All language subtitles for Cosmos.Possible.Worlds.S01E02.The.Fleeting.Grace.of.Habitable.Zone.WEBRip.x264-CAFFEiNE-en

In our galaxy, there
may be ships of other worlds

that dare to venture
into the cosmic deep.

Perhaps they travel
from star to star,

searching for worlds
where life has taken hold.

To get a closer look at the
emergent properties of life

that even they can't predict.

This particular vessel is
on just such a survey mission.

Who, scanning this world, would
have pronounced it a fit nursery for life?

What wild optimist could
have foreseen that peonies

and eagles would one day
spring from this hell hole?

In its infancy,
four billion years ago,

Earth held little
apparent promise.

Now, Venus,
that's more like it.

Back then, it may have had
oceans and land and possibly life.

This long-ago epoch was
Venus' moment to flourish.

Its time in
the habitable zone.

For any world, that's a
period when its relationship to

its star means that it's
not too hot and not too cold.

It's a time in a world's existence
when it can foster and sustain life.

But the grace of the habitable
zone is a fleeting thing

and, for no world,
lasts forever.

We reside in our
star's habitable zone,

but it is moving outwards at the
rate of about three feet per year.

Earth has already passed through
70% of its most hospitable time,

but no need to worry,

that stills leaves us
hundreds of millions of years

to plan and execute
our exit strategy.

Where will we go when the
sun's grace leave us behind

for other worlds and Earth
is no longer a garden for life?

Will our species have set
sail for distant islands in

the vast ocean
of the Milky Way?

There is no refuge
from change in the cosmos.

No safe place to hide for more
than a few hundred million years.

Someday, all of this will surrender
to the churning cycles of birth,

destruction and rebirth
mandated by the laws of nature.

The universe evolves
beautiful things then smashes

them to bits before making new
ones out of the shattered pieces.

Any species that wants
to survive long term on any

possible world, will
have to learn how to engineer

interplanetary and ultimately,
interstellar mass transit.

How do we know this?

The little we've learned
about the universe allows us

glimpses of the future.

I'm not talking about the
near-term where climate change

caused by human activity poses
a danger to our civilization.

If we want to
endure for thousands,

millions even
billions of years,

we'll have to stop dumping
all that carbon dioxide into

the atmosphere, right now.

But I'm gonna give us
the benefit of the doubt

and take the long view.

The sun is aging.

Just like the rest of us.

Someday, it will exhaust
the hydrogen fuel at its core.

Five or six
billion years from now,

the zone of hydrogen fusion
will slowly migrate outward,

an expanding shell of
thermonuclear reactions.

Until the temperatures are less
than about 10 million degrees.

It will go from being a
yellow dwarf to a red giant.

Its gravitational hold on
Venus and Earth will diminish

allowing them to
migrate to a safer distance,

for a little while.

This red giant sun,
ruddy and bloated,

will envelop and
devour the planet Mercury.

The grace of the habitable
zone will be moving outward,

farther and faster.

By now, the intense light
and heat of the sun's expansion

will reach all the way
out to the Jupiter system.

Its clouds of ammonia
and water will escape and

be lost to space as vapor.

And for the first time,
the more dowdy, hidden layers

down beneath Jupiter's gaudy
upper atmosphere will be exposed.

Could we make a home on
one of Jupiter's frozen moons?

The thick layers of ice encasing
Europa and Callisto will defrost,

exposing the liquid oceans
beneath to harsh sunlight,

thousands of times
stronger than before.

This will liberate
large amounts of water vapor,

starting a runaway
greenhouse effect.

Ganymede's once thin atmosphere
will become steamy and dense.

If life was swimming
in those oceans all along,

here's a new chance
to flourish and evolve.

Then Ganymede will
belong to those beings.

It's just as well, because
we'll want our next home

to be at a safer
distance from the sun.

Solar evolution is inevitable,

but we have a billion
years to go house hunting.

Plenty of time to seek
those worlds in the cosmos

that could
become our new homes.

Saturn, what has
the sun done to you?

She's stolen your
glory, your rings.

