All language subtitles for Wonders of the Universe BBC 2011 EP03 Falling BluRay 1080p x264 AC3 EN_Subtitles01.ENG

PROFESSOR BRIAN COX: Why are we here?

Where do we come from?

These are the most enduring
of güestions.

And it's an essential part
of human nature

to want to find the answers.

Now, we can trace our ancestry
back hundreds of thousands of years

to the dawn of human kind.

But in reality, our story extends
far further back in time.

Our story starts
with the beginning of the universe.

It began 13.7 billion years ago.

And today it's filled
with over a hundred billion galaxies,

each containing
hundreds of billions of stars.

In this series,
I want to tell that story.

Because ultimately,
we are part of the universe.

So its story İis our story.

The force at the heart of this story
is gravity.

This fundamental force of nature
built everything we see.

It creates shape and örder

and it initiates patterns
that repeat across the heavens.

But gravity also forges some of the most
alien worlds in the cosmos,

worlds that defy belief.

The guest to understand this fundamental
force of nature

has unleashed a goölden age of
creativity, exploration and discovery.

And it's led to
a far deeper uünderstanding

of our place in the universe.

Every moment of our lives, we experience
a force that we can't see or touch.

Yet this force is able to keep us
firmly rooted to the ground.

İt is, of course, gravity.

But despite its intangible nature,
we always know it's with us.

Now, if was to ask you, "How do you know
that there's gravity around here?"

Then you might say,
"Well, it's obvious.

"You know, I can just do an experiment,
I can drop something."

Well, yes, but actually, gravity
is a little bit more subtle than that.

But to really experience it,
to understand it,

you have to do something pretty extreme.

And this plane has been modified
to help me do it.

Thanks to its flight plan,
iİt's known as the Vomit Comet.

Önce we've climbed to 15,000 metres,

this plane does something
no ordinary Flight would do.

Its engines are throttled back
and the jet falls to Farth.

And then something
gülte amazing happens.

(ALL EXCLAIMING)

MAN: Look at me! Look at me!

I'm now plummeting towards the ground
just like someone's cut the cable.

And you see that I'm not moving
relative to Finstein.

We're all just floating.

MAN: I got it! Oh, intercepted

(LAUGHING)

(ALL EXCLAIMING)

COX: By simply falling
at the same rate as the plane,

for a few fleeting moments,
we were all free of gravity's grip.

(LAUGHING)

But this isn't just a joy ride.

Sorry.

Now, look, there's sornething
very profound here,

because although I'm falling
towards the ground,

as you see,
gravity has completely gone away.

Gravity is not here any more.

I've cancelled gravity out
just by falling.

If you understand that,
then you understand gravity.

So it is possible,
by the simple act of falling,

to get a very different
experfence of gravity.

But this force of nature does more
than just brinmg us back down to Farth.

Gravity also plays a role
on the grandest of stages.

Because across the universe,

from the smallest mote of dust
to the most massive star,

gravity is the great sculptor
that created order out of chaos.

Since the beginning of time, gravity
has been at work in our universe.

From the primordial cloud of gas
and cosmic dust,

gravity forged the stars.

It sculpted the planets and moons

and set them in orbit
around the newly formed suns.

And gravity connects these star systems
together in vast galaxies

and steers them on their journey
through unbounded space.

Over the centuries,
our guüest to ünderstand gravity

has allowed us to explain some
of the true wonders of the universe.

But at a deeper level, that guest
has also allowed us to ask guestions

about the origin and evolution
of the universe itself.

To understand how gravity works
across the universe,

we need look no further
than the ground beneath our feet.

Well, the first scientist to really
think about it

was Isaac Newton back in the 1680s.

And he said this.
"Gravity is a force of attraction

"between all objects."

Now, the force of attraction
between these two rocks

is obviously very small,

almost impossible to measure.

And that's because the force
is proportional

to the masses of the objects.
These things are not very massive.

But there is a more massive rock
around here.

It's the one I'm standing on,
planet Earth.

The mass of our Farth
generates a gravitational pull

strong enougğh to sculpt
the entire surface of the planet.

