Original subtitles

In the lives of every creature on Earth…

…are echoes…

…of events that occurred a long, long time ago.

Events of unimaginable scale…

and violent beauty…

that connect all living things…

…their every action and decision,

their every heartbeat,

to the grandest story ever told.

This is a tale 13.8 billion years in the making…

that has seen billions of stars

and billions of worlds…

live and die…

to create the only planet we know of

that is home to life.

From the stardust that built us…

to the cosmic ingredients that sustain us…

and the starlight that powers it all,

this is the story of our universe.

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?