All language subtitles for How The Universe Works S04E05 Monster Black Hole_ENG_Subtitles01

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A journey to infinity...

and beyond.

A place where the rules
of physics collapse,

where time and space
twist and distort.

Travel back to the past...

..and see into the future.

Enter the most extreme, least
understood place in the universe...

..the heart of
a supermassive black hole.

A black hole -
terrifying and fascinating,

the universe's ultimate enigma.

How can you not love a black hole?
It's the end point of everything.

It's distorting space,
distorting time.

There's some ideas
that if you fall into one,

you could pop out
someplace else in the universe.

It's a science fiction
writer's dream.

And now consider that
these things are real,

that we actually observe
thousands of them, routinely.

Black holes are monsters,
real monsters in our midst,

and they will never
cease to be dramatic.

What would we see if we could
look this monster in the eye?

I would love to have
a trip around a black hole.

Looking out the window, seeing this
scary black disc in front of you,

and marvelling at the gravitational
distortions of light.

And experience this spectacular
manifestation of all the stuff

that I've just calculated
and never seen.

What would we discover

if we could actually
venture inside a black hole?

We're going to find out,

because we're sending
an imaginary probe

to the supermassive black hole
at the centre of the Milky Way.

It's called Sag A*.

It's so far away

that even if the probe could
travel at the speed of light,

it would take
26,000 years to get there.

On the journey, the probe would pass

tens of thousands
of smaller black holes.

We think there is a sort of
a zoo of black hole sizes.

There's hypothetical
microscopic black holes.

There's middleweight black holes
that are formed when stars collapse

and maybe another star
falls onto them.

Then there's the
supermassive black holes.

They're lurking at
the centres of galaxies.

Most black holes are born
when a giant star dies.

When the star collapses,
it all gets blown out

in the most violent fireworks
in the universe.

A super nova,
the explosion of a star,

which shines briefly with
the brightness of 10 billion stars.

After the explosion, gravity
seizes control of the star's core.

A star is already crushing
itself down under gravity,

but what stops it is the pressure
of the light coming out of it.

So if a star can no longer
produce that light,

it's gonna crush itself down.

And it'll get smaller
and smaller and smaller

until finally,
no force can hold it up,

and it just crushes in on itself.

Gravity pulls every speck
of matter inwards,

crushing lumps of solid iron
the size of Mount Everest

down to the size of grains of sand.

You think about solid matter
as being something that's so solid,

so strong, that it can't
compress any more. Think of iron.

But really, iron is mostly space.

The space between the protons

and neutrons at the core
of that iron atom is huge.

So at some point, for some stars,
the compression is so large

that you can end up smashing these
core neutrons and protons together.

What happens next
is not well understood.

Gravity squeezes these
subatomic particles together

in ways that science
has yet to explain.

The inside of a collapsing star
is unimaginable.

There are temperatures and pressures

that we don't really even
have very good numbers for.

We know for a fact that
we will need new physics,

things that we have
not yet discovered

to explain what goes on
inside a black hole.

But we do know that
the giant star is crushed down

to a fraction of its former size.

Although the amount
of stuff inside it,

its mass remains the same.

Such a massive object squeezed
into such a small space

creates a gravitational field
so strong nothing can escape.

The result is a black hole.

Most are roughly 20 times
more massive than the sun.

But at the centre of galaxies,

black holes grow to become
billions of times bigger.

Their size and power is unimaginable,
earning them their own special term.

The coolest word in astronomy
is supermassive black hole.

As you can tell by the name,
this supermassive black hole

is consuming a supermassive
amount of material,

and we know that there's one in
the centre of our Milky Way galaxy.

This supermassive black hole Sag A*

is the final destination
of our imaginary probe.

Supermassive black holes
are actually quite omnivorous.

They like to eat gas but, you know,
if a star comes within reach,

they'll gobble that up, too, or
a planet or a spaceship, whatever.

They're not so fussy.

They even eat each other.

But over billions of years,
many stars could die in one area

and the resulting black holes
can move together

and combine into bigger
and bigger black holes.

Sag A* is an omnivore and a cannibal.

