Original subtitles

What if we're alone in the galaxy?

What if no other intelligent life has ever glimpsed

the beauty of a star rising over a planet's horizon?

For many years, this question was asked, not by scientists,

but by philosophers and theologians.

But then, 50 years ago, an astronomer came up with

a mathematical equation which changed everything.

The equation estimated the number of intelligent civilisations in our galaxy

and it gave the possibility of their existence a scientific legitimacy.

But more incredibly,

this simple equation has gone on to shape the science of a generation.

It's led to new insight into the nature of life, the cosmos and the enigma of intelligence.

And, it's allowing us to speculate

on the true nature of our relationship with the universe.

My name's Dallas Campbell and ever since I first read about the Drake Equation,

I've been intrigued that a simple scientific formula could tell us

so much about the existence of extraterrestrial intelligence.

That it could help us answer what is, perhaps, our most profound question.

When you look up at a clear, desert night sky, like this,

you can start to physically sense just how huge the universe is.

And the few thousand stars you can see are, of course,

just a tiny fraction of the billions of stars that make up our galaxy.

And I don't know about you, but when I look up,

I can't help but wonder what, or who else might be out there.

What I want to find out, is what we do know,

what we can know, and how close we might be to finding an answer.

And that journey starts with a telescope.

50 years ago, one man tried to do something that nobody had ever really tried to do before,

and that's attempt to answer this question in a more scientific and more rational way.

And that attempt happened here,

at the Greenbank Observatory in West Virginia.

In 1960, Doctor Frank Drake was a leading light in the new field of radio astronomy.

With its huge radio dishes, it was revolutionising the way we looked at the universe.

But in April that year, he decided to do something truly extraordinary.

He pointed one of the radio dishes out into space

to listen for signs of extraterrestrial intelligence.

It was a decision that could have labelled him a crank.

It could have ruined his career.

But instead, it was the beginning of a lifelong obsession.

All right, let's go take a look.

Oh, my goodness.

Why is this important? It's probably the most important question there is.

What does it mean to be a human being? What is our future?

Are there other creatures like us?

What have they become? What can evolution produce?

How far can it go? All of that will come out of

learning of the extraterrestrials.

And this will certainly enrich our lives

in a way that nothing else could.

1960 was the beginning of radio astronomy.

New dishes were being built which could search the heavens, not for light, but for faint radio signals

which might reveal new insights about the nature of the universe.

And Drake believed that this meant he could now search for radio evidence of intelligent life.

Quite literally, aliens communicating.

It was such a far-fetched idea, that Frank turned to mathematics,

to create a theoretical framework for his obsession.

Can you just explain the history of the equation?

Well, in 1960, the National Academy of Sciences in the US

asked me to convene a meeting to discuss this whole subject,

to ground it in good, sound science,

and to develop a plan for how to proceed.

So I did that.

I invited everyone in the world who I knew was interested in the subject

to a meeting at Greenbank, all 12 of them.

Just 12 people I knew who were very interested in extraterrestrial life.

And in November of 1961 we convened at the Observatory in Greenbank

and so I thought through what it is you need to know about to be able to

predict how many civilisations there might be to detect in our galaxy.

And I realised that the number of such civilisations depended on seven factors,

and you could even use those factors to form an equation. So I did.

And that became the agenda for the meeting.

This is how those seven factors became the Drake Equation.

He estimated the number of detectable, intelligent communicating civilisations

in the galaxy to be based on the number of stars formed every year...

..multiplied by the fraction of those stars with planets...

..times the number of those planets per solar system with environments suitable for life...

..times the fraction of those planets on which life actually appears...

..multiplied by the fraction of those life-bearing planets on which intelligence arises...

..times the fraction of those that would become

technologically advanced and develop a desire to communicate...

..multiplied by the length of time that they continue to transmit detectable signals into space.

So, with the Drake Equation in place, Frank and his colleagues could start filling in the numbers

and for the first time, make an estimate

for the number of intelligent civilisations in the galaxy.

Can you put the original 1961 estimates into the equation?

One factor that was really well-known was the rate of star formation.

It was about ten per year.

The fraction of stars which have planets -

we had indirect evidence from binary stars.

It was a guess to be about 0.5.

In those days we thought the Earth, and if Mars had been a little more massive, it would have been

able to retain an atmosphere and be suitable for life.

So that, based on our own system, was two.

The chemical experiments in the laboratory suggested that to give it a planet like the Earth,

given some time, by one way or another, life would appear.

So that fraction was one.

That is given enough time it would appear...always appears.

A fraction of these which gave rise to intelligence was a big guess, and still is to this day.

0.5.

