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Human Universe

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The remote island of Rapa Nui
was once home

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to Earth's most isolated
civilisation.

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Famed for their stone effigies,
they lived here for 1,000 years.

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They called the island
the End of the Land.

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Easter Island is, and feels,
isolated.

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It's at least 1,500 miles
to the west,

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to the nearest Pacific island -

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five hours flying time

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from the coast of South America
and Santiago in Chile.

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But on Easter Day, 1722, the
civilisation's solitude was shattered.

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The arrival of a Dutch trading fleet

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was the moment they came
face to face with aliens.

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It turned out to be
a solitary encounter.

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When other ships returned
50 years later,

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the civilisation had fallen.

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It had been pure chance that
they'd met at all,

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such was the island's isolation.

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A pinprick in a vast ocean.

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What then of us on Earth?

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Are we a lone island of life
lost in a vast galaxy?

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Think about this.

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There are billions of habitable
Earth-like worlds out there in the galaxy,

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and yet we are alone.

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Think about this.

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There are billions of habitable
Earth-like worlds out there in the galaxy

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and we are not alone.

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There are others.

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One of these statements is true.

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As far as we know,

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we humans are unique in
the universe.

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One species carried through
space on one tiny planet...

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..amongst the Milky Way's
200 billion stars.

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The question is,
is anyone else staring back?

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Human Uiniverse

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are we alone?

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Edited By
Sirwaan N

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Shiprock
New Mexico

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In New Mexico, the Navajo tribe
believe the stars

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are home
to another consciousness.

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Once a year they come together
to communicate with this entity,

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in a healing ceremony
called Yeibichai.

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It's a nine-day long festival
of ritual and chanting.

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The most sacred of which
is the night-chant

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performed by medicine men
in private,

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never filmed,

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and recorded just once.

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This recording was made by Willard Rhodes
of Colombia University in the early 1940s.

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And he could not have imagined what
was going to happen to it.

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In 1977, the recording was
transferred onto four golden records

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and encased in these covers.

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Today only two of them remain
on Planet Earth.

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The other two are bolted to
the sides of two space probes -

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Voyager 1 and Voyager 2 -

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and are now travelling into
deep space.

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Accompanying the night-chant are an eclectic
mix of images and sounds from Earth.

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'As The Secretary General
of The United Nations,

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'I send greetings on behalf
of the people of our planet.'

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The Voyager's primary mission

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was to explore the outer planets
of the solar system.

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But adding the discs gave
the spacecraft an extra purpose -

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they become Earth's emissaries,

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carrying postcards to our
alien neighbours.

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If they exist.

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But there's more than that -

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there's hope engraved into
this cover, as well.

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Because here is a map,

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this identifies the position
of the Earth in the cosmos.

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These lines point to stars called pulsars
which rotate with a very specific rate.

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So any alien civilisation
that captured this

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would be able to find the
positions of the pulsars

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and all of these lines
point back to Earth.

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And there's also a means of decoding
all that information...here.

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This is a picture
of a hydrogen atom -

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the most common element
in the universe.

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Now hydrogen atoms radiate radio waves with a
very particular wavelength - 21 centimetres.

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That gives you the distance scale -
the key, if you like - to this code.

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So any civilisation that
knows anything about physics,

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which is to say, any
civilisation worth its salt,

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would recognise that
and be able to decode this.

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They would be able to determine
the location of Earth -

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they would be able to find us.

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What a wonderful idea.

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Voyager 2 is now 19 billion
kilometres into its journey.

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But in galactic terms,
it's only just left home...

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..because The Milky Way is a
billion-billion kilometres across.

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In truth, the scientists
and engineers who made that record

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knew that it wouldn't be found,
but that's not the point.

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See the very act of launching it
out into space

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expresses something deep,
something primal.

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It's a feeling we all share -
I certainly feel it -

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and that's that the Navajo
weren't alone in wanting

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to talk to the people out there
amongst the stars.

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'Wouldn't it be lovely to make
contact with another civilisation

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'that has arisen and
evolved independently?'

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Every hour of every day,

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some among us scan the skies

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listening for alien civilisations.

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'The chance of success in,

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'picking up messages directed
our way depends in large part

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'on how serious we are
'at investigating such
possible signals.'

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They call themselves SETI -

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the Search
for Extra-Terrestrial Intelligence.

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Hat Creek
California

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This is the Allen Array
in Northern California,

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and it is SETI's most ambitious
instrument to date.

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This collection of 42
radio telescopes

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is optimised to detect signals
from extra-terrestrial civilisations

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and it's exquisitely sensitive.

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If a signal were beamed to us

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with the sort of power that we can
generate using our current technology

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from any one of the million
or so sun-like stars

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within 1,000 light years of Earth,
then this would hear it.

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This experiment has yet to detect
a call from ET.

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But they live in hope,

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because SETI did once
pick up a tantalising signal.

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On August the 15th, 1977,

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a radio telescope called
the Big Ear detected a radio signal

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from somewhere in the vicinity of
the constellation Sagittarius,

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and this is the printout
from that night.

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You can see that somewhere around
9.45pm Eastern Standard Time

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a very bright radio signal
pulsed in.

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It looks something like this -

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you can sketch it out.

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It was a pulse...

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..with a width of around
72 seconds,

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and a peak intensity -

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the peak brightness -

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was over 30 times the brightness of the
background radio emission from the galaxy.

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So it's fascinating.

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And it came in on a wavelength
that SETI believes

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an intelligent civilisation might choose - the
same wavelength etched into Voyager's golden disc.

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The wavelength was 21 centimetres.

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That's the wavelength of light,

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of radio waves emitted
from hydrogen atoms.

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So the whole sky glows
at that wavelength.

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And, back in the 1950s,
radio astronomers speculated

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that if an alien civilisation
wanted to communicate with us,

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then they might well choose that very special,
natural wavelength to send their message.

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So surprising was this,

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that when it was spotted
a few days later

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by an astronomer called Jerry Ehman

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he circled that pulse -

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the 72-second flash of radio waves -

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and wrote "Wow!" next to it,

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so this has become known
as the Wow! signal.

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Today, over 35 years after
the Wow! signal was detected,

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there's still no satisfactory
explanation.

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It doesn't seem to have been local -
a military signal or a satellite,

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and, indeed, nobody's supposed to
transmit at the hydrogen line frequency,

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it's reserved for radio astronomy.

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But scientific results
have to be repeatable,

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and even though we've turned
our telescopes in the direction

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of Sagittarius many times since,

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nobody has ever heard anything.

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So I suppose it has to remain
just an interesting anomaly.

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For now, we remain in
magnificent isolation...

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..a lone intelligence in a galaxy
that remains quiet.

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But one man more than any other

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is convinced that the great silence

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will not last forever.

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This is not some fantastical idea,

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but a serious scientific quest.

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RECORDING: 'It would be the
greatest bonanza in knowledge

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'you could possibly imagine.

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'A surprise for the
whole civilisation.'

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Dr Frank Drake is SETI's
founding father

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and has spent a lifetime listening.

