good at observing humans.

And one of the interesting philosophical questions

that starts percolating is what makes us,

what is the interesting thing that makes us human?

We tend to think of it,

and you said like there’s three phases.

What’s the thing that’s hard to come by in phase three?

Is it something like scarcity, which is limited resources?

Is it something like consciousness?

Is that the thing that’s very,

that emerged the evolutionary process in biological systems

that are operating under constrained resources?

This thing that feels,

that it feels like something to experience the world,

which we think of as consciousness,

is that really difficult to replicate in artificial systems?

Is that the thing that makes us fundamentally human?

Or is it just a side effect

that we attribute way too much importance to?

Do you have a sense,

if we look out into the future and AI systems

are the ones that are traveling out there

to Alpha Centauri and beyond,

do you think they have to carry

the flame of consciousness with them?

No, not necessarily.

They may do, but they may,

it may not be unnecessarily,

I mean, I guess we’re talking about the difference here

between sort of an AGI, artificial general intelligence,

or consciousness, which are distinct ideas,

and you can certainly have one without the other.

So I could imagine.

I would disagree with this certainly in that statement.

Okay, okay.

I think it’s very possible

in order to have intelligence,

you have to have consciousness.

Okay, well, I mean, to a certain degree,

GPT-3 has a level of intelligence already.

It’s not a general intelligence,

but it displays properties of intelligence

with no consciousness, so.

Again, I would disagree.

Okay, okay.

Well, I don’t know.

Because you said, it’s very nice that you said

it displays properties of intelligence

in the same way it displays properties of intelligence,

I would say it’s starting to display

properties of consciousness.

It certainly could fool you that it’s conscious.

Correct, yeah.

So there’s, I guess, like a Turing test problem.

Like, if it’s displaying all those properties,

if it quacks like a parrot, looks like a parrot,

or quacks like a duck,

things like, isn’t it basically a duck at that point?

So yeah, I can see that argument.

It probably, I mean, certainly as an,

I tried to think about it

from the observer’s point of view as an astronomer.

What am I looking for?

Whether that intelligence is conscious or not

has little bearing, I think,

as to what I should be looking for

when I’m trying to detect evidence of them.

It would maybe affect their behavior

in ways that I can’t predict.

But that’s, again, getting into the game

of what I would call xenopsychology,

of trying to make projections

about the motivations of an alien species

is incredibly difficult.

And similarly, for any kind of artificial intelligence,

it’s unfathomable what its intentions may be.

I mean, I would sort of question

whether it would even be interested

in traveling between the stars at all.

If its primary goal is computation,

computation for the sake of computation,

then it’s probably gonna have a different way of,

it’s gonna be engineering its solar system

and the nearby material around it for a different goal

if it’s just simply trying to increase

computer substrate across the universe.

And that, of course, if that is its principal intention

to just essentially convert dumb matter

into smart matter as it goes,

then I think that would come into conflict

with our observations of the universe, right?

Because the Earth shouldn’t be here if that were true.

The Earth should have been transformed

into computer substrate by this point.

There has been plenty of time

in the history of the galaxy for that to have happened.

So I’m skeptical that we can,

I’m skeptical in the part that that’s a behavior

that AI or any civilization really engages in,

but I also find it difficult to find a way out of it,

to explain why that would never happen

in the entire history of the galaxy

amongst potentially, if life is common,

millions, maybe even billions of instant instantiations

of AI could have occurred across the galaxy.

And so that seems to be a knock against the idea

that there is life else, or intelligent life else

around in the galaxy.

The fact that that hasn’t occurred in our history

is maybe the only solid data point we really have

about the activities of other civilizations.

Of course, the scary one could be that

we just at this stage,

intelligent alien civilizations

just started destroying themselves.

It becomes too powerful.

Everything’s just too many weapons,

too many nuclear weapons,

too many nuclear weapon style systems

that just from mistake to aggression,

like the probability of self-destruction is too high

relative to the challenge of avoiding,

the technological challenges of avoiding self-destruction.

Do you mean that the AI destroys itself,

or we destroy ourselves prior to the advent of AI?

As we get smarter and smarter,

AI, either AI destroys us or other,

there could be just a million,

like AI is correlated,

the development of AI is correlated

with all this other technological innovation.

Genetic engineering,

all kinds of engineering at the nanoscale,

mass manufacture of things that could destroy us,

cracking physics enough to have very powerful weapons,

nuclear weapons, all of it, just too much.

Physics enables way too many things that can destroy us

before it enables the propulsion systems

that allow us to fly far enough away

before we destroy ourselves.

So maybe that’s what happens

to the other alien civilizations.