İt causes water to gouge out
vast canyons.

It sets the limit
for how high mountains can soar.

And it shapes whole continents.

But this invisible force
does more than just shape our world.

The skies are always changing.

The constellations rise and fall
in different places every night

and the planets wander across
the background of the fixed stars.

But throughout human history,
there's been one constant

up there in the night sky.

Because every human that's ever lived

has gazed up at the moon
and seen one face shining back at us.

The reason why we never see
the dark side of the moon

is all down to the subtlety
with which gravity operates.

Millions of years ago,
the moon rotated rapidiy.

But from the moment it was born,
our companlon felt the tug of gravity.

Just as the moon creates great tides
in OuUr oceans,

the Farth caused a vast tide to sweep
across the surface of the moon.

But this tide wasn't in water,
it was in rock.

Imagine that this is the moon
and over there is the Farth.

The Earth's gravity acts on the moon
and stretches it out

into a kind of rugby ball shape.

Now, the size of that tidal bulge
facing the Farth

is something like seven metres in rock.

And then as the moon rotates,

that bulge sweeps
across the lunar surface.

When you imagine
what that would look like here,

you'd see a tidal wave sweep
across this landscape,

with the rock rising and falling
by seven metres.

This massive wave acted like a brake
and gradualiy slowed the moon down.

Eventually, the tidal bulge
became aligned with the Farth,

locking the speed
of the moon's rotation.

So the time it takes
the moon to spin once

is almost the same
as the time it takes to orbit the Farth.

So there is no dark side of the moon,

Just a side that gravity
hides from our view.

The bond that gravity creates
between the Farth and the moon

is repeated across the cosmos.

It's the glue that hold the planets
in orbit around the sun.

And it binds our solar system and
countless other solar systems together

to form galaxies
like our own Milky Way.

But gravity's influence
can be felt even further,

because it controls the fate
of galaxies.

When you look up into the night sky,

then you see the universe
as it looks in visible light,

with the glowing of the stars
and the galaxies.

But that's only part of the story,

because the universe
is full of dust and gas

which you can't see
with a conventional telescope,

but you can see
with a telescope like this.

Radio telescopes,
like the very large array in New Mexico,

are able to peer deep into space

and reveal the incredible
attractive power of gravity.

This is Andromeda,

a spiral galaxy roughly
the same size and mass

as the Milky Way.

This island of over a trillion stars

sits öover two and a half
million light years away.

But every hour, that gap shrinks
by half a million kilometres.

Whilst most galaxies have been
rushing away from each other

ever since they formed
just after the Big Bang,

some galaxies formed so close together

that they are locked
in a gravitational embrace.

Now, the Milky way and Andromeda
are two such galaxies.

And computer simulation suggests
that they will collide together

in around three billion years' time.

I mean, look at that.
That's a simulation

of the Milky Way galaxy and the
Andromeda galaxy colliding together.

And all these wisps of smoke
getting thrown out are stars,

and these are star systems
getting ripped out of the galaxy

and thrown off into interstellar space.

These two islands of hundreds
of billions of suns

have flown through each other.

Gravity has exerted its grasp
and dragged them back again.

Just remember
that we are one of those dots.

Our sun and the EFarth
and the solar system

are either going to be flung out
into interstellar space

or they're going to be in here,
in this maelstrom,

hundreds of billions of suns
swirling around each other

and forming the core of a new galaxy.

But just imagine what it would be like
to gaze up at the sky

as Andromeda approached.
The sky would be ablaze

with the light of hundreds
of billions of suns.

And the imminent collision would provide
the energy to generate the births

of hundreds of millions more.

What a magnificent sight it would be.

But far more magnificent is the
immense scale of gravity's embrace.

It holds galaxies together across
hundreds of billions of kilometres.

And in doing so, it creates
the most magnificent structures.

Our own Milky Way
is part of one of these,

the Virgo cluster.

Every polrnt of light in this image
is not a star but a galaxy.

