All language subtitles for 83C4466A1438C48D2B41364DC0E5E197_eng

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 of 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 pre-scientific 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 Boeheim 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.

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

It's easy to feel smug, right?

Well, the fact is, Martin Boeheim 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 nearly 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.

He 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 have 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.

And 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 standard.

No such rule.

Unlike the outer planets in 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.

The 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 Wicke.

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 months 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
supernovae 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 5 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, Because all such supernovas have

the same wattage, they can travel 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 a thousand 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.

Thirty-five 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
tell-tale traces of this iron in a

thin layer below the surface
of the manganese nodule.

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.

Two 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.

Twenty-six centuries ago, the Assyrian
King S.R.

Hatton 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 tick-tock 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
a thousand 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.

In one whale language.

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

A mother's first words to her newborn
baby.

The brainwaves 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 compress 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.

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.

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.