Why are we here? Where do we come from?
These are the most enduring of questions.
And it's an essential part of human nature to want to find the answers.
And we can trace that ancestry back
hundreds of thousands of years to the dawn of humankind.
But in reality, our story extends far further back in time.
Our story starts with the beginning of the universe.
It began 13.7 billion years ago.
And today it's filled with over 100 billion galaxies,
each containing hundreds of billions of stars.
In the series, I want to tell that story
because ultimately we are part of the universe.
So its story is our story.
It's a story that you couldn't tell without something so fundamental
that it's impossible to imagine the universe without it.
It's woven into the very fabric of the cosmos. Time.
The relentless flow of time has driven the evolution of the universe
and created many extraordinary wonders.
These wonders take us from the very first moments in the life
of the universe to its eventual end.
This is Chankillo on the north-western coast of Peru.
And it's one of South America's lesser known archaeological sites.
But, for me, it is surely one of the most fascinating.
Around 2,500 years ago,
a civilisation we know almost nothing about
built this fortified temple in the desert.
Its walls were once brilliant white and covered with painted figures.
Today, all but the smallest fragments
of the decorations are gone.
The details of this culture and all traces of its language are lost.
And yet, if you stand in the right place, you can still experience
the true purpose of Chankillo,
in just the same way as you could the day that it was built.
But, to do that, you have to be here before the sun rises.
These towers form an ancient solar calendar.
Now, at different times of year,
the sunrise point is at a different place on the horizon.
21st December, which here in the southern hemisphere
is the summer solstice, the longest day,
the sun rises just to the right of the right-most tower.
Then, as the year passes, the sun moves through the towers
until on 21st June, the winter solstice,
the shortest day, it rises just to left of the left-most tower.
Actually just in-between that mountain
you can see in the distance and the left-most tower.
So, at any time of year, if you watch the sun rise,
you can measure its position and you can tell,
within an accuracy of two or three days, the date.
Today's date is September the 15th.
So that means the sun
will rise between the fifth and the sixth towers.
Chankillo still works as a calendar
because the sun still rises in the same place today
as it did when these stones were first laid down.
That's a magnificent sight, as the sun burns through the towers.
You can almost feel the presence of the past here.
Imagine what it must have been like.
Thousands of citizens stood here to greet the sun,
which was almost certainly a deity. Almost certainly their god.
What a magnificent achievement.
Probably one of our earliest attempts
to begin to measure the heavens.
Over the millennia,
that desire to measure what's going on in the sky
has led to modern astronomy
and the foundations of our modern civilisation.
I might build one in my garden.
I want one!
The 13 towers that line this ridge stand testament to our
enduring fascination with the clockwork of the heavens.
And to the direct connection between our lives and the cosmos.
The rising and setting of the sun provides an epic heartbeat
that allows us to mark the passage of time.
A day on Earth is the 24 hours
it takes our planet to rotate once on its axis.
Our months are based on the 29-and-a-half days
it takes the moon to wax and wane in the night sky.
And a year is the 365-and-a-quarter days
it takes us to orbit once around the sun.
These familiar timescales mark the passing of our lives.
But the life of the universe plays out on a much grander scale.
When you look up into the night sky, you don't just see stars.
Those tiny points of light are a million different clocks,
whose lifespans mark out the passage of time over billions,
or even trillions, of years.
This film is about the greatest expanses of time.
The deep time that shapes the universe.
From its fiery beginnings, through countless generations of stars,
planets and galaxies, to its eventual demise,
the fate of the universe is determined by the passage of time.
Timescales in the cosmos seem so unimaginably vast,
it's almost impossible to relate to them.
Yet there are places on Earth
where we can begin to encounter time on these universal scales.
This is Ostional on the northern Pacific coast of Costa Rica.
I've come here to witness a natural event that's been happening
long before there were any humans here to see it.
And I suppose it really is a window
into the distant past of life on our planet.
Once the sun has dipped below the horizon
and the moon conspired to make the tides just right,
this beach is visited by prehistoric creatures.
Under the cover of darkness, they emerge from the ocean.
Playa Ostional is one of the few beaches in the world
where large numbers of sea turtles make their nests.
But what makes this truly remarkable is the sheer length of time
scenes like this have been playing out.
