All language subtitles for BBC.Horizon.2008.What.on.Earth.is.Wrong.with.Gravity.DVBC.XviD.MP3.MVGroup.org-eng

There's a force of nature
that's baffled the most famous
names in the history of science.

Galileo laid the foundations
but didn't get any further.

Newton thought it
was the work of God.

And even Einstein,
Albert Einstein failed to solve it.

It's a mystery that lies
at the heart of everything...

..from the Big Bang
and the beginning of time...

..to the existence
of life on Earth.

From strange
distortions in the cosmos

to the smallest stuff of matter.

It's a puzzle that's led to
the most abusive slanging matches
in modern science.

But I think that
within my lifetime

we may succeed where many of the
greatest brains in history failed,

and finally solve one of the
biggest mysteries of the universe.

I'm Brian Cox,

particle physicist.

I have one of the best jobs
in the world.

I have to find out what are
the fundamental building blocks
of the universe.

How do they stick together, how do
they work and, with a bit of luck,
find out why they're there at all.

I've spent the last ten years
looking at the smallest stuff
in the universe.

But I'm interested in the biggest
questions you could possibly ask.

Why do I exist? Why do you exist?

Why is the Earth the way it is?
Why is the universe the way it is?

Why is the universe built in a way
that life can exist at all?

At the root of all these
questions lies a force of nature

that surrounds us, penetrates us
and binds the galaxy together.

The key
to a much deeper understanding

of the universe, and even our
place within it, is gravity.

It was gravity that made our sun
ignite five billion years ago.

Without gravity
there'd be no planets,

no stars,

no galaxies,

nothing.

If we want to know why
the universe is built the way it is,

we need a complete understanding
of this elusive force.

But there's something missing in
our understanding of what gravity is
and how gravity works.

Getting to the bottom of the problem
has vexed scientists
as far back as the Ancient Greeks.

But in the late 1600s,
in a small village in Lincolnshire,

the question of gravity was
tackled head on by one of
the granddaddies of modern physics.

This is the home
of Sir Isaac Newton.

Film about gravity - apple.

It's a cliche but
the story goes that it was in
this orchard that Newton was sat,

thinking about the universe, and
an apple fell on Newton's head, and
got him thinking about what it is

that makes the apple fall,
what force pulls the apple
towards the ground?

Newton suggested the apple falls
because of a force of attraction

that naturally exists
between the apple and the Earth.

It's this force
that we know as gravity.

But Newton's real genius was
not to just stop with the apple
but to ask the question,

is the same force that
causes the apple to fall
here on Earth also responsible

for the movement of much bigger
things out there in the cosmos?

Newton believed that gravity
is a force that acts
throughout the entire universe.

In 1686, he finally managed
to break it down

into one single
mathematical equation.

Newton's understanding of
gravity is actually
incredibly simple - that the force

between two objects depends on only
two things, the mass of the objects
and the distance they are apart.

So, the more massive the objects,
the stronger the force,

and, the further the objects
are apart, the weaker the force.

See, it's easy to show actually.

Got a pen?

So this is Newton's law of
gravitation.

The force is equal to the masses
of the two objects,

divided by the square of
the distance apart of the objects.

And then there's Newton's
gravitational constant, that just

sets the scale - it tells you
the overall strength of gravity.

With one beautiful bit of maths,
Newton had figured out gravity,

but not just here on Earth.

The Moon seemed to orbit the Earth
exactly as he predicted,

as did the planets
orbiting around the sun.

Newton believed we live in
a universe in which ultimately

the movement of everything
can be predicted.

Newton's universal law of
gravitation is one of the most
important turning points in physics,

and that's because
it really is universal.

It allows you to predict
not only how things move under the
influence of gravity here on Earth

but how the stars and planets
and even galaxies move,
all the way across the universe.

ARCHIVE: Ignition sequence start.

Nearly 300 years after
the falling apple...

..it was Newton's ability to predict
how the Moon orbits the Earth

that allowed us
to take a giant leap.

That's one small step for man,

one giant leap for mankind.

Newton's law of gravity
was crucial in allowing us

to navigate from the Earth
to the Moon.

But we now know
Newton isn't entirely correct.

I've come to El Paso in Texas,
right on the Mexican border.

I'm here to discover
what's wrong with Newton.

Where are the keys?

Now we're all ready and now you're
stopping us. Because it's funny!

We're heading off across America,
to try and solve
the mystery of gravity.

I think the most exciting thing
that we'd ever done, as the human
race, is to land on the Moon.

