Stop for a moment and think of this.
Are we alone in the universe?
It's perhaps the biggest question we've ever asked.
It's not crazy to imagine that some hugely super-human
civilisation exists out there.
They may have been watching the earth for millions of years.
After a long and distinguished career
at the forefront of cosmology,
the Astronomer Royal, Martin Rees, has taken up
the hunt for extraterrestrials.
Absence of evidence is not evidence of absence.
Now, with the help of the BBC's archive...
We can't prove that bug-eyed monsters don't exist.
..Martin's going to take us into his world.
You might think hunting for aliens is just science fiction.
You'd be wrong.
Quite a sight, wasn't it, sir?
A sight I'd rather not be seeing.
It's a vibrant frontier of modern science...
..where fierce debates rage.
It's possible that we are a trillion-to-one fluke.
I think that's an over-hasty conclusion.
By exploring opposing views...
A lot of sloppy thinking is quite accepted about alien intelligence
and I think that is a problem.
..we'll travel to the limits of our understanding about the universe
and our place in it.
It's a journey that, for Martin,
leads to an extraordinary conclusion.
Our idea of what an alien will be is all wrong.
It's not organic beings we should be looking for.
It's machines.
On July 20th, 2015,
Professor Martin Rees joined
some of the greatest minds in science at the Royal Society.
They were launching a £70 million research programme.
The aim? Finding intelligent life in the universe.
It's a huge gamble, of course.
No-one would count on success, but the pay off would be so colossal.
The team are using some of the world's biggest telescopes to hunt for a signal.
It's our best chance yet of finding aliens.
Stakes are so high, and that's why I think there's more interest
and more focus - certainly among mainstream scientists -
on this topic than there ever was in the past.
And we are gradually edging closer to answers.
'With at least two billion stars in our universe,
'somewhere in deep space there are probably planets with
'civilisations built by living creatures.'
As our knowledge of the universe has increased...
..so has our understanding of who or what might be living out there.
Hello!
Aliens have gone mainstream.
That's why scientists like Martin -
more famous for researching the big bang and black holes -
have joined the hunt for extraterrestrials.
Are we alone? Or is there life elsewhere?
It's especially fascinating to us today,
because, for the first time, we have a real chance of answering it,
because of the advances in technology
and in our understanding of life.
But first, there's a problem.
Before we can explore Martin's ideas on aliens,
there's one question all those who look for ET must face.
It's a question famously posed in the most unlikely of settings.
Los Alamos.
Birthplace of the bomb.
The year is 1950...
..and Enrico Fermi, one of the architects of the atomic age,
is taking a break.
Fermi was having lunch with some colleagues.
They were talking about the existence or otherwise of aliens.
And midway through the lunch, Fermi just stopped and said,
"Where is everybody?"
Where indeed.
Fermi's point was that if there ARE lots of alien civilisations
out there, why haven't we found any?
It may seem a simple observation, but for physicist Stephen Webb,
it casts doubt on the idea that we have any cosmic company at all.
Because Fermi did more than just ask the question.
Like all good scientists, he did a spot of maths.
What he did was run through the numbers,
looked at the number of stars in the galaxy, number of planets.
He made an estimate of how many extraterrestrial civilisations
should be out there.
And he came to a large number.
Given the huge scale of the galaxy, Fermi calculated that
there should be loads of alien civilisations out there.
What's more, he reasoned that many of them would
be far more advanced than our own
There are many stars which are quite a bit older than the earth.
Indeed, in our galaxy there are stars two or three billion years older than the sun,
which could perfectly well have evolved planets,
rather like happened here on earth.
And of course you then have to ask, if that were the case,
then the life on those alien planets would have had a head start.
Fermi's conclusion was that aliens should easily have colonised
the galaxy by now - several times over.
In short, there should be space-faring civilisations everywhere.
So Fermi realised that there's something paradoxical about this.
We expect to see them, and we don't.
It's called...guess what? The Fermi Paradox.
And for some, it leads to a stunning conclusion.
It's a surprise to me.
I would expect, if they exist, that we would see them.
We would hear from them.
They could build large structures,
we could see exhaust from anti-matter rockets,
we could see artificial lines in a star's spectrum
that they've put there.
