All language subtitles for What Bothers Physicists About Black Holes (Interview with Brian Cox)

Imagine that you and I are on a mission
to fall into a black hole. It's a bit

nasty around these things. You cease to
stay together.

We're one long string of atoms?

Well, what are we? Yeah, and then the
atoms get separated.

If a black hole will one day end up as
nothing, the normal vacuum of space,

happened to you and me? What happened to
all of that stuff? I mean, this is the

central question.

The laws of nature are quite clear on
this. So that's what bothered everybody.

for a very long time. What happened?
What's the end of the story? I'm so

about this. The video you're about to
watch is a deep dive into the cutting

research happening right now about black
holes.

It's... Awesome. It's the extended cut
of an interview that I did with famous

physicist Dr. Brian Cox for a shorter
Huge If True episode all about what

actually happen if you fell into a black
hole. That episode is incredible, and

I've linked to it in the description.

But there was so much weird and mind
-bending stuff in this conversation that

didn't fit into that shorter episode,
and I knew that you'd want to see it. So

we decided to release the full extended
cut. It's just too cool, and I think

you'll love it. So strap in, because the
cutting edge of black holes is

Great. Would you mind just starting us
out by introducing yourself however you

like? Yeah, I'm Brian Koch.

And if you want the title, the full
title, I'm Professor of Particle Physics

the University of Manchester, Royal
Society Professor for Public Engagement

Science and Visiting Scholar at the
Crick Institute in London.

And how do you describe what you do
every day?

What I do every day?

Physics.

And that's kind of the way that I see
myself. If someone asks me what I do, I

say I'm a physicist.

But actually, of course, most of my time
now is spent on the public engagement

side. And I kind of fell into that
accidentally.

But I still, maybe it's a thing, maybe
there's some deep psychological thing

going on. But I never say TV presenter
or whatever it is. I just say physicist.

Well, that's what I want to talk to you
all about today.

So imagine that you and I are on a
mission to fall into a black hole.

And we have some imaginary spaceship
that can take us as far and as fast as

want. So we get up, we walk outside, we
get into our spaceship.

What now?

What is a black hole and how do we find
them?

So a black hole, it's interesting that
the idea...

The first glimpse of them,
theoretically, came very shortly after

theory of gravity was published, in
1915.

Although it wasn't recognized as such at
the time, this glimpse.

But essentially, what does Einstein's
theory do? It's important for what

follows. It's a theory of space and
time, and how space -time, which is

described as the fabric of the universe,

responds, warps or curves, to matter and
energy in the universe.

So the equations, basically the theory
that Einstein published all those years

ago, will say, give me some distribution
of matter, something like a ball of

matter, and the equations will tell you
how the fabric of the universe is

distorted. And by the way, the force of
gravity in that theory then is the

response of everything else in the
universe to that distortion.

So Einstein would say, what are we
feeling now? Newton would say it's a

between us and the Earth.

But Einstein would say there isn't a
force. What we're responding to the

distortion in the fabric of the universe
created by the Earth.

John Wheeler, actually, the great
physicist, put it beautifully.

He said, matter tells space -time how to
curve, and space -time tells matter how

to move. And that's it. So that's
Einstein's theory.

So in 1916...

shortly after it was published, a man
called Karl Schwarzschild remarkably

managed to solve the equations for a
perfectly spherical, non -spinning ball

matter. It's the simplest thing you
could do, which tells you how space and

are distorted by it. And that's a model
for a star.

It's the simplest thing you could do.

So he solved the equations. It's a
remarkable thing.

In those equations...

there is a description of a black hole,
although it wasn't realized at the time.

It's a remarkable piece, simple piece of
mathematics, actually.

So essentially, what's the idea behind a
black hole?

One way to think about it is that you
could remove, could you remove the star

from this fabric, but leave the
distortion behind?

So if you do that, you get the
description of a black hole. But you

what would you mean? How can that be?

formed in nature so you think about what
a star is then a star is a balancing

act so it's a it's a mainly hydrogen
helium collapsing under its own gravity

that's how our sun formed four and a
half billion years ago so it's

so what stops it collapsing well as it
collapses the core heats up And that

initiates nuclear fusion reactions in
the core. In the case of our sun, it's

hydrogen being fused into helium. That
releases energy, which creates a

which holds the thing up. So it's
balancing, but it needs the fuel.

And it's not infinitely big, of course.
So at some point it runs out of nuclear

fuel. And ultimately, no more fusion
reactions can occur in any star.

And so the star will resume its
collapse.

So the question is, well, is there
something that stops it?

Because if there isn't something that
stops the collapse, then it will

without limits.

And so actually, if you look at the
history of physics in the 20s and 30s,

people were saying, well, we'd like to
avoid this idea that the thing will

collapse without limits.

Because if it does, then Schwarzschild's
equation predicts some very strange

things indeed. And so people kind of
tried to avoid it. It was really

Oppenheimer. and his student Schneider
in the late 30s, just before the Second

World War, that showed that really, with
some assumptions, it looked like a

massive enough star could actually
collapse without limits.

So what does that mean?

Collapse is without limits.

It means that essentially it does what I
said.

You essentially remove the star from the
fabric of the universe, leaving the

distortion behind.

And the black hole, the idea behind the
black hole is... Let's say you take

the sun, the mass of the sun, and you
just collapse it and you keep on

collapsing it.

You get to a point when the radius of
the sun is not 700 ,000 kilometers,

is what it is in miles, half a million
miles.

I'm going to use kilometers because I
can't remember the things in miles. Our

audience will appreciate that. Everyone
can convert it afterwards, right?

So 700 ,000 kilometers.

And you squash it down.

And you squash it and squash it until
its radius becomes three kilometers.

Three.

Then there are several ways to look at
this. One is that on the surface, the

speed you'd have to travel to escape its
gravitational pull, called the escape

velocity, would exceed the speed of
light.

That's one way to think about it.

So even light rays emitted from the
surface, if you could squash it down

far. would just stay there. They would
not escape because they'd be trying to

at the speed of light and the escape
velocity is the speed of light and they

just stop.

So what happens then, if a star
collapses inside that number, which for

of the sun, three kilometers, is called
the Schwarzschild radius, then it will

collapse without limits.

Nothing will stop it.

And for all you will get is essentially
the geometry of space and time, the

curvature. And that's a black hole. So
it's a thing that traps light in that

sense. So you think about that.

If you have this surface, and space and
time are so distorted there, that if you

go in across that surface, called the
event horizon of the black hole, then

can't get out.

One way to think about it is you'd have
to travel faster than light to get out.

