Janna Levin: Black Holes, Wormholes, Aliens, Paradoxes & Extra Dimensions | Lex Fridman Podcast #468

Black holes curve space and time around them in the way that we've been describing.

Things follow along the curves in space.

If the black holes move around,

the curves have to follow them, right?

But they can't travel faster than the speed of light either.

So what happens is

black holes, let's say, move around.

Maybe I've got two black holes in orbit around each other. That can happen.

It takes a while.

A wave is created

in the actual shape of space.

And that wave follows the black holes.

Those black holes are undulating.

Eventually, those two black holes will merge.

And as we were talking about, it doesn't take an infinite time, even though

there's time dilation because they're both so big.

They're really deforming spaceime a lot.

I don't have a little tiny marble falling across an event horizon.

I have two event horizons.

And in the simulations,

you can see it bobble

and they merge together.

They make one bigger black hole.

And then it radiates

in the gravitational waves.

It radiates away all those imperfections

and it settles down to one

quscent perfectly silent black hole that's spinning. Beautiful stuff.

And it emits E= MC² energy.

So the mass of the final black hole

will be less than the sum of the two starter black holes.

And that energy is radiated

away in this ringing of spaceime.

It's really important to emphasize

that it's not light.

None of this has to do

literally with light that we can detect with normal things that detect light.

X-rays form of light.

Gamma rays are a form of light.

Infrared, optical, all this whole electromagnetic spectrum.

None of it is emitted as light. It's completely dark.

It's only emitted in the rippling of the shape of space.

A lot of times it's likened closer to sound.

Technically, we've kind of argued.

I mean, I haven't done an anatomical

calculation, but if you're near enough

to two colliding black holes, they actually ring spaceime in the human auditory range.

The frequency is actually in the human auditory range

that the shape of space could squeeze and stretch your eardrum even in vacuum.

And you could hear literally hear these waves ringing.

The following is a conversation

with Jenna Levan, a theoretical

physicist and cosmologist specializing

in black holes, cosmology

of extra dimensions, topology of the universe,

and gravitational waves in spaceime.

She has also written some incredible

books including how the universe got its spots

on the topic of the shape and the size of the universe,

a mad man dreams of touring machines

on the topic of genius

madness and the limits of knowledge.

Black hole blues and

other songs from outer space

on the topic of LIGO

and the detection of gravitational

waves and black hole survival

guide all about black holes.

This was a fun and fascinating conversation.

This is a Lexman podcast.

To support it, please check out our sponsors in the description.

And now, dear friends, here's Jenna 11.

I should say that you sent me a message

about not starting early in the morning,

and that made me feel like we're kindred spirits.

You wrote to me, "When the great physicist

Sydney Coleman was asked to attend a 9:00 a.m.

meeting, his reply was, "I can't stay up that late." Yeah. So, classic. Sydney was beloved.

I think all the best thoughts, honestly,

maybe the worst thoughts, too, are all come at night.

There's something There's something about the night.

Maybe it's the silence.

Maybe it's the peace all around.

Maybe it's the darkness and you

you could be with yourself and you could think deeply.

I feel like there's stolen hours in the middle of the night because it's not busy.

Your gadgets aren't pinging.

There's really no pressure to do anything but I'm off and awake

in the middle of the night

and so it's sort of like these extra hours of the day.

I think we were exchanging messages at 4 in the morning. Okay.

So in that way, many other ways were kindred spirits. M.

So, let's go in the

one of the coolest objects

in the universe, black holes. What are they?

And maybe even a good way to start is to talk about how are they Yeah.

In a way, people

often confuse how they're formed with

the concept of the black hole in the first place.

So when black holes were first proposed,

Einstein was very surprised

that such a solution could be found so quickly but really thought nature

would protect us from their formation.

And then nature thinks of a way nature thinks of a way to make

these crazy objects which is to kill off a few stars.

But then I think that there's a confusion

that dead stars, these very very massive stars that die

are synonymous with the phenomenon of black hole.

And it's really not the case.

Black holes are more

general and more fundamental

than just the death state of a star.

But even the history of how

people realize that stars could form

black holes is is is

quite fascinating because the entire idea really just started as a thought experiment.

And if you think of it's

1915 1916 when Einstein

fully describes relativity in a way that's the canonical formulation.

It was a lot of changing back and forth before then.

And it's World War I and he gets a message

from the Eastern Front from a friend of his, Carl Shortfield,

who's who solved Einstein's

equations, you know, between

sitting in the trenches

and like cannon fire.

Um, it was joked that he was calculating ballistic trajectories.

He's also perusing the proceedings of the Prussian Academy of Sciences as you do.

and he was an astronomer

um who had enlisted

in his 40s and he finds this really remarkable

solution to Einstein's equations and it's the first exact solution.

He doesn't call it a black hole.

It's not called a black hole for decades.

But what I love about what Schwarz shield did is it's a thought experiment.

It's not about observations.

It's not about making these things in nature.

Um it's really just about the idea.

He sets up this completely untenable situation.

and he says, "Imagine

I crush all the mass of a star to a point."

Don't ask how that's done because that's really absurd.

Um, but let's just pretend

and let's just imagine that that that's a scenario.

And then he wants to decide

what happens to spacetime

if I set up this

confounding but somehow very simple scenario.

And really what Einstein's equations were were telling everybody at the time was that

matter and energy curve space and time

and then curved spacetime tells matter and energy how to fall

once the spacetime shaped.

So he finds this beautiful solution

and the most amazing thing about a solution is he finds this

demarcation which is the event horizon

which is the region beyond which

not even light can escape.

And if you were to ask me today all these

decass crushed to a point.

The black hole is the event horizon.

The event horizon is really just

a point in spaceime or or a region in spaceime.

It's actually in this case a surface in spaceime.

And it marks uh a separation

in events which is why it's called an event horizon.

Everything outside is causally

separated from the inside

in so far as what's inside the event horizon

can't affect events outside.

What's outside can affect events inside.

I can throw a probe

into a black hole and cause something to happen on the inside.

But the opposite isn't true.

Somebody who fell in can't send a probe out.

And this oneway aspect

really is what's profound about the black hole.

Um, sometimes we talk about the black holes being nothing because at the event

horizon there's really nothing there.

Uh, sometimes when we when we think about black holes, we want to imagine

a really dense dead star.

But if you go up to the event horizon,

it's an empty region of spaceime.

It's it's more of a place

than it is a thing.

And Einstein found this fascinating.

He helped get the work published, but he really didn't think

these would form in nature.

I doubt Carl Schwarz shield did either.

