All language subtitles for EA37BC3F6E04279D9FA2489BF3B77506_eng

East Africa.

It's where life's most vital connection
to the universe can be found.

And a very special predator…

named Wa Chini.

Life for a cheetah
is a never-ending search for food…

for vital energy.

And this is one of the hardest places
on Earth for a predator to obtain it.

The blistering sun
has driven away nearly everything

from these dry, desolate plains.

Any creature that remains here
struggles to survive.

Wa Chini's sole focus…

…the only thing driving her…

…is hunger.

This simple, primal impulse

stems from a deep connection
she has to her surroundings

that extends beyond the Serengeti,

beyond our planet

to the universe itself.

Every cell in Wa Chini's body…

is linked to an ancient stream of energy…

…connecting her life

to the heart of a star.

This unbroken stream
spans vast reaches of space…

and stretches back 13.8 billion years.

Ancient energy that existed
at the origin of our universe

powers everything.

Every planet.

Every star.

Every life.

Wa Chini is hunting for energy…

but not just for herself.

A mother of two five-month-old cubs,

she's desperate to feed her hungry family.

It's dry season, and food is scarce.

And yet, energy is more abundant
than ever.

It's just hiding in plain sight.

The largest, brightest, hottest object
in our solar system…

the sun.

Huge loops of searingly hot plasma erupt
from its surface.

Our sun blasts out the energy
of four and a half trillion atomic bombs

every second…

sending more power
to our planet in an hour

than the entire world consumes in a year.

But as impressive
as this gigantic fireball is…

Wa Chini cannot eat sunlight.

She only eats things that run…

like gazelle.

Her spotted coat provides camouflage,

essential for stalking prey.

With few places to hide,
getting closer isn't an option.

Luckily, Wa Chini
has a trick up her sleeve.

Cheetah are the fastest animals on land.

From zero to a hundred
in just three seconds…

but gazelles are a pretty close second.

Wa Chini uses up a lot of energy…

but gains nothing.

An adult cheetah can survive
for over a week without a meal.

But cubs, they can go no longer
than a few days.

And these two
are getting very, very hungry.

Hunting at such great speeds
is incredibly depleting.

Wa Chini's energy reserves
are now dangerously low.

It will be hours
before she has the strength to hunt again.

Wa Chini and her cubs
are running on empty.

Animals all over the planet fight
the same ongoing battle

between consuming…

and using energy.

No matter your strategy,

be it fast or slow,

your next meal is never guaranteed.

Hunger is something
all of us must overcome.

Having recovered from her last chase,

Wa Chini is looking
for her next opportunity.

Like all cheetah mothers,

she's parenting solo.

To keep her young cubs well-fed,

she should make a kill every day.

But it's taken her so long to recover

that the sun is now setting.

As the light fades,

so does this family's hopes of a meal.

As Earth rotates…

the Serengeti turns away from the sun
and into darkness.

It's a powerful reminder
of life's connection to the sun.

Our story is the sun's story.

Long, long ago…

…our solar system was even colder
and darker than it is today.

And yet, these were the perfect conditions
for the birth of a star.

At temperatures close to absolute zero,

the force of gravity began pulling dust
and gas together…

…into a massive cloud.

The cloud collapsed inwards,

crushing itself into
a glowing hot ball of gas.

A protostar.

Like Wa Chini, this star in the making
had a ferocious hunger…

pulling in so much gas
that jets of hot matter

were propelled from its poles,

stretching out light years into space.

The infant star continued to grow
for 30 million years…

…until finally,

it became hot enough
to generate power all on its own.

Our sun.

Its golden rays
have now shone brilliantly and steadily…

for 4.6 billion years.

It's just one star
in a galaxy of billions.

And yet, it is a most special one…

because it is the one
that delivers heat and light…

to this incredible, vibrant planet.

Every living thing in the Serengeti
depends on the sun for its energy.

Wa Chini's cubs are drained,
beyond hungry now.

They need to eat today.

But all Wa Chini can provide this morning
is precious TLC.

In this parched land,

our sun both gives and takes.

Its fierce energy is what life needs.

But it also has the power to destroy.

It was never going to be easy living
this close to a giant nuclear reactor.

To understand the source
of this unbearable heat,

we must peer into the inferno…

…beneath the outer layers
of bubbling hot plasma…

650 thousand kilometers down…

to the core of our sun.

Our star's heart
would seem surprisingly calm…

but on an atomic level, it's pure chaos.

This is the hottest part
of our solar system.

Temperatures here
reach 15 million degrees Celsius…

creating the conditions for an event
that can happen almost nowhere else.

Atoms collide at high speed and fuse…

…releasing pure energy.

This process is called nuclear fusion

and is what makes our sun shine.

In fact, it's what powers
all the stars in our universe.

This energy released by stars can be
traced back to the beginning of time…

when there was no matter,

and all that existed
in the entire universe was energy.

And every bit of it lives on
in our universe today.

As sunlight hits the Serengeti,

energy that's been flowing
for 13.8 billion years

finds its way to Wa Chini and her cubs

and continues its journey
through their environment.

It is never created or destroyed.

It is simply transformed endlessly.

But Wa Chini and her Cubs
can only access this energy in one form…

meat.

And there are rival predators out here…

who could snatch not just her food
but her cubs as well.

If they don't feed soon,

they will die regardless.

It's a meager snack,
but after two days without food,

it's a lifesaver.

But more than 10%
of cheetah kills are stolen.

Wa Chini must defend every scrap
of energy she captures…

…because when energy is scarce,

competition is fierce.

Wa Chini's struggle to survive
and sustain her family is repeated

day after day…

…month after month.

