Original subtitles

PROFESSOR BRIAN COX: Why are we here?

Where do we come from?

These are the most enduring of güestions.

And it's an essential part of human nature

to want to find the answers.

Now, we can trace our ancestry back hundreds of thousands of years

to the dawn of humarıkiınd.

But in reality, our story extends far further back in time.

Our story starts with the beginning of the universe.

It began 13.7 billion years ago.

And today it's filled with over a hundred billion galaxies,

each containing hundreds of billions of stars.

In this series, I want to tell that story.

Because ultimately, we are part of the universe.

So its story İis our story.

İt's a story that we wouldn't be able to tell

were it not for the one thing that cornnects us vividiy to our vast cosmos.

Light.

Light reveals the wonders of the universe in all their glory,

stars that shine with the light of a thousand suns

and vast swirling galaxies.

But light is also a messenger from a long-forgotten era.

And contained in the light from these faraway places

is the story of our universe's origin and evolution.

Through light we can stare back

across the entire history of the universe

and discover how it all began.

And ultimately, see how light breathed life into us.

This is Karnak temple in Egypt.

Built by the ancient pharaohs,

this vast complex was erected to honour Amun-Ra,

god of all gods,

god of the sun.

This worship reaches its peak

during öone fleeting moment in the solar calendar,

an event so brief, it lasts for little more than a minute.

This temple is built to align with an astronomical event

that happens just once a year,

the sunrise at the winter solstice.

Solstice is Latin for "sun stands still",

because as the Farth orbits around the sun and the year passes,

the point at which the sun rises above the eastern horizon moves.

So here in Egypt, in summer the sun rises over in that direction,

and then as summer turns to autumn turns to winter,

the sunrise point drifts along

until today, on December 21st, at 6:30 a.m. in midwinter,

the sun rises exactly between the pillars of this temple.

Just öonce a year for öover 3,000 years,

the sun has risen between the two pillars

and cast its light into the temple.

There it is. The light from our star,

cascading down this magnificent structure.

I mean, you can literally feel the history of this place.

It's easy to forget that this is three and a half thousand years old.

So, in 1500 BC,

the most powerful man on the planet, the pharaoh of Egypt,

would have stood here on December 21st every year,

just to greet and experience the light from Amun-Ra.

This moment that the Fgyptians worshipped instinctively

we now understand in exgulsite detall.

As the Farth journeys through the solar system,

it's bathed in the light of the star that sits at its centre.

(RUMBLING)

This light has travelled some 150 million kilometres

from the surface of the sun.

And at the winter solstice,

that light pours into the temple at Karnak.

Well, this building is, honestly,

the most magnificent structure I've ever seen.

You know, it's not built on the scale of men,

it's built on the scale of gods.

Of one god, Amun-Ra, the god of the sun.

As the sun sinks below the horizon and night falls,

a whole universe of suns fades into view.

We no longer build temples to our sun.

We build machines that allow us to peer deeper into space than ever before,

to far distant suns out there in the galaxy and beyond.

On a night like this,

there are about two and a half thousand stars

visible to the naked eye.

But when we started building telescopes instead of temples,

we discovered that there are billions more.

Every star we see in the night sky

is a sun that sits within our own galaxy,

the Milky Way.

As we step away,

our sun gradually fades to become Just one dot in a sea of stars.

We now know that we are about halfway out from the centre

of this beautiful cosmic structure.

But even though these worlds are many millions of kilometres away,

we know them intimately by their light.

These waves of light are messengers from across the cosmos

and through them we have discovered the wonders of our galaxy.

This is the Lagoon Nebula.

From a distance,

this cloud of dust and gas appears beautiful and serene.

(RUMBLING)

But this a furnace where new stars are forged.

The Lagoon Nebula sits about 5,000 light years from Farth.

But it can still be seen with the naked eye,

because it's 100 light-years across

and brightly lit by the hot, young new star

that sits at its centre,

a giant called Herschel 36.

This newly born star is over 20 times more massive than our sun

and burns much hotter,

which makes the light that pours from its surface blue.

And there are even bigger stars in our galaxy.

Seven and a half thousand light years from Farth

is a star that dwarfs even Herschel 36.

İIts name is Eta Carinae.