Then when it came to the fraction which developed detectable technologies,

was then and now based on our own history, but that one seems to be one.

And at this point we have the rate of production of detectable civilisations.

We conservatively assume that they do not remain detectable forever.

But a favourite guess is 10,000 years for L.

And if we put that in, we get a value N,

which is equal to 50,000 civilisations.

Now that seems like a big number, when you say 50,000.

It is a big number and it's very exciting.

It means there's something to be found out there. We can be far wrong and there's something to be found.

So that's very encouraging to people.

But even though Frank now had a theoretical justification

for his search, he and his colleagues were still a lone voice.

They grabbed telescope time where and when they could,

desperate to find a signal to prove to the world they were right.

But the deafening silence from space was a gift to their critics.

But as the years passed, the scientific mood slowly shifted.

As the astronomers explored more of the universe

and biologists penetrated into the workings of life,

and as our own evolution became clearer, the scientific community

began to feel that Frank wasn't quite so eccentric.

Even though ET had not been heard,

the estimates in Frank's equation made real sense.

And now, 50 years later, his initial radio telescope search of the heavens has become SETI -

the Search for extraterrestrial Intelligence, and boasts its own

multi-million dollar dedicated radio telescope array.

And I'm off to see it with the current director of the Center for SETI Research, Doctor Jill Tarter.

Hi, there. You aren't going anywhere near the ATA, Allen Telescope Array, by any chance, are you?

- You must be Dallas. - Hi, Jill. - It's very nice to meet you.

I'm on my way to the Allen Telescope Array in Hat Creek in Northern California.

And it's the most ambitious SETI project yet.

Built in 2007, the Array is currently made up of 42 small

radio telescopes which can survey the galaxy 24 hours a day.

Computers combine the signals from each dish

to give the equivalent sensitivity of a much larger telescope.

- Well, welcome to Hat Creek. - Thank you for having me.

So why have you got lots of little telescopes as opposed to like a big, Arecibo style dish?

So what we built is a fabulous survey instrument.

You can survey much more of the sky

to a given sensitivity than you can with a big dish.

If you compare what we're doing here with what Frank Drake did 50 years ago,

there's 14 orders of magnitude improvement.

Ten to the 14.

I really get the sense that, for Jill, these are more than just telescopes.

They are the link between modern science and some of the oldest questions on Earth.

After millennia of asking the priests and the philosophers and whoever else we felt was wise,

you know, what we should believe, that suddenly we had some new technology, that is radio telescopes.

And that those telescopes could do an experiment to find the answer.

And I was alive in the very first generation of humans who could do this.

Most of the modern search works in much the same way

as it did back in Frank's day, still based on a single piece of science.

Radio.

Radio waves travel across the distances between the stars across the whole galaxy,

without being absorbed by the dust that's between the stars.

So radio waves are fantastic for long distance inter-stellar communication.

This unique property of radio led Drake to imagine that it would be

far and away the best medium for inter-stellar communication.

But the trouble is that looking for radio signals

isn't quite as simple as we might imagine.

Radio signals, like all electro-magnetic radiation, comes in waves.

And those waves can vary in length from trillionths of centimetres

to kilometres and beyond.

So imagine all those different wavelengths stretched out along this road here.

Let's assume that here we've got visible light and in reality

the wavelength is smaller than the radius of the finest spider silk.

So along this side you've got all the very small stuff.

So you've got ultraviolet. You've got x-rays.

You've got gamma rays.

And on the other side of visible light,

you've got the much bigger stuff.

So you've got infrared, you've got microwave,

you've got radio waves, long waves,

so you can listen to the Radio Four cricket, and very long wave.

But the point is this.

It's a really, really long road

and trying to tune into ET, excuse the cliche,

really is like trying to find a tiny needle in a cosmic-sized haystack.

Back then, SETI could only listen to a tiny section of the spectrum at any one time.

So Drake and his colleagues had to make an educated guess

where to search for extraterrestrial messages.

They knew that every element in the universe has its own unique electromagnetic frequency.

So they made an assumption that if extraterrestrial life

wanted to talk, then surely they'd broadcast on 1420.5 megahertz,

the frequency of the most common atom in the universe, hydrogen.

Hydrogen's the most abundant element in the universe.

So when Frank Drake did his search - and he had one channel -

he chose the frequency of hydrogen - it's universal.

When we were able to look at a little bit more of the spectrum,

we expanded the search to what we call "the waterhole".

Because water is so essential to life, at least as life as we know it,

we said, "Let's look between the hydrogen line, that Frank started at,

"and we'll go up in frequency, 300 megahertz, to the line of the OH Radical."

So H and OH, that's water.