It has gorged on anything
and everything within reach

for at least 12 billion years.

The reason that the black hole
can fit within it

all these enormous amounts
of stuff it's eating

is cos it's like the
ultimate trash compressor.

It just squeezes the matter down
to ridiculously small scales.

So the weight of a black hole

is simply the sum of
everything it's eaten

since the beginning of our universe.

After billions of years of eating,

Sag A* has grown to 4.6 million times
more massive than our sun...

..but it's only 20 times wider.

Outside its black sphere

spins a luminous veil
of stars, dust and gas.

As the probe approaches,
something strange starts to happen.

The probe looks like
it's veering off-course,

even though the
probe's instruments maintain

that it's travelling
in a straight line.

From the probe's perspective,
nothing weird is really happening.

But if you're on the outside,
looking at this probe,

this straight path is not going
to be a straight path.

It's gonna get pulled off
the straight path

by the actual space
around the black hole.

The probe's course hasn't changed,
but the space around it has.

And as space changes,

so does time.

Time flows differently
when you get near a black hole.

If the black hole is spinning,
it drags space around with it.

It is just bizarre and they
take all of our concepts

of common sense
and intuition and everything

and just chuck them
right out the window.

Sag A* distorts space and time.

So as the probe draws closer,
time begins to warp.

At the black hole,

the ultimate science fiction fantasy
becomes reality -

the probe really can
travel back to the future.

*

*

As the imaginary probe nears
the supermassive black hole

at our galaxy's heart,
something strange starts to happen.

The probe experiences
one of the most extreme

and fundamental forces
in the universe.

A force with the power
to twist space

and send the probe
travelling through time.

Gravity is something
incredibly commonplace.

We're always dropping things.

We're not flying off
the surface of the Earth.

It's a part of our lives
from the moment that we're born.

But it turns out
it's a very mysterious

and deep part of the universe.

When something has mass,
it has the ability to bend space.

Before Einstein's theory
of general relativity,

scientists imagined space as a stage
on which the action plays out.

Einstein's genius was to realise

that space itself was
an active member of the cast.

We tend to think of space
as just this stuff around us,

but it's actually kind of a thing,

it has a physical component to it
like a fabric, like a sheet.

The fabric of space is usually flat,

so light travels through it
in a straight line.

But a massive object like the sun,
with its strong gravitational pull,

bends the fabric...

..so the light appears
to bend as it passes the sun.

So light bends,
not because the light bends,

but the space in which the light
is travelling curves itself.

This is why,
as the probe nears Sag A*,

it looks like it's going off-course.

The immense gravity
around the black hole

is warping the fabric of space.

So everything, even the light

that travels through this
warped region of space,

must follow the same curved path.

The amazing thing is

that not only does gravity warp
the light into the black hole,

light coming from farther away
gets bent around it.

And so you could see
this shimmering distortion

against the stars in the background
as a black hole moved in front.

It would almost be like
taking a piece of glass

and moving it across the star field.

The black hole isn't
just bending space,

it's also warping time.

So if we send a probe going
into a black hole,

from our point of view,
we see it falling in.

And we see it falling in
more and more slowly

because its clock is ticking
slower and slower and slower.

That's a bizarre concept,

and it's really hard
to wrap our brains around,

but that is what the math
and physics are telling us.

We experience time as
hours, minutes and seconds.

It seems straightforward,

but actually time is relative,

it changes depending
on where you are.

It seems to the viewer
that this shot

has a picture of a moment
in time and a moment in space,

but it's actually not a moment
in space and a moment in time.

It's spread out in space,

because there's some
depth of field behind me.

But it's also spread out in time,

because the light from
the whiteboard behind me

left the white-board a little bit
earlier than the light from my face.

So when you see an image,

you're really seeing something
that's spread out in space and time.

Space and time are
inextricably linked.

So when gravity bends space,
it also bends time,

and the stronger the gravity,
the more time is distorted.

Time does not flow at the same rate
everywhere in a gravitational field.

The farther down you are into
the gravity, the slower time goes.