There are 2,000 galaxies in this cluster

and they're all bound together
by gravity,

making it the largest structure
in our inter-galactic neighbourhood.

There seems to be no limit
to the reach or power of gravity.

Its influence can be felt across
the vast expanses of space and time.

But there's something
very interesting about gravity,

because it is by far
the weakest force of nature.

I mean, look, I can pick this rock up
off the ground

even though there's an entire planet,
planet Earth tryimg to pull it down.

So, if gravity is so weak,
how come it's so influential?

Gravity may be weak here on Farth,
but it's not so weak across the cosmos.

This invisible force varies
on all the planets in the solar system

and on the exoplanets
we've discovered orbiting other suns.

To experience what gravity feels like
on these worlds,

I need to go for a spin.

This is a centrifuge.
It was built in the 1950s

to test whether fighter pilots
had the right stuff.

But it's going to allow me to feel
what it would be like

to stand on the surface of any
of the planets in the solar system

that are more massive than the Earth.

And in fact,
also what it would be like to stand

on some of the planets
that we've found around distant stars.

TECHNICİAN: Right, I'll have
to strap you in first of all.

Let me see. This one goes here...

This is a gotta-go switch,
it's an emergency switch in case you...

something happens and you release
and the centrifuge will stop.

I was just told by the F-16
fighter pilot who's just been in here

that it's a hundred times
more uncomfortable

than being in a jet fighter.

I was kind of confident
because I've been in jet fighters

and didn't find it too uncomfortable,

but apparently
this is a hundred times worse.

Go ahead.

Doors closed agaln. Provors there.
Systems are there. Doctor, he's ready.

We'll start up the centrifuge, Brian,
and bring you in orbit.

And it happens in three, two,
öne seconds from now.

COX: Zhe first planet
I'm travellirg to is Neptune.

İIts gravity is just fractionally
stronger than here on EFarth.

So this is the gravitational field
on Neptune and you feel,

"You know what,
I could probabiy get used to this.

“I could probabliy live
on the surface of Neptune."

-Can you lift your hands a little?
-There we go.

-Yeah, and down?
-And it is actually guite an effort.

It is noticeably heavier.

It's like having a reasonably
heavy weight in your hand.

To go to 2.56?

Yeah, so now we'll move
from Neptune to Jupiter.

Let's go there.

COX: Jupiter is over 1, 300 times
more massive than the Farth.

But because it's mostly gas,
it's not very dense.

So its gravity is just over twice
as strong at its surface.

Well now, actually it is
gülte difficult to lift my hand.

And that's 2.56.

I wouldn't want to sit here
for half an hour.

TECHNICIAN: Carı you lift both
of your hands above your head?

-See what happens there?
-Let's see, so attualiy...

Just about, but actualiy, it's
an immense amount of hard work.

Though it would be hard work
living on Jupiter.

TECHNICIAN: Zet's go fo 46.

Actually, this is heading
to a planet around...

a planet called OGLE2-TR-L9b,

which is arcund a star
in the constellation of Carina.

It's öone of the exoplanets
we've discovered.

Oh, and there we go.

Now, that is actually beginning
to feel guite unpleasant.

Can you describe what you're feeling?

-A very heavy face.
-Right.

-My head is extremely heavy.
-How about your lungs?

Inhaling, exhaling, breathing?

İt's much harder work.

-I can't lift my hand off my leg.
-Okay.

-And that's at 46.
-Yeah.

But my head and my face
feel very, very heavy.

-Yeah.
-İt's gülte an unpleasant feeling.

We'll go to 5 and let me know
İf you have any visual disturbances.

COX: 7'm now en route
to a newly discovered exoplanet,

WASP-8b.

4.4.

This world sits in the small
and faint constellation of Sculptor.

Auite hard to speak.

It has a gravitational force
nearly five times that of the Farth.

-All right. We'll go to 5 G. Okay?
-I'm very foggy.

-Very foggy.
-Very foggy?

-Still foggy?
-Yeah.

-All right.
-Take it down.

Okay, we'll take you down.

Very interesting.

İt was, wasn't it?