- H2O, yes. - That's a special place.

So if you're trying to guess a magic frequency or a range, where someone

might decide to transmit a signal, that's a good guess.

The spectrum within the waterhole has been the focus of the search for 50 years.

And recently, new advances in computing power have meant

these telescopes can search billions of channels simultaneously.

But, there's a problem.

Since Frank Drake started looking in 1960, they've used thousands of telescope hours to search

for hundreds of different star systems and they've found nothing.

Not a peep.

Silence.

This silence, and the lack of any other evidence

of extraterrestrial life, has become known as the Fermi Paradox.

It's named after the physicist Enrico Fermi,

who first boldly asked, "Where is everybody?"

He pointed out a clear contradiction.

If there are thousands of intelligent civilisations out there,

then at least one must have left some sort of trace.

So what's gone wrong?

Have the scientists led us up the garden path?

Is Frank Drake's Equation just a hope-driven wild overestimation?

Isn't the simplest answer to the Fermi Paradox,

and therefore the most likely, that are no aliens?

We're on our own.

The Fermi Paradox has forced scientists to look closer at the Drake Equation.

Especially at its more speculative elements,

the probability of life beginning and becoming intelligent enough to communicate across the galaxy.

Professor Paul Davies, for one, believes the journey from life's beginnings

to communicating intelligence is fraught with difficulties.

So I asked him to explain the most important barriers to life's development.

One way to think about this is that there's like a great filter

that has to be passed through before you get to the point

of an intelligent civilisation and the first step,

first hurdle, if you like, in the filter

is the transition from non-life to life.

So we can think of this as the first great...

..hurdle that nature has to cross.

So that gives us no life this side. Life.

- So that's the beginning of biology? - That's the beginning of biology.

Big step. I think it could be a very unlikely step, but we don't know.

Then the next might be, say,

multi-cellular organisms.

That's another hurdle that has to be crossed.

And then to get further on,

we need to make the transition to intelligent life.

So intelligence is something that has to evolve, and so it's yet another line in the sand.

That may be a very difficult step.

At the end of this long sequence of hurdles, if you pass through this filter,

then the final goal that we're interested in is the emergence

of technological communicating civilisations, like that up there.

Our lovely telescope.

So if Drake is right, and there are extraterrestrial intelligences elsewhere in the galaxy,

they would all have to overcome those three great filters.

Biogenesis,

the development of multi-cellular life,

and the leap to intelligence.

And that could be almost impossible.

OK, so, this first line in the sand represents the origins of life, biogenesis.

Everything on this side is physics doing its thing,

chemistry doing its thing, and then suddenly...bam!

It turns into biology, the first self-replicating molecules.

And there's loads of good ideas, loads of good science about how this might have happened.

The big question, of course, is, is it common? Does it spring up as soon as the conditions are right?

Or, is life rare or very rare, or even a unique event

that could happen only once in a 13.7 billion year blue moon?

To begin to answer this, we first need to know whether

the kinds of places where life can start are common,

as Drake's Equation would suggest, or rare.

In other words, is Earth a one-off?

To find out, I went hunting for planets around distant stars, known as exoplanets,

at the University of London's Mill Hill Telescope.

One way of detecting exoplanets is what's known as the Transit Method,

and it's a really beautifully simple idea to understand.

If you imagine that this is your star and you're wondering,

"What's going round my star, I can't see it, it's all too small?"

Well, as your exoplanet passes in front of your star, there will be a dip in starlight.

I've got a light meter here, and so imagine that's your telescope, and as the planet passes in between

the telescope and the star, you'll actually be able to see that tiny little dip in starlight.

In practice, even using this small telescope, we can actually see that dip

and infer the existence of a planet orbiting a star far out in the galaxy.

To prove it, the team showed me one

orbiting around a star called HatP14, 650 light years from Earth.

So we started observing just after sunset

and we initially see the amount of light from the parent star.

Then we see it about half an hour later,

just starting to drop as the planet begins to cross the parent star.

Using techniques like this and others,

astronomers have now identified over 450 exoplanets.

A handful of which look like they might be, as Drake put it,

suitable for life.

And they speculate that this is just a tiny fraction of the billions of planets in the galaxy.

So Drake's estimate for Earth-like planets is credible.

And yet, being suitable for life is only the starting point.

Because life still has to actually begin.

And to find out about that,

I've come to southern California and the Scripps Institute in San Diego.

Here, Professor Gerry Joyce believes he could be on the brink

of producing artificial, self-replicating life.

And if he's right, we may understand not only how life started here on Earth,

but also how life might have started elsewhere in the galaxy.

In his lab, he's producing artificial RNA,

which is thought to be the forerunner to DNA.