Now, we actually have clocks
that are accurate enough today

to tell the difference in time
between being in the basement

and being in the attic.
That's really true.

Time really goes faster in the attic
than it does in the basement.

A day spent at the top
of the Empire State Building

will make you a few
billionths of a second older

than someone who stayed
on the ground floor.

That's because
the Earth's gravitational pull

is slightly stronger
on the ground floor,

and the stronger the gravity,
the more time is slowed.

The existence of mass and energy
in space, curves space.

So right now,
I'm curving space-time around me.

And as you get to more
and more massive objects,

that curvature
becomes greater and greater.

So the Earth is curving space-time,
the sun is curving space-time.

And when you get to black holes,
the curvature is incredibly extreme.

As the probe nears
the supermassive black hole,

it starts to travel through time.

It's hard to wrap your mind
around this concept of space-time

and even of black holes,
it's pretty insane.

If I'm near a black hole,

I'm video-conferencing
my mom on a computer,

she would actually see me go,

(SLOW AND DISTORTED) "Hi, Mom."

But I would feel that
my time is running normally,

whereas she is
acting weird, going...

(FAST) "Oh, my goodness,
I'm a little worried about you
because you're speaking so funny."

Close to a black hole,
you really can go back to the future.

And if you go back,
people would say,

"Oh, you look so youthful.
This was a rejuvenating vacation."

I'd be like,
"Yes, because my time slowed down."

As the probe travels closer,
gravity's grip increases,

and time ticks
progressively more slowly.

But the increasing gravity
has another effect...

..it accelerates the probe
towards the black hole.

But in its path is
a cosmic kill-zone...

..a ring of molten dust and gas, tens
of millions of kilometres wide...

..known as the accretion disc.

It threatens to rip
the probe to shreds.

You've got this matter falling
into a black hole, it forms a disc,

and there's friction
inside of this disc.

Things are rubbing
against each other,

and the velocities are so huge
that this disc becomes terribly hot

and it glows when it gets that hot.

And so, ironically,
even though black holes are dark,

as matter falls in, it can light up

and be the most luminous objects
we see in the universe.

The probe plunges headlong towards
this seething disc of matter.

Collision seems inevitable...

..but then
a remarkable thing happens.

Without firing any thrusters
or manoeuvring in any way,

the probe swerves.

Rather than colliding with the
spinning disc, the probe joins it,

its course altered
by an unseen force.

Almost everything in the universe
spins in some way or another.

That is due to angular momentum -

this tendency that once
you get something spinning,

it's gonna stay spinning.

When you think of
that classic example

of an ice skater
spinning on an ice rink,

and as she draws her arms in, she
begins to spin faster and faster.

Think about the scale involved

when you go from a giant star to
a tiny hyper-compressed black hole.

That spin was sped up
and sped up and sped up.

As the matter falls
towards the black hole,

it whirls around faster and faster,
reaching astronomically high speed.

Travelling at close to light speed,

the matter spins too fast
to fall into the black hole.

For example, there's
a very famous ride in fairs

where you can be in a room
and it starts spinning,

and you're pushed against the wall
and the floor recedes.

But you stay up,
you don't slide down.

That same effect can stop you
from falling into a black hole.

Spin something fast enough and
centrifugal force overpowers gravity.

There's this sort of
Yin and Yang tension

between gravity trying
to crush things

and the centrifugal force of spin
trying to blow things apart.

But the black hole doesn't
just spin matter around it,

it spins the fabric
of space around it, too.

Picture a dust devil,
a kind of mini tornado.

The swirling dust reveals
the movement of the unseen wind.

In the same way, the spinning
matter around the black hole

reveals the unseen movement
of space itself.

A spinning black hole creates

a kind of tornado in
the fabric of space and time.

Black holes are weird,
no matter how you look at them.

Everything about them
is just so strange.

But I think the weirdest thing
about them is the fact that

they can drag space and time,
that fabric, around with them,

wrapping themselves in a cloak of
the material of the universe itself.

General relativity tells us that

any massive spinning object,
even the Earth,

should move the space around it
in a process called frame-dragging.