-My face felt a bit saggy there.
-(LAUGHING)

Well, you looked a little different.

That was guite unpleasant
that time, actually.

See, we went very guickly up to 5G.

And what happens is,
well, for me anyway,

was vision becomes very, very foggy.

Just the whole thing just blurs
and blurs and blurs.

So, you realise that we're, obviously,
very finely tuned

to live on a planet that has
an acceleration due to gravity of 1G.

When you got to 2G6, it's difficult.

When you go to 36 and 4G,
it becomes unpleasant.

And 5G, anyway for me,
was on the border of being

so unpleasant that you pass out.

So although gravity feels weak
here on Earth,

it certainly isn't weak
everywhere across the universe.

And that's because gravity
is an additive force.

It scales with mass,

so the more massive the planet or star,
the stronger its gravity.

The body with the strongest gravity
in our solar system is the sun.

Our star has so much mass packed
inside a relatively small space

that it has a gravitational pull
at its surface

28 times that of the Farth.

If I were able to set foot
on this world,

all the blood would be pulled
oUft of my upper body

and I would die in less than a minute.

But our sun's gravitational force
is nothing

compared to the extreme G

found at the surface of öne of the
strangest places in the universe.

Imagine the gravity on a world
with more mass than our sun

crammed into a sphere
Just 20 kilometres across.

We first detected such a wonder
just 40 years ago.

But the story of its discovery
begins over a thousand years earlier.

This is Chaco Canyon in New Mexico,
in the southwestern United States.

And it was home to what's become known
as the Chacoan civilisation.

This is Pueblo Bonito, one of the
so-called Chacoan great houses.

And back in the 1100s, this place
had over 600 rooms.

It's thought that this building
must have been ceremonial

or religious, a cathedral, if you like.

The Chacoan great houses
are aligned with interesting objects

in the skies over the points
at which the sun and moon rise

at important times of the year.

So it seems that by constructing
these grand buildings,

the Chacoans were not only
tryimg to place themselves

at the heart of local culture,

but also to place themselves
at the heart of the cosmos.

Very little is known
about the Chacoan culture

because no written text
has ever been discovered.

But in another part of the canyon,
there is a record of a spectacular event

that they witnessed in the sky in 1054.

I've known about this place
since I was about 12 or 13 years old.

And the reason is this book
and the television series Cosmos,

Carl Sagan's masterpiece,

probably the most important reason
that I got interested in astronomy.

On page 232, there's a picture
that's always fascinated me

and captured my imagination and
it's a photograph of that wall of rock.

And in particular, a painting
that's on the overhang.

Because it's thought that
that painting is a record

of one of the most spectacular
and magical events in the cosmos.

On July 4th, 1054 AD,
a bright new star appeared

and it outshone every other star
in the night sky for over three weeks.

Iİt was so bright that it was visible
in the daytime.

And it's thought that this painting
is the Chacoan peoples' record

of that astronomical event.

Now, the reason we think that is that
using modern computer technigues,

you can wind back the night sky and say,

"Where would the moon have been?
Where would the stars have been?"

And you find that in that direction,
the moon would have risen

and tracked across the night sky
and the new star would have been

very, very close to the crescent moon.

We now know that that new star
was in fact the explosive death

of an old star, a supernova explosion.

A star literally blowing itself apart
at the end ofits life.

Ihroughout a star's life,
there is a constant battle

between energy pushing out
and gravity pushing in.

As long as the star burns,
the two forces balance each other out.

But when it runs out of fuel,
gravity wins and the star collapses

and then explodes
with the brightness of a billion suns.

We can no longer see the supernova
the Chacoans saw,

but we can still marvel
at what it left behind.

This is the Crab Nebula,
the remains of that exploding star

that the Chacoans saw in these skies
a thousand years ago.

Iİt's an expanding cloud of gas and dust,
the remains of that dyirg star.

And the colours are
different chemical elements.

So the orange is hydrogen,
the red is nitrogen

and those filaments of green are oxygen.

While the explosion blew most of the
stellar materlal out into the cosmos

to form this vast nebula,

we now know that this
wasn't the end of the story.