Um I think they thought they were

uh solving theoretical mathematical problems.

Um but not describing

this what turned out to be the end state of gravitational collapse.

And maybe the purpose of the thought experiment was to find the limitations of the theory.

So you you find the most extreme

versions in order to

understand where it breaks down. Yeah.

And it just so happens in this

case that might actually predict these extreme kinds of objects. It does both.

So it also describes the sun from far away.

So the same solution

does a great job

helping us understand the Earth's orbit around the sun. It's incredible.

Does a great job. It's almost overkill.

You don't really need to be that precise as relativity.

Um, and yes, it predicts

the phenomenon of black holes, but doesn't really explain how nature would form them.

But then it also

on top of that does signal the breakdown of the theory.

I mean, you're quite right about that.

It actually says, "Oh, man."

But you you go all the way towards the center

and yeah, this doesn't sound right anymore.

Um, sometimes I liken it to, you know, it's like a dying

man marking in the dirt

that something's gone wrong here, right?

it it it's signaling that that there's some culprit

there's something wrong in the theory and

um and even Roger Penrose

who did this general work trying to

uh the formation of black holes from gravitational

collapse he thought oh yeah there's a singularity

that's inevitable it's in every

there's no way around it once you form a black hole

but he said this is probably just a shortcoming

of the fact that we've forgotten to include quantum mechanics

and that when we do

we'll understand this um differently.

So according to him the closer you get to the singularity the more quantum

mechanics comes into play and therefore

there is no singularity there's something else.

I think everybody would say that.

I think everybody would say

the closer you get to the singularity

for sure you have to include quantum mechanics.

You just can't consistently

talk about magnifying such

small scales, having such enormous

uh ruptures and and

curvatures and energy scales and not include quantum mechanics that that's just inconsistent

with the world as we understand it.

So you've described the

brainbreaking idea that a black hole is

uh not so much a super dense

matter as it's sometimes described, but it's more

akin to, you know, a region

of space time, but even more so just nothing. Yeah, it's nothing.

That that's a thing you seem to like to say.

I do I do like to say that

black holes are no thing. They're nothing. Okay.

So what what what does that mean?

That's that's what I mean.

That's the more profound aspect of the black hole.

So you asked originally

um how do they form?

And I think that that

that even when you try to form them in messy astrophysical

systems, there's still nothing

at the end of the day left behind.

And um this was a very big surprise.

Even though Einstein accepted that this was a true prediction,

he didn't think that that they'd be made.

And it was quite astounding

that that people like Oppenheimer

actually it's probably Oenheimer's

most important theoretical work

um who are thinking

about nuclear physics and quantum mechanics but in the context of these kind of

utopian questions why do stars shine

um why is the sun radiant and hot and

this amazing source of light and it was people like Oenheimer

who began to ask the question well

could stars collapse to form

black holes Could they

become so dense that

uh eventually not even light would escape?

And that's why I think people think

that black holes are these dense objects.

That's often how it's described.

But actually what happens these very massive stars, they're burning thermonuclear fuel.

You know, they're earthfuls of thermonuclear fuel.

They're burning um and

emitting energy in E= MC² energy. So it's fusing.

It's a fusion bomb.

It's a constantly going thermonuclear bomb.

And um eventually it's going to run out of fuel.

It's going to run out of hydrogen, helium, stuff to fuse.

It hits an iron core.

Iron to go past iron with fusion

is actually energetically expensive.

So it's no longer

going to do that so easily.

So suddenly it's run out of fuel.

And if the star is very very very massive, much more massive than our

sun, maybe 20, 30 times the mass of our sun,

it'll collapse under its own weight.

And that collapse is

incredibly fast and dramatic and it creates a shock wave.

So that's the supernova explosion.

So a lot of these

they rebound because once they crunch

they've reached a new critical

uh capacity where they can

reignite to higher elements, heavier elements

and that sets off a bomb essentially.

So, the star explodes

helpfully because that's why you and I are here because

stars send their material back out into space and

you and I get to be made of carbon and oxygen and all this good stuff.

We're not just hydrogen.

So, the suns do that for us.

And then what's left

sometimes ends at a neutron star,

which is a very cool object,

very fascinating object, super dense,

uh, but bigger than a black hole,

meaning it's it's it's

not compact enough to become a black hole.

It's an actual thing.

A neutron star is a real thing.

It's like a giant neutron.

Literally, electrons get jammed into the protons and make this giant nucleus

and this superconducting matter.

Very strange, amazing objects.

But if it's heavier than that the core

and that's you know heavier than twice the mass of the sun

um it will become a black hole and Oenheimer

was wrote this beautiful paper in

1939 with his student

uh saying that they believed

that the end state

of gravitational collapse is actually a black hole.

This is stunning and

really um a visionary conclusion.

Now, the paper is published the same day the Nazis

advance on Poland and so

it does not get a lot of fanfare in the newspapers.

Yeah, we think there's a lot of drama today on social media. Imagine that.

Like here's a guy

who predicts how actually

in nature would be the formation of this most radical of object that broke

even Einstein's brain while

one of the most evil

if not the most evil humans in history

starting a uh the first steps of a global war.

What I also love about that lesson is how agnostic

science is because he was asking these utopian questions as were other people of

the time about the nuclear physics and stars.

You might know this play Copenhagen by Michael Fra.

There's this line that he attributes to Boore and Boore was

the great thinker of early

foundations of quantum mechanics,

Danish physicist, where Boore says to his wife, "Nobody's

thought of a way to kill people using quantum mechanics."

Now, of course, then there's the nuclear bomb.

And what I love about

this was the pressure scientists were under to do something

with this nuclear physics and and to enter this race over

um a nuclear weapon.

But really at the same time, 1939

really uh Oenheimer's thinking about black holes.

There's a there's even a small line in Chris Nolan's film.

It's very hard to catch.

There's a reference to it in the film where he they're sort of joking

well I guess nobody's going to pay attention to your paper now

you know because uh because of the Nazi advance on Poland

that's the other remarkable thing about Oppenheimer

is he's also a central figure in the construction of the bomb

right so it's theory and experiment

clashing together with the geopolitics

exactly so of course Oppenheimer

now known as the father

of the atomic bomb

um he talks about destroyers

of worlds um But it's the same technology

and that's what I mean by science is agnostic, right?

It's the same technology

overcoming a critical mass

um igniting thermonuclear fusion.

Eventually there was a fision the original bomb was a fision bomb and fision

was first shown by

Le Mitner who showed that a certain uranium

when you bombarded it with protons

broke into smaller pieces that

were less than the uranium. Right?

