All language subtitles for Cosmos S01E13 Unafraid of the Dark (1080p x265 10bit)

The dream of
becoming a citizen of the cosmos

was born here,
more than two millennia ago,

in the city of Alexandria,

named after and conceived by
its dead conqueror,

Alexander the Great.

The Ptolemys, the Greek kings

who inherited the Egyptian
portion of Alexander's empire,

built this library

and its associated
research institution.

Rarely, if ever,

before or since,

has there been a government
that was willing to spend

so much of its
gross national product

on the acquisition of knowledge.

And it paid off.

Big time.

Every ship entering
Alexandria's harbor

was searched--
not for contraband,

but for books that might be
copied and stored here,

in what was then
the greatest library on Earth.

Here, Eratosthenes,
one of the chief librarians,

accurately calculated
the size of the Earth

and invented geography.

Pythagoras.

Hypatia.

Euclid.

Euclid set forth
the precepts of geometry

in a textbook that remained
in use for 2,300 years.

The Old Testament Bible
comes down to us

mainly from the Greek
translations made here.

The original manuscripts
of the masterpieces

of Greek
comedy and drama, poetry,

science, engineering,

medicine and history--

the total work product

of the awakening of ancient
civilization-- were kept here.

Estimates vary
on the total number of scrolls.

They range from 500,000

to nearly a million.

And all of it...

all of this

is but a tiny fraction
of the information

that you have at your fingertips
at this very moment.

The collective knowledge
of our species,

our own electronic
Library of Alexandria,

may be accessed by anyone
who has a device

and the interest
and the freedom to do so.

This was not true
in Alexandria,

where knowledge belonged
to the elite.

So in the fourth century AD,

when the mob came
to destroy the library

and the genius
of classical civilization,

there were not enough people
to defend it.

What will happen the next time
the mob comes?

We've come a long way together,

traveling from deep inside
the heart of an atom

clear out
to the cosmic horizon,

and from the beginning of time
to the distant future.

I think we're ready
to perform an experiment.

It's not the kind of experiment
that requires a laboratory.

You can do it in your head.

It's called
a "thought experiment."

Pick a star--

any one of the hundreds
of billions of stars

in our Milky Way Galaxy,

which is just one galaxy

out of the hundred billion
in the known universe.

How about that star?

Or that one?

Okay, this one.

It's orbited by dozens
of planets and moons.

Suppose, on one of them,

there lives
an intelligent species,

one the ten million life-forms
on that planet,

and there's a subgroup
of that species

who believe they have it
all figured out--

their world is the center
of the universe,

a universe made for them,

and that they know everything
they need to know about it--

their knowledge is complete.

How seriously
would you take their claim?

Our ancestors believed

the universe was made for them.

It was natural to assume
that we were at the center.

After all,
it looks like the Sun and stars

all revolve around us.

We still speak
of the Sun "rising."

The architecture of
our language, myths and dreams

comes from
that prescientific age.

This is our planet
as it was known then,

just before Columbus set sail.

This first globe of the Earth
was cutting-edge

when Martin Behaim
made it in 1492.

Like everyone else, he believed

that the jigsaw puzzle
of geography was complete.

There were three continents...

Europe, Africa and Asia,

and only the great world ocean
in between.

Behaim had no clue that North
and South America even existed.

It's easy to feel smug, right?

Well, the fact is Martin Behaim
knew infinitely more

about his world, the Earth,

than we know about ours,
the universe.

A recent lesson in humility

will serve to illustrate.

In 1912, Victor Hess
made a series of voyages

into the sky above Austria,

and found the thing
that scientists love best...

a mystery
that defied understanding

in terms of conventional
scientific wisdom.

And even today,

a century later,
we are still searching

for a complete explanation
of what Hess found.

A new kind of energy
had recently been discovered,

radioactivity.

It was given off

by certain elements,
like radium.

But it was also
found in the air,

even far away
from radioactive rocks.

It was everywhere.

Where did this
strange energy come from?

No one knew.

Hess suspected that it might
come from above the Earth.

To test his hypothesis,
he carried radiation detectors

high into the sky.

During a risky ascent
in a hydrogen balloon,

he attained an altitude
of more than three miles.

When he reached the thin, cold,

upper half of the atmosphere...

he found that the radiation

was more than twice
as strong as on the ground.

