Through the Wormhole (2010–2017): Season 1, Episode 2 - The Riddle of Black Holes - full transcript

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.
♪ Through the Wormhole 1x02 ♪ The Riddle of Black Holes Original air date on June 16, 2010
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.
Black holes
are the most massive objects in the universe.
Some weigh as much as a billion times more than our sun.
But no one really knows how big they are.
All that mass could fit into a space smaller than an atom.
And that's where physics runs off the rails.
Albert Einstein's theory of relativity
explains gravity beautifully,
but it only works for very large objects,
not for tiny building blocks of matter likeke atoms.
We understand so much since Einstein,
but somehow gravity stands apart from our understanding
of everything else in nature.
There's matter on one side,
and there's gravity on the other side.
And there's this great ambition to put those two together,
to understand them as one law of physics.
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,
a notoriously difficult branch of physics.
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.