For more than a decade, I've made programmes about the universe.
And our place within it.
There it is! There it is!
I can see the parachutes.
I've had some remarkable encounters...
I can't believe you can just stand next to a spacecraft.
Release.
.. memorable experiences...
They came down exactly the same. Wow.
.. and explained some beautiful science about how our planet works.
That really is the thin blue line that protects us.
Look at that!
Now, I'm taking a new look at those past programmes.
It's surely as close as I'm going to get to being in space.
I think our knowledge really has moved on since we made these films.
So it's really interesting to revisit
some fundamental questions again.
Are we alone in the universe?
What really is gravity?
Where will the exploration of space take us?
CLOCK TICKS
And what is time?
HIGH-PITCHED BEEPING
Beeping's never good.
I'm back at the Royal Institution to re-watch some of my old films.
And to explore the thing by which we measure our lives.
Time.
It's a concept which is so familiar,
and yet recent discoveries have revealed it to be far stranger
than we could have possibly imagined.
I think the question, "What is time?"
is one of the most fascinating and evocative scientific questions.
Because it's so fundamental to human experience.
Our experience of the world is that the past is written,
it has happened, and the future is yet to be written.
It's open.
CLOCK TICKS
the ticking of the clock?
It's one of the most baffling questions in science.
JAUNTY WHISTLING
Ah, excellent, there you are. Where am I? A bit complicated.
Sort of a spaceship/time machine/slash/swimming pool.
Optional hat stand. I need five minutes of your time and obviously
when I say five minutes, I'm lying. No, no, I'm just going to go give a lecture.
I know, I've just seen it. It's great. But I haven't given it yet.
Tricky to explain. Seen it anyway.
Right, hold on to something, probably your sanity.
Ready?
LOUD CRACKLING
Usually it just twirls around.
It's probably this. Shut up, Brian!
I'm often asked about time travel,
and, yeah, some of it comes from Doctor Who.
It would be great, wouldn't it, to have a TARDIS and to be able
to go back and see some of the great moments in history.
DOCTOR WHO THEME TUNE
It's a tantalising prospect.
But before we can even begin to consider time travel,
we should explore how we experience time.
METALLIC THRUMMING
The way that we experience time and talk about it,
is actually, if you think about it, quite strange.
Because, you know, there are 60 seconds in a minute, 60 minutes
in an hour and 24 of those in a day,
and then there are 365 days in a year.
It's interesting, I think, that most of us have become completely
disconnected from what that's actually telling us.
Which is that we live on a ball of rock,
that is spinning around on its axis
once roughly every 24 hours or so.
And in a plane that can go that fast,
you can really illustrate that.
Because we live on a spinning sphere,
if we turn on the after-burners and chase the setting sun,
something really interesting happens.
This is a Eurofighter Typhoon.
It flies at, at least Mach 1.85, twice the speed of sound.
I can't tell you exactly how fast, because it's classified.
They go up to at least 55,000 feet
but again, I can't tell you, it's classified.
And you can't film down those air intakes
because they're classified as well.
This one is BAE Systems' development aircraft.
I'm going to get in it in a minute,
and it's got all the test software in and the pilot told me that,
you know, it's a bit ropey so press control, alt, delete occasionally
if it all goes funny, and usually it comes back on.
Which is good.
Get in. Feet-wise, comfy? Good. That's it.
That's for, if you need to control it at any point.
It's unlikely. Unlikely.
Have you got a sick bag?
No.
Worst comes to the worst, do it in your glove.
Charlie 69, runway 07, clear take off.
Surface wind 350 degrees, seven knots over.
So, ready? Yeah. Going to go for it.
ENGINES ROAR
There we go. Wahee.
It's every bit as good as you can imagine.
It's beautiful. What a plane.
On the east side, everything's darkening up quite nicely
as the sun starts to set.
And on the ground it's already, it's dark on the ground now,
as far as the sun is concerned.
So, accelerating.
So that's Mach 0.78. Yeah.
And the G-suit is in play here. Yeah.
Turning directly towards the setting sun,
the Typhoon accelerates to catch up with the Earth's spin.
Beneath us, a 6,000 billion, billion-tonne rock
is spinning at 650mph.
But travel faster than the planet's surface
and the normal passage of the day is reversed.
Right, accelerating. Accelerating.
Oh, there we go, that's acceleration. Mach 1.
Through the sound barrier.
As the jet accelerates,
it starts to overtake the spin of the Earth.
Causing the setting sun to rise again.
Starting to grow a little. It is. I can see it.
We're beating the Earth.
Absolutely terrific.
Starting to climb again, you can see it coming up. Yeah.