- All right, so let's replicate some RNA. - OK, fantastic.

- In fact, let's have you replicate some RNA. - So I can do this?

This is OK for me to do, is it?

Yes, I trust you. It's not that hard.

So, we have RNA molecules that can reproduce themselves

and all you need to do is give them the food.

And then a little test tube here that contains their food,

- the building blocks that those molecules use to produce new copies of themselves. - OK.

- And I actually want you to do the replication. - Sure. Just for the sake of argument,

if I went outside and dropped them they won't suddenly devour everything around us

- and start their own culture... - No, out in the wild they wouldn't last

- more than a minute or two. - OK, so they're fragile.

They're very fragile in the face of biology, yeah.

What makes Gerry's RNA unique is that although they're completely artificial,

they are capable of a key characteristic of life -

replicating themselves.

So what's in my test tube?

- I mean, can we say it's life in any way? - They're not alive.

They are a synthetic genetic system.

They are undergoing Darwinian evolution in a self-sustained manner.

And I should say, nothing in the test tube comes from biology. So there's water,

there's some salts, there's the building blocks of RNA,

and then there's the replicator molecules which contain about 80 or 85 different pieces of RNA.

Here's a question. How do I know that they're actually growing?

All I can see is a tiny bit of liquid in the bottom of a test tube?

It is just a very small volume of a clear-coloured solution. So you don't see the molecules.

However, what we've done is put tracers on the molecules.

Either radioactive tracers, which - no offence - we don't trust you with that.

- Right. - Or fluorescent tracers, and then we have analytical tools

that lets us look at their growth characteristics.

So there is ways of actually seeing them doing their thing.

Now it may not look like much,

but this is evidence that Gerry's RNA molecules are actually replicating,

turning basic sugars in the bottom two lines into new RNA at the top.

In terms of that line, that tantalizing line where chemistry turns into biology,

how close are you to that line and can you see yourself going over?

It has a lot of the properties of life, and I suppose the way I would think of things,

even a few years ago, I would have thought something like this would be over the line.

But now, standing right on the line, or right adjacent to the line, I feel it's not over the line.

That it's not just a matter of having a genetic system that can replicate and evolve,

but also the capacity to invent new solutions to new problems that the environment might pose.

So given we've got all this understanding, can we start

to speculate in any meaningful way about how life started on Earth?

- I think that mystery's already put to bed. - Yeah?

I think, you know, there are certainly no show stoppers

in understanding how we get from inanimate chemistry to animate biology,

even though the line hasn't been crossed, literally, in someone's hands.

Or been witnessed other than the life form that we see on this planet.

So I don't think there's mystery about that, but there's still much to be learned.

Understanding the mystery of biogenesis would certainly be

a key step to working out how it might happen elsewhere in the galaxy.

But it doesn't necessarily make biogenesis itself any more likely.

Let's look at the only example we really know - Earth.

It's always been assumed life here on Earth started only once.

So everything, every living thing around us,

is therefore descended from that single moment of biogenesis.

But that view is now being challenged.

All this life around us, all what we see, we know is the same life.

That is, this tree behind me, you and me, these flowers here, the insects and so on,

if you dig into their innards, you look at their DNA, you find they're all interrelated.

So we're all cousins, all life so far studied on Earth,

is related to all other life. So it belongs to a single tree.

And Darwin had this metaphor of a tree,

that it sort of started with some long-ago, precursor organism

and that over billions of years it's diversified and diversified

- into all these different branches. Each branch representing a different species. - That's us up there.

So you've got the mushrooms over there and, you know,

you've got the bacteria up here and the oak trees over here, and so on.

But that's assuming that all life came from a single common origin.

That is, it happened only once on Earth. But how do we know that?

Maybe life happened many times on Earth and maybe instead of being

just one tree of life, there is actually a forest.

So if we confirm this idea of life 2.0, if you like, the separate biogenesis on Earth, can we assume,

with a little more certainty that life is more common in the galaxy, if not the universe, do you think?

It would be inconceivable that life could start twice here on Earth and not at all

on all the other Earth-like planets around the universe.

So all we need is just one example of life, but not as we know it.

Life 2.0. It could be here, it could be on Mars, doesn't matter where it is.

We just want to know that life has happened more than once.

If it's happened twice, it's going to happen all around the universe.

So where do we start looking for life 2.0?

Paul suggested I go looking in the murky world of microbes,

most of which haven't even been classified, let alone analysed.

And he suggested I visit a young biologist in San Francisco.

Doctor Felisa Wolfe-Simon has been searching in the highly toxic depths of California's Mono Lake

and believes she might have found something very unusual.