This is part of one of the oldest life-cycles on Earth.
On nights like these, for the last 100 million years, turtles like this
have been hauling themselves out of the ocean to lay their eggs.
It's an almost incomprehensible timespan.
100 million years ago, there were dinosaurs roaming the Earth,
but the Earth itself looked very different.
South America was not connected to North America.
North America was somewhere over close to Europe.
Australia was connected to Antarctica.
It really is quite...
wonderful to be so close to such an ancient cycle of life.
I can hear breathing, actually.
So, a remarkable experience.
I mean, it really is beautiful to see that.
On one night of many hundreds of millions of nights
stretching back into the past.
And she's gone.
To witness a moment like this
is to open up a connection to the deep past.
To experience timespans far longer than the history of our own species.
Yet even the 100-million-year story of the turtles
only begins to connect us with the vast sweep of cosmic time.
Our entire solar system is travelling
on an unimaginably vast orbit,
spinning around the centre of our galaxy.
It takes 250 million years to make just one circuit of the Milky Way.
In the entire history of the human race,
we've travelled less than a tenth of 1% of that orbit.
These cycles seem eternal and unchanging,
but as the story of time unfolds, a fundamental truth is revealed.
Nothing lasts forever.
This is the most profound property of time.
And it plays out just as vividly here on Earth
as it does in the depths of space.
Well, this is the Perito Moreno Glacier
in Patagonia in southern Argentina.
And it's one of the hundreds of glaciers
that sweep down the continent from the southern Patagonian ice fields.
And, you know, if you carry on that way, south about 1,000 kilometres,
you get to the end of South America.
From then on, there's nothing to the Antarctic.
And it feels like that today.
The glacier is such a massive expanse of ice that, at first sight,
just like the cycles of the heavens, it appears fixed and unchanging.
Yet, seen close-up, it's continually on the move.
As it has been for tens of thousands of years.
WATER CRASHES
The whole face of the glacier is moving into the lake
something like that much every day.
That means that well over a quarter of a billion tonnes of ice
drop off the face of the glacier into the lake every year.
That's about a million tonnes a day. And you can hear it happening.
Just every now and again, you hear this tremendous cracking sound.
It really is like the place is alive.
< CRACKING
THUNDEROUS CRASH
You know, it's quite disturbing when these enormous chunks of ice
fall into the lake.
Although this thing seems stable and the movement seems glacially slow,
actually there can be really violent collapses.
It's an incredibly dynamic place to be.
The movement of the glacier
provides an insight into the nature of time.
It is simply the ordering of events into sequences.
One step after another.
As time passes, snow falls, ice forms,
the glacier gradually inches down the valley
and huge chunks of ice fall into the lake below.
But even this simple sequence contains a profound idea.
Events always happen in the same order.
They're never jumbled up and they never go backwards.
RUMBLING
Now that's something that you would never see in reverse.
But, interestingly, there's nothing in the laws of physics
that describe how all those
water molecules are moving around that prevent them
from all getting together on the surface of the lake,
jumping out of the water, sticking together into a block of ice
and then gluing themselves back on to the surface of the glacier again.
But, interestingly,
we do understand why the world doesn't run in reverse.
There is a reason.
We have a scientific explanation.
And it's called the arrow of time.
We never see waves travelling across lakes,
coming together and bouncing chunks of ice back onto glaciers.
We are compelled to travel into the future.
And that's because the arrow of time dictates that as each moment passes,
things change.
And once these changes have happened, they are never undone.
Permanent change is a fundamental part of what it means to be human.
We all age as the years pass by.
People are born, they live, they die.
I suppose it's part of the joy and tragedy of our lives.
But out there in the universe,
those grand and epic cycles appear eternal and unchanging.
But that's an illusion.
You see, in the life of the universe, just as in our lives,
everything is irreversibly changing.
By building change upon change,
the arrow of time drives the evolution of the entire universe.
And as we look out deep into the cosmos,
we can see that story unfold.
This is an image of a tiny piece of night sky
in the constellation of Leo.
It's actually where the mouth of the lion would be.
And, despite appearances, it is one of the most interesting images
taken in recent astronomical history.
The interesting thing is this little red blob here,
which looks very unremarkable.
