Original subtitles

BRIAN COX: The natural world is beautiful

but complex.

The skies dance with color.

Yeah! Yes!

Shapes of great geometrical beauty

form and disappear.

And the planet itself is constantly transformed.

But this seemingly infinite complexity

is just a shadow of something deeper,

the underlying laws of nature.

The world we live in is beautiful to look at

but it's even more beautiful to understand.

Light is our window on the universe.

By understanding how light is emitted by the sun

and how it interacts with the oceans, atmosphere and life on our planet,

we can explore worlds beyond our solar system,

and even search for the tell-tale signatures of life amongst the stars.

Night on our planet seems eerie,

other, as if all the color has drained away.

But in a few places on Earth, on just a handful of nights in the year,

color bursts through.

10,000 years ago, at the end of the last ice age,

the ice sheets melted

and this part of Iceland rose up and drove the coastline back.

That left the Skoga River to tumble

over the old sea cliffs to form that, Skogafoss,

one of Iceland's great waterfalls.

When the sun, moon and Earth align,

moonlight interacts with the spray at the foot of the falls

to form a moonbow.

Light leaves the sun, travels 93 million miles across space,

and reflects off the surface of the moon and enters the Earth's atmosphere,

bounces in and out of water droplets in the waterfall,

enters my eye, that sends a signal to my brain

and I reconstruct the signal into something beautiful.

But the moonbow isn't just beautiful,

it's physics.

Understanding why something is the color it is tells you something.

It tells you about its structure,

about the processes going on inside, about its history even.

And because light travels freely across the universe,

we can explore distant worlds using light alone,

and we can tell their stories, too.

The reflected light from the moon has its origin in our star, the sun.

Stars illuminate the universe.

They are the source of the light that bathes the planets.

But the processes by which light is emitted by the stars

can be explored here on Earth.

On the 51st of August 2014,

a vast chasm opened up in central Iceland.

At its peak, the Bardarbunga volcano

spewed out 350 cubic meters of molten rock every second,

producing light so bright,

it could be seen from space.

And just like the sun, lava glows because it's hot.

Just look at that.

It's many months since the eruption, but it's steaming away back there.

We're actually fortunate that it erupted here.

The helicopter pilot told me that if it had erupted on the glacier,

then we would have been plunged into perpetual nuclear winter

and civilization would have been destroyed.

That's not actually quite right

but it would have been significantly worse.

The amount of ash that went up into the atmosphere

would have been really considerable.

You get a sense of the power and violence of the Earth.

We're blissfully unaware of it usually.

When it breaks through the surface

you see what it can do.

Today, the lava has cooled into matte black rock

but it's still giving off light.

The thing is, everything is hot,

everything has a temperature.

But if it's cold, it just emits light that we can't see.

This camera can see it, though.

It's called infrared light.

You see there that this lava is glowing brighter than the background,

which means it's hotter.

So, although we can't see it,

everything shines.

Light fills the universe.

Radio waves are light.

X-rays are light.

Visible light is simply the part of the spectrum we can see.

Matter, like lava or you and me,

is made up of electrically charged particles.

Here's one, moving along. Say it's an electron.

Temperature is a measure of how fast those particles are moving around,

how fast they're jiggling.

So, in something hot,

these particles are always bouncing around and changing direction.

Now, here's a fundamental law of the universe.

When a charged particle changes direction,

it emits a light particle called a photon.

Light can be thought of as a stream of photons,

particles whose energy corresponds to their color.

Cooler things, like solid black lava,

emit lower energy photons,

infrared light, which our eyes can't detect.

As things get hotter,

they can radiate higher energy photons.

At 7, 000 degrees Celsius, molten la Va shines

with mainly red light, which our eyes can detect.

The surface of the sun

is 5,500 degrees Celsius,

so it can also produce higher energy green and blue photons

alongside the red.

The white light of the sun is made up of all the colors of the rainbow

and when it reaches the Earth,

those individual colors are revealed.

Photons from the sun rain down and enter water droplets.

They reflect off the rear face,

out of the front again and into your eye.

But the blue photons, the higher energy ones,

behave differently to the green ones

and the yellow ones and the red ones.

They come out at a shallower angle,

and that's why you get the full spectrum of colors

from the white light of the sun.

And it's this light that paints the Earth.

The colors of our planet arise because of the way photons from the sun

interact with the matter from which the Earth is made.

From space, our planet is a blue world

and that blue color arises

because of the way light interacts with water

and the process is linked to one of the planet's greatest migrations.

Every spring, Marine Biologist Oswaldo Vasquez

heads out onto the high seas...