This monster star

is over 100 times more massive than our sun

and burns about four million times brighter,

making it öne of the most luminous stars in the Milky Way.

All we know about these incredible worlds

has been brought to us on wave after wave of light.

Our galaxy is a symphony in light.

The Milky Way is home to 200 billion stars.

But our galaxy is just the beginning.

For each of these stars,

there are a billion more in the universe beyond.

Across the unimaginable reaches of space,

light has allowed us to journey to the most distant galaxies

to see the births and deaths of stars.

No matter how far we follow the light,

no matter how many billions of miles we cross,

the nature of light itself allows us to go on a much richer journey

because to look up and to look out

is to look back in time.

See, those ancient beams of light are messengers from the distant past

and they carry with them a story,

the story of the origin of the universe.

In örder to read this story,

to see how light can transport us to the past,

we must first understand öne of its fundamental properties,

its speed.

Everything in our universe has a speed limit,

even intangible phenomena, like waves of sound and light.

These speed limits are very real physical barrters

and they have profound conseguences for our understanding of the universe.

Today, I'm gorng to try and break öne of those barriers.

This is a Hawker Hunter.

It was built in the 1950s when breaking the sound barrier

Was at the very limit of our technical abilities.

"Sound barrier" is an incredibly evocative term,

it has an almost legendary status in the history of aviation.

But there's nothing fundamental about it.

It's something that you can overcome with some extremely clever engineering

and, in the early days, guilte a lot of courage.

The reason we don't usually think about sound

as having some kind of speed limit, a limiting speed,

is because it is incredibly fast

compared to the things we're used to in everyday life.

But today, we're golng to try and breakit,

I'm going to try and breakit, sat in this marvellous machine.

On Earth, the speed of sound, depending on altitude,

iİs arocund 1200 kilometres per hour,

known as Mach 1.

(TALKING, INDISTINCT)

(WHIRRING)

This jet isn't designed to fly that fast in normal flight.

But there is a way to make it travel faster than sound.

And for that, we need to fliy high.

As the plane flies faster,

it begins to catch up with its own sound.

The sound waves simply can't get out of the way fast enough,

so they begin to pile up at the front of the jet.

But to outrun our sound waves,

we need to push this jet to its absolute limit.

In just seconds, the jet smashes through the sound barrier.

This can be heard from the ground as a sonic boom.

İt was a doddle, actually.

Well, you know, having said that, it was inverted full throttle at 42,000 feet,

but that's a different definition of "doddle".

(LAUGHS)

So this magnificent piece of engineering

is fast enough, if you just push it a little bit,

to outrun its own sound.

So the sound barrier is negotiable. You can smash your way through it.

But the speed oflight, the light barrier,

well, that's a very different story.

Sound has a definite speed that we can measure.

But for thousands of years,

the world's greatest minds thought that light was different,

that it travelled instantaneously from object to eye.

Then, arocund 350 years ago, the truth about light was revealed

through a combination of one man's genius

and the clockwork orbits of the heavens.

Ever since Galileo discovered that Jupiter had moons,

astronomers realised that you could use Jupiter and its moons

as a very precise clock in the sky.

So here's the solar system,

there's the sun, there's the Earth, here's Jupiter,

and here is Jupiter's innermost moon, İo.

Now, it was known that Io takes precisely 42 and a half hours

to orbit around Jupiter.

So, if from the Earth, you see Io emerge from behind Jupiter

at, say, midnight on a Tuesday,

then you know that it should remerge again

at half past six on Thursday afternoon.

Beautiful.

Now, öne of the men charged with making precise tables

of exactly when Io should be seen to emerge from behind Jupiter

was the Danish astronomer Ole Romer.

But he noticed something surprising.

See, depending on the time of year,

Io emerged later than expected or earlier than expected.

Now, Remer's genius was to realise that had nothing to do at all

with the orbit of Io around Jupiter.

It was to do with the orbit of the Earth around the sun.

See, what Remer noticed was that

when the Earth was in a position in its orbit

so that it was close to Jupiter,

then Io emerged earlier than it was expected to.

Then, as the year passed and Earth moved around the sun

and got further away from Jupiter,

Roömer noticed that Io then emerged later than it was expected to.