The conclusion that I would draw from that is that we are alone.
And that's a really, really sad thought.
I think that's an over-hasty conclusion...
..because we've no idea what variety the life out there might take.
If there are aliens out there,
then they're likely to be extremely different from us, in my opinion,
because there could be all kinds of intelligence which would not
manifest itself in any way that we can yet detect.
Indeed, Martin's not ruling out the possibility that we may
someday find evidence that alien civilisations
have visited our solar system.
You could certainly imagine scenarios where some alien
civilisation sent out lots of probes and some of them
came to our solar system.
And therefore we should keep our eyes open for any artefacts
that we might come across orbiting in space or even on one of the planets,
which could be evidence of some kind of external civilisation.
It's an idea that's familiar
from science fiction.
In the film 2001: A Space Odyssey, alien artefacts
were scattered in our solar system,
left by higher civilisations, waiting to be discovered.
It's a long shot, though.
And in the absence of enigmatic monoliths,
we need more solid foundations for our hunt.
Which means starting with something much simpler.
Because intelligence isn't everything.
Consider bacteria. Simple single-celled organisms.
Superficially, nothing special, but these humble life forms could
hold the key to understanding how common life is in the universe.
And if it's just alien bacteria we're looking for,
it might be right under our noses.
For centuries, Mars was the prime candidate for alien life
in our solar system.
In fact, in about 1900, a French foundation had set up
a prize of 100,000 French Francs for the first detection
of extraterrestrial intelligence.
And in the rules for that prize, they excluded Mars
because it was thought too easy to detect life on Mars.
We've just had some amazing photographs sent back
by the American Probe to Mars, Mariner 6.
Nasa's Mariner probes first took us to Mars.
First in 1965...then again in '69.
You can see there some of the dark areas, which may be vegetation.
And at the bottom, you can see the white polar cap,
which has always been thought to be due to some sort of icy or frosty deposit.
But close-up pictures revealed a barren world.
Hopes of Martian life began to slip away.
Well, primitive life, there may be. I don't even think so.
Intelligent life? Certainly not.
So, in other words, you think Mars is a dead planet?
Absolutely dead as a dodo.
It certainly looked as dead as a dodo.
There's nothing. There's not even any desert scrub
clinging to the edge of a cliff.
There's nothing. It's completely bare.
This is Professor Monica Grady.
She's one of a growing number of scientists who believe that, despite appearances,
our solar system may yet turn out to be home to alien life.
15 or so years ago, you were regarded as, at best, fringe,
at worst, lunatic,
if you were going to study these sort of subjects.
It's not hard to see why people were doubtful.
As probe after probe visited the planets in turn,
scientists had grown increasingly confident
that Earth was unique in our solar system
in being home to life.
But for Professor Grady, this just doesn't make sense.
The ingredients of life are really, really simple.
Basically, hydrogen, carbon, oxygen and nitrogen.
And they are the most abundant elements in the solar system.
The most abundant elements in the universe.
So there's no reason why life could not, should not
have got going in places beyond the Earth.
Because it's simply physics and chemistry.
But that raises a big question.
How did physics and chemistry...
..turn into biology?
How was life on Earth first created?
We know that all life on Earth is related.
We share DNA not just with monkeys,
but with all the animals and plant life we see.
Go back far enough
and all living things share the same common ancestor.
A single cell.
What nobody knows yet is where that first cell came from.
The origin of life, everyone has known for a century,
is a key problem in science.
At present, when we only know about life in one place,
we can't rule out the possibility
that the odds against life emerging are zillions to one.
So, do we know anything about how easy it was for that first cell to form?
Well, there is one thing.
On our planet, it happened very early.
4.5 billion years ago, the Earth was formed
from a collapsing cloud of gas and dust.
It was a violent event.
Volcanoes pumped out a toxic atmosphere.
And the young planet was bombarded by asteroids.
Yet in this literal hell on Earth,
chemistry turned into biology.
It was an event that Horizon investigated in 1974.
At the University of California, Stanley Miller is re-creating
the early Earth in a fourth-floor laboratory.
The primitive atmosphere was very different than the one
we have at the present time on the Earth.
But the major difference was that there was no oxygen
and there was an abundance of molecular hydrogen.