Another way to think about it is that
there's a beautiful model, which is my

favorite model. It's called the river
model of a black hole. You can write the

equations, space being like a river that
flows into this thing, kind of like a

sinkhole or something in space.

And the river of space flows at the
speed of light inwards on the horizon.

And then faster than light, inside.

So if you imagine that you're a photon,
a particle of light, you're like a

little fish swimming against the tide.

But if the tide's going at the speed, as
fast as you can swim, the speed of

light, you can't get out.

Not only can you not get out, but you're
going inwards towards something.

And this thing, this something, is
called a singularity.

You say, what is this thing, the
singularity? And I think it's really

to picture it as some infinitely dense
point to which the star collapsed.

When you draw a map of space and time,
what you see really clearly is that this

singularity thing is not a place in
space, it's a moment in time.

And it's in fact the end of time in
Einstein's theory.

So a way that I often kind of picture it
or explain it to myself is that space

and time have become so distorted.

that when you look at it from the
outside, they flip -roll.

So space has become time, and time has
become space.

In the mathematics, if you put a little
graphic up, you'll see that the plus and

minus signs in the Schwarzschilds are
quite reversed, right?

And so they flip around, and so they
change.

So what you thought of as an infinitely
-end place in space to which the star

collapsed has become a moment in time.

And a way to think about why you have to
go to it then, it's really beautiful,

because you think it becomes something
that's in the future for anyone or

anything that crosses the horizon.

It's in the future.

So it's like, if you say, well, I want
to escape this thing, it's like saying,

want to escape tomorrow.

If I said to you, let's run away from
tomorrow, you'd go, I can't run away

tomorrow, it's in the future.

That's what this thing behaves like.

So that's the Einsteinian description of
a black hole.

I want to take that step by step. Yeah,
yeah, there's a lot of it in there, but

it's fun.

Okay, so in order to understand this,
let's imagine that we choose the black

hole at the center of our own galaxy.
Yeah.

Sagittarius A star, I think it's called.
Yeah. I know that we took this picture

of it in 2020.

That is by the Event Horizon Telescope,
Sagittarius A star. What are we looking

at here?

So here, the light, you might say, what
is the light in this picture?

So it's not from the black hole, because
the black hole's trap light.

It's from what's called the accretion
disk around the black hole.

So you have to imagine the material
spiralling around in orbit, around this

dense object, and very violently
orbiting.

And so it heats up and it emits light.

So imagine a flat, thin disk of material
around the black hole.

But this does not look like that.

What you're seeing is the distortion,
the curvature of the light rays.

We said that you might think, well,
light travels in straight lines.

But Einstein's theory says that in the
vicinity of this thing, the fabric of

universe itself is distorted.

So the light, the paths of the light
rays follow the distortion.

That's why in an animation it looks like
it's going over the top and around the

sides at the same time. So what you're
seeing, this famous image of a black

hole, like if you think of the film
Interstellar, that code, by the way, is

implementation of Einstein's equations.

Kip Thorne and others helped him do
that.

So it's really a prediction.

So what you're seeing, if you imagine
this disk of material around this thing,

like picture it in your mind's eye
pattern, then light rays, let's say from

perspective, from behind the black hole,
let's say, on the disk, go around

into your eyes.

Sometimes they orbit and then go around
into your eyes.

And they go into your eyes from every
point on the disk, from underneath and

the top and behind.

So you have light rays going always
around this thing. So you see that.

what you see as an image.

So there's a prediction of Einstein's
theory.

which is a real black hole, should look
like that. It's a characteristic donut

shape that you see.

Well, here's an image with radio
telescopes of such a thing.

And it looks like the prediction. It is
a bit blurry, but, you know, this is at

the center of the galaxy.

Very difficult. This was actually the
second one that was imaged. The first

was in a galaxy called M87, which is 55
million light years away and is bigger

than this one.

Bigger.

So this one's about 6 million times the
mass of the sun, give or take.

The one in M87 is 6 billion times the
mass of the sun. So this is the baby

supermassive black hole that we've got.
So this is my next question.

Our black hole, how big is it compared
to other black holes that we know of?

It's a small -ish one.

And what's the scale?

It's a supermassive black hole. But we
think that I would say all galaxies,

maybe there's an exception or so, but
pretty much all galaxies have

black holes at their centres.

We don't quite know why, actually. We
don't quite know how galaxies form in

early universe. It's one of the...

that the JWST, the James Webb, is
looking at in some detail, the new space

telescope. But to good approximation,
all galaxies have these things.

And they can be different masses.

So as I said, the M87 galaxy has one
that's six billion times the mass rather

than six million times the mass.

But how big is it?

So the number I always remember in my
mind is the Schwarzschild radius of the

sun. which is, as we mentioned, it's the
radius you'd have to squash the sun

down to make a black hole. And it's
three kilometres.

So it goes like the math.

So you can work it out. So if that's six
million times the mass of the sun, then

the Schwarzschild radius is six million
times three kilometres.

It's kind of easy to do the math,
actually.

So that would be the... You might call
it... You have to be careful with your

language. But let's... Let's say that
this thing is, it gives you an idea of

size of this structure.

So the disk outside it is much bigger.

I did the math with Earth's radius.

Yeah. And it seemed to suggest that we
would become a black hole if we

compressed everything on Earth and all
of us into something about the size of a

pea. Yeah, that's from memory about 0 .8
centimeters, I think. Something like

that, just less than a centimeter. So
you're right about that, that big.

Do black holes that small exist?

No, we don't.

I think so.

So even black holes, the mass of the
sun, the sun will not form a black hole.

When it runs out of nuclear fuel, it
will collapse. And there's something

can stop it collapsing.

The force of electrons.

Yeah, it's called the white dwarf star.

It's beautiful calculation, by the way,
that you can do the calculation. It's

great.

So what stops it, as an aside, is that
electrons, there's something called the

Pauli exclusion principle. I read about
this, yeah. So electrons don't want to

be close together, roughly speaking, you
could say it like that.

So as you squash the thing, the
electrons get closer together.

And so they kind of separate away from
each other and go into smaller and

smaller little regions of space because
they're trying to stay away from each

other. But there's also something called
the uncertainty principle, Heisenberg's

uncertainty principle.

So as you confine them in smaller
regions, they start jiggling around

faster. And ultimately, you can reach a
limit where they're essentially trying

to jiggle at the speed of light and they
can't. And so there's a limit to how

much pressure that process can exert.

And it turns out it's 1 .4 times the
mass of the sun, which is called the

Chandrasekhar limit.

So you can do that calculation.

But it's a beautiful calculation because
you could have worked that out.

not knowing that stars exist.