Römer realised that it takes time

for light to travel from Jupiter to the Earth.

So when the Earth is far away from Jupiter,

it takes longer for the light to travel

and therefore you see Io emerge from behind Jupiter

later than you would expect.

Then, when the distance is small,

it takes less time for the light to travel

and you see lo emerge earlier than you might expect.

So Remer had discovered that light doesn't travel instantaneously.

It moves through space with a finite speed.

This remarkable insight led to a measurement of the speed of light.

We now know that light travels at precisely

299,792,458 metres per second.

That means that the time it takes for me to click my fingers,

light has travelled around the Earth seven times.

Or that it travels 10 million million kilometres in one year.

And that's the yardstick we use to measure the universe.

Because 10 million million kilometres is approximately one light year.

The speed of light is the speed limit of the universe

built into the very fabric of space and time itself.

But because light travels at a finite speed,

a light year isn't just a measure of distance.

İt's also a measure of time.

The further away an obfect is,

the further back in time we see it.

Now, the distances that light travels on Earth

are relatively short.

So the time it takes light to travel to our eye

is imperceptible.

But when we look out to space over astronomical distances,

to the stars, planets and galaxies beyond,

then light's finite speed has profound conseguences.

This is Tanzanlia in eastern Africa,

the cradle of humankind.

İIt's here that some of our earliest ancestors walked,

two and a half million years ago.

And our evolutionary journey from the distant past to the present day

ran in parallel with the journey of the light from the stars.

The sun is 150 million kilometres away.

Now, that's very close by cosmic standards.

But light travels at only 300,000 kilometres per second.

So that means that we're seeing the sun as it was in the past,

actually eight minutes in the past.

But when we look beyond our sun to far more distant stars,

we reach further back in time, across the whole of human evolution.

And the deeper into space we look,

the further back in time we see.

As the sun dips below the horizon and night falis,

the universe just fades into view.

And at first you see the bright planets.

I can see Venus over there,

and then the stars appear one by one,

thousands of them shining in the sky.

And then, as it gets darker and darker,

the Milky Way appears.

A vast swathe of billions and billions of suns

as you look out towards the centre of our Milky Way galaxy.

But I think for me the most magical thing you can see in the sky

with the naked eye

is just below the constellation Cassiopeia,

the W of stars in the sky.

There!

Look at that!

Actually, I've got to say, that's amazing. Well...

See that misty patch of light is not a cloud in the sky,

it's not even gas and dust in our galaxy.

That is another galaxy. It's the Andromeda galaxy,

which is roughly the same size as our own,

an island of hundreds and billions of stars,

25 million million million kilometres in that direction.

Like the Milky Way, Andromeda is a spiral galaxy,

two ringed arms circling a light-filled centre.

The core of Andromeda is packed with millions of old red stars.

Very few new stars are born here.

In contrast, its spiral arms shine

with the light from clusters of hot, young, blue stars.

The light that pours from this stellar city

connects us to a remarkable time in the story of human evolution.

The light that I've just captured in my camera

began its journey two and a half million years ago.

At that time, on Earth, there were no humans.

Homo habilis, our distant ancestors, were roaming the plains of Africa.

And as those light rays travelled through the vastness of space,

our species evolved and thousands and thousands

and thousands of generations of humans lived and died.

And then, two and a half million years after their journey began,

these messengers from the depths of space

and from way back in our past

arrived here on Earth

and I just captured them and took that picture.

Light's finite speed opens a window onto the past

and shows us Andromeda as it looked

when our early ancestors walked the Farth

2.5 million years ago.

But by peering further than the naked eye will allow,

we can fourney to a time way before human history,

so far back that we can read the entire history of the universe.

In the last 20 years,

powerful space telescopes have carried us ever deeper into space

and we have become virtual time travellers.

This is Centaurus A, one of our nearest neighbouring galaxies,

only 10 million light years away.

That means that the light began its journey

from these old red and young white, blue stars

only 10 million years ago.

Now, stepping out a little further, just 14 million light years,

there's this beautiful barred spiral galaxy.

And again you can see just lanes and lanes of bright young blue stars.

And this blue light has taken

14 million years to journey across the universe to my eye.

This is NGC 520.

And it's the product of a cosmic collision.