But nobody had ever tried an experiment
to see what would happen in such an atmosphere.
So, at the age of just 23, Stanley Miller decided to do just that.
It was a famous experiment
in our understanding of the origins of life.
So the experiment was to construct the model ocean,
which is the small flask here,
a model atmosphere, which is the large flask
containing the gases of the primitive atmosphere.
So he boiled up the model ocean,
added lightning and sat back to wait.
His flask contained nothing organic at all.
But after just a week, the miniature ocean within it
had turned muddy brown.
He'd created his very own primordial soup,
full of organic compounds.
The building blocks of life.
In fact, the major group of organic compounds
produced by the spark were amino acids.
And one had no right, really, to expect such a result.
Miller had shown just how easily the building blocks of life can form.
We still don't know how those organic chemicals
turned into a living organism.
But we do know that almost as soon as the planet had a solid crust,
life began.
I suspect that we will find that simple life in some form
is something which can form fairly readily,
given the amount of space and time on a young planet.
Biology's early emergence on Earth offers hope
that life might have formed elsewhere in our solar system.
And possibly not too far away.
Because our next-door neighbour had a remarkably similar early life.
Mars was made at the same time as the Earth was made -
so, roughly 4.5 billion years ago.
Made from the same materials, by the same processes.
It did have active volcanoes, it had rain, it had water,
water flowing over its surface.
So for the first billion years of its life, it was like the Earth.
And in the first billion years of Earth, life got going.
But if life did get going on Mars,
it would have soon found it tough-going.
Mars cooled down fast.
Its small size meant it couldn't retain its internal heat.
And with no magnetic field, much of its atmosphere was lost to space.
Could life still be there now?
Until recently, most people would have said no.
But the more we learn about simple bacterial life
of the kind that might have formed on Mars,
the more we realise it's more robust than we ever thought possible.
If you think of the range of environments in which people can survive - you know,
some of us get really sunburnt if we go out into the garden
and the temperature's above about 25 degrees C.
But bacteria is everywhere. I mean, you know, absolutely everywhere -
deep inside nuclear reactors, deep below the surface of the Earth,
in boiling-hot water,
frozen in Antarctica - it's all over the place.
These sorts of microorganisms are called extremophiles.
They love being at these extremes.
In fact, they're so hardy, scientists decided to test them
in the ultimate extreme environment.
Space.
Minus ten, nine, eight. Go from eight and just start. Seven, six...
On February 7th, 2008, the Space Shuttle Atlantis blasted off
with a surprising payload onboard.
..Space Shuttle Atlantis.
Bacteria, taken from the cliffs of Devon.
..A voyage of science to the Space Station.
Devon may be a holiday spot for us,
but for bacteria, these cliffs are a surprisingly harsh place.
When they're not being hit with a hammer,
they're being blasted by sun and salty water.
So a sample of these hardy bacteria
spent 553 days
outside the International Space Station.
Scorched by cosmic rays
and subjected to extreme shifts in temperatures.
When they returned, something was still alive.
Bacteria called OU-20.
Life could survive in space.
Study of extremophiles has shown that it can exist
over a wider range of conditions
than people had thought previously.
And that, of course, is something which is good news
in the sense that it widens the range of possible locations for life,
if we think about the wider galaxy.
And for Monica Grady, these hardy organisms raise a startling possibility.
If bacteria did form on Mars, as they did on Earth,
then maybe they're still there today.
If you look at Antarctica from the air,
you see a barren and desolate place.
You don't see any trees or vegetation.
When you get up close to some of the rocks and break them open,
you can see that there is a colony in there.
A colony of microorganisms called cryptoendoliths
hidden inside the rock.
Maybe they're there on Mars.
And we might not be too far off finding out if it's true.
Right now, the European ExoMars probe
is en route to the red planet...
..where it will scan for biological signatures.
It's then hoped a rover will follow in 2019,
drilling for signs of life in the Martian soil.
And if we find Mars has, at any time, played host to bacteria...
..it will be a game-changer.
As soon as we find a trace of some sort of biology,
we can be almost certain,
almost absolutely 100% certain maybe...
SHE LAUGHS
..that there is going to be physics turning to chemistry,
turning to biology on planets around stars in our own galaxy
and in many, many, many other galaxies.