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So if I'd have asked you back
in the 1960s -

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By the 21st century, do you expect
to have seen a signal? -

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what would you have said?

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I would have said,
"Yes, I expect to succeed."

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Because we were doing a lot
of searching then.

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Does that make you disappointed?

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I'm disappointed, yes,
but not surprised.

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What we've learned over the years

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is that the searching has
to be MUCH more comprehensive,

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than we realised 50 years ago.
Mm.

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But we know it's still doable,

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it just takes much more time
than we imagined.

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Let me show you something.

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This is an orchid.

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A very peculiar and beautiful orchid,

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very fragrant,

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which actually only blooms
two days a year.

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If you would've been here
two days ago,

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you wouldn't have seen this orchid

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and you might've thought
that this plant never blooms.

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Well, so it is with SETI.

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We've learned we must search over
and over and over through the years,

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till we are in the right place
at the right time

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to make the discovery.

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What are they called?
This is called a Stanhopea.

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It has "hope" in its name,

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and we have hope that some day

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we'll be in the right place
at the right time in SETI.

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But Frank wasn't content just
to hang on the line

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waiting for ET's call.

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The equation starts out with
the rate of star formation...

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In 1961, he devised what remains
a useful scientific framework

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for considering how likely it is,
that we share the galaxy with others.

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I realised that there
were seven factors -

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if you knew these factors,
and multiplied them together

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it would give you a prediction of the number
of detectable civilisations in our galaxy.

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The end result is N -
Big N, as we call it -

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which is the number of
detectable civilisations,

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which in its own right
is a very interesting number.

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But, also, it's very important in
guiding us in planning our searches.

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The Drake Equation has become famous

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because it gives us a tool
to continue the search.

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It dares us to answer a series
of provocative scientific questions.

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On the left-hand side is the number
we want to measure -

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the number of intelligent
civilisations in the galaxy

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that we can communicate with.

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But then there's this group of terms

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that really ask questions
about ourselves -

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How likely is it for life
to arise on a planet?

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How special is the Earth?

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How special is the sun?

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How special is the solar system?

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How special is intelligence?

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And then there's this last term, L,

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which perhaps speaks to us most
profoundly of all -

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the lifetime of
intelligent civilisations.

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Do civilisations live
for a long or short time?

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And if it's short,
what is it that destroys them?

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Is it a natural disaster?

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We do, after all,
live in a violent universe.

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Or are they condemned
to destroy themselves?

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We came up with the number 10,000
civilisations in the galaxy,

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and that's sort of stood as
a reasonable number to this day.

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50 years ago, Frank's number
was really an educated guess.

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But our generation is replacing
his hunches with hard data,

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so we can arrive at our own
solution to his equation.

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And we can begin, as Frank did,

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by asking just how rare
is our home planet?

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And the key to understanding that can be found in
the relationship we share with our nearest star.

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The Sacred Valley
Peru

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The Peruvian high Andes,

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home to the mighty Incan Empire,

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a lost civilisation that called
themselves the Children of the Sun

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and worshipped the star
as their god.

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Today, this connection remains
just as vital.

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Angel, come on it's time to get up

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Carmen Pachako and her
family's livelihood

246
00:19:24,201 --> 00:19:26,281
depends entirely on the sun.

247
00:19:37,761 --> 00:19:41,761
Tucked away deep in the Sacred
Valley is an ancient salt mine.

248
00:19:43,121 --> 00:19:47,521
To this day, hundreds of terraces
are tended by the local community.

249
00:20:01,961 --> 00:20:04,961
Carmen's job is to keep
the whole system running.

250
00:20:14,281 --> 00:20:18,761
She floods each terrace in turn with
saline water from the local spring.

251
00:20:25,841 --> 00:20:29,156
The ponds are then left
to evaporate in the sun

252
00:20:29,156 --> 00:20:32,549
leaving behind
a crust of salt crystals.

253
00:20:46,321 --> 00:20:52,761
This place works because, here on Earth, the conditions
are just right for water to exist in three states -

254
00:20:52,761 --> 00:20:56,241
there's liquid, that you can
see in the salt pools,

255
00:20:56,241 --> 00:21:00,081
there's a vapour that can evaporate
up into clouds in the sky,

256
00:21:00,081 --> 00:21:02,121
and a solid as ice and snow,

257
00:21:02,121 --> 00:21:05,281
that you can see over there
on the tops of the mountains.

258
00:21:12,841 --> 00:21:15,561
This constant recycling of water

259
00:21:15,561 --> 00:21:17,641
from one state to another

260
00:21:17,641 --> 00:21:18,881
happens here on Earth

261
00:21:18,881 --> 00:21:22,601
because we receive just the right
amount of energy from the sun.

262
00:21:24,801 --> 00:21:27,921
Can you imagine dragging the
Earth closer to the Sun,

263
00:21:27,921 --> 00:21:29,401
heating it up,

264
00:21:29,401 --> 00:21:31,761
then at some point the temperatures

265
00:21:31,761 --> 00:21:34,201
would rise to 100 degrees
or greater,

266
00:21:34,201 --> 00:21:37,241
all the water would evaporate
or boil away into the atmosphere,

267
00:21:37,241 --> 00:21:39,561
and, in fact, if it got too hot,

268
00:21:39,561 --> 00:21:43,481
then the water molecules themselves
would escape off into space.

269
00:21:43,481 --> 00:21:46,281
Earth would be
a dry and barren rock.

270
00:21:46,281 --> 00:21:49,881
Then, if you imagine dragging
the Earth further out,

271
00:21:49,881 --> 00:21:51,961
further out into the solar system,

272
00:21:51,961 --> 00:21:54,001
then temperatures would drop

273
00:21:54,001 --> 00:21:55,761
and, eventually, they'd be so cold

274
00:21:55,761 --> 00:21:58,041
that all the water would freeze out.

275
00:21:58,041 --> 00:22:00,441
There would be no liquid on
the surface

276
00:22:00,441 --> 00:22:02,761
and, indeed, no clouds
in the atmosphere.

277
00:22:04,161 --> 00:22:06,361
So there's a region
in our solar system,

278
00:22:06,361 --> 00:22:08,521
within which the Earth could orbit

279
00:22:08,521 --> 00:22:13,561
and the conditions would still be right
for liquid water to exist on its surface.

280
00:22:13,561 --> 00:22:16,561
That region is known as
the habitable zone,

281
00:22:16,561 --> 00:22:20,361
because all life on Earth
requires liquid water.

282
00:22:26,161 --> 00:22:30,921
But in the high Andes,
water is relatively scarce.

283
00:22:30,921 --> 00:22:35,561
So, for the Incas,
habitability was important too,

284
00:22:35,561 --> 00:22:38,810
albeit on a more human scale.

285
00:22:39,641 --> 00:22:43,601
This is a natural sink hole cut out
of the limestone of the high Andes.

286
00:22:45,041 --> 00:22:48,161
At some point,
around 500 or 600 years ago,

287
00:22:48,161 --> 00:22:52,681
the Inca modified it by cutting
these circular steps

288
00:22:52,681 --> 00:22:55,361
into the side of the sink hole.