All you need to know about is quantum
mechanics and relativity.

And you can make the calculation, what
is the biggest lump of stuff that can be

held up by this jiggling of electrons?

It turns out it's 1 .4 times the mass of
the sun. Then you look into the sky and

you see there are these things called
white dwarfs, these collapsed stars,

are, and there's none.

More massive than 1 .4 times the mass of
the Sun. So it's very beautiful. And

then you can get neutron stars, which
are held up by the jiggle in the

But ultimately, if you go to something
that's three times the mass of the Sun,

something like that, a bit more, then
nothing stops it collapsing.

And that's when you form a black hole.

So the lightest black holes that we know
of are around that mass.

And then we know of them that are 10,
20, 30 times the mass of the Sun from

collapsed stars.

And then these things, which are
millions of times or even more the mass

sun, which is at the heart of galaxies.

So we've launched in our spaceship. We
are hurtling toward this black hole.

Could you walk us through step by step
what happens from now until when we hit

the event horizon?

Yeah. So the first thing to say is that
it's right at the heart of Einstein's

theory is something called the
equivalence principle, which was the

really led Einstein to the theory itself
of gravity.

And so you don't feel its pull.

What you do is you just fall freely
towards it. So we're falling towards

thing there, and we turn our rocket
motors off.

We can't tell.

We can't look outside.

We can't look out the windows. We're
just in free fall. We're just floating.

So it's like the astronauts on the
International Space Station.

We're just there.

So it's fundamental to Einstein's
theory.

It's very important, actually, for
the...

problems that follow that we're going to
talk about that you just freely fall

towards this thing so we could be
approaching this in this room now and we

have no clue that that's what's
happening and in fact so we're

event horizon of a very big black hole
like this for a black hole of this mass

then we wouldn't even notice something,
according to Einstein's theory, as we

fall across the horizon into the
interior of the black hole.

So we'd fall across the horizon.

From our perspective in this room,
according to Einstein, and we'll go for

caveat a bit later, but according to
Einstein, into the interior of the black

hole we go and we notice nothing.

What about when we're in the accretion
desk?

Wouldn't we be banged around by a lot of
stuff? We might get in a bit of a mess.

But we're talking about the pure
gravitational thing. You're absolutely

It's a bit nasty around these things.

But that's nothing to do with the black
hole itself.

It's nothing to do with the fundamental
physics.

It's all the x -rays and all the nasty
gamma, all the stuff that's been

from all this hot material around it.

So, yes.

That would be a problem. But if we had
a, let's say that our room, this

spacecraft, is magically insulated from
radiation and heat and all those things,

then nothing.

In, we would go into the interior.

The caveat, there's a lot of caveats,
but one thing I should say is that it

matters that that description I've
given, it's for a supermassive black

If this was a smaller black hole, so
smaller, less massive, you know, a few

times the mass of the sun, then at some
point you experience what's called tidal

gravity, tidal forces.

So those are the things that raise the
tides in the oceans of the Earth.

The tidal forces, we will start to, in
our freely falling trajectories towards

the black hole, at some point you start
to get... feel the tides, you start to

get stretched and squashed. And we feel
it. You would start, you'll feel it

eventually. You'll really feel it
eventually because formally, as you get

close to the singularity, you get
infinitely stretched and squashed. So

really feel it. I want to talk about
that inside.

Yes, that's my favorite one. But for a
smaller black hole, as you approach the

horizon, you feel those forces.

But for the big ones, You don't feel the
tights until you've gone into the

interior. So we're moving toward the
event horizon. We're somehow insulated

the messiness of the accretion disk.
We're moving toward it.

I've heard that there's a moment where
the physics of this are such that if you

and I are actually falling in, if we
look to the left and the right, we would

actually see the back of our own heads.

Yeah. Is that anywhere close to correct?
And can you tell me about... the other

little details as we approach the event
horizon that you think are important?

Well, one of the biggest details, it's
not even a detail, it's one of the most

shocking things about this is I've
described this, the earth falling into

black hole.

And we're saying in this room where we
can't see out, what do we feel? What can

we measure?

And the answer is you can't measure
anything and we don't feel anything

get inside and we approach the
singularity for this one.

But from the point of view of someone
outside, the description is very

different.

So what would they see happening to us
as we fall towards this thing? So even

in Einstein's theory with nothing else,
no quantum mechanics or anything.

then what they would see is time tick
more slowly for us.

So they would start to see, as we
approach the black hole, if they could

watches, if we were transmitting to them
or whatever it is, transmitting from

these cameras, we're sending it out to
them.

They would see our time tick more
slowly, more slowly, more slowly.

And they would see our time stop on the
horizon.

So they would never see us fall in.

So from the point of view of someone
outside, nothing goes into the black

ever.

So do they see us imprinted there
forever, or does the light from us

fade? It would fade, because also you
could picture, there are many ways of

picturing it, but you could say this
light is climbing away through this

gravitational field, so it's getting
stretched.

So we get redder and redder and redder,
redshifted, infinitely redshifted.

Time passes more and more slowly until
it stops on the horizon when viewed from

the outside.

From our perspective, we look at our
watches, they go at one second per

And that's absolutely central. There's
nothing weird. Well, there's something

weird there. But there isn't according
to Einstein.

So it's pure.

Einstein's theory.

So that's the first thing to say. And
it's a clue to the interesting things

about what we're going to talk about,
what follows, is that there are

perspectives on what's happening here.

There's a perspective from our point of
view, we're going in for a big black

hole. From the point of view of someone
outside, we never go in.

And that's going to be kind of important
for what follows.

But there's nothing that's not described
by Einstein's theory in that.

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back to Black Hole.

So at this moment, we crossed the event
horizon.

Yeah. And we don't feel that... We could
have crossed it now.

Just now.

Wouldn't notice.

And...

Our experience now is completely inside
the blackness of the black hole from an

outsider's perspective.

Gravity is increasing faster and faster.

And this is where we get to maybe my
favorite word that I have learned in the

process, which is when the, my
understanding of this is when the

feet is so different from the gravity at
your head that you begin to stretch in

a very dramatic way. And this is,
Spaghettification.

Yeah. Could you explain what is
happening here? Yeah. As we get

One way of thinking about it is that,
another way of thinking about it is just

that the distortion in space -time is
not constant over the

length of your body.

So when we're falling in, we might as
well be, this is Einstein's equivalence

principle in action, we might as well be
in flat space because the distortion,

it's like saying, On the surface of the
Earth, if you look at a square mile of

the surface of the Earth, you don't see
the curvature, right? You have to go to

bigger distances to see that you're on a
curved surface.