But what that red blob is is the afterglow
of an enormous cosmic explosion. It's the death of a star.
That was about...
40 or even 50 times the mass of our sun.
Poetically named GRB 090423, it was once a Wolf-Rayet star.
Shrouded by rapidly swirling clouds of gas,
it burned 10,000 times more brightly than our sun.
But because it burned so brightly, it was extremely short-lived.
As it died, the giant star collapsed in on itself.
That caused massive jets of light and stellar material
to be ejected from its poles,
in an explosion that shone with the light of 10 million billion suns.
And it's the afterglow of this catastrophic explosion
that is just visible from our planet as a faint red dot.
But that's not what's so interesting about GRB 090423.
You see, when we look up into the sky, at distant stars and galaxies,
then we're looking back in time
because the light takes time to journey from them to us.
And the light from that red dot has been travelling to us
for almost the entire history of the universe.
You see, what we're looking at here is an event that happened
13 billion years ago.
That's only about 600 million years after the Big Bang.
After the universe began.
So this is something incredibly early in the universe's history.
In fact, this is the oldest single object that we've ever seen.
What we're looking at here is the explosive death
of one of the first stars in the universe.
As it evolves, the universe passes through distinct eras.
Vast ages, whose beginnings and endings
are marked by unique milestones.
The births and deaths of its wonders.
The moment the first stars were born is one of the most important changes
in the evolution of the cosmos.
It signals the end of the Primordial Era
and marks the beginning of the second great age of the universe.
The time in which we live.
The Stelliferous Era -
the age of the stars.
Starlight illuminates the night sky and starlight illuminates our days.
Our sun is just one of 200 billion stars in our galaxy.
Our galaxy is one of 100 billion in the observable universe.
And countless islands of countless stars.
Although the universe is over 13 billion years old,
we still love close to the stars of the Stelliferous Era.
It's an age of astonishing beauty and complexity in the universe.
The cosmos is absolutely awash with stars surrounded by
nebulae and systems of planets.
Countless billions of worlds that we've yet to explore.
But the cosmos isn't static and unchanging.
It won't always be this way.
Because, as the arrow of time plays out,
it produces a universe that is as dynamic as it's beautiful.
We've seen stars born and we've seen stars die.
And we know that tomorrow won't be the same as today
because the arrow of time says
the future will always be different from the past.
But what drives this evolution?
Why is there a difference between the past and the future?
Why is there an arrow of time at all?
We all have an intuitive understanding of the arrow of time.
It seems obvious to us that things change and the future
will be different to the past.
We know that because we see the effects
of the passing years all around us.
This is Kolmanskop, an abandoned diamond mining town
in southern Namibia.
This entire town was founded in 1908,
when a worker who was building the railway from the port of Luderitz
inland into the centre of Namibia found a single diamond
here in this desert.
For 40 years, this was a thriving community of up to 1,000 people.
A place where you could become a millionaire,
picking diamonds out of the sand.
While the money rolled in, they built grand houses
and lived a champagne lifestyle in the desert.
But when the diamonds dried up, the town was abandoned.
And for half a century
it's fallen into disrepair as it's slowly reclaimed by the sands.
The processes at play here at Kolmanskop
are happening everywhere in the universe.
Because it isn't simply permanent change
that's central to the arrow of time.
It's decay.
But the scientific explanation for why that is...
..didn't come from attempting to understand
the effects of time in the universe.
It came from trying to build a faster train.
Back in the 19th century,
engineers were concerned with the efficiency of steam engines.
How hot should the fire be?
What substance should you boil in the steam engine?
Should it be water or something else?
These were profound questions.
And out of those questions arose the science of thermodynamics.
It's when concepts like heat and temperature and energy
entered the scientific vocabulary for the first time.
Now, along with that deeper understanding
emerged what is probably the most important law of physics
for understanding the evolution of the universe
and the passage of time.
It's called the Second Law of Thermodynamics.
The reason the Second Law of Thermodynamics was so profound
was because, at its heart, it contained a radically new concept.
Something physicists call "entropy".
Entropy explains why, left to the mercy of the elements,
mortar crumbles, glass shatters and buildings collapse.
And a good way to understand how is to think of objects
not as single things,
but as being made up of many constituent parts.