And Titan, she's robbed
you of your atmosphere.

Hey.

We're running out of
possible worlds here.

Just in time,
Neptune's moon, Triton,

a world named for the son
of the Roman God, Neptune.

First known to the Greeks
as Poseidon, the God of the Sea.

No one's named this ocean yet,
it only began to exist when

the heat of the red giant
sun melted the ammonia and

water ices of this
once frigid moon.

Our distant descendants will live
to different rhythms than we do.

A day on Triton
will be 144 hours long.

And the winters
will be brutal.

They'll be
nearly 50 years long.

But still, the Triton of a
few billion years from now could

be a great home for us.

It's got everything,

an atmosphere,
water oceans,

the chemical building blocks
would make life possible.

Okay, it's chilly, but not much worse
than upstate New York in January.

And that means, great
skiing all year round.

But one day, the sun will
exhaust itself completely and

the fleeting grace of the
habitable zone will end here, too.

When the sun's torrid
red giant phase is over,

it will strip itself naked,

revealing the small
white dwarf beneath.

A star without even enough energy
left to warm her surviving children.

The moons of the
outer Solar System.

So, if we're looking for
a long lease on a new home.

Say, more than just a
couple hundred million years,

we'd have to
travel even farther out.

We'll have to leave our
Solar System and brave the

vast bottomless ocean
of interstellar space.

I know what you're thinking,

"are we to venture
to the distant stars?"

We once made a few baby
steps to the moon before we lost

our will and scurried back
to the safety of our mother.

What makes us think we could
survive a voyage between the stars?

The nearest of which is 100
million times farther than our moon.

Wouldn't our tiny ships be
swallowed up by the great unknown?

I think we can do it.

Why?

Because we've done it before.

We dream of sailing among
the island worlds of the Milky Way,

catching photons with our sails.

Daring to go tetherless
beyond the point of no return.

We've passed this way before.

Once, there was a people
who chose the unknown.

They risked everything to
go forth on uncharted seas

and their courage
was rewarded.

They found paradise.

I want to tell
you their story.

We call these
people, the Lapita.

But, that was
never their name.

It was just the result
of a misunderstanding made

decades ago when we
first began to discover the

broken shards
of their pottery.

To me, they're not the Lapita,
they are the Voyagers.

A name far
more worthy of them.

About 10,000 years ago,

when the population of settlements
in Southern China began to swell,

there were those who
chose to pioneer the frontier,

farther south to
what is now Taiwan.

And our voyagers
settled there,

happily for
thousands of years,

until the place began
to get too crowded again.

Just as we,
of this planet,

came of age in a
kind of cosmic quarantine.

Cut off from any
hope of knowing about,

much less reaching the
other worlds of the cosmos.

Our distant ancestors
were prisoners of the land.

If you wanted to
travel a great distance,

you had to walk there.

And if you walked
as far as you could,

you would be hemmed
in at the water's edge.

This was before the age of the
great sea-faring civilizations.

The Phoenicians of the
Middle-East and the Minoans of Crete.

And for most of their history,
they hugged the shore.

Their fishing and trading expeditions
were careful to keep land in sight.

For our ancestors,
this was the edge of the cosmic ocean.

We do not know what first
inspired the voyagers to

attempt the
seemingly impossible.

Could they no
longer trust the Earth?

They were living on a
tectonic plate where earthquakes

and volcanic
eruptions were common.

Or did hostile neighbors there
make life intolerable for them?

Did a change in climate
threaten their livelihood?

Were their new
population pressures?

Did they begin to exhaust
the resources of their island

by overhunting
and overfishing?

Or was it simply something
innately human in them that

made them want to
know what was out there?

To reach for the
mysterious distance,

no matter how
dangerous that might be?

Whatever their
motives, over time,

they conquered their fear.

And made preparations to venture
where no one had gone before.

The voyagers used the
careful observations of their

ancestors over generations
to develop navigational

techniques that
are still viable today.

The seasonal migratory flight
patterns of the birds was their GPS.

They also brought high
flying frigatebirds with them,

releasing them at the proper
time to find the shortest

distance to the nearest land.