It's kind of like that. So the
distortion...

the difference in gravitational pull as
you said or the distortion you don't

feel it until it becomes very distorted
or the big gravitational pull when you

get very close to this thing and then
you start to see that and actually it

works it's not only stretching it's also
squashing so the way the tidal gravity

works is to squash in one direction and
pull in the other direction so we are

getting you feel it so you start to feel
this strange

sort of sensation of being stretched and
squashed.

And as you go closer and closer to the
singularity, those effects become much

more extreme.

Until they're so extreme that, first of
all, you cease to stay together.

We're one long string of atoms? What are
we? And then the atoms get separated,

and then the protons, the quarks inside
the protons will get separated.

And ultimately, according to Einstein's
theory, the tidal forces become

infinite.

So formally infinite.

And so everything is gone.

Everything's been ripped apart.

And this is what we call the
singularity. So the whole thing kind of

extreme and breaks down ultimately in
Einstein's picture.

The question that when I began this
story, I wanted to ask you is what is at

center of a black hole? But in doing
this research, I now understand that

talking about the center is also a
little bit incorrect.

Yeah. How should I actually think about
what is happening at that singularity?

Well, I mean, the first thing to say is
we don't know, right?

We can talk about the current research
and speculation.

We don't really have the tools to
describe it.

So a way to think about Einstein's
theory is that, as I mentioned earlier,

tells you how space and time are
distorted.

They also kind of get mixed.

get up from from from the point of view
of someone outside so then you'll see

that space and time are getting warped
and distorted and as i mentioned they

so mixed up that on the horizon you see
that they flip and so the thing to

bear in mind for all that follows with
einstein's theory is this very central

idea that if you're freely falling
through space or over space

-time, if you like, then in the absence
of these tidal effects, you

really cannot tell where you are in the
universe. If you're close to a black

hole, close to a big star, orbiting
around a galaxy, just falling, whatever

is. So I think that's the key idea, the
so -called equivalence principle.

But of course...

As we said before, the thing about a
black hole is that you could say, why

I see these effects on the Earth?

This distortion, this mixing.

And you do.

So you see it in GPS satellites, for
example.

So if you think about what I said, I
said, as you go closer to this thing,

as viewed from the outside, time passes
more slowly.

So you could say, well, why doesn't the
Earth do that? And it does.

So what you see is that time ticks at a
different rate, by which I mean clocks

tick at a different rate, atomic clocks
or biological clocks.

So you age at a different rate in orbit
than you do on the surface of the Earth.

And you're seeing this is the same
effect.

The reason it gets very extreme, I
should say, it's quite a big effect for

near the Earth. So the drift is tens of
thousands of nanoseconds per day.

The difference in the rate that time
passes at the orbit of a

GPS satellite and on the ground.

And we have to accommodate for that when
we deal with GPS. It doesn't work.

There's tens of thousands of nanoseconds
per day, even around the Earth.

So the question of black hole really is,
as you said before, if I could keep the

mass of the Earth the same, but shrink
it down to the size of a pea.

then how does that distortion change as
I go closer and closer to this immensely

massive P thing?

And this is the effect, that time keeps
going more and more slowly from the

perspective of someone outside until you
see it stop on the horizon, which as we

said for the Earth is around a
centimeter, just a little bit less.

So it's kind of not, in some ways, this
behavior of time is not...

unique to a black hole.

It's just that in the black hole, it
becomes extreme because the thing is

completely collapsed.

So we have passed through the event
horizon. We have been spaghettified. We

hit the end of time.

Yeah.

This is a question I think I know the
answer to, but I think it leads us into

our next section.

The question is, can we ever get back
out?

So, yeah. So the answer is, According to
Einstein's theory, no, because

you've gone to the end of time, right?
And there's no way.

Basically, Einstein would say it's all
over.

You've got ripped to bits. Everything
has got ripped to bits. You've gone to

this infinitely distorted space and
time, and it's just done.

What would Stephen Hawking say?

Well, Stephen Hawking initially would
have said, in the 1970s,

Well, we should say, what did Stephen
Hawking discover in the 1970s?

So in his words, he discovered that
black holes ain't so black.

So he said nothing comes out of a black
hole.

Everything that goes in goes to the
singularity. It's gone forever because

black hole lives forever.

Now, Stephen Hawking calculated that if
you do some essentially

quantum mechanics, right, around the
horizon of the black hole. So you think

about what happens.

What does the black hole do?

A way of thinking about this is that in
quantum mechanics, which means in

reality, in nature, empty space isn't
empty. It has a rich structure. So the

vacuum of space has a structure.

And the black hole, you might say, well,
this strange behavior of space and

time, it must do something.

And it does.

It disrupts that structure.

And the result is that...

particle photons, essentially, but
what's called Hawking radiation, is

from the black hole.

So the result, and there are different
ways of thinking about what's happening.

There's the very precise way Stephen
Hawking gave an analogy in his paper.

And he said, it's just an analogy.

And people get very worked up online
when you talk about his analogy, but

Stephen did write it down, right?

So a way to picture the quantum vacuum.

is that you can imagine particles coming
in and out of existence all the time in

the vacuum.

So in accord with the uncertainty
principle, they come in and out and in

like that. You can kind of picture it
like that.

I emphasize it's not supposed to be a
technical description, but you can

picture. So you can picture these in the
vicinity of the horizon.

You can picture that this structure gets
disrupted.

You could have the situation.

where one of these particles is on the
inside and one is on the outside and

we know what's happening to the one on
the inside it's going to the singularity

because we said the river of space is
going fast in there or whatever

way you want to think about it so the
other one is basically made real and and

escaped so that's a picture that steven
himself gave um but the upshot is very

accurate the point is that this particle
has been shaken out of the vacuum And

it's now a real particle when viewed
from the outside.

And it goes away. So what is that? What
particle has been emitted? It's the

temperature. It's glowing.

And so that means it's losing energy.

And so that means it has a lifetime.

So over time, and these are enormous
times, far greater than the current age

the universe for any black hole that we
know of in the universe.

Because we don't know of tiny ones.

So all the ones we know of, the immense
lifetimes, in excess of 10 to the power

of 100 years for these supermassive
ones, right? Ridiculous times.

But ultimately, they have a lifetime.

And that means one day it will be gone,
and space will be all nice and normal

again, right? All you will have left
will be the Hawking radiation that's

emitted over these eons of time.

Okay. I think something is missing from
my understanding of the universe.

I agree with you. Something is missing
in my understanding as well, and

everybody else's.

Here's what I think is missing from mine
right now.

So all of this matter has, including us,
passed through the event horizon, ended

up at the singularity. It is something
in there at the end of time. Yeah, and

would increase the mass of the black
hole, and the black hole would grow.