Like the individual grains that make up this pile of sand.
Now, entropy is a measure of how many ways I can rearrange those
grains and still keep the sand pile the same.
And there are trillions and trillions and trillions
of ways of doing that.
I mean, pretty much anything I do to this sand pile,
if I mess the sand around and move it around,
then it doesn't change the shape or the structure at all.
So, in the language of entropy,
this sand pile has high entropy because there are many, many ways
that I can rearrange its constituents and not change it.
Now let me create some order in the universe.
Now, there are approximately as many sand grains in this sand castle
as there are in the sand pile.
But now, virtually anything I do to it will mess it up,
will remove the beautiful order from this structure.
And because of that, the sand castle has a low entropy.
It's a much more ordered state.
So, many ways of rearranging the sand grains
without changing the structure, high entropy.
Very few ways of rearranging the sand grains
without changing the structure, without disordering it, low entropy.
Imagine I was to leave this castle in the desert all day.
Then it's obvious what's going to happen.
The desert winds are going to blow the sand around
and this castle is going to disintegrate.
Is going to become less ordered. It's going to fall to bits.
But think about what's happening on the fundamental level.
I mean, the wind is taking the sand off the castle
and blowing it over there somewhere and making a sand pile.
There's nothing fundamental in the laws of physics
that says that the wind couldn't pick up some sand from over here,
deposit it here
and deposit it in precisely the shape of a sand castle.
In principle, the wind could spontaneously build a sand castle
out of a pile of sand.
There's no reason why that couldn't happen.
It's just extremely, extremely unlikely because there
are very few ways of organising this sand so that it looks like a castle.
It's overwhelmingly more likely
that when the wind blows the sand around
it will take the low entropy structure of the castle
and turn it into a high entropy structure, the sand pile.
So, entropy always increases. Why is that?
Because it's overwhelmingly more likely that it will.
It seems incredible that a law that says that sand castles
don't spontaneously form on the wind
could solve one of the deepest mysteries in physics.
But by saying entropy always increases,
the Second Law of Thermodynamics is able to explain
why time only runs in one direction.
The Second Law of Thermodynamics, for me, demonstrates everything
that's powerful and beautiful and profound about physics.
You see, here's a law that entered science
as a way of talking about how heat moves around
and the efficiency of steam engines.
But it ended up being able to explain one of the great mysteries
in the history of science.
Why is there a difference between the past and the future?
You see, the second law says
that everything tends from order to disorder.
That means that there is a difference
between the past and future.
In the past, the universe was more ordered.
In the future, the universe will be less ordered.
And that means there's a direction to the passage of time.
So the Second Law of Thermodynamics has introduced the concept
of an arrow of time into science.
The arrow of time has been playing out
in Kolmanskop since the mining facility was abandoned in 1954.
But in the universe,
it's been playing out for almost 14 billion years.
And it will have profound consequences.
Because it means stars cannot shine forever.
Including the star at the centre of our solar system.
At the end of its life, the sun won't simply fade away to nothing.
As it begins to run out of fuel, its core will collapse
and the extra heat this generates
will cause its outer layers to expand.
In around a billion years' time,
this will have a catastrophic effect on our fragile world.
Gradually, the Earth will become hotter and hotter.
So there will be one last perfect day on Earth.
But eventually the existence of all life on this planet
will become impossible.
TICKING
Long after a life has disappeared, the sun will have grown so much
it will fill the entire horizon.
It will become a red giant.
The last phase of its life.
Our planet might not survive to this point.
But, if it does, little more than a scorched and barren rock will remain
to witness the final death throes of our star.
In six billion years, our sun will explode.
Throwing vast amounts of gas and dust out into space,
to form a gigantic nebula.
And at its heart will beat a faintly glowing ember.
All that remains of our once magnificent sun.
It will be smaller than the size of the Earth.
Less than a millionth of its current volume
and a fraction of its brightness.
Our sun will have become a white dwarf.
With no fuel left to burn,
a white dwarf's faint glow comes from the last residual heat
from its extinguished furnace.
The sun is now dead.
Its remains slowly cooling in the freezing temperatures of deep space.
Looking at it from where the Earth is now,
it would only generate the same amount of light
as the full moon on a clear night.
The fate of the sun IS the same as for all stars.
