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

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

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Newton thought it
was the work of God.

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And even Einstein,
Albert Einstein failed to solve it.

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

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

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..to the existence
of life on Earth.

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From strange
distortions in the cosmos

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to the smallest stuff of matter.

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

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But I think that
within my lifetime

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

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

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I'm Brian Cox,

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particle physicist.

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I have one of the best jobs
in the world.

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

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

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

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

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Why do I exist? Why do you exist?

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

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

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

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

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The key
to a much deeper understanding

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

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

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Without gravity
there'd be no planets,

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no stars,

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no galaxies,

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nothing.

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

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we need a complete understanding
of this elusive force.

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

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

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

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

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This is the home
of Sir Isaac Newton.

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Film about gravity - apple.

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

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

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

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Newton suggested the apple falls
because of a force of attraction

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that naturally exists
between the apple and the Earth.

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It's this force
that we know as gravity.

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

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

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

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

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In 1686, he finally managed
to break it down

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into one single
mathematical equation.

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

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

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

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

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See, it's easy to show actually.

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Got a pen?

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So this is Newton's law of
gravitation.

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

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

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

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

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

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but not just here on Earth.

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

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as did the planets
orbiting around the sun.

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Newton believed we live in
a universe in which ultimately

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the movement of everything
can be predicted.

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

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and that's because
it really is universal.

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

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

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ARCHIVE: Ignition sequence start.

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Nearly 300 years after
the falling apple...

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

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that allowed us
to take a giant leap.

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That's one small step for man,

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one giant leap for mankind.

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Newton's law of gravity
was crucial in allowing us

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to navigate from the Earth
to the Moon.

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But we now know
Newton isn't entirely correct.

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

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

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Where are the keys?

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

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

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

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

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

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

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

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Those mirrors have played an
important role

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

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

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

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

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This is a set of mirrors
which are very specially constructed

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so any incoming ray of light
gets reflected exactly back.

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

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not very much larger
than this photograph.

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You can see some of the footprints.

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

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

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

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the distance from the Earth
to the Moon.

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

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

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It can be reflected
by the reflector

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and it then comes right back through
the tube again,

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

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OK, there it is.

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Look at that.

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

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

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'Peter can precisely calculate
the distance to the Moon.

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

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

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We may send out
a thousand million billion photons,

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

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Ten! Or five, or none!

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

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

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

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

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By taking accurate measurements

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of the distance between the Earth
and the Moon,

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

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

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But the results have
thrown up something very odd.

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

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It turns out that simple
Newton's laws of gravity

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really don't answer
all of the questions.

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For the data that existed,
it was good.

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Newton really had a good formula.

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But, as we get
better and better data,

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

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then the Moon is in the wrong place.

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

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

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You've got to
explain your observations.

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

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The observations are so accurate
that we need something else.

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This is an amazing result.

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We've relied on Newton for
300 years -

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his equations certainly
appear to work really well.

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

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

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

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

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

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using something that's
ultimately just an approximation.

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

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

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# Gravity

156
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# Is working against me... #

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

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

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

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

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

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

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

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

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

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

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

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But our journey has only just begun.

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

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

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

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

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

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

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

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

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

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

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

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

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But outside the weather's not good.

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They're not opening
the telescopes tonight.

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00:18:02,733 --> 00:18:05,813
But here's what they saw
all those years ago.

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00:18:05,848 --> 00:18:09,071
Astronomers
were looking into the sky to find

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00:18:09,106 --> 00:18:12,294
distant galaxies,
billions of light years away.

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00:18:12,329 --> 00:18:14,778
And they found this.

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At first sight it looks like
two different galaxies.

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00:18:18,528 --> 00:18:22,139
In fact, they gave them
different names, 957 and 561.

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00:18:22,174 --> 00:18:27,214
But when they
looked more closely they found that
they look identical in every way.

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00:18:27,249 --> 00:18:37,694
It's incredibly strange. It's almost
like there are two twin galaxies,

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00:18:37,729 --> 00:18:41,574
The interpretation is, this is
a picture of one single galaxy.

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00:18:45,733 --> 00:18:49,259
This certainly
confused the astronomers,

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00:18:49,294 --> 00:18:54,014
but they soon realised that the
cause of this strange cosmic mirage

194
00:18:54,049 --> 00:18:57,574
had been predicted
nearly a hundred years ago.

195
00:19:06,334 --> 00:19:10,934
There's one man who, for me,
really did think outside the box.

196
00:19:12,414 --> 00:19:15,459
He was the first
celebrity scientist,

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00:19:15,494 --> 00:19:20,213
hailed by many as the greatest
physicist of all time.

198
00:19:20,248 --> 00:19:24,898
At the turn of the 20th century
it was Albert Einstein

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00:19:24,933 --> 00:19:30,014
who opened our minds to a completely
new way of looking at the universe.

200
00:19:31,094 --> 00:19:35,658
Einstein's universe is
made of something called space time.

201
00:19:35,693 --> 00:19:42,493
Now, space is what we see
around us - it's got
length and breadth and height.

202
00:19:43,534 --> 00:19:47,493
And time...well, it just
ticks along.