289
00:22:55,361 --> 00:22:58,081
There's no consensus as to what
this structure was for,

290
00:22:58,081 --> 00:23:00,561
but one of the more
widely accepted theories is

291
00:23:00,561 --> 00:23:03,801
that it was an agricultural
research station.

292
00:23:03,801 --> 00:23:05,881
So the Inca had built this

293
00:23:05,881 --> 00:23:09,001
in order to generate a series of
different micro climates,

294
00:23:09,001 --> 00:23:10,601
different temperatures,

295
00:23:10,601 --> 00:23:12,681
different amounts of irrigation

296
00:23:12,681 --> 00:23:14,761
to see which crops grew best

297
00:23:14,761 --> 00:23:18,541
in which different conditions.

298
00:23:23,161 --> 00:23:25,601
And so it is,
in our own solar system.

299
00:23:29,961 --> 00:23:32,121
On one extreme lies Mars...

300
00:23:35,681 --> 00:23:38,881
..80 million kilometres further
out from the sun,

301
00:23:38,881 --> 00:23:43,601
its surface is mile after mile
of parched red rock...

302
00:23:45,321 --> 00:23:48,161
..but the surface features
still recall a time

303
00:23:48,161 --> 00:23:50,721
when they were rivers
and flood plains -

304
00:23:50,721 --> 00:23:55,201
evidence of a long oceanic
period before the Red Planet

305
00:23:55,201 --> 00:23:57,761
lost most of its water to space.

306
00:24:03,361 --> 00:24:06,801
Closer to the sun, and on the
inner limits of habitability,

307
00:24:06,801 --> 00:24:08,441
lies Venus.

308
00:24:13,401 --> 00:24:16,921
About the same size as Earth,
its dense atmosphere

309
00:24:16,921 --> 00:24:21,841
sees temperatures soar to over
400 degrees Celsius -

310
00:24:21,841 --> 00:24:23,681
far too hot for water.

311
00:24:26,561 --> 00:24:31,201
But, in 2008, the Venus Express
spacecraft detected a signature

312
00:24:31,201 --> 00:24:36,241
highly suggestive that water once
flowed on the surface here, too.

313
00:24:38,121 --> 00:24:43,721
For a brief moment, billions of
years ago, not one, but three worlds

314
00:24:43,721 --> 00:24:49,088
with oceans and rivers
orbited the sun.

315
00:24:57,321 --> 00:25:00,001
If alien life ever existed
on Mars or Venus,

316
00:25:00,001 --> 00:25:03,481
no trace of it has yet been found.

317
00:25:05,961 --> 00:25:07,681
What is certain, though,

318
00:25:07,681 --> 00:25:10,761
is that our star is central
to the story of life

319
00:25:10,761 --> 00:25:12,441
in our solar system.

320
00:25:14,801 --> 00:25:19,561
But the sun is just one of billions
of stars in the Milky Way...

321
00:25:22,521 --> 00:25:24,361
..so in our hunt for aliens,

322
00:25:24,361 --> 00:25:30,742
we must determine exactly how many of
those stars are capable of supporting life.

323
00:25:51,761 --> 00:25:55,801
I'm going to start with that one -
that's called a red dwarf.

324
00:25:55,801 --> 00:25:57,881
Come here.

325
00:25:57,881 --> 00:25:59,761
This could be the sun.

326
00:25:59,761 --> 00:26:01,241
Are you OK for a big one?

327
00:26:01,241 --> 00:26:03,041
There you go.

328
00:26:03,041 --> 00:26:04,601
This is a little tiny white dwarf.

329
00:26:06,121 --> 00:26:08,001
There's a little white dwarf.
There you go.

330
00:26:08,001 --> 00:26:10,241
Gracias. Thank you.

331
00:26:12,641 --> 00:26:15,001
Can you hold that?
There you go!

332
00:26:19,361 --> 00:26:22,681
So there are 200 billion stars
in our galaxy

333
00:26:22,681 --> 00:26:24,121
of many different types,

334
00:26:24,121 --> 00:26:27,401
and we've got the whole menagerie
represented here -

335
00:26:27,401 --> 00:26:29,361
enormous red stars,

336
00:26:29,361 --> 00:26:30,641
enormous blue stars,

337
00:26:30,641 --> 00:26:32,001
tiny red stars,

338
00:26:32,001 --> 00:26:33,401
tiny white stars.

339
00:26:36,721 --> 00:26:39,321
Now, science is not just about
looking at the stars

340
00:26:39,321 --> 00:26:42,241
and saying, "There's a nice yellow
one. There's a nice blue one."

341
00:26:42,241 --> 00:26:44,601
In fact, the very famous physicist
Ernest Rutherford

342
00:26:44,601 --> 00:26:47,281
who discovered the atomic nucleus
in Manchester

343
00:26:47,281 --> 00:26:50,601
once said all science is either
physics, or stamp collecting.

344
00:26:50,601 --> 00:26:52,881
Stamp collecting is just looking
at the stars,

345
00:26:52,881 --> 00:26:55,487
physics is arranging them
in a pattern

346
00:26:55,487 --> 00:26:58,361
and trying to understand the
pattern. That's what we'll do now.

347
00:26:58,361 --> 00:27:01,361
We're going to make what's called
the Hertzsprung-Russell diagram.

348
00:27:01,361 --> 00:27:02,761
Wish me luck.

349
00:27:02,761 --> 00:27:05,121
You guys go all the way over there.

350
00:27:05,121 --> 00:27:06,761
You go there. Yeah.

351
00:27:06,761 --> 00:27:09,121
You go right over there.

352
00:27:09,121 --> 00:27:10,721
You come in here.

353
00:27:10,721 --> 00:27:13,161
You come here.
You, as well, come here.

354
00:27:16,721 --> 00:27:18,241
There's an orange one.

355
00:27:18,241 --> 00:27:19,641
You go there.

356
00:27:21,721 --> 00:27:22,761
There.

357
00:27:25,281 --> 00:27:26,841
Exactly there.

358
00:27:27,961 --> 00:27:31,281
The Hertzsprung-Russell diagram
allows us to organise the stars

359
00:27:31,281 --> 00:27:33,761
according to their colour
and brightness.

360
00:27:36,041 --> 00:27:37,881
When laid out on a graph,

361
00:27:37,881 --> 00:27:41,081
nearly all the galaxies'
different stars

362
00:27:41,081 --> 00:27:43,361
fall neatly onto a line.

363
00:27:44,761 --> 00:27:47,321
This line is called
the Main Sequence -

364
00:27:47,321 --> 00:27:50,241
these are most of the stars
in the galaxy,

365
00:27:50,241 --> 00:27:53,081
they're burning hydrogen into
helium in their cores.

366
00:27:55,601 --> 00:27:57,921
So this is our familiar sun,

367
00:27:57,921 --> 00:28:00,321
the sun that we see
in the sky every day,

368
00:28:00,321 --> 00:28:02,281
and it sits on the Main Sequence.

369
00:28:02,281 --> 00:28:03,761
If you come with me.

370
00:28:05,481 --> 00:28:07,161
Somewhere around here

371
00:28:07,161 --> 00:28:09,441
a yellow star, an average star.