It happened just in my lifetime
I was just over one year old when
Armstrong and Aldrin touched down.

So I don't remember it, but what
I remember is growing up with it.

Back in '69, Neil and Buzz
left more than footprints behind.

They offloaded a special set of
mirrors that could be used to test
Newton's theory of gravity.

Those mirrors have played an
important role

here at one of the last surviving
outposts of the Apollo
space mission.

This is the McDonald Observatory,
four hours' drive from El Paso.

We've arranged to meet up with
veteran Apollo scientist
Peter Shelus.

This is one of the photographs
which shows this reflector package.

This is a set of mirrors
which are very specially constructed

so any incoming ray of light
gets reflected exactly back.

The reflector on the Moon is really
only about 18 inches square,

not very much larger
than this photograph.

You can see some of the footprints.

You can see a sandwich bag
left on the surface - I don't think
that was anybody's lunch!

The mirrors left on the Moon
allow Peter to make
a very accurate measurement.

Using a telescope with a built-in
laser, Peter can precisely measure

the distance from the Earth
to the Moon.

We orient the telescope
so that it is facing the Moon.

The laser light,
coming out of the telescope,
then goes directly up to the Moon.

It can be reflected
by the reflector

and it then comes right back through
the tube again,

makes its way through the optics
and we sense it inside the building.

OK, there it is.

Look at that.

There's a really big crater,
you can see the shadow in there.

'Timing how long it takes the laser
beam to go out and bounce back,

'Peter can precisely calculate
the distance to the Moon.

'But trying to hit that tiny mirror,
so far away,

'requires very careful alignment
and a bit of perseverance.'

We may send out
a thousand million billion photons,

whereas coming back...coming back
into the telescope might be ten.

Ten! Or five, or none!

So it is still a very hard experiment
because everything has to work
just right.

How accurately can you make
that measurement, off Neil and
Buzz's reflector and back again?

One to three centimetres.
Over a quarter of a million miles.

Over a quarter of a million miles
out, quarter of a million miles back.

By taking accurate measurements

of the distance between the Earth
and the Moon,

day after day, year after year,
for nearly four decades,

an incredibly precise map of
the Moon's orbit has been produced.

But the results have
thrown up something very odd.

The actual orbit of the Moon
is different to that
predicted by Newton.

It turns out that simple
Newton's laws of gravity

really don't answer
all of the questions.

For the data that existed,
it was good.

Newton really had a good formula.

But, as we get
better and better data, we find that that's not exactly right.

If you use Newton's law of gravity
to predict where the Moon should be,

then the Moon is in the wrong place.

Peter's results disagree with
Newton's by about ten metres.

That may not sound much,
but it means Newton got it wrong.

You've got to
explain your observations.

And Newton's gravitational theory
just doesn't do it any more.

The observations are so accurate
that we need something else.

This is an amazing result.

We've relied on Newton for
300 years -

his equations certainly
appear to work really well.

Yet it seems that there's more
to gravity than Newton realised.

Newton's understanding of
gravity was good enough
to allow us to fly from the Earth

to the Moon, to cross a quarter
of a million miles of space

to land on the Moon
and then fly all the way back again.

But it's kind of got to make you
laugh to think that you can go
all the way to the Moon and back

using something that's
ultimately just an approximation.

To find out what on Earth
is wrong with gravity,
we need to go beyond Newton.

The problem lies not so much in what
he understood but in what he failed
to address altogether.

# Gravity

# Is working against me... #

There's a problem with Newton's
theory of gravity,

and that's that it just allows us
to predict how things move
under its influence.

It doesn't say anything about why
gravity exists or even how it works.

It just allows you to calculate
things. Newton knew this, of course.

He essentially just said that
it's down to God.

In fact, he said that the most
beautiful system of the sun,
the planets and the comets

could only
proceed under the dominion and
counsel of an intelligent being.

In other words, I'll give you the
tools to calculate how the objects
move around

but don't ask me how
or why that is, that's down to God.

To solve this fundamental flaw,
we've got to take gravity
out of the hands of the divine.

We've got to discover for ourselves
how gravity works.

But our journey has only just begun.

We've still got
a long way ahead of us.

Set out at three o'clock,
we did it by four,
we'd only lost two men.

It's not about giving information
any more, it's about them feeling
the journey.

That's brilliant! Driving across
the desert to do physics!

Our quest has brought us to
Kitt Peak, about 80 kilometres west
of Tucson in southern Arizona.