So some of that mass that E= MC²

energy had escaped and

it was the first kind of concrete demonstration

of this Einstein's most famous equation.

So all of this comes together

but the story of

um they still weren't called black holes.

This is 1939 and they had these very long-winded

ways of describing the end state the catastrophic

end state of gravitational collapse.

But what you have to imagine is as this star collapses.

So now, so what's the sun?

The sun's a million

and a half kilometers across.

So imagine a star much bigger than the sun. Much bigger radius.

And it's so heavy it collapses. It supernovas.

What's left is still maybe 10 times the mass of the sun.

Just what's left in that core.

And it continues to collapse.

And when that reaches about

60 kilometers across, like just imagine 10 times the mass of the sun citys sized.

That is a really dense object.

And now the black hole essentially has begun to form.

Meaning the curve in spaceime

is so tremendous that not even light can escape.

The event horizon forms.

But the event horizon

is almost imprinted on the spacetime

because the star can't sit there in that dense state

any more than it can race outward at the speed of light

because even light is forced to rain inwards.

So the star continues to fall

and that's the magic part.

The star leaves the event horizon

behind and it continues

to fall and it falls into the interior of the black hole.

Where it goes, nobody really knows.

But it's gone from sight. It goes dark.

There's this quote by John Wheeler who's like granddaddy

of American relativity and he has a line that's something to the effect.

Um, the star like the Cheshire

cat fades from view.

One leaves behind only its grin,

the other only its gravitational attraction.

And he was giving a lecture.

It's actually above Tom's restaurant,

you know, from Seinfeld

near Colombia in New York. Nice.

There was a a place or there still is a place there where

people were giving lectures about astrophysics. And it's 1967.

Wheeler is exhaustively saying this

loaded term, the end state of catastrophic gravitational collapse.

And rumor is that someone shouts from the back row, well, how about black hole?

And um apparently he then foists

this term on the world.

Wheelerhead way of doing that.

Well, I love terms like that.

Big bang, black hole.

There's some I mean, it's just pointing out the elephant in the room and

calling it an elephant.

It is a black hole.

That's a pretty uh

accurate and deep description.

I just wanted to

point out that the

just looking for the first time at a 1939 paper from Oppenheimer.

It's like two page.

It's like three pages.

Oh yeah, it's gorgeous.

The simplicity of some of these that's so gangster.

Just revolutionize all of physics with this with you know Einstein

did that multiple times in a single year. Mhm.

When all thermonuclear sources of energy are exhausted, a sufficiently heavy star will collapse. That's an opener. Mhm.

Unless fision due to rotation,

the radiation of mass

or the blowing off of mass by

radiation reduce the stars mass to orders of that of the sun,

this contraction will continue indefinitely.

And it goes on that way. Yeah.

Now, I have to say that Wheeler,

who actually coins the term

black hole, uh gives Oenheimer

quite a terrible time about this.

He thinks he's wrong.

and they entered what has sometimes been described as kind of a bitter I

don't know if you would actually say feud but there were bad

feelings and um Wheeler actually spent decades

uh saying Oenheimer was wrong and

eventually with his computer

work that early work that Wheeler was doing with computers when he was also

trying to understand nuclear weapons

and in peace time

world found themselves returning again to these astrophysical

questions uh decided that actually Oenheimer had been right.

He thought it was too simplistic,

too idealized a setup that they had used and that if you you looked

at something that was more realistic

and more complicated that it it just simply

it just would go away.

And in fact, he he draws the opposite conclusion.

There's a story that Oppenheimer

was sitting outside of the auditorium

when Wheeler was coming forth

with his declaration that in fact

black holes were the likely end state of gravitational collapse for very very heavy

stars and um when asked about it Oppenheimer

sort of said well I've moved on to other things

because you've written in many places about the human beings behind the science

I have to ask you about this about nuclear weapons

where is the greatest of physicists coming together to create this most terrifying

and powerful of a technology.

And now I get to talk to world leaders for whom this technology

is part of the

tools that is used

perhaps implicitly on the chessboard of geopolitics.

What what can you say

as a person who's a physicist and who have studied the physicists and written

about the physicists the humans behind this

about this moment in human history

when physicists came together

and created this weapon that's powerful enough to destroy all of human civilization.

I think it's an

excruciating moment in in the history of science

and um people talk about

Heisenberg who stayed in Germany and and

uh worked for the Nazis in their own attempt

to build the bomb.

There was this kind of hopeful

talk that maybe Heisenberg

had intentionally derailed the nuclear weapons program.

But I think that's been largely discredited

that he would have made the bomb could he had he not made some

really kind of simple

errors in his original estimates about how much material would be required or how

they would get over the energy barriers.

And that's a terrifying thought.

Um, I I don't know that any of us can really put ourselves in

that position of imagining

that we're faced with that quandry,

having to take the initiative to participate in thinking of a way that quantum

mechanics can kill people

and then making the bomb.

I think overwhelmingly physicists today

feel we should not

continue in the proliferation of nuclear weapons.

Very few um theoretical

physicists want to see this continue.

that moment in history,

the Soviet Union had incredible scientists.

Nazi Germany had incredible scientists

and the United States had incredible scientists.

And it's very easy to imagine that

one of those three

would have created the bomb first,

not the United States.

And how different would the world be?

The game theory of that

I think say the probability is 33%

that it was the United States.

If the Soviet Union

had the bomb, I think I think they would have used it in a

much more terrifying way

in the in the European theater and maybe turn on the United States.

And obviously with Hitler, he would have used it.

I think there's no question he would have used

it to to to

kill hundreds of millions of people.

In the game theory

version, this was the least harmful outcome. Yes. Yes.

But there is no outcome with no bomb

that that any game theorist

would uh I think would play.

But I I think if we just remove the geopolitics

and the ideology and the evil dictators,

all of those people are just scientists.

I think they don't necessarily

even think about the ideology.

And it's a it's a it's a deep lesson about the connection between

great science and the

annoying sometimes evil politicians

that use that science for means that are either good or bad. Mhm.

And the scientists perhaps

don't boy do they even have control of how that science is used. It's hard.

They don't have control. Right.

once it's once it's made, it's no longer scientific

reasoning that dictates the use

or um it's restraint.

But I will say that I do believe that it wasn't a 30

one-third down the line

because America was different and I think that's something we have to think about

right now in this particular climate.

So many scientists fled here.

They fled to here.

Americans weren't fleeing to Nazi Germany.

they came here and and

they were motivated um

by uh it's more than a patriotism,

you know, it was um I mean it was a patriotism

obviously, but it was sort of more than that.