(IN DISTINCT RADIO CHATTER)

It's 11. 11 o'clock.

In search of these waters' most awe-inspiring seasonal visitors.

(LAUGHS)

Humpback whales.

Every year, they make the longest migration of any mammal on Earth,

traveling up to 8,000 kilometers,

from their feeding grounds in the Northern Atlantic,

to the striking blue waters of the Silver Bank Marine Reserve.

OSWALDO: This is the greatest nursery of humpback whales in the world.

85% of the North Atlantic population comes here for breeding,

mating and giving birth.

So, from this place depends the survival of this species.

COX: The whales' life cycle is intricately linked to the interaction

between the light of the sun and the water of the ocean.

OSWALDO: In order to understand their behavior, we need to go beneath,

and to see with our own eyes what is happening there.

Not 'rust on surface, underwater.

(OSWALDO SPEAKING)

(IN DISTINCT)

Yup, yup, yup.

(OSWALDO SPEAKING)

OSWALDO: Slow down, slow down.

Slow down, slow down.

OK.

(WHALE some)

COX: The reason humpbacks come here to give birth

is because the shallow waters around Silver Bank are exceptionally warm.

OSWALDO: Whales are warm-blood animals

and when they give birth they have a very skinny calf with no blubber.

They need warm environment, as they had inside mother.

So, here in Silver Bank, it's warm and it's protected,

so it's suitable for giving birth.

As photons of light rain down onto the ocean,

they strike water molecules,

and some of this energy goes into making them jiggle around,

increasing their speed and therefore their temperature.

But it takes an awful lot of energy to heat the oceans

and so it's only here,

exposed to the full glare of the equatorial sun,

that enough energy is absorbed to raise the water temperature

to a balmy 26 degrees,

the perfect conditions for mothers to raise their calves.

(WHALE some)

OSWALDO: The calves are really very cute because they are like puppies

but, underwater, it weighs one ton. So, it's a big puppy. (CHUCKLES)

But not all of the photons that enter the water are absorbed.

Some of them bounce straight back out again

and it's these photons that reach our eyes

and create the blue of the oceans.

To understand why it's mainly red photons that are absorbed

rather than the blue ones,

we need to take a closer look at the structure of water.

This is called Pingvellir.

That's a rough pronunciation

but in Icelandic it means Parliament Valley

because the Vikings use to meet here

over 1,000 years ago and had the world's first parliament.

The thing is, it's not actually a valley,

in the sense that it wasn't cut by a river

or a glacier.

It was actually formed by the continents themselves

splitting apart.

So, that is the American continental plate,

and that is the Eurasian continental plate.

Now, if you just go about a mile down the road,

this place is flooded, and you can dive in it.

The rift is filled with glacial melt water

that seeps down from Iceland's frozen interior.

The sun's rays are much weaker here

but wherever sunlight hits water molecules

it always produces the same color.

How's that feel?

That's good.

It's quite nice in here actually.

I can't believe this water.

You can see for miles.

I've never seen anything like it.

The reason for that purity

is that the water's come 50 kilometers,

sometimes going deep underground,

and is filtered by these rocks.

So it's some of the coldest,

purest water you can imagine.

It's really, really spectacular.

Look at that. You can see forever.

Descending deeper into the fissure,

the effects on the color of my dry suit

hints at the process by which the oceans

acquire their distinctive blue.

Well, now we're down at about, uh...

Well, 12 meters.

And you see, down here my beautiful red diving suit

is no longer quite as red as it was. (CHUCKLES)

In fact it's looking quite black.

And the reason for that is the structure

of water molecules themselves.

A water molecule is an oxygen

with two hydrogens attached,

and when the light streams into the water,

the red light is just the right energy

to start those molecules vibrating, and they do.

They start going like that,

and like that, and even like that.

So, all the energy in the red light is taken

making the water molecules wobble and vibrate.

The blue light doesn't do that.

So, the blue light can scatter around in the water

relatively unimpeded.

And that's why water is blue.

Cool, isn't it?

(WHALE some)

Vibrations inside the water molecules themselves give the oceans their color.

The weaker bonds between water molecules also absorb some light.

Together these processes absorb so much energy

that there isn't a lot left to increase the sea temperature,

which is why Humpbacks must travel so far

to find water warm enough to give birth.

(DOLPHIN SQUEALING)

Because water is hard to heat up, the temperature of the oceans

remains very stable,

creating the perfect conditions for live to thrive.

Liquid water is the essential ingredient for any life-supporting world.