The radiation
must be coming from above.

That's why its intensity
was weaker on the ground--

the Earth's atmosphere
was absorbing most of it.

Some thought that the radiation
might come from the Sun.

To test that idea,
Hess timed one of his ascents

to coincide
with a solar eclipse.

But the eclipse had
no effect on the radiation.

Hess also found
that the radiation

was just as strong at night
as in daylight.

It was coming from above,
but not from the Sun.

What Hess did not know

was that the solar wind
doesn't move that quickly.

And so, for the wrong reason,

he came
to the right conclusion.

Hess had discovered
cosmic rays--

showers of subatomic particles
that crisscross the universe

at literally the speed of light.

Without the shielding effect
of the Earth's atmosphere,

they would be lethal.

Some cosmic rays
can carry as much energy

as a bullet fired from a rifle.

It would take decades
to trace those cosmic rays

back to a death
of unimaginable violence.

The cosmic rays
that Victor Hess detected

in the skies above Austria
posed a mystery to scientists.

Radioactivity
in minerals on Earth--

like uranium ore--

comes from the disintegration
of atoms.

But cosmic rays were
of a different nature.

They were far more powerful

than anything known
in Hess's world.

Scientists wondered
for two decades

what could possibly produce
cosmic rays.

Enter Fritz Zwicky,

the most brilliant man
you've never heard of.

In 1933,
he and a colleague discovered

that some stars flare up
to become as bright

as their entire galaxy
for a few weeks,

before fading out again.

Fritz Zwicky was
the first person

to understand
what just happened.

He correctly surmised
that this is the way

a massive star dies--
it blows

its guts out into space.

He called this kind of
stellar death a "supernova"...

and predicted
that the dying star would shrink

from about a million miles
across to only ten.

This corpse would be so dense

that a single grain of it
would weigh as much

as the Great Pyramid in Egypt.

It would consist almost entirely

of subatomic particles
called neutrons,

so he named these bizarre
objects "neutron stars."

And 35 years after Zwicky
predicted their existence,

astronomers began to find them.

We call them "pulsars"

when they spin rapidly and emit
regular pulses of radio energy.

Supernovas and neutron stars
could account

for a wide range of cosmic rays,

but not
the most energetic ones.

Nothing yet known to science

can explain them,
and we're fine with that.

It's one of the things
I love about science,

we don't have to pretend
we have all the answers.

Zwicky also came up
with the idea

that the gravity of a galaxy
warps the fabric

of space around it,
to act like a lens.

This distorts
and magnifies light

from any other galaxy lying
directly behind it.

So, astronomers on Earth
would see multiple images

of that same distant galaxy,

deformed,
as in a funhouse mirror.

40 years after this prediction,
we started finding them, too.

And Zwicky made yet another
discovery back in the 1930s.

While studying
the Coma Cluster of galaxies,

he noticed something funny
about the way they moved.

The galaxies were going
way too fast,

so fast that they should've been
flying apart from each other,

because all the stars
in all those galaxies

had far too little gravity
to hold the cluster together.

Zwicky thought

that something else must be
binding them to each other.

That mysterious
missing component

would have to weigh something
like 50 times as much

as the stars themselves.

But no one paid much attention
to this wild notion.

Just another one
of Zwicky's crazy ideas.

In our solar system,

the innermost planet, Mercury,
moves much faster

than the outermost one, Neptune.

And that makes sense, right?

The harder you push or pull on
something, the faster it goes.

The Sun's gravity weakens
with increasing distance,

so, the planets that are farther
from the Sun move more slowly.

Everyone expected that the
outermost stars in a galaxy

would act the same way.

Most of the stars are
concentrated towards the center,

so, their collective gravity
pulls on the other stars

the same way
the Sun pulls on the planets.

But in the 1970s,
when astronomer

Vera Rubin studied
the Andromeda Galaxy,

she discovered that the outer
stars obeyed no such rule.

Unlike the outer planets
of the solar system,

the outer stars in the galaxy
were all going at the same speed

as the stars
that were closer in,

and they were moving way faster
than expected.

"That's funny," Vera thought.

"There must be something weird
about the Andromeda Galaxy."

So she looked at another galaxy.

Same story.

And another.

Vera studied 60 galaxies

and found that all of them

seemed to be violating
the Law of Gravity,

a core principle of physics.