372
00:28:11,601 --> 00:28:13,521
The stars either side of the line

373
00:28:13,521 --> 00:28:15,681
are reaching the end of their lives.

374
00:28:20,121 --> 00:28:23,441
The red giant stars have run
out of hydrogen to burn,

375
00:28:23,441 --> 00:28:27,281
and are swelling in size,
engulfing any nearby planets.

376
00:28:32,441 --> 00:28:34,321
So we can discount the red giants.

377
00:28:34,321 --> 00:28:36,441
Over there. Over there.

378
00:28:38,241 --> 00:28:40,001
Others, like the blue giants,

379
00:28:40,001 --> 00:28:42,961
are so massive that they burn
their fuel quickly...

380
00:28:45,561 --> 00:28:49,521
..collapsing and illuminating the
galaxy in a supernova explosion.

381
00:29:00,081 --> 00:29:02,161
So the search for stars with
habitable planets

382
00:29:02,161 --> 00:29:04,641
must focus on the Main Sequence.

383
00:29:12,081 --> 00:29:14,921
Complex life took three billion
years to evolve -

384
00:29:14,921 --> 00:29:18,601
it wouldn't have time to evolve
around these brightest of stars,

385
00:29:18,601 --> 00:29:20,481
the bright, short-lived stars.

386
00:29:20,481 --> 00:29:22,721
So the white stars can go.

387
00:29:22,721 --> 00:29:24,161
Go on.

388
00:29:28,001 --> 00:29:30,641
If you want to look for planets
that could support life

389
00:29:30,641 --> 00:29:33,441
and civilisations, you'd look at
the sun-like stars -

390
00:29:33,441 --> 00:29:37,001
the G and K stars,
the orange and yellow stars.

391
00:29:39,361 --> 00:29:43,561
These make up one fifth
of all the stars in our galaxy.

392
00:29:44,961 --> 00:29:48,321
But new research suggests
that there's another type of star

393
00:29:48,321 --> 00:29:51,001
that might significantly expand
this number.

394
00:29:52,361 --> 00:29:55,241
Could we find planets around
red dwarfs

395
00:29:55,241 --> 00:29:58,841
that can support complex life
or civilisations?

396
00:29:58,841 --> 00:30:01,961
Well, the jury's still out -
there are big problems.

397
00:30:01,961 --> 00:30:05,881
Red dwarfs - certainly early on in
their lives - are very active stars.

398
00:30:05,881 --> 00:30:07,641
So even though they're dim,

399
00:30:07,641 --> 00:30:10,241
they throw out vast amounts of
radiation,

400
00:30:10,241 --> 00:30:13,561
which many scientists think would
sterilise planets

401
00:30:13,561 --> 00:30:17,041
and prevent life from appearing
on those planets.

402
00:30:20,281 --> 00:30:23,001
But others think that with the right
atmosphere,

403
00:30:23,001 --> 00:30:25,641
a planet could cope with
the radiation.

404
00:30:27,281 --> 00:30:32,345
If they're right, then our odds
of being alone shorten immensely...

405
00:30:32,921 --> 00:30:37,681
..because red dwarfs are by far the
most numerous stars in our galaxy.

406
00:30:47,241 --> 00:30:50,561
So our theoretical search for life
suggests

407
00:30:50,561 --> 00:30:56,405
that there are billions of
potentially habitable star systems...

408
00:30:58,201 --> 00:31:02,739
..and it's to these,
that we must now look.

409
00:31:07,681 --> 00:31:10,201
Trailing behind Earth,
lies a space telescope

410
00:31:10,201 --> 00:31:15,119
nearing the end of its mission
to seek out new worlds.

411
00:31:15,321 --> 00:31:26,274
Known as Kepler, it has stared unblinkingly at 150,000
sun-like and red dwarf stars for over four years.

412
00:31:33,401 --> 00:31:37,281
Kepler looked in the direction
of the constellation of Lyra.

413
00:31:37,281 --> 00:31:39,801
He studied a small patch -

414
00:31:39,801 --> 00:31:42,761
about 0.3% of the entire sky -

415
00:31:42,761 --> 00:31:45,641
and about 3,000 light years deep.

416
00:31:48,041 --> 00:31:50,321
It was looking for a tell-tale,

417
00:31:50,321 --> 00:31:53,201
minute dip in light
from a distant star

418
00:31:53,201 --> 00:31:55,201
that would reveal a new world.

419
00:31:58,601 --> 00:32:01,921
A planet passing in front
of its star.

420
00:32:05,241 --> 00:32:07,481
It found 603 planets,

421
00:32:07,481 --> 00:32:10,321
of which ten were Earth-like

422
00:32:10,321 --> 00:32:14,481
and received about the same amount
of energy from their parent star,

423
00:32:14,481 --> 00:32:17,481
as we do here on Earth -
in other words -

424
00:32:17,481 --> 00:32:20,041
ten Earths within the
habitable zone.

425
00:32:23,441 --> 00:32:27,721
Kepler has proved that our
life-giving planet is not alone...

426
00:32:31,441 --> 00:32:34,761
..and there may be far more out
there waiting to be discovered.

427
00:32:39,161 --> 00:32:42,601
Kepler can only see planets that
pass across the face of the star

428
00:32:42,601 --> 00:32:44,441
as seen from Earth,

429
00:32:44,441 --> 00:32:47,961
and solar systems have many
different orientations.

430
00:32:47,961 --> 00:32:51,841
Also, because it only observed
for around four years,

431
00:32:51,841 --> 00:32:55,281
it can't see planets that have
orbital periods

432
00:32:55,281 --> 00:32:57,481
that last longer than four years.

433
00:32:57,481 --> 00:33:00,961
But, we can correct for all
those things.

434
00:33:04,521 --> 00:33:10,121
And when we do that, we find that
there are 10,000 Earth-size planets

435
00:33:10,121 --> 00:33:14,987
in orbit around Kepler's stars.

436
00:33:15,187 --> 00:33:18,521
But that's just in that
tiny piece of sky -

437
00:33:18,521 --> 00:33:21,761
10,000 Earths...just there...

438
00:33:21,761 --> 00:33:24,361
in a small volume of space.

439
00:33:24,361 --> 00:33:26,401
To get the full picture,

440
00:33:26,401 --> 00:33:29,881
we have to extend that
over the entire sky

441
00:33:29,881 --> 00:33:33,416
and when we do that, we find

442
00:33:33,416 --> 00:33:42,388
that there are ten billion habitable worlds out
there in the Milky Way galaxy around sun-like stars.

443
00:33:43,361 --> 00:33:45,481
And there could be even more.

444
00:33:45,481 --> 00:33:49,321
The red dwarfs,
the so-called M-class stars...

445
00:33:49,321 --> 00:33:52,121
If we admit the possibility
that M stars

446
00:33:52,121 --> 00:33:55,241
might also have habitable
zones around them,

447
00:33:55,241 --> 00:33:59,321
and we can multiply that
by three or four,

448
00:33:59,321 --> 00:34:05,841
that means there might be 30 billion
Earth-like worlds out there in our galaxy.