203
00:19:48,574 --> 00:19:53,954
But in Einstein's universe they're
woven together into a fabric.

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00:19:53,989 --> 00:19:59,334
Space and time are not separate,
they're one and the same thing.

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00:19:59,369 --> 00:20:02,494
And that fabric
is called spacetime.

206
00:20:07,813 --> 00:20:12,773
This strange idea of spacetime
is certainly radical.

207
00:20:17,093 --> 00:20:21,494
In one sweeping action,
Einstein's theory of relativity

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00:20:21,529 --> 00:20:25,093
completely changed
our picture of the universe.

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00:20:27,934 --> 00:20:35,893
Newton's universe was
kind of a stage, an arena
in which everything happens.

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00:20:35,928 --> 00:20:41,219
It was like a box, exactly as
you'd imagine it, and the stars

211
00:20:41,254 --> 00:20:47,979
and the planets and us are just
going about our business
inside the box.

212
00:20:48,014 --> 00:20:54,494
Now, Einstein's genius was to
realise that you don't need a box,
there's just spacetime.

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00:20:54,529 --> 00:20:58,891
And everything that happens in
the universe affects the spacetime,

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00:20:58,926 --> 00:21:03,254
and the spacetime affects everything
that happen in the universe.

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00:21:07,133 --> 00:21:11,093
In Newton's universe
there's just empty space.

216
00:21:12,694 --> 00:21:17,693
The stars and galaxies
have an effect on each other,

217
00:21:17,728 --> 00:21:19,174
but that's it.

218
00:21:21,493 --> 00:21:25,493
Einstein's universe is
completely different,

219
00:21:25,528 --> 00:21:29,494
it has an internal fabric,
the spacetime.

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00:21:30,574 --> 00:21:37,174
The celestial bodies
are all embedded within this fabric,
and they all interact with it.

221
00:21:39,493 --> 00:21:45,854
In Einstein's universe, the planets,
stars and galaxies actually warp,

222
00:21:45,889 --> 00:21:48,973
bend and distort the spacetime.

223
00:21:51,654 --> 00:21:56,773
It's this interaction of matter
with the fabric of the cosmos

224
00:21:56,808 --> 00:22:00,893
that helps explain
the weird sightings on Kitt Peak.

225
00:22:02,494 --> 00:22:08,134
That image of duplicate galaxies
can be explained by the bending
of spacetime.

226
00:22:09,694 --> 00:22:13,259
What's happening is that light from
a distant galaxy

227
00:22:13,294 --> 00:22:18,254
is passing by a galaxy or even
cluster of galaxies on the way
to the Earth.

228
00:22:23,853 --> 00:22:29,054
Now, in that cluster there could
be millions or tens of billions
of stars,

229
00:22:29,089 --> 00:22:32,854
huge amount of mass,
which bends and curves the space.

230
00:22:37,093 --> 00:22:41,413
So the light from the distant galaxy
curves around the cluster.

231
00:22:43,693 --> 00:22:48,013
And from our perspective on Earth
this bending action

232
00:22:48,048 --> 00:22:52,333
causes us to see multiple images
of the distant galaxy.

233
00:22:57,453 --> 00:23:01,773
This explanation has far
wider-reaching implications

234
00:23:01,808 --> 00:23:06,093
than simply describing strange
astronomical oddities.

235
00:23:08,333 --> 00:23:14,614
It lies at the very heart of
Einstein's understanding of gravity.

236
00:23:16,534 --> 00:23:24,454
Einstein believes that it's this
bending of spacetime that actually
explains gravity's existence.

237
00:23:26,093 --> 00:23:28,818
Einstein didn't see gravity
as Newton did,

238
00:23:28,853 --> 00:23:33,973
as a kind of force of attraction
between two bodies,
a star and planet, for example.

239
00:23:34,008 --> 00:23:39,893
He sees gravity as a result of space
and time, of spacetime, being bent.

240
00:23:43,094 --> 00:23:47,894
Einstein says that our planet
is distorting the spacetime.

241
00:23:50,654 --> 00:23:58,613
And it's this curving of the
fabric of the universe that creates
the effect we feel as gravity.

242
00:23:58,648 --> 00:24:03,694
The bigger the mass,
or the nearer you are to an object,
the more curved

243
00:24:03,729 --> 00:24:08,654
the spacetime becomes, and so the
stronger is the effect of gravity.

244
00:24:10,534 --> 00:24:16,774
It sounds impossible to prove,
yet the fact that spacetime is
distorted by the Earth

245
00:24:16,809 --> 00:24:20,854
is something many of us have to
contend with every day,

246
00:24:20,889 --> 00:24:23,534
whether we know it or not.

247
00:24:27,654 --> 00:24:32,934
Einstein's understanding of gravity
is crucial for the correct working

248
00:24:32,969 --> 00:24:37,094
of one of the most useful
innovations of the 20th century.

249
00:24:37,129 --> 00:24:39,658
SATNAV: Select destination.

250
00:24:39,693 --> 00:24:43,853
It's the gadget that's
revolutionised how we get around.

