Imagine somewhere in our universe an utterly strange world.
A place where time could both speed up and slow down.
From where we could journey into the past, and the future.
Somewhere time could even split in two.
Incredibly, this is no alien world.
It's our world.
And it's all around us.
Now, for the first time,
science is enabling us to see what for thousands of years
has remained hidden.
The true nature of time.
We live in a world governed by time.
From the tiniest of cells to the most distant of stars
our entire universe is subject to the beat of a constant clock.
And because time is everywhere, we think we know it.
We know that it's regular and it moves in one direction.
We know that it's universal and eternal.
And we know that it never ever stands still.
But how can we be so sure?
How much of what we think we know about time is really true?
In this programme
I want to get to the bottom of what time really is.
And in doing so I'll be challenging some of our most cherished beliefs.
As a theoretical physicist
it's this hidden time
that has always fascinated me
throughout most of my professional career.
I'm going to explore the very limits of our universe
in order to uncover just what time really is.
And in the process
I'll be revealing an astonishing secret.
Nothing less than our ultimate destiny.
The future of the universe and the fate of time itself.
Of all our assumptions about time
one of the most obvious is that time is regular.
That a minute will always be a minute.
For everyone, everywhere.
Here in the Swiss Alps
I'm searching for a something that challenges this assumption.
Something that if time was as regular as we think it is,
shouldn't exist at all.
Well, I'm now eleven thousand feet above sea level
and I'm out of breath and actually feeling a little bit dizzy.
Now the bad news is
I till have a ways to go to reach the top of the Alps
because what I'm looking for is something
that becomes more plentiful the higher you go.
And this is what I've come to see.
It's a particle counter
telling me that the air around me is full of tiny particles called muons.
They come from all the way out there.
Muons are short lived particles,
formed when cosmic rays from space collide with the upper atmosphere.
But the big mystery is how they come to be down here on Earth.
Because with a lifespan ofjust two millionths of a second,
muons should only live long enough to travel a few hundred metres.
And yet, here they are, after ajourney of several miles.
Something that shouldn't be possible.
So what exactly is going on?
The answer to this mystery,
the reason why muons can reach us at all
is so extraordinary
that from the moment it was first proposed
it literally rewrote the rule book of time.
Less than a hundred miles from the Alps lies the affluent city of Berne.
In the early 1900s
this was home to a young German physicist
who would change the way we looked at time for ever.
His name was Albert Einstein
and he's been my hero for the past fifty years.
In 1905
in this, his first floor apartment,
Albert Einstein put the finishing touches to his radical new theory.
Special Relativity.
One of five papers published by Einstein in 1905,
Special Relativity
would make us think about time in a completely new way.
Einstein's astonishing claim was that time was not regular at all.
It could beat at different rates.
Time changes depending on relative speed.
Imagine for a minute
that my tram is capable of travelling at phenomenal speed.
Just a fraction less than the speed of light.
According to Special Relativity,
the rate at which time flowed on this speeding tram
would depend on whether you were onboard.
Or looking in from the outside.
So while for me
it would seem as though time was passing perfectly normally.
For me, sitting on the pavement,
assuming I could somehow peer inside the tram,
time would assume a totally different quality.
Looking in from the outside
I'd sense that time onboard the tram was passing much more slowly.
That's because, according to Einstein,
the faster an object moves
the slower its time will run
to someone observing from the sidelines.
In other words, time can vary.
It's all a matter of speed.
And that explains the mystery of how our muons reached the Earth.
Because muons travel near the speed of light relative to the Earth,
their clocks have slowed down.
So much so that they exist long enough to reach the Earth and be detected.
Time for our muons has stretched.
It beats very differently to the way it does for us.
Now the effects of Special Relativity are so small
that they have no impact on our daily lives,
but the fact that they are there at all has changed everything.
Because if time is relative,
if time is flexible,
then our belief in the immutability of time is wrong.
And if we can be wrong about something as basic
and as fundamental as this,
then in what other ways might we be mistaken?
Do either of you play cards?
I play a little poker.
You play poker?
So you can shuffle cards, can you?
- Oh no, no. - No?
- I let someone else shuffle. - So do you shuffle like this?
- Yeah. - Yeah?
- That's called the overhand shuffle. - Okay.
'Cause if you don't shuffle cards that well,
you can try - try this one. This one's pretty good.
It makes a complete mess of the deck of cards.
Some cards go back to face and some of them are like back to back.
Our complete trust in temporal orderis
the reason why we delight
in the obvious impossibility of magic tricks.
Back to face, the face to back.