But this galaxy is a hundred million light years away.

That means that the light began its journey from this galaxy to my eye

when the dinosaurs roamed the Earth.

I think it's a beautiful thought that by capturing this faint light

and rebuilding these spectacular images,

we are İn a very real sense connected to these galaxies,

no matter how far away they are across the universe,

connected by the light that's journeyed billions of years to reach us.

But these spectacular galaxies

are not the end of our fourney into the past.

In 2004, we peered further back in time than ever before

and captured the light from the most distant galaxies in the universe.

The image is called the Hubble Ultra Deep Field.

It's a picture take by the Hubble Space Telescope

over a period of 11 days

and it focused its camera on the tiniest piece of sky

just below the constellation of Orion.

Now, it's a piece of sky that you would cover if you took your thumb,

held it in front of your face

and then moved it 20 times further away.

The Hubble captured the faintest lights

from the most distant regions of the universe

and it took this photograph.

Now, almost every point of light in that image

is not a star but a galaxy

of over a hundred billion stars.

The most distant galaxies in that image are over 13 billion light years away.

That means that the faint light from those galaxies

began its journey to Earth 13 billion years ago.

That's over three times the age of the Farth.

Hubble allows us peer back almost to the beginning of time itself.

And out here, in deep space,

it reveals a clue to how our universe began.

When the space telescope stared across the cosmos,

it saw galaxies glow in all different colours.

But when it peered to the very edge of the visible universe,

it captured these images

and saw that every galaxy glowed red.

Written in the red light from these distant worlds

is the story of our universe's origin and evolution.

To reveal it, we must explore one of the most beautiful gualities of light.

For centuries people thought that light just illuminated our world,

you know, allowed us to see and nothing more than that.

But we've since learned that there is a vast amount of information and detail

contained within every beam of light.

And that information is written in colour.

To reveal how colour can unlock the secrets of our universe's creation,

I've come to öne of the most spectacular natural wonders on Farth.

This is Victoria Falls in Zambia.

This waterfall stretches for almost two kilometres,

making it the largest curtain of falling water in the world.

But I'm not here to marvel at the scale of this wonder.

İ've come to see a much more delicate feature

that appears above the water.

These magnificent rainbows

are a permanent feature in the skies above Victorla Falls.

Now, rainbows are a beautiful phenomena.

But I think that they're even more beautiful

when you understand how they're made because they are a visual representation

of the fact that light is made up of, well, all the colours of the rainbow.

Rays of light from the sun bend as they enter the water droplets.

The light beams then reflect off the back of the droplets

and are bent for a second time as they leave.

This bending and reflecting splits the light

and the colours hidden inside the white sunlight are revealed.

But colour can tell us much more.

Because understandıng the reddening of the galaxies

has given us a profound insight into the nature of the universe.

What we see as different colours

are actually different wavelengths of light.

So, blue light has a relatively short wavelength.

And then you go through green and yellow,

all the way to the red end of the spectrum,

which has a very large wavelength.

Starlight is made up of countless different wavelengths.

All the colours of the rainbow.

When light is emitted by a distant star or galaxy,

its wavelength doesn't have to stay fixed.

It can be sguashed or stretched.

And when light is stretched, its wavelength increases

and it moves to the red end of the spectrum.

So the interpretation of the fact that the most distant galaxies appear red

is that the space in between them and us is stretched

during the time it's taken the light to journey over that vast distance.

That means that our entire universe is expanding.

Now, just think about what an exparnıding universe implies.

Because if the galaxies are all rushing away from each other,

that meanrıs that if you rewind time,

then they must have been closer together in the past.

Naturally, if you just keep rewinding,

then you find that at some point ir the past

all the galaxies we can see in the sky

were guite literally on top of each other.

The universe was sguashed down to a point.

That implies that the universe may have had a beginning.

And that is the Big Bang Theory.

Well, that's probably many people's picture of the Big Bang.

You know, this vast explosion that flung matter out into the void.

But that's completely wrong.

As we understand it at the moment, all of space was created at that moment.

So the Big Bang didn't just happen

somewhere out over there in the universe,

it happened everywhere at the same time.

It happened here. So this space here was at the Big Bang.