Since the first telescope was
built here back in the 1950s,

this mountaintop
has witnessed some of the most
important discoveries in cosmology.

Kitt Peak's one of the most
famous observatories in the world.

It's the place where,
about 30 years ago now,

something very strange was observed
about the fabric of the cosmos.

We've come here to see
a little piece of the night sky,
7.8 billion light years from Earth.

That little piece of sky
has given us a glimpse into
the inner workings of gravity.

But outside the weather's not good.

They're not opening
the telescopes tonight.

But here's what they saw
all those years ago.

Astronomers
were looking into the sky to find

distant galaxies,
billions of light years away.

And they found this.

At first sight it looks like
two different galaxies.

In fact, they gave them
different names, 957 and 561.

But when they
looked more closely they found that
they look identical in every way.

It's incredibly strange. It's almost
like there are two twin galaxies,
but actually they found that the light
was absolutely identical from each one and
they are same distance apart.

The interpretation is, this is
a picture of one single galaxy.

This certainly
confused the astronomers,

but they soon realised that the
cause of this strange cosmic mirage

had been predicted
nearly a hundred years ago.

There's one man who, for me,
really did think outside the box.

He was the first
celebrity scientist,

hailed by many as the greatest
physicist of all time.

At the turn of the 20th century
it was Albert Einstein

who opened our minds to a completely
new way of looking at the universe.

Einstein's universe is
made of something called space time.

Now, space is what we see
around us - it's got
length and breadth and height.

And time...well, it just
ticks along.

But in Einstein's universe they're
woven together into a fabric.

Space and time are not separate,
they're one and the same thing.

And that fabric
is called spacetime.

This strange idea of spacetime
is certainly radical.

In one sweeping action,
Einstein's theory of relativity

completely changed
our picture of the universe.

Newton's universe was
kind of a stage, an arena
in which everything happens.

It was like a box, exactly as
you'd imagine it, and the stars

and the planets and us are just
going about our business
inside the box.

Now, Einstein's genius was to
realise that you don't need a box,
there's just spacetime.

And everything that happens in
the universe affects the spacetime,

and the spacetime affects everything
that happen in the universe.

In Newton's universe
there's just empty space.

The stars and galaxies
have an effect on each other,

but that's it.

Einstein's universe is
completely different,

it has an internal fabric,
the spacetime.

The celestial bodies
are all embedded within this fabric,
and they all interact with it.

In Einstein's universe, the planets,
stars and galaxies actually warp,

bend and distort the spacetime.

It's this interaction of matter
with the fabric of the cosmos

that helps explain
the weird sightings on Kitt Peak.

That image of duplicate galaxies
can be explained by the bending
of spacetime.

What's happening is that light from
a distant galaxy

is passing by a galaxy or even
cluster of galaxies on the way
to the Earth.

Now, in that cluster there could
be millions or tens of billions
of stars,

huge amount of mass,
which bends and curves the space.

So the light from the distant galaxy
curves around the cluster.

And from our perspective on Earth
this bending action

causes us to see multiple images
of the distant galaxy.

This explanation has far
wider-reaching implications

than simply describing strange
astronomical oddities.

It lies at the very heart of
Einstein's understanding of gravity.

Einstein believes that it's this
bending of spacetime that actually
explains gravity's existence.

Einstein didn't see gravity
as Newton did,

as a kind of force of attraction
between two bodies,
a star and planet, for example.

He sees gravity as a result of space
and time, of spacetime, being bent.

Einstein says that our planet
is distorting the spacetime.

And it's this curving of the
fabric of the universe that creates
the effect we feel as gravity.

The bigger the mass,
or the nearer you are to an object,
the more curved

the spacetime becomes, and so the
stronger is the effect of gravity.

It sounds impossible to prove,
yet the fact that spacetime is
distorted by the Earth

is something many of us have to
contend with every day,

whether we know it or not.

Einstein's understanding of gravity
is crucial for the correct working

of one of the most useful
innovations of the 20th century.

SATNAV: Select destination.

It's the gadget that's
revolutionised how we get around.

It's what we've relied on
to navigate across America.

SATNAV: Calculating route.

It's the global positioning system,
or GPS.

Right turn in 4.9 miles.

We're heading to GPS headquarters,
just south of Denver, Colorado,

but we're running a bit late.

'Approaching U-turn.'

What were you using,
a GPS satellite navigation system?

Where were you going?
GPS headquarters.

Did you get there on time?

No, we got lost!

in Colorado Springs.

It's a maximum security
military installation.

base without a runway.

It's the home of the
global positioning system.