Is that your resolution?

Because I mean, I think us in the technosignature community

aren’t thinking about this problem seriously enough,

in my opinion.

We should be thinking about what AI is doing to our society

and the implications, what we’re looking for.

And so the only, I think part of this thinking

has to involve people like yourself

who are more intimate with the machine learning

and artificial intelligence world.

How do you reconcile in your mind,

you said earlier that you think

you can’t imagine a galaxy where life and intelligence

is not all over the place.

And if artificial intelligence is a natural progression

for civilizations, how do you reconcile that

with the absence of any information around us?

So any clues or hints of artificial behavior,

artificially engineered stars or colonization,

computer substrate, transform planets, anything like that?

It’s extremely difficult for me.

The Fermi paradox broadly defined

is extremely difficult for me.

And the terrifying thing is one thing I suspect

is that we keep destroying ourselves.

The probability of self-destruction

with advanced technology is just extremely high.

That’s why we’re not seeing it.

But then again, my intuition about why we haven’t

blown ourselves up with nuclear weapons,

it’s very surprising to me from a scientific perspective.

Given all the cruelty I’ve seen in the world,

given the power that nuclear weapons place in the hands

of a very small number of individuals,

it’s very surprising to me that we destroy ourselves.

And it seems to be a very low probability situation

we have happening here.

But, and then the other explanation is the zoo,

is the observation that we’re just being observed.

That’s the only other thing.

It’s just, it’s so difficult for me.

Of course, all of science, everything is very humbling.

It would be very humbling for me to learn

that we’re alone in the universe.

It would change, you know what?

Maybe I do want that to be true

because you want us to be special.

That’s why I’m resisting that thought maybe.

There’s no way we’re that special.

There’s no way we’re that special.

That’s where my resistance comes from.

I would just say, you know, the specialness is something,

we, implicitly in that statement,

there’s kind of an assumption

that we are something positive.

Like we’re a gift to this planet or something

and that makes us special.

But it may be that intelligence is more of an,

it’s like we’re like rats or cockroaches.

We’re an infestation of this planet.

We’re not some benevolent property

that a planet would ideally like to have,

if you can even say such a thing.

We may be not only generally a negative force

for a planet’s biosphere and its own survivability,

which I think you can make a strong argument about,

but we may also be a very persistent infestation

that may, even in, you know, interesting thoughts,

in the wake of a nuclear war,

would that be an absolute eradication of every human being,

which would be a fairly extreme event?

Or would the candela consciousness,

as you might call it, the flame of consciousness,

continue with some small pockets

that would maybe in 10,000 years, 100,000 years,

we’d see civilization reemerge

and play out the same thing over again?

Yeah, that’s certainly,

but nuclear weapons aren’t powerful enough yet.

But yes, but to sort of push back on the infestation,

sure, but the word special doesn’t have to be positive.

I just mean-

I think it tends to imply, but I take your point, yeah.

But maybe, just maybe extremely rare might be.

Yeah, and that, to me, it’s very strange

for me to be cosmically unique.

It’s just very strange.

I mean, that we’re the only thing

of this level of complexity in the galaxy

just seems very strange to me.

I would just, yeah, I do think it depends

on this classification.

I think there is sort of, again,

it’s kind of buried within there as a subtext,

but there is a classification that we’re doing here

that what we are is a distinct category of life,

let’s say, in this case, when we’re talking about intelligence

we are something that can be separated.

But of course, we see intelligence across the animal kingdom

in dolphins, humpback whales, octopuses,

crows, ravens, and so it’s quite possible

that these are all manifestations of the same thing.

And we are not a particularly distinct class,

except for the fact we make technology.

That’s really the only difference to our intelligence.

And we classify that separately,

but from a biological perspective, to some degree,

it’s really just all part of a continuum.

And so that’s why, when we talk about unique,

you are putting yourself in a box which is distinct

and saying this is the only example of things

that fall into this box.

But the walls of that box may themselves be a construct

of our own arrogance that we are something distinct.

But I was also speaking broadly for us,

meaning all life on earth,

but then it’s possible that there’s all kinds

of living ecosystems on other planets and other moons

that just don’t have interest in technological development.

Maybe technological development is the parasitic thing

that destroys the organism broadly.

And then maybe that’s actually one

of the fundamental realities.

Whatever broad way to categorize technological development,

that’s just the parasitic thing that just destroys itself.

It’s a cancer.

We’re floating around, sorry to interrupt.

We’re floating around this idea of the great filter

a little bit here.

So we’re asking, where is this?

Does it lie ahead of us?

Nuclear war may be imminent.

That would be a filter that’s ahead of us.

Or could it be behind us?

