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For more than a decade, I've made
programmes about the universe.
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And our place within it.
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There it is! There it is!
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I can see the parachutes.
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I've had some remarkable
encounters...
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I can't believe you can just
stand next to a spacecraft.
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Release.
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..memorable experiences...
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They came down exactly the same.
Wow.
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..and explained some beautiful
science about how our planet works.
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That really is the thin blue line
that protects us.
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Look at that!
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Now, I'm taking a new look
at those past programmes.
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It's surely as close as I'm going
to get to being in space.
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I think our knowledge really has
moved on since we made these films.
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So it's really interesting
to revisit
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some fundamental questions again.
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Are we alone in the universe?
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What really is gravity?
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Where will the exploration
of space take us?
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CLOCK TICKS
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And what is time?
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HIGH-PITCHED BEEPING
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Beeping's never good.
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I'm back at the Royal Institution
to re-watch some of my old films.
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And to explore the thing
by which we measure our lives.
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Time.
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It's a concept which is so familiar,
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and yet recent discoveries have
revealed it to be far stranger
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than we could have
possibly imagined.
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I think the question,
"What is time?"
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is one of the most fascinating
and evocative scientific questions.
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Because it's so fundamental
to human experience.
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Our experience of the world
is that the past is written,
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it has happened,
and the future is yet to be written.
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It's open.
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CLOCK TICKS
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But what is this thing ultimately
that the clock is doing,
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the ticking of the clock?
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It's one of the most baffling
questions in science.
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JAUNTY WHISTLING
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Ah, excellent, there you are.
Where am I? A bit complicated.
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Sort of a spaceship/time
machine/slash/swimming pool.
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Optional hat stand. I need five
minutes of your time and obviously
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when I say five minutes, I'm lying.
No, no, I'm just going to go
give a lecture.
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I know, I've just seen it. It's
great. But I haven't given it yet.
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Tricky to explain. Seen it anyway.
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Right, hold on to something,
probably your sanity.
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Ready?
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LOUD CRACKLING
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Usually it just twirls around.
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It's probably this.
Shut up, Brian!
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I'm often asked about time travel,
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and, yeah, some of it
comes from Doctor Who.
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It would be great, wouldn't it,
to have a TARDIS and to be able
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to go back and see some of the
great moments in history.
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DOCTOR WHO THEME TUNE
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It's a tantalising prospect.
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But before we can even begin
to consider time travel,
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we should explore
how we experience time.
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METALLIC THRUMMING
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The way that we experience time
and talk about it,
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is actually, if you think about it,
quite strange.
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Because, you know, there are
60 seconds in a minute, 60 minutes
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in an hour and 24 of those in a day,
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and then there are 365 days
in a year.
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It's interesting, I think, that
most of us have become completely
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disconnected from what
that's actually telling us.
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Which is that
we live on a ball of rock,
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that is spinning around on its axis
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once roughly every 24 hours or so.
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And in a plane that can go
that fast,
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you can really illustrate that.
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Because we live on a spinning
sphere,
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if we turn on the after-burners
and chase the setting sun,
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something
really interesting happens.
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This is a Eurofighter Typhoon.
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It flies at, at least Mach 1.85,
twice the speed of sound.
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I can't tell you exactly
how fast, because it's classified.
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They go up to at least 55,000 feet
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but again, I can't tell you,
it's classified.
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And you can't film
down those air intakes
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because they're classified as well.
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This one is BAE Systems'
development aircraft.
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I'm going to get in it in a minute,
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and it's got all the test software
in and the pilot told me that,
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you know, it's a bit ropey so press
control, alt, delete occasionally
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if it all goes funny,
and usually it comes back on.
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Which is good.
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Get in. Feet-wise, comfy? Good.
That's it.
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That's for, if you need to
control it at any point.
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It's unlikely. Unlikely.
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Have you got a sick bag?
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No.
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Worst comes to the worst,
do it in your glove.
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CONTROL TOWER: Charlie 69,
runway 07, clear take off.
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Surface wind 350 degrees,
seven knots over.
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PILOT: So, ready? Yeah.
Going to go for it.
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ENGINES ROAR
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There we go. Wahee.
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It's every bit as good
as you can imagine.
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It's beautiful. What a plane.
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On the east side, everything's
darkening up quite nicely
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as the sun starts to set.
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And on the ground it's already,
it's dark on the ground now,
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as far as the sun is concerned.
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So, accelerating.
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So that's Mach 0.78. Yeah.
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And the G-suit is in play here.
Yeah.
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Turning directly towards
the setting sun,
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the Typhoon accelerates to catch up
with the Earth's spin.
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Beneath us, a 6,000
billion, billion-tonne rock
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is spinning at 650mph.
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But travel faster
than the planet's surface
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and the normal passage of the day
is reversed.
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Right, accelerating. Accelerating.
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Oh, there we go,
that's acceleration. Mach 1.
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Through the sound barrier.
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As the jet accelerates,
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it starts to overtake
the spin of the Earth.
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Causing the setting sun
to rise again.
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Starting to grow a little.
It is. I can see it.
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We're beating the Earth.
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Absolutely terrific.
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Starting to climb again,
you can see it coming up. Yeah.
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That's Mach 1.4.
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So, that's a thousand miles an hour.
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Yeah,
almost a thousand miles an hour.
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And now the sun, it's almost
the full disc over the clouds.
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The sunrise. It is.
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Two sunrises in one day.
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And all you need is the world's
most advanced fighter aircraft.
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There we go.
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Beautiful.
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We've done it,
we've outrun the Earth.
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BRIAN CHUCKLES
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Goodbye, sun! Good.
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Right,
let's get ourselves on our way home.
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I was told that we caused a bit
of an incident in the Isle of Man
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because the sonic boom
did rattle, rattle a few windows.
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So, I apologise to all residents
of the Isle of Man!
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RADIO CHATTER
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This hidden celestial dynamics,
the Earth's spin and its orbit
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00:10:04,320 --> 00:10:08,920
around the sun, delivers our daily
and yearly experience of time.
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Spring goes into summer, and summer
into autumn, and autumn into winter.
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And we experience another season
and another year.
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But, of course,
they're not always the same,
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because every year that passes,
we get older.
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And so in that sense, I think time
connects with the central tragedy
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of human experience,
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the fact that inexorably
and unavoidably
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we get older and ultimately we die.
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So we're born and we die.
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And that's a consequence
of time passing,
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at least from our point of view,
as fragile human beings.
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CLOCK TICKS
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If you want to understand something,
you've got to be able to measure it
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and observe it,
and look at it and quantify it.
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And if you look back at many
ancient civilisations,
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the attempts to measure the
passage of time are rarely small.
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Often, they're massive.
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They're huge temples
that people built.
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So, clearly, there's not only
the practical need to measure
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the passage of time, but there's
some ritual attached to it.
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This is Chankillo on the
northwestern coast of Peru
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and it's one of South America's
lesser known archaeological sites.
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But, for me, it is surely
one of the most fascinating.
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Around 2,500 years ago,
a civilisation
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we know almost nothing about
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built this fortified temple
in the desert.
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Its walls were once brilliant white
and covered with painted figures.
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Today, all but the smallest
fragments of the decorations
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are gone.
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The details of this culture and all
traces of its language are lost.
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And yet, if you stand
in the right place,
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you can still experience
the true purpose of Chankillo
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in just the same way as you could
the day it was built.
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But to do that, you have to be here
before the sun rises.
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WIND WHISTLES AND HOWLS
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These towers form
an ancient solar calendar.
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Now, at different times of year,
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the sunrise point is at a
different place on the horizon.
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Actually, December 21st, which
here in the southern hemisphere
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is the Summer Solstice,
the longest day,
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when the sun rises just to the
right of the rightmost tower.