Because you've gone in.

And also, I think that I know that every
law that we have about the universe

says that information is conserved.

If a black hole will one day end up as
nothing, the

normal vacuum of space, what happened to

you and me? What happened to all of that
stuff? I mean, this is the central

question.

Stephen's initial calculation, 1974,

was that this radiation, the Hawking
radiation, is

informationless, information -free. So
it's not gone away. It's not

the black hole. It turned into the
radiation, right?

But his calculation said there's no
information in that. It's what's called

thermal, purely thermal. Not surprising
if you think about it, because it's been

kind of shaken out of the vacuum of
space.

So it's certainly, you would think, got
nothing to do with the stuff that falls

in. This is something to do with the
horizon.

It's not anything to do with the
singularity, this stuff.

So out it comes, and the calculation is
very clear.

So that would suggest, as you said, that
the information, any record of anything

that fell in will have been erased.

The energy will be the same. The energy
is conserved. The black hole hasn't

vanished. It's turned into radiation.

But the radiation contains no trace of
anything that fell in. That is weird, as

you said.

Because if you think, let's imagine, you
might say, well, what's the difference?

What if I get this piece of paper and
set fire to it? It goes, and there's

stuff, ashes and radiation.

Yes. But in principle, then if you could
just measure everything,

which you can't, but if you could, then
you could reconstruct the information on

the page. And you can see why, because
it's got something.

What's happening when you burn it is
chemical reactions and there's

whatever it is. But you can trace
everything back. So you can say all the

and things are still around and there it
is.

In a black hole, you can't.

So it wasn't surprising.

What was surprising is that it appears
there is a calculation that tells you

that black holes erase everything.

And as you said, the laws of nature are
quite clear on this.

Information does not get destroyed in
the universe. It gets scrambled so you

never reconstruct it, but it doesn't get
destroyed. So that's what bothered

everybody for a very long time.

What happened? What's the end of the
story?

So at the end of the story, we're not at
the end of the story yet, but in 2019,

a series of papers were published.

One of the papers was by Jeff Pennington
and the other one was by another group

of authors.

But those papers suggest that Stephen
missed a bit in his

calculation. Very subtle.

He could have never seen it.

Yeah, I mean, that's why it took, you
know, 50 years, right, to see what he'd

missed. But it turns out that the
radiation is not information free.

At the end of the process, then all the
information about everything that fell

in is imprinted in the radiation, as you
would normally expect.

But you might, but then it becomes
interesting because you say, well, okay,

there's a calculation and there's
mathematics that was done.

But you say, well, what's the picture
then? What happened? Because I

if I take this and throw it into the
black hole, it's gone across the

It's gone to the singularity.

It's definitely true that nothing comes
out of the black hole.

So how is this information about this
thing getting imprinted in the

And it turns out that it's not just...
Initially, quite a few people thought,

well, it must be just right at the end.

When it's all quantum gravity and all
this stuff, so the thing's just about to

disappear back into the universe. And
it's getting hotter and hotter, by the

way, as it gets smaller and smaller. So
there's more and more, it's getting more

and more violent and something weird
happens and everything comes out.

But it was known for a long time, it's
worked by a great physicist called Don

Page, that the problem about the
information and the

structure of space, these problems
occur.

about halfway through the black hole's
life.

So it's called the page time.

So the problems with the information
structure of this thing occur

way before you should be thinking about
quantum gravity and a load of weird

stuff. So there was a big challenge to
physics. It's like we should be able to

calculate stuff when the black hole is
halfway through its life. There's

weird at the horizon.

But yet something weird appears to be
happening. The picture of the thing is

breaking down.

And so then we could skip if you want.

So what is the picture of this? And I
should emphasize the health warning

This is ongoing research.

And there is no agreed upon picture.

And there's some other subtleties we'll
talk about in a minute.

But a picture of what's happening, this
is related to something called the

holographic principle at some level, we
think.

So another discovery that was made in
the 70s, which is quite interesting, by

quite, I'm using it in the American
sense, it's very interesting, is that

Jacob Bekenstein, one of the pioneers
along with Stephen Hawking,

what's called the entropy of a black
hole. So this thing of the temperature,

Stephen calculated the temperature, that
is inscribed on his gravestone in

Westminster Abbey, his equation for the
temperature of a black hole. So it's a

huge fundamental discovery.

Temperature is now, we understand it
now, we didn't, when we first introduced

the concept, we didn't know about atoms
and molecules.

Then we did, and we realised that
temperature is about how fast the

parts jiggle.

around of a thing, right? So this water
here, heated up, the molecules are

jiggling around faster, that's what
temperature is.

This thing, a black hole, think about
what this is.

I said the description of it is just
space and time. That's all it is. It's

geometry.

So immediately we've got the temperature
of a geometry, not a temperature of a

thing made of stuff, but it's just the
temperature of space, right?

So that's kind of interesting.

And then Bekenstein calculates that the
thing as an entropy, which implies that

it hides information from us. There's a
structure, there's information in there.

The entropy turns out to be equal to,
equal to, the surface area of the event

horizon in what's called square Planck
lengths.

So this is a remarkable idea that you
can think of the horizon And I said,

remember, it doesn't really, it's not
really there from our perspective.

I said we could be falling through it
and I wouldn't notice anything,

to Einstein, in we go.

But then you look at it from the outside
and it looks like there's information

encoded on the horizon in pixels that
are one plank length in size.

So what does that mean?

Information's encoded in space somehow,
on the surface?

And also, by the way, It's weird, isn't
it? If I said how much information is

contained in this room, you would say,
well, it's to do with the volume of the

room, right? It's the library. It's how
many books can I fit in the library?

This is saying, no, at a fundamental
level, the amount of information in this

room is determined by the surface area
of the room, not the volume.

So it's almost as if nature has said you
can paper the outside of the library

with the pages of the book.

But there is no interior to this thing.

So you start to get these hints that
there's something very strange going on.

What is happening here?

So we've got this picture now, which was
the 1970s, of this thing that has a

temperature and an entropy, which are
calculated.

And so that kind of is suggestive of
substructure.

But structure of space and time? What do
we mean by that? So nobody knows.

Nobody knew that, right?

Then, so there's another thing that
comes, another property that then comes,

which is why I was careful about us
falling in. And I kept saying, from our

perspective, nothing happens.

So you've got this Hawking radiation.

It's coming from the disruption of the
vacuum in one picture.

So it's all there. And it's coming away
and it's climbing away from this black

hole. It's losing energy.

And so it's very low temperature by the
time you're far away from this thing.

