Original subtitles

[ computerized voice ] hello.

My name is stephen hawking --

Physicist, cosmologist...

And something of a dreamer.

Although I cannot move...

Narrator: ...And I have to speak through a computer...

In my mind, I am free...

...Free to explore the universe

And ask the big questions...

Such as...

Do aliens exist?

If so, where could they be found?

What do they look like?

What are they made of?

Are they intelligent?

And if we met them,

What would it mean for humankind?

Check it out.

Narrator: Wherever I go in the world,

People ask me, "do aliens exist?"

It's a good question, because it cuts to the heart

Of how we see our place in the universe.

Are we alone on our small, round, blue ball?

I think probably not, because of one fact.

The universe is big -- really big.

Our planet is just one of eight in orbit around our sun...

...Which itself is hardly special,

Being one of about 200 billion stars in a vast spiral...

...Our galaxy, the milky way.

It's so big, some days I find it hard to comprehend.

But even the milky way

Is just a tiny drop in the cosmic ocean...

...Just one of 100 billion galaxies

Formed into an enormous web

Stretching away in all directions.

At this scale,

Each point of light is an entire galaxy,

Which not only puts our little world in perspective

But also makes it difficult to believe we really are alone.

So to my mathematical brain,

The numbers alone make thinking about aliens perfectly rational.

The real challenge is to try and work out

What aliens might actually be like,

Living on some far-off world.

Narrator: The possibilities are infinite...

And infinitely intriguing.

Alien life could range

From simple, green slime that doesn't do much but drip

To more advanced animals...

[ creature screeches ]

...Something with a bit more bite.

But, of course, that's just the start

Of what could be out here.

In such a massive universe, it's logical to wonder

If there are intelligent beings,

Perhaps even civilizations

Like those in science-fiction tv shows and movies.

"star wars" and "star trek," two of my personal favorites,

May be closer to reality than we think.

Similar scenarios are at least conceivable.

But think about it more,

And even this is limiting the options.

There could be life-forms so strange

We wouldn't even recognize them as life.

Perhaps there are really exotic creatures

That live at the center of stars...

...Or even huge communities of microorganisms

That look like clouds of cosmic dust.

Maybe aliens live and die so fast

That they come and go in the blink of an eye.

So in such a vast universe with so many possibilities,

How do we know what to look for

Or, for that matter, where to look for it?

The answer is right back where we began.

The information we need is here at home,

For the simple reason that home harbors

The only known examples of life.

The laws of physics appear to be the same everywhere,

So it follows that the laws of life should be universal, too,

Even if the detail is different.

We can use life on earth

As a kind of alien-hunters' handbook --

A field guide to what life actually is and how it works,

No matter where it occurs.

Chapter 1 in our particular case

Takes us back 4.5 billion years

To when the earth was really quite young.

Exactly what triggered life here is still a mystery,

But there are several theories.

The most common one is that life began purely by accident

In pools of primordial soup

Full of chemicals called amino acids.

These molecules would have collided at random

For millions of years

Until the perfect combination just happened --

The ultimate lucky break that started the chain of life.

It is extremely unlikely

That life could spontaneously create itself.

But I don't think that's a problem with this theory.

It's like winning a lottery.

Although the odds are astronomical...

Most weeks someone hits the jackpot.

But there is another intriguing idea called "panspermia,"

Which says that life could have originated somewhere else

And have been spread from planet to planet...

By asteroids.

It seems possible

That lumps of rock could carry frozen organisms inside them --

Organisms able to withstand

Extremes of temperature and the vacuum of space.

If so, asteroids could even now

Be transporting life to other worlds.

Regardless of which theory is right,

Once life begins, the next chapter starts.

That's all about survival.

Survival links you, me, and e.T.,

And it generates rules all of its own.

Survival demands a source of energy --

What we call food -- or else it would grind to a halt.

Once nourished, life can then copy itself

To protect against the death of any one individual.

Ultimately, that leads to evolution --

Evolution that would happen even on alien worlds,

Producing, in some instances,

Animals that I think we would recognize as being alive,

Even if they look a bit strange.

[ creature bellowing ]

So, the next step on our alien hunt

Is to find a place, or places,

Where organisms might find food

And replicate and evolve.