At the centre of the nebula
lies the remnant of the star,

its core crushed
by the force of gravity.

That is a neutron star, an image
taken by the Chandra X-ray satellite.

The central blob there is only
about 20 kilometres across,

but it's got the mass of our sun,
a star the size of a city.

It's spinning at a rate
of over 30 times a second,

1,800 revolutions per minute.

And it really is
an astonishingly alien world.

As the neutron star spins,
jets of particles

stream out from the poles
at almost the speed of light.

These jets are powerful beams
that sweep around as the star rotates.

When the beams sweep across the Farth,
they can be heard as regular pulses.

So we call them pulsars.

But it's not this rhythmic noise
that makes the Crab Pulsar a wonder.

İt's the extraordinary nature
of gravity on this alien world.

If I were to be on its surface,
then the gravitational pull on me

would be a hundred thousand
million times that

that I feel on Earth.

And that means that if I were to jump
from the top of that projection screen

then by the time I hit the ground,

I'd be travelling
at over 4,000,000 miles an hour.

That's a lot of gravity.

Pulsars have such extreme gravity

because they're made of
incredibly dense matter.

To understand why, we have to look
at what gravity can do to matter

at the very smallest scales.

Everything in the universe is made
of atoms.

And until the turn of the 20th century,

it was thought that they were the
smallest building blocks of matter.

I mean, the word itself comes
from the Greek "atomos",

which means indivisible.

But we now know that atoms
are made of much smaller stuff.

Atoms consist of an atomic nucleus
surrounded by a cloud of electrons.

And whilst almost all of the mass
is contained in the nucleus,

it is incredibly tiny
compared to the size of an atom.

I mean, if this were a nucleus then
the cloud of electrons would stretch out

to something like a kilometre away.
I mean, that's from here to that rock.

And electrons on this scale are
incredibly tiny.

There just like specks of dust
and there aren't many of them.

So imagine a giant sphere
centred on the atomic nucleus

stretching out all the way to that rock
and beyond,

with just a few points of dust in it.
That's an atom.

So that means that matter
is almost entirely empty space.

I'm full of empty space,
the Earth is full of empty space.

Everything you can see in the universe
is pretty much just empty space.

So if everything in the universe
is made up of atoms

and atoms are 99.9999 percent
empty space,

then most of the universe is empty.

But in the Crab Pulsar,
the force of gravity is so extreme

that the empty space inside the atoms
is sguashed out of existence.

So all you're left with
is incredibly dense matter.

Imagine this was matter
taken from a neutron star,

then it would weigh
more than Mount Everest.

Or to put it another way, if I took
every human being on the planet

and sguashed them so they were
as dense as neutron star matter,

then we would all fit inside that.

And if I were to drop
my neutron star stuff to the ground,

then it would slice straight through
the Earth like a knife through butter.

Wherever we look in the universe
we see gravity at work.

It creates shape and structure.

It göverns the orbits of every planet,
star and galaxy

in ways we thought
we were able to predict.

But there was a flaw in our
understanding of this force.

And it was exposed by one of
our close neighbours.

This is Mercury.

For thousands of years we've marvelled
as this fleet-footed planet

races across the face of the sun.

But 150 years ago,

astronomers noticed something
strange about Mercury's orbit.

Imagine that this rock is the sun
arıd this is Mercury.

Now, Mercury has guite a complex orbit.

For one thing,
it's not a perfect circle.

It's guite an elongated ellipse.

So at its closest approach to the sun
it's around 46 million kilometres away.

And then it drifts out to something
jJust under 70 million kilometres.

But you can calculate Mercury's orbit
very precisely

using only Newton's laws of gravity.

So astronomers used to predict
the exact time

when you could look up into the sky,
look at the sun

and see the tiny disc of Mercury
pass across its face.

The thing was they never got it right.
They predicted it time and time again,

and every time it happened
they got it slightly wrong,

which was an immense embarrassment.

So what they did was that
rather than guestion Newton,

they invented another planet
and they called it Vulcan.