I would say that finding evidence for life elsewhere
of independent origin would be a huge discovery -
one of the great discoveries of the century, if it happened.
Because it would have these implications about
the likelihood of life existing throughout the entire universe.
These days, most scientists think it's likely
that we do live in a universe teeming with simple life.
But a few cells in a Petri dish
aren't what most people think of when they imagine ET.
So here's the next big question.
If there is primitive life out there,
what are the chances it could have evolved into something
we might truly call an alien?
Again, our Earth offers
the only example of evolution that we can use as evidence.
But this time, things don't look so hopeful.
All we know from the history of life on Earth
is that it took a long time
to get from single-celled life
to the next stage - a multi-cellular one.
And that, of course, suggests that that might involve
some rather improbable change.
For two billion years,
the Earth was home only to simple organisms, like bacteria.
In short, slime.
But then, something happened.
It's thought one primitive cell swallowed another
and the two began working together.
It was the first step on the path to more and more complex organisms
and the huge diversity we see today.
What we don't know is how many of the specific features of the Earth
were crucial in order to allow life
to proceed through its stages of emerging complexity.
And that, therefore, means we don't know for sure
how likely it would be
that life would develop complexity on other planets.
This is a big debate.
For some, the late emergence of complex life on Earth
points to it being a very rare event indeed.
There's a hypothesis - it's called the Rare Earth hypothesis -
that suggests that there's something special about Earth.
This Rare Earth hypothesis claims that an extraordinary
once-in-a-galaxy run of good luck
led to the evolution of our planet's rich and diverse life.
If true, other worlds wouldn't make it past slime.
And slime isn't well suited to interstellar travel.
Some conditions that are part of the Rare Earth hypothesis
don't sound too rare.
We're looking for a star that's been stable for billions of years
and we're looking for a rocky planet with water on there.
But some are trickier.
One in particular takes us back once again
to our Earth's violent formation.
And a day that was responsible for much of what makes Earth so special.
And yet it was just a chance event.
It's believed the Earth once had a twin.
A Mars-sized planet named Theia.
Born in a similar orbit.
The result?
Well, be grateful you weren't there.
Theia was destroyed in the collision.
But the debris coalesced, forming our planet's travelling companion.
The moon.
It's true, moons aren't rare,
but our moon is huge compared to the Earth.
And this may have been vital for complex life.
Because our moon doesn't just give us tides.
The moon plays a key role in stabilising the Earth's axial tilt,
which gives rise to the nice, pleasant seasons that we enjoy.
There's the possibility that the existence of the moon
has helped a long, four-billion-year period of clement weather.
Without the moon, some believe our planet's tilt would have been unstable.
Some years, our seasons would be unbearably hot and long.
Other years wouldn't have seasons at all.
Such an unstable climate might have meant
that complex life never got out of the starting blocks.
Because evolution relies on small changes from one generation to the next.
If that change is useful, the creature is more likely to survive.
But if there were extreme swings in climate -
so extreme that, at times, there was no liquid water -
an adaptation that's useful one year may be wiped out the next.
No long-term stability, no natural selection.
And it's not just the moon.
There are many other examples of our planet's apparent good fortune.
Earth has a system of plate tectonics.
Plate tectonics is important for stabilising Earth's temperature.
The movements of the vast network of rigid plates
that make up our planet's surface...
..create massive volcanic eruptions,
recycling carbon dioxide into the atmosphere.
Today, we think of it as a nasty greenhouse gas.
But throughout the Earth's long history,
carbon dioxide has helped regulate our planet's temperature,
so complex life can survive.
The Rare Earth hypothesis also suggests
that we've a lot to thank Jupiter for.
The gas giant's huge gravitational pull might capture asteroids
that would otherwise be on a collision course with Earth.
It's hard to evolve if icy rocks
constantly rain down on you from above.
The special conditions that led to complex life on Earth go on and on.
And maybe there's only one conclusion.
It's possible that we are a trillion-to-one fluke.
That there's some combination of factors that make Earth special.
My view is that these ideas of a so-called very rare Earth are rather oversold
and that we've learnt that life can exist in a variety of contexts in the Earth.