It was really understanding

the threat of Europe,

uh what was going on in Europe and

um and what that life,

how quickly it turned,

how quickly this freespirited

Berlin culture, you know, was

suddenly in this repressive

and terrifying uh regime.

So, I think that it was a much higher

chance that it happened here in America. Yeah.

And there's something about the American system,

the you know it's cliche to say but the freedom

all the different individual freedoms

that enable a very vibrant

at its best a very vibrant scientific community and that's really exciting

absolutely to scientists and it's very valuable to ma maintain that right

the the vibrancy of the debate of the

funding those mechanisms absolutely the world

flocked here and that won't be the case if

we no longer have intellectual

freedom yeah there's there's something interesting to think about

the tension the cold war between China and the United States in the 21st

century you know some of those same questions some of those ideas will rise

up again and we want to make sure that

um there's a vibrant

free exchange of scientific ideas

I believe most Nobel

prizes come from the United States right

oh yeah I don't have the number but I disproportionately

so disproportionately so in fact a lot of them from

particle physics came from the Bronx

and they were European immigrants.

How do you explain this?

Fled Europe um precisely because of the geopolitics we're describing. Yeah.

And so instead of being Nobel Prize winners from the Soviet Union or from

the Eastern Block, they were from the Bronx.

And that's the thing you write about and we'll return to time and time

again that you know science is done by humans.

And some of those humans are fascinating. There's tensions. There's battles.

There's some are loners.

Some are great collaborators.

Some are tormented, some are easygoing,

all this kind of stuff.

And that's the beautiful thing about it.

We forget sometimes is it's humans

and humans are messy and complicated and beautiful and all of that. Yeah.

Uh so what were we talking about?

Oh, the star is collapsing. Okay.

So can we just

return to the collapse of a star

that forms a black hole?

At which point does the super dense thing become nothing?

if we can just like linger on this concept. Yeah.

So if I were falling into a black hole and I I I

tried really fast right as I crossed

this empty region but this demarcation

I happened to know where it was.

I calculated because there's no line there.

There's no sign that it's there. There's no signpost.

Um I could emit a little light pulse and try to send it outward

exactly at the event horizon.

So it's racing outward at the speed of light.

It can hover there because from my perspective, it's very strange.

The spaceime is like a waterfall

raining in and I'm being dragged in with that waterfall.

I can't stop at the event horizon.

It comes, it goes.

It's behind me really quickly.

That light beam can try to sit there because it's like it's like a

fish swimming against the Niagara,

you know, swimming against the waterfall.

It's like stuck there.

But it's like stuck there.

Um, and so that's one way you could have a little signpost.

You know, if you fly by, you think it's moving at the speed of light.

It flies past you at the speed of light, but it's sitting right there

at the event horizon.

So, you're falling back,

cross the event horizon.

Right at that point, you shoot outwards a photon. Yes.

And it's just stuck there.

It just gets stuck there.

Now, it's very unstable.

So, the star can't sit there is the point.

It It just can't.

So, it rains inward with this waterfall.

But from the outside,

all we should ever really care about is the event horizon because I can't

know what happens to it.

It could be pure matter and antimatter

thrown together which annihilates

into photons on the inside and

loses all its mass into the energy of light.

Won't matter to me because I can't know anything

about what happened on the inside. Okay.

Can we just like linger on this?

So what models do we have about what happens on the inside of the

black hole at that moment?

So I guess that one of the intuitions,

one of the big reminders

that you're giving to us is like,

hey, we know very

little about what can happen on the inside of a black hole.

And that's why we have to be careful about making

it's better to think about the black hole as an event horizon.

But what can we know

and what do we know about the physics of

of space time inside the black hole?

I don't mind being incautious

about thinking about what the math tells us.

So I'm not such a an observer.

I'm very theoretical in my work.

It's really pen on paper a lot.

Um these are thought experiments that I think we we can perform and contemplate.

Um whether or not we'll ever know is another question.

And um so one of the most beautiful things

that we suspect happens on the inside of a black hole is that space

and time in some sense swap places.

So while I'm on the outside of the black hole,

let's say I'm in a nice comfortable space station.

This black hole is maybe

10 times the mass of the sun, 60 kilometers across.

I could be a 100 kilometers out.

That's very, very close. Orbiting quite safely. No big deal.

You know, hanging out.

Uh I don't bug the black hole.

Black hole doesn't bug me.

It won't suck me up like a vacuum or anything crazy.

But uh some my my astronaut friend jumps in.

Um, as they cross the event horizon,

what I'm calling space, I'm looking on the outside at this

spherical shadow of the black hole cast by maybe light around it.

It's a shadow because everything

gets too close, falls in.

It's just this um

uh just contrast against a bright sky.

I think, oh, there's a center of a sphere

and in the center of the sphere is the singularity.

It's a point in space from my perspective,

but from the perspective of the astronaut who falls in,

it's actually a point in time.

So their notions of space and time have rotated

so completely that what I'm calling a direction in space towards the center of

the black hole, like the center of a physical sphere,

they're going to tell me, well, they can't tell me, but they're going to

come to the conclusion, oh no, that's not a location in space.

That's a location in time.

In other words, the singularity

ends up in their future

and they can no more avoid the singularity

than they can avoid

time coming their way.

So there's no shenanigans

you can do once you're inside the black hole to try to skirt it the singularity.

You can't set yourself up in orbit around it.

You can't try to fire rockets and stay away from it because it's in

your future and there's an inevitable

moment when you will hit it.

Usually for a stellar mass black hole, we think it's micros secondsonds.

Micros secondsonds to get from the event horizon to the to the singularity. To the singularity. Oh boy. Oh boy.

So that's describing from the

your astronaut friend's perspective. Yes.

From their perspective, the singularities in their future.

But from your perspective,

what do you see when your

friend falls into the black hole and you're

chilling outside and watching?

So, one way to think about this

um is to is to

think that as you're approaching the black hole,

the astronaut's spaceime is rotating

relative to your spacetime.

So, let's say right now

my left is your right.

We're not shocked by the fact that there's this relativity in left and right. It's completely understood.

And I can perform a spatial

rotation to align my left with your left.

Right now I've completely rotated left out. Right.

Um if I just want to draw a a a

kind of uh compass diagram, not a compass diagram, but you know at the

top of maps there's a northsoutheast west.

But now time is up down

and one direction of space is let's say east west.

As you approach the black hole it's as though you're rotating

in spaceime is one way of thinking about it.

So what is the effect of that?