And they said that there
must be another planet

somewhere in the solar system
which is always invisible from Earth

but which perturbed
Mercury's orbit a bit.

And so that was the reason
their calculations were wrong.

For decades astronomers searched
and searched for Vulcan.

But they never found it
because Vulcan didn't exist.

The explanation, the real explanation,

was even more interesting
than inventing the planet Vulcan.

Because it reguired a modification,
in fact, a complete rewriting

of Newton's law of gravity.

Gravity is not a force pulling us
towards the centre of the Farth

like a giant magnet.

İn a sense,
gravity isn't really a force at all.

Describing the nature of gravity

turned out to be öne of the great
intellectual challenges.

But almost 200 years
after Newton's death,

a new theory emerged.

The new theory,
called General Relativity,

was published in 1915 by Albert Finstein
after 10 years of work.

And it stands to this day
as one of the great achievements

in the history of physics.

See, not only was it able to explain
with absolute precision

the strange behaviour of Mercury,

but it explains to this day
everything we can see

out there in the universe
that has anything to do with gravity.

And most importantly of all,
it explains how gravity actually works.

Gravity is the effect that the
stars, planets and galaxles have

on the very space that surrounds them.

According to Finstein,
space is not just an empty stage,

it's a fabric called space-time.

This fabric can be warped,
bent and curved

by the enormous mass
of the planets, stars and galaxles.

You see, all matter in the universe
bends the very fabric

of the universe itself.

Matter bends space.

I bend space,
these mountains bend space.

But by the tiniest of tiniest
of amounts.

But when you get on to the scale
of planets and stars and galaxies,

then they bend and curve the fabric
of the universe

by a very large amount indeed.

And here is the key idea.
Everything moves in straight lines

oöver the curved landscape of space-time.

So what we see as a planet's orbit
is simply the planet falling

into the curved space-time
created by the huge mass of a star.

This is able to explain
Mercury's erratic orbit.

Because of the planet's
Pproximity to our sun,

the effects of the curvature of
space-time matter far more for Mercury

than for any other planet
in the solar system.

But this idea of curved space
is difficult to imagine.

But if we could only
step outside ofit,

if we could only float above space-time
and look down on it,

this is what our universe
would look like.

You would see the mountains and valleys,

you would see the little
peaks and troughs

created by planets and moons

and you would see these
vast, deep valleys

created by the galaxles.

And you would see planets
and moorns and stars

circling the peaks as they
follow their straight line paths

through the curved landscape
of space-time.

So öone way to think about gravity

is that everything in the universe
is just falling through space-time.

The moon is falling into the valley
created by the mass of the Farth.

The Earth is falling into the valley
created by the sun.

And the solar system is falling

into the valley in space-time
created by our galaxy.

And our galaxy is falling
towards other galaxies in the universe.

Einstein's theory of General Relativity
is so profound and so beautiful

that it can describe the structure
and shape of the universe itself.

But remarkably, the theory
could also predict its own demise.

Because it predicts the existence
of objects so dense and so powerful

that they warp and stretch and bend
the structure of space-time so much

that they can stop time
and that they can swallow light.

There are objects so powerful
that they can tear

all the other wonders
of the universe apart.

Since the dawn of civilisation,

we've peered at the stars
in the night sky

and tracked the movements
of the planets.

We see these familiar patterns repeated
across the whole universe.

But when we train our telescopes

to the stars that orbit
around the centre of our galaxy,

we see something very unusual.

This is one of the most fascinating
and important movies made

in astronomy in the last 10 or 20 years.

This is real data,
every point of light in this movie

is a star orbiting around
the centre of our galaxy.

They're known as the S stars.

Now, our sun takes
around 200 million years

to make its way around the Milky Way.

One of these S stars takes only 15 years
to go around the centre of the galaxy.

It's travelling at three
or four thousand kilometres per second.

Now, by tracking the orbits,
it's possible to work out the mass

of the thing at the centre.

The answer took astronomers
by surprise, I think it's fair to say.