Now, when we go to the case of
the extreme gravity of a black hole,

when we talk about frame-dragging,
we're talking about a region

where the space is actually
being dragged so strongly

that it's impossible
to remain at rest there.

The probe is spinning through
twisted space and time.

Things would look
very warped and distorted.

And what you see in front of you

might even, in fact,
be in back of you.

And much of our intuition for what's
where would actually break down.

Rotating wildly,
twisting space and time,

black holes are not simply monsters

that feast on
everything within reach.

The thing about a black hole

is that they eat like they're
toddlers, they're messy.

So as stuff is falling in,

a lot of it doesn't ever actually
make it inside the black hole.

Physicists estimate that
up to 40% of the dust and gas

in the accretion disc
never enters the black hole.

It's only when you're inside
the black hole that you're doomed.

But just a little bit
outside the black hole,

if you're going around fast enough,

you can exist that way
for a long time.

In fact, black holes
don't just pull material in,

they also blast it out.

This accretion disc is whirling
madly around the black hole.

There's friction,
there are magnetic fields.

And it can twist these up
and they can form

sort of cone-shaped
magnetic cannons

that point out the top
and the bottom of the black hole.

And material can flow along that

and be ejected outward
at almost the speed of light.

These galaxy-sized cannons
are called quasars.

At their heart, powering the blast,
is a supermassive black hole.

If there is a place in the universe
you don't want to be,

it's looking down the barrel

of one of these jets
coming from a black hole.

We see images of galaxies
with supermassive black holes

with jets coming out
and they're hitting galaxies nearby.

And the environment
in that target galaxy

is probably completely
inhospitable for life.

Quasars can rip vast
cavities in galaxies,

preventing stars from forming.

But by blasting matter
far across the universe,

they may provide the raw materials
for the formation of new stars.

Black holes we think of
as destroyers, certainly in movies,

because everything falls into them
and literally, once you're inside,

your future isn't very good.

But we are beginning
to think more and more

that black holes play a central role

in the evolution
of everything we see.

Without black holes, our solar system
may never have formed.

But if our solar system
ever found itself

in the line of fire
of one of these jets...

..we would probably be annihilated.

Luckily, Sag A* seems to be quiet
and our probe is unlikely

to be blasted out into deep space
on a giant magnetic jet.

Still, progress towards
the core is slow.

Suspended between spin and gravity,
the probe spends thousands of years

staring into
the black hole's blank face.

However, gradually, gravity wins,

dragging the probe ever closer
to the edge of oblivion.

To a place where time stands still

and a wall of fire threatens
to obliterate everything.

*

*

The probe is on the precipice...

..about to enter the gaping mouth
of the black hole -

the event horizon.

Black holes have something
called the event horizon,

and it's the point at
which there is no escape

from the gravitational pull
of the black hole.

Once you cross the event horizon,

it's similar to going over the edge
of a waterfall, there's no return.

If you look at this waterfall,
you'll see it's sort of going flat

and then suddenly at the edge,
water's falling steeply down.

The edge of a black hole
is sort of like that.

At the event horizon, suddenly,
space begins to bend deeply in.

Gravity pulls the water across
the edge and down the waterfall

in the same way that
it pulls space and time

over the event horizon
and into the black hole.

Just like a fish exists in water,
everything exists in space-time,

and that includes light.

So a little light ray falling over
the event horizon of a black hole

is never gonna be able
to come back out.

For a fish to travel
back up the waterfall...

..or for light to escape
from a black hole...

..it would have to travel fast enough
to overcome the pull of gravity.

And the stronger the gravity,

the faster the object
needs to travel.

To escape the Earth's gravity,

a rocket must travel
at 11 kilometres per second.

From the far-more massive sun,

the escape velocity soars
to 618 kilometres per second.

Black holes have
gravitational fields

that are so much stronger than that.

In fact, rather than the speed
of a rocket to escape,

even if you go the speed of light,
you'll never get off.

In the few remaining seconds
before the probe tumbles
past the event horizon,

the pull of gravity and
its distortion of space-time

increases dramatically.

Suppose I have a clock
and the probe has a clock

and I can observe
the probe's clock and my clock.