And our observations are limited,
our imaginations are even more limited.
So my view is that we should not be put off
and not take too seriously
the fact that our particular evolutionary track here on Earth
depended on some special conditions.
There's another, more practical reason
that the Rare Earth hypothesis might be overplayed.
Perhaps it underestimates the sheer number and variety
of other worlds in our galaxy.
We've learnt, actually, just in the last few years,
a great deal about our universe
that makes the night sky far more interesting.
100 years ago, people thought that planets were very rare
around other stars.
No-one had found any direct evidence for a planet until 20 years ago.
It was once thought that detecting planets around other stars
would be impossible.
They were just too small and too far away.
But in 1995, the impossible happened.
Two Swiss scientists - Didier Queloz and Michel Mayor -
were monitoring the positions of some 140 stars.
But one of these stars was a puzzle.
On closer inspection, they realised
the sun-like star, 51 Pegasi, was on the move.
In fact, the first reaction that you have at that time is,
"Oh, something is wrong with the experiment".
And you observe it again the day after and the day after
and then it was more and more awful
because it was moving every day.
And you say, "There is really a big problem with the experiment".
Each time they looked, the movement had changed.
Gradually, a pattern emerged.
The star was wobbling around a point.
This could mean only one thing.
51 Peg was not alone.
It was being pushed and pulled by the gravity
of a smaller body we couldn't see.
This was the first planet we'd found orbiting another star.
A huge moment in our hunt for worlds aliens might call home.
It was a completely crazy time, with calls from papers,
from television, from radio, from...from all the world.
And, er...e-mail - 100 email per day, or something like this.
It was absolutely, completely a time
where we had no possibility to work at all.
This planet was too large and too hot to be home to life.
But we've got better at this planet-hunting lark.
Over time, we've found smaller planets,
further out from their parent stars.
Until eventually, in April 2007,
Gliese 581c was discovered.
And scientists thought it just might be capable of supporting life.
European astronomers have spotted a new planet outside our solar system
which closely resembles the planet Earth.
Every time somebody finds an Earth-like planet,
the probability that there is life
somewhere else in the universe goes up a bit.
This latest find has set the world of astronomy alight.
In the last few years, more and more planets have been found.
Many in the so-called Goldilocks Zone -
not too hot and not too cold for liquid water.
The more we look, the more we realise
that Earth-like planets are all over the place.
The universe which we now perceive
is far vaster than it was perceived to be in earlier centuries.
In our galaxy, there are probably
literally a billion planets like the Earth.
We've seen that it's possible simple life is common in the universe.
Complex life could be trickier.
Conditions need to be just right.
But the sheer number of planets we've discovered in our own galaxy
suggests that such conditions could be surprisingly common.
But there's one further leap that needs to happen
before we can hope to make contact with aliens -
the leap to intelligence.
We're not talking about the ability to bash a few rocks together.
We need civilisations that can communicate
across the vastness of space.
So, is it possible to predict
how common intelligent civilisations are in the galaxy?
Fortunately, thanks to astronomer Frank Drake,
we have an equation designed to tell us just that.
And, in, fact this is our number N.
The number of technical civilisations in the galaxy.
The challenge is to give each term a number
and simply multiply them together.
Into the now famous - or infamous - Drake equation
goes everything from astrophysics, through evolutionary biology
to whatever it is that governs
the lifetime of a detectable civilisation.
Not surprisingly, no-one's solved it yet, but anyone can have a go.
It's almost a game the whole family could play.
Get the numbers right, and, bingo!
You know how many communicating civilisations are likely to be out there.
So, in 1981, BBC Horizon locked some of the brightest minds in Nasa
in a room together and asked them to come up with a solution.
Team captain today is John Wolfe.
I think it was Frank Drake himself who said that
this is a rather nice way of fitting
a great deal of ignorance into a very small space.
Some of Drake's variables we know reasonably well.
We know how often stars form.
And these days, we can have a good stab at
how many stars have planets.
Seem to have more consensus... That was easy!
..more consensus there than anywhere. Quickly.
This may reflect the fact that we're moving to the area we know least about.
It's the later terms we know less well.
But scientists don't mind guesswork, provided it's educated guesswork.