A tiny microbe that can survive concentrations of arsenic

that would kill all normal life dead.

And this might imply that it evolved from a totally separate biogenesis.

If it is, then life developed on Earth not once, but twice.

Hi, Felisa. Hello, I'm Dallas.

- Hiya, Dallas. - Nice to meet you.

- Nice to meet you. - Thanks for seeing me.

- So, you've been at Mono Lake. - Yes.

And you've been studying some interesting stuff.

- Yes. - Can I have a look at it? - Absolutely.

Firstly, I should ask you, why Mono Lake? What's important about Mono Lake?

Well, first, since you're in the lab, let's get you the lab coat...

- OK. - ..so we can not just talk about it, but we can actually look at it.

- That would be great, really fantastic. - So why go to Mono Lake?

- Yeah. - So, Mono Lake for many years has been measured

by many different people to be very high in arsenic.

But this isn't polluted arsenic. Nothing has been dumped.

This is a natural, rich arsenic lake.

So this lake has been around for a long time.

- Probably has been enriched in arsenic for most of that time. - So, what have you got to show me?

So, what I wanted to do is first show you, start from kind of the

normal thing we might see at Mono Lake, which is still very unusual.

This is just some gunk from Mono Lake...

Some mud from the bottom of Mono Lake, and essentially you just let it sit on a window sill,

and over time, you see these different colours evolve or develop.

These are different kinds of microbes.

And this is the same source material or the same mud that we've isolated

a potentially very unusual and interesting, let's say, arsenic-utilising organism.

We just want to see what's there.

- Let's have a look. - Absolutely.

So you'll see there's nothing fancy about what we're going to do.

Just take a little bit of the sample.

- Put it on a microscope slide. - Can I have a look?

Please.

Oh, my god. Oh, my god.

The toxic, arsenic-rich mud is actually alive with activity.

It's almost fractal, right.

The closer we go in, the busier it seems to get.

That's...that is extraordinary.

So as we zoom in, you'll see it's just teaming,

literally teaming with life.

That's wild, isn't it?

- That's amazing. - So these are just organisms that were essentially laying in wait in the mud.

Most of these microbes are normal life which have evolved

to live in high levels of toxic arsenic.

But by increasing the levels of arsenic even further,

Felisa believes she may have isolated something very unusual.

So we have, in my group, in my lab,

I've so far looked at a bunch of different microbes, and I was...

The way I went about doing this, we want to give it a lot of arsenic.

- Yes. - We want to really see what can handle a lot of arsenic.

So the more arsenic you give it, the more you're going to say,

actually yeah, this is something different.

It's something that... Different. It's doing something unique.

She's convinced that anything that can survive

this intense arsenic bath would have to be structurally different,

would have unique DNA fundamentally separate

from life as we know it.

If I can concretely say to you, this organism, biochemically,

is completely different than we are at a molecular level,

it's either a deep root, you know, we share a common tree, but it's a deep root on the tree of life.

- Which would be interesting in itself. - Absolutely.

It suggests that while there was really one structural way to make DNA and to make genetic material...

Or there were multiple...

multiple point sources of the origins of life.

And have you found anything like that, or do you think you've found

something that is a prime candidate, if you like, for that?

Well, it's very likely. We think we have an organism.

I think that I've isolated a microbe

that's doing something very different.

It can survive with exceedingly high levels of arsenic

that would be very toxic to you and I and most other life we know.

It seems to be growing in a unique way and hopefully,

very shortly, we'll be making a very interesting announcement.

And that announcement could have a huge impact on the search for extraterrestrials.

Because if life started more than once here on Earth,

then the chances that it started elsewhere in the galaxy

are greatly increased.

But for Drake's estimate to be correct, it's not enough for life to just begin.

Some of that life must develop into intelligent life

capable of communicating across the galaxy.

And to do that, it must first become multi-cellular.

This is the second hurdle or great filter, so everything on this side

is very simple, single-celled life, bacteria and such,

and this is the junction where it suddenly becomes complex,

ultimately blossoming into plant and animal life.

But the big question is, how likely is that?

This is the Mojave Desert,

one of the hottest, most inhospitable places in the world.

And I've been brought here by Doctor Chris McKay of NASA Ames,

who's been studying an unexpected kind of life.

Life that might offer tantalising clues to how we evolved

from single-celled organisms to something much more complex.

Just how hot and dry is it here?

Well, this is the driest part of the Mojave Desert,

and from a microbial point of view

it's dryness, not hotness, that matters.

And we can find a place like this where there's no trees,

no plants and it seems like it's dead.

But it's not. I want to show you something.

Evidence that life is more clever than we think.