As the probe gets nearer and nearer

to the event horizon
of the black hole,

I will observe
the probe's clock actually stop.

Right at the event horizon, time
basically grinds to a complete halt.

So if I were sitting on the
event horizon of a black hole,

or almost on it,
and you looked at me...

..I would just seem frozen to you.

You never actually observe

an object falling into the
event horizon from the outside.

Because it will take longer
than the age of the universe

for us to watch
the object disappear.

Near the black hole's event horizon,

time seems to slow
to a virtual stop...

..and objects appear
to change colour.

As you fell into a black hole,

people would see
you being redshifted.

They would see light coming from you
losing energy,

because it has to climb out of
this incredible well of gravity

to get out of the black hole.

The same phenomenon
occurs with sound.

When a fire engine speeds towards us,
the sound waves compress.

Racing away, they stretch out.

Like sound, light travels in waves.

But instead of changing pitch,
light waves change colour.

Climbing out of the
black hole's gravity,

light waves are
stretched and turn red.

That's why black holes,
in some sense,

sound like the stuff
of science fiction.

But the real universe is
stranger than science fiction,

that's what's so wonderful.

And what's even more wonderful is
we don't know exactly what happens

at the event horizon
of a black hole.

Einstein's theory of
general relativity predicts

the probe will simply glide
through the event horizon.

So this probe, if it's going
past the event horizon,

there's not going to be
a sign post there that says,

"Welcome to the event horizon".

It won't notice anything different.

You just cross this boundary

and then suddenly,
you're cut off from the universe,

never to return again.
That's pretty wild.

But according to
a radical new theory,

the probe's descent into the abyss
won't be a gentle freefall...

..it'll be a baptism by fire
in the ultimate cosmic firewall.

So a computer firewall
is simply supposed to be

an impenetrable barrier,

whereas the black hole firewall
is literally a wall of fire.

And that means that it's not
innocent near the event horizon.

It's not just empty space
with a few soft photons

that you can barely notice.

Rather, there's this hugely dense
radiation bath of photons.

This new theory turns
the event horizon

into the most dangerous
place in the universe.

An inferno of infinite energy

incinerating anything
that touches it.

There is no doubt that
there is a place in space,

the event horizon, the place
from which nothing gets out.

But the million-dollar question is,

what actually happens
there if you jump in?

Some people think that
nothing special happens there,

and other people think

that you actually get
burned up by this firewall.

And what's so embarrassing
about this is,

if you actually want to find out and
decide to jump into a black hole,

you will learn,
but you can't tell anybody else.

The frustrating thing
about black holes is,
because it has this event horizon,

and we know that light cannot
be emitted past that threshold,

even with all of our
advanced telescopes,
it's very difficult to detect.

To resolve what happens
on SAG A*'s event horizon,

we need to build a telescope
as big as the Earth.

It sounds impossible,

but it's already taking shape
at Hawaii's Mauna Kea Observatory.

If you want to see the black hole

at the centre of the galaxy, you
need a really, really big telescope.

We can't build optical
telescopes that big.

And what we do is
we use radio telescopes

and we distribute those telescopes

over thousands of miles
apart from each other.

So we're creating a telescope
that's as big as the Earth itself.

And over here is where
it all comes down.

And inside of this rack,

all of our signals come in
here at eight gigabits per second.

It's the equivalent of
four digital movies per second.

If we sent this back by
your home internet connection,

it would take years
to transmit all of this data.

So what we have to do
is specially package this up

and ship it to our central lab
at MIT where we process this data.

This is essentially the holiest
of holies. This is ground zero.

This is where all
the data come together.

By accumulating
two more years' worth of data,

scientists believe the event horizon
could be brought into focus.

So once the event horizon telescope
gets its final data sets,

we hope to image
something like this.

This is what we wind up seeing,
though, because the intervening gas

to the centre of
our galaxy blurs the image.

But if we take out the scattering,

we wind up being able
to recover the shadow feature.

This is what we're after,
this is the Holy Grail

of the event-horizon telescope.

The event horizon is
already taking shape...

..a black sphere,
27 million kilometres in diameter.

