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There are monsters out in the
cosmos that can swallow entire stars

that can destroy space itself.

Black holes.

For decades, they
remained completely hidden.

But now,

scientists are venturing into
their uncharted territory.

They've discovered that black holes

don't just rule the realm
of stars and galaxies.

They impact all of us here on Earth,

because black holes
just might be the key

to understanding the
true nature of reality.

Space, time, life itself.

The secrets of the cosmos
lie through the wormhole.

Take planet Earth

and squeeze it down to
the size of a marble.

You'll create an object so dense

that not even light, traveling
at 186,000 miles per second,

can escape its extraordinary
gravitational pull.

Its
name --

a black hole.

Astropsicists think that
black holes might form

when giant stars run out of fuel

and collapse under their own weight.

We're not really sure. Why?

Because black holes are places

where the accepted laws
of physics break down.

A few bold thinkers are
now making giant strides

towards understanding what
goes on inside black holes.

And the new laws of physics that emerge

have an astonishing
implication --

you, me, and the world we live in

may be nothing more than an illusion.

In my hometown in
Mississippi, there was a well.

It fascinated me to gaze
into its murky depths

to try and see what lay at the bottom.

I would sit there,
throwing pebbles into it

and trying desperately to
hear a faint splash of water.

But all I got was silence.

One day, I took a
dime-store toy soldier,

made a parachute for it
out of an old handkerchief,

and watched it float down.

I wondered what would happen
to him when he hit the bottom

or if he would just
keep on falling forever

into that impenetrable blackness.

Today, theoretical physicists
are drawn to black holes

like I was to that old well,

trying to understand
how they really work

and what they can tell
us about the universe.

It's one of those things that
sounds like science fiction,

only it's better because,
you know, it's real.

A black hole is the window into a world

that we don't
have the concept --

we don't even have the
mental architecture yet

to be able to envision properly.

You're in this strange
world of strong gravity,

where there are no
straight lines anymore.

You can't even see it.

That is disturbing and
exciting at the same time.

The notion of a black hole

is a natural extension
of the laws of gravity.

The closer you are to a massive object,

the more the pull of its gravity

slows down anything
trying to escape from it.

The surface of the Earth

is 4,000 miles away from its center.

So the force of gravity
up here is not very strong.

Even a kid can resist
it for a second or two.

But if you could squeeze the Earth down

so that all of its mass is
really close to the center,

the force of gravity would
grow incredibly strong.

Nothing could move fast
enough to leave its surface.

Not just a
jumping boy --

even the beams of light
speeding out from his shoes

would be trapped.

So, if you're trying to imagine

creating something so dense
that not even light can escape,

you're trying to get a system so compact

that the speed that it takes
to escape from that object

is greater than the speed of light.

Now, the speed of light is
186,000 miles per second,

so that's going really fast.

Gravity's quite weak. I think
it's surprising, you know.

The whole Earth is
pulling on a rocket ship,

and all it has to do
is go 7 miles per second

to escape from the Earth.

And to get all the way to a black hole,

you'd have to crunch down the entire sun

to be less than a few kilometers across.

Now it would take something

traveling greater than the
speed of light to escape,

so nothing can escape, and
the whole object goes dark.

Christian Ott, an astrophysicist

at the California
institute of Technology,

has been trying to understand

how such strange entities as black holes

might really form in the cosmos.

He studies what goes on

when giant stars run out
of fuel and start to shrink,

a process comparable to the collapse

of an exhausted marathon runner.

So, sometimes you can compare
a star at the prime of its life

to a runner who's just
starting out real fresh,

consuming oxygen aerobically.

And it's the same with stars.

They burn hydrogen into helium slowly,

and they're getting a lot of energy

out of every single
hydrogen nucleus they burn.

After they're done fusing
hydrogen into helium,

they go on to more and
more heavy elements,

and that fuel goes fast and fast.

So, at the end, they end up with iron,

and that's when their --
when their fuel is over,

their fuel is out.

And it's basically
like a marathon runner

hitting a wall in a marathon.

But, unlike a runner

who can restore his
energy with food and drink,

a dying star has no way to
come back from the brink.

Ugh.

There's no more heat generation,

no more energy generation
happening at its core.

So, gravity keeps on pulling in,

and when there's nothing

producing pressure to sustain it,

it will just collapse.

You get a shock wave, and
the shock wave moves out.