251
00:24:45,653 --> 00:24:49,013
It's what we've relied on
to navigate across America.

252
00:24:49,048 --> 00:24:50,818
SATNAV: Calculating route.

253
00:24:50,853 --> 00:24:54,693
It's the global positioning system,
or GPS.

254
00:24:55,894 --> 00:24:59,294
Right turn in 4.9 miles.

255
00:25:01,013 --> 00:25:06,773
We're heading to GPS headquarters,
just south of Denver, Colorado,

256
00:25:06,808 --> 00:25:08,973
but we're running a bit late.

257
00:25:09,008 --> 00:25:10,818
'Approaching U-turn.'

258
00:25:10,853 --> 00:25:14,494
What were you using,
a GPS satellite navigation system?

259
00:25:14,529 --> 00:25:16,973
Where were you going?
GPS headquarters.

260
00:25:17,008 --> 00:25:18,614
Did you get there on time?

261
00:25:18,649 --> 00:25:20,213
No, we got lost!

262
00:25:28,574 --> 00:25:32,934
in Colorado Springs.

263
00:25:33,814 --> 00:25:37,694
It's a maximum security
military installation.

264
00:25:39,494 --> 00:25:41,534
base without a runway.

265
00:25:44,214 --> 00:25:47,933
It's the home of the
global positioning system.

266
00:25:52,054 --> 00:25:56,333
Half an hour late and we're quickly
taken under the wing of
Major Bandit Brant.

267
00:25:59,294 --> 00:26:02,379
Gentlemen. Yes, sir.

268
00:26:02,414 --> 00:26:07,774
Well, welcome to the second space
operations squadron, give you a
tour as we walk down through here.

269
00:26:09,374 --> 00:26:14,854
It's from this one room that the
whole GPS network is controlled.

270
00:26:14,889 --> 00:26:19,454
Running the floor today
is Captain Chris Maddocks.

271
00:26:19,489 --> 00:26:21,779
You must have the biggest impact

272
00:26:21,814 --> 00:26:27,219
of any military crew in the world
on ordinary people.

273
00:26:27,254 --> 00:26:31,813
Typically, civilian users
aren't really our first thought,
because I'm a war fighter.

274
00:26:31,848 --> 00:26:35,414
We think bombs on targets,
planes landing safely.

275
00:26:35,449 --> 00:26:38,418
Soldiers not
getting lost in the desert.

276
00:26:38,453 --> 00:26:44,699
But secondary to that, we do
think there are people using
what is it, Sam Sam or Tom Tom?

277
00:26:44,734 --> 00:26:50,054
Tom Tom. Tom Tom. All these users
have the ability to get from point
A to point B because of what we do.

278
00:26:53,414 --> 00:26:59,494
The global positioning system works
by using a fleet of satellites
orbiting the Earth.

279
00:27:01,093 --> 00:27:05,813
It's these satellites
that are ultimately controlled by
the American military.

280
00:27:06,854 --> 00:27:08,618
How many satellites are up there?

281
00:27:08,653 --> 00:27:13,013
We have 31 satellites up in the
constellation. Minimum is
24 satellites.

282
00:27:13,048 --> 00:27:14,978
So, you can afford
to lose seven of them?

283
00:27:15,013 --> 00:27:18,614
Hopefully not. On your watch,
particularly. Hopefully not.

284
00:27:21,254 --> 00:27:25,413
For the controllers of the GPS,
time is everything.

285
00:27:25,448 --> 00:27:28,818
'US naval observatory master clock,

286
00:27:28,853 --> 00:27:35,494
'at the tone, mountain
daylight time, 18 hours, 48 minutes,
five seconds...'

287
00:27:35,529 --> 00:27:40,173
For the
global positioning system to work,

288
00:27:40,208 --> 00:27:42,219
the clocks on board the satellites

289
00:27:42,254 --> 00:27:46,454
have to be exactly synchronised
with time on Earth.

290
00:27:53,093 --> 00:27:58,693
But for the satellites, orbiting
18,000 kilometres above our planet,

291
00:27:58,728 --> 00:28:02,774
Einstein predicts
something very strange.

292
00:28:04,373 --> 00:28:06,659
He predicts that in orbit,

293
00:28:06,694 --> 00:28:11,653
time itself runs at a different
speed to that on the
Earth's surface.

294
00:28:14,774 --> 00:28:19,894
It's incredible for anyone
to suggest that time goes
at a different rate on the ground

295
00:28:19,929 --> 00:28:21,431
than it does in space.

296
00:28:21,466 --> 00:28:22,899
What's the difference?

297
00:28:22,934 --> 00:28:24,819
Well, the difference is gravity,

298
00:28:24,854 --> 00:28:28,913
the closer you are to the Earth,
the stronger the gravitational field

299
00:28:28,948 --> 00:28:32,938
the further you are up into space
the weaker the gravitational field.

300
00:28:32,973 --> 00:28:38,413
What Einstein said was that the
stronger the gravitational field,
the slower time ticks.

301
00:28:38,448 --> 00:28:41,213
The weaker it is,
the faster time ticks.