And as far as we know, that requires one thing.

[ thunder rumbles ]

Like most people,

I find water both beautiful and fascinating.

But it's also the key to all known forms of life,

From bacteria to blue whales.

Narrator: Find water elsewhere and aliens could exist nearby.

The good news is

That water is very common, indeed...

Out in space.

Frozen water litters the universe,

From tiny, single crystals

To icy comets the size of mountains.

But to find liquid water,

We need somewhere at the right temperature.

Around every star is a region

Where it's not too hot or too cold, but just right...

Like the porridge

In the story of goldilocks and the three bears.

Around our sun,

There are two planets that lie in this "goldilocks" zone --

The earth and mars...

Which is why one day I'm sure we'll pay it a visit.

[ motor whirring ]

Robots have been exploring mars since the '70s,

But they have yet to find life.

I don't think we should give up.

Beneath the martian surface,

Nasa's spirit rover discovered these white salts,

Which are formed in contact with liquid water.

Satellite images reveal drainage patterns and erosion

Of the kinds caused by rivers and oceans.

There may well still be moisture under mars' surface --

Moisture that perhaps could support life.

[ device beeps, radio chatter ]

[ device beeps ]

I hope one day we will find the money

To send men and women to mars.

It would capture the public's imagination

Just as the apollo moon missions captured mine

Back in the '60s.

[ radio chatter ]

If they found even a few martian microbes,

In my opinion,

It would be one of the most exciting discoveries ever made.

But even if mars is barren,

There are other places to look for liquid water.

One of them lies a mere 30 million miles from mars...

On a small, mysterious moon

That orbits the giant planet jupiter.

This is europa.

Europa is tiny --

Just under 2,000 miles in diameter --

And it's very cold --

Minus 260 degrees.

The entire moon is covered

In a layer of ice perhaps 15 miles thick.

But europa may have a hidden heat source

Beneath the surface.

Europa orbits jupiter once every 3.6 days,

In an egg-shaped path.

The gravitational pull from jupiter

Changes constantly,

Stretching, then compressing europa.

This process is like kneading a piece of clay

To make it warm and soft,

And the heat produced may be enough

To melt the underside of the ice sheet...

Creating a hidden ocean of liquid water

Protected from the vacuum of space

By the solid ice above.

If so, there could be aliens living here --

Creatures that have evolved

To exploit this dark and ancient water world.

I think it's even reasonable

To guess at some of their physical features.

[ creature chitters ]

Aliens here would probably swim

In a similar way to our own ocean life,

Since liquid water is the same stuff everywhere.

[ creature chitters ]

They might use chemicals in their skin

To generate their own light,

As many deep-sea creatures do back home.

They might even swim in school-like colonies,

Just as aquatic animals do on earth.

But even if advanced animals do live inside europa,

I think they're unlikely

To be trying to make contact with us anytime soon.

They'd exist cocooned in an icy shell 15 miles thick,

So they'd be blissfully unaware of the universe beyond.

To find them, we'd need to send a mission here,

Which would be even more risky and expensive

Than visiting mars.

I hope one day we will discover europa's secrets.

But before then, it's worth continuing our journey

To search for aliens with a wider outlook.

I think we need to leave our solar system

And voyage into the vastness that lies beyond.

Stars surround us in the universe,

But until recently,

No one knew how many had planets in orbit around them,

Let alone if any of those planets

Could support alien life.

Narrator: Finding out is tough,

Because stars are big and blindingly bright.

Planets are tiny and dark.

Spotting them requires technology

On an enormous scale.

The binocular keck telescope in hawaii,

With its twin 30-foot mirrors,

Is one of the most powerful land-based telescopes

Ever built.

But even this vast machine can't see distant planets.

Instead, it looks for stars that wobble --

The telltale sign of an unseen planet in orbit.

A hammer thrower demonstrates the principle.

As he spins, the hammer pulls on his body

And he wobbles from side to side.

The same thing happens

As a planet swings 'round its star.

Planets also reveal themselves

If they pass between their star and us.

The planet causes regular dimming,

And from the timing, we can even determine

If it's inside the star's "goldilocks" zone.

The first distant planet was discovered

In 1995.