Here on the surface of what looks like a barren desert

we can pick up clear rocks and underneath them,

you can see these layers of green.

This is photosynthesis at its limit.

That's extraordinary, isn't it?

That's thick. There's a colony here.

There's a lot going on. So what is this?

These are single-celled cyanobacteria.

Photosynthetic bacteria.

They take sunlight, they make organic material, they produce oxygen.

Yes, but how are they photosynthesising if they're underneath the rocks?

Presumably it's dark under there.

If you hold these quartz rocks up, you can see that light is coming through.

You can see that sunlight, about a percent or so of the sunlight gets through the rock.

So think of this as a greenhouse.

Light is coming through the glass, the conditions under the rock

are trapping moisture, they're living in little rock greenhouses.

Chris McKay's green smudge is certainly tenacious, but he believes

it also hints at a story much more crucial

to my search for intelligent life in the galaxy -

the story of how simple, single-celled life

became multi-celled and complex.

And that's because of its ability to photosynthesise -

to use sunlight to turn carbon dioxide into food and oxygen.

We think that that ability, photosynthesis,

is going to be widespread.

It's a natural result of living on a planet with sunlight, water...

Combining sunlight and water is a logical thing for an organism to do if it lives on Earth.

The result of that is oxygen.

And that oxygen changes everything.

For most early life, oxygen is toxic.

But, with the arrival of photosynthesis,

oxygen is suddenly pouring into the atmosphere.

Some organisms survive the new levels of oxygen

and find in the process an unexpected reward.

Because using the energy that oxygen releases,

single-celled organisms can supercharge their metabolism.

These organisms are responsible for polluting the Earth.

Billions of years ago, they produced oxygen.

That oxygen changed the environment in a profound way.

It changed the environment in a way that allowed for the development of huge creatures like us.

So, in a sense, we owe our existence to these kind of organisms.

And what's more, according to Chris McKay,

complexity is not only a possibility, it's an inevitability.

Do you think once life gets going, complex life will naturally follow?

Yeah, I think, given an origin of life, photosynthesis will come,

oxygen will come, complex life will come. I think that will be easy.

So, if it's inevitable that simple life will become complex, what of the last great filter?

When I look at the whole story from origin of life, development of complexity,

development of intelligence, I think the hardest step is going to be the final one, intelligence.

I think that's the step that's rare, that's defining.

That separates Earth from the vast majority of other planets.

And for Frank Drake, the likelihood of intelligence arising

was one of the great unknowns of his equation.

He guessed intelligence was common in the galaxy.

But ultimately, that guess was based on a sample of just one. Us.

So this line is what separates us from all other life on Earth,

and I suppose we can call it intelligence.

The big question, of course, is,

is intelligence an evolutionary imperative,

or are we just a once-in-a-galaxy freak of nature?

SQUAWKING

To answer that, I'm off to Cambridge to meet palaeontologist Professor Simon Conway Morris.

He believes intelligence is much more common than we might think.

In fact, to prove it, he's taking me to meet experimental psychologist

Professor Nicky Clayton and one of the cleverest families of creatures on Earth. Corvids.

Better known to you and me as the crow family.

SQUAWKING

- Hi, Nicky. - Hello. - I'm Dallas. How do you do? - Nice to meet you.

Nice to meet you. They are amazing.

It's quite ominous coming here. Just the kind of noise of everything.

You understand why they make appearances in horror movies.

But they're so beautiful.

Are they talking? Are they communicating?

Well, they're communicating, that's for sure,

and there's lots of body language.

If you meant language in a psychological sense, no.

But in a communicative, biological sense, yes.

Nicky and her team have been giving puzzles to

her crows and jays and been finding some impressive results.

So if you give them a tube of water and there's a worm,

the Belgian truffles of the crow world,

floating on the top, but the worm is out of beak reach

because the water level is too low, what they will do is pick up stones

and use the stones as tools to raise the water level

and thereby get the juicy worm at the end of it.

Another experiment reveals a very unexpected human characteristic.

So, one of the things that's thought to sort of make humans special,

of a suite of things that have been claimed, one is theory of mind.

And that's the ability to be able to think about what other people are thinking.

And the jays are very, very good at that. So in one of, perhaps the most striking case of that,

is the case where they hide food, and if another bird is watching them,

they later come back when the other birds have left

and move the food to a new place.

But the really cool thing is that

not all birds do this moving of food to a new place.

It's only those birds who themselves

have been thieves in the past that do it.

So it's not a hard-wired reaction.

It takes a thief to know one, if you like.

And the idea is that that is a special form of this experience projection.

It's reasoning by analogy, based on your own experience.