And that it’s the advent of technology

that is genuinely a rare occurrence in the universe.

And that explains the Fermi paradox.

And so that’s something that obviously people have debated

and argued about in SETI for decades and decades.

But it remains a persistent,

people argue whether it should be really called

a paradox or not.

But it remains a consistent apparent contradiction

that you can make a very cogent argument

as to why you expect life and intelligence

to be common in the universe.

And yet everything, everything we know about the universe

is fully compatible with just us being here.

And that’s a haunting thought.

But I’m not, I have no preference or desire

for that to be true.

I’m not trying to impose that view on anyone.

But I do ask that we remain open-minded

until evidence has been collected either way.

The thing is, it’s one of, if not the,

probably I would argue it’s the most important question

facing human civilization, or the most interesting.


I think scientifically speaking,

what question is more important than,

somehow, there could be other ways to sneak up to it,

but it gets to the essence of what we are,

what these living organisms are.

It’s somehow seeing another kind helps us understand.

It speaks to the human condition,

helps us understand what it is to be human to some degree.

Um, I think, you know, I have tried to remain very agnostic

about the idea of life and intelligence.

One thing I try to be more optimistic about,

and I’ve been thinking a lot with our searches

for life in the universe, is life in the past.

You can, I think it’s actually not that hard

to imagine we are the only civilization

in the galaxy right now living.

Yeah, to this current extent.

But there may be very many extinct civilizations.

If each civilization has a typical lifetime

comparable to, let’s say, AI is the demise of our own,

that’s only a few hundred years of technological development,

or maybe 10,000 years if you go back

to the Neolithic Revolution, the dawn of agriculture.

You know, hardly anything in cosmic time span.

That’s nothing, that’s the blink of an eye.

And so it’s not surprising at all

that we would happen not to coexist with anyone else.

But that doesn’t mean nobody else was ever here.

And if other civilizations come to that same conclusion

and realization, maybe they scour the galaxy around them,

don’t find any evidence for intelligence,

then they have two options.

They can either give up on communication

and just say, well, it’s never gonna happen.

We just may as well just, you know,

worry about what’s happening here on our own planet.

Or they could attempt communication,

but communication through time.

And that’s almost the most selfless act of communication,

because there’s no hope of getting anything back.

It’s a philanthropic gift, almost,

to that other civilization that you can,

maybe it might just be nothing more than a monument,

which the pyramids essentially are,

a monument of their existence,

that these are the things they achieved,

this was their, you know, the things they believed in,

their language, their culture.

Or it could be maybe something more than that.

It could be sort of lessons from what they learned

in their own history.

And so, I’ve been thinking a lot recently about

how would we send a message

to other civilizations in the future?

Because that act of thinking seriously

about the engineering of how we would design it

would inform us about what we should be looking for,

and also perhaps be our best chance, quite frankly,

of ever making contact.

It might not be the contact we dream of,

but it’s still contact.

There would still be a record of our existence,

as pitiful as it might be

compared to a two-way communication.

And I love the humility behind that project,

that universal project.


It’s sort of, it’s humble.

It humbles you to the vast

temporal landscape of the universe,

just realizing our day-to-day lives,

all of us will be forgotten

and it’s nice to think about something

that sends a signal out to other, yeah.

Other life forms.

It was almost like a humility of acceptance as well,

of knowing that you have a terminal disease,

but your impact on the Earth

doesn’t have to end with your death,

that it could go on beyond with what you leave behind

for others to discover with maybe the books you write

or what you leave in the literature.

Do you think launching the Roadster vehicle

out in space would have done better?

Yeah, yeah, the Roadster.

I’m not sure what someone would make of that,

if they found it.

Yeah, that’s true.

I mean, there have been quasi attempts at it

beyond the Roadster.

I mean, there’s like plaques on,

there’s the Pioneer plaques,

there’s the Voyager 2 Golden Record.

It’s pretty unlikely anybody’s gonna discover those

because they’re just adrift in space

and they will eventually mechanically die

and not produce any signal for anyone to spot.

So you’d have to be extremely lucky to come across them.

I’ve often said to my colleagues

that I think the best place is the moon.

The moon, unlike the Earth, has no significant weathering.

How long will the Apollo descent stages,

which are still sun on the lunar surface, last for?

The only real effect is micrometeorites,

which are slowly like dust

smashing against them pretty much.

But that’s gonna take millions,

potentially billions of years to erode that down.

And so we have an opportunity, and that’s on the surface.

If you put something just a few meters beneath the surface,

it would have even greater protection.