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Then, as the year passes,
the sun moves through the towers
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until on June 21st, which is the
Winter Solstice, the shortest day,
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it rises just to the left
of the leftmost tower.
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Actually, just in between that
mountain you can see in the distance
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and the leftmost tower.
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So, at any time of year,
if you watch the sun rise,
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you can measure its position
and you can tell within an accuracy
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of two or three days, the date.
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Today's date is September 15th.
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And so that means
that the sun will rise
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between the fifth
and the sixth towers.
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00:14:03,960 --> 00:14:08,240
Chankillo still works as a calendar
because the sun still rises in
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00:14:08,240 --> 00:14:12,440
the same place today as it did when
these stones were first laid down.
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00:14:18,120 --> 00:14:22,680
That is a magnificent sight
as the sun burns through the towers.
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You can almost feel
the presence of the past here.
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Imagine what it must have been like,
thousands of citizens stood here
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00:14:37,200 --> 00:14:40,280
to greet the sun, which was
almost certainly a deity,
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almost certainly their god.
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What a magnificent achievement.
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00:14:44,920 --> 00:14:48,680
It's probably one of our earliest
attempts to begin to measure
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00:14:48,680 --> 00:14:50,120
the heavens.
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00:15:01,040 --> 00:15:06,000
Time has played a central role
in the drama of human experience
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00:15:06,000 --> 00:15:08,280
for thousands of years.
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00:15:08,280 --> 00:15:11,800
But it's only when we try to measure
it accurately that we start
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00:15:11,800 --> 00:15:13,640
to appreciate its mystery.
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00:15:16,080 --> 00:15:19,920
So the way that traditionally
we measure the passage of time
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00:15:19,920 --> 00:15:23,520
is to look to the heavens
and look to when the sun
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00:15:23,520 --> 00:15:26,880
reaches its highest point in
the sky, and we call that noon.
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00:15:26,880 --> 00:15:32,120
That turns out not to be sufficient
because it's not accurate enough.
215
00:15:32,120 --> 00:15:35,840
The Earth doesn't spin on its axis
at a constant rate.
216
00:15:35,840 --> 00:15:39,520
The Earth wobbles around
by quite a bit, actually.
217
00:15:39,520 --> 00:15:42,960
The Earth's orbit
is not entirely precise.
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00:15:42,960 --> 00:15:44,680
Things change.
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00:15:44,680 --> 00:15:48,240
So if we want to measure
increasingly small time intervals
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00:15:48,240 --> 00:15:51,440
accurately, then the heavens
are not the way to do it.
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00:15:53,160 --> 00:15:55,920
And so we can build
mechanical watches,
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00:15:55,920 --> 00:15:58,440
and that's what we did initially
when we had to measure time
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00:15:58,440 --> 00:16:00,680
more accurately for
navigational purposes.
224
00:16:00,680 --> 00:16:04,920
But even bits of, you know,
cogs and gears and springs,
225
00:16:04,920 --> 00:16:07,960
that's not particularly
accurate either.
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00:16:07,960 --> 00:16:11,320
And so if you really want to start
dividing time up into very
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00:16:11,320 --> 00:16:15,760
small intervals, which we have to do
today for so many reasons,
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00:16:15,760 --> 00:16:18,760
then you need to look
to the subatomic world
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00:16:18,760 --> 00:16:23,680
and you find that in the world of
atoms and subatomic particles,
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00:16:23,680 --> 00:16:28,080
you can identify exquisitely
accurate natural clocks.
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00:16:29,560 --> 00:16:31,840
MILITARY BAND PLAYS
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I'm going to try and answer
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one of the simplest questions
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00:16:36,120 --> 00:16:38,960
you could ask - what time is it?
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These are the early days, right.
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00:16:41,080 --> 00:16:44,800
This is one of the first
television programmes that I made.
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00:16:46,880 --> 00:16:50,120
If there's one place on Earth
where you can come to find the time,
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00:16:50,120 --> 00:16:51,920
it's here in Washington DC.
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00:16:54,800 --> 00:16:57,640
This is the home
of the US Naval Observatory,
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00:16:57,640 --> 00:17:01,200
one of a select bunch of time lords
dotted across the planet
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00:17:01,200 --> 00:17:03,800
who are the keepers
of time on Earth.
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00:17:03,800 --> 00:17:07,840
COMPUTERISED VOICE: Universal Time,
19 hours, 54 minutes exactly.
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00:17:09,680 --> 00:17:12,760
A time now derived
from atomic clocks.
244
00:17:14,080 --> 00:17:16,840
Dennis McCarthy, Director of Time.
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00:17:16,840 --> 00:17:21,800
We defined a time in the 1950s
based on the position of the moon
246
00:17:21,800 --> 00:17:23,680
with respect to the stars.
247
00:17:23,680 --> 00:17:26,640
We needed a more
accurate kind of time.
248
00:17:26,640 --> 00:17:30,840
Not only is it...
does it have to be more accurate
249
00:17:30,840 --> 00:17:33,080
but it has to be more accessible.
250
00:17:34,160 --> 00:17:37,920
That accessible kind of time
is provided by atomic clocks.
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00:17:37,920 --> 00:17:41,560
What we need to tell time
is something which repeats
252
00:17:41,560 --> 00:17:44,920
with great regularity
that you can count on.
253
00:17:44,920 --> 00:17:50,520
How well we can tell time
depends on which atom you're using.
254
00:17:50,520 --> 00:17:55,680
So we choose certain ones to...
to use for keeping atomic time.
255
00:17:57,520 --> 00:18:01,400
Inside the clocks are the atoms
of a rare metal called caesium.
256
00:18:02,920 --> 00:18:06,320
The electrons in the caesium
atoms are made to jump up.
257
00:18:07,560 --> 00:18:10,840
Then as they fall back down,
they give out light.
258
00:18:12,560 --> 00:18:17,440
These light waves peak over
nine billion times every second
259
00:18:17,440 --> 00:18:20,400
and it's this light
that drives the clock,
260
00:18:20,400 --> 00:18:25,000
effectively producing nine billion
ticks for each atomic second.
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00:18:26,560 --> 00:18:29,160
This number never changes,
never alters
262
00:18:29,160 --> 00:18:30,960
and that's why it's so accurate.
263
00:18:32,760 --> 00:18:35,560
So the atomic clock is actually
putting out an electronic signal
264
00:18:35,560 --> 00:18:40,000
which is essentially analogous
to the ticking of a pendulum clock.
265
00:18:40,000 --> 00:18:42,960
You know, a pendulum clock which
might tick once every second
266
00:18:42,960 --> 00:18:44,760
or once every couple of seconds.
267
00:18:44,760 --> 00:18:46,800
This thing is providing us
something
268
00:18:46,800 --> 00:18:49,440
which is going nine billion times
per second.
269
00:18:49,440 --> 00:18:53,840
So it provides us
with a very fine definition of time.
270
00:18:53,840 --> 00:18:57,160
We actually have a number of clocks
at the Naval Observatory
271
00:18:57,160 --> 00:18:59,400
located all over the grounds.
272
00:18:59,400 --> 00:19:01,560
Here's... here's one of them.
273
00:19:01,560 --> 00:19:04,120
This is the master clock system one.
Oh, yeah.
274
00:19:05,680 --> 00:19:08,640
This is the master clock system two.
275
00:19:09,800 --> 00:19:13,240
So if I want an answer to the
question - what time is it?
276
00:19:14,880 --> 00:19:16,600
There it is? That's it.
277
00:19:16,600 --> 00:19:20,120
COMPUTERISED VOICE: Universal Time
20 hours, zero minutes exactly.
278
00:19:21,160 --> 00:19:24,040
Why do I need a clock that accurate?
279
00:19:24,040 --> 00:19:26,400
Well, we do.