302
00:28:46,174 --> 00:28:50,898
The link between the speed of time
and the strength of gravity

303
00:28:50,933 --> 00:28:56,773
is all down to Einstein's prediction
that the Earth distorts
the space time.

304
00:28:58,253 --> 00:29:02,974
If you put something heavy in space
like a planet, a star, the Earth,

305
00:29:03,009 --> 00:29:07,253
then that heavy thing bends
the space, it curves the space.

306
00:29:07,288 --> 00:29:09,773
But space and time
are intimately linked.

307
00:29:09,808 --> 00:29:13,013
So, does the Earth also bend time?

308
00:29:13,048 --> 00:29:14,974
Well, yes, it does.

309
00:29:17,813 --> 00:29:20,499
In the reduced gravity
up in orbit,

310
00:29:20,534 --> 00:29:25,853
time really does tick
a bit faster than time on Earth.

311
00:29:28,733 --> 00:29:30,818
To keep everything in sync,

312
00:29:30,853 --> 00:29:34,978
the controllers have to dial-in
a time correction.

313
00:29:35,013 --> 00:29:39,493
Pretest 35. Check this one, SA step
two, go. Step forward, it's a good
order, no windows.

314
00:29:39,528 --> 00:29:43,253
Step 6 updating on the B string
avtech one's come up and comms good.

315
00:29:43,288 --> 00:29:46,853
You have good visibility
and ascension till 21:52,

316
00:29:46,888 --> 00:29:49,534
and good alt viz at Diego,
no open jobs.

317
00:29:50,774 --> 00:29:55,974
You've got to allow for the fact
that time runs at a different rate
on the ground than it does in orbit,

318
00:29:56,009 --> 00:30:00,613
if you don't,
then your GPS system will drift,
not by a few centimetres,

319
00:30:00,648 --> 00:30:06,053
as you might think, but
by ten, 11, 12 kilometres a day.

320
00:30:07,294 --> 00:30:11,734
This morning we got lost.
It didn't work, can you believe that

321
00:30:11,769 --> 00:30:14,451
And then it took us into a field
about a mile away.

322
00:30:14,486 --> 00:30:17,133
Our response to that is
the constellation is healthy

323
00:30:17,168 --> 00:30:20,134
and producing an
accurate navigation signal.

324
00:30:20,169 --> 00:30:21,854
What you mean is you're an idiot!

325
00:30:24,734 --> 00:30:26,414
With that, it was time to leave.

326
00:30:26,449 --> 00:30:29,613
'Calculating route.'

327
00:30:32,134 --> 00:30:33,454
'Approaching U-turn.'

328
00:30:33,489 --> 00:30:34,774
You got it wrong, again!

329
00:30:46,253 --> 00:30:49,773
The fact that GPS operates
in the way it does,

330
00:30:49,808 --> 00:30:53,258
shows that Einstein's idea of
bending space time

331
00:30:53,293 --> 00:30:58,853
is an accurate description of
how gravity works here on Earth.

332
00:30:58,888 --> 00:31:04,054
But Einstein's understanding
of gravity is not complete,

333
00:31:04,089 --> 00:31:06,413
something is missing.

334
00:31:08,734 --> 00:31:14,933
It may hold true for the Earth
and the other planets even for the
movement of galaxies

335
00:31:14,968 --> 00:31:21,253
but Einstein knew
that his theory of gravity
doesn't apply to the whole universe.

336
00:31:24,934 --> 00:31:29,773
It fails to work in the most violent
and turbulent places in the cosmos.

337
00:31:35,414 --> 00:31:38,893
But if we want a complete
picture of the universe

338
00:31:38,928 --> 00:31:42,134
we must know how
gravity behaves everywhere.

339
00:31:45,933 --> 00:31:49,534
We've come to America's Deep South,
not far from New Orleans.

340
00:31:51,333 --> 00:31:54,093
These are the famous
bayou swamplands of Louisiana.

341
00:31:55,414 --> 00:31:57,179
It's out here

342
00:31:57,214 --> 00:32:04,094
that scientists are trying to peer
deep into the darkest and most
brutal corners of the universe.

343
00:32:05,933 --> 00:32:09,933
Louisiana's one of those places
that you always think of as being...

344
00:32:09,968 --> 00:32:13,499
well, laden with
black magic and things,

345
00:32:13,534 --> 00:32:17,213
certainly not a rational
exploration of the universe.

346
00:32:19,133 --> 00:32:22,259
In these
alligator-infested backwoods,

347
00:32:22,294 --> 00:32:27,174
the final piece in the puzzle of
Einstein's universe
is being put to the test.

348
00:32:28,774 --> 00:32:33,694
This place stands at the leading
edge of the exploration of gravity.

349
00:32:36,293 --> 00:32:38,813
Joe Giami is the head man.

350
00:32:39,934 --> 00:32:43,373
Gravity will probably and hopefully
confuse us for a long time

351
00:32:43,408 --> 00:32:45,459
before we figure out
what it really is,

352
00:32:45,494 --> 00:32:49,133
and scientists are happy when
confused and chasing something fun.