The effect of that is as this astronaut gets closer and closer to the

horizon, part of their space

is rotated into my time and part of their time is rotated into my space.

So in other words, their clocks

seem to be less

aligned with my time.

And the overall effect is that their time seems to dilate.

the spacing between ticks on the clock of their watch, let's say,

um on the on the face of their watch,

uh is is elongated,

dilated relative to mine.

And it seems to me that their watches are running slowly, even though they

were made in the same factory as mine.

They were both synchronized

beautifully and they're excellent Swiss watches.

Um, it seems as though time is elapsing more slowly for my

companion and uh likewise

for them it seems like mine's going really fast.

So years could elapse

in my space station.

My plants come and go. They die. I age faster.

I've got gray hair.

Um, and they're falling in and it's been minutes

in their frame of reference.

Um, flowers in their little rocket ship haven't rotted.

They don't have gray hair.

Their biological clocks have slowown down relative to ours.

Eventually at the event horizon, it's so extreme. It's so slow.

It's as though their clocks have stopped

altogether from my point of view.

And that's to say that it's as though

their time is completely rotated into my space.

And this is connected with the idea that inside the black hole space and

time have switched places.

Um, so I might see them hover there for millennia.

Other astronauts could be born on my space station.

Generations could be populated

there watching this poor astronaut never fall in.

So basically the time

almost comes to a standstill,

but we still they do fall in, right?

They do fall in eventually.

Now that's because they have some mass of their own. Yeah.

So they're not a perfectly

light particle and so

they deform the event horizon a little bit.

You'll actually see the event

horizon bobble and absorb the astronaut.

So in some finite time the astronaut will actually fall in.

So it's a it's like this weird

space-time bubble that we have around us. Mhm.

And then there's a very big

space-time curvature bubble thing from the black hole and they

there's a nice swirly type situation going on.

That's how you get sucked up. Yeah.

So if you're a perfect like

uh infinitely small particle, you would just be take longer and longer

and probably just be

stuck there or something.

But no, there's quantum mechanics. Mhm.

Eventually you'll fall in there.

Any perturbation will only go one way.

It's unstable in one direction.

In one direction only.

Um, but it's it's really

important to remember that from the point of view of the astronaut, not much

time has passed at all.

You just sail right across as far as you're concerned and

nothing dramatic happens here.

You might not even realize

you've come to the event horizon.

You you might not even realize you've crossed the event horizon

because it's there's nothing there. Right?

This is an empty region of spaceime.

There's no marker to tell you you've reached this very dangerous point of no return.

You can fire your rockets

like hell when you're on the outside and maybe even escape, right?

But once you get to that point, there's no amount of energy.

All the energy in the universe will not save you

from uh this demise.

You know, there's different size black holes. Mhm.

And maybe can we talk about the experience

that you have falling into a black hole depending on what the size of

the black hole is? Yeah.

cuz um as I understand if

the the the bigger it

is, the less drastic

the experience of falling into it.

Yeah, that might surprise people.

The bigger it is,

the less noticeable it is that you've

you've crossed the event horizon.

One way to think about it is um curvature

is less noticeable the bigger it is.

So, if I'm standing on a basketball,

I'm very aware I'm I'm balancing on a curved surface.

I my two feet are in different locations

and I really notice.

But on the Earth, you actually have to be kind of clever to deduce

that the Earth is curved.

The bigger the planet,

the less you're going to notice the curvature.

Um the the global curvature.

And it's the same thing with a black hole, a huge huge black hole.

It just is kind of feels like just flat.

You don't really notice.

I'm trying to figure out how the phys because if you don't notice

and there's nothing there

but the physics is weird

in your frame of reference. No.

Well, so another cool thing.

So I'd like to dispel myths. Yeah.

Do you need a minute?

You're holding your head.

There's a sense like you you should be able to know when you're inside

of a black hole when you've crossed the event horizon.

But no, from your frame of reference, you might not be able to know.

Yeah, at first at least, you might not realize what's happened.

There are some hints.

For instance, black holes are dark from the outside,

but they're not necessarily

dark on the inside.

So this is uh

a kind of fascinating

that your experience could be that it's quite bright

inside the black hole because all the light from the galaxy

can be shining in behind you

and it's focusing down because you're all

approaching this really focused region in the interior.

And so you actually see a bright

white flash of light as you approach the singularity.

Um, you know, I kind of uh I joke that it's a, you know,

it's like a near-death experience.

You see the light at the end of the tunnel.

So, you would see millennia pass on Earth.

You could see the evolution of

um the entire galaxy, you know, one big bright flash of light.

So, it's like a near-death experience, but it's a definitely a total death experience.

It goes pretty fast.

But you looking out,

you looking out, everything's going super fast. Yeah.

the clocks um on the earth on the space station

seem to be progressing

very rapidly relative to yours.

The light can catch up to you

and you get this bright beam of light as you see

the evolution of the galaxy

unfold and um I mean it sort of depends on the size of the black

hole and how long

you have to hang around.

The bigger the black hole the longer it takes you

to expire in the center.

Obviously the human uh sensory system we're not able

to process that information correctly

right it would be a microcond

in a right that would be too fast.

Yeah but it would be

wow it' be so cool to get that information

but a big black hole you could actually you know hang around for some months.

So yeah what's uh how are

small black holes versus super massive

uh black holes formed

just so people can kind of load that in.

Are they are they all is it always a star? No.

So this is also why it's important to think of black holes more abstractly.

They are something very profound in the universe and there are probably

multiple ways to make black holes.

Um making them with stars is most plentiful.

There could be hundreds of millions

maybe even a billion black holes in our Milky Way galaxy alone. that many stars.

It's only about 1%

of stars that will

um end their lives in in in a death state that is a black hole.

But we now see and this was really quite a surprise

that there are super massive black holes.

They're billions or even

hundreds of billions of times the mass of the sun and

um uh millions to to tens of billions maybe even hundreds of billions. So extremely massive.

We don't think that the universe has had enough time to make them from

stars that just merge.

We know that two black holes can merge

and make a bigger black hole and then those can merge and make a bigger black hole.

We don't think there's been enough time for that.

So, it's suspected that they're formed very early,

maybe even a hundred

few hundred million years

after the big bang and that they're formed

directly by collapsing out of primordial stuff. Mhm.

that there's a direct collapse

right into the black hole.

So like in the in the very early

universe, these are primordial

black holes from the stars.

Not quite Wait, how how do you get from that soup

black holes right away, right?

So it's odd, but

it's weirdly easier to make a big black hole out of something that's just

the density of air if it's really really as big as what we're talking about.

