Original subtitles

Hello.

My name is Stephen Hawking.

Physicist, cosmologist, and something of a dreamer.

Although I cannot move 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 human kind?"

Check it out!

---- Subtitles and sync ---- * * * brigadir 2010 * * *

Wherever I go in the world people ask me: Do aliens exist?

It's a good question because it comes 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.

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.

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.

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 really 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 hunter's handbook.

A field guide to what life actually is and how it works, no matter where it occurs.

Chapter one 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.

And that's all about survival.

Survival links you, me, and E.T. and it generates rules all of itself.

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.

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.

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.

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.

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 have 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's surface,

moisture that perhaps could support life.

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.

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 a giant planet Jupiter.

This is Europa.

Europa is tiny, just under two thousand miles in diameter and it's very cold.

Minus two hundred and sixty 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.

Aliens here would probably swim in a similar way to our own ocean life

since liquid water is the same stuff everywhere.

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 the'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 that 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 new how many had planets in orbit around them,

let alone if any of those planets could support alien life.

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 build.

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

Instead it looks for stars that wobble.

A tell-tale 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 around 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 its 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 got on the verge of a major breakthrough.

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 probably have legs.

The detail might be different, but legs are a good thing to have on land,

especially if the animal is clinging to the side of a cliff.

If the planet is well lit, eye are almost guaranteed.

They let the 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.

Predators, even alien ones, need forward facing eyes to accurately judge distance,

an essential skill when hunting.

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 Earth-like 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 is likely to exist somewhere.

So there could be, perhaps should 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.

-320 degrees Fahrenheit.

So is there a world of nitrogen oceans, lacking 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 eight gallons.

So let's swap water for liquid nitrogen.

There's also about two pounds of phosphorous, half a pound of salt

enough iron to make a nail,

three pounds of lime, fifteen trace elements which might also work in alien biology,

and then this ...

Carbon.

Forty-five 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.

With the right ingredients ultra low- temperature life might be possible.

If so I think energy would be scarce.

So things around here would move very slowly.

Other possibilities are even stranger.

The astronomists 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.

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.

If the universe is full of intelligent, space faring 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.

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.

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

Look at it from the alien's point of view; what's the point of crossing vast tracks 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 a cover-up they are 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.

Where is everybody?

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

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

Well, except for one mysterious occasion.

On August 16th, 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've sent anything and stop listening for a reply.

Worse, they might well have destroyed themselves in the mean time.

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 to far away in space and time to reach.

But there is one last possibility.

That aliens who've avoided destroying themselves are already colonizing the universe.

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 ageing 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 alone.

Such advanced aliens would perhaps become nomads

looking to conquer and colonize whatever planets they could reach.

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

for materials to build more space ships 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 a blink of an eye.

Like us, the 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 Chirstopher 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

which I think probably do exist.

But in such a massive place as the cosmos we only have to look at ourselves

for a 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.