Half an hour late and we're quickly
taken under the wing of
Major Bandit Brant.

Gentlemen. Yes, sir.

Well, welcome to the second space
operations squadron, give you a
tour as we walk down through here.

It's from this one room that the
whole GPS network is controlled.

Running the floor today
is Captain Chris Maddocks.

You must have the biggest impact

of any military crew in the world
on ordinary people.

Typically, civilian users
aren't really our first thought,
because I'm a war fighter.

We think bombs on targets,
planes landing safely.

Soldiers not
getting lost in the desert.

But secondary to that, we do
think there are people using
what is it, Sam Sam or Tom Tom?

Tom Tom. Tom Tom. All these users
have the ability to get from point
A to point B because of what we do.

The global positioning system works
by using a fleet of satellites
orbiting the Earth.

It's these satellites
that are ultimately controlled by
the American military.

How many satellites are up there?

We have 31 satellites up in the
constellation. Minimum is
24 satellites.

So, you can afford
to lose seven of them?

Hopefully not. On your watch,
particularly. Hopefully not.

For the controllers of the GPS,
time is everything.

'US naval observatory master clock,

'at the tone, mountain
daylight time, 18 hours, 48 minutes,
five seconds...'

For the
global positioning system to work,

the clocks on board the satellites

have to be exactly synchronised
with time on Earth.

But for the satellites, orbiting
18,000 kilometres above our planet,

Einstein predicts
something very strange.

He predicts that in orbit,

time itself runs at a different
speed to that on the
Earth's surface.

It's incredible for anyone
to suggest that time goes
at a different rate on the ground

than it does in space.

What's the difference?

Well, the difference is gravity,

the closer you are to the Earth,
the stronger the gravitational field

the further you are up into space
the weaker the gravitational field.

What Einstein said was that the
stronger the gravitational field,
the slower time ticks.

The weaker it is,
the faster time ticks.

The link between the speed of time
and the strength of gravity

is all down to Einstein's prediction
that the Earth distorts
the space time.

If you put something heavy in space
like a planet, a star, the Earth,

then that heavy thing bends
the space, it curves the space.

But space and time
are intimately linked.

So, does the Earth also bend time?

Well, yes, it does.

In the reduced gravity
up in orbit,

time really does tick
a bit faster than time on Earth.

To keep everything in sync,

the controllers have to dial-in
a time correction.

Pretest 35. Check this one, SA step
two, go. Step forward, it's a good
order, no windows.

Step 6 updating on the B string
avtech one's come up and comms good.

You have good visibility
and ascension till 21:52,

and good alt viz at Diego,
no open jobs.

You've got to allow for the fact
that time runs at a different rate
on the ground than it does in orbit,

if you don't,
then your GPS system will drift,
not by a few centimetres,

as you might think, but
by ten, 11, 12 kilometres a day.

This morning we got lost.
It didn't work, can you believe that

And then it took us into a field
about a mile away.

Our response to that is
the constellation is healthy

and producing an
accurate navigation signal.

What you mean is you're an idiot!

With that, it was time to leave.

'Calculating route.'

'Approaching U-turn.'

You got it wrong, again!

The fact that GPS operates
in the way it does,

shows that Einstein's idea of
bending space time

is an accurate description of
how gravity works here on Earth.

But Einstein's understanding
of gravity is not complete,

something is missing.

It may hold true for the Earth
and the other planets even for the
movement of galaxies

but Einstein knew
that his theory of gravity
doesn't apply to the whole universe.

It fails to work in the most violent
and turbulent places in the cosmos.

But if we want a complete
picture of the universe

we must know how
gravity behaves everywhere.

We've come to America's Deep South,
not far from New Orleans.

These are the famous
bayou swamplands of Louisiana.

It's out here

that scientists are trying to peer
deep into the darkest and most
brutal corners of the universe.

Louisiana's one of those places
that you always think of as being...

well, laden with
black magic and things,

certainly not a rational
exploration of the universe.

In these
alligator-infested backwoods,

the final piece in the puzzle of
Einstein's universe
is being put to the test.

This place stands at the leading
edge of the exploration of gravity.

Joe Giami is the head man.

Gravity will probably and hopefully
confuse us for a long time

before we figure out
what it really is,

and scientists are happy when
confused and chasing something fun.

Rising out of the swamp
in the shape of a giant L,

this is the Laser Interferometer
Gravitational Wave Observatory

or LIGO, for short.

Any signal we see
is gonna be from something really,
really interesting and cool.