But you go in towards it then.

towards the horizon.

If you lowered a thermometer down from
far away, our friends are in a

now, they've got a thermometer and they
lower it down.

The idea is that it sees hotter and
hotter temperatures because you're

closer and closer to this horizon.

So you've got like a fishing rod and
you're sending the thermometer down and

it's going hotter and hotter from the
point of view of someone outside.

From the point of view of someone
falling in, there's no temperature at

You don't see anything. You don't feel
anything. You don't measure any Hawking

radiation. You just go in because you're
in free fall.

So from your perspective, nothing's
happening.

From the outside, you've got this high
temperature.

So from the outside, a description of
what happens to us is different.

The description of what happens to us is
that we get vaporized.

We never get spaghettified.

As I said, you know, the other thing is
we never go in, right? So what happens

to us?

we get vaporized before we cross the
horizon.

And all our ashes and all this stuff
comes out.

And you could collect it and you could
say, well, that's fine.

Great. It's just like burning a piece of
paper.

But Einstein's theory is absolutely
clear that from our perspective, we go

We get spaghettified.

So from our perspective, our demise, the
description of our demise is

spaghettification. Yep.

From the exterior perspective, the
description of our demise is

right? So which one is it?

So you say, well, come on, you either
get incinerated or spaghettified, which

one?

The modern view, at some level, that is
much debated, goes all the way back to

work by Leonard Susskind and Gerard
Verhoeft and some others.

It's called black hole complementarity.

And the idea is that both pictures are
correct.

from different points of view this is
relativity in action right so the idea

both pictures are correct now so there
is some it's not as simple as that

and that even is not simple because
there's other stuff going on here but so

might say well okay so i understand sort
of this idea that the information

essentially you're saying that from the
outside

Things fall in and get scrambled up and
are somehow stored close to the horizon.

And you can obviously imagine these bits
of information coming off the Hawking

radiation. Nothing really goes in.

And so it's fine. I understand how that
stuff got out.

But then the question is, what happens?

What's the description of that from our
perspective going in then? Because we

definitely went in, right? So we've gone
in from our point of view.

What happened?

What's the other description?

Are there two of us?

No, that's a great question. So you
might say, well, we get copied then.

So there's a copy of us, mate. It's like
Len Suskin calls it a quantum Xerox

machine, I think. So he says, is it a
quantum Xerox thing?

Do we get copied?

But there's a very fundamental theorem
in quantum mechanics called the no

-cloning theorem, which says you can't
copy a quantum state.

You can't copy the information.

And this is fundamental.

So this is a problem in quantum
computing when you're trying to... So

copied.

So what's the description? So this is
where we get speculative and we're

to understand what the mathematics is
saying.

One description of our perspective is,
yeah, we go to the singularity, we get

all scrambled up.

And then it looks like...

The interior of the black hole is in
some sense the same place as the

You can almost picture wormholes opening
up from the interior of the black hole

to the exterior.

And very naively, you imagine our bits
of information going through the

wormholes and coming out again.

So we end up outside. The information
ends up outside in the Hawking

How it gets there.

Is it really wormholes that are
connecting the interior?

Is that what's happening?

There is an idea that's been around for
a long time, again, due to Suskind and

others, called ER equals EPR, which is
Einstein -Rosen equals Einstein

and Rosen.

So Einstein -Podolsky and Rosen, a very
famous paper, was about quantum

entanglement in the 30s. They wrote this
paper.

and it was it was they were very
concerned about if you have these um

systems that are so -called entangled
systems then you can make a measurement

this thing over here and instantly this
one which might be a light year away can

will have to reconfigure itself the the
classic example is a quantum coin so you

can have a quantum coin in a quantum
state which can be heads tails plus

heads, let's say that, with a one over
root two, whatever.

So if it's in that state, then it means
that's a full description of the state,

heads, tails, plus tails, heads.

It means that if you separate these
quantum coins, they could be an

right? You separate the quantum coins to
a large distance, then it's still the

case that this thing is in what's called
a superposition of heads and tails.

Then you make a measurement of it, you
make an observation, whatever you want

describe it.

And if that one comes up head, then you
know this one is tails.

Even though before you did anything to
this, they were both in this rather

disentangled state, right? So that
bothered everybody.

Einstein, Fidelsky and Rosen, and they
said maybe there's something else going

on and whatever. But we think that's the
way the world is now.

Einstein -Rosen is the paper that
Einstein and Rosen wrote, noticing that

Schwarzschild description of a black
hole has a wormhole in it.

It's a wormhole. So Einstein -Rosen is a
wormhole.

EPR is quantum entanglement.

So there's been this idea that they're
the same picture.

So you can picture quantum entanglement
somehow.

As a wormhole between the two things?
Linking them, yeah.

So this was an idea from a long time
ago.

So the picture of a black hole is kind
of similar to that in that we're

developing this picture where the
interior of the black hole, when viewed

one perspective, is the exterior of the
black hole when viewed from another

perspective. And so what you're getting
there, we think, and again,

even as I say this, there are papers
being written saying different things.

really cutting edge stuff.

But I think what everybody agrees on,
pretty much, is that you're seeing

something called the holographic
principle at work here.

So it's a dual description of nature.

So there's a very famous paper by
Maldacena.

It's called the ADFCFT Conjecture. And I
think I'm right in saying it's the most

cited paper in all of theoretical
physics.

And it was a very particular model of a
quantum mechanic.

on a surface.

That's what CFP, conformal field theory,
it means. It's quantum capture on a

surface. And a precise proof that
there's a dual description, that this

theory describes an interior geometry of
space, which was not there in

the surface theory.

And the space is called an ADS space, or
antidepressant space, or whatever. But

it's a perfect proof.

There's a one -to -one description
between these two things.

And I think it's fair to say that the
black holes, these strange apparent

paradoxes, are telling us that such a
thing, our universe, can be described in

such a way.

So there are different ways of
describing the same physics.

And they're radically different ways.

Ultimately, the thing is, it shouldn't
be so problematic in that.

In both descriptions, the information
comes out.

But the way it came out is radically
different depending on your point of

And I think most people would say we're
seeing glimpses of some kind of

holographic. They're called holographic,
by the way, because if you think of

what does it mean to have a complete
description of a higher dimensional?

think so let's let's be very concrete
this room so let's say that this

is correct and many people think it is
by the way for this for this room so we

have a surface surrounding the room the
walls and there's a theory that lives

just there and it describes fully
everything that's in the room in that

we're holograms We are both holograms
because we're described by a theory that

lives on a hologram is a piece of film
like that. And it has a perfect, a

perfect hologram would be a perfect 3D
image would be encoded in the surface.