After some initial
healthy skepticism,

her colleagues looked
for themselves,

and found that Vera was right.

It's not that Isaac Newton had
gotten the Law of Gravity wrong;

Vera Rubin had discovered
that the gravity

of something massive
and invisible

was forcing the stars
to go fast.

And then, someone remembered
crazy old Fritz Zwicky,

and the unknown source
of gravity

in the galaxy clusters

that he called "dark matter,"
back in 1933.

Vera Rubin had verified
the existence

of a new, much larger cosmos.

And just like the one
we thought we knew,

it was filled with mystery.

Dark matter
is completely unobservable,

except
for its gravitational effect,

which makes visible stars
and galaxies move faster.

Its nature is another
deep mystery.

Rubin had provided the evidence
for an invisible universe

nearly ten times more massive
than the one we thought we knew.

It was as if we had been
standing on the seashore

at night, mistakenly believing

that the froth on the waves was
all there was to the ocean.

Vera Rubin looked at the stars
and realized

they were merely the foam
on the waves,

and that the greatest part
of the ocean remained unknown.

But wait.

It gets crazier.

Our Milky Way Galaxy,

a few hundred billion stars,

plus the clouds
of gas and dust,

the stuff of once
and future stars--

and about a hundred billion
other galaxies-- all of that,

including those uncounted
billions of trillions

of planets, moons, and comets--

amounts to only five percent
of what is actually there.

Because there's a bigger
unsolved mystery

than dark matter--

dark energy, which makes up
even more of the cosmos

and drives its expansion.

And it was Fritz Zwicky's
supernovas

that lit the way to the
revelation of its existence.

In one scenario, a star consumes
all of its nuclear fuel...

then cools,

and suddenly collapses
under its own gravity.

The star rebounds
in a massive explosion,

leaving behind a neutron star
or a black hole.

Since the mass
of the original star

can fall within a wide range,

its peak brightness
as a supernova

can also vary widely.

So, you can't tell
how far away it is

just from how bright it looks.

A relatively nearby supernova
might appear just as bright

as one that was more powerful,
but farther away.

But there's another kind
of supernova

that comes
in only one strength.

It marks the violent
grand finale

of a tango danced
by a giant star and a dwarf.

As the two stars orbit
closely around each other,

the giant sheds
its outer layers of gas

onto the dwarf.

When the added weight
becomes too much

for it to bear,

the dwarf detonates like a
stupendous thermonuclear bomb.

For a few weeks,

the brilliance
of such a supernova rivals

the combined light
of all the stars in its galaxy.

This kind of supernova

always has the same
maximum power output,

about five billion times
brighter than our Sun.

With big telescopes,

we can see them
in galaxies very far away,

out toward the edge
of the observable universe.

Because all such supernovas
have the same wattage,

they're ideal tools
for measuring distances

to the farthest reaches
of the universe.

We call them
"standard candles."

In 1929, Edwin Hubble discovered
that the universe is expanding.

The distant galaxies are
drifting away from one another.

Later, we learned

that the expansion began
some 14 billion years ago

with the explosive birth
of the universe-- the big bang.

Everybody assumed

that the rate of expansion
would be slowing down,

due to the mutual pull
of gravity

between all the parts
of the universe.

If there is enough dark matter,

its gravity would eventually
bring the expansion to a stop,

and the universe would
then fall back on itself.

In that case, everything
would eventually collapse

in a big crunch.

On the other hand, if the
universe had less dark matter,

the expansion
would continue forever,

just getting slower and slower.

Two competing teams
of astronomers

were observing those supernovas
in distant galaxies.

It turned out to be another one

of those
"that's funny" moments.

In 1998, both teams
independently came

to the same conclusion.

The expansion isn't
slowing down at all...

it's speeding up.

This means the universe will
continue to expand forever.

There seems to be a mysterious
force in the universe,

one that overwhelms gravity
on the grandest scale

to push the cosmos apart.

Most of the energy
of the universe is bound up

in this unknown force.

We call it "dark energy,"

but that name,
like "dark matter,"

is merely a code word
for our ignorance.

It's okay not
to know all the answers.

It's better
to admit our ignorance

than to believe answers
that might be wrong.

Pretending to know everything
closes the door

to finding out
what's really there.

Tonight, our ships sail

into even more exotic waters.