They could read water,
feeling the ocean currents in their

fingertips and the
messages written in the clouds.

These voyagers were scientists
and all of nature was their laboratory.

The Philippine Islands
was where they settled first.

After lingering there
for 1,000 years,

they were ready
to set sail again.

New generations of
voyagers, Polynesians,

mounted successful missions
of exploration to Indonesia.

The Melanesian Islands, Vanuatu,

Fiji, Samoa and
onto the Marquesas.

And then, to the most
isolated island group on Earth,

the Hawaiian Islands.

Tahiti, Tonga, New Zealand,
Pitcairn and Easter Island.

Their empire of water covered
nearly 20 million square miles of sea.

And they accomplished
this without a single nail

or metal tool of any kind.

As contact between the
islands became less frequent,

the language the Polynesians
brought with them evolved into

different tongues in isolation.

Many words changed, but
one word remained the same

in all the languages of
the wide pacific: "Iyar,"

the world for "sail."

Where are we bound for next?

To that place where you
can read the book of worlds.

The ship of the
imagination is on a mission.

Not to any particular world,

but to an empty space
in the interstellar ocean.

Why there?

Come with me.

We're headed to a place
50 billion miles from our sun.

What I'm about to show
you is a gift of thousands

of generations of searchers.

We've been studying light for
millennia and gravity for centuries.

Among Einstein's many
insights was an understanding

of how one could
affect the other.

The way gravity bends
light makes it possible to turn

any star,
including our own,

into a kind of lens
for a cosmic telescope.

One 50 billion miles long.

Our most powerful space-based
telescopes of the present day

can only see the worlds
of other suns as mere dots.

A cosmic telescope could
give us detailed images of

the mountains, oceans,
glaciers and who knows?

Maybe even the
cities of these worlds.

This is the cosmic
telescope's detector array.

Collecting the light
bouncing off a distant world.

It then sends a signal back
to Earth, becoming, in effect,

the telescope's eye piece.

See that brightest
star in the sky?

That's our sun.

And the lens
of this telescope.

So, how can a star,
which you can't see through,

be turned into a lens?

When all the rays of light
from a distant planet pass

very close to the sun,
the sun's gravity bends

those rays ever so slightly.

Where they converge in
space is called the focal point

because that's where the object
you're looking at comes into focus.

So, what can you see through a
50 billion mile long telescope?

Virtually anything you want.

Galileo's best telescope
could magnify an image 30 times,

making Jupiter, say,
appear 30 times closer.

Our cosmic telescope can make
things appear 100 billion times closer.

And we can aim it
at almost any direction.

Our detector array moves
360 degrees around the sun.

There's only one part of the
cosmos that's off-limits to us

and that's the heart
of our own Milky Way Galaxy,

which is just too bright.

Its radiance is blinding.

But with a
telescope like this one,

so much else that has
been foreclosed to us,

would be made visible.

A possible world, perhaps.

The mixture of gases in its
atmosphere can tell us if life is there.

Molecules have
specific color signatures.

If we look at this atmosphere
through a spectroscope,

an instrument that breaks down
light into its constituent colors,

we'll be able to identify the
molecules that make up the atmosphere.

The presence of oxygen and
methane are tell-tale signs of life.

This world is alive and
our cosmic telescope could

give us a complete
picture of its entire surface.

It's not just an
optical telescope,

one that can only
see visible light.

It's also a radio telescope.

Just as it can magnify light from
distant worlds 100 billion times,

it can do the
same for radio waves.

There is something
astronomers call a "water hole."

It's named after that
place where the lions and

the water buffalo
gather to drink and bathe.

It's a region of
the radio spectrum,

where interference is at a
minimum and we can eavesdrop

on even the faintest
transmissions between

far-flung civilizations.

We would need to use all of
our computing power to decrypt

the signals hidden in the noise.

1-4-1-5-9-2-.

And this vast telescope is
also a means for seeing back in time.

You can't look across space
without seeing an object in the past.

That's because the
speed of light is finite.