So it's a perfect 3D image encoded in
this 2D surface.

That really is.

picture that we're talking about here.
You can see it with the event horizon

all the information on the outside and
the interior there and what happens. So

it looks like we're flipping between
descriptions of the world. Does it feel

sometimes like that story about a one
-dimensional being meeting a two

-dimensional being and trying to
describe their circumstances and then

-dimensional being and that we are
somehow like...

seeing the weirdness of our own
experience of dimensionality and that

as you said if someone were viewing us
from a higher dimension they would see

this somehow clearly and i don't really
know what i'm asking no i know you i

know you it's it's kind of yeah you what
we seem to be struggling with yeah is

as you said it's almost the same
struggle as a two -dimensional being

understand a three -dimensional world Or
actually, we do, it's three

-dimensional beings trying to understand
the four -dimensional world, which is

what relativity is. We struggle with it.
It's hard for us.

So this is a level of abstraction
further.

I think one, I saw described, someone
described the black hole. Why are we

glimpsing this deeper structure of
nature when we think about black holes,

are real things?

And I saw someone say it's almost as if
this thing slices through space and

leaves the building blocks of space
dangling right at the horizon.

It's this strange behavior of which
gravity has created this situation where

you start to come face to face with the,
with what?

With the structure of space and time.

So we're talking about, as I said
before, that in retrospect, the hints

there with temperature and entropy and
information in space, encoded

in space. So it looks like we're
starting to glimpse a theory of the

structure of space and time. So this
goes by the name of emergent space

So the picture really would be that you
have a description.

which looks, by the way, for all the
world, like a network of qubits, which

what a quantum computer is.

So it looks like there's a description
of the universe that doesn't have space

and time in it, but it's just a network.

It's just information.

And that goes all the way back to John
Wheeler. We mentioned him once, the

physicist John Wheeler. He had an idea.
He used to call it it from bits.

So it is this, and bits is information.

That's what it looks like we're seeing.

So our window onto this deeper theory,
call it quantum gravity if you like, it

has been very simple questions actually
about black holes, which are real

things. That very simple question from
Stephen Hawking, that's why Hawking's

calculation is so important, because
it's the first glimpse of a problem

with our picture of the world.

And it's a very, very precise glimpse.

It's a precise question.

Does this thing destroy information or
not? If it doesn't, how does the

information get out?

That's a simple question, but it's led
and is still leading, which is why I'm

waving my hands around a lot. You would
get a different, different pictures from

any, any, you know, expert who does the
calculations. I'm not one of those,

right? But if you talk to someone who
does the calculations, they would, not

certain about the physical picture i
think it's fair to say so is it fair to

that the specific research into black
holes the specific questions that we're

asking about black holes are helping us
unlock much much deeper questions about

the universe as a whole exactly it's
very well put and it's wonderful and and

one of the wonderful things is that so
the the techniques that you develop as a

let's say a phd student or a postdoc or
someone who's working in this area the

techniques that you develop to try to
understand what the black hole is doing

are the same techniques you need if you
want to understand how quantum computers

work so and that's a real engineering
question as well as a fundamental

question you know we're trying to build
these things we haven't built one that

works in the way we want to yet but
obviously google and microsoft and ibm

and others are pouring a lot of money
into it because they're profoundly

powerful devices but the insights a lot
of insights now

into how they might work and how we
might build them is coming from this

of emergent space -time so it's the best
example i know of You know, if you say

to a funding agency, I want money to
work on black holes.

They go, well, fortunately, they do give
us the money.

But they often would go, well, is it any
use? I mean, what's the point? You

know, a black hole, does anybody care?

The lesson is that when you study nature
and you go to, you try to

study things that you don't understand,
that pose profound questions.

about our understanding of physics in
this case, then you are, I would say,

likely to learn something useful because
you're studying reality.

And this is the best example of that
that I know.

Because you're studying completely
collapsed stars or the things at the

of galaxies, and you're gaining insight
into quantum computers and networks of

qubits and quantum information.

It's the most wonderful thing. It's
incredible.

So there's one thing I should mention, a
complete picture from the people who

are listening or watching and want to
know more. There's a thing which is

important called the firewall paradox,
as it was initially introduced.

And it hasn't been resolved yet.

And the problem is that when you disrupt
space

in this way, that the black hole does.

And when you try to understand what's
happening to the information and

particles that are on one side of the
horizon and the other side, you know,

Hawking radiation that we discussed
earlier, you do bump up against the

which is that maybe this description of
the equivalence principle and of us

freely falling across the horizon from
our perspective into the interior of the

black hole, maybe that...

doesn't quite stand up.

So maybe you're getting a challenge to
the basis of general relativity.

Maybe it's really true that actually
there isn't an interior of the black

Maybe it's really true that you don't go
in. There isn't an in, right? And so

you'll see if you go and search through
the literature that the firewall paradox

was that these papers were big papers in
this debate.

And then some people thought they were
solved and other people thought they

weren't solved.

And I think it's fair to say that the
jury is still out on these issues.

But the thing to emphasize is it's
really, there's something really

going on here.

And it probably, it almost certainly is
associated with the nature of space and

time themselves or space -time.

It's associated with geometries of space
-time, maybe wormholes, maybe those

kind of things. So it's tremendously
interesting.

And you'll see, it's just wonderful to
dig into this subject because it's so,

so, it develops so fast.

And our understanding is developing so
fast.

But the last thing to say is it does
look like there is a description of the

universe that looks like a giant quantum
computer.

In some sense, which does not imply that
someone built it, right? It doesn't

imply that we're in a simulation.

But it does suggest that there's a good
description of reality that you can

write down in the form of some kind of
network of entangled qubits, which are

presumably the Planck length inside.
Maybe even that's not obvious, right?

something like that.

You know, I came into this story
thinking that I was going to tell about

into a black hole and then eventually
get to the cutting edge of research into

black holes and that that was going to
be the end of the story. But actually

what I'm hearing you say now is that the
cutting edge of research into black

holes is actually a cutting edge of
research into the universe itself.

And that is just incredibly exciting.

It's really beautiful, isn't it?

They're the window, almost like the
Rosetta Stones.

They're allowing us to translate between
different pictures of the universe.

All right. So that's probably where we
end.

If I rewind for a second, one of my
questions to just connect things that I

about the universe, maybe, is what is
the relationship, we think, between the

singularity at the center of a black
hole and the point that Big Banged?

Oh, so...

It's a very good question.

So the singularity inside a black hole
in Einstein's theory is the end of time.