And when it comes to asking if life
would eventually evolve intelligence,
the Nasa scientists were actually quite confident.
It's very natural, I think, to argue that intelligence
with the survival capability that's inherent in it will also follow.
I think that's the usual argument for it being an unity.
In fact, the first guy to get smart is the one that dominates the planet.
That's right. Thank God we were first.
They were equally confident that intelligent life
would go on to develop the ability to communicate across space.
Put it up there, that's good enough. Wait until we get to L.
THEY LAUGH
You might think this would mean that intelligent civilisations are ten a penny.
But the final term, L, causes the team some problems.
It asks us to estimate the lifetime of communicating civilisations.
It soon emerges they're going to chicken out of reaching a conclusion.
So if we were to take that lower value of 100, that says that N is, er...
The average lifetime lies somewhere between a few hundred years
and a few billion.
So the number of civilisations in the galaxy now
is somewhere between a few tens and a few hundred million.
A few tens to a few hundred million
isn't the most exact solution.
The term L is so hard to estimate
because it forces us to ask a very difficult
and rather uncomfortable question.
How long do intelligent civilisations like ours last?
Of course, we know that here on Earth, the amount of time
we've had any kind of civilisation is a few thousand years,
and that is only one millionth of the age of the Earth.
So it's just a sliver.
And we don't know how long it'll last in future.
If civilisations last for only a few hundred years,
then the window of communication is impossibly small.
There are actually people trying to figure out
just how long advanced civilisations might last.
Dr Anders Sandberg works at the Future of Humanity Institute
in Oxford University.
It's his job to think about the myriad ways
a society could destroy itself.
So we humans have mastered this planet,
but in the process, of course,
we caused a lot of extinctions of animals,
and now we're changing the climate and we're developing bioweapons
in the lab that could kill a lot of people.
So we're obviously a danger to ourselves.
So it might be that sufficiently-powerful technologies
mean that a civilisation will start blowing itself up,
or poisoning itself in a very effective way.
And let's not forget, advanced aliens
might have technologies that we haven't even dreamt of yet.
The basic problem here is that powerful technology is dangerous.
And advanced civilisations will have a lot of powerful technologies at their disposal.
Quite a sight, wasn't it, sir?
A sight I'd rather not be seeing.
The truth is, we don't know whether intelligence
might ultimately be fatal.
So we can't know how many civilisations out there
could hold up their end of the conversation.
And this makes our hunt all the more important.
Because if we find advanced aliens, we'll know for certain
that societies can survive their own powerful technologies.
So, how do you go about finding extraterrestrial intelligence?
What we know is that here on Earth,
life has evolved to a kind of intelligence
that can develop a technological civilisation
which would make our activities detectable in principle
to an alien with a big telescope.
So we've learnt that we have become more conspicuous
and that an alien watching the Earth
would realise that something special had happened
in the last few centuries.
Humans have existed for about 200,000 years.
But for most of this time, alien astronomers looking at the Earth
would see little to suggest there's anything intelligent down here.
INSTRUMENTAL
In fact, it wasn't until 80 years ago
that we really screamed our presence to the galaxy.
When we began leaking radio and television signals into space.
So if the Earth's first sign of intelligence
was our making a racket in the radio spectrum,
it's only natural to wonder whether intelligent aliens
would be doing the same.
Listen... CRACKLING
Sound picked up from outer space by radio telescope
for some earthly usage still unknown.
The '50s and '60s saw the construction of radio telescopes
so sensitive, they could tune into signals
from the other side of the galaxy.
The hunt was on.
Into such a dish one day could come a signal
that would reveal the existence of other creatures
unimaginably more intelligent than we are.
It was the radio astronomers who were the first to talk about
doing serious searches for artificial signals.
And the first effort to do this was pioneered by Frank Drake,
who is one of the pioneers of this subject
and is still one of the leaders of it today.
Before he wrote his frustrating equation,
Frank Drake gave birth to Seti -
the Search for Extraterrestrial Intelligence.
We used the 85-foot telescope there
and a special, very sensitive receiver
which was especially designed to detect intelligent signals
rather than the natural emissions radio astronomers normally study.
For the first time, man made a serious attempt
to determine whether he was alone in the universe.
We searched for two months
and studied the two nearest stars which are like the sun.