As I said it makes a total mess.
I'll just show you.
Some of the cards there like face to back
not very good for playing poker or blackjack
but if you press the button here.
Press the button.
Oh... fingers,
they call come out the right way which is rather handy.
- Oh, that's so good. - That's pretty cool, isn't it?
Pretty good.
My job as a magician
is to manipulate people's faith.
Hi, how you doing?
Can I stop you for a moment?
People realise that things can't disappear and reappear.
I'm going to run through the cards and you say stop wherever you like.
If you do yourjob properly
you can make it look as though two things can be in the same place
at the same time.
And to that end essentially
you can make it look as though you're manipulating space and time.
You ever seen magicians use these before?
Yeah, I've seen them.
I'll show you a trick with two of them, okay.
- So can you hold your hand out for me? - Yeah, sure.
A classic way of demonstrating the manipulation of space and time
can be done using the sponge ball trick.
It's a hundred years old, but it's great.
But essentially you take a ball in your own hand
and the spectator holds a ball
and you can do it in such a way
that you can - it looks as though you can manipulate space of time
and it looks as though the ball has disappeared from your hand,
so when the spectator opens their hand suddenly they have two.
That ball has vanished from your hand and it's reappeared in theirs.
But, believe it or not,
this sort of behaviour isn't always an illusion.
Beneath the surface of our on sense world
lies another world
where magical things really do happen.
Where the impossible can be made real.
And where time can perform the most incredible tricks.
That place is inside the atom.
For years
scientists had assumed that in our universe
there was nothing smaller than an atom.
The very word atom in fact comes from the Greek word for indivisible.
Then in 1897,
an Englishman named J. J. Thompson made an astounding discovery,
that inside the atom
there were even smaller particles called electrons.
Thompson's discovery opened the door to the amazing world inside the atom.
A world where everything,
including time,
behaves in a truly alien fashion.
Physicist lan Walmsley
has been studying this microscopic world for almost thirty years.
When we get inside the atom to this world of subatomic particles
the ideas that we have about the way the world
works completely have to change.
We can't think in the same sorts of
come on sense terms that we think of in everyday experience.
In fact, this subatomic universe is so strange
that time becomes chaotic.
A startling discovery that emerged from the study of light.
Light consists of individual particles called photons,
known for their wave-like properties.
Waves have a very interesting sort of phenomenon.
It's called 'interference.'
When two waves come together
they can add together and reinforce one another,
or they can cancel one another out.
And this interference is a ubiquitous property of all waves,
notjust water waves
but also light waves.
But in the early 1900s,
scientists noticed something very odd about these light waves.
Something that proves that time isn't always ordered.
In this reworking of a classic experiment,
once described as 'the most beautiful in physics,'
single photons or particles of light
are fired down a darkened tube towards a camera,
one at a time.
So we have here a very simple apparatus.
It consists of a light bulb at this end
and a camera at the other end that can register the light
and in between
the light encounters a pair of slits etched onto this piece of glass
through which the photons can pass
on their way from the source to the camera.
The purpose of the experiment
is to study the behaviour of photons
as they travel from one end of the tube to the other.
To begin with,
the individual photons are sent through just one of the slits.
Each of these dots
arriving represents a single photon
so most of them are coming along this point,
some of them lie above or below that point,
but the distribution is nice and smooth.
Now the second slit is opened up and the experiment repeated.
Each single photon must still pass through one of the two slits,
so the results should still be the same.
Classical logic would say
that what we would get when we open both slits
is just the sum of these two detection patterns.
But what we actually find is this.
An interference pattern.
Something that should be impossible.
What that implies is that the single photon
is somehow going through both slits at the same time.
It's not making a choice as to go through one or the other,
but is going through both simultaneously.
In other words,
each photon exists notjust in two places,
but also in two times.
So we have this very strange notion
that this single photon can be
in two different places at once. It could be delocalised.
But we can think also of a single photon being in two different times.
So both space and time have become delocalised and fragmented.
On the surface, we feel time is ordered.
But that belies a different reality.
We are totally unaware of the chaos
and unpredictability that lies deep within the atom.
Not surprisingly,
our understanding of time comes from our everyday experience.
And it's for this reason
that we cling to yet another of our assumptions about time.
That it never stands still.
In fact one thing that sets us apart as humans
is the knowledge that time waits for no man.
That time doesn't merely exist but is constantly flowing.
But one discovery proved that this isn't always the case.
TV Doctor Tom Bolton of the University of Toronto
made more than forty observations of Cygnus X One.