280
00:19:26,400 --> 00:19:30,720
If you're using time to measure
distance, which is how the GPS
281
00:19:30,720 --> 00:19:34,040
satellite navigation system works,
then it matters.
282
00:19:34,040 --> 00:19:37,320
If your clock drifts
by one nanosecond,
283
00:19:37,320 --> 00:19:41,360
then your position measurement is
drifting by something like a foot.
284
00:19:43,960 --> 00:19:47,520
Atomic clocks can measure
and divide time into intervals
285
00:19:47,520 --> 00:19:51,040
that are so minuscule that they
are beyond human perception.
286
00:19:52,520 --> 00:19:55,680
But this precision means little
when we begin to consider
287
00:19:55,680 --> 00:19:59,960
the timescales that determine
our ultimate fate - cosmic time.
288
00:20:05,960 --> 00:20:10,360
Timescales in the cosmos
seems so unimaginably vast,
289
00:20:10,360 --> 00:20:12,800
it's almost impossible
to relate to them.
290
00:20:14,720 --> 00:20:18,000
Yet there are places on Earth
where we can begin to encounter
291
00:20:18,000 --> 00:20:20,160
time on these universal scales.
292
00:20:29,000 --> 00:20:32,920
This is Ostional on the northern
Pacific coast of Costa Rica,
293
00:20:32,920 --> 00:20:38,000
and I've come here to witness
a natural event that's been
294
00:20:38,000 --> 00:20:41,000
happening long before there were
any humans here to see it.
295
00:20:42,480 --> 00:20:46,480
And I suppose it really is
a window into the distant past
296
00:20:46,480 --> 00:20:48,120
of life on our planet.
297
00:20:52,320 --> 00:20:54,720
PEOPLE CHAT AND LAUGH
298
00:21:11,400 --> 00:21:13,920
Once the sun has
dipped below the horizon
299
00:21:13,920 --> 00:21:17,840
and the moon conspired
to make the tides just right,
300
00:21:17,840 --> 00:21:21,320
this beach is visited
by prehistoric creatures.
301
00:21:32,560 --> 00:21:35,720
Under the cover of darkness,
they emerge from the ocean.
302
00:21:45,000 --> 00:21:47,920
Playa Ostional is one of the
few beaches in the world
303
00:21:47,920 --> 00:21:51,040
where large numbers of sea turtles
make their nests.
304
00:22:01,640 --> 00:22:05,720
But what makes this truly remarkable
is the sheer length of time
305
00:22:05,720 --> 00:22:08,200
scenes like this
have been playing out.
306
00:22:14,120 --> 00:22:18,400
Well, this is part one of the
oldest life cycles on Earth.
307
00:22:20,000 --> 00:22:24,120
On nights like these for the
last 100 million years,
308
00:22:24,120 --> 00:22:27,560
turtles like this have been hauling
themselves out of the ocean
309
00:22:27,560 --> 00:22:29,440
to lay their eggs.
310
00:22:31,760 --> 00:22:34,360
It's an almost incomprehensible
time span.
311
00:22:34,360 --> 00:22:37,560
I mean, 100 million years ago,
there were dinosaurs roaming
312
00:22:37,560 --> 00:22:41,280
the Earth, but the Earth itself
looked very different.
313
00:22:41,280 --> 00:22:45,360
I mean, South America was not
connected to North America.
314
00:22:45,360 --> 00:22:49,400
North America was somewhere
over close to Europe.
315
00:22:49,400 --> 00:22:51,720
Australia was connected
to Antarctica.
316
00:22:56,560 --> 00:22:58,840
THUNDER RUMBLES
317
00:22:58,840 --> 00:23:01,560
It really is quite
wonderful to be so close
318
00:23:01,560 --> 00:23:05,600
to such an ancient cycle of life.
319
00:23:07,640 --> 00:23:09,920
You can hear her
breathing, actually.
320
00:23:11,440 --> 00:23:13,760
TURTLE EXHALES
321
00:23:21,640 --> 00:23:25,080
So, a remarkable experience.
322
00:23:25,080 --> 00:23:29,760
I mean, it really is beautiful to
see that on the one night
323
00:23:29,760 --> 00:23:32,760
of many hundreds of millions
of nights
324
00:23:32,760 --> 00:23:34,640
stretching back into the past.
325
00:23:42,280 --> 00:23:43,960
And she's gone.
326
00:23:56,440 --> 00:23:59,680
To witness a moment like this
is to open up a connection
327
00:23:59,680 --> 00:24:01,520
to the deep past.
328
00:24:03,960 --> 00:24:08,480
To experience timespans far longer
than the history of our own species.
329
00:24:11,320 --> 00:24:15,160
Yet, even the 100 million year
story of the turtles
330
00:24:15,160 --> 00:24:20,560
only begins to connect us with
the vast sweep of cosmic time.
331
00:24:26,880 --> 00:24:29,760
Our entire solar system
is travelling
332
00:24:29,760 --> 00:24:32,400
on an unimaginably vast orbit,
333
00:24:32,400 --> 00:24:34,960
spinning around the centre
of our galaxy.
334
00:24:42,200 --> 00:24:47,560
It takes 250 million years to make
just one circuit of the Milky Way.
335
00:24:55,560 --> 00:24:58,280
In the entire history
of the human race,
336
00:24:58,280 --> 00:25:02,600
we've travelled less than
a tenth of 1% of that orbit.
337
00:25:15,760 --> 00:25:19,840
The timescales of our galaxy are
almost beyond human comprehension.
338
00:25:22,400 --> 00:25:25,360
But when we extend our gaze
beyond the Milky Way
339
00:25:25,360 --> 00:25:28,520
and out into the universe,
340
00:25:28,520 --> 00:25:32,360
we come face-to-face
with truly deep time.
341
00:25:36,040 --> 00:25:39,480
The time that ticks on your watch
is the time now,
342
00:25:39,480 --> 00:25:41,120
the time of the present.
343
00:25:42,760 --> 00:25:46,160
But the feeling we experience
as the present time
344
00:25:46,160 --> 00:25:48,840
is something we shouldn't
take for granted.
345
00:25:48,840 --> 00:25:53,560
Much of what we believe is in the
present is drawn from the past.
346
00:25:55,160 --> 00:25:58,360
What we feel is happening now
happened a little while ago.
347
00:26:00,800 --> 00:26:03,720
We feel that we experience
a now around us.
348
00:26:03,720 --> 00:26:06,320
Everything we see happened now.
349
00:26:06,320 --> 00:26:10,440
But actually the light coming
from distant things into your eye
350
00:26:10,440 --> 00:26:13,080
takes time to get there.
351
00:26:13,080 --> 00:26:16,320
So...you look at the sun.
352
00:26:16,320 --> 00:26:20,920
The sun is 93 million miles away.
353
00:26:20,920 --> 00:26:25,520
That means light takes over
eight minutes to get from it
354
00:26:25,520 --> 00:26:30,360
into my eyes. So I'm seeing the sun
as it was eight minutes in the past.
355
00:26:30,360 --> 00:26:34,640
It could explode and I wouldn't
notice for eight minutes.
356
00:26:34,640 --> 00:26:37,320
I'd just see that beautiful
image of the setting sun.
357
00:26:40,200 --> 00:26:43,240
The fact that light travels
at a finite speed
358
00:26:43,240 --> 00:26:45,480
offers us a unique opportunity.
359
00:26:46,800 --> 00:26:51,040
It allows us to look back,
not just eight minutes but millions,
360
00:26:51,040 --> 00:26:53,320
even billions of years.
361
00:26:58,680 --> 00:27:02,360
I've come to Baltimore
to look back in time.