449
00:34:18,481 --> 00:34:22,081
We've long suspected that in
a galaxy with so many star systems

450
00:34:22,081 --> 00:34:24,721
Earth couldn't stand alone.

451
00:34:24,721 --> 00:34:27,041
But now we're on the verge of
discovering

452
00:34:27,041 --> 00:34:29,321
not just a handful of other Earths,

453
00:34:29,321 --> 00:34:31,521
but billions of worlds

454
00:34:31,521 --> 00:34:33,881
where water flows freely on
the surface,

455
00:34:33,881 --> 00:34:36,681
and rain falls down from
the skies -

456
00:34:36,681 --> 00:34:39,441
billions of homes for life.

457
00:34:50,921 --> 00:34:53,001
For the first time in human history,

458
00:34:53,001 --> 00:34:56,561
we have the possibility of
glimpsing our planet's twin.

459
00:34:58,881 --> 00:35:00,321
A second Earth.

460
00:35:05,721 --> 00:35:10,969
Perhaps, just perhaps,
we have company.

461
00:35:12,761 --> 00:35:14,961
And it's a lovely thought
that maybe one day

462
00:35:14,961 --> 00:35:18,601
Voyager, our galactic message
in a bottle,

463
00:35:18,601 --> 00:35:21,481
might encounter such a planet.

464
00:35:49,161 --> 00:35:52,481
The sounds of Earth may wash up
on a distant shore.

465
00:35:59,241 --> 00:36:03,641
The question is, will there
be anyone around to listen?

466
00:36:16,001 --> 00:36:21,881
The final turns in the Drake equation shift
the focus from astronomy to biology...

467
00:36:24,481 --> 00:36:30,187
..and they begin by tackling one of the
most enduring mysteries in science -

468
00:36:30,466 --> 00:36:35,881
..the question of how often life
spontaneously arises on a planet.

469
00:36:37,241 --> 00:36:43,201
The problem is that we only have one
example of life anywhere in the universe.

470
00:36:44,441 --> 00:36:46,481
Now you may think that's a
strange thing to say -

471
00:36:46,481 --> 00:36:48,681
there's me, there's fish,

472
00:36:48,681 --> 00:36:51,721
there's coral, insects -

473
00:36:51,721 --> 00:36:53,910
all the living things
you could imagine.

474
00:36:53,910 --> 00:37:01,681
But the remarkable thing is we're all
chemically the same, in a biochemical sense.

475
00:37:01,681 --> 00:37:05,441
We all share the same
basic building blocks.

476
00:37:05,441 --> 00:37:08,801
And that's because
we're all descended

477
00:37:08,801 --> 00:37:13,241
from the same common ancestor
3.8 billion years ago.

478
00:37:24,367 --> 00:37:28,347
Exuma Cays
Bahamas

479
00:37:29,121 --> 00:37:37,281
This is one of the very few places where you can see
living structures reminiscent of early life on Earth.

480
00:37:42,481 --> 00:37:45,601
Well, this alien-looking landscape
that you see here

481
00:37:45,828 --> 00:37:50,166
is made of structures
called stromatolites.

482
00:37:50,921 --> 00:37:53,641
What I'm allowed to do
is break a piece off...

483
00:37:53,641 --> 00:37:55,121
It looks like rock.

484
00:38:01,361 --> 00:38:03,801
But, you see...
it's not really rock,

485
00:38:03,801 --> 00:38:06,761
it's covered in a bit of algae
and it's quite soft to the touch.

486
00:38:06,761 --> 00:38:10,441
They're formed by the action
of bacteria,

487
00:38:10,441 --> 00:38:13,681
specifically, in this case,
Cyanobacteria.

488
00:38:14,761 --> 00:38:18,681
In fact inside Cyanobacteria,
it's now known,

489
00:38:18,681 --> 00:38:21,841
is the place where photosynthesis
first evolved.

490
00:38:21,841 --> 00:38:28,121
Structures like these would have been
the only visible signs of life on Earth

491
00:38:28,121 --> 00:38:31,521
for perhaps two billion years.

492
00:38:31,521 --> 00:38:34,801
This is what the primordial ocean
would have looked like.

493
00:38:43,121 --> 00:38:45,481
Whilst there are no living examples

494
00:38:45,481 --> 00:38:48,121
of what came before
the stromatolites,

495
00:38:48,121 --> 00:38:53,201
we've found clues
that life was around even earlier.

496
00:39:00,561 --> 00:39:02,841
There's very strong evidence

497
00:39:02,841 --> 00:39:05,641
that life on Earth began around
3.8 billion years ago,

498
00:39:05,641 --> 00:39:09,561
which is pretty much as soon as
it could have begun.

499
00:39:09,561 --> 00:39:13,321
So that's taken as one piece
of evidence to suggest that life,

500
00:39:13,321 --> 00:39:16,081
given the right conditions,
is inevitable.

501
00:39:16,081 --> 00:39:18,081
Indeed, there are many scientists

502
00:39:18,081 --> 00:39:23,321
who think that life may be created in a
laboratory in the not-too-distant future.

503
00:39:23,321 --> 00:39:26,281
So that means that most scientists,
I think,

504
00:39:26,281 --> 00:39:30,401
suspect that we will find simple
life somewhere out there.

505
00:39:36,441 --> 00:39:38,681
It's a dizzying thought.

506
00:39:38,681 --> 00:39:43,041
If they're right, and habitable
planets do generate life,

507
00:39:43,041 --> 00:39:47,001
then with billions of such planets
out there in the galaxy,

508
00:39:47,001 --> 00:39:49,961
surely there must've been
a second genesis?

509
00:39:53,441 --> 00:39:56,961
But we must be careful, because
the story of life on this planet

510
00:39:56,961 --> 00:40:02,041
shows that the transition from
single celled life to complex life,

511
00:40:02,041 --> 00:40:04,401
may not have been inevitable.

512
00:40:04,401 --> 00:40:07,961
Life had to overcome
a significant bottleneck.

513
00:40:11,681 --> 00:40:15,801
Everything we would call a complex
living thing today,

514
00:40:15,801 --> 00:40:18,041
shares the same basic structure -

515
00:40:18,041 --> 00:40:21,521
it's built out of cells
called eukaryotic cells.

516
00:40:21,521 --> 00:40:25,521
They're, roughly speaking,
the same in every tree,

517
00:40:25,521 --> 00:40:28,321
every blade of grass, every fish,
every insect

518
00:40:28,321 --> 00:40:31,801
and even in every piece of skin
in my knee -

519
00:40:31,801 --> 00:40:33,401
every cell in my body -

520
00:40:33,401 --> 00:40:35,841
is a eukaryotic cell.

521
00:40:35,841 --> 00:40:39,041
And they're extremely different
to the simple cells,

522
00:40:39,041 --> 00:40:43,721
the bacteria that we've seen
photosynthesising in the stromatolites.

523
00:40:43,721 --> 00:40:46,921
So how did those cells
come to exist?