Come with me.

Only two of
our ships have ventured

into the great dark ocean
of interstellar space.

The longest odyssey
in all of history

was launched back in 1977--

NASA's Voyager 1 and 2.

The Voyagers move
about 40,000 miles an hour.

They gave us
our first close-up look

at Jupiter's Great Red Spot,

a hurricane three times
the size of Earth

and one that's been raging
since at least 1644,

when it was first observed.

For all we know, it could be
thousands of years old.

The Voyagers discovered
the first active volcano

on another world,
on Jupiter's moon Io...

and an ocean
beneath the icy surface

of the moon Europa...

with at least twice as much
water as we have here on Earth.

The Voyagers dared to fly
across Saturn's rings

and revealed that they were
made of hundreds of thin bands

of orbiting snowballs.

On Saturn's giant moon Titan,

Voyager detected an atmosphere
four times denser than Earth's.

That hinted at the existence
of hydrocarbon seas on Titan,

which we later confirmed.

Voyager 2 gave us
our first portrait

of the outermost planet,
Neptune...

where the winds roar
at 1,000 miles per hour...

and its moon Triton,
where geysers

of boiling nitrogen
shoot five miles high.

Voyager successfully completed
its mission of discovery

to the outer planets,

but its odyssey
into the darkness

was just beginning.

35 years after its launch,

Voyager 1 became the first
of our spacecraft

to enter an uncharted realm.

The Sun is constantly
shooting out streams

of charged particles
in all directions,

moving at a million miles
an hour.

This solar wind blows
a vast magnetic bubble,

our heliosphere, that extends
beyond the outer planets.

It pushes out against the
thin gas of interstellar space.

There's a border where
one ends and the other begins.

Voyager 1 reported back
to Earth

that its detectors
were being pummeled

by more and more cosmic rays.

Until then, we didn't know

where the interstellar
ocean began.

Voyager 1 pressed on

past a boundary
we had never crossed before.

The heliosphere shields us from
most of the deadly cosmic rays.

When stormy solar winds blow,

this zone of protection grows;

in calm solar weather,
it shrinks.

When a star goes supernova
in our galactic neighborhood...

the debris
from the exploded star

pushes the heliosphere
back towards the Sun.

If it's strong enough
to push it

all the way back
to Earth's orbit,

our planet gets a radioactive
bath of supernova debris.

Luckily,
this doesn't happen very often.

The last one was perhaps
two million years ago.

A neighboring star explodes
a million years

before there's even such a thing
as the human species.

How can we possibly know this?

Because the dying star
left its traces

miles below the surface
of the ocean.

Manganese nodules,
small rocks like this one,

are scattered over much
of the deep sea floor.

They grow very slowly.

I'm talking a millimeter
in a million years,

layer upon layer.

These nodules grow
in partnership with bacteria

by taking up minerals dissolved
in the seawater.

A supernova produces
a radioactive form of iron,

unlike anything made
by natural processes on Earth.

Researchers found
telltale traces of this iron

in a thin layer
below the surface

of the manganese nodules.

They used the known rate
of growth of the nodules

to date that layer
and to connect it

to the fate of a star
that perished eons ago.

The difference between
seeing nothing but a pebble

and reading the history of
the cosmos inscribed inside it

is science.

The interstellar ocean
is dark and deep.

Out here, the Sun is just
the brightest star in the sky.

Yet the Voyagers maintain
their regular communications

with NASA's
Jet Propulsion Laboratory,

talking back and forth
across the light-hours

that separate these ships
from their home port.

No other objects touched
by human hands

have ever ventured
this far from home.

Even after they lose
their ability

to respond to our command,

the last and,
by far, the longest phase

of the Voyager mission
will begin.

Back in 1979, when both Voyagers
rounded Jupiter,

its massive gravity acted
as a slingshot,

flinging them out
of the solar system

to travel among the stars
of our galaxy

for a billion years.

Carl Sagan recognized
that the Voyager mission

offered two free tickets to
something approaching eternity.

He assembled a small team
to create a message

to any civilization
that might, one day,

encounter
the derelict spacecraft.

26 centuries ago,

the Assyrian king Esarhaddon
wrote...

"I had monuments made of bronze

and inscriptions of baked clay.

I left them in the foundations
for future times."

These hieroglyphics continue
that ancient tradition.