362
00:27:04,840 --> 00:27:09,040
Former director of the Hubble Space
Telescope Steve Beckwith
363
00:27:09,040 --> 00:27:12,120
was responsible for taking
an extraordinary photograph.
364
00:27:13,560 --> 00:27:17,080
As a director, I had at my
discretion 10% of the telescope time
365
00:27:17,080 --> 00:27:19,400
per year, that I could
use for anything.
366
00:27:19,400 --> 00:27:22,920
One year I took all of my time,
in fact I took a little bit more
367
00:27:22,920 --> 00:27:25,440
than all of my time,
and decided that we would devote it
368
00:27:25,440 --> 00:27:28,000
to the deepest picture
ever taken of the universe.
369
00:27:29,720 --> 00:27:34,880
In 2004, Steve pointed the
Hubble Telescope at a tiny piece
370
00:27:34,880 --> 00:27:39,280
of the night sky and took a
picture called the Ultra-Deep Field.
371
00:27:41,600 --> 00:27:44,040
It took a million seconds
of exposure
372
00:27:44,040 --> 00:27:48,000
on the Hubble Space Telescope, the
world's most powerful telescope,
373
00:27:48,000 --> 00:27:52,680
and in this image we can look
back in time 13 billion years.
374
00:27:52,680 --> 00:27:55,880
It's a difficult picture
almost to comprehend, isn't it?
375
00:27:55,880 --> 00:27:59,240
Because in some sense, it's...
3D is the wrong word.
376
00:27:59,240 --> 00:28:02,280
But it's, it's some sense...
Oh, no, it is the right word.
377
00:28:02,280 --> 00:28:04,800
It is 3D.
We are looking back in time.
378
00:28:07,120 --> 00:28:10,520
Every single galaxy in this image
can be dated.
379
00:28:12,280 --> 00:28:13,960
This galaxy emitted its light
380
00:28:13,960 --> 00:28:16,560
when the universe
was 8.8 billion years old.
381
00:28:16,560 --> 00:28:19,960
Then, as you go back in time, this
is a galaxy that emitted its light
382
00:28:19,960 --> 00:28:22,280
when the universe
was 3.3 billion years old.
383
00:28:22,280 --> 00:28:24,320
You can see it looks
completely different.
384
00:28:24,320 --> 00:28:26,160
It's really very chaotic.
385
00:28:26,160 --> 00:28:28,880
And this is one billion years
after the Big Bang.
386
00:28:28,880 --> 00:28:31,240
Very red, a little tail, very small.
387
00:28:33,320 --> 00:28:37,520
The most distant galaxy
in the Ultra-Deep Field
388
00:28:37,520 --> 00:28:40,080
is a red one that's right over here.
This one here?
389
00:28:40,080 --> 00:28:42,720
The light from that was
emitted when the universe
390
00:28:42,720 --> 00:28:44,760
was 700-800 million years old.
391
00:28:45,840 --> 00:28:49,760
So, really, this is one
of the first structures
392
00:28:49,760 --> 00:28:51,800
that formed in the universe?
393
00:28:51,800 --> 00:28:54,040
This is one of the first
structures that formed
394
00:28:54,040 --> 00:28:56,520
and it's one of the first structures
we've been able to see.
395
00:28:56,520 --> 00:28:58,800
In a sense you see this...
396
00:29:00,440 --> 00:29:03,840
..almost, I was going
to say paradoxical,
397
00:29:03,840 --> 00:29:08,880
but strange behaviour of the
universe as revealed by astronomy.
398
00:29:08,880 --> 00:29:14,040
Because I'm trying to say, well,
what does that look like now?
399
00:29:14,040 --> 00:29:16,320
You know, what would
that look like now?
400
00:29:16,320 --> 00:29:20,160
In a sense, it's the wrong
language to use, isn't it?
401
00:29:20,160 --> 00:29:22,520
That's what it looks like now.
That's right.
402
00:29:24,960 --> 00:29:29,960
Steve has turned his photo into
a movie to journey back in time.
403
00:29:31,640 --> 00:29:35,360
You see these little pieces coming
at us? We're going back in time,
404
00:29:35,360 --> 00:29:37,720
and you can see the
three-dimensional effect.
405
00:29:37,720 --> 00:29:40,360
Some of these others
are a little farther back
406
00:29:40,360 --> 00:29:42,760
but here we're going back,
we're probably back now
407
00:29:42,760 --> 00:29:45,520
about three billion years
from the present.
408
00:29:45,520 --> 00:29:48,320
As we keep going
and you get to the smaller ones,
409
00:29:48,320 --> 00:29:51,400
you get back to about
eight or nine billion years.
410
00:29:53,040 --> 00:29:56,280
And then, when we get to the
very tiny most distant ones,
411
00:29:56,280 --> 00:30:00,600
we'll be back probably
ten or 11 billion years in time.
412
00:30:00,600 --> 00:30:03,000
And we're deep into the universe
and we're just looking
413
00:30:03,000 --> 00:30:07,160
at the smallest structures back
in time to about 13 billion years,
414
00:30:07,160 --> 00:30:09,200
and suddenly we run out.
415
00:30:26,560 --> 00:30:29,320
The Hubble Space Telescope
can see galaxies
416
00:30:29,320 --> 00:30:33,160
that are as they were about 500
million years after the Big Bang.
417
00:30:34,800 --> 00:30:37,400
But it can't see
further back than that.
418
00:30:38,520 --> 00:30:41,560
The reason is that the
universe is expanding.
419
00:30:43,520 --> 00:30:46,760
And, so, as the light travels
through the expanding universe,
420
00:30:46,760 --> 00:30:48,800
it gets stretched.
421
00:30:48,800 --> 00:30:51,600
And that means that it gets redder
and redder and redder
422
00:30:51,600 --> 00:30:54,800
until it gets so red
that the Hubble Space Telescope
423
00:30:54,800 --> 00:30:56,600
isn't sensitive to it.
424
00:30:56,600 --> 00:30:59,600
So it can't see any
further away than that.
425
00:31:03,000 --> 00:31:06,480
But a new telescope
with that capability
426
00:31:06,480 --> 00:31:08,800
is due to be launched
later this year.
427
00:31:11,240 --> 00:31:14,800
The James Webb Telescope is going
to be much more sensitive
428
00:31:14,800 --> 00:31:17,200
to those, what we call,
the infrared light,
429
00:31:17,200 --> 00:31:19,160
so the very long wavelengths.
430
00:31:19,160 --> 00:31:23,400
And that means it will be able
to see back past those galaxies
431
00:31:23,400 --> 00:31:26,760
that Hubble can see to the very
early history of the universe.
432
00:31:28,160 --> 00:31:32,760
We'll be able to watch the formation
of the first stars and galaxies.
433
00:31:40,200 --> 00:31:43,400
We're able to look very
far back into the past,
434
00:31:43,400 --> 00:31:45,280
but we can't see into the future.
435
00:31:46,400 --> 00:31:48,240
Which raises the question,
436
00:31:48,240 --> 00:31:50,960
what is the difference
between the two?
437
00:31:50,960 --> 00:31:54,640
Why does time appear to flow
only in one direction?
438
00:31:56,240 --> 00:31:59,800
This question has puzzled
many of science's greatest minds.
439
00:32:02,080 --> 00:32:05,320
All the laws of nature that we
have today that we consider
440
00:32:05,320 --> 00:32:10,480
to be fundamental, so Einstein's
equations or Newton's laws
441
00:32:10,480 --> 00:32:13,920
for that matter, all of them
make no distinction
442
00:32:13,920 --> 00:32:18,480
in the direction of the
flow of time, if you like.
443
00:32:18,480 --> 00:32:24,360
There's only one law of physics that
has an explicit direction of time
444
00:32:24,360 --> 00:32:29,160
in it, and that law is concerned
with something called entropy.