This is what the probe
should see in the final moments

before it enters the abyss.

If there is a firewall lurking
behind this black veil,

the probe will be destroyed.

If not, the probe will glide across
the event horizon without incident...

..only to find itself
in the most bizarre and
most extreme place in the universe...

..where new worlds begin
and the past becomes the present.

*

*

The probe has passed
the point of no return.

It's now inside the
supermassive black hole...

..plunging through a world
of unimaginable extremes.

Everything that falls into
a black hole disappears.

And if it never gets out,
the question is, where does it go?

Here, gravity is so intense
that the fabric of space itself

is pulled inwards at speeds
faster than the speed of light.

The 13-million-kilometre journey
to the black hole centre

will take less than 40 seconds.

But only if the probe can survive
the extreme gravitational forces.

Now, imagine that I've
fallen into a black hole.

The strength of gravity
is gonna be different

if I'm going in feet-first,

because of the extreme
curvature of space-time there.

And because of that,
my feet will have a stronger pull

and you will get
stretched into a form

that's reminiscent of spaghetti.

So we call it spaghettification.

Spaghettification is real.

It happened when Jupiter's gravity
spaghettified Comet Shoemaker-Levy 9

into a chain of fragments in 1994.

In reality, the probe would be
stretched into atom-sized filaments

before it reached
the black hole's centre.

I mean, of course, I could flex
and hold myself together anyway,

but, you know, it's the laws
of physics we're battling with here.

(LAUGHS)

But let's suspend these laws

and equip the probe with
a protective force-field

straight out of science fiction.

It's now halfway from the event
horizon to the black hole's centre.

From this vantage point,

the probe sees something
truly incredible.

If you were talking about
the exact mathematical horizon,

you would see the entire past
of the universe go by.

You would see back to the beginning
of the formation of the black hole.

According to Einstein's equations,

the black hole is
a colossal cosmic museum.

All the light that's fallen in

since the black hole's formation
is still here, sped up,

and stacked in layers.

As the probe plunges deeper,

the battle between gravity
and spin resumes and intensifies.

The centrifugal force
gets relatively stronger

deeper inside the black hole.

And that centrifugal force
slows down the flow of space,

and the place where it slows back
down to the speed of light

is called the inner horizon.

And all kinds of crazy things
happen at the inner horizon.

In this chaotic cosmic blender,

matter gets spun around
and flung back out.

If I actually jump into
a big black hole,

just like if I fell
down a waterfall,

you're gonna be perfectly alive and
well while you're on the way down.

The problems only
come when you reach

what corresponds to
the inner horizon at the base,

where other water and rocks
and things come at you.

Now the probe nears
the inner horizon.

The inner horizons
of rotating black holes

are the most violent places
in our universe.

Wildly energetic particles slam
into the probe at near light-speed.

The black hole,
it's an amazing kind of...

particle accelerator
at the inner horizon.

Particles spewing in all directions,

being accelerated
through each other.

They collide together, they produce
enormous concentrations of energy,

which vastly exceed any energy

in any terrestrial
particle accelerator.

The collisions are comparable
in strength to the Big Bang.

If there is any place
in our universe

where our universe is
making baby universes,
where our universe is reproducing,

I can guarantee to you
that that place is the inner
horizons of black holes.

Because that is the place
where the energies

that are needed to make a Big Bang,
they are produced there.

The idea that a universe can
be born inside a black hole

led scientists to question
the origins of our own universe.

It's actually completely
possible that our Big Bang

is the remnant of a black hole
in some pre-existing universe,

crushing things together,
then spitting out a baby universe.

One of the reasons black holes
are such fascinating objects

for theoretical physicists
is they may provide a guide

to a new understanding
of the universe.

So if we understand black holes,
we may understand the Big Bang.

If we understand the Big Bang,
we may understand our very origins.

As the probe crosses the inner
horizon, everything changes.

The gravity pulling
the probe inward is matched

by the spin pushing it out.

The two opposing forces
are finally balanced.

So what this creates in the centre,

in the very region of
the inner event horizon of
one of these black holes

is sort of like a safe haven,
like the eye of a hurricane.