In 1971
astronomer Tom Bolton embarked on a project
to observe a mysterious x-ray source called Cygnus X One.
An object assumed to be a distant neutron star.
I started to look at Cygnus X One
because I thought it would be a
good opportunity to determine the mass of a neutron star
and nobody had done that yet.
Cygnus X One,
some eight thousand light years away,
is one half of what's called our binary system.
The binary system is a pair of stars
that are gravitationally bound to each other,
er, just like the Earth is bound to the sun
and they orbit er, about their mutual centre of mass.
By measuring the speed and orbit of X One's binary partner,
Tom was able to work out the mass of his neutron star.
But the figure he arrived at was far,
far bigger than the one he'd been expecting.
That turned out to be about ten solar masses,
with a significant error,
but still way too big to be a neutron star.
So I had to start thinking about
what are the alternatives if it's not a neutron star.
There was only one possibility that fitted the data.
But it was something that few people believed actually existed.
As far as I knew
the only object that would fit that description
and produce x-rays was a black hole.
So I said so.
Tom's discovery caused a sensation.
The first incontrovertible proof
that far from being a figment of people's imagination,
black holes were in fact very real indeed.
Since their discovery twenty-five years ago
we now know that the universe is teeming with them.
But it's how black holes affect time that make them so unusual.
Black holes are so massive
that their gravitational pull approaches infinity.
And according to Einstein's second theory,
that of general relativity,
very intense gravity slows time
in a similar way to moving at very high speed.
But if you were to watch someone fall into a black hole
you'd notice that their time was beginning to slow down.
So much so that at the very centre
where the gravitational pull is infinite,
time would stop altogether.
Time would cease to exist.
That there are places where time can come to a grinding halt
seems frankly incredible.
But that's only because we live in such a uniform corner of the galaxy.
Warmed by a benevolent sun, far from any extremes of gravity.
Beyond our everyday environment, time is very different.
Not only is it irregular, it's also chaotic.
It can even stand still.
But for all its vagaries
there's one thing that time never seems to do.
And that's turn back on itself.
Which, when you think about it, is a little odd.
After all my physical environment offers me enormous freedom.
The thing is the laws of physics don't have any problems
with time running backwards.
So we physicists believe that itjust might be possible
to build a time machine.
The only obstacle we face is one of engineering.
That's because the theoretical blueprint
for our time machine already exists.
A machine that's secret lies deep within our microscopic universe.
At the tiniest sub-atomic level,
the fabric of space and time becomes so unstable
that it starts to behave like a foam.
Its surface alive with tiny bubbles
momentarily popping in and out of existence.
We call this quantum state, 'the space time foam.'
It's thought that contained
within this foam are objects called wormholes.
Tiny passageways between two points in space and time.
The secret to building a time machine
is to stabilise the space time foam long enough
to make one of these wormholes permanent.
And the way we do that
is by subjecting it to enormous amounts of energy.
I'm standing one hundred metres above
what will be, when it's finished,
the world's most powerful particle accelerator.
This machine, scientists hope,
will help to unlock some of the secrets
of the mysterious world of sub-atomic particles,
the building blocks of our universe.
This tunnel is twenty-seven kilometres
in circumference and it houses the accelerator.
Inside this chamber
two beams of sub-atomic particles will be travelling in opposite directions,
boosted to near the speed of light.
As the protons within the beams collide,
they shatter into even smaller particles,
releasing bursts of energy roughly half a million times greater
than those inside a nuclear explosion.
But even the most powerful accelerator on this planet
can't produce enough energy to stabilise a space time foam.
To do that,
our particles would have to be moving even faster
and that would require an accelerator of truly enormous proportions.
So big in fact we would need to build it in space.
Now we know
that if you smash particles together at extremely high velocities,
eventually you create something called a 'quark gluon plasma.'
An extremely hot
high energy cauldron of matter
with a temperature exceeding ten trillion degrees.
By adding even more energy,
blasting the plasma with lasers
we can finally stabilise space time foam
long enough to pluck out a miniscule wormhole.
The next task is to enlarge it
and even that is scientifically possible.
In 1948
a Dutch physicist named Hendrick Casimir
introduced us to a mysterious new force called 'negative energy.'
Complete with anti-gravitational properties.
So far
we can only create minute quantities of this in the laboratory,
but one day
if we can create enough negative energy,
we might be able to increase the size of a wormhole.
And this is how we think our wormhole would look.
Each end a sphere held in place by an electric field
invisibly connecting two points in space and time.
By subjecting one end of the wormhole to a huge gravitational field,
we could bring its clock almost to a stop.