And so it raises the prospect of that

if we wanted to send something,

a significant amount of information,

to a future galactic-spanning civilization

that maybe cracks the interstellar propulsion problem,

the moon’s gonna be there for five billion years.

That’s a long time for somebody to come by

and detect maybe a strange pattern

that we draw on the sand,

for them to, you know, big arrow, big cross,

like, look under here,

and we could have a tomb of knowledge

of some record of our civilization.

And so I think it’s,

when you think like that, what that implies to us,

well, okay, the galaxy’s 13 billion years old,

the moon is already four billion years old.

There may be places familiar to us, nearby to us,

that we should be seriously considering

as places we should look for life,

and intelligent life, or evidence of relics

that they might leave behind for us.

So that thinking like that will help us find such relics,

and it’s like a beneficial cycle that happens.

Yes, yeah, exactly.

That enables the science of society better,

like of searching for bios and tech signatures and so on.


And it’s inspiring.

I mean, it’s also inspiring in that we wanna leave

a legacy behind as an entire civilization,

not just in the symbols, but broadly speaking.


That’s the last thing somehow.

Yeah, and I’m part of a team

that’s trying to repeat the Golden Record experiment.

We’re trying to create like an open source version

of the Golden Record that future spacecraft

are able to download,

and basically put in a little hard drive

that they can carry around with them,

and, you know, get these distributed,

hopefully across the solar system eventually.

So it’s gonna be called

the Hitchhiker’s Guide to the Galaxy, right?

Yeah, it could be.

That’s a good name for it.

We’ve been toying a little bit with the name,

but I think probably it would just be Golden Record

at this point, or Golden Record version two or something.

But I think another benefit that I see of this activity

is that it forces us as a species to ask those questions

about what it is that we want another civilization

to know about us.

The Golden Record was kind of funny

because it had photos on it,

and it had photos of people eating, for instance,

but it had no photos of people defecating.

And so I always thought that was kind of funny

because if I was an alien, or if I was studying an alien,

if I saw images of an alien,

I would, I’m not trying to be like a perv or anything,

but I would want to see the full,

I want to understand the biology of that alien.

And so we always censor what we show,

and we should show the whole actual natural process,

and then also say, we humans tend to censor these things.

We tend to not like to walk around naked,

we tend to not to talk about

some of the natural biological phenomena

and talk a lot about others,

and actually just be very,

like the way you would be to a therapist or something,

very transparent about the way we actually operate.

Yeah, I mean, and Sagan had that with the Golden Record.

I think he originally,

there’s a male and a female figure

to pitch on the Golden Record.

And the woman had a genitalia originally drawn,

and there was a lot of pushback

from I think a lot of Christian groups

who were not happy about the idea of throwing this into space

and so eventually they had to remove that.

And so it would be confusing biologically

if you’re trying to study xenobiology of this alien

that apparently has no genitalia,

or the man does, but for some reason the woman doesn’t.

And that’s our own societal and cultural imprint

happening into that information.

That’s, to be fair,

just even having two sexes and predators and prey,

just the whole,

that could be just a very unique Earth-like thing.

So they might be confused about

why there’s like pairs of things.

Like, why are you,

why is there a man and a woman in general?

Like, they could be, I mean,

they could be confused about a lot of things in general.

I don’t think the-

I don’t even know which way to hold the picture.


Or there’s the picture.

They don’t, they might not need,

they might have very different sensory devices

to even interpret this.

Correct, yeah.

If they only have sound

as their only way of navigating the world,

it’s kind of lost to send any kind of,

there’s been a lot of conversation about sending video

and audio and video and pictures.

And I’ve,

that’s one of the things I’ve been

a little bit resistant about in the team

that I’ve been thinking,

well, they might not have eyes.

And so if you lived in,

under Europa’s surface,

having eyes wouldn’t be very useful.

If you lived in a,

on a very dark planet,

on the tidally locked night side of an exoplanet,

having eyes wouldn’t be particularly useful.

So it’s kind of a presumption of us

to think that video is a useful form of communication.

Do you hope we become a multi-planetary species?

So we,

almost sneaking up to that,

but you know,

the efforts of SpaceX, of Elon,

maybe in general,

what your thoughts are about those efforts?

So you already mentioned Starship

will be very interesting for astronomy,

for science in general,

just getting stuff out into space.

But what about the longer term goal

of actually colonizing,

of building civilizations on other surfaces,

on moons, on planets?

It seems like a fairly obvious thing

to do for our survival, right?

There’s a high risk.

If we are committed to trying to keep

this human experiment going,

putting all of our eggs in one basket

is always gonna be a risky strategy to pursue.

It’s a nice basket though, but yeah.

It is a beautiful basket.