And in Einstein's theory alone of the
evolution of the universe, there is

another singularity at the other end of
time, which is the Big Bang singularity,

which you might call, you might be
tempted to call the beginning of time.

It's a very different singularity.

Black holes are...

maximally scrambled information, the
highest entropy things we know of in the

universe. And one of the great mysteries
about the origin of the universe is

it's a very low entropy state.

Broadly speaking, if you want to know
more about that, Sean Carroll actually

writes a lot about this. There's a lot
of interesting stuff to say.

But it's a different kind of
singularity.

And so, are they related?

is the question i would say yeah our
understanding of them surely is um and

but but it's really not clear and when
you add quantum mechanics in then you

begin to ask questions about whether the
big bang thing if there is such a thing

as a singularity in the past is it what
is it at the beginning of time there's a

thing called a no boundary idea that
hawking and others had and Again, all

are off, right? But I think it would be
good.

I think it would be good. It is correct
to say that I'm sure the understanding

of the two is related, but we understand
neither at the moment. I'm

sure that I am garbling fragments of
understanding from things that you have

explained. But does it feel related at
all that there is...

The hologram principle, the hologram
paradox that you described, that we can

described as two -dimensional, that
there can be a two -dimensional kind of

description of a huge amount of mass,
three -dimensional mass that fell into a

black hole, and that we cannot... Is it
possible that we are all living on

the outside of a black hole?

right now what is the question i'm
trying to ask no i think i it's a great

question i i think there is a question
so there is a cosmological horizon there

are different kinds of cosmological
horizons and it is a very good question

but people don't really even know how to
phrase it that but could it be that you

can describe the whole universe in terms
of a quantum theory living on a

boundary of some description.

And I think the guess is yes, the guess.

But we don't even know what we mean by
the boundary.

It's one of the problems here. So the
reason that Maldacena was able

to show this work for this very specific
thing called ADS space is

because there's a boundary you can
identify in that particular.

whereas our universe is digital.

It's not obvious what you mean by a
boundary.

It's not really obvious what question.

As you said, it's hard to find the
words. We don't really know what

we're asking. But that rough picture
that there could be a theory,

a quantum theory somehow, this network
of qubits that gives rise to

geometry, space.

is accepted broadly.

But when you try to get into the detail
of it, it's only been fully realized for

a very specific model, which is kind of
a toy model. It's not our universe. So

it could be that our universe does not
admit that description.

Could be. But it's certainly beyond us
at the moment, technically.

But it's a wonderful thought.

And actually, there's a paper recently.

So people are beginning to use the
Google chip, the Willow chip, which is a

powerful, it's not a quantum computer,
it's a proto -quantum computer kind of

thing. And people have started to use it
because what it is, is a load of qubits

that you can entangle and you can set it
up and it's very well controlled.

So whilst we don't know how to do
quantum calculations on the thing,

what you can do is try to say, well,
Could I set them up so that it's like

emerges from them? And there was a paper
recently where something that was

described in the paper as a one
-dimensional wormhole was made.

It wouldn't be in our university thing,
but it kind of emerged from this

structure. And that's the kind of
picture we're trying to get to.

It's a good paper. It's been peer
-reviewed. It's a controversial paper.

see loads of stuff online.

But it's worth looking at those papers.
And by the time this is sent out, there

might be some other papers. A lot of
people are working on it.

So on also actually building little
clocks, little quantum clocks, tiny

because we don't even know what a clock
is, right, at the most fundamental

level, because we don't know what time
is.

So we're talking about very fundamental
questions about reality.

in this research but it all came from
these that right which is how cool is

it came from thinking about those things
it's so cool and thank you for taking

that question so seriously it's a great
question and i think it's really

instructive that um neither of us
because nobody has the language

when you get into the real detail you're
talking about mathematics ultimately

And even the mathematics is not
complete.

So we're talking about research at the
cutting edge.

And it takes a long time.

I mean, even quantum mechanics, you
think about quantum mechanics, if we

talking about quantum mechanics, this is
a hundred year old theory that's very

well tested and very well understood.

But when you try to put it into language
to speak about it, it's much easier to

write down the equations or something. I
mean, even Feynman.

says that in the Feynman lectures, when
he's talking about this thing called the

double slit experiment, it's a great
description of the way quantum mechanics

behaves. But ultimately, Feynman says,
you know, mathematically, it's the

easiest. I can just write down one line
which tells you how this interference

works and all those things.

But then if you try to say, well, what
does it mean? What happens? What does it

mean for our picture of reality?

Then we're still arguing about that now.

But the math is easy.

Literally worse because here the math is
really difficult and we have no idea

what it's telling us really about
reality.

One of the things that I really admire
about you and your work is that you have

this sense of wonder at the universe.

And I think that the thing I've most
appreciated about it, and I'm sure I

for a lot of people, is that you give
that sense of wonder back to people.

You say, hey, don't you remember what it
was like when you were a little kid

looking up at the sky? And actually, in
fact, as you learn more about the

universe, that sense of wonder can
increase, not decrease.

Yeah. And I think that's really special.
And I think that people need that.

And first, I just wanted to say thank
you.

Thank you. And second, my last question
for you is, how do you

feel when you go outside and look up at
the night sky, given what you

know? Oh, it's a wonderful question.

And you kind of alluded to it earlier
that the

sense of awe and the sense of mystery
and beauty

increases the more you know about what
you're looking at. It doesn't decrease.

The mysteries, the number of mysteries
increases the more you look at it. And

is incomprehensible.

The Milky Way. So it's a beautiful thing
to look at. So anybody watching this,

if it's a clear night and you're away
from the city lights, you can go out.

We've all looked at the Milky Way at
some point.

Even that, if you try and picture what
it is, and you learn that it's a galaxy

of, what, 200 billion, maybe 400 billion
suns.

What does that mean?

200 billion suns.

Most of them have planets.

So it'll be trillions of planets.

It takes light 100 ,000 years to cross
that thing.

None of that is, I think, you can't
internalize even that.

And that's kind of a simple thing
because it's just a galaxy and we know

galaxies. And then you talk about, as
we've talked about, the center of that

galaxy lies this thing, the supermassive
black hole.

And then we don't know. We don't know
what that thing is. You can look towards

it. So you can look towards Sagittarius.

The further south you are, the easier
it'll be to look at. But you can look in

the direction of the centre of the
galaxy.

So you can go out, if you're not too far
north, and look at that.

You can look at it with your eyes and
wonder about it.

So that's what I really believe. I know
Richard Feynman said it many years ago,

and many other people have said it, but
the more...

you understand about nature, the more
mysterious and magical it becomes.

It's a beautiful place, Ben. Thank you
so much for your time.