353
00:32:52,094 --> 00:32:55,658
Rising out of the swamp
in the shape of a giant L,

354
00:32:55,693 --> 00:33:00,694
this is the Laser Interferometer
Gravitational Wave Observatory

355
00:33:00,729 --> 00:33:03,498
or LIGO, for short.

356
00:33:03,533 --> 00:33:08,134
Any signal we see
is gonna be from something really,
really interesting and cool.

357
00:33:08,169 --> 00:33:10,578
Data from those sources
would be valuable

358
00:33:10,613 --> 00:33:13,013
to learn things about
gravity and it's nature.

359
00:33:15,333 --> 00:33:18,733
This machine was built
as an observatory,

360
00:33:18,768 --> 00:33:21,851
a chance to witness
violent galactic events

361
00:33:21,886 --> 00:33:24,934
beyond anything
we've ever seen before.

362
00:33:27,333 --> 00:33:32,734
One of the things I hope to see
is when you get two stars
called neutron stars.

363
00:33:32,769 --> 00:33:37,578
A neutron star is probably twice
or three times as heavy as the sun,

364
00:33:37,613 --> 00:33:42,654
but compressed into a ball
about ten kilometres across,
so the size of a city.

365
00:33:42,689 --> 00:33:45,939
And there are places where there
can be two of those things

366
00:33:45,974 --> 00:33:49,854
orbiting around each other at about
100 or even 1,000 times a second.

367
00:33:53,693 --> 00:33:57,053
The incredibly dense neutron stars
spin round each other,

368
00:33:57,088 --> 00:33:59,333
churning up the space time.

369
00:34:00,934 --> 00:34:04,418
As they spiral in, going
faster and faster,

370
00:34:04,453 --> 00:34:08,753
Einstein predicts this sort of
violent cosmic event

371
00:34:08,788 --> 00:34:13,054
will create something called
gravitational waves.

372
00:34:14,893 --> 00:34:18,573
But what exactly is
a gravitational wave?

373
00:34:18,608 --> 00:34:21,858
It's not that easy to describe.

374
00:34:21,893 --> 00:34:26,774
If a wave came through this room
it'd...what can I say?

375
00:34:26,809 --> 00:34:30,134
Eh...ripples, yeah.

376
00:34:34,893 --> 00:34:37,699
Space time isn't just
something that's...

377
00:34:37,734 --> 00:34:40,694
you know up there
amongst the stars, it's here.

378
00:34:40,729 --> 00:34:44,458
It's in front of me,
and it's inside me.

379
00:34:44,493 --> 00:34:49,098
So, when I move, I disturb it -
I send out ripples in it.

380
00:34:49,133 --> 00:34:52,534
It's just like if I jump into a
swimming pool and start swimming.

381
00:34:52,569 --> 00:34:55,253
I'll send out ripples
on the surface of the water.

382
00:34:55,288 --> 00:34:56,933
It's the same with space time.

383
00:34:59,533 --> 00:35:06,454
In theory, these waves would cause
space and time to stretch and shrink

384
00:35:06,489 --> 00:35:08,573
as they pass through the universe.

385
00:35:10,893 --> 00:35:17,019
These waves are physical distortions
in our reality.

386
00:35:17,054 --> 00:35:23,254
They really are stretching
and contracting the space
and the time that we're in.

387
00:35:31,294 --> 00:35:34,858
But trying to see these
gravitational waves

388
00:35:34,893 --> 00:35:38,978
using the LIGO machine
is proving very difficult.

389
00:35:39,013 --> 00:35:44,454
Gravity waves cause links to
change in one direction
differently than the other direction.

390
00:35:44,489 --> 00:35:45,819
If I were very stretchy,

391
00:35:45,854 --> 00:35:47,898
and a gravitational wave
was going through me,

392
00:35:47,933 --> 00:35:50,733
I would get shorter one way,
and longer the other way.

393
00:35:55,934 --> 00:35:58,058
The machine works by
using a laser beam

394
00:35:58,093 --> 00:36:02,073
to measure the distance between
two sets of mirrors

395
00:36:02,108 --> 00:36:06,054
suspended at the ends of
the two 4km long tubes.

396
00:36:07,294 --> 00:36:09,859
From here you can see
all the key components.

397
00:36:09,894 --> 00:36:13,334
Running off to the right there and
also running down under our feet

398
00:36:13,369 --> 00:36:16,294
are tubes that carry
the light to the end stations.

399
00:36:20,093 --> 00:36:22,299
There's a mirror here and
one 4km that way.

400
00:36:22,334 --> 00:36:26,733
When the gravity
wave comes through the distance
between those mirrors changes.

401
00:36:26,768 --> 00:36:29,813
They're basically just
fancy rulers. That's right.

402
00:36:32,854 --> 00:36:36,258
But even after five years
in continuous operation,

403
00:36:36,293 --> 00:36:41,613
the team hasn't been able to observe
any violent gravitational hotspots.

404
00:36:43,853 --> 00:36:50,014
This is because they still
haven't detected Einstein's
elusive gravitational waves.