So, in some sense, if they're just allowed to directly collapse very early in

the universe's history, they can do that more easily.

Um, and it's so much so that we think that there's

one of these super massive black holes in the center of every galaxy.

So, they're not rare

and we know where they are.

They're in the nuclei of galaxies.

So, they're bound to the very early formation of entire galaxies

in um in a really surprising

and deeply connected way.

I wonder if the

like the chicken or the egg is it

uh like how critical

how essential are the super massive black holes to the formation of galaxies?

Yeah, I mean it's ongoing, right? It's ongoing.

Which came first, the black hole or the galaxy?

Um probably um big early

stars which were just made out of

hydrogen and helium from the big bang.

Um there wasn't anything else, not much of anything else.

um those early stars were forming and then maybe the black holes and kind

of the galaxies were like these

gassy clouds around them.

Um but there's probably a deep relationship

between the black hole powering

jets, these jets blowing material

out of the galaxy

that that shaped galaxies

maybe kind of curbed their growth.

Um and so I think the mechanisms

are still are still ongoing

attempts to understand exactly

the ordering of these things.

Can we get back to spacetime?

Just going back to the beginning of the 20th century.

How do you imagine spacetime?

How do we as human beings supposed to visualize and think about spacetime

where you know time is just another dimension in this 4D space

that combines space and time?

Because we've been talking about morphing in all kinds of different ways.

is a curvature of spacetime

like how do you

how are we supposed to conceive of it?

How do you think of it?

Yeah, time is just another dimension.

There are different ways we can think about it.

We imagine drawing a map of space

and treating time as another direction in map.

But we're limited because as three-dimensional

beings, we can't really draw

four dimensions, which is what I'd require.

three spatial because I'm pretty sure there's at least three.

I think there's probably more,

but um I'm happy just talking about the large dimensions,

the three we see

up, down, right, east, west,

uh north, south, three

spatial dimensions and time is the fourth.

Nobody can really visualize it.

Um but we know mathematically

how to unpack it on paper.

I can mathematically suppress

one of the spatial dimensions and then I can draw it pretty well.

Now the problem is that

we'd call it a ukitian spacetime.

A uklitian spacetime is when all the dimensions are orthogonal

and are treated equally.

Time is not another ukitian dimension.

It's actually a manowskian spacetime.

But it means that the

spacetime, we're misrepresenting it when we draw it, but we're misrepresenting

it in a way that we deeply understand.

I can give you an example.

The Earth, I can project onto a flat sheet of paper.

I am now misrepresenting

a map of the Earth.

And I know that, but I understand the rules for how to add distances

on this misrepresentation because the Earth is not a flat sheet of paper. It's a sphere.

And um and as long as I understand the rules for how I get

from the north pole to the south pole

that I'm moving along really a great arc and I understand that the distance

is not the distance I would measure on a flat sheet of paper

then I can do a really great job with a map

and understanding the rules of

addition multiplication and the geometry is not the geometry of a flat sheet of paper.

I can do the same thing with spacetime.

I can draw it on a flat sheet of paper

but I know that it's not actually a flat uklidian space.

And so my rules for measuring

distances are different than the rules I would use

that for instance cartisian rules of geometry.

I I would know to use the correct rules for manovski

spacetime and and that will allow me to to to to

calculate how long uh time has elapsed

which is now a kind of a length

a space-time length on my map

um between two relative observers.

and I will get the correct answer.

Um but only if I use these different rules.

So then what does

according to general relativity

does uh objects with mass due to the spacetime? Right. Exactly.

So Einstein struggled for this completely

general theory not a specific

solution like a black hole or an expanding spaceime or

galaxies make lenses or those are all solutions.

That's why what he did was so enormous.

It's an entire paradigm

that says over here is matter and energy.

I'm going to call that

the right hand side of the equation.

Everything on the right hand side of Einstein's

equations is how matter and energy are distributed in spaceime.

On the left hand side

tells you how space and time

deform in response to that matter and energy.

And it can be

impossible to solve some of those equations.

What was so amazing about what Shell

did is he found this very elegant simple solution within like a

month of reading um this final formulation.

But Einstein didn't go through and try to find all the solutions.

He sort of gave it to us, right?

He shared this and then

lots of people since

have been scrambling to try to

ah I can predict the curvature of the spaceime if I tell you how

the matter and energy is laid out.

If it's all compact in a spherical

system like a sun

or even a black hole,

I can understand the curves in the spaceime around it.

I can solve for the for the shape of the spacetime.

I can also say, well, what if the universe is full of gas or

light and it's all kind of uniform

everywhere and I'll find a different and equally surprising

solution, which is that the universe would expand.

In response to that, that it's not static,

that the distances between galaxies would grow.

This was a huge surprise to Einstein.

Um, so all of these consequences

of his theory, you know,

came with revelations that were not at all obvious when he first wrote down

um the general theory and he was afraid to take the consequences

of that theory seriously,

which is aen the theory itself

in its scope and grandeur

and power is scary.

So I can understand.

Then there's, you know, the

the edges of the theory where it falls apart.

The consequences of the theory that are extreme, it's hard to take seriously.

So you can sort of empathize. Yeah.

He very much resisted the expansion.

So if you think about 1905

when he's writing these sequence of unbelievable

papers as a 25year-old

who can't get a job, you know, as a physicist and he writes all

of these remarkable papers on relativity and quantum mechanics.

Um and then even

191516 he does not know that there are other galaxies out there.

This this was not known.

People had mused about it.

Um there were these kind of smudges on the sky that

people contemplated what if there are other island universes.

You know going back to Kant thought about this.

But it wasn't until Hubble

it really wasn't until the late 20s

um that it's confirmed

that there are other galaxies. Wow. Yeah.

He didn't obviously there's so much we

think of now that he didn't think of.

So there's no big bang static universe.

But these are all connected. Wow. Yeah.

So he's operating on very little information. Very little information. That's absolutely true.

Actually, one of the things I like to point out is the

idea of relativity was foisted

on people in this kind of cultural way.

But there's many ways in which you could call it a theory of absolutism.

And um the way Einstein

got there with so little information

um is by adhering

to certain very strict absolutes

like the absolute limit of the speed of light

and the absolute constancy

of the speed of light

which was completely bizarre

when it was first uh discovered.

really that was observed

through experiments trying to figure out

um you know what would the relative speed of light be?

It's the only really only massless

particles have this property that they have an absolute speed and if you think

about it it's incredibly strange.

Yeah, it's really strange. Incredibly strange.

And so so from from a theoretical

perspective he he's he takes that seriously.