And it actually blows
up the entire star,

and that's the phenomenon
we call supernova.

The death throes of giant stars

are the most dramatic events
astronomers have ever witnessed.

Chinese stargazers saw
one explode in 1054.

It was so bright, they
could even watch it by day.

Another two blew up
around 400 years ago.

These colossal explosions

leave debris fields of gas and dust

hundreds of light-years across,

still visible and still expanding today.

But what interests
black-hole researchers

is not the explosion.

It's what happens at the
very center of the dying star.

Modern astronomers

have never witnessed a star
in our own galaxy explode.

But theoretical physics predicts
that if a star is large enough,

its collapsing core

should shrink down to form a black hole.

So, imagine the balloon is a star.

And the star stays alive by
burning thermonuclear fuel,

and as it does so,

you get heavier elements like the sponge

and all that energy released,

like the energy released in a bomb.

So, as a star runs out of
fuel, it begins to cool.

And as it cools, it's no longer
supported by all that pressure,

and so it starts to collapse
under its own weight.

And it will continue to
collapse until it gets so small

that now you're running
up against the essure

of crushing the matter together.

And at this stage,

it's a little bigger than
the size of the Earth,

and it's supported by
pushing all of the electrons

in the atoms closer and closer together.

Now, if it's more massive than a
couple of times the mass of the sun,

it will start to collapse even further.

And there is no form of pressure
that can resist this collapse.

And it will continue to collapse down

until it forms a black hole.

But do such strange
crushed corpses of stars

really exist out in the cosmos?

Could they be lurking at the center

of some of those clouds of gas and dust

thrown off in a supernova?

Christian Ott and his
theoretical-astrophysicist group

at caltech

are trying to discover
whether exploding stars

really do form black holes.

Well, I just
generally -- you know,

I'm really excited about
stars that blow up, actually.

First of all, to get a black hole,

you need low, specific angular momentum.

To have a critically
spinning black hole,

you need a lot of
angular momentum, so...

There are two ways to find out

whether black holes really
form when stars blow up.

One is to wait for a supernova
to go off in our galaxy

and use every tool of modern
astronomy to pick it apart.

A galactic supernova would
provide us so much information,

we wouldn't sleep for weeks.

But, unfortunately, it happens

only maybe once or twice per century.

So, Christian and his team are
trying a different approach --

blowing up stars inside
powerful supercomputers.

This is no easy task.

In fact, no one has pulled it off.

But Christian is on his
way to being the first.

So, simulating supernovae
stellar collapse

and black-hole formation

is so hard because it brings
together a lot of physics.

It's general relativity for gravity.

It's fluid dynamics for
the gas that collapses.

It's particle physics.

Doing the simulations,

it's like trying to do a
really good weather forecast.

So far, Christian has failed

to make a virtual star explode

in a way that looks
like a real supernova.

But after years of refining
the physics and the math,

he now thinks he may be the first

to fully understand how
a black hole is born.

Man, that is an event
horizon right there,

and this black hole in the center.

Wow, that's the first
time that we do see this.

What's surprising is

that the most promising simulations

don't actually explode.

They simply collapse.

It's not a bang but a whimper.

Its name -- not
supernova, but unnova.

It's basically just everything

eventually sinks into a black hole,

and the star slowly but
surely just disappears.

It could be true that most stars,

or a large fraction of
stars, just disappear.

We don't have any data on that.
We have never seen an unnova.

If Christian is right and
black holes form silently,

then these cosmic
cannibals could be hidden

in plain sight all around us,

and we might never know it.

Finding black holes is
terribly, terribly difficult.

Even if it wasn't black and
would be radiating energy,

it would still be only,
let's say, 20 miles across.

And even, you know,
at 10 light-years away,

it would be impossible to find

even with the best telescopes we have.

But if black holes are
almost completely elusive,

no one told this man.

He's spent the past 30 years
hunting one, a giant one,

right at the heart of
our own Milky Way galaxy.

And his discovery will
overturn all our ideas

about how the universe really works.

In 1931,

a bell telephone
researcher, Karl Jansky,

was testing a new system
for sending radio messages

across the Atlantic to Europe.

He was plagued by background noise.

After two years of careful work,

Jansky stripped out
most of the interference.

But one strange signal never went away.

It was loudest whenever
his antenna was pointed

at the constellation Sagittarius

at the very heart of the Milky Way.