524
00:40:55,681 --> 00:41:00,601
One popular theory is that it was
two simple cells merging together

525
00:41:00,601 --> 00:41:03,001
that formed what
we'd recognise today

526
00:41:03,001 --> 00:41:05,081
as the complex cells in your body.

527
00:41:07,641 --> 00:41:13,349
Somehow the invader managed to
survive the host cell's defences.

528
00:41:16,001 --> 00:41:20,041
And when the cells reproduced,
they reproduced together.

529
00:41:23,401 --> 00:41:26,321
We still struggle to understand
how this happened,

530
00:41:26,321 --> 00:41:28,361
because it's incredibly unusual.

531
00:41:29,961 --> 00:41:34,841
Here's the point - because every
complex animal and plant

532
00:41:34,841 --> 00:41:37,601
shares that same
basic building block

533
00:41:37,601 --> 00:41:41,241
we are very confident that
it only happened once -

534
00:41:41,241 --> 00:41:44,041
somewhere in the oceans of
the primordial Earth.

535
00:41:45,681 --> 00:41:52,401
Biologists call this merger the Fateful
Encounter hypothesis, for a good reason.

536
00:41:52,401 --> 00:41:56,921
It seems that that kind of merger
between two simpler life forms

537
00:41:56,921 --> 00:41:59,441
may be extremely rare.

538
00:41:59,441 --> 00:42:02,961
The idea that one organism
can get inside another

539
00:42:02,961 --> 00:42:04,801
and doesn't kill it -

540
00:42:04,801 --> 00:42:07,121
that they both survive
to produce something

541
00:42:07,121 --> 00:42:10,281
that's actually capable of
doing magnificent things,

542
00:42:10,281 --> 00:42:13,241
things that are far more
complicated and wonderful

543
00:42:13,241 --> 00:42:16,521
than the two simple building blocks
can manage on their own

544
00:42:16,521 --> 00:42:19,281
seems to be...
It seems to be unlikely,

545
00:42:19,281 --> 00:42:21,401
a "fateful encounter".

546
00:42:21,401 --> 00:42:25,041
If that's the case, then that may
suggest that complex life -

547
00:42:25,041 --> 00:42:29,641
that intelligent life - is extremely
rare INDEED in the universe.

548
00:42:38,201 --> 00:42:40,321
Maybe there is a profound bottleneck

549
00:42:40,321 --> 00:42:43,121
in the evolution of complex
life in the Milky Way.

550
00:42:47,241 --> 00:42:54,227
And perhaps this is why we
continue to bear the great silence.

551
00:43:01,921 --> 00:43:04,481
But life here, did squeeze through.

552
00:43:08,721 --> 00:43:12,081
And the story of our planet
suggests that after it did

553
00:43:12,081 --> 00:43:13,681
all hell broke loose.

554
00:43:16,321 --> 00:43:18,561
So given the right conditions

555
00:43:18,561 --> 00:43:21,841
then 550 million years ago,

556
00:43:21,841 --> 00:43:23,721
at least, here on Earth,

557
00:43:23,721 --> 00:43:26,561
the Cambrian explosion happened

558
00:43:26,561 --> 00:43:28,721
and all the...what Darwin called

559
00:43:28,721 --> 00:43:30,681
"endless forms most beautiful"

560
00:43:30,681 --> 00:43:32,321
that we see on this planet,

561
00:43:32,321 --> 00:43:34,921
emerged almost in the blink
of an eye

562
00:43:34,921 --> 00:43:37,681
including one civilisation,

563
00:43:37,681 --> 00:43:39,281
an intelligent civilisation,

564
00:43:39,281 --> 00:43:41,241
that's managed, ultimately,

565
00:43:41,241 --> 00:43:43,241
to begin to launch spaceships

566
00:43:43,241 --> 00:43:45,841
beyond our solar system into
the stars,

567
00:43:45,841 --> 00:43:47,361
and, it seems,

568
00:43:47,361 --> 00:43:49,521
has also produced aquatic pigs!

569
00:43:50,881 --> 00:43:52,201
Such is the wonder

570
00:43:52,201 --> 00:43:54,081
of evolution by natural selection

571
00:43:54,081 --> 00:43:55,921
which I would argue

572
00:43:55,921 --> 00:43:57,721
is a law of nature.

573
00:43:57,721 --> 00:44:00,001
Anywhere you get the right
conditions

574
00:44:00,001 --> 00:44:01,361
you will get...

575
00:44:01,361 --> 00:44:03,161
You'll get animals like this.

576
00:44:06,921 --> 00:44:11,640
Just 100 million years after
the start of the Cambrian explosion

577
00:44:11,640 --> 00:44:13,721
our ancestors crawled from
the oceans...

578
00:44:21,481 --> 00:44:24,321
And in the cosmic blink of an eye,

579
00:44:24,321 --> 00:44:27,401
evolution threw up an
inquisitive species

580
00:44:27,401 --> 00:44:32,678
prone to asking questions
about the world around it.

581
00:44:40,201 --> 00:44:43,881
If you're interested in communicating
with an alien intelligence

582
00:44:43,881 --> 00:44:47,481
then I suppose a natural question
arises, which is -

583
00:44:47,481 --> 00:44:50,641
Are there animals on Earth
other than ourselves,

584
00:44:50,641 --> 00:44:53,361
that are intelligent enough
to communicate with?

585
00:44:53,361 --> 00:44:56,161
Now, early on in the history
of SETI

586
00:44:56,161 --> 00:44:59,761
there was one animal in particular
that got an iconic reputation -

587
00:44:59,761 --> 00:45:02,881
in fact, Frank Drake, Carl Sagan,
John Lilly,

588
00:45:02,881 --> 00:45:04,801
and the other SETI pioneers

589
00:45:04,801 --> 00:45:08,361
called themselves, named themselves,
after this animal -

590
00:45:08,361 --> 00:45:11,561
they called themselves
The Order of The Dolphin.

591
00:45:11,561 --> 00:45:15,401
And, indeed, in the '60s and '70s,
John Lilly, in particular,

592
00:45:15,401 --> 00:45:18,801
carried out a series of
increasingly eccentric experiments

593
00:45:18,801 --> 00:45:21,161
to try and communicate
with dolphins.

594
00:45:24,481 --> 00:45:29,521
Dolphins remain at the forefront of
inter-species communication efforts.

595
00:45:29,521 --> 00:45:31,281
Where's your giggle?

596
00:45:35,121 --> 00:45:36,801
Good!

597
00:45:36,801 --> 00:45:40,641
So far, there have been
no meaningful conversations -

598
00:45:40,641 --> 00:45:42,161
however there is a dolphin

599
00:45:42,161 --> 00:45:44,761
in the Grassy Key Research Centre
in Florida

600
00:45:44,761 --> 00:45:49,757
that demonstrates
a form of intelligence.

601
00:45:52,241 --> 00:45:55,841
He's a 13-year-old bottlenose
male called Talon.

602
00:45:57,041 --> 00:45:58,761
Good boy.

603
00:46:01,641 --> 00:46:03,521
OK, Brian.

604
00:46:07,521 --> 00:46:09,881
We're going to find out whether
Talon can understand

605
00:46:09,881 --> 00:46:14,691
the abstract concept
of more or less.