So, when we look at the distant galaxies

and we see that they are flying away from us,

that's not because they were flung out

in some massive explosion at the beginning of time.

It's because space itself is stretching

and it's been stretching since the Big Bang.

The universe we see today is a network of galaxies

spanning almost a hundred billion light years.

Bur remarkabiy, the blueprint for this astonishing structure

is written into the very first light released into the universe.

Even more remarkabiy,

it's a blueprint that we can read today.

This first light is no longer visible but it's there.

You fust need to know how to look for it.

This sea of shifting sand is the Namib Desert,

the oldest desert in the world.

And as the wind blows the sand off the top of the dunes,

this landscape is constantly changing.

This world has been sculpted by the sun.

It drives the winds that shape the dunes

and its light paints this place a deep orange.

But even when the sun disappears completely,

this desert is still awash with light and colour.

We just can't see it.

Visible wavelengths of light are just a tiny fraction

of all the light in the universe.

Beyond the visible spectrum,

our world is illuminated by invisible light.

This sand has been under the full glare of the sun all day.

And I can feel the heat radiating off it.

Well, heat is nothing more than a form of light.

Although we don't normally call it light.

It's actually infrared light.

And the only difference between infrared and visible light is the wavelength.

Infrared has a longer wavelength than visible light.

Infrared isn't the end of the story.

There are even longer wavelengths of light.

Throughout most of human history we've been blind

to these more unfamiliar forms of light.

But to detect them you don't need a billion pound satellite

or a telescope built into the side of a mountain.

You just need one of these. A radio.

Because when we tune a radio,

we're tuning in to a form oflight. Radio waves.

(JAZZ MUSIİC PLAYING ON RADIO)

But detecting them and understanding them provides the key

to understanding the origin of the universe.

(STATIC ON RADIO)

And when you detune the radio a bit, you can just hear static.

But about 196 of that static is music to the ears of a physicist.

Because that is stretched light from the Big Bang.

So that sound is the sound of the first light

released at the beginning of the universe.

The reason we can't see this ancient light

is because as the universe expanded, the light waves were stretched

and transformed into radio waves and microwaves.

This first light is called the cosmic microwave background, or CMB.

The CMB fills every part of the universe.

Every second, light from the beginning of time

is raining down on the surface of the Earth in a ceaseless torrent.

If my eyes could only see it, then the sky would be ablaze

with this primordial light both day and night.

These waves have been travelling towards us for over 13 billion years.

They are messengers carrying information about the origin of our universe.

In 2001, a satellite called WMAP took a photograph of our entire sky

to capture this ancient light.

The image reveals that the blueprint of the entire universe

Was created moments after the Big Bang.

This is one of the most important images

of the sky ever taken in the history of science.

It doesn't have the beauty of a spiral galaxy or a nebula,

but to a scientist, to a cosmologist,

it is the most beautiful picture ever taken.

Because it contains a vast amount of information

about the very earliest history of our universe.

When the CMB was first detected,

it appeared that the universe was exactiy the same in all directions.

But WMAP shows us that the early universe was far from uniform.

Some areas were denser than others.

And it's these ripples that seeded all the structure in the cosmos.

The explanation for those ripples in the CMB

is absolutely mind-blowing.

Because it's not that they originated

in the first billion billion billion billionths of a second

after the universe began,

when the whole observable universe

was billions of times smaller than a grain of sand.

And little fluctuations called guantum fluctuations

made little bits of the universe a bit denser.

Those dense regions then got denser and denser

as the universe continued to expand.

And they seeded the formation of the first stars

and the first galaxies in the universe.

The early universe was a hot, almost uniform sea

of matter and radiation.

As the universe expanded,

the slightly denser regions became increasingly dense.

Atoms clumped together to form the first structures.

Over time, these structures grew so massive

that they collapsed under their own gravity.

Hydrogen fused, releasing enormous amounts of energy.

Two hundred million years after the Big Bang,

the first stars in the cosmos burst into life.

Darkness was banished and the cosmos began to fill with light.

Planets formed and fell into orbit around the stars,

and these yourng solar systems orbited the galaxiles.

And the only reason why any of this exists

is because of those tiny density fluctuations

that appeared when the observable universe

was smaller than a grain of sand.