It was a signal unlike
anything a star would make.

Astronomers began to
wonder whether it might come

from an object theorists had
predicted but never detected --

a black hole.

But there was no way to find out.

The center of our galaxy
is hidden from view

by a thick veil of dust.

Then, 25 years ago,

a German astronomer, Reinhard Genzel,

found a way to see through the fog.

The problem is we are
sitting in the Milky Way,

and the galactic center is
sort of just along the way

through the entire plane

of this big spiral
galaxy we're sitting in.

And there's all this gunk,
this dust and this gas,

between us and the galactic center,

so we can't see it in the visible.

But at longer wavelengths,
this dust is not as efficient.

Infrared light, with
its longer wavelength,

is perfect for penetrating the veil.

But it's terrible

at getting through the water
vapor in Earth's atmosphere.

So Reinhard Genzel headed

for the highest and
driest place on Earth --

the Atacama Desert of Chile.

Beginning in 1992,

he and his team at the
Max Planck Institute

began what would become
an enduring campaign

to find out exactly what was causing

the strange noise at the
center of the Milky Way.

In fact, we found in the
center of the Milky Way

a very dense collection of stars.

That's the very center of the Milky Way,

around which, you
know, everything turns.

And then came the
first suspicions --

maybe there is something there.

Reinhard had a hunch that a black hole

could be acting as a
colossal center of gravity,

causing dozens of stars
to whirl around it.

So he settled in for the long haul.

Each year, he took
another set of pictures,

plotting the movement
of that cluster of stars

at our galaxy's heart.

He gathered a large team

to help him handle the
immense amounts of data

and used a new technique
called adaptive optics

to make the images of
these distant stars sharper.

So, if you look at what the
galactic center would look like

in a normal telescope, let's say,

you would get images
which look like that.

The effect of this adaptive optics

you can see on the right-hand side.

It's just amazing how
beautiful that image gets.

It's really the same scene.

You can recognize those two
stars here on the left-hand side

in the blurred
image there --

these two stars on the right-hand side.

As the years went by, a
striking pattern emerged.

Stars were moving --
moving really fast.

This was something that no astronomer

had ever
seen before --

a dozen, then 20, then 30 stars

all swirling at breakneck
speed around a central object

that was completely dark
and tremendously dense.

Could this be the first proof
that black holes existed?

And if so, was there really one here

right in the center of our own galaxy?

What do you do in order to see something

or prove the existence of something

which you can't really see, right?

The black hole, you
would think, is something,

well, by definition,
light can't escape from.

But you have gravity.
Think of the solar system.

Okay, you have the sun in the center,

and then you have the planets.

The outer planets move
very slowly around the sun.

And the closer you come to the
sun, the faster the planets go.

So, suppose in your mind
you switch off the sun.

You would have to conclude
that there is a central object

with one solar mass, around
which the planets orbit.

See, that's what we're doing.

So, these are the stars that are shown.

Here at the very center
here is the radio source,

which we suspect is the
location of the black hole.

This is our best star,

which we have followed for 15
years to trace a full orbit.

This star, known only by the name S2,

was moving at a phenomenal rate.

At its closest approach
to the dark central object,

Reinhard and his team clocked it moving

at 11 million miles per hour.

What we learned from
this is that, indeed,

there's only one
central mass right there

at the position of the radio source,

and that has four million solar masses.

There cannot really be any
believable configuration

which we know of other
than the black hole.

Reinhard Genzel had made

the first definitive
discovery of a black hole.

But more than that, his
team had found an object

that must have swallowed
millions of stars

over its lifetime.

Astronomers call it a
supermassive black hole.

But despite the enormity
of this discovery,

it would be just the first

of many increasingly bizarre
and disturbing findings.

The next was to figure out

what goes on inside a black hole.

What happens to stars,
planets, even people

if they get too close
to this cosmic sinkhole?

No telescope can ever
see inside black holes.

To understand how they twist reality,

we have to stop looking
and learn how to listen.

Lurking at the center of our galaxy

is an object that's completely invisible

but weighs as much
as four million stars.

Astronomers now believe
almost every galaxy has

a supermassive black hole at its core.

So, what are they?

Science fiction sees black
holes as cosmic time machines

or portals to a parallel universe.

But real scientists are finding

that truth is stranger than sci fi.