That's Mach 1.4.
So, that's a thousand miles an hour.
Yeah, almost a thousand miles an hour.
And now the sun, it's almost the full disc over the clouds.
The sunrise. It is.
Two sunrises in one day.
And all you need is the world's most advanced fighter aircraft.
There we go.
Beautiful.
We've done it, we've outrun the Earth.
BRIAN CHUCKLES
Goodbye, sun! Good.
Right, let's get ourselves on our way home.
I was told that we caused a bit of an incident in the Isle of Man
because the sonic boom did rattle, rattle a few windows.
So, I apologise to all residents of the Isle of Man!
RADIO CHATTER
This hidden celestial dynamics, the Earth's spin and its orbit
around the sun, delivers our daily and yearly experience of time.
Spring goes into summer, and summer into autumn, and autumn into winter.
And we experience another season and another year.
But, of course, they're not always the same,
because every year that passes, we get older.
And so in that sense, I think time connects with the central tragedy
of human experience,
the fact that inexorably and unavoidably
we get older and ultimately we die.
So we're born and we die.
And that's a consequence of time passing,
at least from our point of view, as fragile human beings.
CLOCK TICKS
If you want to understand something, you've got to be able to measure it
and observe it, and look at it and quantify it.
And if you look back at many ancient civilisations,
the attempts to measure the passage of time are rarely small.
Often, they're massive.
They're huge temples that people built.
So, clearly, there's not only the practical need to measure
the passage of time, but there's some ritual attached to it.
This is Chankillo on the northwestern 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 it was built.
But to do that, you have to be here before the sun rises.
WIND WHISTLES AND HOWLS
These towers form an ancient solar calendar.
Now, at different times of year,
the sunrise point is at a different place on the horizon.
Actually, December 21st, which here in the southern hemisphere
is the Summer Solstice, the longest day,
when the sun rises just to the right of the rightmost tower.
Then, as the year passes, the sun moves through the towers
until on June 21st, which is the Winter Solstice, the shortest day,
it rises just to the left of the leftmost tower.
Actually, just in between that mountain you can see in the distance
and the leftmost 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 15th.
And so that means that 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 is 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.
It's probably one of our earliest attempts to begin to measure
the heavens.
Time has played a central role in the drama of human experience
for thousands of years.
But it's only when we try to measure it accurately that we start
to appreciate its mystery.
So the way that traditionally we measure the passage of time
is to look to the heavens and look to when the sun
reaches its highest point in the sky, and we call that noon.
That turns out not to be sufficient because it's not accurate enough.
The Earth doesn't spin on its axis at a constant rate.
The Earth wobbles around by quite a bit, actually.
The Earth's orbit is not entirely precise.
Things change.
So if we want to measure increasingly small time intervals
accurately, then the heavens are not the way to do it.
And so we can build mechanical watches,
and that's what we did initially when we had to measure time
more accurately for navigational purposes.
But even bits of, you know, cogs and gears and springs,
that's not particularly accurate either.
And so if you really want to start dividing time up into very
small intervals, which we have to do today for so many reasons,
then you need to look to the subatomic world
and you find that in the world of atoms and subatomic particles,
you can identify exquisitely accurate natural clocks.
MILITARY BAND PLAYS
I'm going to try and answer
one of the simplest questions
you could ask - what time is it?
These are the early days, right.
This is one of the first television programmes that I made.
If there's one place on Earth where you can come to find the time,
it's here in Washington DC.
This is the home of the US Naval Observatory,
one of a select bunch of time lords dotted across the planet
who are the keepers of time on Earth.
Universal Time, 19 hours, 54 minutes exactly.
A time now derived from atomic clocks.
Dennis McCarthy, Director of Time.
We defined a time in the 1950s based on the position of the moon
with respect to the stars.
We needed a more accurate kind of time.
Not only is it... does it have to be more accurate
but it has to be more accessible.
That accessible kind of time is provided by atomic clocks.
What we need to tell time is something which repeats
with great regularity that you can count on.
How well we can tell time depends on which atom you're using.
So we choose certain ones to... to use for keeping atomic time.
Inside the clocks are the atoms of a rare metal called caesium.
The electrons in the caesium atoms are made to jump up.
Then as they fall back down, they give out light.
These light waves peak over nine billion times every second
and it's this light that drives the clock,
effectively producing nine billion ticks for each atomic second.
This number never changes, never alters
and that's why it's so accurate.
So the atomic clock is actually putting out an electronic signal
which is essentially analogous to the ticking of a pendulum clock.
You know, a pendulum clock which might tick once every second
or once every couple of seconds.
This thing is providing us something
which is going nine billion times per second.