Data from those sources
would be valuable

to learn things about
gravity and it's nature.

This machine was built
as an observatory,

a chance to witness
violent galactic events

beyond anything
we've ever seen before.

One of the things I hope to see
is when you get two stars
called neutron stars.

A neutron star is probably twice
or three times as heavy as the sun,

but compressed into a ball
about ten kilometres across,
so the size of a city.

And there are places where there
can be two of those things

orbiting around each other at about
100 or even 1,000 times a second.

The incredibly dense neutron stars
spin round each other,

churning up the space time.

As they spiral in, going
faster and faster,

Einstein predicts this sort of
violent cosmic event

will create something called
gravitational waves.

But what exactly is
a gravitational wave?

It's not that easy to describe.

If a wave came through this room
it'd...what can I say?

Eh...ripples, yeah.

Space time isn't just
something that's...

you know up there
amongst the stars, it's here.

It's in front of me,
and it's inside me.

So, when I move, I disturb it -
I send out ripples in it.

It's just like if I jump into a
swimming pool and start swimming.

I'll send out ripples
on the surface of the water.

It's the same with space time.

In theory, these waves would cause
space and time to stretch and shrink

as they pass through the universe.

These waves are physical distortions
in our reality.

They really are stretching
and contracting the space
and the time that we're in.

But trying to see these
gravitational waves

using the LIGO machine
is proving very difficult.

Gravity waves cause links to
change in one direction
differently than the other direction.

If I were very stretchy,

and a gravitational wave
was going through me,

I would get shorter one way,
and longer the other way.

The machine works by
using a laser beam

to measure the distance between
two sets of mirrors

suspended at the ends of
the two 4km long tubes.

From here you can see
all the key components.

Running off to the right there and
also running down under our feet

are tubes that carry
the light to the end stations.

There's a mirror here and
one 4km that way.

When the gravity
wave comes through the distance
between those mirrors changes.

They're basically just
fancy rulers. That's right.

But even after five years
in continuous operation,

the team hasn't been able to observe
any violent gravitational hotspots.

This is because they still
haven't detected Einstein's
elusive gravitational waves.

This is one piece of nature we
haven't really observed right yet,

to see gravitational waves,
whether they really affect things
here the way we think they do.

We don't know where the sources
are that we're looking for,

so we have to look farther and
farther out until we catch one.

In the most extreme
places in the universe,

Einstein is still on dodgy ground.

As we travel deeper into
space and time

we're beginning to realise that
Einstein's universe may unravel.

But to know the cosmos, we need to
know how gravity works everywhere.

In the most sinister
of cosmic phenomena,

in the dark heart of a black hole,

Einstein has no answers.

And his idea of gravity
completely fails

in the most violent
event in history.

At the Big Bang,
the origin of everything,

the universe was incredibly hot,

incredibly dense and
incredibly small.

All matter was condensed into a
space smaller than a single atom.

And here lies the problem.

Much as he tried,

Einstein never managed to answer the
question of how gravity works

when things get very small.

Einstein gave us a beautiful
theory of gravity,

it tells you how planets orbit
around stars,

it tells you how galaxies
orbit around each other,

it tells you
how the universe evolved.

But Einstein himself knew that
there was a problem,

right at the heart of the theory.

Einstein's theory of gravity
doesn't work at all

if you come into the world
of the small,

so the sub-atomic particles
that make up my body.

Einstein's theory has
nothing to say at all about gravity

in the realm of the atoms
and molecules

and sub-atomic particles
that make up the world.

This is Einstein's greatest failure.

His calculations just come up
"error".

At the smallest scale,
his whole theory simply falls apart.

But we have to know how gravity
works at the smallest distances

if we want to know
how it all began.

Einstein's theory of relativity
just can't provide the answer.

The maths just doesn't work
on the smallest distance scales.

So the answers probably won't lie up
there in the realm of the galaxies,

but in here - in the world of
the atom, the stuff of matter.

This is the world of
quantum mechanics,

which is what I do for a living.

It's in quantum theory
that we hope to find the answers

that Einstein searched for

to understand how gravity behaved
at the very beginning of time.

If we can figure out how gravity
works at the level of the
smallest sub-atomic particles,

then maybe we can finish what
Newton and Einstein started,

and form a complete picture of
this mysterious force of gravity.

To achieve this goal,

we have to try to recreate
the conditions of the Big Bang
here on Earth,

and peer deep into the heart
of the sub-atomic world.

'This place is Fermilab,
and I used to work here.