You're about to enter a world

where the very big and the very small

are indistinguishable,

where reality and illusion
are one and the same.

Astronomer Julie Comerford

has been studying the centers
of dozens of distant galaxies,

trying to find signs of black holes,

hoping to learn more about
these mind-bending objects.

It turns out that in all
or nearly all galaxies,

wherever we look,

they have a central supermassive
black hole at their heart.

Supermassive ones are
the ones that have masses

of anywhere from a
million to a billion times

the mass of the sun.

You can see a supermassive black hole

when gas is falling onto it.

And sort of right before
the gas falls into it,

it gets heated up and
emits a lot of energy

and can appear really bright.

But when Julie
investigates the glowing gas

surrounding these giant black holes,

she finds something totally unexpected.

There's a cosmic dance going on

on a scale that's almost unimaginable.

You saw two peaks in the
light instead of just one.

You'd expect one from one black hole

that's just sitting
at rest in its galaxy,

but we saw two peaks
with different velocities.

And that immediately hit us,

as this has got to be
something interesting.

Julie began thinking

about what would happen
when two galaxies collide.

And if both had black
holes at their centers,

what would happen to
those massive objects?

So, when two galaxies collide,

the black holes
at their center --

instead of crashing in head-on,

they begin this swirl, or dance.

And the way that we can detect
these waltzing black holes

is by looking at the light
that's emitted from them.

So, for the black hole
that's moving towards us,

we detect light that is
at smaller wavelengths,

scrunched up together,
so we see bluer light.

And for the black hole
that's moving away from us,

we see stretched-out,
longer-wavelength light

that appears redder.

So it's this redder and bluer light

that is a telltale signature
of a black-hole waltz.

Every time we see it,

we high-five in the observation room,

and you just can't get over it.

As Julie scans the universe,

she finds the same remarkable dance

happening time and time again.

In galaxy after galaxy,

black holes are paired up

and dancing the cosmic night away.

So, we identified 90 galaxies

from when the universe
was half its present age,

and we found that fully 32
of them, or about a third,

had black holes that exhibited
this blue-and-red signature.

So that was really surprising

that such a high fraction
of the black holes

were not stationary at the
center of the galaxy at all,

that they were undergoing this
waltz with another black hole.

Scientists like Janna Levin believe

the discovery of waltzing black holes

opens up a whole new way
to learn what's inside them,

because their dance
might not only be visible.

It could also be audible.

The scientific visionary Albert Einstein

saw space and time
as a flexible material

that could be distorted by gravity.

A black hole is merely a very
deep well in this material.

When two black holes
come close to one another,

these two orbiting wells

stir up space-time and send out ripples

that can travel clear
across the universe.

And these waves will move
out through the universe,

traveling at the speed of light.

So we can hope to not
see black holes with light

but maybe, in some sense, hear them

if we can pick up the wobbling

of the fabric of space-time itself.

For the past several years,

Janna and her colleagues
have been trying to predict

the sounds black holes make as
they spin around one another.

The calculations are not
for the faint of heart.

Modeling what happens
when two giant objects

create a storm in the sea of space-time

takes some serious math and
months of supercomputing.

This is the orbit of a small black hole

around a bigger black hole,

and it's literally making a
knocking sound on the drum,

where the drum is space-time itself.

Well, it really sounds like
-- sounds like a knocking.

It starts to get a higher
frequency and happen faster,

until it falls into the big black hole

and goes down the throat.

And then the two will ring out together

and form one black hole
at the end of the day.

And then it just sort of,
you know, "brr," chirps up.

Because black holes

stir up the space and
time around them so much,

the orbit of one black
hole around another

looks nothing like the orbit
of Earth around the sun.

An orbit can come in around a black hole

and do an entire circle
as it loops around

before it moves out again.

So instead of getting an oval,

you get a three-leaf clover
that processes around.

This cloverleaf pattern

keeps coming out of the simulations.

Janna was shocked because this picture

of how two of the heaviest
objects in the universe

move around one another

bears an uncanny resemblance to the way

two of the lightest objects
move around one another --

the tiny protons and
electrons inside an atom.

We can build a kind of classical atom

out of a big black hole, like a nucleus,

and a light black hole,
which acts like an electron.

And together, they form
a real atom, in a sense.

How could an object that weighs so much

behave like a subatomic
particle that weighs so little?

When we talk about ordinary
objects, or people even,

they are never exactly the same.