In the morning, look
up at the sun and see it as

it was eight minutes
and 20 seconds ago.

You'll never see
it any other way.

That's because it takes
that long for light from the

sun to travel the
93 million miles to Earth.

And when we look at any
world through this telescope,

we're seeing it in the past.

Now, imagine the cosmic
telescope of another civilization.

Say, one that's 5,000
lightyears from Earth.

The astronomers of that
world could witness the building

of the pyramids in Egypt.

Or follow the Polynesian voyages as they
bravely made their way across the Pacific.

But perhaps the most important
use of the cosmic telescope,

would be our
search for new Earths.

What I can't understand is,
why we haven't built one.

We already know how to do it.

We have the
technology right now.

When would you like
the future to begin?

Okay.

We've got the biggest dreams of
putting our eyes on other worlds.

Traveling to them,
making them our home.

But, how do we get there?

The stars are so far apart.

We would need sailing ships
that could sustain human crews

over the longest
haul of all time.

The nearest star is
four lightyears away.

That's 24 trillion
miles to Proxima Centuri.

Just to give you some idea
of how far away that point

of light really is?

If NASA's Voyager
One spacecraft,

which moves at
a pretty good clip,

38,000 miles an hour,

was headed for
Proxima Centuri?

It would take
70,000 years to get there.

And that's only
the nearest star out of

the hundreds of billions
in our galaxy alone.

So, if we want to endure as
a species beyond the projected

shelf life of our own planet,

we'd better act
like the Polynesians.

We need to take what we know
of nature and build sailing

ships that can ride the light
as they once rode the wind.

These sails are
enormous, miles high,

but they're very thin.

1,000 times thinner
than a garbage bag.

When a photon of light
strikes those magnificent sails

it gives them a little push.

This means then,
in the vacuum of space,

even the tiniest push from a
photon will propel them ever faster,

until they're moving at a significant
fraction of the speed of light.

When you get too far from your
star and the light dwindles,

lasers can do the trick.

If we were to light-sail
our way to Proxima Centuri,

it wouldn't take 70,000 years.

But only 20 years.

Proxima B lies in the
habitable zone of its star.

But we don't yet know
if it could support life.

Does it have the kind of
protective magnetic field that

has sheltered the evolution of
life on the surface of our world?

Another consequence of
Proxima B's close location to its

star is that the planet
is probably tidily locked.

One side
perpetually facing the star.

The other?
Doomed to endless night.

These little
stars may be lukewarm,

but they have a long
future ahead of them.

Trillions of years.

Think of the continuity
and growth potential of

a civilization with a future
measured in trillions of years?

It's always magic hour on
this strip of land that lies

between day and
night of this world.

If Proxima B is habitable,
its life would be confined

to this twilight zone.

It could be a home for
the indigenous life here or

a possible campsite
for our descendants.

The gravity on Proxima B is about
10% greater than ours on Earth.

No real problem for us.

Just a little like
exercising with weights on.

Remote scanning from orbit
found no apparent signs of

life making Proxima B a
waystation on a much grander

interstellar
diaspora of Earthlings.

But for those longer trips?

We're gonna
need a faster boat.

Let's say we found a system
located 100 light-years from home.

One with several
potentially habitable worlds.

For light-sailors, that
would be a 500 year long trip.

Is it possible to build a ship that
could break the cosmic speed limit?

A mathematical physicist,
Miguel Alcubierre of Mexico,

inspired by the original
Star Trek television series,

conceived the calculations
for a ship that could

theoretically travel
faster than the speed of light.

If successful, it could
cut the travel time between

our sun and this distant star system
down to a single year or even less.

But wait a minute, isn't
it a cardinal rule of science

that "thou shalt not
travel faster than light?"

It is.

But here's the thing
about the Alcubierre Drive.

It doesn't move,
the cosmos does.

The ship itself would be enclosed
in its own space-time bubble.

Where it needn't
violate any laws of physics.

Harold White of the United
States ironed out some of the kinks.

Such as prohibitively enormous
energy requirements to fly it.

But it remains far
beyond our immediate grasp.