Since then, hundreds more have been found.

This, I think, is a pretty exciting discovery.

We could be on the verge of a major breakthrough...

Narrator: ...One that will both redefine

Our view of life in the universe

And be a real triumph for science itself.

Somewhere out there, perhaps not so far away,

Is a rocky planet a bit like earth --

A planet with liquid water,

Where life has begun.

Due to the power of evolution,

Aliens here might be surprisingly familiar,

Even if, at first, they seem anything but.

Aliens that eat, for example, need an input orifice,

Or, as most people say, a mouth.

Likewise, if they live on a solid surface,

They'll probably have legs.

The detail might be different,

But legs are good things to have on land,

Especially if the animal

Is clinging to the side of a cliff.

[ creature bellows ]

If the planet is well-lit, eyes are almost guaranteed.

They let a creature accurately sense its environment.

Even the position of the eyes

Will follow the same rules as on earth.

Prey animals tend to have eyes on either side of their head,

Allowing them to look out for predators.

[ creatures screeching ]

Predators, even alien ones, need forward-facing eyes

To accurately judge distance --

An essential skill when hunting.

[ thud ]

Alien struggles of life and death

Are probably happening right now,

Thanks to the universal power of evolution.

But in my opinion, evolution is so remarkable,

We can't really be sure of its ultimate limits.

Life-forms on earthlike planets or in hidden oceans

Are not the only options.

We can go even further into the depths of the universe

In search of other kinds of aliens --

Extraterrestrials that are totally unlike us --

Life...But not as we know it.

I like to think of myself as an optimist,

And so in our vast, ancient universe,

With its countless galaxies,

Almost any life-form that is physically possible...

Narrator: ...Is likely to exist somewhere.

So there could be -- perhap.Shoul be --

Really bizarre aliens

That have followed a different evolutionary path...

...Aliens that don't depend on water,

But on other chemicals instead.

Nitrogen is one possibility.

It's a gas on earth,

But it can exist as a liquid when it's very, very cold --

Minus 320 degrees fahrenheit.

So, is there a world of nitrogen oceans,

Lapping, frozen shores,

Where aliens have evolved

In temperatures that would kill a human instantly?

Life here would need chemistry very different than our own --

A cold-weather remix of the ingredients that make us.

Ingredient number one, of course, is water.

The average male holds 8 gallons.

So, let's swap water for liquid nitrogen.

There's also about 2 pounds of phosphorus,

Half a pound of salt,

Enough iron to make a nail,

3 pounds of lime, 15 trace elements,

Which might also work in alien biology,

And then this...

Carbon, 45 pounds of it.

But what if carbon was switched with something else?

Silicon, perhaps.

Silicon has slightly different properties,

But it could do the same job.

[ wind howling ]

With the right ingredients,

Ultra-low-temperature life might be possible.

If so, I think energy would be scarce,

So things 'round here would move very slowly.

[ wind howling ]

[ creature bellowing ]

Other possibilities are even stranger.

The astronomers searching for far-off planets

Have discovered that many seem to be giant gas planets...

Like our own jupiter and saturn.

Perhaps there are aliens made of gas.

[ thunder crashing ]

Aliens living here would need to consume something.

I imagine they could use the power of lightning storms

That constantly rage on planets like these.

If such extreme life-forms are possible,

Then life elsewhere in the universe

Could be very common, indeed.

There are certainly many more planets

That fall outside the "goldilocks" regions of stars

Than fall inside them.

It suddenly seems like there could be life

Nearly everywhere you look.

But, ultimately, I think it doesn't really matter

What aliens are made of.

To me, it's what they can do that counts.

Are they thinking about the cosmos, too...

...Trying to unlock its secrets just as we are?

In short, has alien life evolved as we have

And developed intelligence?

Narrator: If the universe is full

Of intelligent, spacefaring aliens,

I think at least some of them might be interested in us...

If only as a curiosity.

Of course, many people believe they are already here.

[ country music playing ]

Tales of alien abduction have been common

Ever since I was an undergraduate in the 1950s.

And I watched all those "b" movies, too.

The story always goes the same --

A lone individual on a quiet road at night

Happens to take an unscheduled detour and finds himself lost.