Oceans cover 70% of the Earth's surface,

their distinctive blue broadcasting to the universe

the message that Earth is a possible home for life.

And beyond the waves, on the land,

we see life's other signature color,

a blanket of green plants.

As with all living things, they depend on water to survive,

and when the seasonal rains recede,

the land reverts to the arid colors of the naked earth.

The intense African sun delivers 1,000 watts of solar power

per square meter,

baking the plains of the Serengeti to dust.

Scorched brown, barely a single blade of green grass survives.

For the Masai, the dry season means months of hunger and hardship.

Para Kapooni and his son and brother

must say goodbye to their home valley

and drive their cows across the plains

in search of enough grass and water to keep them alive

until the rains return.

(PARA KAPOONI SPEAKING OWN LANGUAGE)

(COWBELLS RINGING)

At the end of their long journeys,

Masai warriors from across the Serengeti

gather on the banks of Lake Masek.

(KIDS CHATTERING)

(PARA KAPOONI SPEAKING OWN LANGUAGE)

But survival on the plains of the Serengeti

forces Para Kapooni and his family to spend the dry season apart

because while he tends the cattle, his wife, Nura Kapooni,

must stay behind to look after those too young

or too old to make the trip,

and eke out an existence on the brown, lifeless plains.

(NURA KAPOONI SPEAKING OWN LANGUAGE)

With the cows away, the family must survive

on their meager stores of maize flour and water.

(CRYING)

(PARA KAPOONI SPEAKING OWN LANGUAGE)

(THUNDER RUMBLING)

Now, after four long months apart,

things are about to change.

(NURA KAPOONI SPEAKING OWN LANGUAGE)

The coming of the rains means the grass can grow again.

Revived, new shoots emerge,

packed with the green pigment, chlorophyll,

which allows plants to harvest the sun's energy

and the plains are transformed from dusty brown to vibrant green.

In just a few days, the landscape is reborn.

I suppose we think of green as the color of life

but actually it's the color that life throws away,

waste, green photons, reflected back into our eyes.

Plants absorb most of the rest of the rainbow,

the blue and red photons,

and use their energy to power photosynthesis.

Photosynthesis is the process by which plants harness light.

They are the bridge between nuclear reactions

93 million miles away and life on Earth.

Energy released from nuclear fusion reactions in the sun's core

heats everything up and shakes electrons around

and those electrons will emit photons,

which travel across space for eight minutes,

and then hit an electron

in a chlorophyll molecule.

But instead of that energy being dissipated away as heat,

chlorophyll is clever

and ultimately the energy imparted to that electron

is used to do all sorts of clever things

through an intricate piece of machinery.

Split water up, force electrons on to carbon dioxide

and ultimately build sugars, which allows the plant to grow.

COX: On the plains of the Serengeti,

the intricate process of photosynthesis

means Para Kapooni can begin the long journey to rejoin his family.

(NURA KAPOONI SPEAKING OWN LANGUAGE)

COX: After months apart,

the greening of the Serengeti transforms the harshest of environments

into a place the Masai can call home.

(NURA KAPOONI SPEAKING OWN LANGUAGE)

(PARA KAPOONI SPEAKING OWN LANGUAGE)

COX: Animals eat plants that feed on sunlight.

In this way, the sun's energy powers the entire food chain.

But photosynthesis does more than provide life with energy.

Around 2.5 billion years ago,

it began to transform the composition of the Earth's atmosphere itself

by filling it with the waste products, oxygen,

the gas upon which all complex life depends.

Without air to breathe, there would be no intelligent life on Earth.

We rely absolutely on the oxygen

that forms a fifth of the thin blue line

that envelops our planet.

And, perhaps paradoxically,

why the sky is blue is best explained in the dead of night.

It's a beautiful, crisp autumn night here in the south of England.

Rolling hills illuminated by moonlight,

which is the light from the sun reflected off the surface of the moon.

It's quite silent actually, almost eerie.

But out there, the Earth's shadow is racing through space

and actually is just beginning

to cut off the top left-hand corner of the moon.

On a few nights every decade,

the sun, moon and Earth line up

to create one of the wonders of the night sky,

a total lunar eclipse.

You get a real sense of the celestial mechanics

in action during an eclipse.

The sun is somewhere over there behind me,

shining on our planet.

And our planet is casting a shadow through space,

which falls on the surface of our satellite, the moon.

As the Earth moves between the moon and the sun,

it blocks light from falling directly onto the lunar surface.

Now, the moon is completely covered by the Earth's shadow

but it's not completely black.

It's glowing a deep blood red.