The stars Tau Ceti and Epsilon Eridani.
For all we knew then, every star had intelligent civilisations in orbit,
pumping out radio waves.
And just a few days into the search,
it looked like that might be the case.
At one point, we had a very exciting recording on our tape recorder.
The telescope picked up a short, but clearly artificial signal
on a frequency protected for radio astronomy.
The news leaked out.
Journalists started to call up,
asking if Drake had found an alien civilisation on his first go.
Could it really be so easy?
Ten days later and the signal came again.
Only this time, the source was clear.
Analysis of this and further study of the signal
showed it had come not from space,
but rather from a radio station on Earth.
What Drake had discovered was a top-secret U2 spy plane
flying at high altitude.
# I'm sorry...#
Not quite the distant signal they were hoping for.
# That I was such a fool...#
After 300 hours of searching,
we concluded that our two target stars,
Tau Ceti and Epsilon Eridani,
had produced no evidence whatsoever for extraterrestrial radio signals.
It was an inauspicious start to our search.
No aliens, and a false signal.
But Frank had paved the way.
Systematic searches were now possible.
More followed. This time, scanning thousands of stars.
I see two glitches on this one. Yeah, yeah.
Probably a car going by,
or the equipment's screwed up, or something like that.
Still nothing.
But maybe we don't hear anything
because we're going about the search all wrong.
A lot of sloppy thinking is quite accepted about alien intelligence.
And I think that is a problem.
A lot of people, for example, just make bland assumptions
that aliens must, of course, be like us.
Radio signals of the type we churn out
may have been ditched long ago by alien civilisations.
Who knows what technologies they're on to now?
But if they're super-advanced,
they'll probably be doing things on a big scale.
Maybe big enough for us to detect.
Maybe we should look for the side effects of activities.
A super civilisation might be sending off all sorts of radiation,
not because they want to tell us, "We're here,"
but because that's a side effect of what they're actually doing.
It comes down to energy.
As humanity has advanced, we've needed more and more of it.
Fossil fuels may not be the best solution,
so we're turning to wind power, tidal power...
..and the light emitted from our star.
And advanced aliens might have to go to even further lengths
to quench their thirst for energy.
You can get even more energy if you put solar panels in space.
It's day all the time, and there is no atmosphere blocking it.
So the logical endpoint would be
to put solar panels around the entire sun.
Who knows what such a structure would look like?
Indeed, who knows what other strange, supersized technologies
aliens might develop?
But it's likely that from Earth, such megastructures would appear
like nothing we've ever seen before.
And maybe this is how an alien civilisation will reveal itself.
I think we look in every way we can.
Traditionally, we've looked for radio signals.
We should look for optical flashes, we should look for artefacts,
we should look for structures in space
that look manifestly artificial.
Whilst we wait for first contact,
we have time to consider another question.
If any aliens out there are more advanced than we are...
..is it a good idea for us to track them down?
The dangers of alien encounters have certainly
inspired their share of sci-fi films.
Whether they're galactic colonialists,
as in The War Of The Worlds,
taking over our lives one at a time...
You fools! You're in danger!
..like in the classic Invasion Of The Body Snatchers...
They're after all of us! My wife, my children, everyone!
..or simply mindless predators, like in Alien.
SCREAMING
And maybe science fiction wasn't too wide of the mark.
Even top scientists have their concerns.
If aliens decided to visit us, then the outcome might be similar
to when Europeans arrived in the Americas.
That did not turn out well for the Native Americans.
So should we be worried about advertising
our existence to the galaxy?
Martin's not convinced.
I would guess that if there are any aliens out there,
then, if they were advanced, they would know we're here already.
They may have been watching the Earth for millions of years,
realising it's a place where something interesting
might be happening.
So, for that reason, I find it hard to take seriously people
who are worried about sending out some sort of message.
And, anyway, it's already too late.
As soon as we started leaking waves into space,
we said to the galaxy, "We're here."
So what type of entities might be out there, tuning in to our signals?
Who, or indeed what, might we make contact with?
We think we'd know an alien if we saw one.
The classic is ET.
I'll be right here.
He might have a bigger head, short little legs
and long, thin fingers, but the basic body shape
is much like our own.
