[calm music playing]
[chimpanzees screeching]
[chimpanzees hooting]
[clock ticks]
[Freeman] It's morning in the forest.
And for this troop of chimpanzees,
it's time to get out of bed
and get on with the day.
[intriguing music playing]
[chimpanzees screeching]
[Freeman] But when you sleep in a nest 40 meters up in the air,
it can be a bit of a challenge.
[playful music playing]
[chimpanzee howling]
[chirping]
[Freeman] This morning ritual has been playing out like clockwork
for countless generations.
[pensive music playing]
A rhythm driven by one of the most mysterious properties of our universe.
Time.
And time is playing an extra important role
for one female chimp.
Celeste is in her mid-30s,
and she has a ticking clock inside her.
[whooshing]
A clock that was set 13.8 billion years ago.
[heart thumping]
[fizzling, whooshing]
From The Big Bang came atoms…
[zapping]
…and energy…
[rumbling]
…which have journeyed across vast reaches of space.
[dramatic music playing]
And these ingredients
are now assembling…
to create a new life.
In Celeste's womb, a tiny chimpanzee is forming.
[heartbeat thumping softly]
It will be another 150 days before this baby meets the world.
That's the time it takes.
And without time,
nothing in our universe would ever be born.
[heartbeat continues thumping]
From the youngest chimpanzee…
to the oldest black hole.
[fizzling]
[whooshing]
But how did time start in the first place?
Does everything experience time in the same way?
And will our universe's clock ever stop ticking?
[dramatic music playing]
[clock ticking]
[chimpanzees hooting]
[Freeman] The day begins for a chimp much as it does for us.
Breakfast.
[pensive music playing]
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.
[ethereal music playing]
We can't see it.
-[animals growling] -Or hear it.
-[chimpanzee screeches] -We can't influence it in any way.
[elephant growls]
And yet, every heartbeat, every choice and action,
every inaction is a consequence of time's continuous flow.
[whooshing]
It can whiz by or drag on.
But time ticks ever onward.
Stars and planets form, age, and die.
[dramatic music playing]
In their wake, new stars emerge.
And from a rare few,
the most mysterious objects in the universe are born.
Black holes.
[fizzling]
[whooshing]
Time is the cosmic conductor.
[clock ticking]
Nothing can escape its grasp.
[dramatic vocal music playing]
[clock ticks]
[birds chirping]
[chimpanzee hooting]
Although we have devices that can track and measure time…
[dramatic music playing]
…chimps don't.
Celeste and her family use the sun as their guide.
Rising and arcing across the sky.
[hooting]
As it moves…
so do they.
[chimpanzee screeching]
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.
[ominous music playing]
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.
[suspenseful music playing]
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.
[dramatic music playing]
Again and again.
[clock ticking]
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.
[clock ticks]
[ominous music playing]
[clock ticks]
As soon as you leave our home planet…
[clock ticks]
…the 24-hour day no longer applies.
Flying closest to the sun…
[rumbling, whooshing]
…is the planet Mercury.
Compared to us, it rotates at a snail's pace.
Our neighbor Venus spins even slower.
[intense music playing]
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.
[whooshing]
[intense music continues]
[whooshing]
Including planets far beyond our solar system.
[whooshing]
Sixty-three light years away,
orbiting a young star,
is Beta Pictoris b.
It spins so fast…
[whooshing rapidly]
[rumbling]
…it bulges out at the sides.
It is the fastest-spinning world we know of.
[intense music playing]
Here, a day lasts just eight hours.
[clock ticks]
Every planet in our universe spins at its own speed.
[whooshing]
Billions of worlds,
each with their own clock,
ticking away to different rhythms.
[multiple clocks ticking]
But all moving forward on a universal cosmic timeline.
[single clock ticking]
[calm music playing]
[clock ticks]
[chimpanzees screeching]
Back on Earth,
with the sun now almost directly overhead,
the chimps know exactly what time it is.
It's lunchtime.
[calm music continues]
And their crossing of the savanna has been timed to perfection.
[howling]
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.
[dramatic music playing]
Animals of all sizes are tending to their daily tasks.
And each experiences time differently.
For small creatures that live fast, short lives…
[dramatic music intensifies]
…lunchtime can feel like a lifetime.
[elephant snorts]
For slower, longer living things,
an hour can go by in the blink of an eye.
[dramatic music continues]
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…
[dramatic music crescendos]
…those days keep ticking by…
dictating the lives of every chimpanzee.
One in particular.
[low rumbling]
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.
[dramatic music playing]
[ethereal tinkling]
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.
[dramatic music continues]
[chimpanzees hooting]
[clock ticks]
[calm music playing]
As the sunlight wanes,
the chimps instinctively switch gears.
To evening mode.
[chimpanzee yawning]
Nesting calls signal to the whole troop.
[chimpanzees hooting]
It's time to find a safe place to spend the night.
[playful music playing]
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.
[pensive music playing]
But the chimp's innate sense of time
comes from something inside them.
[chimpanzees screeching]
[whooshing]
Deep in their brains is a biological clock.
Bundles of neurons act as a pendulum…
[whooshing]
…controlled by genes that switch on and off…
and a cycle that repeats every 24 hours.
[whooshing continues]
These clock genes create a circadian rhythm in the body
that waxes and wanes in sync with our planet's rotation.