Because the object in the centre
of our galaxy is 4,000,000 times

as massive as the sun

and it fits into a space
smaller than our Solar System.

There's only one thing that anyone
knows of that can be so small

and yet so massive,
and that's a black hole.

So what we're looking at here
is stars swarming like bees

around a supermassive black hole
at the centre of the Milky Way galaxy.

We think black holes can be
smaller than an atom

or a billion times more massive
than our sun.

Some are born when a star dies.

When a star arocund 15 times
the mass of our sun collapses...

all the matter in its core is crushed
into an infinite void of blackness

known as a stellar mass black hole.

Black holes are the most extreme
example of warped space-time.

They have such enormous mass
crammed into such a tiny space

that they curve space-time more
than any öther öbject in the universe.

The immense gravitational pull
of these monsters

can rip a star apart.

They tear matter from its surface
and drag it into orbit.

This super-heated matter spins
around the mouth of the black hole

and great jets of radiation
fire from the core.

Although these jets can be seen
across the cosmos,

the core itself remains a mystery.

Black holes curve space-time so much

that nothing, not even light
Carı escape.

So their interior
is forever hidden from us.

But because we understand
how matter curves the fabric of space,

it is possible to picture
what is happening.

Near black holes, space and time
do some very strange things.

Because black holes are probably
the most violent places we know of

in the universe.

This river provides a beautiful analogy
for what happens to space and time

as you get closer and closer
to the black hole.

Now, upstream of the waterfali,
the water is flowing pretty slowly.

Let's imagine that it's flowing
at three kilometres per hour

and I can swim at four.

So I can swim faster than the flow
and can easily escape the falls.

But as you go further
and further downstream

towards the waterfall in the distance,
the river flows faster and faster.

Imagine I was to decide to jump
into the river

just there on the edge of the falls.

The water is flowing far faster
than I could swim.

So no matter what I did,
no Matter how hard I tried,

I would not be able to swim
back upstream.

I will be carried inexorably
towards the edge

and I would vanish over the falls.

Well, it's the same
close to a black hole.

Because space flows faster
and faster and faster

towards the black hole, literally,
this stuff, my space that I'm in,

flowing over the edge
into the black hole.

And at the very special point
called the event horizon,

space is flowing at the speed of light
into the black hole.

Light itself travelling at 300, 000
kilometres per second

is not golng fast enough
to escape the flow.

And light itself will plunge
into the black hole.

Well, as you fall into a black hole
across the event horizon,

and if you were going feet first,
your feet would be accelerating

faster than your head.

So you will be stretched and you would
be, guite literally, spaghettified.

Now, as you get right to the centre,

then our understanding
of the laws of physics breaks down.

Our best theory of space and time,
Finstein's theory of General Relativity,

says that space and time
become infinitely curved,

that the centre of the hole
becomes infinitely dense.

That place is called the singularity,
and it is the place

where our understanding
of the universe stops.

Gravity is the great creator,
the constructor of worlds.

That's because it's the only force
in the universe

that can reach out across
the vast expanses of space

and pull matter together
to make the planets,

the moons, the stars and the galaxles.

But gravity is also the destroyer.
Because it's relentless.

And for the most massive objects
in the universe,

for the most enormous stars
and the centres of galaxies,

gravity will eventualiy
crush matter out of existence.

Now, the word "beautiful"
is probably overused in physics.

I probabiy overuse it.

But I don't think there is any scientist
who would disagree with its use

in the context of Finstein's
theory of gravity.

Because here is a theory
that describes a universe that is bent

and curved out of shape
bBy every moori, every star

and every galaxy in the sky.

And everything in the universe
has to follow those curves,

from the most massive black hole
to the smallest mote of dust,

even to beams oflight.

But the most tantalising thing
about EFinstein's theory of gravity

is we know that it's not complete.

We know that it's not
the ultimate description

of the structure and shape
of the universe.

And that, for a scientist,
is the most beautiful place to be,

on the border between
the known and the unknown.

That is the true wonder of the universe.

There's so much more
left of it to explore.

(FALLING BY KATE RUSBY PLAYING)