445
00:32:38,720 --> 00:32:42,440
Entropy explains why,
left to the mercy of the elements,
446
00:32:42,440 --> 00:32:47,000
mortar crumbles, glass shatters
and buildings collapse.
447
00:32:50,200 --> 00:32:54,120
And a good way to understand how
is to think of objects
448
00:32:54,120 --> 00:32:58,520
not as single things but as being
made up of many constituent parts,
449
00:32:58,520 --> 00:33:03,160
like the individual grains
that make up this pile of sand.
450
00:33:05,960 --> 00:33:08,880
Now, entropy is a measure
of how many ways
451
00:33:08,880 --> 00:33:13,640
I can rearrange those grains and
still keep the sand pile the same.
452
00:33:13,640 --> 00:33:16,600
And there are trillions and
trillions and trillions
453
00:33:16,600 --> 00:33:18,560
of ways of doing that.
454
00:33:18,560 --> 00:33:21,280
I mean, pretty much anything
I do to this sand pile,
455
00:33:21,280 --> 00:33:23,920
if I mess the sand around
and move it around,
456
00:33:23,920 --> 00:33:27,000
then it doesn't change the shape
or the structure at all.
457
00:33:27,000 --> 00:33:29,960
So, in the language of entropy,
458
00:33:29,960 --> 00:33:32,440
this sand pile has high entropy
459
00:33:32,440 --> 00:33:35,320
because there are many, many ways
that I can rearrange
460
00:33:35,320 --> 00:33:37,600
its constituents and not change it.
461
00:33:38,880 --> 00:33:42,320
But now let me create
some order in the universe.
462
00:33:49,960 --> 00:33:54,400
Now, there are approximately as
many sand grains in this sand castle
463
00:33:54,400 --> 00:33:55,880
as there are in the sand pile.
464
00:33:57,680 --> 00:34:01,120
But now, virtually anything
I do to it will mess it up,
465
00:34:01,120 --> 00:34:05,080
will remove the beautiful
order from this structure.
466
00:34:05,080 --> 00:34:08,920
And because of that, the sand castle
has a low entropy.
467
00:34:08,920 --> 00:34:11,280
It's a much more ordered state.
468
00:34:11,280 --> 00:34:14,720
So, many ways of rearranging
the sand grains
469
00:34:14,720 --> 00:34:18,760
without changing the structure -
high entropy.
470
00:34:18,760 --> 00:34:22,640
Very few ways of rearranging
the sand grains without changing
471
00:34:22,640 --> 00:34:26,520
the structure, without
disordering it - low entropy.
472
00:34:35,480 --> 00:34:38,680
Now, imagine I was to leave this
castle in the desert all day -
473
00:34:38,680 --> 00:34:41,840
then, it's obvious
what's going to happen.
474
00:34:41,840 --> 00:34:44,680
The desert winds are going
to blow the sand around
475
00:34:44,680 --> 00:34:47,560
and this castle
is going to disintegrate.
476
00:34:47,560 --> 00:34:50,440
It's going to become less ordered.
477
00:34:50,440 --> 00:34:52,120
It's going to fall to bits.
478
00:34:55,920 --> 00:35:00,040
But think about what's
happening on the fundamental level.
479
00:35:00,040 --> 00:35:02,720
The wind is taking
the sand off the castle
480
00:35:02,720 --> 00:35:07,240
and blowing it over there somewhere
and making a sand pile.
481
00:35:07,240 --> 00:35:11,360
There's nothing fundamental
in the laws of physics that says
482
00:35:11,360 --> 00:35:15,000
that the wind couldn't pick up
some sand from over here,
483
00:35:15,000 --> 00:35:19,160
deposit it here,
and deposit it in precisely
484
00:35:19,160 --> 00:35:21,240
the shape of a sand castle.
485
00:35:21,240 --> 00:35:25,840
In principle, the wind could
spontaneously build a sand castle
486
00:35:25,840 --> 00:35:27,640
out of a pile of sand.
487
00:35:39,000 --> 00:35:42,360
There's no reason why that couldn't
happen, it's just extremely,
488
00:35:42,360 --> 00:35:46,760
extremely unlikely because there
are very few ways of organising this
489
00:35:46,760 --> 00:35:49,160
sand so that it looks like a castle.
490
00:35:55,960 --> 00:35:58,400
It's overwhelmingly more likely
491
00:35:58,400 --> 00:36:01,520
that when the wind blows
the sand around, it will take
492
00:36:01,520 --> 00:36:03,600
the low entropy structure,
the castle,
493
00:36:03,600 --> 00:36:08,240
and turn it into a high
entropy structure, the sand pile.
494
00:36:15,400 --> 00:36:18,840
So, entropy always increases.
495
00:36:18,840 --> 00:36:20,760
Why is that?
496
00:36:20,760 --> 00:36:24,640
Because it's overwhelmingly
more likely that it will.
497
00:36:34,200 --> 00:36:38,920
There was a tremendous
sandstorm and we all hid,
498
00:36:38,920 --> 00:36:40,760
and it was just vicious.
499
00:36:45,000 --> 00:36:47,360
And when we came out,
500
00:36:47,360 --> 00:36:49,920
we had cameras and we were opening,
taking the lenses off
501
00:36:49,920 --> 00:36:52,160
and just pouring sand out of them!
502
00:37:08,400 --> 00:37:11,880
The Second Law of Thermodynamics,
for me, demonstrates everything
503
00:37:11,880 --> 00:37:16,200
that is powerful and beautiful
and profound about physics.
504
00:37:16,200 --> 00:37:20,360
Here's a law that entered science
as a way of talking about how heat
505
00:37:20,360 --> 00:37:23,760
moves around and the
efficiency of steam engines.
506
00:37:23,760 --> 00:37:29,160
But it ended up being able to
explain one of THE great mysteries
507
00:37:29,160 --> 00:37:31,200
in the history of science.
508
00:37:31,200 --> 00:37:34,880
Why is there a difference
between the past and the future?
509
00:37:34,880 --> 00:37:39,800
You see, the Second Law says that
everything tends from order
510
00:37:39,800 --> 00:37:41,640
to disorder.
511
00:37:41,640 --> 00:37:44,000
That means that there
is a difference
512
00:37:44,000 --> 00:37:45,960
between the past and the future.
513
00:37:45,960 --> 00:37:48,480
In the past,
the universe was more ordered
514
00:37:48,480 --> 00:37:52,480
and in the future,
the universe will be less ordered.
515
00:37:52,480 --> 00:37:56,000
And that means that there's a
direction to the passage of time.
516
00:37:56,000 --> 00:38:00,520
So, the Second Law of Thermodynamics
has introduced the concept
517
00:38:00,520 --> 00:38:03,760
of an arrow of time into science.
518
00:38:05,480 --> 00:38:08,560
The so-called
thermodynamic arrow of time,
519
00:38:08,560 --> 00:38:11,880
this idea that entropy
always increases,
520
00:38:11,880 --> 00:38:18,320
is well understood, but actually its
origin at a deep level
521
00:38:18,320 --> 00:38:20,440
is not so clear.
522
00:38:22,560 --> 00:38:26,720
The reason seems to be
something to do with
523
00:38:26,720 --> 00:38:30,080
the origin of the universe itself
and the presence of this
524
00:38:30,080 --> 00:38:34,240
strange thing called the Big Bang
way back in our past.
525
00:38:34,240 --> 00:38:38,920
Why were things in the past
so beautifully ordered,
526
00:38:38,920 --> 00:38:44,440
that the universe can fall to bits
gently and in the process,
527
00:38:44,440 --> 00:38:47,360
in the transition from order
to disorder,
528
00:38:47,360 --> 00:38:49,120
these tremendous structures,
529
00:38:49,120 --> 00:38:52,480
of which we are
the most magnificent example,
530
00:38:52,480 --> 00:38:55,240
can exist for a brief time
in the universe?