He takes it very seriously and everyone else is trying to come up with

models to make it go away.

Um to make uh the speed of light be a little bit more reasonable

like everything else in the universe.

Um you know if I run at a car, two cars coming at each

other, they're coming at each other faster

than if one of them stops.

It's really a basic observation

of reality right here.

This is saying that if I'm racing at a light beam

um and you're standing still relative to the source,

uh we'll measure the same exact speed of light. Very strange.

And he gets to relativity

by saying, well, what's speed? Speed is distance.

It's space over time.

It's how far you travel.

Um it's the space you travel in a certain duration of time.

And he said, "Well, I bet something must be wrong then with space and time."

So this is an enormous leap.

He's willing to give up

the absolute character of space and time in favor

of keeping the speed of light constant.

How was he able to

intuitit a world of curved spaceime?

Like I think it's like one of the most special leaps

in human history, right?

Cuz you're it's amazing.

like it's very very very

difficult to make that kind of leap.

I I'll tell you it took me I think a long time

to I can't say this is how he got there exactly.

It's not as though I studied

the historical accounts of

or his description of his internal states.

This is more having learned the subject

how I try to tell people how to get there in a few short steps.

Um, one is to start with the equivalence principle

which he called the happiest thought of life.

And the equivalence principle

comes pretty early on in his thinking.

And and um it starts with something like this.

Like right now I think I'm feeling gravity because I'm sitting in this chair

and I feel the pressure of the chair and it's stopping me from falling

and um lie down in a bed and I feel heavy on the bed

and I think of that as

Ein has a beautiful ability to remove

all of these extraneous factors, including atoms.

So, let's imagine instead that you're in an elevator

and you feel heavy on your feet because the floor of the elevator is

resisting your fall, but I want to remove the elevator.

What does the elevator have to do with fundamental properties of gravity?

So, I cut the cable.

Now, I'm falling, but the elevator

is falling at the same rate as me.

So now I'm floating in the elevator.

And if this happened to me,

if I woke up in this state of falling

or floating in the elevator,

I might not know if I was in empty space

just floating um or if I was falling around the earth.

There would actually equivalent situations.

I would not be able to tell the difference.

I'm actually when I get rid of the elevator in this way by cutting

the cable, I'm actually experiencing weightlessness.

And that weightlessness is the purest experience of gravity.

And um and so this idea of falling is actually fundamental.

It's how we talk about it all the time.

The earth is in a free fall around the sun. It's actually falling.

It's not firing engines, right?

It's just it's just falling all the time, but it's just cruising so fast. So actually Yeah.

God, you said so many profound things.

So one of them is

really one of the ways to

spaceime is to be falling.

To be falling that is the purest experience of gravity.

The experience of gravity

uh unfettered uninterrupted by atoms is weightlessness. Yeah.

That observation no it has an unhappy ending.

the elevator story, right? Because of atoms.

Again, that's the fault of

the atoms in your body interacting

electromagnetically with the crust of the earth or the bottom of the building or whatever it is.

Um, but this period of freeall,

so the first observation

is that that is the purest experience of gravity.

Now, I can convince you that things follow along curved paths

because I could take uh, you know, a pen

and if I throw it,

we both know it's going to follow an arc

and it's going to follow an arc until

atoms interfere again and it hits the ground.

But while it's in freef fall

experiencing gravity at its

purest, what the Einsteinian

description would say is it is following the natural

curve in spaceime inscribed by the earth.

So the earth's mass and

shape curves the paths in space

and then those curvatures

tell you how to fall, the paths along which you should fall when you're

falling And so the Earth

has found itself on a free fall

that happens to be a closed circle,

but it's it's actually falling.

The International Space Station uses this principle all the time.

They get the space station up there

and then they turn off the engines.

Can you imagine how expensive it would be if they had to fuel that

thing at all times? Right.

They turn off the engines. They're just falling. Yeah, they're falling.

And they're not that far up.

Um there there are certainly people sometimes say, "Oh, they're so far away they don't feel gravity." Oh, absolutely.

If you stopped the space station, it's going like

17,500 m an hour, something like that.

If you were to stop that,

it would drop like a stone

right to the earth.

So, they're in a state of constant freefall

and they're falling along a curved path.

And that curved path is a result of curving spacetime

and that particular curved path's calculated in such a way that it curves onto itself.

So, you're orbiting, right?

So it has to be cruising

at a certain speed.

So once you get it at that cruising speed, you turn off the engines.

But yeah, to be able to visualize

at the beginning of the 20th century Mhm.

that not you know that

free falling in in in curved spaceime. Mhm.

Boy, the human mind is capable of things.

I mean some of that is

um constructing thought experiments

that collide with our understanding of reality.

Maybe in the collisions, in the contradictions,

you try to think of

extreme thought experiments that

that uh exacerbate that contradiction

and see like, okay, what is actually

is there another model that can incorporate this?

But to be able to do that,

I mean, it's it's kind of inspiring

because, you know, there's probably another general relativity out there. Yeah.

in all not just in physics

in all lines of work in all

scientific pursuits there's certain theories where you're like

okay I just explained

like a big elephant in the room here

that everybody just kind of didn't even

think about there could be

uh for stuff we know about in physics there could be stuff like that

for the origin of life on

everyone's like yeah okay

everyone's like in polite companies Yeah. Yeah. Yeah. Yeah. Somehow it started. Mhm. Right. Nobody knows.

I find it wild that that's so elusive. Yeah. It's it's strange.

And the lab became strange that it's so elusive.

I think it's a general relativity thing.

There's going to be some thing.

It's going to involve aliens and wormholes

and and dimensions that we don't quite understand

or some some field that's bigger than

like it's possible, maybe not.

It's possible that it has

it's a field that is

different that will feel fundamentally

different from chemistry and biology

it'll be maybe through physics again maybe the key to the origin of life

is in physics and the same there it's like a a weird neighbor is consciousness. Mhm.

It's like all right a weird neighbor. Yeah.

It's like okay so we all know

that life started on Earth somehow. Mhm. Nobody knows how. Mhm.

We all know that we're conscious.

We have a subjective experience of things.

Nobody understands that people have ideas and so on.

But it's such a dark

sort of we're entering

a dark room where a bunch of people are whispering about like, "Hey, what's in this room?"

But nobody nobody has a effing clue. Mhm.

So, and then somebody comes along with a general relativity kind of conception

where like it reconceives

everything and you're like ah

it's like a watershed moment. Yeah. Yeah.

It's there and until

we're living in the mo we're living in a time until that theory comes

along and uh it'll be obvious in retrospect,

but right now we're right.