This turns our wormhole into a time machine.
Both ends existing in the same place, but at different times.
Our ability to build such a machine is still some way off.
Butjust knowing that time travel is possible
is enough to turn yet another of our assumptions on its head.
So far we've seen how time,
which appears to be so regular,
can in fact be quite flexible.
We've seen how time can behave in such unpredictable ways.
And as we understand more about time
it's even becoming possible
to solve perhaps the greatest mystery of them all.
Whether time is eternal.
Over the last hundred years
it's becoming increasingly clear that our universe,
and hence time itself, had a beginning.
But that raises another question.
If time had a beginning will it also have an end?
Humanity has long pondered the origins of time and the universe.
Almost every religion that has ever existed
has had its own creation myth.
When I was a child
I remember being so confused about how we got here
and that's because I was brought up in between two faiths
with two very different views on creation.
On the one hand there was Christianity.
At Sunday school I learnt all the Old Testament stories.
Among them the Book of Genesis,
describing how the universe came into being
in a single moment of divine creation.
On the other hand, my parents were both Buddhists.
From then
I discovered that Buddhists believe the universe is timeless,
without either beginning or end.
For some time
I continued to struggle with these two seemingly incompatible doctrines.
Either the universe had a beginning or it didn't.
Either time is eternal or it isn't.
It's only in the last forty years or so
that we think we've found the answer.
An answer that comes from the furthest reaches of space.
The amazing thing about looking up into the night sky
is that it's like gazing at a cosmic map of the past.
Every planet, every star is like a snapshot
taken when their light first left them.
The further the star, the more ancient its origins.
But for centuries
the limits of the universe were a total mystery
until one man peered further into the heavens than ever before.
In doing so
he gave us a better understanding notjust of our universe,
but of time as well.
Perched high in the hills above Los Angeles in southern California,
is the Mount Wilson Observatory.
In 1919
it saw the arrival of an ambitious new astronomer named Edwin Hubble.
Don Nicholson remembers Hubble from regular visits
to Mount Wilson as a young boy.
Hubble, certainly as an astronomer was a very skilled,
a very dedicated, very effective astronomer.
He was highly respected er, for his professionalism.
Hubble's arrival
more or less coincided with completion of the world's
then most powerful telescope.
Capable of looking further into space
and hence further back in time than ever before.
Most astronomers felt that our galaxy was the universe
and for many
that even the solar system was at the centre of that universe.
But on the evening of October 4th 1923,
Edwin Hubble noticed a tiny speck deep within the Andromeda nebula.
Before that time
there was no telescope in the world,
for example, that could resolve individual stars
in these spiral nebula.
And so there was belief that they were simply gaseous objects
in our own galaxy.
But Hubble was able to prove that his speck was indeed a star
and incredibly that it was more than a million light years away,
much too far to be part of our own galaxy.
In one stroke
Edwin Hubble had destroyed the notion that our milky way
was the sum total of the universe.
And if the universe was much bigger,
then it also had to be far, far older.
Every Thursday
a whole bunch of fans congregate at this drag strip
to enjoy the sights,
the smells, the sounds of these muscle cars.
These unmistakeable sounds are created by the same phenomenon
that enabled Edwin Hubble to make his second great discovery.
The sound of a car will always depend on the direction it's travelling.
A car moving towards me sounds high pitched.
But a car moving away from me sounds lower pitched.
This shift in pitch,
known as 'the Doppler Effect'
is due to the fact that at the front of a moving car
sound waves are compressed.
While at the back they're stretched out.
And what's true of sound is also true of light.
As light moves away from us its waves too become stretched.
By measuring this effect called 'the red shift'
in one galaxy after another,
Edwin Hubble realised that not only were they all incredibly distant
they were all moving away from us.
In other words the universe was expanding.
If the universe was expanding,
then it had to be expanding from something.
From an event whose soundtrack is still with us today.
What I'm listening to now are some of the sweetest sounds ever.
The sounds of creation.
Waves of light from the beginning of time have been stretched so much
that we can't really see them anymore.
Instead we can pick some of them up on the radio in the form of static.
Although he didn't know it at the time
Hubble's discovery that the universe was expanding
led to one of the most important breakthroughs ever made about time.
The Big Bang.
Once there was nothing.
Not even time.
But 13.7 billion years ago
it seems that this nothing became everything.
When a tiny dot of infinite density spontaneously expanded
at a phenomenal rate.
Giving birth to the universe and everything within it,
including time.
But if time had a beginning
does that also mean that time will have an end?
Just as many cultures have their own creation myth,
so most also have their own take on how the universe will end.