The Alcubierre Drive Ship
is a gravitational wave making

machine, that compresses
the ocean of space-time

in front of it and expands
that ocean in its wake.

Jet skis for joyriding
through the galaxy and beyond.

Who knows?

Maybe the entire Laniakea supercluster
could one day become our pond.

That's 100,000 galaxies.

Laniakea, the phrase in Hawaiian
for "immeasurable heaven."

An advanced version
of our Alcubierre Drive

could do 600 trillion
miles in the blink of an eye.

Before you know it, you're in the
planetary system of a distant star.

Let's call it,
the "Hoku" system.

A red dwarf star surrounded by a
retinue of rocky and ice giant planets.

Somewhere among them is a world
that we have come to call home.

Our cosmic telescope sifted
through all the stars within

a radius of 100 light years and
pointed the way to this one.

All seven of these planets,
huddle closer to their star

than Mercury does to our sun.

Haumia is just on the outskirts
of Hoku's habitable zone.

Those warm green
colors seem inviting,

but we're not seeing
the tops of forests.

That green comes
from methane and ammonia.

Even at a distance
of only 27 million miles,

the star Hoku is too
weak to keep this planet warm.

We are now in the sweet
spot of Hoku's habitable zone.

And this is the
planet Tangaroa,

where the latest chapter of the
saga of our species is playing out.

It took a few hundred years for
humans to terraform this lifeless world.

But now, even the air
tastes as sweet as home.

But this was only Indonesia.

One of the earlier stops on
our nomadic odyssey throughout

the Milky Way.

There were still so
many islands that lay ahead.

And in this
dream future of ours,

with our faster
than light craft?

There would come a time when
we could place our cosmic telescope

far enough away from our
home planet to see first-hand,

those of our nameless ancestors
who first set sail on unknown seas.

Carl Sagan made this
drawing when he was a child.

Imagining the unfolding of the
next Golden Age of Exploration.

As a scientist, he
played a central role in it.

And now, he speaks
to us out of the past.

About our
dreams of the future.

Are we to
venture out into space?

Move worlds,
re-engineer planets,

spread to
neighboring star systems?

We, who cannot even put
our own planetary home in order,

riven with
rivalries and hatreds.

Despoiling our environment,
murdering one another through

irritation and inattention.

As well as on deadly purpose
and moreover, a species that,

until only recently,
was convinced that the whole

universe was made
for its sole benefit.

I do not imagine that
it is precisely 'we.'

With our present customs and social
conventions who will be out there.

If we continue to accumulate
only power and not wisdom,

we will surely
destroy ourselves.

Our very existence in
that distant time requires

that we will have changed
our institutions and ourselves.

How can I dare to guess
about humans in the far future?

It is, I think, only a
matter of natural selection.

If we become even slightly
more violent, short-sighted,

ignorant and
selfish than we are now.

Almost certainly,
we will have no future.

If you're young, it's
just possible that we will

be taking our first steps
on near-Earth asteroids and

Mars during your lifetime.

By the time we're ready to
settle even the nearest other

planetary systems,
we will have changed.

The simple passage of so many
generations will have changed us.

The different circumstances we will
be living under will have changed us.

We're an adaptable species.

It will not be we
who reach Alpha Centauri

and the other nearby stars.

It will be a
species very like us,

but with more of our strengths
and fewer of our weaknesses.

A species
returned to circumstances,

more like those for which
it was originally evolved.

More confident, far-seeing,
capable and prudent.

The sorts of beings
we would want to represent us

in a universe that,
for all we know,

is filled with
species much older,

much more powerful
and very different.

The vast distances that separate
the stars are providential.

Beings and worlds are
quarantined one from another.

The quarantine is lifted,
only for those with sufficient

self-knowledge and judgement to
have safely traveled from star to star.

Our remote descendants safely
arrayed on many worlds through

the solar system and
beyond will be unified by

their common heritage,
by their regard for their

home planet and by the knowledge
that whatever other life may be,

the only humans in all
the universe come from Earth.

Thank you, mother.

Captioned by
Cotter Captioning Services.