606
00:46:15,201 --> 00:46:18,441
OK, so what we're going to do,
Brian, is put these boards up

607
00:46:18,441 --> 00:46:22,361
and Talon's going to choose the one
that has the least amount of dots.

608
00:46:22,361 --> 00:46:24,881
The dots are randomised
by the computer,

609
00:46:24,881 --> 00:46:27,201
and the side of the correct answer.

610
00:46:27,201 --> 00:46:29,601
So put this one up first.

611
00:46:29,601 --> 00:46:31,801
Oh, yeah.
So always the left first?

612
00:46:31,801 --> 00:46:33,601
Always the left first.

613
00:46:33,601 --> 00:46:35,961
That way if Talon's watching
from the other side -

614
00:46:35,961 --> 00:46:38,361
even though we have these little
blinders -

615
00:46:38,361 --> 00:46:40,281
we're not giving him any kind
of cues,

616
00:46:40,281 --> 00:46:42,721
on which side the correct
answer might be on.

617
00:46:42,721 --> 00:46:44,121
Left board up first...

618
00:46:46,001 --> 00:46:47,561
Yeah. Hi, buddy!

619
00:46:47,561 --> 00:46:49,401
That is Talon. He is looking.

620
00:46:49,401 --> 00:46:53,161
Most humans acquire the ability
to distinguish between

621
00:46:53,161 --> 00:46:56,081
numerical amounts fairly early
in life -

622
00:46:56,081 --> 00:46:58,081
at around the age of six months.

623
00:46:58,081 --> 00:47:00,081
Talon!

624
00:47:00,081 --> 00:47:05,650
The experiment tests if dolphins
share the same cognitive ability.

625
00:47:06,161 --> 00:47:07,281
Less.

626
00:47:07,281 --> 00:47:09,121
Yes!

627
00:47:09,121 --> 00:47:11,601
Yeah, you can move our hands back
out... Excellent!

628
00:47:14,841 --> 00:47:15,881
Less.

629
00:47:18,201 --> 00:47:19,561
Yes!

630
00:47:21,841 --> 00:47:23,681
Yeah, good job, Talon!

631
00:47:26,761 --> 00:47:28,481
This is quite an interesting example

632
00:47:28,481 --> 00:47:30,321
because this one's five and
this one is six

633
00:47:30,321 --> 00:47:32,721
but because of the difference
in area, and placement,

634
00:47:32,721 --> 00:47:35,641
I think it does take a while even
for a human to look at it.

635
00:47:35,641 --> 00:47:39,123
Probably, what we'd do,
is count them.

636
00:47:41,641 --> 00:47:42,961
Less!

637
00:47:43,881 --> 00:47:46,001
Yes.

638
00:47:46,001 --> 00:47:48,641
Straightaway.
You see how quickly he chose that?

639
00:47:48,641 --> 00:47:50,281
That was impressive, actually.

640
00:47:50,281 --> 00:47:53,321
He was actually going for that board
before she even gave him the signal.

641
00:47:55,081 --> 00:47:58,441
It's not known how Talon
processes the information,

642
00:47:58,441 --> 00:48:00,441
but his success rate is interesting.

643
00:48:06,441 --> 00:48:07,961
All right. That was awesome!

644
00:48:07,961 --> 00:48:09,321
Good job, Talon.

645
00:48:10,641 --> 00:48:13,321
What this experiment shows
is that dolphins exhibit

646
00:48:13,321 --> 00:48:16,481
a kind of behaviour that
we associate with intelligence -

647
00:48:16,481 --> 00:48:19,201
scientists call it
relative numerosity -

648
00:48:19,201 --> 00:48:22,961
the ability to say which board
has got more dots on it.

649
00:48:22,961 --> 00:48:24,721
And that's interesting,

650
00:48:24,721 --> 00:48:26,281
because if you ask the question -

651
00:48:26,281 --> 00:48:29,441
Where is the common ancestor between
me and a dolphin?

652
00:48:29,441 --> 00:48:32,921
- you've got to trace the timeline
back about 90 million years.

653
00:48:32,921 --> 00:48:35,361
That's when dinosaurs
were on the Earth.

654
00:48:35,361 --> 00:48:38,921
So our common ancestor certainly
wouldn't be able to do that,

655
00:48:38,921 --> 00:48:41,481
wouldn't exhibit that
kind of intelligence.

656
00:48:41,481 --> 00:48:46,001
So intelligence of a sort has arisen
actually many times on Earth.

657
00:48:47,641 --> 00:48:49,441
But from the point of view of SETI -

658
00:48:49,441 --> 00:48:52,441
the Search for Extra-Terrestrial
Intelligence -

659
00:48:52,441 --> 00:48:54,881
that doesn't matter, at all.

660
00:48:54,881 --> 00:48:57,441
We need a civilisation
that can do astronomy,

661
00:48:57,441 --> 00:48:59,881
that can build radio telescopes
or spacecraft,

662
00:48:59,881 --> 00:49:01,561
that can leave a signature

663
00:49:01,561 --> 00:49:04,281
or send a message
that we can recognise.

664
00:49:07,041 --> 00:49:09,241
This is perhaps the
greatest mystery.

665
00:49:12,401 --> 00:49:17,121
We simply don't know how often
complex, intelligent life...

666
00:49:20,001 --> 00:49:26,073
..develops into a technologically
advanced civilisation.

667
00:49:26,820 --> 00:49:30,401
# I watch the moon
hang in the sky

668
00:49:32,721 --> 00:49:36,081
# I feel the traffic rushing by

669
00:49:39,081 --> 00:49:43,081
# Freight train engine in the night

670
00:49:43,081 --> 00:49:45,041
# I'm still here

671
00:49:46,761 --> 00:49:49,041
# Waiting for you

672
00:49:51,401 --> 00:49:54,241
# I watch the moon hang in the air

673
00:49:57,601 --> 00:50:01,201
# I feel the cool breeze
through my hair

674
00:50:04,161 --> 00:50:07,623
# My eyes' blind by her light's glare

675
00:50:07,961 --> 00:50:11,035
# I'm still here

676
00:50:11,035 --> 00:50:14,224
♪ Waiting for you... ♪

677
00:50:16,001 --> 00:50:17,841
Just three decades ago,

678
00:50:17,841 --> 00:50:20,841
we knew of no planets beyond
our solar system.

679
00:50:22,441 --> 00:50:25,121
Today we've found thousands of them

680
00:50:25,121 --> 00:50:27,961
and suspect that there
are billions more.

681
00:50:29,441 --> 00:50:32,561
Our knowledge of the origin of life
has also deepened,

682
00:50:32,561 --> 00:50:35,681
as has our understanding
of our own evolution.

683
00:50:42,161 --> 00:50:45,201
All this leads me to think
that there must be

684
00:50:45,201 --> 00:50:49,521
at least simple life
elsewhere in the galaxy.

685
00:50:52,201 --> 00:50:55,361
Yet the silence persists.

686
00:50:55,361 --> 00:50:58,161
We remain alone.