I mean, you could try to clone me,

and still the different copies of me

would not be exactly the same.

In that sense, people
and ordinary objects

are not like fundamental particles.

They're distinguishable.

But the black hole is
quite different from that.

Black holes are like
fundamental particles,

and that's very surprising

because they're huge,
macroscopic objects.

Right now, this idea is
only a tantalizing hunch.

But in just five years,
super-sensitive detectors

should be able to pick up
the ripples in space created

by two massive black holes
spinning around one another.

And they'll tell us

whether they really do
behave like tiny atoms.

But this connection between
the very big and the very small

has already sparked a war

between two of the
greatest living physicists.

One of them --
Stephen Hawking.

The other began life as a
plumber in the South Bronx

and is now using black holes to develop

the most revolutionary idea in
physics since Albert Einstein --

an idea that literally
turns reality inside out.

The first step in joining

the physics of the very
large and the very small

came in 1974 from the
mind of Stephen Hawking.

The theory of the very
small, quantum mechanics,

predicts that empty
space should be sizzling

with particles and antiparticles,

popping into existence in pairs

and then annihilating one
another an instant later.

These particles exist
for such a short time,

they're not considered part of reality.

Physicists call them virtual particles.

But Hawking realized

there was one special
place in the universe

where these particles could become real.

Around a black hole,

there is an invisible line in space

called the event horizon.

Outside that line,

the hole's gravity is just
too weak to trap light.

Inside it, nothing can escape its pull.

If a pair of virtual particles fmed

just outside the event horizon,

then one of the pair

might travel across
that point of no return

before being able to recombine,

falling into the black
hole and leaving its partner

to escape as real radiation
-- Hawking radiation.

If Hawking is right,

black holes should
not actually be black.

They should shine ever so faintly.

No one has ever detected
Hawking radiation

from the rim of a black hole.

In fact, it's so faint, and
black holes are so far away,

that it will probably never be possible.

But Jeff Steinhauer
thinks he's found a way

to test Hawking's theory

and send shock waves
through the world of physics.

He's the only person on the planet

who has seen a black hole from up close.

In fact, he's learned how to create one.

My black hole is in no way dangerous.

It's a sonic black hole that
can only absorb sound waves.

It's only made of 100,000 atoms,
which is very little matter.

And I'm sure that my
neighbors would love

that I would put a sonic
black hole around my apartment,

but it's not gonna happen.

When he's not jamming in the basement

of the physics department
at the Technion in Israel,

he's upstairs in his lab.

Jeff Steinhauer's recipe
for making a sonic black hole

begins with a tiny
sample of rubidium atoms

chilled down to minus-459
degrees fahrenheit.

While I was working with
these very cold atoms,

I stumbled across a phenomenon.

When the atoms are actually flowing

faster than the speed of sound,

then, if there are sound waves

trying to travel against the flow,

they can't go forward.

And this is analogous
to a real black hole,

where light waves cannot escape
due to the strong gravitation.

Even though this black hole

traps only sound, not light,

the same laws of quantum
mechanics apply to it

as they do to its cosmic cousins.

If Hawking's theory about
black holes is correct,

Jeff should be able to detect
tiny sound waves escaping.

There should be pairs of sound waves,

one on the right side
and one on the left side.

Due to the quantum physics,
they will suddenly be created.

This is the elusive Hawking radiation.

Jeff has not detected
this elusive radiation yet.

But he believes he should within a year

as he refines his experiment.

No one will await that news

more keenly than Leonard Susskind.

He has spent much of the last 30 years

thinking about Hawking radiation

and being deeply
troubled by what it means.

Today, he is one of the world's
leading theoretical physicists.

But that's not the way he started.

When I was 16 years
old, I was a plumber.

Fixing toilets and sewers and so forth

in tenement buildings in the South Bronx

was not what I wanted to be
doing for the rest of my life.

Whenever I make analogies about physics,

it always seems that they have
something to do with plumbing.

The analogy that I've used
over and over about black holes

is water going down a drain.

The invention of string theory,

which has a lot
to do with tubes --

some people even say

this must've been Susskind the plumber.

Leonard Susskind's
fascination with black holes

began 30 years ago

when he listened to a
talk by Stephen Hawking --

a talk that triggered
a violent reaction.