Without them, there would be no planets or stars and no galaxles.

Our universe would look the same in every direction.

For billions of years, generations of stars lived and died.

And then, nine billion years after it all began

in an unremarkable piece of space in the Orion Spur of the Perseus Arm

of the galaxy called the Milky Way, a star was born that we call the sun,

that illuminated our embryonic solar system with light.

So the light from the star that bathes the Farth has its ultimate origin

in the tiny ripples that appeared in the first moments of our universe's life.

By capturing the light from the skies,

we've been able to tell the story of the universe's origins and evolution,

and it's worth reflecting on what a remarkable thing that is.

You know, little beings like me scurrying around

on the surface of a rock on the edge of one of the galaxies

have been able to understand the very origin and evolution of the universe.

But there's öne more twist to this story.

Because that ability to use light,

to capture it and use it to understand our world,

may have played a key role in the emergence of complex life on Earth.

This is the Yoho National Park in the Rocky Mountains of Canada,

öne of the most spectacular mountain ranges in North America.

A hundred years ago, a fossil field was discovered here at the Burgess Shale

that may reveal how light shaped life on Farth.

This is one of the most important fossil sites in the world.

And actually, it's one of the most important scientific sites of any kind.

And it's not just because of the number and diversity of animals

you find fossilised in these rocks.

It's because of their age.

These fossils are over 500 million years old.

There is virtually no record of complex life on Farth before this time.

İt's as if at one instant in this time we call the Cambrian era,

complex multi-cellular life suddenly emerged,

almost intact, on the planet.

It's called the Evolutionary Big Bang.

This is one of the beautiful animals you find up here in the fossil beds.

It's called a trilobite.

It's a very complex organism.

It's got an external skeleton, it's got jointed limbs,

but perhaps most remarkably, these.

Because these are compound eyes. They were very sophisticated.

And this was one of the first predators

to be able to detect shapes and see movement.

And it could successfully chase its prey.

These creatures were among the first

to harness the light that filled the universe.

Before they emerged, the rise and fall of the sun

and the stars in the night sky simply went unnoticed.

Now, there is a speculative theory that the emergence of the eye

actually triggered the Cambrian explosion,

this Evolutionary Big Bang.

Because once one species got eyes,

then other species had also to develop eyes

to either chase them as predators or evade them as prey.

And that led to an evolutionary arms race.

More and more complex life forms developed.

So the evolution of the eye may have played a fundamental role

in the emergence of complex life on Earth

and could have led to the evolution of our species.

See this little thing, although it looks unimpressive,

may be the most important animal that we've ever discovered in our history.

It's called a pikaia, and it's a little worm-like creature.

But it's thought that this is a chordate,

and that is the branch of life that we're in.

So, it could be that this is our earliest known ancestor.

What's also fascinating is it's also thought

that this may have been able to detect light,

it may have had primitive cells that were sensitive to light

and allowed it, in a very loose sense, to see.

And if that's true, then this little guy may be our direct ancestor.

And those little cells may be the things

that evolved over hundreds of millions of years into our eyes.

Without pikala, we may never have evolved

and developed the ability to see how this story unfolded.

Ünderstanding the universe is like a detective story.

And the evidence has been carried to us across vast expanses of space by light.

We've even been able to capture the light from the beginning of time.

And we've glimpsed in it the seeds of our own origins.

And we've seen things our ancestors wouldn't believe.

Stars being born in distant realms,

alien worlds created by gravity

and spectacular galaxies frozen in time.

But we are not mere witnesses to these evenits.

Because the story of the universe is our story.

We've learned how the dust of the stars makes each and every one of us,

how a simple universal chemistry set makes everything we see.

We've explored how the secrets of deep time

shape the destiny of the universe

and marvelled at the brief flickering moment in which life can exist.

And we've seen how stardust falls

to build the grandest structures in the universe.

We know all this because of messages carrfed on beams of light.

And isn't it a wonderful thing that these biological light detectors

that first emerged half a billion years ago

in the Cambrian explosion

have evolved into those most human of things,

our green, blue and brown eyes that are able to gaze up into the night sky,

capture the light from distant stars and read the story of the universe?

(PURE IMAGINATTION BY MAROON 5 PLAYING)