531
00:38:57,120 --> 00:39:00,800
There are almost more opinions than
there are theoretical physicists
532
00:39:00,800 --> 00:39:02,840
on this question!
533
00:39:04,240 --> 00:39:08,720
The Second Law of Thermodynamics
is an explanation for the arrow
534
00:39:08,720 --> 00:39:12,920
of time, and what makes the past
different from the future.
535
00:39:14,880 --> 00:39:18,880
But it is silent on a question
that excites science fiction writers
536
00:39:18,880 --> 00:39:21,160
and physicists alike.
537
00:39:23,280 --> 00:39:26,160
If I'm in a big audience
of people and someone says,
538
00:39:26,160 --> 00:39:29,040
"Is time travel possible?" there
might be someone who thinks
539
00:39:29,040 --> 00:39:32,800
they know it just adds a bit
of a laugh and chuckles.
540
00:39:32,800 --> 00:39:34,720
It is a very good question.
541
00:39:34,720 --> 00:39:36,920
The answer is,
we don't know for sure.
542
00:39:43,120 --> 00:39:46,360
I think that, ultimately,
543
00:39:46,360 --> 00:39:49,400
the desire to go back in time
544
00:39:49,400 --> 00:39:53,640
is tied in to the tragedy
of human experience.
545
00:39:53,640 --> 00:39:55,440
We've all...
546
00:39:55,440 --> 00:39:58,200
There are not only moments
that we wish we could relive,
547
00:39:58,200 --> 00:40:01,320
there are people that we
wish we could see again.
548
00:40:01,320 --> 00:40:03,800
People who are no longer with us.
549
00:40:03,800 --> 00:40:08,200
So, the idea that somehow the past
might be accessible is extremely
550
00:40:08,200 --> 00:40:10,320
enticing and powerful, emotionally.
551
00:40:13,680 --> 00:40:17,560
But that's impossible if the past
only exists in our memories.
552
00:40:18,960 --> 00:40:21,520
That was the accepted view.
553
00:40:21,520 --> 00:40:23,480
But Einstein changed that.
554
00:40:25,040 --> 00:40:28,400
If we take his Theory of Relativity
at face value,
555
00:40:28,400 --> 00:40:32,200
then every moment of our past
still exists.
556
00:40:37,600 --> 00:40:41,880
We feel as if we move through
space as time ticks by.
557
00:40:43,000 --> 00:40:44,640
But that's an illusion.
558
00:40:44,640 --> 00:40:48,360
The separation of space
and time is false.
559
00:40:48,360 --> 00:40:51,480
The first person to realise that
was Albert Einstein.
560
00:40:51,480 --> 00:40:55,880
He thought deeply about motion,
about the idea that we can't tell
561
00:40:55,880 --> 00:40:57,640
whether we're moving or not.
562
00:40:57,640 --> 00:41:02,200
And he tried to reconcile that with
our picture of the universal laws
563
00:41:02,200 --> 00:41:05,760
of nature, and he found
that he could do,
564
00:41:05,760 --> 00:41:10,880
at the expensive of jettisoning
space and time as separate entities
565
00:41:10,880 --> 00:41:15,880
and merging them together
into a unified whole,
566
00:41:15,880 --> 00:41:19,320
the fabric of the universe
called Spacetime.
567
00:41:22,480 --> 00:41:25,320
As the Earth moves
through Spacetime,
568
00:41:25,320 --> 00:41:29,120
its orbit traces out a spiral
as it circles the sun
569
00:41:29,120 --> 00:41:31,600
and races into the future.
570
00:41:35,840 --> 00:41:38,840
It never returns to the same place
571
00:41:38,840 --> 00:41:41,880
because each moment is
a different location
572
00:41:41,880 --> 00:41:44,120
in the fabric of the universe.
573
00:41:48,480 --> 00:41:51,640
And just as the Earth
travels relentlessly onwards
574
00:41:51,640 --> 00:41:53,920
on its path through Spacetime,
575
00:41:53,920 --> 00:41:55,840
so must we.
576
00:42:11,360 --> 00:42:16,440
So this is how Einstein asks us
to picture the sweep of our lives,
577
00:42:16,440 --> 00:42:19,160
the experience of living.
578
00:42:19,160 --> 00:42:21,920
Our lives are a series of moments
579
00:42:21,920 --> 00:42:25,280
and they're laid out
like places on a map.
580
00:42:28,000 --> 00:42:30,120
There's me as a little baby.
581
00:42:30,120 --> 00:42:32,040
My dad with my grandad.
582
00:42:34,680 --> 00:42:38,200
That idyllic summer some time in the
early '70s in a paddling pool
583
00:42:38,200 --> 00:42:39,880
with my sister.
584
00:42:42,840 --> 00:42:46,040
When I was about four years old.
585
00:42:46,040 --> 00:42:48,840
And the perfect Christmas
with my grandparents
586
00:42:48,840 --> 00:42:51,160
sometime back in the 1970s.
587
00:42:51,160 --> 00:42:56,040
There's me when I was 20 years old
with a ridiculous haircut
588
00:42:56,040 --> 00:42:59,360
playing a gig somewhere in the
middle of Europe.
589
00:42:59,360 --> 00:43:01,000
In Budapest, I think.
590
00:43:04,280 --> 00:43:05,720
Wedding day.
591
00:43:08,640 --> 00:43:11,800
And me in Oldham, where I grew up,
592
00:43:11,800 --> 00:43:14,240
with my little boy, George.
593
00:43:19,280 --> 00:43:21,640
That was a very personal scene.
594
00:43:22,760 --> 00:43:25,680
It was really personal because,
actually, it wasn't long
595
00:43:25,680 --> 00:43:27,160
after my dad had died.
596
00:43:27,160 --> 00:43:31,080
So in my mind, there was,
obviously, as with everyone
597
00:43:31,080 --> 00:43:33,600
who goes through those
experiences as we all do,
598
00:43:33,600 --> 00:43:36,920
there's a, you know,
599
00:43:36,920 --> 00:43:41,160
a reconsideration
or a rethinking of the past.
600
00:43:41,160 --> 00:43:45,000
You find your mind wandering back
into the past and past events.
601
00:43:46,640 --> 00:43:49,480
This isn't exactly like a map.
602
00:43:49,480 --> 00:43:54,080
See, I can return to these places
in space, to Oldham,
603
00:43:54,080 --> 00:43:57,560
to central Europe, to Duluth,
Minnesota where I got married,
604
00:43:57,560 --> 00:43:59,320
back to Oldham again.
605
00:44:00,680 --> 00:44:05,280
But I can't return to these moments,
to these events in Spacetime.
606
00:44:05,280 --> 00:44:09,240
Because of the geometry
of Spacetime itself,
607
00:44:09,240 --> 00:44:13,440
we are compelled to move inexorably
into the future.
608
00:44:18,400 --> 00:44:22,600
What's interesting is that in
Einstein's Theory of Relativity,
609
00:44:22,600 --> 00:44:26,240
the past is not accessible
610
00:44:26,240 --> 00:44:30,520
but it's still there
in a very real sense.
611
00:44:30,520 --> 00:44:35,600
I think the bottom line is,
no, you can't travel into the past.
612
00:44:36,680 --> 00:44:38,400
Probably!
613
00:44:38,400 --> 00:44:43,360
But the explanation for that
is anything but trivial.
614
00:44:46,760 --> 00:44:49,960
But time travel into the future
is a different matter.
615
00:44:49,960 --> 00:44:53,520
We are all travelling
into the future all the time.
616
00:44:53,520 --> 00:44:57,600
But Einstein's Theory of Relativity
tells us that we are each
617
00:44:57,600 --> 00:44:59,600
doing it at different rates.