One day, they must all eventually die
and the cosmos will be plunged into eternal night.
And this is the most profound consequence of the arrow of time.
Because this structured universe that we inhabit,
and all its wonders - the stars, the planets and the galaxies -
cannot last forever.
The cosmos will eventually fade and die.
First will come the end of the Stelliferous Era.
The end of the age of starlight.
The largest stars are the first to disappear,
violently collapsing into black holes.
Just a few million years after their formation.
But long after they're gone, just one type of star will remain.
This is a picture of the nearest star to our solar system,
Proxima Centauri.
It's only 4.2 light years away. But the reason it doesn't stand out
against the much more distant stars in this photograph
is that Proxima Centauri is incredibly tiny.
It's a kind of star known as a red dwarf star.
It's only about 11-12% the mass of our sun.
But to our eyes it would appear to shine 18,000 times less brightly.
But red dwarves do have one advantage over their much more
luminous and magnificent stellar brethren.
And that's because they're so small,
they burn their nuclear fuel incredibly slowly,
so they have lifespans of trillions of years.
And that means that stars like Proxima Centauri
will be the last living stars in the universe.
If we survive into the far future of the universe,
then it's possible to imagine our distant descendants building
their civilisation around red dwarves
to capture the energy from those last fading embers of stars,
just as our ancestors crowded around campfires
for warmth on cold winter's nights.
The reason why Proxima Centauri
burns so slowly is because its small size and low gravity
mean its core is under much lower pressure than larger stars.
This also means that its interior is constantly churning,
whipping up the surface into a fiery turmoil.
Explosive solar flares occur almost continually,
even though it burns so dimly.
But Proxima Centauri will eventually die.
And like our sun, it too will become a white dwarf.
As the age of starlight ends,
all but the dimmest flicker of light in the universe will go out.
The faint glow of white dwarves will provide the only illumination
in a dark and empty void, littered with dead stars and black holes.
By this point, the universe will be 100 trillion years old.
And yet, even now,
the vast majority of its lifespan still lies ahead of it.
There are few places on Earth where you can get an inkling
of what the far future has in store.
This is Namibia's Skeleton Coast,
where the cold water to the South Atlantic
meet the Namib Desert.
And it is one of the most inhospitable places on Earth.
Back in the 17th century,
Portuguese sailors used to call this place the "gates to hell"
because this dense fog
that you see pretty much every morning along this coast,
coupled with the constantly shifting shape of the sandbanks,
meant that over the years,
literally thousands of ships were wrecked along this coastline.
And even if you made it to shore, that wasn't the end of your problems
because the currents are so strong here
that there is no way of rowing back out to sea.
If you look that way,
there's just hundreds of miles of inhospitable desert.
So, it genuinely was a place of no return.
If you were shipwrecked here, this WAS the end of your universe.
This is the Eduard Bohlen.
She was once an ocean-going steamer,
ferrying passengers and cargo between here and Europe.
On 5th September, 1909, she ran aground in thick fog.
Yet, like all the vessels wrecked along this shoreline,
the time it takes her to decay to nothing
will be far longer than her time at sea.
In the far future of the cosmos,
a similar destiny awaits the remaining white dwarves.
A black dwarf will be the final fate of those last stars.
White dwarves that have become so cold
that they barely emit any more heat or light.
Black dwarves are dark, dense decaying balls of degenerate matter.
Little more than the ashes of stars.
Their constituent atoms are so severely crushed
that black dwarves are a million times denser than our sun.
Stars take so long to reach this point,
that after nearly 14 billion years
we believe there are currently no black dwarves in the universe.
But despite never seeing one,
we can still predict how they will end their days.
Just as the iron than makes up this ship
will eventually rust and be carried away by the desert winds,
so we think that the matter inside black dwarves,
the last matter in the universe,
will eventually evaporate away and be carried off
into the void as radiation,
leaving absolutely nothing behind.
With the black dwarves gone,
there won't be a single atom of matter left.
All that will remain of our once rich cosmos
will be particles of light and black holes.
After an unimaginable length of time,
even the black holes will have evaporated
and the universe will be nothing but a sea of photons,
gradually tending towards the same temperature,
as the expansion of the universe cools them towards absolute zero.