405
00:36:50,049 --> 00:36:53,578
This is one piece of nature we
haven't really observed right yet,

406
00:36:53,613 --> 00:36:58,693
to see gravitational waves,
whether they really affect things
here the way we think they do.

407
00:36:58,728 --> 00:37:01,830
We don't know where the sources
are that we're looking for,

408
00:37:01,865 --> 00:37:04,933
so we have to look farther and
farther out until we catch one.

409
00:37:07,974 --> 00:37:11,014
In the most extreme
places in the universe,

410
00:37:11,049 --> 00:37:14,253
Einstein is still on dodgy ground.

411
00:37:19,894 --> 00:37:22,698
As we travel deeper into
space and time

412
00:37:22,733 --> 00:37:27,413
we're beginning to realise that
Einstein's universe may unravel.

413
00:37:30,293 --> 00:37:36,214
But to know the cosmos, we need to
know how gravity works everywhere.

414
00:37:40,173 --> 00:37:43,493
In the most sinister
of cosmic phenomena,

415
00:37:43,528 --> 00:37:46,093
in the dark heart of a black hole,

416
00:37:46,128 --> 00:37:48,973
Einstein has no answers.

417
00:37:51,574 --> 00:37:54,733
And his idea of gravity
completely fails

418
00:37:54,768 --> 00:37:57,893
in the most violent
event in history.

419
00:38:04,813 --> 00:38:07,414
At the Big Bang,
the origin of everything,

420
00:38:07,449 --> 00:38:10,299
the universe was incredibly hot,

421
00:38:10,334 --> 00:38:14,573
incredibly dense and
incredibly small.

422
00:38:19,853 --> 00:38:24,613
All matter was condensed into a
space smaller than a single atom.

423
00:38:25,733 --> 00:38:28,493
And here lies the problem.

424
00:38:31,174 --> 00:38:32,298
Much as he tried,

425
00:38:32,333 --> 00:38:37,254
Einstein never managed to answer the
question of how gravity works

426
00:38:37,289 --> 00:38:40,134
when things get very small.

427
00:38:43,294 --> 00:38:45,874
Einstein gave us a beautiful
theory of gravity,

428
00:38:45,909 --> 00:38:48,419
it tells you how planets orbit
around stars,

429
00:38:48,454 --> 00:38:51,213
it tells you how galaxies
orbit around each other,

430
00:38:51,248 --> 00:38:53,019
it tells you
how the universe evolved.

431
00:38:53,054 --> 00:38:55,414
But Einstein himself knew that
there was a problem,

432
00:38:55,449 --> 00:38:57,218
right at the heart of the theory.

433
00:38:57,253 --> 00:38:59,894
Einstein's theory of gravity
doesn't work at all

434
00:38:59,929 --> 00:39:02,778
if you come into the world
of the small,

435
00:39:02,813 --> 00:39:06,019
so the sub-atomic particles
that make up my body.

436
00:39:06,054 --> 00:39:09,894
Einstein's theory has
nothing to say at all about gravity

437
00:39:09,929 --> 00:39:12,978
in the realm of the atoms
and molecules

438
00:39:13,013 --> 00:39:16,373
and sub-atomic particles
that make up the world.

439
00:39:19,373 --> 00:39:23,613
This is Einstein's greatest failure.

440
00:39:23,648 --> 00:39:27,819
His calculations just come up
"error".

441
00:39:27,854 --> 00:39:34,413
At the smallest scale,
his whole theory simply falls apart.

442
00:39:38,173 --> 00:39:42,213
But we have to know how gravity
works at the smallest distances

443
00:39:42,248 --> 00:39:45,773
if we want to know
how it all began.

444
00:39:49,013 --> 00:39:53,053
Einstein's theory of relativity
just can't provide the answer.

445
00:39:53,088 --> 00:39:57,058
The maths just doesn't work
on the smallest distance scales.

446
00:39:57,093 --> 00:40:02,054
So the answers probably won't lie up
there in the realm of the galaxies,

447
00:40:02,089 --> 00:40:07,454
but in here - in the world of
the atom, the stuff of matter.

448
00:40:10,454 --> 00:40:13,854
This is the world of
quantum mechanics,

449
00:40:13,889 --> 00:40:16,339
which is what I do for a living.

450
00:40:16,374 --> 00:40:20,854
It's in quantum theory
that we hope to find the answers

451
00:40:20,889 --> 00:40:24,179
that Einstein searched for

452
00:40:24,214 --> 00:40:30,939
to understand how gravity behaved
at the very beginning of time.

453
00:40:30,974 --> 00:40:36,493
If we can figure out how gravity
works at the level of the
smallest sub-atomic particles,

454
00:40:36,528 --> 00:40:40,379
then maybe we can finish what
Newton and Einstein started,

455
00:40:40,414 --> 00:40:44,693
and form a complete picture of
this mysterious force of gravity.

456
00:40:48,773 --> 00:40:50,139
To achieve this goal,

457
00:40:50,174 --> 00:40:55,253
we have to try to recreate
the conditions of the Big Bang
here on Earth,

458
00:40:55,288 --> 00:41:00,250
and peer deep into the heart
of the sub-atomic world.