618
00:45:02,920 --> 00:45:06,520
We experience time passing
because we are all travelling
619
00:45:06,520 --> 00:45:08,920
along the time dimension.
620
00:45:10,480 --> 00:45:12,760
But, strangely, Einstein also said
621
00:45:12,760 --> 00:45:16,160
we don't all experience
the same time.
622
00:45:20,600 --> 00:45:23,840
Spacetime can be pictured
as a sort of fabric
623
00:45:23,840 --> 00:45:27,760
where time and space are
inextricably woven together.
624
00:45:29,280 --> 00:45:33,840
As a result, the dimensions of space
and time can get mixed up.
625
00:45:35,880 --> 00:45:38,280
Although we are all travelling
through Spacetime
626
00:45:38,280 --> 00:45:42,680
at the speed of light, it's
the mixing of time and space
627
00:45:42,680 --> 00:45:47,040
that Einstein said causes time to
tick differently for each of us.
628
00:45:50,440 --> 00:45:55,880
For Einstein,
time wasn't like a metronome
629
00:45:55,880 --> 00:45:59,960
that just ticks
the same for everybody.
630
00:45:59,960 --> 00:46:02,400
It's different for you and me,
631
00:46:02,400 --> 00:46:07,360
and everywhere in the universe, the
metronomes tick at different rates.
632
00:46:11,240 --> 00:46:14,720
Einstein said that two people
will only ever agree
633
00:46:14,720 --> 00:46:19,120
on the speed time ticks if they're
standing next to each other.
634
00:46:23,440 --> 00:46:26,760
If I was to fly past you
incredibly fast,
635
00:46:26,760 --> 00:46:30,920
I would see your time
tick much slower than mine.
636
00:46:33,120 --> 00:46:37,120
This idea lies at the heart
of Einstein's Theory of Relativity.
637
00:46:38,680 --> 00:46:43,320
No-one has a right to the... to
claim that their time is THE time,
638
00:46:43,320 --> 00:46:45,520
the absolute time.
639
00:46:45,520 --> 00:46:48,200
It just depends on
who's moving relative to who.
640
00:46:50,200 --> 00:46:53,760
Because of the mixing
of space and time,
641
00:46:53,760 --> 00:46:58,000
time ticks differently for you
relative to other people,
642
00:46:58,000 --> 00:47:01,680
depending on how fast
everyone is moving.
643
00:47:01,680 --> 00:47:03,320
When someone moves relative to me,
644
00:47:03,320 --> 00:47:07,520
they use some of their speed
of light through Spacetime
645
00:47:07,520 --> 00:47:09,280
to move through space.
646
00:47:09,280 --> 00:47:11,880
So they haven't got as much left
to move through time,
647
00:47:11,880 --> 00:47:16,600
and that means that their speed
through time is a bit slower.
648
00:47:16,600 --> 00:47:19,880
They've sort of, in a very real
sense, used a bit of it up.
649
00:47:19,880 --> 00:47:23,520
It's a really profound way
of understanding
650
00:47:23,520 --> 00:47:25,680
Einstein's theory of Spacetime.
651
00:47:27,960 --> 00:47:31,120
And the strange nature of time
doesn't stop there.
652
00:47:32,160 --> 00:47:34,560
It's not just how fast you're moving
653
00:47:34,560 --> 00:47:38,200
but what you're next to
that also affects time.
654
00:47:41,000 --> 00:47:44,800
According to Einstein,
you should see the time tick slower
655
00:47:44,800 --> 00:47:48,840
at my feet
than at the top of my head.
656
00:47:48,840 --> 00:47:53,240
This is because the nearer you are
to a big object like the Earth,
657
00:47:53,240 --> 00:47:57,160
the more bent and warped
is the Spacetime,
658
00:47:57,160 --> 00:47:59,480
and the slower time ticks.
659
00:48:00,760 --> 00:48:03,280
On our planet
the effect is minuscule
660
00:48:03,280 --> 00:48:07,680
but out there in the universe, the
vast mass of the stars and galaxies
661
00:48:07,680 --> 00:48:13,680
bend and warp the Spacetime so much
that time ticks all over the place.
662
00:48:16,000 --> 00:48:19,880
There's a very famous experiment
in 1971 by Hafele and Keating
663
00:48:19,880 --> 00:48:23,040
in which they decided to,
664
00:48:23,040 --> 00:48:26,600
let's say, put Einstein to the test.
665
00:48:26,600 --> 00:48:29,560
They got atomic clocks
and they flew them
666
00:48:29,560 --> 00:48:33,640
around the world on civil airliners
one way, and around the world
667
00:48:33,640 --> 00:48:36,640
on civil airliners the other way,
synchronised them all
668
00:48:36,640 --> 00:48:39,720
before they left and compared
them when they came back.
669
00:48:40,960 --> 00:48:43,360
And the clocks that went eastward
around the world
670
00:48:43,360 --> 00:48:46,400
lost 59 nanoseconds,
671
00:48:46,400 --> 00:48:49,160
59 thousand-millionths
of a second.
672
00:48:49,160 --> 00:48:55,120
And the one that went westward
gained 273 nanoseconds.
673
00:48:56,960 --> 00:49:01,200
The people on those planes
aged at different rates,
674
00:49:01,200 --> 00:49:04,840
the same amount as the shift
in the time difference
675
00:49:04,840 --> 00:49:06,640
is measured by the clocks.
676
00:49:08,000 --> 00:49:11,360
And so we can travel
into the future,
677
00:49:11,360 --> 00:49:14,560
but actually, we can travel
into the future at different rates.
678
00:49:16,200 --> 00:49:20,040
Let's say I get into spacecraft now
and fly off to Alpha Centauri
679
00:49:20,040 --> 00:49:23,200
and come back again.
I can arrange that journey,
680
00:49:23,200 --> 00:49:26,800
and if I can travel fast enough,
such that I come back 1,000 years
681
00:49:26,800 --> 00:49:29,680
in the future or 10,000 years
in the future.
682
00:49:29,680 --> 00:49:32,680
Actually, the closer
I can make it to the speed of light,
683
00:49:32,680 --> 00:49:34,920
the further into the future
I can get.
684
00:49:43,560 --> 00:49:47,400
I think the more
that you know about time,
685
00:49:47,400 --> 00:49:53,360
the more you consider the
fundamental nature of reality itself
686
00:49:53,360 --> 00:49:58,240
and discover that it's nothing
like our experience of the world,
687
00:49:58,240 --> 00:50:01,320
then the more astonished you become!
688
00:50:01,320 --> 00:50:04,040
And at some point,
I'll probably become so astonished
689
00:50:04,040 --> 00:50:06,600
that I'll no longer be
able to speak about it!
690
00:50:09,800 --> 00:50:13,400
Even though physicists are still
grappling with the fundamental
691
00:50:13,400 --> 00:50:18,080
nature of time, we do know
with reasonable certainty
692
00:50:18,080 --> 00:50:20,960
how time will ultimately end.
693
00:50:37,480 --> 00:50:40,960
There are few places on Earth
where you can get an inkling
694
00:50:40,960 --> 00:50:43,960
of what the far future has in store.
695
00:50:43,960 --> 00:50:45,880
HELICOPTER ROTORS WHIR
696
00:50:57,240 --> 00:51:00,560
This is Namibia's Skeleton Coast,
where the cold waters
697
00:51:00,560 --> 00:51:03,440
of the South Atlantic
meet the Namib Desert.
698
00:51:03,440 --> 00:51:07,040
And it is one of the most
inhospitable places on Earth.
