Mickey One

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!

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 in some far off world.

The possibilities are infinite and infinitely intriguing

Alien life could range from a 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 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 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 ET.

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.

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 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.

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 will 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.

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 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.

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-feet 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 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.