All language subtitles for 4FD05F42576CFFADB32BFBBC2E50B9BC_eng

The day begins for a chimp
much as it does for us.

Breakfast.

A critical meal…
when you're eating for two.

Celeste is already an experienced mom.

Her firstborn, Apollo,
is the dominant male of the troop.

And he can be a bit slow
to get going in the morning.

Each chimp is a different age.

Each has a distinct personality.

But all of them are creatures of routine.

Their lives governed
by the passage of time.

We can't see it.

Or hear it.

We can't influence it in any way.

And yet, every heartbeat,
every choice and action,

every inaction is a consequence
of time's continuous flow.

It can whiz by or drag on.

But time ticks ever onward.

Stars and planets form, age, and die.

In their wake, new stars emerge.

And from a rare few,

the most mysterious objects
in the universe are born.

Black holes.

Time is the cosmic conductor.

Nothing can escape its grasp.

Although we have devices
that can track and measure time…

…chimps don't.

Celeste and her family
use the sun as their guide.

Rising and arcing across the sky.

As it moves…

so do they.

Chimps rarely sleep
in the same nest twice.

Each morning,
they head off in search of fresh fruit.

Journeying from one part
of their territory to another.

But right now, the ripest fruit…

is on the other side of an open plain.

Apollo and the strongest members
of the troop go ahead

to make sure it's safe for the others.

Out in the open,

they're vulnerable
to predators, rival chimps,

and the heat of the rising sun.

They need to be quick.

Time is ticking.

The sun traveling across the sky

forms the chimps' basic unit of time.

From sunrise to sunset
and back to sunrise.

The 24-hour day.

But a day
is not actually a measure of time at all.

It's a measure of motion.

As our planet rotates on its axis,

the forest moves through space
at 1,600 kilometers per hour.

It takes 24 hours
for Earth to do one full turn.

Giving the chimps 24 hours of movement,

12 in sunshine and 12 in darkness.

Again and again.

It's our planet's steady spin
that sets Earth's master clock.

And is the chimps' trusted timekeeper.

But this essential cycle
we take for granted…

is not universal.

As soon as you leave our home planet…

…the 24-hour day no longer applies.

Flying closest to the sun…

…is the planet Mercury.

Compared to us,
it rotates at a snail's pace.

Our neighbor Venus spins even slower.

It takes longer to rotate on its axis

than it does to orbit the sun.

Making Venus's day longer than its year.

Each planet has its own unique day length.

Including planets
far beyond our solar system.

Sixty-three light years away,

orbiting a young star,

is Beta Pictoris b.

It spins so fast…

…it bulges out at the sides.

It is the fastest-spinning world
we know of.

Here, a day lasts just eight hours.

Every planet in our universe spins
at its own speed.

Billions of worlds,

each with their own clock,

ticking away to different rhythms.

But all moving forward
on a universal cosmic timeline.

Back on Earth,

with the sun now almost directly overhead,

the chimps know exactly what time it is.

It's lunchtime.

And their crossing of the savanna
has been timed to perfection.

They've hit the jackpot.

These sweet berries
of the African grape tree

are only around for a few weeks.

A rare seasonal gift from the forest.

Where the middle of the day
is a very productive time.

Animals of all sizes
are tending to their daily tasks.

And each experiences time differently.

For small creatures
that live fast, short lives…

…lunchtime can feel like a lifetime.

For slower, longer living things,

an hour can go by in the blink of an eye.

But whether you're living in high speed

or in slow motion,

all life in the forest must adhere
to the same 24-hour day.

And as the world keeps spinning…

…those days keep ticking by…

dictating the lives of every chimpanzee.

One in particular.

At just 15 weeks,

this baby's entire body
could fit in its mother's hand.

For it to fully form,

a cascade
of perfectly timed events must occur.

For the next 130 days,

every minute,
every nanosecond is critical.

New cells divide and grow
with remarkable speed and precision.

Right now,

brain cells are multiplying
at a rate of around 15 million per hour.

All of us, from our very first moments,

have a deep biological relationship
with time.

As the sunlight wanes,

the chimps instinctively switch gears.

To evening mode.

Nesting calls signal to the whole troop.

It's time to find a safe place
to spend the night.

Their bedding needs to be soft but strong.

It doesn't hurt if it tastes good either.

The rhythm of every day in the forest

is determined by the sun's position
in the sky.

But the chimp's innate sense of time

comes from something inside them.

Deep in their brains
is a biological clock.

Bundles of neurons act as a pendulum…

…controlled by genes
that switch on and off…

and a cycle that repeats every 24 hours.

These clock genes create
a circadian rhythm in the body

that waxes and wanes in sync
with our planet's rotation.

Controlling hormones…

…heart rates,

and energy levels.

And right now, the chimps' body clocks
are sending the message,

"It's time to get sleepy."

Not everyone can though.

Celeste's baby's brain is still forming.

With no internal clock of its own,

it relies on its mother's hormones
to keep it synchronized.

But baby doesn't always get the memo.

Lucky for Celeste,

with so much growing to do,

her baby does eventually drift off.

While the chimps go to sleep
high in the treetops…

other forest dwellers are just waking up.

Body clocks tick away

in the cells of plants and animals
throughout the forest.

Clock genes evolved
two and a half billion years ago

in the first living cells.

Those that could anticipate the light
and dark of a day had an advantage.

And as life evolved,

it synchronized to Earth's motion.

So that today,

these clocks exist
in almost every creature on Earth.