It's home to the Tevatron
particle accelerator.

and seeing what comes out.

What we do is we take protons, and
we accelerate them around that way,

and anti-matter protons,
send them around that way,

and they pass by here
50,000 times a second,

very close to the speed of light,

and then we collide them together,
we smash them together.

It's though collisions like these
that the nature of matter
has been revealed.

But the force of gravity still
sits outside what we know.

One of the ways we might
get to the truth about gravity

is to try and fit it
into the beautiful framework we have

that describes the sub-atomic world.

Quantum mechanics predicts
that the force of gravity
should be transmitted by a particle.

We call this particle
the graviton.

If we could just find
these gravitons,

then we might at last arrive
at a quantum theory of gravity,

a universal theory that will
work everywhere in the cosmos.

For eight years,

Greg Landsberg has been using
Fermilab's particle accelerator

to try to create gravitons.

These particles,
though we haven't quite seen them,

so what I'm telling you is...

Haven't quite seen them?!
That's right. It's our hypothesis,

so we don't quite know
if this is true.

on gravitons to see them,

so we have to find some other means.

It's amazing that the way to see
the graviton is by NOT observing it,

by observing it's missing.

To see something that's missing,

Greg is effectively
looking for missing energy.

Typically, when you bash things
together,

the energy of the original particles
should be the same

as the total energy
of all the particles coming out.

But if you were to make a graviton
in that collision,

then our detectors are certainly
not capable of seeing it,

so the graviton will take
energy away from the collision.

Energy will appear to disappear.

So, the old control room.
I haven't been here for years!

So what this picture tells us...
it's called event display.

The height of these bars is how much
energy is released in this collision

in that particular direction.

There's a collision in the middle,
and the stuff's spraying out.

What we're trying to do
is to sum all this energy,

to see if something is missing.

If you look at this display,

you see a lot of energy going
in this direction,

but very little on the other side,
and this yellow bar,

in fact, represents the fraction
of energy which is missing.

So if you see that, that means that
something escaped. That's right.

If gravitons ARE created,

Greg believes the reason
why they would disappear

is because they vanish into a place
beyond our reality,

into some sort of extra dimension.

Now, we're all familiar with
the three dimensions of our world,

you know, there's up and down and
north and south and east and west.

But what scientists like Greg
are proposing

is that there can be extra hidden,
unseen dimensions.

It sounds ridiculous,
and it IS impossible to picture,

but theoretically, it's possible,

and it's also possible that
gravitons, the particles of gravity,

can spend most of their time
in those extra dimensions.

If gravitons really are created,

and they escape in these extra
dimensions, you would never see them.

So although it might sound like a
very odd hypothesis and odd concept,

really, nothing prevents us
of thinking in this direction,

especially if we can
solve these mysteries.

The graviton may really be
the final piece in the puzzle.

Newton could predict
the effects of gravity.

Einstein worked out why it exists.

But by finding a graviton, we might
at last truly understand gravity.

Does Greg stand any chance
of finding his graviton?

You know, it's still just possible.

When this machine started up,
it was very possible,

but it seems now that probably the
Tevatron is just too small to do it.

So we're gonna all move,
I mean myself, Greg,

and pretty much
everyone that works here,

certainly in a couple of years,

we're gonna all move to Geneva where
we've built one of these machines,

but a lot bigger,
and then the search will continue.

We now know exactly where we stand

in our quest for a complete
explanation of gravity.

The solution to
a deeper understanding of gravity

will certainly lie in the world
of the small, the quantum world.

It's in the marriage of Einstein's
theory of gravity with the quantum
theories of sub-atomic particles.

But nobody has any idea
just how long this might take.

We could see something,
a particle accelerator, tomorrow,

that shows us the way to our
quantum theory of gravity.

Or some Einstein, some Newton,
some Galileo, some Da Vinci

could just appear on the scene
and simplify everything.

Understanding how gravity works
everywhere in the cosmos,

and crucially,
at the beginning of time,

will bring us ever closer
to a theory of everything.

Knowing gravity will mean
that we can better understand

why the universe
is built the way it is,

and that's surely
the biggest question you can ask.

But the journey that lies ahead
is not going to be easy.

If there are things
that I listen to,

you listen to, that you think,
"Well, I don't understand that",

then you're in good company,
because nobody understands it.

You dig deeper and it gets more
and more complicated,

and you get confused,

and it's tricky,
and it's hard, right, it's hard,

but it's beautiful.

# The laws of gravity
are very, very strict

# And you're just bending them
for your own benefit...#