687
00:51:12,150 --> 00:51:16,988
Easter Island

688
00:51:18,161 --> 00:51:20,361
It's a puzzle,

689
00:51:20,361 --> 00:51:22,001
but I think Easter Island

690
00:51:22,001 --> 00:51:25,427
may offer us an answer.

691
00:51:26,441 --> 00:51:30,921
The civilisation here survived
in isolation for over 1,000 years...

692
00:51:33,161 --> 00:51:35,361
..until, 300 years ago,

693
00:51:35,361 --> 00:51:37,081
it vanished,

694
00:51:37,081 --> 00:51:42,246
leaving behind only a
handful of stone statues.

695
00:51:44,081 --> 00:51:46,001
What seems to have happened

696
00:51:46,001 --> 00:51:49,721
is that they used the resources
of this tiny island,

697
00:51:49,721 --> 00:51:51,681
chopped all the trees down,

698
00:51:51,681 --> 00:51:54,643
they killed all the animals,
they overused the land,

699
00:51:54,643 --> 00:51:56,279
the population grew too big,

700
00:51:56,279 --> 00:51:57,725
they started warring,

701
00:51:57,725 --> 00:52:02,975
it's thought that they toppled their own
statues in battles between rival villages

702
00:52:02,975 --> 00:52:06,503
and so they essentially
destroyed themselves.

703
00:52:14,001 --> 00:52:19,841
This collapse speaks powerfully to the
last factor in the Drake equation -

704
00:52:19,841 --> 00:52:22,961
the length of time
a civilisation lasts.

705
00:52:35,961 --> 00:52:43,521
Imagine there are, and have been thousands or millions
of civilisations in the history of the Milky Way galaxy -

706
00:52:43,521 --> 00:52:46,441
and imagine their lifetimes
are short.

707
00:52:48,841 --> 00:52:52,761
No matter how they're distributed
in space and time...

708
00:52:54,641 --> 00:52:57,185
..they never overlap.

709
00:52:58,001 --> 00:53:00,721
And I think this is quite
a sobering thought -

710
00:53:00,721 --> 00:53:06,641
the reason we have never and WILL
never hear from any other civilisation,

711
00:53:06,641 --> 00:53:11,041
is because none of them ever last
long enough to contact each other.

712
00:53:27,081 --> 00:53:29,881
But I don't think that's necessarily
the answer.

713
00:53:35,761 --> 00:53:38,761
I think the story of the
Rapa Nui people

714
00:53:38,761 --> 00:53:41,681
hints at something else.

715
00:54:11,521 --> 00:54:16,321
Their island was the final destination
of the human colonisation of Earth.

716
00:54:22,161 --> 00:54:31,015
A journey that took us from our origins
in East Africa to across the planet
in less than 60,000 years.

717
00:54:34,041 --> 00:54:38,001
And I think a sufficiently
advanced alien civilisation

718
00:54:38,001 --> 00:54:40,761
would mirror this
process of colonisation.

719
00:54:42,801 --> 00:54:45,921
In the 1940s, the mathematician
John von Neumann

720
00:54:45,921 --> 00:54:50,721
thought about the possibility that we
could build self-replicating machines -

721
00:54:50,721 --> 00:54:53,561
he called them
Universal Constructors.

722
00:54:53,561 --> 00:54:57,521
So these would be space probes that
could fly out to a solar system,

723
00:54:57,521 --> 00:55:00,521
land on an asteroid, or a moon,
or a planet,

724
00:55:00,521 --> 00:55:04,561
and then mine the resources
they needed to copy themselves.

725
00:55:09,681 --> 00:55:15,521
In this way von Neumann's replicating machines
could spread across the entire galaxy...

726
00:55:16,921 --> 00:55:19,481
..just as humans spread across
the Earth.

727
00:55:22,361 --> 00:55:25,761
Think about how the Polynesians
colonised the Pacific islands -

728
00:55:25,761 --> 00:55:28,161
they sailed across the ocean,

729
00:55:28,161 --> 00:55:32,681
they landed on some uninhabited
rock like Easter Island,

730
00:55:32,681 --> 00:55:35,441
and they used the resources
they found there

731
00:55:35,441 --> 00:55:37,201
to make copies of themselves.

732
00:55:37,201 --> 00:55:38,841
We call it breeding.

733
00:55:41,241 --> 00:55:44,161
Now, modern computer models suggest

734
00:55:44,161 --> 00:55:48,921
that such a strategy would allow an
advanced alien civilisation

735
00:55:48,921 --> 00:55:55,172
to colonise the entire Milky Way
galaxy in only ten million years -

736
00:55:55,172 --> 00:55:58,409
the blink of an eye in cosmic time.

737
00:56:12,441 --> 00:56:14,521
All this sounds
like science fiction,

738
00:56:14,521 --> 00:56:17,041
but if they're possible in principle

739
00:56:17,041 --> 00:56:20,521
then you have to construct
some kind of argument

740
00:56:20,521 --> 00:56:23,439
as to why we don't see them,

741
00:56:23,439 --> 00:56:25,665
and I can't construct one.

742
00:56:25,905 --> 00:56:27,681
It bothers me.

743
00:56:40,041 --> 00:56:43,761
It follows that if such an advanced
civilisation had existed,

744
00:56:43,761 --> 00:56:45,641
we'd know about it.

745
00:56:50,321 --> 00:56:53,761
We'd have encountered one
of von Neumann's machines.

746
00:56:59,641 --> 00:57:03,241
And I think that suggests
that there is only one

747
00:57:03,241 --> 00:57:05,961
technologically advanced
civilisation in the Milky Way,

748
00:57:05,961 --> 00:57:09,561
and there only has ever been one -
and that's us.

749
00:57:09,561 --> 00:57:11,161
We are unique.

750
00:57:19,521 --> 00:57:24,681
Could it be that we alone have passed
through the evolutionary bottlenecks

751
00:57:24,681 --> 00:57:29,401
that seem to have prevented
civilisations from arising elsewhere?

752
00:57:33,561 --> 00:57:35,401
If the answer is yes,

753
00:57:35,401 --> 00:57:39,921
we are the only intelligent
civilisation in the galaxy,

754
00:57:39,921 --> 00:57:44,921
and that makes us indescribably
precious and valuable.

755
00:57:44,921 --> 00:57:48,721
We are the only island of meaning
in an infinite sea of lonely stars.

756
00:57:48,721 --> 00:57:52,441
And without wishing to be overly
romantic or sentimental about it,

757
00:57:52,441 --> 00:57:56,361
that would seem to me to confer
on us a responsibility -

758
00:57:56,361 --> 00:58:01,700
the responsibility to act together
as a civilisation to survive

759
00:58:01,954 --> 00:58:04,361
and, ultimately, to explore
those stars.

760
00:58:08,801 --> 00:58:11,641
"As The Secretary General
of the United Nations

761
00:58:11,641 --> 00:58:15,161
"I send greetings on behalf
of the people of our planet."

762
00:58:24,241 --> 00:58:27,921
SMALL CHILD: 'Hello, from
the children of Planet Earth...'

763
00:58:28,121 --> 00:58:34,840
End