So it provides us with a very fine definition of time.
We actually have a number of clocks at the Naval Observatory
located all over the grounds.
Here's... here's one of them.
This is the master clock system one. Oh, yeah.
This is the master clock system two.
So if I want an answer to the question - what time is it?
There it is? That's it.
Universal Time 20 hours, zero minutes exactly.
Why do I need a clock that accurate?
Well, we do.
If you're using time to measure distance, which is how the GPS
satellite navigation system works, then it matters.
If your clock drifts by one nanosecond,
then your position measurement is drifting by something like a foot.
Atomic clocks can measure and divide time into intervals
that are so minuscule that they are beyond human perception.
But this precision means little when we begin to consider
the timescales that determine our ultimate fate - cosmic time.
Timescales in the cosmos seems 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,
and 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.
Well, this is part 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 time span.
I mean, 100 million years ago, there were dinosaurs roaming
the Earth, but the Earth itself looked very different.
I mean, 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.
You can hear her breathing, actually.
TURTLE EXHALES
So, a remarkable experience.
I mean, it really is beautiful to see that on the 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.
The timescales of our galaxy are almost beyond human comprehension.
But when we extend our gaze beyond the Milky Way
and out into the universe,
we come face-to-face with truly deep time.
The time that ticks on your watch is the time now,
the time of the present.
But the feeling we experience as the present time
is something we shouldn't take for granted.
Much of what we believe is in the present is drawn from the past.
What we feel is happening now happened a little while ago.
We feel that we experience a now around us.
Everything we see happened now.
But actually the light coming from distant things into your eye
takes time to get there.
So... you look at the sun.
The sun is 93 million miles away.
That means light takes over eight minutes to get from it
into my eyes. So I'm seeing the sun as it was eight minutes in the past.
It could explode and I wouldn't notice for eight minutes.
I'd just see that beautiful image of the setting sun.
The fact that light travels at a finite speed
offers us a unique opportunity.
It allows us to look back, not just eight minutes but millions,
even billions of years.
I've come to Baltimore to look back in time.
Former director of the Hubble Space Telescope Steve Beckwith
was responsible for taking an extraordinary photograph.
As a director, I had at my discretion 10% of the telescope time
per year, that I could use for anything.
One year I took all of my time, in fact I took a little bit more
than all of my time, and decided that we would devote it
to the deepest picture ever taken of the universe.
In 2004, Steve pointed the Hubble Telescope at a tiny piece
of the night sky and took a picture called the Ultra-Deep Field.
It took a million seconds of exposure
on the Hubble Space Telescope, the world's most powerful telescope,
and in this image we can look back in time 13 billion years.
It's a difficult picture almost to comprehend, isn't it?
Because in some sense, it's... 3D is the wrong word.
But it's, it's some sense... Oh, no, it is the right word.
It is 3D. We are looking back in time.
Every single galaxy in this image can be dated.
This galaxy emitted its light
when the universe was 8.8 billion years old.
Then, as you go back in time, this is a galaxy that emitted its light
when the universe was 3.3 billion years old.
You can see it looks completely different.
It's really very chaotic.
And this is one billion years after the Big Bang.
Very red, a little tail, very small.
The most distant galaxy in the Ultra-Deep Field
is a red one that's right over here. This one here?
The light from that was emitted when the universe
was 700-800 million years old.
So, really, this is one of the first structures
that formed in the universe?
This is one of the first structures that formed
and it's one of the first structures we've been able to see.
In a sense you see this...
.. almost, I was going to say paradoxical,
but strange behaviour of the universe as revealed by astronomy.
Because I'm trying to say, well, what does that look like now?
You know, what would that look like now?
In a sense, it's the wrong language to use, isn't it?
That's what it looks like now. That's right.
Steve has turned his photo into a movie to journey back in time.
You see these little pieces coming at us? We're going back in time,
and you can see the three-dimensional effect.
Some of these others are a little farther back
but here we're going back, we're probably back now
about three billion years from the present.
As we keep going and you get to the smaller ones,
you get back to about eight or nine billion years.
And then, when we get to the very tiny most distant ones,
we'll be back probably ten or 11 billion years in time.
And we're deep into the universe and we're just looking
at the smallest structures back in time to about 13 billion years,
and suddenly we run out.
The Hubble Space Telescope can see galaxies
that are as they were about 500 million years after the Big Bang.
But it can't see further back than that.
The reason is that the universe is expanding.
And, so, as the light travels through the expanding universe,
it gets stretched.
And that means that it gets redder and redder and redder
until it gets so red that the Hubble Space Telescope
isn't sensitive to it.