I wouldn’t wanna,

I personally have no interest in living on Mars

or the moon.

I would like to visit,

but I would definitely not wanna spend

the rest of my life and die on Mars.

It’s a,

I mean, it’s a hell hole.

Mars is a very, very different,

I think the idea that this is gonna happen

in the next 10, 20 years

seems to me very optimistic.

Not that it’s insurmountable,

but the challenges are extreme

to survive on a planet like Mars,

which is like a dry, frozen desert

with a high radiation environment.

It’s a challenge of a type we’ve never faced before.

So it’s, I’m sure human ingenuity

can tackle it,

but I’m skeptical that we’ll have thousands of people

living on Mars in my lifetime.

But I would relish that opportunity

to maybe one day visit such a settlement

and do scientific experiments on Mars

or experience Mars,

do astronomy from Mars,

all sorts of cool stuff you could do.

Sometimes you see these dreams

of outer solar system exploration

and you can fly through the clouds of Venus

or you could just do these enormous jumps

on like these small moons

where you can essentially jump as high as a skyscraper

and traverse the moon.

So there’s all sorts of wonderful ice skating on Europa,

might be fun.

So don’t get me wrong,

I love the idea of us becoming interplanetary.

I think it’s just a question of time.

Our own destructive tendencies,

as you said earlier,

are at odds with our emerging capability

to become interplanetary.

And the question is,

will we get out of the nest before we burn it down?

And I don’t know,

obviously I hope that we do,

but I don’t have any special insight that,

there is a problem,

there is somewhat of a

annoying intellectual itch I have

with the so-called doomsday argument,

which I try not to treat too seriously,

but there is some element of it that bothers me.

The doomsday argument basically suggests

that you’re typically,

the mediocrity principle,

you’re not special,

that you’re probably gonna be born

somewhere in the middle of all human beings

who will ever be born.

You’re unlikely to be one of the first 1% of human beings

that ever lived

and similarly the last 1% of human beings

that will ever live,

because you’d be very unique and special if that were true.

And so by this logic,

you can sort of calculate

how many generations of humans you might expect.

So if there’s been,

let’s say 100 billion human beings

that have ever lived on this planet,

then you could say to 95% confidence,

so you divide by 5%,

so 100 billion divided by 0.05

would give you 2 trillion human beings

that would ever live,

you’d expect by this argument.

And so if each,

let’s say each planet,

in general the planet has a 10 billion population,

so that would be 200 generations of humans

we would expect ahead of us.

And if each one has an average lifetime,

let’s say 100 years,

then that would be about 20,000 years.

So there’s 20,000 years left in the clock.

That’s like a typical doomsday argument type,

that’s how they typically lay it out.

Now you can,

a lot of the criticisms of the doomsday argument

come down to what are you really counting?

You’re counting humans there,

but maybe you should be counting years

or maybe you should be counting human hours

because what you count makes a big difference

to what you get out on the other end.

So this is called the reference class.

And so that’s one of the big criticisms

of the doomsday argument.

But I do think it has a compelling point

that it would be surprising

if our future is to one day blossom

and become a galactic spanning empire,

trillions upon trillions upon trillions of human beings

will one day live across the stars

for essentially as long as the galaxy exists

and the stars burn.

We would live at an incredibly special point in that story.

We would be right at the very, very, very beginning.

And that’s not impossible,

but it’s just somewhat improbable.

And so part of that sort of irks against me,

but it also almost feels like a philosophical argument

because you’re sort of talking about

souls being drawn from this cosmic pool.

So it’s not an argument that I lose sleep about

for our fate of the doomsday,

but it is somewhat intellectually annoying

that there is a slight contradiction

now it feels like with the idea

of a galactic spanning empire.

Yeah, but of course there’s so many unknowns.

I for one would love to visit even space,

but Mars, just imagine standing on Mars

and looking back at Earth.


I mean.

The incredible sight.

It would give you such a fresh perspective

as to your entire existence and what it meant to be human.

And then come back to Earth,

it would give you a heck of a perspective.

Plus the sunset on Mars is supposed to be nice.

I loved what William Shatner said after his flight.

His words really moved me when he came down.

And I think it really captured the idea

that we shouldn’t really be sending engineers

or scientists into space.

We should be sending our poets

because those are the people when they come down

who can truly make a difference

when they describe their experiences in space.

And I found it very moving reading what he said.

Yeah, when you talk to astronauts,

when they describe what they see, it’s like this,

like they discovered a whole new thing

that they can’t possibly convert back into words.


It’s beautiful to see.

Just as a quick, before I forget, I have to ask you,

can you summarize your argument against the hypothesis

that we live in a simulation?