At the height of the eclipse,

the only photons reaching the moon

have passed through the atmosphere of our planet.

It's red because of the way that light interacts with the Earth's atmosphere.

Imagine that rain of photons passing through the atmosphere from the sun,

all the colors of the rainbow.

Well, the blue photons, the higher energy photons,

have a higher probability of bouncing off the molecules

in the Earth's atmosphere.

So they scatter around.

That just leaves the lower energy red photons,

have a much lower probability of bouncing around,

and therefore can pass through the Earth's atmosphere

relatively unscathed.

So they're the ones that make it onto the moon's surface

and reflect back into my eye.

And that's why, in a lunar eclipse,

you get a blood-red moon.

And by day,

the blue photons the atmosphere scatters are what paint the skies blue.

So, when you look up to the sky on a summer's day

and see that deep blue,

what you're actually seeing is blue photons

scattering around off the molecules in the atmosphere.

Red, green, blue. The primary colors of our planet.

The Earth is painted by the photons

that rain down from the surface of the sun.

But for us to see them,

those photons must take one final journey.

(SALMA SPEAKING BENGALI)

COX: Salma lives with her seven-year-old son, Magidal,

on the banks of the Gorai River in Bangladesh.

(SALMA SPEAKING BENGALI)

COX: This is a vibrant place to grow up.

But unlike the other children, Magidal can't experience it.

(SALMA SPEAKING BENGALI)

COX: For us to see, photons must travel into our eyes.

But Magidal was born with severe cataracts.

The lenses of his eyes are so clouded,

he's been effectively blind since birth.

(FATHER SPEAKING BENGALI)

COX: But today, Magidal's life is about to change.

His family are making the eight-hour journey to the capital, Dhaka,

because this afternoon, Magidal will undergo surgery

designed to restore his sight.

(DOCTOR SPEAKING BENGALI)

COX: If the surgery is successful,

replacing his faulty lenses with artificial ones

will allow light to travel directly into Magidal's eyes.

It's at the back of the eye

that photons collide with cells in the retina

sensitive to red, green and blue light,

and trigger the nerve impulses that allow us to see in color.

(BICYCLE BELL RINGING)

(SALMA SPEAKING BENGALI)

(DOCTOR SPEAKING BENGALI)

COX: For the first time in his life,

photons are able to enter Magidal's eyes unimpeded.

For the first time in his life,

he can see.

(SPEAKING BENGALI)

COX: Our eyes reveal to us the colors of the Earth.

The first step towards understanding their meaning.

The blue that signals the presence of liquid water.

The green that marks out our planet as a home for complex life.

And, in this most distant image of the Earth ever taken,

from six billion kilometers away by the Voyager spacecraft.

The sunlight bouncing off our atmosphere

reveals our planet as a pale blue dot,

hanging in the void of space.

And even from this distance, anyone who happened to be looking

could tell our planet contained the ingredients for life.

Because in the most delicate color signals,

we have measured with precision what the universe is made of.

And those signals can be glimpsed at the very edge of our own atmosphere.

BECKY. What are we drawing? OCEANIA: A sun dragon!

- What's a sun dragon? - It's just like a sun,

and it's got smoke coming out of its mouth

'cause it's starting to make fire on the world.

(ROARS)

Now, let's just do the fire.

BECKI: We need to get ready to go, don't we?

Push!

COX: For seven years, the Nation family

have been consumed by an obsession,

ready to drop everything at a moment's notice

in pursuit of a light show like no other.

I'm an aurora chaser!

COX: They've left their home on the Sussex coast

for the cold climes of northern Norway...

73, 98, 97.

69, 98, 100.

COX: Spending their weekends

chasing one of the planet's most extraordinary phenomena,

the Northern Lights, Aurora Borealis.

It's an addiction, it's an absolute full-blown addiction.

It's a buzz and it's a rush of adrenaline

and it's a holding of your breath and...

(IN HALES) Wow.

COX: The aurora was once thought to be caused

by dragons fighting in the sky.

But today, we know its ethereal light is created by charged particles

known as the solar wind

interacting with the gases of the upper atmosphere.

BECKI: Well, our eldest, Aurora, she's 11.

She's fascinated by,

"Why do those different gases make those different colors?"

She's quite fascinated by them.

Oshey, she likes the pink 'cause she likes pink.

It's her favorite color, so pink's cool.

Anything else, just wake me up if it goes pink.

And Lyrica is quite a fact box on everything.

She can explain to you what causes an aurora,

where it comes from,

the technical names and, you know, what the magnetic field does,

and how it stops the solar wind from harming us.