If I were the thief, I would do X and therefore I'll move it.

- Your corvid is your sort of ZX81 and we're a kind of iPad, maybe. - Well, in my view...

- Not me personally. - My view is, I mean,

these and maybe a few other groups, maybe the elephants also,

I think the dolphins are just on the threshold

of what we were only 100,000 years ago.

- This is what I want to know. - Very exciting, isn't it? - Super exciting.

What makes this especially exciting is that crows are so far from us on the evolutionary tree.

And this suggests that intelligence is evolutionarily convergent,

that intelligence is such a good solution to living in our complex world

that evolution will fall upon it time and time again

in many different organisms.

Just like that other great evolutionary success story, the eye.

- What could be more different than an octopus to ourselves? - Yeah, yeah.

But now what I'm going to show you is in fact just in this area here.

It's not for the squeamish.

This is the eye of the octopus.

If I was to dissect out that eye,

it would be, in certain respects,

almost indistinguishable

from our eyes.

Built on a so-called camera principle.

And there are many ways of building eyes, but this camera eye,

remember, is in an animal which is

a close relative of the garden snail.

- So we can say that eyes are convergent. - Eyes are convergent.

Because it happens lots of different times.

Yeah, and we shouldn't be surprised, because eyes are a good trick.

Now, if the crow's behaviour really implies that intelligence

is convergent, then it has serious implications for our search.

Because not only would it lend support to the idea

that aliens would evolve intelligence,

it might allow us to imagine how they think, too.

At least, if I'm right about the convergence, one could say, you know,

after all, they come from the same universe with the same periodic table,

governed by the same evolution.

Even if there wasn't a hand to shake of the alien,

we would still know each other.

Simon's research really lends intriguing support

to the more speculative parts of the Drake Equation.

But there's one final element that's less certain.

L. The length of time a civilisation might last.

Maybe galactic civilisations last just a short blink of the eye.

Which means that perhaps there's

yet another great filter ahead in our future.

The question is, is the eerie silence

because we're alone in the universe, or is it because

there are many civilisations that emerge, but they don't last long?

That they get wiped out fairly soon after they arise.

When you say wiped out, what kind of thing are we talking about?

Well, I suppose we can think of manmade disasters, like the release of some

genetically-engineered organism that just infects us all,

or nuclear war, or there could be natural disasters,

like the impact of an asteroid or comet

or the explosion of a nearby star as a supernova.

There are many ways that we could meet our demise.

Does this explain the conundrum of why we haven't heard from any extraterrestrial life?

The so-called Fermi Paradox?

If civilisations disappear quickly, then we are unlikely to hear their short bursts of radio.

MUFFLED RADIO NOISE

But there may be another reason.

If the value of L was large, we might not hear ET because

our radio technology might be much too primitive.

After all, radio's only been around about 100 years

and already it's changed many times.

Now, this little diddy radio here is tuned to AM,

which is where medium wave and long wave radio stations broadcast.

And you can hear it. It's low quality and consequently rarely used now by any broadcaster.

MURKY DISTORTION

But nowadays, of course,

we don't use AM as much, because we've got FM,

Frequency Modulation, which of course gives us a much better signal.

RAPID BURSTS OF CLEAR RECEPTION

FM is a newer technology, it's clear as a bell, and as you can hear, it's very, very busy.

And this is the thing. Our technology is constantly changing,

so it's very likely that an extraterrestrial technology is going to be hugely different from ours.

So in the same way that an AM receiver can't pick up FM, maybe SETI are listening in the wrong way.

I always kind of assume that, well,

we're just expecting everyone else out there

to have our technology where we are.

Are we being quite anthropocentric about the way we look for...?

Well, how would you look in a way that you don't know anything about?

- Exactly, yeah. - You have to use the tools that we have.

We have to base it on what we know.

And in fact, it might well be that in some other planet,

it's the Institute of Ancient Instruments

that is broadcasting SETI signals.

But back at Greenbank, Frank Drake believes the real reason

we haven't heard anything is much, much more simple.

But even if we haven't, obviously, you know,

despite what people may think they see or believe happens,

you know, other civilisations haven't come here, why haven't we been able to detect them?

I mean, forget about space travel. But why?

Why haven't we detected them? That's easy. We just haven't tried enough.

We, I think, have again been mislead by unfortunate...

exuberant claims by myself and other colleagues that we've done a lot of searching, and we haven't.

We've looked carefully at only a few thousand stars on a very small number

of the channels that are possible in the electromagnetic spectrum.

And that's just hardly even a start.

If you take perhaps reasonable or even optimistic values for the factors that go into the equation,

it suggests that right now, there maybe only 10,000 civilisations we can detect in the galaxy.