Although some creatures prefer day
and others night…

all life is dancing to the same beat.

Thanks to cellular clocks

that tick in time
with the spin of our Earth.

As yesterday becomes a memory…

…another new day begins in the forest.

A fresh cycle,

and yet, no clock can ever truly be reset.

And there are subtle clues
all around the forest that reveal why.

Nothing is the same today
as it was yesterday.

Least of all Apollo,

who seems to have woken up
on the wrong side of the bed.

When he's in a bad mood…

the rest of the group
just need to keep their heads down.

He soon finds a target
for his rage, though.

Some of the younger chimps
have found honey for breakfast.

And they forgot
to invite Apollo to join them.

You soon learn, never get
on the wrong side of the dominant male.

He's got a nasty bite.

Thankfully, it's not too serious.

With a bit of care,
this wound should heal.

But wounds leave behind scars,

etched into the chimps' bodies.

Indelible marks of the past that reveal
the one universal truth about time.

It has a direction.

You can never go back in time…

…only forward into the future.

This is time's arrow,

and it leaves scars on everything

across Earth…

…and beyond.

Our moon is pockmarked with battle scars
that tell stories of ancient events.

So too are the planets.

Their surfaces testament to a lifetime
of bombardment by asteroids and comets.

But perhaps the most impressive
impact crater in our solar system

belongs to a moon of Saturn.

Mimas.

The Herschel crater
is 130 kilometers across.

Whatever created this enormous scar…

must have come close
to shattering the moon to pieces.

Mimas lives to tell the tale.

But events like this are irreversible.

And they differentiate the past
from the present.

Impact craters are timestamps

that mark a unique moment in history.

We can never revisit the moment
they were created.

But we can piece together traces
of past events

and map a course back through time.

Before craters.

Before planets.

Before stars.

Back to a time before time.

Our universe had a beginning.

A very big bang…

that created three-dimensional space

and time.

But space and time are not separate.

Time is woven
into the fabric of the universe.

Bound to space
as our universe's fourth dimension.

The Big Bang
set the universe's clock ticking.

Propelling everything into the future.

It created the arrow of time.

From our universe's very first moments…

…it pushes us all into the future,

causing everything to grow,

age…

…and change.

From childhood…

…to adulthood,

we all travel through life
in the same direction.

Getting older day by day.

And with age comes wisdom

as youthful innocence
is replaced by experience.

Time's arrow leads us through
these stages of life.

It shapes us.

Defines who we are.

From our first moments…

to our last.

Chimps rarely live past the age of 40.

Nothing is immortal.

Everything that exists in our universe
has a finite lifespan.

Including, perhaps, the universe itself.

Today, the galaxies are filled with stars.

But 95% of stars that will ever exist
have already been born.

So, as our universe
journeys into the future…

…the stars…

…one by one, will blink out…

…leaving the universe
to face an ever-darkening future,

stretching out for trillions,

that's thousands of billions, of years.

The age of starlight

will be followed by a dark age
of black holes.

These monsters feed on the remnants
of dead stars and planets.

And as they do,

their ever-increasing gravity scars
the very fabric of the universe.

Distorting both space and time.

The edge of a black hole,
called the event horizon,

is a region where gravity
has become so strong

it causes time
to slow down practically to a standstill.

But even black holes
can't escape time's arrow.

In the far, far future…

…when there are no stars
or planets left to consume,

they will begin to starve.

And slowly…

very slowly,

they will shrink.

When they die,

no one truly knows what comes next.

But it could be the end of our universe.

Here on Earth, none of us can slow
the passage of time.

And one of Celeste's aunts
is reaching the end of her time.

Retreating from the group,
she heads into the forest alone.

She has lived many years.

But this day will be her last.

While the world continues to spin,

her body lies still.

But time doesn't just carry us
toward endings.

It also creates beginnings.

As days turn into weeks
and weeks into months,

there are big changes
for one special chimpanzee.

Say hello to Cosmo.

Her brain and limbs are now fully formed.

And her eyes are ready to see the world.

The exact timing
of her birth is impossible to know.

But she could be born any day now.

She's been in the womb for eight months.

But her journey began long, long ago.

The elements that made her
came from dying stars.

The water that flows through her body
came from distant worlds.

The energy that powers her muscles
came from the heart of our sun.

But it's that most mysterious ingredient,

the one that started ticking
13.8 billion years ago…

that has led all other ingredients
to this moment.

In this place.

On this planet.

Another sunrise, another morning.

And this one is extra special.

Welcome to Earth, Cosmo.

This precious moment
will never be repeated for Celeste.

But Cosmo's journey has just begun.

It will take around three months

for her body clock to synchronize
to the rhythm of the planet,

one year before she can truly communicate,

and perhaps 15 years
until she is fully grown.

So much lies ahead.

Like Cosmo,

our universe is still in its infancy

at the beginning
of an unimaginably long lifespan.

We are living in the age of starlight.

A moment when time's arrow
has filled the universe with beauty…

…and wonder.

But it's a brief window of time

that will never be repeated
in the history of our universe.

No one can slow the passage of time,

nor should we try.

Because without time,

there would be no now.

No moment in the sun.

No moments, period.

Without time,

there would be no life.

Next in the story of our universe,

Earth's seasons.

Like a mother bear raising her cubs…

…we all experience
our planet's yearly transformations.

But what created Earth's seasons?

How are they connected
to the formation of our moon?

And why does only our planet
have conditions just right for life?