I first heard Stephen
Hawking give a lecture

up in San Francisco,

in which he made this
extraordinary claim

that black holes seem to violate

the very, very fundamental
principle of physics

called conservation of information.

Seven years after his
groundbreaking work

on black-hole radiation,

Hawking had taken the idea
to its logical conclusion.

For every ounce of material

a black hole absorbed into its core,

it would radiate away an
equivalent amount of energy

from its event horizon.

But since there is no physical link

between the center of a black
hole and its event horizon,

the two processes could
not share any information.

Now, this was a disaster
from the point of view

of the basic principles of physics.

The basic principles of physics say

that you can't lose information.

Let me give you an exale.

Here's a sink of water.

Imagine sending in a message
into that sink of water

in the form of morse code
by dropping in this red ink.

Drip, drip, drip, drop, drip.

You see the red ink swirling around,

but if you wait a few
hours, what will happen

is that red ink will get
diffused throughout the water.

You might say, well, my goodness,

the information
is clearly lost --

nobody can reconstruct it now.

But down at the very core
of physical principles,

no, that information is there.

If you could watch
every single molecule,

you could reconstruct that message.

It may be much too hard for human beings

to be able to reconstruct and
to follow all those motions,

but physics says it's there.

But Stephen Hawking claimed

there are special places in the universe

where that law can be broken.

What happens when the information

goes down the black hole?

The answer, according to Stephen,

was it goes down the drain

and disappears completely
from our universe.

This was a fundamental violation

of the most sacred principle of physics.

And I was personally, truly shocked.

If what Hawking claimed was right,

it would mean most of modern physics

had to be seriously flawed.

Black holes would spend
their lives eating stars

and leave no record of what they'd done.

Nothing else in the universe does this.

The fiery blast of a nuclear bomb

might vaporize everything in sight,

but all that information
is still in this universe,

no matter how scrambled.

Black holes, according to Hawking,

don't scramble information.

They completely destroy it.

That was 1981,

and from that time
forward, I was hooked.

I could not let go of the
question of black holes.

This squabble soon grows
beyond these two men

and engulfs all of physics.

At stake is more than just
bragging rights for the winner.

It turns out to affect the very
way we perceive the universe.

There may be 100 million black holes

scattered across the Milky Way.

Anything that strays too close

to these dark remnants
of burned-out stars

will be pulled in by an
intense gravitational field.

But what actually happens

to the stuff that
falls into a black hole?

Is it simply wiped out of existence,

or do black holes remember?

These are the battle lines

of the
black-hole war --

a battle with repercussions

that the men who started it

could never have imagined.

It's a war between two giant minds.

On one side, the famous
physicist Stephen Hawking,

on the other, Leonard Susskind,

one of the creators of string theory.

Stephen Hawking argues

black holes destroy what
they swallow without a trace.

Leonard Susskind passionately disagrees.

But for 10 years,

he struggled to find anything wrong

with Hawking's concept

of how black holes radiate
away the matter they swallow.

It was thought to be inconceivable

that somehow the things
which fell into the black hole

could have anything to do
with the Hawking radiation,

which was coming out
from very, very far,

from where the particles fell in.

Then he began looking at
the problem in a new way.

Call it the
dead-and-alive paradox.

It's a cosmic thought experiment

starring an astronaut named Alice,

her friend Bob, and a black hole.

Bob is orbiting the
black hole in a spaceship,

and Alice decides to
jump into the black hole.

What does Bob see, and
what does Alice see?

Well, Bob sees Alice falling
toward the black hole,

getting closer and closer to
the horizon, but slowing down.

Because the gravity of the black hole

severely distorts space and
time near the event horizon,

Einstein's theory of relativity predicts

that Bob will see Alice
moving slower and slower,

until she eventually stops.

So, from Bob's point of view,

Alice simply becomes completely immobile

with a big smile on her face.

And that's the end of the story.

It takes forever for Alice to
fall through the black hole.

On other hand,

Alice has a completely different
description of what happens.

She just falls completely
cleanly through the horizon,

feeling no pain, no bump.

It's only when she
approaches the interior

when she starts to feel uncomfortable.

And at that point, she starts
to get more and more distorted,

and I don't want to go into
detail what happens to her.

It's not pretty.

These two descriptions
of the same events

appear to be at odds.

In one, Alice is stuck
at the event horizon.

In the other, she sails right through.

In one version, she dies.

In the other, she's
frozen in time but alive.