So it can't see any further away than that.
But a new telescope with that capability
is due to be launched later this year.
The James Webb Telescope is going to be much more sensitive
to those, what we call, the infrared light,
so the very long wavelengths.
And that means it will be able to see back past those galaxies
that Hubble can see to the very early history of the universe.
We'll be able to watch the formation of the first stars and galaxies.
We're able to look very far back into the past,
but we can't see into the future.
Which raises the question,
what is the difference between the two?
Why does time appear to flow only in one direction?
This question has puzzled many of science's greatest minds.
All the laws of nature that we have today that we consider
to be fundamental, so Einstein's equations or Newton's laws
for that matter, all of them make no distinction
in the direction of the flow of time, if you like.
There's only one law of physics that has an explicit direction of time
in it, and that law is concerned with something called 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.
But 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.
Now, 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.
It's going to become less ordered.
It's going to fall to bits.
But think about what's happening on the fundamental level.
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, 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.
There was a tremendous sandstorm and we all hid,
and it was just vicious.
And when we came out,
we had cameras and we were opening, taking the lenses off
and just pouring sand out of them!
The Second Law of Thermodynamics, for me, demonstrates everything
that is powerful and beautiful and profound about physics.
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 the future.
In the past, the universe was more ordered
and in the future, the universe will be less ordered.
And that means that 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 so-called thermodynamic arrow of time,
this idea that entropy always increases,
is well understood, but actually its origin at a deep level
is not so clear.
The reason seems to be something to do with
the origin of the universe itself and the presence of this
strange thing called the Big Bang way back in our past.
Why were things in the past so beautifully ordered,
that the universe can fall to bits gently and in the process,
in the transition from order to disorder,
these tremendous structures,
of which we are the most magnificent example,
can exist for a brief time in the universe?
There are almost more opinions than there are theoretical physicists
on this question!
The Second Law of Thermodynamics is an explanation for the arrow
of time, and what makes the past different from the future.
But it is silent on a question that excites science fiction writers
and physicists alike.
If I'm in a big audience of people and someone says,
"Is time travel possible?" there might be someone who thinks
they know it just adds a bit of a laugh and chuckles.
It is a very good question.
The answer is, we don't know for sure.
I think that, ultimately,
the desire to go back in time
is tied in to the tragedy of human experience.
We've all...
There are not only moments that we wish we could relive,
there are people that we wish we could see again.
People who are no longer with us.
So, the idea that somehow the past might be accessible is extremely
enticing and powerful, emotionally.
But that's impossible if the past only exists in our memories.
That was the accepted view.
But Einstein changed that.
If we take his Theory of Relativity at face value,
then every moment of our past still exists.
We feel as if we move through space as time ticks by.
But that's an illusion.
The separation of space and time is false.
The first person to realise that was Albert Einstein.
He thought deeply about motion, about the idea that we can't tell
whether we're moving or not.
And he tried to reconcile that with our picture of the universal laws
of nature, and he found that he could do,
at the expensive of jettisoning space and time as separate entities
and merging them together into a unified whole,
the fabric of the universe called Spacetime.
As the Earth moves through Spacetime,
its orbit traces out a spiral as it circles the sun
and races into the future.
It never returns to the same place
because each moment is a different location
in the fabric of the universe.
And just as the Earth travels relentlessly onwards
on its path through Spacetime,
so must we.
So this is how Einstein asks us to picture the sweep of our lives,
the experience of living.
Our lives are a series of moments
and they're laid out like places on a map.
There's me as a little baby.
My dad with my grandad.
That idyllic summer some time in the early '70s in a paddling pool
with my sister.
When I was about four years old.
And the perfect Christmas with my grandparents
sometime back in the 1970s.
There's me when I was 20 years old with a ridiculous haircut
playing a gig somewhere in the middle of Europe.
In Budapest, I think.
Wedding day.
And me in Oldham, where I grew up,
with my little boy, George.
That was a very personal scene.
It was really personal because, actually, it wasn't long
after my dad had died.
So in my mind, there was, obviously, as with everyone
who goes through those experiences as we all do,
there's a, you know,
a reconsideration or a rethinking of the past.
You find your mind wandering back into the past and past events.
This isn't exactly like a map.
See, I can return to these places in space, to Oldham,
to central Europe, to Duluth, Minnesota where I got married,
back to Oldham again.
But I can't return to these moments, to these events in Spacetime.
Because of the geometry of Spacetime itself,
we are compelled to move inexorably into the future.
What's interesting is that in Einstein's Theory of Relativity,
the past is not accessible
but it's still there in a very real sense.
I think the bottom line is, no, you can't travel into the past.