They are inscribed on the cover
of a message designed

to be read by the beings
of other worlds and times.

What could we possibly
have in common

with an alien civilization

with its own separate
evolutionary history

and one so far advanced
beyond us

that they can patrol
interstellar space?

One thing at least,

a universal language...

science.

It's hard to break the bonds
of gravity.

You can only sail
the cosmic seas

if you speak mathematics
and physics.

Hydrogen is the most common
element in the universe.

The electron in a hydrogen atom

flips the direction of its spin

at a constant rate,
or frequency.

Hydrogen atoms are
like tiny natural clocks--

tick... tock.

Now we have a unit of time
in common

with the extraterrestrials.

This will come in handy
when we get to the next level

of the message.

Here's our return address
in space.

Pulsars are rapidly-spinning
neutron stars

that give off regular bursts
of radio waves.

You can set your clock by them.

The Sun is at the center
of this diagram,

and the lines point
to the 14 nearest pulsars.

A simple code labels each pulsar
with its unique frequency,

using the ticktock
of the hydrogen atom

as the unit of time.

So alien astronomers could use
this diagram

to locate the home star
of the Voyager spacecraft

in our galaxy.

They could also tell

how long ago the spacecraft
was launched.

And that's important
because the Voyager record

has a projected shelf life
of 1,000 million years.

Become an extraterrestrial
archaeologist

for a few moments.

An artifact has been fished out
of the interstellar ocean.

It was made by beings

that lived
about a billion years ago.

What would you make of them
and their world?

They've sent us their music

and greetings
in 59 human languages.

Hello from the
children of planet Earth.

And one whale language.

And a sound essay that includes
a Saturn V rocket launch.

A mother's first words
to her newborn baby.

Oh, come on now.

Be a good boy... be a good boy.

The brain waves of a young
woman newly fallen in love.

And the sound of a pulsar.

All of that will live
for a billion years.

How long is a billion years?

If you can press all the
time since the Big Bang,

the explosive birth
of the universe,

into a single Earth year,

a billion years is
about one month of that year.

What was happening on Earth
a billion years ago?

Most of Earth's land was amassed
into a supercontinent

called Rodinia.

It was a barren desert--
no animals, no plants.

A billion years ago,
there wasn't enough oxygen

in our atmosphere
to form an ozone layer,

and without it,
ultraviolet radiation

prevented life
from colonizing the land.

Rodinia probably looked
more like Mars

than present-day Earth.

The giant world ocean
produced huge rainstorms

causing flooding and erosion.

Glaciers formed, and their
slow but relentless movements

carved the land
into new shapes.

Single-celled organisms
dominated the oceans,

but some existed in colonies
called "microbial mats,"

and the first multicellular
organisms would soon evolve.

And a billion years from now,

what will Earth be like...

long after our cities,
the Egyptian pyramids,

the Rocky Mountains
have all been eroded to dust?

There are few things
we can say with confidence

about such a far distant time.

The only thing
we can say for sure

is that Earth as we know it
will be so changed

that we would
scarcely recognize it as home.

But even a thousand
million years from now,

something of who we were
and the music that we made

in that long-ago spring...

will live on.

In that distant future,
our Sun will have completed

another four orbits around
the center of the galaxy...

...and the Voyagers will have
ventured far from the Sun.

Carl Sagan was a member
of Voyager's imaging team,

and it was his idea that Voyager
take one last picture.

A generation before,

an astronaut on the last
Apollo flight to the Moon

had taken a picture
of the whole Earth--

the planet
as a world without borders.

It became an icon
of a new consciousness.

Carl realized the next step
in this process.

He convinced NASA to turn
the Voyager 1 camera

back towards Earth when the
spacecraft went beyond Neptune

for one last look homeward
at what he called...

the pale blue dot.

That's here.

That's home.

That's us.

On it, everyone you love,

everyone you know,

everyone you ever heard of,

every human being who ever was,

lived out their lives.

The aggregate
of our joy and suffering,

thousands of confident
religions, ideologies,

and economic doctrines,

every hunter and forager,

every hero and coward,

every creator and destroyer
of civilization,

every king and peasant,

every young couple in love,

every mother and father,
hopeful child,

inventor and explorer,

every teacher of morals,
every corrupt politician,

every superstar,
every supreme leader,

every saint and sinner
in the history of our species,

lived there...

on a mote of dust

suspended... in a sunbeam.

