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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 humankind?
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 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 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.
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
Inds
caused by rivers and oceans.
There may well still be moder m-
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
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.
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 dcovery.
We could be 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'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.
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.
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 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
LifeBut 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 --
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
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,
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.
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.
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.
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.
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 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 se.
So, the lack of alien contact
Raises
a serious scientific problem.
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.
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
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.
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 delop
Into sometng
we wldn't wa 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 mitht 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.
