Original subtitles

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)