That's one in ten million stars.

We have to look at ten million stars before we have a good chance of succeeding. We have a long way to go.

Hearing Frank say this made me realise

that the one thing I hadn't done was actually look myself.

And almost exactly 50 years after Frank's first search,

he and I have been given an exceptional opportunity.

This is the Robert Byrd Telescope.

The largest, steerable radio telescope in the world.

And we're going to use its incredible radio sensitivity

to perform a landmark experiment.

So here we are actually in the mission control of the Greenbank telescope.

We're going to be redoing the original project with Frank. Frank's over here, come with me.

We're going to look at the stars from his original search

that Frank still believes are good candidates for intelligent life.

Here we are, 50 years later looking at the same two stars.

Apart from obviously the sort of anniversary, does it make sense to look at those two stars?

Yes. But there is a catalogue called the HabCat Catalogue,

which is the Habitable Stars Catalogue.

And there are five stars in that catalogue that are considered

the prime candidates, and two of them are these two.

As the telescope locked onto the star, I had to admit to feeling a surge of adrenalin.

- Just a single beep, beep, beep would change everything. - Here we go.

- We've started, folks. - Are we on?

- We're on. - OK.

- Good luck, everyone. - So here is hydrogen

coming from the Milky Way and so we know now that everything is OK.

Now we're looking at the star.

Well, you get the excitement that goes with doing SETI the first time.

Maybe the whole world is going to change.

I remember Carl Sagan doing this with me once and

he was sure we were going to find something within the first hour.

After the first hour he sort of started nodding off

and he got the newspaper and started reading it!

We're starting to get the first data in now.

STATIC

What's it doing?

You so want there to be something. Every time you see one of those

blips in the line, you just want it to be...to be real.

STATIC

Just a few minutes into the search, and an unexpected peak crops up

amongst the normal background signal.

- So, an extraterrestrial signal would be broader. - It would be broader.

But disappointingly, it turns out to be merely interference.

- So we're saying no extraterrestrials? - Yeah.

How do you feel about... are you sort of disappointed?

No... It's... You...

It's like buying a ticket in the lottery.

If you're going to be disappointed that every ticket loses,

you shouldn't be in the business.

That's the difference between me and you,

because you can be very pragmatic about it

and say, "Well, it's OK, it's like a lottery ticket.

"Two chances a million." I'm...

You know, that's my first search, and I'm disappointed

because I secretly, deep down, wanted to hear a signal.

Well, don't be depressed. Your reaction is very standard.

Everybody thinks that there's going to be a success on the first search.

I told you about Carl Sagan.

It took him one hour to go from wild excitement to, "Ugh, let's go home."

I guess that's the ultimate question, isn't it? Is it worth it?

- Yeah. Is it worth that much effort? - And is it worth that much effort?

Yeah. People in SETI think the ultimate impact on society

is great enough to justify 50 years of failures.

I shouldn't call them failures.

- Lack of success! - Observations.

50 years on, and that lack of success might, to some, suggest a lost cause -

a lottery in which any jackpot might not even exist.

But these SETI types are made of sterner stuff.

And what's more, where some see failure, they see hope.

I think everything we've learned about Earth

builds in us an intuition that life is common.

But it's important to emphasise that at this point,

it is just an intuition.

We don't have any hard facts,

and that's what this horse race is all about.

Is to get some hard facts, some scientific facts,

to try to understand, is life on Earth a rare, unusual, unique story?

Or is the events that unfolded on this planet

a common story that occurred many times in many different places?

To me, the thing that SETI brings out

is the intrinsic connection that we have with the cosmos.

I mean, we are star stuff studying the stars.

If you see yourself in that kind of a larger perspective,

it really does change what you think about other humans on this planet.

I think Frank Drake summed it up very well when he said

that SETI is really a search for ourselves -

who we are and where we fit in to the universe.

And that's why it's great to do, even if it's a needle in a haystack search

without any guarantee there's a needle out there.

It's good that we should ask questions like, what is life?

What is intelligence? What is the destiny of mankind?

These are all very healthy, particularly for young people, to deliberate on.

So is it worth it?

Is the optimism of Frank's estimate

and the search for extraterrestrial intelligence naive?

Or is it enough that through the process of looking,

we learn more about ourselves and what it means to be human.

To be honest, I still don't know.

What I do know is that after some 50 years of searching, we're just beginning to find

some real, tangible evidence that life COULD exist beyond the Earth.

And if you want to know what I believe,

I agree with Arthur C Clarke, when he said,

"Sometimes I think we're alone, sometimes I think we're not.

"But either way, the implications are staggering."