But Martin thinks this is about as far from what an actual alien
might look like as it could be.
A clue to what we might find, lies in our own species' future.
It's taken us a few hundred years to evolve
our technological civilisation.
It's changing very fast,
and if we think of what's going to happen in the next century,
one scenario is that intelligence of the organic kind
may be near its limit with humans.
We like to think we're a pretty smart species.
As evidence, we might point to our technological achievements.
Our computers and sophisticated artificial intelligence, perhaps?
But maybe they're getting so good that our robot servants
will soon be our robot masters.
The future intelligence in our solar system may lie
not with organic life on Earth, but with these entities which are
electronic, rather than chemical,
like what goes on in our human skulls.
Martin's point is that it looks like it won't be long
before the robots here on Earth are much smarter than we are.
And if this happens,
it's likely that THEIR culture will dominate ours.
But what does this have to do with aliens?
Well, if it does turn out that humanity's role is to act
as the midwives to a new robotic super species,
there's no reason other worlds won't have followed a similar path.
If there were another planet on which evolution had tracked
what happens on Earth, then there are two options.
Either it hasn't yet got to
the stage of emergent intelligence - we see no signal from it -
or it's got to the stage when the machines have taken over.
What is most unlikely is that we would find another planet
whose evolution was so synchronised with ours
that we would observe it in just the few centuries
when the dominant feature is organic intelligent civilisation.
If Martin's right, in our first encounter with aliens
we might be dealing not with organisms,
but with super-advanced artificial intelligences.
And this might give us cause for concern.
After all, in films like The Terminator,
when the machines took control, it didn't turn out well for the humans.
And, actually, maybe they underestimated the dangers.
It might all depend
on why the robots were built in the first place.
So you might want to use an autonomous weapon for warfare.
And it's very convenient if it can build more of itself.
And you could programme it to attack your enemies.
So what if you let them loose and they attacked everybody else,
and then you went extinct?
So now you have these mindless machines
going around killing off young civilisations.
The idea that self-replicating killer robots roam throughout space
is called the Berserker Hypothesis, after the novels by Fred Saberhagen.
If true, maybe we should turn off our transmitters
and sit in the dark with our fingers crossed, hoping the machines
have been too busy causing destruction elsewhere to notice us.
And even if the robots aren't programmed killers,
we could still be in trouble.
And this might not be deliberate at all.
The software is really smart and you give it an order
and it implements the order faultlessly,
except that it wasn't in the way you wanted.
And it converts the planet into paperclips,
and then the rest of the galaxy into paperclips,
because that was the order - "Make more paperclips."
Whilst we can't do anything about how aliens may create
their AI, Martin thinks that we at least should proceed with caution.
We've got to ensure that the way in which innovation leads
from the limited-capacity artificial intelligence we have today,
to the more powerful ones, is moderated and regulated,
just like we already have to moderate and regulate
the way biotech is used.
Whether benevolent or not, one thing's for sure -
if we encounter such beings,
they would be unlike anything we've ever seen before.
We are thinking about the possibility of entities who may
be able to grasp concepts which are as far beyond the human mind
as quantum theory is beyond a monkey's mind.
So, are these entities out there?
We've seen how scientists think our universe
might be teeming with life.
And perhaps somewhere it's evolved,
and gone on to do things that dwarf our own achievements.
But we've also seen that there are an awful lot of barriers
to intelligent civilisations.
It feels like we're on the brink.
There is a huge truth to discover.
A truth that tells us not just what's out there,
but what might lie ahead for us down here on Earth.
Whatever we find, one thing is certain -
the answer will change our understanding
of our place in the universe for ever.
Were it the case that the origin of life,
or the origin of intelligent life, were an extremely rare phenomenon
so that we were, in a sense, unique, or unique in our galaxy,
then our fate matters not just to us,
but maybe in a sense of cosmic importance,
and the greening of the galaxy could then start with us.
But, of course, if there were life everywhere in our galaxy -
as there may well be -
it would, in a sense, force us to be somewhat more cosmically modest.
But the upside would be that,
instead of there just being lifeless planets and stars
orbiting around in the galaxy,
we would realise that we were in a far more interesting cosmos
than one in which life is limited to one place.