The Earth is a very small stage

in a vast, cosmic arena.

Think of the rivers of blood

spilled by all those
generals and emperors

so that in glory and triumph

they could become
the momentary masters

of a fraction... of a dot.

Think of the endless
cruelties visited

by the inhabitants
of one corner of this pixel

on the scarcely
distinguishable inhabitants

of some other corner.

How frequent
their misunderstandings,

how eager they are
to kill one another,

how fervent their hatreds.

Our posturings,

our imagined self-importance,

the delusion that we have
some privileged position

in the universe,

are challenged
by this point of pale light.

Our planet...

is a lonely speck in the great,

enveloping cosmic dark.

In our obscurity,

in all this vastness,

there is no hint that help
will come from elsewhere

to save us from ourselves.

The Earth is the only world
known so far to harbor life.

There is nowhere else,

at least in the near future,

to which our species
could migrate.

Visit, yes.

Settle, not yet.

Like it or not,

for the moment, the Earth
is where we make our stand.

It has been said that
astronomy is a humbling

and character-building
experience.

There is perhaps
no better demonstration

of the folly of human conceits

than this distant image.

To me, it underscores
our responsibility

to deal more kindly
with one another

and to preserve and cherish

the pale blue dot,

the only home we've ever known.

How did we,

tiny creatures living
on that speck of dust,

ever manage to figure out
how to send spacecraft

out among the stars
of the Milky Way?

Only a few centuries ago,
a mere second of cosmic time,

we knew nothing
of where or when we were.

Oblivious to the rest
of the cosmos,

we inhabited a kind of prison--

a tiny universe

bounded by a nutshell.

How did we escape
from the prison?

It was the work
of generations of searchers

who took five
simple rules to heart.

Question authority.

No idea is true
just because someone says so,

including me.

Think for yourself.

Question yourself.

Don't believe anything
just because you want to.

Believing something
doesn't make it so.

Test ideas
by the evidence gained

from observation
and experiment.

If a favorite idea fails
a well-designed test,

it's wrong!

Get over it.

Follow the evidence,
wherever it leads.

If you have no evidence,
reserve judgment.

And perhaps the most
important rule of all...

Remember, you could be wrong.

Even the best scientists

have been wrong
about some things.

Newton, Einstein,

and every other great scientist
in history,

they all made mistakes.

Of course they did--
they were human.

Science is a way to keep
from fooling ourselves...

and each other.

Have scientists known sin?

Of course.

We have misused science,
just as we have

every other tool
at our disposal,

and that's why we can't afford

to leave it in the hands
of a powerful few.

The more science
belongs to all of us,

the less likely
it is to be misused.

These values
undermine the appeals

of fanaticism and ignorance

and, after all,

the universe is mostly dark,

dotted by islands of light.

Learning the age of the Earth
or the distance to the stars

or how life evolves--

what difference does that make?

Well, part of it depends
on how big a universe

you're willing to live in.

Some of us like it small.

That's fine.

Understandable.

But I like it big.

And when I take all of this
into my heart and my mind,

I'm uplifted by it.

And when I have that feeling,
I want to know that it's real,

that it's not just something
happening inside my own head,

because it matters what's true,

and our imagination is nothing

compared with
Nature's awesome reality.

I want to know
what's in those dark places,

and what happened
before the Big Bang.

I want to know what lies
beyond the cosmic horizon,

and how life began.

Are there other places
in the cosmos

where matter and energy
have become alive...

and aware?

I want to know my ancestors--

all of them.

I want to be
a good, strong link

in the chain of generations.

I want to protect my children

and the children
of ages to come.

We, who embody
the local eyes and ears

and thoughts and feelings
of the cosmos,

we've begun to learn the story
of our origins--

star stuff contemplating
the evolution of matter,

tracing that long path by which
it arrived at consciousness.

We and the other living things
on this planet

carry a legacy
of cosmic evolution

spanning billions of years.

If we take that knowledge
to heart,

if we come to know and love
nature as it really is,

then we will surely be
remembered by our descendants

as good, strong links
in the chain of life.

And our children will continue
this sacred searching,

seeing for us as we have seen
for those who came before,

discovering wonders
yet undreamt of...

in the cosmos.