Well, this it was obvious

to no one that spacetime

was curved, but even Newton understood something wasn't right.

So, he knew there was something missing.

And I think that's always

fascinating when we're in

a situation where we're pressure testing our own ideas.

He did something remarkable,

Newton did, with his theory of gravity.

Just understanding that the same phenomena was at work

with the earth around the sun as the apple falling from the tree. That's insane.

That's a huge leap.

Understanding that mass, inertial

mass, what makes something hard to push around

is the same thing that

feels gravity in at least in the Newtonian

picture in that simple way. Unbelievable leap. Absolutely genius.

But he didn't like

that the apple fell from the tree

even though the earth wasn't touching it.

Yeah, the action at a distance thing.

The action at a distance thing.

That is weird, too.

Well, but that is a really weird one. It's really weird.

But see, Einstein solves that.

Relativity solves that because

it says the Earth

created the curve in space.

The apple wants to fall freely along it.

The problem is the trees in the way.

The tree is the problem.

The tree is actually accelerating the apple.

It's keeping it away from its natural state of weightlessness

in a gravitational field.

And as soon as the tree lets go of it, the apple will simply

fall along the curve that exists.

I would I would love it if somebody went back to Newton's time

and told him all this.

Probably some like some like hippie would be like

it's a gravity is just the curvature in space time, man.

I wonder if he would be able to I don't think there's you know

every idea has its time.

He might not he might not even be able to load that in.

I I mean that

sometimes even the greatest geniuses

I mean you can't

like you need too out of context.

You need to be standing on the shoulders of giants

and on the shoulders of those giants and so on.

I heard that Newton used that as an unkind

remark to his competitor Hook.

Oh no, the people talk even back then. Trash talking.

This is one of the hilarious

things about humans in general, but scientists too, like these huge minds.

There's these moments in history where

you'll see this in

this in universities, but everywhere else too.

Like you have gigantic

minds obviously also coupled with

everybody has an ego

and like sometimes it's just the same soap opera

that played out amongst humans everywhere else

and so you're thinking about the biggest

cosmological objects and forces

and ideas and you're still

like jealous and right

I know your your office is bigger than my office.

I know this chair

this or or maybe

uh you got married to

this person that I was always in love with

the betrayal of something.

The one woman in the department. Yeah.

The one woman in the department. Yeah.

And it's just I mean but that is also the fuel of innovation

that jealousy that tension that's

well you know the expression I'm sure um the battles are so bitter in

academia because the stakes are so low.

That's a beautiful way to phrase it.

But also like we shouldn't forget I mean

that I love seeing that even in academia

because it's humanity the silliness

it's there is a degree to academia

where the reason you're able to think about some of these grand ideas

is because you still allow yourself to be childlike.

Oh yeah, there's a childlike nature to be ask

questions but children can also be like children children.

So like you don't I think when

um in in in a corporate context and maybe the world gets

forces you to behave you're supposed to be a certain kind of way

there's some aspects and it's a really beautiful aspect to preserve and to celebrate

in academia is like you're just

allowed to be childlike

in your curiosity and your exploration

you're just exploring asking the biggest questions

the best scientists I know

often ask the simplest questions questions.

Um they're they're really

um first of all there's probably some confidence there,

but also they're never

going to lie to themselves

that they understand something that they don't understand.

So even this idea that Newton didn't understand the apple falling

from the tree, he

had he lived another

couple hundred of years, he would have invented relativity

because he never would have lied to himself that he understood it.

he would have kept asking this very simple question.

Um, and uh, I think that there is this childlike beauty to that. Absolutely. Yeah.

Just some of the topics,

I don't know why I'm stuck to those two topics of origin of life

and consciousness, but there's I'll talk about this.

Some of the most brilliant people I know

are stuck just like with Newton and Einstein.

They're stuck on that.

This doesn't make sense.

I know a bunch of brilliant biologists,

physicists, chemists, they're thinking about the origin of life.

They're like, "This doesn't

I know how evolution works.

I know how the biological systems work.

How genetic information propagates,

but like this this part, the singularity

at the beginning doesn't make sense. We don't understand.

We can't create in the lab.

They're bothered come every single day.

They're bothered by it.

And that being bothered by that tension, by that gap in knowledge is uh

yeah, that's the catalyst.

That's the fuel catalyst for the discovery.

But the discovery yeah absolutely the discovery is going to come because somebody couldn't

sleep at night and couldn't rest.

So in that way I think black holes are a kind of

portal into some of the biggest mysteries of our universe.

So it is a it's a good terrain on which to explore these ideas.

So can can you speak about some of the

mysteries that the black holes present us with?

Yeah, I think it's important

to separate the idea that there are these astrophysical

states that become black holes

um from being synonymous with black holes because black holes are kind of this

this larger um idea

and uh they might have been made primordally

when the big bang happened and

they're there's something flawless

about black holes that makes them

um unlike anything else.

So, uh they're flawless in the sense that

you can completely understand a black hole by looking at just its charge,

electric charge, its mass, and its spin.

And every black hole with that charge, mass, and spin is

identical to every other black hole.

You can't be like, "Oh, that one's mine. I recognize it.

It has this little feature, and that's how I know it's mine." They're featureless.

They you you try to put

uh Mount Everest on a black hole and it will shake it off

in these gravitational waves.

It will radiate away

this imperfection until it settles down to be a perfect black hole again.

So there's something about them that is unlike

and another reason why I don't like to call them objects in a traditional

sense unlike anything else

in the universe that's macroscopic.

It's kind of a little bit more like a fundamental particle.

So, an electron is described by a certain short list of properties.

Charge, mass, spin, maybe some other quantum numbers.

That's what it means

to be an electron.

There's no electron that's a little bit different.

You can't recognize your electron.

They're all identical in that sense.

Um, and and so in some

very abstract way, black holes

share something in common with microscopic fundamental particles.

And so what they tell

us about the fundamental

laws of physics um can be very

profound and it's why

even theoretical physicists, mathematical

physicists, not just astronomers

who use telescopes, they

rely on the black hole

as a terrain to perform their thought experiments.

And and it's because there's something fundamental about them. Yeah.

General relativity means quantum mechanics

means singularity and sadly

heartbreakingly so it's out of reach

for experiment at this moment but

but within reach for theoretical

it's in reach for for thought experiments

for thought experiments which are quite beautiful

well on that topic I have to ask you about

the paradox the information

paradox of black holes what is it so

this is what catapulted

Hawkings fame when he was a young

researcher, he was thinking about black holes

and wanted to just add a little smidge of quantum mechanics,