Is it similar to our discussion about the Doomsday Clock?

No, it’s actually pretty more similar

to my agnosticism about life in the universe.

And it’s just sort of remaining agnostic

about all possibilities.

The simulation argument,

sometimes it gets mixed.

There’s kind of two distinct things that we need to consider.

One is the probability that we live in so-called base reality

that we’re not living in a simulated reality itself.

And another probability we need to consider

is the probability that that technology is viable,

possible, and something we will ultimately choose

to one day do.

And those are two distinct things.

They’re probably quite similar numbers to each other,

but they are distinct probabilities.

So in my paper I wrote about this,

I just tried to work through the problem.

I teach astrostatistics,

I was actually teaching it this morning.

And so it just seemed like a fun case study

of working through a Bayesian calculation for it.

Bayesian calculations work on conditionals.

And so when you hear,

what kind of inspired this project

was when I heard Musk said was like a billion to one chance

that we don’t live in a simulation.

He’s right if you add the Bayesian conditional,

and the Bayesian conditional is conditioned upon the fact

that we eventually develop that technology

and choose to use it,

or it’s chosen to be used by such species,

by such civilizations.

That’s the conditional.

And you have to add that in

because that conditional isn’t guaranteed.

And so in a Bayesian framework,

you can kind of make that explicit.

You see mathematically explicitly

that’s a conditional in your equation.

And the opposite side of the coin is basically

in the trilemma that Bostrom originally put forward

is options one and two.

So option one is that you basically never develop

the ability to do that.

Option two is you never choose to execute that.

So we kind of group those together

as sort of the non-simulation scenario, let’s call it.

And so you’ve got non-simulation scenario

and simulation scenario.

And agnostically, we really have to give the,

how do you assess the model,

the a priori model probability of those two scenarios?

It’s very difficult and we can,

I think people would probably argue

about how you assign those priors.

In the paper, we just assigned 50-50.

We just said, this hasn’t been demonstrated yet.

There’s no evidence that this

is actually technically possible,

but nor is it that it’s not technically possible.

So we’re just gonna assign 50-50 probability

to these two hypotheses.

And then in the hypothesis

where you have a simulated reality,

you have a base reality set at the top.

So there is, even in the simulated hypothesis,

there’s a probability you still live in base reality.

And then there’s a whole myriad of universes beneath that,

which are all simulated.

And so you have a very slim probability

of being in base reality if this is true.

And you have a 100% probability of living in base reality,

on the other hand, if it’s not true

and we never develop that ability

or choose never to use it.

And so then you apply this technique

called Bayesian model averaging,

which is where you propagate the uncertainty

of your two models to get a final estimate.

And because of that one base reality

that lives in the simulated scenario,

you end up counting this up

and getting that it always has to be less than 50%.

So the probability you live in a simulated reality

versus base reality has to be slightly less than 50%.

Now that really comes down to that statement

of giving it 50-50 odds to begin with.

And on the one hand, you might say,

look, David, I work in artificial intelligence,

I’m very confident that this is gonna happen,

just of extrapolating of current trends.

Or on the other hand, a statistician would say,

you’re giving way too much weight

to the simulation hypothesis

because it’s an intrinsically highly complicated model.

You have a whole hierarchy of realities

within realities within realities.

It’s like the Inception-style thing, right?

And so this requires hundreds, thousands,

millions of parameterizations to describe.

And by Occam’s razor, we would always normally penalize

inherently complicated models as being disfavored.

So I think you could argue I’m being too generous

or too kind with that.

But I sort of want to develop

the rigorous mathematical tools to explore it.

And ultimately, it’s up to you to decide

what you think that 50-50 odds should be.

But you can use my formula to plug in whatever you want

and get the answer, and I use 50-50.

So, and, but in that first pile,

with the first two parts that the bossman talks about,

it seems like connected to that

is the question we’ve been talking about,

which is the number of times at bat you get,

which is the number of intelligent civilizations

that are out there that can build such simulations.

That’s, it seems like very closely connected

because if we’re the only ones that are here

and can build such things, that changes things.

Yeah, yeah.

I mean, yeah, the simulation hypothesis

has all sorts of implications like that.

I’ve always loved, as Sean Carroll points out,

a really interesting contradiction, apparently,

with the simulation hypothesis

that I speak about a little bit in the paper.

But he showed that, or pointed out,

that in this hierarchy of realities,

which then develop their own AIs within the realities,

and then they, or really ancestor simulations,

I should say, rather than AI,

they develop their own capability to simulate realities.

You get this hierarchy,

and so eventually there’ll be a bottom layer,

which I often call the sewer of reality.