459
00:41:00,285 --> 00:41:05,213
'This place is Fermilab,
and I used to work here.

460
00:41:06,854 --> 00:41:10,694
It's home to the Tevatron
particle accelerator.

461
00:41:16,853 --> 00:41:19,739
and seeing what comes out.

462
00:41:19,774 --> 00:41:23,814
What we do is we take protons, and
we accelerate them around that way,

463
00:41:23,849 --> 00:41:26,974
and anti-matter protons,
send them around that way,

464
00:41:27,009 --> 00:41:30,293
and they pass by here
50,000 times a second,

465
00:41:30,328 --> 00:41:32,738
very close to the speed of light,

466
00:41:32,773 --> 00:41:35,813
and then we collide them together,
we smash them together.

467
00:41:37,974 --> 00:41:43,133
It's though collisions like these
that the nature of matter
has been revealed.

468
00:41:46,174 --> 00:41:50,753
But the force of gravity still
sits outside what we know.

469
00:41:50,788 --> 00:41:54,840
One of the ways we might
get to the truth about gravity

470
00:41:54,875 --> 00:41:58,893
is to try and fit it
into the beautiful framework we have

471
00:41:58,928 --> 00:42:00,374
that describes the sub-atomic world.

472
00:42:05,773 --> 00:42:12,814
Quantum mechanics predicts
that the force of gravity
should be transmitted by a particle.

473
00:42:15,934 --> 00:42:20,314
We call this particle
the graviton.

474
00:42:20,349 --> 00:42:24,659
If we could just find
these gravitons,

475
00:42:24,694 --> 00:42:30,013
then we might at last arrive
at a quantum theory of gravity,

476
00:42:30,048 --> 00:42:35,333
a universal theory that will
work everywhere in the cosmos.

477
00:42:40,054 --> 00:42:42,219
For eight years,

478
00:42:42,254 --> 00:42:46,013
Greg Landsberg has been using
Fermilab's particle accelerator

479
00:42:46,048 --> 00:42:51,259
to try to create gravitons.

480
00:42:51,294 --> 00:42:54,053
These particles,
though we haven't quite seen them,

481
00:42:54,088 --> 00:42:56,138
so what I'm telling you is...

482
00:42:56,173 --> 00:42:58,733
Haven't quite seen them?!
That's right. It's our hypothesis,

483
00:42:58,768 --> 00:43:01,294
so we don't quite know
if this is true.

484
00:43:01,329 --> 00:43:04,938
on gravitons to see them,

485
00:43:04,973 --> 00:43:07,499
so we have to find some other means.

486
00:43:07,534 --> 00:43:12,574
It's amazing that the way to see
the graviton is by NOT observing it,

487
00:43:12,609 --> 00:43:14,374
by observing it's missing.

488
00:43:16,733 --> 00:43:19,618
To see something that's missing,

489
00:43:19,653 --> 00:43:27,013
Greg is effectively
looking for missing energy.

490
00:43:27,048 --> 00:43:29,498
Typically, when you bash things
together,

491
00:43:29,533 --> 00:43:33,673
the energy of the original particles
should be the same

492
00:43:33,708 --> 00:43:37,813
as the total energy
of all the particles coming out.

493
00:43:39,213 --> 00:43:41,418
But if you were to make a graviton
in that collision,

494
00:43:41,453 --> 00:43:45,233
then our detectors are certainly
not capable of seeing it,

495
00:43:45,268 --> 00:43:49,013
so the graviton will take
energy away from the collision.

496
00:43:49,048 --> 00:43:53,333
Energy will appear to disappear.

497
00:43:56,413 --> 00:43:59,573
So, the old control room.
I haven't been here for years!

498
00:44:01,814 --> 00:44:06,538
So what this picture tells us...
it's called event display.

499
00:44:06,573 --> 00:44:10,814
The height of these bars is how much
energy is released in this collision

500
00:44:10,849 --> 00:44:12,059
in that particular direction.

501
00:44:12,094 --> 00:44:14,374
There's a collision in the middle,
and the stuff's spraying out.

502
00:44:14,409 --> 00:44:17,494
What we're trying to do
is to sum all this energy,

503
00:44:17,529 --> 00:44:19,391
to see if something is missing.

504
00:44:19,426 --> 00:44:21,218
If you look at this display,

505
00:44:21,253 --> 00:44:24,539
you see a lot of energy going
in this direction,

506
00:44:24,574 --> 00:44:28,179
but very little on the other side,
and this yellow bar,

507
00:44:28,214 --> 00:44:31,498
in fact, represents the fraction
of energy which is missing.

508
00:44:31,533 --> 00:44:35,974
So if you see that, that means that
something escaped. That's right.

509
00:44:40,294 --> 00:44:42,899
If gravitons ARE created,

510
00:44:42,934 --> 00:44:46,858
Greg believes the reason
why they would disappear

511
00:44:46,893 --> 00:44:51,694
is because they vanish into a place
beyond our reality,

512
00:44:51,729 --> 00:44:55,054
into some sort of extra dimension.