And when I say "unimaginable period of time," I really mean it.
It's 10,000 trillion trillion
trillion trillion trillion trillion trillion trillion years.
How big's that number?
If I were to start counting with a single atom representing one year
then there wouldn't be enough atoms in the entire universe
to get anywhere near that number.
Once the very last remnants
of the very last stars have finally decayed away to nothing,
and everything reaches the same temperature,
the story of the universe finally comes to an end.
For the first time in its life,
the universe will be permanent and unchanging.
Entropy finally stops increasing
because the cosmos cannot get any more disordered.
Nothing happens and it keeps not happening.
Forever.
It's what's known as the heat death of the universe.
An era when the cosmos will remain vast and cold and desolate
for the rest of time.
But that's because there is no difference between the past,
the present and the future.
There's no way of measuring the passage of time
because nothing in the cosmos changes.
The arrow of time has simply ceased to exist.
It's an inescapable fact of the universe,
written into the fundamental laws of physics.
The entire cosmos will die.
Every single one of the 200 billion stars in our galaxy will go out.
And just as the death of the sun means the end of life on our planet,
so the death of every star
will extinguish any possibility of life in the universe.
The fact that the sun will die and it will incinerate the Earth
and obliterate all life on our planet in the process,
might sound a bit depressing to you.
You might legitimately ask,
"Well, surely you could build a universe in a different way?
"Surely you could build it
"so it didn't have to descend from order into chaos?"
Well, the answer is no,
you couldn't, if you wanted life to exist in it.
The arrow of time,
the sequence of changes that slowly leads the universe to its death,
is the very same thing that creates the conditions
for life in the first place.
Because it takes time for matter to form
and it takes time for gravity to pull it together
into stars and planets.
The arrow of time creates a bright window
in the universe's adolescence.
During which, life is possible.
But it's a window that doesn't stay open for long.
As a fraction of the lifespan of the universe,
as measured from its beginning to the evaporation
of the last black hole,
life, as we know it, is only possible for one thousandth
of a billion billion billionth billion billion billionth
billion billion billionth of a per cent.
And that's why, for me,
the most astonishing wonder of the universe isn't a star
or a planet or a galaxy.
It isn't a thing at all.
It's an instant in time.
And that time is now.
Humans have walked the Earth for just the smallest fraction
of that briefest of moments in deep time.
But in our 200,000 years on this planet,
we've made remarkable progress.
It was only 2,500 years ago that we believed that the sun was a god
and measured its orbit with stone towers,
built on the top of a hill.
Today, the language of curiosity is not sun gods, but science.
And we have observatories that are almost infinitely more sophisticated
than the 13 towers, that can gaze out deep into the universe.
And, perhaps even more remarkably,
through theoretical physics and mathematics,
we can calculate what the universe will look like
in the distant future.
And we can even make concrete predictions about its end.
And I believe it's only by continuing
our exploration of the cosmos
and the laws of nature that govern it,
that we can truly understand ourselves
and our place in this universe of wonders.
And that's what we've done in our brief moment on Planet Earth.
In 1977, a space probe called Voyager 1
was launched on a grand tour of the solar system.
And it visited the great gas giant planets -
Jupiter and Saturn - and made some wonderful discoveries
before heading off towards interstellar space.
13 years later, after its mission was almost over,
it turned around and took one last picture of its home solar system.
This is that picture.
And the beautiful thing about this picture
is this single pixel of light
suspended against the blackness of space.
Because that pixel, that point, is Planet Earth.
The most distant picture of our planet ever taken.
6 billion kilometres away.
And whilst I suppose it has very limited scientific value,
for me, this tiny point of light
is the most powerful and profound demonstration
of perhaps the most human of qualities.
Our unique ability to reflect on the universe's existence
and our place within it.
Just as we, and all life on Earth, stand on this tiny speck
adrift in infinite space, so life in the universe will only exist
for a fleeting bright instance in time
because life, just like the stars and the planets and the galaxies,
is just a temporary structure on the long road from order to disorder.
But that doesn't make us insignificant
because we are the cosmos made conscious.
Life is the means by which the universe understands itself.
And, for me, our true significance lies in our ability
and our desire to understand and explore this beautiful universe.
Subtitles by Red Bee Media Ltd