And in there,
things are a lot calmer

and you could imagine
actually navigating,

once you get through
the crazy region on the outside.

Inside the eye of the storm,

the probe heads
for the black hole's heart -

the singularity.

Here, space and time and our
understanding of the universe ends.

Inside the inner event horizon
of a spinning black hole,

you can look at the singularity,
it's over there in a ring.

The actual thickness
of the ring is zero.

It is a circle of points

of infinite mathematical thickness

and infinite curvature
of space-time.

This was once a massive star,
crushed down to an infinitely small,

infinitely dense point
in space and time.

Spinning at
astronomically high speed,

centrifugal force transforms
this point into a ring

which warps
the space and time around it.

And it turns out that around
the singularity there's a region

where we have, what in the jargon
is called, a closed timelike curve.

Which is a fancy way of saying,
"You can enter this region,

you can zoom around
and then you can come out,

and you come out
before you went in."

So you can basically visit
the past version of yourself

before you ever entered.

OK. (LAUGHS)

General relativity predicts
that the singularity will bend

space and time to such an extent

that if the probe took
a trip around the ring,

it could come back to
a time before it set off.

But this probe is heading
straight through the ring.

There's this idea that
a black hole is punching a hole

in the fabric of space and time.

And that it might be
punching a second hole

someplace very far away.

And that if you fall
into the black hole,

you will come out on the other side,
somewhere light years away,

even though it didn't take you
any time to traverse that distance.

We call this a wormhole

because it's like a worm
eating its way through an apple.

But could the probe
survive the journey?

What goes into a singularity
may come out somewhere else,

but what comes out is not gonna
have much of a relationship

to what went in.

It will be not only spaghettified,
but essentially destroyed.

If you want to go somewhere else,
take an airplane.

There's another theory that
a singularity isn't a wormhole,

it's a white hole.

A white hole is basically a
black hole played backward in time.

So a white hole is a singularity

that sort of spits out
into the universe

and pushes things away from it
rather than pulling them in.

The singularity spits out a universe,

a process bearing a striking
similarity to the Big Bang.

Our Big Bang emerged, at least
classically, from a singularity.

And it's not lost on people

that the end point of
a black hole is a singularity.

Is there a connection
between the two? Maybe.

But in reality,
scientists are not sure

that this infinitely dense
and infinitely small singularity

at the centre of a black hole
exists at all.

Infinities popping up in physics

really just tell us that we have
no clue what we're talking about.

We've never seen anything
actually infinite in physics.

So my own personal guess is
that there are no singularities.

And that whenever we see an infinity
pop out of our equations,

it's just nature telling us that...

(MIMICS BUZZER) "You were wrong."

Einstein's general relativity
commits suicide, if you will,

at singularities.

It can't continue space-time
beyond singularities.

How that plays out...

..don't know.
We don't know what happens to it.

This is the end of the probe's
extraordinary journey.

It has reached the end
of space and time

and the limit of human knowledge.

Certainly, right now, black holes
are the bad boys of physics.

They break every rule we know,

and that just shows us
our own limitations.

It's not the black hole's problem,

we have not gotten far
enough to explain them.

And that will continuously
challenge us and pull us

in a real way into
the heart of a black hole.

On our own journey
into the black hole's heart,

we've discovered it's more than the
veracious monster of science fiction.

It's a time machine...

..and a cosmic museum...

..a destroyer
and a creator of worlds,

and the universe's ultimate enigma.

Understand black holes

and we will truly understand
how the universe works.

The math is bizarre,
the observations are difficult,

and the concepts are mind-shredding.
Who wouldn't love that?

I think a lot of people
love black holes

just because they're big
and scary and fun.

But we physicists love them
also for a different reason,

which is that it's the most
extreme physical systems

that usually give us the best clues
about how nature works.

Black holes have driven
our imagination

beyond where it
would have gone before.

Nature is much more
imaginative than we are.

And every time we explore nature,
we're surprised.

So truth is far
stranger than fiction,

and the real universe exceeds

even the wildest imaginings of
the wildest science fiction writer.

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