But then Leonard
Susskind suddenly realized

how to resolve this paradox
and win the black-hole war.

Well, I began to think
that some of the ideas

that we had developed for string theory

could help resolve this
problem, this paradox.

One way of thinking about string theory

is that elementary particles are
simply more than meets the eye.

You see this propeller here?

This propeller -- when it's
spinning very, very rapidly,

all you see is the central hub.

It looks like no more
than a simple particle.

But if you had a
really high-speed camera

that could catch it as it was spinning,

you would discover that there's
more to it than you realized.

There's the blades.

And the blades would
make it look bigger.

In string theory,

an elementary particle has
vibrations on top of vibrations.

It's as though this propeller

had, on the ends of its
blades, more propellers.

And those propellers had propellers

on the ends of their
blades, out to infinity,

each propeller going faster
than the previous one.

As you would catch it with a
higher- and higher-speed camera,

you would see more and more
structure come into focus,

and the particle would seem to grow.

It would grow endlessly

until it filled up the whole universe.

Leonard realized

that a black hole is like
an ultra-high-speed camera.

It appears to slow objects down

as they approach the event horizon.

Time for another thought experiment.

The black hole, Bob, and Alice are back,

but this time, Alice has an airplane

powered by a string-theory propeller.

For Alice, not much changes.

She sits in the cockpit

and flies right over the event horizon,

all the time seeing just the
central hub of her propeller.

And she meets the same horrible fate

at the heart of the black hole,

this time accompanied
by some plane debris.

Bob's view is very different.

So, first he sees the first propeller

come into existence.

Then later when it's
slowed down even further,

he begins to see the outer propellers

come into existence sort of one by one.

And the effect is for
the whole propeller

to get bigger and bigger
and bigger and grow

and eventually be big enough
to cover the whole horizon.

These two views no longer
seem so irreconcilable.

Alice is either squished at
the center of the black hole

or smeared all over the event horizon.

Leonard has a name for this
new way of seeing things --

the holographic principle.

I began to think,
hey, wait a minute --

this sounds awfully
much like a hologram.

There's Alice at the center,

and if I look at the -- let
me not call it the horizon.

Let me just call it
the surface, the film.

All you see is a
completely scrambled mess,

and somehow they're representing
exactly the same thing.

Leonard's
idea --

that the event horizon of a black hole

is a two-dimensional representation

of a three-dimensional
object at its center --

solves the problem of information loss.

Every object that
falls into a black hole

leaves its mark both at the central mass

and on the shimmering
hologram at the event horizon.

When the black hole

emits Hawking radiation
from the horizon,

that radiation is connected
to the stuff that fell in.

Information is not lost.

In 2004 at a scientific
conference in Dublin,

Hawking conceded defeat.

Black holes do not destroy information.

Leonard Susskind had
won the black-hole war.

But he'd done much more than that

because the theory does not
merely apply to black holes.

It forces us to picture
all of reality in a new way.

It's as if there were two versions

of the description of you and
me and what's in this room,

one of them being

the normal, perceived,
three-dimensional reality

and the other being a
kind of holographic image

on the walls of the
room, completely scrambled

but still with the same,
exact information in it.

That idea has now --
it's not an idea anymore.

It's a really basic principle of physics

that information is stored
on a kind of holographic film

at the edges of the universe.

In a sense,

three-dimensional space is
just one version of reality.

The other version exists
on a flat, holographic film

billions of light-years away
at the edge of the cosmos.

Why these two realities seem to coexist

is now the biggest puzzle
physics needs to solve.

One of the big challenges
that comes out of all of this

is understanding space itself.

Why is space three-dimensional

when all of the information
that's stored in that space

is stored as a
two-dimensional hologram?

A black hole raises these challenges

and really sharpens these challenges

because it's practically a place

where ordinary space
doesn't exist anymore.

So, if I'm asked questions
about how space emerges,

I will simply have to say,
well, we're thinking about it.

We don't understand it.

Black holes have been
a source of fascination

for almost a century.

We've thought of them as time machines,

shortcuts to parallel universes,

as monsters that will
one day devour the Earth.

Well, any of these ideas may
turn out to be true one day.

But right here, right now,

black holes have a profound
effect on you and me.

Their shimmering, holographic surfaces

seem to be telling us

that everything we think is
here is mirrored out there

at the very edge of
our mysterious universe.