It’s like the worst layer where it’s the most pixelated

it could possibly be, right?

Because each layer is necessarily

going to have less computational power

than the layer above it.

Because not only are you simulating that entire planet,

but also some of that’s being used

for the computers themselves that those are simulated.

And so that base reality, or sorry,

the sewer of reality is a reality

where they are simply unable

to produce ancestor simulations

because the fidelity of the simulation is not sufficient.

And so from their point of view,

it might not be obvious that the universe is pixelated,

but they would just never be able

to manifest that capability.

What if they’re constantly simulating,

because in order to appreciate the limits of the fidelity,

you have to have an observer.

What if they’re always simulating

a dumber and dumber observer?

What if the sewer has very dumb observers that can’t,

like scientists that are the dumbest possible scientists.

So it’s very pixelated, but the scientists are too dumb

to even see the pixelations.

That’s like built into the universe

always has to be a limitation on the cognitive capabilities

of the complex systems that are within it.

Yeah, so that sewer of reality,

they would still presumably be able

to have a very impressive computational capabilities.

They’d probably be able to simulate galactic formation

or this kind of impressive stuff,

but they would be just short of the ability

to however you define it,

create a truly sentient conscious experience in a computer.

That would just be just beyond their capabilities.

And so Carol pointed out that if you add up all the,

you count up how many realities there should be,

probabilistically, if this is true,

over here, the simulation hypothesis or scenario,

then you’re most likely to find yourself in the sewer

because there’s just far more of them

than there are of any of the higher levels.

And so that sort of sets up a contradiction

because then you live in a reality

which is inherently incapable

of ever producing ancestor simulations.

But the premise of the entire argument

is that ancestor simulations are possible.

So there’s a contradiction that’s been introduced.

There’s that old quote, we’re all living in the sewer,

but some of us are looking up at the stars.

This is maybe more true than we think.

To me, so there’s of course physics

and computational fascinating questions here,

but to me, there’s a practical psychological question

which is how do you create a virtual reality world

that is as compelling,

and not necessarily even as realistic,

but almost as realistic,

but as compelling or more compelling than physical reality?

Because something tells me it’s not very difficult.

In the full history of human civilization,

that is an interesting kind of simulation to me

because that feels like it’s doable

in the next hundred years,

creating a world where we all prefer

to live in the digital world.

And not like a visit,

but like it’s like you’re seen as insane.

No, like you’re required.

It’s unsafe to live outside of the virtual world.

And it’s interesting to me from an engineering perspective

how to build that,

because I’m somebody that sort of loves video games

and it seems like you can create incredible worlds there

and stay there.

And it’s a different question

than creating a ultra high resolution,

high fidelity simulation of physics.

But if that world inside a video game

is as consistent as the physics of our reality,

then you can have your own scientists in that world

that trying to understand that physics world.

It might look different.

I’m presuming that eventually forget,

give it long enough,

they might forget about their origins

of being once biological

and assume this is their only reality.

Especially if you’re now born,

well, certainly if you’re born,

but even if you were eight years old or something

when you first started wearing the headset.

Yeah, or you have a memory wipe when you go in.

I mean, it also kind of maybe speaks to this issue

of like Neuralink and how do we keep up with AI in our world?

If you want to augment your intelligence,

perhaps one way of competing

and one of your impetuses for going into this digital reality

would be to be competitive intellectually

with artificial intelligences

that you could trivially augment your reality

if your brain was itself artificial.

But I mean, one skepticism I’ve always had about that

is whether it’s more of a philosophical question,

but how much is that really you if you do a mind upload?

Is this just a duplicate of your memories

that thinks it’s you versus truly a transference

of your conscious stream into that reality?

And I think when you,

it’s almost like the teleportation device in Star Trek,

but with teleportation, quantum teleportation,

you can kind of rigorously show that,

as long as all of the quantum numbers

are exactly duplicated as you transfer over,

it truly is from the universe’s perspective

in every way indistinguishable from what was there before.

It really is, in principle, you

and all the sense of being you

versus creating a duplicate clone

and uploading memories to that human body or a computer

that would surely be a discontinuation

of that conscious experience

by virtue of the fact you’ve multiplied it.

And so I would be hesitant about uploading for that reason.

I would see it mostly as my own killing myself

and having some AI duplicate of me

that persists in this world,

but is not truly my experience.

Typical 20th century human

with an attachment to this particular

singular instantiation of brain and body.

How silly humans used to be.

Used to have rotary phones and other silly things.

You’re an incredible human being.

You’re an educator, you’re a researcher.

You have an amazing YouTube channel.