In the 11th century,
the ancient Norse myth of Ragnarok
predicted that the universe and time along with it,
would end in a desperate battle between the forces of good and evil.
It was believed that this apocalypse
would be preceded by something called, 'the winter of winters.'
An epic ice age,
during which all the stars would gradually vanish from the sky.
How the universe will end
continues to preoccupy us over a thousand years later.
In 1988,
physicist Saul Perlmutter joined this quest
to discover the fate of the cosmos.
It seems like a really philosophical question
er, is the universe going to last for ever
or is it some day going to come to an end?
But in just the last - last few decades
we finally have the -
both the intellectual tools that Einstein gave us
and the practical measurement tools.
Saul believed that the destiny of our universe
was linked to the rate at which it was expanding.
Since the 1930s we've known that the universe is expanding
and everybody's understanding was that it would be slowing down
in that expansion
because all of the stuff in the universe
would gravitationally attract all the other stuff
and so would slow the expansion down little by little.
This would result in the universe collapsing back in on itself
in something called, 'the Big Crunch.'
Bringing time to an abrupt and violent halt.
Are there any decisions coming up?
Are there any other ones that
we're actually going to have to decide something about?
To discoverjust when the universe and time would end,
Saul and his team began to hunt for extremely rare objects known as
'supernovae.'
The aftermath of exploded stars.
There are two things you need to know
about a given supernova when - once -
- you've discovered one.
First its peak brightness.
That tells you how far away it is
and hence how far back in time the explosion occurred.
The other thing
is you want to look at its colour through its spectrum
and the more it's been shifted to the red - it's called Red Shift,
the more the universe has stretched since the time of that explosion.
Painstakingly,
Saul and his team begin to discover one supernova after another.
After several years of the - of the supernova hunting
we had built up a sample of some forty two supernova
and we were finally ready to go back -
- to ask that question that we began the project with.
What is the fate of the universe?
But the answer they came up with came as something of a shock.
When we finally graphed the results we found a very surprising result.
Apparently the universe is not slowing down.
It was actually speeding up and that was the big surprise.
In other words
the universe wasn't headed for a big crunch at all.
So what will its fate be?
Saul's discovery has helped scientists
to map out how time and the universe will evolve.
An incredible space epic separated into five long ages.
The first of these was the Primordial Age,
starting with the Big Bang and the birth of time.
Lasting only 350 thousand years, that's long gone.
We're now 13.7 billion years into the second age
and it's only just beginning.
We live in something called the Stelliferous Era.
An epoch
that has brought us notjust the stars and the planets,
but also every speck of matter in the universe.
One day,
a hundred million, million years from now,
a mere finger click in the life of the universe,
this golden age will come to an end.
In its place will come the Degenerate Age.
When the last stars burn out and die.
When the planets fall from their orbits
and in the darkness of space matter begins to decay.
After a truly unimaginable length of time only black holes remain.
A fourth age that far exceeds all the time that has ever gone before.
But even black holes don't last for ever.
Little by little their thermal energy will leak away.
Until ultimately they too disappear.
So what does this mean for the future of time?
Does the death of our universe
mean that time is destined to run out,
or is time really eternal, without end?
Even as the last black hole evaporates,
a fifth and final age is beginning.
The age of the photon
in which time finally fragments into total disorder.
When all that remains of our cosmos
are invisible,
indestructible, low energy light particles.
For Saul Perlmutter,
this cold chaos represents the ultimate destiny for time.
This particular picture of the - of the future of the universe,
and we don't know if this will be the final answer,
would have time lasting for ever.
There'll be no end to the universe in this particular scenario.
So it seems as if both religious traditions
that I grew up with are in some sense correct.
Time is eternal as the Buddhists believe,
but time also came into being at a precise moment,
and that fits well with the story of Genesis.
As we look out to the vastness of time that lies ahead
we begin to notice something truly incredible.
As we move from one age of the universe to the next
we see that the nature of time itself begins to change.
Time evolves.
Ultimately
the strange and chaotic behaviour that we can only glimpse inside the atom
may in general become the nature of time throughout the entire cosmos
and if we could somehow hang around to experience it
we might not even recognise it as time at all.
Because just as particles can be in many places at once,
so in our quantum cosmos
we might uncover many universes,
each one with a time of its own.
So this new perspective of time
over the whole life of the cosmos,
makes us look at our time from a new point of view.
The time that we feel passing,
the time that we know and trust,
may be something of an illusion.
An illusion that allows us to make sense of our place
in this tiny corner of the cosmos.