Probably!
But the explanation for that is anything but trivial.
But time travel into the future is a different matter.
We are all travelling into the future all the time.
But Einstein's Theory of Relativity tells us that we are each
doing it at different rates.
We experience time passing because we are all travelling
along the time dimension.
But, strangely, Einstein also said
we don't all experience the same time.
Spacetime can be pictured as a sort of fabric
where time and space are inextricably woven together.
As a result, the dimensions of space and time can get mixed up.
Although we are all travelling through Spacetime
at the speed of light, it's the mixing of time and space
that Einstein said causes time to tick differently for each of us.
For Einstein, time wasn't like a metronome
that just ticks the same for everybody.
It's different for you and me,
and everywhere in the universe, the metronomes tick at different rates.
Einstein said that two people will only ever agree
on the speed time ticks if they're standing next to each other.
If I was to fly past you incredibly fast,
I would see your time tick much slower than mine.
This idea lies at the heart of Einstein's Theory of Relativity.
No-one has a right to the... to claim that their time is THE time,
the absolute time.
It just depends on who's moving relative to who.
Because of the mixing of space and time,
time ticks differently for you relative to other people,
depending on how fast everyone is moving.
When someone moves relative to me,
they use some of their speed of light through Spacetime
to move through space.
So they haven't got as much left to move through time,
and that means that their speed through time is a bit slower.
They've sort of, in a very real sense, used a bit of it up.
It's a really profound way of understanding
Einstein's theory of Spacetime.
And the strange nature of time doesn't stop there.
It's not just how fast you're moving
but what you're next to that also affects time.
According to Einstein, you should see the time tick slower
at my feet than at the top of my head.
This is because the nearer you are to a big object like the Earth,
the more bent and warped is the Spacetime,
and the slower time ticks.
On our planet the effect is minuscule
but out there in the universe, the vast mass of the stars and galaxies
bend and warp the Spacetime so much that time ticks all over the place.
There's a very famous experiment in 1971 by Hafele and Keating
in which they decided to,
let's say, put Einstein to the test.
They got atomic clocks and they flew them
around the world on civil airliners one way, and around the world
on civil airliners the other way, synchronised them all
before they left and compared them when they came back.
And the clocks that went eastward around the world
lost 59 nanoseconds,
59 thousand-millionths of a second.
And the one that went westward gained 273 nanoseconds.
The people on those planes aged at different rates,
the same amount as the shift in the time difference
is measured by the clocks.
And so we can travel into the future,
but actually, we can travel into the future at different rates.
Let's say I get into spacecraft now and fly off to Alpha Centauri
and come back again. I can arrange that journey,
and if I can travel fast enough, such that I come back 1,000 years
in the future or 10,000 years in the future.
Actually, the closer I can make it to the speed of light,
the further into the future I can get.
I think the more that you know about time,
the more you consider the fundamental nature of reality itself
and discover that it's nothing like our experience of the world,
then the more astonished you become!
And at some point, I'll probably become so astonished
that I'll no longer be able to speak about it!
Even though physicists are still grappling with the fundamental
nature of time, we do know with reasonable certainty
how time will ultimately end.
There are few places on Earth where you can get an inkling
of what the far future has in store.
HELICOPTER ROTORS WHIR
This is Namibia's Skeleton Coast, where the cold waters
of 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 Edward 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.
And in the far future, long after our own sun has run out of fuel,
a similar destiny awaits the universe's last stars.
A black dwarf will be the final fate of those last stars -
white dwarfs that have become so cold that they barely emit
any more heat or light.
Black dwarves are dark, dense, decaying bowls 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 takes 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 that 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.
There were wild dogs everywhere, actually, when we were filming that.
And so they... Standing there on my own and they're all gone,
they're all in the helicopter, and I thought,
I really hope they come back
because the dogs are circling, you know.
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 is that number?
Well, 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.
CLOCK TICKS SOFTLY
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.
Nothing happens,
and it keeps not happening forever.
People always ask me, actually, why do you smile when you talk about
the inevitable decay of the universe and the dissolving of everything
that we hold most dear into a bath of radiation
that will... will fade?
So even the afterglow of our presence in the universe
will become undetectable and there will be no memory at all...
of everything or anything that we've created.
There will be no imprint left of us at all in the far future.
Why do you smile?
And I just think it's quite funny.
That's why I smile, I think!
It certainly does take us down a peg or two, doesn't it?
You know, I want to build a statue of myself, a grand celebration,
a permanent monument of my achievements.
There will be no such permanent monument of your achievements.
Don't worry about the statues. Don't worry about them.
They're all going to dissolve into a bath of photons!