Controlling hormones…
[chimpanzee screeching]
…heart rates,
and energy levels.
And right now, the chimps' body clocks are sending the message,
"It's time to get sleepy."
[moans]
Not everyone can though.
[heartbeat thumping softly]
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.
[insects chirping]
[pensive music playing]
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.
[bat chittering]
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.
[dramatic music playing]
Thanks to cellular clocks
that tick in time with the spin of our Earth.
[whooshing]
[clock ticks]
As yesterday becomes a memory…
[pensive music playing]
…another new day begins in the forest.
[chimpanzees hooting]
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.
[grunts]
When he's in a bad mood…
the rest of the group just need to keep their heads down.
[chimpanzees hooting]
[ominous music playing]
[Apollo grunting]
He soon finds a target for his rage, though.
[bees buzzing]
Some of the younger chimps have found honey for breakfast.
[ominous music continues]
And they forgot to invite Apollo to join them.
[chimpanzee hooting]
[ominous music crescendos]
[chimpanzees screeching]
You soon learn, never get on the wrong side of the dominant male.
[hooting]
[chimpanzees screeching]
[solemn music playing]
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…
[sound effects playing in reverse]
…only forward into the future.
[clock ticking continuously]
This is time's arrow,
and it leaves scars on everything
across Earth…
[clock ticking rapidly]
…and beyond.
[rapid ticks morph into rhythmic music]
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.
[rhythmic music continues]
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.
[intense electronic music playing]
Mimas lives to tell the tale.
But events like this are irreversible.
[whooshing]
And they differentiate the past from the present.
[intriguing music playing]
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.
[sound effects playing in reverse]
Before planets.
Before stars.
Back to a time before time.
Our universe had a beginning.
[explosion rumbles]
[dramatic music playing]
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.
[dramatic music continues]
Bound to space as our universe's fourth dimension.
The Big Bang set the universe's clock ticking.
Propelling everything into the future.
[zapping]
[dramatic music crescendos]
It created the arrow of time.
[insects, birds chirping]
From our universe's very first moments…
[clock ticks]
[calm music playing]
…it pushes us all into the future,
causing everything to grow,
age…
[clock ticks]
…and change.
[clock ticks]
From childhood…
[clock ticks]
…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.
[chimpanzee grunting]
Time's arrow leads us through these stages of life.
[calm music continues]
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.
[solemn music playing]
Everything that exists in our universe has a finite lifespan.
Including, perhaps, the universe itself.
[whooshing]
Today, the galaxies are filled with stars.
But 95% of stars that will ever exist have already been born.
[solemn music continues] -[clock ticks]
So, as our universe journeys into the future…
[clock ticks]
…the stars…
-[clock ticks] -…one by one, will blink out…
[clock ticks]
…leaving the universe to face an ever-darkening future,
stretching out for trillions,
that's thousands of billions, of years.
[solemn music continues]
The age of starlight
will be followed by a dark age of black holes.
[eerie music playing]
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.
[zapping, whooshing]
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.
[eerie music crescendos]
But even black holes can't escape time's arrow.
[solemn music playing]
In the far, far future…
[clock ticking]
…when there are no stars or planets left to consume,
they will begin to starve.
And slowly…
very slowly,
they will shrink.
[suspenseful music playing]
When they die,
no one truly knows what comes next.
But it could be the end of our universe.
[insects, birds chirping]
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.
[somber music playing]
Retreating from the group, she heads into the forest alone.
She has lived many years.
But this day will be her last.
[somber music continues]
While the world continues to spin,
her body lies still.
[somber music crescendos]
[whooshing]
But time doesn't just carry us toward endings.
It also creates beginnings.
[ethereal music playing]
As days turn into weeks and weeks into months,
there are big changes for one special chimpanzee.
[whooshing]
[intriguing music playing]
[heartbeat thumping softly]
Say hello to Cosmo.
Her brain and limbs are now fully formed.
And her eyes are ready to see the world.
[intriguing music continues]
The exact timing of her birth is impossible to know.
But she could be born any day now.
[dramatic vocal music playing]
She's been in the womb for eight months.
But her journey began long, long ago.
[whooshing, explosion rumbles]
The elements that made her came from dying stars.
[whooshing]
The water that flows through her body came from distant worlds.
[dramatic music playing]
The energy that powers her muscles came from the heart of our sun.
[explosion rumbles]
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.
[ethereal music playing]
On this planet.
-[birds chirping] -[chimpanzees hooting]
Another sunrise, another morning.
[calm music playing]
And this one is extra special.
Welcome to Earth, Cosmo.
[Cosmo grunting]
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.
[Cosmo grunting]
[whooshing]
Like Cosmo,
our universe is still in its infancy
at the beginning of an unimaginably long lifespan.
[majestic music playing]
We are living in the age of starlight.
A moment when time's arrow has filled the universe with beauty…
[penguins squawking]
…and wonder.
[majestic music continues]
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.
[whooshing]
Next in the story of our universe,
Earth's seasons.
[playful music playing]
Like a mother bear raising her cubs…
[cub groans]
…we all experience our planet's yearly transformations.
[bear roars]
But what created Earth's seasons?
[rumbling]
[crashing]
How are they connected to the formation of our moon?
And why does only our planet have conditions just right for life?
[cub whines]
[dramatic music playing]