699
00:51:07,040 --> 00:51:10,960
Back in the 17th century, Portuguese
sailors used to call this place
700
00:51:10,960 --> 00:51:15,080
The Gates to Hell because
this dense fog that you see
701
00:51:15,080 --> 00:51:20,080
pretty much every morning along this
coast, coupled with the constantly
702
00:51:20,080 --> 00:51:24,520
shifting shape of the sandbanks,
meant that over the years
703
00:51:24,520 --> 00:51:27,840
literally thousands of ships
were wrecked along this coastline.
704
00:51:34,040 --> 00:51:37,480
And even if you made it to shore,
that wasn't the end of your problems
705
00:51:37,480 --> 00:51:39,880
because the currents
are so strong here
706
00:51:39,880 --> 00:51:43,440
that there is no way
of rowing back out to sea.
707
00:51:43,440 --> 00:51:46,360
If you look that way,
there's just hundreds of miles
708
00:51:46,360 --> 00:51:48,080
of inhospitable desert.
709
00:51:51,040 --> 00:51:55,400
So, it genuinely was
a place of no return.
710
00:51:55,400 --> 00:51:59,280
If you were shipwrecked here,
this was the end of your universe.
711
00:52:11,200 --> 00:52:13,200
This is the Edward Bohlen.
712
00:52:13,200 --> 00:52:17,120
She was once an ocean-going steamer
ferrying passengers and cargo
713
00:52:17,120 --> 00:52:18,880
between here and Europe.
714
00:52:24,400 --> 00:52:27,840
On 5th September 1909,
she ran aground in thick fog.
715
00:52:34,520 --> 00:52:38,560
Yet, like all the vessels wrecked
along this shoreline, the time it
716
00:52:38,560 --> 00:52:43,520
takes her to decay to nothing will
be far longer than her time at sea.
717
00:52:48,320 --> 00:52:53,000
And in the far future, long after
our own sun has run out of fuel,
718
00:52:53,000 --> 00:52:57,120
a similar destiny awaits
the universe's last stars.
719
00:53:01,160 --> 00:53:05,400
A black dwarf will be the final
fate of those last stars -
720
00:53:05,400 --> 00:53:08,680
white dwarfs that have become
so cold that they barely emit
721
00:53:08,680 --> 00:53:11,080
any more heat or light.
722
00:53:15,240 --> 00:53:20,760
Black dwarves are dark, dense,
decaying bowls of degenerate matter,
723
00:53:20,760 --> 00:53:23,800
little more than
the ashes of stars.
724
00:53:26,040 --> 00:53:29,520
Their constituent atoms
are so severely crushed
725
00:53:29,520 --> 00:53:33,440
that black dwarves are a
million times denser than our sun.
726
00:53:35,520 --> 00:53:38,200
Stars takes so long
to reach this point
727
00:53:38,200 --> 00:53:40,440
that after nearly 14 billion years,
728
00:53:40,440 --> 00:53:44,680
we believe there are currently
no black dwarves in the universe.
729
00:53:46,200 --> 00:53:48,920
But despite never seeing one,
we can still predict
730
00:53:48,920 --> 00:53:50,960
how they will end their days.
731
00:53:52,320 --> 00:53:55,880
Just as the iron that makes up
this ship will eventually rust
732
00:53:55,880 --> 00:53:59,280
and be carried away
by the desert winds,
733
00:53:59,280 --> 00:54:04,000
so we think that the matter inside
black dwarves, the last matter
734
00:54:04,000 --> 00:54:09,720
in the universe, will eventually
evaporate away and be carried off
735
00:54:09,720 --> 00:54:12,320
into the void as radiation,
736
00:54:12,320 --> 00:54:15,840
leaving absolutely nothing behind.
737
00:54:21,160 --> 00:54:26,120
There were wild dogs everywhere,
actually, when we were filming that.
738
00:54:26,120 --> 00:54:31,680
And so they... Standing there
on my own and they're all gone,
739
00:54:31,680 --> 00:54:34,960
they're all in the helicopter,
and I thought,
740
00:54:34,960 --> 00:54:37,560
I really hope they come back
741
00:54:37,560 --> 00:54:41,760
because the dogs are circling,
you know.
742
00:54:45,960 --> 00:54:48,160
With the black dwarves gone,
743
00:54:48,160 --> 00:54:50,840
there won't be a single atom
of matter left.
744
00:54:53,640 --> 00:54:56,720
All that will remain
of our once-rich cosmos
745
00:54:56,720 --> 00:54:59,960
will be particles
of light and black holes.
746
00:55:07,160 --> 00:55:10,200
After an unimaginable
length of time,
747
00:55:10,200 --> 00:55:14,040
even the black holes will
have evaporated and the universe
748
00:55:14,040 --> 00:55:18,080
will be nothing but a sea of photons
749
00:55:18,080 --> 00:55:21,360
gradually tending towards
the same temperature,
750
00:55:21,360 --> 00:55:25,960
as the expansion of the universe
cools them towards absolute zero.
751
00:55:34,920 --> 00:55:38,320
And when I say unimaginable
period of time, I really mean it.
752
00:55:38,320 --> 00:55:41,960
It's 10,000 trillion, trillion,
trillion, trillion, trillion,
753
00:55:41,960 --> 00:55:44,880
trillion, trillion, trillion years.
754
00:55:44,880 --> 00:55:47,440
How big is that number?
755
00:55:47,440 --> 00:55:51,800
Well, if I were to start counting
with a single atom representing
756
00:55:51,800 --> 00:55:56,960
one year, then there wouldn't be
enough atoms in the entire universe
757
00:55:56,960 --> 00:56:00,200
to get anywhere near that number.
758
00:56:00,200 --> 00:56:02,960
CLOCK TICKS SOFTLY
759
00:56:05,960 --> 00:56:10,520
Once the very last remnants
of the very last stars have finally
760
00:56:10,520 --> 00:56:14,640
decayed away to nothing,
and everything reaches the same
761
00:56:14,640 --> 00:56:19,120
temperature, the story of the
universe finally comes to an end.
762
00:56:23,560 --> 00:56:25,840
For the first time in its life,
763
00:56:25,840 --> 00:56:28,360
the universe will be
permanent and unchanging.
764
00:56:30,920 --> 00:56:32,920
Nothing happens,
765
00:56:32,920 --> 00:56:36,040
and it keeps not happening forever.
766
00:56:47,080 --> 00:56:50,440
People always ask me, actually,
why do you smile when you talk about
767
00:56:50,440 --> 00:56:55,040
the inevitable decay of the universe
and the dissolving of everything
768
00:56:55,040 --> 00:56:59,120
that we hold most dear
into a bath of radiation
769
00:56:59,120 --> 00:57:01,840
that will... will fade?
770
00:57:01,840 --> 00:57:05,400
So even the afterglow of our
presence in the universe
771
00:57:05,400 --> 00:57:09,360
will become undetectable and
there will be no memory at all...
772
00:57:09,360 --> 00:57:12,480
of everything or anything
that we've created.
773
00:57:12,480 --> 00:57:16,400
There will be no imprint
left of us at all in the far future.
774
00:57:16,400 --> 00:57:18,120
Why do you smile?
775
00:57:18,120 --> 00:57:20,320
And I just think it's quite funny.
776
00:57:20,320 --> 00:57:22,600
That's why I smile, I think!
777
00:57:22,600 --> 00:57:26,240
It certainly does take us down
a peg or two, doesn't it?
778
00:57:26,240 --> 00:57:32,040
You know, I want to build a statue
of myself, a grand celebration,
779
00:57:32,040 --> 00:57:34,920
a permanent monument
of my achievements.
780
00:57:34,920 --> 00:57:38,200
There will be no such permanent
monument of your achievements.
781
00:57:38,200 --> 00:57:40,960
Don't worry about the statues.
Don't worry about them.
782
00:57:40,960 --> 00:57:44,640
They're all going to dissolve
into a bath of photons!