513
00:44:56,693 --> 00:45:00,339
Now, we're all familiar with
the three dimensions of our world,

514
00:45:00,374 --> 00:45:04,214
you know, there's up and down and
north and south and east and west.

515
00:45:04,249 --> 00:45:07,098
But what scientists like Greg
are proposing

516
00:45:07,133 --> 00:45:11,153
is that there can be extra hidden,
unseen dimensions.

517
00:45:11,188 --> 00:45:15,174
It sounds ridiculous,
and it IS impossible to picture,

518
00:45:15,209 --> 00:45:17,658
but theoretically, it's possible,

519
00:45:17,693 --> 00:45:21,214
and it's also possible that
gravitons, the particles of gravity,

520
00:45:21,249 --> 00:45:25,734
can spend most of their time
in those extra dimensions.

521
00:45:25,769 --> 00:45:27,498
If gravitons really are created,

522
00:45:27,533 --> 00:45:31,853
and they escape in these extra
dimensions, you would never see them.

523
00:45:31,888 --> 00:45:36,173
So although it might sound like a
very odd hypothesis and odd concept,

524
00:45:36,208 --> 00:45:39,533
really, nothing prevents us
of thinking in this direction,

525
00:45:39,568 --> 00:45:42,134
especially if we can
solve these mysteries.

526
00:45:46,133 --> 00:45:50,333
The graviton may really be
the final piece in the puzzle.

527
00:45:52,173 --> 00:45:55,373
Newton could predict
the effects of gravity.

528
00:45:55,408 --> 00:45:59,099
Einstein worked out why it exists.

529
00:45:59,134 --> 00:46:05,974
But by finding a graviton, we might
at last truly understand gravity.

530
00:46:06,009 --> 00:46:09,053
Does Greg stand any chance
of finding his graviton?

531
00:46:09,088 --> 00:46:11,338
You know, it's still just possible.

532
00:46:11,373 --> 00:46:13,858
When this machine started up,
it was very possible,

533
00:46:13,893 --> 00:46:20,374
but it seems now that probably the
Tevatron is just too small to do it.

534
00:46:20,409 --> 00:46:22,871
So we're gonna all move,
I mean myself, Greg,

535
00:46:22,906 --> 00:46:25,334
and pretty much
everyone that works here,

536
00:46:25,369 --> 00:46:27,139
certainly in a couple of years,

537
00:46:27,174 --> 00:46:31,133
we're gonna all move to Geneva where
we've built one of these machines,

538
00:46:31,168 --> 00:46:34,133
but a lot bigger,
and then the search will continue.

539
00:46:40,174 --> 00:46:43,859
We now know exactly where we stand

540
00:46:43,894 --> 00:46:48,533
in our quest for a complete
explanation of gravity.

541
00:46:53,294 --> 00:46:56,859
The solution to
a deeper understanding of gravity

542
00:46:56,894 --> 00:47:01,258
will certainly lie in the world
of the small, the quantum world.

543
00:47:01,293 --> 00:47:08,654
It's in the marriage of Einstein's
theory of gravity with the quantum
theories of sub-atomic particles.

544
00:47:11,294 --> 00:47:16,033
But nobody has any idea
just how long this might take.

545
00:47:16,068 --> 00:47:20,981
We could see something,
a particle accelerator, tomorrow,

546
00:47:21,016 --> 00:47:25,954
that shows us the way to our
quantum theory of gravity.

547
00:47:25,989 --> 00:47:30,681
Or some Einstein, some Newton,
some Galileo, some Da Vinci

548
00:47:30,716 --> 00:47:35,373
could just appear on the scene
and simplify everything.

549
00:47:37,613 --> 00:47:42,093
Understanding how gravity works
everywhere in the cosmos,

550
00:47:42,128 --> 00:47:44,734
and crucially,
at the beginning of time,

551
00:47:46,013 --> 00:47:51,073
will bring us ever closer
to a theory of everything.

552
00:47:51,108 --> 00:47:56,134
Knowing gravity will mean
that we can better understand

553
00:47:56,169 --> 00:48:01,219
why the universe
is built the way it is,

554
00:48:01,254 --> 00:48:06,334
and that's surely
the biggest question you can ask.

555
00:48:07,654 --> 00:48:11,573
But the journey that lies ahead
is not going to be easy.

556
00:48:11,608 --> 00:48:15,338
If there are things
that I listen to,

557
00:48:15,373 --> 00:48:18,753
you listen to, that you think,
"Well, I don't understand that",

558
00:48:18,788 --> 00:48:22,133
then you're in good company,
because nobody understands it.

559
00:48:22,168 --> 00:48:24,893
You dig deeper and it gets more
and more complicated,

560
00:48:24,928 --> 00:48:26,099
and you get confused,

561
00:48:26,134 --> 00:48:28,694
and it's tricky,
and it's hard, right, it's hard,

562
00:48:28,729 --> 00:48:30,734
but it's beautiful.

563
00:48:33,093 --> 00:48:38,859
# The laws of gravity
are very, very strict

564
00:48:38,894 --> 00:48:45,854
# And you're just bending them
for your own benefit...#