Looking to young people, if you were to give them advice,

how can they have a career that maybe is inspired by yours,

inspired by wandering curiosity,

a career they can be proud of or a life they can be proud of?

What advice would you give?

I certainly think in terms of a career in science,

one thing that I maybe discovered late,

but has been incredibly influential on me

in terms of my own happiness and my own productivity

has been this synergy of doing two passions at once,

one passion in science communication

and another passion research

and not surrendering either one.

And I think that tends to be seen as something

that’s an either or.

You have to completely dedicate yourself to one thing

to gain mastery in it.

That’s a conventional way of thinking about both science

and other disciplines.

And I have found that both have been elevated

by practicing in each.

And I think that’s true in all assets of life.

I mean, if you want to become the best researcher

you possibly can, you’re pushing your intellect

and in a sense your body to a high level.

And so to me, I’ve always wanted to couple that

with training of my body, training of my mind

and other ways besides from just what I’m doing

when I’m in the lecture room or when I’m in my office,

you know, calculating something.

Focusing on your own development

through whatever it is, meditation,

for me it’s often running, working out

and pursuing multiple passions

provides this almost synergistic bliss

of all of them together.

So often I’ve had some of the best research ideas

from making a YouTube video and trying to communicate an idea

or interacting with my audience

who’ve had a question that sparked a whole trail of thought

that led down this wonderful intellectual rabbit hole

or maybe to a new intellectual discovery

can go either way sometimes with those things.

And so thinking broadly, diversely

and always looking after yourself

in this highly competitive

and often extremely stressful world that we live in

is the best advice I can offer anybody

and just try, if you can, it’s very cheesy

but if you can follow your passions, you’ll always be happy.

Trying to sell out for the quick cash out,

for the quick book out can be tempting in the short term.

Looking for exomoons was never easy

but I made a career not out of discovering exomoons

but out of learning how to communicate

the difficult problem

and discovering all sorts of things along the way.

We shot for the sky

and we discovered all this stuff along the way.

We discovered dozens of new planets

using all sorts of new techniques.

We pushed this instrumentation to new places

and I’ve had an extremely productive research career

in this world.

I’ve had all sorts of ideas working on techno signatures.

It’s, you know, thinking innovatively pushes you

into all sorts of exciting directions.

So just try to, yeah, it’s hard to find that passion

but you can sometimes remember it when you were a kid,

what your passions were

and what fascinated you as a child.

For me, as soon as I picked up a space book

when I was five years old, that was it.

I was hooked on space

and I almost betrayed my passion at college.

I studied physics,

which I’ve always been fascinated by physics as well.

But I came back to astronomy because it was my first love

and I was much happier doing research in astronomy

than I was in physics

because it spoke to that wonder I had as a child

that first was the spark of curiosity for me in science.

So society will try to get you to look at hot Jupiters

and the advice is to look for the cool worlds instead.

What do you think is the meaning of this whole thing?

Have you ever asked yourself why?

It’s just a ride.

That’s how I think it.

It’s just a ride, we’re on a roller coaster

and we have no purpose.

It’s an accident in my perspective.

There’s no meaning to my life.

There’s no objective deity

who is overwatching what I’m doing

and I have some fate or destiny.

It’s all just riding on a roller coaster

and trying to have a good time

and contribute to other people’s enjoyment of the ride.

Yeah, try to make it a happy accident.

Yeah, yeah, I see no fundamental providence in my life

or in the nature of the universe.

And you just see this universe

as this beautiful cosmic accident

of galaxies smashing together,

stars forging here and there

and planets occasionally spawning maybe life

across the universe.

And we are just one of those instantiations

and we should just enjoy this very brief episode

that we have.

And I think trying to look at it much deeper than that

is to me, it’s not very soul satisfying.

I just think enjoy what you’ve got and appreciate it.

It does seem noticing that beauty

helps make the ride pretty fun.

Yeah, absolutely.

David, you’re an incredible person.

I haven’t covered most of the things

I wanted to talk to you about.

This was an incredible conversation.

I’m glad you exist.

I’m glad you’re doing everything you’re doing

and I’m a huge fan.

Thank you so much for talking today.

This was amazing.

Thank you so much, Lex.

It’s a real honor, thank you.

Thanks for listening to this conversation

with David Kipping.

To support this podcast,

please check out our sponsors in the description.

And now let me leave you with some words from Carl Sagan.

Perhaps the aliens are here,

but are hiding because of some Lex Galactica,

some ethic of non-interference with emerging civilizations.

We can imagine them, curious and dispassionate,

observing us as we would watch a bacterial culture

in a dish to determine whether this year,

again, we managed to avoid self-destruction.

Thank you for listening and hope to see you next time.