[ birds, crickets chirping ]

[ whirring ]

[ wind howling ]

I'm always a bit suspicious when I hear these tales.

Look at it from the aliens' point of view.

What's the point of crossing vast tracts of the universe

In a high-tech ship

Just to abduct some lone earthling?

In my opinion, if aliens are here,

I suspect the newspapers would be full of the story.

And if governments are involved in their cover-up,

They're doing a much better job at it

Than they seem to do at anything else.

So, the lack of alien contact

Raises a serious scientific problem.

Narrator: Where is everybody?

We've been listening to space for over 40 years.

And in all that time, we've picked up nothing.

Well, except for one mysterious occasion.

[ computers beeping, whirring ]

On August 16, 1977, a radio telescope in ohio

Picked up a signal that became famous.

The telescope listened to space

By scanning the skies as the earth rotated.

And just once,

It recorded a signal that got everyone excited --

The "wow!" signal, as it became known.

The signal was a steady source of radio waves,

Just the kind an alien race might send,

Because it stands out

From the radio static that fills the universe.

A computer recorded the signal as six letters and numbers.

Astronomer jerry ehman saw the data

And wrote one word in the margin.

Ehman and others subsequently searched

The same patch of sky many times...

But found nothing.

The "wow!" signal had vanished.

The whole mysterious episode reveals

That making contact with aliens via radio

Is always going to be difficult.

In such a vast universe,

Messages take a long time to reach their destination.

The "wow!" signal appeared to come from a star system

200 light years away.

So it took at least 200 years to reach us.

If we sent a reply,

It would take another 200 years to reach them,

By which time they might have forgotten they sent anything

And stopped listening for a reply.

Worse, they might well have destroyed themselves

In the meantime.

The human race very quickly discovered

The power of the atom bomb.

If the same holds for intelligent aliens,

Then they might not last long.

Perhaps they all blow themselves up

Soon after they discover that "e" equals "m.C." squared.

If civilizations take billions of years to evolve

Only to vanish virtually overnight,

Then, sadly, we've next to no chance of hearing from them.

They are simply too far away in space and time to reach.

But there is one last possibility --

That aliens who have avoided destroying themselves

Are already colonizing the universe.

[ siren wailing ]

Narrator: The human race has only two options

When it comes to looking for advanced aliens.

We can listen, or we can be more active

And broadcast our willingness to talk.

We'd have to think very carefully

About what we might say.

I think this might be just a little too risky.

We only have to look at ourselves

To see how intelligent life might develop

Into something we wouldn't want to meet.

We humans are already capable

Of manipulating the course of our own evolution.

Exactly the same, presumably,

Would be true of advanced extraterrestrials.

Ultimately, they could halt aging

And become virtually immortal.

What's more, they might have reached that point

Millions of years ago.

It might sound unlikely, but if you think about it logically,

Alien technology should be as extraordinary to us

As a rocket ship to a caveman.

I imagine they might exist in massive ships like these,

Having used up all the resources

From the home planet below.

Such advanced aliens would perhaps become nomads

Looking to conquer and colonize

Whatever planets they can reach.

If so, it makes sense for them to exploit each new planet

For materials to build more spaceships

So they could move on.

Who knows what the limits would be?

Perhaps their capabilities would only be limited

By how much power they could harness and control.

And that could be far more than we might first imagine.

For example, it might be possible

To collect the energy from an entire star.

To do that, they could deploy millions of mirrors in space,

Encircling the whole sun

And feeding the power to one single collection point.

Such power might make it possible

To walk the very fabric of space

And create a portal called a wormhole.

This portal would act like a shortcut,

Allowing them to travel huge distances

In the blink of an eye.

Like us, they would probably have evolved

From a species used to exploiting whatever it can.

So, if aliens ever visit us,

I think the outcome would be much as when

Christopher columbus first landed in america...

...Which didn't turn out very well for the native americans.

So the journey that started with the search for water

Has led us to far-off worlds

That I think probably do exist.

In such a massive place as the cosmos,

We only have to look at ourselves

For proof that extremely unlikely things

Can and do happen all the time.

Let's just hope that if aliens do find us,

They'll come in peace.

-- Captions by vita -&www.M

Captions paid for by discovery communications