COX: But the aurora is elusive.

To see it, conditions have to be just right.

BECKI: Shall we go build a snowman?

COX: Clear, dark skies must combine with strong solar winds.

(CHATTERING)

Mum, aren't you going to burn it?

COX: All the family can do is wait.

Ooh! Ooh, ooh, ooh!

I can see some uprights there.

Oh, wow!

BECKI: Oh, yeah! MR NATION: Here we go, look at it!

BECKI: Beautiful! Look at it!

Look how bright that is up there, look!

Yeah! Yes! (LAUGHS)

Now, that's what I'm talking about!

Look! (GASPS) Ooh!

Look! Look! Look! Look! Look!

Corona, corona! Look at it!

MR NATION: Look at the reds at the top!

BECKI: Stunning! MR NATION: Wow!

Oh! Oh! Oh! Oh, look at that!

And on the left, on the left, look there's some pink as well...

BECKI: Yay! (INDISTINCT)

COX: But the aurora isn't simply beautiful.

It contains information.

As charged particles strike gas atoms,

a photon of light is released.

And because the atoms of every element have a unique structure,

each one gives off a photon of a unique color.

The green comes from oxygen atoms, pink from nitrogen.

BECKY. Yes:!

COX: The colors dancing across the sky

reveal the composition of our atmosphere.

And it's these fingerprints encoded in photons of light

that have shown us the entire universe.

In the last few 100 years,

astronomers have gazed out from the edges of our home world

and dreamt of a universe beyond.

In the shadow of the Eiger, that is the Sphinx,

and, despite appearances, isn't the lair of some alpine super villain.

It's an observatory.

It was built in 1937,

and since then, astronomers have been coming here

from all over the world to look at the night sky.

And by decoding messages hidden in the light reaching our telescopes,

we've discovered the true nature of the cosmos.

That's an aurora in a box.

It's a tube full of hydrogen gas that's heated up.

And what you're seeing in that pinky-red color

are the fundamental laws of nature themselves in action.

See, they tell you that a single proton,

which is a nucleus of hydrogen, and a single electron

can only behave in certain ways.

The electrons can only go in certain places around the proton.

So, when you heat them up, they can only jump high up.

And then when they cool down,

they can only fall back in a specific way,

releasing light of a particular energy which equals a particular color.

And those laws don't just apply here on Earth,

they apply everywhere across the universe.

So, anywhere that you see glowing hydrogen gas,

let's say, in a nebula heated up by young stars,

then you'll see that specific color.

Vast clouds of glowing hydrogen

create some of the most spectacular sights in the cosmos,

their pink hue revealing the identity of the gas

from which they're made.

And what's true for nebulae is true for everything in the universe.

By analyzing the light from the stars,

we know that they're not just twinkling lights in the sky.

They are other suns made out of the same stuff as ours,

and if there are other suns, then there must be other planets,

maybe even other Earths.

By understanding the origin of the colors of our world,

the blue of its oceans,

the green of its life

and the colors dancing in its atmosphere,

we've uncovered the color signature of a life-supporting planet.

And because we understand the signature of our own world,

we can look for worlds like ours elsewhere in the cosmos.

But here's what I think is the most wonderful thought of all.

When you look out

to those distant star systems and planets,

you're connected to them, see?

An electron somewhere out there radiated a photon

which hit an electron in your eye.

Alien photons crossing light years of space

entering your retina,

and carrying stories of distant worlds.

In the constellation of Pegasus, around a sun-like star,

there's a planet called Osiris.

It's way closer to its parent star than Mercury is to our sun

but it's a massive gas giant, a hot Jupiter.

And by measuring the light that shines through its atmosphere,

we've found that the atmosphere's full of hydrogen and methane

and water.

And just 24 light years away, in the constellation of Scorpius,

there's a small rocky world,

one of the most Earth-like worlds we know.

It orbits around a red dwarf star,

which is one of three stars in the system.

A planet with three suns in the sky.

In the last 20 years, we've found hundreds of planets around distant suns.

We've begun to analyze their atmospheres

and search for life-giving water.

Science is about gathering data,

information about the natural world, and trying to understand it.

When put like that, it seems a bit dry.

But when that information carries stories of alien worlds

around distant suns hundreds of light years away,

that's a whole different thing.

Astronomy turns data into dreams,

dreams of worlds of ice and snow,

dreams of worlds with hemispheres in perpetual day

and permanent night.

Dreams of worlds with moons and moonbows,

and perhaps, just perhaps, alien astronomers,

observing the light passing through the atmosphere of our blue world,

and dreaming of us.