Every meal is a fight.

In the battle between using
and acquiring energy…

Wa Chini is only just breaking even.

Dry season on the Serengeti
is defined by constant hunger.

But change is in the air.

The sun's heat has pulled
what moisture there is high into the sky.

And what goes up

must eventually come down.

Rains sweep across the plains

and bring dry season to an end.

As the clouds clear,

a glimmer of hope appears.

A single blade of grass
cannot feed Wa Chini's family…

but deep within its cells

lies the answer to their hunger.

Here, there's a hidden world.

Microscopic stacks called grana bask
in the warm rays from the sun.

Their surface is covered with a forest
of tiny, light-harvesting proteins

that capture energy from our nearest star.

They're packed with
the green pigment chlorophyll,

which absorbs rays of light.

Through the magic of photosynthesis…

water combines with carbon dioxide…

and sunbeams are spun into sugar.

In a matter of days,
the once parched plains are painted green.

Billions of blades of grass
now soak up the boundless sunlight.

And the universe's energy
becomes embedded in the landscape.

There's only one problem.

Cheetahs can't eat grass.

But far away in the northern woodlands,

there are beasts…

that do.

Hundreds of thousands of them.

Wildebeest.

They have wide mouths,
flexible lips, and four stomachs

that are perfectly adapted
to eating grass.

The massive herds
are constantly on the move

in search of fresh grazing.

To find the grass, they follow the rain.

Driven, like all of us…

by hunger.

But if there is one rule in the Serengeti,

it's that food never comes easy.

The Mara River…

home to some
of the largest crocodiles on Earth.

It's a serious roadblock

in the wildebeests' quest
for vital energy.

To the south, Wa Chini spends
every available moment

scouring the plains for something edible.

After six months surviving
on a meager diet,

one of her cubs
has managed to grow bigger…

…and is even learning
some hunting skills of her own.

But the other cub is nowhere to be seen.

Just five percent of cheetah cubs
make it into adulthood.

Most lose their lives
to hungry lions and hyenas.

This cub's future is far from guaranteed…

even when energy is tantalizingly close.

Amassed on the banks of the Mara,

the wildebeest have
nowhere to go but forward.

But someone needs to be first.

One and a half million wildebeest

make this journey each year.

And here, the battle between using
and consuming energy…

plays out on an epic scale.

For those lucky enough to make it across,

this is only the beginning.

Now, they must travel
hundreds of kilometers

day and night

for over two months…

to get to the grassy plains.

Wa Chini eagerly awaits
the arrival of the wildebeest,

but there is another migration
taking place that is critical

to the survival of both animals.

It's the journey
of unfathomable distance and time.

And without it, every creature
on the Serengeti would go hungry.

In the core of our sun,

as atoms collide and fuse,

photons are released and stream outwards.

These tiny packages of light energy
have zero mass

and travel at the speed of light.

But inside the unbelievably dense core,

they're restrained, absorbed, scattered.

A trip that would normally take
just two seconds can take a million years.

It's a mind-boggling torturous struggle
to escape the sun.

But slowly, the photons do rise

upward through the sun's layers

toward its raging hot surface…

where they can finally be set free.

They radiate out in all directions…

as starlight…

traveling 150 million kilometers
in just over eight minutes.

Arriving just in time…

to meet the wildebeest
at the end of their journey.

Each individual blade of grass absorbs
ten quadrillion photons every second…

capturing enough energy overall
to feed these massive herds.

From star…

…to grass…

to wildebeest…

sunlight now provides them
with power to move…

to grow…

to reproduce.

And the longer
they're out on the plains eating,

the longer they're available to be eaten.

Rich, delicious, plentiful energy

is finally within striking distance.

But with three million eyes watching…

Wa Chini needs to move fast.

Luckily, she's a cheetah.

At last, Wa Chini
gets a taste of starlight.

With every bite,

proteins and fats imbued
with cosmic energy

enter Wa Chini's bloodstream.

Their final destination
are her body's cellular power plants,

mitochondria…

where one last transformation
will take place.

Within each mitochondrion
is a surging landscape.

Canyons of membranes rippling
with complex chemistry.

It's here that the energy-rich food
reacts with oxygen

and is finally broken down…

releasing our universe's energy
directly into Wa Chini's cells…

…powering every action and thought,

every little movement.

The journey from star to cell is complete.

Energy that once lit up the universe

now gives Wa Chini and her cub
the gift of life.

In green season,

hunger is just a memory.

Across the Serengeti,
energy is continually transformed…

passing from one life to another,

nourishing the entire ecosystem.

Our sun is the ultimate provider.

Everything feeds on starlight.

The trouble is,
there's nothing to feed the sun.

And in five billion years,

it will run out of fuel.

As its core collapses,

the sun will expand…

and become a red giant…

that will devour the inner planets,
Mercury and Venus.

As it balloons out toward Earth,

the extreme gravity
will rip our moon to shreds…

…leaving a ring of moon rock around Earth.

The ultimate fate of our planet
is unknown.

But there will be one last sunrise…

before our star's outer layers blow away,

and it takes its final breath.

All that will remain is a dying ember,

a white dwarf,

barely the size of our Earth,
surrounded by a vast glowing cloud.

A beacon to the universe.

We were here.

But right now,

our star continues to shine down on us…

…and will for billions of years to come,

its energy a vital force for all life.

Next in the story of our universe,

whether you are a blazing star…

a vast black hole,

or a chimpanzee learning the ropes,

everything needs time.

But what do you really know
about this mysterious dimension?

Why does everything
have a past, present, and future?

And would any of us be here…

without time?